WLAN 802.11n/ac RF PHY Layer Transmitter Testing

This page covers RF and PHY conformance tests for 11n device testing and 11ac device testing. These compliance tests are used for transmitter and receiver measurements of IEEE 802.11n/802.11ac compliant devices. These tests are useful for test and measurements related to 802.11n and 802.11ac products. 802.11ac standard-based products support RF frequencies up to 6GHz and also support MIMO.

Transmitter tests include transmit Spectrum Mask, Spectral Flatness, Center Frequency Tolerance, Packet Alignment, Symbol Clock Frequency Tolerance, and Modulation Accuracy (Center frequency leakage and Constellation EVM). Table 1 (below) mentions the limits for these 11ac transmitter conformance tests.

Transmit Spectrum Mask

• Go through 11ac spectral mask for limits defined for 20 MHz, 40 MHz, 80 MHz, and 160 MHz channel bandwidths.
• The 11ac transmitter device radiation should conform to the defined mask.
• Measurements should be carried out with 100 kHz RBW and 30 kHz VBW.
• 80 + 80 MHz Non-contiguous Spectrum Mask measurement also needs to be done.

Spectral Flatness

• The allowed spectral flatness limit is 2dB from max./min. values.
• This is a measurement of the power of each subcarrier with respect to the average power over a set of subcarriers as per the specified range.
• This is similar to 11n.

Transmitter Relative Constellation Error (RCE) OR Error Vector Magnitude (EVM)

The method is the same as 11n.

• Channel estimation is done using the preamble sequence only.
• Pilot subcarriers are used for phase tracking (or phase rotation).
• A minimum of 16 data symbols are used in a frame, and the RMS average over at least 20 frames is taken.

The following table mentions the EVM limits for different MCS (modulation and code rates).

Table 1: EVM Limits for 802.11n and 802.11ac

11ac Receiver Tests

The receiver tests include Minimum input level sensitivity, Adjacent channel rejection, Non-adjacent channel rejection, and Receiver maximum input level. Table 2 (below) mentions the limits for these 11ac receiver conformance tests.

Min. Input Level Sensitivity

Table 2 (below) mentions the minimum sensitivity levels at various modulation-code rates for different bandwidths as supported by the 11ac device. At the input levels mentioned in the table, PER (Packet Error Rate) should be less than 10% with a PSDU length of 4096 octets. This is for non-STBC modes with an 800ns Guard Interval and BCC coding. Technical specifications are the same as 802.11n with the addition of MCS and Bandwidths specific to 802.11ac.

Table 2: Minimum Sensitivity Levels for 802.11ac

Adjacent and Non-Adjacent Channel Rejection

The following table mentions the limits for adjacent channel rejection and non-adjacent channel rejection for different bandwidths.

Table 3: Adjacent and Non-Adjacent Channel Rejection Limits

| Modulation-code rate | Adjacent channel rejection(dB) | Non-adjacent channel rejection(dB) | | :------------------- | :----------------------------- | :--------------------------------- | ---------------- | --------- | | | 20/40/80/160 MHz | 80+80 MHz | 20/40/80/160 MHz | 80+80 MHz | | BPSK 1/2 | 16 | 13 | 32 | 29 | | QPSK 1/2 | 13 | 10 | 29 | 26 | | QPSK 3/4 | 11 | 8 | 27 | 24 | | 16QAM 1/2 | 8 | 5 | 24 | 21 | | 16QAM 3/4 | 4 | 1 | 20 | 17 | | 64QAM 2/3 | 0 | -3 | 16 | 13 | | 64QAM 3/4 | -1 | -4 | 15 | 12 | | 64QAM 5/6 | -2 | -5 | 14 | 11 | | 256QAM 3/4 | -7 | -10 | 9 | 6 | | 256QAM 5/6 | -9 | -12 | 7 | 4 |

The following test procedure is followed to determine adjacent channel rejection and nonadjacent channel rejection:

1. Set the desired signal to 3dB higher than the min. sensitivity level.
2. Apply an interfering signal of the same bandwidth as the desired signal in the adjacent or nonadjacent frequency. The interfering signal should be OFDM compliant with a 50% min. duty cycle.
3. Increase the power of the interfering signal until a PER value of 10% is achieved. Set the length of the PSDU equal to 4096 octets.
4. The power difference at the output between the interfering signal and the desired signal is the rejection as needed.

11n, 11ac RF PHY Layer Conformance Testing Solutions

The following test and measurement instruments are ideal for conformance testing of 802.11n and 802.11ac products. These are useful for 11n/11ac device testing and measurements. These RF and baseband instruments are ideal for 11n/11ac RF and PHY conformance testing or compliance testing. The solutions are packaged into 802.11ac signal generation and signal analysis hardware as well as software.

Table 4: 802.11n/ac Conformance Testing Solutions