Directional antennas in sensor networks are receiving increasing interest and research due to the potential to increase throughput and reduce delay and interference, while requiring lower transmission power. Considering the stringent operation requirements (low duty-cycle) as MAC congestion problems in large multi-hop networks, WSN performance can benefit enormously from such directional capabilities together with an intelligent design. This paper investigates the introduction of switched beam directional antennas in sensor networks using a synchronised sleep/awake contention-base MAC (DirC-MAC) and real available hardware solutions. The control simplicity, small size and low cost makes switched beam antenna technology an attractive and suitable solution for sensor nodes. By means of modelling off-the-shelf sensor node architecture and the use of network simulation this paper shows significant improvements (up to 4 times more throughput and half battery used) may be achieved using directional antennas compared to the omnidirectional alternative. This paper emphasises the use of more realistic radio channel assumptions and addresses the impact of directional antennas in contention-based MACs analysing the performance of different handshaking mechanisms.

No abstract

No abstract

This paper addresses the trend in Wireless Sensor Network applications of increasing node density and multi-hop communications that result into extremely challenging design constraints. SSAS, an adaptive hybrid localised sink-oriented Routing/MAC protocol is proposed. It offers a self-configuration scalable solution for large random sensor networks and attempts to alleviate multi-hop congestion problems. The strength of the SSAS protocol is based on the scheduled access at the sinks and the enhancement of the number of one-hop sinks' neighbours by profiting directional antenna capabilities. By means of modelling off-the-shelf sensor node architecture with realistic radio channel assumptions and the use of network simulations, this paper shows significant improvements of SSAS (such as 10 times higher network lifetime) compared to other techniques such as pure contention-based alternative (C-MAC), B-MAC and LEACH. I. INTRODUCTIONWith cost and size of the nodes decreasing due to the technology advances, more applications consider deployment of large multi-hop wireless sensor networks (WSN). Commonly, these are nodes-to-sink (converge-casting) applications where sensed data must be delivered to designated gateway nodes (sinks) that serve as fusion centres, but also distribute control information and application requirements to the sensor nodes. This process may involve the use of multi-hop links and can lead to congestion problems (overhearing, collisions, buffer overflow and energy drain) the major impact of which occurs closer to the sinks. Sensor nodes have limited energy supply and a general approach to maximise the network lifetime is the imposition of sleep/wake cycles. Under decreasing active times, efficient contention MAC protocols attempt to maximise the use of the shared channel to achieve application requirements (throughput, delay, lifetime) but using minimal resources. However, as multi-hop is increased in larger networks congestion problems are likely to appear. More precisely, nodes that are closer to the sinks become more saturated with the forwarding task but with reduced chances of competing for access to the channel. These nodes restrict the network time operation.In this situation, the network could benefit from the use of a TDMA-based protocol that is naturally energy preserving, exempt of contention mechanisms and does not suffer from collisions. However, creating and maintaining a TDMA schedule in a multi-hop nodes-to-sink application can be extremely complex if slots need to be allocated more than one-hop away. The effect of clock drift can also be considerable with low duty-cycle MACs as can topology changes or node mobility. In such situations network design

No abstract