Z-MAC is a hybrid MAC protocol for wireless sensor networks. It combines the strengths of TDMA and CSMA while offsetting their weaknesses. Nodes are assigned time slots using a distributed implementation of RAND. Unlike TDMA where a node is allowed to transmit only during its own assigned slots, a node can transmit in both its own time slots and slots assigned to other nodes. Owners of the current time slot always have priority in accessing the channel over non-owners. Therefore, under low contention where not all owners have data to send, non-owners can “steal ” time slots from owners. This has the effect of switching between CSMA and TDMA depending on contention. Z-MAC is robust to topology changes and clock synchronization errors; in the worst case its performance falls back to that of CSMA. We implemented Z-MAC in TinyOS and evaluated its channel utilization, energy, latency and fairness over single-hop, twohop and multi-hop sensor network topologies constructed using Mica2. The result shows that Z-MAC has remarkably better data throughput than existing sensor MAC protocols while consuming comparable energy (over three times better throughput under high contention).

Energy is a critical resource in sensor networks. MAC protocols such as S-MAC and T-MAC coordinate sleep schedules to reduce energy consumption. Recently, lowpower listening (LPL) approaches such as WiseMAC and B-MAC exploit very brief polling of channel activity combined with long preambles before each transmission, saving energy particularly during low network utilization. Synchronization cost, either explicitly in scheduling, or implicitly in long preambles, limits all these protocols to duty cycles of 1–2%. We demonstrate that ultra-low duty cycles of 0.1% and below are possible with a new MAC protocol called scheduled channel polling (SCP). This work prompts three new contributions: First, we establish optimal configurations for both LPL and SCP under fixed conditions, developing a lower bound of energy consumption. Under these conditions, SCP can extend lifetime of a network by a factor of 3–6 times over LPL. Second, SCP is designed to adapt well to variable traffic. LPL is optimized for known, periodic traffic, and long preambles become very costly when traffic varies. In one experiment, SCP reduces energy consumption by a factor of 10 under bursty traffic. We also show how SCP adapts to heavy traffic and streams data in multi-hop networks, reducing latency by 85 % and energy by 95 % at 9 hops. Finally, we show that SCP can operate effectively on recent hardware such as 802.15.4 radios. In fact, power consumption of SCP decreases with faster radios, but that of LPL increases.

This paper explores applications and challenges for underwater sensor networks. We highlight potential applications to off-shore oilfields for seismic monitoring, equipment monitoring, and underwater robotics. We identify research directions in shortrange acoustic communications, MAC, time synchronization, and localization protocols for high-latency acoustic networks, longduration network sleeping, and application-level data scheduling. We describe our preliminary design on short-range acoustic communication hardware, and summarize results of high-latency time synchronization.

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This report summarizes our research directions in underwater sensor networks. We highlight potential applications to off-shore oilfields for seismic monitoring, equipment monitoring, and underwater robotics. We identify research directions in short-range acoustic communications, MAC, time synchronization, and localization protocols for highlatency acoustic networks, long-duration network sleeping, and application-level data scheduling. 1

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This paper proposes a simple protocol for low-power sensor networks with battery-operated sensing devices. The sensors are expected to become active only when certain events in the environment occur. Therefore, a scheme for the application and medium access cycles is developed which avoids common problems of energy loss due to idle actions. Subsequently, the protocol is evaluated according to sensor lifetime. In contrast to common performance analysis, the approach considers the application behavior as a main impact on the sensor lifetime. Capabilities to save energy are derived. 1

Abstract — Notoriously, energy-efficient MAC protocols cause high latency of packets. Such delays may well increase when a routing protocol is applied. Therefore, quantifying the endto-end delay and energy consumption when low duty cycle MAC and routing protocols are jointly used, is of particular interest. In this paper, we present a comprehensive evaluation of the MERLIN (MAC and Efficient Routing integrated with support for localization) protocol. MERLIN integrates MAC and routing features into a single architecture. In contrast to many sensor network protocols, it employs a multicast upstream and multicast downstream approach to relaying packets to and from the gateway. Simultaneous reception and transmission errors are notified by using asynchronous burst ACK and negative burst ACK. A division of the network into timezones, together with an appropriate scheduling policy, enables the routing of packets to the closest gateway. An evaluation of MERLIN has been conducted through simulation, against both the SMAC and the ESR routing protocols,which is an improved version of the DSR algorithm. The results illustrate how both SMAC and ESR, jointly used in low duty cycle scenarios, can cause an impractical and very high end-to-end delays. MERLIN, as an integrated approach, notably reduces the latency, resulting in nodes that can operate in a very low duty cycle. Consequently, an extension of the operative lifetime of the sensor network is achieved.

An algorithm for self-scheduling of node access and self-configuration of routes to data collectors in wireless sensor networks is proposed and described. The algorithm relies on the robustness and stability of the self-synchronisation of unnamed pulse coupled oscillators. Results of an initial simulation of a protocol based on the algorithm are reported. The results indicate that the protocol is resilient in the presence of low levels of mobility and noise. Plans to perform more realistic future tests including a full implementation are outlined. I

This thesis describes the design and development of the SmartBadge; an electronic replacement for the standard paper name badge worn at conferences and similar events. Both hardware and software have been designed for the SmartBadge; the hardware has been developed around a CC1010 microcontroller and RF transceiver. Attached to this are an infrared transceiver, an LCD display, some LEDs, buttons and a piezoelectric buzzer. There is also an antenna for the RF transceiver whose design is the result of SuperNEC [1] simulations. Protocol software development has focussed on the communication between a SmartBadge and other badges and base stations, yet there is still space available in the CC1010s flash memory to develop applications beyond the business card exchange example developed to demonstrate the communication software. The SmartBadge communicates with other badges by using the infrared transceiver. In the business card application a SmartBadge is worn by a person and is collecting the ID and a time counter from SmartBadges worn by other facing people as this person mingles through a conference or similar event. This data is then collected in real time using the RF transceiver to communicate with base stations which would be scattered around the venue. The RF network has been designed as a single hop network and a new Medium Access Control (MAC) protocol has been designed to allow the SmartBadges to share the links to the base stations while conserving as much energy as possible. This protocol is called Uplink MAC (or U-MAC) and is described in section 6.2. i ii