UWB Propagation Phenomena and Multipath Channel Model for IEEE 802.15.3

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [UWB Propagation Phenomena] Date Submitted: [4July, 2002; r1: 7 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 is relevant to propagation laws in multipath and hence for 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 propagation law. this leads to a theory for the connection and to a generalized propagation law model that offers a better understanding of UWB multipath channels model which can 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. Time Domain Corporation

2. UWB Propagation Phenomena Kai Siwiak Time Domain Corporation 7 July, 2002: IEEE 802.15-02/301r2 Time Domain Corporation

3. Overview • High resolution UWB propagation measurements reveal a close connection between propagation law and multipath • A theory based on measurements leads to a generalized multipath propagation law model • Result has implications on receiving signals, RAKE gain and understanding of the UWB channel and channel models Time Domain Corporation

4. UWB Propagation Measurements • A set of UWB propagation measurements [1] were carried out using a UWB pulse transmitter and a UWB scanning receiver • The data were processed using the CLEAN algorithm [2] to extract: • ‘Strongest pulse power density’ vs. distance • ‘Total power density’ vs. distance • RMS delay spread vs. distance Time Domain Corporation

5. 0 -10 Power, strongest pulse, dB . -20 -30 -40 1 10 100 Distance, m Strongest pulse vs. Distance The indoor UWB measurements [1] reveal that the “strongest pulse power density” propagates approximately as 30 log(d), distance d is meters Time Domain Corporation

6. Indoor Channel Impulse Response Channel pulses (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] Time Domain Corporation

7. 0 -10 Total power, dB . -20 -30 -40 1 10 100 Distance, m 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 Time Domain Corporation

8. 80 60 Delay spread, ns 40 20 0 0 10 20 30 Distance, m RMS Delay Spread vs. Distance The same measurements [1] further reveal that the rms delay spread varies approximately as t0d, distance d is in meters, and here t0=3 nano seconds Time Domain Corporation

9. Initial Assumptions • A simple ‘Gedankenexperiment’ leads us to conclude that in a lossless 3-d environment of copolarized scatterers, total power propagates with inverse square of distance P(d) = Ptx/4pd2 • We further assert that the multipath power delay profile is exponentially distributed [3] S = e-t/trms/trms Time Domain Corporation

10. Dissipative Losses • There are additional dissipative losses of the form e-2ad which will increase the rate of signal attenuation beyond free space loss • Dissipative lass basis for a very simple UWB propagation law [5] which modeled successive wall reflections as homogeneous attenuation • Here, however a nepers/m, is actual dissipative I2R loss constant for total power propagation Time Domain Corporation

11. t0 ó -t/trms ô 1 = = 1-exp(-t0/trms) e dt P1 ô trms ô õ 0 Model Parameters • Rays or pulses arrive at uniform rate 1/t0 • For this measurements set, trms=t0d • The fractional power density associated with strongest ray P1 is Time Domain Corporation

12. Propagation Law • Pulses propagate as P1(d) = [Ptx/4pd2][1- exp(-t0/trms)]e-2ad where trms=t0d • The value of t0/t0 establishes the transition between free space and higher order power law • When t0/t0d is small (increasing d) we use the approximation ex = 1+ x Time Domain Corporation

13. Deriving Higher Order Power Law • Substituting P1(d) = [Ptx/4pd2][t0/t0d]e-2ad • ... and we have the theoretical basis for inverse 3rd power propagation law in multipath scattering for this data set: P1(d) = [Ptx/d3][t0/4pt0]e-2ad Time Domain Corporation

14. Relation to Outdoor Propagation • Outdoors, the delay spread increases approximately with the square root of distance [4] • 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: Poutside(d) = CPtx/d 2.5 Time Domain Corporation

15. Model Constants • The theory can be generalized to non-uniform arrival rates for rays and other data sets • Values of trms(d), and hence t0 = 3 ns and t0=3 nshere, can be derived directly from UWB pulse propagation measurements • Dissipation factor 20alog(e) dB/m is found from the propagation of total power density, here a<0.006 nepers/m (<0.05 dB/m) Time Domain Corporation

16. Implications to RAKE Gain • The maximum possible RAKE gain based on this measurement set is the ratio of ‘total power density’ to ‘single pulse power density’ Gmax,RAKE = 10 log(d) indoors Gmax,RAKE = 5 log(d) outside • Propagation measurements are dependent on how the power is collected with respect to multipath in the receiver Time Domain Corporation

17. Summary • Generalized propagation law in multipath is P1(d) = [Ptx/4pd2][1- exp(-t0/trms(d))]e-2ad • Which with this indoor data set for d>>t0/t0 reduces to P1(d) = [Ptx/d3][t0/4pt0]e-2ad • Maximum possible indoor RAKE gain here is Gmax,RAKE = 10 log(d) • The propagation law is general: also applies to narrow band signal propagation Time Domain Corporation

18. Conclusions • A theoretical basis for propagation law in scattering was derived, general model proposed • Propagation model can be applied to other data sets • Propagation law, attenuation losses, multipath delay spread, and RAKE gain are closely connected • Has implications on UWB channel models: channel model must couple propagation law, dissipative losses and multipath correctly Time Domain Corporation

19. 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 Time Domain Corporation