Spectral Control Issues for TGg May 2002 Spectral Control Issues for TGg Steve Halford Michael Seals Mark Webster Jim Zyren Steve Halford, Intersil

Motivation for Spectral Control May 2002 Motivation for Spectral Control Adjacent Channel Interference Number of comments in LB33 on ACI OFDM to OFDM, OFDM to CCK, CCK to OFDM Issue also raised in January 802 meeting See IEEE 802.11-02/043 & 044 FCC Forbidden Band Compliance A few comments in LB33 question FB compliance DOC 02/220r0 showed +20 dBm possible for OFDM This document presents some follow up to support 02/220 Steve Halford, Intersil

Adjacent Channel Interference May 2002 Adjacent Channel Interference Interference depends on Tx spectrum & power Receiver reduces with filtering & processing 802.11a spacing is 20 MHz Mask allows for more ACI than 802.11b Need to ‘skip’ adjacent channels for adjacent AP’s ACI/ACR issue is not as critical Physical separation will reduce interference 802.11b spacing is 25 MHz Fewer channels so cannot avoid adjacent freq ACI/ACR is important issue to resolve Affects 802.11g & legacy 802.11b systems Steve Halford, Intersil

Approaches for ACI Spectral Mask… or, Adjacent Channel Rejection Test… May 2002 Approaches for ACI Spectral Mask… TGg draft uses 802.11b for Barker/CCK & PBCC modes TGg draft uses 802.11a mask for OFDM Different spacing & number of channels provides motivation to consider a different mask? or, Adjacent Channel Rejection Test… Specifies the level of adjacent channel interference tolerated by receiver 802.11a also specifies an alternate channel rejection Spectral Mask Advantages Approach is implementation independent Protects legacy systems from interference Steve Halford, Intersil

Spectral Control via Masks May 2002 Spectral Control via Masks TGg Draft Spec allows for two different mask Both masks are relative to peak of the main lobe Picture of Masks Steve Halford, Intersil

May 2002 Simulation Model Used Steve Halford, Intersil

Power Amplifier Model P_sat= 24.2 dBm P_1dB = 21.5 dBm May 2002 Steve Halford, Intersil

802.11a Mask Limit for OFDM Measured EVM = -12.55 dB (measured for May 2002 802.11a Mask Limit for OFDM Measured EVM = -12.55 dB (measured for BPSK modulation) Back-off from 1-dB Compression Point= 1.59 dB Back-off from Saturation Point= 4.29 dB Steve Halford, Intersil

May 2002 ACI Results for 802.11a Mask Receive Filter Spectral Response Transmit Spectrum PSD of Received Adjacent Channel Signal Main Channel Receives -12.6 dBm from Adjacent Channel Adjacent Channel Rejection = 32.6 dB Steve Halford, Intersil

802.11b Mask Limit for QPSK Back-off from 1-dB Compression May 2002 802.11b Mask Limit for QPSK Back-off from 1-dB Compression Point= 1.15 dB Back-off from Saturation Point= 3.85 dB Steve Halford, Intersil

May 2002 ACI Results for QPSK Receive Filter Spectral Response Transmit Spectrum PSD of Received Adjacent Channel Signal Main Channel Receives -19.4 dBm from Adjacent Channel Adjacent Channel Rejection = 39.74 dB Steve Halford, Intersil

Comparison of ACI Results May 2002 Comparison of ACI Results Waveform Power out (dBm) ACI (dBm) ACR (dB) Limit OFDM 19.91 -12.66 32.57 .11a Mask QPSK 20.35 -19.39 39.74 .11b Mask Output power for OFDM near that of QPSK About 0.45 dB added back-off More forgiving mask of OFDM increases ACI About 6.5 dB more than current 802.11b Are changes needed to protect 802.11b? Steve Halford, Intersil

Solutions to reduce ACI May 2002 Solutions to reduce ACI Could increase ACR spec for .11g Helps future 802.11g systems Doesn’t help current 802.11b radios Adopt a different spectral mask Select mask to control amount of ACI Protects legacy 802.11b networks Will reduce the total output power Steve Halford, Intersil

Meeting mask corners requires large back-off May 2002 Why not use .11b mask? Suggested by several voters Shape was selected to fit single carrier Corners of mask too restrictive for OFDM Requires a back-off of 6.64 from 1 dB compression Resulting ACI is -34.72 dBm (15 dB less than QPSK) Meeting mask corners requires large back-off Steve Halford, Intersil

From Comment #123-127 under Clause 19 Tab IEEE DOC 802.11-02/209r6 May 2002 Karaoguz Mask Mask proposed in LB 33 comments Proposed by J. Karaoguz, C. Hansen, & others From Comment #123-127 under Clause 19 Tab IEEE DOC 802.11-02/209r6 “First, the transmit spectral mask of the OFDM signal should be modified such that the transmitted spectrum shall have a 0 dBr bandwidth not exceeding 18 MHz, -30 dBr at 11 MHz frequency offset, -38 dBr at 20 MHz frequency offset, and -47 dBr at 30 MHz frequency offset and above.” Steve Halford, Intersil

Results for Karaoguz Mask May 2002 Results for Karaoguz Mask Back-off from 1-dB Compression Point= 5.8 dB Back-off relative to .11a mask = 4.2 dB ACI reduced to -28.2 dBm-- 8.8 dB below QPSK ACI Steve Halford, Intersil

Potential 802.11g OFDM Mask 0 dB for -9 to 9 MHz May 2002 Potential 802.11g OFDM Mask 0 dB for -9 to 9 MHz 20 dB down by 11 MHz offset 50 dB down by 29.5 MHz offset Steve Halford, Intersil

Results for proposed mask May 2002 Results for proposed mask Back-off from 1-dB Compression Point= 3.0 dB Back-off relative to .11a mask = 1.4 dB ACI reduced to -19.4 dBm -- Equal to QPSK ACI Steve Halford, Intersil

Proposed Mask: J. Karaoguz May 2002 ACI with Various Mask Waveform Power out (dBm) ACI (dBm) ACR (dB) Limit OFDM 18.50 -19.41 37.91 Proposed .11g Mask 15.68 -28.2 42.98 Proposed Mask: J. Karaoguz 19.91 -12.66 32.57 .11a Mask 14.22 -34.74 48.94 .11b mask QPSK 20.35 -19.39 39.74 .11b Mask Proposed masks lower ACI to same or better level than 802.11b Proposed masks fit OFDM better than .11b Output power is reduced by 1.4 dB in our mask Still have better theoretical range than 802.11a Steve Halford, Intersil

May 2002 EVM Limits Steve Halford, Intersil

Error Vector Magnitude May 2002 Error Vector Magnitude Specification on the transmit quality Mean Square Receiver of the constellation at receiver Requirement depends on data rate For many data rates, EVM limits transmit power more than mask Data Rate Relative Error (dB) 6 -5 9 -8 12 -10 18 -13 24 -16 36 -19 48 -22 54 -25 Steve Halford, Intersil

EVM Limits This limit applies to center channel & edge channels May 2002 EVM Limits Waveform Power out (dBm) EVM (dB) Added Back-off Over .11a mask OFDM -- 54 Mbps 15.73 -25.34 4.18 OFDM -- 48 Mbps 16.98 -22.23 2.93 OFDM -- 36 Mbps 17.99 -19.14 1.92 OFDM -- 24 Mbps 19.15 -16.05 0.76 This limit applies to center channel & edge channels Steve Halford, Intersil

Back-off from 1 dB compression May 2002 Summary of Results Waveform Power out (dBm) ACI (dBm) Back-off from 1 dB compression (dB) Limit QPSK 20.35 -19.39 1.12 .11b channel OFDM -- 54 Mbps 15.73 -25.34 5.77 EVM OFDM -- 48 Mbps 16.98 -22.77 4.52 OFDM -- 36 Mbps 17.99 -19.65 3.51 OFDM -- 24 Mbps 18.50 -19.41 3.00 Proposed Mask OFDM -- 18 Mbps OFDM -- 12 Mbps OFDM -- 9 Mbps OFDM -- 6 Mbps Steve Halford, Intersil

May 2002 Forbidden Band & OFDM Steve Halford, Intersil

Forbidden Band Limits FCC Limits power into forbidden bands May 2002 Forbidden Band Limits FCC Limits power into forbidden bands Average Power must be less than -41.25 dBM/MHz 47 CFR 15.205 & 15.209 Two ‘edge’ channels are 22 MHz & 21.5 MHz away from forbidden bands Channel 1 (2412 MHz) -- 22 MHz away Channel 11 (2462 MHz) -- 21.5 MHz away Steve Halford, Intersil

802.11b FB Compliance .11b mask provides a ‘guide’ to meeting May 2002 802.11b FB Compliance .11b mask provides a ‘guide’ to meeting Mask Compliance = FB Compliance some cases 3-dB of Margin often used for FCC testing -- Allows for process variations Back-off from 1-dB compression point = 2.67 dB Back-off from full saturation = 5.37 dB Steve Halford, Intersil

OFDM & FB Compliance Back-off from 1-dB compression point = 5.57 dB May 2002 OFDM & FB Compliance Back-off from 1-dB compression point = 5.57 dB 3-dB of Margin often used for FCC testing -- Allows for process variations Back-off from full saturation = 8.23 dB Additional back-off of 2.86 dB over QPSK Additional back-off of 3.94 dB over 802.11a mask Steve Halford, Intersil

Conclusions 802.11a mask not optimal @ 2.4 GHz May 2002 Conclusions 802.11a mask not optimal @ 2.4 GHz 802.11b mask is too restrictive for OFDM Our proposed mask reduces ACI to same level as 802.11b Requires 1.4 dB back-off over 802.11a mask EVM requirements already restrictive for some rates OFDM will satisfy Forbidden Band Back-off of 2.86 dB relative to QPSK Steve Halford, Intersil