Research On Transmission Of B-CDMA Overlaying GSM And Its Key Techniques

With the rapid development of mobile communication systems, the existing GSM and narrowband CDMA cellular system cannot solve the contradiction between the limited frequency source and the increased mobile users. Furthermore, the network technique only support the voice service cannot meet the communication requirements of people. People hope to obtain multimedia service such as packet data, video and picture phone etc besides voice service. All these need operators and researchers to look after the mobile communication scheme which optimizes spectrum efficiency and expands system capacity to accommodate more users in major metropolitan markets. To solve these issues, a new idea i.e. co-frequency transmission technique is proposed. It can not only realize the smooth transition from 2G to 3G but also optimize spectrum efficiency and expand system capacity to accommodate more users in major metropolitan markets.Firstly this paper researches present mobile communication technique of enhancing system capacity, next further researches basic principles of TDMA and CDMA system. Based on these researches a new scheme is proposed that let Broadband code division multiple access (B-CDMA) system overlay on an existing narrowband digital cellular system (i.e. GSM). To realize the object of this research, we must solve some problems better such as the relationship between the spread spectrum processing gain and system complexity, the choice of spread spectrum codes etc. All these problems can be solved by existing theories and techniques and need not establish new system info, so this technique scheme is feasible. Then the present capacity of GSM and CDMA system is analyzed and the cellular system total capacity adopting this co-frequency transmission scheme will be discussed in detail. It can be estimated that such an overlay has the potential of enhancing the overall spectrum efficiency and system capacity and it can provide for the flexibility of spectrum utilization. Finally this scheme will be simulated and then we analyze the relationship between spread spectrum processing gain, system capacity and mutual interference according to simulation results.