One of the options that is most likely to be incorporated into the 5G technologies that are being developed for the 5G cellular telecommunications systems is a millimetre wave capability.
With spectrum being in short supply below 4GHz, frequencies extending up to 60GHz are being considered.
5G millimetre wave basics
One of the interfaces being considered for 5G mobile communications uses millimetre wave frequencies.
It is estimated that bandwidths of several GHz may be required by operators to provide some of the extremely high data rates being forecast.
Currently frequency below 4GHz are being used by cellular communications systems, and by the very nature, these frequencies could only offer a maximum bandwidth of 4 GHz, even if they were all clear for use which is obviously not possible.
By having a 5G millimetre wave interface, much wider bandwidths are possible, and there are several candidate millimeter bands that are being considered for allocation to this type of service.
5G millimeter wave propagation
The propagation characteristics of millimetre wave bands are very different to those below 4GHz. Typically distances that can be achieved are very much less and the signals do not pass through walls and other objects in buildings.
Typically millimetre wave communication is likely to be used for outdoor coverage for dense networks - typically densely used streets and the like. Here, ranges of up to 200 or 300 metres are possible.
One of the issues of using millimetre wave signals is that they can also be affected by natural changes such as rain. This can cause a considerable reduction in signal levels for the duration of the precipitation. This may result in reduced coverage for some periods.
Often these 5G millimetre wave small cells may use beamforming techniques to target the required user equipment and also reduce the possibility of reflections, etc.
Millimetre wave coverage
Simulations have shown that when millimetre wave small cells are set up they provide a good level of coverage. Naturally, typically being lower down than macro cells, the coverage will not be as good, but when considering the level of data they can carry, they provide an excellent way forwards for meeting the needs of 5G systems.
A further issue to be considered when looking at 5G millimetre wave solutions is that they will incur a much greater number of handovers than a normal macro cell. The additional signalling and control needs to be accommodated within the system. Also backhaul issues need to be considered as well.
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