Traditional contention-based random-access wireless MAC protocols such as IEEE 802.11 DCF are designed for single-hop wireless networks and do not perform well in multi-hop scenarios due to inefficiency in their medium reservation mechanisms. In this paper, we introduce a new MAC protocol, called EMAC, which improves the efficiency of wireless medium reservation for general asynchronous multi-hop wireless networks. By exploiting limited routing information at the MAC layer, EMAC enables multiple asynchronous stations along a delivery path to cooperate in their random medium access. In particular, a control frame can travel across a multi-hop path composed of asynchronous nodes, and make synchronized medium reservations for an upcoming data frame transmission. This distributed cooperation at the MAC layer can greatly improve the medium reservation efficiency by reducing intra-flow contentions. Simulation results show that EMAC can improve end-to-end throughput compared to IEEE 802.11 DCF in chain scenarios by up to 85% and can avoid throughput starvation in cross scenarios.

The use of asynchronous duty-cycling in wireless sensor network MAC protocols is common, since it can greatly reduce energy consumption and requires no clock synchronization. However, existing systems using asynchronous duty-cycling do not efficiently support broadcast-based communication that may be used, for example, in route discovery or in network-wide queries or information dissemination. In this paper, we present the design and evaluation of ADB (Asynchronous Duty-cycle Broadcasting), a new protocol for efficient multihop broadcast in wireless sensor networks using asynchronous duty-cycling. ADB differs from traditional multihop broadcast protocols that operate above the MAC layer, in that it is integrated with the MAC layer to exploit information only available at this layer. Rather than treating the data transmission from a node to all of its neighbors as the basic unit of progress for the multihop broadcast, ADB dynamically optimizes the broadcast at the level of transmission to each individual neighbor of a node, as the neighbors asynchronously wakeup. We evaluate ADB both through ns-2 simulations and through measurements in a testbed of MICAz motes using TinyOS, and compare its performance to multihop broadcast based on X-MAC and on RI-MAC. In both evaluations, ADB substantially reduced energy consumption, network load, and delivery latency compared to other protocols, while achieving over 99% delivery ratio.

Duty cycling is a widely used mechanism in wireless sensor networks (WSNs) to reduce energy consumption due to idle listening, but this mechanism also introduces additional latency in packet delivery. Several schemes have been proposed to mitigate this latency, but they are mainly optimized for light traffic loads. A WSN, however, could often experience bursty and high traffic loads, such as due to broadcast or convergecast traffic. In this paper, we present a new MAC protocol, called Demand Wakeup MAC (DW-MAC), that introduces a new low-overhead scheduling algorithm that allows nodes to wake up on demand during the Sleep period of an operational cycle and ensures that data transmissions do not collide at their intended receivers. This demand wakeup adaptively increases effective channel capacity during an operational cycle as traffic load increases, allowing DW-MAC to achieve low delivery latency under a wide range of traffic loads including both unicast and broadcast traffic. We compare DW-MAC with S-MAC (with and without adaptive listening) and with RMAC using ns-2 and show that DW-MAC outperforms these protocols, with increasing benefits as traffic load increases. For example, under high unicast traffic load, DW-MAC reduces delivery latency by 70% compared to S-MAC and RMAC, and uses only 50% of the energy consumed with S-MAC with adaptive listening. Under broadcast traffic, DW-MAC reduces latency by more than 50% on average while maintaining higher energy efficiency.

Duty-cycle MAC protocols have been proposed to meet the demanding energy requirements of wireless sensor networks. Although existing duty-cycle MAC protocols such as S-MAC are power efficient, they introduce significant end-to-end delivery latency and provide poor traffic contention handling. In this paper, we present a new duty-cycle MAC protocol, called RMAC (the routing enhanced MAC protocol), that exploits cross-layer routing information in order to avoid these problems without sacrificing energy efficiency. In RMAC, a setup control frame can travel across multiple hops and schedule the upcoming data packet delivery along that route. Each intermediate relaying node for the data packet along these hops sleeps and intelligently wakes up at a scheduled time, so that its upstream node can send the data packet to it and it can immediately forward the data packet to its downstream node. When wireless medium contention occurs, RMAC moves contention traffic away from the busy area by delivering data packets over multiple hops in a single cycle, helping to reduce the contention in the area quickly. Our simulation results in ns-2 show that RMAC achieves significant improvement in end-to-end delivery latency over S-MAC and can handle traffic contention much more efficiently than S-MAC, without sacrificing energy efficiency or network throughput.

Simulation and physical implementation are both valuable tools in evaluating ad hoc network routing protocols, but neither alone is sufficient. In this paper, we present the design and performance of PRAN, a new system for the physical implementation of ad hoc network routing protocols that unifies these two types of evaluation methodologies. PRAN (physical realization of ad hoc networks) allows existing simulation models of ad hoc network routing protocols to be used - without modification - to create a physical implementation of the same protocol. We have evaluated the simplicity and portability of our approach across multiple protocols and multiple operating systems through example implementations in PRAN of the DSR and AODV routing protocols in FreeBSD and Linux using the standard existing, unmodified ns-2 simulation model of each. We illustrate the ability of the resulting protocol implementations to handle real, demanding applications by describing a demonstration with this DSR implementation transmitting real-time video streams over a multihop mobile ad hoc network; the demonstration features mobile robots being remotely operated based on the real-time video stream transmitted from the robot over the network. We also present a detailed performance evaluation of PRAN to show the feasibility of our architecture

Distributed wavelet processing within sensor networks holds promise for reducing communication energy and wireless bandwidth usage at sensor nodes. Local collaboration among nodes de-correlates measurements, yielding a sparser data set with significant values at far fewer nodes. Sparsity can then be leveraged for subsequent processing such as measurement compression, de-noising, and query routing. A number of factors complicate realizing such a transform in real-world deployments, including irregular spatial placement of nodes and a potentially prohibitive energy cost associated with calculating the transform in-network. In this paper, we address these concerns head-on; our contributions are fourfold. First, we propose a simple interpolatory wavelet transform for irregular sampling grids. Second, using ns-2 simulations of network traffic generated by the transform, we establish for a variety of network configurations break-even points in network size beyond which multiscale data processing provides energy savings. Distributed lossy compression of network measurements provides a representative application for this study. Third, we develop a new protocol for extracting approximations given only a vague notion of source statistics and analyze its energy savings over a more intuitive but naïve approach. Finally, we extend the 2-dimensional (2-D) spatial irregular grid transform to a 3-D spatio-temporal transform, demonstrating the substantial gain of distributed 3-D compression over repeated 2-D compression.

Summary form only given. Recent advances in technology have made low-cost, low-power wireless sensors a reality. A network of such nodes can coordinate among themselves for distributed sensing and processing of certain phenomena. We propose an architecture to provide a stateless solution in sensor networks for efficient addressing and routing. We name our architecture TreeCast. We propose a unique method of address allocation, building up multiple disjoint trees which are geographically inter-twined and rooted at the data sink. Using these trees, routing messages to and from the sink node without maintaining any routing state in the sensor nodes is possible. Next, we use this address allocation method for scoped addressing, through which sensor nodes of a particular type or in a particular region can be targeted. Evaluation of our protocol using ns-2 simulations shows how well our addressing and routing schemes perform.