UC Santa Cruz

This paper demonstrates that a pre-scheduled (primary) mobile user can receive information along with another user by taking advantage of transmit beamforming and multiuser diversity concepts. The motivation for combining these two approaches is to show that even in a time-sharing scheduling system (like many current systems), opportunistic users can also be scheduled without interfering with the pre-scheduled mobile users and still have good performance. The practicality of this approach is shown in the small amount of feedback required to take advantage of multiuser diversity, so long as we have full channel knowledge for the primary user. Once the channel of the primary user is known, the nullspace of its channel is used to maximize the received signal-to-noise ratio of the selected opportunistic user, given the small amount of feedback. A lower-bound for the signal-to-interference-plus-noise ratio (SINR) is derived and verified via simulation, and different approaches are then considered for the problem of selecting the appropriate secondary user conditions and ensure a logarithmic increase of SINR as a function of the number of mobile users.