effect of closed loop power control on the ul rssi

7/23/2019 Effect of Closed Loop Power Control on the UL RSSI

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Effect of Closed Loop Power Control on the UL RSSI

The Received Signal Strength Indicator (RSSI) in the uplink is also affected by the parameter settings that govern closed loop power control in LTE Immediately after the !E completes anRR" connection with the e#ode$% the !E uses closed loop power control on both% the &!""'

and the &!S"'

1. PUSCH

In particular% the power that the !E transmits the &!S"' with is given by

The power control formula for the uplink for the &!S"' in LTE can be broken into five key parts The first part is the amount of additional power that is needed based on the sie of the R$

allocation The higher the number of R$s% the higher the power that is re*uired



The second part is called &+ It is basically the assumed interference that the !E is e,pected to

overcome &+ is composed of two subcomponents The first is called &+-#ominal-&!S"' and

it is communicated over SI$. It is valid for all !Es in the cell The second component is called&+-!E-&!S"' and it is a !E/specific value It is optional

The third part of this e*uation is the &ath Loss (&L) and the impact of the &L or 0lpha &L is 1ustcalculated% but the 0lpha value communicated to the !E in SI$. If the 0lpha value is set to 2%

then all of the &L needs to be taken into account in the power control formula Some vendorsmight not allow you to change this value% though (as it is hardcoded)

The fourth part is an 3"S/specific component If the e#$ wants the !E to ad1ust its power

based on the 3"S that is assigned% it will be taken into account here

Lastly is the f(i) value% which is simply the closed/loop feedback This is the additional power the !E will add to the transmission based on specific feedback by the e#$

'ence% for the &!S"'% two parameters affect the !E transmit power% and therefore% our !LRSSI

a) &4-nominal-&!S"'

b) 0lpha

2. PUCCH:

The power control formula for the uplink for the &!""' in LTE can be broken into four key

parts The first part is called &+ It is basically the assumed interference that the !E is e,pected

to overcome &+ is composed of two subcomponents The first is called &+-#ominal-&!""'and it is communicated over SI$. It is valid for all !Es in the cell The second component is

called &+-!E-&!S"' and it is a !E/specific value It is optional The second part of this

e*uation is the &ath Loss (&L) and the impact of the &L or 0lpha (the same value used for the

&!S"' 5 See above/) The third part is an 3"S/specific component If the e#$ wants the !E toad1ust its power based on the 3"S that is assigned% it will be taken into account here Lastly is

the f(i) value% which is simply the closed/loop feedback This is the additional power the !E will

add to the transmission based on specific feedback by the e#$ This value is different for eachformat type of the &!""' 0 different value is given to the !E in SI$. for formats 2% 2a% 2b% .%

.a and .b



'ence% the parameters that controls the transmit power in the &!""' are

a) &4-nominal-&!""'

b) 0lpha

The higher the value of &!""' and the higher the value of &!S"'% the more power the !E willtransmit% the better the !L $LER% the higher the throughput and the higher the !L SI#R

'owever% in high capacity cell% this might not be true and the opposite effects might be

encountered E,amples of such situations are 0irports% events% convention centers% etc It isrecommended to analye the !L RSSI in these types of venues during high capacity scenarios

and ad1ust accordingly $ear in mind that the 0lpha value affects both% the &!""' and the

&!S"'

� Lauro

UL Throughput Troubleshootng

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by Lauro

• + "omments

Several are the conditions that produce low throughput in the uplink This blog shows a simpleflowchart that attempts to guide you while troubleshooting cells with poor performance in theuplink #ote that the flowchart is not comprehensive but rather an informative guide for you to

start



Lauro

Upln! Throughput Troubleshootng

by Lauro

• + "omments

In this blog we will briefly describe general troubleshooting guidelines for uplinkthroughput in LTE networks with MIMO 2x2. The reader is advised to look for particularcounters and paraeters in their respective OEM!s docuentation to address each ofthe areas explored below.

The general troubleshooting strategy is described below and the covered reasons forbad throughput are shown in the figure below.

"igure #. Low Throughput causes in the $plink for LTE networks.

Step 1: Identify cell with low UL (uplink) throughput

a% The first thing is to identify those cells with low throughput. &hat is considered as lowthroughput is a threshold defined by your network policies and best practices 'it alsodepends on your design paraeters%. (eports should be run for a significant nuber ofdays so that data is statistically valid.

Step 2: Identify Uplink interference


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a% (un a report for ())I in the uplink. Most OEM provide with counters and or tools toassess the ())I in a span of days. *ells with uplink interference are those whose ())Ivalues are high 'higher than +,-d/ for instance%.

b% Typical scenarios where these values are high are indoor environents 'i.e.0 arenas/

airports/ etc.%

c% *oon sources of interference in the 1-- M3 band 'LTE deployent in the $)4%are0 high values of traffic in the uplink/ external source of interference/ high valuesof P0-nominalPUCCH and P0-nominalPUSCH '*onsult your technical lead on thesettings of these paraeters%

Step 3: BLER !lue"

a% (un a report for LE( in the cells identified. The LE( should be saller or e5ualthan #-6. If the value is larger/ then/ there is an indication of bad (" environent.

b% Typical causes of bad LE( are uplink interference/ bad coverage 'holes in thenetwork/ etc.%

Step #: Low $e%!nd

a% (un a report using the counters provided by the OEM to find

2 Maxiu nuber of ((* connections supported per cell 'paraeter or feature%

. Maxiu nuber of ((* connections active per cell

6 4verage nuber of ((* connections active per cell

7 Maxiu nuber of users per TTI supported per cell 'paraeter or feature%

8 Maxiu nuber of users scheduled per TTI in the cell's% of interest

9 4verage nuber users scheduled per TTI in the cell's% of interest

b% If the axiu nuber of ((* connections active per cell is close or e5ual to theaxiu nuber of ((* connections supported/ then. The cause for low throughput is

load.

c% 4 high nuber of scheduled users per TTI does not necessarily ean that deand isthe cause for low throughput.

Step &: Scheduler 'ype

a% "ind the scheduler types your OEM supports



b% )elect the one that is ore convenient for the type of cell you are investigating.Exaples of schedulers are0 round robin/ proportional fairness/ axiu *7I/ e5ualopportunity/ etc. OEMs allow you to switch the scheduler in your network butrecoend one in particular.

c% The wrong scheduler ay be the reason for bad throughput.

Step : ower *e!droo%

a% (un a report to find out the average power headroo that $Es have in your network.

b% 4 low value of power headroo eans that $Es do not have available power totransit in the uplink and hence/ the throughput is low.

c% Low values of power headroo are 8 d or saller.

d% Typical causes of low power headroo are uplink interference and7or incorrect power control paraeter settings/ to ention a few.

Step +: ,ther

a% (un a 9)&( report or ask your OEM to run it for you.

b% igh values of 9)&( result in low throughput due to losses.

c% *heck your backhaul capacity. Often ties/ the backhaul links are shared aongultiple (4Ts. Make sure your backhaul is properly diensioned.

4t the end of this ethodology/ you will be able to deterine if the reasons for lowthroughput in your cells is one of the following or a cobination/ thereof0

+ LE( 'bad coverage%

+ $plink Interference 'high ())I%

+ Low :ower headroo

+ )cheduling algorith

+ Low ;eand

+ Other '9)&(/ ackhaul capacity%



-regunt!". !%igo"/

Lauro

H"ndo#er P"r"$eters %P"rt & of &'

by Lauro

• . "omments

(lter Coeffcent for E#ent "&

4nce the !E is configured to do measurements% the !E starts measuring reference signals from

the serving cell and any neighbors it detects The ne,t *uestion is whether the !E should look at

1ust the current measurement value% or if the recent history of measurements should be

considered LTE% like other wireless technologies% takes the approach of filtering the currentlymeasured value with recent history Since the !E is doing the measurement% the network conveys

the filtering re*uirements to the !E in an RR" "onnection reconfiguration message

The !E filters the measured result% before using for evaluation of reporting criteria or formeasurement reporting% by the following formula

where

• 3n is the latest received measurement result from the physical layer:

• ;n is the updated filtered measurement result% that is used for evaluation of reporting

criteria or for measurement reporting:

• ;n/2 is the old filtered measurement result% where ;+ is set to 32 when the first

measurement result from the physical layer is received: and

•

a < 2 = .(k=7)

% where k is the flterCoeffcent for the corresponding measurement *uantityreceived by the *uantity"onfig

Then% the !E adapts the filter such that the time characteristics of the filter are preserved at

different input rates% observing that the flterCoeffcent k assumes a sample rate e*ual to .++ ms

The parameter >a? defines the weight given to current value and (2/a) (ie% the remaining weightis given to the last filtered value) ;or e,ample% if filter coefficient k < 7% then a < @A(7=7) <2=.


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This means that new measurement has half the weight and the last filtered measurement gets the

other half of the weight

E,ample of ;ilter coefficient values are

•"ase 2 value k < B % a < C% ;n < D 4ld C #ew

• "ase . value k < 7% a < @% ;n < @ 4ld @ #ew

4ptimiation Rules

a) 0 high value of the parameter fltercoeffcent will provide higher weight to old

measurements (more stringent filter)(the opposite is true)

b) The higher the values of fltercoeffcent the higher the chances of eliminating fast fading

effects on the measurement reports

2 This eliminates reporting a cell which RSR& was suddenly changed due to multipath orfast fading

. Fhich in turns eliminates the chances to handover to a cell which RSR& was strong for

some milliseconds

6 Therefore reducing the chances for &ing/&ong effects

c) 0 value of B is typically used in the network although a value of 29 might also be used indense urban areas

Lauro

Cell R"dus n LTE %P"rt 1 of &'

by Lauro

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The cell radius in LTE is affected and=or determined by three factors

a) The &reamble ;ormat

b) The "yclic Shift the corresponds to the Gero"orrelationGone"onfig parameter and%

c) The "ell Radius &arameter


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0) &reamble ;ormat

LTE ;HH supports four preamble formats (as of today% not all of them currently supported by the

e*uipment manufacturers) The preamble consists of a cyclic prefi, (to handle multipath

interference) followed by an B++ s se*uence In preamble formats . and 6% the se*uence isrepeated The total length of the cyclic prefi, and the se*uence(s) determines how long it takes to

transmit the preamble Since the actual physical transmission occurs in units of sub/frames (2

ms)% the remaining time determines how far away the !E can be without overlapping another!EJs access attempt (the guard time) ;or further details% refer 6K&& TS 69.22 / &hysical

"hannels and 3odulation

The operator typically must pick a preamble format to determine the coverage area desired In

the event of remote sites deployment% the length of the fiber to the remote cells must beconsidered as part of the cell radius (this includes Histributed 0ntenna Systems /H0S/ ) Since

the speed of electromagnetic waves over fiber is only two thirds of the speeds in free space% the

total cell radius reduces to the values shown in the table below

effect of closed loop power control on the ul rssi

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