Detection methodologies to overcome Non line of Sight (NLOS) in Adhoc Networks: A Survey

In Vehicular Ad-hoc networks (VANETs) one of the pioneer applications is exchange of emergency messages to identify the location information of the emergency and nonemergency vehicles. But, the presence of obstacles like building infrastructure, trucks and other environmental factors can create Non Line Of Sight (NLOS) which prevents the direct communication between the two vehicles even though the vehicles are within the communication range. So the exchange of emergency message is being prevented in reaching the vehicle user within stipulated period of time resulting in fatal accidents because of the wrong conclusion taken by the vehicle users. This situation has to be handled with at most attention as it involves human lives. This paper focuses on analyzing the various methodologies devised by the researchers in localizing the NLOS nodes with their merits and demerits.