# Energy Efficient Multicast Communication in Cognitive Radio Wireless Mesh Network
## 2 Related Work  
Energy efficient multicasting in wireless networks is a multi-faceted problem that can be addressed in several ways, to name a few, including optimization of transmission power [3], optimization of routing paths [4], and spectrum and bandwidth optimization for multicast sessions [5]. CR is considered a promising candidate technology to be used in this field. However, these results in [3; 4; 5] are not applicable to the CRN because of its unique features in terms of spectrum availability. Thus, it is essential to develop new protocols and algorithms for multicasting in CRNs. Over the last few years, many studies have been reported on multicast communication in CRNs. A multipath on-demand routing protocol for CRNs has been presented in [6]. The protocol is based on the Artificial Intelligence Reinforcement Learning Method and aims to increase throughput and reduce end-to-end delays. Results have shown that, particularly in the case of high primary user (PU) activity, the proposed protocol is superior to current state-of-the-art protocols. A multicast scheduling technique for a single cell CR-WMN is proposed in [7]. In this technique, client nodes assist the base station in delivering the multicast data over orthogonal channels to reduce total multicast time. Network coding is also utilized for a further reduction in overall multicasting time. The authors of [8] have also used network coding for multicasting in CRNs with the goal of minimizing total transmission cost (amount of transmitted data) while taking into account both channel uncertainty and node mobility. A random network coding-based multicasting strategy is presented in [9], and the aim was again to reduce the total number of transmissions (amount of data). An optimization method for multicast scheduling in CRNs using network coding was presented in [10]. In this optimization problem, several considerations, including protection of the PU and fairness, were taken into account. Two methods were proposed: a greedy method based on centralized optimization and a stochastic optimization-based online method. An optimization problem is presented in [11] which jointly defines multicast routes and channel assignments with the goal of increasing multicast throughput in multi-hop CRNs. In [12], the implementation of multicast non-orthogonal multiple access (NOMA) in CRNs is explored. Significant performance gains were achieved by CR user scheduling through cooperative NOMA. Other multicasting strategies inspired by NOMA are proposed for CRNs [13; 14]. A multicast tree construction method is proposed in [15] such that the total bandwidth used by the multicast tree is reduced to meet the predetermined _Quality of Service_ (QoS) requirements. The authors presented two approaches to solve this problem based on a minimal spanning tree so that time slots are allocated to tree links in a manner that reduces bandwidth usage. A minimum tree-based multicast routing protocol is proposed in [16]. The contribution of this paper was to increase the total throughput and the delivery rate of the packets. The authors of [17] presented a problem related to joint power and rate allocation with a goal of maximizing the average multicast rate in CRNs while guaranteeing QoS in terms of the probability of service failure. A hidden node problem for multichannel multicast transmission is raised in [18], and a local multicast concept is introduced to address this issue. A channel assignment algorithm is presented for this purpose that considers both partially overlapping as well as orthogonal channels. The authors in [19] proposed a multi-channel multicast problem for a multi-radio network of wireless mesh nodes with directional antennas. The goal was to reduce interference by selecting the best multicast session tree, channel, and antenna beams. A survey article [20] has been referred to for a more detailed review of multicast communication in CRNs. In Table 1, the above related work is summarized as follows.