Frequency-Domain Turbo Equalization for MIMO Underwater Acoustic Communications

This paper investigates a low-complexity frequency-domain turbo equalization (FDTE) based on linear minimum mean square error (LMMSE) criterion for single-carrier (SC) multiple-input multiple-output (MIMO) underwater acoustic communications (UAC). The receiver incorporates both the equalizer and the decoder which exchange the extrinsic information on the coded bits for each other to implement the iterative detection. The channel impulse responses (CIRs) required in the equalization are estimated in the frequency domain (FD) by inserting the well-designed pilot blocks which are frequency-orthogonal Chu sequences. The proposed SC-MIMO-FDTE architecture is applied to the fixed-to-fixed underwater data gathered during SPACE08 ocean experiments in October 2008, where multiple transducers and hydrophones are deployed in communication ranges of 200m and 1000m, and the channel bandwidth is 9.765625 kHz. The phase shift keying (PSK) signals are transmitted from multiple transducers in various block sizes. The proposed transceiver has been demonstrated to improve the bit-error-rate (BER) performance significantly by processing the QPSK data blocks with block length of 1024 in 200m and 1000m ranges. The average BERs obtained by turbo detection with 3 iterations can achieve approximately 1.4 × 10-4 for the 200m system and 4.4 × 10-5 for the 1000m system

A New Class of Multiple-rate Codes Based on Block Markov Superposition Transmission

Hadamard transform~(HT) as over the binary field provides a natural way to implement multiple-rate codes~(referred to as {\em HT-coset codes}), where the code length $N=2^p$ is fixed but the code dimension $K$ can be varied from $1$ to $N-1$ by adjusting the set of frozen bits. The HT-coset codes, including Reed-Muller~(RM) codes and polar codes as typical examples, can share a pair of encoder and decoder with implementation complexity of order $O(N \log N)$. However, to guarantee that all codes with designated rates perform well, HT-coset coding usually requires a sufficiently large code length, which in turn causes difficulties in the determination of which bits are better for being frozen. In this paper, we propose to transmit short HT-coset codes in the so-called block Markov superposition transmission~(BMST) manner. At the transmitter, signals are spatially coupled via superposition, resulting in long codes. At the receiver, these coupled signals are recovered by a sliding-window iterative soft successive cancellation decoding algorithm. Most importantly, the performance around or below the bit-error-rate~(BER) of $10^{-5}$ can be predicted by a simple genie-aided lower bound. Both these bounds and simulation results show that the BMST of short HT-coset codes performs well~(within one dB away from the corresponding Shannon limits) in a wide range of code rates

Performance analysis of IRA codes for underwater acoustic OFDM communication system

Recently, multicarrier modulation in the form of orthogonal frequency division multiplexing (OFDM) has been actively investigated in underwater acoustic communications for its effective algorithms to handle the channel time-variability. In order to improve the performance of the underwater acoustic OFDM communication system, the irregular repeat accumulate (IRA) code as a channel coding scheme is proposed in this paper. We analyzed the effect of parameters of the IRA code on the performance of the system. Computer simulation has been implemented and the sea trial has been carried out in shallow water acoustic channels near Xiamen port. The simulation results show that the IRA coding scheme has improved the SNR (signal noise ratio) performance of the system at range of 14dB to 16dB compared with the system without coding and the BER performance of the IRA code will get improvement with the increase of the code length and the iteration of decoding to a certain degree, and then tends to stable. Field test experiment results obtained with the IRA code are provided, demonstrating the feasibility of the proposed channel coding for underwater acoustic OFDM communication system

NB-JNCD Coding and Iterative Joint Decoding Scheme for a Reliable communication in Wireless sensor Networks with results

Privacy threat is a very serious issue in multi-hop wireless networks (MWNs) since open wireless channels are vulnerable to malicious attacks. A distributed random linear network coding approach for transmission and compression of information in general multisource multicast networks. Network nodes independently and randomly select linear mappings from inputs onto output links over some field. Network coding has the potential to thwart traffic analysis attacks since the coding/mixing operation is encouraged at intermediate nodes. However, the simple deployment of network coding cannot achieve the goal once enough packets are collected by the adversaries. This paper proposes non-binary joint network-channel coding for reliable communication in wireless networks. NB-JNCC seamlessly combines non-binary channel coding and random linear network coding, and uses an iterative two-tier coding scheme that weproposed to jointly exploit redundancy inside packets and across packets for error recovery

Applied research on RA codes in underwater acoustic ofDM communication system

正交频分复用(OrTHOgOnAl frEQuEnCy dIVISIOn MulTIPlEXIng,OfdM)技术由于具有频谱利用率高、抗多径能力强等优点,成为当前水声通信的研究重点和热点,但较高的峰均功率比(PEAk-TO-AVErAgE POWEr rATIO,PAPr)严重影响了水声OfdM通信系统的性能。采用重复累积码(rEPEAT ACCuMulATE,rA)作为信道编码方案,并用线性反馈移位寄存器(lInEAr fEEdbACk SHIfT rEgISTErS,lfSr)代替原rA码结构中的累加器,再通过选择映射(SElECTIVE MAPPIng,SlM)方法降低系统的峰均功率比。计算机仿真和水池实验结果表明,采用改进结构的rA码结合SlM技术能有效降低水声OfdM系统的PAPr,提高系统的性能,具有很好的应用前景。Orthogonal frequency division multiplexing(ofDM) technology has become the research focus and hotspot of underwater acoustic communications owing to its advantages such as high spectrum efficiency and robustness to multipath fading,but it possesses high peak-to-average power ratio(PAPR) which severely degrades the performance of Underwater Acoustic ofDM Communication System.In this paper,repeat accumulate(RA) code is adopted as the channel coding scheme,and linear feedback shift registers(LFSR) is used to replace the accumulator of original RA code structure,then selective mapping(SLM) method is also adopted to reduce the PAPR of system.Computer simulation and experimental results show that modified RA code and SLM can effectively reduce the PAPR and improve the per-formance of underwater acoustic ofDM communication system,which have a very good application prospect.研究基金访问学者项目(2011631504); 中央高校基础研究基金项目(201112G020和201212G012); 国家自然科学基金项目(41176032

Performance Analysis of Repeat-Accumulate Codes over Shallow Water Acoustic Channels

针对浅海水声信道的强多途、长时延、严重衰落等特点,需采用性能好、能够实现线性编译码便于实时处理的信道纠错码技术以提高水声通信系统可靠性的问题,提出重复累积(rEPEAT-ACCuMulATE,rA)码作为浅海水声信道的纠错码方案。建立rA码在浅海水声信道中的仿真模型,比较其在不同浅海水声信道模型下的性能,通过水池数据传输实验研究编译码参数对rA码性能的影响,并以水下图像传输实验进一步验证该编码方案。仿真和实验结果表明:rA码在浅海水声通信系统中具有较强的纠错能力,选择合适的参数会进一步提高编码增益。与TurbO码和ldPC码的编译码复杂度对比,rA码能够实现线性时间编译码,算法复杂度低,硬件实现简单,在水声通信中具有非常好的应用前景。Due to a large delay spread caused by multipath propagation and severe attenuation of the channel conditions,the Repeat-Accumulate(RA) code with short length codes,good performance and easy implementation has been proposed to enhance the reliability of the shallow water acoustic(SWA) communication system.A system model including RA coding over the SWA channels was established.As a comparison,the performance of RA codes under different ocean acoustic channel conditions was presented.The experiment in the pool was carried out to show how the encoding and decoding parameters affect the performance of RA codes,which was verified by the image transmission over channels in the pool tank.The simulation and experimental results show that RA codes have a strong error correction capability and the codes with appropriate parameters would further improve the coding gain,while they enjoy encoding and decoding in linear time and have simple hardware implementation,which have a good applied prospect in underwater acoustic communication system.国家自然科学基金资助项目(41176032);中央高校基本科研业务费专项资金资助项目(2010121032)(20112G020);厦门大学基础创新科研基金资助项目(201112G020

Ciphered BCH Codes for PAPR Reduction in the OFDM in Underwater Acoustic Channels

We propose an effective, low complexity and multifaceted scheme for peak-to-average power ratio (PAPR) reduction in the orthogonal frequency division multiplexing (OFDM) system for underwater acoustic (UWA) channels. In UWA OFDM systems, PAPR reduction is a challenging task due to low bandwidth availability along with computational and power limitations. The proposed scheme takes advantage of XOR ciphering and generates ciphered Bose–Chaudhuri–Hocquenghem (BCH) codes that have low PAPR. This scheme is based upon an algorithm that computes several keys offline, such that when the BCH codes are XOR-ciphered with these keys, it lowers the PAPR of BCH-encoded signals. The subsequent low PAPR modified BCH codes produced using the chosen keys are used in transmission. This technique is ideal for UWA systems as it does not require additional computational power at the transceiver during live transmission. The advantage of the proposed scheme is threefold. First, it reduces the PAPR; second, since it uses BCH codes, the bit error rate (BER) of the system improves; and third, a level of encryption is introduced via XOR ciphering, enabling secure communication. Simulations were performed in a realistic UWA channel, and the results demonstrated that the proposed scheme could indeed achieve all three objectives with minimum computational powerThis research was funded by a grant from the Spanish Ministry of Science and Innovation in the framework of the project “NAUTILUS: Swarms of underwater autonomous vehicles guided by artificial intelligence: its time has come” (PID2020-112502RB / AEI / 10.13039/501100011033). Partial funding for open access charge: Universidad de Málag