The following is a summary of an article in ericsson review December 28, 2011
In
locations where the number of users are high a densified infrastructure can
provide the increase in NW capacity that is needed. This can be achieved with a
layered cell structure meaning that multiple and equally available cells have overlapping
coverage areas. Typically, the
traditional macro cell transmitting with high power over a large coverage area
is complemented with pico cells transmitting with low power over a smaller
coverage area that is geographically covering a part of the coverage area of
the macro cell. In addition to simply selecting the cell with the strongest
signal, the cell selection algorithm should in this case also incorporate cell congestion
and backhaul capacity. Heterogeneous network deployment can be achieved with
two different approaches, resource partitioning and soft-cell schemes:
·
Resource
partitioning can be achieved in either the frequency or the time domain which
in reality creates separate cells with individual system information and synchronization signals transmissions.
·
In
shared cell or soft cell schemes, the low power pico cells are part of the
macro cell but with a Cell Specific Reference signal (CRS) which determines
which part of the System Information that is relevant. Also, a Demodulation
specific Reference Signal (DM-RS) is used to determine which transmission point
(macro or pico cell) the terminal should use.
Heterogeneous deployments that use soft cells can provide
greater mobility robustness than deployments with separate cells. This is
important, especially when moving from a low-power node to the macro. In
separate cell deployment, a handover procedure is required to switch serving
cells. If, during the time it takes to perform the handover procedure, the
terminal has moved too far into the macro area, it may drop the downlink
connection from the low-power node before handover is complete – leading to a
radio-link failure. In soft-cell deployment, the transmission point that should
be used for downlink transmission can be changed rapidly without a handover
procedure – thus reducing the probability of dropped connections.
the article in its entirety can be found at
heterogeneous_network_deployments_lte
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