LTE Capacity/Throughput Optimisation: How to improve capacity and data rates in LTE

hi everybody welcome to our today’s
tutorial and today our topic is Lte capacity optimisation but before I go
deeper into the details I would like you to subscribe to our Channel and also
press the bell icon because that will help you notify about our new videos and at
the end of today’s lecture there will also be details about our
upcoming online optimisation course which covers the entire scope of
optimization of LTE. So let’s begin with LTE capacity optimization and the main
factors in LTE capacity optimisation or capacity or DL/UL Throughput are reference signal SINR, PDCCH capacity, PUCCH capacity
and we have specific parameters and procedures for downlink throughput
or data rate We have separate procedures
parameters for uplink. In addition to this we have other factors such as spectral efficiency and other factors that affect LTE capacity so
let’s dig in to our LTE capacity lecture and start with our first topic. So our
first topic is reference signal SINR RS refers to reference signal. The SINR of reference signal plays a very important role
in terms of your LT capacity and throughput performance in the downlink and
your overall metric structure because the overall network structure. This resource element that
basically enables the mobile to detect the cell signals and basically then
perform any other actions in terms of that. Also it will affect the UE
CQI and the factors affecting RS SINR can be coverage, Downlink interference, terrain, clutter and also grid structure issue or anything but RS SINR is a very important factor and you need to optimise it in order to
optimise your capacity. The next factor which is some people said at the heart
of LTE and the way LTE provides the shared channel throughput is PDCCH. PDCCH capacity is extremely important in LTE because PDCCH provides you DCI that is Downlink Control Information and in downlink control
information you have all the information regarding the grants when a particular
user has been granted resources in downlink or when a particular user has
been granted resources in the uplink also it gives you information about the
acknowledgement for the hybrid retransmission it also gives you
information about other factors so there are different formats for this DCI that
is we have format zero, one, two and three. The zero part is for your
uplink grant basically if you have been granted a resource an uplink then you
have format one that is for your downlink resource and mean that eNodeB allocated a resource
in downlink for the UE. then format 1 is divided into basically
there’s 1a which is for preamble for your PRACH and two and three are also defined for different downlink mechanisms. The question of how PDCCH capacity is
calculated – This is also a very interesting aspect. PDCCH capacity is
usually calculated in terms of CCEs CCE is your control channel
elements so I will explain you in terms of LTE resource block and how CCE works.
PDCCH has four formats that 0 1 2 & 3 and these PDCCH formats then correspond to a particular CCE format so basically you
have 1 2 4 & 8 CEEs and relevant aggregation. so if we are using PDCCH format 0
we will have 1 control channel element if we are using format 2 then we have 2 CCEs, for format 3, we have 4 and for format 4 we have 8 CCEs In LTE, we aggregate these control channel elements
to provide the PDCCH information and in each CCE we have nine resource element
groups and in each resource element group we have four resource elements. Now what do you mean by resource element in LTE. Resource element is basically your
OFDM symbol in time domain mapped onto a sub carrier. So basically this is how PDCCH information is mapped on to your CCE. So what happens in LTE that if you have
PDCCH congestion. For example you have used up all the PDCCH resources
then you cannot inform your your UE regarding an uplink or downlink grant
so even if you have resources in your downlink shared channel then you
will not be able to inform the UE regarding any any data that needs to be
transmitted either in the downlink or in the uplink. In terms of calculating how much
resources we need to allocated for PDCCH , CCEs and then PDDCH boost, will go through another lecture but for now this is how PDCCH works and this is how PDCCH capacity impacts LTE throughput
in general and if you go into further detail into PDCCH, PDCCH congestion
basically will cause direct impact on to your bit rate. Next we have PUCCH
capacity that is your physical uplink control channel and physical uplink
control channel also affects your throughput both in uplink and downlink. There are three formats
for this as well namely 1 2 & 3 so in the first format we have
scheduling request, in the second format we have CQI that is the channel
quality indicator and in the third part you have other different elements
included into it. If you have PUCCH capacity issues you
cannot have a scheduling request sent to your enodeB and in the second case, you cannot have your CQI sent to the eNodeB. Now what parameters we usually optimize in terms
of handling PUCCH capacity capacity so we have a parameter which describes how
many physical resource block you allocate to this CQI format 2 then
we have our time period periodic so we have periodic time period for SR for
scheduling request and basically for CQI and the default idea is that we use 10
millisecond. Therefore in each 10 millisecond we have one SR and we have 1 CQI. we can change
that parameter as well if we see that the radio conditions are not that
basically feasible and coming back to PDCCH. In PDCCH we have
two aspects the one is your common common channel and then is user
specific and what LTE specifications have done is that this common channel is
limited to these two formats to basically ensure that they have better
radio performance and the user specific can use all the four formats so this
was something about PDCCH capacity, PUCCH capacity and RS SINR now we will move on to basically what are the factors that impact your
downlink throughput and what are the factors that affect uplink throughput.
let’s see what we have for downlink data rate optimization and uplink data rate
optimization first we will discuss uplink and we will go from what are the
issues and how we basically resolve or optimize them. Number one issue that
can come in downlink throughput is your high BLER. BLER is your block error
rate and that is the main you can say KPI on which the entire LTE coding
and rated adaptation and modulation selection works.
Low BLER is mostly caused by when your UE is an low coverage area and
coverage issues can be caused by a number of factors that can include parameter optimisation, coverage optimisation. Next we have
bad CQI and bad CQI can result from coverage issues, it can
also result from downlink interference issues then we have scheduling algorithms
parameters that decide what kind of scheduling algorithm are being used. Number four is
PDCCH and PRB high resource utilisation so if you are running
low on PDCCH and on your resource block resources then your utilisation would be higher and any utilisation above 80 % will cause you throughput issues
This would also result in cell throughput issues and as well as user specific throughput
issue as well. Next we have transmission modes we have 3
transmission modes one is called single-user mimo then we have
transmit diversity and then multi-user mimo. We also have
single input multiple output SIMO mode as well so all of
these transmission modes basically provide you with different kind
of data rates for example in diversity you have the same data being transmitted
through multiple transmission ports and in your multi-user mimo you have your
spatial multiplexing and your data rate is much higher but these have specific
SINR targets and in order to optimize your network so that your
connection you have not have radio link losses and also you have the maximum
throughput you need to optimize those SINR thresholds to switch from one
transmission mode to another and you must have your dynamic switching on as
well another aspect in downlink throughput as
we would not be covering the entire aspects in this short video but another
aspect which we can check in the network is how much of usage is on 64 QAM that is
quadrature amplitude modulation because the higher the modulation schemes higher
the data rate you will get and if your CQI is consistently in the bad region so
for example you have this normal distribution and
this is your basically majority of your CQI is in the bad part so this will
result as per the code and modulation adaptation
you will not have your majority of the users on high modulation schemes and
therefore your spectral efficiency and your data throughput will go down so we
need to check these kind of things for your throughput and second is your TCP
and UDP impact as well most importantly if you’re
having a TCP low throughput in your drive testing you can check and use your
UDP and if you are improving have improve results in UDP then you need to
check your TCP settings as well these are some of the factors that impact on
your downlink throughput there are a number of hardware factors which can
also impact on your downlink and the parameters that include in downlink are
as I told about the SINR thresholds then you have your scheduling scheme parameter
then you have your code format indicator parameter then you have your power
control parameters so these are the parameters that you may use to optimize
your downlink throughput then we come to our uplink throughput and in uplink
throughput we have similar problems such as BLER and bad CQI then we have
scheduling issues and majority of those issues are basically related similar to
coverage or your uplink interference and stuff like that some of the parameters
that we can use in uplink are related to your uplink power control and that is
your p0nominal for your uplink control channel or p0nominal for your
uplink shared channel then we have our fractional power control factor alpha
and we have also got of a fractional factor for the proportional fair
scheduling scheme. this is a very brief summary of the
throughput factors in LTE and definitely you will need to work in detail to get to
the bottom of the issue and apply the knowledge accordingly so now I will let
you know about the LTE training the comprehensive LTE training that we will
be publishing and we will be publishing it in the third week of March and
you can visit our website which is given in the video detail section and
have a look out on the third week of March and that video will be available
online it will be several hours of optimisation training for LTE and it will be
the only training of LTE available online at a very very minimal cost so we want
everybody to learn LTE optimize it and also have it at your doorstep so
subscribe to the channel hit the bell icon and keep looking out for new videos
from our channel thank you so much for your time. See you next time!


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