Signature Waveform Mismatch Research Articles

Multiple access interference suppression for CDMA systems via [formula omitted]-minimization

A key problem in code-division multiple access (CDMA) system is to mitigate the multiple access interference (MAI) from other users while detecting the desired user. The performance of the conventional minimum output energy (MOE) multiuser detector for CDMA system significantly degrades in the presence of signature waveform distortions induced by multipath propagation or timing asynchronism. In this paper, a robust linear programming (ROLP) algorithm for blind multiuser detection is proposed. Different from the existing MOE-based multiuser detection techniques, the proposed ROLP minimizes the ℓ∞-norm of the output to exploit the non-Gaussianity of the communication signals. To achieve robustness against signature waveform mismatch, the proposed method constrains the magnitude response of any signature vector within a specified uncertainty set to exceed unity. The uncertainty set is modeled as a rhombus, which differs from the spherical uncertainty region widely taken in the existing robust multiuser detectors. The resulting optimization problem is reformulated into a linear programming program and hence can be solved efficiently. The proposed ROLP is computationally simpler than its robust counterparts that requires solving a second-order cone programming. Simulation results demonstrate the superiority of the ROLP over several robust detectors, which indicate that its performance approaches the optimal performance bound.

Second-Order Cone Programming Based Robust Blind Multiuser Detector for CDMA Systems

In this paper, we propose a robust blind multiuser detector for code-division multiple access (CDMA) systems against signature waveform mismatch (SWM) derived from the influences of time asynchronization or channel distortion. This blind detection method with SWM problem is formulated as blind source separation (BSS) model subject to the second-order cone (SOC) constraint. The resulting blind separation based on SOC programming problem is solved by approximate negentropy maximization using quasiNewton iterative methods. Theoretical analysis and simulation results show that the performance of the proposed blind detector is superior to those of the existing methods.

Blind RLS-Based Detection Using GSC with DF for STBC MC-CDMA Systems Under Mismatched Channel Estimation

Under Rayleigh fading channels, a common problem with blind multiuser space-time block coded (STBC) multicarrier code division multiple access (MC-CDMA) detectors is that their performance is very sensitive to the signature waveform mismatch (SWM) induced by channel estimation distortion. This paper presents a robust detector using the generalized sidelobe canceller with a double-feedback filter that effectively mitigates the channel estimation distortion for the STBC MC-CDMA system during multipath fading. Numerical simulations show that the proposed detector substantially provides robustness against small-to-medium SWM scenarios for a downlink STBC MC-CDMA system.

The Subspace-Based Linear Conjugate CMA in BPSK-Modulated MC-CDMA Systems

A subspace-based linear conjugate constant modulus algorithm (CMA) for blind adaptive multiuser detection in BPSK-Modulated MC-CDMA systems is proposed. First, a linear conjugate CMA algorithm is presented which jointly elaborates the received signal and its complex conjugate to utilize the information contained in the pseudo-autocorrelation of the observable, thus is capable of achieving much better performance. Second, to further improve the performance, the subspace method is applied to the linear conjugate CMA algorithm to obtain a subspace-based linear conjugate CMA algorithm, which mitigates the influence of the noise subspace. Finally, an improved projection approximation subspace tracking with deflation algorithm is proposed for adaptive signal subspace estimation to reduce the computational complexity. The proposed algorithm provides an improved robustness against the signature waveform mismatch, good tracking capability in dynamic environment and better output signal-to-interference-plus-noise-ratio and bit error rate performance. The superiority of the proposed algorithm is demonstrated through computer simulations.

Robust MOE Detector for DS-CDMA Systems with Signature Waveform Mismatch

In this letter, a decision-directed MOE detector with excellent robustness against signature waveform mismatch is proposed for DS-CDMA systems. Both the theoretic analysis and computer simulation results demonstrate that the proposed detector can provide better SINR performance than that of conventional detectors.

Blind Linear MMSE Receivers for MC-CDMA Systems

This paper studies blind constrained minimum output energy (CMOE)-based and subspace-based linear minimum mean-squared-error (LMMSE) detectors for multi-carrier code division multiple access (MC-CDMA) systems. By imposing quadratic weight constraint, the CMOE detector is made more robust against signature waveform mismatch, and a better performance over the standard CMOE detector is obtained. Because of separation of signal and noise subspaces, the more complicated subspace-based LMMSE detector has better performance than the CMOE detector. The recursive subspace tracking algorithms are also investigated for the subspace-based MMSE receiver. Numerical results show that the steady-state performance of the robust CMOE detector is close to the subspace-based MMSE method. The blind mode decision-directed LMMSE detection is studied where the blind detectors are used for initial adaptation. Numerical simulations illustrate that the blind mode decision-directed MMSE detection substantially improves the system performance when the frequency-selective channel is slowly-varying

Robust blind multiuser detection against signature waveform mismatch based on second-order cone programming

Blind signal detection in multiuser code division multiple access (CDMA) system is particularly attractive when only the desired user signature is known to a given receiver. A problem common to several existing blind multiuser CDMA detectors is that the detection performance is very sensitive to the signature waveform mismatch (SWM) which may be caused by channel distortion. In this paper, we consider the design of a blind multiuser CDMA detector that is robust to the SWM. We present a convex formulation for this problem by using the second-order cone (SOC) programming. The resulting SOC problem can be solved efficiently using the recently developed interior point methods. Computer simulations indicate that the performance of our new robust blind multiuser detector is superior to those of many existing methods.

Blind multiuser detection: a subspace approach

A new multiuser detection scheme based on signal subspace estimation is proposed. It is shown that under this scheme, both the decorrelating detector and the linear minimum-mean-square-error (MMSE) detector can be obtained blindly, i.e., they can be estimated from the received signal with the prior knowledge of only the signature waveform and timing of the user of interest. The consistency and asymptotic variance of the estimates of the two linear detectors are examined. A blind adaptive implementation based on a signal subspace tracking algorithm is also developed. It is seen that compared with the previous minimum-output-energy blind adaptive multiuser detector, the proposed subspace-based blind adaptive detector offers lower computational complexity, better performance, and robustness against signature waveform mismatch. Two extensions are made within the framework of signal subspace estimation. First, a blind adaptive method is developed for estimating the effective user signature waveform in the multipath channel. Secondly, a multiuser detection scheme using spatial diversity in the form of an antenna array is considered. A blind adaptive technique for estimating the array response for diversity combining is proposed. It is seen that under the proposed subspace approach, blind adaptive channel estimation and blind adaptive array response estimation can be integrated with blind adaptive multiuser detection, with little attendant increase in complexity.