MIMO-Based Rate Adaptation to Enhance TCP Throughput over Wireless Fading Channels

We study the performance of TCP (transmission control protocol) over a wireless fading link using MIMO (multiple input multiple output) technology. MIMO technology using multiple transmit and receive antennas can potentially mitigate the effect of fading by providing diversity gain and/or increase the throughput by providing multiplexing gain. Given the number of transmit and receive antennas, there exists a tradeoff between the diversity and multiplexing gains. We study the effect of the so-called diversity-multiplexing tradeoff on the throughput of TCP. We demonstrate by cross-layer simulations involving the physical and transport layers that diversity gain is more useful to enhance TCP throughput when the signal-to-noise ratio (SNR) is low, and multiplexing gain is more useful when SNR is high. Our results indicate that there exist SNR levels at which switching from diversity-providing schemes to multiplexing schemes would provide enhanced TCP throughput. We propose a cross-layer rate-switching scheme to enhance TCP throughput over a wide range of SNR values.