Convolutional Channel Coding Research Articles

SDR implementation and real-time performance evaluation of 5G channel coding techniques

This article presents a study on the real-time performance and practical implementation of several 5G channel coding candidates including low-density parity check (LDPC), polar, turbo, and convolutional channel codes. The experiment was conducted using a wireless communication transceiver system implemented on a software defined radio (SDR) platform called Universal Software Radio Peripheral (USRP). The system was implemented using Matlab software and included scrambling, channel coding, interleaving, and required synchronization and estimation blocks. Various sets of system and channel parameters were tested, including the impact of information block sizes, code lengths, and modulation orders on the performance of each channel coding technique. The study also evaluated the impact of hardware impairments and the required blocks to mitigate them. The results indicated that polar codes had the best performance, while other codes had trade-offs for various system parameters. The study concludes that polar codes with cyclic redundancy check-successive cancellation list (CRC-SCL) are the most reliable 5G channel coding candidates.

Design and Analysis of Joint Source-Channel Code System with Fixed-Length Code

As the demands of multimedia and data services increase, efficient communication systems are being investigated to meet the high data rate requirements. Joint source-channel coding (JSCC) schemes were proposed for improving overall system performance. However, existing JSCC systems may suffer a symbol error rate (SER) performance loss when residual source redundancy is not fully exploited. This paper presents a novel, low-complexity JSCC system, which consists of a fixed-length source block code and an irregular convolutional channel code. A simple approach is proposed to design source codes that minimize the SER of source detection and guarantee the convergence of iterative source-channel decoding (ISCD). To improve the waterfall performance of ISCD, the channel code is optimized by using the extrinsic information transfer (EXIT) chart and the concept of irregular code. The channel code is constituted by recursive non-systematic convolutional (RNSC) subcodes. The weights of subcodes are optimized to make the EXIT curves of the channel decoder and the source decoder well-matched, and therefore, a near-capacity performance is achieved. Simulation results show that the proposed system achieves more than 1 dB gains and 0.3 dB gains compared to the separate source-channel code system and the other optimal JSCC systems, respectively. Additionally, the performance of the proposed system is within 1 dB deviation from the Shannon limit capacity.

Iterative Threshold Channel Estimation in ORGV Convolutional Code MISO-OFDM System

ABSTRACT In the orthogonal frequency division multiplexing (OFDM) transmission system, when the digital symbols are transmitted in the wireless channel, it would be affected by a lot of noise interference due to the unsatisfactory condition characteristics of the wireless channel itself, therefore, the symbol error and bit error would be generated. To achieve a certain bit error rate (BER) under the condition of known signal-to-noise ratio (SNR), convolutional channel coding and block interleaver should be utilized to further reduce the BER. Moreover, convolutional code is almost utilized in all wireless communication systems. This paper proposes a convolutional code channel estimation method in multiple-input single-output (MISO)-based OFDM (MISO-OFDM) system with frequency-shift m-sequence (FSMS) as guard interval (GI) for avoiding inter-symbol interference (ISI). The proposed space-frequency block code (SFBC) MISO-OFDM system achieves higher transmit diversity gains and better BER performance. Simulation results verify that the proposed iterative threshold channel estimation (ITCE) method in octal representation generation vector (ORGV) convolutional code 4 × 1 MISO-OFDM system provides good BER and normalized mean squared error (NMSE) performance with significant coding gains in both static and dynamic multipath channels.

FPGA Implementation of MIMO System using Xilinx System for Video Transmission

In this paper, we have introduced an architecture for real-time video transmission over multiple- input multiple-output (MIMO) wireless communication systems. We employ the 2x1 and 2x2 Alamouti MIMO technique to develop a transmission system and implement the design on FPGA using Xilinx System using the modeling and simulation capabilities of MATLAB. Furthermore, according to the contribution to the reconstructed video quality, we apply unequal error protection strategy using STBC space-time codes for each video bitstream. We present a solution using FPGA as target platform (instead of software), for implementing algorithms for transmission of educational videos using MIMO systems. In our proposed system, we have provided the system performance of a joint MPEG-2 coding scheme with convolutional channel coding and space time block coding (STBC) techniques, associated with suitable modulation method (QAM and BPSK), for video data transmission over a wireless MIMO system with Rayleigh fading noises. Simulation results show the quality of the reconstructed image can be significantly improved over only using space time coding. The comparison has been done on the basis of quality of reproduced image by measuring image PSNR based on SNR and BER value for different system model is realized over Xilinx Virtex-4 XC4VFX100FFG1517-11C FPGA based WRAP board. Keywords: FPGA (Field Programmable Gate Arrays); STBC (Space Time Block Coding), Bit error rate(BER), FPGA, Peak to signal noise ratio (PSNR), Multiple input multiple output (MIMO), WRAP board, Joint source channel coding, Space time block coding(STBC).

Robust Ultra-Low Latency Soft-Decision Decoding of Linear PCM Audio

Applications such as professional wireless digital microphones require a transmission of practically uncoded high-quality audio with ultra-low latency on the one hand and robustness to error-prone channels on the other hand. The delay restrictions, however, prohibit the utilization of efficient block or convolutional channel codes for error protection. The contribution of this work is fourfold: We revise and summarize concisely a Bayesian framework for soft-decision audio decoding and present three novel approaches to (almost) latency-free robust decoding of uncompressed audio. Bit reliability information from the transmission channel is exploited, as well as short-term and long-term residual redundancy within the audio signal, and optionally some explicit redundancy in terms of a sample-individual block code. In all cases we utilize variants of higher-order linear prediction to compute prediction probabilities in three novel ways: Firstly by employing a serial cascade of multiple predictors, secondly by exploiting explicit redundancy in form of parity bits, and thirdly by utilizing an interpolative forward/backward prediction algorithm. The first two presented approaches work fully delayless, while the third one introduces an ultra-low algorithmic delay of just a few samples. The effectiveness of the proposed algorithms is proven in simulations with BPSK and typical digital microphone FSK modulation schemes on AWGN and bursty fading channels.

Self-Encoded Multiple Access Multiuser Convolutional Codes in Uplink and Downlink Cellular Systems

Self-encoded spread spectrum eliminates the need for traditional pseudo noise (PN) code generators. In a self-encoded multiple access (SEMA) system, the number of users is not limited by the number of available sequences, unlike code division multiple access (CDMA) systems that employ PN codes such as m-, Gold or Kassami sequences. SEMA provides a convenient way of supporting multi-rate, multi-level grades of service in multimedia communications and prioritized heterogeneous networking systems. In this paper, we propose multiuser convolutional channel coding in SEMA that provides fewer cross-correlations among users and thereby reducing multiple access interference (MAI). We analyze SEMA multiuser convolutional coding in additive white Gaussian noise (AWGN) channels as well as fading channels. Our analysis includes downlink synchronous system as well as asynchronous system such as uplink mobile-to-base station communication.

Integrated joint source-channel symbol-by-symbol decoding of variable-length codes using 3-D MAP sequence estimation

Most of multimedia schemes employ variable-length codes (VLCs) like Huffman code as core components in obtaining high compression rates. However VLC methods are very sensitive to channel noise. The goal of this paper is to salvage as many data from the damaged packets as possible for higher audiovisual quality. This paper proposes an integrated joint source-channel decoder (I-JSCD) at a symbol-level using three-dimensional (3-D) trellis representation for first-order Markov sources encoded with VLC source code and convolutional channel code. This method combines source code and channel code state-spaces and bit-lengths to construct a two-dimensional (2-D) state-space, and then develops a 3-D trellis and a maximum a-posterior (MAP) algorithm to estimate the source sequence symbol by symbol. Experiment results demonstrate that our method results in significant improvement in decoding performance, it can salvage at least half of (50%) data in any channel error rate, and can provide additional error resilience to VLC stream like image, audio, video stream over high error rate links.

Rotated Walsh-Hadamard Spreading with Robust Channel Estimation for a Coded MC-CDMA System

We investigate rotated Walsh-Hadamard spreading matrices for a broadband MC-CDMA system with robust channel estimation in the synchronous downlink. The similarities between rotated spreading and signal space diversity are outlined. In a multiuser MC-CDMA system, possible performance improvements are based on the chosen detector, the channel code, and its Hamming distance. By applying rotated spreading in comparison to a standard Walsh-Hadamard spreading code, a higher throughput can be achieved. As combining the channel code and the spreading code forms a concatenated code, the overall minimum Hamming distance of the concatenated code increases. This asymptotically results in an improvement of the bit error rate for high signal-to-noise ratio. Higher convolutional channel code rates are mostly generated by puncturing good low-rate channel codes. The overall Hamming distance decreases significantly for the punctured channel codes. Higher channel code rates are favorable for MC-CDMA, as MC-CDMA utilizes diversity more efficiently compared to pure OFDMA. The application of rotated spreading in an MC-CDMA system allows exploiting diversity even further.We demonstrate that the rotated spreading gain is still present for a robust pilot-aided channel estimator. In a well-designed system, rotated spreading extends the performance by using a maximum likelihood detector with robust channel estimation at the receiver by about 1 dB.

Turbo detection of convolutionally coded and differentially modulated signals

In an uncoded digital transmission system with M-PSK or M-DPSK, respectively, always a performance difference in the required signal-to-noise ratio (SNR) of up to 3 dB occurs, if M-DPSK is detected noncoherently. This difference still remains in coded systems based on convolutional codes with classical soft decision Viterbi decoding. In this contribution, the combination of differential modulation and convolutional channel coding is re-interpreted as a concatenated coding scheme. In this case, the differential modulation system is considered as the inner code and the convolutional code as the outer code. Before this background, turbo decoding is applied at the receiver resulting in an SNR gain of more than 3.5 dB compared with classical soft decision Viterbi decoding. Thus, the transmission system with differential modulation performs even better than the corresponding system with non-differential modulation.

Trellis source codes designed by conjugate gradient optimization

Time-invariant trellis codes for stationary, ergodic, discrete-time sources are designed by unconstrained, nonlinear optimization of the performance in a simulated source encoding with the Viterbi algorithm. A nonderivative conjugate directions algorithm and a conjugate gradient algorithm with restarts are applied to design low-constraint-length, unit-rate, binary codes for the memoryless Gaussian source. The latter algorithm is also used to design codes for the memoryless Laplacian source and a third-order autoregressive model for speech. Good codes are tabulated and compared to other known results on a performance versus complexity basis. Those for the Gaussian source are tested in a joint (tandem) trellis-coding system with known convolutional channel codes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Rotationally Invariant Convolutional Channel Coding with Expanded Signal Space - Part I:180°

Convolutional channel coding with expanded signal space improves error performance of synchronous data links without sacrificing data rate or requiring more bandwidth. Due to the phase ambiguity(ies) in the expanded signal space, it is desirable to design the code' to be transparent to signal element rotations. In this paper, design rules and procedures for 180° rotationally invariant codes are presented. In a companion paper, we extend these rules and procedures to codes which are transparent to 90, 180, and 270° signal element rotations. We illustrate these rules and procedures by designing simple codes that achieve coding gain of 3-4 dB. These are the codes of practical interest. Codes with higher coding gain can be obtained using the same rules and procedures. Both feedforward and feedback codes are considered.

Rotationally Invariant Convolutional Channel Coding with Expanded Signal Space - Part II: Nonlinear Codes

This is the second paper on rotationally invariant convolutional channel coding with expanded signal space. Signal space with 90, 180, and 270° phase ambiguities is generally preferred to signal space with only 180° phase ambiguity. In this paper, design rules and procedures for 180° rotationally invariant convolutional codes in the previous paper are extended to rotationally invariant codes with expanded signal space having 90, 180, and 270° phase ambiguities. As in the previous paper, we illustrate these rules and procedures by designing simple codes with coding gain of 4 dB. Nonlinear convolutional codes result from these design rules and procedures. These simple nonlinear convolutional codes are being considered as international standards on voiceband modems at rate greater than or equal to 9.6 kbits/s. Codes with higher coding gain can be obtained using the same rules and procedures. Both feedforward and codes are considered. In addition, a new class of codes described as generalized feedback is also considered.