Asynchronous diversity receiving scheme and analysis on cooperative relay networks简

The transmission antennas of cooperative systems are spatially distributed on multiple nodes, so the received signal can be asynchronous due to propagation delays. A receiving scheme for cooperative relay networks is proposed, multiple asynchronous signals are reconstructed at the receiver by forward and backward interference cancellation, which can obtain gains of cooperative transmission diversity with obvious delay and with no requiring timing synchronization or orthogonal channelization between relays. Analysis and simulation show that the bit error rate（BER） of the proposed scheme is similar to Alamouti code, and the scheme has the diversity order of orthogonal transmission scheme accompanied by minimal BER losses. It is demonstrated that the performance can be further improved by adding an error correcting code（ECC）.     

一种 1x2x4分布式空时编码异步协作方案

协作分集技术可以有效提高移动通信系统的容量和可靠性。近年来,分布式空时码（DSTC）被广泛应用到协作分集系统以实现空间分集增益。然而,时间异步和频率异步会使正交DSTC的码字结构受到破坏,严重影响系统性能。本文针对时间异步的协作通信系统,提出一种基于分布式Alamouti STBC的1x2x4异步协作方案。对这种方案进行了理论分析和算法推导,并且重新定义了中继节点归一化后的发射信号幅度。仿真结果表明该方案的误比特率性能具有明显优势,能在时间异步的协作通信系统中很好地发挥多天线接收性能。     

A Semi-Orthogonal Distributed Alamouti Space-Time Codes Design

In this paper, a novel semi-orthogonal distributed Alamouti space-time codes transmission protocol is proposed for a four nodes cooperative communication system consisting of one source, one destination and two semi blind relays over block fading channels. In particular, by semi-orthogonal we mean two orthogonal frequency bands are invoked, one of which is for the transmission by the source node, while the other one is shared simultaneously by the two relay-destination links. Moreover, analytical performances of the proposed semi-orthogonal scheme are investigated in this paper. Specifically, the theoretical expressions of the exact SER and diversity order are presented. Our proposed scheme is capable of achieving higher spectral efficiency and remaining the same diversity order compared to the existing orthogonal one, while attaining better symbol error rate performance and higher diversity order against the non-orthogonal design. Finally, simulation results prove the correctness of the above conclusions and also verify our derivation for the analytical performances.     

Regenerative Cooperative Diversity with Path Selection and Equal Power Consumption in Wireless Networks

Recently developed cooperative protocol with distributed path selection provides a simple and practical means of achieving full cooperative diversity in wireless networks. While the best path selection method can significantly improve bit error rate (BER) performance, it may cause unequal power consumption among relay nodes, which may reduce the lifetime of energy-constrained networks. A path selection method under the equal power constraint has been developed for the amplifyand- forward (AF) protocol, but there is no such method for the decode-and-forward (DF) protocol. In this paper, we develop a distributed path selection method with an equal power constraint for the DF protocol. We also analyze the BER performance of our path-selection method. Numerical results demonstrate that the proposed method can guarantee equal power consumption, while achieving full diversity as the best path selection method and providing significant performance gain relative to noncooperative communication.     

BER-Constrained Incremental Relaying with Relay Selection in Cooperative Wireless Networks

One of the main drawbacks of cooperative communication systems with half-duplex relaying is inefficient use of spectrum. Incremental relaying is an effective technique that overcomes this limitation, particularly in the high-SNR regime. In this paper, for a multi-relay cooperative network with arbitrary number of relay nodes, we propose a spectrally-efficient incremental relaying scheme that eliminates redundant relay transmissions such that an average end-to-end bit error rate (BER) constraint is satisfied. For detect-and-forward relaying, under the assumption of error propagation from the relays to the destination, we analyze the performance of the system in terms of the end-to-end BER, the average spectral efficiency and the outage probability for Rayleigh fading environment. The performance of the system depends on a single threshold employed by the relays and the destination. We optimize this threshold such that the average spectral efficiency of the system is maximized under an average end-to-end BER constraint. This optimization criterion results in a constant-BER, variable-spectral efficiency relaying scheme. The proposed scheme makes use of spectrum as efficiently as possible, while providing the required quality of service at the destination.     

空时分组码在编码协作通信中的性能研究

为提高系统性能,有效抵抗衰落,提出了采用空时分组码的双中继编码协作通信系统,并给出了中继点使用Alamouti码的发送方式。根据源点和中继点产生LDPC码的整体校验矩阵,导出了目的点进行联合迭代译码所需的初始化消息。理论分析和数值模拟表明,在相同条件下,采用Alamouti码可以明显提高系统性能。当误比特率达到10-4,Alamouti码编码协作通信系统较相应的普通编码协作具有1.6 dB增益。     

Cooperative communications with multilevel/AES-SD4-CPFSK in wireless sensor networks

In this paper, a new joint multilevel data encryption and channel coding mechanism is proposed, which is called ??multilevel/advanced encryption standard?Csystematic distance 4?Ccontinuous phase frequency shift keying?? (ML/AES-SD4-CPFSK). In the proposed scheme, we have not only taken advantage of spatial diversity gains but also optimally allocated energy and bandwidth resources among sensor nodes as well as providing high level of security and error protection for cooperative communications in wireless sensor networks. Relay protocols of cooperative communications, such as amplify-and-forward and decode-and-forward with/without adversary nodes, have been studied for 4CPFSK, 8CPFSK, and 16CPFSK of ML/AES-SD4-CPFSK. We have evaluated the error performances of multilevel AES for data encryption, multilevel SD-4 for channel coding, and various CPFSK types for modulation utilizing cooperative communications in wireless sensor networks. According to computer simulation results, significant diversity gain and coding gain have been achieved. As an example, bit error rate (BER) performance of 10^?5 value has been obtained at a signal-to-noise ratio (SNR) of ?6?dB for SD-4-CPFSK scheme in a compared related journal paper, whereas in our proposed system, we have reached the same BER value at a SNR of ?23?dB with amplify-and-forward with direct path signal protocol in 16-level AES, two-level SD-4 coded 16CPFSK, and at the same time, we have reached the same BER value at a SNR of ?22?dB with amplify-and-forward without direct path signal protocol in 16-level AES, two-level SD-4 coded 16CPFSK.     

Frequency Offset Estimation by Multi-Band Averaging Method: A New Approach for MB-OFDM Based Ultra-Wideband Communication System

In this literature, we present a new method for estimating the coarse frequency offset in multi-band orthogonal frequency division multiplexing (MB-OFDM) based ultra-wideband (UWB) communication systems. The proposed training based coarse frequency offset (CFO) estimator performs an averaging of initial estimate over the multiple bands of transmission during estimation process. The proposed multi-band averaging provides an improved estimation of approximately three times for band group 1 (BG1) compared to our earlier proposed scheme. To prove the efficiency of the proposed scheme, the Cramer Rao lower bound (CRLB) of the estimation error is calculated and compared with the simulation results. We illustrate the performance of MB-OFDM system in terms of bit-error rate (BER) with multi-band averaged frequency synchronization (MBAFS) and compare with earlier reported results for 100,000 noisy realizations in UWB channel model 2 (CM2).     

虚拟多天线无线传感器网络

提出一种基于虚拟多天线技术的分布式和协作的无线传感器网络,分析了该虚拟多天线无线传感器网络的性能。同点到点的无线传感器网络相比较,在天线传输信号能量相同的情况下,虚拟多天线无线传感器网络的误比特概率(BER)更小;或者在同样误比特概率情况下,虚拟多天线无线传感器网络的天线传输信号能量更低。这些特性能够提高无线传感器网络的性能或延长无线传感器网络的使用寿命。     

A Cyclic Shift Relaying Scheme for Asynchronous Two-way Relay Networks

Perfect time synchronization among multiple relay nodes is quite difficult to realize in distributed relay networks. In this paper, we proposed a cyclic prefix (CP) assisted cyclic shift relaying (CFR) scheme for asynchronous two-way amplify-and-forward (AF) relay networks over flat fading channels. In the proposed scheme, a CP is inserted at the two source nodes to combat the asynchronous delays. Each relay amplifies the received mixed asynchronous signals after CP removal, and a cyclic delay is introduced to further improve the system performance. With the CP and the cyclic delay, the multiple flat fading relay channels are transformed into a multipath fading channel. As a result, low complexity frequency domain equalizers, such as zero-forcing and minimum mean square error (MMSE) equalizer, can be used to recover the transmit signal. Furthermore, the performance of the proposed CFR scheme with MMSE equalizer is analyzed and closed-form expression for the lower bound of uncoded bit error rate (BER) performance is derived. Based upon this lower bound, we also investigate the power allocation among the sources and the relays to improve the system performance. Finally, extensive numerical results are provided to show the BER and frame error rate performance of the proposed CFR scheme.     

Distributed polar-coded OFDM based on Plotkin’s construction for half duplex wireless communication

A Plotkin-based polar-coded orthogonal frequency division multiplexing (P-PC-OFDM) scheme is proposed and its bit error rate (BER) performance over additive white gaussian noise (AWGN), frequency selective Rayleigh, Rician and Nakagami-m fading channels has been evaluated. The considered Plotkin’s construction possesses a parallel split in its structure, which motivated us to extend the proposed P-PC-OFDM scheme in a coded cooperative scenario. As the relay’s effective collaboration has always been pivotal in the design of cooperative communication therefore, an efficient selection criterion for choosing the information bits has been inculcated at the relay node. To assess the BER performance of the proposed cooperative scheme, we have also upgraded conventional polar-coded cooperative scheme in the context of OFDM as an appropriate bench marker. The Monte Carlo simulated results revealed that the proposed Plotkin-based polar-coded cooperative OFDM scheme convincingly outperforms the conventional polar-coded cooperative OFDM scheme by 0.5 ~ 0.6 dBs over AWGN channel. This prominent gain in BER performance is made possible due to the bit-selection criteria and the joint successive cancellation decoding adopted at the relay and the destination nodes, respectively. Furthermore, the proposed coded cooperative schemes outperform their corresponding non-cooperative schemes by a gain of 1 dB under an identical condition.     

Distributed Space-Time Cooperative Systems with Regenerative Relays

This paper addresses some of the opportunities and the challenges in the design of multi-hop systems that utilize cooperation with one or two intermediate regenerative relays to provide high-quality communication between a source and a destination. We discuss the limitations of using a distributed Alamouti scheme in the relay channel and the additional complexity required to overcome its loss of diversity. As an alternative to the distributed Alamouti scheme, we propose and analyze two error aware distributed space-time (EADST) systems built around the Alamouti code. First, using a bit error rate based relay selection approach, we design an EADST system with one and two regenerative relays that rely on feedback from the destination and we show that the proposed system improves on the distributed Alamouti scheme. In addition, we prove that the proposed one relay EADST system collects the full diversity of the distributed MISO channel. Second, we introduce an EADST system without feedback in which the relaying energies depend on the error probabilities at the relays. Numerical results show that both EADST systems perform close to the error probability lower bound obtained by considering error-free reception at the relays     

Joint Hadamard transform and Alamouti scheme for wireless communication system

In this letter, the joint of Hadamard transform and Alamouti scheme is proposed. By applying Hadamard transform in the Alamouti scheme, two points of constellation can be merged into one symbol. This symbol is used for input of Alamouti scheme without changing the behavior of Alamouti scheme. System model for joint Hadamard transform and Alamouti scheme is also suggested and formulated. Simulation results show that the bit error rate (BER) performance of the proposed scheme outperforms the original Alamouti scheme.     

BER performance enhancement for secure wireless communication systems based on DCSK-MIMO techniques under Rayleigh fading channel

There has been a growing interest in the use of chaotic techniques for enabling secure communication in recent years. This need has been motivated by the emergence of a number of wireless services which require the channel to provide very low bit error rates (BER) along with information security. As more and more information is transacted over wireless media, there has been increasing criminal activity directed against such systems. This paper investigates the feasibility of using chaotic communications over Multiple-Input-Multiple-Output (MIMO) channels. We have studied the performance of differential chaos shift keying (DCSK) with 2×2 Alamouti scheme and 2×1 Alamouti scheme for different chaotic maps over additive white Gaussian noise (AWGN) and channels disturbed by Rayleigh fading. Both the inherently wideband DCSK modulation and the space-time block code (STBC) are techniques that can mitigate the effect of multipath fading. The use of these schemes allows us to enhance security without degrading the BER performance for Rayleigh fading channels. We have employed an exact method to analyze the performances of DCSK communication system over fading channel. Our simulations indicate that the combination of the STC and tent map provides the best BER performance in addition to security when compared to the choice of other maps. Hence, this study shows that the use of these schemes can allow the user to enhance security without degrading the BER performance while communicating over these channels.     

Residual Synchronization Error Elimination in OFDM Baseband Receivers

It is well known that an OFDM receiver is vulnerable to synchronization errors. Despite fine estimations used in the initial acquisition, there are still residual synchronization errors. Though these errors are very small, they severely degrade the bit error rate (BER) performance. In this paper, we propose a residual error elimination scheme for the digital OFDM baseband receiver aiming to improve the overall BER performance. Three improvements on existing schemes are made: a pilot‐aided recursive algorithm for joint estimation of the residual carrier frequency and sampling time offsets; a delay‐based timing error correction technique, which smoothly adjusts the incoming data stream without resampling disturbance; and a decision‐directed channel gain update algorithm based on recursive least‐squares criterion, which offers faster convergence and smaller error than the least‐mean‐squares algorithms. Simulation results show that the proposed scheme works well in the multipath channel, and its performance is close to that of an OFDM system with perfect synchronization parameters.     

DF模式协同通信的节点选择策略研究

在协同网络中,为了解决如何从所有候选协同节点中选择适当的协同节点进行协同通信的问题,提出了一种基于DF模式的协同节点选择策略,即根据即时信道信息来选择最优的协同节点。理论分析和仿真结果证明,该选择策略能够获得良好的性能,且候选节点在不同位置时采用路径取小准则是最优的方案。     

非理想载波同步物理层网络编码误比特性能分析

采用相干检测的物理层网络编码系统的误比特性能与载波同步精度密切相关,收发双方的载波同步误差将引起系统性能恶化。本文研究了残余载波同步误差对采用相同星座和正交星座BPSK信号的两种物理层网络编码双向中继系统误比特性能的影响。首先基于最大似然准则推导了存在残余载波同步误差时中继节点及源节点处接收信号的判决区域,然后运用Craig极坐标法分析了系统多址接入、广播阶段及总的端到端误比特性能,得出了精确的误比特率表达式,文中的分析方法可推广到采用其他调制方式的物理层网络编码系统。计算机仿真表明:文中的理论分析与仿真结果完全吻合,所推导的理论公式可以效地评估BPSK调制物理层网络编码系统的误比特性能;正交星座系统对载波同步误差更为敏感,相同的同步误差对正交星座系统的性能恶化更为严重。      

Differential Modulation and Relay Selection With Detect-and-Forward Cooperative Relaying

In this paper, we consider the bit error rate (BER) performance analysis of a cooperative relay communication system with differential modulation and selective relaying, where the best relay is selected to forward the signals from the source to the destination. The advantage of differential modulation is that it allows noncoherent detection without requiring the full channel-state information (CSI), as obtaining CSI in a cooperative communication system at each node is a complicated and costly task. We consider a simple detect-and-forward (DetF) relay system and take into account the effect of imperfect detection at the relay. We derive the average bit error probability of the DetF relay scheme by using the closed-form relay link signal-to-noise ratio (SNR). Based on the analysis, we show that the proposed system with $N$ relay nodes and the simple relay selection can achieve a total diversity gain of $N + 1$. The BER performance of the system is also evaluated by simulation. It is shown that the analysis matches well with the simulation results.      

Capacity of distributed PHY-layer sensor networks

Sensor networks are comprised of nodes with minimal baseband and RF functionalities. In such networks, it is assumed that a source sensor communicates with a target sensor over a number of relaying sensors by utilizing distributed low-complexity space-time encoding techniques, hence the resulting communication scenario is a generalized form of orthogonalized multiple-input multiple-output (MIMO) channels. The contributions of this paper are the derivation of the Shannon capacity in terms of natural units per second per Hertz for such space-time encoded distributed communication scenarios. Closed-form capacity expressions are derived for ergodic flat-fading Rayleigh and Nakagami channels, as well as the communication-rate outage probabilities for aforementioned channels. It is shown that the distributed Alamouti scheme yields the best performance over ergodic channels. In the case of nonergodic channels, the 3/4-rate sporadic space-time block code (STBC) is shown to give optimum performance. Finally, Monte Carlo simulations are used to assess the performance of distributed multistage sensor networks. It is shown that notable power savings can be achieved, compared to the traditional single-link sensor networks.     

Flexible decision-aided maximum likelihood phase estimation in coherent optical phase-shift-keying systems

Decision-aided maximum likelihood (DA-ML) phase estimation has been applied in coherent optical communication systems due to its high computational efficiency. However, conventional DA-ML scheme only assumes constant phase noise within each observation block, thus causing block length effect (BLE) which degrades system performance. In this paper, we take into account the time-varying laser phase noise and propose a flexible DA-ML phase estimation method for carrier phase recovery in coherent optical phase-shift-keying systems so as to eliminate BLE. Weighted coefficients based on ML criterion are introduced to strengthen the estimation accuracy. The statistical property of phase estimation error is derived, and the bit error rate (BER) performance is also evaluated. Numerical simulation results show that our flexible DA-ML scheme is very robust against time-varying phase noise. Compared with conventional DA-ML receiver, it can significantly reduce the phase estimation variance, improve the BER performance and increase the laser linewidth tolerance. By adopting the flexible DA-ML method with a relatively larger block length, BLE can be effectively eliminated. Thus, the BER performance can be significantly improved without carefully finding out the optimum block length or the optimum forgotten factor.