Space-time Minimum Mean Square Error Research Articles

A Space-Time Signal Decomposition Algorithm for Downlink MIMO DS-CDMA Receivers

We propose a dimension reduction algorithm for the receiver of the downlink of direct-sequence code-division multiple access (DS-CDMA) systems in which both the transmitters and the receivers employ antenna arrays of multiple elements. To estimate the high order channel parameters, we develop a layered architecture using dimension-reduced parameter estimation algorithms to estimate the frequency-selective multipath channels. In the proposed architecture, to exploit the space-time geometric characteristics of multipath channels, spatial beamformers and constrained (or unconstrained) temporal filters are adopted for clustered-multipath grouping and path isolation. In conjunction with the multiple access interference (MAI) suppression techniques, the proposed architecture jointly estimates the direction of arrivals, propagation delays, and fading amplitudes of the downlink fading multipaths. With the outputs of the proposed architecture, the signals of interest can then be naturally detected by using path-wise maximum ratio combining. Compared to the traditional techniques, such as the Joint-Angle-and-Delay-Estimation (JADE) algorithm for DOA-delay joint estimation and the space-time minimum mean square error (ST-MMSE) algorithm for signal detection, computer simulations show that the proposed algorithm substantially mitigate the computational complexity at the expense of only slight performance degradation.

BLIND PARALIND MULTIUSER DETECTION FOR SMART ANTENNA CDMA SYSTEM OVER MULTIPATH FADING CHANNEL

This paper links the multipath smart antenna CDMA system signal detection problem to the PARAllel profiles with LINear Dependencies (PARALIND), and derives a deterministic blind PARALIND algorithm whose performance is very close to nonblind space-time minimum mean square error (ST-MMSE) method. The blind PARALIND algorithm has the better performance than space- time matched filter. The proposed PARALIND algorithm also works well in array error condition. Most notably, it does not require knowledge of the DOA (Direction Of Arrival) and channel fading information.

Multistage MMSE PIC Space–Time Receiver With Non-Mutually Exclusive Grouping

The arrival of new data services for wireless mobile communications requires an efficient use of the available bandwidth. Interference-limited cellular systems based on code-division multiple access (CDMA) can benefit from multiuser detection (MUD) and beamforming with antenna array to reduce multiple-access interference. Group-based techniques have been proposed to reduce the complexity of space-time MUD and have been shown to provide a performance-complexity tradeoff between matched filtering and full MUD. In this paper, the intergroup interference, which is a limiting factor in group-based systems, is reduced using multistage parallel interference cancellation after group-based minimum mean square error (MMSE) linear filtering. In addition, the extra resources that are available at the receiver are exploited by sharing users among groups. The proposed receiver is shown to converge, as the number of stages increases, to the full space-time MMSE linear MUD filter. The results show that the new approach provides bit error rate (BER) performance close to the full MUD receiver at a fraction of the complexity.

Convolutionally Coded Adaptive Space-Time MMSE Receiver for W-CDMA Systems in Multipath Channels

In this paper, we consider the use of convolutionally coded adaptive space-time minimum mean-square error (MMSE) receiver for wideband code division multiple access (W-CDMA) systems in multipath channels. In the adaptive space-time MMSE receiver, antenna array processing is combined with MMSE multiuser detection (MUD). Simulations are carried out to evaluate the performance in the directional multi path quasi-static Rayleigh fading channels. Simulation results show that substantial performance improvement may be obtained by using convolutional codes jointly with the adaptive space-time MMSE receiver. Only requirement to implement the receiver is a training sequence and a priori knowledge of the users’ timing for only the strongest path.

Performance analysis of space-time MMSE multiuser detection for coded DS-CDMA systems in multipath fading channels

This paper investigates the use of convolutional coding in space-time minimum mean-square-error (MMSE) multiuser-based receivers over asynchronous multipath Rayleigh fading channels. We focus on the performance gain attained through error control coding when used with binary-phase-shift-keyed modulation (BPSK) and multiuser access based on direct sequence-code-division multiple access (DS-CDMA). In our analysis, we derive an approximation for the uncoded probability of bit-error in multipath fading channels. This bit-error rate (BER) approximation is shown to be very accurate when compared to the exact performance. For a convolutionally coded system, we obtain a closed form expression for the bit-error rate upper bound. This error bound is noted to be tight as the number of quantization levels increased beyond eight. Using our theoretical results, we obtain an estimate for the achieved user-capacity that accrues due to error control coding. It is found that using convolutional coding with 3-bit soft-decision decoding, a user-capacity gain as much as 300% can easily be achieved when complete fading state information plus ideal channel interleaving are assumed.

A novel blind space-time multiuser detector for DS-CDMA system

In this letter, a novel blind space-time multiuser detector, called space-time constrained minimum output energy (ST-CMOE) detector, is proposed. It can achieve the same performance as the training based space-time minimum mean square error (ST-MMSE) detector. An adaptive version of the proposed ST-CMOE detector is also presented. Simulation shows that, the adaptive ST-CMOE detector can work well in a dynamic multiple-access channel.

Linear space-time multiuser detection for multipath CDMA channels

We consider the problem of detecting synchronous code division multiple access (CDMA) signals in multipath channels that result in multiple access interference (MAI). It is well known that such challenging conditions may create severe near-far situations in which the standard techniques of combined power control and temporal single-user RAKE receivers provide poor performance. To address the shortcomings of the RAKE receiver, multiple antenna receivers combining space-time processing with multiuser detection have been proposed in the literature. Specifically, a space-time detector based on minimizing the mean-squared output between the data stream and the linear combiner output has shown great potential in achieving good near-far performance with much less complexity than the optimum space-time multiuser detector. Moreover, this space-time minimum mean-squared error (ST-MMSE) multiuser detector has the additional advantage of being well suited for adaptive implementation. We propose novel trained and blind adaptive algorithms based on stochastic gradient techniques, which are shown to approximate the ST-MMSE solution without requiring knowledge of the channel. We show that these linear space-time detectors can potentially provide significant capacity enhancements (up to one order of magnitude) over the conventional temporal single-user RAKE receiver.

Adaptive space-time reduced-length MMSE receiver for interference suppression in DS/CDMA

The authors present an adaptive space-time reduced-length minimum mean-squared error (MMSE) receiver to suppress co-channel interference in the near-far environment for an asynchronous direct-sequence code-division multiple-access (DS/CDMA) system. Simulation results show that better bit-error rate and faster and more stable convergence are achieved over the existing full- and reduced-length MMSE receivers.