2D-RAKE Receiver Research Articles

Application of a Novel Antenna Diversity Technique for WCDMA Systems

Abstract WCDMA is one of the key technologies of third-generation mobile communication. In this paper we study a new antenna diversity technology for WCDMA systems. The antenna diversity is based on log-likelihood ratio (LLR) which is better than that based on signal-to-noise ratio (SNR) in bit error rate performance. So the average bit-error rate (BER) performance of MQAM WCDMA systems combined with space-time block coding (STBC), 2D-RAKE receiver and the new LLR technology on correlated Nakagami fading channels has been investigated. The expressions of generalized selective combining (GSC) schemes based on Symbol-LLR (SLLR) and Bit-LLR (BLLR) are derived. Furthermore, the resolve expression of BER for a 16QAM WCDMA system with BLLR scheme in receive correlated Nakagami fading channel is presented. The simulation results show that the BLLR scheme is optimum since it minimizes the BER of WCDMA systems. With the increase of the multipath components, the performance of system is improved significantly. Moreover, the system which possesses the smaller rate of average path decay factor exhibits the higher diversity order.

A New Combination of RAKE Receiver and Adaptive Antenna Array Beamformer for Multiuser Detection in WCDMA Systems

The aim of this paper is to combine smart antenna beamforming and RAKE receiver in wideband code division multiple access (WCDMA). The proposed method combines spatial diversity as well as temporal diversity to improve the performance and overcome both interferences and multipath fading. This investigation has focused on one of the new proposed blind beamforming algorithms. It is based on constrained constant modulus (CCM) algorithm which is used for deriving a recursive-least-squares (RLS-) type optimization algorithm. We illustrate the comparison of bit error rate (BER) of the proposed receiver with simple correlator and also 1D-RAKE receiver in multiuser detection (MUD) WCDMA. The simulation results show that the proposed 2D-RAKE receiver offers lower BER rather than conventional ones, that is, it is an effective solution for decreasing the effect of interference and increasing the capacity, in a joint state.

2D Rake Receiver for MIMO Channels: Optimum Algorithm with Minimum Complexity

This article presents the original results of the synthesis and noise immunity analysis of the optimum rake-type receiver with minimum complexity properties for MIMO systems. In this approach we apply the fully generic Gaussian MIMO channel model with a separable covariance matrix in the time and space domains. The advantages of this model for statistical aspects of MIMO communications are shown.

A New Blind 2D-RAKE Receiver Based on CMA Criteria for Spread Spectrum Systems Suitable for Software Defined Radio Architecture

Spread Spectrum (SS) has been widely used for various wireless systems such as cellular systems, wireless local area network (LAN) and so on. Using multiple antennas at the receiver, two-dimensional (2D) RAKE is realized over the time- and the space-domain. However, it should be noted that the 2D-RAKE receiver must detect the bit timing prior to the RAKE combining. In case of deep fading, it is often difficult to detect it due to low signal-to-noise power ratio (SNR). To solve this problem, we propose a new blind 2D-RAKE receiver based on the constant modulus algorithm (CMA). Since it does not need a priori bit timing detection, it is possible to compensate frequency selective fading even in very low SNR environments. The proposed method is particularly suitable for the software defined radio (SDR) architecture. The performance of the proposed method is investigated through computer simulations.

Coherent Code Tracking for Spatial Transmit Diversity DS-CDMA Systems

Spatial transmit diversity schemes are now well integrated into third-generation cellular mobile communication system specifications. When DS-CDMA-based technology is deployed in typical macro- and microcell environments, multipath diversity and spatial diversity may be exploited simultaneously by a 2D RAKE receiver. The work presented in this paper focuses on taking advantage of spatial transmit diversity in synchronising the 2D RAKE structure. We investigate the use of coherent and noncoherent techniques for tracking the timing parameters of each multipath component. It is shown that both noncoherent and coherent techniques benefit from transmit diversity. Additionally the performance gap between these two techniques increases with the number of antennas.

Joint Effects of Dynamic Time Slot Scheduling Schemes and Soft Handoff on the Performance of TDD DS-CDMA Systems with 2D Rake Receivers

In this paper, we derive analytical expressions to assess the performance of Time Division Duplexing (TDD) Direct Sequence-Code Division Multiple Access (DS-CDMA) systems with coherent bi-dimensional (2D) Rake receivers. Considering either hexagonal macrocellular and microcellular cross-shaped networks, we propose and evaluate different approaches to model the effects of the intercellular multiple access interference (MAl) on the performance of DS-CDMA systems with 2D Rake receivers. These results are then used on the performance comparison between coherent and optimum 2D Rake receivers. It is shown that soft handoff allows gains of 2 dB in the Signal-to-Interference-plus-Noise-Ratio (SINR) at the 2D Rake receiver output. Simulation results, ratified by theoretical upper bounds, show that the dynamic time slot allocation schemes allow considerable increase of the SINR at the receiver output with a concomitant improvement on the throughput.

Hotelling's generalized distribution and performance of 2D-RAKE receivers

Two-dimensional (2D) RAKE (2D-RAKE) receivers process signals in both time and space to improve the performance of code-division multiple-access (CDMA) systems. We establish the connection between the 2D-RAKE signal-to-interference-ratio (SIR) output statistics and the generalized Hotelling's (1947, 1951, 1931) T/sup 2//sub 0/ (in the complex case) distribution. We study this distribution and offer new simple explicit closed-form expressions (in terms of hypergeometric functions) for its probability density function (PDF) and cumulative distribution function (CDF). Based on that, we derive the outage probability of dual-branch 2D-RAKE receivers over Rayleigh-fading channels. Some numerical examples for particular cases of interests are plotted and discussed.

BER performance of 2D-RAKE receivers in DS-CDMA over frequency-selective, slow Rayleigh fading channels

In this letter, we extend the method that has been proposed in the literature for calculating the bit error probability of two-dimensional (2D) RAKE receivers in asynchronous direct sequence code-division multiple access (DS-CDMA) over flat, slow Rayleigh fading channels to the case of frequency-selective, slow Rayleigh fading channels. We also compute and plot the lower bound on the performance that can be achieved in the above system.

Performance of coherent DS-CDMA with 2D-RAKE receiver

The bit error rate (BER) of a coherent digital signal code-division multiple access system with a 2D-RAKE receiver is evaluated in a Rayleigh fading multipath channel. The numerical results indicate that, compared with the conventional RAKE receiver, the 2D-RAKE receiver could provide a significant capacity gain which is sensitive to the selection of spatiotemporal diversity fingers.