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1.
The network coding is a new technology in the field of information in 21st century. It could enhance the network throughput and save the energy consumption, and is mainly based on the single transmission rate. However, with the development of wireless network and equipment, wireless local network MAC protocols have already supported the multi-rate transmission. This paper investigates the optimal relay selection problem based on network coding. Firstly, the problem is formulated as an optimization problem. Moreover, a relay algorithm based on network coding is proposed and the transmission time gain of our algorithm over the traditional relay algorithm is analyzed. Lastly, we compare total transmission time and the energy consumption of our proposed algorithm, Network Coding with Relay Assistance (NCRA), Transmission Request (TR), and the Direct Transmission (DT) without relay algorithm by adopting IEEE 802.11b. The simulation results demonstrate that our algorithm that improves the coding opportunity by the cooperation of the relay nodes leads to the transmission time decrease of up to 17% over the traditional relay algorithms. 相似文献
2.
A Two-hop Wireless Network (TWN) is the basic topology structure that provides network coding opportunity for improving throughput. Network coding on a homogeneous TWN, in which all the data flows have the same packet size and all the links have the same transmission rate, has been extensively investigated. In this paper, network coding on more practical heterogeneous TWNs, featured by various packet sizes and transmission rates, is studied. Based on the Markov model, the throughput of the proposed network coding scheme, together with the throughput gain, is derived, which matches the simulation results very well. Numerical analyses indicate that, encoding the packets with close size and close transmission rate and enlarging buffer size at the relay node help in improving the throughput gain. 相似文献
3.
In this paper,a network scenario of two-way relaying over orthogonal frequency division multiplexing(OFDM) is considered,in which two nodes intend to exchange the information via a relay using physical-layer network coding(PLNC).Assuming that the full channel knowledge is available,an optimization problem,which maximizes the achievable sum rate under a sum-power constraint,is investigated.It is shown that the optimization problem is non-convex,which is difficult to find the global optimum solution in terms of the computational complexity.In consequence,a low-complexity optimal power allocation scheme is proposed for practice implementation.A link capacity diagram is first employed for power allocation on each subcarrier.Subsequently,an equivalent relaxed optimization problem and Karush-Kuhn-Tucker(KKT) conditions are developed for power allocation among each subcarrier.Simulation results demonstrate that the substantial capacity gains are achieved by implementing the proposed schemes efficiently with a low-complexity computational effort. 相似文献
4.
The smart grid has caught great attentions in recent years, which is poised to transform a centralized, producer-controlled network to a decentralized, consumer- interactive network that's supported by fine-grained monitoring. Large-scale WSNs (Wireless Sensor Networks) have been considered one of the very promising technologies to support the implementation of smart grid. WSNs are applied in almost every aspect of smart grid, including power generation, power transmission, power distribution, power utilization and power dispatch, and the data query processing of 'WSNs in power grid' become an hotspot issue due to the amount of data of power grid is very large and the requirement of response time is very high. To meet the demands, top-k query processing is a good choice, which performs the cooperative query by aggregating the database objects' degree of match for each different query predicate and returning the best k matching objects. In this paper, a framework that can effectively apply top-k query to wireless sensor network in smart grid is proposed, which is based on the cluster-topology sensor network. In the new method, local indices are used to optimize the necessary query routing and process intermediate results inside the cluster to cut down the data traffic, and the hierarchical join query is executed based on the local results.Besides, top-k query results are verified by the clean-up process, and two schemes are taken to deal with the problem of node's dynamicity, which further reduce communication cost. Case studies and experimental results show that our algorithm has outperformed the current existing one with higher quality results and better efficiently. 相似文献
5.
In this paper,we consider a cognitive radio system with energy harvesting,in which the secondary user operates in a saving-sensing-transmitting(SST) fashion.We investigate the tradeoff between energy harvesting,channel sensing and data transmission and focus on the optimal SST structure to maximize the SU's expected achievable throughput.We consider imperfect knowledge of energy harvesting rate,which cannot be exactly known and only its statistical information is available.By formulating the problem of expected achievable throughput optimization as a mixed-integer non-linear programming one,we derive the optimal saveratio and number of sensed channels with indepth analysis.Simulation results show that the optimal SST structure outperforms random one and performance gain can be enhanced by increasing the SU's energy harvesting rate. 相似文献
6.
In this study, a Multi-Layer BP neural network (MLBP) with dynamic thresholds is em-ployed to build a classifier model. As to the design of the neural network structure, theoretical guidance and plentiful experiments are combined to optimize the hidden layers’ parameters which include the number of hidden layers and their node numbers. The classifier with dynamic thresholds is used to standardize the output for the first time, and it improves the robustness of the model to a high level. Finally, the classifier is applied to forecast box office revenue of a movie before its theatrical release. The comparison results with the MLP method show that the MLBP classifier model achieves more satis-factory results, and it is more reliable and effective to solve the problem. 相似文献
7.
The difference in link condition of broadcast/ multicast users and the limitation of uplink resource, make it difficult to utilize adaptive modulation and coding (AMC) in the enhanced multimedia broadcast and multicast service (E-MBMS) network. To obtain the improvement of system throughput, this study proposes an adaptive modulation and coding scheme based on partial feedback, by which only partial users whose channel qualities are lower than the system threshold need to make a response to the modulation coding scheme (MCS) adaptation procedure. By this investigation, an adaptive scheme can be introduced in the E-MBMS network. Both the theoretical analysis and simulation results demonstrate the efficiency of the proposed strategy, in which the performance is close to the ideal one and has a significant throughput improvement when compared with that of the fixed MCS transmission scheme. 相似文献
8.
Euee S.Jang 《中兴通讯技术(英文版)》2012,(2):19-24
Recent advances in reconfigurable computing have led to new ways of implementing complex algorithms while maintaining reasonable throughput.Video codecs are becoming more complex in order to provide efficient compression for video with ever-increasing resolution.This problem is compounded by the fact that spectra of video decoding devices has become wider in the move from traditional TV to cable and satellite TV,IPTV,mobile TV,and Internet media.MPEG is tackling this problem with a reconfigurable video coding(RVC) framework and is standardizing a modular definition of tools and connections.MPEG’s work started with video coding and has recently extended to graphics data coding.RVC will be supported by non-MPEG standards such as the Chinese audio-video standard(AVS).This article gives a brief background to the reconfigurable codec framework.The key to this framework is reconfigurability and reducing granularity to find commonality between different standards. 相似文献
9.
10.
To solve the slow congestion detection and rate convergence problems in the existing rate control based fair data collection schemes, a new fair data collection scheme is proposed, which is named the improved scheme with fairness or ISWF for short. In ISWF, a quick congestion detection method, which combines the queue length with traffic changes of a node, is used to solve the slow congestion detection problem, and a new solution, which adjusts the rate of sending data of a node by monitoring the channel utilization rate, is used to solve the slow convergence problem. At the same time, the probability selection method is used in ISWF to achieve the fairness of channel bandwidth utilization. Experiment and simulation results show that ISWF can effectively reduce the reaction time in detecting congestion and shorten the rate convergence process. Compared with the existing tree-based fair data collection schemes, ISWF can achieve better fairness in data collection and reduce the transmission delay effectively, and at the same time, it can increase the average network throughput by 9.1% or more. 相似文献
11.
本文研究了利用network coding的多速率多播最大吞吐量问题.与以往研究重点集中在单速率多播中的network coding研究工作不同,本文考虑了链路的异构性问题并采用多速率多播来解决该问题.首先文中形式化地描述了多速率多播最大可得吞吐量问题,并证明了在分层独立和层速率固定条件下,利用network coding的多速率多播最大吞吐量问题是NP-hard类问题,同时给出了最大吞吐量的上界.此外本文同时也研究了分层相关和层速率可变情况下的最大吞吐量问题. 相似文献
12.
多速率多播最大吞吐量问题研究 总被引:1,自引:0,他引:1
该文研究了利用network coding的多速率多播最大吞吐量问题.与以往研究重点集中在单速率多播中的network coding研究工作不同,该文考虑了链路的异构性问题并采用多速率多播来解决该问题.文中形式化地描述了多速率多播最大可得吞吐量问题,并证明了在分层独立和层速率固定条件下,利用network coding的多速率多播最大吞吐量问题是NP-hard类问题,同时给出了最大吞吐量的上界.该文同时还研究了分层相关和层速率可变情况下的最大吞吐量问题,并提出了一种满足公平性的近似算法. 相似文献
13.
On average throughput and alphabet size in network coding 总被引:1,自引:0,他引:1
Chekuri C. Fragouli C. Soljanin E. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2006,52(6):2410-2424
We examine the throughput benefits that network coding offers with respect to the average throughput achievable by routing, where the average throughput refers to the average of the rates that the individual receivers experience. We relate these benefits to the integrality gap of a standard linear programming formulation for the directed Steiner tree problem. We describe families of configurations over which network coding at most doubles the average throughput, and analyze a class of directed graph configurations with N receivers where network coding offers benefits proportional to /spl radic/N. We also discuss other throughput measures in networks, and show how in certain classes of networks, average throughput bounds can be translated into minimum throughput bounds, by employing vector routing and channel coding. Finally, we show configurations where use of randomized coding may require an alphabet size exponentially larger than the minimum alphabet size required. 相似文献
14.
Network planning in wireless ad hoc networks: a cross-Layer approach 总被引:10,自引:0,他引:10
Wu Y. Chou P.A. Qian Zhang Jain K. Wenwu Zhu Sun-Yuan Kung 《Selected Areas in Communications, IEEE Journal on》2005,23(1):136-150
In this paper, the network planning problem in wireless ad hoc networks is formulated as the problem of allocating physical and medium access layer resources or supplies to minimize a cost function, while fulfilling certain end-to-end communication demands, which are given as a collection of multicast sessions with desired transmission rates. We propose an iterative cross-layer optimization, which alternates between: 1) jointly optimizing the timesharing in the medium access layer and the sum of max of flows assignment in the network layer and 2) updating the operational states in the physical layer. We consider two objectives, minimizing aggregate congestion and minimizing power consumption, respectively, corresponding to operating in a bandwidth-limited regime and in an energy-limited regime. The end result is a set of achievable tradeoffs between throughput and energy efficiency, in a given wireless network with a given traffic pattern. We evaluate our approach quantitatively by simulations of community wireless networks and compare with designs that decouple the layers. We demonstrate that significant performance advantages can be achieved by adopting a full-fledged cross-layer optimization. Furthermore, we observe that optimized solutions generally profit from network coding, physical-layer broadcasting, and traffic-dependent physical states. 相似文献
15.
We investigate the multicast throughput of a butterfly network, which may be a promising topology for network coding application in next‐generation wireless communication systems. The butterfly network consists of two sources, two destinations and a relay, where each destination requires decoding of data from two independent sources. It is assumed that all the nodes are operated in half‐duplex mode. Each end‐to‐end packet transmission should be completed in a two‐phase period. In order to reduce processing complexity and multiple interference, other nodes should keep silent when the relay transmits a signal. By using Avestimehr, Diggavi and Tse's deterministic model, we first introduce a deterministic butterfly network and demonstrate that its maximal multicast rate region can be achieved by employing a network coding policy. According to the results obtained in deterministic case, we then put forward a near‐optimal design on the transmitted signal and decoding scheme for Gaussian scenarios based on a nested lattice code. It is proved that the gap between the achievable rate region and an outer bound is less than 3bits/s/Hz, which is not related to the signal‐to‐noise ratio. That is, the proposed scheme can approach the maximal multicast throughput. Finally, numerical results demonstrate that the gap is robust to both channel gains and time division of the two phases. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
16.
Daisuke Umehara Satoshi Denno Masahiro Morikura Takatoshi Sugiyama 《Ad hoc Networks》2011,9(2):164-179
Deployment of wireless relay nodes can enhance system capacity, extend wireless service coverage, and reduce energy consumption in wireless networks. Network coding enables us to mix two or more packets into a single coded packet at relay nodes and improve performances in wireless relay networks. In this paper, we succeed in developing analytical models of the throughput and delay on slotted ALOHA (S-ALOHA) and S-ALOHA with network coding (S-ALOHA/NC) for single-relay multi-user wireless networks with bidirectional data flows. The analytical models involve effects of queue saturation and unsaturation at the relay node. The throughput and delay for each user node can be extracted from the total throughput and delay by using the analytical models. One can formulate various optimization problems on traffic control in order to maximize the throughput, minimize the delay, or achieve fairness of the throughput or the delay. In particular, we clarify that the total throughput is enhanced in the S-ALOHA/NC protocol on condition that the transmission probability at the relay node is set at the value on the boundary between queue saturation and unsaturation. Our analysis provides achievable regions in throughput on two directional data flows at the relay node for both the S-ALOHA and S-ALOHA/NC protocols. As a result, we show that the achievable region in throughput can be enhanced by using network coding and traffic control. 相似文献
17.
Alireza Shafieinejad Faramarz Hendessi Faramarz Fekri 《Wireless Personal Communications》2013,72(4):2185-2214
In this paper, first, we propose Star-NC, a new network coding (NC) scheme for multiple unicast sessions in an n-input n-output star structure. Then, we evaluate the network throughput of this coding scheme in wireless mesh network over the traditional non-NC transmission. Our scheme benefits from the proximity of all the nodes around the relay node and employs a more general form of overhearing different from other schemes such as COPE. We found that the gain of our NC scheme depends on both the star size and the routing pattern of the unicast transmissions. Based on this, we identify both the situations which the maximum gain is achievable and a lower bound for the expected value of the gain in the case of random routing pattern. Next, we propose an analytical framework for studying throughput gain of our Star-NC scheme in general wireless network topologies. Our theoretical formulation via linear programming provides a method for finding source-destination routes and utilizing the best choices of our NC scheme to maximize the throughput. Finally, we evaluate our model for various networks, traffic models and routing strategies over coding-oblivious routing. We also compare the throughput gain of our scheme with COPE-type NC scheme. We show that Star-NC exploits new coding opportunities different from COPE-type NC and thus can be used with or without this scheme. The results show that Star-NC has often better performance than COPE for a directional traffic model which is a typical model in wireless mesh networks. Moreover, we found that, joint Star and COPE-type NC has better throughput performance than each of Star or COPE alone. 相似文献
18.
Modern wireless communication networks frequently have lower application throughput due to higher number of collisions and subsequent retransmission of data packets. Moreover, these networks are characterized by restricted computational capacity due to limited node‐battery power. These challenges can be assessed for deploying fast, reliable network design with resource‐restrained operation by means of concurrent optimization of multiple performance parameters across different layers of the conventional protocol stack. This optimization can be efficiently accomplished via cross‐layer design with the aid of network coding technique and optimal allocation of limited resources to wireless links. In this paper, we evaluate and analyze intersession coding across several source–destination pairs in random access ad hoc networks with inherent power scarcity and variable capacity links. The proposed work addresses the problem of joint optimal coding, rate control, power control, contention, and flow control schemes for multi‐hop heterogeneous networks with correlated sources. For this, we employ cross‐layer design for multiple unicast sessions in the system with network coding and bandwidth constraints. This model is elucidated for global optimal solution using CVX software through disciplined convex programming technique to find the improved throughput and power allocation. Simulation results show that the proposed model effectively incorporates throughput and link power management while satisfying flow conservation, bit error rate, data compression, power outage, and capacity constraints of the challenged wireless networks. Finally, we compare our model with three previous algorithms to demonstrate its efficacy and superiority in terms of various performance metrics such as transmission success probability, throughput, power efficiency, and delay. 相似文献
19.
Petrovic D. Ramchandran K. Rabaey J. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2006,52(6):2649-2657
The drive toward the implementation and massive deployment of wireless sensor networks calls for ultralow-cost and low-power nodes. While the digital subsystems of the nodes are still following Moore's Law, there is no such trend regarding the performance of analog components. This work proposes a fully integrated architecture of both digital and analog components (including local oscillator) that offers significant reduction in cost, size, and overall power consumption of the node. Even though such a radical architecture cannot offer the reliable tuning of standard designs, it is shown that by using random network coding, a dense network of such nodes can achieve throughput linear in the number of channels available for communication. Moreover, the ratio of the achievable throughput of the untuned network to the throughput of a tuned network with perfect coordination is shown to be close to 1/e. This work uses network coding to leverage the fact that throughput equal to the max-flow in a graph is achievable even if the topology is not know a priori. However, the challenge here is finding the max-flow of the random graph corresponding to the network. 相似文献
20.
Cross-Layer Design of Wireless Mesh Networks with Network Coding 总被引:1,自引:0,他引:1
We investigate the optimal design of a multihop wireless mesh network equipped with multiple orthogonal wireless channels and multiple radios. Specifically, we focus on solutions that can efficiently utilize the limited resource to support multiple unicast applications by routing and network coding. We propose a cross-layer optimization framework where the broadcasting feature of the wireless environment, which plays an important role in realizing the achievable gain of network coding, is taken into account. Moreover, we propose a network code construction scheme based on linear programming, with which the possible achievable Coding+MAC gain could be significantly increased. Delay constraints are also included in the network code construction formulation so that the possible impact of the extra decoding delay to the TCP/IP performance can be reduced without changing the upper-layer protocols. The proposed network design based on cross-layer optimization results in significant increase in network throughput. 相似文献