Adaptive Dly-ACK for TCP over 802.15.3 WPAN

The Dly-ACK scheme in IEEE 802.15.3 is designed to reduce the overhead of the ACK and improve the channel utilization. However, the way to use the Dly-ACK is open for implementation. In this paper, we first investigate the problems of applying the fixed Dly-ACK scheme to the TCP stream and show that the TCP performance is rather poor. Then, we propose two enhancement mechanisms for TCP with Dly-ACK over the 802.15.3 system. The first one is to request the Dly-ACK frame adaptively or change the burst size of Dly-ACK according to the queue size. The second is a retransmission counter to enable the destination DEV to deliver the packets to the upper layer timeously and in orderly fashion. Simulation results show that, with our enhancements, the TCP throughput can be improved more than 40% compared with the conventional Imm-ACK. We also investigate the impacts of some important system parameters such as the buffer size on the TCP performance. Some guidelines for the Dly-ACK design are given. Finally, it is worth pointing out that our enhancements are compatible with the standard.