An Iterative Interference Alignment Scheme for the SISO Interference Channel

In this paper, we propose a novel iterative interference alignment (IA) scheme for the single-input single-output (SISO) interference channel system using minimum total mean square error criterion under the individual transmitter power constraints. We show that interference alignment under such criterion could be realized through an iterative algorithm. The convergence of the proposed algorithm is discussed. We also proposed a robust MMSE-based iterative design with imperfect channel state information. Simulation results, compared with several existing IA schemes, have shown that the proposed method could effectively improve the BER performance of the SISO interference channel system while maintaining the same degree of freedom as Cadambe?CJafar scheme. The proposed robust MMSE-based iterative interference alignment scheme is shown to be less sensitive to channel estimation error.     

Design and Performance Analysis of Soft Decision-Based Network-Assisted Interference Cancellation and Suppression Scheme

Recently, 3rd Generation Partnership Project (3GPP) has developed a network-assisted interference cancellation and suppression scheme to reduce the effect of interference. In this paper, we propose an advanced receiver based on soft decision to reduce the interference from the neighbor cells. The proposed receiver can suppress and cancel the interference by calculating the unbiased estimation value of the interference signal using the minimum mean square error or the interference rejection combining receiver. The interference signal is updated using soft information expressed by the log-likelihood ratio. We perform the system-level simulation based on 20 MHz bandwidth of a 3GPP LTE-Advanced sidelink system. The simulation results show that the proposed receiver can improve the signal-to-noise-plus-interference ratio, throughput, and spectral efficiency of a conventional system.

     

GF(q)‐based precoding: information theoretical analysis and performance evaluation

In this paper, a new precoding scheme that is based on the operations in Galois field of size q = 2^m(GF(q)) is proposed. Generally, precoding is a processing technique at transmitters to match the input signal to the channel in order to achieve optimal channel capacity through fully utilizing space, time, and frequency diversity. Precoding schemes can be divided into two main categories: linear precoding and nonlinear precoding. It has been shown from an information theoretical aspect that both the linear and nonlinear precoding schemes can achieve the optimal channel capacity. Our proposed GF(q)‐based precoding scheme is a nonlinear precoding technique, and the idea originates from finite inputs of the modulated symbols. When representing the modulated symbols and the elements in precoding matrix with the finite elements in Galois field of size q, and applying the operations defined in GF(q), we can obtain the precoded symbols that contains information of the original symbols. Starting from binary symmetry channel to additive Gaussian white noise channels, we have demonstrated that the proposed GF(q)‐based precoding schemes can enhance the system mutual information when the original finite inputs are not uniformly distributed. In addition, inspired by the mutual information analysis in binary symmetry channel, we investigated the selection of the precoding matrix in GF(q)‐based precoding schemes. As mutual information indicates the information about the source carried by the symbols of the channel output, greater mutual information enables the receivers to recover more information about the original source. To further utilize the greater mutual information brought by the proposed GF(q)‐based precoding schemes, we proposed a novel‐receiving structure by exchanging soft information between the GF(q) decoding block and channel decoding block. Simulation results show that the proposed iterative receiver improves the system bit error rate performance by 1 and 2 dB at the bit error rate level of 10 ^− 6 with binary phase shift keying and quadrature phase shift keying modulations, respectively. Inspired by the encouraging results of greater mutual information and better bit error rate performance, we are convinced that the proposed GF(q)‐based precoding schemes can be extended to fading channels and multiple input–multiple output systems to further approach channel capacity. Copyright © 2016 John Wiley & Sons, Ltd.     

Performance Investigation of Space‐Time Block Coded Multicarrier DS‐CDMA in Time‐Varying Channels

In this letter, we evaluate the system performance of a space‐time block coded (STBC) multicarrier (MC) DS‐CDMA system over a time selective fading channel, with imperfect channel knowledge. The average bit error rate impairment due to imperfect channel information is investigated by taking into account the effect of the STBC position. We consider two schemes: STBC after spreading and STBC before spreading in the MC DS‐CDMA system. In the scheme with STBC after spreading, STBC is performed at the chip level; in the scheme with STBC before spreading, STBC is performed at the symbol level. We found that these two schemes have various channel estimation errors, and that the system with STBC before spreading is more sensitive to channel estimation than the system with STBC after spreading. Furthermore, derived results prove that a high spreading factor (SF) in the MC DS‐CDMA system with STBC before spreading leads to high channel estimation error, whereas for a system with STBC after spreading this statement is not true.     

双向MIMO中继网络中采用信道独立预编码的自干扰消除技术

双向中继网络在提高频谱效率的同时会引入额外的自干扰,本文针对放大转发（AF）模式下双向多输入多输出（MIMO）中继网络中的自干扰抵消问题,从消除信道估计误差引入的剩余自干扰着手,提出一种采用信道独立预编码的盲干扰抵消（BIC）方案。新方案在源节点对信息进行行空间预编码,从而构建不依赖于MIMO信道矩阵的期望信号子空间和自干扰子空间,实现未知信道状态下自干扰抵消和期望信号分离,从而消除非理想信道估计带来的剩余自干扰信号。在此基础上,以最大化有效信噪比为目标设计最佳预编码,通过推导可达和速率的闭合表达式,分析不同方案下信道估计误差对可达和速率的影响。仿真结果表明,新方案在不同的信道估计误差下,能够实现完美自干扰消除,其检测性能和容量均优于基于信道估计的自干扰消除方案。      

Intercarrier Interference Suppression for OFDMA Uplink in Time- and Frequency-Selective Fading Channels

This paper investigates intercarrier interference (ICI) suppression and channel estimation for the uplink of an orthogonal frequency-division multiple-access (OFDMA) system in a time- and frequency-selective fading channel. In such a doubly selective channel, channel variations within each OFDMA block disrupt the orthogonality among subcarriers and leads to ICI. We develop an appropriate signal model for the OFDMA uplink in a doubly selective fading channel and propose a minimum mean square error (MMSE) scheme and an MMSE successive detection (MMSE-SD) scheme to suppress ICI. It is shown that the MMSE scheme is the optimal linear scheme in terms of maximizing achievable data rate and that the MMSE-SD scheme is able to further remove ICI and exploit the Doppler diversity embedded in time-varying channels. As an essential component in ICI suppression, channel estimation is also considered. A basis expansion model (BEM) is formulated for the OFDMA uplink channel, and a pilot-aided channel-estimation algorithm is developed to track users' channels in the time domain. Simulation results are presented to illustrate the overall performance improvements that can be obtained from using the proposed ICI suppression and channel-estimation schemes.      

LTE同频干扰环境下干扰抑制检测算法的研究

基于上行干扰抑制合并技术（IRC）提出了两种干扰检测算法。第一种改进方案需要预先知道目标小区和干扰小区信道状态信息,第二种改进方案在不知道目标小区和干扰小区信道状态信息的情况下,通过盲估的方法进行计算。这两种算法都能有效抵御同频干扰,并减少误码率。     

Time‐domain equalizer for multicarrier systems in impulsive noise

In multicarrier communication systems, a time‐domain equalizer (TEQ) can be applied to shorten the channel impulse response and to eliminate inter‐symbol interference (ISI). However, the presence of impulsive noise in the channel may paralyze the operation of TEQs and subsequently lead to poor error performance. In this paper, a multicarrier receiver that incorporates a constant false alarm rate algorithm and an iterative estimation technique (CFAR‐IET) in conjunction with a TEQ is proposed to increase the robustness of the receiver against impulsive noise. Furthermore, an improved version of the CFAR‐IET‐TEQ scheme, which uses the buffering, sorting, removing and amplitude averaging (BSRA) processes, is presented. Performance comparisons of the proposed schemes with the existing Gaussian‐optimized schemes are made. Simulation results show that the BSRA‐IET‐TEQ scheme is an effective approach to reduce symbol error rate (SER) in impulsive channels while performing satisfactorily in Gaussian channels. Copyright © 2011 John Wiley & Sons, Ltd.     

Performance analysis for relay networks with hierarchical support vector machines

In this paper, we consider a cooperative relay scheme for a mobile network with MIMO technology. The channel capacity for two well‐known relaying schemes are investigated: analogue relaying (amplify and forward) and digital relaying (decode and forward) from a mobile device to the base station through a relay node. In order to further increase the channel capacity, we propose an efficient hierarchical procedure based on support vector machine, namely hierarchical support vector machines (HSVM), to estimate the wireless networks condition approximately and design two ways (matched filter and minimum mean square error filter) of increasing the channel capacity according to the estimated wireless network condition. The proposed HSVM can estimate the wireless networks condition in much shorter time compared with the traditional minimum mean square error scheme without incurring much estimation error, which is spatial, useful for delay sensitive communication. For digital relaying, the effect of imperfect channel decode is also addressed. Our numerical results demonstrate the reduction of estimation complexity by adopting HSVM and the significant improvement of network capacity by applying the matched filter weight at relay nodes according to the network estimation. Copyright © 2011 John Wiley & Sons, Ltd.     

Two signaling schemes for improving the error performance of frequency division duplex (FDD) transmission systems using transmitter antenna diversity

We propose two signaling schemes that exploit the availability of multiple (N) antennas at the transmitter to provide diversity benefit to the receiver. This is typical of cellular radio systems where a mobile is equipped with only one antenna while the base station is equipped with multiple antennas. We further assume that the mobile-to-base and base-to-mobile channel variations are statistically independent and that the base station has no knowledge of the base-to-mobile channel characteristics. In the first scheme, a channel code of lengthN and minimum Hamming distanced _minN is used to encode a group ofK information bits. Channel code symbolc _i is transmitted with thei th antenna. At the receiver, a maximum likelihood decoder for the channel code provides a diversity ofd _min as long as each transmitted code symbol is subjected to independent fading. This can be achieved by spacing the transmit antennas several wavelengths apart. The second scheme introduces deliberate resolvable multipath distortion by transmitting the data-bearing signal with antenna 1, andN–1 delayed versions of it with antennas 2 throughN. The delays are unique to each antenna and are chosen to be multiples of the symbol interval. At the receiver, a maximum likelihood sequence estimator resolves the multipath in an optimal manner to realize a diversity benefit ofN. Both schemes can suppress co-channel interference. We provide code constructions and simulation results for scheme 1 to demonstrate its merit. We derive the receiver structure and provide a bound on the error probability for scheme 2 which we show to be tight, by means of simulations, for the nontrivial and perhaps the most interesting caseN=2 antennas. The second scheme is backward-compatible with two of the proposed digital cellular system standards, viz., GSM for Europe and IS-54 for North America.     

多波束移动卫星系统的自适应开环预编码方法

对于卫星移动通信系统,由于卫星与地面终端之间的相对运动以及星地间传输延迟,传统的基于理想信道信息的预编码方法是不适用的。针对这一问题,提出了一种基于开环信道估计的预编码方法。卫星端利用开环获取的部分信道信息实现多波束联合预编码,并导出了系统传输速率的闭合解析表达式。此外,为了克服强干扰环境下多波束预编码系统性能恶化问题,提出了一种自适应预编码传输方法。卫星发射机依据开环获得的慢时变用户位置信道信息和信道统计量信息,自适应地选择预编码方法或传统频率复用方法,实现最优的系统性能。理论分析和仿真结果表明,与传统的干扰抑制方法相比,所提方法能实现更优的系统性能,同时也克服了传统预编码方法的局限性。     

突发通信中基于叠加训练的信道估计方案

针对无线突发通信中频带利用率低、信道参数获取困难等问题,提出了一种应用于突发通信的叠加训练信道估计与检测方案。该方案将信息和训练叠加发送,通过预失真发送信息符号使得训练与信息在频域正交,收端采用一阶统计信道估计和最大似然符号检测,并设计了抗直流干扰的信道估计方案。仿真表明,新方案在消除训练序列的频带开销的情况下获得了较好的信道估计和符号检测性能,与采用时分复用训练的方案相比,其有效吞吐率更优。     

Spectral efficiency evaluation of full‐duplex mode of communications based on SLNR approach

Full‐duplex (FD) mode of communication with efficient transmission scheme is a promising approach for 5G wireless systems by improving the spectral efficiency. This can be attained by making use of various precoding approaches. We propose a new co‐channel interference (CCI)‐aware improvement to signal‐to‐leakage‐and‐noise ratio (SLNR) technique and a suppression filter at the receiver to whiten the interference for the downlink channel. As well, for the uplink (UL) communication, we propose a self‐interference (SI)‐aware enhancement to SLNR scheme and designing a precoder using self‐interference plus noise covariance matrix. The total spectral efficiency is obtained from the sum‐rates of both downlink and uplink communication systems. Simulation results verify that the spectral efficiency (SE) of FD using the proposed scheme performs well relative to the half‐duplex system for all Rician factor and for small powers at the base station (BS) and UL communication channel users. Moreover, as the number of users grows, which entails that as the number of receiving antennas greater than the number of antennas at the BS the SLNR scheme still works, nonetheless, zero‐forcing (ZF) and block‐diagonalization (BD) precoding schemes failed. This is due to the fact that designing a precoder based on SLNR scheme supports multiple numbers of antennas at the base station and users compared with ZF and BD by compromising the interference and noise. However, for the cases of ZF and BD approaches failed due to both schemes require the number of transmit antennas at the BS to be larger than the sum of the receiving antennas at all users.     

Investigation on outage capacity of spectrum sharing system using CSI and SSI under received power constraints

In this paper, we have investigated the outage capacity of secondary user for opportunistic spectrum sharing under the joint peak and average received power constraints for Rayleigh fading environment. Under this communication scenario, on detecting the licensed primary user inactive, the secondary unlicensed users transmit data/information in the licensed frequency band such that no or minimum interference may be experienced by the primary user. The soft sensing information (SSI) and secondary user’s channel state information is used to obtain the closed form expressions for the ergodic and outage capacity using truncated channel inversion with fixed rate technique under the joint peak and average received power constraints. Numerically simulated results are provided to demonstrate the improvement in outage capacity of secondary user under the proposed spectrum sharing scheme. Moreover, the proposed scheme is also compared with other conventional spectrum sharing schemes to illustrate the benefits of SSI and received power constraints on the outage capacity of secondary user.

     

5G多载波通信中信道估计干扰抑制均衡算法

传统5G多载波通信中信道估计干扰抑制算法存在着均衡性能较差的问题,表现为误码元数与误码率偏高,因此文章提出5G多载波通信中信道估计干扰抑制均衡算法。该算法首先对干扰项进行过采样处理,引入预处理矩阵以减小模损失的影响,对信道估计干扰进行均衡抑制。仿真实验结果表明,在信噪比相同的情况下,5G多载波通信中信道估计干扰抑制均衡算法的误码元数比两种传统算法分别低了161、192,其误码率分别低了24%、31%,均衡性能较好。     

Channel estimation and interference suppression for uplink CDMA mobile communication systems

Wireless communications for mobile telephone and data transmission is currently undergoing very rapid development. Code division multiple‐access (CDMA) implemented with direct sequence spread spectrum signaling is among the most promising multiplexing technologies for cellular telecommunications services. In this paper, jointly period inserted pilot symbols assisted recursive (PIPSAR) channel estimation and interference suppression techniques are proposed for uplink CDMA mobile communication systems. The uplink CDMA mobile communication system model is described in the form of space‐time domain through antenna array and multipath expression. Interference suppression is achieved by using adaptive minimum mean squared error (MMSE) digital filters that span several successive received chip oversampling vectors of a symbol interval. PIPSAR techniques are used to estimate channel parameters. The correlation between the successive periods is considered to further improve the performance of the proposed scheme. Analysis and simulations are used to evaluate the performance of the proposed scheme. Copyright © 2004 John Wiley & Sons, Ltd.     

Interference management schemes for multi‐user cooperative wireless networks

Cooperative communication is a promising technique for future wireless networks. It can be used in improving communication reliability and enhancing spectrum efficiency by using the broadcast nature of radio communication and exploiting cooperative diversity. However, its performance gain degrades in the presence of co‐channel interference, which makes it essential to propose interference mitigation schemes. In this paper, we introduce three cooperative communication schemes with interference management for multi‐user cooperative wireless networks. The first scheme (best relay selection) is used as a performance benchmark because it completely avoids the interference problem by using the Frequency‐Division Multiple Access technique. The second scheme (best available relay selection) maximizes the received signal‐to‐noise ratio while keeping the interference levels below a certain threshold, and the third scheme (General Order Relay and User Selection) is based on iterative resource allocation algorithm. We derive exact closed‐form expressions of average bit error probability, outage probability, and average consumed power for the proposed schemes. Simulations are used to validate the analytical results. The results confirm the advantage of the proposed cooperation schemes in enhancing the system performance and improving the interference management. Copyright © 2015 John Wiley & Sons, Ltd.     

双选择信道中的时间偏移广义频分复用通信

当信道存在时间-频率双选择性时,严重的子载波间干扰和子符号间干扰将导致广义频分复用(GFDM)系统性能显著下降.为此,该文提出一种时间偏移GFDM系统(TO-GFDM),通过对传统GFDM系统的原型滤波器进行时间偏移,来提高双选择信道下GFDM系统的性能.该文推导了GFDM信号在双选择信道中的平均信干比公式,并提出基于离散导频的联合迭代信道估计与符号检测算法,该算法利用信道估计器与串行干扰消除符号检测器之间的信息交换,逐步减小干扰信号,提高信道估计与符号检测的精度.理论分析与仿真实验结果表明,在双选择信道条件下,时间偏移GFDM比传统的GFDM具有更高的平均信干比和误码率性能;并且,联合迭代信道估计与符号检测算法能有效降低系统误码率.     

双选择信道中的时间偏移广义频分复用通信

当信道存在时间-频率双选择性时,严重的子载波间干扰和子符号间干扰将导致广义频分复用(GFDM)系统性能显著下降。为此,该文提出一种时间偏移GFDM系统(TO-GFDM),通过对传统GFDM系统的原型滤波器进行时间偏移,来提高双选择信道下GFDM系统的性能。该文推导了GFDM信号在双选择信道中的平均信干比公式,并提出基于离散导频的联合迭代信道估计与符号检测算法,该算法利用信道估计器与串行干扰消除符号检测器之间的信息交换,逐步减小干扰信号,提高信道估计与符号检测的精度。理论分析与仿真实验结果表明,在双选择信道条件下,时间偏移GFDM比传统的GFDM具有更高的平均信干比和误码率性能;并且,联合迭代信道估计与符号检测算法能有效降低系统误码率。     

On the performance of two‐user full‐duplex network‐coded cooperation

In this paper, we propose two schemes based on a full‐duplex network‐coded cooperative communication (FD‐NCC) strategy, namely, full‐duplex dynamic network coding (FD‐DNC) and full‐duplex generalized dynamic network coding (FD‐GDNC). The use of full‐duplex communication aims at improving the spectrum efficiency of a two‐user network where the users cooperatively transmit their independent information to a common destination. In the proposed FD‐NCC schemes, the self‐interference imposed by full‐duplexing is modeled as a fading channel, whose harmful effect can be partially mitigated by interference cancellation techniques. Nevertheless, our results show that, even in the presence of self‐interference, the proposed FD‐NCC schemes can outperform (in terms of outage probability) the equivalent half‐duplex network‐coded cooperative (HD‐NCC) schemes, as well as traditional cooperation techniques. Moreover, the ?‐outage capacity, that is, the maximum information rate achieved by the users given a target outage probability, is evaluated. Finally, we examine the use of multiple antennas at the destination node, which increases the advantage of the FD‐NCC (in terms of the diversity‐multiplexing trade‐off and ?‐outage capacity).