一种弱安全网络编码的改进方法

改进了弱安全网络编码。为提高网络编码的安全性,利用流密码防止窃听,利用纠错码防止污染,将二者结合,则可以达到同时防止窃听和污染的目的。在攻击者可以窃听网络任意信道和污染指定数量比特的情况下,仍达到弱安全的要求由信源向信宿安全无误地传输信息。仿真结果表明,该方法与普通的网络编码相比,仅多用很少时间即令网络编码的安全性大为提高,较好地保护了信息。     

防窃听和污染攻击的安全网络编码

搭线窃听和污染攻击是安全攻击中的2种重要手段。研究表明,网络编码自身的数据融合特性能够达到一定的安全传输效果。针对污染攻击和搭线窃听攻击,在此提出一种能够防御全能窃听和污染攻击的安全网络编码。在攻击者具有全能窃听能力以及污染部分链路,该方案通过对传输的信息进行哈希达到了防污染攻击的效果,对全局编码向量进行加密实现了防污染攻击,该方案适用于攻击者窃听能力较强并且具有污染攻击威胁的网络中。分析结果表明,该方案是有效的。     

基于纠错算术码的信源信道自适应联合编解码系统

对信源信道自适应联合编码方法进行了研究,提出了一种新的基于纠错算术码的联合信源信道编解码系统。该系统在编码端利用算术码内嵌禁用符号实现信源信道一体式编码,即利用马尔科夫信源模型和根据信道状态信息自适应地调整禁用符号概率大小从而调整编码码率来实现信道自适应;在解码端,推导出了基于MAP的解码测度数学公式并基于此测度公式提出了一种改进的堆栈序列估计算法。与传统的信道自适应编码算法不同,该自适应编码算法只需调整一个参数:禁用符号,且理论上可获得连续可变的编码码率。实验结果表明,与经典的Grangetto联合编码系统以及分离编码系统相比,所提出的编码系统具有明显改善的性能增益。     

类卷积译码的容错解扰算法

针对自同步扰码系统的联合信源信道译码问题,本文将自同步扰码看作一种特殊的卷积编码,提出了类似卷积译码的软输入软输出(SISO)自同步去扰算法。该算法利用信源冗余更新扰码序列的外信息,在信道译码时作为先验信息进行译码,实现了自同步去扰与信道译码之间的软信息交互,充分利用了信源冗余信息,使得接收系统的性能得到了有效提升。仿真结果表明,在TPC编码条件下,当信源冗余度为70%时,联合信源信道译码的性能增益约为4.1dB。相比于单一纠错编码系统,当通信系统中存在自同步扰码时,联合信源信道译码具有更大的性能增益。      

基于LDPC码的小波图像传输码率优化

LDPC码是一种具有低复杂度,强纠错能力的信道分组编码结构,SPIHT算法是嵌入式小波图像压缩编码中性能较好的一种。文中充分考虑SPIHT算法和LDPC码的特性,提出了根据信源编码后的数据在解码重建时的重要程度进行不等纠错保护的信源信道联合编码方案。实验表明,该方案有利于压缩图像在噪声信道上的可靠传输,提高系统整体纠错性能。     

基于多描述的联合信源信道编码

在实时通信系统中,传统的联合信源信道编码方法在分组编码长度有限的情况下,不可避免地会存在残余误差,从而影响了整体性能。提出了一种基于多描述源编码的联合信源信道编码方法,此方法不仅可以利用分组编码的纠错能力,也可以利用多描述源编码的鲁棒性。通过具有代表性的高斯信号编码序列在有损网络信道中的传输仿真,可以看出,此方法相对于传统的联合信源信道编码方法,可提供更好的信噪比性能。     

高斯窃听信道中删余Polar码的设计方法研究

本文针对高斯窃听信道模型下的物理层安全问题,提出一种基于删余Polar码的、拥有编码比特的可信度计算的物理层安全编码方案。方案考虑到信道噪声对译码结果的影响,通过Bhattacharyya参数评估各信息比特的恢复差错概率,并将这恢复差错概率应用于编码比特的可信度计算。理论证明所提出的方案可使窃听者保持较高误码率,同时合法用户在高于自身信噪比门限时保证较低误码率。数值仿真结果表明所提出的安全编码方案能够有效地减小安全间隙。当窃听信道质量比合法信道质量稍差时窃听者误码率能迅速逼近0.5,而合法信道的误码率能够降到10-5以下,大大地降低了Bob和Eve间的安全间隙。      

无线视频传输中的信源信道联合编码的研究

文章在研究信源信道联合编码方法的基础上,介绍了信源信道联合编码的产生背景、研究意义、应用环境,指出了信源信道联合编码在通信系统中的实际应用。结合编码码流的自身特点,给出了一种以图片组为单位的码流重要性模型,并根据此模型使用不同码率的Turbo码对H.264编码码流进行不等差错保护。     

RS编码和纠错算法

几乎所有的现代化通信系统都把纠错编码作为一个基本组成部分。RS码由于具有强有力的纠错功能，已经被NASA、ESA、CCSDS等空间组织接受，用于空间信道纠错。本文简单论述了RS编码原理，纠错算法及工作流程，能使大家初步了解RS编码。     

防窃听的安全网络编码

网络编码的思想得到了广泛的关注,网络编码的各种应用问题相继提出,其中网络编码中的安全是网络编码的重要应用领域。安全网络编码大体上分为两方面,反篡改数据和反窃听数据。反篡改数据也就是网络纠错,反窃听数据就是防搭线窃听的安全网络编码。文章论述了防窃听的安全网络编码的模型、理论、构造、发展,对抗搭线窃听的安全网络编码进行了重点分析。     

Resilient Network Coding in the Presence of Byzantine Adversaries

Network coding substantially increases network throughput. But since it involves mixing of information inside the network, a single corrupted packet generated by a malicious node can end up contaminating all the information reaching a destination, preventing decoding. This paper introduces distributed polynomial-time rate-optimal network codes that work in the presence of Byzantine nodes. We present algorithms that target adversaries with different attacking capabilities. When the adversary can eavesdrop on all links and jam links, our first algorithm achieves a rate of , where is the network capacity. In contrast, when the adversary has limited eavesdropping capabilities, we provide algorithms that achieve the higher rate of . Our algorithms attain the optimal rate given the strength of the adversary. They are information-theoretically secure. They operate in a distributed manner, assume no knowledge of the topology, and can be designed and implemented in polynomial time. Furthermore, only the source and destination need to be modified; nonmalicious nodes inside the network are oblivious to the presence of adversaries and implement a classical distributed network code. Finally, our algorithms work over wired and wireless networks.     

On Metrics for Error Correction in Network Coding

The problem of error correction in both coherent and noncoherent network coding is considered under an adversarial model. For coherent network coding, where knowledge of the network topology and network code is assumed at the source and destination nodes, the error correction capability of an (outer) code is succinctly described by the rank metric; as a consequence, it is shown that universal network error correcting codes achieving the Singleton bound can be easily constructed and efficiently decoded. For noncoherent network coding, where knowledge of the network topology and network code is not assumed, the error correction capability of a (subspace) code is given exactly by a new metric, called the injection metric, which is closely related to, but different than, the subspace metric of KÖtter and Kschischang. In particular, in the case of a non-constant-dimension code, the decoder associated with the injection metric is shown to correct more errors then a minimum-subspace-distance decoder. All of these results are based on a general approach to adversarial error correction, which could be useful for other adversarial channels beyond network coding.      

A novel scheme for protecting receiver's location privacy in wireless sensor networks

Due to the open nature of a sensor network, it is relatively easy for an adversary to eavesdrop and trace packet movement in the network in order to capture the receiver physically. After studying the adversary's behavior patterns, we present countermeasures to this problem. We propose a locationprivacy routing protocol (LPR) that is easy to implement and provides path diversity. Combining with fake packet injection, LPR is able to minimize the traffic direction information that an adversary can retrieve from eavesdropping. By making the directions of both incoming and outgoing traffic at a sensor node uniformly distributed, the new defense system makes it very hard for an adversary to perform analysis on locally gathered information and infer the direction to which the receiver locates. We evaluate our defense system based on three criteria: delivery time, privacy protection strength, and energy cost. The simulation results show that LPR with fake packet injection is capable of providing strong protection for the receiver?s location privacy. Under similar energy cost, the safe time of the receiver provided by LPR is much longer than other methods, including Phantom routing [1] and DEFP [2]. The performance of our system can be tuned through a few system parameters that determine the tradeoff between energy cost and the strength of location-privacy protection.     

Zero-error network coding for acyclic networks

Consider transmitting a set of information sources through a communication network that consists of a number of nodes. Between certain pair of nodes, there exist communication channels on which information can be transmitted. At a node, one or more information sources may be generated, and each of them is multicast to a set of destination nodes on the network. In this paper, we study the problem of under what conditions a set of mutually independent information sources can be faithfully transmitted through a communication network, for which the connectivity among the nodes and the multicast requirements of the source information are arbitrary except that the connectivity does not form directed cycles. We obtain inner and outer bounds on the zero-error admissible coding rate region in term of the regions /spl Gamma//sub N//sup */ and /spl Gamma/~/sub N//sup */, which are fundamental regions in the entropy space defined by Yeung. The results in this paper can be regarded as zero-error network coding theorems for acyclic communication networks.     

Almost-Everywhere Secure Computation with Edge Corruptions

We consider secure multi-party computation (MPC) in a setting where the adversary can separately corrupt not only the parties (nodes) but also the communication channels (edges), and can furthermore choose selectively and adaptively which edges or nodes to corrupt. Note that if an adversary corrupts an edge, even if the two nodes that share that edge are honest, the adversary can control the link and thus deliver wrong messages to both players. We consider this question in the information-theoretic setting, and require security against a computationally unbounded adversary.In a fully connected network the above question is simple (and we also provide an answer that is optimal up to a constant factor). What makes the problem more challenging is to consider the case of sparse networks. Partially connected networks are far more realistic than fully connected networks, which led Garay and Ostrovsky [Eurocrypt’08] to formulate the notion of (unconditional) almost everywhere (a.e.) secure computation in the node-corruption model, i.e., a model in which not all pairs of nodes are connected by secure channels and the adversary can corrupt some of the nodes (but not the edges). In such a setting, MPC among all honest nodes cannot be guaranteed due to the possible poor connectivity of some honest nodes with other honest nodes, and hence some of them must be “given up” and left out of the computation. The number of such nodes is a function of the underlying communication graph and the adversarial set of nodes.In this work we introduce the notion of almost-everywhere secure computation with edge corruptions, which is exactly the same problem as described above, except that we additionally allow the adversary to completely control some of the communication channels between two correct nodes—i.e., to “corrupt” edges in the network. While it is easy to see that an a.e. secure computation protocol for the original node-corruption model is also an a.e. secure computation protocol tolerating edge corruptions (albeit for a reduced fraction of edge corruptions with respect to the bound for node corruptions), no polynomial-time protocol is known in the case where a constant fraction of the edges can be corrupted (i.e., the maximum that can be tolerated) and the degree of the network is sublinear.We make progress on this front, by constructing graphs of degree O(n ^? ) (for arbitrary constant 0<?<1) on which we can run a.e. secure computation protocols tolerating a constant fraction of adversarial edges. The number of given-up nodes in our construction is μn (for some constant 0<μ<1 that depends on the fraction of corrupted edges), which is also asymptotically optimal.     

A separation theorem for single-source network coding

In this paper, we consider a point-to-point communication network of discrete memoryless channels. In the network, there are a source node and possibly more than one sink node. Information is generated at the source node and is multicast to each sink node. We allow a node to encode its received information before loading it onto an outgoing channel, where the channels are independent of each other. We also allow the nodes to pass along messages asynchronously. In this paper, we characterize the admissibility of single-source multi-sink communication networks. Our result can be regarded as a network generalization of Shannon's result that feedback does not increase the capacity of a discrete memoryless channels (DMCs), and it implies a separation theorem for network coding and channel coding in such a communication network.     

A minimum mean-squared error relay for the two-way relay channel with network coding

In this letter, we consider the two-way relay channel (TWRC) employing network coding. In TWRC, a conventional relay first decodes symbols from each user and combines (network coding) them using, for example, the XOR (eXclusive OR) operation. However, it may be suboptimal for the relay to use this concatenated approach, when the channels are noisy and the cost criterion is source distortion. Instead, we propose a new relay scheme that generates network coded symbols by performing symbol estimation and network coding operation jointly, in order to minimize the source distortion at the users.     

Rateless Coding and Relay Networks

A framework for coding over relay channels using rateless codes is the intersection of two active areas of research in communications; namely relay networks and rateless coding. We demonstrate that there is a very natural and useful fit between these two areas and describe some design challenges and implementation considerations for this framework. The use of relays in wireless communication networks provide a new dimension to the design space of wireless networks that promises enhancements to both the coverage and throughput of the network. In its simplest form, a relay network is a collection of terminals that are able to transmit, receive, and possibly assist the reliable delivery of information from source terminals to destination terminals. Thus, communication of data through a wireless relay network is not required to be direct; it may pass through a number of other terminals, though direct communication from source to destination is not precluded. In fact, it is possible to simultaneously use single-hop, i.e., direct, and multihop communications paths.     

Byzantine Agreement Given Partial Broadcast

This paper considers unconditionally secure protocols for reliable broadcast among a set of n players, where up to t of the players can be corrupted by a (Byzantine) adversary but the remaining h = n - t players remain honest. In the standard model with a complete, synchronous network of bilateral authenticated communication channels among the players, broadcast is achievable if and only if 2n/h < 3. We show that, by extending this model by the existence of partial broadcast channels among subsets of b players, global broadcast can be achieved if and only if the number h of honest players satisfies 2n/h < b + 1. Achievability is demonstrated by protocols with communication and computation complexities polynomial in the size of the network, i.e., in the number of partial broadcast channels. A respective characterization for the related consensus problem is also given.     

基于8PSK的MLC-STBC在瑞利衰落信道中的性能

文章提出了在瑞利信道中,8PSK调制模式下多级编码空时分组编码级联的MLC-STBC方案,并在系统码率为2.032bit/s、发射天线为2、接收天线数目为1的条件下,分别对多级编码和MLC-STBC级联编码进行了仿真。仿真结果表明,基于8PSK,在瑞利衰落下利用旋转距离度量规则选择分量码码率的MLC-STBC系统,能获得比较理想的系统增益。