WLC13-5: Downlink Capacity Improvement Through Orthogonal Code Hopping Multiplexing and Multiple Scrambling Codes in CDMA Systems

We compare the performance of the downlink capacity improvement schemes based on orthogonal code hopping multiplexing (OCHM) and multiple scrambling codes (MSC). Both OCHM and MSC have been proposed in order to overcome a code-limitation problem in CDMA downlink. However, both schemes exhibit different characteristics. In order to increase user capacity in CDMA downlink, OCHM allocates a random hopping pattern using a set of orthogonal codes instead of orthogonal code for each connection and MSC allocates a non-orthogonal codeword to each connection. In the OCHM scheme, hopping pattern (HP) collisions may degrade the system performance. The HP collisions in OCHM systems differ from the hits in frequency- hopping (FH) systems because it can be effectively controlled through synergy and perforation techniques. In OCHM, the receiver requires additional energy for a given frame error rate (FER) due to the HP collision. In the MSC scheme, inner-cell interference is induced by non-orthogonal codewords and it degrades the performance. Numerical examples show that the OCHM-based system is more effective than the MSC-based system.