On the Performance of Timing Synchronization and OOK Pulse Bandwidth

1. On the Performance of Timing Synchronization and OOK Pulse Bandwidth Date: 2017-01-16 Authors: Eunsung Park, LG Electronics

2. Overview • In this contribution, we deal with the timing synchronization and the OOK pulse bandwidth and show some performance results to provide insights on them • To this end, we first go through several assumptions such as • Wake-up frame structure • OOK symbol computation • Then, we investigate possible options of the wake-up preamble part for the timing synchronization • Finally, we compare the PER performance among them considering various OOK pulse bandwidths, i.e., the number of available subcarriers, k Eunsung Park, LG Electronics

3. Wake-Up Frame • We assume that the wake-up frame consists of wake-up preamble and wake-up payload • Wake-up preamble further falls into two parts, and the purpose of each part is • Detection and timing synchronization • Signal power measure for calculating a threshold used for decoding and transmission for short control information • Wake-up payload conveys control information • Except for the first preamble part, i.e., the preamble part for the detection and timing synchronization, the wake-up frame is computed by utilizing the OOK symbol as shown in the next slide • The signal structure for the first preamble part is different according to the option as depicted in slide 5 and 6 Detection & Synch. Signal power measure & Short control information Control information Wake-up preamble Wake-up payload Eunsung Park, LG Electronics

4. OOK Symbol • In this contribution, several OOK pulse bandwidths are considered such as 4MHz (k=13), 5MHz (k=16), 8MHz (k=26) and 10MHz (k=32) • As shown in the PER performance for the perfect synchronization in Appendix A, the performance of 1% PER is enhanced as k increases but it no longer gets better when k is larger than 26 • Also, the larger bandwidth OOK symbol has, the more power receiver consumes • LNA consumes more power for the signal which utilizes larger bandwidth • On the other hand, in [2], the case of k=1 has a poor performance • Also, the less bandwidth OOK symbol has, the sharper filter receiver requires • Thus, in this contribution, we do not consider the pulse bandwidth larger than 10MHz or less than 4MHz and just deal with the above candidates for simplicity • Also, for the ON-symbol, the frequency domain sequence optimized (or sub-optimized) in terms of the PAPR is applied to each pulse bandwidth • Similar to [1], OOK symbol is generated using 802.11 OFDM transmitter Eunsung Park, LG Electronics

5. Preamble Part for Timing Synchronization • We have three options • Option 1 : OOK symbol based signal • It is composed of several OOK symbols which are also used in the other parts • The transmitter just needs to be capable of generating the OOK symbols • Option 2 : Periodic signal in the time domain • Similar to the legacy STF, it is composed of a periodic signal which has a period less than 3.2us • In this contribution, by using an approach similar to generating Manchester coding based signal [3], 1.6us periodic signal is computed and applied • Option 3 : A certain sequence based signal in the time domain • By employing a single carrier transmitter, a certain sequence based signal in the time domain is sent • In this contribution, we apply Golay sequence as in 11ad in order to exploit a good autocorrelation property of Golay sequence when performing timing synchronization at the receiver. Eunsung Park, LG Electronics

6. Simulation Environment • Each part of the wake-up frame has the following length • Each option for the synchronization has the following structure • Option 1 : two ON-symbols (8us) + one OFF-symbol (4us) • Last OFF-symbol may have a positive effect on the timing synchronization and detection • Also, it can be used to indicate the WUR frame • Option 2 : five 1.6us signals (8us) + one OFF-symbol (4us) • Option 3 : two 64 length Golay sequence based signals (6.4us) + one OFF-symbol (4us) • 64 length Golay sequence [-1,-1,1,-1,1,-1,-1,-1,1,1,-1,1,1,-1,-1,-1,-1,-1,1,-1,1,-1,-1,-1,-1,-1,1,-1,-1,1,1,1,-1,-1,1,-1,1,-1,-1,-1,1,1,-1,1,1,-1,-1,-1,1,1,-1,1,-1,1,1,1,1,1,-1,1,1,-1,-1,-1] • OOK symbol is decoded in the frequency domain • Performance may be degraded if the signal decoding is preformed in the time domain since the noise in adjacent tones that cannot be perfectly removed by the filter which is not sharp enough affects the performance • SNR is defined considering 20MHz • PER performance for the wake-up payload will be shown in TGn D channel Signal power measure / Short control information (6 symbols, all ON-symbols) Detection & Synch (About 3 symbols) Control information (48 symbols) Wake-up preamble Wake-up payload Eunsung Park, LG Electronics

7. Simulation Results – Comparison amongOptions for Timing Synchronization k = 13 k = 16 Eunsung Park, LG Electronics

8. Simulation Results – Comparison amongOptions for Timing Synchronization k = 26 k = 32 Eunsung Park, LG Electronics

9. Discussion • We assume the target PER of 1% or 10% • For the timing synchronization, all options have similar PER performance and the PER performance gap less than 1dB comparing with the perfect synchronization case • However, the transmit complexity is different according to the option • Option 1 is the simplest one since the transmitter only needs to be possible to send the OOK symbol by using the conventional 802.11 OFDM transmitter • Option 2 needs a procedure which generates a periodic signal as well as the OOK symbol, but the transmitter can use the conventional 802.11 OFDM transmitter • Option 3 may need the most complex procedure at the transmitter since a single carrier transmission is required Eunsung Park, LG Electronics

10. Simulation Results – Comparison amongVarious OOK Pulse Bandwidths Option 1 Option 2 Eunsung Park, LG Electronics

11. Simulation Results – Comparison amongVarious OOK Pulse Bandwidths Option 3 Eunsung Park, LG Electronics

12. Discussion • For the OOK pulse bandwidth, there is a trade-off between the PER performance and the power consumption assuming the target PER of 1% • When k=13, it has an advantage of the power consumption but its PER is the worst in all options • When k=16, it achieves a better PER performance than that of k=13 with relatively low power consumption • The cases of k=26 and 32 have a similar PER performance and they overwhelm other cases in all options • Considering the power consumption issue, the case of k=26 may be better than k=32 • On the other hand, if we see the target PER of 10%, the case of k=13 may be the best in most cases in terms of both the PER performance and the power consumption Eunsung Park, LG Electronics

13. Conclusions • Assuming the target PER of 1% • If we focus only on the PER performance, we can choose the following case • 8MHz pulse bandwidth (k=26) with option 2 for timing synchronization • However, since the power consumption is a dominant factor in 11ba, 4MHz pulse bandwidth (k=13) can be preferred rather than other cases • If the case of k=16 has an allowable power consumption, then 5MHz pulse bandwidth (k=16) can be selected • On the other hand, in terms of the complexity at the transmitter, option 1 is the most favorable and option 2 is relatively comparable • Thus, considering all of the factors such as the PER performance, the power consumption and the transmit complexity, it may be advisable to apply the following cases to 11ba • 4MHz pulse bandwidth (k=13) with option 1 for the timing synchronization • 5MHz pulse bandwidth (k=16) with option 1 or option 2 for the timing synchronization • Note that considering the UMi channel as shown in Appendix B, we don’t have any choice but to apply 8MHz pulse bandwidth (k=26) with option 3 for timing synchronization • Only the cases of k=26 and 32 with option 3 achieve 1% PER and other cases can not meet it in the UMi channel • The case of k=32 with option 3 can be excluded considering the power consumption and its worse performance than that of the case of k=26 with option 3 • Assuming the target PER of 10% • If we focus only on the PER performance, we can choose the following case • 4MHz pulse bandwidth (k=13) with option 3 for timing synchronization (low power consumption is also achieved) • If we also think about the transmit complexity, it may be advisable to apply the following case to 11ba • 4MHz pulse bandwidth (k=13) with option 1 for the timing synchronization (actually, comparable PER with 4MHz w/option 3) • Note that we can have the same conclusions even in the UMi channel as shown in Appendix B Eunsung Park, LG Electronics

14. References [1] IEEE 802.11-16/0341r0 - LP-WUR (Low-Power Wake-Up Receiver) Follow-Up [2] IEEE 802.11-16-0865-01-0wur-performance-investigation-on-wake-up-receiver [3] IEEE 802.11-16-1144-00-0wur-further-investigation-on-wur-performance Eunsung Park, LG Electronics

15. Appendices Eunsung Park, LG Electronics

16. Appendix A Eunsung Park, LG Electronics

17. Appendix B – PER in the UMI Channel Perfect synch. Option 1 Eunsung Park, LG Electronics

18. Appendix B – PER in the UMI Channel Option 2 Option 3 Eunsung Park, LG Electronics