Cooperative diversity with incremental redundancy turbo coding for quasi-static wireless networks

Channel coding is a fundamental procedure in wireless telecommunication systems and has a strong impact on the data transmission quality. This effect becomes more important when the transmission must be characterised by low latency and low bit error rate, as in the case of vehicle-to-everything (V2X) services. Thus, V2X services must use powerful and efficient coding schemes. In this paper, we thoroughly examine the performance of the most important channel coding schemes in V2X services. More specifically, the impact of use of 4th-Generation Long-Term Evolution (4G-LTE) turbo codes, 5th-Generation New Radio (5G-NR) polar codes and low-density parity-check codes (LDPC) in V2X communication systems is researched. For this purpose, we employ stochastic propagation models that simulate the cases of line of sight (LOS), non-line of sight (NLOS) and line of sight with vehicle blockage (NLOSv) communication. Different communication scenarios are investigated in urban and highway environments using the 3rd-Generation Partnership Project (3GPP) parameters for the stochastic models. Based on these propagation models, we investigate the performance of the communication channels in terms of bit error rate (BER) and frame error rate (FER) performance for different levels of signal to noise ratio (SNR) for all the aforementioned coding schemes and three small V2X-compatible data frames. Our analysis shows that turbo-based coding schemes have superior BER and FER performance than 5G coding schemes for the vast majority of the considered simulation scenarios. This fact, combined with the low-complexity requirements of turbo schemes for small data frames, makes them more suitable for small-frame 5G V2X services.

Polar codes are the first provably capacity-achieving forward error correction codes. To improve decoder throughput, the symbol-decision SC algorithm makes hard-decision for multiple bits at a time. In this paper, we prove that for polar codes, the symbol-decision SC algorithm is better than the bit-decision SC algorithm in terms of the frame error rate (FER) performance because the symbol-decision SC algorithm performs a local maximum likelihood decoding within a symbol. Moreover, the bigger the symbol size, the better the FER performance. Finally, simulation results over both the additive white Gaussian noise channel and the binary erasure channel confirm our theoretical analysis.

MIMO systems (with multiple transmit and receive antennas) are becoming increasingly popular, and many next-generation systems such as WiMAX, 3-GPP LTE and IEEE802.11 n wireless LANs rely on the increased throughput of MIMO systems with up to four antennas at receiver and transmitter. High throughput implementation of the detection unit for MIMO systems is a significant challenge. This challenge becomes still harder, because the above mentioned standards demand support for multiple modulation and coding schemes. This implies that the MIMO detector must be dynamically reconfigurable. Also, to achieve required bit error rate (BER) or frame error rate (FER) performance, the detector has to provide soft values to advanced forward error correction (FEC) schemes like turbo Codes. This paper presents an ASIC implementation of a novel MIMO detector architecture that is able to reconfigure on the fly and provides soft values as output. The design is implemented in 45 nm predictive technology library, and has a parallelism factor of four. The detector has many qualities of a systolic architecture and achieves a continuous throughput of 1 Gbps for QPSK, 500 Mbps for 16-QAM, and 187.5 Mbps for 64-QAM. The total area is estimated to be approximately 70 KGates equivalent, and power consumption is estimated to be 114 mW.

MIMO systems (with multiple transmit and receive antennas) are becoming increasingly popular, and many next-generation systems such as WiMAX, 3-GPP LTE and IEEE802.11n wireless LANs relay on the increased throughput of MIMO systems with up to four antennas at receiver and transmitter. High throughput implementation of the detection unit for MIMO systems is a significant challenge especially for higher order modulation schemes. To achieve superior Bit Error Rate (BER) or Frame Error Rate (FER) performance, the detector has to provide soft values to advanced Forward Error Correction (FEC) schemes like Turbo Codes. This paper presents a systolic soft detector architecture for high dimensional (eg. 4times4, 64-QAM) MIMO systems. A Single detector core achieves, throughput of 215 Mbps and power consumption of 23.6 mW, whiles using only 33.1 K gate equivalent (for l <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> norm). Impressive SNR gains of almost 2 dB are observed with respect to the hard detection counterpart over a block fading channel (at an FER of 1%). Additionally, the architecture can be stacked to give linear increase in throughput with linear increase in hardware resources.

We consider the design of adaptive hybrid automatic retransmission request (ARQ) with incremental redundancy (IR) in which the transmission rates of different blocks in one hybrid ARQ process can be different. The throughput of adaptive IR hybrid ARQ in block fading channels is formed based on the renewal-reward theorem. Two types of input signals are considered, namely, Gaussian inputs and practical turbo coded modulation. For Gaussian inputs, the error probability after each transmission is obtained from the outage rate. For turbo coded modulation, we obtain the error rate after each transmission block by applying union-Bhattacharyya (UB) bound for parallel channels. The throughput optimization is then formed to seek the optimal transmission rates. The results show that adaptive IR HARQ provides higher throughput than non-adaptive IR HARQ and chase combining in the moderate-to-high SNR region.

This paper uses the reconstruction-computation-quantization (RCQ)paradigm to decode low-density parity-check (LDPC) codes. RCQ facilitates dynamic non-uniform quantization to achieve good frame error rate (FER) performance with very low message precision. For message-passing according to a flooding schedule, the RCQ parameters are designed by discrete density evolution. Simulation results on an IEEE 802.11 LDPC code show that for 4-bit messages, a flooding Min Sum RCQ decoder outperforms table-lookup approaches such as information bottleneck (IB) or Min-IB decoding, with significantly fewer parameters to be stored. Additionally, this paper introduces layer-specific RCQ, an extension of RCQ decoding for layered architectures. Layer-specific RCQ uses layer-specific message representations to achieve the best possible FER performance. For layer-specific RCQ, this paper proposes using layered discrete density evolution featuring hierarchical dynamic quantization (HDQ) to design parameters efficiently. Finally, this paper studies field-programmable gate array (FPGA) implementations of RCQ decoders. Simulation results for a (9472, 8192) quasi-cyclic (QC) LDPC code show that a layered Min Sum RCQ decoder with 3-bit messages achieves more than a 10% reduction in LUTs and routed nets and more than a 6% decrease in register usage while maintaining comparable decoding performance, compared to a 5-bit offset Min Sum decoder.

Polar codes under cyclic redundancy check-aided successive cancellation list (CA-SCL) decoding can outperform the turbo codes and the LDPC codes when code lengths are configured to be several kilobits. In order to reduce the decoding complexity, a novel tree-pruning scheme for the SCL/CA-SCL decoding algorithms is proposed in this letter. In each step of the decoding procedure, the candidate paths with metrics less than a threshold are dropped directly to avoid the unnecessary computations for the path searching on the descendant branches of them. Given a candidate path, an upper bound of the path metric of its descendants is proposed to determined how much pruning this candidate path would affect frame error rate (FER) performance. By utilizing this upper bounding technique and introducing a dynamic threshold, the proposed scheme deletes as many as possible of the redundant candidate paths while keeping the performance deterioration in a tolerant region, thus it is much more efficient than the existing pruning scheme. With only a negligible loss of FER performance, the computational complexity of the proposed pruned decoding scheme is only about 40% of the standard algorithm in the low signal-to-noise ratio (SNR) region (where the FER under CA-SCL decoding is about 0.1 ~ 0.001), and it can be very close to that of the successive cancellation (SC) decoder in the moderate- and high-SNR regions.

The paper presents a novel cooperative coding scheme using punctured serial concatenated convolutional codes (SCCC). We evaluate its performance in terms of frame error rate (FER) under two cooperation protocols: a decode-and-forward protocol in conjunction with automatic repeat request (ARQ), by which the relay sends an acknowledge bit (ACK) back to the source to indicate whether its data packet is correctly decoded; an adaptive amplify-and-forward protocol, where the amplifying relay node cooperates to forward the message only when the inter-user link gain is above a certain threshold. In both cases, the destination makes the decision on each transmitted bit after appropriately combining signals and performing iterative decoding. Simulation results show that SCCC-based cooperative coding achieves full spatial diversity and exhibits a similar FER performance to that using parallel concatenated convolutional codes (PCCC). At the price of channel feedback, the adaptive decode-and-forward algorithm demonstrates a relatively lower FER than the adaptive amplify-and-forward scheme. Amplified cooperation experiences severe performance degradation due to the inefficiency of repetition coding and error propagation, especially when the quality of the source-relay link deteriorates; however, if the threshold for carrying cooperation is carefully selected, the adaptive amplify-and-forward protocol can perform comparably to the decode-and-forward protocol.

In this paper, we propose a novel multihop transmission scheme using selective network coding (NC) and differential modulation (SNC-DM) for two-way relay networks (TWRNs) when neither the source nodes nor the relay nodes know the channel state information (CSI). We first develop a bidirectional transmission scheme using NC where the information exchange in a two-way multihop relay network with the arbitrary number of hops can be completed in four transmission phases. As a result, the maximum achievable throughput does not decrease as the number of hops increases. To overcome the error propagation in the multihop transmission with decode-and-forward (DF) protocol in wireless fading channels, a selective NC scheme is proposed. In addition, we apply differential modulation in the proposed scheme to avoid channel estimation in the multihop networks. The performance of the proposed scheme is analyzed, and a closed-form frame error rate (FER) expression is derived. It is shown that the proposed scheme achieves significant improvements in both FER performance and network throughput compared to the conventional multihop DF scheme in TWRNs. The analytical results are verified through numerical simulations.

Hybrid ARQ (HARQ) has been shown to be an effective transmission strategy to improve the performance and capacity of relayed transmission in cooperative wireless networks. In contrast to the conventional HARQ, the retransmitted packets in cooperative systems do not need to come from the original source but could instead be sent by relays that overhear the transmission. This paper proposes an improved HARQ scheme with an adaptive relaying protocol (ARP). The proposed HARQ- ARP scheme combines the retransmission mechanisms (repetition coding and incremental redundancy), the distributed turbo coding (DTC) and the adaptive relaying strategy. They can effectively avoid the problem of both error propagation and noise amplification encountered in current cooperative communication systems. A performance analysis is carried out for the proposed scheme. The analysis and simulation results show that the proposed HARQ scheme can achieve a superior frame error rate (FER) to the existing HARQ relaying methods in all signal to noise ratio (SNR) regions.

The inner decoder of the Davey-MacKay (DM) construction for combating insertions, deletions and substitution errors, has high complexity and produces bursts of output likelihoods of greatest uncertainty in the vicinity of insertions and deletions. We therefore propose (i) a lookup-table-based implementation of the inner decoder to reduce its complexity, (ii) the use of interleaved LDPC codes as outer codes in the DM construction to spread the uncertain likelihoods produced by the inner decoder over several constituent LDPC codewords. Simulation results show that the proposed lookup table approach reduces the complexity of the inner decoder considerably while a significant improvement in frame error rate (FER) performance can be obtained with small interleaving depths. Our lookup table approach culminates in an iterative decoding scheme which yields improved FER performance over its non-iterative counterparts, yet with only a modest increase in decoding complexity, when the insertion/deletion probability is small.

One of the promising techniques to achieve high-speed data transmission in limited bandwidth is multi-input multi-output (MIMO) multiplexing. In MIMO multiplexing, signal separation/detection is one of the most important signal processing parts, so that the signal separation/detection schemes have been vigorously researching. Recently, as a promising signal separation/detection scheme, frequency-domain iterative interference cancellation (FD-IIC) has been proposed. FD-IIC can achieve good transmission performance which is close to lower bound when QPSK is used. However, the accuracy of signal separation/detection significantly degrades in case of high data modulation. Therefore, in this paper, to improve the accuracy of signal separation/detection, we propose layered-symbol iterative interference cancellation (LSIC). We consider single-carrier (SC) MIMO multiplexing and the achievable frame error rate (FER) performances with LSIC are evaluated by computer simulation to show that LSIC can provide better FER performance than FD-IIC.

Increasing the performances of turbo codes used in communication systems is an important issue at the moment. The method used for trellis termination influences the code performances. This paper describes and compares (in terms of bit error rate - BER and frame error rate - FER) four types of these methods: without trellis termination, termination only of the first trellis, post-interleaver flushing and dual termination. Turbo code performances are evaluated for two lengths of S-random interleaver, using binary phase-shift keying (BPSK) modulation, over Additive White Gaussian Noise (AWGN) channel. The simulations were performed for two generating matrices of the component encoders and the decoding algorithm we have used is a version of Max-Log-MAP.

A novel polar coded hybrid-ARQ (PC-HARQ) transmission with chase combining utilizing powerful successive cancellation list decoder (HARQ-CC-SCL) is explored. We propose that by applying the distance spectrum of polar code to evaluate its frame error rate, the bounds of throughput and average transmission number can be derived. Then, this letter proposes an adaptive scheme combining the list size-manageable SCL decoding with ARQ protocol. Simulations indicate that the proposed HARQ-CC-SCL obtains a considerable throughput improvement of PC-HARQ-CC system, and approaches those of HARQ schemes with incremental redundancy through less transmission times for each packet. Meanwhile, the adaptive version achieves high throughput and good flexibility in practical applications without significant increase of complexity.

In this paper some simple channel models taking into account the corresponding BER (bit error rate) and FER (frame error rate), for an advanced 3G (WCDMA) receiver, using chip level equalizer and turbo coding, are considered. The conventional RAKE receiver is used as a reference. On the basis of the obtained models parameters, some corresponding FER bounds are evaluated and compared