Throughput Performance of Spread Spectrum Multiple Access Packet Radio Networks.

摘要

In this dissertation, an integrated model of an unslotted spread spectrum multiple access (SSMA) packet radio network is developed. The model combines a detailed model of the radio channel, accounting for the effect of multi-user interference, with a network model that traces the evolution of the number of interfering transmissions and accounts for the half-duplex nature of the radios. A new analysis of the performance of a Viterbi decoder in a packet radio environment allows the model to be used for a system with convolutional Forward Error Correction (FEC) coding. The synchronization process is also analyzed and incorporated into the integrated model. The model makes use of several approximations for tractability. A discrete event simulation is used to validate these approximations. The integrated model leads to numerical results which show the throughput and the probability of success for a packet as a function of the channel level and network level parameters. Specifically, for the radio channel, these parameter include the modulation format, the received signal power, the spread spectrum bandwidth expansion, and the presence or absence of FEC coding. Also, the throughput is found as a function of the synchronization parameters, such as the detection thresholds and correlation times, for several different synchronization circuits and preamble structures. At the network level, the parameters are the traffic rate and the network size. The random access protocols considered include unslotted ALOHA and channel load sensing, which is an extension of carrier sensing to an SSMA network. (jhd)