project: ieee p802.15 working group for wireless personal area networks (wpans)

July 9, 2002

J.M. Cramer, TRW Space and Electronics

IEEE 802.15-SG3a-02/325

Submission

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)(WPANs)

Submission Title: [An Evaluation of Indoor Ultra-Wideband Communication Channels]Date Submitted: [8 July, 2002]Source: [R. Jean-Marc Cramer]Company [TRW Space & Electronics]Company []Address [One Space Park DriveMail Stop 02/2743Redondo Beach, CA 90278 ]Voice [310-812-9073], FAX: [] E-Mail:[[email protected]]Re: []Abstract: []Purpose: [UWB channel model presentation.]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.

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

An Evaluation of Indoor Ultra-Wideband Communication Channels

R. Jean-Marc Cramer

[email protected]

9 July, 2002

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Overview

• Introduction and motivation– UWB propagation experiment

• UWB array signal processing– Application to measured data

• Channel models for UWB signal propagation• Conclusions

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Introduction and Motivation• Accurate models of the propagation channel are

required for the design of UWB systems– UWB radio algorithm verification and design trades– Performance prediction

• Previous studies have reported characterizations of more narrowband channels– These studies may not adequately reflect the bandwidth-

dependent effects of the propagation of UWB signals.

• Propose channel models of the form:

where the pulse shape and amplitude are dependent on the particular multipath component

n n nn

r t a p t

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

UWB Propagation Experiment• Measurements made at 14 different locations in an office building• At each location data collected on a 7x7 array of sensors with 6”

spacing– Array located 1.65 meters above the floor and 1.05 meters below the ceiling

∙

4 4.5 5 5.5 6 6.5 7 7.5 8-6

-4

-2

0

2

4

Time (ns)

Sig

nal A

mpl

itud

e (V

olts

)

Pulse at 1m separation from the transmit antenna(Direct path pulse)

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

15 20 25 30 35 40 45 50 55

Am

pli

tud

e

Time (nanoseconds)

-0.1

-0.05

0

0.05

0.1

15 20 25 30 35 40 45 50 55

Am

pli

tud

e

Time (nanoseconds)

-0.1

-0.05

0

0.05

0.1

15 20 25 30 35 40 45 50 55

Am

pli

tud

e

Time (nanoseconds)

(1,7)

(7,7)

6 in.

(1,1)

(7,1)

6 in.

Typical Received Signal Profiles

Measurement array

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Sensor-CLEAN Algorithm• Processed the measured data with a variation of the

CLEAN algorithm• Delay-and-sum beamforming used as a first step

– Constructed beamformer response over of direction and time• Signal detection at peak in the response over time and angle

– Only assumption on the incident signal is that it exists in a short window of time at beamformer output• No canonical wave shape is assumed• Permits study of incident waveform shape and signal statistics

• Iteratively reduce sensor data based on detected signal locations (peaks in the beamformer output)– Generate updated beamformer output and repeat until residual

threshold is satisfied

• Refer to the algorithm used here as Sensor-CLEAN– Relaxation step conducted directly on the sensor data

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

UWB Channel Modeling

• UWB signal processing techniques applied to measured propagation data

• Resulting recovered UWB signal information used to study– Received waveform shapes– Path-loss models– Clustering models for indoor signal propagation– Spatio-temporal distributions of the received signal

energy– Ray tracing based on single bounce elliptical

models– UWB channel synthesis

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Application of Algorithm to Measured Data• Recover measurement locations from time-of-arrival and

azimuth angle-of-arrival of first detected signal• Corresponding direct path length is 1 / 1 metersLOS d sd n n f c

Location dL OS (m.) AOA (o)P 5.47 49B 16.92 191F2 5.61 203H 10.20 149C 17.23 198F1 8.68 172L 7.04 136N 5.29 107A 16.13 184E 13.54 156M 13.07 255T 10.48 293U 10.57 41W 8.87 327

• X indicates recovered measurement locations• Squares are actual measurement locations

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Recovered Signals at Location P• Plot shows recovered signal amplitude versus time and azimuth at P

– Dependence on elevation angle has been integrated out

• Existence of clusters of multipath signals is noted is the plots

LOS signal at 5.47m and 49o

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Recovered Signals at Location H


July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Recovered Signals at Location M


July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Recovered LOS Waveforms

• Each plots displays two curves corresponding to the waveform recovered by processing algorithms using different time windows

– A larger window gives more complete picture of isolated signals– Smaller window is better for resolving dense multipath

• Compare to direct path waveform shown earlier

-3

-2

-1

0

1

2

3

4

0 0.5 1 1.5 2 2.5 3 3.5 4

Rec

over

ed s

igna

l am

plit

ude

(Vol

ts)

Time (ns)

dLOS = 5.47 mLocation P

-8

-6

-4

-2

0

2

4

6

8

0 0.5 1 1.5 2 2.5 3 3.5 4R

ecov

ered

Sig

nal A

mpl

itud

e (V

olts

)Time (ns)

dLOS = 5.61 mLocation F2

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Clustering Models for UWB Propagation

• Previous models for indoor propagation reported the existence of clusters of multipath components

• This model is justified for the UWB channel by the apparent existence of clusters seen in the scatter plots– Further justified by use of a sliding window on the recovered

signal information over time and angle

• Assume channel impulse response is separable as a function of time and azimuth angle:

• Final cluster locations determined by manual inspection of the recovered signal locations over time and angle– 65 clusters identified at 14 different measurement locations

( , ) ( ) ( )h t h t h

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Clustering Models for UWB Propagation

29328126925624423222020819518317115914613412211097.785.473.2

6148.836.624.412.2

0

Angle-of-Arrival (degrees)

Sliding window over the recovered signals at location M shows theexistence of clusters of multipath

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Clustering Models for UWB Propagation• Model the received signal amplitude by a Rayleigh

distributed RV with MS value given by,

– is the average power in first arrival of first cluster– The variable Tl represents the arrival time of the lth cluster– The variable kl is the arrival time of the kth signal within the lth

cluster, relative to Tl

• The parameters and determine the inter-cluster (cluster) and intra-cluster (or ray) rates of decay– The exponent is generally determined by building

architecture– The exponent is determined by objects close to the receive

antenna

/ /2 2 0,0 l klTkl e e

2 0,0

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Inter-Cluster Decay Rate

10-3

10-2

10-1

100

101

102

0 50 100 150 200

LS

= 30.4 ns

Nor

mal

ized

Rel

ativ

e E

nerg

y

Relative Delay (ns)

med

= 25.3 ns

mean

= 30.5 ns

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Intra-Cluster Decay Rate

10-3

10-2

10-1

100

101

102

0 50 100 150 200 250 300

med

= 78.2 ns

mean

= 84.1 ns

Me

dian

gam

ma

- re

lativ

e

Relative Delay (ns)

Nor

mal

ized

Rel

ativ

e In

ter-

Clu

ster

Ene

rgy

LS = 97.8 ns

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Energy Deviation from Mean

• Deviation from the mean is hypothesized to follow Rayleigh dist• This distribution represents best-fit to the recovered UWB signal

information when considering Rayleigh, lognormal, Nakagami-m and Rician distributions

Pro

babi

lity

Den

sity

Volts

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.5 1 1.5 2 2.50

0.01

0.02

0.03

0.04

0.05

0.06

0 0.5 1 1.5

Pro

babi

lity

Den

sity

Volts

2

222

, 0.46x

x

xf x e

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Cluster Angle-of-Arrival

• Cluster angle-of-arrival is hypothesized to follow a uniform distribution

• Ray angle-of-arrival is hypothesized to follow a Laplacian distribution, according to

• Recovered ray or intra-cluster arrivals were tested against Gaussian and Laplacian hypothesis.– Best fit distribution and resulting standard deviation were

reported. – Laplacian with =38° is the best fit distribution.

2 /1

2p e

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Cluster and Ray Angles-of-Arrival

-180 -135 -90 -45 0 45 90 135 1800

20

40

60

80

100

Cluster Angle-of-Arrival Relative to Reference Cluster

CD

F (

%)

0

0.005

0.01

0.015

0.02

-180 -135 -90 -45 0 45 90 135 180

p()

(Degrees)

=38

• Distribution of cluster angles is relatively uniform below 135o

• Additional measurement would probably provide clusters above 135o

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Rate of Signal Arrivals

• Signal inter-arrival times are hypothesized to follow an exponential rate law according to,

where is the cluster arrival rate and is the ray arrival rate

• Following this model, best-fit distributions were determined for recovered UWB signal arrival times– Faster arrival rates were found than in previous reports

• Could be due at least in part to finer time resolution

1

1,

1

1,

|

|

l l

kl k l

T Tl l

kl k l

p T T e

p e

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Ray Arrival Rates

10-4

10-3

10-2

10-1

100

0 10 20 30 40 50

1/ = 2.30 ns

1/ = 5.41 ns

1 -

CD

F

Delay (ns)

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

UWB Channel Parameter Summary

• Many potential reasons for differences in the values.– Finer time resolution of UWB signals.– Larger fractional bandwidth and better penetration

performance of UWB signals.– Differences in the building materials and/or architecture.– Differences in the orientation of the transmitter and the

receiver

• Bottom line: More UWB studies need to be made before concrete conclusions can be drawn

Parameter UWB Propagation Spencer et al. Spencer et al. Saleh-Valenzuela¡ 27.9 ns 33.6 ns 78.0 ns 60 ns° 84.1 ns 28.6 ns 82.2 ns 20 ns1=¤ 45.5 ns 16.8 ns 17.3 ns 300 ns1=̧ 2.3 ns 5.1 ns 6.6 ns 5 ns¾ 37o 25.5o 21.5o -

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

UWB Channel Synthesis• Synthesis of UWB channels permits accurate simulations of

UWB systems• Multipath arrivals for two UWB channels synthesized from the

clustering model parameters are shown below

0

50

100

150

200

250

300

3500 45 90 135 180 225 270 315 360

Tim

e-of

-Arr

ival

(ns

)

Angle-of-Arrival (Degrees)

0

100

200

300

400

5000 45 90 135 180 225 270 315 360

Tim

e-of

-Arr

ival

(ns

)

Angle-of-Arrival (Degrees)

July 9, 2002


IEEE 802.15-SG3a-02/325

Submission

Conclusions

• UWB signal processing techniques applied to data measured on an array of sensors

• Resulting received signal information used to develop models of the indoor UWB propagation channel– Comparisons drawn with more narrowband channel models

• UWB channel parameters derived from measurements taken in a single building with a single type of UWB pulse– Building architecture and the geometry of the experiment can impact

the received signal statistics– Statistics of other UWB waveforms may be different

• Main result may be development of techniques for analysis and processing of UWB signals– Techniques can be applied to other UWB waveforms

project: ieee p802.15 working group for wireless personal area networks (wpans)

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