The basics of cell splitting is to reduce the strength of signal of an
antenna, this reducing the area of coverage for the antenna. thus the capacity
provided by an antenna over a large area is now concentrated in a small area.
Obviously, if this were all that were done, then blank spots would be introduced
and in order to remove these extra antennas need to be introduced into the network.
this adds extra capacity to the whole cell. In some situations extra capacity is
needed for parts of the cell and a second option is to introduce additional small
cells on to of the original cell. This adds capacity but care is required regarding
the interference between the two cells.
There are only 3 ways for a MNO to add capacity to a mobile network.
- Improve the spectral efficiency, using modulation techniques that maximize
the number of bits sent per cycle. They can also employ multiplexing schemes
so that there are no "gaps" in the channels when there is demand on other
- Add more spectrum. This can be by gaining more spectrum overall. Or using
what they have in a better way. There is much re-factoring of 2G to 4G and
soon removing 3G to free up this for 4G or 5G. However not all frequency is
equal with lower frequencies more useful in rural areas, and higher frequencies
provide capacity in urban areas
- More cells working a lower power can allow spectrum to be reused more
Many diagrams of cell coverage show regular hexagonal coverage but in reality
demand is not uniform within a cell. Masts that are directional, maybe along a road,
can add capacity to the users of the road but add no extra capacity to the
surrounding fields. Below are 4 cases of where extra capacity is required
for a particular need and extra small cells are added to the network.
- As the user moves to the edge of a cell, at a maximum distance from all
of the masts the mobile device can see. The signal to noise ration is at a
maximum and so modulation must be slowed to make signals readable, to reduce
the errors. The addition of a small cell at the worst point can add capacity
to the network.
- For a building, in an urban environment, the damand within the buiding
and it's environs may be a hot spot within the larger cell coverage area. A small
cell targetted at providing mobile phone coverage for that buiding will
server the users within the building and allow the users away from the building
more network capacity.
- Similar to the above situation but with periodic demand. Events such as
football matches where 50,000 supporters want to use their phone would
hit the standard phone coverage cell. Extra small cell(s) add capacity for the
duration of the event. Similarly for music festivals, which may be located
in rural environments may not have suitable capacity for an influx of 20,000
people when the usual population is 200. Also the frequency used in a rural
environment will typically be 800/900MHz so for the festival duration
extra small cells using the 2.1/2.6GHz frequencies would add capacity for the
- Very busy streets such as Oxford Street in London have a high demand, even
given the overall high demand in the Central London area. To get capacity along
Oxford Street, a number of small uni-directional cells can be installed using the
higher frequencies. The shopper will have an increased number of handovers between these
linear cells but as they will be travelling slowly (walking) it will not be an issue.
For a fast car driver this would be more difficult to acheieve.