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Cwte_Wi-Fii6-presentation_dec_7_2021

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Cwte_Wi-Fii6-presentation_dec_7_2021

  1. 1. RF DESIGN CHALLENGES AND TESTING Center of Wireless Technologies Colloquium Technical University of Eindhoven 7th December, 2020 WI-FI6 / 802.11AX
  2. 2. • Masters in Electrical Engineering - Mixed Signal Microelectronics(MSM), TU/E, 2011 • Wireless engineer at TP Vision(formerly Philips TV’s), 2013-2015 – Evaluated the first 802.11ac radio systems for Smart TV product line – Wireless peripherals development (BT audio, RF4CE/BLE remote control) • Systems engineering at Qorvo, 2015-2020 – Wi-Fi- IOT coexistence solutions (patent) – IOT Design win in Amazon products – Wi-Fi filters and FEM development • Wi-Fi Architect at Liberty Global-Current – Looking into Wi-Fi6 based CPE and mesh systems for home segment Love affair with wireless technologies still strong! ABOUT ME 2 MAYUR SARODE
  3. 3. This presentation will highlight Wi-Fi6 RF design challenges and discuss some test results measured with commercial Wi-Fi6 routers. To support new features, Wi-Fi chipset / RFFE* vendors had to make significant improvements on Wi-Fi6 hardware design. Key features promised by Wi-Fi6 standard • OFDM improvement • 1024 QAM modulation (MCS11/10) • OFDMA scheduling • UL/DL MU-MIMO • TWT and BSS coloring PRESENTATION ABSTRACT RFFE: RF Front End 3
  4. 4. THE WI-FI6 PROMISE 4 Graphic source: Wi-Fi alliance
  5. 5. Wi-Fi6 R1 Wi-Fi6E Wi-Fi6 R2 WI-FI TIMELINE 5 2019 2020 2021 UL MU-MIMO Preamble Puncturing 6 GHz spectrum DL/UL OFDMA DL MU-MIMO 2015 DL MU-MIMO Wi-Fi5 802.11n 802.11ac 802.11ax 2009 MIMO Wi-Fi4
  6. 6. FREQUENCY BANDS WI-FI6/E 6 2.4- 2.48 GHZ 5.17-5.33 GHz 5.490-5.835 GHz 5.925 – 6.425 GHz • With the opening up of 6 GHz band, routers/APs moving towards Tri-band architecture – Bandpass filters necessary to separate out the bands • Wi-Fi transceivers need to support 6GHz bands – Separate silicon Vs 5 GHz transceiver update Legacy & IOT Low latency/ high throughput applications Legacy and High throughput applications Dual band Tri band
  7. 7. Wi-Fi6 DESIGN Amplitude Time Spatial Frequency RF PERFORMANCE METRICS 7 Output power Spectral mask/flatness Inter Carrier interference Adjacent channel interfere Antenna isolation Timing drift Carrier Frequency accuracy UL MU-MIMO UL OFDMA 8 spatial streams 1024 QAM OFDM DL-OFDMA
  8. 8. EVM | CFO | SNR SOME TERMINOLOGY 8 EVM -35 dB (MCS11/MCS10) CFO 2.4 GHz: +/- 25 ppm 5 GHz: +/- 20 ppm SNR 35 dB Error Vector Magnitude (EVM) Carrier Frequency Offset (CFO) Signal to Noise Ratio (SNR) SNR
  9. 9. WI-FI IMPAIRMENTS Graphic source: wlanpedia 9 • WI-Fi6 MCS11/10 index mandates a tough -35 dB EVM limit • System design goal – Meet EIRP limits by maximizing transmit power and designing Omni-directional antennas Wi-Fi chipset Front End Module Filtering & Matching Antenna 2.4 GHz X 4 5 GHz X 8 iPA LO leakage TX PATH
  10. 10. • ¼ of 802.11ac Subcarrier spacing – Local Oscillator with low phase noise to minimize ICI – Sensitive to Carrier Frequency Offset • 77% increase in OFDM data channels – Impact on frequency synthesizer/mixer design • 4 times larger FFT size – 160 MHz bandwidth mandatory – 30% more efficient than 802.11ac – Longer symbol duration – Higher power consumption and larger area 802.11 AX OFDM ICI: Inter Carrier Interference FFT: Fast Fourier Transform 10 Sub carrier spacing 312.5 KHz 78.125 KHz FFT size(max) 512 2048 Orthogonal Frequency Division Multiplexing Graphic source: wlanpedia
  11. 11. iPA + RFFE • Wi-Fi6 demands tighter EVM (-43 dB) on Front end PA – Designed to work with 10 dB return loss (VSWR=2:1) antennas • 80/160 MHz bandwidth operation – 0.1 dB amplitude droop causes 6 dB EVM degradation • Higher current to meet linearity requirements→ DPD saves the day! POWER AMPLIFIER 11 Transmit Power→ EVM → PA power profile PA frequency response Source: Litepoint EVM → Amplitude Distortion →
  12. 12. • Allows for significant power savings when used with an external non-linear FEM – Reduces system power consumption for MIMO systems • 7% of the total CPE power budget (0.5W per chain) – Better thermal management for CPE devices • Contribute to smaller and greener CPE devices in the future! DIGITAL PRE DISTORTION 12 Wi-Fi chipset DPD + Non-linear PA External FEM = Wi-Fi chipset implements a PA gain/phase correction algorithm to improve cascaded PA’s linearity FEM: Front End Module Wi-Fi chipset Highly Linear PA
  13. 13. SPECTRAL SHAPING/TX POWER DPD IMPROVEMENTS Source: Qorvo 13 Spectral Shaping • Increase MCS11/10 coverage ( larger TX power) • Improve spectral mask – meet FCC band-edge requirements at higher TX power for channel 1 and 11 TX power improvement
  14. 14. ORTHOGONAL FREQUENCY DIVISON MULTIPLE ACCESS 802.11AX OFDMA 14 User 1 • Resource Units (RU) as small as 2 MHz – 37 simultaneous users in 80 MHz band! • Ideal for applications requiring low latency/jitter • Basis for Preamble puncturing – Potential to improve 80/160 MHz channel utilization RU OFDMA MU- MIMO SU- MIMO Wi-Fi vendor’s special sauce Graphic source: wlanpedia
  15. 15. • RU size is dynamically reconfigured over time • Different MCS rates/output power per user! 802.11AX OFDMA Source: Litepoint 15
  16. 16. • AP adjusts power level for each Resource Unit(RU) • PA’s may need upto 12 dB better linear range to avoid co-channel interference • Degradation in EVM of lowered power RU’s expected OFDMA DOWNLINK Graphic source: Litepoint 16 TX power@AP Resource Units 12 dB
  17. 17. DYNAMIC POWER CONTROL • Similar to 4G LTE uplink communication – GPS guided clocks to sync all devices • 802.11ax AP’s/routers dependent on their own built-in oscillators as the reference – Clients adjust their internal clock and frequency references by extracting offset information via TRIGGER they receive OFDMA UPLINK 17 RX power@AP Users TRIGGER Graphic source: Litepoint RXpower@AP Users Noise floor BEFORE POWER CONTROL AFTER POWER CONTROL
  18. 18. TRIGGER FRAME CONTROL OFDMA UPLINK Graphic source: Litepoint 18 • Inter Carrier Interference causes – Receiver compression, Signal leakage, CFO RSSI accuracy • RSSI measurement accuracy:+/- 2dB • Transmit power accuracy: +/- 3dB Timing/Frequency Error • Transmit within < 0.4 usec relative to TRIGGER frame • Relative Frequency Error< +/-350 Hz (0.07 ppm@ 5.2 GHz) TRIGGER TRIGGER FRAMES ALSO USED in UL MU-MIMO!
  19. 19. TRIGGER DL & UL MU-MIMO 19 • 4 users (2 spatial stream) support on the 5 GHz band – Upto 12 spatial streams ( 4 in 2.4 GHz, 8 in 5 GHz band) • Challenge to integrate many antennas in a small CPE devices – minimum 20 dB antenna-antenna isolation necessary • MU-MIMO uses TRIGGER frames to synchronize uplink from stations RX power@AP Time WI-FI6 TX beamforming Upto 3 dB higher gain More accurate beam steering USER 1 USER 2 USER 3 USER 4 Graphic source: Litepoint freq
  20. 20. OFDM TEST SETUP WI-FI6 PHY TESTING 20 • Fully CONDUCTED black-box test-setup to measure critical PHY level properties of Wi-Fi5/6 design (without antenna) – Data Modulation Code Scheme(MCS) count – Data Error Vector magnitude (EVM) – Carrier Frequency Offset (CFO) – Signal to Noise Ratio (SNR) • Measurements done with MATLAB WLAN tool box – Captures TCP I/Q samples from Spectrum Analyser(SA) • Variable attenuator introduced to induce MCS drop REFERENCE 2.4 GHz Channel 1 HT 20 5 GHz Channel 36 HT40 ASUS RTAX88U Wi-Fi station BLACK BOX testing
  21. 21. TIME DOMAIN • Analysis done on Data packets collected during 25 msec TCP session WI-FI PACKETS Graphic source: Litepoint 21
  22. 22. Sl no PPDU Format Frame Type L-SIG EVM (rms) L-SIG EVM (max) MCS SNR Data EVM Stream 1: (RMS) Data EVM Stream 2: (max) Data EVM Stream 2: (RMS) Data EVM Stream 2: (max) CFO (Hz) PPM Spatial Streams 4 HE-SU ampdu -41.2 -34.4 11 36.12 -0.6 0 -37.3 -28.8 -18694.5 -8 2 12 HE-SU ampdu -40.3 -33.7 11 36.1 -0.6 0 -38.9 -31.4 -18708.2 -8 2 24 HE-SU ampdu -41 -35.1 11 36.48 -0.7 0 -38.4 -29.1 -18654.3 -8 2 37 HE-SU ampdu -39.1 -34.4 11 34.53 -0.6 0 -37.1 -26.7 -18600.8 -8 2 45 HE-SU ampdu -41.5 -34.4 11 33.91 -0.7 0 -37.4 -23.8 -18677.9 -8 2 DATA PACKET ANALYSIS MATLAB SIGNAL PROCESSING 22 EVM/Constellation diagram • Key Wi-Fi6 PHY parameters are measured and averaged over multiple data packets ( >100) MCS 11 constellation diagram MCS 11 Spectral Mask
  23. 23. 0 5 10 15 20 25 30 35 40 45 50 0 6 9 12 15 18 24 27 30 33 36 42 Packets [%] Attenuation [dB] MCS rates ASUS RTAX88U (MU-MIMO/TX beamforming OFF) MCS 11 MCS 10 MCS 9 MCS 8 MCS 7 MCS 6 MCS 5 MCS 4 MCS SELECTION ASUS RTAX88U 23 5 GHz • 10% of the Data packets (HE-SU) are sent on MCS11 index -25 dBm MU-MIMO DISABLED BEAMFORMING DISABLED
  24. 24. EVM ASUS RTAX88U 24 MCS11 MCS 10 MCS 9 MCS 8 MCS 7 MCS 6 MCS 5 MCS 4 MCS 3 MCS 2 MCS 1 MCS 0 -35 -35 -32 -30 -27 -25 -22 -19 -16 -13 -10 -5 802. 11 ax EVM regulatory limit 5 GHz -25 dBm MU-MIMO DISABLED BEAMFORMING DISABLED PASS at all attenuation points NOT PASS at all attenuation points
  25. 25. CFO • CFO well within the spec! ASUS RTAX88U 25 5 GHz MU-MIMO DISABLED BEAMFORMING DISABLED -25 dBm
  26. 26. • Investigate Wi-FI6 receiver performance for adjacent channel rejection. Impact on – BSS color implementation – Dynamic Bandwidth selection • Benchmark RF specs. on Downlink use cases – Introduce butler matrix to test MIMO – Evaluate selection of SU-MIMO, OFMDA, MU-MIMO mode of transmission • Create a “Black box” testing methodology for Uplink uses cases CONCLUSION 26
  27. 27. Same spec but smaller RBW • 802.11 ac: 312.5 RBW • 802.11ax: 78.125 RBW LO LEAKAGE SPEC Source: Litepoint and Rhode & Schwarz 27 Ptot= transmit power per antenna (dBm)
  28. 28. PASS FAIL criteria • CFO – 2.4 GHz:+/- 25 ppm* – 5 GHz: =/- 20 ppm IEEE 802.11AX 28 20 MHz BW spectral mask EVM Vs MCS rate *Parts Per Million
  29. 29. • https://www.litepoint.com/wp-content/uploads/2018/12/PA-Testing-Application-Notes-092517.pdf • https://www.litepoint.com/wp-content/uploads/2019/09/Wi-Fi-6-OFDMA-App-Notes-091319- web.pdf • https://www.qorvo.com/design-hub/technical-articles/the-new-wi-fi-6-standard-combining- software-and-hardware-for-best-in-class-solutions • http://download.ni.com/evaluation/rf/Introduction_to_WLAN_Testing.pdf APPENDIX 29

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