Efficient broadcast for wireless ad hoc networks with a realistic physical layer

In this paper, we investigate the low coverage problem of efficient broadcast protocols in wireless ad hoc networks with realistic physical layer models. To minimize energy consumption, efficient protocols aim to select small set of forward nodes and minimum transmission radii. In ideal physical layer model, nodes within forward nodes’ transmission ranges can definitely receive packets; therefore energy efficient protocols can guarantee full coverage for broadcasting. However, in networks with a realistic physical layer, nodes can only receive packets with probability. We present an analytical model to show that the transmission radii used for nodes can be used to establish a tradeoff between minimizing energy consumption and ensuring network coverage. We then propose a mechanism called redundant radius, which involves using two transmission radii, to form a buffer zone that guarantees the availability of logical links in the physical network, one for broadcast tree calculation and the other for actual data transmission. With this mechanism, we extend well-known centralized protocols, BIP and DBIP, and corresponding localized protocols, LBIP and LDBIP. The effectiveness of the proposed scheme in improving network coverage is validated analytically and by simulation.     

On broadcasting with cooperative diversity in multi-hop wireless networks

Cooperative diversity facilitates spatio-temporal communications without requiring the deployment of physical antenna arrays. While physical layer studies on cooperative diversity have been extensive, higher layer protocols which translate the achievable reduction in the SNR per bit for a given target BER, into system wide performance enhancements are yet to mature. The challenge is that appropriate higher layer functions are needed in order to enable cooperative diversity at the physical layer. We focus on network-wide broadcasting with the use of cooperative diversity in ad hoc networks. We design a novel distributed network-wide broadcasting protocol that takes into account the physical layer dependencies that arise with cooperative diversity. We perform extensive simulations that show that our protocol can outperform the best of the noncooperative broadcasting protocols by: (a) achieving up to a threefold increase in network coverage and, (b) by decreasing the latency incurred during the broadcast by about 50%. We also construct an analytical model that captures the behavior of our protocol. Furthermore, we show that computing the optimal solution to the cooperative broadcast problem is NP-complete and construct centralized approximation algorithms. Specifically, we construct an O(N ^epsi)-approximation algorithm with a computational complexity of O(N4/epsi); we also construct a simpler greedy algorithm.. The costs incurred with these algorithms serve as benchmarks with which one can compare that achieved by any distributed protocol     

Efficient geocasting with multi-target regions in mobile multi-hop wireless networks

Geocasting, a variation on the notion of multicasting, is a mechanism to deliver messages of interest to all nodes within a certain geographical target region. Although several geocasting protocols have already been proposed for multi-hop wireless networks, most of these algorithms consider a “single” target region only. Here, when more than one target regions need to receive the same geocast messages, multiple transmissions need to be initiated separately by the message source. This causes significant performance degradation due to redundant packet transmissions, and it becomes more severe as the number of target regions increase. To solve this problem, we propose a basic scheme and its variations which utilize the geometric concept of “Fermat point” to determine the optimal junction point among multiple geocast regions from the source node. Our simulation study using ns-2 shows that the proposed schemes can effectively reduce the overhead of message delivery while maintaining a high delivery ratio in mobile multi-hop wireless networks.     

Efficient delay based scheduling with fairness in multi-hop wireless mesh networks

Some scheduling algorithms have been designed to improve the performance of multi-hop wireless mesh networks (WMNs) recently. However the end-to-end delay is seldom considered as the complexity of multi-hop topology and open wireless shared channel. This article proposes an efficient delay based scheduling algorithm with the concept of buffer-data- hops. Considering the demand satisfaction factor (DSF), the proposed algorithm can also achieve a good fairness performance. Moreover, with the interference-based network model, the scheduling algorithm can maximize the spatial reuse, compared to those graph-based scheduling algorithms. Detailed theoretical analysis shows that the algorithm can minimize the end-to-end delay and make a fair scheduling to all the links.     

Efficient broadcasting protocols for regular wireless sensor networks

The wireless sensor network (WSN) has attracted lots of attention recently. Broadcast is a fundamental operation for all kinds of networks and it has not been addressed seriously in the WSN. Therefore, we propose two types of power and time efficient broadcasting protocols, namely one‐to‐all and all‐to‐all broadcasting protocols, for five different WSN topologies. Our one‐to‐all broadcasting protocols conserve power and time by choosing as few relay nodes as possible to scatter packets to the whole network. Besides, collisions are carefully handled such that our one‐to‐all broadcasting protocols can achieve 100% reachability. By assigning each node a proper channel, our all‐to‐all broadcasting protocols are collision free and efficient. Numerical evaluation results compare the performance of the five topologies and show that our broadcasting protocols are power and time efficient. Copyright © 2005 John Wiley & Sons, Ltd.     

Experimental investigation of wireless link layer for multi-hop oceanographic-sensor networks

A wireless link layer designed for a spatially distributed, ad hoc multi-hop wireless sensor network for use in oceanography is described.     

Efficient multicasting and broadcasting in layer 2 provider backbone networks

Ethernet has grown from its roots in LANs to contend in previously unchartered territory of MANs and WANs. A slew of projects underway in the IEEE 802 standards bodies plan to groom Ethernet with carrier grade features like high availability, fault management, and resiliency thus far found only in other circuit-switched technologies. These include, among others, IEEE 802.1ag (connectivity fault management), IEEE 802.1ad (provider bridges), and IEEE 802.1ah (provider backbone bridges). IEEE 802.1ah addresses the service and MAC address scalability of provider backbone bridges. Since Ethernet has been architected and designed for a shared medium, it inherently handles broadcast and multicast traffic very efficiently, unlike layer 3 technologies, where multicasting and broadcasting rely on using multiple point-to-point connections. With IEEE 802.1ah, Ethernet would be able to provide millions of service instances in a provider backbone network. While flooding of frames in a LAN may provide for good multicasting, flooding of data in a MAN or WAN could mean huge bandwidth wastages, especially when the remote peers are geographically distant, and the traffic is not necessarily destined to any of its local ports of the peers. In this article we explore technologies to Address efficient multicasting in provider backbone networks. We also consider extending this technology to address unknown unicast floods and efficient proxy of customer multicast frames.     

多跳无线传感器网络吞吐量分析

针对无线传感器网络这种典型多跳网络的吞吐量进行了理论分析,提出了在线性网络路由的情况下的网络吞吐量的计算模型,并通过NS-2仿真模拟进行了验证。发现吞吐量随着网络节点数目的增加而呈现出一种类似于简谐振动的变化,并且最终收敛到一个稳定值。这一规律揭示了无线传感器网络的节点行为特征与网络吞吐量之间的内在联系,对网络性能的优化具有指导性的帮助。     

Ripple: a wireless token-passing protocol for multi-hop wireless mesh networks

This work presents a wireless token-passing protocol, named Ripple, for wireless mesh networks (WMNs). In contrast to existing random-access approaches, Ripple uses a decentralized controlled-access approach to protect nodes from unintentional packet collisions and maximize the spatial reuse. The performance of Ripple under an error-free wireless channel was investigated and the accuracy of the analysis was verified by simulation. Simulation results also indicated that Ripple achieved throughput, stability, and QoS enhancement than that of 802.11 DCF under a highly loaded situation.     

Segment cooperation communication in multi-hop wireless networks

Cooperative communication could enhance the performance of wireless communications by allowing nodes to cooperate with each other to provide spatial diversity gain. In cooperative communications, rational helper selection is an important issue to obtain good cooperative gain at destinations. There are many works on this topic; however, most of them are based on hop-by-hop model and few works investigate how to select helpers for the nodes in a multi-hop path to optimize the end-to-end performance. The helper selection for one node could affect the helper selection for other nodes on the same route and in turn affect end-to-end performance. In other words, the traditional hop-by-hop helper selection methods could not lead to optimal performance in multi-hop environments. To solve this, this paper firstly defines a novel cooperation mode, named segment cooperation, and deduces the capacity and outage probability of cooperation segment. Then new performance metrics, end-to-end capacity and end-to-end outage probability, are defined to measure the end-to-end performance of multi-hop route. Finally, a segment cooperation method is proposed to maximize these metrics.     

多跳多中继无线网络中的协作波束形成技术

针对多跳多中继无线网络中的协作波束形成技术进行研究.在基于放大转发机制的三跳协作通信系统中,对2个中继节点簇的协作波束形成矢量进行联合设计,以求在目标节点获得最大的接收信噪比.该方法首先将原始优化问题加以推导简化,然后应用半定规划方法求解获得协作波束形成矢量的次优解,并结合对分搜索算法加以改进.仿真结果表明,提出的协作波束形成方法可取得明显优于固定放大增益中继策略的接收信噪比.     

Capacity of FH wireless multi-hop networks

In this article, the capacity of wireless multi-hop networks with the frequency hopping (FH) technique is derived. Different from the previous work based on non- spread spectrum (SS) system, this study is based on frequency hopping spread spectrum (FHSS) and the retransmission mechanism. The analysis results show that the normalized transport capacity decreases as 1/(Mλ) , when the total available frequency band is divided into M sub-bands for frequency hopping and the nodes are randomly distributed in space according to a Poisson point process with intensity λ . In this work, the best transmission range per hop to get the maximum capacity is also derived. Besides, the results summarize how the capacity of FH wireless multihop networks is affected by the outage probability, target signal to interference plus noise ratio (SINR) and other system parameters.     

SWIPT in multi-hop amplify-and-forward wireless sensor networks

ABSTRACT

Energy harvesting (EH) is an eminent solution to perpetuate the lifetime of energy-constrained relay nodes in wireless sensor networks (WSNs). This paper considers a multi-hop amplify-and-forward (AF) network in which relay nodes with EH capability harvest energy inherent in the source transmitted radio frequency (RF) signal and use the harvested energy for signal transmission. Based on the time switching and power splitting EH receiver designs, we have examined the performance of, (i) time switching based relaying (TSR) and (ii) power splitting based relaying (PSR) protocols in multi-hop AF network, with throughput as the figure of merit. The numerical analysis reveals that, PSR outperforms TSR at high signal-to-noise ratio (SNR) whereas TSR outperforms PSR at low SNR, in multi-hop AF-WSNs with energy harvesting.     

Analysis of TCP performance on multi-hop wireless networks: A cross layer approach

In Multi-Hop Wireless Networks (MHWNs), wireless nodes cooperate to forward traffic between end points that are not in direct communication range. Specifically, traffic is forwarded from a source towards its destination through intermediate nodes that form a wireless multi-hop chain. Researchers have studied the performance of TCP over chains discovering properties such as how the number of hops reduces chain throughput as neighboring links contend for the shared medium. Moreover, the presence of hidden terminals has also been shown to negatively affect performance of example chains. In this paper, we leverage recent characterization of how competing wireless links interact to develop an in-depth analysis of TCP performance over wireless chains. In particular, there are a number of possible modes of interference between competing links with distinct implications on performance and fairness; to our knowledge, this is the first work that studies the impact of these different modes on TCP chain performance. We classify chains according to interference modes considering both the forward (data) and reverse (acknowledgment) traffic. Chain geometry limits the types of chains that arise most frequently in practice. We evaluate TCP performance over the most frequently occurring chain types and observe significant performance differences between chains that have the same hop count. Different four-hop chains, for example, show a throughput difference of up to 25% and a retransmission overhead difference of over 90%. We discuss the implications of these differences on network performance: specifically, route instability and bandwidth usage generated. We extend this analysis to two single-hop TCP flows and quantify the effect of interference interactions between two flows. This study is a first step towards completely understanding the performance of multiple TCP flows over multiple hops in a MHWN.     

Design guidelines for routing protocols in ad hoc and sensor networks with a realistic physical layer

We present guidelines on how to design network layer protocols when the unit disk graph (UDG) model is replaced by a more realistic physical layer model. Instead of merely using the transmission radius in the UDG model, physical, MAC, and network layers share the information about a bit and/or packet reception probability as a function of distance between nodes. We assume that all nodes use the same transmission power for sending messages, and that a packet is received when all its bits are correctly received. The MAC layer reacts to this probabilistic reception information by adjusting the number of acknowledgments and/or retransmissions. We observe that an optimal route discovery protocol cannot be based on a single retransmission by each node, because such a search may fail to reach the destination or find the optimal path. Next, we discuss that gaining neighbor knowledge information with "hello" packets is not a trivial protocol. We describe localized position-based routing protocols that aim to minimize the expected hop count (in case of hop-by-hop acknowledgments and fixed bit rate) or maximize the probability of delivery (when acknowledgments are not sent). We propose a guideline for the design of greedy position-based routing protocols with known destination locations. The node currently holding the message forwards it to a neighbor (closer to the destination than itself) that minimizes the ratio of cost over progress, where the cost measure depends on the assumptions and metrics used, while the progress measures the difference in distances to the destination. We consider two basic medium access layer approaches, with fixed and variable packet lengths. This article serves as a preliminary contribution toward the development of network layer protocols that match the assumptions and criteria already used in simulators and ultimately in real equipment.     

Distributed fault-tolerant topology control in wireless multi-hop networks

In wireless multi-hop and ad-hoc networks, minimizing power consumption and at the same time maintaining desired properties of the network topology is of prime importance. In this work, we present a distributed algorithm for assigning minimum possible power to all the nodes in a static wireless network such that the resultant network topology is k-connected. In this algorithm, a node collects the location and maximum power information from all nodes in its vicinity, and then adjusts the power of these nodes in such a way that it can reach all of them through k optimal vertex-disjoint paths. The algorithm ensures k-connectivity in the final topology provided the topology induced when all nodes transmit with their maximum power is k-connected. We extend our topology control algorithm from static networks to networks having mobile nodes. We present proof of correctness for our algorithm for both static and mobile scenarios, and through extensive simulation we present its behavior.     

On the connectivity of wireless multi-hop networks with arbitrary wireless channel models

Considering a wireless multi-hop network where a total of n nodes are randomly, independently and uniformly distributed in a unit square in R² and each node has a uniform transmission power, a fundamental problem is to investigate the connectivity of such networks. In this letter, we prove that the probability of having a connected network and the probability of having no isolated node asymptotically converges to the same value as n goes to infinity for an arbitrary wireless channel model satisfying certain intuitively reasonable conditions.     

Neighbor caching in multi-hop wireless ad hoc networks

We propose a neighbor caching strategy to overcome the overhead of multi-hop wireless communications. Neighbor caching makes a node able to expand its caching storage instantaneously by storing its data in the storage of idle neighbors. We also present the ranking based prediction that selects the most appropriate neighbor which data can be stored in. The ranking based prediction is an adaptive algorithm that adjusts the frequency of neighbor caching and makes neighbor caching flexible according to the idleness of nodes.     

编码感知多跳无线网络安全路由协议

分析了网络编码系统DCAR"编码+路由"发现过程存在的安全问题,提出了适用于编码感知安全路由协议的安全目标,设计了基于DCAR的编码感知安全路由协议DCASR,DCASR协议利用密码学机制保证可信路由建立和正确编码机会发现。为建模多跳无线网络特征和分析路由协议安全性,引入线程位置和线程位置相邻概念扩展安全系统逻辑LS2,提出了分析路由协议安全性的逻辑LS2-RP。LS2-RP用线程邻居集及邻居集的变化描述多跳无线网络的动态拓扑关系,用广播规则模型化多跳无线网络广播通信特征。最后,用LS2-RP协议编程语言描述了DCASR协议,用LS2-RP的谓词公式和模态公式描述DCASR协议的安全属性,用LS2-RP逻辑证明系统分析了DCASR协议的安全性,证明DCASR协议能够满足安全目标。     

Cooperative quadrature physical layer network coding in wireless relay networks

This paper proposes a cooperative quadrature physical layer network coding (CQPNC) scheme for a dual‐hop cooperative relay network, which consists of two source nodes, one relay node and one destination node. All nodes in the network have one antenna, and the two source nodes transmit their signals modulated with quadrature carriers. In this paper, a cooperative quadrature physical layer network coded decode‐and‐forward (DF) relay protocol (CQPNC‐DF) is proposed to transmit the composite information from the two source nodes via the relay node to the destination node simultaneously to reduce the number of time slots required for a transmission. The proposed CQPNC‐DF relay protocol is compared with time‐division multiple‐access amplify‐and‐forward (TDMA‐AF), TDMA‐DF, cooperative network coded DF (CNC‐DF) and cooperative analog network coded AF (CANC‐AF) relay protocols to demonstrate its effectiveness in terms of bit error rate (BER) and system throughput under different propagation conditions. The simulation results reveal that the proposed CQPNC‐DF relay protocol can significantly improve the network performance. Compared with two TDMA schemes and CNC‐DF, the proposal can provide up to 100% and 50% throughput gains, respectively. Moreover, no matter what the scene, the proposed scheme always has the lowest BER in the low SNR region. Copyright © 2013 John Wiley & Sons, Ltd.