Trickle-based interference cancellation schemes for CDMA systems

In this paper, we introduce a novel approach to interference cancellation (IC) for code division multiple access (CDMA) uplink transmission. Several models combining principles of serial (SIC) and parallel (PIC) interference cancellation are discussed. The proposed scheme is derived from the analysis of these hybrid models and applies a user configuration algorithm (termed “trickle”) in order to provide improved bit-error-rate (BER) performance. The algorithm utilizes an adaptive matrix to compute the required configuration to be used for the subsequent interference cancellation stage. We demonstrate that significant performance improvements can be achieved over various hybrid schemes. A reduced-complexity version of the trickle algorithm is also introduced where the processing delay is greatly reduced while maintaining similar performance. We present several numerical examples through which we demonstrate the efficacy of the proposed algorithms relative to existing interference cancellation algorithms.     

基于软判决的MMSE-OSIC接收机

串行干扰相消接收机是广泛应用于多输入多输出系统中的一种接收端信号处理与检测技术。在串行干扰相消接收机中,先检测的层的判决准确性会对后续层的检测产生影响。检测过程中产生的判决误差,将对后续层的检测引入残留干扰,进而影响后续层检测的正确性,造成差错传播。本文提出一种基于软判决的最小均方误差检测带排序串行干扰相消接收机,可以有效减轻基于硬判决方法的带排序串行干扰相消接收机的差错传播问题。在重构干扰信号时,该接收机使用根据软判决信息得到的符号期望,替代硬判决方法,能够有效降低干扰相消时各层之间由判决误差引起的残留干扰;该接收机还可以精确估计残留干扰的功率以及各层数据流的后处理信干噪比,改善了基于硬判决方法的串行干扰相消接收机存在的各层后处理信干噪比估计值偏大的问题。可靠性更高的软判决结果有效降低了残留干扰,更精确的各层后处理信干噪比抑制了残留干扰对后续数据流检测的影响,提高了判决结果和排序过程的准确性。仿真结果证明,基于软判决的最小均方误差检测带排序串行干扰相消接收机可以有效避免差错传播的产生,因而获得较大的性能提升。      

Degrees of freedom of MIMO interference channel with distributed space-time interference alignment

In the context of K-user MIMO interference channel (IC),achievable degrees of freedom (DoF) were investigated with distributed space-time interference alignment (DSTIA).By precoding with distributed current and outdated channel state information at the transmitters (CSIT),new tradeoff regions between achievable DoF and CSI feedback delay/frequency were achieved for MISO system.The impact of the number of transmit antennas on achievable DoF in the MISO system was analyzed,revealing that DoF results approach to the outer bound as the number of transmit antennas increases.Further,the impact of the number of receive antennas on achievable DoF was characterized,deriving the range of CSI feedback delay that preserves achievable DoF in the MIMO system.Theoretical and numerical analyses show that,the proposed DSTIA scheme can achieve better sum-DoFs by eliminating inter-user interference perfectly,tighten the gap between achievable DoF and outer bound,as well as improve the achievable rate of the system.     

Rate Optimization to Minimize Distortion for Source-Channel Coded H-BLAST with SIC Decoding

As joint source and channel coding schemes, layered transmission schemes for a successive refinable source (SRS) are recently studied over quasi-static fading channels. In this letter, we consider spatial layered transmission for a SRS with successive interference cancellation (SIC) decoder over quasistatic multi-input multi-output (MIMO) fading channels. We show that if the distortion function can be factorized, the minimum average distortion can be obtained by individual rate optimization for each layer when zero-forcing (ZF) SIC receiver is employed over Rayleigh fading channels.     

Interference cancellation schemes for MIMO MC-CDM in fading channels

A novel interference cancellation (IC) scheme for MIMO MC-CDM systems is proposed. It is shown that the existing IC schemes are suboptimum and their performance can be improved by utilising some special properties of the residual interference after interference cancellation.     

Interference Cancellation in CDMA Systems Employing Complementary Codes Under Rician Fading Channels

The ideal correlation properties of single user code division multiple access (CDMA) systems with complementary codes (CC) are lost by multiple access interference and near–far effects in downlink frequency selective fading channels. This severity in interference has motivated to develop ways to overcome the threats with suitable suboptimal interference cancellation schemes. In this paper, we propose successive interference cancellation (SIC) for downlink CDMA systems with CC to improve the system capacity and reduce error rate under near–far situations. Theoretical study and extensive simulations were conducted to verify the effectiveness of proposed SIC under frequency selective Rician fading channels in achieving frequency diversity gain, close to theoretical lower bound in complementary coded CDMA (CC-CDMA) systems.     

Optimal Lattice-Reduction Aided Successive Interference Cancellation for MIMO Systems

In this letter, we investigated the optimal minimum-mean-squared-error (MMSE) based successive interference cancellation (SIC) strategy designed for lattice-reduction aided multiple-input multiple-output (MIMO) detectors. For the sake of generating the MMSE-based MIMO symbol estimate at each SIC detection stage, we model the so-called effective symbols generated with the aid of lattice-reduction as joint Gaussian distributed random variables. However, after lattice-reduction, the effective symbols become correlated and exhibit a non-zero mean. Hence, we derive the optimal MMSE SIC detector, which updates the mean and variance of the effective symbols at each SIC detection stage. As a result, the proposed detector achieves a better performance compared to its counterpart dispensing with updating the mean and variance, and performs close to the maximum likelihood detector.     

Approximate Minimum BER Power Allocation for MIMO Spatial Multiplexing Systems

Precoding for multiple-input multiple-output (MIMO) spatial multiplexing generally requires high feedback overhead and/or high-complexity processing. Simultaneous reduction in transmitter complexity and feedback overhead is proposed by imposing a diagonal structural constraint to precoding, i.e., power allocation. Minimum bit-error rate (MBER) is employed as the optimization criterion, and an approximate MBER (AMBER) power-allocation algorithm is proposed for a variety of receivers, including zero-forcing (ZF), successive interference cancellation (SIC), and ordered SIC (OSIC). While previously proposed precoding schemes either require ZF equalization for MBER, or use a minimum mean-squared error (MMSE) criterion, we provide a unified MBER solution to power allocation for ZF, SIC, and OSIC receiver structures. Improved error-rate performance is shown both analytically and by simulation. Simulation results also indicate that SIC and OSIC with AMBER power allocation offer superior performance over previously proposed MBER precoding with ZF equalization, as well as over MMSE precoding/decoding. Performance under noisy channels and power feedback is analyzed. A modified AMBER algorithm that mitigates error propagation in interference cancellation is developed. Compared with existing precoding methods, the proposed schemes significantly reduce both transmit processing complexity and feedback overhead, and improve error-rate performance     

基于干扰消除辅助稀疏连接神经网络的大规模MIMO信号检测

近年来,深度学习成为无线通信领域的关键技术之一。在基于深度学习的一系列MIMO信号检测算法中,大多未充分考虑相邻天线之间的干扰消除问题,无法彻底消除多用户干扰对误码率性能的影响。为此,该文提出一种将深度学习与串行干扰消除(SIC)算法进行结合的方法用于大规模MIMO系统上行链路信号检测。首先,通过优化传统的检测网络(DetNet)及改进ScNet检测算法,该文提出一种基于深度神经网络(DNN)的检测算法,称为ImpScNet。在此基础上,进一步将SIC思想应用到深度学习框架结构设计中,提出一种基于深度学习的大规模MIMO多用户SIC检测算法,称为ImpScNet-SIC。此算法在每个检测层上分为两级,其中,第1级由该文提出的ImpScNet算法提供初始解,再将初始解解调至相应的星座点上作为SIC的输入,由此构成该算法的第2级。此外,在SIC中也使用了ImpScNet算法估计传输符号,以便获得最优性能。仿真结果表明,与已有的各种典型代表算法相比,该文所提ImpScNet-SIC检测算法特别适合大规模MIMO信号检测,具有收敛速度快、收敛稳定及复杂度相对较低的优势,并且在10–3误码率上有至少0.5 dB以上的增益。     

On Multiple Access Using H-ARQ with SIC Techniques for Wireless Ad Hoc Networks

In this paper, we consider non-orthogonal multiple access (NOMA) for wireless ad hoc networks over block fading channels where the performance is limited by interference and fading. In order to provide a reasonable performance, we can use re-transmission and interference cancellation techniques. Re-transmission techniques can provide a diversity gain over fading channels, while the successive interference cancellation (SIC) can improve the signal to interference ratio (SIR). Using the information outage probability, we show that the NOMA approach with re-transmissions can perform better than the orthogonal multiple access (OMA) approach with re-transmissions when the signal to noise ratio (SNR) is low. It is also shown that the outage probability of the NOMA with SIC is lower than that of OMA when the rate is sufficiently low where SIC can be facilitated.     

Evaluation of a DS/CDMA multiuser receiver employing a hybrid formof interference cancellation in Rayleigh-fading channels

This paper assesses the performance of a multiuser detection DS/CDMA receiver based on a hybrid scheme of successive interference cancellation (SIC) and parallel interference cancellation (PIC). Two configurations of the proposed hybrid IC are presented and compared with existing SIC and PIC schemes. The performance criteria used for comparison are complexity, delay, power control requirements, and average bit-error rate (BER) performance obtained by simulation in Rayleigh-fading channels with additive white Gaussian noise (AWGN). The suggested hybrid IC combines good average BER performance, short delay, acceptable complexity, and also operates under slow power control     

Space–Time Turbo Equalization With Successive Interference Cancellation for Frequency-Selective MIMO Channels

This paper addresses the issue of iterative space–time equalization for multiple-input–multiple-output (MIMO) frequency-selective fading channels. A new soft equalization concept based on successive interference cancellation (SIC) is introduced for a space–time bit-interleaved coded modulation (STBICM) transmission. The proposed equalizer allows us to separate intersymbol interference (ISI) and multiantenna interference (MAI) functions. Soft ISI is successively suppressed using a low-complexity suboptimum minimum mean square error (MMSE) criterion. The decoupling of ISI and MAI offers more flexibility in the design of the whole space–time equalizer. Different multiantenna detection criteria can be considered, ranging from simple detectors to the optimal maximum a posteriori (MAP) criterion. In particular, we introduce two soft equalizers, which are called SIC/SIC and SIC/MAP, and we show that they can provide a good performance-to-complexity tradeoff for many system configurations, as compared with other turbo equalization schemes. This paper also introduces an MMSE-based iterative channel state information (CSI) estimation algorithm and shows that attractive performance can be achieved when the proposed soft SIC space–time equalizer iterates with the MMSE-based CSI estimator.      

Multistage soft decision equalization technique for MIMO systems in frequency selective channels

This article proposes a multistage soft decision equalization （SDE） technique for block transmission over frequency selective multi-input multi-output （MIMO） channels. Using the Toeplitz structure, the general signal model can be converted into a series of small-sized sub-signal models. For each sub-signal model, soft interference cancellation （SIC） is used firstly to remove partial effects of interfering symbols, then max-log-map sphere decoder is performed to get the desired a posteriori information. Simulation shows that with lower complexity the proposed method outperforms the probability data association SDE and the Schnorr-Euchner sphere decoder.     

Soft-decision multistage multiuser interference cancellation

Successive interference cancellation (SIC) refers to a family of low-complexity multiuser detection methods for direct-sequence code-division multiple-access systems. The performance of multistage SIC depends on the decision function used in the interference cancellation iterations, e.g., hard, soft, or linear decision functions. Due to error propagation, multistage SIC with hard data bit decisions may perform more poorly than multistage SIC with linear or soft decision functions. We propose and analyze a family of generalized unit-clipper bit decision functions that better combine linear and hard decisions. Performance within 0.4 dB of the single-user bound can be obtained. We then make robust the above soft-decision SIC to time-delay errors as large as half a PN chip and evaluate its performance.     

大规模MIMO系统中的一种自适应SIC检测算法

与传统系统相比,大规模多入多出（MIMO）系统能更加有效地提高频谱效率。利用传统的最小均方误差（MMSE）信号检测算法求解大规模MIMO系统,虽然检测结果接近最优,但是矩阵的求逆运算导致计算的复杂度非常高。提出了一种自适应排序干扰消除（SIC）检测算法,在逐次超松弛（SOR）迭代运算的基础上,通过干扰消除降低待检测矩阵的维度。通过仿真分析,得出所提算法的复杂度低于Jacobi、SOR检测算法,且在迭代次数较少的情况下,算法的误码率（BER）性能明显优于SOR检测算法。     

Analysis on the Diversity-Multiplexing Tradeoff for Ordered MIMO SIC Receivers

The diversity-multiplexing tradeoff for multiple-input multiple-output (MIMO) point-to-point channels and multiple access channels were first proposed and studied by Zheng and Tse recently. While the optimal tradeoff curves for MIMO channels have been explicitly explored, those corresponding to some suboptimal and practical MIMO schemes are still open. One such important problem is the diversity-multiplexing tradeoff for a V-BLAST type system employing ordered successive interference cancellation (SIC) receivers with zero forcing (ZF) or minimum mean square error (MMSE) processing at each stage. In this paper, we take a novel geometrical approach and rigorously verify that under general settings, the optimal ordering rule for a V-BLAST SIC receiver will not improve its performance regarding diversity-multiplexing tradeoff in point-to- point channels. The same geometrical tool is then applied to MIMO spatial-division multiple access channels, leading to some first results in this area. Particularly, we reveal that when the rates of data streams are fixed (i.e., zero spatial multiplexing gain), the diversity order is not improved by user ordering.     

Joint Design of Groupwise STBC and SIC Based Receiver

In this letter, we propose a simple groupwise space-time block code (GSTBC) which can be easily applied to a large number of transmit antennas and be effectively decoded by a low complexity successive interference cancellation (SIC) based receiver. The proposed GSTBC and SIC based receiver are jointly designed and the diversity repetition in GSTBC is used to induce the dimension expansion that can be exploited by the SIC based receiver to suppress interfering signals as well as to obtain diversity gain. Our proposed scheme provides a near maximum likelihood (ML) performance while keeping a reasonably low complexity at the receiver.     

A matrix-algebraic approach to successive interference cancellationin CDMA

In this paper, we describe linear successive interference cancellation (SIC) based on matrix-algebra. We show that linear SIC schemes (single stage and multistage) correspond to linear matrix filtering that can be performed directly on the received chip-matched filtered signal vector without explicitly performing the interference cancellation. This leads to an analytical expression for calculating the resulting bit-error rate which is of particular use for short code systems. Convergence issues are discussed, and the concept of ϵ-convergence is introduced to determine the number of stages required for practical convergence for both short and long codes     

Low‐complexity linear group‐SIC detectors

In this paper, we consider a linear group polynomial expansion successive interference cancellation (GPE‐SIC) detector in a synchronous CDMA system. It is a hybrid detector, which combines parallel and successive cancellation techniques in order to extract the advantages of both schemes. We use the fact that even if the cross‐correlation matrix of the system is not diagonal dominant, the sub‐matrices corresponding to different groups can be forced to be diagonal dominant by suitable grouping of users to approximate the decorrelator/MMSE detector by a low‐complexity polynomial expansion detector. The latter is computationally very efficient if the cross‐correlation matrix of users within the same group is diagonal dominant. Simulation results showed that the (GPE‐SIC) detector has the same performance as the linear group decorrelator successive interference cancellation (GDEC‐SIC) detector but with low‐computational complexity. Copyright © 2006 John Wiley & Sons, Ltd.     

Performance tradeoffs among low‐complexity detection algorithms for MIMO‐LTE receivers

The upcoming Third‐Generation Partnership Project—Long‐Term Evolution (3GPP‐LTE) cellular standard will employ spatial multiplexing to significantly increase the data rates. Detection of the spatially multiplexed signals is an essential issue in the design of an LTE receiver. In this paper, we evaluate the performance–complexity tradeoffs for a set of low‐complexity multiple input multiple output (MIMO) detection algorithms in a realistic LTE downlink system. Specifically, antenna correlation and channel estimation errors have been considered for a practical MIMO‐LTE receiver. An LTE downlink model has been implemented in order to evaluate three types of detectors: linear, unsorted successive interference cancellation (SIC), and ordered SIC. Our simulation results show that the unsorted SIC detectors present a very poor performance–complexity tradeoff. Besides, linear detectors are shown to be the best candidates as the performance improvement for the ordered SIC detectors is not significant in a realistic scenario. Copyright © 2009 John Wiley & Sons, Ltd.