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1.2.1. Wireless Networks

Establishing Wireless Network Communication

Wireless communication can be via different media such as ultrasound, infrared or electromagnetic radio waves. Radio waves are the most suitable for LBS as the other media have more problems e.g. with walls and other obstacles.

Common wireless networks today can be classified by two means. One classifier is the network range which is also induced by the network's purpose and the physical limitations of radio waves. The other classifier is the networks topology, whether the network consists of a large infrastructure of mostly im-mobile network-nodes and the mobile clients access only the nodes or the clients form an "Ad-Hoc" network by beeing the nodes themselfes.

Classification of Wireless NetworksClassification of Wireless Networks

Wireless Network Topologies

Radio waves do have a limited range. No matter which technologies and thus what ranges can be reached with a wireless radio transmission, for establishing communication between multiple components as a network three strategies are available: cellular infrastructure networks, Ad-Hoc networks and hybrid networks.

Infrastructure and AdHoc Wireless NetworksInfrastructure and AdHoc Wireless Networks

Cellular Infrastructure Networks are probably the most common way of overcoming the limited range problem. The mobile terminals, e.g. cell phone or PDA, communicate with base station. The base stations themselves are again connected to a network which can also be connected to other networks like the internet. Cell phone technologies like GSM work exactly this way. Usually is the base station network covering a whole country. In dense populated areas there are usually more base stations then on the countryside where fewer buildings or other obstacles are interfering with the propagation of the radio waves.

Ad-Hoc Networks are linking devices like computers or PDAs directly without a base station or access point. Common examples are Bluetooth devices communicating with each other or mobile computers which use just their wireless network capabilities to exchange data directly. To overcome the limited range problem, devices can not only do their own communication but act also as a relay-station and forward other messages.

Hybrid Networks are combining the two above technologies. Thus a cellular network can be extended into regions where no base station is reachable. The base stations can also then provide access to other networks like the internet.

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