Soft Decision Viterbi Decoding Research Articles

Low Complexity Signal Detection for Massive MIMO in B5G Uplink System

Massive Multiple Input Multiple Output (M-MIMO) is realized as a mandatory technique for Beyond Fifth Generation (B5G) wireless networks. In next-generation node B (gNB) uplink transmission, M-MIMO requires a low-complexity signal detection scheme with an increased number of antennas to attain high channel capacity and reliability. To attain close-optimal performance in these B5G systems, the Minimum Mean Square Error (MMSE) detection scheme is preferred at the gNB but it demands a complex matrix inversion concerning the number of users. Hence, this article proposes a Modified Weighted Two Stage (MWTS) iterative algorithm with an appropriate initial solution to realize MMSE detection at reduced complexity. MWTS detection algorithm is formulated by integrating the first half iteration phase of weighted two stage with the previous phase and ignoring the second half iteration. Further to improve the performance of the B5G system, a low-complexity soft decision Viterbi decoder is introduced at gNB. With K users, the proposed modifications display a reduction in computational complexity of 4K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> +16K as compared to the weighted two stage algorithm of 7K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> +8K. Simulation results confirm that the proposed MWTS algorithm yields lower complexity and near-optimal performance close to MMSE detection.

A High-throughput Parallel Viterbi Algorithm via Bitslicing

In this work, we present a novel bitsliced high-performance Viterbi algorithm suitable for high-throughput and data-intensive communication. A new column-major data representation scheme coupled with the bitsliced architecture is employed in our proposed Viterbi decoder that enables the maximum utilization of the parallel processing units in modern parallel accelerators. With the help of the proposed alteration of the data scheme, instead of the conventional bit-by-bit operations, 32-bit chunks of data are processed by each processing unit. This means that a single bitsliced parallel Viterbi decoder is capable of decoding 32 different chunks of data simultaneously. Here, the Viterbi’s Add-Compare-Select procedure is implemented with our proposed bitslicing technique, where it is shown that the bitsliced operations for the Viterbi internal functionalities are efficient in terms of their performance and complexity. We have achieved this level of high parallelism while keeping an acceptable bit error rate performance for our proposed methodology. Our suggested hard and soft-decision Viterbi decoder implementations on GPU platforms outperform the fastest previously proposed works by and , achieving 21.41 and 8.24 Gbps on Tesla V100, respectively.

Trellis coded quadrature spatial modulation

In this paper, a novel multiple-input multiple-output (MIMO) transmission scheme called trellis coded quadrature spatial modulation (TC-QSM), is proposed. In the proposed scheme, trellis coded modulation (TCM) principle is applied to the emerging quadrature spatial modulation (QSM) scheme, and a trellis encoder and a QSM mapper are jointly designed to benefit from both coding and multiplexing gains. At the receiver side, a soft-decision Viterbi decoder is used along with a QSM decoder to obtain the optimum error performance. Considering our design criterion, TC-QSM schemes are designed for different number of trellis states, transmit antennas and spectral efficiencies. The pairwise error probability (PEP) of the TC-QSM scheme is derived over quasi-static Nakagami-m, Rician and Rayleigh fading channels and an upper bound on the average bit error probability (BEP) is obtained. Through comprehensive Monte Carlo simulations, the effect of signal and spatial bits on uncoded and trellis coded SM and QSM schemes over Nakagami-m and Rician fading channels are investigated for different fading parameters. Moreover, the error performance of the TC-QSM and SM with trellis coding (SM-TC) schemes are compared for different spectral efficiency values, where it is revealed that the proposed TC-QSM scheme provides an interesting trade-off between performance and implementation cost, and achieves an improved error performance over reference schemes including SM, QSM and SM-TC.

Enhanced 2/3 four-ary modulation code using soft-decision Viterbi decoding for four-level holographic data storage systems

An enhanced 2/3 four-ary modulation code using soft-decision Viterbi decoding is proposed for four-level holographic data storage systems. While the previous four-ary modulation codes focus on preventing maximum two-dimensional intersymbol interference patterns, the proposed four-ary modulation code aims at maximizing the coding gains for better bit error rate performances. For achieving significant coding gains from the four-ary modulation codes, we design a new 2/3 four-ary modulation code in order to enlarge the free distance on the trellis through extensive simulation. The free distance of the proposed four-ary modulation code is extended from 1.21 to 2.04 compared with that of the conventional four-ary modulation code. The simulation result shows that the proposed four-ary modulation code has more than 1 dB gains compared with the conventional four-ary modulation code.

A pipelined 8-bit soft decision viterbi decoder for IEEE802.11ac WLAN systems

Recently, IEEE802.11ac, which can support ultra high speed data communications up to 1Gbps with low power consumption, has been drawing much attention in the consumer electronic field. In the IEEE802.11ac system, one of the critical implementation issues is to find the optimum architecture of demodulator satisfying the speed requirement. A Viterbi decoder is an essential part for error correction in the demodulator and has a design problem with respect to hardware costs as well as decoding speed. Among various functional blocks in the Viterbi decoder, both hardware complexity and decoding speed highly depend on the architecture of ACS. Because of a feed-back structure, it is very difficult for the ACS to perform its task at a high data rate at low power. Substantial previous works have been presented in order to enhance the decoding speed or to reduce the hardware costs. However, the approaches are insufficient to meet the high-speed and low-cost requirements of a high-level soft decision (up to 8 bits) Viterbi decoder for IEEE802.11ac systems. In this paper, therefore, we propose a cost-efficient high-level soft decision Viterbi decoder with a multi-stage pipelined ACS for IEEE802.11ac systems. From the implementation and verification results under 0.13μm CMOS technology, we find that the proposed architecture can meet the required data rate of IEEE802.11ac and reduce the hardware complexity by about 70% and 90% compared with conventional single-stage pipelined ACS and look-ahead ACS structures, respectively.

Soft-Decision Viterbi Decoding Scheme and a New Reliability Metric for 4/6 Modulation Code in Holographic Data Storage

A soft-decision Viterbi decoding for a 4/6 modulation code is proposed in a holographic data storage system. Since the previous proposed soft-decision Viterbi decoding does not support a higher rate modulation codes than 1/2 rate modulation codes, we propose a new reliability metric to support the 4/6 modulation code. The reliability metric is used to calculate the branch metric on the trellis. For a better coding gain, we find a symbol mapping method for the modulation code which provides a large free distance on the trellis to have the enhanced error correcting capability. Simulation results show that the proposed scheme has about 2 dB coding gains than the conventional soft-decision Viterbi decoding scheme.

Soft-Decision Viterbi Decoding Scheme and a New Reliability Metric for 4/6 Modulation Code in Holographic Data Storage

Soft-Decision Viterbi Decoding Scheme and a New Reliability Metric for 4/6 Modulation Code in Holographic Data Storage

軟判定ビタビ復号を用いた4 値FSK 無線伝送システムの特性評価

軟判定ビタビ復号を用いた4 値FSK 無線伝送システムの特性評価

Variable wordlength soft-decision Viterbi decoder for power-efficient wireless LAN

This paper describes the design of a new, variable wordlength, soft-decision Viterbi decoder that can significantly reduce power dissipation in wireless local area network (LAN) hardware. By taking into account the dynamic range of the time-varying channel coefficients, the quantization level is adjusted to suit the observed instantaneous link quality, i.e., the decoder wordlength is adjusted to maintain efficient throughput requirements and low power dissipation. A dynamic voltage scaling is applied with a variable wordlength to significantly reduce power consumption in the soft-decision Viterbi decoder. Unlike the conventional 8-bit fixed-wordlength decoder, our radix-4 Viterbi decoder can reduce power consumption by up to 35% under AWGN and multipath fading channel conditions.

Bit-error ratio performance for radio over multimode fibre system using coded orthogonal frequency division multiplexing

In this study, a performance evaluation of radio over multimode fibre system using coded orthogonal frequency division multiplexing (COFDM) is presented. The performance analyses based on bit-error ratio (BER) are extensively investigated. In addition, the effect of fibre length on BER performance is presented. Moreover, the effect of the exponent refractive index profile of the multimode fibre on the BER of COFDM is studied considering maximum likelihood ratio and sub-optimal simplified log likelihood ratio as a soft-bit metrics for soft-decision viterbi decoding.

New Trellis Code Design for Spatial Modulation

Spatial modulation (SM), in which multiple antennas are used to convey information besides the conventional M-ary signal constellations, is a new multiple-input multiple-output (MIMO) transmission technique, which has recently been proposed as an alternative to V-BLAST (vertical Bell Labs layered space-time). In this paper, a novel MIMO transmission scheme, called spatial modulation with trellis coding (SM-TC), is proposed. Similar to the conventional trellis coded modulation (TCM), in this scheme, a trellis encoder and an SM mapper are jointly designed to take advantage of the benefits of both. A soft decision Viterbi decoder, which is fed with the soft information supplied by the optimal SM decoder, is used at the receiver. A pairwise error probability (PEP) upper bound is derived for the SM-TC scheme in uncorrelated quasi-static Rayleigh fading channels. From the PEP upper bound, code design criteria are given and then used to obtain new 4-, 8- and 16-state SM-TC schemes using quadrature phase-shift keying (QPSK) and 8-ary phase-shift keying (8-PSK) modulations for 2,3 and 4 bits/s/Hz spectral efficiencies. It is shown via computer simulations and also supported by a theoretical error performance analysis that the proposed SM-TC schemes achieve significantly better error performance than the classical space-time trellis codes and coded V-BLAST systems at the same spectral efficiency, yet with reduced decoding complexity.

BER Performance Analysis of CDMA Reverse Link under AWGN Channel

bit error rate (BER) performance of the Code Division Multiple Access (CDMA) cellular system based on IS-95 standard in the presence of an additive white Gaussian noise (AWGN) and interference has been investigated in this paper. The performance is evaluated under two types of decision feedback receivers for the CDMA reverse link. These two feedback receivers are: (a) Hard decision Viterbi decoder in which coded bit is estimated based on Hamming Distance method and (b) Soft decision Viterbi decoder in which Euclidean Distance method is used for coded bit estimation. The comparison of these two techniques of decision feedback receivers of CDMA is done under AWGN channel. The performance of CDMA system is shown in graphs between BER versus Energy per bit to Noise Ratio i.e. Eb/No ratio. KeywordsBER, Chip Rate, Chip period, Eb/No, PN codes.

Performance Enhancement of Wireless Communication Systems using Transmit and Receive diversity

In this paper, we describe the concatenation of Turbo/Convolutional codes with transmit and receive diversity schemes by using Space-Time Block Code. It is shown that, by using two transmit antennas and one/or two receive antenna, large coding gain for the bit error rate is achieved over the system without diversity. Simulation results show that, by using systems with transmit and receive diversity, high gain can be achieved with very low complexity. It turns out that at BER = 10−4, the gain of 9 dB can be achieved for system using STTD transmit diversity only (without using any channel codes) and 2 dB gain can be achieved over channel coding systems using hard-decision decoding with much lower complexity. The most important conclusion is that, using soft-decision decoding systems enhanced with transmit diversity can provide very high coding gain; e.g., in convolutional coded system using soft-decision Viterbi decoder, the coding gain is 12 dB over uncoded system and 5 dB over hard-decision decoding in flat fading channel, while the coding gain is about 13 dB for turbo coded systems using soft-decision decoding based on SOVA algorithm with transmit diversity and the coding gain is 15 dB if the decoder is based on Log-MAP algorithm. In systems using transmit and receive diversity, the coding gain is much higher, e.g., for convolutional-coded systems, the coding gain is 20 dB, while for turbo-coded systems using SOVA and Log-MAP algorithms, the coding gain are a little more than 20 dB and 21 dB, respectively.

Double Space Time Transmit Diversity OFDM System with Antenna Shuffling in Spatial Correlated Frequency Selective MIMO Channels

In this paper, we study low complexity transceiver for double space time transmit diversity (DSTTD) and orthogonal frequency division multiplexing (OFDM) system with antenna shuffling. Firstly, we propose a novel antenna shuffling method based on the criterion of minimizing the condition number of channel correlation matrix. The condition number is an indicator about the quality of the channel. By selecting the minimum of condition number which has better channel quality, consequently, a linear detector with respect to this new channel may achieve better performance results. A low complexity variant of the condition number calculation is also proposed, and it is shown that this criterion can be reduced to the minimum mean square error (MMSE) based criterion. Furthermore, the weighted soft decision Viterbi decoding is applied to mitigate noise enhancement inherent to zero forcing (ZF) and MMSE linear receivers and improve error rate performance. Next, we propose an algorithm to reduce the amount of feedback by exploiting the fact that the channel frequency responses across OFDM subcarriers are correlated. In the proposed algorithm, subcarriers are clustered in blocks, which are allocated the same shuffling pattern with the largest number of the shuffling patterns in the cluster. This way, the signaling overhead can be reduced in comparison with each subcarrier based feedback. Extensive simulations show that the proposed techniques for DSTTD-OFDM system outperform other existing techniques under both uncorrelated and highly spatial correlated frequency selective MIMO fading channels.

Evaluation of mobile ultra wideband modems in dense multipath-part 2: performance of DSSS/Rake modems

This paper presents a comparative analysis of the performance of three UWB (ultra wideband) DSSS (direct sequence spread spectrum)/Rake modems used to communicate with mobile platforms over new mobile outdoor and indoor dense multipath UWB channel models developed in a companion paper. The Rake modems analyzed differ in the techniques used to estimate the channel and are called decision-directed parallel- probe and serial-probe modems. The performance analysis includes the effects of time-selective distortion and noise on the estimated tap weights wherein the time constant of the tap weight measurements and the number of Rake taps are optimized. Numerical results are presented for 2 GHz bandwidth transmitted signals, a 7.5 GHz carrier frequency, and channel BPSK symbol rates of .15, 1.5, and 15 Megasymbols/sec. The well known rate 1/2, constraint length 7 convolutional code using 3 bit soft decision Viterbi decoding is assumed. One moving and one stationary platform are postulated, with a velocity of 100 ft/sec for the outdoor channel and 5 ft/sec for the indoor channel. Required values of Es/No to achieve 10-6 decoded error rate are computed as a function of multipath spread.

Architectures for the Implementation of a OFDM-WLAN Viterbi Decoder

This paper describes the design of a soft decision Viterbi Decoder for orthogonal frequency division multiplexing-based wireless local area networks and evaluates different architectural options by means of their field programmable gate-array (FPGA) implementation. A finite precision analysis has been performed to reduce the data-path widths under the specifications of IEEE 802.11a and Hiperlan/2 standards. Four implementation strategies (register exchange, trace back, trace back with double rate memory read and pointer trace back) for the survivor management unit have been evaluated together with two different normalization methods for the add---compare---select unit. The results of the implementation in FPGA have been given and it is shown that register exchange and pointer trace back architectures with pre-normalization in the add---compare---select unit achieve the best performance. Both architectures can decode 200 Mbps in a Virtex-4 device with lower latency that the conventional trace back one and pointer trace back exhibits the lowest power consumption, these characteristics make them suitable for future multiple-output multiple-input WLAN systems.

Coded Decision-Directed Channel Estimation for Coherent Detection in Terrestrial DMB Receivers

This paper proposes a coded decision-directed (DD) channel-estimation method with two-dimensional averaging for T-DMB receivers. Since the noncoherent differential demodulation of existing T-DMB receivers can not track channel variation, it may not work well in fast-fading channels. To overcome this problem, coherent detection based on channel estimation is introduced. The proposed method re- modulates the output of the soft-decision Viterbi decoder for coded DD channel estimation to obtain more accurate decision symbols than hard-decision symbols. To both mitigate the effects of noise and smooth incorrectly-estimated coefficients, the estimated channel coefficients are two- dimensionally averaged. The enhanced accuracy leads to the high-performance DQPSK demodulation robust to Doppler spread and noise. The proposed method may also contribute to the launch of the future T-DMB service of providing a higher data rate. Simulation results show that the proposed scheme performs much better than the conventional method, especially at high speed-moving receivers.

Soft-Decision Viterbi Decoding for 2/4 Modulation Code in Holographic Memory

The signal quality of holographic memory is lowered by the thermal noise and shot noise of a detector, and the reproduced image distortion caused by the shrinkage of a medium. For the improvement of signal quality, soft-decision Viterbi decoding was performed after 2/4 modulation coding. For the 2/4 modulation code, a new two-dimensional reliability was defined. A method of soft-decision Viterbi decoding, which uses this reliability as the value for soft decision, was proposed. In our record/reproduction experiment using this method, the reduction in bit error rate and effectiveness of soft-decision Viterbi decoding were verified.

Low complexity radix-4 butterfly design for the soft-decision Viterbi decoder

This study presents a new radix-4 butterfly design for Viterbi decoders. The branch symmetry of the proposed radix-4 butterfly is exploited to design a low-complexity radix-4 butterfly module to simplify the implementation of the soft-decision Viterbi decoder. By exploiting the branch symmetry, only a half of branch metrics need to be computed, while other metrics can be derived from the computed branches. Therefore, the branch metric computation of the radix-4 butterfly can be reduced by a factor of 2. Considering the convolutional code in the DAB system as an example, experimental results indicate that the proposed radix-4 butterfly design can reduce the number of FPGA slices of the radix-4 butterfly module by 24% over the conventional design.

On Optimal Stepsize for Soft Decision Viterbi Decoding

This letter presents a method of finding the optimal quantization stepsize that minimizes quantization loss and maximizes coded BER performance. We define 'Information Error Rate'(IER) and obtain the equation of the modified constraint length (K m ) to obtain an upper bound of coded BER performance of a I bit quantized soft decision Viterbi decoder. Using IER and K m , we determine the optimal quantization stepsize of a 2 bit and 3 bit quantized soft decision decoding system in an AWGN channl with respect to SNR, and verify our strategies by simulation results.