A Novel Algorithm Of WCDMA Base Station Testing

Wideband Code Division Multiple Access(WCDMA) is the most popular 3G standard, and both the number of operators and that of subscribers rank No.1 over the world. Accurately measuring the transmitting signals of WCDMA base station is meaningful to the deployment and optimization of WCDMA networks. Thus, it makes practical sense to develop signal analyzers to support WCDMA standards.Besides a deep study on WCDMA downlink physical layer protocols, the function blocks that signal analyzer should provide are defined and described, referring to the field test requirements and the functions of similar products in markets. Then, the algorithms like cell search, frequency offset compensation and channel estimation involved in WCDMA downlink signal processing are introduced in detail.Composite error vector magnitude(C-EVM) is one of the most important performance indexes to assess WCDMA radio frequency(RF) signal quality. The measurement of C-EVM is much more complicated than that of EVM, because it is necessary to search out all the activated code channels and calculate their power before reconstructing the reference signal. And the variable length of spreading codes used in WCDMA further increase the complexity. Based on the detailed analysis of the WCDMA signal characteristics, a measurement solution to Composite EVM is proposed in this paper. Power and modulation error rate(MER), are jointly utilized to identify the spreading code between the root and leaves. The characteristic that spreading codes of root and leaves cannot exist simultaneously is exploited to optimize the search strategy and reduce the search complexity.The simulation results demonstrate that the proposed solution can accurately measure the C-EVM of WCDMA downlink signals and meets the requirements of practical application. The scheme has been successfully implemented in practical products, and the performance index keeps pace with counterparts in markets.