Throughput performance of direct spread Slotted-Aloha packet networks
Vincent Barnes, William P. Osborne · 16th International Communications Satellite Systems Conference · 1996
The throughput performance of direct spread Slotted-Aloha systems is evaluated and compared with the normalized throughput of a narrowband system to determine the extent to which the 'softer' collision characteristics of the spread system can improve throughput. This paper simulates a DS/SSMA packet network using the Signal Processing Workstation software. The packet throughput of a rate 1/2 convolutionally coded DS/SSMA Slotted Aloha packet network, using soft decision Viterbi decoding, is determined and compared to the existing analytical results. The simulations show the 'so called' Improved Gaussian Approximation (IGA) does indeed provide accurate results for an uncoded system. However, when soft decision Viterbi decoding is used, the channel exhibits a decrease in performance of approximately 0.5 dB compared to the results predicted by the IGA model. Despite this, the simulations show the DS/SSMA Slotted-Aloha system can support more traffic than an equivalent narrowband network. The throughput of the direct spread channel is approximately 50 percent for packet lengths of approximately 1000 bits and 70 percent for packet lengths on the order of 100 bits. (Author)