Uplink throughput in a single-macro cell/single-micro cell CDMA system, with application to data access points

Building upon the study of a single-macrocell/single-microcell CDMA system in (S. Kishore et al, IEEE Trans. on Wireless Comms., vol.2, no.2, p.364-374, 2003), we examine the performance of a specific example of such a two-tier system. In particular, the microcell base is converted into a data access point. Data access points (DAPs) are limited-range base stations that provide high-speed access to one user at a time. The microcell (or DAP) user operates on the same frequency as the macrocell users and has the same chip rate. However, it adapts its spreading factor (and thus its data rate) in accordance with interference conditions. By contrast, the macrocell serves multiple simultaneous data users, each with the same (fixed) rate. We analyze the achievable throughput for individual microcell users and present a simple, accurate approximation for its probability distribution. We also present average throughputs, both per-user and total. Our numerical results highlight the impact of a desensitivity parameter used in the base-selection process.