Space-division multiple access
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In traditional mobile cellular network systems the base station has no information on the position of the mobile units within the cell and radiates the signal in all directions within the cell in order to provide radio coverage.
This results in “wasted” power and transmission where there are no mobile units to reach as well as interference to adjacent cells using the same frequency, so called co-channel cells. Likewise, in reception, the antenna receives signals coming from all directions including noise and interference signals.
By using smart antenna technology and exploiting spatial information of the location of mobile units within the cell have led to the development of space-division multiple access (SDMA) techniques. The radiation pattern of the base station, both in transmission and reception is adapted to each user to obtain highest gain in the direction of the mobile user. This is often done using phased array techniques.
[edit] See also
In GSM cellular networks, the base station is aware of the mobile phone's position by use of a technique called Timing Advance (TA). The Base Transceiver Station (BTS) can determine how far the Mobile Station (MS) is from the base by the reported TA. This information, with other parameter settings, can then be used to power down the BTS or MS power if the power control feature is implemented in the network. In general BTS & MS power control are implemented in any modern network. Especially MS as this ensures a better battery life for the MS and thus a better user experience with the MS (not always charging the battery). This is why it is safer to have a BTS close to you as the MS will be powered down as much as possible. There is more power being transmitted from the MS than you receive from the BTS even if you are 6m away from a mast.
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