Time-Domain-CFP-Response

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Time-Domain-CFP-Response] Date Submitted: [4 January, 2005] Source: [Vern Brethour, Adrian Jennings] Company: [Time Domain Corp.] Address: [7057 Old Madison Pike; Suite 250; Huntsville, Alabama 35806] Voice: [Vern: (256) 428-6331; Adrian: (256) 428-6326], E-Mail: [vern.brethour@timedomain.com; adrian.jennings@timedomain.com] Re: [802.15.4a CFP] Abstract: [802.15.4a CFP response from Time Domain. An impulse radio nominally occupying 3 – 5 GHz with 4 ns chip times using 40 chips/symbol and 300 ns quiet time between symbols.] Purpose: [Response to WPAN-802.15.4a CFP] 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 individuals or organization. The material in this document is subject to change in form and content after further study. The contributors reserve the right to add, amend or withdraw material contained herein. Release: The contributors acknowledge and accept that this contribution becomes the property of IEEE and may be made publicly available by P802.15. Vern Brethour, Adrian Jennings (Time Domain)

2. Proposal:Single Band UWB Alternate Physical Layer for TG 802.15.4a Vern Brethour, Adrian Jennings (Time Domain)

3. Proposal Contents • General Overview • Proposal Principles • Regulatory Flexibility • Performance • Evaluation Matrix (in backup slides) Vern Brethour, Adrian Jennings (Time Domain)

4. General Overview • Impulse radio • Single band nominally from 3 to 5 Ghz. • 4 ns chip times • 40 chips per symbol • 300 ns quiet time between symbols • Max symbol integration = 64 (data) • Max symbol integration = 256 (acquisition) Vern Brethour, Adrian Jennings (Time Domain)

5. Proposal Principles • The most important part of a proposal is the signal as it appears on the air. For most signal definitions, there are many ways to build a radio, and as many corresponding performance results. However, as a standard, we can define a signal which will forever limit the systems ultimate performance. (For example, by not using all reasonably available bandwidth.) Vern Brethour, Adrian Jennings (Time Domain)

6. The need for robust links • There is already a 15.4a radio at 2.54GHz. We must be substantially better than that radio. • This proposal provides the opportunity for maximum performance by occupying as much bandwidth as reasonable. Vern Brethour, Adrian Jennings (Time Domain)

7. Regulatory Flexibility • There are fundamentally two approaches to UWB regulatory flexibility: • 1) using multiple bands. • 2) longer chip times. • Using long chip times allows for filters if needed and does little harm if not needed. Vern Brethour, Adrian Jennings (Time Domain)

8. Regulatory Flexibility • This proposal occupies all of the spectrum between the ISM bands and the UNII bands • This proposal allows ample (4 ns) chip time to accommodate spectral shaping if necessary. • This proposal also allows a future (optional) band between 6 and 10 GHz. Vern Brethour, Adrian Jennings (Time Domain)

9. Support for positioning • There are already radios which do the low data rate communications job without positioning. • Excellent positioning performance will be the key differentiator for 15.4a. • Use of as much bandwidth as reasonable gives the best positioning performance. Vern Brethour, Adrian Jennings (Time Domain)

10. What about the “simple radio” approach? • Vocabulary is important here. Words like “simplicity” imply virtue. Words like “crude” and “unsophisticated” might be used by others to describe the same radio. • The critical issue is that there will be other users of the spectrum and the 4a standard must use spectrum and air time efficiently and effectively. • A proposed standard which we think implies a “simple and virtuous” radio might be viewed by others as spectrally wasteful and unworthy of letter ballot approval. Vern Brethour, Adrian Jennings (Time Domain)

11. What does “simple radio” mean? • A “simple radio” to our customers doing system integration, is a radio with the lowest chip count, the least number of passives and the most forgiving antenna driver. • The integration customer does not (and should not) care how hard we have to work to implement the design inside of our chip. Vern Brethour, Adrian Jennings (Time Domain)

12. Performance: the optimistic story. • A “marketing style” link budget looks very optimistic even for 250 Kbyte links at 100 meters, the link budget shows over 6dB of margin. Vern Brethour, Adrian Jennings (Time Domain)

13. Link Performance: A realistic story. • Performance predicted by the link budget is optimistic primarily due to the use of “2” for the path loss exponent. • Links inside buildings with interior walls, will suffer path loss exponents more like “3”. Vern Brethour, Adrian Jennings (Time Domain)

14. Link Performance • A more realistic idea of performance is available by scaling the results of the simulations done for 802.15.3a to longer ranges and lower data rates. • The 802.15.3a DS proposal uses signaling similar to this proposal, so I will scale from simulations reported in 802.15.04.0483r5 (McLaughlin, November 2004). Vern Brethour, Adrian Jennings (Time Domain)

15. Scaling the DS results: • The DS radio is simulating a 11.8 meter link in CM4 at 110 Mbit/sec with a 90% packet success rate. • Going from a link distance of 11.8 meters to 100 meters would seem to require less than 20 dB of additional processing gain. BUT that’s with a path loss exponent of 2. • A path loss exponent of 3 requires 28 dB of processing gain. Vern Brethour, Adrian Jennings (Time Domain)

16. How much integration is needed for 28 dB of processing gain? • Each time we double the integration, we get another 3dB of processing gain. • For 28 dB, we need to do 10 doublings, or an integration rate of 1024. • Integration rate 1024 will take the 110 Mbit/sec rate down to 107 Kbit/sec. Vern Brethour, Adrian Jennings (Time Domain)

17. Noticeable difference: Vern Brethour, Adrian Jennings (Time Domain)

18. Even the Scaled Simulation is a very optimistic result: • The DS radio that this prediction rests on is a very fancy radio: • 16 Rake taps • 31 tap decision feedback equalizer • Constraint length 6 convolutional code with Viturbi decoder • RF front end with 6.6 dB noise figure Vern Brethour, Adrian Jennings (Time Domain)

19. Link budgets do not address acquisition. • Acquisition will usually be the performance limiter at long range. • The Acquisition decision needs an additional 6 dB of processing gain over data demodulation. Vern Brethour, Adrian Jennings (Time Domain)

20. We must acquire without benefit of a trained equalizer. • Equalizers are fine, but only after they have been trained. • If the spacing between pulsing events is too short, the resulting inter symbol interference makes trouble for acquisition. • This proposal uses a relatively long (300 ns) distance between pulse events to handle large channel delay spreads without an equalizer. Vern Brethour, Adrian Jennings (Time Domain)

21. Applications need robust links. • The applications can stand low data rates, so this proposal uses data symbol integration of 64 and acquisition symbol integration 256. • The long acquisition integration puts a burden on crystal tolerance (2 ppm) that not all vendors will want to deal with, so shorter integration modes will also be supported. Vern Brethour, Adrian Jennings (Time Domain)

22. Clear Channel Assessment • This is a hard problem for all UWB approaches. • We should not ignore it. • Detection of energy at the chipping rate (as in the 15.3a DS proposal) is doable, but not reliable. • We may need relief from the MAC. Vern Brethour, Adrian Jennings (Time Domain)

23. Simultaneously Operating Piconets • The long symbol (40 chips) enables good orthagonality between piocnets. • Different piconets use slightly different chipping rates like the 15.3a DS proposal. • Bits are modulated onto symbols using only BPSK so all of the symbol orthogonality is used for piconet isolation. Vern Brethour, Adrian Jennings (Time Domain)

24. Power control is the key to compatibility with 15.3a • This proposal is set up for 100 meter links. • Many applications will have shorter links. • For shorter links, we turn down the Tx power. • Power control gives superior compatibility with all services. Vern Brethour, Adrian Jennings (Time Domain)

25. Proposal Summary • Impulse radio • Single band nominally from 3 to 5 Ghz. • 4 ns chip times • 40 chips per symbol • 300 ns quiet time between symbols • Max symbol integration = 64 (data) • Max symbol integration = 256 (acquisition) Vern Brethour, Adrian Jennings (Time Domain)

26. Backup Slides Vern Brethour, Adrian Jennings (Time Domain)

27. Evaluation Matrix Vern Brethour, Adrian Jennings (Time Domain)

28. Self Evaluation – General Solution Criteria Vern Brethour, Adrian Jennings (Time Domain)

29. Self Evaluation – PHY Protocol Criteria Vern Brethour, Adrian Jennings (Time Domain)