无阈下信道签名方案及其应用

介绍了开展封闭阈下信道签名研究的意义，综述了它们新的研究成果和应用。最后提出了若干有待进一步研究的问题。     

Enhancing multi-hop communication over multi-radio multi-channel wireless mesh networks: A cross-layer approach

The multi-channel multi-radio technology represents a straightforward approach to expand the capacity of wireless mesh networks (WMNs) in broadband wireless access scenarios. However, the effective leveraging of this technology in WMNs requires (i) enhanced MAC protocols, to coordinate the access to multiple channels with a limited number of radio interfaces, and (ii) efficient channel allocation schemes, to mitigate the impact of co-channel interference. The design of channel assignment schemes and MAC protocols is strictly interrelated, so that joint design should be considered to optimize the mesh network performance. In this paper, a channel assignment and fast MAC architecture (CAFMA) is proposed, which exploits the benefits provided by the multi-channel multi-radio technology to (i) enhance the performance of multi-hop communications, (ii) maximize the resource utilization, and (iii) support differentiation of traffic classes with different quality of service (QoS) requirements. CAFMA is designed with a cross-layer approach and includes (1) a novel MAC scheme, which provides multi-channel coordination and fast data relaying over multi-hop topologies, and (2) a distributed channel allocation scheme, which works in cooperation with the routing protocol. Simulation results confirm the effectiveness of CAFMA when compared with other single-layer and cross-layer solutions for multi-radio multi-channel WMNs.     

ICRN功率分配与中继选择联合优化

针对工业认知无线电网络中出现的无线干扰和冲突严重,特别是工业现场的金属环境和移动特性造成多径与阴影衰落,从而使得传输可靠性难以保证的问题,引入感知信道概率及信道可用度概念,提出一种联合优化中继选择与功率分配的算法。该算法给出3种认知中继选择方案,分别是信道增益最大准则、最近准则及调和平均准则,并在源节点和所选中继节点之间进行最优功率分配,以最小化网络中断概率。仿真结果表明,与平均功率分配算法相比,所提算法能更好地降低系统中断概率,提高传输可靠性。     

一种虚拟信道动态调度方案在CCSDS AOS中的分析

本文分析了高级在轨系统中常用的几种虚拟信道调度策略。针对同步/异步混合调度策略中同步业务流和异步业务流占用物理信道比率这一关键问题,提出了一种基于各用户的数据速率(实时数据)和剩余数据量(回放数据)的实时动态调度方案,保证同步/异步业务流高效、公平的共用同一物理信道。     

一种MIMO-OFDM系统空频分组码相位校正技术

对于MIMO-OFDM系统,本文指出如果直接将空频分组码SFBC与使用了跨符号插值信道估计算法和“增/扣脉冲”同步技术的OFDM方案相结合,那么由后者引入的时域循环移位操作会破坏SFBC算法对于信道假设的有效性,从而导致空频分组码译码性能下降。针对这一现象,本文提出了一种频域相位校正的方法,使得校正后的等效频域信道能重新满足空频码对于信道的要求,进而使这类MIMO-OFDM系统在工程中更具有实用价值。     

Dynamically adaptive channel reservation scheme for cellular networks

In personal communications networks (PCN) supporting network-wide handoffs, new and handoff requests compete for connection resources in both mobile and backbone networks. Forced call terminations due to handoff call blocking are generally more objectionable than new call blocking. In general, most of the previously proposed schemes for radio channel allocation in cellular networks reduce handoff call blocking probability substantially at the expense of increasing the new call blocking probability by giving higher priority to handoff calls over new calls in admission control. This reduces the total admitted traffic and results in inefficient utilization of wireless channels. The tradeoff between the new and handoff calls blocking probabilities should be defined on importance basis. In this paper, we propose a performance metric equation that makes a trade off between the two probabilities depending on the network preferences. Using this equation, we study the performance of various proposed channel reservation schemes. Also in this paper, a new dynamically adaptive channel reservation scheme (DACRS) is developed and compared with other schemes proposed in the literature. The DACRS assigns handoff-reserved channels to new calls depending on the locality principle in which the base station with the help of location estimation algorithms in the mobile location center predicts the position of the mobile terminal. Eventually, the DACRS is designed to improve channel utilization while satisfying the QoS of the calls. As will be shown analytically and through simulation, the DACRS outperforms current reservation schemes and results in more statistical gain, and powerful channel utilization.     

Performance analysis of a threshold based distributed channel allocation algorithm for cellular networks

Rapid advances of the handheld devices and the emergence of the demanding wireless applications require the cellular networks to support the demanding user needs more effectively. The cellular networks are expected to provide these services under a limited bandwidth. Efficient management of the wireless channels by effective channel allocation algorithms is crucial for the performance of any cellular system. To provide a better channel usage performance, dynamic channel allocation schemes have been proposed. Among these schemes, distributed dynamic channel allocation approaches showed good performance results. The two important issues that must be carefully addressed in such algorithms are the efficient co-channel interference avoidance and messaging overhead reduction. In this paper, we focus on our new distributed channel allocation algorithm and evaluate its performance through extensive simulation studies. The performance evaluation results obtained under different traffic load and user mobility conditions, show that the proposed algorithm outperforms other algorithms recently proposed in the literature.     

Joint channel estimation algorithm via weighted Homotopy for massive MIMO OFDM system

Massive (or large-scale) multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system is widely acknowledged as a key technology for future communication. One main challenge to implement this system in practice is the high dimensional channel estimation, where the large number of channel matrix entries requires prohibitively high computational complexity. To solve this problem efficiently, a channel estimation approach using few number of pilots is necessary. In this paper, we propose a weighted Homotopy based channel estimation approach which utilizes the sparse nature in MIMO channels to achieve a decent channel estimation performance with much less pilot overhead. Moreover, inspired by the fact that MIMO channels are observed to have approximately common support in a neighborhood, an information exchange strategy based on the proposed approach is developed to further improve the estimation accuracy and reduce the required number of pilots through joint channel estimation. Compared with the traditional sparse channel estimation methods, the proposed approach can achieve more than 2 dB gain in terms of mean square error (MSE) with the same number of pilots, or achieve the same performance with much less pilots.     

Effects of the pricing and cooperative advertising policies in a two-echelon dual-channel supply chain

The rapid development of e-commerce has reduced the intermediary channels between manufacturers and consumers and changed consumption patterns. However, channel conflicts occur when manufacturers engage in direct sales. Using traditional and direct online channels as its setting, this paper evaluates the impact of price schemes and cooperative advertising mechanisms on dual-channel supply chain competition. Our analysis offers structural and quantitative insights into the interplay between upstream and downstream entities in the supply chain, helping managers to understand the interplay between the upstream and downstream entities of a dual channel structure.     

蜂窝网中基于分布式约束满足算法的改进信道分配

随着蜂窝网业务需求的不断增长,如何利用有限的信道资源在各小区间进行复用,以便既能避免移动用户之间的干扰,又能满足所有移动用户的话务请求,使蜂窝系统容量大大增加,已成为一项重要研究课题。此类问题属于NP-hard的信道分配问题(Channel Assignment Problem,CAP),将CAP问题形式化为分布式约束满足问题(DC-SP),然后提出基于改进现有的信道分配策略,以获得更高的信道利用率、较令人满意的系统服务质量,尽可能满足所有用户的话务请求。将利用尽可能简单、搜寻时间短的算法,并将现有的benchmark问题进行仿真。实验表明,该方案对有效改进信道分配问题,充分利用有限的信道资源,降低系统的阻塞率,有着较好的应用前景。     

基于集群技术的无线数据传输系统设计

介绍了一种基于集群通信技术的无线网络数据传输技术。论述了以集群通信技术业务信道为基础的无线网络数据传输系统,给出了网络结构、通信过程以及业务信道数据传输格式和集群系统所用的信令格式,提出了业务信道数据传输差错控制和超时处理的几种方案。     

基于软件无线电平台的信道模拟技术实现

信道模拟技术的研究与实现对无线通信系统的开发具有重要意义;在研究现有信道模型的基础上,提出了基于DSP＋FPGA平台的信道模拟技术。将复杂的信道模型算法置于计算功能强大的DSP中来实现;利用FPGA控制时序和DDR存储;通过AD9952提供FPGA工作时钟,同时控制输出信号读取时钟;由AD9777完成输出信号的数模转换。模拟了瑞利（Rayleigh）、莱斯（Ricean）N种信道。     

基于叠加训练序列的MIMO信道估计算法

针对提高无线信道的传输性能,提出了改进的基于叠加训练序列的MIMO信道估计算法。利用训练序列与信息序列的不相关特性,在没有带宽损失的情况下初步估计出信道参数;然后利用加权因子对信道参数在相邻信号段之间进行加权平均,得到最终的信道参数。与以往的叠加训练序列估计方法比较,利用算法具有更低的估计均方误差,且适用于时变信道。通过计算机仿真结果表明,估计方法提高了信道传输精度和性能。     

一种无线信道模型的特征分析

本文针对实际的无线信道中可能出现的一些色散现象，提出了一种具有抛物线相位特性的无线信道模型。并分析了此种信道模型的频域和时域特征。通过计算机仿真验证了信道模型的特征．仿真结果表明了对于信道模型的理论分析结果的正确性。     

一种无线信道模型的特征分析

本文针对实际的无线信道中可能出现的一些色散现象,提出了一种具有抛物线相位特性的无线信道模型,并分析了此种信道模型的频域和时域特征。通过计算机仿真验证了信道模型的特征,仿真结果表明了对于信道模型的理论分析结果的正确性。     

Channel correlated refinement for color interpolation with quincuncial patterns containing the white channel

In this paper, a refinement scheme considering channel correlation is presented for a color filter array (CFA) sensor with the white (W) channel. Differently from the Bayer CFA, which has the red, green, and blue (R, G, and B) channels only, the R, G, B, and W channels can be alternately assigned to each grid to form new CFA patterns. However, the resolution degradation of the interpolated results in the pattern with the R, G, B, and W channels is more prominent than that in the Bayer pattern, because channel correlated errors in the high frequency, which originate from errors during the color interpolation process, such as false color and aliasing artifacts along the edges and in the details, are magnified. The proposed refinement scheme is applied to the three CFA patterns, which contain the W channel of the quincuncial structure. The interpolated W channel has more high frequency than the other interpolated R, G, and B channels, because the W channel occupies the largest pixel samples in the patterns. Thus, the W channel is eventually utilized to improve the R, G, and B channels by applying the edge adaptive refinement considering channel correlation based on high frequency reconstruction. First, the CFA patterns are partially interpolated to generate quincuncial patterns with the same structures of the Bayer pattern. Then, the edge adaptive color interpolation is applied to each pattern. Finally, the smoothing filter based on robust estimator is adopted for the refinement of the color difference image between the degraded color channel and the high resolution W channel. Experimental results of the proposed scheme are shown in comparison with the results of the conventional methods.     

WLAN与蜂窝混合网络有效的信道切换策略

针对无线局域网WLAN(Wireless Local Area Network)与蜂窝混合网络,提出一种具有抢占蜂窝网络信道的切换策略。当使用蜂窝信道的终端移入WLAN覆盖区域时,只有在该终端所使用的信道被抢占时,该机制才进行垂直切换以减少因切换造成的时延与丢包;建立了该切换策略的三维马尔可夫模型,分析了WLAN网络的终端数、蜂窝信道的利用率、信道接入请求阻塞率、信道抢占率与信道被抢占率的性能。详细的仿真结果证明了提出的模型的有效性,当WLAN覆盖面积比例为0.2时,信道抢占概率最大;当终端移动速度达到100km/h时,信道被抢占的概率是移动速度为20km/h的3倍;提出的信道切换策略与随机切换策略相比,显著地降低了业务的丢包率与传输时延。     

A new framework for robust speech recognition in complex channel environments

Channel distortion is one of the major factors which degrade the performances of automatic speech recognition (ASR) systems. Current compensation methods are generally based on the assumption that the channel distortion is a constant or slowly varying bias in an utterance or globally. However, this assumption is not sustained in a more complex circumstance, when the speech records being recognized are from many different unknown channels and have parts of the spectrum completely removed (e.g. band-limited speech). On the one hand, different channels may cause different distortions; on the other, the distortion caused by a given channel varies over the speech frames when parts of the speech spectrum are removed completely. As a result, the performance of the current methods is limited in complex environments. To solve this problem, we propose a unified framework in which the channel distortion is first divided into two subproblems, namely, spectrum missing and magnitude changing. Next, the two types of distortions are compensated with different techniques in two steps. In the first step, the speech bandwidth is detected for each utterance and the acoustic models are synthesized with clean models to compensate for spectrum missing. In the second step, the constant term of the distortion is estimated via the expectation-maximization (EM) algorithm and subtracted from the means of the synthesized model to further compensate for magnitude changing. Several databases are chosen to evaluate the proposed framework. The speech in these databases is recorded in different channels, including various microphones and band-limited channels. Moreover, to simulate more types of spectrum missing, various low-pass and band-pass filters are used to process the speech from the chosen databases. Although these databases and their filtered versions make the channel conditions more challenging for recognition, experimental results show that the proposed framework can substantially improve the performance of ASR systems in complex channel environments.     

基于自适应高斯混合模型特征映射的说话人确认

为了解决电话语音说话人确认系统中信道非线性失真导致系统性能下降的问题,提出一种消除信道影响的特征映射方法.采用高斯混合模型建立语音模型,通过最大后验概率自适应某种信道的语音模型,两种模型间相应高斯类的差异描述了该信道对于不同语音的影响.由此得出信道映射规则进行参数补偿,消除训练和测试语音中不匹配的影响.在NIST 1999年和2004年男性说话人的数据库上进行的实验表明,此方法使系统的等错误率分别改善了14.7%和15.18%.     

On the optimal,fair and channel-aware cognitive radio network reconfiguration

In this work, we focus on the Joint Channel Assignment and Routing (JCAR) problem in Cognitive Radio Networks (CRNs) and especially on the optimal reconfiguration of secondary networks under the presence of primary users. Secondary CRN users need to adapt their transmission channels promptly, while effectively limit additional or escalating system modifications triggered by the intertweaved primary user activity. Our approach takes into consideration the underlying spectrum switching dynamics and concurrently aims at a fair resource allocation among the active network flows. We take an optimization perspective and formulate the JCAR and network reconfiguration problems as mixed integer linear programs, addressing fairness concerns as well. We propose a heuristic approach which is based on a sequential reduced search space methodology, in order to obtain efficiently solutions of otherwise tough and demanding reconfiguration problems. The operation, effectiveness and performance of the proposed mechanisms are evaluated through analysis and simulations under various working conditions. The obtained numerical results indicate the benefits of the proposed schemes in terms of overhead performance and their scaling properties with respect to more realistic and thus demanding topologies.