Decision-feedback differential demodulation of bit-interleavedcoded MDPSK

A novel simple receiver structure for M-ary differential phase shift keying (MDPSK) transmission over flat Rayleigh fading channels without channel state information is proposed. Convolutional codes are used for error correction and bit-interleaving as an appropriate means to combat the effects of fading, and the hard decisions of the Viterbi algorithm are fed back during the decoding process in order to improve the calculated bit metric. Iterative decoding with this decision-feedback differential demodulation, (DF-DM) results in significant power efficiency gains compared to those achieved using conventional differential demodulation, while the computational complexity remains low     

基于判决反馈的TurboDPSK

本文针对衰落信道中DPSK(differential phase-shift keying)信号的特点,提出了一种基于判决反馈的Turbo DPSK解调/译码算法,它利用判决反馈进行衰落信道的估计并计算信息比特的似然比.与基于BCJR(Bahl-Cocke-Jelinek-Raviv)的Turbo DPSK解调/译码算法相比,它可以大大降低运算复杂度,减少迭代译码过程中所需的存储空间.仿真结果表明,采用这种新的迭代解调/译码算法可以获得和基于BCJR的迭代解调/译码算法几乎一样的性能.     

Soft multiuser demodulation and iterative decoding for FH/SSMA with a block turbo code

The number of users that can be supported by frequency-hopped, spread-spectrum multiple-access systems can be increased greatly by using multiuser demodulation and iterative decoding. In the receiver employed hard-decision multiuser demodulation followed by iterative decoding, users exchange decoded information with each other. Additional information from multiuser demodulation in the first decoding iteration is limited by the hard-decision output of the multiuser demodulator. The error-correction used was an errors-and-erasures Reed-Solomon (RS) decoder. We revisit hard-decision demodulation and conventional RS decoding. Hard-decision multiuser demodulation is modified to provide a soft output, which is then given to a nonbinary block turbo code with shortened RS codes as the constituent codes. An iterative multiuser decoding algorithm is developed to do soft multiuser interference cancellation. This soft receiver with soft demodulation and decoding is shown to be more resistant to multiuser interference and channel noise, especially at lower values of signal-to-noise ratio. The results show a great improvement in the ability of the system to support more users (more than three times in some cases), as compared with systems that erase all hits or employ hard-decision multiuser demodulation followed by RS code. We examine the proposed method for synchronous as well as asynchronous frequency-hopped systems in both AWGN and fading channels.     

联合迭代解调译码算法的短波FH/OFDM系统的性能分析

该文提出了一种基于联合迭代解调译码的短波跳频OFDM系统,并在其接收端采用非相干序列检测和迭代译码相结合的联合迭代解调译码算法。该联合迭代解调译码算法可以降低差分检测时所导致的性能损失,同时,也可以提高短波FH/OFDM系统的可靠性。仿真结果表明：该方法可使其系统在短波信道中获得较好的比特误码性能,当Eb/N0＝5.5 dB时,其系统的比特误码率可达到10-5,数据传输速率达到8.912 kb/s,显然,该联合迭代译码解调算法是适合短波FH/OFDM系统的。     

Low complexity decision-aided decoder for turbo DPSK

A new decision-aided soft a posteriori probability (APP) algorithm for iterative differential phase-shift keying (DPSK) signal demodulation/decoding in a Rayleigh flat-fading channel is presented. Compared with conventional APP algorithms for iterative DPSK, the new algorithm results in considerably lower decoding cost yet can achieve nearly the same performance     

Turbo decodulation: iterative combined demodulation and source-channel decoding

We propose the combination of iterative demodulation and iterative source-channel decoding as a multiple turbo process. The receiver structures of bit-interleaved coded modulation with iterative decoding (BICM-ID), iterative source-channel decoding (ISCD), and iterative source coded modulation (ISCM) are merged to one novel turbo system, in which in two iterative loops reliability information is exchanged between the three single components, demodulator, channel decoder and (softbit) source decoder. Simulations show quality improvements compared to the different previously known systems, which use iterative processing only for two components of the receiver.     

迭代硬判决反馈的LDPC级联MDPSK解调译码算法

该文给出了瑞利衰落信道条件下LDPC级联MDPSK的接收机结构,研究了在不考虑信道状态条件下基于硬判决反馈的迭代检测译码算法,该算法相对于传统的差分解调和译码,复杂度几乎没有增加。仿真结果表明,这种方法在迭代4次的情况下,在误比特率为10-4时与传统的解调方法相比,可以提供2.2dB的增益。     

使用软输入硬输出译码的联合MSDD迭代译码解调器

该文提出了一种使用软输入硬输出(SIHO)Viterbi译码联合多符号差分检测系统(MSDD)的差分解调算法,这种简化算法有前向反馈迭代和后向反馈迭代算法。仿真结果表明,使用后向反馈迭代的DQPSK解调时比相干解调在性能上只恶化1.1dB。还给出了用于卫星通信的FPGA实现的解调器实测结果,其性能比本文提供的仿真结果恶化约0.5dB。     

BICM-ID的MPSK星座映射

在分析了星座映射对比特交织编码调制迭代译码影响的基础上,给出了迭代解调和解码时,星座映射的设计准则,进而给出了一种新的迭代解码的8PSK映射方案.新方案不但满足最大平方欧氏距离(MSEW)映射,在高信噪比时具有较好的性能,而且提高了解调器软信息的输出质量,因而在低信噪比时也具有较好的性能.性能分析和仿真结果表明所给方案的有效性.     

Doubly Iterative Equalization of Continuous-Phase Modulation

In this paper, a doubly iterative receiver is proposed for joint turbo equalization, demodulation, and decoding of coded binary continuous-phase modulation (CPM) in multipath fading channels. The proposed receiver consists of three soft-input soft-output (SISO) blocks: a front-end soft-information-aided minimum mean square error (MMSE) equalizer followed by a CPM demodulator and a back-end channel decoder. The MMSE equalizer, combined with an a priori soft-interference canceler (SIC) and an a posteriori probability mapper, forms a SISO processor suitable for iterative processing that considers discrete-time CPM symbols which belong to a finite alphabet. The SISO CPM demodulator and the SISO channel decoder are both implemented by the a posteriori probability algorithm. The proposed doubly iterative receiver has a central demodulator coupled with both the front-end equalizer and the back-end channel decoder. A few back-end demodulation/decoding iterations are performed for each equalization iteration so as to improve the a priori information for the equalizer. As presented in the extrinsic information transfer (EXIT) chart analysis and simulation results for different multipath fading channels, this provides not only faster convergence to low bit error rates, but also lower computational complexity.     

SVD iterative decision feedback demodulation and detection of coded space-time unitary differential modulation

A new suboptimal demodulator based on iterative decision feedback demodulation (DFD), and a singular value decomposition (SVD) for estimation of unitary matrices, is introduced. Noncoherent communication over the Rayleigh flat-fading channel with multiple transmit and receive antennas, where no channel state information (CSI) is available at the receiver is investigated. With four transmit antennas, codes achieving bit-error rate (BER) lower than 10/sup -4/ at bit energy over the noise spectral density ratio (E/sub b//N/sub o/) of -0.25 dB up to 3.5 dB, with coding rates of 1.6875 to 5.06 bits per channel use were found. The performance is compared to the mutual information upper bound of the capacity attaining isotropically random (IR) unitary transmit matrices. The codes achieve BER lower than 10/sup -4/ at E/sub b//N/sub o/ of 3.2 dB to 5.8 dB from this bound. System performance including the iterative DFD algorithm is compared to the one using Euclidean distance, as a reliability measure for demodulation . The DFD system presents a performance gain of up to 1.5 dB. Uncoded systems doing iterative DFD demodulation and idealized pilot sequence assisted modulation (PSAM) detection are compared. Iterative DFD introduces a gain of more than 1.2 dB. The coded system comprises a serial concatenation of turbo code and a unitary matrix differential modulation code. The receiver employs the high-performance coupled iterative decoding of the turbo code and the modulation code. Information-theoretic arguments are harnessed to form guidelines for code design and to evaluate performance of the iterative decoder.     

Multiuser demodulation and iterative decoding for frequency-hoppednetworks

Demodulation and decoding for frequency-hopped spread-spectrum multiple-access (FH/SSMA) systems have been traditionally conducted by conventional single-user (noncollaborative) demodulation and error- and erasure-correcting decoding techniques. In this paper, we study the demodulation and decoding aspects of collaborative multiuser reception for FH/SSMA and propose methods which increase the number of users the system can support. In particular, we propose and analyze the optimum maximum a priori probability demodulation of multiple symbols or type, and the use of iterative multiuser decoding after the demodulation. Since hits from one or two other users are the most likely hit events in FH/SSMA, the joint demodulation of two or of three users is performed based on likelihood ratio tests. M-ary frequency-shift keying modulation with noncoherent demodulation and Reed-Solomon codes with hard-decision minimum distance decoding are used in the FH/SSMA system. Results are derived for both synchronous and asynchronous frequency-hop systems. The performance of the proposed multiuser detector in additive white Gaussian noise and flat Rayleigh fading channels is evaluated. Scenarios when all simultaneous users or only a subset of them are collaboratively demodulated and decoded are simulated     

高速通信系统中Turbo乘积码的研究

Turbo乘积码是一类易于硬件实现高速迭代译码的分组码。对Turbo乘积码软输入软输出迭代译码算法进行了分析。将Turbo乘积码与QAM调制结合起来,提出了一种简化的、便于硬件实现的联合解调译码方案。仿真结果表明这种简化方案对译码性能影响很小。     

适用于BICM-ID系统的星座成形方法

结合几何成形与概率成形的思想,提出了一种适用于比特交织编码调制系统的星座成形映射方法。该方法基于实用信号星座,通过不使用部分能量较大的信号点并利用多对一的映射关系,使发送信号逼近最佳输入概率分布。利用解调器和译码器之间的迭代译码,该方法可方便地获得成形增益。基于容量和外信息转移图分析,给出了信号星座和信号到符号映射的优化方法。理论分析和仿真结果表明,在高斯白噪声信道和独立Rayleigh衰落信道下,该映射方法利用大信号星座在采用迭代译码的比特交织编码调制系统中均能取得优于传统Gray映射的误码性能,且随着调制阶数的增大可进一步提高成形增益。     

CPM调制的迭代检测技术

CPM信号具有包络恒定、峰均比小、功率利用率高的优点。针对CPM信号的特征,比较了最大似然序列检测Viterbi算法和逐符号的最大后验概率(MAP)解调算法的特点,重点研究了使用迭代检测技术进行软输入输出解调及译码的MAP解调方法。在AWGN信道条件下对CPM全响应和部分响应信号进行了误码性能仿真,结果表明采用相干解调和译码,迭代检测方案可得到较高的编码增益。     

Iterative demodulation/decoding methods based on Gaussian approximations for lattice based space-time coded systems

In this letter, we study iterative demodulation and decoding methods for lattice based space-time coded systems concatenated with convolutional codes. We first apply the optimal MAP demodulation and the suboptimal linear MMSE methods to lattice based space-time demodulation and decoding. We then propose two other methods based on the idea of soft interference cancellation and in one method vector Gaussian approximation is used and in the other method scalar Gaussian approximation is used. We also present the EXIT chart analyses for the performance analyses for these iterative methods. Both theoretical and simulation results show that the performance of the vector Gaussian approximation method is the same as that of the linear MMSE method but in some cases the vector Gaussian approximation method has lower complexity. The complexity of the scalar Gaussian approximation method is the lowest among these different methods and grows linearly with the transmission rate while it still has an acceptable performance. Full diversity and full rate lattice based space-time coding is compared with the BLAST scheme and simulations show that the former has a better performance than the later even with the proposed suboptimal iterative demodulation and decoding methods.     

Constellation mapping for space-time matrix modulation with iterative demodulation/decoding

The mapping from binary sequences to space-time matrices is an important issue in designing space-time coded multiple-antenna systems where different mapping schemes may lead to different bit-error-rate (BER) performance. In this letter, we use a binary switching algorithm to investigate the mappings of bit-interleaved coded modulation with iterative demodulation/decoding (BICM-ID) for space-time modulation. Both coherent and noncoherent space-time modulation in the cases of no a priori information and perfect a priori information of the coded bits for the demodulator are considered.     

一种新的解调译码方案

提出了一种多码元差分检测与软判决译码相结合的解调译码方案。该方案利用差分编码后载波相位之间的相关性,将多阶差分的联合信息用于Viterbi算法,从而实现了多码元检测与Viterbi软判决译码的结合。对该方案进行了计算机仿真,仿真结果表明,在误比特率为10~(-4)时,在AWGN信道中相对于传统的差分检测结合软判决译码,性能提高约1．6dB,在Rician衰落信道中性能同样有明显改善。该方案实现简单。对于功率受限的卫星通信系统,具有重要意义。     

Staggered interleaving and iterative errors- and-erasures decoding for frequency-hop packet radio

Information about the reliabilities; of the received symbols is very beneficial in frequency-hop communication systems. This information, known as side information, can be used to erase unreliable symbols at the input to an errors-and-erasures decoder. For slow-frequency-hop systems it is common that special redundant symbols, referred to as side-information symbols, are included in each dwell interval, and the demodulation of these symbols provides the side information. The corresponding decrease in the number of message symbols that can be sent in each dwell interval makes it desirable to develop alternative methods that do not require side-information symbols. In this paper, one such alternative is proposed, and its performance is evaluated for channels with partial-band interference. It is shown that staggered interleaving of Reed-Solomon code words and iterative errors-and-erasures decoding facilitates the erasure of unreliable symbols without the need for side-information symbols. The performance of this method is compared with the performance of systems that employ standard block interleaving and errors-only decoding or errors-and-erasures decoding with side information obtained from test symbols.     

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