The IEEE 802.11 Standard specifies a minimum receiver sensitivity that all 802.11 devices must achieve. This sensitivity is specified as a receive power (in dBm) in which a device must achieve no worse than a 10% packet-error-rate (PER) for PPDU receptions of 1000 octets. The receiver minimum input sensitivity requirements are specified in Section 22.214.171.124 of 802.11-2012 and are reproduced here:
|Rate||Modulation / Coding||Minimum Sensitivity (dBm)|
|6 Mbps||BPSK 1/2||-82|
|9 Mbps||BPSK 3/4||-81|
|12 Mbps||QPSK 1/2||-79|
|18 Mbps||QPSK 3/4||-77|
|24 Mbps||16-QAM 1/2||-74|
|36 Mbps||16-QAM 3/4||-70|
|48 Mbps||64-QAM 1/2||-66|
|54 Mbps||64-QAM 2/3||-65|
The values specified in this table recognize that higher rate transmissions require higher SNR (and therefore higher delivered power) than lower rate transmissions.
Receiver Sensitivity Test
To test the Mango 802.11 Reference Design Rx PHY against these measures, we use the Keysight N4010A Wireless Connectivity Test Set to generate known-good 1000 octet transmissions and deliver those transmissions to WARP v3 at a specified power. Then, we use the WLAN Experiments Framework to measure PER.
- Construct PPDU waveforms in MATLAB for each PHY rate that have the following characteristics:
- 1000 octet PPDU length (i.e., a 972 byte payload + 14 byte MAC header + 4 byte FCS)
- 10 different scrambling sequence start points to generate waveforms with different peak-to-average-power (PAPR) features
- Load each waveform in to the N4010A's volatile memory as segment files.
- Create N4010A sequence files that send each waveform segment 1000x in a row
- Use WLAN Experiments Statistics to determine how many of the transmissions were fully received with a good FCS.
We have used the above steps determine the Mango 802.11 Reference Design's receive sensitivity across 7 different WARP v3 kits and RF interfaces.
The above plots shows the results of this experiment. In particular, notice the receive powers that cross the 10% PER horizontal line -- these can be compared directly to the minimum sensitivity values specified by the standard. Specifically,
|Rate||Modulation / Coding||Minimum Sensitivity (dBm)||Mango 802.11 Sensitivity (dBm)||Difference|
|6 Mbps||BPSK 1/2||-82||-85||3dB better than minimum|
|9 Mbps||BPSK 3/4||-81||-83||2dB better than minimum|
|12 Mbps||QPSK 1/2||-79||-83||4dB better than minimum|
|18 Mbps||QPSK 3/4||-77||-81||4dB better than minimum|
|24 Mbps||16-QAM 1/2||-74||-78||4dB better than minimum|
|36 Mbps||16-QAM 3/4||-70||-75||5dB better than minimum|
|48 Mbps||64-QAM 1/2||-66||-71||5dB better than minimum|
|54 Mbps||64-QAM 2/3||-65||-69||4dB better than minimum|
Rx Power Accuracy
Because the N4010A lets us accurately specify a power level at which a transmission is delivered to the antenna port of WARP v3, we can also test the Mango 802.11 Reference Design's ability to estimate receive power from the transceivers RSSI circuit.
The above plot shows measured receive power vs. actual receive power controlled by the N4010A. Each line represents a different WARP v3 kit and frequency band (2.4GHz or 5GHz).