Power-controlled CDMA Research Articles

MULTIUSER INTERFERENCE SUPPRESSION TECHNIQUES FOR DIRECT-SEQUENCE CDMA COMMUNICATION SYSTEMS

In this paper, several techniques for multi-user interference suppression from power-controlled direct-sequence CDMA systems are proposed and the emphasis is on the one-shot structure. The proposed schemes arise from the optimum detector that takes into account the existence of power-controlled chip-synchronous multi-user interference and white Gaussian noise. Restricting the multi-user interference to the power-controlled chip-synchronous case strongly reduces the complexity of the optimum detector. For more reduction in the complexity, some approximations of the obtained techniques are also considered. It is shown that in asynchronous CDMA systems and in the presence of white Gaussian noise, the proposed detectors outperform the correlator with comparable complexity

Power-Controlled CDMA Cell Sectorization with Multiuser Detection: A Comprehensive Analysis on Uplink and Downlink

We consider the joint optimization problem of cell sectorization, transmit power control and multiuser detection for a CDMA cell. Given the number of sectors and user locations, the cell is appropriately sectorized such that the total transmit power, as well as the receiver filters, is optimized. We formulate the corresponding joint optimization problems for both the uplink and the downlink and observe that in general, the resulting optimum transmit and receive beamwidth values for the directional antennas at the base station are different. We present the optimum solution under a general setting with arbitrary signature sets, multipath channels, realistic directional antenna responses and identify its complexity. We propose a low-complexity sectorization algorithm that performs near optimum and compare its performance with that of optimum solution. The results suggest that by intelligently combining adaptive cell sectorization, power control, and linear multiuser detection, we are able to increase the user capacity of the cell. Numerical results also indicate robustness of optimum sectorization against Gaussian channel estimation error.

Effects of the BS power and soft handoff on the outage and capacity in the forward link of an SIR-based power-controlled CDMA system

In the forward link of a signal-to-interference ratio (SIR)-based fast power-controlled CDMA system, the fraction of base station (BS) power allocated to a mobile station (MS) is considered as a key factor affecting the system performance. By using our proposed macrodiversity non-orthogonality factor, we establish a unified analytical model to characterize the distribution of the fraction of BS power allocated to an MS in either the non-soft handoff mode or the soft handoff mode. By using that distribution and limiting the maximum fraction of BS power available to an MS, a closed-form expression of the capacity at a certain outage probability is obtained. The effects of system parameters, such as the available Rake fingers, the soft handoff threshold, the unbalance of the BS power, and the power control error, on the capacity are investigated from the viewpoint of the limitation on the fraction of BS power allocated to an MS. Simulation results show that soft handoff does not always improve capacity and the capacity gain may result depending on the choice of the system parameters

Performance and capacity improvements of subchannel power-controlled MC-CDMA system under multipath channels

In this paper, a novel subchannel transmission power control algorithm for MC-CDMA system is proposed. Subchannel power-controlled OFDM and CDMA techniques are combined to realise power-controlled MC-CDMA system. This improves BER performance and hence the capacity. A transmission power control method is implemented in the OFDM system, which transmits data with variable power level for each subcarrier based on the received SNR. This scheme enhances the network capacity by reducing the BER.

EFFECTIVE ADMISSION CONTROL FOR POWER-CONTROLLED DS-CDMA SYSTEMS

Effective call admission control (CAC) is one of the most important techniques to provide the desired quality of service (QoS) in wireless networks. This paper investigates the call admission control problem for the power-controlled CDMA systems. With a macroscopic description for the power control problem, the call admission control for the power-constrained system is analyzed and an admissibility condition is derived. Based on the derived condition, we propose two CAC algorithms. One is an interactive method that provides the optimum performance, but requires some information exchange between base stations. The other can be implemented in a distributed manner and provide a reasonable performance. Through simulations, we show that the proposed algorithms provide an improved performance.

Capacity estimation of a SIR-based power-controlled cellular CDMA system with base station diversity in a multipath fading environment

This article estimates the reverse link capacity of an SIR-based power-controlled code-division multiple access system in a multiple cells environment. The effect of multipath fading on the interference statistics is explicitly accounted for and mobiles are assumed to connect to a base station based on minimum attenuation criterion.

Theoretical analysis of reverse link capacity for an SIR-based power-controlled cellular CDMA system in a multipath fading environment

Capacity estimation in a code-division multiple-access system is closely related to power control schemes, which complicates the analysis due to the interaction between the signal power and the interference from other users and from other paths. For a signal-to-interference ratio (SIR)-based power control scheme, most previous work has been restricted to a single-cell system or to a multiple-cell system neglecting the effect of multipath fading. This paper is to give a theoretical foundation to the possible reverse link capacity of a multiple-cell system with perfect SIR-based power control, assuming two different multipath Rayleigh fading channel models: uniform and exponential power delay profiles. The effects of the numbers of resolvable propagation paths and RAKE fingers, and other system parameters such as the required E/sub b//I/sub 0/, the processing gain, and the maximum allowable transmit power of a mobile station, are investigated. The results are compared between single- and multiple-cell systems. When the number of resolvable paths is one or the number of Rake fingers is one, the link capacity becomes zero in a multiple-cell environment. This can be avoided by the use of antenna diversity. Antenna diversity reception is found to linearly increase the link capacity as the number of antennas increases.

Erlang capacity of ATM-based CDMA satellite system

The capacity and throughput of an ATM-based CDMA system offering flexible access rates on demand are analysed. Extending the existing analysis of traffic capacity of a power-controlled CDMA cellular system, it is shown that offering multiple access rates may result in higher throughput efficiency. An example given of a satellite system shows that the gain in capacity may be some 10%.

Corrections to "Spectral Efficiency of a Power-Controlled CDMA Mobile Personal Communication System"

Corrections to "Spectral Efficiency of a Power-Controlled CDMA Mobile Personal Communication System"

Other-cell interference in cellular power-controlled CDMA

An improved series of bounds is presented for the other-cell interference in cellular power-controlled CDMA. The bounds are based on allowing control by one of a limited set of base stations. In particular, it is shown that the choice of cellular base station with least interference among the set of N/sub c/>1 nearest base stations yields much lower total mean interference from the mobile subscribers than the choice of only the single nearest base station.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>