Uplink Users Research Articles

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.

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 user's 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.

Uplink user capacity in a CDMA macrocell with a hotspot microcell: exact and approximate analyses

This paper studies the number of voice users (user capacity) supported on the uplink of a single-macrocell/single-microcell code-division multiple-access system. A microcell is embedded within a larger macrocell and operates over the same bandwidth as the larger cell. Analytic methods are presented for computing user capacity which account for propagation loss, multiple-access interference, power control, and random locations of user terminals, as well as two distinct methods by which users select base stations (tiers). Along with the exact user capacity, a technique for making accurate approximations is also presented. Simulation results verify both the exact and approximate analytical methods. This simulation is also employed to study the capacity gains of a third, more optimal, tier-selection scheme. These results point to differences in capacity performance based on the tier-selection method, as well as on the traffic density within the hotspot region.

Modeling and prediction of the wireless vector channel encountered by smart antenna systems

AbstractIn this paper, a Kalman‐filter‐based, vector autoregressive (VAR) model is used to forecast mobile user uplink spatial signatures and improve downlink signal‐to‐interference ratio in time‐division duplex (TDD) systems. Results are presented from computational electromagnetic (CEM) simulations of a smart antenna system operating at 1.8 GHz in an urban microcellular environment. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 35: 281–283, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10582

OFDM uplink for interactive broadband wireless: analysis and simulation in the presence of carrier, clock and timing errors

This paper is concerned with the performance of OFDM when used as a modulation and access technique for the uplink of an interactive broadband wireless system or in the return link of a terrestrial television system. In such an application, the uplink performance becomes strongly dependent on the discrepancies related to the carrier frequencies, sampling frequencies and time references used by different users. In addition, different uplink subcarriers will see different channels since individual subcarriers are allocated to different users. The main purpose of this paper is to provide the analytical tools necessary to quantify the performance of such an uplink by taking into consideration the error sources indicated above. The analysis is made from the uplink users' perspective; i.e. the results are presented with the subcarrier index as a parameter. Average uplink user performance is obtained by averaging over the tone index. Extensive computer simulations have been carried out and the results are in strong agreement with the analytical predictions.