Correlated fading and antenna directionality in multiuser detection

We investigate detection of multiple users at a base station array of antennas, isotropic or directional, with overlapping beam patterns. The question is whether the increased diversity obtainable by isotropic antennas can compensate for the loss of antenna gain. We also account for limited angle spread of the arriving signals, which correlates the gains and reduces diversity. We consider the multiuser detection algorithm to be maximum likelihood and present new expressions for the resulting symbol error rate in correlated fading. Among other features, they show that each user's performance depends on the angle spreads of all users. We also demonstrate that a circular array of directional antennas with overlapping beams can achieve the same level of diversity as a circular array of isotropic antennas.