Ad-hoc network is a network created without any central control or management. This network is based of mobile nodes, which use wireless interface to transfer of data packets. Nodes in network are able to work as routers and they can route packets for other nodes. Ad-hoc connection is based on peer-to-peer type of communication. To provide a connection among mobile units it is not used any cable infrastructure and there is no central control to manage a creation of connections and to support the coordination and communication. Furthermore, there is no intervention from operators.
In general, in ad-hoc networks all devices, which share a common space, will also share common channel and they will be equivalent in this sharing each other.
These networks can be applied for network creation in such areas, where there is no infrastructure available, for example by emergency operations in far-away areas and for wireless public access in metropolitan areas – access nodes can serve as fixed relay stations for packet routing among each other [27]. On local level they are used for connection of notebooks, palmtops, e.g. at the conference, creation of home network, creation of personal networks and also for surroundings monitoring and realization of WLAN networks.
Wireless Local Area Network (WLAN) as a main representative of Ad-hoc networks can operate in two configurations, either as independent configuration (ad-hoc) – stations communicate directly and there is no necessity to install any supporting infrastructure, or as distributive system configuration – configuration expects existence of access point (AP), which at the same time works as a base radio station and as a data bridge. Wireless local networks can be divided into radio technology networks and infrared (IR) technology networks. IEEE 802.11 (WiFi), HIPERLAN and Home RF standards belong to radio technology networks [28].
Bluetooth technology represents the next radio technology of a short range, it has to be able to work in ad-hoc networks, which can be either independent, or works like a part of IP networks in all over the world, eventually as combination of both possibilities. The goal of this technology is to replace the cable connection among electronic devices by radio channel by means of cheap radio chip. The key characteristics of this technology are robustness, small complexity, low power and small price. Bluetooth works in ISM (Industrial-Scientific-Medical) band of 2.4 GHz and uses frequency hopping to eliminate of interference and fading. Coverage is about 10 meters (possible connection through walls of building), transmission rate is 780 kbps (one-direction transmission is 721 + 57.6 kbps, symmetric transmission is 432.6 kbps).
The following table presents bit rates survey, which networks technologies of particular generations can ensure.
Distribution of technology |
Maximal bit rate downlink/uplink [Mbit/s] |
|
2G/2.5G/2.75G |
GPRS |
0.080/0.040 |
EDGE |
0.236/0.236 |
|
EDGE Evolution |
1.9/0.9 |
|
3G/3.5G/3.9G |
UMTS |
0.384/0.384 |
HSPA |
14.4/5.75 |
|
HSPA+ |
56/22 |
|
LTE |
360/80 |
|
Flash – OFDM |
15.9/5.4 |
|
WiMAX |
144/35 |
|
4G |
LTE Advanced |
1 Gbit/s fixed connections and 100 Mbit/s mobile |
WiMAX IEEE 802.16m |
||
Others |
WiFi 802.11b,g |
54/54 |
WiFi 802.11n |
600/600 |