International Journal of Computer Applications (0975 – 8887) Volume 39– No.10, February 2012 18 Effect of Communication Range with Node Cooperation in Wireless Passive Sensor Networks 1 Farman Ullah, 2 Aamir Khan 1,2 COMSATS Insititute of IT Quaid Avenue, Wah Cantt. Pujnab, Pakistan Imdad Ullah SEECS, NUST, Islamabad, Pakistan Hasan Farooq Universiti Tecknologi Petronas, Malaysia ABSTRACT Node cooperation is considered in this paper in the existence of two relaying protocols i.e. “Amplify and Forward (AF)” also called “Store and Forward (SF)” and the second relaying protocol is “Decode and Forward”. The two stated protocols are different from each other and perform different operations on received data before retransmitting to next hop. Also the selection of each protocol is varying in accordance to the dis- tance of a sensor node from the destination node (RF source). It is suggested in this literature that a relay node close to the source node will employ Decode and Forward and if it is close to the destination node, then Amplify and Forward will be employed. This work is achieved by first modelling an empirical system consists of single relay, source and destina- tion. And the two relaying protocols (SF and DF) were modelled and implemented. This approach is then extended for three relay nodes and the two sets of relaying nodes were implemented again on every single node and then the output performances were compared. Finally using analytical ap- proach, the communication range or the capacity of RF source to charge the sensor nodes in certain area was also evaluated and it is considered that the relay nodes within the prescribed range are successfully charged in charging stage. And in communication stage, the relay node was allowed to keep at various distances from the source node and evaluate the per- formance of each relaying protocol on a particular distance from source and destination. 1. INTRODUCTION In wireless sensor networks, signal is severely degraded by the multipath signals which can be compensated with the use of diversity. Taking the advantageous of diversity, the destina- tion node accumulates or combines all the received signals received via independent links and makes the final decision upon the transmitted bits. This characteristic of sensor net- works is called the cooperative attempt and is always there when they are active. Sensor nodes, with this property en- hance their quality of service and offer good BER compare to the conventional mode of communication. The senor nodes make use of their processing capabilities to locally carry out simple calculations and send out only interested data [5]. This approach or capability of WPSN can offer spatial diversity against fading in a wireless channel [22]-[23]. If there is no direct line of sight or having difficulty in communication, then one sensor node help another, called relay node in order to accomplish transmission from source to the desired destina- tion [23]. This cooperative behaviour is adopted by each sensor node in the network along with the normal communi- cation responsibility. Node Cooperation results in various trades off in terms of resources e.g. data rate and transmit power. Because in coop- erative mode if there are “N” number of sensor nodes, then the total power would be divided into “N” number of portions and with that individual part of the total power, the data would be transmitted to each node. Hence, total power available at the single node divided and thus it is reduced for all users because of diversity [24]. The scenario that this work will consider would assume that all nodes work in the same band and therefore the source node will behave in broadcast manner, while the destination node is in multiple channel access mode as depicted in the following figure 1. Channel between each pair of node is in- dependent and have random effect on data. Broadcast Multi Access Channel 1 Channel 2 Channel 3 Source Node Relay Node Destination Node Figure 1: A 2 hops relaying system 1.1. Relaying Protocols The two approaches are employed by the relaying nodes named as Amplify-and-Forward (AF) or Repeater and De- code-and-Forward (DF) in order to accomplish their job in the case when channel is severely fading. The need of two ap- proaches arises when signal is very week and is unable to reach the destination node. The factors that weaken the signal are path loss (Large Scale Fading (LSF)) e.g. Reflection, Dif- fraction, Scattering etc. and Small Scale Fading (SSF) e.g. Rayleigh, Ricean, Nakagami, Doppler Spectrum, Autoregres- sive Model etc. [25]-[26] that could be resolved through the use of space, time and multiple antenna diversities. In a very simple case shown below is the 4 nodes system. In which two terminals T1 and T2 transmit to the destination terminals T3 and T4 respectively. But due to broadcast nature of wireless communication system, they also share resources with other nodes coming in the range of WPSN field [25] such as shown in Fig 3.2 and jointly communicate the data.