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A feasibility study of intrabuilding wireless communications using low level nominal 60 GHz radiation Siu, Frederick Wing Cheung 1988

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A FEASIBILITY STUDY OF INTRABUILDING WIRELESS COMMUNICATIONS USING LOW LEVEL NOMINAL 60 GHz RADIATION by FREDERICK WING CHEUNG SIU B.A.Sc The University of B r i t i s h Columbia, 1975 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF ELECTRICAL ENGINEERING We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA January 1988 ©Frederick Wing Cheung Siu 1988 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of £1^ c TCA L- £(V G Q The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date J > ^ '8 / DE-6(3/81) ABSTRACT The RF ( r a d i o f r e q u e n c y ) a s p e c t o f an IWC ( i n d o o r w i r e l e s s c o m m u n i c a t i o n ) s y s t e m w h i c h o p e r a t e s i n t he 60 GHz range i s d e s i g n e d and i m p l e m e n t e d . The o v e r a l l s y s t e m s h o u l d be c a p a b l e of p r o v i d i n g i n d o o r o f f i c e c o m m u n i c a t i o n s f o r a maximum o f 200 b a s i c r a t e ISDN ( i n t e g r a t e d s e r v i c e s d i g i t a l n e t w o r k ) s u b s c r i b e r s , and BER ( b i t e r r o r r a t e ) o f 1 0 - 6 o r l e s s . The s y s t e m f e a s i b i l i t y s t u d y i s b a s e d on t he a s s u m p t i o n s of u s i n g BPSK ( b i n a r y phase s h i f t k e y i n g ) m o d u l a t i o n , DSCDMA ( d i r e c t sequence code d i v i s i o n m u l t i p l e a c c e s s ) s p r e a d s p e c t r u m t e c h n i q u e and an EIRP ( e f f e c t i v e i s o t r o p i c a l l y r a d i a t e d power) o f 100 m i l l i w a t t o r l e s s . A l i n e of s i g h t scheme i s a d o p t e d w h i c h makes use o f a p r o p a g a t i o n a r r a n g e m e n t t h a t c o n f i n e s t h e r a d i a t i o n t o a r e g i o n o f space s e l d o m o c c u p i e d i n t he open o f f i c e e n v i r o n m e n t . The d e s i g n of an a p p r o p r i a t e a n t e n n a s y s t e m w h i c h meets s u c h a r e q u i r e m e n t i s p r e s e n t e d . U s i n g t he s p e c i a l l y d e s i g n e d a n t e n n a s and c o m m e r c i a l l y a v a i l a b l e m i l l i m e t r i c wave componen ts , a one d i r e c t i o n b a s i c RF s y s t e m i s i m p l e m e n t e d . The i n d o o r p r o p a g a t i o n c h a r a c t e r i s t i c s and f a d i n g s t a t i s t i c s o f t he s y s t e m a r e e x p e r i m e n t a l l y o b t a i n e d . I t i s f o u n d t h a t t he f a d i n g i s R i c i a n , w i t h a K r a t i o ( f a d i n g s i g n a l p o w e r / s t e a d y s i g n a l power ) o f l e s s t h a n - 2 0 . 2 d B , and t h a t t he RF s y s t e m c a n s u p p o r t t he t y p e of c o m m u n i c a t i o n s e r v i c e p r o p o s e d . - i i -TABLE OF CONTENTS Page ABSTRACT 1 3 ; TABLE OF CONTENTS i i i LIST OF SYMBOLS AND ABBREVIATIONS v LIST OF ILLUSTRATIONS i x ACKNOWLEDGEMENT x i 1. INTRODUCTION 1 1.1 Background 1 1.2 P o t e n t i a l applications 5 1.3 Thesis objective 5 1.4 Thesis outline 7 2. OVERALL SYSTEM CONSIDERATIONS 9 2.1 Functional requirements 9 2.2 Environmental requirements 9 2.3 Global system performance requirements 11 3. INITIAL SPREAD SPECTRUM MULTIPLE ACCESS CONSIDERATIONS 13 3.1 Problems of Indoor Wireless Communications 13 3.2 Properties of spread spectrum multiple access 13 3.3 Preliminary design considerations 17 3.3.1 Type of modulation and SSMA 17 - i i i -Page 3.3.2 B i t error rate and code length 18 3.3.3 Fading 25 4. RADIO FREQUENCY SYSTEM DESIGN 27 4.1 General 27 4.2 Choice of operating frequency 28 4.3 Proposed radio frequency system 30 4.4 Signal power requirements 32 5. ANTENNA SYSTEM DESIGN 36 5.1 General 36 5.2 Antenna systems considered 36 5.3 F i n a l system engineering d e t a i l 40 5.4 Construction d e t a i l 46 6. TESTS OF THE RF SYSTEM 49 6.1 General 49 6.2 Signal l e v e l s 49 6.3 Crossp o l a r i z a t i o n discrimination 52 6.4 Radiation patterns 52 6.5 Propagation c h a r a c t e r i s t i c s 60 6.6 Fading s t a t i s t i c s 6° 7. CONCLUSIONS AND RECOMMENDATIONS 64 7.1 Conclusions 64 7.2 Recommendations for further research 65 8. REFERENCES 6 9 i - i v -L I S T OF SYMBOLS AND ABBREVIATIONS 2B+D An ISDN recommended s y s t e m c o n f i g u r a t i o n w i t h 2 v o i c e and one d a t a c h a n n e l s commonly r e f e r r e d t o as b a s i c - r a t e ISDN a R a d i u s o f i n n e r c o n d u c t o r o f c o a x i a l c a b l e a ^ S p e c u l a r component o f R i c i a n f a d i n g b R a d i u s o f o u t e r c o n d u c t o r o f c o a x i a l c a b l e B j + B 2 S u s c e p t a n c e o f r a d i a l l i n e to c o a x i a l l i n e s t r u c t u r e BER B i t e r r o r r a t e BPSK B i n a r y phase s h i f t k e y i n g BW B a n d w i d t h CAD/CAM Computer a i d e d d e s i g n / m a n u f a c t u r i n g CCD Charge c o u p l e d d e v i c e CCITT C o n s u l t a t i v e commi t t ee of i n t e r n a t i o n a l t e l e p h o n e and t e l e g r a p h CDMA Code d i v i s i o n m u l t i p l e - a c c e s s C^ Code number i C . Code number j 2 CW C o n t i n u o u s wave dB D e c i b e l dBm D e c i b e l w i t h r e f e r e n c e t o a m i l l i w a t t ECM E l e c t r o n i c c o u n t e r measure E IRP E f f e c t i v e i s o t r o p i c a l l y r a d i a t e d power £ q F r e e s p a c e p e r m i t t i v i t y R e l a t i v e p e r m i t t i v i t y o r d i e l e c t r i c c o n s t a n t o f m a t e r i a l E S i g n a l power s t r e n g t h s EW E l e c t r o n i c w a r f a r e - v -c FHCDMA F • C • C • GHz R H(2) o I F ISDN ISM IWC I o J o k K K KBPS KHz K LAN O p e r a t i n g f r e q u e n c y F r e q u e n c y h o p p i n g code d i v i s i o n m u l t i p l e a c c e s s F e d e r a l C o m m u n i c a t i o n s C o m m i s s i o n Fade m a r g i n G i g a - h e r t z G a i n of node a n t e n n a G a i n of s u b s c r i b e r a n t e n n a Gap of r a d i a l l i n e H a n k e l f u n c t i o n o f t he s e c o n d k i n d o f o r d e r z e r o I n t e r m e d i a t e f r e q u e n c y I n t e g r a t e d s e r v i c e s d i g i t a l n e t w o r k I d u s t r i a l S c i e n t i f i c and M e d i c a l Band I n d o o r w i r e l e s s c o m m u n i c a t i o n s M o d i f i e d B e s s e l f u n c t i o n of t he f i r s t k i n d o f o r d e r z e r o B e s s e l f u n c t i o n of the f i r s t k i n d o f o r d e r z e r o I n t e g e r s u c h t h a t 2 -1=L, the code l e n g t h B o l t z m a n n ' s c o n s t a n t , random component . _,. . ,. , . Power r a t i o of . - _ i n a R i c i a n f a d i n g s p e c u l a r component K i l o - b i t p e r s e c o n d K i l o - h e r t z M o d i f i e d B e s s e l f u n c t i o n o f t he s e c o n d k i n d s of o r d e r z e r o Code l e n g t h , s p r e a d r a t i o , s p r e a d g a i n o r p r o c e s s g a i n (when e x p r e s s e d i n dB) L o c a l a r e a n e t w o r k - v i -hi N a t u r a l l o g a r i t h m LOG L o g a r i t h m L P I Low p r o b a b i l i t y o f i n t e r c e p t m M e t r e mm M i l l i m e t r e MBPS M e g a - b i t p e r s e c o n d MHz M e g a - h e r t z MMIC M o n o l i t h i c m ic rowave i n t e g r a t e d c i r c u i t MSK Minimum s h i f t k e y i n g ^ f a d e N o i s e component due t o f a d i n g N . N o i s e component due t o i n t e r f e r e n c e s i n t N N o i s e component due t o t h e r m a l e f f e c t N •TJ— T w o - s i d e d s p e c t r a l d e n s i t y o f w h i t e G a u s s i a n n o i s e n F r e e s p a c e i n t r i n s i c impedance P Number of p a i r s o f s u b s c r i b e r s P g P r o b a b i l i t y o f e r r o r P G P a t h g a i n PG P r o c e s s g a i n , e q u i v a l e n t t o s p r e a d r a t i o e x p r e s s e d i n dB PN P s e u d o - n o i s e PR P s e u d o - r a n d o m P T T r a n s m i t power Q A n g l e , phase a n g l e Q ( x ) Q f u n c t i o n r e p r e s e n t i n g t he i n t e g r a l o f one t a i l o f n o r m a l d i s t r i b u t i o n f r om x t o 0 0 - v i i -r Random component o f R i c i a n f a d i n g ( G a u s s i a n d i s t r i b u t e d ) RCL R e c e i v e d c a r r i e r l e v e l RF R a d i o f r e q u e n c y RJ,^(T) N o r m a l i z e d a u t o c o r r e l a t i o n of t he i t h code w i t h a t ime d e a l y o f t R^^(T) N o r m a l i z e d c r o s s c o r r e l a t i o n o f the i t h code w i t h j t h code w i t h a t i m e d e l a y o f T SAW S u r f a c e a c o u s t i c wave SSMA S p r e a d s p e c t r u m m u l t i p l e a c c e s s T P e r i o d of d a t a s t r e a m T Room t e m p e r a t u r e 25°C o r 298°K TE T r a n s v e r s e e l e c t r i c mode TH Time h o p p i n g TM T r a n s v e r s e m a g n e t i c mode F r e e s p a c e p e r m e a b i l i t y UPS U n i v e r s a l p o r t a b l e s e r v i c e Y A d m i t t a n c e __ i ^. c random component . „ . . Y V o l t a g e r a t i o o f . - i n a R i c i a n f a d i n g ° s p e c u l a r component Y B e s s e l f u n c t i o n of t he s e c o n d k i n d o f o r d e r z e r o o Z C h a r a c t e r i s t i c impedance o f c o a x i a l c a b l e - v i i i -LIST OF ILLUSTRATIONS Page Figure 2.1 Proposed RLAN system 10 Figure 3.3.1 T y p i c a l autocorrelation output 19 Figure 3.3.2.1 Phasor representation of R i c i a n fading 22 Figure 4.3.1 RF system configuration 31 Figure 4.3.2 V e r t i c a l r a d i a t i o n pattern required for node antenna 33 Figure 4.4.1 Signal to thermal noise r a t i o through various stages of the receiver 33 Figure 5.2.1 Cross section view of a double r e f l e c t o r system for omnidirectional h o r i z o n t a l pattern and narrow v e r t i c a l pattern 39 Figure 5.2.2 Array of d i e l e c t r i c rod antennas using simple amplitude and phase feed 41 Figure 5.3.1 Cross section view of the node antenna 42 Figure 5.3.2 Equivalent transmission l i n e problem i n the analysis of node antenna structure 44 Figure 5.3.3 A coaxial to r a d i a l l i n e junction 44 Figure 5.4.1 Subscriber d i e l e c t r i c antenna construction d e t a i l . . 47 Figure 5.4.2 Node antenna construction d e t a i l 48 Figure 6.1.1 Functional block diagram of RF system (with only one subscriber shown) 50 - i x -Page F i g u r e 6 . 1 . 2 A one d i r e c t i o n " b a r e bone " RF s y s t e m u s e d f o r RF i n v e s t i g a t i o n 51 F i g u r e 6 . 3 . 1 A p l o t o f c r o s s p o l a r i z a t i o n d i s c r i m i n a t i o n o f t he a n t e n n a s y s t e m 53 F i g u r e 6 . 4 . 1 R a d i a t i o n p a t t e r n s of node a n t e n n a 54 F i g u r e 6 . 4 . 2 R a d i a t i o n p a t t e r n s of s u b s c r i b e r d i e l e c t r i c 55 t o r e c t a n g u l a r r o d a n t e n n a f o r v a r i o u s E p l a n e o r t o 6 . 4 . 6 H p l a n e f l a r e s 59 F i g u r e 6 . 6 . 1 S e t - u p u s e d t o o b t a i n e x p e r i m e n t a l d a t a f o r RF f a d i n g e s t i m a t i o n 61 F i g u r e 6 . 6 . 2 C o m p a r i s o n o f c u m u l a t i v e p r o b a b i l i t y d i s t r i b u t i o n o f the measured RCL a g a i n s t t h e o r e t i c a l R i c i a n d i s t r i b u t i o n w i t h d i f f e r e n t K v a l u e s 63 - x -ACKNOWLEDGEMENT This author would l i k e to express his gratitude to Dr. Kharadly who has kindly provided supervision and guidance. Dr. Kharadly's invaluable ideas and suggestions have been a central force of motivation. Thanks are also due to the author's employer, B r i t i s h Columbia Telephone Company for support. In particular to Mr. W. Robinson and Mr. G. Ross for their pioneering efforts i n setting up this program, Mr. G.E. Valde and Mr. D.A. Calder for approving i t , Mr. N. Owen, Mr. D.A. Chang, Mr.A. Au and Mr. F. Schell for supervising i t . Helpful discussions and constructive c r i t i c i s m from Dr. Lee, Mr. J. Loo and Mr. S. Liang are appreciated. Thanks are also due to Mrs. G a i l Schmidt for typing, Mr. A. MacKenzie and his staff for metal work and project l o g i s t i c s support. - x i -1 CHAPTER 1 INTRODUCTION 1.1 B a c k g r o u n d Modern s o c i e t y has e n t e r e d t h e i n f o r m a t i o n age [ 1 ] . As t he i n f o r m a t i o n g r o w t h c o n t i n u e s so w i l l t he demand f o r c o m m u n i c a t i o n s . Some c u r r e n t e v e n t s a f f e c t i n g t he e v o l u t i o n o f c o m m u n i c a t i o n s a r e t he a d v e n t of ISDN ( i n t e g r a t e d s e r v i c e s d i g i t a l n e t w o r k ) [2] , t he d e r e g u l a t i o n o f the c o m m u n i c a t i o n i n d u s t r y and t he r a p i d i t y o f changes o f t e c h n o l o g y . These i m p l y t h a t d i g i t a l r a t h e r t h a n a n a l o g c o m m u n i c a t i o n w i l l p r e v a i l and t h a t t e l e c o m m u n i c a t i o n o p e r a t o r s ( s u c h as t e l e p h o n e c o m p a n i e s ) and v e n d o r s ( s u c h as t e l e c o m m u n i c a t i o n equ ipmen t m a n u f a c t u r e r s ) w i l l p r o s p e r i n a c o m p e t i t i v e e n v i r o n m e n t o n l y i f t h e y e x c e l i n a p p l y i n g new t e c h n o l o g i e s t o p r o v i d e e f f i c i e n t and e c o n o m i c a l c o m m u n i c a t i o n s e r v i c e s . The need f o r e f f i c i e n t c o m m u n i c a t i o n s i s most a c u t e i n modern o f f i c e s where 95% o f a c t i v i t i e s a r e i n f o r m a t i o n i n t e n s i v e . I n t h e U . S . A . , t he o f f i c e w o r k e r s make up more t h a n 40% of t he t o t a l work f o r c e [ 1 ] . I n C a n a d a , where b u s i n e s s e s a r e more s e r v i c e o r i e n t e d , t he p e r c e n t a g e i s p r o b a b l y even h i g h e r . B u s i n e s s e s r e a l i z e t h a t o f f i c e p r o d u c t i v i t y i s one of the key f a c t o r s a f f e c t i n g p o t e n t i a l p r o f i t o r l o s s . O f f i c e a u t o m a t i o n s , of w h i c h c o m p u t e r i z a t i o n i s o n e , a r e supposed t o i n c r e a s e o f f i c e p r o d u c t i v i t y . To r e a l i z e the p r o j e c t e d p r o d u c t i v i t y improvement due t o common d a t a b a s e o r f a c i l i t y s h a r i n g , e f f i c i e n t c o m m u n i c a t i o n s i n t h e f o r m o f L A N ' s ( l o c a l a r e a n e t w o r k s ) l i n k i n g t h e compu te rs o r t e r m i n a l s t o g e t h e r a r e r e q u i r e d [6] . B i g b u s i n e s s e s s u c h as Dow C h e m i c a l [3] and X e r o x have p l a n n e d and c o o r d i n a t e d LAN i n s t a l l a -2 t i o n s ; most o t h e r L A N ' s a r e i n s t a l l e d i n a h a p h a z a r d manner w i t h l i t t l e r e g a r d f o r s t a n d a r d s o r p l a n s f o r g row th [ 4 ] . I t i s a n t i c i p a t e d t h a t t h e s e w i l l be r e p l a c e d s h o r t l y t o c o n f o r m to r e c o g n i z e d s t a n d a r d s . The i l l u s i o n , t h a t L A N ' s b u i l t u s i n g t w i s t e d p a i r s a r e i n e x p e n s i v e , i s s h a t t e r e d when u s e r s s u f f e r f r om a r e c u r r i n g expense of r e l o c a t i o n . M o t o r o l a e s t i m a t e s t h i s r e l o c a t i o n c o s t a t $1000 t o $1400 p e r t e r m i n a l a t an a v e r a g e f r e q u e n c y o f once e v e r y e i g h t months [ 5 ] . When t h e s e r e l o c a t i o n e x p e n s e s a r e i n c l u d e d , a c a b l e LAN c a n be v e r y e x p e n s i v e i n d e e d . O t h e r d i s a d v a n t a g e s o f a c a b l e LAN a r e : - P r e w i r i n g i s n e c e s s a r y - Growth i s i n f l e x i b l e - B a n d w i d t h i s l i m i t e d by c a b l e c h a r a c t e r i s t i c s - R e l o c a t i o n i n v o l v e s e x c e s s i v e down t i m e - L a c k of p o r t a b i l i t y . The p r o s p e c t o f u s i n g r a d i o t o r e p l a c e c a b l e f o r LAN a p p l i c a t i o n l o o k s v e r y p r o m i s i n g [ 5 , 7 ] . A r a d i o L A N , e s p e c i a l l y t he t y p e p r o p o s e d h e r e , has a h i g h e r s t a r t - u p c o s t bu t o f f e r s a d v a n t a g e s such a s : - Low o r no r e l o c a t i o n c o s t [5] , so t h a t a f t e r s e v e r a l y e a r s of o p e r a t i o n , o v e r a l l c o s t w i l l be even l o w e r t h a n t h a t of a c a b l e s y s t e m . - Growth i s f l e x i b l e and o v e r l o a d c a n be accommodated by g r a c e f u l d e g r a d a t i o n . - Medium t o h i g h speed d a t a t r a n s f e r i s p o s s i b l e . - P o r t a b i l i t y and f r e e d o m f rom messy c a b l i n g . - S e l f a d d r e s s i n g c a p a b i l i t y . - P r e w i r i n g i s no t r e q u i r e d . 3 The u t i l i z a t i o n o f RF t e c h n o l o g y f o r b o t h v o i c e and d a t a t r a n s m i s s i o n i n t he i n d o o r e n v i r o n m e n t i s r e c e i v i n g much a t t e n t i o n [ 1 0 ] , j u d g i n g by t h e abundan t r e c e n t l i t e r a t u r e on t he s u b j e c t [10 t o 2 0 , 2 2 ] . R e c e n t i n v e s t i g a t i o n s on i n d o o r w i r e l e s s c o m m u n i c a t i o n s have f o c u s s e d o n : - P r o p a g a t i o n c h a r a c t e r i s t i c s . E m p i r i c a l d a t a of f r e e s p a c e l o s s i n d o o r does no t f o l l o w the s i m p l e - _ r u l e bu t r a t h e r ( d i s t a n c e ) 2 - w h e r e n can v a r y f r om 1 t o 6 [ 12 ,13 ] d e p e n d i n g on t he ( d i s t a n c e ) b u i l d i n g c h a r a c t e r i s t i c s . - Time d e l a y s p r e a d o f the m u l t i p a t h s i g n a l s . T h i s c o u l d c a u s e i n t e r - s y m b o l i n t e r f e r e n c e and l i m i t t h e r a t e of d a t a commun ica -t i o n s . Some e x p e r i m e n t s [18] measured t h i s d e l a y s p r e a d . - F a d i n g s t a t i s t i c s and m o d e l s . E m p i r i c a l d a t a o f r e c e i v e d s i g n a l l e v e l a r e s t a t i s t i c a l l y a n a l y z e d [20] . M o d e l s o f the f a d i n g phenomenon have a l s o been p r o p o s e d [ 1 4 ] . - T e c h n i q u e s f o r o v e r c o m i n g t h e u n p r e d i c t a b l e f a d i n g . S p r e a d s p e c t r u m i s a p o p u l a r method [ 1 8 , 1 9 , 2 0 ] . A n t e n n a d i v e r s i t y ( s w i t c h i n g and c o m b i n i n g ) [ 1 5 , 1 6 , 1 9 ] i s a n o t h e r . A l s o l e a k y f e e d e r s have been p r o p o s e d [ 1 3 ] . The i d e a o f c o m b i n i n g SS ( s p r e a d s p e c t r u m ) t e c h n i q u e and RF f o r i n d o o r o f f i c e c o m m u n i c a t i o n s comes f r o m P a h l a v a n ' s p a p e r [ 1 1 ] . The s y s t e m p r o p o s e d i n the p r e s e n t work d i f f e r s f r o m o t h e r r e s e a r c h e s i n IWC ( i n d o o r w i r e l e s s c o m m u n i c a t i o n s ) i n s e v e r a l r e s p e c t s . These a r e : 4 - The o p e r a t i n g f r e q u e n c y i s i n t he oxygen a b s o r p t i o n b a n d ; i t i s p r o p o s e d f o r s e l f c o n t a i n e d , s h o r t r a n g e , low power , w i d e b a n d and p r i v a t e o p e r a t i o n . - S p r e a d s p e c t r u m t e c h n i q u e s , i n p a r t i c u l a r , BPSK-DSCDMA ( b i n a r y phase s h i f t k e y i n g , d i r e c t sequence code d i v i s i o n m u l t i p l e a c c e s s ) i s p r o p o s e d t o p r o v i d e s i m u l t a n e o u s a c c e s s f o r as many as 200 s u b -s c r i b e r s w i t h an a v e r a g e BER ( b i t e r r o r r a t e ) o f 1 0 _ b o r l e s s . The a n t i - f a d i n g p r o p e r t y i s u s e d t o r e d u c e the e f f e c t o f f a d i n g [ 2 3 ] . - The s y s t e m i s c o m p a t i b l e w i t h ISDN t e c h n o l o g y . F o r t h i s s t u d y i t i s assumed t h a t e a c h s u b s c r i b e r w i l l need 2B+D ISDN c h a n n e l s c a r r y i n g a t r a f f i c w h i c h i s e q u i v a l e n t t o a 192 KBPS ( k i l o b i t p e r s e c o n d ) d a t a s t r e a m . The b u s i n e s s p o t e n t i a l o f L A N ' s i s p r o j e c t e d t o e x c e e d $1 b i l l i o n a n n u a l l y f o r t h e n e x t f i v e y e a r s i n t h e U . S . A . a l o n e [ 5 ] . The p o s s i b i l i t y o f c a p t u r i n g a f r a c t i o n o f t h i s ma rke t i s enough m o t i v a t i o n f o r t h i s p r o j e c t . B e f o r e d e r e g u l a t i o n , t he i m b a l a n c e o f l o c a l and l o n g d i s t a n c e s e r v i c e s was a r t i f i c i a l l y m a i n t a i n e d t h r o u g h m o n o p o l y . N a t u r a l l y , the i n i t i a l r e s p o n s e t o d e r e g u l a t i o n has been a s u r g e o f a c t i v i t i e s p r o v i d i n g new s e r v i c e s i n t h e more l u c r a t i v e l o n g d i s t a n c e s e r v i c e s . I t i s n a t u r a l t o p r o j e c t t h a t r a t e r e b a l a n c i n g w i l l e v e n t u a l l y even ou t t h i s i m b a l a n c e and t h a t l o c a l s e r v i c e s w i l l t h e n become the n e x t a r e a of k e e n c o m p e t i t i o n . T h i s p r o j e c t a ims t o p r o v i d e a s a l e a b l e p r o d u c t i n t h i s p o t e n t i a l l y huge l o c a l a c c e s s and d i s t r i b u t i o n m a r k e t . On a more p h i l a n t h r o p i c b a s i s , t h i s p r o j e c t c o n t r i b u t e s t o t h e p o s s i b i l i t y o f r e a l i z i n g UPS ( u n i v e r s a l p o r t a b l e s e r v i c e s ) as a n a t u r a l e v o l u t i o n of c o m m u n i c a t i o n s e r v i c e s [ 9 ] . 5 1.2 P o t e n t i a l A p p l i c a t i o n s The t a r g e t e d marke t i s f o r o f f i c e i n d o o r c o m m u n i c a t i o n s . W i t h p r o p e r m o d i f i c a t i o n s , the a p p l i c a t i o n s p e c t r u m c a n s p r e a d t o : - A t e m p o r a r y , f a s t d e p l o y a b l e c o n f e r e n c e ne two rk f o r a few hund red u s e r s w i t h i n a l a r g e open s t r u c t u r e . - C e l l u l a r r a d i o t e l e p h o n e and m o b i l e c o m m u n i c a t i o n s . - H i g h s e c u r i t y ne two rk f o r b a n k i n g . S e c u r i t y i s p r o v i d e d by d a t a e n c r y p t i o n i n a d d i t i o n t o s p e c t r u m s p r e a d i n g ( w h i c h p r o v i d e s p r i v a c y ) . - C o v e r t m i l i t a r y c o m m u n i c a t i o n s s u c h as EW ( e l e c t r o n i c w a r f a r e ) , ECM ( e l e c t r o n i c c o u n t e r m e a s u r e ) , L P I ( l o w p r o b a b i l i t y o f i n t e r c e p t ) sys tems e t c . . - Robo t c y b e r n e t i c s i n CAD/CAM ( compu te r a i d e d d e s i g n / m a n u f a c t u r i n g ) . I n t e r f e r e n c e r e s i s t a n c e p r o v i d e d by s p e c t r u m s p r e a d i n g i s r e q u i r e d f o r r e l i a b l e c o m m u n i c a t i o n s and c o n t r o l s of r o b o t s . J a p a n ' s e x p e r i e n c e [8] o f r o b o t a c c i d e n t s c a u s e d by e l e c t r o n i c smog, c l e a r l y d e m o n s t r a t e s t h i s p o t e n t i a l n e e d . 1 .3 T h e s i s O b j e c t i v e T h i s t h e s i s p r e s e n t s an i n v e s t i g a t i o n of the f i r s t s t a g e of a two s t a g e p r o j e c t . The o v e r a l l p r o j e c t g o a l i s t o d e t e r m i n e t h e f e a s i b i l i t y o f p r o v i d i n g ISDN ( i n t e g r a t e d s e r v i c e s d i g i t a l n e t w o r k ) c o m p a t i b l e RLAN ( r a d i o l o c a l a r e a n e t w o r k ) s e r v i c e s u s i n g low l e v e l ( l e s s t h a n 100 m i l l i w a t t o f E I R P ( e f f e c t i v e i s o t r o p i c a l l y r a d i a t i o n p o w e r ) ) m i l l i m e t r i c wave and SSMA ( s p r e a d s p e c t r u m m u l t i p l e a c c e s s ) f o r IWC ( i n d o o r w i r e l e s s c o m m u n i c a t i o n ) . 6 The s c o p e o f t he o v e r a l l p r o j e c t i s q u i t e l a r g e , e n c o m p a s s i n g b o t h RF ( r a d i o f r e q u e n c y ) and SSMA ( s p r e a d s p e c t r u m m u l t i p l e a c c e s s ) w o r k s , so t h a t a d i v i s i o n o f t he p r o j e c t i n t o two s t a g e s i s a p p r o p r i a t e . The o b j e c t i v e of t h i s t h e s i s i s to i n v e s t i g a t e RF s y s t e m f e a s i b i l i t y . The RF s t u d y , h o w e v e r , canno t be c o n d u c t e d s e p a r a t e l y f r o m the o v e r a l l s y s t e m c o n s i d e r a t i o n s s i n c e s u c h c o n s i d e r a t i o n s d i c t a t e t h e RF s y s t e m r e q u i r e m e n t . An RF s y s t e m i s e n g i n e e r e d a s s u m i n g t h a t t he o v e r a l l s y s t e m - u s e s BPSK ( b i n a r y phase s h i f t k e y i n g ) and DSCDMA ( d i r e c t sequence code d i v i s i o n m u l t i p l e a c c e s s ) . - c o v e r s a c i r c l e of 20 me t re r a d i u s on t he same f l o o r i n a modern o f f i c e ( o r f a c t o r y ) w i t h l a r g e " o p e n " f l o o r p l a n . - accommodates a maximum o f 200 s u b s c r i b e r s each c a r r y i n g 192 KBPS and meets a BER p e r f o r m a n c e r e q u i r e m e n t o f 1 0 " b o r l e s s . S p r e a d s p e c t r u m m u l t i p l e a c c e s s i s u s e d t o overcome f a d i n g and i n t e r f e r e n c e . The s e v e r i t y of f a d i n g a f f e c t s t he o v e r a l l s y s t e m v i a b i l i t y . F o r t h i s r e a s o n a l i n e of s i g h t r a t h e r t h a n a s i g n a l f l o o d i n g scheme w i l l be u s e d f o r s i g n a l t r a n s m i s s i o n . An a n t e n n a s y s t e m s a t i s f y i n g t h i s l i n e of s i g h t r e q u i r e m e n t i s cus tom d e s i g n e d and c o n s t r u c t e d . A m i n i m a l RF s y s t e m i s t h e n i m p l e m e n t e d u s i n g c o m m e r c i a l l y a v a i l a b l e m i l l i m e t r i c wave components and t he c u s t o m d e s i g n e d a n t e n n a s . The l a s t p a r t o f t he i n v e s t i g a t i o n i s t he d e t e r m i n a t i o n of the c h a r a c t e r i s t i c s and t he s e v e r i t y of f a d i n g . E x p e r i m e n t a l measurements a r e t h e n u s e d t o v e r i f y p e r f o r m a n c e and t o e s t a b l i s h RF s y s t e m f e a s i b i l i t y . 7 1.4 T h e s i s O u t l i n e C h a p t e r 1 g i v e s an i n t r o d u c t i o n and b a c k g r o u n d on t h e o v e r a l l p r o j e c t , d i f f e r e n t i a t e s i t f r o m s i m i l a r r e s e a r c h e s and l i s t s i t s p o t e n t i a l a p p l i c a t i o n s . T h e s i s o b j e c t i v e d e f i n e s t he g o a l o f t h i s e x p e r i m e n t and t he o u t l i n e s k e t c h e s t he t h e s i s o r g a n i z a t i o n . C h a p t e r 2 d e f i n e s the s y s t e m s i z e , p e r f o r m a n c e r e q u i r e m e n t s and the assumed o p e r a t i n g e n v i r o n m e n t . C h a p t e r 3 l o o k s i n t o t he d i f f i c u l t i e s of i n d o o r r a d i o t r a n s m i s s i o n and t he j u s t i f i c a t i o n s of u s i n g s p r e a d s p e c t r u m m u l t i p l e a c c e s s . The f u n c t i o n o f code d i v i s i o n m u l t i p l e a c c e s s i s e x p l a i n e d u s i n g a n o n r i g o r o u s a n a l o g y . A s s u m i n g a BPSK-DSCDMA ( b i n a r y phase s h i f t k e y i n g , d i r e c t sequence code d i v i s i o n m u l t i p l e a c c e s s ) s y s t e m , the i m p o r t a n t s i g n i f i c a n c e o f f a d i n g i s i l l u s t r a t e d by c a l c u l a t i o n s of code l e n g t h r e q u i r e d u n d e r t h r e e c o n d i t i o n s , the f i r s t a s s u m i n g no f a d i n g , the s e c o n d a s s u m i n g m i n o r R i c i a n f a d i n g and t he t h i r d a s s u m i n g a R a y l e i g h f a d i n g . I n C h a p t e r 4 t h e c h o i c e of the o p e r a t i n g f r e q u e n c y i s d i s c u s s e d , a s i m p l e h e t e r o d y n e RF s y s t e m i s p r o p o s e d a n d , b a s e d on a v a i l a b l e componen ts , an RF s i g n a l power budge t f o r t he RF s y s t e m i s c a l c u l a t e d . From t h i s c a l c u l a t i o n , the r e q u i r e d comb ined g a i n of node and s u b s c r i b e r a n t e n n a i s d e t e r m i n e d . C h a p t e r 5 summar i zes t he a n t e n n a s y s t e m r e q u i r e m e n t s , d i s c u s s e s some p o s s i b i l i t i e s and t he s e l e c t e d s y s t e m i s e n g i n e e r e d . A n a l y t i c d e t e r m i n a t i o n o f the i n p u t impedance a t v a r i o u s p l a n e s of r e f e r e n c e s i n t h e node a n t e n n a s t r u c t u r e i s a v a i l a b l e i n t h e l i t e r a t u r e . The s i z e ( r a d i u s ) and d e p t h of p r o t r u s i o n o f p r o b e , s i z e ( r a d i u s ) o f c o a x i a l a p e r t u r e and p o s i t i o n of 8 s h o r t i n g p l u n g e r s can be v a r i e d to p r o v i d e impedance m a t c h i n g . C o n s t r u c t i o n d e t a i l s o f node and s u b s c r i b e r antennas a r e a l s o i n c l u d e d . C h a p t e r 6 p r e s e n t s the t e s t r e s u l t s of the RF s y s t e m . I n d o o r f r e e space p r o p a g a t i o n c h a r a c t e r i s t i c s and l o s s e s t h r o u g h v a r i o u s b u i l d i n g m a t e r i a l s a r e d e t e r m i n e d . The g a i n s and r a d i a t i o n p a t t e r n s of the node a n t e n n a and s u b s c r i b e r d i e l e c t r i c r o d antennas a r e e x p e r i m e n t a l l y measured and r e c o r d e d . A l a r g e number of e m p i r i c a l d a t a of R C L ' s ( r e c e i v e d c a r r i e r l e v e l s ) a r e s t a t i s t i c a l l y a n a l y z e d to d e t e r m i n e the c h a r a c t e r i s t i c s and the e x t e n t of f a d i n g . C h a p t e r 7 c o n c l u d e s t h a t the RF sys tem o p e r a t i n g i n the assumed e n v i r o n m e n t i s p o s s i b l e . Recommendations f o r f u r t h e r r e s e a r c h a r e made w i t h r e g a r d to c o s t r e d u c t i o n p o s s i b i l i t i e s i n RF sys tem i m p l e m e n t a t i o n and the m e r i t s o f o t h e r SSMA t e c h n i q u e s such as FHCDMA ( f r e q u e n c y h o p p i n g ) o r H y b r i d FH-DSCDMA. P r o s and cons of u s i n g o t h e r m o d u l a t i o n schemes , e r r o r d e t e c t i o n or c o r r e c t i o n c o d i n g and p r o t o c o l i m p l e m e n t a t i o n e t c . a r e a l s o d i s c u s s e d . A l i s t of r e f e r e n c e s i s p r e s e n t e d i n C h a p t e r 8. 9 CHAPTER 2 OVERALL SYSTEM REQUIREMENTS 2 .1 F u n c t i o n a l R e q u i r e m e n t s T h e r e i s s u f f i c i e n t e v i d e n c e t h a t ISDN w i l l be i m p l e m e n t e d w o r l d w i d e [ 2 ] . A c c o r d i n g l y , t he v e r y f i r s t r e q u i r e m e n t f o r t h i s s y s t e m i s ISDN c o m p a t i b i l i t y . F i g u r e 2 .1 shows t he p r o p o s e d RLAN c o n f i g u r a t i o n . The s y s t e m p r o v i d e s f u l l d u p l e x w i r e l e s s i n d o o r c o m m u n i c a t i o n s f o r a maximum of 200 s u b s c r i b e r s v i a a p o i n t t o m u l t i p o i n t s t a r c o n f i g u r a t i o n . The d a t a r a t e f r o m e a c h s u b s c r i b e r i s assumed t o be 192 K B P S , e q u i v a l e n t t o 2B+D ISDN c h a n n e l s . The a r e a o f c o v e r a g e w o u l d be a p p r o x i m a t e l y a c i r c l e o f 20 m e t r e s r a d i u s on t h e same f l o o r . The c e n t r a l node p r o v i d e s a s y n c h r o n o u s m u l t i p l e a c c e s s f o r a l l t he s u b s c r i b e r s . I t a l s o p r o v i d e s s w i t c h i n g i n t e r n a l l y f o r a l l t h e s u b s c r i b e r s as w e l l as e x t e r n a l l y t o t e l e p h o n e t r u n k s o r d a t a l i n k s . O t h e r a u x i l i a r y f u n c t i o n s s u c h a s s i g n a l l i n g , a l a r m s u p e r v i s i o n , i m p l e m e n t a t i o n of s t a n d a r d c o m m u n i c a t i o n p r o t o c o l and e r r o r d e t e c t i o n o r c o r r e c t i o n c o d i n g e t c . , a r e a l s o r e q u i r e d . 2 . 2 E n v i r o n m e n t a l R e q u i r e m e n t s The s y s t e m i s i n t e n d e d t o o p e r a t e i n a modern o f f i c e e n v i r o n m e n t . A t y p i c a l o f f i c e comp lex i s c h a r a c t e r i z e d by a w i d e open f l o o r p l a n , m e a s u r i n g a p p r o x i m a t e l y 40 m e t r e x 40 m e t r e w i t h a f i n i s h e d c e i l i n g h e i g h t o f a t l e a s t 2 . 4 4 m e t r e s (8 f e e t ) . I n d i v i d u a l o f f i c e s o r w o r k s t a t i o n s a r e fo rmed by p a r t i t i o n s w h i c h a r e u s u a l l y 1 .5 me t res (5 f e e t ) h i g h . 10 A PC PC PH L PHX SUBSCRIBER NO. 1 SUBSCRIBER'NO. 2 \ NODE ANTENNA / PC L PH SUBSCRIBER NO. M FLOOR i FLOOR J FLOOR K MAIN FRAME COMPUTER SWITCHING PROTOCOL SIGNALLING & ALARM SUPERVISORY —TO/FROM TELEPHONE TRUNKS _AND DATA LINKS TO/FROM ALARM SURVEILLANCE AND CONTROL EQUIPMENT LEGEND: M t NUMBER OF SUBSCRIBERS 20 < M < 200 i , J & K NEED NOT BE ALL DIFFERENT PC • PERSONAL COMPUTER PH = PHONE Figure 2.1 - Proposed RLAN System 11 By r e s t r i c t i n g t he EIRP ( e f f e c t i v e i s o t r o p i c a l l y r a d i a t e d power ) t o a l e v e l b e l o w 100 m i l l i w a t t (+20 dBm) , i t i s h i g h l y p r o b a b l e t h a t t he s y s t e m can o p e r a t e w i t h o u t f r e q u e n c y l i c e n s i n g o r code r e g u l a t i o n s [ 5 9 ] . A n o t h e r f a c t o r f a v o u r i n g l ow s i g n a l s p e c t r a l d e n s i t y o p e r a t i o n i s t he a l l e v i a t i o n of o f f i c e w o r k e r s ' c o n c e r n of r a d i a t i o n h a z a r d . I n summary, t he s y s t e m ough t t o o p e r a t e i n a p o w e r - l i m i t e d bu t w i d e b a n d w i d t h c o n d i t i o n . I t s h o u l d be n o n - i n t e r f e r i n g , i n t e r f e r e n c e r e s i s t a n t and a b l e t o m a i n t a i n p e r f o r m a n c e i n an i n d o o r o f f i c e e n v i r o n m e n t . H e a l t h r e l a t e d c o n c e r n s of i n d o o r r a d i a t i o n , w h e t h e r f ounded o r u n f o u n d e d , a l s o need t o be a d d r e s s e d . One s o l u t i o n w o u l d be t o c o n f i n e r a d i a t i o n t o a r e g i o n o f space s e l d o m o c c u p i e d by the o f f i c e w o r k e r s . The r e q u i r e m e n t s of l ow s p e c t r a l d e n s i t y , w ide b a n d w i d t h , a n t i - f a d i n g and a n t i - i n t e r f e r e n c e s u g g e s t t he use o f s p r e a d s p e c t r u m t e c h n i q u e s . 2 . 3 G l o b a l S y s t e m P e r f o r m a n c e R e q u i r e m e n t s The most c r i t i c a l p e r f o r m a n c e f o r d i g i t a l c o m m u n i c a t i o n i s BER ( b i t e r r o r r a t e ) . I f t h i s s y s t e m I s t o f u n c t i o n as a h i g h p e r f o r m a n c e medium t o h i g h speed R L A N , t he BER s h o u l d be k e p t r e a s o n a b l y low ( 1 0 - b o r l e s s ) . T h i s i s t he " r a w " BER a f t e r d e s p r e a d i n g bu t b e f o r e e r r o r c o r r e c t i o n o r d e t e c t i o n . As m e n t i o n e d i n S e c t i o n 2 . 1 , s t a n d a r d p r o t o c o l s u c h as X . 2 5 and e r r o r d e t e c t i o n o r c o r r e c t i o n c o d i n g need t o be i n c o r p o r a t e d (bu t t hey a r e no t c o n s i d e r e d h e r e ) . The i n c o r p o r a t i o n of p r o t o c o l and e r r o r d e t e c t i o n o r c o r r e c t i o n c o d i n g w i l l e n s u r e d a t a i n t e g r i t y so t h a t t he f i n a l BER w i l l a l w a y s be e x t r e m e l y s m a l l . The p e n a l t y i s r e t r a n s m i s s i o n s w h i c h s l o w down 12 t he r a t e of d a t a t r a n s f e r . To m a i n t a i n an a c c e p t a b l e e f f i c i e n c y , t he raw BER s h o u l d no t e x c e e d 1 0 " 6 . The O c t o b e r 1984 CCITT recommenda t i ons have a l l o w e d 64 KBPS f o r c o d i n g o f v o i c e s i g n a l bu t a t p r e s e n t t h i s can a l r e a d y be a c c o m p l i s h e d u s i n g o n l y 32 KBPS so t h a t t he v a c a n c y c a n p r o b a b l y be u s e d f o r e r r o r c o d i n g , p r o t o c o l i m p l e m e n t a t i o n , a l a r m s u p e r v i s o r y and o t h e r h o u s e k e e p i n g f u n c t i o n s . 13 CHAPTER 3 I N I T I A L SSMA CONSIDERATIONS 3 .1 P r o b l e m s o f I n d o o r W i r e l e s s C o m m u n i c a t i o n s The d i f f i c u l t i e s o f IWC a r e u n p r e d i c t a b l e f a d i n g and i n t e r f e r e n c e [ 1 1 ] . RF p r o p a g a t i o n i n d o o r i s c h a r a c t e r i z e d b y : - M u l t i p a t h f a d i n g due t o t h e s c a t t e r i n g o f RF s i g n a l by w a l l s , w i n d o w s , f u r n i t u r e as w e l l as random s c a t t e r i n g by o f f i c e w o r k e r s . - Shadow f a d i n g and a t t e n u a t i o n due t o b l o c k a g e of RF s i g n a l by f i x e d o b j e c t s s u c h as p a r t i t i o n s , p o s t s and w a l l s . - I n t e r f e r e n c e f r o m o t h e r s u b s c r i b e r s u s i n g t h e same s y s t e m and i n t e r f e r e n c e f r om o t h e r RF sys tems s h a r i n g the same b u i l d i n g . S e v e r a l methods c o u l d be u s e d t o r e d u c e t he e f f e c t o f f a d i n g . D i v e r s i t y s w i t c h i n g o r c o m b i n i n g [15] i s one and SSMA i s a n o t h e r . 3 . 2 P r o p e r t i e s o f SSMA The p r o p e r t i e s of SSMA a r e u t i l i z e d t o combat the u n p r e d i c t a b l e f a d i n g o f i n d o o r t r a n s m i s s i o n [ 2 3 ] . These p r o p e r t i e s a r e : - a n t i - i n t e r f e r i n g and n o n - i n t e r f e r i n g - a n t i - m u l t i p a t h O t h e r u s e f u l p r o p e r t i e s a r e : - f l e x i b l e g r o w t h and g r a c e f u l o v e r l o a d d e g r a d a t i o n - low s i g n a l power s p e c t r a l d e n s i t y - p r i v a c y a g a i n s t c a s u a l e a v e s d r o p p i n g . 14 A l t h o u g h s p r e a d s p e c t r u m t e c h n i q u e s have been and s t i l l a r e c o n f i n e d t o m i l i t a r y a p p l i c a t i o n s , the a p p l i c a t i o n s p e c t r u m i s s p r e a d i n g t o t he c o m m e r c i a l a r e a . One s t r o n g e v i d e n c e i s t he r e c e n t F . C . C . ( F e d e r a l C o m m u n i c a t i o n s C o m m i s s i o n ) a p p r o v a l o f the ISM ( I n d u s t r i a l , S c i e n t i f i c and M e d i c a l ) and amateur bands f o r s p r e a d s p e c t r u m a p p l i c a t i o n [ 2 6 ] . The r e g u l a t o r y body must have r e g a r d e d SS as a b e t t e r a l t e r n a t i v e , o t h e r w i s e i t w o u l d no t have a p p r o v e d o r e n c o u r a g e d i t s u s e b e f o r e i t s f u l l d e v e l o p m e n t . A n o t h e r e v i d e n c e i s t he announcement by a c o n s o r t i u m o f J a p a n e s e , German, F r e n c h and D u t c h m a n u f a c t u r e r s i n c l u d i n g G r u n d i g A . G . Thomson -B rand t and N . V . P h i l i p s , on t h e i r i n t e n t i o n to d e v e l o p SS h i g h f i d e l i t y d i g i t a l b r o a d c a s t . These a r e p r o b a b l y e a r l y i n d i c a t i o n s t h a t b roadband low s p e c t r a l d e n s i t y SS sys tems w i l l soon be r e p l a c i n g c o n v e n t i o n a l h i g h power n a r r o w band s y s t e m s . The l i t e r a t u r e abounds w i t h SS r e s e a r c h e s and r e f e r e n c e s [27 t o 46] h e r e a r e o n l y a p a r t i a l l i s t r e l e v a n t t o t h i s w o r k . S i n c e t he p r o p e r t i e s of CDMA a r e q u i t e c r i t i c a l t o t he d e s i g n of t he o v e r a l l s y s t e m , the o p e r a t i o n o f CDMA d e s e r v e s some e x p l a n a t i o n s . The o p e r a t i n g p r i n c i p l e o f CDMA c a n b e s t be i l l u s t r a t e d by an a n a -l o g y . Imag ine a room f i l l e d w i t h P (an i n t e g e r > 2) p a i r s of p e r s o n s . I t i s d i f f i c u l t o r even i m p o s s i b l e t o have a l l P p a i r s t r y i n g t o c o n v e r s e a t t h e same t i m e . Howeve r , i f each p a i r o f the P p a i r s c o n v e r s e i n a l a n g u a g e o f t h e i r own, i t i s p o s s i b l e t o have a l l P p a i r s c o m m u n i c a t i n g s i m u l t a n e o u s -l y . T h i s i s p o s s i b l e p r o v i d e d t h a t a l l P l a n g u a g e s a r e r a d i c a l l y d i f f e r e n t . A measure of s i m i l a r i t y ( o f random p r o c e s s e s ) i s c o r r e l a t i o n . F o r s i m p l i c i -t y assume P = 3 and t h e l a n g u a g e s u s e d a r e E n g l i s h , C h i n e s e and A r a b i c . The 15 a u t o c o r r e l a t i o n ( i . e . E n g l i s h x E n g l i s h , C h i n e s e x C h i n e s e o r A r a b i c x A r a b i c ) s h o u l d be l a r g e compared t o c r o s s c o r r e l a t i o n s ( i . e . E n g l i s h x C h i n e s e , E n g l i s h x A r a b i c , A r a b i c x C h i n e s e ) . The E n g l i s h r e c e i v e r w i l l e x t r a c t t he E n g l i s h i n f o r m a t i o n t h r o u g h a u t o c o r r e l a t i o n and i g n o r e t h e sum o f c r o s s c o r r e l a t i o n s of E n g l i s h x C h i n e s e and E n g l i s h x A r a b i c as n o i s e . I n o r d e r t o make t he r e c o v e r e d i n f o r m a t i o n t o n o i s e r a t i o h i g h , i t i s n e c e s s a r y t o have an a u t o c o r r e l a t i o n of a l m o s t one w h i l e k e e p i n g t he sum o f c r o s s c o r r e l a t i o n s a l m o s t z e r o on a n o r m a l i z e d b a s e . C a r r y i n g t h i s a n a l o g y t o CDMA, the code d i v i s i o n i s a n a l o g o u s t o l a n g u a g e d i v i s i o n . I n p a r t i c u l a r , f o r DSCDMA ( d i r e c t sequence code d i v i s i o n m u l t i p l e a c c e s s ) , the 2P s u b s c r i b e r s a r e a s s i g n e d p a i r w i s e a PR (pseudo random) o r PN (pseudo n o i s e ) c o d e , i . e . t h e y a r e g i v e n the a l g o r i t h m f o r g e n e r a t i n g t he PN code ( a n a l o g o u s t o b e i n g t a u g h t a l a n g u a g e ) . The code g e n e r a t o r s a t t h e t r a n s m i t and r e c e i v e end a r e assumed s y n c h r o n i z e d . A t t he t r a n s m i t end s p e c t r u m s p r e a d i n g i s a c c o m p l i s h e d by m u l t i p l y i n g t he d a t a s t r e a m by t h e PN c o d e . D e s p r e a d i n g a t t he r e c e i v e end i s a c c o m p l i s h e d by c o r r e l a t i o n w i t h t he same c o d e . The n o r m a l i z e d a u t o c o r r e l a t i o n s h o u l d be a l m o s t u n i t y and n o r m a l i z e d c r o s s - c o r r e l a t i o n s h o u l d be a l m o s t z e r o . I n a d d i t i o n , i n o r d e r t o be a b l e t o d i s c r i m i n a t e a g a i n s t echoes o r d e l a y e d r e p l i c a s o f a t r a n s m i s s i o n c a u s e d b y r e f l e c t i o n , m u l t i p a t h f a d i n g o r l o s s o f c o d e s y n c h r o n i z a t i o n , a u t o c o r r e l a t i o n R( T ) (where x i s the t ime d e l a y ) s h o u l d be a l m o s t z e r o f o r i + 0 . I n summary t he d e s i r a b l e p r o p e r t i e s of codes c . , c . a r e : 16 ^ , ( - 0 - / C . ( t ) C . ( t - T ) d t i j o 1 J R. . ( x ) » 0 f o r a l l t and A T R . . ( T ) = / C . ( t ) C * ( t - T ) d t 0 R . . ( x ) ** 0 f o r x * 0 i i v R . . ( T ) » 1 f o r T = 0 i i A A where T = p e r i o d o f d a t a s t r e a m , t = t i m e d e l a y . The d e s i g n of t h e s e PN codes i s most c r i t i c a l f o r CDMA o p e r a t i o n . A good s u r v e y o f codes s u i t a b l e f o r DSCDMA i m p l e m e n t a t i o n i s g i v e n by P u r s l e y and S a r w a t e [ 2 5 ] . F o r G o l d codes o r max ima l l e n g t h codes [25] t h e r a t i o of R i i ( 0 ) t o R ^ C x ) i s L = 2 -1 where L i s t he code l e n g t h . T h i s i n t e g e r L i s a l s o known as the s p r e a d r a t i o , s p r e a d g a i n o r p r o c e s s g a i n (when e x p r e s s e d i n d B ) , o f the s p e c t r u m s p r e a d i n g . I n a t y p i c a l DSCDMA s y s t e m , o n l y a p p r o x i m a t e l y 5% o f t he t o t a l L pseudorandom codes a r e a s s i g n e d t o t he 2P s u b s c r i b e r s . When t h e s y s t e m expands beyond t he 2P l i m i t , t he l a r g e r e s e r v e of u n a s s i g n e d codes can be u s e d t o accommodate o v e r l o a d . The i n t e r f e r e n c e n o i s e , c a u s e d by t he summa-t i o n of c r o s s - c o r r e l a t i o n s w i l l o f c o u r s e be e x p e c t e d t o i n c r e a s e above t h e d e s i g n e d l i m i t . T h i s f e a t u r e of t r a d i n g p e r f o r m a n c e d e g r a d a t i o n f o r s y s t e m 17 o v e r l o a d i s c a l l e d g r a c e f u l d e g r a d a t i o n . F o r t e l e c o m m u n i c a t i o n o p e r a t o r s , s u c h as ma jo r t e l e p h o n e c o m p a n i e s , s e r v i c e e x p a n s i o n beyond d e s i g n l i m i t i s o f t e n t h e norm r a t h e r t h a n e x c e p t i o n . Such g r a c e f u l o v e r l o a d i s an e x t r e m e l y d e s i r a b l e f e a t u r e . A p r i v a t e ( b u t no t s e c u r e ) s y s t e m i s p o s s i b l e s i n c e t he code s p r e a d has the ne t e f f e c t o f t r a d i n g r e d u c t i o n o f s i g n a l power s p e c t r a l d e n s i t y f o r i n c r e a s e of b a n d w i d t h . I t i s d i f f i c u l t i f no t i m p o s s i b l e f o r a c a s u a l e a v e s d r o p p e r t o t r y t o e x t r a c t m e a n i n g f u l i n f o r m a t i o n f r o m w ide band low s p e c t r a l d e n s i t y n o i s e l i k e t r a n s m i s s i o n . S e c u r i t y however i s no t p o s s i b l e [25] w i t h o u t a d d i t i o n a l d a t a e n c r y p t i o n b e c a u s e t he PN o r PR code i s p e r i o d i c and i t s a l g e b r a i c s t r u c t u r e o r g e n e r a t i o n a l g o r i t h m c a n s t i l l be d e c i p h e r e d by t e c h n i c a l l y e q u i p p e d e a v e s d r o p p e r s . 3 . 3 P r e l i m i n a r y D e s i g n C o n s i d e r a t i o n s 3 . 3 . 1 Type o f m o d u l a t i o n and SSMA The c h o i c e o f t he t y p e o f m o d u l a t i o n and SSMA depends on v a r i o u s p a r a m e t e r s s u c h as b i t e r r o r r a t e , RF b a n d w i d t h , RF s i g n a l power , t y p e of f a d i n g and t y p e of t r a f f i c e t c . A p r o p e r c h o i c e c a n be made o n l y a f t e r c o n s i d e r a t i o n of t h e s e p e r t i n e n t f a c t o r s . T h i s w i l l be f u r t h e r d i s c u s s e d i n C h a p t e r 7 . S i n c e t h e work h e r e o n l y c o n c e r n s RF f e a s i b i l i t y , t he r e l a t i v e l y s i m p l e D i r e c t Sequence Code D i v i s i o n M u l t i p l e A c c e s s (DSCDMA) u s i n g B i n a r y P h a s e S h i f t K e y i n g (BPSK) i s a s s u m e d . T h i s i s s i m p l e o n l y i n t h e s e n s e t h a t f a s t s e t t l i n g f r e q u e n c y s y n t h e s i z e r s o r s w i t c h e s a r e no t r e q u i r e d . 18 3 . 3 . 2 B i t e r r o r r a t e and code l e n g t h P e r f o r m a n c e i s b e s t gauged by BER ( b i t e r r o r r a t e ) . F o r BPSK m o d u l a t i o n t he p r o b a b i l i t y o f e r r o r P g i s g i v e n by [ 6 1 ] , P = BER = Q(j _ ! ) N o N 0 w h e r e — i s t h e t w o - s i d e d s p e c t r a l d e n s i t y o f G a u s s i a n w h i t e n o i s e . E g i s t he s i g n a l power s t r e n g t h and Q i s the f u n c t i o n d e f i n e d a s 2 a oo Q ( x ) - 1 / e 2 d a x N 0 F o r B P S K DSCDMA t h e e x p r e s s i o n f o r P i s s t i l l v a l i d i f — , t he e 2 n o i s e t e r m , i s g e n e r a l i z e d t o i n c l u d e N , , N . , and N c , w h i c h a r e t he » o t h ' i n t f a d e n o i s e components due t o t h e r m a l e f f e c t s , i n t e r f e r e n c e ( f r o m c o - s y s t e m u s e r and o t h e r s y s t e m s ) and f a d i n g , r e s p e c t i v e l y . I n t e r m o d u l a t i o n n o i s e i s assumed t o be c o m p a r a t i v e l y s m a l l a n d , t h e r e f o r e i g n o r e d . N . i s c a u s e d by t he n o n - o r t h o g o n a l i t y o f t he s p r e a d i n g c o d e s , i . e . , i n t t h e c r o s s - c o r r e l a t i o n o f s u b s c r i b e r i w i t h o t h e r s u b s c r i b e r s i s non z e r o , and u s u a l l y depends on t he t y p e of s p r e a d code u s e d . A s s u m i n g an ML ( m a x i m a l l e n g t h ) b i n a r y s e q u e n c e , t h e m a g n i t u d e o f s i d e l o b e e n e r g y i s y-( w h e r e L=2 - 1 i s t h e code l e n g t h ) o f t he magn i t ude of a u t o c o r r e l a t i o n peak as shown i n F i g . 3 . 3 . 1 . N „ , i s c a u s e d by t h e n o n - z e r o a u t o c o r r e l a t i o n o f s i g n a l w i t h t he f a d e 19 R ^ ( T ) N o r m a l i z e d A u t o c o r r e l a t i o n • 1 .0 t i m e d e l a y T LEGEND: L = 2 - 1 i s t h e s p r e a d r a t i o o r s p r e a d g a i n = c h i p p e r i o d F i g u r e 3 . 3 . 1 - T y p i c a l a u t o c o r r e l a t i o n o u t p u t 20 d e l a y e d r e p l i c a s of i t s e l f p l u s the summat ion of n o n - z e r o c r o s s - c o r r e l a t i o n o f s i g n a l w i t h f a d e d r e p l i c a s of o t h e r s i g n a l s . F o r m a x i m a l l e n g t h s e q u e n c e , when t he d e l a y i s l a r g e r t h a n 1 c h i p p e r i o d , ( w h i c h i s assumed t o be ^- o f t he d a t a p e r i o d T ) , the a u t o c o r r e l a t i o n o r c r o s s - c o r r e l a t i o n i s i o f t h e a u t o c o r r e l a t i o n p e a k . M u c h w o r k i n t h e l i t e r a t u r e i s d i r e c t e d t o e s t i m a t i n g t he N,. , and ° f a d e N . c o m p o n e n t s . D i s c u s s i o n o f t h e v a l i d i t y o f t r e a t i n g t h e s e n o i s e i n t components as G a u s s i a n n o i s e i s p r e s e n t e d i n [ 2 8 ] . V a r i o u s m e t h o d s , s u c h as moment s p a c e i n e q u a l i t i e s [ 4 0 ] , c h a r a c t e r i s t i c f u n c t i o n [33] and compute r s i m u l a t i o n a r e a v a i l a b l e . W h i l e t he i d e a m igh t be s i m p l e , the m a t h e m a t i c a l a n a l y s i s c o u l d ge t u n t r a c t a b l e , e s p e c i a l l y i f non G a u s s i a n s t a t i s t i c s a r e i n v o l v e d . D e p e n d i n g on t h e r e l a t i v e l e v e l o f t h e s e t h r e e n o i s e c o m p o n e n t s , a s y s t e m c o u l d be c l a s s i f i e d as t h e r m a l n o i s e l i m i t e d (when N ^ d o m i n a t e s ) , i n t e r f e r e n c e l i m i t e d ( w h e n N ^ n f c d o m i n a t e s ) o r f a d i n g l i m i t e d (when N ^ a ^ e d o m i n a t e s ) . W i t h p r o p e r RF d e s i g n , N ^ i s u s u a l l y s m a l l . To i l l u s t r a t e t he i m p o r t a n c e o f f a d i n g , t he code l e n g t h s r e q u i r e d a r e c a l c u l a t e d u n d e r t h r e e c o n d i t i o n s : 1 . N o - f a d i n g F o r a s y n c h r o n o u s BPSK-DSCDMA o p e r a t i n g i n a no f a d i n g e n v i r o n m e n t , t h e r e c e i v e r i s o p e r a t i n g i n an i n t e r f e r e n c e l i m i t e d c o n d i t i o n and i t s p e r f o r m a n c e i s g i v e n by T u r i n [28] -1-1 SNR M - l o _3L 2 E s J 21 where SNR = s i g n a l t o n o i s e r a t i o . M = number o f u s e r s L = s p r e a d r a t i o . N A s s u m i n g s m a l l ( t y p i c a l o f a p r o p e r l y d e s i g n RF s y s t e m ) , t he s i n t e r f e r e n c e l i m i t e d - 1 SNR M-l 3L 3L M-l F o r a s p e c i f i e d P , and k n o w i n g t he t y p e o f m o d u l a t i o n (BPSK i n t h i s c a s e ) p g = Q(7 SNR) M - l 199 L = — SNR = — x 2 2 . 5 6 = 1497 3 3 k T h e s m a l l e s t i n t e g e r k s u c h t h a t 2 - 1 > 1497 i s k = 1 1 , so t h a t s p r e a d r a t i o L = 2 0 4 7 . 2 . R i c i a n f a d i n g F o r t h e s y s t e m o p e r a t i n g i n a R i c i a n f a d i n g e n v i r o n m e n t , t he e v a l u a t i o n o f t he p r o b a b i l i t y o f e r r o r and s i g n a l t o n o i s e r a t i o i s g i v e n by [30] [33] and [ 4 2 ] . S i n c e t he o b j e c t i v e h e r e i s t o d e t e r m i n e f e a s i b i l i t y , a s i m p l i f i e d a p p r o a c h y i e l d i n g a p e s s i m i s t i c bu t c o n s e r v a t i v e r e s u l t can be u s e d . F i g u r e 3 . 3 . 2 . 1 shows t he p h a s o r r e p r e s e n t a t i o n o f a R i c i a n f a d i n g p r o c e s s a 2 2 v a o x 2v - t . JL) exp ( - 1-) I o ( — i ) r 2 r 2 r 2 P(v) = — exp ( -2 Figure 3.3.2.1 - Phasor representation of R i c i a n fading 23 T h e a s s u m p t i o n s f o r r a r e t h a t t he magn i t ude | r | f o l l o w s a G a u s s i a n d i s t r i b u t i o n and t he phase of r f o l l o w s a u n i f o r m d i s t r i b u t i o n o v e r t he 0 t o 2u i n t e r v a l . The p r e s e n c e o f t he f a d e d s i g n a l has two s i g n i f i c a n t e f f e c t s : 1 . I t changes t h e o b s e r v a b l e s i g n a l f r o m t h e s p e c u l a r component [ a g | t o |I s + r|. 2 . I t i n c r e a s e s t he n o i s e l e v e l . The w o r s t c a s e SNR o c c u r s when | a g + r | i s m i n i m u m and t he t o t a l n o i s e l e v e l i s a t a p e a k . S i g n a l l e v e l | a + r | i s a t a minimum when a and r i s 180° ou t of s s p h a s e . T h e n o i s e l e v e l p e a k s when r p l u s t h e sum o f a l l o t h e r u s e r i n t e r f e r e n c e s add i n phase a - r a - r /SNR S S w o r s t c a s e / . r l , 7 . / N + - + r - ( m - l ) mr L L L F o r the non f a d e d c a s e •^SNR - S = /3Q.71 where N i s t he t h e r m a l p l u s i n t e r f e r e n c e n o i s e . d e f i n i n g Y = — a 1 - Y /SNR w o r s t c a s e 1 + y( ^ U ( ^ ) / 3 0 . 7 1 2047 To m a i n t a i n a BER p e r f o r m a n c e of 1 0 " 24 /§NR " > Z22.56 so _ , 1 ~ — > 4.75 w o r s t c a s e 1 + y( ) y < 9.76% T h i s shows t h a t up t o 9.76% o f f a d i n g can be t o l e r a t e d . 3. R a y l e i g h f a d i n g F o r t h e same s y s t e m o p e r a t i n g i n a R a y l e i g h f a d i n g e n v i r o n m e n t M - l G a r d n e r [34] g i v e s t h e a s y m p t o t i c P as P " —. T h i s a s y m p t o t i c P c a n n o t e e Li e be i m p r o v e d by i n c r e a s e o f SNR above a " s a t u r a t e d SNR t h r e s h o l d " . F o r P = 10"6 & M = 200 e L has to be a t l e a s t 199 x 10 6 k = t h e s m a l l e s t i n t e g e r l a r g e r t h a n l o g 2 L = 28 so t h a t L , the code l e n g t h o r s p r e a d r a t i o i s L = 2 2 8 - l = 2.684 x 10 8 . T h e s e t h r e e c a l c u l a t i o n s show t h a t f o r t he t y p e o f s y s t e m p r o p o s e d h e r e , f a d i n g i s an i m p o r t a n t c o n s i d e r a t i o n . I f t h e r e i s m i n o r R i c i a n f a d i n g , minimum b a n d w i d t h o f 2 x 192 x 2047 KHz = 786 MHz w i l l s u f f i c e , w h e r e a s w i t h R a y l e i g h f a d i n g , f o r t h e s y s t e m t o meet t h e same BER r e q u i r e m e n t , t he minimum b a n d w i d t h needed w i l l be 2 x 192 x 2.684 x 10 KHz = 1.03 x 10 5 GHz . I t i s no t v e r y l i k e l y s u c h a b a n d w i d t h c a n be met by any RF d e s i g n a t a l l n o r a r e t h e r e ha rdwa re f a s t enough f o r t he s p r e a d i n g code i m p l e m e n t a t i o n . E i t h e r a r e l a x a t i o n o f BER o r some f o r m of d i v e r s i t y t o i m p r o v e the r e c e i v e r p e r f o r m a n c e i s n e e d e d . 25 3 . 3 . 3 F a d i n g K e n n e d y [ 6 0 ] a n d S c h w a r t z e t a l . [ 21 ] g i v e a v e r y g o o d p h e n o m e n o l o g i c a l and m a t h e m a t i c a l a c c o u n t of f a d i n g . A s i m p l i f i e d a p p r o a c h i s t a k e n h e r e by c l a s s i f y i n g f a d i n g b r o a d l y i n t o two c l a s s e s ( a l t h o u g h i n a s t r i c t s e n s e , R a y l e i g h f a d i n g c o r r e s p o n d s to t he s p e c i a l c a s e o f R i c i a n f a d i n g w i t h l a r g e K = r a n d o m / s p e c u l a r power r a t i o ) : 1 . R a y l e i g h f a d i n g - where t h e r e i s no s t a b l e s t r o n g p a t h , a l l p a t h s a r e s t a t i s t i c a l l y random i n b o t h phase and a t t e n u a t i o n . 2 . R i c i a n f a d i n g - where t h e r e i s one s t a b l e s t r o n g s i g n a l ( t h e s p e c u l a r component ) and a l l f a d i n g p a t h s a r e s m a l l i n c o m p a r i s o n t o i t . The p e r f o r m a n c e o f SSCDMA u n d e r t h e s e two c o n d i t i o n s [27 t o 3 0 , 3 3 , 38 and 40 to 46] has been m o d e l l e d and i n v e s t i g a t e d w i t h t he f o l l o w i n g c o n c l u s i o n s : a . R a y l e i g h f a d i n g i s d e t r i m e n t a l t o SSCDMA. I t i s i m p o s s i b l e t o m a i n t a i n a low BER u n l e s s an e x c e p t i o n a l l y l o n g code r e q u i r i n g an a l m o s t i n f i n i t e l y l a r g e b a n d w i d t h i s u s e d o r some o t h e r method o f r e d u c i n g t he e f f e c t o f f a d i n g s u c h as d i v e r s i t y s w i t c h i n g o r c o m b i n i n g i s u s e d . b . R i c i a n f a d i n g c a n be t o l e r a t e d by DSCDMA, p r o v i d e d t he K r a t i o f a d e d component s i g n a l p o w e r / s t a b l e component s i g n a l power i s no t t o o l a r g e . B u l t i t u d e and Mahmoud f o u n d t h a t [20] f o r 8 0 0 / 9 0 0 MHz, i n d o o r f a d i n g i s R i c i a n i n t h e a b s e n c e of m o b i l e b l o c k a g e r e g a r d l e s s of w h e t h e r o r no t t h e r e i s l i n e - o f - s i g h t be tween t r a n s m i t t e r and r e c e i v e r . I t i s no t c e r t a i n i f t h i s i s a l s o t r u e f o r 60 GHz. Howeve r , b l o c k a g e of s i g n a l by m o b i l e o b j e c t s s u c h as human b e i n g s c o u l d s u b s t a n t i a l l y r e d u c e t h e ma in s i g n a l , h e n c e i n c r e a s e K and change t he s t a t i s t i c s f r om R i c i a n t o R a y l e i g h . To 26 m i n i m i z e t he amount o f f a d i n g , a l i n e - o f - s i g h t p a t h i s p r e f e r r e d . The RF s y s t e m must p r o p a g a t e t h r o u g h some c l e a r s p a c e i n o r d e r t o a v o i d s c a t t e r i n g and b l o c k a g e . A t 55 GHz , the c l e a r a n c e ( 0 . 6 x f i r s t F r e s n e l zone ) r e q u i r e d a t t h e m id p o i n t o f a 20 me t re l i n k , wou ld be l e s s t h a n 7 cm [ 6 2 ] . A s s u m i n g t h e a v e r a g e o f f i c e w o r k e r ' s h e i g h t t o be 1 .75 m e t r e s ( 5 ' 9 " ) , t he l a y e r of s p a c e f r o m 6 f e e t t o 8 f e e t i s f r e e and c l e a r . T h i s l a y e r of space can s e r v e as a c o m m u n i c a t i o n s p a c e . To ge t a r o u n d o b s t a c l e s s u c h as o c c a s i o n a l p o s t s o r p i l l a r s , r e f l e c t o r s c o u l d p r o b a b l y be u s e d . 27 CHAPTER 4 RADIO FREQUENCY SYSTEM DESIGN 4 . 1 G e n e r a l The u t i l i z a t i o n of r a d i o f r e q u e n c y l i n k s f o r b o t h v o i c e and d a t a t r a n s m i s s i o n s i s r a p i d l y becoming an I m p o r t a n t a r e a of IWC. Mos t r e s e a r c h e s [10 t o 20] a r e i n t he VHF (150 M H z ) , UHF (450 M H z ) , 900 MHz o r 1.2 t o 1.7 GHz b a n d s . RF p r o p a g a t i o n i n t he i n d o o r e n v i r o n m e n t i s r e g a r d e d as u n p r e d i c t a b l e . Cus tom p r o p a g a t i o n s t u d y o r d e s i g n f o r i n d i v i d u a l b u i l d i n g s i s j u s t too e x p e n s i v e . The most common method t o p r o v i d e i n d o o r p r o p a g a t i o n c o v e r a g e i s t o f l o o d t he i n d o o r a r e a w i t h s i g n a l u s i n g h i g h power (1 t o 10 w a t t s ) t r a n s m i t t e r s . Such a method i s s i m p l e but w a s t e f u l o f s i g n a l e n e r g y . I t does no t t r y t o r e d u c e the e f f e c t o f f a d i n g . O f t e n , i t c r e a t e s more t r o u b l e as the randomly s c a t t e r e d s i g n a l s add up t o an u n p r e d i c t a b l e l e v e l a t t he r e c e i v e r . I n f a c t , i n s i d e b u i l d i n g s u s i n g a s i g n a l f l o o d i n g scheme, " d e a d s p o t s " and deep f a d e s have been o b s e r v e d [ 1 2 ] . The a p p r o a c h t a k e n h e r e d i f f e r s i n t h e s t r a t e g y u s e d to h a n d l e t he u n p r e d i c t a b i l i t y o f i n d o o r p r o p a g a t i o n . By c o n f i n i n g t he s i g n a l t o a r e g i o n of space s e l d o m o c c u p i e d o r p e r t u r b e d , i t i s p o s s i b l e t o r e d u c e t he amount of f a d i n g due t o random s c a t t e r i n g . S i g n a l e n e r g y w a s t a g e i s a l s o m i n i m i z e d . A n o t h e r i m p o r t a n t f a c t o r i s t he l o n g t e r m e f f e c t o f m i l l i m e t r i c wave r a d i a t i o n on human b e i n g s . A l t h o u g h the RF r a d i a t i o n l e v e l i s w e l l w i t h i n t h e l i m i t c o n s i d e r e d s a f e by r e g u l a t o r y b o d i e s , o v e r a l o n g t e r m t h e r e i s no c o n c l u s i v e e v i d e n c e of i t s e f f e c t on h e a l t h . T h e r e a r e s i m p l y no t e s t s c o n d u c t e d l o n g enough t o d e t e c t any c o r r e l a t i o n ( o r t he l a c k of c o r r e l a t i o n ) 28 be tween h e a l t h damages and RF r a d i a t i o n . A s y s t e m w h i c h m i n i m i z e s u s e r s ' , e x p o s u r e t o r a d i a t i o n w o u l d be p r e f e r a b l e i n te rms o f p r u d e n c e and r e s p o n s i b l e e n g i n e e r i n g . 4 . 2 C h o i c e o f O p e r a t i n g F r e q u e n c y H u i s h and P u g l i e s e [22] d i d some i n d o o r p r o p a g a t i o n s t u d i e s a t 60 G H z . S p r e a d s p e c t r u m t e c h n i q u e s were no t c o n s i d e r e d i n t h e i r s y s t e m . They c o n c l u d e d t h a t any m i l l i m e t r i c f r e q u e n c y c o u l d be u s e d f o r f u t u r e d e v e l o p m e n t s . I n f a c t 3 0 - 3 5 GHz was s u g g e s t e d f o r l o w e r c o s t . The r e a s o n s f o r c h o o s i n g 60 GHz i n t h i s e x p e r i m e n t a r e : - t h e need t o r e - u s e t h e same f r e q u e n c y on d i f f e r e n t f l o o r s i n a b u i l d i n g o r i n b u i l d i n g s of c l o s e p r o x i m i t y can be s a t i s f i e d more r e a d i l y u s i n g a h i g h e r o p e r a t i n g f r e q u e n c y . A t t e n u a t i o n o f RF s i g n a l t h r o u g h m a t e r i a l i s p r o p o r t i o n a l t o • H i g h ^ w a v e l e n g t h f r e q u e n c y s i g n a l c a n be e a s i l y c o n t a i n e d w i t h i n t h e b u i l d i n g w a l l s and f l o o r s . W i t h low f r e q u e n c y s i g n a l s u c h as t he 900 MHz s y s t e m [63] p r o p o s e d by T e l e s y s t e m s SLW I n c . , p o t e n t i a l s u b s c r i b e r s w o r r y a b o u t m u t u a l i n t e r f e r e n c e . F o r s u c h a s y s t e m , some fo rm of code r e g u l a t i o n o r f r e q u e n c y c o - o r d i n a t i o n i s n e e d e d t o a v o i d c a t a s t r o p h i c p e r f o r m a n c e d e g r a d a t i o n when i d e n t i c a l s ys tems a r e o p e r a t e d i n a m u l t i - s t o r e y b u i l d i n g . F o r p r i v a t e , low range o p e r a t i o n , h i g h e r o p e r a t i n g f r e q u e n c y i s p r e f e r r e d . 29 - H i g h e r f r e q u e n c y s i g n a l p r o p a g a t e s l i k e r a y [64] and r e q u i r e s l e s s c l e a r a n c e f o r t h r e a d i n g t h r o u g h o f f i c e s p a c e f o r l i n e of s i g h t c o v e r a g e . - E l e c t r i c a l l y l a r g e s t r u c t u r e g i v i n g h i g h d i r e c t i v i t y i s p o s s i b l e w i t h p h y s i c a l l y s m a l l c o m p o n e n t s . - B a n d w i d t h c o n s i d e r a t i o n s . From S e c t i o n 3 . 3 . 2 , the s p r e a d r a t i o L o r PG ( p r o c e s s g a i n ) r e q u i r e d f o r o p e r a t i o n i n a c h a n n e l e x h i b i t i n g m i n o r R i c i a n f a d i n g c h a r a c t e r i s t i c s i s 2 0 4 7 . The m i n i m u m BW ( b a n d w i d t h ) r e q u i r e d t o s u p p o r t a d a t a r a t e o f R ^ i s 2 x R ^ x L = 2 x 192 x 2047 KHz = 786 MHz. T h i s 786 MHz r e p r e s e n t s t he ma in l o b e n u l l t o n u l l BW. To i n c l u d e t h e f i r s t s i d e l o b e a d o u b l i n g of BW i s needed so t h a t BW s h o u l d be 1 .5 GHz. RF sys tems a r e u s u a l l y c l a s s i f i e d as e i t h e r w i d e o r n a r r o w band by r a t i o ( f i s t h e c e n t r e f r e q u e n c y ) . Nar row band sys tems u s u a l l y have c l e s s t h a n 20% a n d a r e r e l a t i v e l y e a s y to d e s i g n . D e s i g n o f w i d e band c sys tems i s more d i f f i c u l t [52] b e c a u s e b r o a d b a n d i n g i n v o l v e s i n c r e a s i n g t h e d e g r e e s o f f r e e d o m ( b y i n t r o d u c i n g more c o m p o n e n t s w i t h v a r i a b l e p a r a m e t e r s ) . The PG e s t i m a t e i s b a s e d on a R i c i a n f a d i n g w i t h s p e c u l a r r a t i o o f 9.7% o r l e s s . I f t he r a t i o e x c e e d s 9.7% a n o t h e r d o u b l i n g o r even q u a d r u p l i n g o f BW m i g h t be r e q u i r e d . I n o r d e r t o keep t he RF s y s t e m na r rowband even f o r t he w o r s t c a s e , an o p e r a t i n g f r e q u e n c y o f a n o m i n a l 60 GHz i s p r e f e r r e d . 30 4 . 3 P r o p o s e d RF S y s t e m A h e t e r o d y n e s y s t e m i s p r o p o s e d . I t i s shown i n F i g u r e 4 . 3 . 1 . I n o r d e r t o be a b l e t o o p e r a t e a l i n e o f s i g h t s y s t e m , the 1 me t re o f s p a c e j u s t be low the c e i l i n g , u n o c c u p i e d by o f f i c e w o r k e r s , i s r e s e r v e d f o r RF t r a n s m i s s i o n . The c e n t r a l node and t he s u b s c r i b e r s a r e l i n k e d t o g e t h e r on t h e same h o r i z o n t a l p l a n e . The c e n t r a l node a n t e n n a w i l l be mounted 0 . 3 m e t r e be low t h e c e i l i n g . The s u b s c r i b e r a n t e n n a w i l l be mounted a t t h e same h e i g h t , on a p o l e . The p o l e has s p r i n g l o a d e d t e l e s c o p i c ends w h i c h g i v e t h e p o l e m e c h a n i c a l s t a b i l i t y when s t r u t t e d f i r m l y a g a i n s t f l o o r and c e i l i n g . RF f r o n t end equ ipment s u c h as LO ( l o c a l o s c i l l a t o r ) , up o r down c o n v e r t e r s ( m i x e r s ) , I F ( i n t e r m e d i a t e f r e q u e n c y ) a m p l i f i e r s , c i r c u l a t o r s , s p l i t t e r s and RF f i l t e r s a r e so s m a l l t h a t t h e y can be i n t e g r a t e d w i t h the a n t e n n a s . The IF w i l l t h e n be c o n n e c t e d t o t h e n o n - R F equ ipment s u c h as PSK m o d u l a t o r and code m u l t i p l i e r v i a c o a x i a l c a b l e s . I t i s no t p r a c t i c a l t o r u n RF c o n n e c t i o n s o v e r any d i s t a n c e b e c a u s e wavegu ide a t t e n u a t i o n i s s u b s t a n t i a l (more t h a n 1 d B / m ) , and RF power i s e x p e n s i v e . A 30 m i l l i w a t t RF s o u r c e c o s t s abou t $2000 bu t one of 100 m i l l i w a t t c o s t s o v e r $ 1 5 , 0 0 0 . E x t r e m e l y n a r r o w beamwid th and low s i d e l o b e s a r e d e s i r a b l e f o r s i g n a l e n e r g y s a v i n g . Howeve r , t h e s e a r e c o n f l i c t i n g r e q u i r e m e n t s as n a r r o w beam i s u s u a l l y a c c o m p a n i e d by h i g h s i d e l o b e s . A l s o when t he beams a r e too n a r r o w ( e . g . n u l l t o n u l l beamwid th of l e s s t h a n one d e g r e e ) , o r i e n t a t i o n o f a n t e n n a becomes d i f f i c u l t and even m i n o r m e c h a n i c a l d i s t u r b a n c e s , c o u l d r e s u l t i n l a r g e RCL ( r e c e i v e d c a r r i e r l e v e l ) f l u c t u a t i o n s . 31 LEGEND: f1 = 56 GHz f 2 = 52 GHz C x ( t ) = PSEUDORANDOM BINARY SEQUENCE CODES d x ( t ) = TRANSMIT DATA STREAM = 192 KBPS d x ( t ) = RECEIVE DATA STREAM = 192 KBPS PSK MOD = PHASE SHIFT KEYING MODULATOR PSK DEM = PHASE SHIFT KEYING DEMODULATOR UCM = UP CONVERSION MIXER DCM = DOWN CONVERSION MIXER BPF = BAND PASS FILTER WITH ± 2 GHz BANDWIDTH IF FLTR = INTERMEDIATE FREQUENCY FILTER IF = INTERMEDIATE FREQUENCY = 2 GHz AMP = AMPLIFIER CIRC = CIRCULATOR Figure 4.3.1 - RF system configuration 32 F o r t h e c e n t r a l node a n t e n n a t h e h o r i z o n t a l ( a z i m u t h a l ) p a t t e r n s h o u l d be o m n i d i r e c t i o n a l . The v e r t i c a l r a d i a t i o n p a t t e r n s h o u l d be c o n f i n e d t o a n a r r o w beam as shown i n F i g . 4 . 3 . 2 w i t h n u l l t o n u l l beamwid th o f a p p r o x i m a t e l y 6° bu t a compromise of s i d e l o b e l e v e l r e l a x e s t he n u l l t o n u l l beamwid th t o 22° [ 6 8 ] . F o r t he s u b s c r i b e r a n t e n n a , t he compromised p a t t e r n i s a n u l l t o n u l l beamwid th o f abou t 10° ( b o t h h o r i z o n t a l and v e r t i c a l ) . S i d e l o b e l e v e l s s h o u l d be k e p t l o w , p r e f e r a b l y - 2 0 dB o r l e s s . S i n c e d i s c r i m i n a t i o n a g a i n s t r e f l e c t e d r e p l i c a of s i g n a l s i s h e l p f u l i n r e d u c i n g o v e r a l l i n t e r f e r e n c e , c r o s s p o l a r i z a t i o n d i s c r i m i n a t i o n w o u l d be u s e f u l to c o u n t e r m u l t i p a t h f a d i n g . The a n t e n n a s y s t e m s h o u l d be l i n e a r l y p o l a r i z e d r a t h e r t h a n c i r c u l a r l y p o l a r i z e d , i n c o n t r a s t t o t h a t of low f r e q u e n c y t r a n s m i s s i o n s u c h as a c o r d l e s s t e l e p h o n e w h i c h i s b e t t e r s e r v e d by p o l a r i z a t i o n i n s e n s i t i v e a n t e n n a sys tems [ 1 0 , 6 4 ] . 4 . 4 S i g n a l Power R e q u i r e m e n t s  F r e e s p a c e l o s s C o n f i n i n g t h e p a t h l e n g t h t o 20 m e t r e s , f r e e s p a c e l o s s i n dB = 20 l o g ( _ * _ ) 4-rtJl \ = 3 x 1 0 8 m = 5 .357 mm I = 20 m e t r e s 56 x 1 0 9 F r e e s p a c e l o s s = - 9 3 . 4 3 dB 33 F i g u r e A . 4 . 1 - S i g n a l t o t h e r m a l n o i s e r a t i o t h r o u g h v a r i o u s s t a g e s o f t h e r e c e i v e r . 34 R e c e i v e r t h r e s h o l d ( s e n s i t i v i t y ) T h i s i s c o n t r o l l e d by t he S N R ( s i g n a l t o n o i s e r a t i o ) r e q u i r e d a t t he I F s t a g e i . e . b e f o r e d e s p r e a d i n g . The SNR a f t e r d e s p r e a d i n g , f o r i n t e r -f e r e n c e l i m i t e d o p e r a t i o n was d e r i v e d i n S e c t i o n 3.3.2. i = 4.752 = 13.5 dB i n t I n o r d e r t o a v o i d o p e r a t i n g t h e r e c e i v e r i n a t h e r m a l n o i s e l i m i t e d S S S c o n d i t i o n , t he ==- needs t o be 10 dB b e t t e r t h a n ^ . i . e . ~ = 23.5 d B . N t h i n t t h g When i m p r o v e m e n t due t o s p e c t r u m s p r e a d i n g i s i n c l u d e d , =. a t t he IF s t a g e \ h = (23.5 - 33.1)dB = -9.6 dB F o r t h e t h e r m a l n o i s e s o u r c e a t room t e m p e r a t u r e T , t he n o i s e s p e c t r a l d e n s i t y i s = N ° i s * P ° W f = KT T - 25° c e l s i u s = 298° K e l v i n and b a n d w i d t h K i s the B o l t z m a n n ' s c o n s t a n t = -174 dBm/Hz F o r 1.5 GHz BW ( t h i s w i l l i n c l u d e ma in s i g n a l p l u s the f i r s t s i d e l o b e ) , the t h e r m a l n o i s e f l o o r = -174 + 91.8 = - 82.2 dBm A c c o r d i n g t o t he m a n u f a c t u r e r ' s s p e c i f i c a t i o n s , the c o n v e r s i o n l o s s o f the b a l a n c e d m i x e r i s a t most 7.5 dB w i t h NF ( n o i s e f i g u r e ) o f 5.5 d B . G a i n of I F a m p l i f i e r i s 30 d B , w i t h NF o f 2 d B . U s i n g F r i i ' s f o r m u l a [56] t h e n o i s e f i g u r e of m i x e r and I F a m p l i f i e r i n c a s c a d e i s : 35 ( N FIF AMP"1] N F ( M I X E R + IF AMP) N F M I X E R + " = 8 ' 3 5 d B MIXER R e f e r r i n g t o F i g . 4 . 4 . 1 on page 3 3 . — " — + ""(MIXER + IF AMP) " 9- 6 + 8- 3 5 " - U 2 5 D B .-. RF s i g n a l l e v e l , RCL = - 8 2 . 2 - 1 .25 = - 8 3 . 4 5 dBm. A s s u m i n g 10 mW (+ 10 dBm) f o r t r a n s m i t power , and a l l o w i n g 20 dB f o r f a d e m a r g i n , p l u g g i n g i n a l l t he s i g n a l l e v e l s i n the e q u a t i o n g i v e s P m + Gm  + G„ + P 0 - F „ = RCL T T R G M +10 + G m + G„ - 9 3 . 4 3 - 20 = - 8 3 . 4 5 dBm T R .-. G_ + G_ = 1 0 3 . 4 3 - 8 3 . 4 5 dBm T R = 20 dB where P T = t r a n s m i t power o f node a n t e n n a G T = g a i n of node a n t e n n a G R = g a i n of s u b s c r i b e r a n t e n n a P = p a t h g a i n G F ^ = f a d e m a r g i n s RCL = r e c e i v e d c a r r i e d l e v e l . The comb ined t r a n s m i t and r e c e i v e a n t e n n a g a i n w i l l have t o e x c e e d 20 dB i n o r d e r t o meet t h i s b u d g e t . 36 CHAPTER 5 ANTENNA SYSTEM DESIGN 5 .1 G e n e r a l The v a r i o u s c o n s i d e r a t i o n s so f a r r e q u i r e t h a t t he a n t e n n a s y s t e m s a t i s f y the f o l l o w i n g r e q u i r e m e n t s : Node A n t e n n a S u b s c r i b e r A n t e n n a P o l a r i z a t i o n L i n e a r V e r t i c a l o r H o r i z o n t a l Same as node a n t e n n a G a i n Combined node and s u b s c r i b e r g a i n s h o u l d e x c e e d 20 dB n u l l t o n u l l beamwid th V e r t i c a l 22 d e g r e e o r l e s s h o r i z o n t a l o m n i d i r e c t i o n a l abou t 10 d e g r e e s b o t h v e r t i c a l & h o r i z o n t a l s i d e l o b e l e v e l As low as p o s s i b l e p r e f e r a b l y no t h i g h e r t h a n - 20 dB M a x . power h a n d l i n g c a p a b i l i t y 100 mw 100 mw O p e r a t i n g f r e q u e n c y range 51 - 59 GHz 51 - 59 GHz M e c h a n i c a l To be mounted n e a r c e i l i n g To be mounted on p o l e s A d d i t i o n a l r e q u i r e m e n t s a r e low c o s t , s i m p l e m a n u f a c t u r i n g and most i m p o r t a n t , s i m p l e o p e r a t i o n . T h i s e x c l u d e s a n t e n n a f e e d s w h i c h use c o m p l i c a t e d a m p l i t u d e o r phase c o n t r o l , s u c h as t he S y n a p s i s t e m p r o p o s e d by B r o a d c o m I n c . [78] . 5 . 2 A n t e n n a Sys tems C o n s i d e r e d S e v e r a l a n t e n n a d e s i g n s have been c o n s i d e r e d . 37 A . F o r t he s u b s c r i b e r l o c a t i o n s . - An open wavegu ide can a c t as an a n t e n n a but w ide beamwid th and low g a i n make i t u n s u i t a b l e f o r e f f i c i e n t s i g n a l power e x p e n d i t u r e [ 7 1 ] . - A h e l i c a l beam a n t e n n a i s a l s o p o s s i b l e bu t the s m a l l p h y s i c a l s i z e s and t he d i f f i c u l t y o f f e e d i n g i t p r e c l u d e s i t s use [ 7 0 ] . - A d i e l e c t r i c r o d a n t e n n a i s i n e x p e n s i v e , f a i r l y easy t o make and a p a t t e r n m e e t i n g o v e r a l l s y s t e m r e q u i r e m e n t c a n be e n g i n e e r e d r e a d i l y [ 7 6 , 7 7 ] . B . F o r t he node l o c a t i o n . - A L u n e b e r g l e n s [74] s y s t e m mounted n e a r t h e c e i l i n g can be u s e d as a node a n t e n n a . The l e n s f o c u s e s i n c o m i n g beams o n t o t h e l e n s s u r f a c e d i a m e t r i c a l l y a c r o s s . A s e c o n d a r y c o l l e c t i o n s y s t e m r e d i r e c t s t he RF s i g n a l s f r o m the l e n s s u r f a c e t o a c e n t r a l f e e d . C o v e r a g e i s p r o v i d -ed by f l o o d i n g o f t he l o w e r s p h e r e . T r a n s m i s s i o n t h r o u g h s u c h a s t r u c t u r e m igh t r e s u l t i n uneven " h o t " and " c o l d " s p o t s . The l e n s c o n s t r u c t i o n r e q u i r e s low l o s s d i e l e c t r i c m a t e r i a l s w i t h a c c u r a t e l y c o n t r o l l e d d i e l e c t r i c c o e f f i c i e n t s . The d i e l e c t r i c c o e f f i c i e n t s r e q u i r e d f o r e a c h l a y e r o f the m u l t i - l a y e r e d " o n i o n " c o n s t r u c t i o n a r e d i f f e r e n t and v a r y be tween 1.0 t o 2 . 0 . The a r t i f i c i a l d i e l e c t r i c s r e q u i r e d a r e m a n u f a c t u r e d by s u s p e n s i o n o f a c o n t r o l l e d d e n s i t y o f f i n e m e t a l l i c p a r t i c l e s i n low l o s s foam w h i l e t he foam i s s t i l l i n l i q u i d f o r m . I t i s d i f f i c u l t t o e c o n o m i c a l l y m a n u f a c t u r e r e l i a b l y c o n s i s t e n t a r t i f i c i a l d i e l e c t r i c s of a s p e c i f i e d d i e l e c t r i c c o n s t a n t . F o r t h i s r e a s o n , Emerson and Cumming I n c . has s t o p p e d m a n u f a c t u r i n g t h e a r t i f i c i a l d i e l e c t r i c m a t e r i a l s s u i t a b l e f o r L u n e b e r g l e n s 38 f o r L u n e b e r g l e n s c o n s t r u c t i o n . Such an a n t e n n a s y s t e m i s v u l n e r a b l e t o s i g n a l b l o c k a g e by o f f i c e w o r k e r s . - A d o u b l e r e f l e c t o r a n t e n n a s y s t e m . The node a n t e n n a s y s t e m i s made up o f two r e f l e c t o r s and as i l l u s t r a t e d by the r a y t r a c e i n F i g . 5 . 2 . 1 , the c o n t o u r of t he two r e f l e c -t o r s c a n be d e s i g n e d t o make t he beamwid th r e a s o n a b l y n a r r o w . The d i f f i c u l t y of e x c i t i n g T M 0 1 mode s i n g u l a r l y makes t h i s sy tem u n s u i t a b l e . I n a c i r c u l a r w a v e g u i d e , the dominan t mode i s T E ] ^ . T M 0 ^ i s t he n e x t h i g h e r o r d e r mode. The d o u b l e r e f l e c t o r s y s t e m [72] i s d e s i g n e d t o o p e r a t e w i t h TMQI mode. I t i s n e c e s s a r y t o e x c i t e t h e TMQX mode w i t h o u t e x c i t i n g t he T E j ^ mode. D e s i g n o f a f e e d t r a n s i t i o n t h a t c o n v e r t s TEQI mode i n a r e c -t a n g u l a r w a v e g u i d e t o TM 0 x mode i n a c i r c u l a r wavegu ide i s a v a i l a b l e [ 7 3 ] . I n t h e c i r c u l a r w a v e g u i d e , i t i s p o s s i b l e t o gua rd a g a i n s t p o s s i b l e mode c o n v e r s i o n by means of mode s u p p r e s s o r . A n o t h e r t e c h n i q u e i s t o change t h e overmoded o p e r a t i o n (TMQI + T E ^ ) i n t o a s i n g l e mode ( T M 0 1 ) o p e r a t i o n by e n g i n e e r i n g a moda l i n v e r s i o n . I n a n o r m a l open homogeneous c i r c u l a r w a v e -g u i d e , t he o r d e r of t he f i r s t few modes a r e T E ^ , TMnj. , T E 2 i , e t c * M o d a l i n v e r s i o n , t he change of mode o r d e r t o TMQI> T E I I > 1^21 e t c . , can be a c c o m -p l i s h e d by p a r t i a l l y l o a d i n g t he c e n t r e o f the wavegu ide w i t h a d i e l e c t r i c m a t e r i a l o f d i e l e c t r i c c o n s t a n t o f abou t 50 [53] . I t i s d i f f i c u l t t o ge t l o w l o s s m a t e r i a l w i t h s u c h a h i g h d i e l e c t r i c c o n s t a n t . A l s o f o r t he o p e r a t i n g f r e q u e n c y of 55 GHz , t he t o l e r a n c e s on t h e r e f l e c t o r s u r f a c e i s ± 0 . 2 mm. The f e e d t r a n s i t i o n , mode s u p p r e s s o r , the moda l i n v e r t o r and t he r e f l e c t o r s r e q u i r e p r e c i s i o n m a c h i n i n g and e l e c t r o - f o r m i n g . A r r a y o f d i e l e c t r i c r o d 39 F i g u r e 5 . 2 . 1 - C r o s s s e c t i o n v i e w of a d o u b l e r e f l e c t o r s y s t e m f o r o m n i -d i r e c t i o n a l h o r i z o n t a l p a t t e r n and n a r r o w v e r t i c a l p a t t e r n 40 As i l l u s t r a t e d by F i g u r e 5 . 2 . 2 , t he i d e a h e r e i s t o f i r s t e n g i n e e r a d i e l e c t r i c r o d a n t e n n a w i t h a w i d e b e a m - w i d t h i . e . u s i n g a f a i r l y s h o r t d i e l e c t r i c r o d [ 76 ] [ 77 ] . N e x t , an a r r a y p a t t e r n i s d e s i g n e d t o make the v e r t i c a l p a t t e r n n a r r o w . Howeve r , u s i n g s i m p l e a m p l i t u d e and phase f e e d , a n a r r o w a r r a y p a t t e r n i s no t p o s s i b l e w i t h o u t a c o r r e s p o n d i n g l y l a r g e s i d e l o b e . The use o f an e l a b o r a t e f e e d i s e x c l u d e d f r om S e c t i o n 5 . 1 . The c h o s e n node a n t e n n a s y s t e m A s e c t o r a l h o r n i s a w e l l e s t a b l i s h e d d e s i g n [68] . By e x t e n d i n g t he S e c t o r i n t o a f u l l 2TI r a d i a n , a b i c o n i c a l h o r n ( o r V - g r o o v e d p u l l e y shaped) s t r u c t u r e i s o b t a i n e d . The v e r t i c a l beam p a t t e r n can be o p t i m i z e d f o r n a r r o w n e s s and low s i d e l o b e . T h i s d e s i g n i s c h o s e n f o r t h e s i m p l i c i t y of m a n u f a c t u r e , f e e d and s i d e l o b e l e v e l c o n t r o l . 5 . 3 F i n a l S y s t e m E n g i n e e r i n g D e t a i l The node a n t e n n a i s p h y s i c a l l y made up o f 3 p a r t s : the top p l a t e , the b o t t o m p l a t e and a s m a l l p robe as shown i n F i g . 5 . 3 . 1 . The p robe a t p l a n e A - A i s an a n t e n n a r a d i a l l y r a d i a t i n g i n t h e p r e s e n c e o f two c i r c u l a r p l a t e b o u n d a r i e s . L e t t he i n p u t impedance be Z . S i m i l a r l y , A. t h e p r o b e a t p l a n e B - B i s a n a n t e n n a r a d i a t i n g i n a r e c t a n g u l a r w a v e g u i d e a n d s e e s Z a s t h e i n p u t i m p e d a n c e . The c o a x i a l c a b l e p o r t i o n h a s B c h a r a c t e r i s t i c s impedance Z Q 2 i e e a r o where An = n a t r u a l l o g a r i t h m f u n c t i o n b = r a d i u s of o u t s i d e c o n d u c t o r Al d i e l e c t r i c r o d a n t e n n a s LEGEND: CIRC = C i r c u l a t o r A , B , C a r e s i m p l e 3 dB s p l i t t e r s d i s t h e d i s t a n c e o f s e p a r a t i o n be tween r o d a n t e n n a s F i g u r e 5 . 2 . 2 - A r r a y o f d i e l e c t r i c r o d a n t e n n a s u s i n g s i m p l e a m p l i t u d e and phase f e e d . 42 F i g u r e 5 . 3 . 1 - C r o s s s e c t i o n v i e w of the node a n t e n n a 43 a = r a d i u s of i n n e r c o n d u c t o r e = d i e l e c t r i c c o n s t a n t o f m a t e r i a l i n s i d e t h e c o a x i a l l i n e , r The d e s i g n t h e n can be r e d u c e d t o an e q u i v a l e n t t r a n s m i s s i o n l i n e c i r c u i t p r o b l e m as shown i n F i g . 5 . 3 . 2 . The d e s i g n of c e n t r a l node a n t e n n a can be a n a l y t i c a l l y d i v i d e d i n t o t h r e e r e g i o n s : i ) t h e r e g i o n above p l a n e A - A . i i ) the r e g i o n be tween p l a n e A-A and B - B . i i i ) t he r e g i o n be low p l a n e B B . The o b j e c t i v e of t he d e s i g n i s t o a c h i e v e e f f i c i e n t e n e r g y t r a n s f e r o v e r w i d e b a n d w i d t h i . e . a ma tch of i n p u t impedances o v e r as b r o a d a b a n d w i d t h as p o s s i b l e . The t r a n s m i s s i o n l i n e e q u i v a l e n t p r o b l e m i s t o match Z a n d Z o v e r a l e n g t h A o f t r a n s m i s s i o n l i n e of c h a r a c t e r i s t i c impedance A B V R e g i o n i ) c a n be a n a l y z e d by c o n s i d e r i n g t he p robe as a c y l i n d r i c a l a n t e n n a r a d i a t i n g i n t o an i n f i n i t e r a d i a l l i n e , a s s u m i n g t h e edge e f f e c t s of t h e end of the r a d i a l l i n e i s n e g l i g i b l e . T h i s i s v a l i d s i n c e t he r a d i a l l i n e i s assumed t o be matched t o f r e e s p a c e by t he f l a r i n g o f the r a d i a l s t r u c t u r e . W i l l i a m s o n [58] has a n a l y z e d t h i s r a d i a l l i n e j u n c t i o n . H i s r e s u l t s a r e : F o r a p e r f e c t l y matched r a d i a l l i n e , t he a d m i t t a n c e Y seen a t t he c o a x i a l p o r t o f t he j u n c t i o n w i t h the c e n t r e c o n d u c t o r e x t e n d e d a c r o s s the gap h ( F i g u r e 5 . 3 . 3 ) c a n be shown t o be 2 . H ( 2 ) ( k b ) Y = 12 _ x { j Q ( k a ) Y 0 ( k b ) - J Q ( k b ) Y Q ( k a ) } T ) 0 k h A n 2 ( b / a ) H Q ( 2 ) ( k a ) + j B i + jB2 A B F i g u r e 5 . 3 . 2 - E q u i v a l e n t t r a n s m i s s i o n l i n e p r o b l e m i n t h e a n a y l s i s of node a n t e n n a s t r u c t u r e i n f i n i R a d i a l l i n e y 1 , To i n f i n i t y gap h c o a x i a l f e e d r a d i u s b r a d i u s a F i g u r e 5 . 3 . 3 - A c o a x i a l t o r a d i a l l i n e j u n c t i o n 45 2TC where B 1 = - c o t k h n o A n ( b / a ) - K_(q k b ) ruk h I n 2 ( b / a ) m = 1 q 2 V q m k a ) U m V q m k b ) V q m k a ) } q = m / k h 2% k = — i s t he wave number 0^ — = T) = i n t r i n s i c impedance of f r e e s p a c e . e 0 J i s B e s s e l f u n c t i o n of the f i r s t k i n d o f o r d e r z e r o , o Y i s B e s s e l f u n c t i o n o f t he s e c o n d k i n d o f o r d e r z e r o , o I i s m o d i f i e d B e s s e l f u n c t i o n of the f i r s t k i n d o f o r d e r z e r o , o K i s m o d i f i e d B e s s e l f u n c t i o n o f t he s e c o n d k i n d o f o r d e r z e r o , o (2) H i s H a n k e l f u n c t i o n o f t he s e c o n d k i n d o f o r d e r z e r o . O R e g i o n i i i ) c a n be a n a l y z e d by c o n s i d e r i n g t he i n p u t a d m i t t a n c e of a c o a x i a l l y f e d c y l i n d r i c a l monopo le i n a r e c t a n g u l a r w a v e g u i d e . A g a i n W i l l i a m s o n [57] has p r e s e n t e d some a n a l y t i c a l r e s u l t s w h i c h c a n be u s e d t o c a l c u l a t e t he i n p u t a d m i t t a n c e . 46 F o r t he s u b s c r i b e r l o c a t i o n s d i e l e c t r i c r e c t a n g u l a r r o d a n t e n n a a r e u s e d . A p r o p e r c h o i c e o f r o d l e n g t h and t a p e r o r f l a r e t o g i v e t h e d e s i r e d beamwid th and s i d e l o b e l e v e l c o n t r o l i s n e e d e d . T h i s i s d e t e r m i n e d e x p e r i m e n t a l l y by m e a s u r i n g t h e r a d i a t i o n p a t t e r n of s e v e r a l d i f f e r e n t r o d t a p e r o r f l a r e . 5 . 4 C o n s t r u c t i o n D e t a i l s F i g u r e 5 . 4 . 1 shows t he d e t a i l o f t he s u b s c r i b e r a n t e n n a . The d i e l e c t r i c m a t e r i a l i s p o l y s t y r e n e w i t h d i e l e c t r i c c o n s t a n t of 2 . 5 . S e v e r a l f l a r e a n g l e s i n E and H p l a n e were e x p e r i m e n t e d and a 10° E p l a n e f l a r e was c h o s e n . Such an a n t e n n a has a l m o s t i d e n t i c a l E and H p l a n e r a d i a t i o n p a t t e r n and a s i d e l o b e l e v e l l o w e r t h a n - 2 5 d B . F i g u r e 5 - 4 . 2 shows t he d e t a i l o f the node a n t e n n a , t e f l o n t a p e i s u s e d t o f i l l t h e c o a x i a l p a r t t o p r o v i d e s u p p o r t f o r t he p r o b e . Low l o s s foam i s shaped t o p r o v i d e p r o p e r s e p a r a t i o n ( 1 . 6 mm) be tween t he top and b o t t o m p l a t e s . The f l a r e a n g l e and l e n g t h o f the r a d i a l l i n e s t r u c t u r e a r e d e s i g n e d u s i n g s e c t o r a l h o r n d e s i g n d a t a [ 6 8 ] . 47 a i s t h e n a r r o w d i m e n s i o n and b i s t h e b r o a d d i m e n s i o n i n s i d e t h e r e c t a n g u l a r w a v e g u i d e F i g u r e 5 . 4 . 1 - S u b s c r i b e r d i e l e c t r i c a n t e n n a c o n s t r u c t i o n d e t a i l NOTE: 1 H i g h g l o s s f i n i s h f o r i n s i d e s u r f a c e s i n r e g i o n A 2 M a t e r i a l : - B r a s s 174 mm DIA 50 mm DIA 13 mm REGION A NOTE 1 144 mm DIA F i g u r e 5 . 4 . 2 - Node a n t e n n a c o n s t r u c t i o n d e t a i l 3 mm co 49 CHAPTER 6 TESTS ON THE RF SYSTEM 6 .1 G e n e r a l F i g u r e 6 . 1 . 1 i s a b l o c k d i a g r a m o f t he RF s y s t e m show ing o n l y one s u b s c r i b e r and t h e n o d e . The components a r e q u i t e e x p e n s i v e . I n o r d e r t o k e e p t h e c o s t o f t h i s e x p e r i m e n t r e a s o n a b l e , o n l y one d i r e c t i o n o f t r a n s m i s s i o n I s i m p l e m e n t e d and o n l y e s s e n t i a l components a r e p u r c h a s e d . The " b a r e bone" s y s t e m u s e d f o r t h i s e x p e r i m e n t i s shown i n F i g u r e 6 . 1 . 2 . The RF band p a s s f i l t e r and I F f i l t e r s have been l e f t o u t . I n a r e a l s y s t e m , t h e y a r e e s s e n t i a l and c a n n o t be o m i t t e d . I n t h i s e x p e r i m e n t o n l y CW ( c o n t i n u o u s wave) i s u s e d and t he IF a m p l i f i e r BW i s no t w i d e r t h a n 5 G H z . The t h e r m a l n o i s e l e v e l i s no t h i g h enough t o drown ou t t he s i g n a l , so t h a t i t i s s a f e t o l e a v e them o u t . The i n c l u s i o n of the one dB a t t e n u a t o r w i t h the IF a m p l i f i e r i s n e c e s s a r y b e c a u s e i t p r o v i d e s a l o a d m a t c h i n g f o r t h e m i x e r o u t p u t and I F a m p l i f i e r i n p u t . W i t h o u t t he 1 dB a t t e n u a t o r , t he I F a m p l i f i e r e x h i b i t e d u n s t a b l e o s c i l l a t i o n c a u s e d by p o s i t i v e f e e d b a c k . 6 . 2 S i g n a l L e v e l s The measured RF power a t v a r i o u s p o i n t s a r e a l s o shown i n F i g u r e 6 . 1 . 2 . U s i n g t h e method o f s u b s t i t u t i o n , t he a n t e n n a g a i n and p a t h l o s s can be a c c u r a t e l y d e t e r m i n e d . The p r o c e d u r e i s as f o l l o w s : 50 LEGEND: ANT = A n t e n n a CIRC = C i r c u l a t o r BPF = Band p a s s f i l t e r UCM = Up c o n v e r s i o n m i x e r DCM = Down c o n v e r s i o n m i x e r FLTR = F i l t e r L . O . = L o c a l o s c i l l a t o r I F = I n t e r m e d i a t e f r e q u e n c y AMP = A m p l i f i e r SUB = S u b s c r i b e r F i g u r e 6 . 1 . 1 - B l o c k d i a g r a m o f RF s y s t e m ( w i t h o n l y one s u b s c r i b e r s h o w n ) . 51 2.25 METERS TWO 25 dB GAIN HORNS i / VARIABLE ATTENUATOR •DIELECTRIC ROD ANTENNA LOAD dB I.L. CIRCULATOR LOCAL OSCILLATOR DOWN CONVERSION MIXER WITH I.L. OF 6.5 dB. 1 dB ATTENUATOR ^ 1 ^ " NODE ANTENNA I.L. +14.5 dBm LOCAL OSCILLATOR ^ - U 20 dB V IF AMP -19.5 dBm LEGEND: I.L. = INSERTION LOSS F i g u r e 6.1.2 - A o n e - d i r e c t i o n " b a r e b o n e " s y s t e m u s e d f o r RF i n v e s t i g a t i o n 52 - u s i n g a p a i r o f known g a i n a n t e n n a s s u c h as s t a n d a r d g a i n h o r n s , and i n s t a l l i n g them 2 . 2 5 m e t r e s a p a r t , t he RCL ( r e c e i v e d c a r r i e d l e v e l ) i s f i r s t r e c o r d e d . - s i m u l a t e t he combined a n t e n n a g a i n and s p a c e l o s s by means of an a c c u r a t e l y c a l i b r a t e d a t t e n u a t o r . F rom t h i s , the f r e e s p a c e l o s s can be d e t e r m i n e d . - s u b s t i t u t i n g one g a i n h o r n w i t h an a n t e n n a of unknown g a i n , the g a i n of t he a n t e n n a c a n be d e t e r m i n e d by n o t i n g t he RCL c h a n g e . The r e s u l t s show t h a t : - f r e e s p a c e l o s s i s i n v e r s e l y p r o p o r t i o n a l t o t h e s q u a r e o f the d i s t a n c e . - t h e g a i n o f t he d i e l e c t r i c r o d a n t e n n a i s 1 2 . 5 d B . - the g a i n of the node a n t e n n a i s 9 . 5 d B . 6 . 3 C r o s s p o l a r i z a t i o n D i s c r i m i n a t i o n B o t h n o d e a n t e n n a a n d s u b s c r i b e r a n t e n n a a r e s e n s i t i v e t o p o l a r i z a t i o n c h a n g e s . A 90° r o t a t i o n (E and H swap) w i l l c a u s e a p p r o x i m a t e l y 30 dB o f a t t e n u a t i o n . A 10° o f f s e t w i l l c a u s e abou t 5 dB of a t t e n u a t i o n . F i g u r e 6 . 3 . 1 g i v e s a p l o t o f p o l a r i z a t i o n d i s c r i m i n a t i o n a g a i n s t the a n g l e o f o f f s e t . 6 .4 R a d i a t i o n P a t t e r n s The r a d i a t i o n p a t t e r n o f t he node and s u b s c r i b e r a n t e n n a s a r e m e a s u r e d and r e c o r d e d i n F i g u r e 6 . 4 .1 to F i g u r e 6 . 4 . 6 . The a n t e n n a u n d e r t e s t i s . mounted h o r i z o n t a l l y on a r o t a t i n g p l a t f o r m i n s i d e an a n e c h o i c chamber . The p l a t f o r m r o t a t e s abou t a v e r t i c a l a x i s . 53 20.0 30.0 10.0 50.0 60.0 DEGREE OF O F F S E T 70.0 80.0 90.0 F i g u r e 6 . 3 . 1 - A p l o t o f t he of c r o s s p o l a r i z a t i o n a n t e n n a s y s t e m d i s c r i m i n a t i o n 54 Legend: rad ia l scale=10dB/inch or ig in set at -48.5dB sol id l ine: E - p l a n e dashed line: H - p l a n e F i g u r e 6 . 4 . 1 - R a d i a t i o n p a t t e r n of node a n t e n n a 55 Legend: r ad ia l scale=10dB/inch sol id l ine: E - p l a n e dashed l ine: H - p l a n e F i g u r e 6 . 4 . 2 - R a d i a t i o n p a t t e r n of 10 deg ree E f l a r e 56 Legend: radial scale=10dB/inch solid line: E-plane dashed line: H-plane F i g u r e 6 . 4 . 3 - R a d i a t i o n p a t t e r n o f 20 d e g r e e E f l a r e 57 Legend: radial scale=10dB/inch solid line: E-plane dashed line: H-plane F i g u r e 6 . 4 . 4 - R a d i a t i o n p a t t e r n a t 30 d e g r e e E f l a r e 58 Legend: radial scale=10dB/inch solid line: E-plane dashed line: H-plane F i g u r e 6 . 4 . 5 - R a d i a t i o n p a t t e r n o f 40 d e g r e e E f l a r e 59 Legend: radial scale=10dB/inch solid line: E-plane dashed line: H-plane F i g u r e 6 . 4 . 6 - R a d i a t i o n p a t t e r n o f 30 d e g r e e H f l a r e 60 A standard gain horn, placed at a distance of 1 metre away, i s used as a transmit source. The received s i g n a l l e v e l i s measured using an RF power meter. (HP 432A with suitable power sensor). I t i s assumed that the s i g n a l i s f ar enough away from the horn that i t can be treated as a plane wave, and the r a d i a t i o n pattern i s independent of the r a d i a t i o n pattern of the standard gain horn used. 6.5 Propagation C h a r a c t e r i s t i c s Through Various Building Materials and Obstacles [22]  Most bui l d i n g materials are "opaque" to the 55 GHz m i l l i m e t r i c wave. Double glazed glass windows cause 3 to 7 dB l o s s . Construction lumbers such as Douglas F i r or Hemlock 2 x 4's attenuate the s i g n a l by 15 to 20 dB. A 1 cm. thick gypsum wall board attenuates the s i g n a l by 10 dB. A two inch aerated concrete block attenuates i t by more than 30 dB. Human body attenuates the s i g n a l by as much as 25 dB. The s i g n a l at 55 GHz just do not have any penetrating power. This reaffirms the decision to use a d i r e c t l i n e of sight transmission. Coverage by flooding w i l l need a much higher l e v e l of power transmission. 6.6 Fading S t a t i s t i c s The one d i r e c t i o n RF system i s set up as shown i n Figure 6.6.1 inside the microwave laboratory. The received IF s i g n a l l e v e l i s recorded while free t r a f f i c inside the laboratory i s allowed. No noticeable s i g n a l l e v e l changes were observed unless the passers-by d e l i b e r a t e l y block the signal with t h e i r hands raised up. The record was run for 3 days and the results sampled i n 1 minute i n t e r v a l s . These samples were then used to construct a t - 1 pa > cd M C/3 H H Pd > I—! S3 13 a o o > > o -o z z a H O H M CD rr CO w 1.9 Metres tn CD tn o 13 ?a 2 H ^ H : > co CO pa cn s w o cn Q O Co H pa cn a pa pa cn pa 62 p l o t of c u m u l a t i v e p r o b a b i l i t y v e r s u s RCL as shown i n F i g u r e 6 . 6 . 2 u s i n g a t h i r d o r d e r p a r a m e t r i c p o l y n o m i a l f i t . . i J . _« « . , c „ 2 random s i g n a l T h e R i c i a n d i s t r i b u t i o n f o r v a r i o u s v a l u e s o f K=Y = — r — ^ r = — r s t e a d y s i g n a l power r a t i o a r e a l s o p l o t t e d [ 7 9 ] . An e s t i m a t e of t he R i c i a n p a r a m e t e r K c a n be deduced u s i n g K o l m o g o r o v S m i r n o v goodness o f f i t t e s t [75] . I t can be s t a t e d w i t h 95% c o n f i d e n c e t h a t K i s l e s s t h a n - 2 0 . 2 d B . 1 .0 p O O OUB *_>!llg|1 o MEASURED o R I C I A N K-18DB A" " R" 1C1 AN"K- 20D6 R I C I R N K-25DB ° ' ° -3 5-3 0 -2 5 -2.0 -l'.5 -l'.O -0.5 0.0 0.5 l'.O 1.5 2.0 2.5 3.0 3.5 DB W . R . T . MEDIAN F i g u r e 6 . 6 . 2 - C o m p a r i s o n of c u m u l a t i v e p r o b a b i l i t y d i s t r i b u t i o n o f t he measured RCL a g a i n s t t h e o r e t i c a l R i c i a n d i s t r i b u t i o n w i t h d i f f e r e n t K v a l u e s 64 CHAPTER 7 CONCLUSION AND RECOMMENDATIONS 7 .1 C o n c l u s i o n R e s u l t s o f t h i s RF i n v e s t i g a t i o n a r e : 1 . The use o f DSCDMA i s e f f e c t i v e o n l y a g a i n s t R i c i a n f a d i n g o f low K r a t i o ( - 2 0 . 2 dB o r l e s s ) . F o r h i g h K r a t i o , t he s p r e a d g a i n and hence t h e b a n d w i d t h needed i s so l a r g e t h a t no p h y s i c a l l y r e a l i z a b l e c h a n n e l o r t r a n s m i s s i o n medium c a n meet t he r e q u i r e m e n t . I n t he d e s i g n of t he RF s y s t e m , a l i n e of s i g h t t r a n s m i s s i o n scheme r a t h e r t h a n s i g n a l f l o o d i n g scheme i s c h o s e n s i n c e t he f o r m e r a c t i v e l y t r i e s t o r e d u c e t h e amount o f f a d i n g . E f f i c i e n t s i g n a l power e x p e n d i t u r e and r e d u c t i o n of h e a l t h h a z a r d due t o r a d i a t i o n a l s o f a v o u r s u c h a scheme. 2 . T y p i c a l o f f i c e s have a c e i l i n g h e i g h t o f a t l e a s t 8 f e e t . The r e g i o n o f s p a c e be tween c e i l i n g and 6 f e e t h e i g h t can be u s e d as a c o m m u n i c a t i o n s p a c e . T h i s s p a c e w o u l d be s e l d o m d i s t u r b e d o r o c c u p i e d by o f f i c e w o r k e r s . F a d i n g c a u s e d by random s c a t t e r i n g i s m i n i m i z e d . 3 . I t i s f e a s i b l e t o d e s i g n and c o n s t r u c t an a n t e n n a s y s t e m t h a t c o n f i n e s t h e r a d i a t i o n w i t h i n t h e c o m m u n i c a t i o n s p a c e . I n e x p e n s i v e d i e l e c t r i c r o d a n t e n n a s can be u s e d as t he s u b s c r i b e r a n t e n n a s . An a n t e n n a fo rmed by c o a x i a l t o a f l a r e d r a d i a l l i n e s t r u c t u r e can be u s e d as t he node a n t e n n a . Beamwid th and s i d e l o b e l e v e l o f the node a n t e n n a c a n be a p p r o x i m a t e l y d e s i g n e d u s i n g s e c t o r a l h o r n d a t a . The comb ined g a i n of t h e node and s u b s c r i b e r a n t e n n a e x c e e d s the d e s i g n e d r e q u i r e m e n t w h i c h 65 i s d e t e r m i n e d by b a l a n c i n g a s i g n a l power budget of the RF s y s t e m w i t h an a l l o w a n c e o f 20 dB f o r f a d e m a r g i n . 4 . O v e r a l l RF s y s t e m f e a s i b i l i t y i s c o n t r o l l e d by the K r a t i o . T h i s K r a t i o i s e s t i m a t e d by s t a t i s t i c a l l y a n a l y z i n g t he d a t a o f e x p e r i m e n t a l l y r e c o r d e d r e c e i v e d c a r r i e r l e v e l . I t c a n be c o n c l u d e d w i t h 95% c o n f i d e n c e t h a t K i s l e s s t h a n - 2 0 . 2 d B , t hus e s t a b l i s h i n g t h e o v e r a l l RF s y s t e m f e a s i b i l i t y . I n summary, i t c a n be c o n c l u d e d t h a t i t i s f e a s i b l e t o use low l e v e l 60 GHz r a d i a t i o n f o r i m p l e m e n t a t i o n o f RLAN s e r v i n g up t o 200 s u b s c r i b e r s , e a c h demand ing 2B+D ISDN c h a n n e l s and BER of 1 0 " 6 . The RF s y s t e m i s based on a n a r r o w beam l i n e o f s i g h t t r a n s m i s s i o n scheme. By c o n f i n i n g t h e RF s i g n a l t o a c o m m u n i c a t i o n s p a c e s e l d o m o c c u p i e d by o f f i c e w o r k e r s , i t i s p o s s i b l e t o u t i l i z e s i g n a l power e f f i c i e n t l y , m i n i m i z e o f f i c e w o r k e r s ' e x p o s u r e t o r a d i a t i o n and r e d u c e random f a d i n g . E x p e r i m e n t a t i o n w i t h a s i m p l e h e t e r o d y n e RF s y s t e m made up o f c o m m e r c i a l l y a v a i l a b l e m i l l i m e t r i c w a v e c o m p o n e n t s a n d c u s t o m d e s i g n e d a n t e n n a s c o n f i r m s o v e r a l l RF f e a s i b i l i t y . 7 . 2 Recommendat ions Recommenda t ions f o r f u r t h e r r e s e a r c h a r e : a ) I n t h e RF a r e a C o s t r e d u c t i o n p o s s i b i l i t y s u c h as - MMIC ( m o n o l i t h i c m i c r o w a v e i n t e g r a t e d c i r c u i t ) - C o n s t r u c t i o n u s i n g p l a s t i c m o u l d i n g and e x t r u s i o n i n c o m b i n a t i o n w i t h m e t a l p l a t i n g . 66 - U t i l i z a t i o n of l o w e r o p e r a t i n g f r e q u e n c i e s s u c h as 20 t o 40 GHz r a n g e . - F u r t h e r b r o a d e n i n g o f b a n d w i d t h f o r p o s s i b l e s y s t e m e x p a n s i o n o r w i d e band h i g h speed d a t a c o m m u n i c a t i o n s . b) I n SSMA a r e a - Compare the v a r i o u s SSMA schemes f o r an opt imum c h o i c e . F o r e x a m p l e , " n e a r - f a r " p r o b l e m ( r e f e r r i n g t o t he c a p t u r e of t he node r e c e i v e r by a s t r o n g s u b s c r i b e r s i g n a l ) i s a s i g n i f i c a n t o b s t a b l e when DSCDMA i s a p p l i e d t o a c e l l u l a r m o b i l e t e l e p h o n e s y s t e m w i t h l a r g e c e l l s where p a t h d i s t a n c e s c a n v a r y as much as h u n d r e d f o l d , s u c h as f r o m 0 .1 km t o 10 km [ 3 2 ] , [35 t o 3 7 ] . FHCDMA ( f r e q u e n c y h o p p i n g ) c a n a v o i d t h e " n e a r - f a r " c a p t u r e bu t t he h a r d w a r e r e q u i r e -ment of a f a s t r i s i n g and f a s t s e t t l i n g f r e q u e n c y s y n t h e s i z e r m igh t a l s o l i m i t t h e p e r f o r m a n c e . The FHCDMA m a i n t a i n s a low c r o s s c o r -r e l a t i o n n o i s e by a v o i d a n c e of e n e r g y s p i l l o v e r f r o m one f r e q u e n c y s l o t t o v a r i o u s o t h e r s l o t s by f r e q u e n c y h o p p i n g . O t h e r schemes s u c h as t ime h o p p i n g ( w i t h f a s t s w i t c h i n g ha rdwa re r e q u i r e m e n t ) o r h y b r i d scheme m i x i n g f r e q u e n c y h o p p i n g , t ime h o p p i n g and d i r e c t s e q u e n c e s m u l t i p l e a c c e s s s h o u l d a l s o be c o n s i d e r e d . A h y b r i d s y s t e m o f FH and DS c o u l d a c h i e v e a p e r f o r m a n c e s p e c i f i c a t i o n t h a t i s no t a c h i e v a b l e by e i t h e r FH o r DS a l o n e [ 6 5 ] . The t r a n s m i t t e r and r e c e i v e r w i l l n e c e s s a r i l y be more c o m p l i c a t e d , bu t by d i v i d i n g t h e o v e r a l l p e r f o r m a n c e r e q u i r e m e n t , t he p e r f o r m a n c e r e q u i r e m e n t s of the DS p o r t i o n o r FH p o r t i o n can each be r e l a x e d t o e a s i l y a t t a i n a b l e l e v e l s . 67 c ) I n m o d u l a t i o n c h o i c e s A l t h o u g h a PSK scheme i s assumed f o r s i m p l e d e s i g n e x p e d i e n c y a t t h i s s t a g e , o t h e r schemes s u c h as d i f f e r e n t i a l P S K , n o n - c o h e r e n t BFSK o r even f a n c i e r schemes s u c h as MSK (minimum s h i f t k e y i n g ) , M -a ry P S K , M-a ry FSK e t c . , p r o v i d i n g s p e c t r a l e f f i c i e n y o r p e r f o r m a n c e improvement a t t he c o s t o f t r a n s m i t t e r and r e c e i v e r c o m p l e x i t y , d e s e r v e c a r e f u l c o n s i d e r a t i o n . d ) I n a r e a o f c o d i n g d e s i g n The c o d i n g i s a most c r i t i c a l a r e a o f SS d e s i g n . A g a i n , a l t h o u g h ML code i s assumed f o r t h i s w o r k , v a r i o u s o t h e r c o n s i d e r a t i o n s [39] d e s e r v e a c l o s e r l o o k . The d e s i r a b l e f e a t u r e s o f a good SS code a r e : - s i m p l i c i t y of g e n e r a t i o n - l o n g sequence - low c o s t - f a s t s y n c h r o n i z a t i o n a c q u i s i t i o n and l o n g ( p r e f e r a b l y i n f i n i t e ) s y c h r o n i z a t i o n l o c k - i n t ime - good c o r r e l a t i o n p r o p e r t i e s - d i f f i c u l t t o d e c i p h e r . These a r e u s u a l l y c o n f l i c t i n g r e q u i r e m e n t s . A p r o p e r c h o i c e of code i s t o t a l l y d i c t a t e d by t h e s y s t e m r e q u i r e m e n t s , w h i c h a r e q u i t e a p p l i c a t i o n s p e c i f i c . F o r m i l i t a r y c o m m u n i c a t i o n s , p r o b a b l y f a s t s y n c h r o n i z a t i o n and n o n - d e c i p h e r a b i l i t y a r e p r i o r i t i e s w h i l e o t h e r f e a t u r e s a r e no t t o o c r i t i c a l . H o w e v e r , f a s t s y n c h r o n i z a t i o n r e q u i r e s t he p r e s e n c e of some d i s t i n c t f e a t u r e s i n t he code w h i c h w i l l make i t e a s i e r t o d e c i p h e r . F o r t h e i n d o o r o f f i c e n e t w o r k p r o p o s e d by t h i s w o r k , i t m igh t be a c c e p t a b l e t o 68 r e l a x t he c o v e r t n e s s r e q u i r e m e n t t o t r a d e f o r a f a s t a c q u i s i t i o n and s i m p l e c o d e s t r u c t u r e . The c o m b i n a t i o n s a r e many and d e s e r v e c a r e f u l c o n s i d e r a t i o n s . e ) A u x i l i a r y f u n c t i o n s V a r i o u s f u n c t i o n s s u c h as p r o t o c o l i m p l e m e n t a t i o n , s w i t c h i n g , a l a r m s u r v e i l l a n c e and s i g n a l l i n g e t c . , need t o be i n c o r p o r a t e d i n t he o v e r a l l s y s t e m d e s i g n . The OSI (open s y s t e m i n t e r c o n n e c t ) s t a n d a r d s h o u l d be o b s e r v e d . I t i s a l s o recommended t h a t , i f p o s s i b l e , t h e s e f u n c t i o n s s h o u l d be imp lemen ted on a m o d u l a r b a s i s so t h a t a change of t e c h n o l o g y i n one a r e a w i l l no t o u t d a t e t he w h o l e s y s t e m . Upgrade c a n be f a c i l i t a t e d by modu le r e v i s i o n . f ) C h o i c e o f t e c h n o l o g y A t p r e s e n t i t seems CCD ( c h a r g e c o u p l e d d e v i c e s ) [66] and SAW ( s u r f a c e a c o u s t i c w a v e ) [ 6 7 ] d e v i c e s a r e p o t e n t i a l c a n d i d a t e s f o r i m p l e m e n t a t i o n of SSMA r e c e i v e r s . An i n t e l l i g e n t d e c i s i o n on w h i c h t e c h n o l o g y t o p u r s u e , i s p o s s i b l e o n l y a f t e r c a r e f u l i n v e s t i g a t i o n s and e v a l u a t i o n s . g) T r a d e o f f o f b a n d w i d t h t o s y s t e m s i z e A 2B+D d a t a f o r m a t f o r 200 s u b s c r i b e r s i s assumed f o r t h i s s t u d y . I t s h o u l d be p o s s i b l e t o s e r v e 20 s u b s c r i b e r s e a c h r e q u i r i n g a 1 .544 MBPS c h a n n e l as an a l t e r n a t i v e . A l s o , a m i x o f 1.544 MBPS and 192 K B P S , w i t h c o r r e s p o n d i n g a d j u s t m e n t i n t he t o t a l number of s u b s c r i b e r s t o be s e r v e d , w o u l d be a n o t h e r p o s s i b l e s y s t e m c o n f i g u r a t i o n . I t i s s t r o n g l y recommended t h a t f u r t h e r work be a l l o w e d t o c o n t i n u e t o d e v e l o p a p r o t o t y p e and e v e n t u a l l y p roduce a s a l e a b l e p r o d u c t i n t he up a n d coming R L A N ' s m a r k e t . 69 CHAPTER 8 REFERENCES 1 . "The o f f i c e o f t h e f u t u r e " , U h l i g , F a b e r & B a i r , N o r t h H o l l a n d P u b l i s h i n g Company, 4 t h p r i n t i n g 1 9 8 2 . 2 . " ISDN i n t h e O f f i c e " - H i co m " S p e c i a l i s s u e t e l e c o m , r e p o r t and S iemens M a g a z i n e COM, December 1 9 8 5 . 3 . M.W. Rahm, " B r o a d b a n d N e t w o r k : A u s e r p e r s p e c t i v e " , IEEE Comm. M a g . , V o l . 2 2 , N o . 7 . , J u l y 1984 . 4 . S o f t w a r e C a n a d a , "Mos t L A N ' s w i l l need r e p l a c e m e n t s h o r t l y " , D e c / J a n . 1 9 8 7 , P . 2 . 5 . C a n a d i a n D a t a s y s t e m , May 8 6 , " B u i l d i n g L A N ' s w i t h o u t c a b l e s " , by C h r i s Gower R e e s . 6 . The F i n a n c i a l P o s t , 8 6 - 0 6 - 2 1 , S p e c i a l q u a r t e r l y r e p o r t , " L o c a l a r e a ne two rk v i t a l t o au tomated o f f i c e " , by B r u c e G a t e s . 7 . The F i n a n c i a l P o s t , 8 6 - 0 3 - 2 2 , S p e c i a l r e p o r t f r o m I n t e r n a t i o n a l D a t a C o r p . Canada L t d . , O f f i c e a u t o m a t i o n and compu te r n e t w o r k s , " M a r k e t f o r l o c a l a r e a n e t w o r k r i s i n g " . 8 . 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