多载波CDMA容量的研究

该文对多载波CDMA容量规划进行了详细的理论和数学分析，推导出多载波CDMA上下行链路的容量的表达式，利用拉格朗日乘数求极值的方法，分别得到多载波CDMA话音和数据业务上下行链路最大容量；同时得出一个非常重要的结论：只有当即基站最大发射功率平均分配给每个子载波时，多载波CDMA系统才能获得最大的容量。该文还对影响容量的因素进行了仿真，各业务的容量随平均路径损耗的增加急剧下降。由此揭示了容量和覆盖的内在关系：容量和覆盖是相互制约的一对矛盾，容量的增加就意味着覆盖的减小，反之亦然。无论上下行链路，当功率达到一定程度时，再通过增大功率来提高容量并不是行之有效的方法。最后，通过对GSM，WCDMA，多载波CDMA 3个系统容量的比较，得出多载波CDMA下行链路频谱效率为WCDMA频谱效率的1.7倍，GSM 的2.7倍；上行链路频谱效率为WCDMA频谱效率的2.1倍，GSM 的2.4倍的结论。

Research on Capacity of Multicarrier CDMA

Theorelical and mathematical analyses of multicarrier CDMA capacity planning are proposed and the expressions of capacity for multicarrier CDMA are derived both in uplink and downlink. Through extremum of a multivariate function (by Lagrange multipliers), the maximum capacity of multicarrier CDMA is achieved from the viewpoint of voice and data, respectively. Simultaneously, the important conclusions are got for multicarrier CDMA: when BS maximum transmit power is average distributed for all subcarriers, the maximum of capacity is achieved. Simulation results show that capacity of all kinds of service will decrease rapidly as average path loss increase. The essence is opened out between capacity and coverage: capacity and coverage restrict each other, decreasing in capacity means extend in coverage, and vice versa. When transmit power is in higher level, increasing power is not an effective way to improve capacity. From comparison between GSM, WCDMA and multicarrier CDMA, the conclusion are achieved that the spectrum efficiency of multicarrier CDMA is 1.7 times that of WCDMA, and 2.7 times that of GSM in downlink; and 2.1 time that of WCDMA, and 2.4 times that of GSM in uplink.