Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [ How Energy Detector

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [How Energy Detector handles Inter-Pulse Interference?] Date Submitted: [12 May 2005] Source: [Francois Chin, Lei Zhongding, Yuen-Sam Kwok, Xiaoming Peng] Company: [Institute for Infocomm Research, Singapore] Address: [21 Heng Mui Keng Terrace, Singapore 119613] Voice: [65-68745687] FAX: [65-67744990] E-Mail: [chinfrancois@i2r.a-star.edu.sg] Re: [] Abstract: [Presents signaling options to achieve precision ranging with both coherent and non-coherent receivers] Purpose: [To discuss which signal waveform would be the most feasible in terms of performance and implementation trade-offs] 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. Francois Chin (I2R)

2. Objectives • CMOS technology imposes max PR interval limit • Inter-pulse interference expected • Important for energy detector to handle inter-pulse interference in order to function in various multipath channels Francois Chin (I2R)

3. Ternary Signaling - Synchronisation with Energy Detector Pulse Repetition Interval ~ 30ns 1 2 3 4 5 6 7 8 30 31 ………………………… Non-inverted pulses are blue, Inverted pulses are green. Synchronisation / Ranging preamble = Binary Base Sequence repeated For K times… …………… …………… ................. Symbol Interval ~940ns Symbol Interval ~940ns Francois Chin (I2R)

4. Soft output RAKE combiner Noncoherent detection of OOK Soft Despread LPF / integrator BPF ( )2 ADC Sample Rate 1/Tc {1,-1} Binary Sequence Figure 1. The block diagram of energy detection receiver using soft despreader and RAKE combiner How Energy Detector despread? Ternary Seq [+ - - 0 0 0 + - 0 + + + 0 + 0 - 0 0 0 0 + 0 0 - 0 - + 0 0 - - ] After Square Law & Integration in PRI Unipolar M-Seq [+ + + 0 0 0 + + 0 + + + 0 + 0 + 0 0 0 0 + 0 0 + 0 + + 0 0 + + ] Bipolar M-Seq [+ + + - - - + + - + + + - + - + - - - - + - - + - + + - - + + ] Francois Chin (I2R)

5. Synchronisation with Energy Detector in AWGN Before Depreader – Unipolar M-Seq [+ + + 0 0 0 + + 0 + + + 0 + 0 + 0 0 0 0 + 0 0 + 0 + + 0 0 + + ] repeated 4x Despread Sequence – Bipolar M-Seq [+ + + - - - + + - + + + - + - + - - - - + - - + - + + - - + + ] Francois Chin (I2R)

6. How Energy Detector handle inter- pulse interference? Pulse Repetition Interval ~ 30ns d5 d1 d2 d3 d4 d6 d7 Ternary signaling Non-inverted pulses are blue, Inverted pulses are red. PRI T8 T6 T5 T7 T1 T2 T3 T4 Let’s zoom into the channel details … … … PRI T1 T2 T3 T4 Francois Chin (I2R)

7. = complex channel samples @ 500MHz Energy Integration in PRI @ TX Ternary codes Multipath Channel d5 d1 d2 d3 d4 d6 d7 … … … Pulse Repetition Interval 30ns PRI T1 T2 T3 T4 @ RX (assume noiseless case) Received signal matrix (PRI/column) Take the 3rd PRI as example Francois Chin (I2R)

8. Energy Integration in PRI (some noise due to cross terms) After square-law device at 3rd PRI Apply integration over PRI = Column Sum The soft ADC value for 3rd PRI: Each PRI contains partial energy from previous pulses More noise due to cross terms Multipath energy spread each PRI Francois Chin (I2R)

9. Energy Detector Sees An Equivalent Unipolar Sequence after integration in PRI Pulse Repetition Interval ~ 30ns d5 d1 d2 d3 d4 d6 d7 Ternary signaling Non-inverted pulses are blue, Inverted pulses are red. After Square Law & Integration in PRI cj=dj2 Sequence become Unipolar e1 e2 e3 c5 c1 c2 c3 c4 c6 c7 More Noise due to cross terms + PRI T1 T2 T3 T4 integrator Output is a convolution of the equivalent Unipolar Sequence with a PRI-spaced tap-delay-line channel, each tap comprising multipath energy within a correponding PRI Francois Chin (I2R)

10. Soft output e1 e1 e2 e2 e3 e3 RAKE combiner Noncoherent detection of OOK Soft Despread PRI PRI LPF / integrator BPF ( )2 ADC T1 T1 T2 T2 T3 T3 T4 T4 Sample Rate 1/Tc {1,-1} Binary Sequence Figure 1. The block diagram of energy detection receiver using soft despreader and RAKE combiner In Multipath Channels … Ternary Seq [+ - - 0 0 0 + - 0 + + + 0 + 0 – 0 0 0 0 + 0 0 - 0 - + 0 0 - - ] Unipolar M-Seq [+ + + 0 0 0 + + 0 + + + 0 + 0 + 0 0 0 0 + 0 0 + 0 + + 0 0 + + ] Despread Sequence = Bipolar M-Seq [+ + + - - - + + - + + + - + - + - - - - + - - + - + + - - + + ] Francois Chin (I2R)

11. e1 e2 e3 PRI T1 T2 T3 T4 Sliding Correlator Output @ PRI …. Synchronisation in Multipath Channels Equivalent to Simple RAKE combining at the despreader output (in fact, simple summation across despreader output) can be used to collect energy across PRI Francois Chin (I2R)

12. Summary • Square Law / Envelope Detector effectively convert a ternary sequence to a Unipolar Sequence • Energy integration in PRI converts the multipath channels into a PRI-spaced tap-delay-line channel , each tap comprising multipath energy within a correponding PRI • Energy collector / integrator Output is a convolution of the equivalent Unipolar Sequence with the PRI-spaced tap-delay-line channel • Simple RAKE combining at the despreader output (in fact, simple summation across despreader output, no need RAKE coefficients) can be used to collect energy across PRI • Energy Detector can handle inter-pulse interference just as normal direct sequence spread spectrum systems Francois Chin (I2R)

13. Appendix Francois Chin (I2R)

14. Ternary – Bipolar – Unipolar Conversion Ternary ± → + 0 → - Bipolar This is in fact m-Sequences! + → + - → 0 Unipolar Francois Chin (I2R)

15. Properties of M-Sequence Transmit – Unipolar M-Seq [+ + + 0 0 0 + + 0 + + + 0 + 0 + 0 0 0 0 + 0 0 + 0 + + 0 0 + + ] repeated 4x Receive – Bipolar M-Seq [+ + + - - - + + - + + + - + - + - - - - + - - + - + + - - + + ] ZERO autocorrelation Francois Chin (I2R)

16. Properties of M-Sequence Transmit – Bipolar M-Seq [+ + + - - - + + - + + + - + - + - - - - + - - + - + + - - + + ] repeated 4x Receive – Unipolar M-Seq [+ + + 0 0 0 + + 0 + + + 0 + 0 + 0 0 0 0 + 0 0 + 0 + + 0 0 + + ] ZERO autocorrelation Francois Chin (I2R)

17. Properties of M-Sequence Transmit – Bipolar M-Seq [+ + + - - - + + - + + + - + - + - - - - + - - + - + + - - + + ] repeated 4x Receive – Bipolar M-Seq [+ + + - - - + + - + + + - + - + - - - - + - - + - + + - - + +] HIGH peak LOW autocorrelation Francois Chin (I2R)

18. How to make use of these properties? Francois Chin (I2R)

19. Synchronisation Preamble • M-sequences has excellent autocorrelation properties • Synchronisation / Ranging Preamble is constructed by repeating the base sequence • Common Signaling (Mode 1) • Ternary for e.g. Beacon Packet • Receiver-specific signaling (Mode 2) • Ternary for Energy Detector • Bipolar for Coherent and Differential Chip Detectors • Long preamble for distant nodes is constructed by further symbol repetition Francois Chin (I2R)

20. Ranging: Code Sequences for different Receiver Criteria/Target – ZERO autocorrelation sidelobes for best leading edge detection Francois Chin (I2R)

21. Communication: Code Sequences for different Receiver Criteria/Target – Max SNR and min inter-sequence interference after despreading Francois Chin (I2R)

22. Snychronisation: Code Sequences for different Receiver Criteria/Target – balance max post-despreading SNR and low auto-correlation sidelobes Francois Chin (I2R)