Many recent advances in MAC protocols for wireless sensor networks have been proposed to reduce idle listening, an energy wasteful state of the radio. Low-Power-Listening (LPL) protocols transmit packets for U s (the "interlistening interval"), thereby, allowing nodes to sleep for long periods of time between channel probes. The interlistening interval as well as the particular type of LPL protocol should be well matched to the network conditions. In this paper, we propose network-aware adaptation of the specific succession of repeated packets over the U interval (the "MAC schedule"), which yields significant energy savings. Moreover, some LPL protocols interrupt communication between the sender and the receiver after the data packet has been successfully received. We propose a new and simple adaptation of the "transmit/receive schedule" to synchronize nodes on a slowly changing path so that energy consumption and delay are further reduced, at no cost of overhead in most cases. Our results show that using network-aware adaptation of the MAC schedule provides up to 30 percent increase in lifetime for different traffic scenarios. Additional adaptation of the transmit/receive schedule to automatically synchronize the nodes can reduce packet delivery delays by up to 50 percent, providing an additional decrease in energy consumption of 18 percent.

Energy efficiency is of the utmost importance in wireless sensor networks. The family of Low-Power-Listening MAC protocols was proposed to reduce one form of energy dissipation-idle listening, a radio state for which the energy consumption cannot be neglected. Low-Power-Listening MAC protocols are characterized by a duty cycle: a node probes the channel every t_i {\rm s} of sleep. A low duty cycle favors receiving nodes because they may sleep for longer periods of time, but at the same time, contention may increase locally, thereby reducing the number of packets that can be sent. We propose two new approaches to control the duty cycle so that the target rate of transmitted packets is reached, while the consumed energy is minimized. The first approach, called asymmetric additive duty cycle control (AADCC), employs a linear increase/linear decrease in the t_i value based on the number of successfully received packets. This approach is easy to implement, but it cannot provide an ideal solution. The second approach, called dynamic duty cycle control (DDCC) utilizes control theory to strike a near-optimal balance between energy consumption and packet delivery successes. We generalize both approaches to multihop networks. Results show that both approaches can appropriately adjust t_i to the current network conditions, although the dynamic controller (DDCC) yields results closer to the ideal solution. Thus, the network can use an energy saving low duty cycle, while delivering up to four times more packets in a timely manner when the offered load increases.

Low-power-listening MAC protocols were designed to reduce idle listening, a major source of energy consumption in energy starved wireless sensor networks. Low-power-listening is a MAC strategy that allows nodes to sleep for tis (the ldquointer-listeningrdquo time) when there is no activity concerning them. It follows that a node has to occupy the medium for at least tis to guarantee that its destination will probe the channel at some point during the transmission. Low-power-listening protocols have evolved with the introduction of new radios, and the most recent contributions propose to interrupt communication between the sender and the receiver after the data packet has been successfully received and acknowledged. This results in significant energy savings because a sending node does not need to send for full tiperiods. We propose a new and simple approach to synchronize nodes on a slowly changing routing tree so that energy consumption is further reduced at the sending node, and the delay is considerably less. Our method allows the nodes to use a lower duty cycle, at no cost of overhead in most cases. Simulation and implementation results show that energy consumption can be reduced by a significant factor (dependant on ti) and delay by at least 18%.

Energy efficiency is of the utmost importance in wireless sensor networks. The family of low-power-listening MAC protocols was proposed to reduce one form of energy dissipation-idle listening, a radio state for which the energy consumption cannot be neglected. Low-power-listening (also called channel probing) MAC protocols are characterized by a duty cycle: a node probes the channel every tis of sleep. A low duty cycle favors receiving nodes because they may sleep for longer periods of time, but at the same time, contention may increase locally, thereby reducing the number of packets that can be sent. We propose a new approach to dynamically control the duty cycle so that the target rate of transmitted packets is reached, while the consumed energy is minimized. Our approach utilizes control theory and adapts it to the control of tifor low-power-listening MAC protocols in wireless sensor networks. Results show that this approach can appropriately adjust tito the current network conditions.

Car crashes claim the lives of more than 100,000 people every year in the US alone. Forming ad-hoc networks among vehicles traveling on a highway can be very helpful to avoid such deadly accidents and pile-ups. In this paper, we define two classes of applications for such networks: safety-related applications and Internet connectivity. We also propose a new model for highway traffic and events that can be used to automatically generate movement files readable by the NS-2.28 simulator. Through simulations of such vehicular networks using flooding and IEEE 802.11 for safety-related applications, we attempt to answer the fundamental question: are highway vehicular networks feasible and efficient for safety purposes