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: Simulation results of non-coherent reception based system proposed for the Low Rate alt-PHY (802.15.4a) Date Submitted: 15th July 2005 Source: Patricia Martigne Company: France Telecom R&D Address: 28 Chemin du Vieux Chêne – BP98 – 38243 Meylan Cedex - France Voice: +33 4 76 76 44 03 E-Mail: patricia.martigne@francetelecom.com Abstract: Simulation results related to low rate and ranging applications Purpose: This document shows some simulation results obtained for non-coherent receivers using UWB-IR technology as proposed by FT R&D fellows 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

2. UWB-Impulse Radio (IR) with Time-Hopping codingnon-coherent reception Simulations performed by Patricia MARTIGNE, Benoit MISCOPEIN, Jean SCHWOERER

3. CONTENT • General description of the system • Focus on the synchronization process, including simulation results • Specificities for ranging applications, including first simulation results • Conclusion

4. UWB-IR based system Impulse-radio (IR)based: • Very short pulses  Reduced ISI • Robustness against fading • Episodic transmission (for LDR) allowing long sleep-mode periods and energy saving Time Hopping coding: • Multiple access management • Timing approach used for efficient synchronization • Smoothing the spectrum Low-complexity implementation (OOK modulation, pulse repetition for robustness of the transmitted symbol) • General description • Synchronization process • Ranging applications • Conclusion

5. 1- General description UWB-IR based system • 8 pulses per symbol • Use of an 8-ary Time Hopping code of length 8 • Use of such a TH code combined with the band plan may allow to handle the SOP issue • Code order and length are scalable to meet different requirements • Tp = 1ns, Tc = 20 ns, Tf = 160 ns, Tsymbol = 1080 ns PRP ± TH Tp Tc Tf

6. 1- General description UWB-IR Transmitter • Main Goal : "Low cost & low consumption". • Pulses are generated in baseband. • No mixer, no VCO but pulse shaping. • Simple control logic and "reasonable" clock frequency (Crystal) PSDU Data Clock F < 100 MHz Control Logic BaseBand signal PA (option) Pulse shaper Pulse Generator RF Signal

7. 1- General description UWB-IR Receiver • Energy detection technique rather than coherent receiver, for relaxed synchronization constraints. • Threshold detection (no A/D conversion). • The threshold is set by the demodulation block at each symbol time, if needed. • Synchronization fully re-acquired for each new packet received (=> no very accurate timebase needed).

8. 1- General description UWB-IR non-coherent Receiver • Reception • performs an energy detection • and creates a {thresholder , timebase} couple, • in order to timestamp the threshold crossings. BPF Time stamps Synchro / demodulation : Communication applications ( )2 LPF / 2-4ns integrator Analog comparator Time base 1-2ns accuracy 1st path detection Ranging applications

9. 1- General description UWB-IR non-coherent Receiver Digital signal processing Analog signal conditioning Time base Each time the signal amplitude exceeds a given threshold, a timestamp is associated to this event and can be exploited by the digital part.

10. 1- General description UWB-IR non-coherent Receiver Symbol detection

11. Synchronization algorithm for non-coherent receivers During a synchronization preamble of unmodulated symbols, the algorithm used consists in • parsing the received timestamps, • so as to identify a known Time Hopping sequence. Simulations have been performed to validate the performances of such an algorithm, in terms • of accuracy, and • of mean elapsed time in acquisition. • General description • Synchronization process • Ranging applications • Conclusion

12. i Detected edge for t_pos(i) i No edge detection for t_pos(i) 2- Synchronization process Packet Acquisition & Synchronization The synchronization algorithm • detects the threshold crossings, and • updates an assumption matrix, which can also be viewed as a tree exploration Δ3,4 Δ2,3 2 3 4 Δ1,2 Δ2,3 ? 3 ? Time base origin determination = Δ3,4 4 Δi,j = Known time offset between the pulses appearance, with respect to the TH code.

13. 2- Synchronization process Packet acquisition & Synchronization The threshold level is set to detect a number of crossings consistent with the expectations (known time hopping sequence) For any tested Channel Model, the synchronization is properly acquired (during the Synch preamble) Measured accuracy is around several 100s of ps.

14. 2- Synchronization process Time needed for synchronization

15. 2- Synchronization process Time needed for synchronization Simulation results • The synchronization is quickly acquired : • in CM1 condition it is acquired in less than 2 symbol times for a range of50 meters • in CM2, CM3 or CM5 condition it is acquired in less than 5 symbol times for a range of30 meters The synchronization is achievable within the 32 bytessynchronization preamble.

16. 2- Synchronization process Time accuracy during synchronization Simulation results • Timing retrieval accuracy : the tolerance window, set up for the timestamps validation, is centered around the theoretical position and is set to a width of 1.25ns mean synchronization accuracy obtained in this simulation is 625ps • This value is precise enough to ensure a correct data demodulation • Considering that 625 ps represents a distance of 19 cm, this accuracy is fully consistent with the UWB-IR ranging capabilities.

17. 2- Synchronization process Accuracy vs. tolerance width (for CM2)

18. 2- Synchronization process Accuracy vs. tolerance width (for CM2) Simulation results • CM2 model, • 30 meter range, • several widths have been tested for the tolerance window: wt = 16, 20, 32, 40 • For each width, a standard deviation has been computed. • Mean elapsed time to acquire the synchronization (tsynch) as well as the related standard deviation for each window width are gathered in the table. • To illustrate the tolerance window width dependance of the synchronization accuracy, each case is represented by a centered normal distribution on the figure. • When setting the window width from 2.5 ns to 1 ns, the standard deviation of the synchronization error is divided by 2 but the required time for acquisition encounters a 40 % increase. • Tslot/32 = 1.25 ns appears as an acceptable value in this case.

19. Ranging applications Once the synchronization is acquired, the system may be used either for communication applications or for ranging applications (slide 8). The latter one is particularly challenging for non-coherent receivers when accurate ranging measurements (less than 1 meter accuracy) are aimed at. The ranging technique is based on the synchronization acquisition algorithm, aiming at detecting the direct path. • General description • Synchronization process • Ranging applications • Conclusion

20. 3- Ranging applications UWB-IR non-coherent receiver for ranging BPF ( )2 Filtering + Assumption/path selection Time base 1-2ns accuracy Assumption path synchronization Matrix LPF / 2-4ns integrator Analog comparator Time stamping "Path-arrival dates" table 1D to 2D Conversion

21. 3- Ranging applications Leading edge detection Simulation results • Simulations have been performed for CM1 model, over a 50µs preamble (40 symbols) • They provide the accuracy in 1st path detectionobtained for a given Signal to Noise Ratio at the receiver antenna (input to the band pass filter) • Graphs are given for a (SNR)ANT between -9,5dB and -1dB (corresponding to a Esymbol/E0 ranging from around 20dB to 28dB)

22. 3- Ranging applications Leading edge detection Simulation results

23. 3- Ranging applications Leading edge detection Simulation results Some more simulations are on going • to obtain results with other channel models • to have a look at the accuracy obtained with longer preambles (500µs, 4ms)

24. 4- Conclusion UWB-IR non-coherent schemes for IEEE 802.15.4a targeted applications The proposed non-coherent reception concept • has an efficient behaviour in synchronization, using a time-stamping process with less than 700ps accuracy (accuracy for the detection of the strongest path) • provides 1st path-detection for ranging applications with an accuracy of typ. some hundreds of ps • is still simple-designed, meeting 802.15.4a PAR goals of low complexity and low cost. • General description • Synchronization process • Ranging applications • Conclusion

25. 4- Conclusion UWB-IR non-coherent schemes for IEEE 802.15.4a targeted applications This first set of simulations is showing the relevance of considering this kind of UWB-IR non-coherent receivers, using Time Hopping coding, when drafting the 15.4a standard. • General description • Synchronization process • Ranging applications • Conclusion