GSM GPRS EDGE Base Station Troubleshooting Guide


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GSM GPRS EDGE Base Station Troubleshooting Guide

  1. 1. GSM/GPRS/EDGE Base Station Troubleshooting Guide – utilizing Anritsu’s Handheld BTS Master™, Cell Master™, or Spectrum Master™ with Options 40/41 Start Here Troubleshooting Hints Locating Over-the-Air Test Spots OTA Signal Quality Test Use BTS Over-the-Air (OTA) tests to spot- These two tables provide guidance from the first indication of a fault, a poor Key Performance To test a BTS Over-the-Air (OTA) it is Carrier to Interference (C/I) check a transmitters’ coverage and signal Indicator (KPI), to the BTS or Spectrum Master test, and finally, to the field replaceable unit. necessary to find a good location. To find a Base Station Identity Code (BSIC) quality. Use the Direct Connect tests to check Power good OTA test site, look for a place squarely Rx transmitter power and when the OTA test Key Performance vs. Phase Freq Origin in the sector, a block or two from the tower, C/I Power Occ BW EVM Noise results are ambiguous. Indicators vs. Test Time Error Error Offset and away from surfaces that may reflect radio Floor (Slot) waves. A good location will have a C/I ratio OTA Start Call Blocking or Denial better than 20 dB. A directional antenna for Time Slot Shortage x x x x x x the BTS Master will help to screen out unwanted signals and improve the OTA C/I UL Interference x x xx Find location several blocks from reading. tower, square to face, and Call Drop away from reflective surfaces Radio Link Timeout x x x xx xx x x x In some urban areas, locating a good OTA site can be difficult. In these cases, it may be UL Interference x x x xx quicker to hook up to the BTS for testing. DL Interference xx x x x x x x x Start Found good Direct Connect Test vs. BTS Field Freq Ref Radios MCPA Filters Antenna Antenna spot? N Transmitter Replaceable Units Down Tilt Test The Carrier to Interference (C/I) ratio Power x xx x x indicates the quality of the received signal. Y This measurement can be used to locate a Power vs. Time (slot) x xx x x good spot for OTA testing. It also can be used Occupied Bandwidth (OCC BW) xx x x x to identify areas of poor signal quality. Freq. Phase Error xx x Fix frequency Error The Base Station Identity Code (BSIC) gives reference Error Vector Magnitude (EVM) x xx x x Passes? N xx the base station id. The Network Color Code Frequency Error xx (NCC) identifies the owner of the network. Y Origin Offset The Base Station Color Code (BCC) identifies Carrier to Interference Ratio (C/I) x x x x xx the sector. Occupied Rx Noise Floor xx Bandwidth x = probable, xx = most probable Anritsu BTS Master™ Guidelines: Passes? N Pass/Fail screen provides status of BTS C/I ratios for OTA signal quality testing should be higher than 20 dB. Y GSM/GPRS/EDGE BTS Block Diagram Direct Connect Transmitter Tests C/I ratios for coverage testing, should be Transmitter tests can be run while hooked up higher than10 dB over 95% of the coverage to the: Phase area. Error A. Output of the BTS (Point “A”). BSIC, NCC, and BCC numbers should be as Passes? N B. Test port (Point “B”) which is specified by the network operator. essentially the output of all of the Consequences: Y amplifiers. C/I ratios under 20 dB will prevent accurate C. Output of the power amplifiers (Point OTA signal quality testing. EDGE data rates Power “C”). will also be affected. vs. Time Passes? N The goal of these measurements is to increase C/I ratios under 10 dB will cause coverage voice coverage, data rate, and EDGE capacity issues including dropped calls, blocked calls, Y by accurate power settings, low out-of- and other handset reception problems. channel emissions, and good signal quality. BSIC, NCC, and BCC faults indicate coverage Good signals allow the cell to have better Origin issues that lead to dropped calls. capacity and a better return on investment. Offset Passes? N The antenna is the last link in the Common Faults: transmission path. If hooked up at point “A”, For OTA signal quality testing, the C/I ratio Y it is helpful to sweep the antenna(s) at the will vary with location. Be aware that same time, to ensure a high quality signal. interference or a faulty BTS may cause a low Start C/I. EVM Direct Connect For coverage and BSIC issues, check for a Passes? Transmitter N weak signal or excessive coverage from Test another sector. Check antenna down tilt, BTS Y power, BTS signal quality, and look for interference. Done Visit us at
  2. 2. GSM/GPRS/EDGE Base Station Troubleshooting Guide – utilizing Anritsu’s Handheld BTS Master™, Cell Master™, or Spectrum Master™ with Options 40/41 Cell Size Guard Period Measurements Out-of-Channel Emissions Signal Quality Tests Signal Quality Tests for EDGE Power Meter Measurements Power vs. Time (Slot) Occupied Bandwidth (Occ BW) Phase Error (for GSM) Error Vector Magnitude (EVM) Average Burst Power Power vs. Tiime (Frame) Frequency Error Pass Fail Mode Origin Offset Power versus Time (Slot and Frame) should Occupied Bandwidth is a measurement of Phase Error is a measure of the phase Error Vector Magnitude (EVM) measures the be used if the GSM base station is setup to the spectrum used by the carrier. The difference between an ideal and actual GMSK difference between an ideal and an actual 8-PSK The High Accuracy Power Meter can turn RF power off between timeslots. When occupied bandwidth contains 99% of the modulated voice signal. Phase Error signal. EVM measurements are required for the measure RF power to an accuracy of ± 0.16 used OTA, this measurement can also spot signal’s RF power. measurements are required for the GMSK 8-PSK modulated signals used for EDGE data dB. Traffic channels may need to be changed GSM signals from other cells. modulated signals used for GSM voice transmissions. to BCCH channels for the duration of the test. transmissions. Average Burst Power is discussed to the left. Average Burst Power, shown to the right, can be used in-service on all channels. Guidelines: Most network operators set Guidelines: The GSM signal should be Guideline: Occupied bandwidth should be Guideline For GSMK signals, phase error Guideline For 8-PSK signals, EVM should be: their base stations to within ±1.0 dB of within the GSM mask, and EDGE signals should be: Less than 7% for EVM (rms), measured between 230 kHz and 280 kHz for GSM signals. • specification. should be within the EDGE mask. The signal’s • Less than 5% for RMS Phase Error before any passive combiners off-time must coincide with the mask. • Less than 20% for Peak Phase Error • Less than 22% for EVM (pk), measured before any passive combiners Consequences: High or low values will Consequences: Violations of the mask Consequences: Excessive occupied Consequences: Poor signal quality leading Consequences: Dropped calls, blocked calls, create larger areas of cell-to-cell interference create dropped calls, low capacity, and small bandwidth can create interference with to dropped calls, blocked calls, and missed low data rate, and low sector capacity. and create lower data rates near cell edges. service area issues. adjacent channels or be a sign of poor signal handoffs. Low values create dropouts and dead zones. quality, leading to dropped calls. Common Faults: Common faults include Common Faults: Small violations of the Common Faults: Check for proper carrier Common Faults: Phase faults can be Common Faults: Radio units, power lack of amplifier calibration, radio drift, large mask during on-time indicate EVM (see EVM) filtering and distortion caused by high caused by distortion in the radio units or amplifiers, filters and antenna system can cause VSWR errors, damaged connectors, and issues. If the off-time misses the mask, look amplifier power levels. Faulty radios, filters, power amplifier. Trace the fault through the EVM faults. Trace the fault through the signal damaged antennas. for radio timing issues. If a second set of off- and bad antennas can also cause occupied signal chain to find the faulty Field chain to find the faulty Field Replaceable Unit. times is visible OTA during what should be on- bandwidth problems. Replaceable Unit. time, look for excessive GSM coverage. Frequency Error is a check to see that the Pass Fail Mode (shown on the previous page Origin Offset is a measure of the DC power Rx Noise Floor Rx Noise Floor (continued) carrier frequency is precisely correct. The as the BTS Master screen) is a way to set up leaking through local oscillators and mixers. When looking for uplink interference a good Guideline: Less than approximately –100 BTS Master can accurately measure Carrier common test limits, or sets of limits, for each This fault lowers signal quality and is normally first step is to check the Rx Noise Floor. To do dBm received noise floor when no calls are Frequency Error OTA if it is GPS enabled or in instrument. caused by radio units and up-converters. this, hookup to a Rx test port, or the Rx up. GPS holdover. antenna, for the affected sector and make measurements on the receive channel when Consequences: Call blocking, denial of Guideline: Frequency Error should be less Guideline: A green “Pass” field is required Guideline: Origin Offset should be less than - calls are not up. services, call drops, low data rate, and low than ± 0.05 ppm. for all tests. 30 dB for EDGE measurements. capacity. Look first for a high received Rx noise floor by using the GSM channel power measurement Common Faults: Receiver de-sense from Consequences: Calls will drop when Consequences: Inconsistent settings Consequences: Origin Offset faults will lower on the uplink channel. co-channel interference, in-band interference, mobiles travel at higher speed. In some between base stations, leading to inconsistent EVM and Phase Error measurements and create or passive intermodulation. Also check for signals outside the Rx channel cases, cell phones cannot hand off into, or out network behavior. higher dropped call rate. but still passed through the Rx filter. These Intermodulation products can cause of the cell. signals can cause receiver de-sense, a interference and in turn may be caused by a reduction in receiver sensitivity that combination of strong signals and corrosion. Common Faults: First, check the reference Common Faults: Failures come from BTS Common Faults: Origin Offset is created in effectively lowers the cell’s receive coverage. This corrosion can be in the antenna, frequency and the reference frequency aging, hard faults, and variable standards. the radio units Amplifiers and passive connectors, or nearby rusty metal. This issue distribution system. Check the backhaul and if components do not create is often called the rusty bolt syndrome. used, the GPS. this error. ® Anritsu. All trademarks are registered trademarks of their respective companies. Data subject to change without notice. For the most recent specifications visit: Document No. 11410-00466, Rev A Printed in the United States 2008-10