Research On Link Adaption Schemes Based On Cross-layer Design

The evolution of wireless communication results in a vigorous growth of multimediaservice which means the wireless communication services turn to multimedia data service,high speed image transmission and so on rather than low speed voice service step by step.While the contradiction among the limitation of the radio resources, the complexity ofwireless communication environment and the severe demand for quality of service formultimedia services deepens, the disadvantage of traditional layered structure emerges.Besides, since higher transmission rate and faster movement speed make the wirelesschannel more complex, how to enhance the performance of radio link becomes one ofhotspot issues of wireless communication. The link adaption mechanism based oncross-layer design allows information sharing between phycial layer and data link layer,and optimizes them to achieve higher spectral efficiency under limited radio resources.Adaptive Modulation and Coding (AMC) and Automatic Repeat request (ARQ) aremost widely used among link adaption. In this article, we use the above two technologiesto discuss cross-layer link adaption mechanism including selecting switching thresholdsfor modulation and coding scheme and average packet error rate in Physical layer in orderto optimize spectral efficiency and throughput.Firstly, we introduce a kind of cross-layer design by combining AMC and ARQ,whose performance is compared with AMC-only and ARQ-only schemes and we come upwith two modified cross-layer schemes to enhance average spectral efficiency. Then, weuse a Finite State Markov Chain model to describe the behavior of the channel and thequeue considering the combined affection of a limited queue and AMC, and obtain aclosed-form expression of real average throughput. Based on the analysis of FSMC, weintroduce a cross-layer design combining AMC and the dynamic queue at data link layer, and compare the performance of cross-layer design and layered design using simulation,which quantify the gain in average throughput via optimizing the average packet error rateat Physical layer. At last, we add the ARQ technology into the cross-layer designcombining AMC and the dynamic queue, and propose a modulation and coding schemeselection method considering the channel state information and the queue state.Simulation shows this new cross-layer design can improve the average throughputefficiently.