A wireless sensor network (WSN) (sometimes called a wireless sensor and actor network(WSAN)) are spatially distributed autonomous sensors to monitor physical or environmental conditions, such as temperature, sound, pressure, etc. and to cooperatively pass their data through the network to a main location. The more modern networks are bi-directional, also enabling control of sensor activity. The development of wireless sensor networks was motivated by military applications such as battlefield surveillance; today such networks are used in many industrial and consumer applications, such as industrial process monitoring and control, machine health monitoring, and so on.

Current research topics in Wireless sensor Networks

1. Power Management
2. Localisation
3. Routing
4. Deployment Technique

Power Management

Sensor network is composed of a large number of sensor nodes that are densely deployed either inside the environment or close to it. The position of sensor nodes need not be engineered or predetermined. This allows random deployment in inaccessible terrains or hazardous environments. Some of the most important application areas of sensor networks include military, natural calamities, health, and home. When compared to traditional ad hoc networks, the most noticeable point about sensor networks is that , they are limited in power, computational capacities, and memory. Hence optimizing the energy consumption in wireless sensor networks has recently become the most important performance objective.

Localization

Location information is used to detect and record events, or to route packets using geometric-aware routing. Manual configuration of locations is not feasible for large-scale networks or networks where sensors may move. Providing each sensor with localization hardware (e.g., GPS) is expensive in terms of cost and energy consumption. A more reasonable solution to the localization problem is to allow some nodes (called seeds) to have their location information at all times, and allow other nodes to infer their locations by exchanging information with seeds

Routing

Efforts are being made to design routing protocols for WSN which are energy efficient. Following are some energy efficient routing protocols proposed for WSN.

1. Data-centric protocols

1.1 Flooding and gossiping
1.2 Sensor protocols for information via negotiation
1.3 Directed Diffusion
1.4 Rumor Routing
1.5 Gradient-based routing
1.6 CADR
1.7 COUGAR
1.8 ACQUIRE

2. Hierarchical protocols

2.1. LEACH
2.2 PEGASIS and Hierarchical-PEGASIS
2.3 TEEN and APTEEN
2.4 Energy-aware routing for cluster-based sensor networks
2.5 Self-organizing protocol

3. Location-based protocols

3.1. MECN and SMECN
3.2. GAF
3.3. GEAR

4. Network flow and QoS-aware protocols

4.1 Maximum lifetime energy routing
4.2 Maximum lifetime data gathering
4.3 Minimum cost forwarding
4.4 SAR
4.5 Energy-aware QoS routing protocol
4.6 SPEED