一种基于CoMP的随机接入方案

提出了一种新的基于协作多点传输和接收（CoMP）技术的多发随机接入流程,并根据 随机接入的目的和业务类型设计了接入优先级,在此基础上设计了一种新的随机接入方案, 对 不同类型的随机接入请求提供不同的接入机制,以保证边缘用户的接入性能和满足不同业务 的QoS需求。仿真结果表明,与LTE标准随机接入方案相比,该方案对系统整体接入性能略有 提高,且大大提高了边缘高优先级用户的接入性能。     

TD-LTE系统随机接入过程碰撞问题研究

随机接入是移动通信系统媒体接入控制的一项重要技术,文章在分析传统的随机接入前导码管理方案优缺点的基础上,提出了一种改进的基于码字共享的前导码管理方案,并通过matlab仿真对比该方案与传统方案性能优劣情况。结果表明:该方案能够在减少系统资源的情况下,有效提升接入成功率,降低碰撞的概率。     

TD-SCDMA随机接入信道的分析

给出了TD-SCDMA(时分双工同步码分多址)系统中一种新的随机接入方案,对该方案进行了理论分析 和计算机仿真,得到了随机接入信道吞吐率和时延公式,并将其数值计算结果与计算机仿真结果以及原方案计算 机仿真结果进行了对比。     

MIMO系统下随机接入的实现及吞吐量研究

随机接入技术作为LTE系统中的关键技术之一,接入成功率关系到传输时延,LTE系统下的随机接入所采用的传统冲突解决算法主要是基于网络层的重传机制。提出了一种MIMO下的随机接入实现方案,基站端可以利用多天线接收和先进的MIMO信号处理技术的结合,进而联合高层解决冲突,仿真结果表明了该方案可以显著地提高系统的吞吐量。     

Implement of MIMO System for Random Access and Research of Throughput

随机接入技术作为LTE系统中的关键技术之一,接入成功率关系到传输时廷,LTE系统下的随机接入所采用的传统冲突解决算法主要是基于网络层的重传机制.提出了一种MIMO下的随机接入实现方案,基站端可以利用多天线接收和先进的MIMO信号处理技术的结合,进而联合高层解决冲突,仿真结果表明了该方案可以显著地提高系统的吞吐量.     

卫星物联网混合随机接入技术

在卫星物联网(IoT)场景中,随着终端数量不断增加,频谱资源日益紧张。传统的随机接入技术频谱利用率较低,使得传统随机接入协议不适用于未来卫星IoT的高并发业务需求。同时,卫星通信链路长,开放性强,难以保证特种终端信号的安全性。对此,本文提出一种适用于卫星IoT的混合随机接入方案。该方案引入重叠传输的容量提升与安全性优势,利用扩频码对瞬时功率谱密度的控制能力,构造功率域非正交接入条件,并通过接收端的迭代分离实现稳健接收。对本文所提方案的吞吐量性能进行闭式解推导分析与计算机仿真,结果表明,与传统的随机接入协议相比,所提方案可提高系统吞吐量。同时,相较于常用信号隐藏方法,所提方法利用常规接入数据包的功率优势,强化了波形隐藏效果,提升了特种信息接入的安全性。     

基于OFDM系统的随机信道接入方案

双忙音多址信道接入(DBTMA)协议是一种信道利用率较高的无线局域网信道随机接入控制方案。但是, 该协议的硬件实现复杂度较高。该文在对DBTMA协议进行简单修改的基础上,结合节能意识多址接入(PAMAS) 协议提出了一种基于OFDM系统的DBTMA信道接入系统,并对此系统做了简要分析。分析结果显示,该文提出的随机信道接入系统的性能良好且实现方式简单。     

LTE网络端MAC状态研究与设计

针对目前LTE系统网络端MAC子层状态划分的不明确性,提出了在LTE系统通信过程中网络端MAC层状态划分的方案.该方案将网络端MAC层划分为4个状态,设计了状态转移过程及随机接入流程,由此实现了MAC状态转移方案.通过TTCN与SDL协仿真的测试,证明了状态转移及随机接入流程设计的正确性,为LTE系统的通信实现提供有效方案.     

MIMO-OFDM系统中跨层媒体接入控制

针对MIMO-OFDM系统,提出了一种基于时隙ALOHA协议的随机接入方案,该方案利用一个简单的中心控制器和物理层的自适应调制技术以及MIMO迫零信号检测算法,在媒体接入控制层提供多包接收能力,解决包冲突问题。在满足用户BER要求的前提下,研究了系统最大化吞吐量时,接入同一子载波的最优用户数,并为此设计最佳的接入请求概率。仿真结果表明,最优接入天线数大约为接收天线数的四分之三,此时可以获取最大的吞吐量。     

TD-LTE随机接入过程的研究与分析

随机接入是移动通信系统中终端(UE)与基站建立上行同步和连接的一个非常重要的过程.文章主要研究时分-长期演进(TD-LTE)上行随机接入技术的设计.考虑到基于竞争模式的随机接入过程适用的普遍性,文章从随机接入的应用场景和类型出发,重点讨论基于竞争模式下的随机接入过程,并详细地分析了随机接入过程中的具体流程及实现方案.     

A Co ding Scheme for Noisy Image Based on Layer Segmentation

Heavy noises distribute in the images when imaging in a poor environment. The randomness of noises makes pixels distributing singularly, which weakens the 1-D piecewise smooth property of original scenes. Thus, wavelets-based compression method no longer works well. In this paper, a layer segmentation based compression scheme is proposed for gray images. Image textures and some high frequency noises are described in a high fre-quency layer while the coarse part of the image is described in the low frequency layer. The high frequency layer is represented by a joint dictionary, and the low frequency layer is coded with the traditional wavelets. The proposed scheme is tested on nature images and synthetic images. The results show that the proposed scheme achieves better rate-distortion performance compared with several com-peting compression systems. Besides, further degradation of edges is avoided by the proposed compression scheme.     

延迟容忍网络自适应差错控制方法

根据延迟容忍网络的时延较大、误码率较高等特点,在现有的传输控制层和MAC层差错控制的基础上改进,结合IEEE 802.11 DCF机制的特点,提出一种基于MAC层丢包率的自适应差错控制方案.该方案能有效改善延迟容忍网络的传输时延,满足对时延要求比较敏感的业务的要求.     

Guide to MPEG-1 audio standard

This paper is designed to help the reader to unravel the ISO MPEG-1 standard for compressing digital audio data. In comparison to the standards for video, little additional information is available on this standard. The standard describes the implementation of three compression schemes called layer 1, layer 2 and layer 3. The layer 1 scheme is the simplest to implement but its efficiency is not as good as the other layers. The layer 3 scheme provides the best performance at low bit rates but it is also the most difficult one to implement. The compression techniques used psychoacoustic models for predicting the human auditory response to the noise that is introduced by the coding scheme. Using these models, the characteristics of the compression scheme can be changed dynamically in order to minimize the audibility of these noise impairments. The implementation of two such psychoacoustic models are described in the standard     

WAVELET－BASED FINE GRANULARITY SCALABLE VIDEO CODING

This letter proposes an efficient wavelet-based fine Granularity Scalable(FGS)coding scheme,where the base layer is encoded with a newly designed wavelet-based coder,and the entancement layer is encoded with Progressive Fins Granularity Scalable(PFGS)coding.This algorithm involves multi-frame motion compensationk,rate-distortion optimizing strategy with Lagrangian cost function and context-based adaptive arithmetic coding.In order to improve efficiency of the enhancenent layer coding,an improved motion estimation scheme that uses both information from the base layer and the enhancement layer is also proposed in this letter.The wavelet-based coder significantly improves the coding efficiency of the base layer compared with MPEG-4 ASP(Advanced Simple Profile)and H.26L TML9.The PFGS coding is a significant improvement over MPEG-4 FGS coding at the enhancement layer.Experiments show that single layer coding efficiency gain of the proposed scheme is about 2.0-3.0dB and 0.3-1.0dB higher than that of MPEG-4 ASP and H.26L TML9,respectively.The overall coding efficiency gain of the proposed scheme is about 4.0-5.0dB higher than that of MPEG04 FGS.     

TCP over optical burst-switched networks with controlled burst retransmission

For optical burst-switched (OBS) networks in which TCP is implemented at a higher layer, the loss of bursts can lead to serious degradation of TCP performance. Due to the bufferless nature of OBS, random burst losses may occur, even at low traffic loads. Consequently, these random burst losses may be mistakenly interpreted by the TCP layer as congestion in the network. The TCP sender will then trigger congestion control mechanisms, thereby reducing TCP throughput unnecessarily. In this paper, we introduce a controlled retransmission scheme in which the bursts lost due to contention in the OBS network are retransmitted at the OBS layer. The OBS retransmission scheme can reduce the burst loss probability in the OBS core network. Also, the OBS retransmission scheme can reduce the probability that the TCP layer falsely detects congestion, thereby improving the TCP throughput. We develop an analytical model for evaluating the burst loss probability in an OBS network that uses a retransmission scheme, and we also analyze TCP throughput when the OBS layer implements burst retransmission. We develop a simulation model to validate the analytical results. Simulation and analytical results show that an OBS layer with controlled burst retransmission provides up to two to three orders of magnitude improvement in TCP throughput over an OBS layer without burst retransmission. This significant improvement is primarily because the TCP layer triggers fewer time-outs when the OBS retransmission scheme is used.     

一种基于信道特征参数的无线通信密钥生成方法

无线通信由于自身传输信道的开放性,其安全问题相对于有线通信更为突出。物理层安全技术利用无线通信信道天然的多径时变特性,可为无线传输提供物理层加密,因而近年来得到快速发展。针对传统物理层安全中密钥生成速率低、频分双工系统不适用等问题,提出了一种基于信道特征参数的无线通信密钥生成方法。基于宽带信号对多径的辨识力,利用各径间相对时延生成初始密钥,结合码本进行密钥长度扩展,从而生成最终密钥。通过数值分析证明,相对于传统物理层密钥生成方式,所提方法能显著提高密钥生成速率,同时,基于时延信道特征的互易性,该方法可适用于时分双工和频分双工无线通信系统的物理层加密。     

粒度区分和可调的无线流媒体可靠传输策略

为实现无线接入流媒体可靠传输和降低应用层设计复杂度,提出结合交织编码和RS编码,实现对应用层数据有效的分帧/重组,区分数据重要级别并采用不平等粒度的保护,支持根据信道状况对保护粒度和帧长度的自适应调节.该策略增强了传输层功能,实现了灵活的数据保护方式,显著提高了无线流媒体的传输质量.     

MIMO-OFDM中基于业务类型的跨层资源分配研究

提出了一种基于PHY层和MAC层的跨层资源自适应方案。该方案首先把业务类型划分为实时业务和非实时业务,并在此基础上针对业务类型在MAC层对分组进行调度和在PHY层对子载波和功率分配。     

基带芯片物理层控制方案的设计

对多核基带芯片物理层控制方案进行了简单的讨论,提出了一种用于GSM移动终端基带芯片物理层控制(L1C)的方案,根据GSM的帧结构设计了基时钟电路,并以物理层信号处理流程为依据,建立了物理层上下行的调度时序,初步完成了基带芯片SoC系统多核之间的任务调度和时序控制。     

A scalable and format-compliant encryption scheme for H.264/SVC bitstreams

SVC (Scalable Video Coding) is designed to adapt to heterogeneous networks and various terminal devices. This paper presents an encryption scheme for SVC bitstreams which retains the valuable scalability properties of SVC. To this end, we explore PACSI (Payload Content Scalability Information) and RTP (Real-time Transport Protocol) payload format such that encrypted bitstreams are SVC format-compliant. Specifically, the proposed scheme processes the base layer and enhancement layers in different ways. For the base layer, the scheme encrypts VCL (video coding layer) NALU (Network Abstract Layer Unit) into either SEI (Supplement Enhancement Information) NALU or PACSI NALU. For an enhancement layer, the scheme replaces a coded slice in scalable extension NALU with an encryption of PACSI NALU. Thus, the proposed encryption scheme preserves SVC scalability and format-compliance. It produces encrypted bitstreams which have the original SVC structure without emulation markers or illegal codewords for any standard decoder. The analysis and experiments indicate that our algorithm is cost-effective and secure against chosen plaintext attack.