Wireless Ad Hoc and Sensor Networks

Background on Networking 37sensor node is more energy-constrained compared to an ad hoc network.Although traditional networks aim to achieve high QoS provisions, WSNprotocols must focus primarily on power conservation. Therefore, WSNsmust have an inbuilt power or energy monitor and smartness that willgive an end user the option of prolonging network lifetime at the cost oflower throughput or higher transmission delay. Many research works inthe literature, which are covered in the book, are engaged in developingschemes that fulfill these requirements.WSNs are used to monitor a wide variety of ambient conditions thatinclude temperature, humidity, vehicular movement, pressure, soil makeup,and so on, besides many military applications, such as battlefield surveillance,reconnaissance mission and terrain, ammunition targeting, battledamage assessment, nuclear, biological, and chemical attack detectionas well as water quality monitoring etc. There are a number of homeapplications such as home automation and smart environment. Sensornodes in a WSN can be used for continuous assessment of process/systemhealth, event detection, location sensing, and control of actuators.A WSN design is influenced by many factors that include hardwareconstraints, transmission media, power consumption, network topology,scalability, and fault tolerance. Though many researchers have addressedmany of these factors, none of these studies has a full integrated view ofall factors (Akyildiz et al. 2002).Sensor nodes can fail or be blocked because of lack of power, causingproblems to the functioning of the network. The reliability Ri( k)or faulttolerance of a sensor node is modeled (Hoblos et al. 2000) using thePoisson distribution to capture the probability of not having a failurewithin the time interval ( 0, k)asR( k)= e−λ iki(1.14)where λ i and k are the failure rate of sensor node i and the time instant,respectively. Protocols and algorithms have to be designed to address thelevel of fault tolerance required by the sensor networks.A WSN is supposed to have several hundred or thousand sensor nodes.Therefore, the protocols and algorithms should be scalable, which is amajor problem observed in ad hoc networks. The density can range froma few sensor nodes in a region, which can be less than 10 m in diameter.The density can be calculated according to (Bulusu et al. 2001) as2γ( R) = ( NπR )/ A(1.15)where N is the number of sensor nodes in a geographical region A, andR, the radio transmission range. The term γ( R)provides the number ofnodes within the transmission radius of each node in region A.