Test-and-Measurement » Wi-Fi 8 EVM & RCPI Accuracy: 802.11bn Test & Measurement

Wi-Fi 8 EVM & RCPI Accuracy: 802.11bn Test & Measurement

wifi 8 evm error vector magnitude rcpi accuracy wi-fi 8 wlan test and measurement

Introduction : In the quest for Ultra-High Reliability (UHR), Wi-Fi 8 (IEEE 802.11bn) places unprecedented demands on hardware performance. While previous generations allowed for some margin of error, the complex modulation schemes and multi-access point coordination in Wi-Fi 8 require extreme precision in signal generation and power reporting. Two critical metrics for conformance are Error Vector Magnitude (EVM) and Received Channel Power Indicator (RCPI) accuracy.

Wi-Fi 8 EVM (Error Vector Magnitude)

EVM is a measure of modulation quality and error. It quantifies how far the actual captured signal constellation points are from their ideal “perfect” positions. In Wi-Fi 8, high EVM can lead to packet loss, reducing the very reliability the standard aims to achieve.

Wi-Fi 8 introduces four new Modulation and Coding Schemes (MCS 17, 19, 20, and 23) to fill the SNR gaps between legacy levels. Testing EVM for these levels ensures that the hardware can handle the finer grained rate adaptation without introducing noise. Following table EVM requirements to be met by Wi-Fi 8 hardware devices and Access Points.

EVM Compliance Limits

ModulationCoding RateWi-Fi 8 MCSEVM Limits (non-ELR MU PPDU)
BPSK1/20-5 dB
QPSK2/317 (New)-12 dB
16QAM5/620 (New)-20 dB
256QAM3/423 (New)-30 dB
1024QAM5/611-35 dB
4096QAM5/613-38 dB

Note: For Enhanced Long Range (ELR) PPDUs, the limits are significantly relaxed to -4 dB (BPSK) and -5 dB (QPSK), as these modes prioritize signal “reach” over density.

RCPI (Received Channel Power Indicator) Accuracy

While Wi-Fi has used RSSI (Received Signal Strength Indicator) for years, RSSI is often a proprietary, uncalibrated relative value. RCPI is a standardized, absolute measure of the received RF power in dBm.

Wi-Fi 8 Requirement: IEEE 802.11bn is the first standard to introduce a mandatory PHY layer requirement to test the accuracy of RCPI. The device must measure power specifically over the UHR-STF (Short Training Field) or UHR-LTF (Long Training Field) and report the average power across all active receive chains.

RCPI Compliance Limits:

  • Accuracy Requirement: The reported RCPI value must be accurate within +/- 5 dB.
  • ELR Adjustment: For ELR PPDUs, the reported value must be 3 dB less than the measured power (to account for the 3 dB power boost in the preamble fields).

Wi-Fi 8 Test tool providers

Wi-Fi 8 Solution ProviderKey offeringsPurpose
Rohde & SchwarzCMP180 / CMX500Non-signaling and signaling testers for high-speed EVM measurement and RCPI validation.
KeysightM9484C VXG / N9021B MXAHigh-performance signal generators and analyzers with dedicated Wi-Fi 8 (802.11bn) software options.
LitePointIQxel-MW 7GA industry-standard tester for production environments, optimized for 802.11be (Wi-Fi 7) and early 11bn (Wi-Fi 8).
AnritsuMT8862AWireless Connectivity Test Set designed for testing the actual performance of Wi-Fi devices in a signaling mode.
National InstrumentsPXIe-5841 (VST)Vector Signal Transceivers used for lab-grade research and characterization of Wi-Fi 8 chipsets.

References for further study

  1. IEEE P802.11bn Draft Amendment
  2. Rohde & Schwarz White Paper - Setting New Performance Standards with IEEE 802.11bn Version 2.00
  3. IEEE 802.11-2020 Standard
  4. Wi-Fi Alliance UHR Marketing Requirements