Optimal multiple access to data access points in tiered CDMA systems

This work studies a specific two-tier CDMA system in which a microcell attracts only a small number of users and gives them high-speed access while the umbrella macrocell serves multiple simultaneous low-rate users. The microcell, referred to as a data access point (DAP), operates on the same frequency as the macrocell and uses the same chip rate. The DAP users adapt their spreading factor in accordance with interference conditions, whereas the macrocell users have a fixed data rate. The analysis here presents a scheduling method that maximizes the total DAP throughput. The schedule indicates which DAP users should be given access and at what data rate. We also devise a second access scheme which maximizes throughput while ensuring each user is assigned one slot per frame. Our results show that the DAP can support at most two simultaneous users. Further, throughput gains of optimal access are more evident when the DAP contains multiple potential users.