To overcome the defect that IEEE 802.11 Wireless Local Area Network (WLAN) does not provide link adaptation scheme, a joint Medium Access Control (MAC) layer and physical (PHY) layer cross layer link adaptation scheme (CLLA) is proposed. The proposed CLLA scheme, which takes channel interference into consideration and distinguishes collision lose and interference lose, provides mathematical description of PHY layer and MAC layer respectively. CLLA also deduces the relationship of two layers in term of throughput. CLLA selects rate adaptively to improve throughput. Simulation results and comparisons with existed schemes prove that the proposed CLLA scheme not only adapts interference and channel variation, but also improves system throughput obviously.

IEEE 802.11 Medium Access Control (MAC) protocol provides a competition-based distributed channel access mechanism for mobile stations to share the wireless medium in wireless Ad Hoc networks. Under the precondition of variable packet length, an energy analytical method was proposed, which calculated the energy efficiency of the basic, the RTS/CTS (Request To Send/Clear To Send) and the hybrid access mechanisms of the IEEE 802.11 Distributed Coordination Function (DCF). Furthermore, the effects of the network size, the average packet length, maximum backoff time, and the initial contention window on the energy efficiency of IEEE 802.11 DCF were explored in detail. Correctness and effectiveness of the proposed analytical method were verified through detailed simulation results.