Evaluation of 16 kbit/s digital voice transmission for mobile radio

In this paper 16 kbit/s digital voice transmission with conventional channel spacing of 25 kHz, employing a 16 kbit/s adaptive delta modulation (ADM) coder-decoder (CODEC) is evaluated. The main characteristics of narrow-band digital FM modulation schemes, such as tamed FM, Gaussian filtered minimum shift keying (GMSK), four-level FM and phase locked loop-quaternary phase shift keying (PLL-QPSK), are compared by laboratory tests. Digitized voice quality in a digital channel incorporating a 16 kbit/s ADM CODEC and GMSK coherent detection was compared with voice quality of a conventional analog FM channel. Bit error ratio (BER) performance is shown to depend primarily on demodulation schemes. Digital voice quality is inferior to that of analog voice with an opinion score difference of about 0.5 in fading environments. This kind of digital voice transmission will be applicable for those systems that require high security at an expense of speech quality.     

Improved performance of coded digital FM

The performance of convolutionally encoded narrow-band digital FM with Viterbi decoding was considered in some detail by Simon (1983) for a noncoherent limiter/discriminator (L/D) with integrate and dump (I&D) bit detection. Employing a new threshold receiver which averages the output of the I&D detector with the output of a sample and hold (S&H) detector, a 3-dB improvement over Simon's results for the bit error probability with FM clicks is shown to be achievable. At low error rates, the performance of this new receiver is, moreover, comparable to that obtained when the clicks are exactly removed by Simon's hypothetical “genie”     

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.     

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。     

M-QAM系统中QC_LDPC译码性能研究

研究了M-QAM与QC-LDPC结合的调制编码系统的性能。详细推导M-QAM软解调的后验概率计算公式,得出正方形星座软解调时,解映射搜索点数由M可降低为M～(1/2)的结论。通过仿真,对调制阶数对系统性能的影响进行了评估。QC-LDPC译码采用M.Mansour最新提出的P-TDMP算法,仿真结果显示,P-TDMP算法比传统的置信传播译码算法有一定的性能增益,它还提高了硬件实现的并行度,降低了系统的开销。     

Performance analysis of Viterbi decoding for 64-DAPSK and 64-QAMmodulated OFDM signals

The multilevel modulation techniques of 64-quadrature amplitude modulation (QAM) and 64-differential amplitude and phase-shift keying (DAPSK) have been proposed in combination with the orthogonal frequency-division multiplexing (OFDM) scheme for digital terrestrial video broadcasting (DTVB). With this system a data rate of 34 Mb/s can be transmitted over an 8-MHz radio channel. A comparison of these modulation methods in the uncoded case has been presented by Engels and Rohling (see European Trans. Telecommun., vol.6, p.633-40, 1995). The channel coding scheme proposed for DTVB by Schafer (see Proc. Int. Broadcasting Convention, Amsterdam, The Netherlands, p.79-84, 1995) consists of an inner convolutional code concatenated with an outer Reed-Solomon (RS) code. In this paper the performance of the convolutional codes is analyzed for the two modulation techniques. This analysis includes soft decision Viterbi (1971) decoding of the convolutional code. For soft decision decoding of DAPSK modulated signals a new metric is developed     

Channel coding for satellite mobile channels

The deployment of channel coding and interleaving to enhance the bit-error performance of a satellite mobile radio channel is addressed for speech and data transmissions. Different convolutional codes (CC) using Viterbi decoding with soft decision are examined with inter-block interleaving. Reed-Solomon (RS) codes with Berlekamp-Massey hard decision decoding or soft decision trellis decoding combined with block interleaving are also investigated. A concatenated arrangement employing RS and CC coding as the outer and inner coders, respectively, is used for transmissions via minimum shift keying (MSK) over Gaussian and Rayleigh fading channels. For an interblock interleaving period of 2880 bits, a concatenated arrangement of an RS(48,36). over the Galois field GF(256) and punctured PCC(3,1,7) yielding an overall coding rate of 1/2, provides a coding gain of 42dB for a BER of 10^?6, and an uncorrectable error detection probability of 1–10^?9.     

JTIDS系统的RS码性能分析

介绍了JTIDS战术数据链系统的基本结构和原理,分析了JTIDS战术数据链中的RS纠错编译码以及MSK调制解调技术,研究了RS码在高斯白噪声情况下的抗噪声性能,建立了系统的性能分析模型,并使用Matlab进行了仿真,仿真结果验证了分析结论.     

Joint data detection and channel estimation for coded and uncoded continuous phase modulation signals

The performance of decision‐directed approach for joint data detection and channel estimation for continuous phase modulation (CPM) signal is limited because of an inevitable decision delay, which results in a trade‐off between data detection and channel estimation. In this paper, a novel hard output demodulation that solves the conflict requirement on the decision delay by predicting the channel coefficients over a given observation interval through a Kalman filter is proposed for uncoded CPM signal. The prediction guarantees high channel tracking capability and meanwhile maintains the accuracy of data detection. The proposed hard output demodulator is further extended to design a soft‐input soft‐output demodulator for serially concatenated CPM signal, which allows iterative processing. The convergence behavior of the proposed iterative receiver is presented. Simulation results show that the proposed demodulators provide improved performance in terms of bit error rate over some existing algorithms. Copyright © 2014 John Wiley & Sons, Ltd.     

Soft decision metric generation for QAM with channel estimation error

The channel code bit log likelihood ratio (LLR) for soft decision decoding is derived for quadrature amplitude modulated signals (QAM). The effect of imperfect channel knowledge on soft decision decoding performance is studied. Our results indicate this effect increases with channel estimation error and/or QAM modulation level. A metric based on generalized log likelihood ratio (GLLR) is derived for soft decision channel decoding with imperfect channel knowledge. Numerical results show that the GLLR-based metric outperforms the conventional minimum distance decoding metric that does not take into account channel estimation error.     

Broad-band OFDM radio transmission for multimedia applications

Future multimedia services will require the transmission of very high data rates over broad-band radio channels. In order to provide these services to mobile users, an appropriate transmission technique has to cope with frequency-selective and time-variant radio channels. The computation complexity for an equalizer increases in a frequency-selective radio channel for high data rate applications. Furthermore, the overhead for channel estimation procedures increases in time-variant channels. To overcome these drawbacks orthogonal frequency division multiplexing (OFDM) has been considered for broadband applications in many publications. The objective of this paper is to describe the large potential, the flexibility and adaptivity of the OFDM transmission technique in frequency-selective and time variant radio channels. Several technical aspects of OFDM transmission systems are discussed, especially the topics of differential modulation for which we compare different demodulation methods and channel coding with soft decision decoding. For higher level differential modulation, multilevel coding is taken into consideration     

Performance evaluation of COFDM for digital audio broadcasting. I.Parametric study

This paper describes the performance of COFDM (coded orthogonal frequency division multiplexing) for digital audio broadcasting (DAB) over various multipath mobile radio channels. COFDM is a channel coding and modulation scheme which mitigates the adverse effects of fading by using wideband multicarrier modulation combined with time interleaving and a convolutional error correcting code. A guard interval is inserted at the transition between successive symbols to absorb the intersymbol interference created by the time domain spread of the mobile radio channel. The decoding process is performed using differential demodulation in conjunction with a soft decision Viterbi decoder. The COFDM evaluation is done by means of computer simulations. A parametric study of the proposed COFDM system is done in this first of a series of papers to determine the optimal system parameter values for operation at a radio frequency of 1.5 GHz. The results show that the parameter values proposed in the standard are indeed well suited for operation at 1.5 GHz. Using the set of optimal parameter values found, the COFDM performance is then evaluated in mobile radio channels typical of different geographical environments. Simulation results confirm the benefit that the system gains from frequency diversity found in the urban and hilly terrain areas     

Iterative multiuser detection

Communication channels that involve both error-control coding and multiple-access signaling are of increasing interest in applications such as cellular telephony, wireless computer networks, and broadband local access. Optimal data detection and decoding in such channels generally require a level of computational complexity that is prohibitive for these types of applications. Turbo multiuser detection (MUD) addresses this problem by applying turbo principle of iteration among constituent decision algorithms, with intermediate exchanges of soft information about tentative decisions. This principle is applied in this paper by considering MUD and error-control decoding as the two constituent decision algorithms. The resulting iteration between soft MUD and soft channel decoding yields good results. This article reviews this area outlining both the basic principles involved and the basis for low-complexity turbo multiuser detectors that require minimal increased complexity over that of the standard channel decoder.     

Single carrier digital terrestrial television broadcasting

A transmission system for digital terrestrial television broadcasting has been designed. This system is based on the European cable system but uses stronger error correction and better equalization. The stronger error correction is a concatenation of Reed Solomon coding RS [204,188,17] and convolutional coding with R_conv=1/2, 2/3, 3/4, 5/6 and 7/8. The algorithm which is used for convolutional decoding is the Viterbi algorithm. To provide the Viterbi decoder with soft decision information, every symbol bit will be expanded with two soft decision (reliability) bits. The modulation scheme of the terrestrial transmission system is 64-QAM square root raised cosine filtered with a roll off factor α=0.15. The mapping of the symbols into the 64-QAM constellation is a Gray-mapping over the complete I,Q-plane. In this paper the performances of the terrestrial transmission system are simulated and analyzed     

Channel coding for narrow-band Rayleigh fading with robustnessagainst changes in Doppler spread

For digital transmission over frequency-nonselective fading channels, data security can be obtained by error correction coding, but the coding scheme has to be adapted to the channel properties. For many vehicular applications, the range of possible vehicle speeds is large and in the UHF band the resulting Doppler frequency may not be small relative to the symbol rate-suggesting a differential detection scheme. Therefore, the channel coding should be robust against changes in Doppler spread. A combination of a convolutional code (soft-decision decoding) and a Reed-Solomon (RS) code is considered, and the performance in a narrow-band Rayleigh-fading channel with differential quaternary phase shift keying (DQPSK) modulation without interleaving is evaluated as a function of signal-to-noise ratio (SNR) and Doppler spread by computer simulations. This transmission scheme is proved to have good performance over a large variety of vehicle speeds     

基于脉冲位置调制的无线光通信多级编码调制及其多阶段解调译码算法

针对无线光通信脉冲位置调制(PPM)与信道编码的结合应用,提出了一种多级编码调制方案,利用多级编码的多级标签结构,将PPM符号所对应的分组比特分拆到不同子码通道的码字中,同时结合PPM的信号集分割和极大似然检测解调方法,推导了方案的多阶段解调译码算法。在弱湍流大气条件下的仿真分析表明,PPM多级编码调制相对单级编码调制在误码率10-6下获得0.85 dB以上的增益,且可实现对不同重要程度信息段的不等差错保护。在分量码码型给定的条件下,按纠错能力逐级配置分量码并采用所推导的多阶段解调译码,可为系统提供更好差错性能,优于直接的并行译码方法。     

On the performance of spectrally efficient trellis coded FMmodulation employing noncoherent FM demodulation

The authors analyze the problem of noncoherent FM demodulation of trellis-coded continuous-phase M-ary FSK (frequency-shift keying). The FM demodulation process is divided into two parts, the first being the actual noncoherent FM demodulation and the second being trellis decoding of the data. Upper bounds on the bit error rate as well as the 99% energy bandwidth are determined for the codes under consideration. In particular, the authors consider the trellis codes with rates 1/2 and 2/3 and symmetric and asymmetric signal constellations. Upper bounds on the probability of error are obtained for the symmetric and the optimum asymmetric cases. The optimum asymmetry is one which minimizes the bit error probability. The performance of this system is compared to that of the standard continuous phase modulation techniques employing noncoherent detection     

基于网络编码的协作HARQ协议

该文基于网络编码技术提出了一种新的协作HARQ协议。在中继节点的协助下两个用户与基站进行通信。中继节点响应基站的重传请求,对两用户的增加冗余帧采用物理层网络编码即信号重叠调制技术进行处理,然后发送至基站。基站对接收信号采用多用户联合检测以及联合软判决译码。在平坦瑞利衰落信道下,该网络编码协作HARQ协议较传统的非协作HARQ协议可获得较大的性能改善,其性能接近没有采用网络编码的协作HARQ协议,且需要较少的硬件和带宽资源。     

RoFSO系统中4FSK仿真及其误比特率性能分析

将射频技术应用到自由空间光通信具有独到的优势。为了研究自由空间光载射频技术,在四进制频移键控调制解调理论基础上,以自由空间光通信为应用背景,采用仿真,从时域角度对四进制频移键控系统进行了编码及解码研究,并推导了经过高斯噪声和瑞利信道后系统误比特率及信道容量。两种解调法的系统误比特率仿真结果表明,当信噪比为12dB时,过零检测法的系统误比特率达到10-15,明显优于相干解调法。     

Readable erasures improve the performance of Reed-Solomon codes (Corresp.)

Since well-known decoding algorithms [1],[2] are able to correct both character errors and character erasures withq-ary Reed-Solomon codes, some modulation and demodulation schemes designed to be used with such codes provide a channel that hasqinputs andq + 1outputs,qof which correspond to theqinputs and one of which corresponds to the "erasure" symbol. This correspondence points om the relative advantages offered by a slightly more refined demodulation scheme, which creates a digital channel that hasqinputs and2_{q}outputs,qof which correspond to "strong" receptions of the inputs andqof which correspond to "weak" receptions of the inputs. For decoding purposes, allqweak outputs may be treated as erasures, but the fact that the channel now provides additional information facilitates improved decoding performance by reading the weak characters under the erasures.