Venkatesh Rajendran

Energy-efficient collision-free medium access control for wireless sensor networks

The traffic-adaptive medium access protocol (TRAMA) is introduced for energy-efficient collision-free channel access in wireless sensor networks. TRAMA reduces energy consumption by ensuring that unicast, multicast, and broadcast transmissions have no collisions, and by allowing nodes to switch to a low-power, idle state whenever they are not transmitting or receiving. TRAMA assumes that time is slotted and uses a distributed election scheme based on information about the traffic at each node to determine which node can transmit at a particular time slot. TRAMA avoids the assignment of time slots to nodes with no traffic to send, and also allows nodes to determine when they can become idle and not listen to the channel using traffic information. TRAMA is shown to be fair and correct, in that no idle node is an intended receiver and no receiver suffers collisions. The performance of TRAMA is evaluated through extensive simulations using both synthetic- as well as sensor-network scenarios. The results indicate that TRAMA outperforms contention-based protocols (e.g., CSMA, 802.11 and S-MAC) as well as scheduling-based protocols (e.g., NAMA) with significant energy savings.

Energy-efficient, application-aware medium access for sensor networks

We introduce FLAMA (flow-aware medium access), an energy-efficient medium-access control (MAC) protocol designed for wireless sensor networks. FLAMA achieves energy efficiency by preventing idle listening, data collisions and transmissions to a node that is not ready to receive packets. It adapts medium access schedules to the traffic flows exhibited by the application. FLAMA is simple enough so that it can be run by nodes with limited processing, memory, communication, and power capabilities. We evaluate the performance of FLAMA through simulations and test-bed experimentation. Simulation results indicate that, in terms of reliability, queuing delay and energy savings, FLAMA outperforms TRAMA, the first traffic-adaptive, schedule-based MAC proposed for sensor networks, and S-MAC, a contention-based energy-efficient MAC. FLAMA achieves significantly smaller delays (up to 75 times) when compared to TRAMA with significant improvement in energy savings and reliability, demonstrating the importance of application awareness in medium access scheduling. Our simulation and test-bed results show that FLAMA achieves better end-to-end reliability with significant energy savings compared to S-MAC

Combining source- and localized recovery to achieve Reliable multicast in multi-hop ad hoc networks

This paper proposes a novel reliable multicast transport protocol for multi-hop, wireless ad hoc networks (or MANETs). To recover from the different types of losses that may occur in MANETs, our Reliable Adaptive Congestion-controlled Transport protocol, or Re-ACT, combines source-based congestion- and error control with receiver-initiated localized recovery. While the latter attempts to recover localized losses (e.g., caused by transmission errors), the former is invoked only for losses and congestion that could not be recovered locally (e.g., caused by global congestion). Loss differentiation is an important component of ReACT and uses medium access control (MAC) layer information to distinguish between different types of losses. Through extensive simulations, we evaluate ReACT’s performance under a variety of MANET scenarios, including different offered load and mobility conditions, and compare it against a strictly end-to-end (i.e., no localized recovery) scheme. Our results show that ReACT is the best performer in terms of reliability. Our results also showcase the effect of ReACT’s local recovery mechanism which quickly corrects error- and path breakage induced losses and thus manages to prevent the source from reducing its rate unnecessarily , thus achieving significant throughput improvement with lower overhead when compared to the strictly end-to-end protocol.

Energy-efficient channel access scheduling for power-constrained networks

We introduce the distributed energy-aware node activation (DEANA) channel access protocol for power-constrained networks. Conventional channel access protocols waste energy during periods of idle listening and collisions. In DEANA, the radio is switched to a low-power, stand-by mode when a node is not transmitting or receiving, which makes DEANA very attractive for sensor networks. Using an analytical model, we show that the proposed approach can achieve significant energy savings (up to 95%).

DYNAMMA: A DYNAmic Multi-channel Medium Access Framework for Wireless Ad Hoc Networks

This paper introduces a scheduled-access, multi-channel medium access control (MAC) framework for wireless multi-hop ad hoc networks (MANETs). The proposed framework dubbed dynamic multi-channel medium access, or DYNAMMA, features: (1) ability to dynamically adapt to application-specific traffic patterns, (2) collision-free, multi-channel operation, (3) energy efficiency, and (4) minimum signaling overhead. We evaluate DYNAMMA through extensive simulations and compare its performance against scheduled-access (e.g., TRAMA) and contention-based (e.g., 802.11) MAC protocols for different application scenarios. Our results show that DYNAMMAs ability to perform collision-free transmission over multiple channels significantly increases system capacity through higher channel utilization and spatial re-use. When compared to TRAMA, DYNAMMAs efficiency in terms of signaling overhead yields considerable energy savings as well as queueing delay reduction. We also present an implementation of DYNAMMA over an Ultra-Wideband (UWB) radio testbed. Our UWB testbed results indicate that DYNAMMA can achieve both high channel utilization (close to 90% for our experiments) and high energy efficiency (nodes, on average, sleep one third of the time).

The Multi-Channel Flow-Aware Medium Access Control protocol for wireless sensor networks

We introduce the multi-channel flow-aware medium access control protocol, or (MFLAMA), an energy-efficient, schedule-based, multi-channel medium-access control (MAC) protocol designed for data gathering applications in wireless sensor networks. MFLAMA improves the channel utilization by establishing collision-free transmission schedules across multiple channels. Energy efficiency is achieved by preventing packet collisions, idle listening, and transmissions to a node that is not ready to receive packets. We evaluate MFLAMA through extensive simulations and quantify the improvement in channel utilization through the use of multiple channels. Our results indicate that as we increase the number of orthogonal channels used for communication, there is significant improvement in channel utilization and queueing delay. However, we notice a ldquodiminishing returnsrdquo effect as we increase the number of channels, i.e., the performance improvements observed decrease with the number of channels beyond a certain threshold. This threshold depends on the topology and traffic flow patterns being used.