The Capacity Region of a Spread Spectrum Multiple-Access Channel

Spread spectrum communication systems offer a number of advantages in multiple access situations, compared with alternative approaches. A major disadvantage of spread spectrum is the low spectral efficiency due to mutual interference from other users of the system. In theory channel coding can increase this efficiency to about 70% for asynchronous systems, and 100% for synchronous systems. The channel capacity, and hence the spectral efficiency, is obtained here for the general case of a synchronous OR channel supporting n users with different data rates. The form of the results shows clearly how the interference from one user can be traded for that of another. Some alternative models are also investigated, primarily to show the effect of changes in the model on the capacity region.