# Minimum Interference Channel Assignment Algorithm for Multicast in a Wireless Mesh Network
## 2 Related Work  
In this section, we review some of the related works in the area of channel assignment for multicast in multi-channel multi-radio WMNs. It is widely considered that there are two different types of channels in the study of channel assignment for multi-channel and multi-radio WMNs: orthogonal channels and partially-overlapped channels. In 802.11b/g network environments the use of 11 channels from channel number 1-11 is allowed [22]. Based on the IEEE 802.11b/g standard, if the channel gap is greater than, or equal, to 5 then two channels are non-overlapping. This means that three channel numbers 1, 6, and 11 are non-overlapping channels in 802.11b/g. Orthogonal channels can completely eliminate network interference between two nodes and dramatically increase network throughput. However, only three orthogonal channels are not enough to assign them to the network interfaces of wireless nodes to get rid of network interference completely. Thus, most of the studies of channel assignment consider partially-overlapping channels. Previous studies on channel assignment problems in multi-channel multi-radio WMNs have been studied substantially for unicast communications [5; 6; 7; 8; 9; 10; 11; 12; 13; 14]. However, recent studies on the channel assignment problem in WMNs focus on multicast manner [15; 16; 17; 18; 19; 20; 21; 22; 23]. Therefore, our work focuses on the channel assignment problem for multicast in WMNs. In [17], authors presented the MCM algorithm. The MCM algorithm is a channel assignment algorithm for multicast in multi-channel multi-radio wireless mesh network environments. This algorithm first constructs a multicast tree for multicast communications from a source to multi-receivers. In the multicast tree, there are three kinds of nodes: a source, relay nodes, and multi-receivers. A source node usually generates data packets, and a relay node receives packets from its relay node and forwards them to its children. Lastly, there are several receivers that just receive data from its parent node. In this algorithm, they assume each wireless node has two network interfaces: one for sending packets to its children and the other for receiving data from its relay node. Thus, each node needs two-channel information for these network interfaces. The main goal of MCM is to assign channel numbers to the sending and receiving interfaces, respectively, without network interference. The MCM algorithm uses an interference factor to estimate the level of interference between two nodes. The interference factor [17] is defined as the ratio of the interference range by the transmission range. The interference factor is also closely connected with channel separation [29] between two nodes. In the previous research, they conducted real experiments to measure the interference factor between two wireless peer-to-peer links. Table 1 shows the interference factors in an IEEE 802.11b network. As seen from this table, we can know that the interference range decreases as the channel separation increases. For instance, if the channel separation is greater than, or equal to, 5 then the interference factor value is zero, which means there is no interference between the two nodes. An example of channel assignment by MCM is shown in Figure 1. In this example, S is a source node, C, D, and F are multi-receivers, and A, B, and E are relay nodes. The black-colored numbers represent the channel number for each node's sending interface and the red-colored number represents the channel number for each node's receiving interface. The MCM channel assignment algorithm considers only one-hop neighboring nodes to decide the influence of interference. This approach may yield the HCP. The HCP takes place when two different nodes which are away from each other with a two-hop distance use the same channel, thus these two nodes can interfere with themselves. For example, node A receives packets from node S on channel 1, which means node A is located in the source node's transmission range.