Minimum power energy spanners in wireless ad hoc networks

A power assignment is an assignment of transmission power to each of the nodes of a wireless network, so that the induced communication graph has some desired properties. The cost of a power assignment is the sum of the powers. The energy of a transmission path from node u to node v is the sum of the squares of the distances between adjacent nodes along the path. For a constant t > 1, an energy t-spanner is a graph G′, such that for any two nodes u and v, there exists a path from u to v in G′, whose energy is at most t times the energy of a minimum-energy path from u to v in the complete Euclidean graph. In this paper, we study the problem of finding a power assignment, such that (1) its induced communication graph is a ‘good’ energy spanner, and (2) its cost is ‘low’. We show that for any constant t > 1, one can find a power assignment, such that its induced communication graph is an energy t-spanner, and its cost is bounded by some constant times the cost of an optimal power assignment (where the sole requirement is strong connectivity of the induced communication graph). This is a significant improvement over the previous result due to Shpungin and Segal in Proceedings of 28th IEEE INFOCOM, pp 163–171, (2009).     

Utilizing detours for energy conservation in mobile wireless networks

Autonomous robotic systems have been gaining the attention of research community in mobile ad hoc network since the past few years. While motion cost and communications cost constitute the primary energy consumers, each of them is investigated independently. By taking into account the power consumption of both entities, the overall energy efficiency of a system can be further improved. In this paper, the energy optimization problem of radio communication and motion is examined. We consider a hybrid wireless network in two scenarios: first, a single autonomous mobile node communicating with multiple static relays through single hop, and secondly, a single mobile node communicating with a static base station via a mobile relay. The mobile node interacts with the relays within its vicinity by continuously transmitting high-bandwidth data, e.g. triggered by a multimedia application like video surveillance. The goal is to find the best paths such that the energy consumption for both mobility and communications is minimized for all mobile nodes. We introduce Radio-Energy-Aware (REA) path computation strategy by utilizing node mobility. Given the starting point, the target point and the position of the relays, our simulation results show that the proposed strategy improves the energy efficiency of mobile node compared to Motion-Energy-Aware (MEA) path constructed based only on the mobility cost.     

Joint mobile wireless energy transmitter and data collector for rechargeable wireless sensor networks

Wireless Networks - Energy efficiency and data gathering are the primary goals of wireless sensor networks (WSNs), challenging. Mobile sink and mobile chargers are two promising techniques for data...     

Adaptive clustering for mobile wireless networks

This paper describes a self-organizing, multihop, mobile radio network which relies on a code-division access scheme for multimedia support. In the proposed network architecture, nodes are organized into nonoverlapping clusters. The clusters are independently controlled, and are dynamically reconfigured as the nodes move. This network architecture has three main advantages. First, it provides spatial reuse of the bandwidth due to node clustering. Second, bandwidth can be shared or reserved in a controlled fashion in each cluster. Finally, the cluster algorithm is robust in the face of topological changes caused by node motion, node failure, and node insertion/removal. Simulation shows that this architecture provides an efficient, stable infrastructure for the integration of different types of traffic in a dynamic radio network     

Tracking mobile users in wireless communications networks

Tracking strategies for mobile wireless networks are studied. A cellular architecture in which base stations that are interconnected by a wired network communicate with mobile units via wireless links is assumed. The cost of utilizing the wireless links for the actual tracking of mobile users is considered. A tracking strategy in which a subset of all base stations is selected and designed as reporting centers is proposed. Mobile users transmit update messages only upon entering cells of reporting centers, while every search for a mobile user is restricted to the vicinity of the reporting center to which the user last reported. It is shown that, for an arbitrary topology of the cellular network (represented by the mobility graph), finding an optimal set of reporting centers is an NP-complete problem. Optimal and near-optimal solutions for important special cases of the mobility graph are presented     

Minimum delay routing for wireless networks with STDMA

STDMA emerges as a promising channel access technique for providing Quality of Service (QoS) guarantees in multi-hop ad hoc networks such as community mesh and sensor networks. The contention-free channel access combined with spatial reuse of the channel provide significant benefits in the energy/throughput trade-off. On the other hand, the time-multiplexed communication introduces extra delay on the packets when relayed by intermediate nodes. Hence in large wireless sensor networks or mesh networks, where data is routed over several hops before reaching the data sink, STDMA protocols may introduce high end-to-end latency due to the reservation-based access policy. We argue that a suitable routing protocol specifically designed for reservation-based Medium Access Control (MAC) protocols can alleviate their high-latency drawback. Following this argument, we propose first such routing algorithms working on top of a generic STDMA MAC protocol. First, we consider routing with data fusion and present our GreenWave routing idea. We show that our algorithm significantly reduces the end-to-end delay when compared to routing over the shortest-hop paths. Second, we consider routing without data fusion, by taking into account the effect of congestion along the paths on the end-to-end delays. We provide a QIP formulation of the problem, and present a lower bound and a heuristic algorithm to bound the optimal solution. Based on the centralized heuristic algorithm, we propose a distributed, dynamic routing protocol GreenWave routing with Congestion and Flow control (GWCF), which uses a novel congestion and flow control technique utilizing the underlying contention-free protocol. We show by simulations that GWCF routing significantly improves the end-to-end delay while increasing the network throughput when compared to routing over shortest paths.

Infrastructure-based MAC in wireless mobile ad-hoc networks

The IEEE 802.11 standard is the most popular Medium Access Control (MAC) protocol for wireless local area networks. However, in an ad-hoc environment, the Point Coordination Function (PCF), defined in the standard, cannot be readily used. This is due to the fact that there is no central authority to act as a Point Coordinator (PC). Peer-to-peer ad-hoc mode in the IEEE 802.11 standard only implements the Distributed Coordination Function (DCF). In this paper, an efficient and on-the-fly infrastructure is created using our proposed Mobile Point Coordinator (MPC) protocol. Based on this protocol, we also develop an efficient MAC protocol, namely MPC–MAC. Our MAC protocol extends the IEEE 802.11 standard for use in multi-hop wireless ad-hoc networks implementing both the DCF and PCF modes of operation. The goal, and also the challenge, is to achieve QoS delivery and priority access for real-time traffic in ad-hoc wireless environments while maintaining backward compatibility with the IEEE 802.11 standard. The performance of MPC–MAC is compared to the IEEE 802.11 DCF-based MAC without MPC. Simulation experiments show that in all cases the use of PCF benefits real-time packets by decreasing the average delay and the discard ratio. However, this may come at the expense of increasing the average delay for non-real-time data. On the other hand, the discard ratio for both real-time and non-real-time packets improves with the use of PCF. Therefore, our MPC–MAC outperforms the standard DCF IEEE 802.11 MAC protocol in multi-hop ad-hoc environments.     

Minimum cost localization problem in wireless sensor networks

Localization is a fundamental problem in wireless sensor networks. Current localization algorithms mainly focus on checking the localizability of a network and/or how to localize as many nodes as possible given a static set of anchor nodes and distance measurements. In this paper, we study a new optimization problem, minimum cost localization problem, which aims to localize all sensors in a network using the minimum number (or total cost) of anchor nodes given the distance measurements. We show this problem is very challenging and then present a set of greedy algorithms using both trilateration and local sweep operations to address the problem. Extensive simulations have been conducted and demonstrate the efficiency of our algorithms.     

Optimization energy consumption with multiple mobile sinks using fuzzy logic in wireless sensor networks

Wireless Networks - Each sensor in WSNs receives data from the limited area under its coverage. The received data is processed by the sensor; then, it is wirelessly transmitted to the sink....     

Link energy minimization for wireless networks

In this paper, we formalize the problem of minimizing the energy dissipated to successfully transmit a single information bit over a link, considering circuit power consumption, packetization and retransmission overhead, bit/packet error probability, and the duty cycle of the transceiver. We optimize the packet length and transmit power as a function of distance between the transmitter and the receiver for different modulation schemes. We propose a general unconstrained energy consumption model that provides a lower bound on the energy dissipated per information bit. A practical unconstrained physical layer optimization scheme is also provided to illustrate the utilization of the model. Furthermore, minimized energy consumptions of different modulation schemes are compared over an additive white Gaussian noise (AWGN) channel. We extend this general energy consumption model by considering two particular constraints: fixed average power and fixed average rate. We explore the impact of the average power and the information rate constraints on energy consumption and determine the optimum constellation size, packet length, and duty cycle.     

Improving performance of TCP over mobile wireless networks

Mobile IP is a network layer protocol for handling mobility of hosts in the Internet. However, mobile IP handoff causes degradation of TCP performance. Hence, there is a need for improving performance of TCP over mobile IP in wireless mobile networks. We propose an approach which handles losses due to both wireless link errors and host mobility. To handle losses due to host mobility, a method for seamless handoff is proposed. Empirical results show that the scheme provides substantial improvement of performance.

Monte Carlo localization for mobile wireless sensor networks

Localization is crucial to many applications in wireless sensor networks. In this article, we propose a range-free anchor-based localization algorithm for mobile wireless sensor networks that builds upon the Monte Carlo localization algorithm. We concentrate on improving the localization accuracy and efficiency by making better use of the information a sensor node gathers and by drawing the necessary location samples faster. To do so, we constrain the area from which samples are drawn by building a box that covers the region where anchors’ radio ranges overlap. This box is the region of the deployment area where the sensor node is localized. Simulation results show that localization accuracy is improved by a minimum of 4% and by a maximum of 73% (average 30%), for varying node speeds when considering nodes with knowledge of at least three anchors. The coverage is also strongly affected by speed and its improvement ranges from 3% to 55% (average 22%). Finally, the processing time is reduced by 93% for a similar localization accuracy.     

Analysis of link lifetime in wireless mobile networks

Link lifetime (LL) analysis is crucially important in designing and evaluating wireless mobile network protocols. Although a considerable amount of research has been conducted on this issue, the current paper studies several aspects of link lifetime for the first time, e.g. a closed form expression for the probability distribution of the residual link lifetime (RLL) for the constant velocity mobility model is obtained, which facilitates marginal studies on the behavior of link lifetime. As a case, using a tail analysis of LL and RLL distributions, we analytically prove that they are heavy-tailed. Using this outcome, a self-similar behavior in the traffic pattern of a sample delay tolerant network is justified analytically. To extend the model, the effect of stationary nodes, the effect of buffer zone, and the effect of link establishment policies between different node categories on the link lifetime are investigated. Extensive simulation experiments are performed to validate the obtained analytical results and derivations precisely. Moreover, simulation results confirm that the analytic results can also be used for two well known mobility models (random waypoint and random direction) with a negligible error.     

A distributed routing algorithm for mobile wireless networks

We present a loop-free, distributed routing protocol for mobile packet radio networks. The protocol is intended for use in networks where the rate of topological change is not so fast as to make flooding the only possible routing method, but not so slow as to make one of the existing protocols for a nearly-static topology applicable. The routing algorithm adapts asynchronously in a distributed fashion to arbitrary changes in topology in the absence of global topological knowledge. The protocol's uniqueness stems from its ability to maintain source-initiated, loop-free multipath routing only to desired destinations with minimal overhead in a randomly varying topology. The protocol's performance, measured in terms of end-to-end packet delay and throughput, is compared with that of pure flooding and an alternative algorithm which is well-suited to the high-rate topological change environment envisioned here. For each protocol, emphasis is placed on examining how these performance measures vary as a function of the rate of topological changes, network topology, and message traffic level. The results indicate the new protocol generally outperforms the alternative protocol at all rates of change for heavy traffic conditions, whereas the opposite is true for light traffic. Both protocols significantly outperform flooding for all rates of change except at ultra-high rates where all algorithms collapse. The network topology, whether dense or sparsely connected, is not seen to be a major factor in the relative performance of the algorithms.The work of A. Ephremides was supported in part by the National Science Foundation under grants D-CDR-8803012 and EEC94-02384.     

An Aloha protocol for multihop mobile wireless networks

An Aloha-type access control mechanism for large mobile, multihop, wireless networks is defined and analyzed. This access scheme is designed for the multihop context, where it is important to find a compromise between the spatial density of communications and the range of each transmission. More precisely, the analysis aims at optimizing the product of the number of simultaneously successful transmissions per unit of space (spatial reuse) by the average range of each transmission. The optimization is obtained via an averaging over all Poisson configurations for the location of interfering mobiles, where an exact evaluation of signal over noise ratio is possible. The main mathematical tools stem from stochastic geometry and are spatial versions of the so-called additive and max shot noise processes. The resulting medium access control (MAC) protocol exhibits some interesting properties. First, it can be implemented in a decentralized way provided some local geographic information is available to the mobiles. In addition, its transport capacity is proportional to the square root of the density of mobiles which is the upper bound of Gupta and Kumar. Finally, this protocol is self-adapting to the node density and it does not require prior knowledge of this density.     

Secure routing in mobile wireless ad hoc networks

We discuss several well known contemporary protocols aimed at securing routing in mobile wireless ad hoc networks. We analyze each of these protocols against requirements of ad hoc routing and in some cases identify fallibilities and make recommendations to overcome these problems so as to improve the overall efficacy of these protocols in securing ad hoc routing, without adding any significant computational or communication overhead.     

An image processing inspired mobile sink solution for energy efficient data gathering in wireless sensor networks

Wireless Networks - This paper presents a gradient-based multi-hop clustering protocol combined with a mobile sink (MS) solution for efficient data gathering in wireless sensor networks. The main...     

Online energy aware routing in wireless networks

Online energy aware routing in wireless networks is the problem of finding energy efficient routes that maximize the network lifetime without the knowledge of future message flows. To maximize network lifetime, the paths for message flows are chosen in such a way that the total energy consumed along the path is minimized while avoiding energy depleted nodes. Finding paths which consume minimum energy and finding paths which do not use energy depleted nodes lead to conflicting objectives. In this paper, we propose two-phased energy aware routing strategies that balance these two conflicting objectives by transforming the routing problem into a multi-metric widest path problem. We find that the proposed approaches outperform the best-known algorithms in the literature. We also demonstrate a simple but insightful relationship between the total energy required along a path and the minimum remaining energy of a node along the path. We further exploit this relationship to show that staying within the solution space of paths with high residual energy and low total energy provides much improved lifetimes in general.