IEEE 802.11-18/0101r0 TSF Timer Accuracy Discussion
Delve into the discussion surrounding the TSF timer accuracy requirement in the IEEE 802.11-18/0101r0 document, focusing on the proposed inclusion of the TSF timer in WUR beacons for synchronizing with AP timers. The need for high-precision reference oscillators, specific clock frequencies, and the implications of maintaining TSF timer accuracy within 100 ppm are explored.
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Jan. 2018 doc.: IEEE 802.11-18/0101r0 Discussion on TSF Date: 2018-01-10 Authors: Name Affiliations Address Phone email Ming Gan ming.gan@huawei.com David Xun Yang Huawei Technologies, Co. LTD. Submission Slide 1 Ming Gan et al. (Huawei)
Jan. 2018 doc.: IEEE 802.11-18/0101r0 Introduction TSF timer is proposed to be included in WUR beacon [1-3] It helps the WURx synchronize to the AP s timer Current spec. states that the accuracy of the TSF timer shall be no worse than 100 ppm In this contribution, we focus on The TSF timer accuracy requirement Submission Slide 2 Ming Gan et al. (Huawei)
Jan. 2018 doc.: IEEE 802.11-18/0101r0 TSF timer accuracy To keep high transmit center frequency and symbol clock, a high- precision reference oscillator is required for every 802.11 PHY The worse accuracy shall be less than 20 ppm~25 ppm Typical reference clock frequencies are 22 or 44 MHz (802.11b), and 20, 40 or 80 MHz (802.11a or 802.11g) At the beginning, 1588 in the upper layer was proposed to maintain timer in the MAC layer To further reduce power and cost, the MAC-layer TSF timer is derived from a separate reference oscillator Generally speaking, the TSF is based on a 1-MHz clock and "ticks" in microseconds. Each STA maintains a TSF timer with modulus 264counting in increments of microseconds non-DMG STA s TSF timer shall be accurate to within 100 ppm Submission Slide 3 Ming Gan et al. (Huawei)
Jan. 2018 doc.: IEEE 802.11-18/0101r0 TSF timer accuracy Extreme low power oscillator (LPO) The 32.768 kHz LPO clock is used when the STA stays in doze state where the radio, analog domains, and most of the linear regulators are powered down. It allows the power management sequencer to wake-up the chip and transition to Active mode. A maximum drive level is of a mere 1 uW [6] However, LPO still can keep the frequency stability less than 100 ppm based on the existing commercial oscillator datasheets [5] Some LPO accuracy even goes down to 10 ppm 100 KHz oscillator keeps frequency stability within about 30 ppm Hence, it is not reasonable to assume the TSF timer accuracy for WUR is 500ppm as [4] Hence, it is nature to keep the TSF timer accuracy within 100 ppm as today s WiFi devices Otherwise, it brings serious time drift issue and requires frequent synchronization actions Submission Slide 4 Ming Gan et al. (Huawei)
Jan. 2018 doc.: IEEE 802.11-18/0101r0 SP Do you agree to maintain the TSF timer accuracy in the MAC layer for WUR STA within 100 ppm? Submission Slide 5 Ming Gan et al. (Huawei)
Jan. 2018 doc.: IEEE 802.11-18/0101r0 Reference [1] 17/1004r4 Consideration on WUR frame format [2] 17/1645r3 WUR frame format Follow up [3] 20170221 Intel WUR Beacon Follow up [4] 17/1384r0 WUR Synchronization [5] https://www.mouser.com/Passive-Components/Frequency-Control- Timing-Devices/Oscillators/Standard-Clock-Oscillators/_/N- 7jdva?P=1yzmo0z&FS=True [6] Clock solutions for WiFi (IEEE 802.11) http://application- notes.digchip.com/031/31-20310.pdf Submission Slide 6 Ming Gan et al. (Huawei)
