Troubleshooting-Installing an RF link Issue : 5.3.x Rev 2 Authors : Matt Olson/Dave Sida Date : 30th July 2004 Axxcelera Broadband Wireless 175 Science Parkway Rochester, New York 14620 support@axxcelera.com www.axxcelera.
Axxcelera Broadband PLEASE READ THESE SAFETY PRECAUTIONS RF Energy Health Hazard Professional installation required. The radio equipment described in this guide uses radio frequency transmitters. Although the power level is low, the concentrated energy from a directional antenna may pose a health hazard. Use the following chart for determining the minimum safe distance. Do not allow people to come within the minimum safe distance of the antenna while the transmitter is operating.
Axxcelera Broadband FCC Notice, USA The AB-Access units comply with Part 15 of the FCC rules. Operation is subject to the following three conditions: • • • This device may not cause harmful interference. This device must accept any interference received including interference that may cause undesired operation. Units with support for an external antenna must be professionally installed. This device is specifically designed to be used under Part 15, Subpart E of the FCC Rules and Regulations.
Axxcelera Broadband CONTENTS CONTENTS ..................................................................................................................................... 4 1 CHANGE HISTORY................................................................................................................. 7 2 INTRODUCTION ...................................................................................................................... 8 3 ALIGNING AN SU................................................
Axxcelera Broadband 7.1.23 7.1.24 7.1.25 7.1.26 7.1.27 7.1.28 7.1.29 7.1.30 7.1.31 7.1.32 7.1.33 8 RSSI...................................................................................................................................... 20 Path loss in excess of FSL (estimate) ................................................................................... 20 Downlink RSSI Fade Margin ............................................................................................... 21 TX maximum backoff .
Axxcelera Broadband 10.1.8 AGC...................................................................................................................................... 32 10.1.9 Nominal TX chain attenuation.............................................................................................. 32 10.1.10 Actual TX chain attenuation ............................................................................................ 32 10.1.11 Digital baseband attenuation...........................................
Axxcelera Broadband 1 CHANGE HISTORY REVISION DATE EDITOR DESCRIPTION Draft 1 14th Aug 2002 MOlson First Draft Draft 2 5th Nov 2002 DSida Edits to section 3 (link status) Draft 3 15th Nov 2002 MOlson Numerous updates Draft 4 20th Nov 2002 DSida Edits to sections 7,8,9 Draft 5 2nd Dec 2002 DSida Edits to sections 4,5,6 Draft 6 31st Mar 2003 MOlson Updates for 5.2.x release Draft 7 29th Apr 2004 Molson Updates for 5.3.6 5.3.
Axxcelera Broadband 2 INTRODUCTION This document’s purpose is to help troubleshoot radio problems with the AB-Access and AB-Extender products. This document should only be used with System Software 5.1.5 or above, because some of the CLI commands described here are either different or not supported by earlier software revisions. Troubleshooting-Installing an RF link -8- Issue: 5.3.
Axxcelera Broadband 3 Aligning an SU This section will discuss how align the antenna for optimal signal strength. Line of Sight (LOS) The first step is being able to see the tower or building the AP is mounted on. This should be possible in most deployments, however there could be times that you will not be able to see this far due to weather or you are unable to pick out the exact building or tower that the AP is mounted on. There for we described 2 methods to initially align an SU. 3.1.
Axxcelera Broadband 3.1.2 GPS/Compass alignment A GPS (Global Positioning System) can be used to align the unit by taking a waypoint at the AP. This will allow you to get the proper bearing to the AP from the building the SU is on. Then by holding the GPS next the SU you can turn the SU to the proper bearing. This can also be done with a compass if the bearing has been defined by looking at a map. Or if the installer knows the general direction of the Access Point.
Axxcelera Broadband 4 Fine tuning an SU This section will discuss how to fine tune your SU alignment for optimal performance. Fine tune alignment The easiest and fastest way to fine tune the antenna is to look at the RSSI of the SU. This can be done by using the command hmm modem rssi repeatedly until you have found the best possible RSSI for the SU. 4.1.1 Procedure Once you have either eyeballed or used a GPS to align the SU then you can use the following steps to fine tune the alignment. 1. 2. 3.
Axxcelera Broadband 6. 7. 8. 9. Once you have located the bearing of the best RSSI tighten the screws that allow the radio to turn on the horizontal axis. Now have the installer slowly tilt the SU on the vertical axis (tilt bracket is required for vertical axis adjustments). While you are continuously checking the RSSI. If the RSSI gets worse have him stop and start tilting it the other direction following the same procedure as in step 7.
Axxcelera Broadband 5 SU signal quality After you have adjusted the SU to receive a good RSSI you will want to look at the quality of the signal. This is done by using a few commands at the SU. Procedure 1. Check the quality of the signal (not the strength) by looking at the hmm modem mmse. This take 1000 samples of the modem mean square error rate, and report the average and the number of samples over 50. See chart below to identify if out is good or bad.
Axxcelera Broadband NOTE: If you are using anything other than the normal SU antenna that has a gain of 18 dBi you will need to account for the difference in antenna gain yourself. For example if you have an Extender SU with a 23 dBi antenna you will need to add 5 dB to the number, so the example would be 10.2 dB and not 5.2 dB. It also assumes that the SU and AP are set to transmit at the same power. If no modifications have been made to the channels.
Axxcelera Broadband 6 Troubleshooting SU link from AP This section will show you how to identify an SU that is having problem from an AP. Identify SU The hmm mac stats of the AP can identify that there is a problem in the sector, but is unable to identify which SU is having a problem. Follow the steps below to identify which SU is having a problem. 1. To identify a problem SU you can use the pnms sector command which will give you 5 vital statistics for each SU in the sector.
Axxcelera Broadband 3. Once you have identified the SU you can focus on troubleshooting that particular SU. Refer to section Fine tuning an SU and SU signal quality for pointers on what to look for while troubleshooting an SU. Troubleshooting-Installing an RF link - 16 - Issue: 5.3.
Axxcelera Broadband 7 Link status The link status command will display the most common information needed to characterize how a radio link is performing. The command is implemented on both APs and SUs. However, some of the information is subtly different between the two unit types. AP Link Status 192.168.100.
Axxcelera Broadband 7.1.6 Radio Temperature Radio Temperature displays the internal temperature of the radio in degrees Celsius. It is followed by an indicator to tell you if the temperature is acceptable. Possible indicators are good, marginal and bad. 7.1.7 TX maximum backoff TX maximum backoff displays the maximum system backoff that can be placed in the system.conf file for a given band. 7.1.8 TX current backoff TX current backoff displays the system backoff that is currently in the unit.
Axxcelera Broadband alone it is not possible to determine which AP-SU radio link/links is/are having a problem. A high value for this measurement simply means that at least one radio link supported by that AP has an upstream problem. The Aggregate Uplink Cell Error Rate measurement is a more sensitive indicator of upstream radio problems than the Aggregate Downlink Cell Error Rate measurement. SU Link Status 192.168.3.
Axxcelera Broadband 7.1.17 Radio Channel Mask Radio Channel Mask displays the current channel mask. The channel mask determines which channels will be scanned in dynamic mode and when the survey web page is used. 7.1.18 Correlation sequence Correlation sequence displays whether or not the SU modem has detected a downstream burst (the “training/correlation sequence”) from the AP modem. This has to happen before the MAC can delay compensate.
Axxcelera Broadband backoff, and the AP and SU having the same channels.conf file (where applicable). A very high value here can also indicate a hardware fault. 7.1.25 Downlink RSSI Fade Margin The Downlink RSSI fade margin is the amount by which the RSSI can fall (in dB) before the radio link will fail totally. The minimum fade margin recommended by Axxcelera is 10dB, although units at maximum range will have slightly less than this at best.
Axxcelera Broadband 7.1.32 Downlink Cell Error Rate Downlink Cell Error Rate is the downlink cell error rate for a specific AP-SU radio link. This is displayed in % and is based on CELL RXOK, RXMISSED, and RXBAD from the SU’s MAC stats. It is followed by an indicator to tell you if the error rate is acceptable. This is actually measuring the percentage of cells received in error, and this type of error indicates a downstream radio problem.
Axxcelera Broadband 8 Modem RSSI RSSI is the Receiver Signal Strength Indicator for an SU, and is displayed in dBm. RSSI is not available on an AP, because all SUs transmit so that there signal is received at the AP in the range of -71 to -78. The RSSI is displayed by the “hmm modem rssi” command, but is also displayed by the “hmm link status” and “hmm modem txpower” commands. SU Modem RSSI 192.168.3.254 hmm> modem rssi mean actual RX chain attenuation +35.375 dB demod gain stage OUT actual RX gain +80.
Axxcelera Broadband 9 Mac stats The MAC stats show the RF-link statistics. It is one of the primary tool for diagnosing RFproblems. The “hmm link status” command reports some error rates based on the MAC stats, but these are sampled over a very short period of time, and only show the performance at that instant. In contrast, the “hmm mac stats” command can be used to look at average error rates over any period of time.
Axxcelera Broadband ticks UTOPIA interface # of 20 mS ticks since last received… Utopia tx UTOPIA interface # of ticks since the last cell was transmitted from the UTOPIA interface (to the air interface) Utopia rx UTOPIA interface # of ticks since the last cell was received at the UTOPIA interface (from the air interface) FDHDR RXOK UTOPIA interface # of ticks since the last FDHDR was received OK from the air interface Free list UTOPIA interface Relates to internal pointers, and is not releva
Axxcelera Broadband Acknowledgements received from the SU. These are generated by the SU when it receives a valid cell or cells in the downstream portion of the frame. 9.1.3.2 TX Acknowledgements transmitted by the AP. These are generated by the AP when it receives a valid cell or cells from an SU in the upstream portion of the previous frame. 9.1.4 CELLS CELLS are the number of ATM CELLS that have been transmitted from, or received by the MAC, and carried by the RF link. 9.1.4.
Axxcelera Broadband 9.1.8 dup The “dup” count represents cells that have been received with their sequence number to low, i.e. cells that have been received multiple times (because they were re-transmitted over the RF link). There are two mechanisms that cause duplicates; CELL errors and ACK errors. These are described below. Duplicates caused by CELL errors Up to 6 cells can be sent from any unit in a single burst.
Axxcelera Broadband MAC used (i.e. 5.6km, 8.0km or 11.4km). The FDHDR error rate should be less than 1/10000 for a good link. Between 1/10000 and 1/1000 is marginal, and an error rate higher than 1/1000 is bad. 9.1.9.2 TX The FDHDR TX counter should never increment because an SU cannot transmit FDHDRs. 9.1.10 RGR Reservation (Grant) Request (Rx) / Reservation (Grant) Request Acknowledgement (Tx) 9.1.10.1 RX Reservation Request Acknowledgment received by the SU.
Axxcelera Broadband The upstream cell retransmission rate (i.e. average for this SU-AP link) can be calculated approximately from the “tx” and “CELL TX” counts, as follows: Upstream Cell Re-Transmission Rate = (( CELL TX – tx ) / tx ) x 100% A value of 0% means that cells are only sent once, a value of 100% means that on average each cell is sent twice, and a value of 500% means that every cell is sent six times - the maximum.
Axxcelera Broadband 10 Modem txpower The “hmm modem txpower” command is available on both APs and SUs. AP Modem Txpower 192.168.100.200 hmm> modem txpower corrected FCC backoff tx attenuation nominal TX chain attenuation actual TX chain attenuation digital baseband attenuation nominal TX power actual TX power +17.466 dB 16 dB +16.937 dB +0.638 dB +1.000 dBm +0.
Axxcelera Broadband FCC High-Band = +14dBm (+14dBm for AB-Extender) FCC Mid-Band = +8dBm ( +4dBm for AB-Extender) FCC Low-Band = +1dBm ( -2dBm for AB-Extender) The nominal TX power value also takes into account any deviations from the standard FCC limits, such as a System Backoff adjustment or a non-FCC power scheme. Nominal TX power can therefore be used to see if the AP and SUs in a sector are using the same power scheme, e.g.
Axxcelera Broadband 10.1.8 AGC The AGC Rx pointer is the number of 2dB attenuator pads currently switched into the SU’s receive path. The AGC Tx pointer is the number of 2dB attenuator pads currently switched into the SU’s transmit path. 10.1.
Axxcelera Broadband 10.1.14 Actual TX power Actual TX power is the actual power level (dBm) being transmitted from the SU radio. The difference between the actual and actual (AP) TX powers represents the amount by which the SU transmit power can increase before it is capped. A small difference indicates that if the RSSI drops then the SU may not be able to transmit at the correct level, and the signal from this SU may be too weak when it arrives at the AP receiver. This is likely to cause RF problems.
Axxcelera Broadband 11 Modem mmse The modem mmse command measures the modem’s mean-squared-error (MSE) for each burst, which can be used to determine the quality of the signal being received. The mean squared error indicates how closely the received data coincides with the four QPSK constellation points, the expected data values. A high MSE indicates that the received signal quality is poor, either because there is noise/interference on the signal, or because the signal level is incorrect.
Axxcelera Broadband 12 PNMS Sector The pnms status command retrieves the RF related stats from an entire sector with one command. It is only available on an AP. It scans the sector up to MID and display results for each SU that responds. Values are updated every 10 minutes and are only updated when there is sufficient traffic to make the calculations meaningful. For the first 10 minutes the unit is powered up the values will be zero. AP pnms sector 192.168.2.
Axxcelera Broadband 13 Survey Scan A Survey Scan can be conducted from the CLI or the web interface. This feature is only applicable to FPGA APs and SUs. The "survey scan" CLI command and 'radio survey' web page now provide additional data on RF energy in each channel. Continuous or bursty energy can be detected, regardless of the source (i.e. it does not have to be Axxcelera equipment), providing it is present during the scan.
Axxcelera Broadband 3. Click on SU and AP Radio Survey scan. 4. The survey page is displayed. It will take up to 2 minutes to appear so be patient. 5. Once you are finished click on Click here to exit. Troubleshooting-Installing an RF link - 37 - Issue: 5.3.
Axxcelera Broadband CLI 192.168.2.2> survey scan Please wait while a channel scan is performed by this AP. This will take up to 1 minute to perform.
Axxcelera Broadband 14 Modem msreg 6 1 The modem msreg 6 1 command will display the RX digital AGC level. This is a fine gain adjustment. It is the only dynamic gain adjustment on APs. SUs also have a course gain adjustment, the Radio AGC, which adjusts the gain over a wide range. On SUs the Rx digital AGC does not assist in debugging, because of the presence of the Radio AGC. However, for APs it indicates if the received signal is too strong or too weak.
Axxcelera Broadband 15 Modem rxdc stats The “hmm modem rxdc stats” command can help to spot intermittent problems with radio links. It displays the number of times the receiver dc offsets were recalibrated, and for what reason, e.g. AP/SU modem rxdc stats 192.168.100.200 hmm> modem rxdc stats TRIGGER : TEMPERATURE FDHDR ERROR CELL ERROR FREQUENCY : 1 0 0 OFFSET I Q : MIN :0 :3 ACK ERROR 0 MAX 0 4 The stats can be reset to zero with the “hmm modem rxdc stats z” command.
Axxcelera Broadband 16 Bun list channels Bun list channels can be used to determine which PVC (SU) traffic is coming from. This command is somewhat obsolete with the introduction of the “pnms sector” command in the 5.2.x and later releases. 192.168.100.
