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UWB Measurements and Channel Modeling


This page summarizes our work on UWB channel measurements and modeling, sponsored by the DARPA NETEX program.

Numerous indoor UWB measurements were taken by researchers of the Time Domain Laboratory and the Mobile and Portable Radio Research Group of Virginia Tech as a part of a collaborative research effort within the DARPA NETEX program. A large number of LOS and NLOS measurements were taken using a pulse generator capable of generating approximately Gaussian shaped pulses each with a duration of less than 200 picoseconds, a 20 GHz digital sampling oscilloscope (effective sampling rate of 80 GHz), and either a set of TEM horn antennas or a set of biconical antennas. We focus on biconical antennas in this work. To understand fading in a local area, the measurements taken at most locations consisted of 49 different measurement points in a square 90 cm x 90 cm grid, where each point was spaced 15 cm apart.

 


LARGE SCALE MODELING

Some Measured Path Loss Exponents for the NLOS and LOS cases:


Large Scale Path Loss Parameters (Total)

 

Bicone

TEM

 

n

s(dB)

n

s(dB)

LOS

1.3

2.6

1.3

2.8

NLOS

2.3

2.4

2.4

5.1

Large Scale Path Loss Parameters (Peak)

 

Bicone

TEM

 

n

s(dB)

n

s(dB)

LOS

2

0.71

2

-

NLOS

2.7-4.3

2.97-3.98

3.35

6.3

The variation of measured path loss with frequency and distance for different scenarios are shown in the figures below:

SMALL SCALE MODELING

Three key small scale parameters to be modeled:

  • RMS Delay Spread

  • Mean Excess Delay

  • Number of Multipath components

Some of the observed statistics for the Indoor measurements taken at MPRG, Virginia Tech, are shown in the Table below:


 

Bicone

 

TEM

 

15 dB

20 dB

 

15 dB

20 dB

 

NLOS

LOS

NLOS

LOS

 

NLOS

LOS

NLOS

LOS

Mean Excess Delay

1.6e-8

5.19E-09

2.01E-08

1.05E-08

 

2.36E-09

5.52E-10

5.59E-09

1.22E-09

Max Excess Delay

6.57E-08

2.84E-08

7.86E-08

5.68E-08

 

1.61E-08

2.65E-09

4.31E-08

1.24E-08

RMS Delay Spread

1.37E-08

5.41E-09

1.62E-08

8.50E-09

 

3.27E-09

7.53E-10

7.09E-09

1.70E-09

Number of Paths

72.8415

24.2753

153.9571

64.5884

 

28.7333

6.4188

99.1556

15.7607

Inverted Paths

49.00%

47.61%

49.30%

48.68%

 

50.71%

39.54%

49.81%

43.93%

Inverted Energy

44.23%

45.02%

45.36%

45.63%

 

34.26%

24.19%

37.67%

25.97%

 

The CDFs of the RMS delay spread, Mean Excess Delay and the Number of Paths are shown in the Figures below:

The CDFs of the total received energy for a 7 x 7 grid of points is shown in the figure below. We see that the spatial variation in received power (fading) is less than 5 dB in almost all cases. This is a major advantage of impulse radio, assuming that it is possible for all the received energy to be captured.

A new model for the indoor UWB channel was proposed. It was observed that the channel impulse response contained two clusters of multipath arrivals as seen in the figure below:

Therefore, the model channel impulse response was generated using a weighted sum of clusters of Poission arrivals, with parameters chosen to match the statistics of the data accurately. A more complete explanation can be found in the draft submitted to the APS/URSI Symposium in Monterey CA, Jun 20-27, 2004. We have observed that the new channel model matches the measured data closely in terms of RMS delay spread, mean excess delay, number of paths and the fraction of energy captured by a Rake receiver as shown in the Table below:


Table: Comparison of accuracy of Saleh-Valenzuela model and 2-cluster model

RMS delay spread

Mean Excess Delay

Number of Paths
Measured 16.0 ns 18.7 ns 138
Saleh-Valenzuela 15.0 ns 18.9 ns 198
2-cluster model 15.8 ns 19.2 ns 125

Bibliography: Channel Measurement and Models

[1] Cassioli, D., Win, M.Z., Molisch, A.F., "A Statistical Model for the UWB Indoor
Channel," IEEE VTS 53rd Vehicular Technology Conference, 2001, Spring, vol. 2,
pp. 1159-1163.

[2] Cramer, J.M., Scholtz, R.A., Win, M.Z., "Spatio-Temporal Diversity in Ultra-wideband
Radio," IEEE Wireless Communications and Networking Conference,
1999, vol. 2, pp. 888-892.

[3] Cramer, J.M., Scholtz, R.A., Win, M.Z., "On the Analysis of UWB Communication
Channels," IEEE Military Communications Conference, 1999, vol. 2, pp. 1191-1195.

[4] Cramer, R.J.-M., Win, M.Z., Scholtz, R.A., "Impulse Radio Multipath
Characteristics and Diversity Reception," IEEE International Conference on
Communications, 1998, vol. 3, pp. 1650-1654.

[5] Cramer, R.J.-M., Win, M.Z., Scholtz, R.A., "Evaluation of the Multipath
Characteristics of the Impulse Radio Channel," The Ninth IEEE International
Symposium on Personal Indoor and Mobile Radio Communications, 1998, vol. 2,
pp. 864-868.

[6] Foerster, J.R., "The Effects of Multipath Interference on the Performance of UWB
Systems in an Indoor Wireless Channel," IEEE VTS 53rd Vehicular Technology
Conference, 2001, Spring, vol. 2, pp. 1176-1180.

[7] Ghassemzadeh, S.S., Jana, R., Rice, C.W., Turin, W., Tarokh, V., "A Statistical Path
Loss Model for In-Home UWB Channels," IEEE Conference on Ultra Wideband
Systems and Technology, 2002.

[8] Hovinen, V., Hämäläinen, M., Pätsi, T., "Ultra Wideband Indoor Radio Channel
Models: Preliminary Results," IEEE Conference on Ultra Wideband Systems and
Technology, 2002.

[9] Keignart, J., Daniele, N., "Subnanosecond UWB Channel Sounding in Frequency
and Temporal Domain," IEEE Conference on Ultra Wideband Systems and
Technology, 2002.

[10] Kissick, W.A. (Ed), "The Temporal and Spectral Characteristics of
Ultrawideband Signals," NTIA Report 01-383, Jan. 2001.

[11] Kunisch, J., Pamp, J., "Measurement Results and Modeling Aspects for the UWB
Radio Channel," IEEE Conference on Ultra Wideband Systems and Technology,
2002.

[12] Lee, H., Han, B., Shin, Y., Im S., "Multipath Characteristics of Impulse Radio
Channels," IEEE VTS 51st Vehicular Technology Conference, 2000, Spring, vol. 3,
pp. 2487-2491.

[13] Prettie, C., Cheung, D., Rusch, L., Ho, M., "Spatial Correlation of UWB Signals
in a Home Environment," IEEE Conference on Ultra Wideband Systems and
Technology, 2002.

[14] Qiu, R.C., "A Theoretical Study of the Ultra-wideband Wireless Propagation
Channel Based on the Scattering Centers," IEEE VTS 48th Vehicular Technology
Conference, 1998, vol. 1, pp. 308-312.

[15] S. Venkatesh, J. Ibrahim and R.M. Buehrer, "A New Model for Ultra Wideband Indoor NLOS Channels",
Submitted to 2004 Antennas and Propagation Society Conference, Monterey California June 20-27, 2004




Mobile & Portable Radio Research Group
Virginia Tech
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FAX: (540) 231-2968
Email: mprg@vt.edu