On a Reduced‐Complexity Inner Decoder for the Davey‐MacKay Construction

The Davey‐MacKay construction is a promising concatenated coding scheme involving an outer 2^k‐ary code and an inner code of rate k/n, for insertion‐deletion‐substitution channels. Recently, a lookup table (LUT)‐based inner decoder for this coding scheme was proposed to reduce the computational complexity of the inner decoder, albeit at the expense of a slight degradation in word error rate (WER) performance. In this letter, we show that negligible deterioration in WER performance can be achieved with an LUT as small as 7·2^k+n–1, but no smaller, when the probability of receiving less than n–1 or greater than n+1 bits corresponding to one outer code symbol is at least an order of magnitude smaller than the WER when no LUT is used.     

Near-capacity coding in multicarrier modulation systems

We apply irregular low-density parity-check (LDPC) codes to the design of multilevel coded quadrature amplitude modulation (QAM) schemes for application in discrete multitone systems in frequency-selective channels. A combined Gray/Ungerboeck scheme is used to label each QAM constellation. The Gray-labeled bits are protected using an irregular LDPC code with iterative soft-decision decoding, while other bits are protected using a high-rate Reed-Solomon code with hard-decision decoding (or are left uncoded). The rate of the LDPC code is selected by analyzing the capacity of the channel seen by the Gray-labeled bits and is made adaptive by selective concatenation with an inner repetition code. Using a practical bit-loading algorithm, we apply this coding scheme to an ensemble of frequency-selective channels with Gaussian noise. Over a large number of channel realizations, this coding scheme provides an average effective coding gain of more than 7.5 dB at a bit-error rate of 10/sup -7/ and a block length of approximately 10/sup 5/ b. This represents a gap of approximately 2.3 dB from the Shannon limit of the additive white Gaussian noise channel, which could be closed to within 0.8-1.2 dB using constellation shaping.     

Improved Performance Upper Bounds for Terminated Convolutional Codes

In this letter, we propose tight performance upper bounds for convolutional codes terminated with an input sequence of finite length. To obtain the upper bounds, a weight enumerator is defined to represent the relation between the Hamming distance of the coded output and the Hamming distance of the input bits of the code. The upper bounds on frame error rate (FER) and average bit error rate (BER) are obtained from the weight enumerator. A simple method is presented to compute the weight enumerator of a terminated convolutional code based on a modified trellis diagram.     

Reliable communication over channels with insertions, deletions,and substitutions

A new block code is introduced which is capable of correcting multiple insertion, deletion, and substitution errors. The code consists of nonlinear inner codes, which we call “watermark"” codes, concatenated with low-density parity-check codes over nonbinary fields. The inner code allows probabilistic resynchronization and provides soft outputs for the outer decoder, which then completes decoding. We present codes of rate 0.7 and transmitted length 5000 bits that can correct 30 insertion/deletion errors per block. We also present codes of rate 3/14 and length 4600 bits that can correct 450 insertion/deletion errors per block     

A Novel M‐ary Code‐Selected Direct Sequence BPAM UWB Communication System

In this letter, a novel M‐ary code‐selected direct sequence (DS) ultra‐wideband (UWB) communication system is presented. Our purpose is to achieve a high data rate by an M‐ary code‐selected direct sequence bipolar pulse amplitude modulation (MCSDS‐BPAM) scheme. In this system, a particular DS code sequence is selected by the log₂M/2 bits from the DS gold code set. This scheme can accomplish both a high data rate without increasing the system bandwidth or changing the pulse shape and improve the BER with an increase of modulation level M even at a lower signal‐to‐noise ratio (SNR). The receiver signal processing algorithm is given for an MCSDS‐BPAM UWB system over an ideal AWGN channel and correlation receivers.     

The outage capacity of linear space-time codes

An inner space-time code, i.e., one that is complemented by an outer error-control code, calls for vastly different design strategies than a space-time code that stands alone. This letter investigates the design of a linear inner space-time code for a t-input r-output Rayleigh fading channel by examining its outage capacity, which assumes an idealized outer code. We show that a linear space-time code with rate R相似文献   

Selective serial concatenation of turbo codes

A serial concatenation scheme consisting of a Bose-Chaudhuri-Hocquenghem (BCH) outer code and a turbo inner code is proposed. We first establish that only a small number of bit positions at the turbo decoder output are likely to be in error at high signal-to-noise ratios. A double-error correcting BCH outer code is used to protect these particular error prone bits. Simulation results for an additive white Gaussian noise (AWGN) channel show that the bit-error rate (BER) floor of the turbo code can be lowered by using this serial concatenation scheme. The proposed technique offers higher throughput efficiency and lower complexity than other serial concatenation schemes     

Improved space-time codes using serial concatenation

In this letter, a new family of space-time codes is proposed. These codes employ a serially concatenated coding scheme with a standard space-time code as the outer code and a very simple rate-1 recursive code as the inner code. Adding this simple rate-1 recursive inner code does not decrease the bit rate and introduces only negligible complexity increase to the transmitter when compared to cases with standard space-time codes. An interleaver is embedded between the inner coder and the outer coder and the size of this interleaver determines the performance gain. We also provide a relatively low complexity iterative decoding procedure. For applications which can tolerate delay, significant gain can be achieved with the proposed approach     

A Simple Space-Time-Frequency Block Code Scheme for Four Transmit Antennas

It is well known that the full rate and full diversity complex space-time block code (STBC) is not existed for four transmit antennas. In this letter, we propose a simple quasi-orthogonal space-time-frequency block code (QO-STFBC) scheme with four transmit antennas and n _R receive antennas, where every two transmit antennas constitute one group and each group transmits signals over different subcarriers. The receiver can separate the received signals from each group via odd/even index FFT operation. After recombining the separated received signals with received antennas, an equivalent half rate orthogonal STFBC (O-STFBC) can be used for decoding. Thus, the full rate and full diversity are achieved at the transmitter and receiver, respectively. Simulation result shows that the proposed QO-STFBC scheme has better performance than the other schemes, in rate 2 layered Alamouti scheme is about 4 dB, full rate QO-STBC scheme is about 5 dB and half rate O-STBC scheme is about 7 dB at 10^?3 BER for the transmission of 2 bits/s/Hz.     

On the probability of symbol error in Viterbi decoders

An upper bound is derived on the probability that at least one of a sequence of B consecutive bits at the output of a Viterbi (1979) decoder is in error. Such a bound is useful for the analysis of concatenated coding schemes employing an outer block code over GF(2^B) (typically a Reed-Solomon (RS) code), an inner convolutional code, and a symbol (GF(2^B)) interleaver separating the two codes. The bound demonstrates that in such coding schemes a symbol interleaver is preferable to a bit interleaver. It also suggests a new criterion for good inner convolutional codes     

Performance of Unequally Punctured Convolutional Codes

In practical applications, some coded symbols are unequally punctured for rate matching of terminated convolutional codes. In this letter, performance upper bounds are proposed for a terminated convolutional code punctured with an arbitrary pattern. To obtain the upper bounds, a weight enumerator is defined to represent the relation between the Hamming weight of the coded outputs and that of the selected input information bits. A method is presented to compute the weight enumerator based on a modified trellis diagram. Simulation and numerical analysis show that the proposed bounds are tight to the performance of terminated convolutional codes.     

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.     

一种用于军事光纤通信系统的新型前向纠错码的研究

光纤信道具有比传统电缆信道更高的信号传输速率和更大的带宽,当采用光纤调制解调器进行电光信号转换时,可以使用具有较多冗余位的编码方式来保证信号传输的准确性和可靠性。论文研究了一种以BCH作内码、Hamming码作外码的新型前向纠错码,该码使用三级编码和两次交织技术构成了串行级联线性友,可以有效地将信号传输过程中所产生的较长突发错误交织成较短的随机错误,并使交织后可能出现的误码个数在所设计编码的纠错能力范围内,从而可在译码时实时地纠正这些错误。论文探讨了这种前向纠错码的编、译码算法,采用了软硬件较易实现的逐步判决逐步译码算法。计算机模拟结果表明该级联码具有较强的纠错功能,可应用于对信号传输的准确性和实时性都具有特殊要求的军事光纤通信系统。     

Coded diversity for cooperative MISO based wireless sensor networks

Motivated by the recent works on cooperative MIMO, this letter presents a coded diversity based cooperative protocol for wireless sensor networks. In densely deployed sensor networks, nearby nodes form a cluster of virtual antenna array to provide independent fading paths. The source node encodes the information bits with any channel code and forwards a portion of the codeword towards the cooperating nodes. The source and the cooperating nodes transmit different portion of the codeword to achieve a coded diversity at destination. Analysis and simulation show that our proposal can achieve full diversity when code rate is below a certain threshold.     

Improving the Error Rate Performance of Turbo Codes using the Forced Symbol Method

This letter presents a method that significantly improves the error rate performance of turbo codes, especially in the error flare region, without changing the basic encoder structure. This method applies repeated decoding, with one or more symbols being forced to certain values, when an error is detected. This forces the decoder to output alternate sets of decisions that can then be checked for errors. The effectiveness of this method is demonstrated by its ability to lower the error flare by several orders of magnitude as soon as the error flare region is encountered. For the DVB-RCS 8-state, rate 1/2, double-binary turbo code and packets of 1504 information bits (MPEG-size), this method yields performance about 0.4 dB from the sphere-packing bound down to a packet error rate of 10-7.     

删余型Turbo码分量编码器盲识别算法

摘 要:无法获得完整的递归系统卷积码(Recursive System Code,RSC)码字,传统的盲识别方法就不适用于删余型Turbo码的识别。于是该算法在识别序列的构造上进行了改进,针对Turbo码在删余位上的码字与对应的RSC码有所区别的情况,将该位上的码字视为“0”和“1”等概率出现的误码,从而对删余位进行归零处理并选取合适的截取序列进行匹配度计算,根据最后匹配度的总分布情况对删余型Turbo码分量编码器的参数进行识别。仿真结果表明针对码长为256,码率为1/2的删余型Turbo码,在最大误比特率不超过0.033的情况下正确识别率能保持在80%以上。      

Medical data transmission using the product of TLDPC and BCH error control coding systems with two interleavers

Medical data are very precious since it has the most sensitive data of patient which can save them. If it is handled wrongly or it is manipulated, then it could result in permanent problems or even it can result in fatal. So medical data widely used in a digital format with error detection and correction codes (EDC) in its transmission and storage process. EDC is a method of adding redundant bits to the static message bits to enhance the reliability of binary digital data broadcast while the medical data communication medium adds the errors in the course of transmission. In the proposed method, we use Bose–Chaudhuri–Hocquenghem codes (BCH) as an outline algorithm and trellis Low‐Density Parity Check code (TLDPC) as an inner algorithm along with two interleavers. Product of BCH code and TLDPC code with interleavers can control more errors as compared with its plain code and product of RS‐Hamming code. MATLAB used as a simulation tool. Plain BCH code is simulated first, and then plain LDPC code is simulated for the same information. Finally, the product of BCH and TLDPC with two interleavers is imposed on the same information. The result of our research work shows enhancement in bit error rate (BER) compared to other plain and product codes from 10^?2 to 10^?3. Also, frame error rate (FER) is improved in 0.5 scaling factors when compared with other trellis decoders. Hence, this proposed system can be utilized in an application where less error rate and high accuracy of information transmission between medical data processing systems are required.     

Performance of RS coded M-ary modulation with and without symbol overlapping

In this paper, we present analytical bit error probability results for M-ary modulation concatenated with Reed Solomon (RS) codes. The analysis of bit error probability is nontrivial as the number of bits per symbol for the RS codes may not be an integer multiple of the number of bits per symbol for a modulation symbol. We propose a Markov chain technique which allows analytical evaluation of the bit error probability for such cases. The performance of RS coding with coherent biorthogonal, coherent/non-coherent orthogonal modulation over an additive white Gaussian noise (AWGN) channel is evaluated. Simulation of the bit error probability of RS code concatenated with a Nordstrom Robinson (NR) code as an inner code is performed and compared with the case of biorthogonal modulation. From the results, we notice that a stronger inner code gives better bit error probability. In addition, the throughput of the coded system with biorthogonal modulation over an AWGN channel is discussed. For a Rayleigh flat fading and block fading channel, we analyze the bit error probability of RS codes concatenated with biorthogonal modulation. From the result, we notice that a stronger outer code gives a better bit error probability for the case of Rayleigh flat fading channel.     

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