Open Collections

Asynchronous hopping and code diversity in frequency hopped code division multiple access systems

University of British Columbia

This thesis is about Frequency Hopped-Code Division Multiple Access (FH-CDMA) systems. More specifically, it studies the packet error rates and system performance of FHCDMA systems with guard times. In the past, a number of simplifying assumptions have been made in the studies of these systems. This work investigates the effects of these simplifying assumptions by deriving exact expressions, which do not make these assumptions, and comparing the results using both methods. By considering edge effects due to the inclusion of guard times, it is shown that the probability of codeword error can be significantly lower. Furthermore, it is found that the independence assumption, where frequency hits within a packet is assumed are independent, leads to larger probability of codeword error. On the other hand, system performance measures such as normalized maximum local traffic and throughput are not significantly altered by these simplifying assumptions. In addition, this work also proposed a new diversity scheme in FH-CDMA systems, which we refer to as code diversity. In such a diversity scheme, the transmitters are allowed to transmit in more than one frequency bin simultaneously. A variety of decoding schemes, including some with optimal bit error rate (BER) performance, for the code diversity system are proposed and studied. It is shown that the code diversity scheme can have a lower BER than conventional FH-CDMA systems and that such a method of transmitting can be used to establish priority classes among the users in the system. It is further shown that error control coding can be included in the code diversity transmission scheme to further improve the BER performance. The performance of several code diversity schemes is studied in a Rayleigh fading and additive white Gaussian noise environment. From the analysis of the various schemes it is found that code diversity can improve the BER.

Thesis/Dissertation

application/pdf

2009-04-20

For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.

http://hdl.handle.net/2429/7432

Electrical and Computer Engineering

University of British Columbia

UBCV

DSpace