International Journal of Computer Applications (0975 – 8887) Volume 136 – No.7, February 2016 20 Exploration of Various Network Coding Schemes to Improve Performance in Wireless Multihop Networks Sunil Bajeja Asst. Prof. – FCA Marwadi Edu. Fou. Grp of Inst. Rajkot Atul Gosai, PhD Associate Prof. – CSD Saurashtra University Rajkot ABSTRACT Network coding is a collection of techniques in which a node is allowed to combine, encode and send one or more packets as a single encoded packet instead of sending individually. It improves throughput, packet delivery ratio and efficiency of the system. The inherent broadcasting nature of wireless mediums helps us to adopt network coding very easily. At the same time, as it reduces the number of transmissions, it reduces the probability of various losses due to transmission impairments, channel contentions and route failures. This paper discusses various well known network coding schemes.. Network coding is broadly classified into global and local network coding. Network coding is also classified into binary – Xor based and random linear coding based network coding. Further to these, based upon the applications, Network coding schemes are classified for unicast, multicast and broadcast applications. In each of these categories, network coding is explained in the reference of inter-session network coding and intra-session network coding. Keywords Network Coding, Random Linear Network Coding, Binary Network Coding, Unicast, Multicast, Broadcast, Inter-Session, Intra-Session, COPE, MORE 1. INTRODUCTION Network coding refers to the coding at a node of a specific network. Coding can be either mathematical, substitution or permutation. The basic idea behind network coding is to reduce the number of transmissions. In the earlier days of wireless networking, network suffers from various transmission issues like loss of signal called attenuation, change in signal shapes called distortion, modification of signal called noise. At the same time, when multiple nodes want to communicate all together, they content for the channel which either create problem like hidden or exposed stations or in critical cases collision. Several approaches have been proposed to make the networks robust against such issues. But the ultimate solution is to transmit more in less number of packets. At application layer, data compression can be done. At physical layer, multiplexing our signals at various unique frequencies can be done to generate a composite signal. But what about the middle three layers? Network Coding targets the reduction in number of transmissions corresponding to each of the intermediate layers which are data link layer, network layer and physical layer. This paper discussed network coding at various layers of TCP/IP protocol suite [1]. Lets understand basic need of network coding with a simple example shown in figure 1 which shows a network scenario without network coding. Figure 1. Network without Network Coding Here node 1 and node 2 want to exchange message S1 and message S2 respectively. The chain topology is formed using intermediate relay node R. in 1 st time slot, node 1 sends S1 to node R. in 2 nd time slot, node R sends S1 to node 2. In 3 rd time slot, node 2 sends S2 to node R and in 4 th time slot, node R sends S2 to node 1. In this way, in 4 transmissions both the messages are exchanged. Our goal is to reduce this requirement to the best by reducing number of transmissions [1].The following sections show various ways of implementing network coding at various layers. 2. NETWORK CODING AT PHYSICAL LAYER PNC - Physical layer network coding is developed for wireless networks. PNC performs network coding when electromagnetic signals are superimposed on each other to form a composite signal which can be transmitted as a single signal. In wireless communication, there are various transmission impairments like attenuation, distortion, noise, cross talk occur which may change the information being transmitted. Interference is considered as a destructive element as it changes the signal and so destructs the information insides. When multiple transmitters transmit signals to various receivers, A receiver may receive signal from its own transmitter as well as from few of the others. The signals from other transmitters are often considered as interferences. When collision occurs, none of the packets can be received correctly due to corruption in both the signals. The same interference can be well treated to take advantage of combining more than one signal. The network coding at physical layer is based on showing positive attitude towards the composite signals. The only difference here is the composite signal is made here is intentional and is reversible[2]. Figure 2. Physical Layer Network Coding