The Analysis And Implemetation Of The PDCP Protocol Stack Based On The Arm Platform In WCDMA System

With the rapid development of wireless multimedia, besides traditional wireless voice Communication services, wireless network has began to support the increasingly multimedia services, such as images, video, and so on. Because of the addition of these new types of services, the data amount of wireless communication network is increasing rapidly, which make the scarce radio spectrum resources tenser. In order to solve this problem, on the one hand, better signal modulation methods, like OFDM modulation scheme, are researched so that more information can be carried in the certain band; on the other hand, the transmitted packet can be compressed to reduce the amount of data, improving the resource utilization of the frequency band. Usually, there are two data packet compression methods: information load compression and packet header compression.In today’s wireless network, various multimedia related protocol packets become the main transfer objects in the radio channel, these protocol packets often carry long protocol header bytes. Typical, such as the RTP voice packet, it usually has only15to20bytes voice data as payload; however, its protocol header can take as much as40bytes on the basis of IPv4standard, which make a great waste of valuable wireless channel resources. In order to achieve header compression, one of the3G standards, WCDMA communication system, separate a packet data convergence protocol layer on the user plane of the data link layer, which is specifically responsible for the compression operation to the header of the packet data transmission in the wireless link, to improve the transmission efficiency of packet data flow on the radio interface.This article is committed to the research and development work for Packet Data Convergence Protocol (PDCP) layer in the WCDMA system, based on the ARM9microprocessor embedded operating system platform. On the basis of a comprehensive and systematic analysis of ROHC, an entire ROHC system structure is designed and implemented. In this structure the total ROHC compression and decompression functions are realized on the ARM platform. Meantime, a test of compression efficiency and robustness of this new system is taken. Simulation shows that ROHC indeed have good performance on compression efficiency and robustness.Moreover, an improvement for ROHC protocol in multicast transmission environment is proposed in this article. In this scheme compression side can implement context synchronization function in transmission system by sending periodic refresh messages. Then a simulation of initial time loss of new comer and the throughput of the entire multicast system is taken using the improved ROHC protocol.The simulation results show that these improvements are feasible and effective to improve the throughput of multicast transmission channel.