Group-wise Successive Interference Cancellation Research Articles

RIS-Aided Multiuser MIMO-OFDM With Linear Precoding and Iterative Detection: Analysis and Optimization

In this paper, we consider a reconfigurable intelligent surface (RIS) aided uplink multiuser multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) system, where the receiver is assumed to conduct low-complexity iterative detection. We aim to minimize the total transmit power by jointly designing the precoder of the transmitter and the passive beamforming of the RIS. This problem can be tackled from the perspective of information theory. But this information-theoretic approach may involve prohibitively high complexity since the number of rate constraints that specify the capacity region of the uplink multiuser channel is exponential in the number of users. To avoid this difficulty, we formulate the design problem of the iterative receiver under the constraints of a maximal iteration number and target bit error rates of users. To tackle this challenging problem, we propose a groupwise successive interference cancellation (SIC) optimization approach, where the signals of users are decoded and canceled in a group-by-group manner. We present a heuristic user grouping strategy, and resort to the alternating optimization technique to iteratively solve the precoding and passive beamforming sub-problems. Specifically, for the precoding sub-problem, we employ fractional programming to convert it to a convex problem; for the passive beamforming sub-problem, we adopt successive convex approximation to deal with the unit-modulus constraints of the RIS. We show that the proposed groupwise SIC approach has significant advantages in both performance and computational complexity, as compared with the counterpart approaches.

Modelling and Simulation of Interference Cancellation Receiver for MIMO Multicarrier CDMA based Cognitive Radio

In this paper, modeling and simulation of a receiver with interference cancellation technique for the downlink transmission of multiple input multiple output (MIMO) multicarrier code-division multiple access (MC-CDMA) based cognitive radio is investigated. Synchronous transmission of multiple users’ signals over frequency selective Rayleigh channel is considered. Linear MMSE frequency domain equalization is utilized to overcome channel effect. Orthogonal Variable Spreading Factor (OVSF) codes are used to support users of different data bit rates. An adaptive subcarrier deactivation method is proposed for deactivating a set of subcarriers used for downlink transmission by the cognitive radio base station that overlap with primary user’s transmission in order to avoid causing interference to the primary user. Orthogonality between the spreading codes is lost due to subcarrier deactivation which causes interference among secondary cognitive radio users. In this paper a modified Group-wise Successive Interference Cancellation (m-GSIC) technique is proposed to suppress the interference caused due to subcarrier deactivation. The simulation results show that the proposed interference cancellation technique results in better BER performance over conventional interference cancellation techniques

ML Detection with Successive Group Interference Cancellation for Interleaved OFDMA Uplink

To mitigate the interference caused by multiple carrier frequency offsets (CFO) of distributed users, a maximum likelihood (ML) detection with group-wise successive interference cancellation (GSIC) is proposed for interleaved Orthogonal Frequency Division Multiplexing Access (OFDMA) uplink. By exploiting the interference characteristics and the finite alphabet property of transmitted symbols, the proposed scheme first extracts the block diagonal of the frequency domain channel matrix and then employs ML detection via sphere decoding in each block. The decisions obtained from the detected blocks are used to mitigate the interference to the residual blocks. Numerical results show that the proposed scheme outperforms both the minimum mean square error (MMSE) detection and parallel interference cancellation (PIC) with affordable computational complexity.

Analysis of the Linear GSIC Multiuser Detector Using a Matrix Iterative Approach

In this work, we use a new approach that relies on the theory of matrix iterative analysis to study the convergence behavior of the linear group-wise successive interference cancellation (GSIC) detector. Particularly, we show that the linear GSIC detector is in fact a realization of a modified block successive over-relaxation (BSOR) iterative method where the relaxation factor is a matrix instead of scalar. Consequently, to study the convergence behavior of the GSIC detector, we propose two new corollaries that extend the famous work of Kahan (Varga, Matrix iterative analysis, 2000) to the case where the relaxation factor is a matrix instead of a scalar. Using the two new corollaries we develop two new conditions of convergence for the linear GSIC detector. Simulation results are in excellent agreement with theory.

A Chip-Level BSOR-Based Linear GSIC Multiuser Detector for Long-Code CDMA Systems

We introduce a chip-level linear group-wise successive interference cancellation (GSIC) multiuser structure that is asymptotically equivalent to block successive over-relaxation (BSOR) iteration, which is known to outperform the conventional block Gauss-Seidel iteration by an order of magnitude in terms of convergence speed. The main advantage of the proposed scheme is that it uses directly the spreading codes instead of the cross-correlation matrix and thus does not require the calculation of the cross-correlation matrix (requires floating point operations (flops), where is the processing gain and is the number of users) which reduces significantly the overall computational complexity. Thus it is suitable for long-code CDMA systems such as IS-95 and UMTS where the cross-correlation matrix is changing every symbol. We study the convergence behavior of the proposed scheme using two approaches and prove that it converges to the decorrelator detector if the over-relaxation factor is in the interval ]0, 2[. Simulation results are in excellent agreement with theory.

ICA based GSIC receiver for multirate DS-CDMA systems

In this paper, we propose an Independent Component Analysis (ICA) based Group-wise Successive Interference Cancellation (GSIC) receiver for multi rate DS-CDMA communication systems. By describing the multi rate DS-CDMA data model in terms of ICA model, we show that ICA can be employed for multiuser detection within a group of GSIC receiver. The advantage of ICA technique is that it is a blind approach based on independence of input signals. The multirate DS-CDMA system has been simulated using multiple processing gain and simulations have been carried out for both single path and multi path propagation conditions. It is shown that the proposed method exhibits good bit error rate performance.

Capacity regions and optimal power allocation for groupwise multiuser detection

In this letter, optimal power allocation and capacity regions are derived for groupwise successive interference cancellation (GSIC) systems operating in multipath fading channels, under imperfect channel estimation conditions. It is shown that the impact of channel estimation errors on the system capacity is two-fold: It affects the receiver performance within a group of users, as well as the cancellation performance (through cancellation errors). An iterative power allocation algorithm is derived, based on which it can be shown that that the total required received power is minimized when the groups are ordered according to their cancellation errors, and the first detected group has the smallest cancellation error. Performance/complexity tradeoff issues are also discussed by directly comparing the system capacity for different implementations: GSIC with linear minimum-mean-square error (LMMSE) receivers within the detection groups; GSIC with matched filter (MF) receivers; multicode LMMSE systems; and simple all MF receivers systems.

MMSE‐based groupwise successive interference cancellation scheme for multirate CDMA systems

AbstractIn this work, group‐wise successive interference cancellation (GSIC) scheme for multi‐rate CDMA systems is proposed. A multi‐rate CDMA system is a CDMA system that can support voice users together with data users which may have different data rates. In the proposed group‐wise detection, users with the same information rate are grouped and detected together. Users with the highest information rate are detected first, neglecting the presence of the other users in the system. Interference between the groups is cancelled in a successive order. The proposed scheme is based on the minimum mean square error (MMSE) criterion. We also studied the decision feedback interference cancellation for multi‐rate CDMA systems. The performance of the proposed detection scheme is compared with that of conventional detector, the decorrelating detector, and the linear MMSE detector for multi‐rate CDMA systems. The proposed scheme achieves better performance than the above‐mentioned detectors. The proposed scheme also provides significantly high spectral efficiency under certain conditions. The algorithms in the proposed scheme are suitable for both terrestrial and satellite applications of multi‐rate CDMA systems. Copyright © 2003 John Wiley & Sons, Ltd.