Javad Vazifehdan

Energy-Efficient Reliable Routing Considering Residual Energy in Wireless Ad Hoc Networks

We propose two novel energy-aware routing algorithms for wireless ad hoc networks, called reliable minimum energy cost routing (RMECR) and reliable minimum energy routing (RMER). RMECR addresses three important requirements of ad hoc networks: energy-efficiency, reliability, and prolonging network lifetime. It considers the energy consumption and the remaining battery energy of nodes as well as quality of links to find energy-efficient and reliable routes that increase the operational lifetime of the network. RMER, on the other hand, is an energy-efficient routing algorithm which finds routes minimizing the total energy required for end-to-end packet traversal. RMER and RMECR are proposed for networks in which either hop-by-hop or end-to-end retransmissions ensure reliability. Simulation studies show that RMECR is able to find energy-efficient and reliable routes similar to RMER, while also extending the operational lifetime of the network. This makes RMECR an elegant solution to increase energy-efficiency, reliability, and lifetime of wireless ad hoc networks. In the design of RMECR, we consider minute details such as energy consumed by processing elements of transceivers, limited number of retransmissions allowed per packet, packet sizes, and the impact of acknowledgment packets. This adds to the novelty of this work compared to the existing studies.

Reincarnation in the Ambiance: Devices and Networks with Energy Harvesting

Miniaturization of devices with higher computational capacity coupled with advancement in communication technologies is driving the growth of deployment of sensors and actuators in our surroundings. To keep up the pace with this growth, these tiny, battery-powered devices need small-sized and high-energy density batteries for longer operational time, which calls for improvement in battery technologies. An alternative is to harvest energy from the environment. An important aspect of energy harvesting is that the devices go through birth and death cycles with respect to their power unlike battery powered ones. Another important aspect is that contextual information is also generated while devices harvest energy from their ambiance. In this article we provide a comprehensive study of various types of energy harvesting techniques. We then provide some models used in energy harvesting systems and the design of such systems. We also throw light on the power management and networking aspects of the energy harvesting devices. At the end we discuss the major issues and avenues for further research.

An Analytical Energy Consumption Model for Packet Transfer over Wireless Links

We provide a detailed analytical model for estimating the total energy consumed to exchange a packet over a wireless link. Our model improves many of the current models by considering details such as consumed energy by processing elements of transceivers, packet retransmission, reliability of links, size of data packets and acknowledgments, and also the data rate of wireless links. To develop the model, we use experimental results based on IEEE 802.15.4 devices to show that consumed energy for receiving erroneous packets is comparable to the consumed energy for receiving error-free packets.

Energy-aware routing algorithms for wireless ad hoc networks with heterogeneous power supplies

Although many energy-aware routing schemes have been proposed for wireless ad hoc networks, they are not optimized for networks with heterogeneous power supplies, where nodes may run on battery or be connected to the mains (grid network). In this paper, we propose several energy-aware routing algorithms for such ad hoc networks. The proposed algorithms feature directing the traffic load dynamically towards mains-powered devices keeping the hop count of selected routes minimal. We unify these algorithms into a framework in which the route selection is formulated as a bi-criteria decision making problem. Minimizing the energy cost for end-to-end packet transfer and minimizing the hop count are the two criteria in this framework. Various algorithms that we propose differ in the way they define the energy cost for end-to-end packet traversal or the way they solve the bi-criteria decision making problem. Some of them consider the energy consumed to transmit and receive packets, while others also consider the residual battery energy of battery-enabled nodes. The proposed algorithms use either the weighted sum approach or the lexicographic method to solve the bi-criteria decision making problem. We evaluate the performance of our algorithms in static and mobile ad hoc networks, and in networks with and without transmission power control. Through extensive simulations we show that our algorithms can significantly enhance the lifetime of battery-powered nodes while the hop count is kept close to its optimal value. We also discuss the scenarios and conditions in which each algorithm could be suitably deployed.

Extending WPANs to Support Multi-Hop Communication with QoS Provisioning

Wireless Personal Area Networks (WPANs) usually have very limited coverage. In this paper, we focus on methods to extend this range through multi-hop communication crossing several inter-connected WPANs called piconets. Multi-hop communication between piconets is possible through the bridge devices. While extending the range of WPANs, bridge devices become the capacity bottlenecks for these connected piconets. Therefore, an unoptimized resource allocation mechanism involving the bridges could degrade system performance severely. In this work we propose a novel resource allocation mechanism that outperforms other schemes proposed so far. Moreover, our scheme is QoS aware due to its cross-layer design. In our proposed scheme, resource allocation cooperates with the route discovery process to mitigate collisions due to inter-piconet resource reservations. Simulation results show that our approach significantly increases network capacity. This work is expected to pave the way for QoS support in WPANs.

Symbol Error Rate of Space-Time Coded Multi-Antenna Wireless Cooperative Networks

In this paper, we propose a generalized cooperative signal transmission model for wireless networks. In this model, the source, the destination, and an arbitrary number of relay nodes may have multiple antennas. The source node uses an orthogonal space- time block code for signal transmission over its multiple antennas to each of the relays and the destination node. Each relay performs a linear processing on the received signals and transmits the processed samples to the destination after encoding them using an orthogonal space-time block code. We analyze the performance of the proposed cooperative model by finding an approximate formula for its symbol error rate at high signal to noise ratios, which determines the total diversity order of the cooperative network. The achieved results show that various cooperative structures with different numbers of relay nodes and different numbers of antennas at each of the source, the destination and the relays, can have the same error rate performance at high signal to noise ratios.

Performance Evaluation of multi-hop Detect-and-Forward and Amplify-and-Forward wireless transmission systems

In this paper we propose a new scheme for multi-hop forwarding in wireless networks. This new scheme is based on detection and forwarding of the received messages at the physical layer, without further processing at the higher layers. We derive a new expression for the symbol error rate in this proposed multi-hop detect-and-forward network by modeling the transmission line as a Markov Chain. The derived expression is quite general with respect to the (de) modulation scheme and the channel model. We compare the error rate performance of the proposed multi-hop detect-and-forward scheme with the earlier in the literature proposed multi-hop amplify and forward scheme. For the case of slow-varying flat-fading Rayleigh channels, our analytical and simulation results show that these two systems have surprisingly close performance at a wide range of signal to noise ratios.

On the lifetime of node-to-node communication in wireless ad hoc networks

Lifetime of node-to-node communication in a wireless ad hoc network is defined as the duration that two nodes can communicate with each other. Failure of the two nodes or failure of the last available route between them ends their communication. In this paper, we analyze the maximum lifetime of node-to-node communication in static ad hoc networks when alternative routes that keep the two nodes connected to each other are node-disjoint. We target ad hoc networks with random topology modeled as a random geometric graph. The analysis is provided for (1) networks that support automatic repeat request (ARQ) at the medium access control level and (2) networks that do not support ARQ. On the basis of this analysis, we propose numerical algorithms to predict at each moment of network operation, the maximum duration that two nodes can still communicate with each other. Then, we derive a closed-form expression for the expected value of maximum node-to-node communication lifetime in the network. As a byproduct of our analysis, we also derive upper and lower bounds on the lifetime of node-disjoint routes in static ad hoc networks. We verify the accuracy of our analysis using extensive simulation studies.

Performance evaluation of power-aware routing algorithms in Personal Networks

Personal Networks (PN) is a concept in the area of modern communication networks in which devices belonging to a person cooperate to offer services to the person regardless of their geographical locations. A PN may consist of several ad-hoc sub-networks (or clusters) which are interconnected through infrastructure networks such as the Internet. Failure of personal devices due to battery shortage is one of the main threads for service availability in PNs. Power-aware routing (PAR) has been proposed as an effective scheme to prolong the lifetime of battery-operated nodes in wireless ad-hoc networks. This scheme, however, could be utilized in PNs as well, since a PN cluster can be modeled as a wireless ad-hoc network. Aiming at prolonging the lifetime of nodes in PNs, in this paper we propose a PAR algorithm for PNs and we evaluate and compare its performance with the performance of other PAR algorithms proposed so-far for wireless ad-hoc networks. We analyze the effect of node density, routing overhead, heterogeneity of PN nodes in terms of their power supplies, and communication pattern within PN clusters on the performance of the PAR algorithms. Taking into account various parameters, we show that in a PN environment, our proposed scheme can profoundly extend the lifetime of PN nodes compared to the other algorithms. We also show that there can be an optimal value for route refresh interval, as a parameter which affects the generated routing overhead, and the node density of PN clusters, in such a way that the network lifetime is maximized.

Minimum energy cost reliable routing in ad hoc wireless networks

Energy-aware routing is an effective way to extend the operational lifetime of wireless ad hoc networks. In this paper, we propose a new energy-aware routing scheme called Reliable Minimum Energy Cost Routing (RMECR). RMECR finds routes which require least amount of energy for reliable packet transfer in ad hoc networks. It defines the energy cost of packet forwarding by a node as the fraction of remaining battery energy which is consumed by a node to forward a packet. This includes the energy consumed for retransmission of the packet as well, when the packet or its acknowledgment is lost. We show that RMECR can effectively reduce the energy consumption of nodes and balance the traffic load among them. Furthermore, RMECR is able to find reliable routes, in which constituent links require less number of packet retransmissions due to packet loss. This in turn decreases the latency of packet delivery and saves energy as well.