Wireless video transmission using feedback-controlled adaptive h.264 source and channel coding

For wireless video, the present paper demonstrates that combining adaptive source and channel coding can provide a robust service over a wide range of transmission channel conditions. Various feedback-controlled adaptive coding solutions are considered for orthogonal frequency-division multiplexing-based systems. At the receiver, the reliabilities of subchannels (SCHs) are estimated and decisions are fed back to the transmitter to adapt modulation modes and channel code-rates to provide reliable transmission and yet avoid over-protection. The resulting available transmission capacity (which can vary widely with channel conditions) can inform an online collaborating source coder which itself exploits the available feedback to reduce error propagation. To ensure further improvement for fading channels, an efficient low-delay retransmission arrangement is also considered in which only the contents of unreliable SCHs within an erroneous packet are retransmitted. Simulation results demonstrate that such collaborative adaptive source and channel coding can provide efficient use of a continuously varying wireless channel.     

一种利用数据分类和RS误码保护的H.263++抗误码算法

从最新的H.263 Annex V选项出发，提出了一个基于数据分类封装和编码信息RS误码保护的抗误码算法，在不过多增加码率的前提下，提供更强的误码抵抗力，实验结果表明，本编码算法在高衰码的无线信道条件下具有比以前一般算法更好的适应性和更强的健壮性。     

Integrated channel assignment and data aggregation routing problem in wireless sensor networks

In wireless sensor networks, data aggregation routing could reduce the number of data transmission so as to achieve efficient total energy consumption. However, this kind of data aggregation introduces data retransmission that is caused by co-channel interference from neighbouring sensor nodes. Hence, more data aggregation leads to more extra energy consumption and significant retransmission delay from retransmission. This could jeopardise the benefits of data aggregation. One possible solution to circumvent retransmission caused by co-channel interference is to assign different channel to every sensor node that is within each other's interference range on the data aggregation tree. As the number of non-overlapping channels is limited in wireless networks, it is unlikely that we could assign a different channel to every sensor node on the data aggregation tree. Then, an interesting problem is to perform data aggregation routing in conjunction with channel assignment to minimise total transmission power under limited number of non-overlapping channels. This problem is an NP-complete problem. We devise heuristic algorithm, Iterative Channel Adjustment Data Aggregation Routing algorithm (ICADAR), and other three heuristics, to tackle this problem. From the simulation results, the ICADAR algorithm outperforms the other three algorithms under all experimental cases.     

Multi-channel medium access control protocol with channel distribution for mobile ad hoc networks

This study proposes a novel multi-channel medium access control protocol for mobile ad hoc networks that enables nodes to transmit packets in distributed channels. In our protocol, the ad hoc traffic indication message window is divided into two windows. The first window is called the deciding channel window (DCW). Source and destination nodes can negotiate with each other in deciding a channel that can be used to compete for the final data channel in the DCW. The second window is called the exchanging packet window (EPW). Pair source and destination nodes can compete to obtain a channel to transfer packets in the EPW. This mechanism can distribute pair source and destination nodes to compete for a data channel. Hence, because of this, collisions can be avoided greatly and throughput can be increased. The simulation results show that our protocol successfully exploits the use of the bandwidth of multiple channels effectively.     

基于校验式判决的LDPC码编码的HARQ协议

针对RB-HARQ协议系统开销巨大的问题,提出一种基于校验式判决的HARQ协议.该协议根据不成立的校验式与错误比特之间的关系,将一部分不成立的校验式的序号通过反馈信道反馈给发射机,发射机按照一定的规则将这些校验式所包含的某些比特确定为重传比特,重新发送给接收端,接收端将重传的比特与先前发送的码字进行最大比合并,最后进行译码.数值仿真结果表明,由于只需要反馈一部分校验式的序号,该协议能够有效降低系统的开销,其吞吐量性能能够接近RB-HARQ协议.     

基于分组差错控制的轨道交通ATS信号可靠组播技术研究

为解决轨道交通中ATS信号组播丢包问题,拟定一种基于分组差错控制的可靠组播传输协议。该协议不需要路由器的支持,在每个接收节点都定义一个申请重传权值列表,根据组播丢包情况,动态更新接收节点的权值列表,从而为接收节点选择最佳的重传请求处理节点,以提高数据重传效率。仿真实验表明：在多个分组中,将该文所提出的基于分组差错控制的可靠组播传输协议应用于轨道交通中ATS信号仿真系统中,与传统的可靠组播传输协议相比,能有效减少差错修复时延,并提高系统整体的吞吐率。     

Differentiated cooperative multiple access for multimedia communications over fading wireless networks

The quality of service (QoS) support for multimedia communications faces a big challenge in a fading wireless network. On one hand, conventional automatic repeat request (ARQ) schemes are not effective for small-scale fading channels with correlated errors due to consecutive retransmission failures. On the other hand, large-scale fading due to propagation loss or shadowing severely limits transmission range. A novel differentiated cooperative medium access control (MAC) protocol, called DC-MAC, is proposed to enhance the QoS support for multimedia communications while supporting service differentiation based on the IEEE 802.11e architecture. By enabling cooperative ARQ, the retransmission is initiated from an appropriate transmission queue of an appropriate relay node instead of the original source. Since unnecessary and useless retransmissions may intensify the node contention and degrade the system performance contrarily, a novel negative acknowledgement feedback mechanism is introduced for loss distinguishing and channel estimation such that cooperative retransmission will be employed only when necessary and only by competent nodes. Extensive simulations are conducted on the OPNET platform to analyse the performances of DC-MAC under both small-scale and large-scale fading. Simulation results show that the proposed scheme significantly improves the performances of both multimedia applications and best-effort data applications in terms of throughput, delay and coverage with moderate user contention.     

HARQ Optimization for PDCP Duplication-Based 5G URLLC Dual Connectivity

Packet duplication (PD) with dual connectivity (DC) was newly introduced in the 5G New Radio (NR) specifications to meet the stringent ultra reliable low latency communication (URLLC) requirements. PD technology uses duplicated packets in the packet data convergence protocol (PDCP) layer that are transmitted via two different access nodes (ANs) to the user equipment (UE) in order to enhance the reliability performance. However, PD can result in unnecessary retransmissions in the lower layers since the hybrid automatic retransmission request (HARQ) operation is unaware of the transmission success achieved through the alternate DC link to the UE. To overcome this issue, in this paper, a novel duplication-aware retransmission optimization (DRO) scheme is proposed to reduce the resource usage induced by unnecessary HARQ retransmissions. The proposed DRO scheme can minimize the average channel use while satisfying the URLLC requirements. The proposed DRO scheme derives the optimal HARQ retransmission attempts for different ANs by solving a nonlinear integer programming (NLIP) problem. The performance of the proposed DRO scheme was evaluated using MATLAB simulation and is compared to the existing 5G HARQ support schemes. The simulations results show that the proposed DRO scheme can provide a 14.71% and 15.11% reduced average channel use gain compared to the selective data duplication upon failure (SDUF) scheme and latency-aware dynamic multi-connectivity algorithm (LADMA) scheme, respectively, which are the existing 5G PD schemes that use HARQ.     

Distributed truncated ARQ protocol for cooperative diversity networks

Automatic repeat request (ARQ) retransmission in user cooperative networks, which use amplify-and-forward as a relaying strategy is dealt with. In contrast to the conventional environments, where the source responds in a retransmission demand, in cooperative systems this requirement can also be satisfied by a relay node. In addition, if a relay node can be selected according to the instantaneous channel conditions, the source is not always the optimal responder. The problem under consideration here is to find the retransmission combination which optimises the performance under a given delay quality-of-service constraint. It will be shown that the optimal combination depends on the number of available relays, the total number of retransmissions and the average signal-to-noise ratio. We provide an analytical framework for the definition of the optimal combination in function of these three system parameters. Since the practical ad hoc networks are not centralised and do not have an external control, a distributed truncated ARQ protocol is further proposed to apply the decided retransmission combination.     

Iterative optimization for joint design of source and channel codes using genetic algorithms

Abstract

This paper presents a novel algorithm for the joint design of source and channel codes. In the algorithm, channel‐optimized vector quantization (COVQ) and rate‐punctured convolutional coding (RCPC) are used for design of the source code and the channel code, respectively. We employ the genetic algorithm (GA) to prevent the design of COVQ from falling into a poor local optimum. We also adopt the GA to reduce the computational time needed for realizing the unequal error protection scheme best matched to the COVQ. Both the GA‐based source coding and channel coding scheme are then iteratively combined to achieve a near global optimal solution for the joint design. Numerical results show that the algorithm can be an effective alternative for applications where high rate‐distortion performance and low computational complexity are desired.     

Quasi-Cyclic LDPC Codes for the Magnetic Recording Channel: Code Design and VLSI Implementation

By implementing a field-programmable gate array (FPGA)-based simulator, we investigate the performance of randomly constructed high-rate quasi-cyclic (QC) low-density parity-check (LDPC) codes for the magnetic recording channel at very low block sector error rates. On the basis of extensive simulations, we conjecture guidelines for designing randomly constructed high-rate regular QC-LDPC codes with low error floor for the magnetic recording channel. Experimental results show that our high-rate regular QC-LDPC codes do not suffer from error floor, at least at block error rates of 10^-9, and can realize significant coding gains over Reed-Solomon codes that are used in current practice. Furthermore, we develop a QC-LDPC decoder hardware architecture that is well suited to achieving high decoding throughput. Finally, to evaluate the implementation feasibility of LDPC codes for the magnetic recording channel, using 0.13 mum standard cell and memory libraries, we designed a read channel signal processing datapath consisting of a parallel max-log-MAP detector and a QC-LDPC decoder, which can achieve a throughput up to 1.8 Gb/s     

Concatenated coded modulation techniques and orthogonal space-time block codes in the presence of fading channel estimation errors

Performance of coding and modulation systems in fading channels is usually analysed under the assumption that the receiver has perfect knowledge of channel condition. However, various shortcomings in practical channel estimation techniques lead to imperfections, resulting in channel estimation errors. The authors analyse a practical coding and modulation scheme for multiple-antenna systems considering channel estimation errors. The novelty of this study resides in providing error probability bounds for concatenated trellis coded modulation (TCM) or bit-interleaved coded modulation (BICM) schemes with orthogonal space--time block codes (OSTBC) under imperfect channel estimation assumption. Moreover, our analytical results quantify the performance degradation associated with various levels of channel estimation error variance. The authors also show that if channel estimation quality does not improve sufficiently with SNR, there would be error floor in performance, such that the coded system could get outperformed by a system with differential signalling that requires no channel estimation. Simulation results are presented, which confirm the validity of the analytical results.     

提高MPEG-2信噪比可分级视频编码效率的研究

采用信噪比可分级性的双层视频编码可以用于提供在信道资源不可靠情况下视频信号的恢复,然而,信噪比可分级编码的这一优点是以增加总比特率为代价的。针对这一问题,提出了一个新的基于率失真理论的优化方法,称为最优系数调整法。实验表明采用该方法可以提高编码效率并且效果优于传统的Thresholding算法。     

Using Embedded Dynamic Random Access Memory to Reduce Energy Consumption of Magnetic Recording Read Channel

Although the performance of a magnetic recording read channel can be improved by employing advanced iterative signal detection and coding techniques, the method nevertheless tends to incur significant silicon area and energy consumption overhead. Motivated by recent significant improvement of high-density embedded dynamic random access memory (eDRAM) towards high manufacturability at low cost, we explored the potential of integrating eDRAM in read channel integrated circuits (IC) to minimize the silicon area and energy consumption cost incurred by iterative signal detection and coding. As a result of the memory-intensive nature of iterative signal detection and coding algorithms, the silicon cost can be reduced in a straightforward manner by directly replacing conventional SRAM with eDRAM. However, reducing the energy consumption may not be trivial. In this paper, we present two techniques that trade eDRAM storage capacity to reduce the energy consumption of iterative signal detection and coding datapath. We have demonstrated dDRAM's energy saving potential by designing a representative iterative read channel at the 65 nm technology node. Simulation shows that we can eliminate over 99.99% of post-processing computation for dominant error events detection, and achieve up to a 67% reduction of decoding energy consumption.     

Efficient secure channel coding based on quasi-cyclic low-density parity-check codes

A secure channel coding (joint encryption-channel coding) scheme provides both data security and reliability in one combined process to achieve faster processing and/or more efficient implementation. The issue of using quasi-cyclic low-density parity-check (QC-LDPC) codes in a symmetric-key secure channel coding scheme is addressed. A set of this class of LDPC codes has recently been recommended by the NASA Goddard Space Flight Center for near-earth and deep-space communications. The proposed scheme provides an efficient error performance, an acceptable level of security and a low-complexity practicable implementation. The results indicate that the proposed scheme can efficiently employ large QC-LDPC codes to achieve a relatively smaller secret-key size to be exchanged by the sender and the receiver, and higher information rates in comparison with the previous symmetric-key McEliece-like schemes. Simulation results indicate that there is no trade-off between the error performance and the security level of the proposed scheme unlike that of the previous ones. These characteristics make the proposed scheme suitable for high-speed communications, such as satellite communication systems.     

光通信系统中一种新颖的级联码型

基于级联码对光通信系统中级联码特性和ITU-T G.975.1中两种超强前向纠错(SFEC)码型进行分析和研究后,提出了一种新颖的RS(255,239) BCH(1023,963)级联码型.仿真表明,该码型与ITU-T G.975.1中RS(255,239) CSOC(k0/n0=6/7,J=8)码相比较,具有更低的冗余度和更好的纠错性能,并且在经过三次迭代且误码率(BER)为10-12时其净编码增益(NCG)比ITU-T G.975.1中RS(255,239) CSOC(k0/n0=6/7,J=8)码和BCH(3860,3824) BCH(2040,1930)码要分别大0.60 dB和0.57 dB.因而,它更适用于超长距离、超大容量和超高速的光通信系统中,并可以作为SFEC码的一种候选码型.     

Performance of Reed?Solomon codes using the Guruswami?Sudan algorithm with improved interpolation efficiency

List decoding is a novel method for decoding Reed-Solomon (RS) codes that generates a list of candidate transmitted messages instead of one unique message as with conventional algebraic decoding, making it possible to correct more errors. The Guruswami-Sudan (GS) algorithm is the most efficient list decoding algorithm for RS codes. Until recently only a few papers in the literature suggested practical methods to implement the key steps (interpolation and factorisation) of the GS algorithm that make the list decoding of RS codes feasible. However, the algorithm's high decoding complexity is unsolved and a novel complexity-reduced modification to improve its efficiency is presented. A detailed explanation of the GS algorithm with the complexity-reduced modification is given with simulation results of RS codes for different list decoding parameters over the AWGN and Rayleigh fading channels. A complexity analysis is presented comparing the GS algorithm with our modified GS algorithm, showing the modification can reduce complexity significantly in low error weight situations. Simulation results using the modified GS algorithm show larger coding gains for RS codes with lower code rates, with more significant gains being achieved over the Rayleigh fading channels.     

Measurements of radio channels and bit error rate estimation of IEEE802.16 standard in semi-rural environment at three frequencies in the 2?6 GHz frequency band

Simultaneous measurements with 10 MHz bandwidth at 2.5, 3.5 and 5.8 GHz were performed in a rural/semi-rural environment in the UK. The measurements were processed to generate power delay profiles to estimate the root mean square delay spread of the channel. The frequency range of the orthogonal frequency division multiplexing (OFDM) symbol bandwidth that has dropped below a predefined level, termed herein as average fade bandwidth, and the corresponding level crossing are employed to quantify the severity of frequency selectivity. The channel data were used to estimate the bit error rate, for the 256 carrier-OFDM IEEE802.16 standard using a frequency domain channel simulator especially designed for the study. It was found that the performance of quasi-stationary wireless broadband systems depends mainly upon the frequency selectivity and the channel coding rate with 1/2 rate coding giving a superior performance to 3/4 rate coding. Puncturing was found to weaken the capability of forward error correction coding in the presence of series of deep fades in the channel transfer function.     

Use of Low-Density Parity-Check Codes for Dominant Error Events Detection and k-Constraint Enforcement

In this paper, we propose to leverage the simple and explicit parity checks inherent in low-density parity-check (LDPC) codes to detect dominant error events without code rate penalty. This is enabled by enforcing a very weak constraint on the LDPC code parity check matrix structure. Such a constraint can be readily satisfied by most structured LDPC codes reported in the open literature, such as quasi-cyclic (QC) LDPC codes. Moreover, this zero-redundancy dominant error events detection can be extended to handle the bit errors that occur when deliberate bit-flipping is used to enforce -constraints. We have demonstrated the effectiveness of the proposed method in computer simulations.     

Application-controlled handover for heterogeneous multiple radios over fibre networks

The wired-wireless integration network can be categorised as fixed mobile convergence (FMC). FMC means the convergence of the existing wired network and wireless network. Therefore a mobile device needs the function of connection and control to the FMC infrastructure. An application-controlled handover is developed, which keeps channel continuity in the wired-wireless synergy network environment that consists of 3G (UMTS) t WLAN t WPAN (UWB) and optical fibre network. A handover mechanism transmits and receives data by using the proposed application selection criteria. It maintains the channel and the seamless transmission from mobile device to the remote optical fibre network, to provide real-time service continuity for multimedia traffic. The results show that application-controlled handover has a reduction up to 83% in packet drop, 74% reduction in bit error rate, 85% reduction in power consumption and 100% enhancement in application response time (delay) as compared with the network without handover technique.