Here we have screen shot path profile for PTP 550, the radios are 49 km in range and have channel bonding enabled with Two 40 MHz channel size selected, the overall throughput is 490 Mbps , however the actual radio in the field were deployed in two 20 MHz since they could not find clean 40 MHz channels. Hence we will assume LINKPlanner predicts 245.3 Mbps with two 20 MHz Channel
LINKPlanner Profile
From spectrum analyzer we can see there are not many 40 MHz opportunities. Using traditional single radio, the operator would have been force to use 30 or 20 MHz single radio. Here using channel bonding two 20 MHz are configured.
Wireless Throughput Link Test
Here, we have Wireless link test results; topline throughput is 217 Mbps compared to LINKPlanner profile which suggests 245 Mbps
Here are some reason why there are gaps and how to close them gap and make accurate predication
- Making Correction to LINKplanner project: There are many fields like Tx Power, Interference, Max modulation rate, that have default options filled in. However by adding correct field such as Interference level, Max modulation mode obtained from radio, the LINKPlanner will start to predict more accurately.
- Review MCS Rates on Radio: In Wireless Link Test , we have MCS Downlink/Uplink mentioned , here we observe that radio DL/UL is not always on DS9 it fluctuates between DS9 to DS7, more percentage breakdown can be viewed in Monitor-> Performance Data to get a more clearer understanding on the level of interference
- ARQ in PTP 550: ARQ retry mechanism is used between the radios to ensure all packet pass through successfully. LINKPlanner does not account for this re-transmission of packets, if for example there are lot of packets drops, then all those packets need to be re-transmitted again. Hence the overall throughput will drop from expected number. This packet loss information can also be found in Monitor -> Performance Data section.
- Understanding SNR vs SINR: SNR (Signal to Noise Ratio), in this we only consider RSSI and noise floor level, it does not consider Interference level which varies with time. SINR (Signal to Interference Noise Ratio) takes current interference level at center frequency and calculated SINR (see attached spectrum analyzer image to show difference between Noise level and Interference level), we will have another post covering this topic in detail soon. Having high SNR and low SINR indicated high interference environment.
Spectrum Analyzer
|
Radio |
RSSI |
Noise Floor Level |
Interference level |
SNR (RSSI-Noise Level) |
SINR (RSSI-Interference Level) |
|
Radio 1 |
-57 |
-93 |
-83 |
36 |
26 |
|
Radio 2 |
-59 |
-96 |
-84 |
37 |
25 |
In future, we will be covering more section, such as what does the right bar in spectrum analyzer mean and how we can use it to analyze the network.
Thanks
Sagar