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Radio technologies usually associated with mobile telephony can also be used to provide services to homes and offices. GSM and CDMA are capable of providing voice telephony and low-rate Internet connectivity. For example, CDMA is being used in this way is to provide a CDMA mobile phone for both home and mobile use. The customer is charged the same rates as for wireline (POTS) calls if they use the phone within a small, geographically defined, 'home' range - and mobile rates if they use it outside this range.
'3G' wireless technologies promise higher bandwidths for data in the future. Both CDMA and GSM can be used for higher bandwidth data too - for instance GSM's GPRS (General Packet Radio Service). But no matter what radio technology is used, a greater communications bandwidth requires a greater usage of radio spectrum. With finite spectrum, large-scale use of more spectrum can only be achieved by increasing the number of base stations to reduce the cell size. More spectrum is available in higher frequencies, but this means shorter wavelengths and so greater attenuation by buildings and trees. Frequencies of 30 GHz have wavelengths of 1 cm - which requires a line-of-sight path between the customer antennae and the base-station, again - necessitating the installation of more base stations, which typically need to be connected to fiber and have battery backed up power supplies.
As base stations and mobile technologies proliferate and their costs fall, it will be increasingly attractive to provide services via radio which were previously supplied by twisted pair telephone circuitry. In addition to providing telephone and data services to fixed locations, GSM and other mobile phone technologies are widely used for applications such as vending machines or taxi-request units in shopping centers, where the calls are short and the mobile technology saves the costs of cabling and line rental.
Applications
These technologies are generally only suitable for deployment by telecommunications carriers who invest large sums of money to provide coverage of particular areas. They require significant investment and are suitable for connecting to tens of thousands of customers in a reliable, cost-effective manner.
Ideally the infrastructure would provide communications of all conceivable sorts. The most demanding applications might be a single household or business requiring several Megabits per second of bi-directional communication for Internet access, together with several 4 to 8 Megabit per second downstream data-paths for broadcast video, Near Video On Demand (NVOD) or Video On Demand (VOD) plus telephony and upstream channels for controlling VOD data streams.
1. Near Video On Demand - NVOD
NVOD is very different from VOD. NVOD involves making one or more popular movies available on multiple 'broadcast' channels, with each channel starting the movie at, for instance, ten minutes later then the previous channel. This enables a viewer to start viewing within ten minutes, and to take a break from the movie and return to the same point at intervals of ten, twenty or thirty minutes etc.
2. Video On Demand - VOD
Video On Demand does not involve broadcast. Each customer receives their own MPEG-2 compressed video program from a remote video server, with full control over programming, fast-forward, rewind etc. VOD was first conceived as an extension of cable television and video-cassette rental several years before the Internet and World Wide Web became prominent. Properly considered, VOD is indistinguishable from the World Wide Web with full MPEG-2 video. Its scope goes far beyond movies, and includes all existing broadcast video programming plus unique capabilities such as personalized camera angles and replays of live or recorded sports events, and novel material involving games and stories with multiple plots. All this material should be able to contain links to the World Wide Web. So the term VOD could be seen as an early 1990's term for a technology which is yet to be deployed commercially and would ideally be similar or identical to broadband ('broadband' means greater than 2 Megabits per second) Internet.
In the early 1990s, when HFC and ADSL technologies and networks were being planned by telecommunications carriers and cable TV operators, the Internet was used by only a fraction of the population and it was widely believed that Internet usage would not be as important as the demand for video programming, particularly on a VOD basis. By 2001, Internet usage was an established mass-market industry, detracting to a certain extent from the time spent with television and videos. VOD has not been deployed on a large scale commercial basis - due to factors including the technical difficulties and lack of standards for the massive server systems required and the lack of standardized set-top boxes to support it. Additionally, HFC networks were only widely deployed and used for cable modem Internet services from about 2000 onwards, with ADSL's widespread deployment beginning in late 2000.
Ordinary cable TV with fifty or so channels can be delivered with analogue video signals - or digitally with more channels - via HFC cable, satellite or other broadcast technologies. NVOD requires so many channels that it is only practical to deliver it digitally. VOD requires a 'channel' for each customer - and whether the medium is shared, as in HFC or LMDS or a provides a dedicated path to each customer, as with ADSL, FTTC or FTTH, digital video must be used. Video servers are digital devices - but they are extremely technically demanding and it could be 2003 or later before it is practical to deploy server systems capable of meeting the demands of tens or hundreds of thousands of individual customers.
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