# Energy Efficient Multicast Communication in Cognitive Radio Wireless Mesh Network
## 1 Introduction  
Multicasting is a fundamental networking primitive that is used by a wide range of applications. The fundamental idea of multicasting is to facilitate group communication by allowing the transmission and routing of packets to various destinations while using as few resources as possible, such as energy consumption, necessary bandwidth, and relay nodes. However, with the rise of low-power gadgets, efficient resource usage has become even more crucial. Cognitive radio technology has been recognized as a key enabler for next-generation wireless communication and effective spectrum usage. This helps us to minimize energy usage for transmission even further. This technology allows the nodes equipped with a cognitive radio to utilize the unused portion of the licensed spectrum in an opportunistic manner. The availability of these unused portions of the spectrum is dependent on the usage pattern of the licensed user. This varies in time and location, due to which a cognitive radio may observe a different set of available channels (which is referred to as spectrum heterogeneity). This raises several challenges for cognitive radio networks [1]. This paper is interested in the multicast problem in cognitive radio wireless mesh network (CR-WMNs). Although a lot of research has already been done on multicasts in wireless networks, these findings cannot be applied due to the spectrum heterogeneity associated with CR-WMNs. This is because the properties of this kind of network may result in the transmission of the same frame multiple times over multiple channels depending on the availability of the channels at different nodes. Furthermore, most of the previous work done, which will be discussed later, focused towards either improving the throughput or decreasing the latency of the transmission for multicast session which is not applicablefor an environment with low power devices. Keeping in view the current proliferation of low power devices, we considered the reduction of energy consumption to be the prime objective of this work. In this work, how to minimize these multiple transmissions of the same frame in order to reduce the energy consumption for multicast communication in CR-WMNs has been studied. To have a better understanding of multimedia communication over the CR-WMNs, a survey article presented by [PERSON] et al. in [2] had been referred to. For this purpose, first, an energy consumption model has been developed for multicast communication and an optimization problem designed to construct an energy efficient multicast tree while considering the spectrum heterogeneity property of CR-WMNs. Subsequently, rather than developing a single layer approach that solely focuses on multicast routing, a cross-layer heuristic approach is proposed to solve this optimization problem. The proposed approach considers the routing and channel assignment mechanism to construct an energy efficient multicast tree in CR-WMNs. In the proposed technique, for a given multicast session, a node level is defined for each node in the CR-WMN. The node level is determined on the basis of the node's distance in terms of the number of hops from the source node (with the farthest node being assigned the highest level). A mechanism to select the forwarding nodes and assign channels to these nodes is then introduced for each level. This mechanism starts from the highest to the lowest level and ultimately results in the construction of a multicast tree. The decision to select the forwarding nodes and assign channels to these nodes is carried out in such a way that a frame is transmitted a minimum number of times to reach all its intended receiving nodes while taking care of spectrum heterogeneity. The main contribution of this paper can be summarized as follows:  
1. A multicasting problem for CR-WMNs is established to reduce the amount of energy used during a multicast session. 2.