水声信道中的迭代分组判决反馈均衡器

 与传统的时域均衡相比,频域均衡为单载波传输系统提供了一种计算更为有效的方法。该文对有大多径时延和多普勒频移的水声信道中的频域分组迭代判决反馈均衡器(IB-DFE)进行了研究,提出了一种联合迭代均衡和频域信道估计(JECE)算法,分析了JECE算法的性能以及不同数据参数对IB-DFE性能的影响,并计算了IB-DFE的计算复杂度。仿真结果表明,所提出的JECE算法对时变水声信道有更好的适应性。与TD-DFE相比,IB-DFE有3.6 dB以上的信噪比增益和约19%的复杂度增益,而且随着多径时延和多普勒频移的增加,这种性能增益会进一步增加。     

Shifted Known Symbol Padding for Efficient Data Communication in a WLAN Context

To allow for a computationally efficient equalization scheme for the frequency-selective transmission channels encountered in wireless local area network (WLAN) applications, cyclic prefix (CP) block transmission schemes have been proposed, such as single-carrier CP (SC-CP) and multi-carrier CP (MC-CP) transmission, also known as orthogonal frequency division multiplexing (OFDM). In this letter, however, we focus on the known symbol padding (KSP) transmission scheme. In this scheme known padded sequences can be exploited for synchronization as well as for channel estimation. However, to simultaneously allow for low-complexity frequency-domain equalization and accurate channel estimation within the KSP context, a modified KSP scheme is proposed, namely shifted KSP (S-KSP). Comparing different block transmission schemes in the WLAN context, the S-KSP scheme is shown to offer a very good performance.     

Redundant Paraunitary FIR Transceivers for Single-Carrier Transmission Over Frequency Selective Channels With Colored Noise

Recently, the use of redundant memoryless single-carrier transmitters has been reported as an efficient choice to reduce distortions introduced by finite-impulse response (FIR) channels. In this work, redundant FIR transceivers are proposed to address not only channel frequency selectivity but additive colored noise, which strongly degrades the performance of memoryless transceivers. The transmitter is shown to be paraunitary, resulting in a simple receiver. The proposed system is optimized like a modulated filter bank. Channel shortening and post-combiner equalizers are used to improve system performance. Comparisons with recent proposed schemes are presented, illustrating the efficiency of the new structure for selective channels with colored noise.     

空间相关莱斯衰落信道下基于部分信道信息的多用户预编码与调度算法

在空间相关的莱斯衰落信道模型下,针对多用户MIMO(Multiple-Input Multiple-Output)系统潜在的多用户分集增益和空间分集增益,该文提出了一种基于部分信道信息的多用户预编码与调度算法。结合部分瞬时信道信息和统计信息,利用约束最大似然估计对各用户信道矢量进行估计,然后利用估计的各用户信道调度多个用户进行预编码。仿真结果表明,该方案以较少的反馈开销,获得了较大的性能增益。     

Space-frequency block code for single-carrier FDMA

A full-diversity space-frequency block code (SFBC) for single-carrier frequency-division multiple access (SC-FDMA) systems is presented. The code is designed for two transmit antennas and preserves the low envelope fluctuations of SC signals. The good performance of the proposed scheme over multiple-input multiple-output (MIMO) channels, both in static and in high-speed mobility scenarios, is proved.     

Performance of a hybrid multilevel error control with an early-stop ARQ protocol for wireless ATM networks

This paper proposes an effective hybrid multilevel error control (HMEC) with an early-stop automatic repeat request (ARQ) scheme for wireless asynchronous transfer mode (ATM) networks. In this scheme, the source traffic is segmented into a number of blocks, each with m cells, then encoded into k(k>m) cells. The transmission of one block may be finished as long as m out of the k cells are received correctly. The ARQ protocol is applied only when too many cells are dropped or corrupted due to uncorrectable error in the radio channel. This paper also provides a detail study of the proposed scheme. In particular, the throughput efficiency with parameters (m,k) are derived analytically for the white Gaussian and Rayleigh fading channels. Simulation results show a very close match with theoretical results. All the results show that the HMEC scheme can reduce cell-retransmission probability and improve network throughput over a wide range of channel error rates when appropriate values of parameters m and k are chosen.     

Optimization of Training and Scheduling in the Non-Coherent SIMO Multiple Access Channel

Channel state information (CSI) is important for achieving large rates in MIMO channels. However, in time-varying MIMO channels, there is a tradeoff between the time/energy spent acquiring channel state information (CSI) and the time/energy remaining for data transmission. This tradeoff is accentuated in the MIMO multiple access channel (MAC), since the number of channel vectors to be estimated increases with the number of users. Furthermore, the problem of acquiring CSI is tightly coupled with the problem of exploiting CSI through multiuser scheduling. This paper considers a block-fading MAC with coherence time T, n uncoordinated users-each with one transmit antenna and the same average power constraint, and a base station with M receive antennas and no a priori CSI. For this scenario, a training-based communication scheme is proposed and the training and multiuser-scheduling aspects of the scheme are jointly optimized. In the high-SNR regime, the sum capacity of the non-coherent SIMO MAC is characterized and used to establish the SNR-scaling-law optimality of the proposed scheme. In the low-SNR regime, the sum-rate of the proposed scheme is found to decay linearly with vanishing SNR when flash signaling is incorporated. Furthermore, this linear decay is shown to be order-optimal through comparison to the low-SNR sum capacity of the non-coherent SIMO MAC. A by product of these SNR-asymptotic analyses is the observation that non-trivial scheduling (i.e., scheduling a strict subset of trained users) is advantageous at low SNR, but not at high SNR. The sum-rate and per-user throughput are also explored in the large-n and large-M regimes. Non-coherent capacity, training, multiple access channel, multiuser scheduling, opportunistic scheduling.     

Orthogonal spectral precoder for minimizing adjacent channel leakage ratio in OFDM based cognitive radio

One of the major drawback of an orthogonal frequency division multiplexing based cognitive radio is high out‐of‐band leakage that can severely affect primary users operating in adjacent bands. The paper aims to design a new spectral precoding scheme that minimizes Adjacent Channel Leakage Ratio (ACLR) while retaining the orthogonality among data symbols. The problem is formulated as trace ratio minimization subjected to unitary constraint that can be effectively solved using iterative methods. The proposed precoder's error performance is similar to uncoded orthogonal frequency division multiplexing system due to orthogonal multiplexing. Also, it is practically realizable due to lower complexity. The scheme also extends for distinct ACLR requirements in upper and lower adjacent bands. A relative important factor is introduced so as to flexibly control the interference leakage in upper and lower adjacent channels. An algorithm is suggested for choosing suitable values of this factor. Simulation results display the superiority of proposed scheme over existing techniques in terms of ACLR and throughput. Copyright © 2016 John Wiley & Sons, Ltd.     

Channel Adaptive Shortest Path Routing for Ad Hoc Networks

1　IntroductionAdhocnetworksareformedwithoutrequiringthepreexistinginfrastructureorcentralizedadminis tration ,incontrasttocellularnetworks.Asidefromtheoriginalmilitaryapplication ,ithasapplicationinpublicsafetyandcommercialareas,butadaptiveprotocolsarerequiredinorderforthemtodoso .Twoimportantcharacteristicsofacommunicationlinkinadhocnetworksareitsunreliabilityanditsvariability .Thelinksinsuchanetworkareunreli ablebecauseoffading ,interference,noise,andper hapsthefailureofthetransmittingorrec…     

Cross-Layer MAC Protocol and Holistic Opportunistic Scheduling with Adaptive Power Control for QoS in WiMAX

Providing quality of service (QoS) to different service classes with integrated real-time and non-real-time traffic is an important issue in broadband wireless access networks. Opportunistic MAC (OMAC) is a novel view of communication over spatiotemporally varying wireless link whereby the multi-user diversity is exploited rather than combated to maximize bandwidth efficiency or system throughput. It combines cross-layer design features and opportunistic scheduling scheme to achieve high utilization while providing QoS support to various applications. Channel characteristics, traffic characteristics and queue characteristics are the essential factors in the design of opportunistic scheduling algorithms. In this paper, we propose a cross-layer MAC scheduling framework in WiMAX point-to-multipoint (PMP) systems and a corresponding opportunistic scheduling algorithm with an adaptive power control scheme to provide QoS support to the heterogeneous traffic. Extensive simulation experiments have been carried out to evaluate the performance of our proposal. The simulation results show that our proposed solution can improve the performance of the WiMAX PMP systems in terms of packet loss rate, packet delay and system throughput.     

A satellite switched CDMA system for fixed service communications

Satellite-switched code-division multiple access is a system proposed for geostationary fixed satellite service. SS/CDMA provides both multiple access and switching to a multibeam satellite. In this article we present the system architecture and performance. The SS/CDMA consist of the common air interface (CAI) and the onboard code switching mechanism. The CAI provides signaling control and traffic channels. Traffic channel access and modulation is based on a spectrally efficient CDMA scheme. The satellite code-division switch (CDS) routes calls from an uplink to a downlink beam without onboard demodulation and channel decoding. This system operates with demand assignment control; that is, channel bandwidth and switch connections are only assigned per user request. The system can offer a wide variety of bit rates with wireline quality of service. The services provided are circuit-switched calls for voice data and video, and packet-switched for data. As shown, the proposed SE-CDMA can achieve high capacity and very low bit error rates at low signal-to-noise ratio. Also, the innovative switching technique can provide low complexity and achieve high throughput for all services     

AWGN和Rayleigh信道下的自适应多级编码系统设计

基于信道容量规则和分组分割,构造自适应于AWGN和Rayleigh两种信道的多级编码系统,为移动信道编码调制系统的设计度量提供参考。提出利用信道状态信息的软判决支路度量计算公式,分析分组分割方案的自适应特性,比较软、硬判决译码对系统性能的影响,结果表明本文提出的自适应系统比未编码系统获得可观的编码增益。     

频率选择性信道下单载波空时分组编码传输系统中的信道估计技术

在频率选择性信道下给出了单载波频域均衡系统结合空时分组编码传输基于训练序列的最优信道估计算法。由于选取具有恒幅特性的Chu序列作为训练序列,因此这一算法能够实现信道估计的最小均方误差,并作了理论证明。最后,对本方案的性能进行了仿真比较,仿真的结果证实了本方案的优点。     

Optimization and performance evaluation of multicarriertransmission

Optimization of the performance of multicarrier transmission over a linear dispersive channel is presented. The optimum data and power assignment to the subcarriers are derived for both the conventional error probability criterion, and a new criterion based on the normalized mean-square error. The assignments and algorithms hold for channels where performance is degraded by additive noise, intersymbol and interchannel interference. Lower bounds on throughput are derived and are used to compare multicarrier performance with conventional single-carrier quadrature amplitude modulation (QAM) with both linear and decision feedback equalization. It is seen that multicarrier transmission can provide a significant improvement at low and intermediate channel signal-to-noise ratios. As an example, the optimization is applied to the high-speed digital subscriber loop, and multicarrier transmission is demonstrated to be superior to decision feedback equalized single-carrier QAM     

Frequency resource allocation strategy with QoS support in hybrid cellular and Device‐to‐Device networks

Hybrid networks, comprising a conventional cellular network overlaid with Device‐to‐Device (D2D), offer efficient way to improve system throughput. In this paper, a novel orthogonal frequency‐division multiple access channel‐assignment method is proposed for hybrid network. The proposed approach is optimal in terms of throughput and is subjected to a sensible QoS requirement, which guarantees that macrocell and D2D achieve a prescribed data rate and outage probability, respectively. Our solution consists of two phases. In the first phase, the minimum sub‐channels are allocated to the macrocell to satisfy their data rate requirements. This problem is mapped to the 0‐1 Knapsack Problem and solved by integer programming based Lagrange dual approach. In the second phase, the redundant sub‐channels are allocated to D2D pairs to maximize the throughput of D2D networks. An interference management scheme is proposed to guarantee the outage probability of D2D communications. A cluster is taken as the unit for frequency reuse among D2D pairs. The problem of clustering is mapped to the MAX k‐CUT problem in graph theory and is solved by graph‐based heuristic algorithm. Extensive simulations demonstrate the superior performance of the proposed solution compared with the existing scheme. Copyright © 2014 John Wiley & Sons, Ltd.     

Robust QoS Control for Single Carrier PMP Mode IEEE 802.16 Systems

The IEEE 802.16 WirelessMAN standard provides a comprehensive quality-of-service (QoS) control structure to enable flow isolation and service differentiation over the common wireless network interface. By specifying a particular set of service parameters, the media access control (MAC) mechanisms defined in the standard are able to offer predefined QoS provisioning on a per-connection basis. However, the design of efficient, flexible, and yet robust MAC scheduling algorithms for such QoS provisioning still remains an open topic. This paper proposes a new QoS control scheme for single-carrier point-to-multipoint mode wireless metropolitan area network (WirelessMAN) systems, which enables the predefined service parameters to control the service provided to each uplink and downlink connection. By MAC-PHY cross-layer resource allocation, the proposed scheme is robust against particular wireless link degradation. Detailed simulation experiments are presented to study the performance and to validate the effectiveness of the proposed QoS control scheme.     

A cooperative multi-group priority MAC protocol for multi-packet reception channels

Medium access control (MAC) protocol design for cooperative networks over multi-packet reception (MPR) channels is a challenging topic, but has not been addressed in the literature yet. In this paper, we propose a cooperative multi-group priority (CMGP) based MAC protocol to exploit the cooperation diversity for throughput enhancement over MPR channels. The proposed approach can bypass the computationally-intensive active user identification process. Moreover, our method can efficiently utilize the idle periods for packet relaying, and can thus effectively limit the throughput loss resulting from the relay phase. By means of a Markov chain model, the worstcase throughput analysis is conducted. The results allow us to investigate the throughput performance of the proposed CMGP protocol directly in terms of the MPR channel coefficients. Simulation results confirm the system-wide throughput advantage achieved by the proposed scheme, and also validate the analytic results.     

Optimization for faster-than-Nyquist signaling based combining under multi-path channel

We propose a faster-than-Nyquist (FTN) signaling based combining scheme to increase the achievable rate for the single-input-single-output (SISO) system and the single-carrier system under the multi-path channel, where the combining scheme aims to combine the signals received at all symbol periods during the channel length for each transmitted symbol. An important feature of the FTN signaling based combining scheme is that the transmitter ceases the transmission for b symbol periods after transmitting each symbol. By proposing the optimization algorithm for finding the optimum b that maximizes the achievable (information) rate, we propose in this paper the optimal FTN signaling based combining scheme. We first establish the optimization problem and then present a theorem for proving the existence of the optimum b that maximizes the lower bound of the average achievable (information) rate. On the basis of this theorem, we present the steps of the proposed optimization algorithm. Numerical results are provided, and they confirm that the proposed optimization algorithm can find the optimum b.     

MIMO-CDMA系统的分数间隔空频均衡接收方案

该文提出了两种适用于宽带单载波多用户MIMO-CDMA系统下行链路的分数间隔空频均衡接收方案,并进行了理论推导。第1种接收方案采用分数间隔空频均衡器对MIMO频率选择性衰落信道进行均衡,从而恢复了扩频码的正交性,减小了码间干扰和共道干扰。第2种方案在假设接收端已知各用户扩频码的前提下,将分数间隔空频均衡器与频域并行干扰消除器结合,能够进一步消除天线间干扰,提高系统性能。仿真结果表明,这两种分数间隔空频均衡接收方案都比传统的频域均衡接收方案在性能上有很大的提高,并且复杂度也比较低。     

Single-carrier frequency-domain equalization for space-timeblock-coded transmissions over frequency-selective fading channels

We propose an Alamouti-like scheme for combining space-time block-coding with single-carrier frequency-domain equalization. With two transmit antennas, the scheme is shown to achieve significant diversity gains at low complexity over frequency-selective fading channels