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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks ( WPANs )

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks ( WPANs ) Submission Title: [ FSK PHY Channelization and Data Rate Proposal ] Date Submitted: [March 19th, 2013] Source: [Andy Bottomley] Company [ Microsemi ]

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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks ( WPANs )

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  1. Project: IEEE P802.15Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [FSKPHYChannelization and Data Rate Proposal] Date Submitted: [March 19th, 2013] Source: [Andy Bottomley] Company [Microsemi] Address [15822 Bernardo Center Dr, Ste B, San Diego, CA, 92127] Voice:[+01-858-675-3485] FAX :[+01-858-675-3450] E-Mail:[andy.bottomley@microsemi.com ] Re: [In response to TG4q PAR] Abstract: [] Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15. Andy Bottomley (Microsemi)

  2. FSKPHY Recommendation • To facilitate ultra low power 802.15.4q devices powered by coin-cell batteries and/or energy harvesting, it is recommended that an FSK PHY is adopted. • Adoption of an FSK PHY would be in-line with current PHY amendments (802.15.4g & 802.15.4k) • This presentation proposes channel spacing, data rates and modulation indexes for 802.15.4q Andy Bottomley

  3. Channel Spacing Proposal • Channel spacing of 500kHz can support data rates of 400kbps facilitating low energy per bit data transfer • Higher data rates can provide lower energy per bit at the expense of higher peak power. A data rate of 400kbps provides a good compromise between low peak power and low energy per bit (see #15-13-0052-00-004q). Above 400kbps the peak power increases with a diminishing improvement in overall energy per bit). • Channel spacing of 250kHz can support 200kbps & supports more channels and improved sensitivity modes • Both 500kHz & 250kHz channel spacing coexist well with O-QPSK 2MHz channel spacing Andy Bottomley

  4. Modulation Index Definition Review • fd = max peak deviation frequency • h = modulation index • M = 2 or 4 (2-FSK or 4-FSK) • Example of 2-FSK & 4-FSK with the same modulation index and same data rate Andy Bottomley

  5. The Choice of 2-FSK or 4-FSK • 2-FSK or 4-FSK could both be used for the 400kbps ‘Low Energy Mode’ (2-FSK 400ksps & 4-FSK 200ksps) • The 99% occupied bandwidth of 2-FSK or 4-FSK @ 400kbps is approximately the same with a modulation index of 0.7 • The Eb/No is the same with a modulation index of 0.7 • The digital timing recovery may consume a little less current when supporting a 4-FSK symbol rate of 200ksps compared to a 2-FSK symbol rate of 400ksps but this may be offset by the extra complexity required to support a multi-level system • As there appears to be no significant performance benefit in using 4-FSK over 2-FSK it is proposed that 2-FSK is used for all modes Andy Bottomley

  6. Channel filter 3dB double side bandwidth = 500kHz • 3rd order Butterworth channel filter • BT = 1 • 0.7 is the optimal modulation index for an Eb/No of 9.2dB at 0.1% BER Andy Bottomley • Eb/No Sweep of Modulation Index for 2-FSK400kbps ‘Low Energy Mode’

  7. Eb/No Sweep of Modulation Index for 2-FSK 200kbps Mode • Channel filter 3dB double side bandwidth = 250kHz • 3rd order Butterworth channel filter • BT = 1 • 0.7 is the optimal modulation index for an Eb/No of 9.2dB at 0.1% BER Andy Bottomley

  8. BT = 1 Andy Bottomley • Occupied Bandwidth vs Modulation Index for 2-FSK400kbps mode • Occupied bandwidth increases with modulation index

  9. BT = 1 Andy Bottomley • Occupied Bandwidth vs Modulation Index for 2-FSK 200kbps mode • Occupied bandwidth increases with modulation index

  10. 2-FSK, 400kbps, Modulation Index 0.7 2-FSK, 200kbps, Modulation Index 0.7 • Modulation Index Summary • Modulation index of 0.7 provides best Eb/No performance: • 9.2dB Eb/No at 1e-3 BER for 2-FSK 200kbps mode, BT=1 • 9.2dB Eb/No at 1e-3 BER for 2-FSK 400kbps mode, BT=1 Andy Bottomley

  11. Further Consideration for Modulation Index Selection • The Modulation Index may be reduced in order to tighten up the transmitted spectrum at the expense of sensitivity degradation • Local regulations may restrict the minimum ACPR (Adjacent Channel Power Ratio) or band edge power levels? Using a lower BT=0.5 or adding a guard band may be required • The choice of frequency offset in the channel due to Xtal variations should be considered once a specification has been agreed upon. • 802.15.4-2011 section 15.3.3 states a GFSK 950MHz symbol rate accuracy of +/-40ppm • 802.15.4g draft v7 provides an equation for specifying the transmitter frequency tolerance as a function of symbol rate, modulation index and carrier frequency. The maximum frequency tolerance is +/-50ppm. • Ability of the system to reject adjacent and alternate channel interferers (see next slide) Andy Bottomley

  12. Adjacent Channel & Alternate Channel Rejection Requirements • 802.15.4-2011 specifies 0dB & 24dB ACR & ALTCR using a modulated interferer • 802.15.4g draft v7 specifies 10dB & 30dB ACR & ALTCR using a CW at centre of channel • Simulation results in the next slide are used to guide the requirement chosen for 802.15.4n Andy Bottomley

  13. ACR& ALTCRSimulation Results for 2-FSK200kbpsMode, 250kHzChannelization • Conditions: BT = 1, modulation index 0.7 (99% occupied bandwidth 291kHz), 3rd order Butterworth channel filter 250kHz +/-10%, the modulated interferer is the same as the wanted signal • Both the modulated and CW interferer rejection requirements are met • The margin for passing the modulated interferer is small Andy Bottomley

  14. Proposal for Channel Rejection Specification • Based on the simulation results it is recommended that the 802.15.4g rejection specification is used: ACR 10dB & ALTCR 30dB using a CW interferer • This facilitates a simple 3rd order channel filter with +/-10% bandwidth tolerance and offers some margin in meeting the interferer requirements when a modulation index of 0.7 is used Andy Bottomley

  15. Note 1: A spreading factor of 8, 4 & 2 is to be offered for this mode as an alternative way to generate lower data rates and spread the spectrum Andy Bottomley • Summary of FSK PHY Proposal • 500kHz channelization to support 400kbps ‘Low Energy Mode’ • 250kHz channelization to support greater number of channels • Spreading option to provide extra robustness to interference • Gaussian filter with BT=1 (lower BT could be possible)

  16. 4-FSK, 400kbps, Modulation Index 0.7 2-FSK, 400kbps, Modulation Index 0.7 Supporting Slides Andy Bottomley

  17. Comparing Occupied Bandwidth vs Modulation Index for 2-FSK 400kbps & 4-FSK 400kbps • At a modulation index of 0.7 the 99% emission bandwidth is similar Andy Bottomley

  18. 4-FSK 400kbps (200ksps) Modulation Index Sweep Andy Bottomley

  19. 4-FSK 400kbps (200ksps) Occupied Bandwidth with Modulation Index Andy Bottomley

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