Research And Implementation On Automatic Selective Repeat In WLAN Systems

Wireless local area network (WLAN) is becoming more and more popular as one kind of broadband wireless access technology. With the rapid development of mobile communications, the further applications of it were highly expected, such as mobile Internet, wireless image transmission etc. It is expected to support all kinds of new applications which require different quality of service (QoS). There are inborn shortcomings on QoS in IEEE 802.11 standard when it was used in wide area network, for example, DCF is excellent when the user load is low. However, the throughput and waiting time approximations will deteriorate rapidly when the load increases greatly. Since different kinds of services often differ in sensibility to the network characteristic such as transmission time lag, the demands for the network manager to differentiate their administration among those services are coming forth. We could no longer treat all the data packets in the same way, which will absolutely impose a negative influence on the transmission capability. In the data link layer, transmission different policies should be adopted as services varies. So, highly efficient ARQ that differentiates in disposal of different services becomes necessary and important. This paper introduces the main Automatic Repeat request technologies used currently in wireless communication system: MR_ARQ (Multiple Rejects ARQ),RLP (Radio Link Protocol) and Selective Repeat ARQ with Partial Bitmap. Based on the fact above, one Multiple Rejects ARQ algorithm was presented which has economic spending. It can save much up-bandwidth, more adapt to the future network. This paper discusses the mechanism, describes the arithmetic of the solution in detail. Furthermore, the arithmetic simulation is carried out to support the improved method in this paper. The simulation analysis proves that the proposed scheme could achieve remarkable performance gain than the conventional ARQ schemes. In this paper, it illustrates the Best-Effort RLC entity based on this ARQ algorithm which is designed for the wireless local area network system. Furthermore, the Best-Effort RLC entity and the Reliable RLC entity are combined in the whole plat in order to distinguish different kinds of services at the same time. Besides, some optimized algorithms are included such as combine / de-combine, zero cost copy. The analysis shows this scheme not only has much less complexity for implementation, but could achieve reasonable performance. Finally, this paper makes it clear how to realize the scheme under VxWorks real time operation system.