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We propose an orthogonal code hopping multiple access (OCHMA) scheme in order to improve the capacity of an uplink-synchronized code division multiple access (CDMA) systems. When orthogonal codes (OCs) are used for channelization in uplink-synchronized CDMA systems, a finite set of OCs tends to severely limit the capacity gain of the uplink-synchronized CDMA systems. The OCHMA system allows each user to use a different OC for each symbol according to an allocated hopping pattern (HP). It also allows multiple users to use the same OC at a specific symbol time, which is called an HP collision. Thus, the proposed OCHMA scheme can accommodate more users than the number of available OCs. We analyze the capacity of the OCHMA scheme and compare the performance of the OCHMA with that of conventional schemes including the system using multi-scrambling codes (MSC) which have also been proposed to overcome a code-limited situation.
Date of Publication: November 2009