基于LDPC码的单载波频域均衡系统

该文设计了一种联合判决-反馈均衡的单载波频域均衡(SC-FDE)系统,该系统用固定波形的短pn序列取代常规SC-FDE系统中的循环前缀(CP),并以多个短pn序列组成的长PN序列作信道训练从而解决快变信道的初始估计和跟踪问题。针对该系统,一种在时域内对接收的多个训练序列进行平均,然后提出了在频域对信道信息进行估计的信道训练算法,该算法与传统SC-FDE系统相比,其计算复杂度较低。另外,提出了一种增加纵向校验的LDPC码用于该系统中降低信噪比门限,提高系统的整体性能。仿真结果表明在多径衰落信道中,此系统可获得较为理想的结果。     

On channel estimation using optimal training sequences in Cyclic-Prefix-based Single-Carrier systems with Space-Time Block-Coding

In this paper, a new scheme that combines Space-Time Block-Coding （STBC） based on an Alamouti-like scheme and the Least Squares （LS） channel estimation using optimal training sequences in Cyclic-Prefix-based （CP）／Single-Carrier （SC） systems is proposed. With two transmit antennas, based on Cramer-Rao lower bound for channel estimation, it is shown that the Periodic Complementary Set （PCS） is optimal over frequency-selective fading channels. Compared with the normal scheme without STBC, 3dB Mean Square Error （MSE） performance gains and fewer restrictions on the length of channel impulse response are demonstrated.     

基于级联变系数训练序列和预增强技术的直接检测光OFDM系统实验研究

分析了直接检测光OFDM(DDO-OFDM)传输系统中由数模转换器和光纤链路中的光纤色散所致的OFDM信号高频衰减现象,以及经光纤传输后在光电检测时存在的子载波间互拍干扰现象。提出使用级联变系数训练序列和预增强结构的光OFDM(O-OFDM)信号来降低传输系统所受到的影响。理论分析和实验验证表明,级联变系数训练序列和预增强结构的基带OFDM信号在DDO-OFDM传输系统中,接收灵敏度比常规的交叉型训练序列结构的OFDM信号要高。说明基于级联变系数训练序列和预增强结构的O-OFDM信号的传输性能在抵抗子载波间互拍干扰(SSMI)和频率选择性衰减(FF)方面要优于常规的交叉型训练序列结构的O-OFDM信号。     

TURBO AIDED CYCLIC PREFIX RECONSTRUCTION FOR CODED SINGLE-CARRIER SYSTEMS WITH FREQUENCY-DOMAIN EQUALIZATION （SC-FDE）

In this paper, a Turbo aided Cyclic Prefix (CP) reconstruction scheme, termed Turbo- CPR, is proposed for Single-Carrier systems with Frequency-Domain Equalization (SC-FDE) that employ insufficient CP in the transmitter. In Turbo-CPR, the decoder output is incorporated in the process of equalization, i.e. Turbo equalizer is employed. It is shown in the simulation results that Turbo-CPR not only recovers the performance loss due to insufficiency of CP, but also provides extra gains over the lower bound of performance for conventional CP reconstruction schemes.     

A New ICI Matrices Estimation Scheme Using Hadamard Sequence for OFDM Systems

The intercarrier interference (ICI) matrix for the orthogonal frequency division multiplexing (OFDM) systems usually has a fairly large dimension. The traditional least-square solution based on the pseudo-inverse operation, therefore, has its limitation. In addition, the provision of a sufficiently long training sequence to estimate the complete ICI matrix is not feasible, since it will result in severe throughput reduction. In this paper, we derive a lower bound for the mean-square estimation error among the least-square ICI matrix estimators using different training sequences and prove that the minimum mean-square error (MMSE) optimality is attained when the training sequences in different OFDM blocks are orthogonal to each other, regardless of the sequence length. We also prove that the asymptotical mean-square estimation error using the maximal-length shift-register sequences ($m$-sequences) as in the existing communication standards is 3 dB larger than that using the perfectly orthogonal sequences for ICI matrix estimation. Thus, we propose to employ the training sequences based on the Hadamard matrix to achieve a highly efficient and optimal ICI matrix estimator with minimum mean-square estimation error among all least-square ICI matrix estimators. Meanwhile, our new scheme involves only square computational complexity, while other existing least-square methods require the complexity proportional to the cube of the ICI matrix size. Analytical and experimental comparisons between our new scheme using Hadamard sequences and the existing method using$m$-sequences (pseudo-random sequences) show the significant advantages of our new ICI matrix estimator. The proposed method is most suitable for OFDM systems with large amount of subcarriers, using high order of subcarrier modulation, and designed for high-end of RF frequency band, where accurate ICI estimation is crucial.     

一种低复杂度的MIMO-OFDM信道估计新方法

该文基于m序列设计了一种适合多天线收发-正交频分复用(MIMO-OFDM)系统的时域信道估计新方法.在时域OFDM符号之间插入附加循环前缀(CP)的m序列作为训练序列,在接收端将去掉循环前缀的接收序列与指定的循环移位m序列作相关运算,然后利用m序列的二值自相关特性获得信道的冲激响应估计,从而得到信道的频率响应估计.理论分析和仿真结果都表明:在频率选择性信道中,新方法在系统开销小、计算复杂度低的情况下可以取得比传统算法更好的性能.     

OFDM系统信道盲估计的一种新算法

利用循环前缀（CP）引入的信息冗余，在利用接受信号的二阶统计特性实现正交频分复用（OFDM）系统信道盲估计的子空间算法基础上，采用矩阵变换的方法，改善信息序列的非周期相关函数，推导出信道估计的新算法。     

基于辅助数据的SC-FDE系统频域LS信道估计

通过对单载波频域均衡(SC-FDE)系统的分析得出了对最小二乘(LS)信道估计中采用的训练帧的要求, 从理论上推导了不计循环前缀(CP)能量损失的条件下, SC-FDE系统采用LS方法估计信道的性能界。文中指出, Newmann序列适合作为SC-FDE系统频域LS信道估计的训练帧。理论分析和仿真结果都表明, 采用Newmann序列可以达到LS信道估计的性能界。     

A pilot-assisted non-Cyclic Prefixed MIMO-SCFDE system

A non-Cyclic Prefixed Multiple-Input Multiple-Output Single-Carrier Frequency-Domain Equalization (non-CP MIMO-SCFDE) system based on a recursive algorithm of Joint Channel Es- timation and Data Detection (recursive-JCEDD) is proposed in this paper. Unlike the traditional CP MIMO-SCFDE system, the transmitted block of the proposed system is designed in the way that block-type pilot sequences and Single-Carrier (SC) information sequences have been arranged alter- nately without any cyclic prefix before each ...     

Blind coding classification in the presence of interference in MIMO systems using ML algorithm

This paper presents a framework for coding classification in multiple‐input multiple‐output (MIMO) systems in the presence of inter‐user interference (IUI). This framework is performed at the receiver beginning with a signal separation step. The signal separation is implemented with a multi‐user kurtosis (MUK) algorithm. The classification step estimates the code parameter (CP) using the maximum‐likelihood (ML) method applied to the covariance matrix of the received signal without a priori knowledge about the transmitted signal. Experimental results show that the proposed coding classifier is easy to implement and efficient for the classification of the CP over Rayleigh fading channels in the presence of time and frequency offsets. Furthermore, the success rate of code classification is high at low signal‐to‐noise ratios (SNRs). The signal separation increases the probability of true classification.     

Subspace-based noise variance and SNR estimation for MIMO OFDM systems

This paper proposes a subspace-based noise variance and Signal-to-Noise Ratio （SNR） estimation algorithm for Multi-Input Multi-Output （MIMO） wireless Orthogonal Frequency Division Multiplexing （OFDM） systems. The special training sequences with the property of orthogonality and phase shift orthogonality are used in pilot tones to obtain the estimated channel correlation matrix. Partitioning the observation space into a delay subspace and a noise subspace, we achieve the measurement of noise variance and SNR. Simulation results show that the proposed estimator can obtain accurate and real-time measurements of the noise variance and SNR for various multipath fading channels, demonstrating its strong robustness against different channels.     

一种利用循环前缀改善OFDM各级系统性能的方法

近年来,正交频分复用(OFDM)技术已被越来越多的人所关注,并且在IEEE 802.11无线局域网中得到实际应用.在经典的OFDM系统中,接收端恢复信号时,只是对去掉循环前缀(CP)的信号进行处理,而没有考虑循环前缀中的部分有用信息.文章提出了一种基于LS(Least Squares)准则,利用循环前缀恢复发送信号的方法,并给出这种方法的仿真结果.结果表明,当循环前缀长度较大时,文章方法得到的误码率明显低于传统方法.     

EFFICIENT CYCLIC PREFIX RECONSTRUCTION USING DECISION FEEDBACK FILTER FOR CODED SINGLE-CARRIER SYSTEMS WITH FREQUENCY-DOMAIN EQUALIZATION （SC-FDE）

In this paper, an efficient Cyclic Prefix （CP） reconstruction scheme is proposed for Single-Carrier systems with Frequency-Domain Equalization （SC-FDE） that employ insufficient length of CP at the transmitter. By utilizing a decision feedback filter to cancel the residual InterSymbol Interference （ISI） in the equalized signal, the proposed scheme can effectively lower the low bound of performance for the CP reconstruction schemes and can greatly improve the Bit Error P~te （BER） performance of SC-FDE systems. In addition, the existing methods and the proposed scheme are also optimized. It is shown in the simulation results that, when the Signal-to-Noise Ratio （SNR） exceeds a certain threshold, the proposed scheme can achieve the low bound of performance for the existing methods. Moreover, by increasing the number of iteration or through optimization, the low bound can be outperformed.     

一种新的关键词确认方法

本文提出了一种新的基于模型距离矩阵的关键词确认算法,并给出模型距离的定义及其训练方法,利用模型相对距离矩阵对语音识别结果进行确认.对于关键词库较大的关键词检出系统,通过对关键词分段,得到扩展的模型距离矩阵确认算法,使得大词表确认问题得到很好的解决,并能够获得和小词表系统一样的确认效果.为了对关键词库进行方便的操作,模型距离矩阵的更新算法使得用户可以很方便地修改关键词库内的关键词,而不必重新训练整个模型距离矩阵.     

A low‐complexity MSK‐based M‐ary cyclic‐shift keying transceiver for direct sequence spread spectrum system over multipath fading channels

In this paper, a low‐complexity spread spectrum system with M‐ary cyclic‐shift keying (MCSK) symbol spreading is proposed. In addition, by using the minimum‐shift‐keying (MSK) as the chip‐level modulation, we obtain a high‐rate QPSK‐MCSK transceiver scheme which not only provides a constant‐envelop and continuous‐phase transmitted signal, but can also achieve a better performance than the conventional direct sequence spread spectrum (DSSS) system. At the transmitter, the data stream is first mapped into QPSK‐MCSK symbols in terms of orthogonal Gold code sequences, then followed by the cyclic prefix (CP) insertion for combating the interblock interference, and finally applying the MSK scheme to maintain the constant‐envelope property. The receiver first performs MSK demodulation, then CP removal, and finally the channel‐included MCSK despreading and symbol demapping. Furthermore, the single input single output (SISO) QPSK‐MCSK transceiver can be easily extended to the multiple input single output (MISO) case by incorporating the space–time block coding for high‐link quality. Simulation results show that the proposed SISO and MISO QPSK‐MCSK systems significantly outperform the conventional DSSS counterparts under the AWGN channel, and attain a more robust performance under the multipath fading channel. Copyright © 2011 John Wiley & Sons, Ltd.     

OFDM系统在循环前缀不足时的两种高效迭代均衡方法

本文提出两种新的用于循环前缀(CP)不足时正交频分复用(OFDM)系统的迭代均衡方法。首先,我们提出并行迭代均衡(PIE)方法,该方法分别使用时域判决反馈方法和频域并行迭代方法来消除符号间干扰(ISI)和子载频间干扰(ICI)。为了改进PIE的性能,提出基于高斯-塞德尔迭代的串行迭代均衡(SIE)方法。在不增加计算复杂度的情况下,SIE具有比PIE更快的收敛速度。仿真结果表明,新方法可以在几次迭代后得到接近CP足够情况下的系统性能,PIE的性能与传统的迭代干扰消除方法相同,而SIE则提供好得多的收敛性能。     

矩形窗正交时频空检测算法

针对正交时频空(Orthogonal Time Frequency Space, OTFS)调制系统采用矩形窗函数时,信道矩阵结构复杂导致的鲁棒性差的问题,提出了一种基于时域处理和酉近似消息传递的检测算法。该算法首先添加循环前缀,将时域信道转换为分块对角矩阵;然后应用酉变换和近似消息传递建立迭代检测算法。仿真结果表明,所提检测算法能够在不增加复杂度的条件下有效提升检测精度和鲁棒性,特别是存在信道编码的条件下表现出2 dB的性能增益,使得该算法更适用于杂散多径、高速移动等环境,具有较高的应用价值。     

基于叠加训练的非合作多用户/MIMO信道估计

提出一种基于叠加训练的单载波非合作多用户/MIMO系统的迭代信道估计与检测方案。首先利用变换域方法构造具有零周期互相关特性的训练序列,从而消除多天线间的相互干扰,实现基于一阶统计量的信道估计。然后采用联合符号检测的迭代信道估计方法,利用检测序列作为额外的“训练序列”来降低信息序列自身干扰。与现有的叠加训练信道估计方案比较,新方案中训练序列构造更加灵活,在低信噪比下信道估计均方误差和误码率性能更优,且复杂度更低,仿真结果表明了该方案的有效性。     

Sensing OFDM systems with timing and frequency offset for cognitive radio networks

In this paper, we consider the detection of orthogonal frequency division multiplexing with timing and frequency offset for cognitive radio over fast time‐varying multipath channels. By making different assumptions on the availability of the timing and frequency offset at the secondary user, we derive two algorithms based on likelihood ratio test and generalized likelihood ratio test, respectively and theoretically obtain the detection performances of them. The proposed algorithms jointly utilize energy of observations and correlation of the cyclic prefix (CP) data. The extensive simulations show that the two algorithms outperform the other CP‐based methods, perform well at very low signal to noise ratio (SNR) and are robust to the CP ratio. Copyright © 2012 John Wiley & Sons, Ltd.     

Timing synchronizer and its architecture for OFDM-based high-throughput millimeter wave systems

In this work, a new symbol time synchronization and its architecture design for high-throughput millimeter wave systems based on orthogonal frequency-division multiplexing (OFDM) are introduced. Complementary Golay sequences with good signal properties are popular training sequences used for the preamble design of a multi-gigabit communication system, which is the promising technology for future 5G communications. The basic idea of our contribution is to obtain a time estimate based on the aperiodic autocorrelation function (ACF) of complementary Golay sequences. Besides, achieving low power consumption and less chip area remains the challenge of high-throughput millimeter wave systems. To achieve over 2.64 GSamples/s throughput requirement, the proposed algorithm is especially suitable for the parallel design architecture of very high throughput receivers. Moreover, the complexity is further reduced by employing the correlation characteristic of the ACF of complementary Golay sequences and the regularity of the algorithm. Simulations confirm the advantages of the proposed synchronizer.