Performance of WiMAX over MIMO Nakagami Fading Channels in Cross layer

This paper presents an optimal adaptive modulation (AM) algorithm using a cross-layer approach which combines truncated Automatic repeat request (ARQ) protocol and packet combining. Transmissions are performed on WiMAX over multiple-input multiple output (MIMO) Nakagami fading channels. Orthogonal frequency division multiplexing (OFDM) system is used. The data is transmitted in the form of packets. Here the retransmitted packets are not necessarily modulated using the same modulation format as in the initial transmission. Compared to traditional approach, cross-layer design based on the coupling across the physical and link layers has proven to yield better performance in wireless communications. However, there is lack for the performance analysis and evaluation of such design when the ARQ protocol is used in conjunction with packet combining.Indeed, previous works addressed the link layer performance of AM with truncated ARQ but without packet combining. In addition, previously proposed AM algorithms are not optimal and can provide poor performance when packet combining is implemented. Packet loss rate resulting from the combining of packets modulated with different constellations can be well approximated by an exponential function.This model is then used in the design of an optimal AM algorithm for systems employing packet combining,WiMAX and MIMO antenna configurations,considering transmissions over Nakagami fading channels.Numerical results are provided for operation with or without packet combining, and show the enhanced performance and efficiency of the proposed algorithm in comparison with existing ones.