Interference analysis of CDMA network using existing integrated wireless distribution systems in subways

With the rapid development of CDMA networks and increasing penetration of subways in various cities in China, it has become an important task to extend CDMA coverage into the underground. Thus, it makes great economical sense if CDMA signals can be distributed over existing integrated wireless distribution systems that were originally designed for GSM and paging signals. However, in order to ensure stable operations of all systems involved, it is necessary to analyze interaction and interference among them. In this paper, the existing integrated distribution system of Shanghai subway is first described and characterized, followed by an analysis of three factors that could impair the normal operations of the systems once the CDMA system is introduced: spurious emission, inter-modulation interaction and receiver overload. Based on the analysis, we outline requirements on the system design as well as precautionary measures to be considered. It is concluded that it is feasible for a new CDMA system to share the existing distribution system in an area covered by multiple systems, provided that the possible sources of interferences are carefully analyzed and taken into consideration when designing and deploying the CDMA system.