Interactions between transmission power and TCP throughput fairness in wireless CDMA networks

TCP protocols have scarce performance when transmitting over wireless channels. In fact, wireless medium is characterized by multipath fading and high time variability which lead to a great amount of losses in the transmitted packets. In such environments many new problems arise, the most serious of which are the decrease of throughput performance and the unfairness due to the great difference in the Round Trip Times (RTTs) of the connections sharing the same wireless link. In particular, the unfairness is related to the fact that the lower is the RTT of a connection, the higher is its throughput. In literature many solutions aimed at improving TCP fairness through modifications of the congestion avoidance algorithm have been proposed. However, all these solutions are not suitable for wireless networks because they still interpret transmission losses as congestion clue while it is not. In this paper it is demonstrated that the unfairness problem can be solved through appropriate power management. In particular, by letting connections with longer RTT transmit with stronger power, the proposed approach tries to increase the fairness. The performance evaluation is carried out using the NS2 Simulator and interesting simulation results are provided. In particular, it can be observed that, if compared to standard wireless CDMA solutions for transmission over wireless networks, the proposed approach allows to guarantee a good level of throughput and a higher fairness.