Ad Hoc Networks
Ad Hoc Networks

The main characteristic of ad hoc network topology is that there is no central control unit as in case of infrastructure network. That means there is no base station as in case of conventional cellular network (GSM, UMTS, LTE) or no access points as in case of WiFi (Wireless Fidelity) technology, which should control and manage the network. In addition, while in cellular networks the mobile station send/receive data and control information solely to/from base station, in ad hoc network all mobile stations are equal and can communicate between themselves. The important notion is that ad hoc network is only of temporal duration, not permanent as in case of infrastructure network.

The meaning “ad hoc” is taken from Latin, which stands for “to this”. To be more specific, ad hoc means something created without planning.

At the beginning, the idea behind ad hoc network was to connect several UEs that were in communication distance with each other (this is also definition of ad hoc network in WiFi based on IEEE 802.11 standards). In other words, only those UEs that were close enough can exchange data. In addition, formerly known ad hoc networks supported in WiFi were supposed to be mostly fixed, that is, the UTs were immobile.

Since the new trends in telecommunications industry is to allow all users mobility, network topology can change very often in sense that direct communication with individual UEs does not have to be available all the time. The networks supporting ad hoc topology together with users’ mobility emerged and became known as a Mobile Ad Hoc Network (MANET). The MANETs are distinguished especially by mobility of terminals (that is why we call them “mobile” ad hoc networks) and by multihop communication. Like in case of relays in LTE-A, the multihop communication means that the source and destination stations do not have to be in communication distance. In order to send data between them, the packets have to be retransmitted through several neighbour stations. The comparison of ad hoc topology and infrastructure networks is depicted in Figure 28.

The comparison of ad hoc and infrastructure topologies

The advantages and disadvantages of ad hoc networks in comparison to infrastructure networks are stated below.

- Simplicity in terms of network building since there are no central nodes
- Presence of external network is not necessary
- Easy to setup and simple to configure and install
- Cheap and fast deployment where needed

- UE can communicate only with other UE, which is in communication distance (applied only to single hop fixed ad hoc networks based on WiFi standard)
- High interference could be generated as UEs are using the same frequency bandwidth
- Frequent topological changes due to UEs’ mobility and necessity to keep track concerning the available path between individual UEs => high signalling overhead (applied only to MANET)
- Power constrains
- Security issues and protection against various attacks

The ad hoc and especially MANET networks can be used in many scenarios:

- Military communication and operations
- Emergency services (search and rescue operations, disaster recovery, policing and fire fighting)
- Commercial and civilian environments (dynamic database access, mobile offices, sport stadium, trade fairs, etc.)
- Home and enterprise networking (home/office wireless networking, conferences, meeting rooms, personal area network, construction sites, etc.)
- Education (University and campus, virtual classrooms)

In order to manage communication in ad hoc based networks and to address its many challenges, wireless MAC (Medium Access Control) protocols and appropriate routing protocol (in case of MANET) has to be implemented. These will be explained in the following chapters.