OFDM-based turbo-coded hierarchical and non-hierarchicalterrestrial mobile digital video broadcasting

The feasibility of terrestrial digital video broadcast (DVB) to mobile receivers is studied and turbo coded performance enhancements are proposed. Initially, the MPEG-2 codec is subjected to a rigorous bit error sensitivity investigation, in order to assist in designing various error protection schemes for wireless DVB transmission. The turbo codec is shown to provide signal-to-noise ratio (SNR) performance advantages in excess of 5-6 dB over conventional convolutional coding both in terms of bit error rate and video quality. Our experiments suggested that-despite our expectations-multi-class data partitioning did not result in error resilience improvements, since a high proportion of relatively sensitive video bits had to be relegated to the lower integrity subchannel, when invoking a powerful low-rate channel codec in the high-integrity protection class. Nonetheless, DVB transmission to mobile receivers is feasible, when using turbo-coded OFDM transceivers at realistic power-budget requirements under the investigated highly dispersive fading channel conditions. It is interesting to note furthermore that the 5-6 dB SNR improvement due to turbo coding allows us to invoke for example the double-throughput 16-level quadrature amplitude modulation (16-QAM) mode instead of the standard convolutional-coded 4-QAM mode. This facilitates doubling the bit rate and hence improving the video quality     

Design, analysis, and performance evaluation for BICM-ID withsquare QAM constellations in Rayleigh fading channels

We consider bit-interleaved coded modulation with iterative decoding (BICM-ID) for bandwidth-efficient transmission over Rayleigh fading channels. We propose the design criteria that utilize a large Hamming distance inherited in a low-rate code and a new labeling technique designed specifically for fading channels. This results in a large coding gain over noniterative coded modulation and performance close to that of “turbo” coded modulation with less complexity. We also show that BICM-ID designed for fading channels usually has a very good performance over the additive white Gaussian noise (AWGN) channel while the converse is difficult to achieve. When combined with signal space diversity, diversity order can be improved to twice the diversity order of conventional BICM-ID; therefore, the code complexity can further be reduced while maintaining the same level of performance. Specifically, with the bandwidth efficiency of 2 bits/s/Hz over Rayleigh fading channels, a bit error rate (BER) of 10^-6 can be achieved with 16-QAM, a four-state rate 1/2 code at E_b/N₀ of about seven dB. We also derive performance bounds for BICM-ID with and without signal space diversity over Rayleigh fading channels, which can be easily extended for other types of fading channels     

比特交织Turbo编码调制的8PSK符号映射

基于对Turbo编码器输出的系统比特和校验比特的不等错误保护(UEP),提出了一种新的比特交织Turbo编码调制(BITCM)的8PSK符号映射方案,即对于码率为1/3的Turbo码,校验比特映射到8PSK星座点中具有较好传输性能的比特位置上,而系统比特映射到较差传输性能的比特位置上。实现新映射方案的关键是比特交织器的设计。仿真结果表明,新的映射方案在AWGN信道下,误码率为10-3时,可获得大于0.2dB的信噪比增益,而这一增益的获得并没有牺牲频谱效率和增加系统的复杂性。     

Bit-interleaved coded modulation with iterative decoding using constellation shaping over Rayleigh fading channels

We propose to investigate the performance of bit-interleaved coded modulation with iterative decoding (BICM-ID) over Rayleigh fading channel by using constellation shaping (CS). The (CS) is implemented by inserting shaping block codes between mapping and channel coding functions, in order to generate non-equiprobable distribution of a 16-ary QAM signal constellation. Simulation results carried out on 2-bit/s/Hz 16-QAM BICM-ID indicate that is possible to obtain a gain of 1.2 dB at a BER of 10^-3 compared to the equiprobable 16-QAM BICM-ID schemes. It is also shown that, the error floor level can reduced by applying the signal space diversity technique.     

Hamming Coding of DCT-Compressed Images Over Noisy Channels

Theoretical and simulation results of using Hamming codes with the two-dimensional discrete cosine transform (2D-DCT) at a transmitted data rate of 1 bit/pixel over a binary symmetric channel (BSC) are presented. The design bit error rate (BER) of interest is 10^-2. The (7, 4), (15, 11), and (31, 26) Hamming codes are used to protect the most important bits in each 16 by 16 transformed block, where the most important bits are determined by calculating the mean squared reconstruction error (MSE) contributed by a channel error in each individual bit. A theoretical expression is given which allows the number of protected bits to achieve minimum MSE for each code rate to be computed. By comparing these minima, the best code and bit allocation can be found. Objective and subjective performance results indicate that using the (7, 4) Hamming code to protect the most important 2D-DCT coefficients can substantially improve reconstructed image quality at a BER of 10^-2. Furthermore, the allocation of 33 out of the 256 bits per block to channel coding does not noticeably degrade reconstructed image quality in the absence of channel errors.     

Unequal error protection for MPEG-2 video transmission over wireless channels

This paper proposes an unequal error protection (UEP) method for MPEG-2 video transmission. Since the source and channel coders are normally concatenated, if the channel is noisy, more bits are allocated to channel coding and fewer to source coding. The situation is reversed when the channel conditions are more benign. Most of the joint source channel coding (JSCC) methods assume that the video source is subband coded, the bit error sensitivity of the source code can be modeled, and the bit allocations for different subband channels will be calculated. The UEP applied to different subbands is the rate compatible punctured convolution channel coder. However, the MPEG-2 coding is not a subband coding, the bit error sensitivity function for the coded video can no longer be applied. Here, we develop a different method to find the rate-distortion functions for JSCC of the MPEG-2 video. In the experiments, we show that the end-to-end distortion of our UEP method is smaller than the equal error protection method for the same total bit-rate.     

Optimal precoding for orthogonalized spatial multiplexing in closed-loop MIMO systems

In this paper, we propose a new precoding algorithm for orthogonalized spatial multiplexing (OSM) systems over flat-fading multiple-input multiple-output (MIMO) channels. The OSM scheme was recently introduced for closed-loop MIMO systems which allows single symbol decodable maximum likelihood detection. To further improve the performance of the OSM system, we propose a new precoding method by maximizing the minimum Euclidean distance between constellation points in the effective channel. In order to efficiently identify the parameters of a precoder which maximizes the minimum distance, we introduce a partitioning approach. Through analysis, it is shown that one real value parameter and two bits are required for feedback information for precoding in 16-QAM systems. Simulation results demonstrate that our algorithm provides 9 dB and 7.5 dB gains at a bit error rate (BER) of 10^-4 over the conventional OSM systems for 4-QAM and 16-QAM, respectively. We also confirm that the performance of the proposed scheme is the same as that of the optimum closed-loop MIMO systems in terms of the minimum distance. Consequently, our precoding algorithm significantly improves the system performance with a small increase of feedback amount.     

纠错码性能仿真中的误码率估计

在纠错码性能仿真中,一般是给定信噪比后,由实测的错误信息比特数与发达信息比特总数相比来估计误码率的,这种方法在大码长或者极低误码率情况下。可信程度不高。本文提出用仿真数据计算后验概率分布参数的方法来直接估计纠错误码率及其置信区间,给出了误码率的上界,由少量测试数据仍然可以获得比较可靠的误码率估计,由于这种后验估计考虑了信道特性,所以适用于任意广义信道模型。     

Multilevel coded modulation for unequal error protection andmultistage decoding .I. Symmetric constellations

In this paper, theoretical upper bounds and computer simulation results on the error performance of multilevel block coded modulations for unequal error protection (UEP) and multistage decoding are presented. It is shown that nonstandard signal set partitionings and multistage decoding provide excellent UEP capabilities beyond those achievable with conventional coded modulation. The coding scheme is designed in such a way that the most important information bits have a lower error rate than other information bits. The large effective error coefficients, normally associated with standard mapping by set partitioning, are reduced by considering nonstandard partitionings of the underlying signal set. The bits-to-signal mappings induced by these partitionings allow the use of soft-decision decoding of binary block codes. Moreover, parallel operation of some of the staged decoders is possible, to achieve high data rate transmission, so that there is no error propagation between these decoders. Hybrid partitionings are also considered that trade off increased intraset distances in the last partition levels with larger effective error coefficients in the middle partition levels. The error performance of specific examples of multilevel codes over 8-PSK and 64-QAM signal sets are simulated and compared with theoretical upper bounds on the error performance     

基于误码率的软件无线电射频干扰效应分析

针对通信系统工作过程中受到外界电磁干扰而无法通信的问题,研究了基于软件无线电的电磁干扰效应及误码特征。通过分析典型软件无线电电磁信号传输特性及其信息链路电磁干扰耦合路径,设计了软件无线电通信干扰实验系统。该系统利用Simulink软件观测、记录通信信号眼图、星座图信息等受扰特征,并通过分析接收信号的误码率,给出了不同干扰信号对通信系统的影响规律：当同频干扰功率达到-40 dBm时通信开始出现误码,干扰功率每增加5 dB,误码率增加一个量级,干扰功率增加到-18 dBm时,误码率达到阈值0.25;邻频干扰误码率随干扰功率变化趋势与同频干扰一致,但出现误码的最小干扰功率更大;带外强干扰信号也会影响通信系统可靠性,在相同误码率情况下,需要更大的干扰信号功率且大小与信号频偏成正比。     

Bandwidth‐efficient turbo coding over Rayleigh fading channels

Introduced in 1993, turbo codes can achieve high coding gains close to the Shannon limit. In order to design power and bandwidth‐efficient coding schemes, several approaches have been introduced to combine high coding rate turbo codes with multilevel modulations. The coding systems thus obtained have been shown to display near‐capacity performance over additive white Gaussian noise (AWGN) channels. For communications over fading channels requiring large coding gain and high bandwidth efficiency, it is also interesting to study bit error rate (BER) performance of turbo codes combined with high order rectangular QAM modulations. To this end, we investigate, in this paper, error performance of several bandwidth‐efficient schemes designed using the bit‐interleaved coded modulation approach that has proven potentially very attractive when powerful codes, such as turbo codes, are employed. The structure of these coding schemes, termed ‘bit‐interleaved turbo‐coded modulations’ (BITCMs), is presented in a detailed manner and their BER performance is investigated for spectral efficiencies ranging from 2 to 7 bit/s/Hz. Computer simulation results indicate that BITCMs can achieve near‐capacity performance over Rayleigh fading channels, for all spectral efficiencies considered throughout the paper. It is also shown that the combination of turbo coding and rectangular QAM modulation with Gray mapping constitutes inherently a very powerful association, since coding and modulation functions are both optimized for operation in the same signal‐to‐noise ratio region. This means that no BER improvement is obtainable by employing any other signal constellation in place of the rectangular ones. Finally, the actual influence of the interleaving and mapping functions on error performance of BITCM schemes is discussed. Copyright © 2002 John Wiley & Sons, Ltd.     

Combined turbo coding and unitary space-time modulation

Space-time coding is well understood for high data rate communications over wireless channels with perfect channel state information. On the other hand, channel coding for multiple transmit antennas when channel state information is unknown has only received limited attention. A new signaling scheme, named unitary space-time modulation, has been proposed for the latter case. In this paper, we consider the use of turbo coding together with unitary space-time modulation. We demonstrate that turbo coded space-time modulation systems are well suited to wireless communication systems when there is no channel state information, in the sense that the turbo coding improves the bit error rate (BER) performance of the system considerably. In particular, we observe that the turbo-coded system provides 10-15 dB coding gain at a BER of 10/sup -5/ compared to the unitary space-time modulation for various transmit and receive antenna diversity cases.     

Coded overlapped code division multiplexing system with Turbo product structure

Coded overlapped code division multiplexing system with Turbo product structure (TPC-OVCDM) is introduced, and trellis coded modulation (TCM) code is employed as error correcting code for uncoded overlapped code division multiplexing (OVCDM) system. In such a scheme, row code and column code are TCM and OVCDM spreading code, respectively. Data bits are only encoded directly by TCM and transformed into a matrix. Each column of this matrix is then permuted by symbol interleaver before being encoded by OVCDM spreading code. During iterative decoding process in the receiver, two constituent decoders use symbol by symbol BCJR algorithm in the log domain. The order of decoding two sub-codes is determined by the encoding order. The proportion of TCM coding and OVCDM coding affects system performance. For fixed coding structure and symbol interleaver, the performance of TPC-OVCDM systems of different proportions of additive white Gaussian noise (AWGN) channel have been simulated. The results show that TPC-OVCDM system of reasonable proportion can achieve significant coding gain, compared with uncoded OVCDM system under the condition of same spectral efficiency at bit error rate (BER) level of 10-5 .     

高阶调制系统下LDPC码优化设计

为了提高编码调制系统的整体编码增益,提出一种高阶调制系统下LDPC码的度分布优化方法.根据高阶调制符号中不同比特的误比特特性,将调制符号所经历信道建模为一组对称二进制输入加性高斯信道.在此基础上,推导了高阶调制系统下LDPC码高斯近似密度进化分析方法,并得到译码收敛条件.结合度分布约束关系及译码收敛条件,提出高阶调制系统下LDPC码的度分布优化问题及差分进化实现方法.仿真结果表明,设计的LDPC码在高阶调制系统中的渐进性能和误码性能优于基于比特优化映射的编码调制方案.     

100 Gbit/s Nyquist-WDM PDM 16-QAM Transmission over 1200 km SMF-28 with Ultrahigh Spectrum Efficiency

Nyquist wavelength-division multiplexing (N-WDM) allows high spectral efficiency (SE) in long-haul transmission systems.Compared to polarization-division multiplexing quadrature phase-shift keying (PDM-QPSK),multilevel modulation,such as PDM 16 quadrature-amplitude modulation (16-QAM),is much more sensitive to intrachannel noise and interchannel linear crosstalk caused by N-WDM.We experimentally generate and transmit a 6 × 128 Gbit/s N-WDM PDM 16-QAM signal over 1200 km single-mode fiber (SMF)-28 with amplification provided by an erbium-doped fiber amplifier (EDFA) only.The net SE is 7.47 bit/s/Hz,which to the best of our knowledge is the highest SE for a signal with a bit rate beyond 100 Gbit/s using the PDM 16-QAM.Such SE was achieved by DSP pre-equalization of transmitter-side impairments and DSP post-equalization of channel and receiver-side impairments.Nyquist-band can be used in pre-equalization to enhance the tolerance of PDM 16-QAM to aggressive spectral shaping.The bit-error ratio (BER) for each of the 6 channels is smaller than the forward error correction (FEC) limit of 3.8 × 10-3 after 1200 km SMF-28 transmission.     

Information Theoretic Foundations of Adaptive Coded Modulation

In wireless/mobile communications, terminals adapt their rate and transmit power or, more in general, their coding and modulation scheme, depending on the time-varying channel conditions. This paper presents, in a tutorial form, the information theoretic framework underlying such ldquoadaptive modulationrdquo techniques. First, we review fading channel models, channel state information assumptions, and related capacity results. Then, we treat the case of input power constraint, where the optimal input distribution is Gaussian. Finally, we address the case of discrete modulations. In order to treat the latter, we make use of the recently developed method of ldquomercury-waterfillingrdquo, based on the relationship between mutual information and minimum mean-square error (MMSE) estimation of the channel input from the channel output. While the traditional design of adaptive modulation schemes based on uncoded bit-error rate (BER) involves the optimization over a discrete set of signal constellations, when powerful (i.e., capacity approaching) coding schemes are used the corresponding adaptive coded modulation design becomes surprisingly simple. The regime of very powerful coding is justified by the use of modern coding schemes, such as turbo codes and low-density parity-check codes, able to perform close to channel capacity at very small BER.     

BER analysis of QAM on fading channels with transmit diversity

In this letter, we derive analytical expressions for the bit error rate (BER) of space-time block codes (STBC) from complex orthogonal designs (COD) using quadrature amplitude modulation (QAM) on Rayleigh fading channels. We take a bit log-likelihood ratio (LLR) based approach to derive the BER expressions. The approach presented here can be used in the BER analysis of any STBC from COD with linear processing for any value of M in an M-QAM system. Here, we present the BER analysis and results for a 16-QAM system with i) (2-Tx, L-Rx) antennas using Alamouti code (rate-1 STBC), ii) (3-Tx, L-Rx) antennas using a rate-1/2 STBC, and iii) (5-Tx, L-Rx) antennas using a rate-7/11 STBC. In addition to being used in the BER analysis, the LLRs derived can also be used as soft inputs to decoders for various coded QAM schemes, including turbo coded QAM with space-time coding as in high speed downlink packet access (HSDPA) in 3G.     

Concatenation of trellis coded modulation and space-time block codes for high data rate on wireless systems using multiple antenna elements

Performance results using concatenation of high-rate pragmatic TCM (trellis coded modulation) codes with a simple high-rate space-time block code operating on a multiple input/multiple output (MIMO) channel with 4 transmit and 4 receive antennas are presented. Four TCM encoders feed 4 data streams consisting of 32-QAM symbols into a simple Alamouti — like space-time code, spreading the data over 4 transmit antennas. In this way an overall data rate of 8 information bits per channel use is obtained. Perfect channel state information (CSI) at the receiver is assumed for all investigations. Using 4 receive antennas with a low complexity zero-forcing (ZF) receiver we get diversity order of approximately 6. Compared with coded V-BLAST (Foschini, 1996) operating on the same information bit rate and decoder complexity, our system performs much better for all types of spatially correlated and uncorrelated MIMO channels under investigation.     

A noise resistant synchronization scheme for HDTV images

A method that increases the error resistance of the HDTV system and offers graceful picture degradation in the presence of bit errors, is presented. Due to the nature of the presently proposed compression schemes for HDTV systems, an error in a data bit does not only affect the block the bit belongs to, but unfortunately the effects of this error may perpetuate to the following blocks. This is because a bit error may cause loss of synchronization between the data bits and the picture blocks they represent. Our method restricts the effects of a bit error to a picture block whose size is significantly smaller than those used by the HDTV systems. We achieve synchronization by transmitting a header-word for each such synchronization block. Each header-word contains the number of data bits representing the compressed block. This header-word is protected by two levels of FEC code. To decrease the number of extra bits needed by the header-words, two different synchronization block sizes are used, a relatively small block size for the reference frames and a larger size for the inter-frames. The resulting method improves the quality of the picture in the presence of errors and defers the SNR at which the HDTV picture suddenly deteriorates by 2.5 to 3 dB. It also allows operation at higher order modulation transmission schemes, e.g., 32-QAM instead of 16-QAM, without the requirement of increased signal power     

Multistage recursive interleaver for turbo codes in DS-CDMA mobileradio

A multistage recursive block interleaver (MIL) is proposed for the turbo code internal interleaver. Unlike conventional block interleavers, the MIL repeats permutations of rows and columns in a recursive manner until reaching the final interleaving length. The bit error rate (BER) and frame error rate (FER) performance with turbo coding and MIL under frequency-selective Rayleigh fading are evaluated by computer simulation for direct-sequence code-division multiple-access mobile radio. The performance of rate-1/3 turbo codes with MIL is compared with pseudorandom and S-random interleavers assuming a spreading chip rate of 4.096 Mcps and an information bit rate of 32 kbps. When the interleaving length is 3068 bits, turbo coding with MIL outperforms the pseudorandom interleaver by 0.4 dB at an average BER of 10^-6 on a fading channel using the ITU-R defined Vehicular-B power-delay profile with the maximum Doppler frequency of f_D = 80 Hz. The results also show that turbo coding with MIL provides superior performance to convolutional and Reed-Solomon concatenated coding; the gain over concatenated coding is as much as 0.6 dB