pathbalance problem analysis

White Paper:

Path_Balance (PB)

Abstract

The purpose of this document is to provide the local office and operator with a method to troubleshoot and analyze poor PB issues on CTU2s and CTUs.

Justin Annes and Julien Drouet Revision 1.0

Initial Release

BTS Center of Excellence Global Telecom Solutions Sector

Motorola, Inc November 23, 2004

Troubleshooting guide for poor PB

Page 2 of 19 Motorola General Business Use

Revision History Date Version Issued By Changes

23 Nov 2004 1.0 J. Annes

J. Drouet

Original

References Ref. Version Issued By Title

1 V8.15.0 (2002-06) 3GPP ESTI 5.08

3rd Generation Partnership Project; Technical Specification Group GSM/EDGE

Radio Access Network; Radio subsystem link control

(Release 1999)

2 GSR6 (HII) 02 May 2003 68P02901W56-M Maintenance Information

GSM Statistics Application

3 68P02902W02-A GSD Documentation Service Manual Horizonmacro outdoor Category 523 Maintenance Information

(Maint.) Chapter 3 - FRU replacement procedures

4 68P02902W96 -B GSD Documentation Service Manual: Horizon II macro

Chapter 7: FRU replacement procedures

5 1.0 BTS CoE DE IOI Debug Guide

6 1.0 BTS CoE DE TX Antenna VSWR and Reverse Power Paper

Table of Contents

1. Overview ................................................................................................................ 3 2. Description of the path balance statistic ................................................................. 4 3. Possible sources for poor PB ................................................................................. 6 4. Data and information to be gathered...................................................................... 8

4.1. General information.......................................................................................... 8 4.2. TEST #1: Calibration issue............................................................................... 9 4.3. TEST #2: Cabinet/Cabling issue .................................................................... 14 4.4. TEST #3: Environment issue.......................................................................... 15

APPENDIX 1 ................................................................................................................. 18

https://mynetworksupport.motorola.com/showcontent.asp?id=6249



1. Overview Path balance (PB) is usually monitored by customers to ensure optimal performance of the network. This document is going to provide customers or local office an understanding of the variables that affect PB and how the number is calculated. Additionally this document will provide an analytical and systematic method to identifying the root cause of poor PB. Understanding the scope of the problem Customers and local offices need to understand the scope of the PB issue and the extent of the problem. PB alone should not be used to identify faulty components of a BTS. However, PB could help identify issues such as inaccurate calibrations. An occurrence of poor PB along with another bad statistic, will typically point to another issue. It is important to identify if the problem is isolated to a single radio or if the problem is present on all the radios of the site: If the problem exists on one radio, customers can try to change the configuration of the

site (e.g. move the RTF of the poor PB DRI to another DRI) and check if the problem followed the RTF or stayed on the DRI.

If the problem is on all or multiple radios of the site then focusing on the cabinet cabling, the surf, and the environment might shorten the investigation.

NOTE: Poor path balance alone is not a reason to suspect a problem with the network/radio. The limit of 11010 is not a hard limit, only a guide and is highly dependant on how well the equipment has been setup. Past investigation have concluded that radios are returned only to find the problem is due to improper site configuration/cabinet calibration or bad cabling. Recalibration and verification of the poor PB radios Performing a cabinet offset calibration (TX/BAY CAL) on the radio exhibiting the problem can quickly resolve the problem since invalid/inaccurate calibration has been identified as a recurrent issue on customers networks. First step should always be to verify and calibrate when troubleshooting poor PB. Poor installation/maintenance (Cabling) During initial installation/deployment, it is critical that care is taken on the equipment. Damaged connectors, cables, poor ANT VSWR and dropped equipment can lead to poor PB statistics. A regular maintenance schedule is recommended to inspect and identify faulty components before a problem becomes worse. Presence of interference in the RF environment Sometimes poor cell planning or the presence of other equipment near by, transmitting at the same frequency of the wireless equipment can result in interferences. When another piece of equipment or equipment not meeting ETSI guides for spurious emission generates power in either the TX or RX operating frequency of the radio, this will increase the rx_lev the power measured by the mobile or the BTS. These types of interference will typically also cause IOI ad BER issues, if the interfere signal is large enough. However smaller levels on interference might only cause 1-4dB of error. Tools are available to scan the RF environment of the site and check if poor PB is due to an abnormally noisy RF environment. The remaining of this document will describe in detail how to proceed in the poor PB investigation and will provide tools and tips to root cause the poor PB issue.



2. Description of the path balance statistic As required in ETSI 05.08 [REF 1], one task of the BSS is to generate raw statistics for reporting network performance. The OMC-R processes these raw statistics to create custom statistics. One of these statistics is path balance (PATH_BALANCE). This measurement is known at the OMC as PATH_BALANCE [REF 2]. The Path balance (PB) statistic provides an indication of the RF link between the MS and BTS. In order to optimize the RF link, one has to make sure that all path losses in RX and TX are accounted for. If an imbalance of loss is reported in either the RX or the TX, it can indicate an invalid power level reading, an invalid calibration, a failed RF component of the BTS, or an unaccounted piece of equipment such as a preamp. An operator may be able to use the PATH_BALANCE statistic to identify a fault in the RX or TX signal path. The OMC PATH_BALANCE metric is a statistic derived on a timeslot basis and calculated using four parameters:

1. Mobile Tx power The TX power level reported by the MS (ms_txpwr_dBm) 2. Mobile Rx power The RX power level reported by the MS (ms_rxlev__dBm) 3. BTS Tx power The TX power level reported by the BTS (bts_txpwr_dbm) 4. BTS Rx Power The RX power level reported by the BTS (bts_rxlev_dbm)

To calculate path_balance:

path_balance = ((ms_txpwr_dbm ms_rxlev_dbm) (bts_txpwr_dbm bts_rxlev_dbm)) +110

or

path_balance = path_loss_difference + 110

Path_loss_difference = uplink path loss downlink path loss

uplink path loss = mx_txpwr_dbm ms_rxlev_dbm downlink path loss = bts_txpwr_dbm bts_rxlev_dbm

Note: Path balance expects one stage of combining at the bts when calculating bts_txpwr_dbm. If there is no combining or there are two stages of combining, then the PB number will be off by at least 3. Amplifiers external to the cabinet; mast mount pre-amps, power amps excreta, are not included in the calculation and will have a larger impact on the PB number. If any of this is the case then expect the PB number to ALWAYS be off from the nominal 110 by as much error as the additional component is adding/subtracting in gain.

bts_txpwr_dbm = (maximum output power of BTS) (TX power of the call)

If down link power control is used then the bts_txpwr_dbm value will change over time.



Maximum Output Power of BTS is a constant calculated by the Software and assumes there is one stage of combining and that the calibration has been done to get the output power to the correct value. If there is an extra stage of combining, there will be approximately a 3 dB difference in the path balance calculation.

TX Power of the Call - The amount of attenuation that has been placed on the call. This will be the value that is sent from the Software to the radio.

Uplink path loss is the signal loss from the mobile to the BTS.

Downlink path loss is the signal loss from the BTS to the mobile.

When investigating path_balance issues keep in mind the following:

Uplink Receive Power - Reported by the BTS XCVR as the RXLEV seen at the antenna port of the BTS.

o Relies on a proper RX Bay Level Offset Procedure having been run to accurately measure the gain of the components between the radio and the antenna port.

Uplink Transmit Power - Reported by the mobile in the uplink SACCH

Downlink Receive Power - Reported by the mobile in the uplink SACCH

Downlink Transmit Power - Calculated based upon two pieces of information. First is the XCVR type as an index into a look-up table which gives the maximum power level for this radio type. The second is the downlink transmit power level being commanded for that timeslot transmitting to the mobile. This calculation does not take into account the following pieces of information:

o Relies on the Tx Cell Site Offset Procedure being run to get to those power levels mentioned below

o Does not take into account any other BTS configurations that may result in a change in output power (2nd stage of combining, preamp, repeater, etc.)

The ideal path_balance number is 110 as this will indicate that the RF loss of the downlink is exactly equal to the RF loss of the uplink. However it is important to note that always achieving a number of 110 might not be possible because this number takes into account the variation of different mobiles, tolerances of the BTS TX and RX power reporting, and losses in the antenna TX and RX paths. At peak network loads, this number might be seen to drop. This is not an indication of a failure only an indication of a raised noise level of the



RF environment. In-band interference in the receive or transmit frequencies can also cause a path balance number to be less than optimal, as the mobile or the BTS will measure a higher rxlev than expected. The mobile TX and RX power levels are averaged over a period of time. Typically hundreds to thousands of mobiles will connect to a radio over a long period of time. Since there is a large sample of mobiles reporting TX and RX power levels, these number should show a normal distribution meaning that over time inaccuracies in any one mobile will have little affect on the PB number. This means that it takes an error at the BTS TX and/or RX path loss or power reporting to cause a continuous change in the PB number. If a TX loss problem exists then the number will typically increase, if TX gain problem then the number will decrease, if an RX loss problem then the number will typically decrease, if an RX gain problem then the number will typically increase. If there is also an IOI issue then there is either a problem with the RX path or interference on the RX frequency. PB acceptable limit: There is a range in which if exceeded the OMC software will peg the statistic. This range is 100 to 120 or 11010. The more the path balance number deviates from the ideal 110 number, the more likely there is a problem with the equipment. However this number when slightly out of range does not indicate a failure of the equipment. Also a wrong PB number might only indicate that a component such as a preamp is unaccounted for. Typically if the number is significantly far away from 110, then the poor path_balance will be accompanied by another bad statistic such as high IOI, high BER or a high number of dropped calls. Note that it is acceptable to have PB values varying throughout the day since there will most likely be more interferences in the natural environment during peak hours of the day than during non-peak hours. 3. Possible sources for poor PB There are three different possible known sources of poor PB: Invalid or inaccurate TX/BAY CAL

o If the radio is a new spare it comes with default CAL data and must be TX and RX offset calibrated within the slot it will function in

o If the radio was swapped from one slot to another and preserve bay level cal feature is not enabled, a recalibration of the TX and RX is necessary to achieve more accurate PB stats

o If an expansion cabinet is added to the configuration it might be necessary to recalibrate the TX and RX

o If external combining, filtering or amplification is added to the configuration a TX or RX calibration is required. In some cases this might be impossible

HW/Connection problem with the cabinet slot/cabling/antenna: An element in the received path might have failed, or might not be used or installed correctly: backplane, cabling, bad connectors, a bad duplexer

HW problem with the DRI: A HW component of the transceiver (CTU or CTU2) can have failed which results in abnormal noise in the transceiver or loss of output power.

In this document, we will describe how to identify if the high IOI problem falls in one of these categories. Your investigation will follow the graph below.



Yes

Yes

No

Yes

Poor PBI detected?

No

Yes

TEST #3 Section 4.4: Is the problem due

to other HW failure?

No TEST #4 Section 4.5: Is the problem due to the environment

TEST #2 Section 4.3: Is the

calibration data accurate?

- Contact the local office to see if there is a know issue affecting the PB number and to see if an SR has already been opened -Open an SR (provide a description of the problem and attach the logs you gathered during your investigation) AND -Contact the network optimization team

- Contact the network optimization team and/or - Modify the frequencies to be used on this sector

Section 4.1: Gather generic configuration information on

the radio and the site.

Calibrate the radio and monitor the

PB again

Return or fix the faulty

equipment and monitor the PB again

No Yes TEST #1 Section 4.2: Is the VSWR

good?

Fix VSWR issue and

monitor PB



4. Data and information to be gathered WARNING: Throughout this procedure, keep logs of all MMI commands and all the results or you tests.

4.1. General information In this section, we want to have a snapshoot of:

the radios state and configuration, and

the sites performance.

Please answer the following questions below before you change anything in the site:

Is there TX combining or is there an amp in the TX or RX after the cabinet?

How many radios/sectors are affected?

What type of radio is affected (CTU, CTU2, both)?

For all radios affected, get OMC INTF_ON_IDLE statistic.

Monitor PB, BER, call drop rates and IOI performance, if High IOI please see IOI white paper

Did the problem start after an upgrade, a cell replanning, or HW change?

Check with the Local Office if there is a known issue

Run the following commands for the site at the MMI-RAM:

disp_proc 0

disp_proc

state

disp_cell_status

disp_gsm_cell

disp_hop

disp_hop active

state rtf * *

disp_neighbor

disp_act_alarm

Run (at the MMI-RAM) the following commands for ALL DRIs/RTFs that of the site:

disp_rtf_chan

disp_eq rtf

disp_eq dri full

disp_cal_data dri

Provide a map showing where the sites are and their respective frequencies.



4.2. TEST #1: Check Antenna VSWR

The fist step due to convenience is to check the VSWR of the affected antenna. It has been seen in some cases that poor antenna VSWR can lead to bad path_balance numbers. An instrument is required to place between the antenna and the BTS to measure VSWR. A good VSWR should be less than 2.61 or a return loss higher than 6dB.

If there is a VSWR problem, then the result for TEST #1 is NO and you should resolve the VSWR issue and monitor the PB again. Please refer to REF 6, which is a paper written to resolve VSWR issues.

Otherwise if VSWR is ok go to (4.3) below

4.3. TEST #2: Calibration issue

In this section, we will verify that the calibration data is valid for the antenna and branch(es) being used. (Note: It is recommended to calibrate all antennas but in some cases, only the antenna being used is calibrated by the customer).

4.3.1. Verification that the calibration data is valid

Verification that the calibration data is valid:

(a) CTU radio At the EQCP MMI prompt, enter the following commands:

EQCP TEST > calchk EQCP TEST > RX Branch 1: CAL CHECKSUM RX Branch 2: CAL CHECKSUM AIC YES 0001 AIC YES 0007 AGC YES d3f0 AGC YES b845 BAY YES 7f3b BAY YES 7f3b BBG YES 002a (This is for both branches.) DCO YES 3ef0 DCO YES 169b FREQ YES ffe3 FREQ YES fe21 IFG YES 0006 IFG YES 0005 RSSI YES a19a RSSI YES a0ce TX CAL CHECKSUM DET YES 5865 PWR YES 04a2 TX YES 0000 VVA YES a3c7

Verify that the "CAL" value for the row titled BAY is "YES".

If there is a NO, then the result for TEST #2 is NO and you should recalibrate the radio and monitor the PB again. If IOI is also occurring then please reference the IOI white paper and perform specific tasks.

Otherwise if calibration data is ok go to (4.3.2) below



(b) CTU2 radio At the DSP MMI prompt, run the following commands:

CTU2.carA.ts_0>chg Enter Password: pizza Access Level 3 Granted CTU2.carA.ts_0>cal_status tall Cal Ca Br Status Result Valid Checksum Ver S/HC --------------------------------------------------------------------- RF Lop A 0 pass valid 0x0672d5b5 1 / 1 RF Lop B 0 pass valid 0x0d7b5025 1 / 1 RX RF A 0 pass valid 0x2ae0b9fc 1 / 1 RX RF A 1 pass valid 0x2bb91f4a 1 / 1 RX RF B 0 pass valid 0x2c1ed905 1 / 1 RX RF B 1 pass valid 0x2b063b6b 1 / 1 RX IF A 0 pass valid 0xc8bc3caf 1 / 1 RX IF A 1 pass valid 0xc8d99f37 1 / 1 RX IF B 0 pass valid 0xc8dadb3f 1 / 1 RX IF B 1 pass valid 0xc8bfbd0a 1 / 1 RX FR A 0 pass valid 0xa8fe3af6 1 / 1 RX FR A 1 pass valid 0xa8e8ba39 1 / 1 RX FR B 0 pass valid 0xa8fb5db7 1 / 1 RX FR B 1 pass valid 0xa8f593e0 1 / 1 RX CAB A 0 pass valid x53703256 0 / 1 0RX CAB B 0 pass valid 0x45562835 0 / 1 TX VVA A 0 pass valid 0xb0be7eb2 1 / 1 TX VVA B 0 pass valid 0x96686359 1 / 1 TX DSA A 0 pass valid 0x01a775df 1 / 1 TX DSA B 0 pass valid 0x01a7863a 1 / 1 TX FP A 0 pass valid 0x09e81286 1 / 1 TX FP B 0 pass valid 0x07c8ee22 1 / 1 TX Ver A 0 pass valid 0x064b1162 1 / 1 TX Ver B 0 pass valid 0x063b5e9a 1 / 1 TX CAB A 0 pass valid 0x019e2da9 1 / 1 TX CAB B 0 pass valid 0x01bd2da9 1 / 1 PA Det A 0 pass valid 0x15cc24be 1 / 1 PA Det B 0 pass valid 0xd7dc8932 1 / 1 PA VVA A 0 pass valid 0xda5d5f94 1 / 1

Verify that the rows for the "RX CAB A" and RX CAB B values are pass and valid.

If this is not the case, then the result for TEST #2 is NO and you should recalibrate the radio and monitor the PB again. If IOI is also occurring then please reference the IOI white paper and perform specific tasks.

Otherwise if calibration data is ok go to (4.3.2) below



4.3.2. Manual verification

It is important to verify that the bay level offset is accurate. This procedure can be performed to manually identify an invalid offset as an invalid offset can cause PB issues. A RX calibration that is off by 10dB will result in a path_balance that is 10 worse than normal.

WARNING: Be sure to take the radios connected to this duplexer out of service so that the TX power is off.

For verification of the cabinet calibration follow the following procedure:

(1) This procedure requires a signal generator to inject a RF signal into the antenna (ANT) port of the duplexer. Therefore radio must be taken out of service.

At the RSS MMI prompt:

MMI-RAM 1015 -> lock pchn

Example:

MMI-RAM 1015 -> lock 52 pchn 0 0 6

This command must be entered for each time slot of each DRI connected to the duplexer. There should be no TX power into the duplexer.

(2) Disconnect the antenna from the duplexer

(3) Attach a good RF cable from the signal generator to the ANT port using appropriate adapters

(4) Set the signal generator to a power level of -70dBm and the frequency of the desired RX channel to be measured. See appendix for a list of ARFCNs and corresponding frequencies. For this example we will use ARFCN 512 1710.2MHz

(5) Log into the radio and set the ARFCN being measured. For this example it is 512. At the EQCP TTY ts a chan 512 .

(6) Now measure RXLEV. For CTU use self cal rx_lev, for CTU2 use rxlev.

(a) CTU Radio EQCP > .gsmfw

EQCP > test

WARNING: The EQCP is now in test mode.

EQCP TEST > ts a chan 512

EQCP TEST >

The data for all timeslots has been changed.

EQCP TEST >

EQCP TEST > self cal rx_lev

EQCP TEST >



Power into radio: (AIC is assumed out.)

B1 Rx Lev: -66.1049 dBm

B2 Rx Lev: -105.4468 dBm

Power into cabinet:

B1 Rx Lev: -71.4258 dBm

B2 Rx Lev: -112.6094 dBm

EQCP TEST >

(b) CTU2 Radio CTU2.carA.ts_0> CTU2.carA.ts_0>ch Enter Password: pizza Access Level 3 Granted CTU2.carA.ts_0>set_c cara Setting carrier to carrier A CTU2.carA.ts_0> CTU2.carA.ts_0>ts a chan 512 Name rx_synth_channel TS 0 1 2 3 4 5 6 7 ------- -------- -------- -------- -------- -------- -------- -------- -------- State OVRD OVRD OVRD OVRD OVRD OVRD OVRD OVRD OVRD 200 200 200 200 200 200 200 200 rt 21b 21b 21b 21b 21b 21b 21b 21b Decimal Equivalent OVRD 512 512 512 512 512 512 512 512 rt 539 539 539 539 539 539 539 539 Freq. 1710.2 1710.2 1710.2 1710.2 1710.2 1710.2 1710.2 1710.2 Name tx_synth_channel TS 0 1 2 3 4 5 6 7 ------- -------- -------- -------- -------- -------- -------- -------- -------- State OVRD OVRD OVRD OVRD OVRD OVRD OVRD OVRD



OVRD 200 200 200 200 200 200 200 200 rt 21b 21b 21b 21b 21b 21b 21b 21b Decimal Equivalent OVRD 512 512 512 512 512 512 512 512 rt 539 539 539 539 539 539 539 539 Freq. 1805.2 1805.2 1805.2 1805.2 1805.2 1805.2 1805.2 1805.2 CTU2.carA.ts_0>

CTU2.carA.ts_0>rxlev

TS 0

------- --------

Hex b9a1

Dec 47521

dBm -70.371

TS 0

------- --------

Hex 8736

Dec 34614

dBm -120.789

CTU2.carA.ts_0>

(7) The CTU command will report both the cabinet and the radio power measured. The CTU2 command will report only the cabinet power measured. The cabinet power reading should be -70dBm +/-4dB or between -66 to -74dBm.

(8) If diversity is used, connect the signal generator to the appropriate diversity connection on the SURF or SURF2. Repeat the procedure to measure reported power on all utilized branches.

(9) Using a power meter and proper couple verify the TX power level.

If the radio reads a value that is off by more than 4dB on the main or diversity path, then the result for TEST #2 is NO and you should monitor the PB again with the new RX calibration offset values.

Other wise continue to section 4.3.3

4.3.3. Recalibration of the radio Re-calibrate the radio according to the procedure described in REF [3] (CTU) or REF[4] (CTU2) and then run the disp_cal_data dri command at the MMI-RAM.



Verify that the new calibration offsets are not too different from the initial ones you got in Section 4.1 for this radio. To do that, use the CheckRecalibration_v01.xls excel spreadsheet that can be found at http://compass.mot.com/go/153741877.

(1) Select the radios frequency (850, 900, 1800, or 1900)

(2) Copy and paste the initial and new values into the spreadsheet

(3) Look at the differences between the initial and new data. If the difference for the antenna being used is more than 2 dB for most of the offsets, the result for TEST #2 is NO and you should monitor the PB again with the new RX calibration offset values.

Otherwise run section 4.4 below.

4.4. TEST #3: Cabinet/Cabling issue In this section we will discuss the various items that could be broken or damaged on the cabinet. In many situations all that is required is a close inspection of the cabinet looking for damaged connectors and cables. There are three places to look to identify this type of failure: TX path, RX path and the combined TX/RX path. There are two other possibilities, though less likely, in which interference can be generated. These are after the duplexer combining and a bad SURF/SURF2.

TX Path

Lock the radio and power down.

Inspect the short TX cable that goes from the CTU/CTU2 to the duplexer. Make sure there are no cuts or frays or places where it looks like the cable is coming apart. If there is damage replace the cable.

If the short TX cable looks ok, remove the cable connecting the CTU/CTU2 to the duplexer. Inspect the center conductor on the cable, the CTU/2, and the duplexer. If there is damage to the cable or the cables center conductor is bent, replace the cable. If it looks like the CTU/CTU2 connector is damaged or loose, return the CTU/CTU2 for repair and note the damaged connector on the RMA. Inspect the duplexer center conductor and return if there is damage or if the connector is bent.

Inspect any other cables that might be used in the TX path such as cables connected to combiners, add-on VSWR units, and external filters.

RX Path

Lock the radio and power down.

Pull out the radio and inspect the connectors on the back of the radio for damage. Replace if damaged and make note of it on the RMA.

Remove the RX cable, for the desired path, from the duplexer and SURF. Inspect the cable for damage and cuts. If it looks like the cable is breaking near the connector, it is bad. Replace this cable as necessary. Also inspect the N-Type connector on the SURF/SURF2 and the duplexer. Look closely at the center conductor to see if there is any damage. If one prong is bent or missing or if the prongs are spread far apart, then the connector is bad. Replace the unit and mark the reason on the RMA.

If it is ok to take down the entire site, the SURF/SURF2 can be removed to inspect the SURF connectors. Again, look for any damage to this connector. Look closely to see if prongs are bent or missing and center conductor is ok.

http://compass.mot.com/doc/154299383/CheckRecalibration_v01.xlshttp://compass.mot.com/go/153741877



In some cases an external LNA is used before the duplexer to improve the sensitivity. If this is the case try removing the LNA for a period of time to see if the interference goes away. If an LNA is used, it is important to calibrate the cabinet with the LNA connected to account for the extra gain.

RX/TX Path

Remove the ANT connector from the duplexer. Inspect both the antenna feeder cable connector and the duplexer connector. Look closely for bent or missing pins/prongs. If there is damage replace either the cable or duplexer. Measure the VSWR of the antenna. If the VSWR is worse than 2.33 then inspect all cabling to and including the antenna. Check for bad lightening arresters or other bad connectors.

External Combining, Filtering, Amplification

Motorola certifies all equipment used on the cabinet to ensure that a minimum amount of interference exits. If add-on combining is used, it is important that (1) the part is rated to handle the power and (2) the part does not generate any additional interference. If interference is detected on a cabinet, and the problem does not appear to be related to the environment, then try removing any external components not supplied by Motorola for a period of time to see if the interference subsides.

SURF/SURF2

It is possible but not likely that the SURF/SURF2 might generate interference in the form of an oscillation. There is no record of this type of occurrence but you can check it in two ways.

1. The SURF/SURF2 can be swapped with another SURF/SURF2 to see if the problem clears. This will require a cabinet TX and BAY RX offset calibration. If the interference clears by simply swapping the SURF then return the SURF/SURF2 for repair and note the failure on the RMA.

If you have found a faulty cable, connector, equipment, etc. then the answer to TEST #3 is YES - replace the faulty part and re calibrate both the TX and BAY offsets. If no faulty equipment is found the answer to TEST #3 is NO, continue to section 4.5

4.5. TEST #4: Environment issue In this section, we will check that there is not a signal in the radios environment at the frequency (or frequencies) which the radio is tuned to.

4.5.1. Use of a spectrum analyzer For this procedure, you will have to power down the whole sector for approximately 15 minutes

(1) Using the output of the disp_gsm_cell command, get the list of frequencies the radio exhibiting poor PB uses.

(2) Turn off all of the radios of the site.



(3) Using the diversity path of the SURF or SURF2, connect the sector of interest to port 0B of the SURF/SURF 2.

(4) Connect the spectrum analyzer to the expansion port B of the Surf/Surf 2.

(5) Look for obvious spurs or humps in the noise floor on or near the center frequency, narrow the span to 1MHz to determine how close to on-channel the noise/spurs are.

Start with a wide bandwidth, this picture shows what a typical noisy site might look like.

Set the bandwidth to 1MHz to see if the spur lands on the RX channel you are investigating. In this case

the interfere is just left of center. This picture shows interference on the desired frequency.



This is what a clean or ideal environment should look like.

If you find spurs or humps on the frequencies being used by the radio then the answer to TEST #4 is YES. Otherwise, its NO.



APPENDIX 1 ARFCN to Frequency Calculation: The carrier spacing is 200 kHz. The carrier frequency is designated by the absolute radio frequency channel number (ARFCN). If we call Fl(n) the frequency value of the carrier ARFCN n in the lower band, and Fu(n) the corresponding frequency value in the upper band, we have: E-GSM Fl(n) = 890 + 0.2*n

Fl(n) = 890 + 0.2*(n-1024) 1 n 124 975 n 1023

Fu(n) = Fl(n) +45

DCS 1800 Fl(n) = 1710.2 + 0.2*(n-512) 512 n 885 Fu(n) = Fl(n) +95



APPENDIX 2 QUICK GUIDE FOR FIELD ENGINEER

PB Issue Site Investigation Steps Poor Path Balance:

1. Collect two weeks Path Balance data of sites (900 & 1800 CTU-Horizon) with low path balance and high IOI from OMC. Analyze the PB trend chart. Collect log data and alarm info from both MCUF and CTU. Also collect IOI, BER and TCH_RF_Loss rate. If Path Balance is only slightly bad then there is no issue. Also if there are extra combining or amplification after the BTS then do not pay attention to the Path Balance statistic.

2. Check the antenna VSWR. If VSWR is worse then 2.61:1 or return loss is worse than 6dB then resolve VSWR issue. If not continue investigation.

3. Manually verify the BAY and TX CAL for accuracy. Inject a sigen into the ANT port at the appropriate frequency and power level to verify RX cal. If inaccurate perform BAY/TX CAL. Always perform BAY/TX CAL when replacing or swapping radios. Check the TX power out of the radio and then out of the duplexer. If out of the radio is 2dB low need to return radio. If the power out of the duplexer is more than 2dB lower that the radios output power then return the duplexer. There should be some loss through the duplexer. Only a high dB error will result in a PB error.

4. Site investigation, visual check all RF connections on the suspect base station, make sure all connections work, and there are no bent connectors, check below items:

a. Antenna connector (7/16 type); b. DCF connector (N type, SMA, 7/16 type); c. CTU Output connector (SMA type); d. SURF RF connector (N type); e. Check the VSWR, should be 2.33 or less

5. If the site has two stages antenna combining or combining after the duplexer then must accept path_balance error of 3-4. If an LNA or preamp is used on the RX then must accept 10-20 path_balance error. If a repeater or external PA is used on the TX then must accept 10-20 path_balance error.

6. Change antenna of the DRI, to see if the problem clears

7. Swap radio to another slot, re-calibrate and monitor statistics.

Note: If there is high IOI, then most likely there is low path_balance, and the problem is at the RX or interference. If there is only a path_balance problem then the issue is most likely due to a hardware issue, meaning cables, antenna, duplexer, or CTU/CTU2. It is normal for path balance to vary throughout the day as the RF interference increase along with the traffic load. Do not replace CTU/CTU2 if path_balance varies only a little.

pathbalance problem analysis

Documents

poor pb page

poor pb issues

occurrence of poor pb

root cause of poor pb

overview path balance

general information

problem customers

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