Single user TCP downstream throughput probability models in IEEE802.11b WLAN system

Single User, Transmission Control Protocol Downstream Throughput (TCPDST) probability models in an IEEE802.11b WLAN have been developed, validated and evaluated for performance. Measurement of single user TCPDST were taken using Tamosoft throughput test while that of signal to noise ratio (SNR) were taken using inSSIDer 2.1. The Tamosoft throughput tests were conducted using different quality of service (QoS) traffic. These QoS traffic (which were sent through an infrastructure based network) correspond to different wireless multimedia tags. Measurements were taken in free space, small offices and open corridor environments. By assuming a normal distribution, single user TCPDST Cumulative distribution function (CDF) probability models were developed for different signal categories namely: (i) all the SNR considered, (ii) strong signals only, (iii) grey signals only and (iv) weak signals only. The models were validated and their performances evaluated using root mean square (RMS) errors. RMS errors were computed by comparing model predicted values with validation data. The RMS errors for single user CDF all signals model was 0.1466%. RMS errors for strong signals models, grey signals model and weak signals model respectively were 0.1466%, 0.6756% and 0.1233% indicating acceptable performances. All signals, strong signals, grey signals and weak signals CDF probability models predicted probabilities of obtaining TCPDST values greater than 5Mbps as 74.79%, 90.55%, 13.00% and 4.77% respectively while probabilities of obtaining TCPDST values less than 2Mbps were predicted as 4.91%, 0.00%, 18.98% and 52.41% respectively. These probability models will provide additional useful information needed to design efficient distributed data networks. Keywords: Throughput, TCP, WLAN, probability model

Empirical Investigation on the Dependence of TCP Upstream Throughput on SNR in an IEEE802.11b WLAN System

An empirical investigation on the dependence of TCP upstream throughput against signal to noise ratio (SNR) in an IEEE802.11b WLAN system was carried out in various environments and varieties of QoS traffic. The TCP upstream throughput (TCPupT) was measured for various SNR observed. An Infrastructure based IEEE802.11b WLAN system having networked computers on which measurement software were installed, was set up consecutively in various environments (open corridor, small offices with block walls and plaster boards and free space). Empirical models describing the TCPupT against SNR for different signals ranges (all ranges of signals, strong signals only, grey signals only and weak signals only) were statistically generated and validated. Our results show a strong dependence of TCPupT on the received SNR which varied as the SNR values changed from high (strong signals) through low (grey signals) to very low (weak signals). Our models showed lower RMS errors when compared with other similar models. We observed RMS errors of 0.5431955Mbps, 0.447938789Mbps, 1.04536603Mbps and 0.4503096Mbps for all SNR model, strong signals model, Grey signals model and Weak signals model respectively. Our models will provide researchers and WLAN systems users with a tool to estimate TCPupT in a real network in various environments by monitoring the SNR