Ad Hoc Networks
Mesh network

Mesh network is a perspective topology combining characteristics of infrastructure and ad hoc networks. Similarly as in infrastructure network, the mesh network is composed of central nodes (e.g., base stations, access points, etc.) that provide connectivity, for example, to the Internet. Nevertheless, the main difference in comparison to cellular networks is that in mesh network the UE can attach to other UE. These UEs can then communicate between themselves without intervention of the central node. When compared to ad hoc and MANET networks, the mesh network topology is supposed to be permanent and individual nodes in the network are mostly fixed. Still, mesh network also inherent the paradigm of multihop communications when data can be sent via several nodes to reach their destination. Consequently, optimal routing path (if UE is out of central node’s range) has to be found by means of specific routing protocols similarly as in case of MANET or WSN.

The mesh topology is supported in WiFi technology by IEEE 802.11s amendment. While legacy user equipments (i.e., equipments supporting already existing standards such as IEEE 802.11a/b/g) can use mesh, it can not serve as an intermediate node between the UE and the access point. In addition, the mesh topology is also considered in WiMAX technology based on IEEE 802.16d standard where fixed topology is assumed. Nevertheless, more recent standards supporting mobility (IEEE 802.16e/j/m) excludes mesh and use only infrastructure topology such as PMP and relay due to high complexity of mesh implementation.

The advantages of mesh are the following:

- Increase of coverage since UEs out of access point coverage can connect to it with help of their neighbours (i.e., no additional access points have to be installed).
- High flexibility and reliability (several possible routes to access point can be found).

The disadvantages of mesh are following:

- The UE can be used for data transmission of other UE. Thus, intermediate UE will consume more battery energy.
- Throughput degradation if the same data are transmitted more than once between source and destination stations due to multihop communications.
- Higher overhead than in case of infrastructure network (it is necessary to maintain available routes).

An example of mesh structure and communication between individual stations