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UBC Theses and Dissertations

Multi-receiver performance of slotted Aloha multiple access with direct sequence spread-spectrum signalling for wireless in-building networks Au, Andrew W. Y.


Recently, indoor networks trend towards the use of radio technology because of the user terminal portability and location flexibility it offers. The distributed architecture allows wireless terminals to interconnect to a backbone local area network via multiple receivers, easing network configuration and mobility management relative to the centralized approach. To combat both multipath and multiaccess interference, we consider a wireless in-building network where all terminals employ a common spreading sequence for direct sequence spread spectrum (SS) signalling in the physical layer, and the slotted Aloha protocol for multiple access. The objective of this thesis is to model and analyze the performance of such a system. The bit-error rate at the receiver is derived to study the capture effect of SS signalling technique with respect to different terminal locations in a room. Using theoretical analysis and simulations, we prove that this system is always stable under slotted Aloha multiple access, and achieves a high channel throughput approaching the number of receivers present, and a finite packet waiting time under heavy traffic. However, the near-far effect results in uneven performance at different locations. Among several strategies developed for combating the near-far problem, random signal selection with power control is capable in reducing the variation in the receiver capturing probability over different locations under heavy traffic, whereas power control only is suitable for light traffic. An infinite population model in an infinitely large room is used to study the placement of receivers. A ratio of receiver separation distance to separation distance between packet transmissions of 0.8 guarantees an average receiver throughput of at least 50% and a standard deviation in the receiver capturing probability of at most 10% of the average among all terminal locations. The square and interlaced receiver placement patterns are found to give very similar performance. These results are further shown to be applicable also for a finite population model in a room of limited size.

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