TX performance typically involves a sweep of TX power versus Spectral Emission Mask (SEM) and Error Vector Magnitude (EVM) identifying the maximum transmit power at each EVM limit.
The SEM limit is a function of operating band and bandwidth, while the EVM limit is a function of modulation. Measurement of these requires transmitting modulated packets from the Device Under Test (DUT) and using a Vector Signal Analyzer (VSA) to measure EVM and SEM. The transmit power of the DUT should be swept until either SEM or EVM compliance fails.
The following table summarizes the EVM requirement as a function of modulation for Orthogonal Frequency Division Multiplexing (OFDM) modulation types.
| MCS index | Modulation | Code rate | EVM (dB) |
|---|---|---|---|
| 0 | BPSK | 1/2 | -5 |
| 1 | QPSK | 1/2 | -10 |
| 2 | QPSK | 3/4 | -13 |
| 3 | 16-QAM | 1/2 | -16 |
| 4 | 16-QAM | 3/4 | -19 |
| 5 | 64-QAM | 2/3 | -22 |
| 6 | 64-QAM | 3/4 | -25 |
| 7 | 64-QAM | 5/6 | -27 |
For Direct-sequence Spread Spectrum (DSSS)/Complementary Code Keying (CCK) modulation types, the EVM limit is -9 dB.
Use the Wi-Fi® Radio test sample to control the TX parameters of the DUT. For example, the following sequence transmits an MCS0 IEEE 802.11n packet at 15 dBm on channel 7 in the 2.4 GHz band:
wifi_radio_test init 7
wifi_radio_test tx_pkt_tput_mode 1
wifi_radio_test tx_pkt_mcs 0
wifi_radio_test tx_power 15
wifi_radio_test tx 1To set the next value in sweep (for example, to 16 dBm), use the following sequence:
wifi_radio_test tx 0
wifi_radio_test tx_power 16
wifi_radio_test tx 1