Rahul Shah

Energy aware routing for low energy ad hoc sensor networks

The recent interest in sensor networks has led to a number of routing schemes that use the limited resources available at sensor nodes more efficiently. These schemes typically try to find the minimum energy path to optimize energy usage at a node. In this paper we take the view that always using lowest energy paths may not be optimal from the point of view of network lifetime and long-term connectivity. To optimize these measures, we propose a new scheme called energy aware routing that uses sub-optimal paths occasionally to provide substantial gains. Simulation results are also presented that show increase in network lifetimes of up to 40% over comparable schemes like directed diffusion routing. Nodes also burn energy in a more equitable way across the network ensuring a more graceful degradation of service with time.

Data MULEs: modeling and analysis of a three-tier architecture for sparse sensor networks

Abstract This paper presents and analyzes a three-tier architecture for collecting sensor data in sparse sensor networks. Our approach exploits the presence of mobile entities (called MULEs) present in the environment. When in close range, MULEs pick up data from the sensors, buffer it, and deliver it to wired access points. This can lead to substantial power savings at the sensors as they only have to transmit over a short-range. This paper focuses on a simple analytical model for understanding performance as system parameters are scaled. Our model assumes a two-dimensional random walk for mobility and incorporates key system variables such as number of MULEs, sensors and access points. The performance metrics observed are the data success rate (the fraction of generated data that reaches the access points), latency and the required buffer capacities on the sensors and the MULEs. The modeling and simulation results can be used for further analysis and provide certain guidelines for deployment of such systems.

Exploiting mobility for energy efficient data collection in wireless sensor networks

We analyze an architecture based on mobility to address the problem of energy efficient data collection in a sensor network. Our approach exploits mobile nodes present in the sensor field as forwarding agents. As a mobile node moves in close proximity to sensors, data is transferred to the mobile node for later depositing at the destination. We present an analytical model to understand the key performance metrics such as data transfer, latency to the destination, and power. Parameters for our model include: sensor buffer size, data generation rate, radio characteristics, and mobility patterns of mobile nodes. Through simulation we verify our model and show that our approach can provide substantial savings in energy as compared to the traditional ad-hoc network approach.

When does opportunistic routing make sense

Different opportunistic routing protocols have been proposed recently for routing in sensor networks. These protocols exploit the redundancy among nodes by using a node that is available for routing at the time of packet transmission. This mitigates the effect of varying channel conditions and duty cycling of nodes that make static selection of routes not viable. However, there is a downside as each hop may provide extremely small progress towards the destination or the signaling overhead for selecting the forwarding node may be too large. In this paper, we provide a systematic performance evaluation, taking into account different node densities, channel qualities and traffic rates to identify the cases when opportunistic routing makes sense. The metrics we use are power consumption at the nodes, average delay suffered by packets and goodput of the protocol. Our baseline for comparison is geographic routing with nodes being duty cycled to conserve energy. The paper also identifies optimal operation points for opportunistic routing that minimizes the power consumption at nodes.

On the performance of geographical routing in the presence of localization errors [ad hoc network applications]

In this paper, a detailed study of the performance of geographic routing protocols in the presence of localization errors is carried out. Both analytical and simulation results illustrate the major impact or localization errors on the protocol goodput and route discovery energy. The performance metrics observed were the packet delivery ratio and the power consumed at a node for routing. It is shown that significant performance deterioration occurs with location errors as low as 20% of a nodes radio range with no other obstacles in the network. To counteract this degradation, an enhancement is proposed that increases the error tolerance to about 40% radio range and in addition improves the performance consistently for any location error. Furthermore, the effect of obstacles in conjunction with location errors on the routing performance is also investigated.

Joint optimization of a protocol stack for sensor networks

In this work, we present protocols for routing, MAC and power-control in sensor networks and jointly optimize these protocols. The joint optimization aims to capture the impact of cross-layer interaction on the efficiency and performance of the protocol stack. We model the protocol stack as a whole, rather than a collection of individually modeled layers. In our model, the protocol stack has tunable parameters that affect the operation of each layer to achieve globally specified performance and efficiency. In the paper, we begin by presenting the randomized protocols at each layer that exploit node density in order to achieve reliable communication. First, we present a region-based opportunistic routing protocol. Then, at the medium access layer, we consider an asynchronous rendezvous scheme called TICER. Third, a randomized sleep discipline is set forth that allows nodes to power down periodically. Finally, we combine the routing, MAC and power-control protocols to obtain a constrained optimization problem. Results show that it is possible to minimize energy consumption while satisfying application requirements on end-to-end delay.

Modeling and analysis of opportunistic routing in low traffic scenarios

Opportunistic routing protocols have been proposed as efficient methods to exploit the high node densities in sensor networks to mitigate the effect of varying channel conditions and non-availability of nodes that power down periodically. They work by integrating the network and data link layers so that they can take a joint decision as to the next hop forwarding node based on its availability and suitability as a forwarder. This cross-layer integration makes it harder to optimize the protocol due to the dependencies among the different components of the protocol stack. In this paper, we provide a framework to model opportunistic routing that breaks up the functionality into three separate components and simplifies analysis. The framework is used to model two variants of opportunistic routing and is shown to match well with simulation results. In addition, using the model for performance analysis yields important guidelines for the future design of such protocols.

Altruists in the PicoRadio sensor network

Self-configuring wireless sensor networks are a fascinating emerging technology: the vision is to spread out hundreds or thousands of small, cheap, battery-driven, and self-configuring nodes bearing a wireless modem to accomplish a given task jointly. An important concern is network lifetime: as nodes run out of power the connectivity decreases and the network can finally be partitioned and become dysfunctional. In this paper we present the BWRC PicoRadio approach to wireless sensor networking. Furthermore, we introduce the general concept of altruistic nodes and apply this to the routing protocol of PicoRadio (the energy aware routing protocol, EAR). The concept of altruists is a lightweight approach for exploiting differences in node capabilities. We show that the altruist approach can achieve significant gains in terms of network lifetime over the already lifetime-optimized EAR protocol of PicoRadio.

Data link layer design for wireless sensor networks

This paper presents the architecture of data link layer for wireless sensor networks. Requirements are specified and the functional description is given. The relationship between different subsystems is also discussed. The designed data link layer has ultra-low power consumption. It is distributed, simple and robust. Additionally, it requires no synchronization.