Iterative nonlinear detection for SFBC SC–FDMA uplink MIMO transmission systems

Single‐carrier frequency division multiple access (SC‐FDMA) systems with space frequency block coding (SFBC) transmissions achieve both spatial and frequency diversity gains in wireless communications. However, SFBC SC‐FDMA schemes using linear detectors suffer from severe performance deterioration because of noise enhancement propagation and additive noise presence in the detected output. Both issues are similar to inter‐symbol‐interference (ISI). Traditionally, SC‐FDMA system decision feedback equalizer (DFE) is often used to eliminate ISI caused by multipath propagation. This article proposes frequency domain turbo equalization based on nonlinear multiuser detection for uplink SFBC SC‐FDMA transmission systems. The presented iterative receiver performs equalization with soft decisions feedback for ISI mitigation. Its coefficients are derived using minimum mean squared error criteria. The receiver configuration study is Alamouti's SFBC with two transmit and two receive antennas. New receiver approach is compared with the recently proposed suboptimal linear detector for SFBC SC‐FDMA systems. Simulation results confirm that the performance of the proposed iterative detection outperforms conventional detection techniques. After a few iterations, bit‐error‐rate performance of the proposed receiver design is closely to the matched filter bound. Copyright © 2016 John Wiley & Sons, Ltd.     

Novel Turbo Receiver for MU-MIMO SC-FDMA System

Single carrier-frequency-division multiple access (SC-FDMA) has been adopted as the uplink transmission standard in fourth-generation cellular networks to facilitate power efficiency transmission in mobile stations. Because multiuser multiple-input multiple-output (MU-MIMO) is a promising technology employed to fully exploit the channel capacity in mobile radio networks, this study investigates the uplink transmission of MU-MIMO SC-FDMA systems with orthogonal space-frequency block codes (SFBCs). It is preferable to minimize the length of the cyclic prefix (CP). In this study, the chained turbo equalization technique with chained turbo estimation is employed in the designed receiver. Chained turbo estimation employs a short training sequence to improve the spectrum efficiency without compromising the estimation accuracy. In this paper, we propose a novel and spectrally efficient iterative joint-channel estimation, multiuser detection, and turbo equalization for an MU-MIMO SC-FDMA system without CP-insertion and with short TR. Some simulation examples are presented for the uplink scenario to demonstrate the effectiveness of the proposed scheme.     

Analysis of receiver algorithms for lte LTE SC-FDMA based uplink MIMO systems

This letter derives mathematical expressions for the received signal-to-interference-plus-noise ratio (SINR) of uplink Single Carrier (SC) Frequency Division Multiple Access (FDMA) multiuser MIMO systems. An improved frequency domain receiver algorithm is derived for the studied systems, and is shown to be significantly superior to the conventional linear MMSE based receiver in terms of SINR and bit error rate (BER) performance.     

ICI problem and compensation in MIMO SC‐FDMA system with SC‐SFBC scheme

In this paper, we address the ICI (intercarrier interference) problem and compensation in MIMO (multiple input multiple output) SC‐FDMA (single carrier frequency division multiple access) system that exploits SC‐SFBC (single carrier‐space frequency block coding) scheme. Recently, SC‐FDMA technique has received more attention due to the low PAPR (peak to average power ratio) property. However, SC‐FDMA system is sensitive to phase noise and CFO (carrier frequency offset) which is unavoidable in wireless communication systems. Phase noise and CFO introduce CPE (common phase error) as well as ICI into the received signal and seriously degrade the system performance. Therefore, analysis and suppression of these interferences are of great importance. In this paper, we analyze the interferences in MIMO SC‐FDMA system with SC‐SFBC. Then a new ICI estimation and suppression method is proposed to suppress the interferences. Instead of directly estimating the CFO and phase noise, which is pretty difficult and complex, this algorithm exploits block‐type pilots, which is a common pilot pattern in wireless communication systems, such as LTE standard, to estimate the interferences. After that the interferences are suppressed by the inverse matrix method. Simulation results show that the system performance is significantly improved. Copyright © 2010 John Wiley & Sons, Ltd.     

Output MAI distributions of linear MMSE multiuser receivers inDS-CDMA systems

Multiple-access interference (MAI) in a code-division multiple-access (CDMA) system plays an important role in performance analysis and characterization of fundamental system limits. We study the behavior of the output MAI of the minimum mean-square error (MMSE) receiver employed in the uplink of a direct-sequence (DS)-CDMA system. We focus on imperfect power-controlled systems with random spreading, and establish that in a synchronous system (1) the output MAI of the MMSE receiver is asymptotically Gaussian, and (2) for almost every realization of the signatures and received powers, the conditional distribution of the output MAI converges weakly to the same Gaussian distribution as in the unconditional case. We also extend our study to asynchronous systems and establish the Gaussian nature of the output interference. These results indicate that in a large system the output interference is approximately Gaussian, and the performance of the MMSE receiver is robust to the randomness of the signatures and received powers. The Gaussianity justifies the use of single-user Gaussian codes for CDMA systems with linear MMSE receivers, and implies that from the viewpoints of detection and channel capacity, signal-to-interference ratio (SIR) is the key parameter that governs the performance of the MMSE receiver in a CDMA system     

Information Capacity of the Space Division Multiple Access Mobile Communication System

An expression for the Shannon capacity lower bound of the space division multiple access (SDMA) mobile communication channel with interference is shown. The bound is tightly approaching the Shannon capacity of the orthogonal SDMA system over Gaussian channel with no interference. The information capacity of the SDMA system with adaptive MMSE receivers is presented as well. The SDMA system with MMSE receivers achieves at least 50% of the orthogonal SDMA system capacity for the input signal to noise ratio of practical interest in cellular mobile communications (10–30dB).     

New transmit schemes and simplified receivers for MIMO wireless communication systems

In this paper, optimized transmit schemes for multiple-input multiple-output (MIMO) systems with simplified receivers are proposed for the downlink of high-speed wireless communication systems. In these systems, MIMO signal preprocessing is performed at the transmitter or base station with the receiver at the mobile station having a simplified structure that requires only limited signal processing. An important potential application for our transmit MIMO techniques is in the downlink of high-speed wireless communication systems with Vertical Bell Laboratories Layered Space-Time (V-BLAST) or a similar technique utilized in the uplink, creating a high-speed duplex system with a simplified mobile station transceiver structure. Two approaches are introduced and these depend on whether or not receive diversity is employed at the receiver. Both methods require that channel state information be available at the transmitter. In addition, some important associated issues such as peak-to-average power ratio requirements at the transmitter and robustness to downlink channel errors are also investigated and various solutions are proposed. Simulation results are provided and these show that performance improvement can be achieved when compared with other MIMO transmit schemes.     

Soft‐output MMSE V‐BLAST receiver with MMSE channel estimation under correlated Rician fading MIMO channels

For wireless multiple‐input multiple‐output (MIMO) communications systems, both channel estimation error and spatial channel correlation should be considered when designing an effective signal detection system. In this paper, we propose a new soft‐output MMSE based Vertical Bell Laboratories Layered Space‐Time (V‐BLAST) receiver for spatially‐correlated Rician fading MIMO channels. In this novel receiver, not only the channel estimation errors and channel correlation but also the residual interference cancellation errors are taken into consideration in the computation of the MMSE filter and the log‐likelihood ratio (LLR) of each coded bit. More importantly, our proposed receiver generalizes all existing soft‐output MMSE V‐BLAST receivers, in the sense that, previously proposed soft‐output MMSE V‐BLAST receivers can be derived as the reduced forms of our receiver when the above three considered factors are partially or fully simplified. Simulation results show that the proposed soft‐output MMSE V‐BLAST receiver outperforms the existing receivers with a considerable gain in terms of bit‐error‐rate (BER) performance. Copyright © 2011 John Wiley & Sons, Ltd.     

基于DFT扩频的广义多载波频分多址上行链路传输方案——DFT-S-GMC

针对宽带移动通信上行链路传输,提出一种基于离散傅立叶变换(DFT)的广义多载波(GMC)频分多址方案--DFT-S-GMC.该传输方案采用DFT进行频域扩频,采用逆滤波器组变换(IFBT)实现频分复用和频分多址.理论分析和仿真表明,与现有主流上行多址方案(如OFDMA和DFT-S-OFDMA)相比,该方案具有较低的峰均比,并且对由上行用户间的定时和频率同步误差导致的多址干扰有较强的顽健性.     

The BER analysis of OFDMA and SC‐FDMA under pilot‐assisted channel estimation and pilot jamming in rayleigh slow‐fading channel

In this paper, the authors derived the analytical bit error rate expressions for orthogonal frequency division multiple access and single‐carrier frequency‐division multiple access (SC‐FDMA) in Rayleigh slow‐fading channel for binary phase‐shift keying/quadrature phase‐shift keying/16‐quadrature amplitude modulations under pilot jamming and pilot symbol‐assisted channel estimation. Beginning with the bit error rate analysis from the general case of pilot symbol‐assisted channel estimation technique in Rayleigh slow‐fading channel, the expressions are first modified for different modulations and then further customized to account for the Zero‐Forcing equalization in frequency or time direction with application respectively to orthogonal frequency division multiple access or SC‐FDMA without and with pilot jamming. Piecewise‐linear interpolation is used for its simplicity. The simulation results match perfectly with the theoretical predictions except for some discrepancies with SC‐FDMA, which imply that the generalized equations developed here have to be further modified to account for system‐specific features like discrete Fourier transform precoding for SC‐FDMA. Copyright © 2016 John Wiley & Sons, Ltd.     

MIMO系统中一种子空间追踪的盲空时多用户检测方法

文章提出在空时分组编码的MIMO系统中利用OPAST这种子空问追踪算法进行盲空时多用户检测.仿真结果表明,这种子空间追踪算法可以联合实现平坦瑞利衰落信道估计和空时多用户检测.针对不同的空时分组编码的MIMO通信系统模型,这种盲自适应空时多用户检测方法可以抵抗严重的远近效应和抑制多址干扰,并具有很好的动态跟踪能力.     

Monte Carlo FEXT cancellers for DSL channels

Crosstalk coupling is a severe impairment to transmission on twisted-pair copper cables such as digital subscriber telephone loops (DSLs). In this paper, we investigate the problem of far-end crosstalk (FEXT) cancellation for DSL. We propose a new soft interference canceller for coordinated self-FEXT cancellation across multiple twisted-pairs. The proposed receiver treats the FEXT-impaired channel as a multiple-input multiple-output (MIMO) channel; it uses the sequential Monte Carlo (SMC) technique to exploit the sequential structure inherent in iterative cancellation techniques for MIMO decoding. On telephone loops with strong FEXT, the proposed algorithm shows 0.5-dB coding gain with respect to previously proposed techniques. Furthermore, being soft-input-soft-output in nature, the proposed SMC receiver can iteratively exchange extrinsic information with a MAP decoder to successively cancel FEXT, leading to a turbo FEXT canceller.     

MC–CDMA receiver design using recurrent neural networks for eliminating multiple access interference and nonlinear distortion

Multicarrier code division multiple access (MC–CDMA) is a promising wireless communication technology with high spectral efficiency and system performance. However, all multiple access techniques including MC–CDMA were most likely to have multiple access interference (MAI). So this paper mainly aims at designing a suitable receiver for MC–CDMA system to mitigate such MAI. The classical receivers like maximal ratio combining, minimum mean square error, and iterative block–decision feedback equalization fail to cancel MAI when the MC–CDMA is subjected to severe nonlinear distortions, which may occur due to saturated power amplifiers or arbitrary channel conditions. Being highly nonlinear structures, the neural network receivers such as multilayer perceptron and recurrent neural network could be better alternative for such a case. The feasibility, efficiency, and effectiveness of the proposed neural network receiver are studied thoroughly for MC–CDMA system under different nonlinear conditions.     

Multiuser OFDM Using Cyclic Time Shift for Wireless Uplink Broadcasting

A combination of orthogonal frequency division multiplexing (OFDM) with frequency-division multiple access (FDMA) called orthogonal frequency-division multiple access (OFDMA) is regarded as a promising solution for improving the performance of interactive wireless broadcasting systems. This paper presents our investigation into reducing the multiple access interference (MAI) introduced by symbol timing misalignment in an OFDMA uplink system. To combat the MAI, we provide a new OFDMA symbol frame employing a simple symbol repetition coupled with a cyclic time shift for typical OFDMA uplink scenarios. Theoretical analysis and computer simulations are used to assess the performance of the proposed OFDMA uplink system. It is found that this scheme can decrease the probability of destroying the orthogonality among the users and provide the MAI-free reception.     

Performance analysis and design optimization of LDPC-coded MIMO OFDM systems

We consider the performance analysis and design optimization of low-density parity check (LDPC) coded multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems for high data rate wireless transmission. The tools of density evolution with mixture Gaussian approximations are used to optimize irregular LDPC codes and to compute minimum operational signal-to-noise ratios (SNRs) for ergodic MIMO OFDM channels. In particular, the optimization is done for various MIMO OFDM system configurations, which include a different number of antennas, different channel models, and different demodulation schemes; the optimized performance is compared with the corresponding channel capacity. It is shown that along with the optimized irregular LDPC codes, a turbo iterative receiver that consists of a soft maximum a posteriori (MAP) demodulator and a belief-propagation LDPC decoder can perform within 1 dB from the ergodic capacity of the MIMO OFDM systems under consideration. It is also shown that compared with the optimal MAP demodulator-based receivers, the receivers employing a low-complexity linear minimum mean-square-error soft-interference-cancellation (LMMSE-SIC) demodulator have a small performance loss (< 1dB) in spatially uncorrelated MIMO channels but suffer extra performance loss in MIMO channels with spatial correlation. Finally, from the LDPC profiles that already are optimized for ergodic channels, we heuristically construct small block-size irregular LDPC codes for outage MIMO OFDM channels; as shown from simulation results, the irregular LDPC codes constructed here are helpful in expediting the convergence of the iterative receivers.     

Iterative Joint Tone-Interference Cancellation and Decoding for MIMO-OFDM

In this paper, multi-input–multi-output orthogonal frequency-division multiplexing (MIMO-OFDM) is considered in the presence of multipath fading and multitone interference (MTI). The MIMO-OFDM system makes joint use of channel coding and orthogonal space–frequency block coding (OSFBC) on the transmit side and iterative processing on the receiver side for robustness and improved performance against the fading and MTI effects of the channel. The new iterative receiver is implemented by either an optimal a posteriori probability (APP) space–frequency detector or a soft-information-aided minimum-mean-squared-error (MMSE) combiner at its front end and a soft-input–soft-output channel decoder at its back end. An approximate error performance analysis is provided for the OSFBC-OFDM system under maximum-likelihood decoding to illustrate the interference mitigation efficiency of the system. Then, the two iterative receivers are compared in terms of their computational complexities and bit error rate (BER) performances. As depicted in the BER graphs, both iterative receivers provide an improvement in performance after only a few detection/decoding iterations. It is also shown that despite its suboptimality, the MMSE receiver has the potential to achieve a BER performance close to that of the APP detector at a significantly lower cost.      

Channel-Aware ALOHA-Based OFDM Subcarrier Assignment in Single-Cell Wireless Communications

Usually, centralized channel state information (CSI) is assumed to exploit the multiuser diversity with a smart transmission scheduler. However, such centralized CSI can be impractical for a broadband wireless communication system with a large number of mobile users (MUs). In this paper, we propose a decentralized method to exploit the multiuser diversity in a single cell scenario with orthogonal frequency-division multiplexing (OFDM) based downlink. The central part of our approach is the channel-aware ALOHA-based OFDM subcarrier assignment. According to it, each MU measures the channel at all OFDM subcarriers and tries to obtain proper ones by sending a service-request packet through the corresponding orthogonal uplink subchannel. This packet is sent when the measured channel-fading level exceeds a predetermined threshold xi. The base station processes these request packets with a collision-reception model, and assigns the corresponding subcarrier(s) to the MU whose request packet has been successfully received. Two implementation algorithms are developed, by solving the problem of optimization of xi under different system configurations. Computer simulations show that in comparison with the standard round-robin method, the proposed algorithms offer a substantial data-rate improvement, especially when the correlation property of the OFDM subcarriers is properly exploited     

A new subspace method for blind estimation of selective MIMO‐STBC channels

In this paper, a new technique for the blind estimation of frequency and/or time‐selective multiple‐input multiple‐output (MIMO) channels under space‐time block coding (STBC) transmissions is presented. The proposed method relies on a basis expansion model (BEM) of the MIMO channel, which reduces the number of parameters to be estimated, and includes many practical STBC‐based transmission scenarios, such as STBC‐orthogonal frequency division multiplexing (OFDM), space‐frequency block coding (SFBC), time‐reversal STBC, and time‐varying STBC encoded systems. Inspired by the unconstrained blind maximum likelihood (UML) decoder, the proposed criterion is a subspace method that efficiently exploits all the information provided by the STBC structure, as well as by the reduced‐rank representation of the MIMO channel. The method, which is independent of the specific signal constellation, is able to blindly recover the MIMO channel within a small number of available blocks at the receiver side. In fact, for some particular cases of interest such as orthogonal STBC‐OFDM schemes, the proposed technique blindly identifies the channel using just one data block. The complexity of the proposed approach reduces to the solution of a generalized eigenvalue (GEV) problem and its computational cost is linear in the number of sub‐channels. An identifiability analysis and some numerical examples illustrating the performance of the proposed algorithm are also provided. Copyright © 2009 John Wiley & Sons, Ltd.     

Iterative Group-Blind Multiuser Detection and Decoding With Signal Rank Estimation for Coded CDMA Systems

In this paper, a turbo receiver structure is proposed for the uplink of coded code-division multiple-access (CDMA) systems in the presence of unknown users. The proposed receiver consists of two stages following each other. The first stage performs soft interference cancellation and group-blind linear minimum mean square error (MMSE) filtering, and the second stage performs channel decoding. The proposed group-blind linear MMSE filter suppresses the residual multiple-access interference (MAI) from known users based on the spreading sequences and the channel characteristics of these users while suppressing the interference from other unknown users using a subspace-based blind method. The proposed receiver is suitable for suppressing intercell interference in heavily loaded CDMA systems. Since the knowledge of the number of unknown users is crucial for the proposed receiver structure, a novel estimator is also proposed to estimate the number of unknown users in the system by exploiting the statistical properties of the received signal. Simulation results demonstrate that the proposed estimator can provide the number of unknown users with high accuracy; in addition, the proposed group-blind receiver integrated with the new estimator can significantly outperform the conventional turbo multiuser detector in the presence of unknown users.      

Capacity Improvement for TDD-MIMO Systems via AR Modeling Based Linear Prediction

The quality of channel state information (CSI) affects the performance of multiple input multiple output (MIMO) systems which employ multi-elements antenna arrays at both the transmitter and the receiver. In a time division duplex (TDD) systems, the CSI for downlink can be obtained from uplink channel using reciprocity principal. However, the performance of a MIMO system can be degraded due to channel impairments especially in fast fading scenarios when the CSI obtained from uplink is used for downlink transmission. In this paper, we study performance of autoregressive (AR) modeling based MIMO channel prediction under varying channel propagation conditions (mobile speed, multipath number and angle spread) and prediction filter order. Our simulation results show that using the predicted CSI for downlink provides capacity improvement compared to conventional method.