LTE Coverage Optimisation : How to improve coverage in LTE radio network in UL and DL


Our today’s topic is LTE Coverage
optimisation. It is a very important aspect in an LTE network from the initial planning phase to deployment phase and on-going optimisation phase of the network. We will be covering a number of topics within LTE coverage optimisation
and those are listed now on the screen. number one is how to detect UL and DL coverage problems. This would include from which KPIs, information elemects which be used to detect the issue. Secondly we will have a look at Imbalance between downlink and uplink and
imbalances that can occur between transmission elements. Thirdly
we will discuss overshooting and overlapping problems and then we will
have a look at extended coverage and then we would analyse cell border adjustment. Finally in end we will look at the parameters that can we can use to
optimise LTE. By the end of this video you will
have essential info to optimise coverage and coverage parameters. So let’s
get to our first topic So the question is how we detect that we
have a coverage problem We would need to know in terms of RSRP what defines a coverage problem In terms of RSRP, if it is less than -120 dbm, it is considered a coverage hole and in terms of weak coverage, the RSRP is less than -105 dbm This is regarding the downlink so this is your
coverage hole and this is you have weak coverage problem
so in optimizing Coverage you have to have a balance between the coverage and
the interference because if you are increasing transmission power then you are also increasing interference so we go back to a question that how we detect
coverage problems. In the downlink considering this is your base station
and this is your UE. So how to detect it that we have a LTE Coverage hole. One of the best ways is using drive testing. If you are drive testing a site or a cluster of sites, you will get get that information where you
have handover failures where you can see in the drive test areas where you have coverage issues. You can also see them through the KPIs so
for example for a number of neighbouring sites there is one specific area at a given inter-site distance where you are having a lot of IRAT handovers
so in that situation that shows you that you most probably have an LTE coverage hole. This would also sometime point out in terms of weak coverage you would have frequent handovers towards the other LTE sites and you would have low throughput and you have RSRP issues. So this is how you detect a downlink coverage issue. What about uplink? So in LTE we have
a factor called power headroom and power headroom report is sent by the UE
towards the eNobeB of the and in that power headroom report, the UE informs about how much
room it has for reaching its maximum transmission power so basically eNobdB knows if the UE is transmitting on maximum power or
something below. So basically power headroom has a range from from a -20db to
+40db and if we normalise this it will give us a range of -5db to 20 DB so
your eNodeB would know from that power headroom that if your UE is already
transmitting on maximum power and if yes then it is in a part where there is weak coverage. secondly we have SINR thresholds for Physical Uplink shared channel We also have RSSI thresholds for Uplink shared channels. So eNodeB can know from these thresholds as well that UE may be facing an uplink coverage issue. So these are the ways to detect downlink and uplink coverage
issues in LTE So let’s move towards the next topic
that is overshooting and overlapping. Lets discuss overlapping and overshooting.
First we discuss overlapping. Overlapping basically means that in LTE that you have in one coverage area,
there is no dominant server. In this case, there is a lot of pilot pollution and there are strong reference signals from different cells are within a certain
power range. So there is no dominant server and you can have strong signals for a number
of eNodeBs and this will result in downlink interference and in the end
basically will result in the low throughput and sometimes it can
result in radio link failure as well so what are the criteria that basically we
use to decide that we have an overlapping issues so the general rule
of thumb is that if in an area for example this is a coverage area and
we have this coverage area more than three RS which are basically greater
than -105dbm and the strongest reference signal is not more than 6db higher. So we have three strong RS within a range of 6db. For example strongest RS at -81dbm and weakest at -87dbm. So from -81dbm to -87dbm, we have three reference signals. This would result in Pilot pollution and DL interference So how to control these factors and Pilot pollution. Bascially you can use azimuth change, E-tilting You can also use height reduction and sometimes you can reduce the power of the reference signal as well or you can adjust using power boost for the RS , power of traffic signal and
common channels or even the ratio the power used by shared channel, PDCCH and RS. So this was overlapping issue. In terms of Overshooting it occurs when your the signals from your base
station are reaching places where they are not supposed to so basically they have
the case of more coverage then you have predicted or then you have expected. This can be caused by first of all may be due to bad modelling
secondly because of wrong parameter settings in terms of E-tilting, in terms of
height in terms of some other power parameters we need to see that how
basically we could optimize that but how to detect overshooting. We can detect it by drive testing, we can detect it by propagation delay matrix. So you
get these propagation delay matrices in your OSS KPIs. From these matrices, you can get the information about how far the cell is getting traffic from and
overshooting cells basically cause a lot of problems in terms of handovers
because Handover relationships are defined and in terms of normal coverage
relationships like the way you have modelled the coverage, how you expect it and if a site is
providing signals where it is not supposed to then the neighbouring sites
will not be added in its neighbours and you might have a handover failure.
The third part is Timing Advance. From Timing Advance, we even get this information from
your timing advance as well. that is first of all in your random
access message and in your connection acceptance message as well you can get
that information and you can also check that you have an overshooting cell. DT is the most common method but you use these two as well for your
overshooting issues and again you can use tilting you can use parameter
optimisation to reduce your coverage and improve your network performance. So now
let’s move to it Imbalance in DL and UL and then we would move to TRX imbalance as well So lets discuss DL and UL Imbalance. So if you have an UL imbalance, and that is the most common case, then it means that you have an UL limited network or you have an UL limited coverage and that means that your RSRP from DL is greater than -105 dbm,
your power Headroom which we discussed earlier which your UE sends to your eNodeB to inform how much power is left before reaching UEs maximum power Power head room3db Received interference is below -105 dbm, SINR>3db and DL RSRP

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One thought on “LTE Coverage Optimisation : How to improve coverage in LTE radio network in UL and DL

  1. We have added customised subtitles in the Video to help you better understand the content. Please switch on the subtitles from the caption/subtitle button. Thanks

  2. Suggest if possible use a bigger board, have some pictures on a second board and switch if can. Increase volume. You know your stuff for sure. Please keep it up. i am in Montreal and trying to do something similar for microwave transmission but we will see.

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