Direct-sequence code-division multiple-access (DSCDMA) cellular systems, such as wideband CDMA (WCDMA), are limited in performance by interference. Linear equalization, such as generalized Rake (G-Rake) receivers and transversal chip equalizers, can theoretically provide significant gains in performance by suppressing interference. In this paper, an adaptive G-Rake receiver is developed, employing practical algorithms for finger placement and weight computation. Finger placement is determined by selecting delays from a candidate set using a "maximal-weight" criterion. Weight computation includes estimation of an impairment covariance matrix using a parametric approach. While described in the context of the downlink, these algorithms can be used in the uplink as well. Both single-antenna and dual-antenna receivers are considered. Link and system performance are evaluated for the downlink, showing significant gains in high-rate coverage.

In this paper we present the main concepts of high speed packet access evolution currently being standardized in 3GPP. In general HSPA evolution consists of introduction of MIMO, higher order modulation, and protocol optimizations and optimizations for voice over IP. We describe these improvements in detail and show that HSPA Evolution can reach performance comparable to those of long term evolution of UMTS terrestrial radio access network in a 5 MHz deployment.

Own-cell interference limits capacity and coverage in the WCDMA enhanced uplink, and the use of interference cancellation (IC) techniques is required to provide high-data-rate availability. For a typical uplink WCDMA system with mixed traffic generated by few high-data-rate users and many low-rate users (e.g., voice users), this paper considers an IC receiver that cancels the high-data-rate signals prior to low-rate traffic reception. The IC receiver provides substantial capacity gains and the benefits of cancellation can be seen as increased achievable data rate for a fixed voice load and/or increased voice load for a target data load. For example, with a data rate of 1.5 Mbps, voice capacity gains are between 60% and 80%. In low voice load, the achievable data rate exceeds 3.5 Mbps. Due to the nature of traffic in WCDMA networks and the option of a short transmission time interval (TTI) for high-data-rate transmission in WCDMA Release 6, this IC scheme is an attractive solution for implementation in base station receivers. In addition, this paper considers also an uplink receiver that cancels the control channels of all users in the cell. Capacity gains are substantial in cells highly loaded with low-rate users

We develop a parametric receiver for packet data systems based on the generalized Rake (G-Rake) formulation. The focus here is on multi-antenna receivers to exploit both the spatial and temporal dimensions in suppressing interference. We extend previous G-Rake formulations to multi-antenna reception and propose an adaptive, parametric form to handle the (potentially) rapid interference variation in packet data systems. This parametric form estimates an impairment covariance matrix using a model, and calculates the model parameters based solely on short-term received data. The parameter calculation involves least-squares fitting of a short-term estimated impairment covariance matrix to the model. Simulation of a two-antenna G-Rake receiver shows that significant gains in performance are possible in both the uplink and downlink

In direct-sequence code-division multiple-access (DS-CDMA) systems, signal quality estimation is an important receiver function used for power control and rate adaptation. Signal quality is usually measured in terms of a signal-to-interference ratio (SIR). Typically, a short term signal power estimate and a long term interference power estimate are used. As a result, estimation error is mostly due to the short term signal power estimate. In this paper, we consider both subtractive and multiplicative forms of bias removal for SIR estimation, and show that multiplicative bias removal provides lower root-mean-square (rms) error. These bias removal forms are developed for a traditional SIR estimation approach that has been extended to account for interference correlation across Rake fingers due to receive filtering or dispersion. The extension provides an SIR estimation approach suitable for use in conjunction with generalized Rake reception, which also accounts for interference correlation.

This paper deals with finder placement for Rake receivers, which is a key aspect in the design of receivers for spread-spectrum communications. Finger placement is typically performed using a path searcher, which estimates the power/delay profile (PDP) of the received signal to determine where signal energy is present. A commonly used finger placement approach is to place fingers at delays corresponding to the peaks of the PDP, with a restriction that fingers he no closer than some minimum spacing. Another approach is to place fingers on an equally-spaced grid of delays. For the typical urban (TU) channel model, we quantify performance of the two approaches in terms of acquired signal-to-noise ratio (SNR) and modem bit- error-rate (BER). We show that performance depends primarily on minimum finger spacing and number of fingers. The grid approach performs well when there are enough fingers to collect most of the signal energy. For a channel model in which path delays vary dynamically, we find that the grid approach provides robust performance.

The paper considers joint channel estimation and data sequence detection for multipath radio channels with multiple antennas at the transmitter and/or receiver. An iterative space-time receiver based on the expectation-maximization algorithm is proposed. We examine the performance of this receiver for transmit diversity and space-time coding methods over Rayleigh fading channels. Simulation results show that the receiver can often achieve near-coherent performance with modest complexity and using very few pilot symbols.

Most analytical studies of the performance of space diversity systems on fading channels assume a very rich multipath environment. In certain wireless applications, however, the number of significant multipath components can be small. In this letter, we consider a multipath channel in which the signal propagates from the transmitter to the receiver via L discrete paths which are uniformly distributed about the transmitter and receiver. For this channel, we study the effects of the number of multipath components and antenna array size on the error probability and outage capacity of space diversity systems. We observe that performance is significantly influenced by the presence of a channel with few multipath components.

An adaptive receiver based on per-survivor processing is proposed for detecting space-time trellis codes transmitted over time-selective flat-fading channels, and its performance is examined through simulations. Results suggest that the new receiver can outperform iterative approaches based on Kalman filtering and the expectation-maximization algorithm, at the cost of increased receiver complexity.

This paper considers joint channel estimation and data detection for multipath radio channels with multiple antennas at the transmitter and/or receiver. An iterative space-time receiver based on the expectation maximization (EM) algorithm is described and performance is investigated on fast fading channels for several transmit diversity and space-time coding schemes.