1. doc.: IEEE 802.15-02/301r0 Submission July 2002 Time Domain Corporation Slide 1 Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title:[UWB Propagation Phenomena] Date Submitted:[4 July, 2002] Source: [Kai Siwiak] Company [Time Domain Corporation] Address [7057 Old Madison Pike, Huntsville, AL 35806] Voice [256-990-9062] E-Mail: [ kai.siwiak@timedomain.com ] Re: [Response to the Call for Contributions on UWB Channel Models (IEEE P802.15-02/208r1-SG3a).] Abstract:[This contribution exposes a behavior of UWB signals in multipath which may be relevant to path loss and multipath models intended for evaluating UWB physical layer submissions for a high-rate extension to IEEE 802.15.3. ] Purpose:[A connection is shown between measured multipath delay spread and the power laws of propagation. A theory for the connection is proposed which offers a better understanding of UWB multipath channels model that could be used to compare different UWB PHYs.] 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. doc.: IEEE 802.15-02/301r0 Submission July 2002 Time Domain Corporation Slide 2 UWB Propagation Phenomena Kai Siwiak Time Domain Corporation 4 July 2002

3. doc.: IEEE 802.15-02/301r0 Submission July 2002 Time Domain Corporation Slide 3 Overview High resolution UWB propagation measurements reveal a close connection between propagation power law and multipath delay spread Suggests a theoretical basis for power laws observed in multipath Has implications on receiving signals, RAKE gain and understanding of channel models

4. doc.: IEEE 802.15-02/301r0 Submission July 2002 Time Domain Corporation Slide 4 UWB Propagation Measurements A set of UWB propagation measurements [1] were carried out using a UWB impulse transmitter and a UWB scanning receiver The data were processed using the CLEAN algorithm [2] to extract: –Strongest impulse power density vs. distance –Total power density vs. distance –RMS delay spread vs. distance

5. doc.: IEEE 802.15-02/301r0 Submission July 2002 Time Domain Corporation Slide 5 -40 -30 -20 -10 0 110100 Distance, m Power, strongest impulse, dB. The indoor UWB measurements [1] reveal that the “strongest impulse” power density propagates approximately as 30 log(d), distance d is meters Strongest Impulse vs. Distance

6. doc.: IEEE 802.15-02/301r0 Submission July 2002 Time Domain Corporation Slide 6 Indoor Channel Impulse Response Channel Impulses (left) are processed with CLEAN algorithm to obtain CIRs (right). The total power density represented by the CIR can then be reported Source: Yano [1]

7. doc.: IEEE 802.15-02/301r0 Submission July 2002 Time Domain Corporation Slide 7 -40 -30 -20 -10 0 110100 Distance, m Total power, dB. Total Power Density vs. Distance The same measurements [1] reveal that the “total power density” propagates approximately as 20 log(d), distance d is meters, and with smaller variance

8. doc.: IEEE 802.15-02/301r0 Submission July 2002 Time Domain Corporation Slide 8 0 20 40 60 80 0102030 Distance, m Delay spread, ns RMS Delay Spread vs. Distance The same measurements [1] further reveal that the rms delay spread varies approximately as  0 d, distance d is in meters, and here  0 =3

9. doc.: IEEE 802.15-02/301r0 Submission July 2002 Time Domain Corporation Slide 9 Discussion A simple ‘Gedankenexperiment’ leads us to conclude that in a lossless 3-d environment of copolarized scatterers the total power density propagates, on the average P(d) = P tx /4  d 2 We further assert that the multipath power delay profile is exponentially distributed [3] S = e -t/  rms /  rms

10. doc.: IEEE 802.15-02/301r0 Submission July 2002 Time Domain Corporation Slide 10 Discussion Impulses are of finite duration t 0 and, from this measurements set,  rms   d The power density fraction associated with our single finite impulse P  is P1P1 0 t0 t0 e -t/  rms      dt   1 – exp(-t 0 /  rms ) 1  rms

11. doc.: IEEE 802.15-02/301r0 Submission July 2002 Time Domain Corporation Slide 11 Discussion The propagation of the single impulse is P 1 (d) = [P tx /4  d 2 ][ 1 – exp(-t 0 /  rms ) ] Since t 0 /  rms is small, we use the approximation e x = 1+x and recall that  rms   d

12. doc.: IEEE 802.15-02/301r0 Submission July 2002 Time Domain Corporation Slide 12 Discussion Substituting P 1 (d) = [P tx /4  d 2 ][ t 0 /  rms d ]... and we have the theoretical basis for inverse 3 rd power propagation law in multipath scattering for this data set: P 1 (d) = [P tx /d 3 ][ t 0 /4  rms ]

13. doc.: IEEE 802.15-02/301r0 Submission July 2002 Time Domain Corporation Slide 13 Discussion Outdoors, the delay spread increases approximately with the square root of distance [4] So applying the same analysis, power density (in the absence of dissipative losses) gives a plausible inverse 2.5 power propagation law for this mechanism alone: P outside (d) = CP tx /d 2.5

14. doc.: IEEE 802.15-02/301r0 Submission July 2002 Time Domain Corporation Slide 14 Discussion There are additional dissipative losses, e -  d, but for relatively small  d can be treated same way, and will increase rate of signal attenuation beyond the free space rate A simple indoor UWB path loss model [5] for impulses, which treats propagation through walls same as dissipation per impulse, reduces to inverse 3 rd power for small distances

15. doc.: IEEE 802.15-02/301r0 Submission July 2002 Time Domain Corporation Slide 15 Implications to Propagation Results The maximum possible RAKE gain based on this measurement set can be cast as the ratio of ‘total power density’ to ‘single impulse power density’ so G max,RAKE = 10 log(d) Propagation measurements are dependent on how the power is collected with respect to multipath in the receiver

16. doc.: IEEE 802.15-02/301r0 Submission July 2002 Time Domain Corporation Slide 16 Conclusions A theoretical basis for propagation power law in scattering was derived Power law, attenuation losses, and multipath delay spread are closely connected Has implications on UWB channel models: channel model must correctly connect propagation law, dissipative losses and delay spread

17. doc.: IEEE 802.15-02/301r0 Submission July 2002 Time Domain Corporation Slide 17 References [1]S. M. Yano: “Investigating the Ultra-wideband Indoor Wireless Channel” Proc. IEEE VTC2002 Spring Conf., May 7-9, 2002, Birmingham, AL, Vol. 3, pp. 1200-1204 [2]J.A. Högbom, “Aperture Synthesis with a Non-Regular Distribution of Interferometer Baselines”, Astron. and Astrophys. Suppl. Ser, Vol. 15, 1974 [3]William C. Jakes, Microwave Mobile Communications, 1974, IEEE Press Reprint [4]Private e-mail communication with Henry L. Bertoni, 6 June 2002 [5]K. Siwiak, A. Petroff, “A Path Link Model for UWB Pulse Transmissions,” Conference Proceedings of the IEEE VTC-2001, Rhodes, Greece, May 6-9, May 2001