基于交叉传输的水声通信网络MAC协议

为了解决传统TDMA协议在水下环境信道利用率低的问题,提出了交叉传输的TDMA (I-TDMA)协议.该协议利用水声信道长传输时延的特性,采用数据分组交叉传输的方法改善信道利用率,同时引入了拓扑扩展和循环同步机制,增强了网络系统的可扩展性.仿真结果表明,该协议与传统的TDMA协议相比减少了数据分组时延以及同步开销,具有更好的性能.     

多幅度数字脉冲间隔调制的水下无线光通信研究

为了研究适用于水下无线光通信的调制方式,采用分析水下无线光通信的信道模型、并推导该信道中用多幅度数字脉冲间隔调制方式的误包率表达式、带宽利用率和功率利用率的方法,对不同调制方式进行了理论分析比较.结果表明,多幅度数字脉冲间隔调制的带宽利用率和功率利用率最高.这一结果对选择适合用于水下无线光通信的调制方式是有帮助的.     

视频压缩与信号复接系统设计

为了满足视频信号传输的高实时性,提高无线信道的利用率,设计并实现了一种以专用视频压缩芯片ADV202实现视频信号压缩,并采用FPGA为信号复接单元的视频压缩与信号复接系统。系统中通过ADV202实现了基于JPEG2000的视频数据压缩,保证了信号传输的高实时性;并通过FPGA实现对压缩数据的复接,提高了无线信道的利用率。     

链路层中速率自适应方法研究

速率自适应技术是一种链路自适应方法,它在特定时间内根据信道质量状况选择最佳的数据发送速率。对于支持多速率传输的无线系统来说,采用速率自适应技术之后系统能够在很好地保证服务质量的同时有效地增大网络吞吐量,提高无线链路的利用率,更好地利用时变信道的有限带宽。文章将速率自适应过程划分为信道质量估计和速率选择两个阶段,并对它们分别进行了详细分析,进而得出了速率自适应技术的基本研究方法。     

适用于AMI的有线无线融合数据传输方法

针对AMI的需求和有线/无线系统各自的不足,提出了一种适用于AMI的有线无线融合的数据传输系统及方法.该系统将有线传输和无线传输有机地结合起来,实现了系统与环境和信道特性相适应的传输方案的灵活选择;采用OFDM技术,增强了系统的抗干扰性能,提高了数据传输率;通过多种调制模式的设计,使系统在可靠稳定的前提下拥有尽可能高的速率;通过有线无线的基带复用,简化了系统设计,节约了系统成本.     

针对块稀疏信道的估计算法

无线多径信道中存在着块稀疏结构。针对块稀疏信道中分块信息是否已知的不同场景,分别提出了两种基于块稀疏贝叶斯学习(BSBL)框架的OFDM系统信道估计算法。这两种算法根据边界最优(BO)方法估计信道分块的稀疏度参数,提升算法运算速率。为进一步提升信道估计性能,在基于BSBL框架算法仅利用导频信号估计信道的基础上,又提出了基于联合块稀疏贝叶斯学习(JBSBL)的信道估计新算法,该算法利用导频与数据子载波实现信道的联合估计。仿真结果表明,与传统的最小二乘算法比较,本文提出的算法均可获得很好的信道估计性能,且基于JBSBL的信道估计算法性能更佳。      

基于IP over TS系统网段内地址扩展技术的研究

针对IP over TS 系统研究同一网段内的地址扩展技术,分析常用的链路扩展方法,在无线链路传输中针对该方法所导致的信道有效占有率不稳定且不足提出邻接表法.为了增强邻接表法的地址扩展灵活性将邻接表法改进为自适应邻接表法.测试结果表明,自适应邻接表法解决了同一网段内的地址扩展问题.同时提高了无线信道有效数据的占有率和稳定性.     

机会网络视频数据的分块渐进传输新方法

各类移动多媒体智能终端的普及使得设备间的自组织机会通信成为国际研究热点,而移动节点间的机会通信方式已无法满足日益增长的多媒体传输需求.面向机会组网与视频内容传输问题,基于机会网络实际通信能力计算,提出了一种视频分块大小最优化计算方法,使机会网络通信能力得到最大化利用;提出了一种能够实现渐进式接收视频分块的路由调度算法,建立分块紧缺度模型,引导分块在目标节点趋于均匀分布.实验结果表明,该方法能在恶劣通信环境下实现高效的视频数据预览与传输,可为相关视频内容的无线移动传输提供支持.     

一种基于OFDM信号加窗设计的实现方法

给出一种基于OFDM信号加窗设计的FPGA的具体实现方法,并通过无线传输信号在加窗前后带外能量大小的比较,说明该方法可以迅速地降低无线传输信号的带外能量,减少无线传输信号的带外辐射,降低无线信道污染以及对周围设备的干扰.     

多天线OFDM系统中的自适应子信道分配和天线选择

针对多用户MIMO-OFDM系统,提出自适应子信道分配算法.首先将相邻的子载波分块成若干子信道,在分配子信道的时候优先考虑平均信道容量小的用户,并且将相对利用度大的子信道分配给该用户,从而在频谱利用率和公平性上具有较好的性能.为了降低发送端的硬件复杂度以及非线性因素的影响,将自适应信道分配和发送天线选择相结合,提出联合自适应子信道分配和天线选择算法.仿真结果表明,本文提出的联合算法具有较高的频谱效率和较低的中断概率.     

Noncoherent block detection in the presence of DC offset

In this paper, we deal with noncoherent detection of a digitally phasor block-modulated signal in the additive white Gaussian noise channel when a direct-current (DC) offset is present in the receiver baseband processing. By processing the received baseband signal block by block, a generalized linear transform is used to remove the offset prior to data detection, thereby releasing the succeeding detection process from the threat of DC offset. Operating on transform output blocks, a generalized maximum-likelihood scheme is developed for noncoherent data detection without a priori knowledge of channel amplitude and phase. When all the signaling blocks are confined within the space expanded by the basis vectors obtained from the onset-removal transform matrix, the proposed detection scheme can exploit the advantage of performing data detection and estimation on channel amplitude and phase jointly in the maximum-likelihood sense. It is analytically shown that the block detection scheme provides the bit error performance asymptotically approaching that of the corresponding ideal coherent phase-shift-keyed (PSK) detection in the absence of DC offset when the block length is increased. An iterative detection scheme is also modified from the block detection scheme to simplify the realization complexity. Both block and iterative detection schemes are shown to outperform the conventional training-sequence-aided PSK detection scheme under the same transmission throughput efficiency.     

iFrag: interference-aware frame fragmentation scheme for wireless sensor networks

Reliable data transmission is a fundamental challenge in resource-constrained wireless sensor networks. In current implementations, a single bit error requires retransmitting the entire frame. This incurs extra processing overhead and power consumption, especially for large frames. Frame fragmentation into small blocks with individual error detection codes can reduce the unnecessary retransmission of the correctly received blocks. The optimal block size, however, varies based on the wireless channel conditions. In this paper, we propose an interference-aware frame fragmentation scheme called iFrag. iFrag dynamically adjusts the number of blocks inside a frame based on current channel conditions, and effectively addresses all challenges associated with such dynamic partitioning. Through analytical and experimental results, we show that iFrag achieves up to \(3\times\) improvement in goodput when the channel is noisy, while reducing the delay by 12 % compared to other static fragmentation approaches. On average, it shows a 13 % gain in goodput across all channel conditions used in our experiments. Our testbed results also show that iFrag lowers the energy consumed per useful bit by 60 %, as improved data transmission reliability reduces the number of frame retransmissions which increases the motes energy efficiency.     

Intercarrier interference in MIMO OFDM

In this paper, we examine multicarrier transmission over time-varying channels. We first develop a model for such a transmission scheme and focus particularly on multiple-input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM). Using this method, we analyze the impact of time variation within a transmission block (time variation could arise both from Doppler spread of the channel and from synchronization errors). To mitigate the effects of such time variations, we propose a time-domain approach. We design ICI-mitigating block linear filters, and we examine how they are modified in the context of space-time block-coded transmissions. Our approach reduces to the familiar single-tap frequency-domain equalizer when the channel is block time invariant. Channel estimation in rapidly time-varying scenarios becomes critical, and we propose a scheme for estimating channel parameters varying within a transmission block. Along with the channel estimation scheme, we also examine the issue of pilot tone placement and show that in time-varying channels, it may be better to group pilot tones together into clumps that are equispaced onto the FFT grid; this placement technique is in contrast to the common wisdom for time-invariant channels. Finally, we provide numerical results illustrating the performance of these schemes, both for uncoded and space-time block-coded systems.     

基于块调制的MIMO-OFDM系统

该文在MIMO-OFDM系统中提出基于块调制的OFDM算法,降低了循环前缀(CP)所占的系统开销。在每个发射天线,将P个OFDM符号联合调制组帧后共用一个CP,到达接收天线后,接收帧经过分解可得到P个接收数据块,各数据块无相互间干扰。其中第p个接收数据块等于各个发射天线的第p个OFDM符号通过MIMO信道后到达接收天线的和,该文算法与传统MIMO-OFDM系统本质上传输方式相同,因而传输性能也相同,而频带效率则明显提高。     

A digital transmission system with very high immunity to dynamicmultipath distortion

This paper describes a novel solution to the problem of bandwidth-efficient digital signal transmission in the presence of dynamic multipath distortion. A burst transmission is comprised of two consecutive data blocks with identical data that have been processed differently. The two data blocks are transmitted adjacent to each other in time so that the time-variable transmission channel will apply approximately the same linear distortion to each block. At the receive site, the two blocks are captured and processed together to cancel the effects of the linear distortion, while adding the signal energy from each block     

Fast turbo codes with space‐time block codes in fast fading channels

In this paper, space‐time block coding has been used in conjunction with Turbo codes to provide good diversity and coding gains. A new method of dividing turbo encoder and decoder into several parallel encoding and decoding blocks is considered. These blocks work simultaneously and yield a faster coding scheme in comparison to classical Turbo codes. The system concatenates fast Turbo coding as an outer code with Alamouti's G2 space‐time block coding scheme as an inner code, achieving benefits associated with both techniques including acceptable diversity and coding gain as well as short coding delay. In this paper, fast fading Rayleigh and Rician channels are considered for discussion. For Rayleigh fading channels, a fixed frame size and channel memory length of 5000 and 10, respectively, the coding gain is 7.5 dB and bit error rate (BER) of 10^?4 is achieved at 7 dB. For the same frame size and channel memory length, Rician fading channel yields the same BER at about 4.5 dB. Copyright © 2013 John Wiley & Sons, Ltd.     

Low-Complexity Channel Estimation for Wireless Block Transmission Systems in Time-and Frequency-Selective Rayleigh Fading Channels

Mobility-induced Doppler spread and multipath propagation introduce the time- and frequency-selectivity (doubly selectivity) in fading channels. Based on the complex exponential basis expansion model (BEM) to approximate the doubly selective channel (DSC), a low-complexity channel estimation scheme for block transmission systems over DSC are developed in this paper. Using the developed scheme, the long data block is divided into a few short data subblocks in terms of the maximum normalized Doppler frequency and block length, and each subblock is performed to respective channel estimation. Thus the total calculation complexity is effectively decreased because the number of the BEM channel coefficients to estimate is greatly reduced for each sub-block. Moreover, by utilizing these channel estimation values to refit the true channel, we can obtain better channel estimation. Besides, the normalized mean square error (NMSE) expressions for the developed scheme and the existing scheme are derived in detail, respectively. Compared to the existing scheme, the proposed scheme has lower calculation complexity and superior performance. The simulation results verify the effectiveness of the developed scheme, and the theory values of the derived NMSE accord with corresponding simulation values.     

Signal Processing for Passive Radar Using OFDM Waveforms

Passive radar is a concept where illuminators of opportunity are used in a multistatic radar setup. New digital signals, like Digital Audio/Video Broadcast (DAB/DVB), are excellent candidates for this scheme, as they are widely available, can be easily decoded to acquire the noise-free signal, and employ orthogonal frequency division multiplex (OFDM). Multicarrier transmission schemes like OFDM use block channel equalization in the frequency domain, efficiently implemented as a fast Fourier transform, and these channel estimates can directly be used to identify targets based on Fourier analysis across subsequent blocks. In this paper, we derive the exact matched filter formulation for passive radar using OFDM waveforms. We then show that the current approach using Fourier analysis across block channel estimates is equivalent to the matched filter, based on a piecewise constant assumption on the Doppler-induced phase rotation in the time domain. We next present high-resolution algorithms based on the same assumption: first we implement MUSIC as a 2-D spectral estimator using spatial smoothing; then we use the new concept of compressed sensing to identify targets. We compare the new algorithms and the current approach using numerical simulation and experimental data recorded from a DAB network in Germany.      

基于频谱感知的业务分割-合并的弹性光网络资源分配策略

针对弹性光网络中业务分割的资源分配策略消耗更多保护带与设备端口,浪费频谱资源和增加网络能耗的问题,该文提出一种频谱感知的业务分割再合并的资源分配策略。为新业务分配频谱资源时,先计算路径上总链路剩余频谱连续度,选择使剩余频谱连续度最大频谱块传输业务;当路径上频隙数不满足业务传输需求空闲频谱块时,将该业务分割为多个子业务,尽可能选取使剩余频谱连续度最大的多个频谱块承载各子业务。当监视到子业务传输路径上有可用频隙数满足业务传输所需空闲频谱块时,计算剩余频谱连续度作为子业务合并触发的判决条件,将子业务再合并后继续传输。仿真结果表明该文提出的策略能有效降低网络的带宽阻塞率,并节约网络的能耗。     

Transform domain inter-block interleaving schemes for robust image and video transmission in ATM networks

Data interleaving schemes have proven to be an important mechanism in reducing the impact of correlated network errors on image/video transmission. Current interleaving schemes fall into two main categories: (a) schemes that interleave pixel intensity values and (b) schemes that interleave JPEG/MPEG transform blocks. The schemes in the first category suffer in terms of lower compression ratio since highly correlated information in the spatial domain is de-correlated prior to compression. The schemes in the second category interleave DCT transformed blocks. In this case, in the absence of ARQ, if a packet is lost, an entire block may be lost thus yielding poor image quality and making the error concealment task difficult. Interleaving transform coefficients is tricky and error concealment in the presence of lost coefficients is challenging. In this paper, we develop three different interleaving schemes, namely Triangular, Quadrant, and Coefficient, that interleave frequency domain transform coefficients. The transform coefficients within each block are divided into small groups and groups are interleaved with the groups from other blocks in the image, hence they are referred to as inter-block interleaving schemes. The proposed schemes differ in terms of group size. In the Triangular interleaving scheme AC coefficients in each block are divided into two triangles and interleaving is performed among triangles from different blocks. In the Quadrant interleaving scheme, coefficients in each block are divided into four quadrants and quadrants are interleaved. In the Coefficient interleaving scheme, each coefficient in a block is a group and it is interleaved with the coefficients in other blocks. The compression ratio 3 of the proposed interleaving schemes is impressive ranging from 90 to 98% of the JPEG standard compression while providing much higher robustness in the presence of correlated losses. We also propose two new variable end-of-block (VEOB) techniques, one based on the number of AC coefficients per block (VAC-EOB) and the other based on the number of bits per block (VB–EOB). Our proposed interleaving techniques combined with VEOB schemes yield significantly better compression ratios compared to JPEG (2–11%) and MPEG-2 (3–6.7%) standards while at the same time improve the resilience of the coded data in the presence of transmission errors.