Capacity and error rate of spatial CDMA for multiple antenna multiple accessing

Pulse radio has been considered a power efficient method for communication in a multiple path fading environment. We extend the method to the use of multiple transmitters per user, and the use of receiver arrays distributed over a geographic area. We show that we can obtain a linear growth in transmission capacity if we use multiple receivers. We explore the notion of spatial capacity, similar to the earlier results for point-to-point communications with multiple antenna elements (MAE). Since spatially separated users each uses a different set of paths to reach a receiver, we can imagine that the multipath “impairment” actually could be used to our advantage to improve capacity and reduce transmission errors. In effect, each user has a multipath transmission signature that helps to distinguish its information transmission. This transmission signature becomes more complex when we have multiple receivers at the base station, and multiple transmitters at the user. The signature can be seen as a spatial CDMA code, and the use of MAE actually increases the multiple access capacity linearly with the multiplicity of antennas. We study the spectral characteristics of monocycle pulses and other bandwidth efficient pulse shapes. We propose a novel technique of using a convolution formula for the Poisson shot noise process to calculate the probability distribution of multiple access interference (MAI). The technique analyses the Poisson process. Using the distribution, we calculate the channel capacity of spatial CDMA for various pulse shapes. We show that spatial CDMA provides high capacity wireless multiaccess communications