Capacity and delay of hybrid wireless broadband access networks

An optical network is too costly to act as a broadband access network. On the other hand, a pure wireless ad hoc network with n nodes and total bandwidth of W bits per second cannot provide satisfactory broadband services since the pernode throughput diminishes as the number of users goes large. In this paper, we propose a hybrid wireless network, which is an integrated wireless and optical network, as the broadband access network. Specifically, we assume a hybrid wireless network consisting of n randomly distributed normal nodes, and m regularly placed base stations connected via an optical network. A source node transmits to its destination only with the help of normal nodes, i.e., in the ad hoc mode, if the destination can be reached within L (L /spl geq/ 1) hops from the source. Otherwise, the transmission will be carried out in the infrastructure mode, i.e., with the help of base stations. Two transmission modes share the same bandwidth of W bits/sec. We first study the throughput capacity of such a hybrid wireless network, and observe that the throughput capacity greatly depends on the maximum hop count L and the number of base stations m. We show that the throughput capacity of a hybrid wireless network can scale linearly with n only if m = Ω(n), and when we assign all the bandwidth to the infrastructure mode traffics. We then investigate the delay in hybrid wireless networks. We find that the average packet delay can be maintained as low as Θ(1) even when the per-node throughput capacity is Θ(W).     

Novel Section‐Based Joint Network Coding and Scheduling Scheme in WMNs: JNCS

Guaranteeing quality of service over a multihop wireless network is difficult because end‐to‐end (ETE) delay is accumulated at each hop in a multihop flow. Recently, research has been conducted on network coding (NC) schemes as an alternative mechanism to significantly increase the utilization of valuable resources in multihop wireless networks. This paper proposes a new section‐based joint NC and scheduling scheme that can reduce ETE delay and enhance resource efficiency in a multihop wireless network. Next, this paper derives the average ETE delay of the proposed scheme and simulates a TDMA network where the proposed scheme is deployed. Finally, this paper compares the performance of the proposed scheme with that of the conventional sequential scheduling scheme. From the performance analysis and simulation results, the proposed scheme gives more delay‐ and energy‐efficient slot assignments even if the NC operation is applied, resulting in a use of fewer network resources and a reduction in ETE delay.     

无线网络编码增益感知的低时延路由协议

降低无线网络数据包传递时延对实时应用有重要的意义.该文提出了一种编码增益的计算方法和编码图的简化方法,并基于此提出了编码增益感知的路由协议CGAR(Coding Gain Aware Routing).CGAR利用网络编码增益和无线链路的期望传输次数ETX(Expected Transmission Count)计算传递一个来自新流的数据包所需要的时间,并以此为选路度量,旨在降低数据传递时延.仿真试验表明,CGAR的时延优于COPE和DCAR协议.     

Delay analysis in practical wireless network coding

Network coding provides a powerful mechanism for improving performance of wireless networks. In this paper, we present an analytical approach for end‐to‐end delay analysis in wireless networks that employs inter‐session network coding. Prior work on performance analysis in wireless network coding mainly focuses on the throughput of the overall network. Our approach aims to analyze the delay of each flow in the network. The theoretical basis of our approach is network calculus. In order to use network calculus to analyze the performance of traffic flows in the network, we have to address three specific problems: identifying traffic flows, characterizing broadcast links, and measuring coding opportunities. We propose solutions for these problems and discuss the practical issues when applying the approach in practice. We make three main contributions. First, we obtain theoretical formulations for computing the queueing delay bounds of traffic flows in wireless networks with network coding. Second, with the formulations, we figure out the factors that affect the queueing delay of a flow and find that first‐in first‐out scheduling cannot fully exploit the benefit of network coding. Third, in order to exploit our findings, we introduce a new scheduling scheme that can improve the performance of current practical wireless network coding. Copyright © 2012 John Wiley & Sons, Ltd.     

Hierarchy schedule-sensing protocol for CDMA wireless data-centric networks with multiple packet collision and capture effect

This paper focuses on performance analysis of a CDMA wireless data network based on hierarchy schedule-sensing (HSS) protocol, in which a common-code permission frame beacon is used to schedule request transmissions to avoid packet collisions. To further reduce scheduling delay, hierarchical group-based coding is adopted in the scheme. The performance of such a network is evaluated considering packet collisions with and without packet capture effect using a two-dimensional Markovian chain model. In particular, this paper will study the impact of multiple packet-collision effect on network performance with the help of the average packet-collision rate derived explicitly in the paper. The obtained results show that, despite its low implementation complexity, the HSS protocol is a fairly robust medium-access control protocol featuring uniformly high throughput and short delay even under very high traffic load, which especially suits data-centric wireless networks with relatively small coverage area and great node density.     

A one-hop opportunistic network coding algorithm for wireless mesh networks

This paper proposes a Bearing Opportunistic Network (BON) coding procedure that operates in wireless multihop networks over multiple unicast sessions and it introduces very low overhead to the network. The BON coding is used to increase network performance in terms of a higher throughput and a lower delay. It can be seen as an independent layer in the communication stack, relying solely on information that is on the node itself. The proposed coding procedure is easy to implement and deploy. The performance evaluation of the BON coding procedure was performed in a dedicated simulation model. The comparison was made to the well-known network coding procedure COPE and the case where network coding is not used at all. Results show that BON coding increases the network goodput and decreases the delay in comparison to COPE and case where network coding is not used.     

Efficient scalable video multicast based on network-coded communication

In order to increase the efficiency of mobile video transmission in a 5G network, this paper investigates a cooperative multicast of scalable video using network coding with adaptive modulation and coding over dedicated relay-based cellular networks. Different scalable video layers prefer different protection degrees, and user equipments (UEs) in different locations experience different packet loss rates in wireless networks. Guaranteeing that all UEs experience a certain level of video quality is one of the biggest challenges in scalable video multicast. Using the number of satisfied UEs as a metric, the proposed efficient scalable video multicast based on network-coded cooperation (SVM-NC) scheme, combined with adaptive modulation and coding, enhances the attainable system performance under strict time and bandwidth resource constraints for guaranteed smooth playback. Various simulations were performed for performance evaluation. The proposed scheme ensures that the expected percentage of satisfied UEs approximately achieves the maximum number of UEs in a multicast group by using network-coded cooperation over dedicated relay-based cellular networks. In addition, the peak signal-to-noise ratio metric is asymptotic to the maximum performance of high-resolution video quality offered by service providers.     

AEETC—adaptive energy-efficient timing control in wireless networks with network coding

Energy is a scarce resource in wireless networks. Network coding has been proposed recently as a means to reduce the number of transmissions and energy consumption. In this paper, we introduce timing control into network coding to further enhance its performance. It is found that when bandwidth is sufficient, the extra delay introduced by waiting for additional data to perform network coding will increase the number of codings without affecting system throughput. Both delay and throughput suffers when bandwidth is insufficient. An adaptive energy-efficient timing control algorithm called AEETC is proposed which can automatically adjust local node’s transmission behavior on the basis of the network traffic conditions. Simulation results demonstrate that AEETC increases network coding by 7% to 60% for light network load and is able to provide good performance in terms of delay, throughput and the number of successful codings.     

On the path-loss attenuation regime for positive cost and linear scaling of transport capacity in wireless networks

Wireless networks with a minimum inter-node separation distance are studied where the signal attenuation grows in magnitude as 1/ρ/sup δ/ with distance ρ. Two performance measures of wireless networks are analyzed. The transport capacity is the supremum of the total distance-rate products that can be supported by the network. The energy cost of information transport is the infimum of the ratio of the transmission energies used by all the nodes to the number of bit-meters of information thereby transported. If the phases of the attenuations between node pairs are uniformly and independently distributed, it is shown that the expected transport capacity is upper-bounded by a multiple of the total of the transmission powers of all the nodes, whenever δ>2 for two-dimensional networks or δ>5/4 for one-dimensional networks, even if all the nodes have full knowledge of all the phases, i.e., full channel state information. If all nodes have an individual power constraint, the expected transport capacity grows at most linearly in the number of nodes due to the linear growth of the total power. This establishes the best case order of expected transport capacity for these ranges of path-loss exponents since linear scaling is also feasible. If the phases of the attenuations are arbitrary, it is shown that the transport capacity is upper-bounded by a multiple of the total transmission power whenever δ>5/2 for two-dimensional networks or δ>3/2 for one-dimensional networks, even if all the nodes have full channel state information. This shows that there is indeed a positive energy cost which is no less than the reciprocal of the above multiplicative constant. It narrows the transition regime where the behavior is still open, since it is known that when δ<3/2 for two-dimensional networks, or δ<1 for one-dimensional networks, the transport capacity cannot generally be bounded by any multiple of the     

网络-信道联合编码的DmF协作通信技术

提出了一种采用网络-信道编码的解调前传(DmF)协作通信方案.与译码前传(DF)相比,DmF协作方式在中继处只对信号进行解调而非译码,因此,大大降低了中继节点的复杂度.在由两个用户、一个中继节点和一个基站组成的通信模型中,采用LDPC信道编码与网络编码结合的方式,构造了一种DmF协作传输方式.在基站处,通过构造的H矩阵对来自两用户及中继的信号进行联合译码.仿真结果表明:所给方案的性能优于非协作方式及无网络编码的协作通信方式,随着信噪比的增加这种优势会更加明显;另外,DmF的性能与DF的非常接近,但其设备复杂度却大大降低,因此DmF比DF方式更具实用性.同时,该方案在降低设备复杂度、减少延迟、有效对抗无线信道慢衰落、提高通信性能及频谱利用率等方面都是非常有效的.     

一种提高协作通信性能的新方法

传统的无线通信中,由于外部环境的干扰,信道的不稳定,网络的中断率比较高。在信道条件较差时,通信性能较差。本文利用无线通信节点间的合作,通过不同节点对信息的中继放大、解码（或者网络编码）,对直接传输的无线信道性能进行改进,大大提高了网络性能,降低网络的中断率;通过比较不同频谱效率下的不同转发方式的中断率性能,选择合适的传输方法。仿真实验得到：频谱效率小于一定值的情况下,利用放大和网络编码转发方式的性能大大高于直接传输方式。     

D2D网络中基于牺牲节点的网络编码协作重传策略

针对D2D无线网络中多终端并发协作重传过程中平均解码时延较高的问题,提出了一种牺牲节点的协作重传策略.在重传阶段,发送终端在立即可解网络编码(Instantly Decodable Network Coding,IDNC)图上根据接收终端与发送终端的链路质量、终端数据包权重和接收终端的连通度选择出发送终端的最优编码包,以降低系统的平均解码时延.同时,利用部分接收终端对最优编码包的无效解码和不可解码的特性,扩展了备选协作终端,使更多的终端参与到协作传输过程.仿真结果表明,所提策略有效降低了系统的平均解码时延和重传次数.     

Wireless network coding in slotted aloha with two-hop unbalanced traffic

This paper deals with two representative unbalanced traffic cases for two-hop wireless relay access systems employing network coding and a slotted ALOHA protocol. Network coding is a recent and highly regarded technology for capacity enhancement with multiple unicast and multisource multicast networks. We have analyzed the performance of network coding on a two-hop wireless relay access system employing the slotted ALOHA under a balanced bidirectional traffic. The relay nodes will generally undergo this unbalanced multidirectional traffic but the impact of this unbalanced traffic on network coding has not been analyzed. This paper provides closed-form expressions for the throughput and packet delay for two-hop unbalanced bidirectional traffic cases both with and without network coding even if the buffers on nodes are unsaturated. The analytical results are mainly derived by solving queueing systems for the buffer behavior at the relay node. The results show that the transmission probability of the relay node is a design parameter that is crucial to maximizing the achievable throughput of wireless network coding in slotted ALOHA on two-hop unbalanced traffic cases. Furthermore, we show that the throughput is enhanced even if the traffic at the relay node is unbalanced.     

On the improvement of scaling laws for large-scale MANETs with network coding

This paper investigates the problem of how much benefit network coding can contribute to the network performance in terms of throughput, delay, and storage requirements for mobile ad hoc networks (MANETs), compared to when only replication, storage and forwarding are allowed in relay nodes. We characterize the throughput-delay-storage tradeoffs under different node mobility patterns, i.e., i.i.d. and random walk mobility, with and without network coding. Our results show that when random linear coding instead of replication is used in MANETs, an order improvement on the scaling laws of MANETs can be achieved. Note that previous work showed that network coding could only provide constant improvement on the throughput of static wireless networks. Our work thus differentiates MANETs from static wireless networks by the role network coding plays.     

Topology-Transparent Transmission Scheduling Algorithms in Wireless Ad Hoc Networks

1　Introduction　A Mobile Ad Hoc Network (MANET) is formed by acluster of mobile hosts and can be rapidly deployed withoutany established infrastructure or centralized administration.The design of transmission scheduling is a key design prob lem in Ad Hoc networks. Many topology dependent trans mission scheduling algorithm have been proposed to minimizethe time division multiple access frame length, in whichchanges of topology inevitably require recompilations oftransmiss…     

Performance optimization of wireless local area networks through VLSI data compression

In contrast to wireline communication, the physical bandwidth of RF wireless communication systems is relatively limited and is unlikely to grow significantly in the future. Hence it is advantageous to increase the effective bandwidth of communication channels at the expense of complex processing at both the sending and receiving entities. In this paper we present a real-time, low-area, and low-power VLSI lossless data compressor based on the first Lempel–Ziv algorithm (Ziv and Lempel, 1977) to improve the performance of wireless local area networks. Our architecture can achieve an average compression rate of 50 Mbps thus providing sufficient performance for all current and most foreseeable future wireless LANs. Since the architecture including a dictionary contains less than 40 K transistors and consumes approximately 70 mW in 1.2 CMOS, it enables low-cost, adaptive, and transparent data compression to be employed in wireless LANs. Its small size allows it to be implemented on an ASIC, as part of a new DSP, or in configurable FPGA technology. To estimate the impact of VLSI compression, we use network simulations to analyze the performance and the power consumption of the compression in the context of a WLAN protocol. In particular, we consider the proposed IEEE WLAN protocol standard 802.11 (IEEE Standard Group, 1994). The compression ratio is modeled as a random variable with a Gaussian distribution based on empirical studies (Cressman, 1994; Pawlikowski et al., 1995). Our results show that efficient real-time data compression can greatly improve the throughput and the delay of a medium-to-heavily loaded network while minimizing the average power vs. throughput ratio.     

Delay Optimal Scheduling in a Two-Hop Vehicular Relay Network

We study a scheduling problem in a wireless network where vehicles are used as store-and-forward relays, a situation that might arise, for example, in practical rural communication networks. A fixed source node wants to transfer a file to a fixed destination node, located beyond its communication range. In the absence of any infrastructure connecting the two nodes, we consider the possibility of communication using vehicles passing by. Vehicles arrive at the source node at renewal instants and are known to travel towards the destination node with average speed v sampled from a given probability distribution. The source node communicates data packets (or fragments) of the file to the destination node using these vehicles as relays. We assume that the vehicles communicate with the source node and the destination node only, and hence, every packet communication involves two hops. In this setup, we study the source node’s sequential decision problem of transferring packets of the file to vehicles as they pass by, with the objective of minimizing delay in the network. We study both the finite file size case and the infinite file size case. In the finite file size case, we aim to minimize the expected file transfer delay, i.e., expected value of the maximum of the packet sojourn times. In the infinite file size case, we study the average packet delay minimization problem as well as the optimal tradeoff achievable between the average queueing delay at the source node buffer and the average transit delay in the relay vehicle.     

Asymptotic Distortion Performance of Source-Channel Diversity over Multihop and Relay Channels

A key challenge in the design of real-time wireless multimedia systems is the presence of fading coupled with strict delay constraints. A very effective answer to this problem is the use of diversity achieving techniques to overcome the fading nature of the wireless channels caused by the mobility of the nodes. The mobility of the nodes gives rise to the need of cooperation among the nodes to enhance the system performance. This paper focuses on comparing systems that exhibit diversity of three forms: source coding diversity, channel coding diversity, and user cooperation diversity implemented through multihop or relay channels with amplify-and-forward or decode-and-forward protocols. Commonly used in multimedia communications, performance is measured in terms of the distortion exponent, which measures the rate of decay of the end-to-end distortion at asymptotically high signal-to-noise ratio (SNR). For the case of repetition coding at the relay nodes, we prove that having more relays is not always beneficial. For the general case of having a large number of relays that can help the source using repetition coding, the optimum number of relay nodes that maximizes the distortion exponent is determined in this paper. This optimum number of relay nodes will depend on the system bandwidth as well as the channel quality. The derived result shows a trade-off between the quality (resolution) of the source encoder and the amount of cooperation (number of relay nodes). Also, the performances of the channel coding diversity-based scheme and the source coding diversity-based scheme are compared. The results show that for both relay and multihop channels, channel coding diversity provides the best performance, followed by the source coding diversity.     

多源多目的模型中网络编码的时延性能分析

研究表明基于无线信道的广播特性,网络编码技术能够显著降低多播通信中的传输时延。多源多播模型中,在任一源节点已知其他源节点信息的条件下,现有传输方案能够确保系统时延最小化。本文在其他源节点信息未知时,对现有多源多目的单中继模型应用网络编码后的时延性能进行分析,并将该模型推广到多中继模型,提出了基于网络编码和机会中继选择策略的MR-OPP-NC方案,并在译码转发机制下,利用中断概率量化了应用网络编码前后的时延性能,仿真表明本文所提MR-OPP-NC方案与未使用网络编码的机会中继方案相比较,能获得显著的时延增益。      

Performance analysis of slotted ALOHA and network coding for single-relay multi-user wireless networks

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.