H.V. Poor

Soft handoff and uplink capacity in a two-tier CDMA system

This paper examines the effect of soft handoff on the uplink user capacity of a CDMA system consisting of a single macrocell in which a single hotspot microcell is embedded. The users of these two base stations operate over the same frequency band. In the soft handoff scenario studied here, both macrocell and microcell base stations serve each system user and the two received copies of a desired users signal are summed using maximal ratio combining. Exact and approximate analytical methods are developed to compute uplink user capacity. Simulation results demonstrate a 20% increase in user capacity compared to hard handoff. In addition, simple, approximate methods are presented for estimating soft handoff capacity and are shown to be quite accurate.

Downlink user capacity in a CDMA macrocell with a hotspot microcell

This paper examines the downlink user capacity in a CDMA system composed of a macrocell and a microcell, where both cells use the same frequency channel. The effect of channel dispersion on the number of simultaneous users supported is studied for three different downlink power control methods. Channel dispersion produces in-cell interference and variable fading of the received signal power. Novel analytical methods are developed to account for both effects; these techniques derive user capacity for any delay profile using the results for the uniform delay profile. The downlink user capacities for the three power control methods are compared to the uplink user capacity under the same channel conditions. The results point to the need for fast power control to obtain uplink-limited performance.

Uplink user capacity in a CDMA system with hotspot microcells: effects of finite transmit power and dispersion

This paper examines the uplink user capacity in a two-tier code division multiple access (CDMA) system with hotspot microcells when user terminal power is limited and the wireless channel is finitely-dispersive. A finitely-dispersive channel causes variable fading of the signal power at the output of the RAKE receiver. First, a two-cell system composed. of one macrocell and one embedded microcell is studied and analytical methods are developed to estimate the user capacity as a function of a dimensionless parameter that depends on the transmit power constraint and cell radius. Next, novel analytical methods are developed to study the effect of variable fading, both with and without transmit power constraints. Finally, the analytical methods are extended to estimate uplink user capacity for multicell CDMA systems, composed of multiple macrocells and multiple embedded microcells. In all cases, the analysis-based estimates are compared with and confirmed by simulation results.

User capacity in a CDMA macrocell with a hotspot microcell: effects of transmit power constraints and finite dispersion

This paper examines the uplink user capacity in a CDMA system composed of one macrocell and one microcell when user terminal power is limited and the wireless channel is finitely-dispersive. A finitely-dispersive channel causes variable fading of the signal power at the output of the RAKE receiver. Analytical methods are developed to compute the user capacity as a function of a dimensionless parameter that depends on the transmit power constraint and cell radius. Additionally, a novel analytical method is developed to study the effect of variable fading due to a finite number of multipaths. This technique derives the user capacity for any delay profile using the results for the uniform multipath channel. Simulation results confirm the accuracy of these simple analytical solutions.

Uplink throughput in a single-macrocell/single-microcell CDMA system with application to data access points

This paper studies a two-tier code-division multiple-access (CDMA) system in which the microcell base is converted into a data access point (DAP), i.e., is a limited-range base station that provides 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. The achievable throughput for individual microcell users is examined and a simple accurate approximation for its probability distribution is presented. Computations for average throughputs, both per-user and total, are also presented. The numerical results highlight the impact of a desensitivity parameter used in the base-selection process.

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.