Achievable performance gain of IEEE 802.11 multi-rate link adaptation algorithm with cross-layer design

Link quality based rate adaptation which aims at link throughput optimization has been used widely for IEEE 802.11 networks. However, from system perspective network performance is affected by not only link quality but also random channel access at the MAC layer. Selection of transmit mode for optimal link throughput can cause performance loss of MAC throughput. In this paper we investigate this issue and propose a generalized cross-layer rate adaptation algorithm which considers jointly link quality at the physical layer and random channel access at the MAC layer to optimize network throughput. The objective is to examine the potential benefits that can be offered by cross-layer design. An efficient analytic model is proposed to evaluate rate adaptation algorithms operated under dynamic channel and multi-user access environments. The proposed rate adaptation algorithm is compared to the link throughput optimization based rate adaptation algorithm. It is found that rata adaptation by optimizing link layer throughput can result in large performance loss at the MAC layer, which can not be compensated by the means of optimizing MAC access mechanism alone. Numerical results show that the cross-layer design can achieve consistent and considerable performance gains of up to 20%. Therefore cross-layer rate adaptation design is promising and deserves to be exploited in practical rate adaptation design for IEEE 802.11 networks.