This chapter explains the importance of channel bit error rate (BER) in 802.11 networks and proposes a joint physical layer-Medium access control (MAC) cross-layer design (CLD) framework for improving WLAN performance. It describes the principle of operation of the channel-aware buffer unit multiple access protocol. The chapter shows that the proposed CLD framework and algorithms. It discusses the benefits and practical implications of the proposed CLD framework. The chapter provides a simulation model to study the performance of the proposed CLD. The motivation for implementing a wireless channel BER in ns-2.31 was to verify the accuracy of ns-2.31 results and to model CLD more accurately. For the implementation of the proposed CLD framework, two algorithms, namely, channel prediction and the MAC protocol modeling, are described. The CLD was evaluated by measuring network mean throughput, packet delay, mean deviation of throughput fairness, and packet drop ratio. The proposed CLD significantly reduces packet drops, leading to overall network throughput improvement.