MC-CDMA and its relation to general multiuser/multisubchannel transmission systems

A general model for multiuser/multisubchannel transmission systems is derived. This model can be used to compare various existing transmission systems and those proposed for future mobile radio communications in a basic way. It allows conclusions with respect to the complexity of the algorithms at the receiving side and the overall performance to be expected. It incorporates all known basic techniques which can be used to separate the users of a mobile communication system and to create subchannels for a “parallel” transmission of symbol blocks from an arbitrary user to another. The basic techniques range from FDM/FDMA to CDM/CDMA and OFDM to OCDM. The core of this model, the “channel matrix”, is used to describe the differences and commonalities of these basic techniques. It is demonstrated that the basic effect of combinations, which allow a tradeoff between performance and complexity, becomes easy to estimate. Furthermore it is pointed out that many different techniques become equivalent, also in the case case of frequency selective radio channels, as long as multiuser receiving algorithms are assumed. As a special example of a general multiuser/multisubchannel transmission system MC-CDMA (multicarrier code division multiple access) is considered in more detail. Some conclusions concerning channel coding are also made