We all are using mobile phones. But many of us don't know how the communication actually happens so for this purpose I'm writing this post. Hope you get some useful information from this post. Now coming to the point.
At first glance, the transmission path of mobile communications appears simple: Digital radio signals are transmitted from one mobile phone to another or to a landline telephone. In reality, however, speech and data will pass through a number of intermediate stations before reaching the called party. The transmission path of mobile communications spans the distance from the mobile phone to the base station of the radio cell in which the caller is located. From there, the information must be transmitted – at times over great distances – to the radio cell in which the called party is located. This is done by the use of mobile switching centre's.
Mobile switching centres
The mobile phone base station receives the radio signal of a mobile phone – and the information to be transmitted – with its receiving antenna. It relays this signal, via a traditional cable connection or a microwave link, to the mobile switching centre. The mobile switching centre is responsible for routing calls and handling the entire connection, including ringing through to the end connection. It also carries out services such as call forwarding, call waiting or conference calls. Additionally, it registers the billing data.
The mobile switching centre will either hand the call over to the traditional fixed network or to another mobile switching centre that will transmit the call to the base station closest to the called party. It is from here that it can reach the mobile phone.
The transmission path in mobile communications
Microwave links
The data transmission between the base stations and the mobile switching centres uses either traditional cable connections or microwave links. Microwave links will send and receive signals on frequencies in the gigahertz range via circular parabolic antennas. Signals are sent in the microwave range between 2 GHz and 60 GHz. Microwave links always require a direct line-of-sight connection, so the data is generally transmitted via so-called microwave radio relays. These are often installed on rooftops together with base stations. The microwave radio relays receive and amplify the microwave signals and retransmit them to the next relay. Maximum distances here depend on the frequency. For frequencies of 2 GHz, they can be between 40 km and 100 km. For higher frequencies, the maximum distance is shorter, comprising about 30 km for 10 GHz.
Handover Mechanism
Mobile phones are not the only mobile element in the communication process; the mobile transmission path also adapts dynamically. This means that the transmission path of the information changes depending on the location of the caller and the called party. Whenever a subscriber moves from one radio cell to another during a call, the system will automatically switch over to the adjacent radio cell (called a handover) and finish the connection to the old cell without the mobile phone user noticing anything.
The transmission quality is the deciding factor in the decision whether to hand over the connection or not. If this falls below a certain limit or if changing the radio cell will improve the transmission quality, a handover to the next cell will take place.
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