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View Full Version : UMTS Radio Network Planning , Design and Optimization



mansoor2
2008-10-03, 11:12 AM
UMTS radio network planning and optimization is altogether a vast
and interesting field.
It involves the simple work of deploying the Node-B's and RNC's but,
hold on...!!
Complex estimations of various radio network parameters, Dimensioning,
Detailed Planning and Optimization of radio network, Network simulation
softwares and Field measurements are involved in enforcing the
simplicity mentioned earlier!! The goal is to get sufficient coverage
and capacity by maintaining the lowest possible deployment costs.
Dimensioning:
In this phase the basic general properties of the "would-be"
network is investigated.
This initial phase of Network Planning includes calculating the
approximate number of Node-B's required, deciding the antenna heights
and the network configuration parameters keeping in mind the kind of
mobile services the service provider advertised to offer their
customers!
Detailed Planning:
Usually a site-survey is done at first to get to know about the
geographical locations,
traffic volume in different areas.Topology planning and configuration
planning is
done in this stage.Power budget calculation, also called as link budget
is done by taking all the available radio parameters that include
information of different gains and losses in the communication path of
the radio link.
Cell breathing should be taken into account while calculating
cell range in UMTS network.When the traffic in the cell increases, the
sensitivity of the Node-B decreases
because of the increased interference and so the UE will require more
power to
remain connected to the cell.And when there is not much load in the
cell, the interference would be low and the UE can use the same power
to connect to that particular cell even from a longer distance.This
variation in cell ranges is called as cell breathing.
Simply put, cell capacity influences cell coverage area.So one of the
parameter in link budget is Interference margin.
<i>MInterference, dB = 1...3 dB (20...50% Load).</i>

Usually in RF Network planning, they start with uplink because
the downlink is normally adjusted to balance the uplink by selecting
the appropriate power amplifier at the base station. Near cell edges,
the users transmit with full power to reach the Node-B and the inner
loop power control mechanism in uplink causes a problem, because the UE
cannot respond to power control commands due to limitations in
transmission power capacity. This should be taken into account while
calculating link budget, and it is done by introducing a Power control
headroom margin also called as Fast fading margin, which guarantees
continuous service for users in cell edges.
The Fast fading margin or Power control headroom is given by

<i>MFastFade, dB = 2...5 dB.</i>

In UMTS, coverage and capacity planning are interrelated and
cannot be done separately
because of cell breathing phenomenon and they are done in planning
phase called topology planning. In coverage planning accurate cell
ranges are calculated from power budget calculations provided in
configuration planning phase. Normally, cell coverage's are made to
overlap excessively to give high service probability to users in cell
edges, thus providing soft handover resulting in macro-diversity
gains.But more number of soft handovers implies significant cost in the
capacity. After measuring the pilot strength in the area, the size of
handover zones within the cell footprint should be decreased. Handover
zones should be shifted from high-traffic areas to low-traffic areas
but at the same time should be strategically placed to get the
advantage of macro-diversity gains
for UEs in cell edges.
The detailed planning phase includes usage of Network
simulation soft wares for coverage and capacity estimations. The inputs
include user traffic distributions and other network specific
parameters. Simulations are mainly done to know the optimal number of
Node-B's required,UE transmit powers etc.Simulation results are used
for optimizing the network. However simulations are also done in
parallel to actual planning before the network is actually launched.
Base station locations should be selected so that they are always
placed on the traffic hot spots, since this offers the best link budget
for the mobile users served by those base stations.
Field measurements are performed to study soft handover areas, network interference,
and call drops that happen in the real network.Field measurements are mostly performed
when planned coverage and propagatiion channel characteristics are examined in an already operational network.

Before the network is launched code and parameter planning are
needed. Certain amount of Channelisation codes(OVSF codes or walsh
codes) are allocated for each cell to separate users in downlink
direction. Optimization:

The actual parameters being used in the real network are fine
tuned for better performance. The power control parameters, number of
channelisation codes being used in a particular cell and other critical
parameters that have a great impact on the performance are optimized
from the network simulation software and field measurements.Use of
WCDMA repeaters is one way to increase coverage and capacity in an easy
and affordable way.The article discussed only about Interference
margin, Power control headroom margin and soft handover macro diversity
gains.

RF engineer
2009-10-18, 11:22 PM
Dear mansoor i would like to ask you do you have a document contain that you mentioned .thanks in advance

Mazari
2009-10-19, 02:29 PM
Did you forget to attach the document ??