Performance analysis of Viterbi decoder using channel stateinformation in COFDM system

This paper relates to the application method of channel state information (CSI) to the Viterbi (maximum likelihood) decoder in the digital terrestrial television broadcasting system. The proposed Viterbi decoder uses the CSI derived from the pilots inserted in the transmitter of the COFDM (coded orthogonal frequency division multiplexing) system. The CSI is calculated by interpolation using the pilots in the receiver. The active real (I) and imaginary (Q) data after equalization are transferred to the branch metric calculation block that decides the euclidean distance for soft decision decoding and also the estimated CSI values are transferred to the same block. After calculating the euclidean distance for the soft decision decoding, the euclidean distance of the branch metric is multiplied by CSI. To do so, new branch metric values that consider each carrier state information are obtained. We simulated this method in Rayleigh fading defined in the ETSI standard. From the simulation, this method has better performance of about 0.15 dB to 0.7 dB and 2.2 dB to 2.9 dB in the Rayleigh channel than that of conventional soft decision Viterbi decoding with or without a bit interleaver where the constellation is QPSK, l6-QAM and 64-QAM     

The Effect of Metric Modification on the Performance of TCM and Concatenated Systems Over Rayleigh Fading Channels

The performance improvement of conventional TCM schemes over frequency nonselective slow Rayleigh fading channels, caused by a slight modification on the metric calculation of the Viterbi decoder, is investigated in this paper. A statistical analysis of the Euclidean distances at the input of the Viterbi decoder is carried out to explain this improvement. Furthermore, the performance improvement of two concatenated coding systems incorporating the above modification, under the same conditions, is studied. The performance of the TCM and the concatenated systems is evaluated by Monte Carlo simulation. The results show that the examined systems, using the proposed modification on the metric calculation, achieve BER performances comparable to other codes and systems, especially designed for fading channels.     

Space–Time Code Design for CPFSK Modulation Over Frequency-Nonselective Fading Channels

We derive a novel space–time code-design criterion for continuous-phase frequency-shift keying (CPFSK) over frequency-nonselective fading channels. Our derivation is based on a specific matrix that is related to the input symbols of the CPFSK modulators. With this code-design criterion, we propose a simple interleaved space–time encoding scheme for CPFSK modulation over frequency-nonselective correlated fading channels to exploit potential temporal and spatial diversity advantages. Such an encoding scheme consists of a ring convolutional encoder and a spatial encoder, between which a convolutional interleaver is placed. A decoding algorithm that generates symbol metrics for the Viterbi decoder of convolutional codes from the spatial modulation trellis is examined. Simulation results confirm that the advantages of combination of the interleaved convolutional encoding (for temporal diversity) and the spatial encoding (for spatial diversity) are promising for various system parameters.     

An optimal circular Viterbi decoder for the bounded distance criterion

We propose a Viterbi-type decoder for tailbiting trellis codes that works by traversing the tailbiting circle somewhat more than once. The traversal is the least possible for any bounded distance Viterbi decoder. Procedures are given that compute this minimum. Unlike previous decoders of the type, the new scheme does not suffer limit cycles or from pseudocodewords. The bit-error rate is compared to that of Bahl-Cocke-Jelinek-Raviv and maximum-likelihood decoding.     

一种M-FSK信号的能量度量Viterbi软译码算法性能分析

Viterbi译码算法广泛应用于无线数字通信系统,一般采用比特对数似然信息(LLR)作为译码器的输入。针对M-FSK信号,该文提出一种采用信号解调得到的M维能量信息,直接作为译码器分支度量值,并给出了相应的Viterbi译码算法。在加性高斯白噪声(AWGN)和瑞利(Rayleigh)衰落信道下对所提算法的BER性能进行了理论推导,得到了闭合表达式。通过仿真验证了理论推导的正确性,与常规Viterbi算法相比,所提算法避免了比特LLR和分支度量值的计算,降低了算法复杂度和减少了信息损失,提高了M-FSK信号软解调Viterbi译码算法的BER性能,是一种更适用于工程实现的M-FSK信号的Viterbi译码算法。     

Space-time code design for CPFSK modulation over frequency-nonselective fading channels

We derive a novel space-time code (STC) design criterion for continuous-phase frequency-shift keying (CPFSK) over frequency-nonselective fading channels. Our derivation is based on a specific matrix that is related to the input symbols of the CPFSK modulators. With this code-design criterion, we propose a simple interleaved space-time encoding scheme for CPFSK modulation over frequency-nonselective correlated fading channels to exploit potential temporal and spatial diversity advantages. Such an encoding scheme consists of a ring convolutional encoder and a spatial encoder, between which a convolutional interleaver is placed. A decoding algorithm that generates symbol metrics for the Viterbi decoder of convolutional codes from the spatial modulation trellis is examined. Simulation results confirm that the advantages of the combination of the interleaved convolutional encoding (for temporal diversity) and the spatial encoding (for spatial diversity) are promising for various system parameters.     

Forward Error Correction Coding for Fading Compensation in Mobile Satellite Channels

Fading in mobile satellite communications severely degrades the performance of data transmission. The channel is modeled with nonfrequency selective Rice and Rayleigh fading. Also, stored channel simulation is used for hardware data transmission. FEC coding with Viterbi decoding of convolutional codes, and Berlekamp-Massey decoding of Reed-Solomon codes, are used to compensate for the fading. In addition to interleaving, channel state and erasure information improve the performance of the decoder. The BER after decoding is calculated for specific codes on several channels and for different transmission schemes. Using very simple channel state and erasure information gives 2-7 dB additional coding gain. These gains have been verified by hardware data transmission on synthetic fading channels and stored mobile satellite channels.     

Low-complexity turbo equalization and multiuser decoding for TD-CDMA

The authors propose a low complexity multiuser joint parallel interference cancellation (PIC) decoder and turbo decision feedback equalizer for code division multiple access (CDMA). In their scheme, an estimate of the interference signal (both multiple-access interference and intersymbol interference) is formed by weighting the hard decisions produced by conventional (i.e., hard-output) Viterbi decoders. The estimated interference is subtracted from the received signal in order to improve decoding in the next iteration. By using asymptotic performance analysis of random-spreading CDMA, they optimize the feedback weights at each iteration. Then, they consider two (mutually related) performance limitation factors: the bias of residual interference and the ping-pong effect. The authors show that the performance of the proposed algorithm can be improved by compensating for the bias in the weight calculation, and they propose a modification of the basic PIC algorithm, which prevents the ping-pong effect and allows higher channel load and/or faster convergence to the single-user performance. The proposed algorithm is validated through computer simulation in an environment fully compliant with the specifications of the time-division duplex mode of third-generation systems, contemplating a combination of time-division multiple access and CDMA and including frequency-selective fading channels, user asynchronism, and power control. The main conclusion of this work is that, for such application, soft-input soft-output decoders (e.g., implemented by the forward-backward BCJR algorithm) are not needed to attain very high spectral efficiency, and simple conventional Viterbi decoding suffices for most practical settings.     

General approach to implementing analogue Viterbi decoders

Commercial realisations of analogue Viterbi decoder are available for magnetic read channels. However, these implementations are restricted to a particular coding scheme. The authors present a general approach to the implementation of analogue Viterbi decoders having arbitrary coding schemes. The proposed method exploits the ability of simple analogue circuits to perform the required mathematical functions. Simulation results are presented for a 0.8 μm BiCMOS process     

Super-orthogonal differential space-time trellis coding and decoding

In this paper, a differential space-time trellis-coded scheme based on super-orthogonal space-time trellis codes (SOSTTCs) is proposed. It achieves full diversity and provides an improved coding gain. Based on the per-survivor processing (PSP) technique, a low-complexity suboptimal differential decoder is developed. In slow fading channels, it can approach the performance of SOSTTC with coherent decoding. Furthermore, in time-varying channels, a bank of recursive least square (RLS) type channel predictors are incorporated into the Viterbi decoder to track the channel variance and the RLS predictors do not need training data and channel statistics. The performance analysis is given. Simulation results are presented to illustrate our analytical results and they show that our scheme can achieve a good performance in both slow fading and time-varying fading channels with modest complexity.     

Low bit-rate cloud-based image coding in the wavelet transform domain

The rapid growth of image resources on the Internet makes it possible to find some highly correlated images on some Web sites when people plan to transmit an image over the Internet. This study proposes a low bit-rate cloud-based image coding scheme, which utilizes cloud resources to implement image coding. Multiple- discrete wavelet transform was adopted to decompose the input image into a low-frequency sub-band and several high-frequency sub-bands. The low-frequency sub-band image was used to retrieve highly correlated images (HCOIs) in the cloud. The highly correlated regions in the HCOIs were used to reconstruct the high-frequency sub-bands at the decoder to save bits. The final reconstructed image was generated using multiple inverse wavelet transform from a decompressed low-frequency sub-band and reconstructed high-frequency sub-bands. The experimental results showed that the coding scheme performed well, especially at low bit rates. The peak signal-to-noise ratio of the reconstructed image can gain up to 7 and 1.69 dB over JPEG and JPEG2000 under the same compression ratio, respectively. By utilizing the cloud resources, our coding scheme showed an obvious advantage in terms of visual quality. The details in the image can be well reconstructed compared with both JPEG, JPEG2000, and intracoding of HEVC.     

Hybrid ARQ schemes employing coded modulation and sequencecombining

In this paper, we propose and analyze two hybrid automatic-repeat-request (ARQ) schemes employing bandwidth efficient coded modulation and coded sequence combining. In the first scheme, a trellis-coded modulation (TCM) is used to control channel noise; while in the second scheme a concatenated coded modulation is employed. The concatenated coded modulation is formed by cascading a Reed-Solomon (RS) outer code and a block coded modulation (BCM) inner code. In both schemes, the coded modulation decoder, by performing sequence combining and soft-decision maximum likelihood decoding, makes full use of the information available in all received sequences corresponding to a given information message. It is shown, by means of analysis as well as computer simulations, that both schemes are capable of providing high throughput efficiencies over a wide range of signal-to-noise ratios. The schemes are suitable for large file transfers over satellite communication links where high throughput and high reliability are required     

Multistage decoding for internally bandwidth efficient coded Poisson fiber-optic CDMA communication systems

We consider the structure and performance of a multistage decoding scheme for an internally bandwidth efficient convolutionally coded Poisson fiber-optic code division multiple access (CDMA) communication system. The decoder is implemented electronically in several stages in which in each stage, the interfering users' coded bit decisions obtained in the previous stage is applied for computing the likelihood of the coded symbols of the desired user. The first stage is a soft-input Viterbi decoder for the internally coded scheme, in which the soft-input coded symbol likelihood values are computed by considering the multiuser interference as a noise signal. The likelihood of coded symbol computed in each stage is then entered into the convolutional decoder for the next bit decisions. The convolutional codes that are used for demonstrating the performance of the multistage decoder are super orthogonal codes (SOCs). We derive the bit error rates (BERs) of the proposed decoder for internally coded Poisson fiber-optic CDMA systems using optical orthogonal codes (OOCs) along with both ON-OFF keying (OOK) and binary pulse position modulation (BPPM) schemes. Our numerical results indicate that the proposed decoding scheme substantially outperforms the single-stage soft-input Viterbi decoder. We also derive the upper bound on the probability of error of a decoder for the known interference case, which is the ultimate performance of a multiuser decoder, and compare the result with that of the soft-input Viterbi decoder.     

Design of a 20-mb/s 256-state Viterbi decoder

The design of high-throughput large-state Viterbi decoders relies on the use of multiple arithmetic units. The global communication channels among these parallel processors often consist of long interconnect wires, resulting in large area and high power consumption. In this paper, we propose a data transfer oriented design methodology to implement a low-power 256-state rate-1/3 Viterbi decoder. Our architectural level scheme uses operation partitioning, packing, and scheduling to analyze and optimize interconnect effects in early design stages. In comparison with other published Viterbi decoders, our approach reduces the global data transfers by up to 75% and decreases the amount of global buses by up to 48%, while enabling the use of deeply pipelined datapaths with no data forwarding. In the register-transfer level (RTL) implementation, we apply precomputation in conjunction with saturation arithmetic to further reduce power dissipation with provably no coding performance degradation. Designed using a 0.25 /spl mu/m standard cell library, our decoder achieves a throughput of 20 Mb/s in simulation and dissipates only 0.45 W.     

High rate concatenated coding systems using bandwidth efficienttrellis inner codes

High-rate concatenated coding systems with bandwidth-efficient trellis inner codes and Reed-Solomon (RS) outer codes are investigated for application in high-speed satellite communication systems. Two concatenated coding schemes are proposed. In one the inner code is decoded with soft-decision Viterbi decoding, and the outer RS code performs error-correction-only decoding (decoding without side information). In the other the inner code is decoded with a modified Viterbi algorithm, which produces reliability information along with the decoded output. In this algorithm, path metrics are used to estimate the entire information sequence, whereas branch metrics are used to provide reliability information on the decoded sequence. This information is used to erase unreliable bits in the decoded output. An errors-and-erasures RS decoder is then used for the outer code. The two schemes have been proposed for high-speed data communication on NASA satellite channels. The rates considered are at least double those used in current NASA systems, and the results indicate that high system reliability can still be achieved     

Hybrid block-convolutional rate-½ coding strategy forconstant envelope (CE)Q2PSK

The authors address the problem of trellis coding on multidimensional signal space for incorporation into a 4D quadrature-quadrature phase-shift keying (Q²PSK) communication system. A low-complexity rate-½ hybrid block-convolutional coding scheme is proposed, to be utilised in a constant envelope (CE)Q²PSK system configuration. The encoder and decoder designs have been structured to facilitate simple implementation with standard components. The bit error rate performance of the proposed coding scheme is studied by means of simulation on a non-frequency selective Rician fading channel assuming coherent detection. The benefits of the use of channel state information (CSI) in conjunction with maximum-likelihood Viterbi decoding are also considered     

Hybrid-ARQ scheme using different TCM for retransmission

A new hybrid automatic repeat-request (ARQ) scheme that uses supplementary trellis codes for retransmission is described. In this scheme, supplementary codes are designed to compensate for the squared free distance (d/sub free//sup 2/) of the trellis code used for the previous transmission. Differently encoded codewords are combined and decoded by the same Viterbi decoder at the receiver. This scheme provides improved (d/sub free//sup 2/) upon retransmission compared with that provided by the conventional trellis coded hybrid-ARQ scheme where the same coding scheme is used for all transmissions.     

A simple remedy for the exaggerated extrinsic information produced by the SOVA algorithm

In this paper, we propose a novel and simple approach for dealing with the exaggerated extrinsic information produced by the soft-output Viterbi algorithm (SOVA). The proposed remedy is based on mathematical analysis and it involves using two attenuators, one applied to the immediate output of the SOVA and another applied to the extrinsic information before it is passed to the other decoder (assuming iterative decoding). The use of these attenuators aims at reducing the inherent strong correlation between the intrinsic information (input to the SOVA) and extrinsic information (output of the SOVA). We examine the modified SOVA (MSOVA) on additive white Gaussian noise (AWGN) and flat fading channels for parallel concatenated codes (PCCs) and serial concatenated codes (SCCs). We show that the MSOVA provides substantial performance improvements over both channels. For example, it provides improvements of about 0.8 to 1.0 dB at P/sub b/ = 10/sup -5/ in AWGN, and about 1.4 to 2.0 dB at P/sub b/ = 10/sup -5/ on fading channels. We also show that there are cases where the MSOVA is superior to the a posteriori probability (APP) algorithm. With this motivation, we extend the proposed modification to the APP algorithm with favorable results. We demonstrate that the modified APP (MAPP) provides performance improvements between 0.3 to 0.6 dB at P/sub b/ = 10/sup -5/ relative to the APP. We lastly mention that the proposed modifications, while they provide considerable performance improvements, keep the complexity of these decoders almost the same, which is remarkable.     

A Viterbi Decoder with Efficient Memory Management

This paper proposes a new architecture for a Viterbi decoder with an efficient memory management scheme. The trace‐back operation is eliminated in the architecture and the memory storing intermediate decision information can be removed. The elimination of the trace‐back operation also reduces the number of operation cycles needed to determine decision bits. The memory size of the proposed scheme is reduced to 1/(5×constraint length) of that of the register exchange scheme, and the throughput is increased up to twice that of the trace‐back scheme. A Viterbi decoder complying with the IS‐95 reverse link specification is designed to verify the proposed architecture. The decoder has a code rate of 1/3, a constraint length of 9, and a trace‐forward depth of 45.     

A Novel Cooperative Communication System Based on Multilevel Convolutional Codes

The authors propose a system where single antenna mobile users share antennas to transmit their information cooperatively to the common base station. Each mobile user overhears the coded information transmitted by other users, detects it and further encodes it along with its own information. The encoding is done using multilevel coding scheme with convolutional codes as component codes. The proposed system considers the self-information of user u at level u to reduce complexity while decoding. The coded symbols are mapped to M-ary quadrature amplitude modulation constellation using multi-resolution modulation partitioning. This enables the component codes to be designed for lower order constellation. Each cooperative user transmits multilevel coded symbols to the common base station, thus creating transmit diversity. The base station receives noisy superposition of independent Rayleigh faded signals transmitted by cooperative users and pass it through a multistage decoder. The multistage decoder employs maximum likelihood based Viterbi decoder at each stage to detect the information of each user. The Viterbi decoder applies max-log approximation to reduce the branch metric complexity. The proposed cooperative multilevel coding system outperforms non-cooperative multilevel coding system and is less complex than the existing cooperative multilevel coding system.