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UBC Theses and Dissertations

Modeling and performance analysis of in-building distributed WLAN using CSMA with spread spectrum signaling Tang, Lawrence


In recent years, application of wireless technology in local area networks has become prominent due to its flexibility and ability to support portable terminals. This thesis considers a wireless local area network in a room with multiple stations accessing multiple radio bridges which are interconnected by a backbone network. Direct sequence spread spectrum signaling with a common spreading code and carrier sensing multiple access are employed. This system is analyzed with respect to uplink performance only as well as uplink/downlink performance. The 1-persistent carrier sensing multiple access protocol performs well in the uplink model. However, it does not yield satisfactory results in the uplink/downlink model. In particular, the 1-persistent protocol is unable to balance uplink/downlink channel access, giving the uplink traffic much higher throughput than downlink traffic. This unbalanced channel access problem is solved by using a dual persistency carrier sensing protocol, which is shown to balance uplink and downlink throughput. The relationships between packet duplications, hidden terminals and multiple packet receptions in the distributed wireless local network architecture are illustrated via eight system parameters. In particular, the number of radio bridges, the carrier sensing threshold and the type of power control method have the greatest influence on the system performance. These three parameters directly affect packet duplications, multiple packet receptions, the number of hidden terminals in the system, and the received signal-to-noise ratio and interferenceto- signal ratio at each receiver. In both the uplink only and uplink/downlink models, a higher number of radio bridges is found to be desirable since it allows multiple packet receptions. A moderate carrier sensing threshold is preferred since a low value causes packet duplications whereas a high value causes the system to saturate. Power-controlled transmission is desirable in terms of fairness because it equalizes capturing probabilities with respect to stations' distances from the radio bridges. Hidden terminals, which are detrimental to conventional carrier sensing systems, have a less detrimental effect in distributed wireless local area networks with multiple radio bridges due to the possibility of multiple packet receptions.

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