空时分组码在Nakagami衰落下的信道容量

空时编码技术将信道编码技术和天线分集技术结合,在不牺牲带宽的情况下,大幅度地增加了无线通信系统的信道容量,而Nakagami衰落信道能够准确表示实际衰落环境。基于此研究了空时分组码在Nakagami衰落的信道容量。首先将Nakagami信道等效为一个m分集系统通过瑞利信道,推导出Nakagami衰落下空时分组码瞬时信噪比的概率密度函数表达式,进一步推出Nakagami衰落下空时分组码信道容量的表达式,并对其进行了仿真和分析。     

Rayleigh衰落信道下空时网格码的性能研究

为了比较准确地评价空时网格码(STTC)的编码性能.利用矩量母函数(MGF)分析方法,推导出了在不相关Rayleigh衰落信道中STYC成对差错概率的单变量积分形式的准确表达式,通过对STYC成对差错概率(PEP)的研究,发现利用PEP单变量积分形式能够更精确地估计STTC的性能.同时研究了编码器状态数、收发天线数和天线相关系数对STTC影响,并基于此分析了其误码率和误帧率性能,最后给出Rayleigh衰落条件下的空时网格编码的误码率和误帧率性能仿真结果,验证了理论分析的有效性.     

频率选择性衰落信道中一种低复杂度的正交空时分组码译码算法

针对正交空时分组码在频率选择性衰落信道中正交性被破坏的问题,该文提出了一种基于干扰对消的译码方案。该方案借鉴D-BLAST系统的检测方法,采用干扰抵消和干扰置零方法消除多径干扰,从而有效地检测出期望信号。理论分析和系统仿真表明,与迭代干扰抵消算法相比,该译码方案在有效地改善系统误码性能的同时,降低了译码复杂度,尤其适用于信道阶数较小的环境。     

Feedback Communications over Fading Channels

A communication system using noiseless feedback for Rayleigh fading channels is proposed. Pilot tone signaling is used to provide channel amplitude and phase information for the detection of antipodal signals. Channel estimates generated in the receiver are fed back to control the transmitter power and rate. Power division and rate control rules are derived, and it is shown that definite performance improvement over diversity systems is obtained. Because of the requirement of small loop propagation delays, the technique is mainly applicable to low data rate multitone modems for short range HF channels.     

Sequential Decoding of Convolutional Codes for Rayleigh Fading Channels

The performance of sequential decoding of long constraint length convolutional codes is evaluated for Rayleigh fading channels. Sequential decoding is not practical below a certain theoretical signal-to-noise ratio, and these theoretical limits are calculated for a number of modulation methods and code rates. As an example, with BPSK modulation, soft decisions and code rate 1/2, the theoretical signal-to-noise ratio per information bit is 5.7 dB. Above this limit the bit error rate can be made arbitrarily small by increasing the constraint length at no significant complexity cost. Furthermore, it is shown that with carefully chosen quantization steps, 8 level uniform quantization gives a negligible loss also for sequential decoding on a Rayleigh fading channel. Simulation results using 8 level quantization correspond well with the theoretical performance bounds. Also, the performance on a correlated channel with finite interleaving has been obtained. With an interleaver depth of 50×50 and a normalized doppler frequency equal to 0.01 we are only 0.5 dB away from the performance with perfect interleaving. Finally, bit error rate results show this scheme to compete well with Turbo codes.     

衰落信道下卷积码的软判决译码

本文将交织、信道输出软信息、信道特征软信息相结合,研究Rayleigh衰落信道下卷积码的Viterbi软判决译码,在利用和不利用信道状态信息(CSI)两种情况下给出软判决的支路度量计算公式和性能仿真结果,计算了卷积码的性能上界;研究了解调器输出量化门限(量化级数目、量化间距)对译码性能的影响.结果与硬判决译码及AWGN信道的相关结论进行了比较.     

衰落信道下基于线性预测的迭代解调及译码技术:Turbo DPSK

本文针对移动通信中常见的衰落信道的特点,提出了一种基于信道增益线性估计的Turbo DPSK解调、译码技术.其特点是在进行信道增益的线性估计时无需知道信道的自相关函数,可简化接收机的复杂度.同时在系统中引入Per-Survivor Process(PSP)和迭代译码技术,充分利用每次迭代后的信息进一步提高系统的性能.计算机仿真表明,采用这种基于线性信道估计的Turbo DPSK系统有很好的抗衰落性能.     

Adaptive Modulation over Nakagami Fading Channels

We first study the capacity of Nakagami multipath fading (NMF) channels with an average power constraint for three power and rate adaptation policies. We obtain closed-form solutions for NMF channel capacity for each power and rate adaptation strategy. Results show that rate adaptation is the key to increasing link spectral efficiency. We then analyze the performance of practical constant-power variable-rate M-QAM schemes over NMF channels. We obtain closed-form expressions for the outage probability, spectral efficiency and average bit-error-rate (BER) assuming perfect channel estimation and negligible time delay between channel estimation and signal set adaptation. We also analyze the impact of time delay on the BER of adaptive M-QAM.     

一种适用于频率选择性衰落信道的Turbo-BLAST系统

该文提出了一种适用于频率选择性无线衰落信道的Turbo-BLAST方案。在发送端联合采用了随机分层空时编码和分组线性星座预编码OFDM以充分利用多径和空间分集;在接收端比较了两种类型的Turbo接收机,一种是基于最小均方误差准则的软输入软输出的检测模块,它有较低的计算复杂度;另一种采用了类似球形解码的检测模块,它有很好的性能但需要较高的计算复杂度。仿真结果表明该文提出的方案能在保持BLAST高数据速率的同时充分利用信道环境提供的多径和空间分集。     

未知相位信道下 Turbo码编码DPSK信号的联合迭代解调解码

本文提出了未知相位信道下Turbo码编码DPSK信号的联合迭代解调解码算法 .推导了未知相位信道的最大后验概率 (MAP)算法 ,推导表明该MAP算法同样可用前向、后向递推方程来有效实现 .其次 ,采用等效信道的方法将未知相位信道的Turbo码解码问题化为AWGN信道下Turbo码的解码问题 .最后 ,引进了联合迭代解调解码算法 ,可用于Turbo码的解调解码 .模拟表明本文算法可有效用于未知相位信道Turbo码的解码     

Joint Relay and Antenna Selection in MIMO PLNC Inter-vehicular Communication Systems over Cascaded Fading Channels

We investigate the joint relay and antenna selection performance in a multiple input multiple output (MIMO) Vehicle-to-Vehicle (V2V) communication system employing physical layer network coding (PLNC) with amplify-and-forward (AF) scheme at the relay antenna. Analytic results are derived under the cascaded Nakagami-m fading channel model assumption, which covers cascaded Rayleigh and conventional cellular channel models as well. We evaluate the performance of the system in terms of joint outage probability of sources and derive closed-form expressions for lower and upper bounds while an exact expression is found as a single integral form. Besides, the asymptotic diversity order is analyzed and quantified as a function of number of relays and antennas installed on the source and relay vehicles, and channel parameters. Finally, we verify the analytic derivations by computer simulations. Our results show that the outage probability performance decreases with the increasing cascading degrees of the channels but joint relay and antenna selection enhances the performance of the system superbly with the increasing number of relays and antennas. Also it is shown throughout all the simulation results, the lower bound for the joint outage probability seems to consistently be well tight for large SNR. Therefore it can be used for practical design of inter-vehicular communication systems which contain multiple relays and antennas.     

Joint Data and Kalman Estimation for Rayleigh Fading Channels

Channel estimation is an essential part of many detection techniques proposed for data transmission over fading channels. For the frequency selective Rayleigh fading channel an autoregressive moving average representation is proposed based on the fading model parameters. The parameters of this representation are determined based on the fading channel characteristics, making it possible to employ the Kalman filter as the best estimator for the channel impulse response. For IS-136 formatted data transmission the Kalman filter is employed with the Viterbi algorithm in a Per-Survivor Processing (PSP) fashion and the ove rall bit error rate performance is shown to be superior to that of detection techniques using the RLS and LMS estimators. To allow more than one channel estimation per symbol interval, Per-Branch Processing (PBP) method is introduced as a general case of PSP and its effect on performance is evaluated. The sensitivity of performance to parameters such as fading model order and vehicle speed is also studied.     

联合译码在图像无线传输中的应用

对Turbo码编码结构作了适当调整,进行信道编码的不仅有信源编码信息还有信源信息的统计特性,将信源编码后码流中存在的残留冗余特性应用到被传输的信源编码信息在进行Turbo码译码的算法中,给出了实验结果。通过结果比较发现,改进算法提高了Turbo码译码的纠错性能。     

非平稳信道下LDPC码低复杂度滑窗置信传播联合信道估计与译码算法

随着移动通信应用场景的持续增多,非平稳信道成为越来越常见的传输环境,而非平稳信道下的可靠传输依赖于准确的信道估计。基于信源编码中用于信源参数估计和信源相关性估计的滑窗置信传播(SWBP)算法,该文提出一种非平稳信道下LDPC码的联合信道估计与译码(JCED)算法;同时,分别基于交叉熵和离散傅里叶变换提出两种在每轮JCED迭代中自适应设置滑窗长度的快速算法。仿真结果表明,在无导频辅助的前提下,所提算法具有接近理想信道估计下置信传播译码的性能以及高效率、低复杂度、强鲁棒性和不导致错误平层等优点。     

非平稳信道下LDPC码低复杂度滑窗置信传播联合信道估计与译码算法

随着移动通信应用场景的持续增多,非平稳信道成为越来越常见的传输环境,而非平稳信道下的可靠传输依赖于准确的信道估计.基于信源编码中用于信源参数估计和信源相关性估计的滑窗置信传播(SWBP)算法,该文提出一种非平稳信道下LDPC码的联合信道估计与译码(JCED)算法;同时,分别基于交叉熵和离散傅里叶变换提出两种在每轮JCED迭代中自适应设置滑窗长度的快速算法.仿真结果表明,在无导频辅助的前提下,所提算法具有接近理想信道估计下置信传播译码的性能以及高效率、低复杂度、强鲁棒性和不导致错误平层等优点.     

Turbo Decoding of Super-Orthogonal Space-Time Trellis Codes in Rayleigh Fading Channels

Space-time trellis codes have shown to provide a good performance in Rayleigh fading channels. Recently Super-orthogonal space-time trellis codes have shown to outperform these codes, and also provide a systematic design method to maximize diversity and coding gain in quasi-static Rayleigh fading channels. We investigate the performance of these new codes in rapid Rayleigh fading channels and further propose two concatenated versions of these codes. We further investigate the effect of imperfect channel state information on one of the concatenated versions. Some simulation results of the various concatenated schemes in quasi-static and rapid Rayleigh fading channels are presented. Jayesh N. Pillai received the B.Tech degree in Electrical and Electronic Engineering from the University of Calicut, Kerala, India in 2001. He is currently pursuing an MScEng degree in Electronic Engineering at the School of Electrical, Electronic and Computer Engineering at the University of KwaZulu-Natal, Durban, South Africa. His research interests are in the area of wireless communications, including multiple-antenna systems, space-time coding and channel coding. Stanley Henry Mneney obtained his B.Sc.(Hons) Eng. Degree from the University of Science and Technology, Kumasi in Ghana in 1976. In 1979 he completed his M.A.Sc. from the University of Toronto in Canada. In a Nuffic funded project by the Netherlands government he embarked on a sandwich Ph.D. programme between the Eindhoven Univesity of Technology and the University of Dar es Salaam, the latter awarding the degree in 1988. His co-supervisors were Prof Jens Arnbak and Prof Ramje Prasad representing the two Universities. The research area was on the application satellite technology to provide low cost systems and services to the rural population in the developing countries.Prof Mneney has taught at the Universities of Dar es Salaam, Nairobi, Durban Westville and he is currently an Associate Professor and Deputy Head of School of Electrical, Electronic and Computer Engineering at the University of KwaZulu-Natal in South Africa. His research interest includes Signal and Image processing, radio propagation and communication systems.     

Trained Space-Time Block Decoding for Flat Fading Channels with Frequency Offsets

Space-time block coding (STBC) is a recent appealing solution to the problem of exploiting transmit diversity in multi-antenna systems for communications over flat fading channels. In a standard STBC scheme the receiver requires Channel State Information (CSI), which can be acquired via training at the expense of a reduced information rate. Alternatively, the requirement of CSI can be avoided altogether by using differential encoding. The existing trained or differential schemes for STBC assume that the channel is time-invariant during the transmission of at least two data blocks. However, wireless channels may often be time varying owing to frequency offsets induced by either Doppler shifts or carrier frequency mismatches. In this paper we present a simple trained STBC scheme for fading channels with frequency offsets. This revised version was published online in July 2006 with corrections to the Cover Date.     

On Joint Order Statistics in Correlated Nakagami Fading Channels

In this letter, the joint probability density function (pdf) of the order statistics for a set of correlated Nakagami-m fading channels is derived. This result is useful in analyzing the performance of a variety of diversity schemes which involve branch selection. The derivation also yields a computationally efficient method for obtaining the marginal pdf of the p-th order statistic for a set of correlated Nakagami-m fading channels.     

相关衰落MIMO信道下的联合天线子集选择

针对相关衰落MIMO信道下的联合天线子集选择,提出了2种选择算法。首先,在已知精确信道知识的情况下,选择算法选择以使接收数据流的SNR最大化和瞬时误差概率即误符号率最小化的天线子集,从而得到平均SNR增益改善的解析表达式;其次,当信道迅速变化时,在已知信道统计知识的情况下,选择算法选择以使全部可能信道实现的平均误差概率最小化的天线子集,从而得到编码增益,在极端相关信道条件下,也可以得到分集增益;基于2种选择算法的性能分析和仿真结果验证了本文提出算法的有效性。