RF Optimization Guide.pdf

7/30/2019 RF Optimization Guide.pdf

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Goal Setting

1. Coverage Area: measured in terms of Mobile Receive Power, adequate

Ec/Io, Mobile Transmit Power;

2. Voice quality criteria: measured in terms of Frame Erasure Rate (FER)

on the forward/reverse links;3. System performance criteria: target call completion, call drop rates and

handoff factor;

4. Packet data service performance: individual throughput/sector

throughput, SCH FER for both forward/reverse;

Primary objectives of network optimization are to identify and eliminate

any hardware and database implementation errors and arrive a set of

optimal operating parameters and equipment settings (e.g. antenna tilts,

azimuths, and SIF power settings) to provide an acceptable level of

performance according current condition.

That acceptable level of performance can be specified and measured in

terms of a combination of the following:


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Goal Set Addition by CDMA2000 1x

With the Packet data service introduced in CDMA2000 1X system, some new

measurable levels in data optimization goal setting are listed following:

1. Target SCH FER: Higher target FER takes advantage of presence of RLPabove the physical layer, results in air-link capacity improvement and low

user data throughput. Recommendation for the SCH FER is ranged from

5% to 10% for all rates.

2. User throughput: Single user data throughput under the different RF

condition (Stationary, single dominant Pilot, Near Cell, Mid-Cell, Far Cell,

during maintenance window).

3. Sector throughput: Multi-users data throughput on same cell/sector under

the ideal RF condition (Ec/Io of 4 to 6 dB and Rx Power of 45 to

55dB, single dominant Pilot, stationary mobile, during maintenancewindow).


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Interference


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Handoff


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Window SearchingSRCH_WIN_A


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Window SearchingSRCH_WIN_N & SRCH_WIN_R


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Call Processing


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Coverage Optimization

The purpose of the initial coverage test is to

characterize the coverage and performance of agroup (cluster) of cells (have been passed

functional tests for both voice and data service)

that provide contiguous coverage. The initialcoverage test will identify predicted (via

simulation) problems and record new problems

measured during the initial drive test, a callsampling benchmark and data throughput are

initialized in the test.


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BTS Site Audit

Installation & environment Checking

Define BTS position (latitude longitude)with GPS

Check antenna position (height,bore/orientation, and tilting)

Measure output of LPA (Tx) Measure feeder loss (VSWR)


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Generate Drive ( Metric) Routes

Obtain road maps for the cluster area and identify drivetest or metric routes for the cluster.

Metric routes should focus on traversing the coveragearea. The route should go through all sectors and extendto the edge of the predicted coverage areas (use thesimulation outputs to guide this part of the activity) andinto coverage areas of surrounding tier sites (far enoughto enter into soft handoff with the first tier sites).

Special attention should be paid to points or routes ofextreme interest such as stadiums, arenas, interstate or

major highways, and locations where many users maycongregate. The customer should be consulted to helpprioritize these areas.

Drive routes should be designed so they can be

completed in a single shift. Include time for breaks,lunches, dinners, etc.


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Tools preparation

Agilent E6474A

Post-processing tools(Actix), includingplotter and/or printer

Test Phones

The rightconfiguration shall besure during thepreparation, such asGPS setting, data logmask, test phonesetting etc.


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Collect Performance and System

Stability DataReal time Drive Data Collection

Sampling call statisitcs set up rate/drop rate BSS system monitoring hardware fault/outage

DM monitoring test system properly working

Post Drive Data Collection

Drive test data for all test mobiles Agilent data should be retrieved if the tool was used

during the drive test

CDLs for the ESNs that were used, and for the durationof the drive test

Event logs for the period of the drive test should becollected


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Evaluate System Stability Data

This procedure includes verification that

the system was stable during datacollection.

System stability can be quickly verified forthe time during which data was collected

by using the Performance Management

Reports (PM Reports)


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Process and Plot Performance Data,

Calculate Call Statistics Forward link performance plots:

Mobile receive Power,

Combined EcIo FCH FER

SCH FER

Data Throughput

Reverse link performance plots: Mobile Transmit Power

FCH FER

SCH FER

Data Throughput Call setup rate

Call drop rate

Call Originate/Terminate Failed


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Forward link performance evaluation

Evaluation of Mobile Received Power: The following table shows suggestedcutoff levels for acceptable signal strength based upon the number of pilotscontributing to that composite measurement.

Evaluation of Ec/Io:Ec/Io is a measurement of usable energy in each chip (for a specific PN) ascompared to the total noise at a particular location. This value is used totrigger handoffs at the mobile.

Any areas where all pilots are consistently below Tadd are a problem;

Areas that have multiple pilots present, where all pilots fluctuate betweenTadd+3dB and Tdrop-3dB are areas referred to as non-dominant pilotareas;

These locations should be noted in the PRM;

Evaluation of FFER: All locations where FER rises above 2% should be aPRM entry.


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Reverse link performance

evaluation Evaluation of Mobile Transmit Power: Assuming

that the IS-95 link balance equation is adheredto, and using the lower limit of 87 dBm for an

acceptable forward link receive level, any areas

where Mobile Transmit levels exceeds + 14 dBmshould be a PRM entry.

Evaluation of RFER: Similar to the forward link, if

FER on the reverse link rises above 2% in anarea, this area deserves to be an entry in the

PRM.


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RF Network Optimization


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Data Analysis

Neighbor List Check

Cell Radius Checks RF Coverage Problems


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Neighbor Lists Check

Adjacent sectors at the same site should be included in each others neighborlists, and be positioned at the top of the list. For six sector system, sectors onthe other side of the site should be maintained, in general, in the top 11entries in the neighbor list.

Sectors pointing towards each other should be in each others neighbor lists.

Sectors pointing into the same coverage areas should be in each othersneighbor lists. These should be prioritized based upon amount of coverageoverlap.

Special cases may include: Sectors facing in the same direction (azimuth) where one sector overshoots

another site: If there is desired coverage overlap, then the sectors should beneighbored.

Sectors separated by terrain obstacles: For example, if there are two clusters, butthey are separated by a mountain range and could not enter into soft handoff witheach other because their coverage footprints do not overlap, there is no need to putthem in each others neighbor lists. Make use of the elevation data or use the Best

Server Ec/Io image to determine whether coverage footprints overlap. Additional checks for neighbor list development are listed here:

Verify that reciprocal neighbors are entered into each others sectors neighbor lists.

Verify that neighbors for a specific sector are within the cell radius limits (eliminatedistant neighbors).


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RF Coverage Problems

Poor RF Coverage Next To Cell Site

Evaluating Coverage At The Limits of thePredicted Coverage Area

Poor RF Coverage Inside The PredictedCoverage Area, But Not Next

Pilot Pollution

Infrastructure Issues

Subscriber Test Unit Issues


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Poor RF Coverage Next To Cell Site

Identify if any obstacles;

Identify antenna configuration and installation, such as

mount on the top of building, but not close enough to theedge; antenna title, height etc;

Check event log, alarms, CDLs to find if any hardware

errors, and if the site taking the test call; Investigate database errors related to mobile receive

levels, such as SIF pilot power settings;

Investigate data collection equipments, method,processes deployed in the data collection and post-processing tools.


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Evaluating Coverage At The Limits of the

Predicted Coverage Area The best indicator to use to determine whether or not

coverage can be improved at the limits of the network is

mobile transmit power (mobile Tx). Typically the reverselink (mobile -> base station) is the limiting link due topower restrictions of the mobile.

Refer to the predicted mobile transmit power requiredimage and compare that to the measured data. Iffollowing cases is met, The measured and predicted data are within 6 dB of each other;

The mobile Tx level is high, (over +17 dBm).Then, the network can be considered to be nearing itscoverage limit.


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Evaluating Coverage At The Limits of the

Predicted Coverage Area How to confirm the issue is really a coverage problem: Verify that themobile receive and transmit level (path balance) comply to the IS-95specification at the start of a call:

Mobile Tx (dBm) = - Mobile Rx (dBm) 73 + NOM_PWR (dB) +

INIT_PWR (dB) If the measured data does not adhere to this equation within 6 dB, then

there may be excessive interference on either the forward or reverse link, orthere may be equipment problems that require investigation.

If the data conforms to the guideline, firstly investigate if mobile TX powerhave any headroom available, if yes, changing the SIF pilot power and/orantenna pointing angles may improve the problem area; if not, an antennaangle change (azimuth or tilt) might provide some incremental improvement,and this shall be under investigation, and it is no meaning to changing theforward link power.

A clear understanding of the limits of a networks coverage is key tostreamlining the optimization activity and to avoid wasting effort in areasthat arent predicted to be covered.

Collection of data outside of the predicted coverage area will skew thestatistics of the overall drive. Data collected in the uncovered areas should

be removed from the reporting of statistics and performance trends,especially for warranty testing purposes.


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Poor RF Coverage Inside The Predicted Coverage Area,

But Not Next

Step 1: Verify Existence of Coverage Problem Areas

Verify that areas exhibiting low Rx values and correspondingly high Tx values insidethe predicted area of coverage are actually performing poorly.

The forward and reverse link Frame Erasure Rates (FER) should be evaluated.

Generally, areas where forward FER values exceed 2 percent should be investigated.Step 2: Identify Candidate PNs Serving, or Which Should Serve, The Problem Area

Make a list of all PNs and their corresponding Ec/Io values serving the problem area.There may be problems with specific sectors not transmitting or neighbor lists maynot be accurate and therefore not reported by the PSMMs. These situations shouldbe investigated and corrected.

Step 3: Evaluate PN Plots for Sectors Serving the Problem Area The PN plots for individual sectors should be examined to determine the

reasonableness of each sectors coverage footprint.

PNs exhibiting any of these characteristics should be investigated to determine ifobstacles are causing localized degradations in mobile receive/transmit levels that

could be worked around by raising antennas, changing pointing angles, or increasingSIF pilot powers. Slight path imbalances can occur on the forward and reverse linksdue to multi-path conditions caused by natural (terrain, trees) or man made (buildings)obstacles.

A fair evaluation of the PN plots requires that the data being evaluated adequatelycover the area of interest (sufficient drive routes). An incomplete data set might make

a sector that actually has a good coverage footprint look like it is incomplete.



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But Not Next

Step 4: Identify Which PNs Can Be Improved Using Mobile Tx As Guide To determine which sites/sectors should be changed, one should consider the following questions

for each site/sector serving the poor coverage area:

Is the coverage problem very localized, and would re-directing the RF energy into theproblem area with a change in antenna azimuth or tilt help? If so, which sector would providethe most improvement (based on distance between the candidate antennas and problemarea and angle off main antenna beam bore)?

Is the coverage problem more widespread, and would a broader correction (increase) of SIFpilot power in the entire area be a better solution? If so, which sector would provide the mostimprovement (based on relative distances from the problem area and candidate servers)?

Whether the best correction is a change in antenna pointing angle or SIF pilot power, whatpenalty would be paid, in terms of degrading other areas, if the modification(s) wereimplemented?

Step 5: Determining Power and Tilt changes SIF Power Changes

Permanent changes in SIF pilot power should be directed toward affecting a widespreadcoverage problem area where a particular PN serves. The diagnosis should indicate that anincrease of a particular sectors power level will not adversely affect surrounding or adjacentareas (i.e. introduce pilot pollution or non-dominant conditions).

To make a noticeable change in the coverage, a minimum SIF change of 2 dB should beinvestigated. A rule of thumb would be to try increments of 3 dB to see useful improvements.It is recommended that the power differences between adjacent sectors on the same cell sitedo not exceed 6dB. This large variation could cause degradation in system performancewhen a CDMA system becomes loaded.

Antenna Pointing Angle Changes

Redirecting antennas will reallocate the RF energy in a most efficient manner. This solution

should be considered for acute, focused problem areas requiring substantial correction. Ingeneral, implementation of antenna angle changes is more timely and costly than SIF powerchanges.


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Pilot Pollution

Pilot pollution (too many pilots) can be defined as theexistence of four or more pilots with Ec/Io values greater

than Tadd. To correct this problem the engineer needsdecrease the amount of energy to the problem area.

Lack of dominance can be defined as low Ec/Io levels,

numerous pilots with similar values of Ec/Io, and four ormore pilots above the Tadd threshold. To correct thisproblem the engineer needs to make up to three of thepilots in the area stronger or the other ones weaker.

These changes will create pilot dominance in the areaand reduce the number of pilots that appear in the activeset, therefore reducing the amount of interference in thearea.


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Pilot Pollution

Action : Verify the neighbor list is complete

Verify there are no PN reuse issues Create data table

Determine line of sight

Identify overshooting sites

Determine corrective action Evaluate recommendations

Implement changes



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Infrastructure IssuesDuring the optimization, problems may be encountered in areas where the RF coverage isadequate and Ec/Io for all pilots is good. When problems are encountered in good RF coverage

areas, focus should turn to identifying potential infrastructure problems.



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Infrastructure IssuesProblems That Can Be Diagnosed Using CDLs/CFCs


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Subscriber Unit Issues

Call statistics are typically used to gaugenetwork performance and partially verify the

contractual warranty performance agreement.Sometimes the statistics can be skewed due toone or more poor performing mobiles. Identifyingand removing any problematic mobiles will moreaccurately represent system call statistics. Theperformance should be monitored for all mobilesused in drive testing. Sometimes one mobile

may be testing in particularly poor RF coverage,therefore do not assume the mobile is bad bylooking at only one drive test.


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Data throughput Troubleshooting

Lots of events will contribute to low data throughput, here we candivide them into three sections: RF problem, Resource Problem andEquipment Errors.

As for Resources problem, we shall check if enough resources suchas Channel element, WC and Packet pipe configured in yoursystem, if no, it is better to re-design the data resourceconfiguration.

RF problem includes bad RF environment, mobile state (speed,handoff state) and low RF budget can be obtained because of thehigh noise floor. So for the low data throughput troubleshooting,basically, we shall have a good optimization job for IS95 voiceoptimization. Re-optimization for IS95 voice will be needed as the

coverage changed and also expected data throughput cannot beobtained.

Equipment Errors including setting errors and hardware errors, suchas TCP window size setting, ftp server setting, physical link betweenMS and terminal etc.


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Data throughput Troubleshooting

The following is the check list for data throughput troubleshooting:

RF enviroment checking (Ec/Io, RSSI, Dorminant pilot or pilotpollution)

RF budget checking (GLI RF load manager reports, BBX RSSImin)

FCH/SCH FER checking(FCH FER not exceed 1%, SCH FER notexceed 5%)

RLP statistic checking (NAK statistic, Reset statistic, Retransmisson

statistic) Resource availble checking (resgrp, walsh code, packetpipe)

Mobile state checking (Mobile speed and handoff state)

Multiplex option checking

TCP window size checking FTP server configuration checking

CDL/CFC Analysis and Application


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CDL/CFC Analysis and ApplicationWhen combined with information from Performance Management statistics, the CDLmay help answer the following types of questions:

Why did a specific call disconnect?

What are the reasons for abnormal disconnects?

RF Loss - associated with call setup, with a handoff event, with suspect equipment, witha specific MS?

L2 failure - associated with call setup, with a specific MS? BTS Link failure - associated with call setup, with suspect equipment, with a specific

MS?

MS failed to get on TCH - associated with call setup, with hard handoff, with suspectequipment, with a specific MS?

What are the possible reasons for exceptionally short call durations? Are they due tobusy at the destination (for mobile originations), ring no answer, or application of errortone or RANN to the circuit by the MSC? Are they due to the MS invoking a featurerather than requesting a call, or because of defective equipment degrading voicequality? Are they due to release by the calling party before the connection is complete?

Are calls disconnecting soon after a handoff attempt fails, possibly because the voice

quality degraded? Are calls disconnecting soon after a successful handoff or during a handoff procedure,

possibly because the voice quality degraded or RF Loss occurred?

Are an exceptional number of failures associated with a particular piece of equipment?

So CDL/CFC are useful for Optimization Engineer to distinguish call failures/drops dueto parameter, coverage problems or Hardware errors.

Final Coverage survey and


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Final Coverage survey and

Warranty Verification

Data collection, data processing and

generation of reports

Special evaluation(s) for contractual

warranty certification

Final documentation of network

configuration and performance


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Thats all & thank you & remember.

impossible is nothing

Documents

RF Optimization Guide.pdf