Research On Datalink Layer QoS In Broadband Wireless IP Mobile Communication System

The development of wireless communication and broadband technologies makes broadband wireless communication network the first choice in the filed of personal communication and wireless services. The wireless channel places fundamental limitations on the performance of wireless communication systems. This makes high speed data transmission a big challenge in wireless network. ARQ(Automatic-Repeat-reQuest) can greatly improve the reliability of data transmission. Multi-rejects ARQ which combines the strong points of MR ARQ and HIPERLAN can effectively improve the throughput in the wireless datalink layer. Multi-ARQ supplies us several RLC entities which are different in the mechanisms of data sending and acknowledge and forms the basic frame of wireless datalink layer QoS. A wireless datalink layer QoS framework is developed based on diffserv architecture of IP QoS and Multi-ARQ technology. This QoS module together with RLC sub layer provides upper layer multi-user and multi-service QoS control. Congestion control is an important function of QoS. This paper discusses TCP's slow start, congestion avoidance, fast retransmission and fast recovery algorithms, develops a congestion control method for wireless networks based on multi-rejects ARQ algorithm. According to RED algorithm, this method controls the congestion through the ARQ send window, the length of segmentation queue and the link-layer retransmission rate. The simulation proves this method can improve the link throughput.