REG : [LAA-WiFi coexistence] How wifi will sense channel busy in presense of Wifi and in presence of LTE?

[saumil shah]

Dear All,

I am working on study of LAA-Wifi coexistence. Lets consider 2 scenarios.
Scenario 1 ) Operator A - LTE and Operator B - wifi
Scenario 2 ) Operator A - wifi and Operator B - wifi

In the first scenario wifi will defer to LTE node if received power from LTE node will be higher than -62 dbm as it's a different technology.
In second scenario wifi will defer to another wifi AP if received power will be higher than -82 dbm and not -62 dbm , right?

What i mean by defer is that node finds channel busy and will not transmit to prevent collision when other node is transmitting.

But when i am running simulation with scenario 2 i found from phy_log that from one AP to another AP rxpower is -67.36 dbm. So as per my understanding both AP should defer to each other and they will transmit almost half of the time and throughput should be almost half of what is maximum throughput.

----Signal arrival Log--------
#time(s) nodeId type sender endTime(s) duration(ms)     powerDbm
2.014007945 0 wifi 1 2.014059945 0.052000000 -67.365724283
2.014007945 2 wifi 1 2.014059945 0.052000000 -72.377338385
2.014007945 3 wifi 1 2.014059945 0.052000000 -47.028696637

2.056835523 1 wifi 0 2.057039523 0.204000000 -67.365724283
2.056835523 3 wifi 0 2.057039523 0.204000000 -79.066971121
2.057195523 2 wifi 0 2.057239523 0.044000000 -43.046879651

Node 0 and Node 1 are APs and as we can see from above log that from one to another AP rxpower is -67.36 dbm. Though they are differing, i am getting quite high throughput around 50 Mbps as shown below.

Running simulation for 10 sec of data transfer; 12 sec overall
Operator A: Wi-Fi; number of cells 1; number of UEs 1
Operator B: Wi-Fi; number of cells 1; number of UEs 1

Total txop duration: 0 seconds.
Total phy arrivals duration: 0 seconds.
--------monitorA----------
Flow 1 (11.0.0.1:49153 -> 17.0.0.2:9) proto UDP
Tx Packets: 63327
Tx Bytes: 94990500
TxOffered: 75.9924 Mbps
Rx Bytes: 63478500
Throughput: 50.7828 Mbps
Mean delay: 94.3117 ms
Mean jitter: 0.152057 ms
Duration: 9.94295 s

Rx Packets: 42319

--------monitorB----------
Flow 1 (12.0.0.1:49153 -> 18.0.0.2:9) proto UDP
Tx Packets: 63545
Tx Bytes: 95317500
TxOffered: 76.254 Mbps
Rx Bytes: 64008000
Throughput: 51.2064 Mbps
Mean delay: 93.6147 ms
Mean jitter: 0.150181 ms
Duration: 9.97711 s

Rx Packets: 42672

Can anyone help me understand this behavior ? Or my understanding is wrong?

Best Regards
Saumil Shah

[Rediet]

Hello Saumil,

When using the code, I had noticed that it didn't use the PreambleThreshold attribute (maybe because the aim wasn't to check Wi-Fi <-> Wi-Fi sensitivity). So there isn't the -82dBm limit; it is as if Wi-Fi STAs/APs had ideal preamble detectors.

As for the observed 50 Mbps, I don't see the problem with it since you only have one STA per BSS. With a total of 2 DL transfers over both BSSs you should have a little less than half the total throughput that a single STA would have (since they are within deferal range). This is the case since it's around 100/120 Mbps for 1 STA in 11n.

Rediet

[saumil shah]

Hello Rediet,

Thank you for clearing the preamble threshold attribute doubt. I also agree both BSSs are within the deferral range so throughput should be little less than half.

As per standard i think for 802.11n max throughput without MIMO is 65 Mbps for 20 MHz bandwidth with long guard interval and in my simulation i am using SISO channel only with 1 transmitter and 1 receiver. So why i was expecting throughput around 30 Mbps as it is little less than half the total throughput single STA would have.

Best Regards
Saumil Shah

[Rediet]

Strange indeed. Try performing step by step debug, while focusing on how the PHY has been configured. Maybe there is something that's overwriting your parameters. 

Best Regards
Saumil Shah