# On Applicability of Network Coding Technique for 6 LoWPAN-based Sensor Networks
## 2 Related Work  
Most network coding solutions are dedicated for wireless ad-hoc networks; however, other applications are also possible. For instance, networks with overlay P2P services, as presented in [11; 12], are a good example of encoding the streams of data that are shared between different positions in the Internet, in order to increase file sharing efficiency. But, due to overhearing, wireless medium gives natural opportunity for network coding. One of the most influential, practical inter-session network coding mechanisms, named COPE, was proposed by [PERSON] et al., in [13]. COPE was elaborated to improve the throughput of IEEE 802.11-based ad-hoc wireless network. The opportunistic unicast packet encoding is performed based on bitwise XOR (Exclusive Or) operations. A similar approach can be found in [14], where also XOR encoding is executed, not in a whole network, but in the so-called capacity region. The NC operations are based on flows instead of individual packets. Both of the solutions ([13; 14]) give significant network throughput improvements (from 20 to 80%). A couple of extensions of COPE that offer throughput improvement are presented, for example, in [15; 16; 17]. Distinctly fewer solutions are devoted to network coding for wireless sensor networks. It should be noticed that sensor motes are characterized by restricted memory resources, which limit the space that is required for efficient network coding operation. In [18], [PERSON] et al., proposed a combined network coding and multipath routing scheme for underwater sensor networks, which is efficient for error recovery and energy consumption. The reliable data dissemination protocol, which uses adaptive network coding to reduce broadcast traffic in sensor networks, is proposed in [19]. This technique is based on the dynamic adjustment of a number of coefficients, and then, the number of packets that can be encoded depending on link density (number of neighboring nodes). Similarly, in [20], network coding is used for the management of available energy during broadcast transmission in a sensor network. It is based on a cross-layer approach that supports the random linear network coding at the network layer, allowing for the cooperation with the MAC layer's forwarding and scheduling schemes, in order to determine whether and how broadcast packets are encoded. The enhancement of the sensor network lifetime, using duty cycle and network coding, was also discussed in [21; 27; 28]. Some recent papers are also focused on the increase in the transmission reliability in sensor networks. [PERSON] et al., in [22], proposed a broadcast protocol that uses an inter-session network coding scheme, based on the sliding encoding window, which positively influences the efficiency of packet streams transmission. A very interesting solution is presented by [PERSON] et al., in [23]. To increase a packet delivery ratio in 6 LoWPAN-based sensor network, the authors proposed the intra-session network coding to encode the fragments of IPv6 packets that are typically sent in 6 LoWPAN-based networks. To decrease an overhead, which is caused by the coding vector that is attached to each encoded packet, 2-byte field of powers of coefficients from Vandermonde matrix are attached, instead of full coefficient vectors. This solution allows for avoiding the retransmissions of frames, and therefore for decreasing overall traffic in a lossy sensor network. One of the important issues in sensor networks is a scalability problem. A lot of sensors can be deployed in some region; thus, networks are often organized hierarchically using clustering approach. The NC technique application in cluster-based, error-prone networks is discussed in [29], where the impact of cluster size on approximate decoding performance and data transfer rate is analytically studied. To improve the decoding performance of approximate decoding, a position information matrix (PIM) is used.