网格编码调制结合低密度校验码的应用方案设计及性能分析

提出一种利用网格编码调制将低密度校验码与高阶数字调制相结合的应用方法，其中在网格编码调制中采用递归系统卷积码进行编码用以实现基于对数似然比的软译码方法，构造了低密度校验码和网格编码调制相结合的编译码系统。仿真结果表明，该方案将低密度校验码的高编码增益与多元调制的高频谱利用率有效结合在一起，是一种功率和频谱高效的编码调制方式，比传统的网格编码方式有更好的性能。     

基于LDPC码的BICM系统性能分析

低密度校验码(LDPC)由于其编码增益高、译码速度快、性能接近香农限的优点,目前得到学术界的广泛关注.文中简单介绍了LDPC码及其译码算法,在此基础上结合比特交织编码调制(BICM)系统,并在算法上作出了相应改进.仿真结果表明,在高斯信道、充分交织瑞利信道、相关瑞利衰落信道下,此算法正确有效.     

基于迭代的置信传播编码调制在瑞利衰落信道中的性能

该文提出一种结合低密度校验码(LDPC)和MQAM星座的置信传播编码调制方案,并对其在瑞利衰落信道下成对差错概率及最优星座选择进行了分析。为防止过多错误反馈造成译码失效,提出采用内、外双重迭代方式提高系统的鲁棒性。同时把LDPC码校验矩阵作为迭代终止判决准则,降低了迭代算法的平均复杂度。与其他3种方案相比,仿真结果证明了该方案能显著提高系统性能。     

基于LDPC码有效编码算法的编码调制系统

低密度奇偶校验码(LDPC码)的直接编码运算量较大,采用基于下三角矩阵的有效编码算法,通过重排列的顺序得到一个新的校验矩阵,以控制编码运算量为线性复杂度。编码后经过BPSK调制,采用对数域的BP译码算法进行解码。仿真结果表明,在AWGN信道下该系统有较好的误码率性能。     

一种LDPC编码慢跳频系统迭代信道估计译码算法

低密度奇偶校验码(LDPC, Low Density Parity Check)的和积译码算法(SPA, Sum-product Algorithm)在加性高斯白噪声信道中具有很好的译码性能,但需要已知信道状态信息。提出了一种在部分频带干扰条件下LDPC编码慢跳频(SFH, Slow Frequency Hopping)系统的迭代信道估计译码算法。该算法利用迭代译码过程中产生的比特后验信息作为信道估计器的先验信息辅助信道估计,进而更新下一次译码的初始信息。仿真结果显示,该算法性能逼近已知信道信息时的性能,而且每跳所含的符号数很少,不需要插入导频,增大了传输功率效率。另外,相对于SPA算法运算量增加不大,实现简单。     

LDPC码在水下激光通信中的研究

为了研究低密度奇偶校验码在水下激光通信系统中的性能,采用软判决迭代译码算法对系统误比特率进行了仿真,并对水下激光通信的信道模型和低密度奇偶校验码的编译码方式进行了探讨.在一定码长和调制阶数条件下,当信号光子数ns增大时,可以使误比特率降到10-5以下.结果表明,通过利用光电检测输出的软信息进行低密度奇偶校验软判决译码可以明显地降低系统误比特率.     

《电路与系统学报》2004年（第9卷）总目录

混沌吸引子周期轨道理论研究(II)┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅丘水生1(基于校验矩阵构造BCM网格的一般方法┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅康桂华，张朝阳，仇佩亮1(基于低密度校验码的OFDM编码调制译码算法┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅徐志江，李式巨，官军1(1OFDM系统中低复杂度联合译码和信道估计方法研究┅┅┅┅┅┅┅┅┅┅┅王东明，赵军辉，高西奇，尤肖虎1(1结合STBC的一种分层空时编码结构模型┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅┅兰洋，程时昕…     

基于低密度校验码的OFDM编码调制译码算法

低密度校验码(LDPC)具有编码增益高、译码速度快、性能接近Shannon限的优点。LDPC码应用于OFDM，能有效地提高多径环境下OFDM的BER性能。本文首先简单介绍LDPC码及其概率域上的译码算法，在此基础上对译码算法作融合，阐述概率似然比的译码算法。为了把LDPC应用于OFDM系统上，提出了多电平调制下的LDPC译码的算法。仿真结果表明，在AWGN和Rayleigh信道下，此算法正确有效。     

弱湍流条件下LDPC码室内FSO通信系统调制性能分析

为了克服光在弱湍流大气条件传输时,光强闪烁造成的突发错误,理论分析了基于开关键控、脉冲位置调制、差分脉冲位置调制和数字脉冲间隔调制方式的自由空间光通信系统性能。首先推导了无线光通信未编码系统在各调制方式下的平均误比特率公式;在此基础上,将低密度奇偶校验码和置信传播算法应用到无线光通信系统中,研究了相应系统模型下的译码,并在大气湍流信道中进行了理论分析和实验仿真验证。结果表明,脉冲位置调制可获得最好的误比特率性能;采用低密度奇偶校验的大气弱湍流光通信系统比未编码的通信系统性能好,并且可以有效地增加信噪比增益,能够提高系统的抗干扰能力,在无线光通信系统中将有一定的应用前景。     

瑞利信道上的8PSK网格编码系统

网格编码调制(TCM)是近年来提出的一种新的组合编码调制技术,在不降低信息传速率,不扩展占用频带的前提下,它能获得可观的编码增益。本文讨论了8PSK网格编码系统在瑞利信道上的性能,在此基础上提出了一种改进的编码系统,计算机模拟结果表明该系统在瑞利信道下具有较好的性能。     

基于非编码信息匹配的自适应Turbo TCM编码调制方案

本文提出了一种通过调整非编码信息量,并与信号映射相结合来改变编码、调制模式的自适应Turbo TCM编码调制方案,称之为基于非编码信息匹配的自适应Turbo TCM编码调制方案.由于将Turbo码和TCM编码调制技术相结合得到的Turbo TCM编码调制方案的带宽效率高,所以,在慢时变无线衰落信道中,自适应Turbo TCM编码调制的平均频谱效率也将很高.给出了该方案的工作原理、设计方法,并通过蒙特卡洛(Monte Carlo)仿真研究了该方案的性能.与现有编码调制方案相比,该方案具有频谱效率高、易于设计和实现的优点.     

残余频偏对重叠复用信号接收性能的影响分析

主要研究AWGN信道下,残余频偏对重叠时分复用(OvTDM)信号接收的性能影响;同传统的QAM技术相比,OvTDM是一种可以获得高频谱效率的传输技术,它通过引入符号码间串扰,并利用符号间互扰的约束特性来实现更高传输速率。在一个实际通信系统中,接收信号不可避免的会受到系统载波频偏的影响,从而影响信号的接收性能。因此,分析了系统残余频偏对OvTDM的性能影响,对比了相同条件下QAM信号性能,研究结果表明,在相同的信噪比和残余频偏条件下,OvTDM信号具有更好的误码性能。     

MIMO-OFDM系统中的一种空时频编码方案

基于MIMO-OFDM系统,本文提出了一种空时频编码方案,其利用扩展码,使数据符号在空域、时域、频域得到扩展,通过设置合适的参数,能够在频率选择性衰落信道下获得满空间分集和满频率分集,同时该方案的编解码复杂度不高。仿真结果表明,该方法在低信噪比下,也具有良好的误码率性能。     

基于分集技术的低速调制解调器设计分析

针对层反射信道中深衰落和时变色散特性,提出了一种适应该信道的调制解调器系统设计方案。介绍了分集技术、差分相干检测技术和定时提取等关键技术。给出了系统实现及性能测试结果分析。利用思博伦通信公司的SR5500信道模拟器,测试了该方案在高斯信道和变参信道上的性能,得到了良好的误码特性曲线,实际工程证明了其有效性。     

一种新颖的TD-LTE系统上行小区间干扰管理方法

For OFDM based system with Single-Frequency Networking (SFN), ICI (inter-cell interference), especially uplink ICI, becomes a bottleneck to improve system performance. Since the conventional interference management scheme with OI (overload indicator) can not show the instantaneous ICI, this paper proposes a method to reduce ICI by utilizing channel reciprocity of TD-LTE system. In the proposed scheme, UE shall make a decision whether to reduce its power or not after predicting the instantaneous ICI level according to the scheduling results. The system simulation results show that the proposed scheme can reduce the uplink ICI effectively and improve the system performance such as system spectrum efficiency, 10% user throughput, 50% user throughput, packet drop rate etc. significantly while keep 5% cell edge user throughput loss less than 5%. For example, the proposed scheme improved system spectrum efficiency about 50% and 50% user throughput gain is larger than 140%. Meanwhile, the proposed scheme controls the system ICI level and variance effectively. The mean system ICI level and variance are reduced by 4.5dB and 18dB respectively. The proposed scheme can be joint implemented with those existing ICI mitigation methods such as (soft) frequency reuse, power control etc. to further improve the system performance.     

一种结合自适应信道估计的差分TC-OFDM系统

本文结合正交频分复用(OFDM)、格形编码调制(TCM)与差分编码,提出一种使用子信道交织技术的差分TC—OFDM系统,并在此基础上将信道估计引入系统接收机,提出了与解码相联合的SEWRLS自适应信道估计方法。计算机仿真结果表明,本文提出的联合系统能有效地克服宽带无线通信中的多径衰落,并在快衰落环境中具有很强的抗信道干扰能力。     

TIME-FREQUENCY 2-D LMS BASED LONG-RANGE CHANNEL PREDICTION FOR WIRELESS OFDM SYSTEMS

Adaptive modulation can optimize the spectrum efficiency and system performance with the channel state information achieved by the long-range channel prediction.To avoid re-estimating channel correlation function as the channel statioharity varies and to track the channel adaptively, LMS (Least-Mean-Square) based long-range channel prediction is discussed in the existing literature, but it needs long observation interval to reach the convergence.Given that all OFDM (Orthogonal Frequency Division Multiplexing) subcarriers have the identical time-domain correlation and sta- tionarity during the same time interval,this paper proposed a 2-D LMS based predictor which updates the filter weights in both time and frequency domain.The proposed scheme can effectively decrease the observation intervals and significantly speed up the convergence than the conventional LMS and Parallel LMS (PLMS).Complexity analysis and simulation results prove that the proposed scheme can improve the BER (Bit Error Rate) performance and spectrum efficiency with negligible complexity increase.     

失真自适应接收机技术及信号形式选择

对流层散射信道是一种典型的多径衰落信道,多径传播造成了信号的深衰落和多径扩散。而多径扩散现象的存在,会使速率高、码元窄、频谱宽的信号遭受频率选择性衰落的影响,造成传输中的信号码元之间产生码间干扰,严重影响信息传输质量。在此提出了一种基于失真自适应接收技术和3/4占空半余弦信号形式的数字接收机方案,能够自适应地跟踪失真信号的变化而进行最佳相干接收,使系统具有稳定的通信性能。     

Buffer-aware resource scheduling scheme for LTE-A uplink relay-assisted network

Due to the constraint of single carrier frequency division multiple access （SC-FDMA） adopted in long term evolution （LTE） uplink, subcarriers allocated to single user equipment （UE） must be contiguous. This contiguous allocation constraint limits resource allocation flexibility and makes the resource scheduling problem more complex. Most of the existing work cannot well meet UE＇s quality of service （QoS） requirement, because they just try to improve system performance mainly based on channel condition or buffer size. This paper proposes a novel resource scheduling scheme considering channel condition, buffer size and packet delay when allocating frequency resource. Firstly, optimization function is formulated, which aims to minimize sum of weight for bits still left in UE buffer after each scheduling slot. QoS is the main concern factor here. Then, to get packet delay information, this paper proposes a delay estimation algorithm. Relay node （RN） is introduced to improve overall channel condition. Specific RN selection strategy is also depicted in the scheme. Most important of all, a creative negotiation mechanism is included in the subcarrier allocation process. It can improve the overall system throughput performance in guarantee of user＇s QoS requirement. Simulation results demonstrate that the scheme can greatly enhance system performance like delay, throughput and jitter.     

Frequency domain pre-equalization with transmit precoding for MIMO broadcast wireless channels

Recent research has shown that frequency domain pre-equalization (FDPE) can provide broadcast transmissions over multi-input multi-output (MIMO) frequency selective channels, where the multiple receivers need limited processing. In this paper, we consider the combination of FDPE with parallel and successive Tomlinson-Harashima Precoding (THP) and propose two novel FDPE MIMO schemes, which are referred to as FDPE-P-THP and FDPE-S-THP, respectively, based on the minimum mean square error (MMSE) criterion. The ordering algorithm in the FDPE-S-THP scheme is considered and it is shown that the system with even a randomly selected order can perform almost as well as that with the optimal one. This paper further develops an accurate theoretical performance analysis methodology for the proposed FDPE-THP schemes. Numerical results along with analytical results demonstrate the significant performance improvement of our proposed schemes compared to the conventional FDPE MIMO schemes. The channel estimation errors and channel variation effects on the proposed system are also investigated. It is shown that the performance degradation due to channel variation can be efficiently reduced by applying channel prediction.