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

Summary

This video script delves into LTE Coverage optimisation, crucial from planning to ongoing phases of an LTE network. It covers detection of uplink and downlink coverage issues, imbalances, overshooting, overlapping, and cell border adjustments. The script explains using KPIs and elements like RSRP and power headroom for detection, and discusses techniques to manage overlapping and overshooting. It also addresses DL/UL imbalances, TX imbalances, and the use of specific parameters for coverage extension and adjustment. The goal is to equip viewers with the knowledge to optimize LTE coverage and parameters effectively.

Takeaways

• 📡 Detecting LTE Coverage Issues: RSRP less than -120 dBm indicates a coverage hole, while RSRP less than -105 dBm signifies weak coverage.
• 🔍 Balance Between Coverage and Interference: Optimizing LTE requires a balance to avoid increasing interference with transmission power.
• 🚗 Drive Testing for Coverage Holes: Drive testing can identify handover failures and areas with coverage issues, including IRAT handovers.
• 📶 Uplink Coverage Detection: Power headroom reports from UE to eNodeB can indicate weak uplink coverage when UE is transmitting at maximum power.
• 🔄 Overlapping and Overshooting Problems: Overlapping occurs when there is no dominant server leading to interference, while overshooting is when signals reach unintended areas.
• 🛠️ Adjusting Overlapping: Techniques like azimuth change, E-tilting, height reduction, and power adjustments can control overlapping issues.
• 🔎 Detecting Overshooting: Drive testing and propagation delay matrices can help identify overshooting and its impact on handover failures.
• ⚖️ DL and UL Imbalance Detection: UL imbalance is common, indicated by good DL coverage but poor UL performance, while DL imbalance is the opposite.
• 🔄 TX Imbalance Issues: Different performance between multiple radio transmission elements can point to hardware or cable issues.
• 🌐 Extended Cell Coverage: LTE can extend up to 100km using specific PRACH formats and special subframe configurations, but may face issues like time delay and low SINR.
• 🔄 Cell Border Adjustment: Parameters like qrxlevmin and a2threshold can be adjusted to optimize cell coverage areas based on network requirements.

Q & A

What is the main focus of the video script provided?

The main focus of the video script is LTE Coverage optimisation, covering various aspects from initial planning to ongoing optimisation of an LTE network.

What are the key topics discussed in the script for LTE coverage optimisation?

The key topics discussed include detecting UL and DL coverage problems, imbalance between downlink and uplink, overshooting and overlapping problems, extended coverage, cell border adjustment, and parameters for optimising LTE.

What is considered a coverage hole in terms of RSRP?

In terms of RSRP, a coverage hole is defined as an area where the RSRP is less than -120 dBm.

How can imbalance between downlink and uplink be detected?

Imbalance can be detected through various methods such as observing handover failures, low throughput, and specific KPIs related to IRAT handovers, as well as analyzing power headroom reports and SINR thresholds for Physical Uplink Shared Channels (PUSCH).

What is overshooting in the context of LTE coverage?

Overshooting occurs when signals from the base station reach areas where they are not supposed to, resulting in more coverage than predicted or expected, which can cause issues with handovers.

What are some methods to control overlapping issues in LTE coverage?

Methods to control overlapping issues include azimuth change, E-tilting, height reduction, adjusting the power of the reference signal, and modifying the power used by shared channel, PDCCH, and RS.

How can extended cell coverage be achieved in LTE?

Extended cell coverage can be achieved by using specific PRACH formats and special subframe formats that allow for coverage of different radii, up to the maximum cell radius as per 3GPP standards.

What are the potential issues that can arise from extending cell coverage?

Potential issues include increased time delay, loss of orthogonality of the Zadoff-Chu (ZQ) sequence preamble due to long delays, and low SINR for PRACH and other channels due to large distances.

What parameters are used to adjust cell coverage borders in LTE?

Parameters used to adjust cell coverage borders include qrxlevmin, which is the minimum RSRP required to access an LTE cell, and a2threshold, which is the RSRP threshold after which the LTE UE would switch to WCDMA due to weak LTE coverage.

What is the purpose of PDCCH boost in LTE coverage optimization?

PDCCH boost is used to provide coverage to the Physical Downlink Control Channel (PDCCH) because it does not use beamforming or advanced antenna techniques like the downlink shared channel, resulting in a coverage gap.

What are some of the downlink parameters discussed in the script for LTE coverage optimization?

Some of the downlink parameters discussed include qrxlev, reference signal power, P alpha, P beta, and the parameters for uplink power control such as pnominal PUCCH and pnominal PUSCH.

Outlines

00:00

📡 LTE Coverage Optimization Basics

The script introduces the concept of LTE Coverage Optimization, emphasizing its importance from the initial planning to the ongoing optimization phase. It outlines the key topics to be covered, including detecting uplink and downlink coverage issues, identifying imbalances, addressing overshooting and overlapping problems, extending coverage, adjusting cell borders, and optimizing parameters. The first topic delves into detecting coverage problems using KPIs and RSRP thresholds, highlighting the significance of a balanced approach between coverage and interference. Drive testing is mentioned as a method to identify coverage holes and weak coverage areas, with specific RSRP values indicating such issues.

05:01

🔍 Detecting and Addressing Overlapping and Overshooting

This paragraph discusses the problems of overlapping and overshooting in LTE networks. Overlapping occurs when there is no dominant server within a coverage area, leading to pilot pollution and downlink interference, which can degrade throughput and cause radio link failures. The criteria for identifying overlapping issues are provided, including the presence of multiple strong reference signals within a 6dB range. Solutions such as azimuth change, E-tilting, height reduction, and power adjustments are suggested to mitigate these issues. Overshooting is identified as signals reaching unintended areas, potentially causing handover failures and timing advance issues. Detecting overshooting can be done through drive testing and propagation delay matrices, with parameter optimization and tilting recommended as corrective measures.

10:03

🚦 Imbalance Issues in DL and UL Coverage

The script addresses the imbalances that can occur between the downlink and uplink coverage, as well as transmission elements (TRX imbalance). UL imbalance is characterized by good downlink coverage but poor uplink performance, indicated by specific thresholds for RSRP, power headroom, received interference, and UL SINR. DL imbalance, on the other hand, is identified by a surplus of power headroom and a low SINR, suggesting coverage issues on the downlink. The importance of hardware checks and network modeling in resolving these imbalances is highlighted. TRX imbalance is discussed as a hardware or cable issue causing mismatched coverage performance between transmission elements.

15:12

🌐 Extended Cell Coverage and Border Adjustment

The script explores the concept of extending cell coverage in LTE networks, noting the maximum cell radius as per 3GPP standards. It explains the use of PRACH formats and special subframe formats to achieve extended coverage, discussing the potential problems associated with this, such as time delay, loss of orthogonality in ZQ sequence preambles, and low SINR for PRACH and other channels. The importance of network planning to accommodate these issues is emphasized. Additionally, the script covers the adjustment of cell coverage borders using parameters like qrxlevmin and a2threshold, which can be tweaked to meet network requirements and performance criteria.

20:15

🛠️ LTE Coverage Optimization Parameters

This paragraph delves into the specific parameters used for LTE coverage optimization, starting with qrxlev, which is the minimum RSRP required to access an LTE cell. The script explains the relationship between the Information Element (IE) obtained from drive testing and the qrxlev parameter. It also discusses reference signal power and the associated parameters P alpha and P beta, which are crucial for power distribution in OFDM symbols. The paragraph further covers uplink power control parameters such as pnominal PUCCH and PUSCH, and SINR targets for PUSCH, which are integral to power control mechanisms. The script also mentions the use of PDCCH boost to address coverage gaps between shared channels and PDCCH, noting the importance of this topic for future discussion.

25:17

📚 Conclusion and Invitation to Further Training

The script concludes by summarizing the coverage optimization topics discussed and inviting viewers to subscribe to the channel for more training on LTE, 5G, and other related subjects. It also mentions an upcoming detailed parameter optimization training to be published, indicating the intention to cover these topics in greater depth in the future.

Keywords

💡LTE Coverage Optimisation

LTE Coverage Optimisation is the process of enhancing the geographical reach and quality of an LTE network's signal. It is a central theme of the video, as it discusses various strategies to improve the network's performance from initial planning to ongoing maintenance. The script mentions detecting coverage problems, balancing interference, and adjusting cell borders as part of this process.

💡RSRP (Reference Signal Received Power)

RSRP is a key performance indicator used to measure the power level of the reference signal received in an LTE network. In the script, RSRP values are used to define coverage problems, such as a coverage hole being indicated by an RSRP less than -120 dBm, and weak coverage by an RSRP less than -105 dBm.

💡Imbalance

Imbalance refers to the unequal performance between the downlink and uplink of an LTE network. The script discusses how imbalances can occur due to various factors, such as transmission power and interference levels, and how they can be detected and addressed through parameters like power headroom and SINR thresholds.

💡Overshooting

Overshooting is a phenomenon where the signal coverage extends beyond the intended area, causing issues like unnecessary interference and handover problems. The script explains how overshooting can be detected through methods like drive testing and propagation delay matrices, and how it can be mitigated through parameter optimization.

💡Overlapping

Overlapping occurs when multiple cells have strong signals within the same area, leading to pilot pollution and interference. The script describes how overlapping can be identified by the presence of multiple reference signals within a 6 dB range and how it can be managed through techniques like azimuth change and power adjustments.

💡Cell Border Adjustment

Cell Border Adjustment is the process of fine-tuning the boundaries of a cell's coverage area to optimize network performance. The script mentions parameters like qrxlevmin and a2threshold that can be adjusted to control cell size and ensure seamless network operation.

💡Drive Testing

Drive testing is a common method used to assess the quality of an LTE network's coverage by physically driving through the area and recording signal data. The script highlights its use in detecting coverage holes, handover failures, and other issues that affect network performance.

💡Power Headroom

Power headroom is a measure of the difference between the current transmission power and the maximum transmission power of a UE (User Equipment). The script explains how the power headroom report sent by the UE to the eNodeB can indicate whether the UE is in an area of weak coverage.

💡SINR (Signal-to-Interference-plus-Noise Ratio)

SINR is a critical metric used to assess the quality of a signal in the presence of interference and noise. The script discusses SINR thresholds for uplink shared channels as a way to detect uplink coverage issues, with a low SINR indicating potential problems.

💡PRACH (Physical Random Access Channel)

PRACH is a channel used by UEs to access the network. The script mentions different PRACH formats that can be used to extend cell coverage, but also notes potential issues such as time delay and low SINR that can arise with extended coverage.

💡PDCCH (Physical Downlink Control Channel)

PDCCH is a channel used to transmit control information in the downlink direction. The script points out that PDCCH does not benefit from beamforming or advanced antenna techniques like the downlink shared channel, leading to a potential coverage gap that can be addressed with PDCCH boost.

Highlights

LTE Coverage optimisation is essential from the initial planning phase to deployment and ongoing optimisation phases.

Detecting UL and DL coverage problems involves analyzing KPIs and information elements.

RSRP values less than -120 dBm indicate a coverage hole, and values less than -105 dBm indicate weak coverage.

Balance between coverage and interference is crucial during optimization to prevent increased transmission power from boosting interference.

Drive testing is an effective method for detecting LTE coverage holes and handover failures.

Power headroom reports from UEs help eNodeB determine if UEs are transmitting at maximum power, indicating potential weak coverage areas.

Overlapping in LTE occurs when there is no dominant server, leading to pilot pollution and downlink interference.

Overshooting is identified by signals reaching unintended areas, potentially causing handover failures.

Imbalance between DL and UL can be detected through various thresholds and parameters, indicating network limitations.

TX imbalance arises when different radio transmission elements from the same antenna system perform differently.

Extended cell coverage in LTE can reach up to 100km using specific PRACH formats and special subframe configurations.

Time delay, preamble orthogonality, and low SINR are challenges faced when extending cell coverage.

Cell border adjustment can be managed using parameters like qrxlevmin and a2threshold to meet network requirements.

Parameters such as qrxlev, reference signal power, and P alpha/beta are fundamental for downlink coverage optimization.

PUCCH and PUSCH power control parameters are essential for maintaining uplink transmission quality.

SINR targets for PUSCH at different stages are utilized by the power control mechanism for optimal performance.

PDCCH boost is used to bridge the coverage gap between shared channels and PDCCH due to the lack of advanced antenna techniques for PDCCH.

Transcripts

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 room < -3db

Received Interference Power < -105dbm but your UL SINR is less than -5db

so this shows that you have a good downlink

You have low interference but you have poor UL both in terms of PHR and SINR. So this is UL imbalance.

usually it is the case that we have better Downlink coverage because eNodeB

is transmitting at a much higher power and we have this problem usually at the cell edge

If we have this problem, then we either have to limit the DL coverage

or we can have a Drive test to check in which areas we are having this imbalance issue.

These imbalance issues can also be caused because of hardware issues for example

diversity issues in your eNodeB, combiner or other losses in the

uplink direction in your hardware so we alsoneed to check those. Second is DL imbalance

DL imbalance is in the case where your power headroom > 3db

Received interference is below -105 dbm, SINR > 3db and DL RSRP <-110 dbm

In this case, your DL has the coverage issues and your network is DL limited

We need to check whether the cell is able to transmit on max EIRP

or is there some issue with the hardware.

or is there some issue with the modelling of the network coverage

This is how you detect an imbalance between DL and UL.

We have another issue known as TX imbalance

The problem arises when there are more than one radio transmission elements e.g TX1/TX2

from the same antenna system have different performance. This may be because of feeder loss or any other issues.

but when one TX element will be providing you better coverage and the other one with poor coverage.

In some of the optimisation tools, you can detect these issues and they are represented

as coverage from TX1, TX2 and so on. From here you can directly see if there is a coverage mismatch between the two elements. If there is, it directly points to a

hardware issue or a cable issue and you need to check that. So this was over imbalance issues and our next we'll

discuss extended cell coverage and then Cell border adjustment. So let's discuss extended cell range and

then we will see how we adjust cell borders. So in LTE max cell radius can be 100km as per 3GPP standards

PRACH - Physical Random Access Channel has different formats for cell extension

in LTE and if you want to optimise your coverage extension so you have limited number of

PRACH formats that you can use to basically have an extended cell coverage.

of different radius. so it is a combination between PRACH formats and also special subframe format.

So for these two, when you design your network, you will choose a format

a combination of PRACH and special subframe to provide coverage to

particular radius and for PRACH format you have 0 1 2 & 3 which have adjustable

radius this is how you configure it and what are the problems which we can face if you extend

cell coverage. The first one is the time delay. if your PRACH is being sent from

for example a distance of 30 or 40 kilometers. In this case, it may happen that

it would not reach the enodeB within the PRACH symbol period and therefore

it will be discarded so we need to plan the network and we need to plan the

PRACH and special subframe structure accordingly. The second problem is

basically orthogonality of the ZQ sequence preamble.

All the users using PRACH preamble have orthogonality in terms of ZQ sequence however if the time delay

are too long then basically the cyclic prefix which is basically

used to counter these delays and multipath propogration will not be able to work as we the total delay would surpass

CP added in the OFDM symbol and has we would have issues in

using and decoding the preamble. The third issue is SINR of PRACH and other channels being too low

because the distance is large and therefore you will be having an UL limited system

where the SINR is low and therefore we would need to allocate more Uplink resources

to counter the time delay and also to counter the low Uplink SINR problems

For adjusting cell coverage borders, basically what we do is we have two

parameters we will discuss this parameter when we go to the parameter

section but the two main parameters are qrxlevmin and then we have a2threshold.

qrxlev is basically the minimum RSRP required to access an LTE cell

a2threshold is the RSRP threshold after which the LTE UE would go to WCDMA network due to weak LTE coverage

We can use these parameters to adjust coverage areas as per the network requirement.

The rule of thumb is to keep the parameters same but we can

decrease or increase the value of these parameters to adjust coverage area.

For example if you have an uplink limited system and you are having coverage issues

, radio link failures then you can reduce the cell size or you can increase your cell size

if the performance of the cell is satisfactory and also meets a hysteresis criteria above the acceptance threshold

then you can also increase the cell size using these two parameters

so now lets go to parameters section and see what parameters we can use

for our basics LTE Coverage optimisation . So we are in the last part that is

parameters. First we will discuss the downlink parameters

The first parameter is a very basic parameter as discussed and that is

qrxlev and that is basically minimum RSRP required to access an LTE network cell.

An interesting part is the Information element you see in the drive testing for this parameter, you have to multiply that to get

multiply it by 2 to know your parameter value of qrxlev. For example and IE of -65 would mean a min RSRP of -130dbm

then you have your reference signal power and along with reference signal power you also

have some parameters called P alpha and P beta these are have some

relationship in terms of how we distribute the power in OFDM symbol.

because the symbol power should remain constant however some of the OFDM symbols contain the high power RS signal

and the remaining symbols do not contain high power RS symbols

so these are the ratios of how to divide the power between RS and other channels. We discuss all of this in our detail Parameter Optimisation training which is due to be published in March.

Then we have the parameters such ponominal PUCCH and ponominal PUSCH which are used for uplink power control.

These parameters define the power levels which enodeB tries to maintain with UL power control

For PUCCH the value of the parameter is -117dbm and for shared channel it is -103dbm

These are default preferred value and may be optimised as per the requirement

If we go in to more detail in power control, then we have

target for SINR of PUSCH at different stages. We have initial SINR target

for PUSCH SINR and also min and max SINR targets for PUSCH.

These SINR targets are used by power control.

So these are some of the parameters used for

coverage and you can use them or optimizing your coverage and also they

play a part in your power control as well and we will definitely discuss

power control in much more detail in one of our optimisation programs. One thing which I also wanted to mention was weeping basically aggregate different

PDCCH boost which is done by aggregating CCE's to provide boost to PDCCH coverage

This is because PDCCH does not use any beamforming or advanced antenna techniques

as compared to their extensive use for downlink shared channel

Therefore there is a coverage gap between the shared channels and the PDCCH

therefore we use a PDCCH boost I will do a separate blog on

that because that is a very important topic. So thats it for our coverage

optimization I hope you have liked our video. Please do subscribe to our Channel

and also have a look at our website for upcoming trainings on LTE, 5G and other topics

thank you so much and let's meet another day for another lecture.