A CDMA-distributed antenna system for in-building personal communications services

To investigate applications of spread spectrum code division multiple access (CDMA) technology to in-building personal communications services (PCS), comprehensive studies have been conducted for a CDMA PCS distributed antenna system in the 1.8 GHz band. The CDMA PCS distributed antenna system was set up with three nodes, each having two time-delayed elements, in a Qualcomm two story office building in San Diego. This paper presents measurement and modeling results on coverage, voice quality (frame error rate), reduction of transmit power, and path diversity for the in-building CDMA PCS distributed antenna system. Wideband CDMA signal coverage was predicted by using a ray tracing tool to find optimum placement of the distributed antennas. Using three nodes mounted in the ceiling space between the first and second floors, with each active element transmitting at -5 dBm in the system, the ray-tracing prediction shows good signal coverage in both floors of the building. The prediction results are confirmed by measurements at numerous discrete points with a standard deviation of 3.3 dB. Measurements using various combinations of number of nodes and delay elements showed significant time and path diversity advantages for the CDMA-distributed antenna system in indoor radio environments. Trade-offs between diversity gain and self-interference due to uncaptured finger energy in fringe areas are discussed.