What Is Communications System?
Communications system is a system consisting of two ends, transmitter and receiver, in between which there is a channel. Antenna is a transducer, which is a device that transmits and receives radio waves. It converts radio waves to electric signal by induction and vice versa.
Nowadays mobile phones use full duplex (i.e. the use of two different frequencies simultaneously) to transmit data. This means mobile phones can process two frequencies together, one is for transmitting signal (talking) and one is for receiving signal (listening). The network coverage of mobile phones is determined by the number of 'cells'. Cells are small partitions that a city is divided into, whereby each cell consists of a tower and a small building with radio equipment. Mobile phones operate within cells and can switch cells as they move around to enable continuous conservation. Same frequency can be reused in non-adjacent cells.
Typically there are 832 radio frequencies in a city, which can be divided into 395 full duplex voice channels and 46 control channels. The available number of frequency is increased by 2G technology with digital transmission methods. The most popular one is GSM, which stands for Global System for Mobile communications. Voice data is compressed by an analogue-to-digital converter so that less space is taken and less travel time. GSM uses encryption (for security) and operates in 900MHz or 1800MHz. The main network providers in the UK, like T-Mobile and Orange, work on the 1800MHz bandwidth while O2 and Vodafone use 900MHz bandwidth. Within the bandwidth, each frequency is identified by Mobile Telephone Switching Office and signal transmitted from each user is differentiated by a specific code. This specific code or System Identification Code (SIC) is assigned by the network provider and is searched by control channel when the phone is switched on. When a phone call is made, the mobile phone sends SID along with registration request to Mobile Telephone Switching Office (MTSO) which will keep track of your phone location and save it in the database . When a phone call is made to you, the MTSO will search your location, before picking an available frequency pair for your phone to receive the call.
By setting a resonant frequency, only certain bandwidth(s) will be allowed to work with this antenna . Radio waves are more reliable because it travels at higher speed and low energy loss through air. However, it is not penetrable, where signal is absorbed by rocks and soils and partially reflected when it encounters a surface. So it makes underground communication difficult.
How is it related to London Underground?
London Underground is the oldest underground railway in the world . With 402km/249miles in length of networks , it has become the 2nd longest metro in the world . On average, 1065 million passengers are carried each year3 . It shows how important the Tube is to Londoners.
However, London's underground railway is lacking network coverage, unlike its counterparts in Glasgow, Washington DC, Stockholm, Beijing, Tokyo and Moscow. At present, there is hardly any cellular connection that is the simplest communication technology available on the underground tube, let alone the 4th generation cellular wireless standards .
Communication underground is useful to Londoners in many ways. Apart from being a platform of idea exchange, some research has shown that 6 out 10 passengers would like to have mobile phone coverage on the Tube . The figures are expected to increase prominently following the upcoming Olympic Games in 2012.
However, further research has shown that a lack of credible proposals from suppliers has been the main factor of the delay of implementation of underground communication network by London's underground authorities .
After 4 months indulging ourselves researching and finding solutions to the problem, we finally came up with report and this website. They should draw readers' understanding, first on communications in general, then the impediments to the existence of underground communication, before arriving at a solution to this problem. Hopefully this will give an insight to all readers about communications in general and how it is useful to our lives!
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