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

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Discussions on SFD sequence length for LECIM FSK-PHY] Date Submitted: [Dec. 2011] Source: Mi-Kyung Oh, Sangsung Choi, Kwang-Roh Park (ETRI) Voice: +82 42 860 5680, FAX: +82 42 860 5218, E-Mail: ohmik@etri.re.kr Re: [802.15.TG4k] Abstract: This contribution is prepared to discuss about SFD sequence length for FSK PHY. Purpose: 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. Mi-Kyung Oh, Sangsung Choi (ETRI)

2. Outline • The goal of this document is to discuss about SFD detection capability depending on the sequence length for LECIM FSK PHY. Mi-Kyung Oh, Sangsung Choi (ETRI)

3. FSK Packet Format • PHY packet format • Reliability features in harsh LECIM environments • Preamble: multiple repetition of “01010101” • SFD: 2-octet is enough for reliable operation?? • PHR: FEC, Spreading • PSDU: FEC, Spreading, P-FSK PHY Layer Preamble PSDU SFD PHR FEC, Spreading, P-FSK FEC, Spreading Multiple repetition of “01010101” ?? Mi-Kyung Oh, Sangsung Choi (ETRI)

4. SFD Detector • One example: correlator-based SFD detector • Detection occurs when the correlator output exceeds the threshold SFD sync. position Detection threshold • SFD detection threshold • - If it is set to high value, the missing rate increases and false alarm rate decreases. • - If it is set to small value, the false alarm rate increases and missing rate decreases. Mi-Kyung Oh, Sangsung Choi (ETRI)

5. Simulations on SFD Detector • Simulation environments • Packet format: • Preamble: 8-octet (8 multiples of “01010101”) • SFD: 2-octet, 3-octet, 4-octet, 5-octet, 6-octet • Data: 127-octet random data • Modulation: 2-level FSK • Demodulation: non-coherent & hard decision for simplicity • SFD detector: correlator-based detector Mi-Kyung Oh, Sangsung Choi (ETRI)

6. Simulations on SFD Detector • False alarm rate • In this simulation, we consider only the case when the SFD correlator output has its maximum during preamble. • Comment: If the detection threshold is used, the false alarm rate becomes dependent on missing rate. Max. value occurs in preamble duration Real SFD sync. position => False alarm SFD correlator output at SNR=3dB Preamble duration Mi-Kyung Oh, Sangsung Choi (ETRI)

7. Simulations on SFD detector • Simulation results: False alarm rate • Longer SFD sequence gives better performance Performance difference is relatively small Mi-Kyung Oh, Sangsung Choi (ETRI)

8. Discussions (1) • Good channel environments with high EIRP • Operating SNR would be high • Non-coherent FSK receiver requires 11dB @ BER 10-5 • PHR & PSDU recovery • The FSK basic feature is enough • No need for FEC, spreading or P-FSK • SFD detection • False alarm rate is negligible at high operating SNR • SFD sequence : 2-octet would be enough Mi-Kyung Oh, Sangsung Choi (ETRI)

9. Discussions (2) • Harsh channel environments with low EIRP • Operating SNR would be low: e.g., SNR ≤ 4dB • PHR & PSDU recovery • The FSK selection features should be used • FEC, spreading, P-FSK • Once SFD detection is successful, PHR & PSDU have capabilities of restoring information bits at low SNR. • SFD detection • False alarm rate becomes one of main factors for packet recovery at low operating SNR • 2-octet SFD sequence: false alarm rate is relatively high at low SNR Mi-Kyung Oh, Sangsung Choi (ETRI)

10. Discussions (3) • The SFD part is required to have similar capability compared with PHR & PSDU parts in harsh environments • It can be possible by lengthening the SFD sequence. • Repetition of 4g SFD sequence with length 16 as in the doc. 774-01 • It will be good for 15.4g interoperability. • SFD detector can use full SFD sequence or part of SFD sequence according to its capability and channel condition • How many repetitions? • 2 repetitions (4-octet SFD) would be suitable since 5-octet SFD and 6-octet SFD do not give the dramatic performance enhancement. Mi-Kyung Oh, Sangsung Choi (ETRI)

11. Discussions (4) • Still, 4-octet SFD is not enough at low SNR and the false alarm rate is relatively high. • Once SFD detection with false alarm occurs, the receiver starts to recover PHR & PSDU bits. • It entails unnecessary energy consumption. • Validity check for PHR can stop this unnecessary PSDU recovery. • Simple validity check method for PHR • Parity check • How many parity bits? • Need more discussions Mi-Kyung Oh, Sangsung Choi (ETRI)

12. Conclusions • SFD sequence • Simulation results show that 4-octet SFD is suitable • SFD Pattern: 2 repetitions of 4g SFD sequence • However, long SFD sequence may not be required at high SNR  can we select 2-octet SFD and 4-octet SFD according to channel condition? • Validity check for PHR • Simple parity check can stop PSDU recovery to conserve energy even if SFD detection with false alarm occurs Mi-Kyung Oh, Sangsung Choi (ETRI)