RSSI and power levels (dBm) report lower than expected value

RSSI and power levels (dBm) report lower than expected values

TITLE: RSSI and power levels (dBm) report lower than expected values

PRODUCTS: Canopy AP's, SM's, 10/20 Mbps BH's


PROBLEM DESCRIPTION: RSSI and dBm values displayed are less than expected when performing installations with new radios. Reports from the field show that newer radios report 10-15 dB less than older installations located in the same physical area. The power is reported less however the Jitter, link efficiency, and throughput are not.

HOW to TROUBLESHOOT: Compare older and newer installation results. Note that the installations must be physically near each other and registered to the same AP. You may not get completely accurate comparisons unless you bring two radios to the same location for the comparison.

HOW ISSUE WAS RESOLVED/WORK AROUND: dBm and RSSI will vary for each radio. Do not rely only on dBm and RSSI to determine if you will perform an installation. In addition, do not mistake link quality for dBm & RSSI values. The key is to get the jitter as low as possible and the efficiency over 90% in 2-level communication (1X). It is recommended that you get the best possible link efficiency in 1x mode prior to enabling 2x.

Motorola Canopy suggests that when performing the installation you focus on the lowest jitter value. Notice, some adjustments will lower the initial power but it may also lower the jitter (this is a good thing). After achieving the lowest jitter then perform a link test to get the link efficiency. There may be further adjustments to get the efficiencies above 90% so perform those while also monitoring the jitter. Once these two values achieve the maximum potential you will want to document the power & RSSI.

**Again, you may notice a 10-15 dB difference but this shouldn't be cause for alarm. The important thing is that with each installation you document the jitter, efficiency, dBm, and RSSI. After the installation is complete you can only bench mark this link against itself. It is not unlikely that you will see a 10-15 dBm differential in areas where you have other installations. The data you record during the installation for the link can be used as a reference if the customer reports an issue with their link. With this data you may be able to see what possibly changed after installation when the radio had its best values.

Regarding 2x link efficiency; you may find that it is difficult to gauge the link quality in 2x when it states <90% and you are use to 90-100% (1X) benchmarks. It is recommended that when reviewing link tests in 2x you look at the throughput. If you are passing more data in 2x than in 1x then you should keep the link at 2x. If the link is reporting 40-70% and passing less traffic in 2x than in 1x then it is best to keep it at 1x and work towards 100% efficiency. Keep in mind that Canopy doesn't pass errored packets so a poor efficiency in 2x while passing twice the traffic and keeping jitter low is the goal for 2x installations. The difference between the two efficiencies is that 2x has a higher Bit Error Rate (BER) than 1x.