**3. Channel assignment problem**

In this section, the medium access issues encountered by IEEE 802.11-based single-radio single-channel WMNs are presented, and a multiple-channel approach using multiple radios to overcome these problems is discussed. The key issue of channel assignment in Multi-Radio Multi-Channel (MRMC) WMNs is presented, along with its objectives and constraints.

### **3.1. IEEE 802.11 medium access issues**

Since the WMN has to provide access to broadband Internet, it is expected to have higher bandwidth. Even though the physical layer can support very high bit rate, current MAC protocols are not able to utilize the entire bandwidth provided by the physical layer. The main reason for this poor performance is the suboptimal media access protocols, which were primarily designed for single-hop networks [1].

#### *3.1.1. Hidden and exposed terminal problems*

IEEE 802.11 Distributed Coordination Function (DCF) is one such widely accepted MAC protocol but, when used in a multihop network scenario, it results in poor performance and is therefore unacceptable. The reason is that some nodes remain starved due to hidden and exposed terminals in a multihop environment. Figure 2 illustrates these problems [1].

Node 2, which is outside the interference range of Node 3 and unaware of the ongoing transmission at Node 3, continues to send RTS to Node 1 causing collision. This is a case of the hidden terminal problem.

Node 4 is prevented from transmitting because of the neighboring transmission at Node 3. This is a case of the exposed terminal problem.

**Figure 2.** Hidden and exposed terminal problems [1]

required in HMCP is not needed in TICA.

**3. Channel assignment problem** 

**3.1. IEEE 802.11 medium access issues** 

primarily designed for single-hop networks [1].

*3.1.1. Hidden and exposed terminal problems* 

This is a case of the exposed terminal problem.

the hidden terminal problem.

constraints.

**b. Breadth First Search - Channel Assignment (BFS-CA)** 

A co-ordination protocol is required to decide what channel to assign to the fixed interface, and also for enabling neighbors of a node X to know about the channels used by fixed interface of node X. Time synchronization and coordination between mesh nodes which is

BFS-CA [20] is a centralized, interference-aware algorithm aimed at improving the capacity of the WMN backbone and at minimizing interference. This algorithm is based on an extension to the conflict graph concept called the Multi-radio Conflict Graph (MCG) where the vertices in

BFS-CA requires certain number of MRs with certain number of radio interfaces to be placed at certain hops from the gateway, whereas TICA simply requires all MRs to have four data radios, does not require any careful router placement strategy, and works with any

In this section, the medium access issues encountered by IEEE 802.11-based single-radio single-channel WMNs are presented, and a multiple-channel approach using multiple radios to overcome these problems is discussed. The key issue of channel assignment in Multi-Radio Multi-Channel (MRMC) WMNs is presented, along with its objectives and

Since the WMN has to provide access to broadband Internet, it is expected to have higher bandwidth. Even though the physical layer can support very high bit rate, current MAC protocols are not able to utilize the entire bandwidth provided by the physical layer. The main reason for this poor performance is the suboptimal media access protocols, which were

IEEE 802.11 Distributed Coordination Function (DCF) is one such widely accepted MAC protocol but, when used in a multihop network scenario, it results in poor performance and is therefore unacceptable. The reason is that some nodes remain starved due to hidden and

Node 2, which is outside the interference range of Node 3 and unaware of the ongoing transmission at Node 3, continues to send RTS to Node 1 causing collision. This is a case of

Node 4 is prevented from transmitting because of the neighboring transmission at Node 3.

exposed terminals in a multihop environment. Figure 2 illustrates these problems [1].

the MCG represent edges between radios instead of edges between mesh routers.

placement of routers as verified by a comprehensive performance evaluation.
