A NEW PACKET CDMA NETWORK WITH HIGH CAPACITY

Abstract

A new packet CDMA network has been looked into. Three types of codes are used to encode a packet before transmission: mobile codes (MCs) for communication purposes, transmitter codes (TCs) as pilot signals and common codes (CCs) for registration or location updating. MCs appear in both uplink and downlink communications while TCs and CCs appear only in downlink and uplink communications respectively. In the analysis, signal-to-noise ratio (SNR) expressions have been derived. It was found that the uplink case is the limiting case. For non-fading channels, the capacity can be very high when the code length used is large. For conventional lengths in use now, the system is able to support comfortably more than 100 users in a cell. For fading channels, the capacity is very small. But on application of RAKE receivers, the performance improves tremendously. As the number of RAKE fingers increases, the performance approaches the non-fading case. The optimum number of RAKE fingers to use takes into consideration the multipath fading environment and also the number of fading paths encountered.