Project Title: Concepts for Ultra Wideband Radio Systems (CUBS) Distribution: CUBS ... · 2005-02-09 · Project Title: Concepts for Ultra Wideband Radio Systems (CUBS) Distribution:

Project Title: Concepts for Ultra Wideband Radio Systems (CUBS)

Distribution: CUBS

Document Id:

Document Title: UWB Channel Measurements at Oulu University Hospital

Work Area: CUBS/WP6 – radio channel modeling

Editor: Lassi HENTILÄ

Authors: Lassi HENTILÄ, Harri VIITTALA, Matti HÄMÄLÄINEN

Version: Ver. 0.4.

Last Save Date: 04.08.2004

File Name: Hospital_meas_report_A.doc

Abstract: This document reports an ultra wideband radio channel measurement campaigns performed at the Oulu University Hospital. Radio channel sounding were carried out in frequency domain using vector network analyzer. The frequency band of interest was 3.1 GHz to 6.0 GHz. This document will be updated after the final results are available.

Keywords: ultra wideband, radio channel modeling, measurement, indoor, hospital

Document History:

Ver. 0.1. 19.07.2004 Document created Ver. 0.2. 28.07.2004 First version Ver. 0.3. 02.08.2004 Preliminary results added Ver. 0.4 04.08.2004 Document uploaded to CUBS web-site

Centre for Wireless Communications

UNIVERSITY OF OULU Centre for Wireless Communications 04.08.2004 2 / 24

TABLE OF CONTENTS

TABLE OF CONTENTS........................................................................................ 2

1. INTRODUCTION......................................................................................... 3 2. MEASUREMENTS........................................................................................ 4

2.1. Measurement setup...................................................................................................4 2.2. Measurement parameters.........................................................................................4 2.3. Parameters and reference measurement................................................................6

3. ENVIRONMENTAL PARAMETERS.......................................................... 8 3.1. Operating room L4 (K6 234)..................................................................................8 3.2. X-ray examination room (N4 111).......................................................................10 3.3. Intensive care unit 2 (N5 223) ..............................................................................11

4. PRELIMINARY RESULTS.......................................................................... 11 4.1. Channel characteristics...........................................................................................14 4.2. Path Loss..................................................................................................................15

5. CONCLUSIONS ...........................................................................................18 6. REFERENCES..............................................................................................19 7. APPENDICES .............................................................................................. 20


1. INTRODUCTION

Ultra wideband (UWB) technology is breaking itself through in a short range data communications and positioning applications. To gain as much as possible of the technique precise radio channel models are needed. A hospital is a potential environment where UWB can be used in the future applications due to its very low, noise-like power spectral density which minimized the radio interference caused to the other sensitive medical devices.

In this document an UWB radio channel measurement campaign performed at the Oulu University Hospital is presented. Transfer functions of the predefined channels were measured using a conventional vector network analyzer (VNA) sounder, thus VNA is used for both transmission and reception. The frequency sweeping measurement technique covered a band from 3.1 to 6.0 GHz. The measurement setup, parameters, environments, measurement positions and some preliminary results are presented in this document. Final channel parameters and models will be presented in a later version of this document after the data is totally analysed.


2. MEASUREMENTS

2.1. Measurement setup

The channel sounder is built over the vector network analyzer (VNA). The diagram of the channel sounding system is presented in Figure 1.

Figure 1. Radio channel sounding system and post-processing process.

The measurement system is controlled by a personal computer through the LabView program. The controlling software takes care of the analyzer settings, timings, data storage, etc. functions during the measurements.

VNA is operating in a single stepping sweep mode and it was sweeping the frequency band using 1601 points to measure the channel frequency response (transfer function).

The probing signal (output of the VNA) is amplified to the predefined level using Agilent 83017A wideband amplifier. The antennas in the system are CMA-118/A conical antennas. Antenna type has typically an omni-directional radiation pattern with a constant phase centre which is requirement for the antenna to be used in channel sounding.

The receiving antenna is placed onto a moving antenna carriage which takes 5 centimetres steps controlled by LabView. The length of the carriage is approximately 2.5 meters.

Data post-processing is done in Matlab using the software that is developed in the project.

2.2. Measurement parameters

There are few main parameters that need to be selected before the measurements can be carried out. The used measurement setup utilized the parameters shown in , and are next discussed. When specifying and building up the test setup, and also during the test


measurements, those parameters have to be monitored to guarantee the correct operation of the system.

Table 1. Measurement setup parameters

Parameter Value

Frequency band 3.1–6.0 GHz

Bandwidth 2.9 GHz

Number of points over the band 1601

Sweep time 800 ms

Dynamic range 80 dB

Average noise floor –90 dB

Transmitted power (amplifier output) 21 dBm

Amplifier gain (mean) 32 dB

TX cable loss (max) 6 dB

RX cable loss (max) 15 dB

Antenna gain 0 dBi (typical)

EIRP (min) 0 dBm = 1 mW

The frequency sweeping time is set to 800 ms. The sweeping time depends only on the number of the measured frequency points within the band to be swept. The transmitted power levels reported are typical output powers of the amplifiers. Cables and the adapters connected cause excess attenuation to the transmitted signal level. Effective isotropic radiated power (EIRP) is calculated taking all the losses and gains into account. The same transmission power level has been used in all measurements. The system calibration has been done to compensate the frequency dependent variation and attenuation caused by the adapters and cables. The dynamic range mentioned in Table 1 is reduced to the output of the RX antenna. Specified dynamic range for the network analyzer is 100 dB [1], but the cable losses diminish the achievable dynamic range.

Maximum alias-free detectable delay maxτ is defined by the number of frequency points per sweep N and by the used bandwidth B as [1]

BN /)1(max −=τ . (1)

Using the parameter values from Table 1, (1) gives theoretical upper bound for the maximum detectable delay, maxτ =1600/(2.9 GHz) = 551.7 ns =̂ 165.5 m. This is quite reasonable value for hospital indoor environments.

To detect possible channel fluctuation, 20 sweeps was recorded at each antenna location. The RX-antenna carriage positions inside rooms were determined by measuring distances to walls using a laser ranging device. The manufacturer’s specification of the laser device is 3 mm measurement accuracy (typically).


2.3. Parameters and reference measurement

The amplifier, the cables and the whole measurement system were measured independently before the measurement campaign at the same frequency band. The reference measurement was performed in an anechoic chamber at the University of Oulu.

Figure 2 illustrates the reference measurements when the link distance between the antennas was 1.0 m. Figure 3 and Figure 4 show the system’s transfer function and impulse response in the chamber, respectively. Basically, the result is a response of the antenna plus some reflections from the roof and back wall of the chamber (See Figure 4 from markers 3 to 5). Since the reflections are 35 dB under the LOS (line-of-sight) peak, their effect is insignificant in the channel modelling point of view. The reference measurement is taken into account in the data post-processing by reducing the free space loss (at distance 1 m) from the reference measurement and compensating the result at each measured sweep in the raw data.

The frequency responses of the amplifier and the cables are shown in Appendix 1.

Figure 2. Reference measurements in an anechoic chamber.


Figure 3. Reference measurement, a transfer function.

Figure 4. Reference measurement, an impulse response.


3. ENVIRONMENTAL PARAMETERS

The UWB radio channel measurements presented in this document have been performed at the Oulu University Hospital . The measured environments were operating room (leikkaussali), x-ray examination room (natiiviröntgen) and intensive care unit 2 (ICU, teho-osasto). Environmental parameters and locations of the measurements are discussed in the following chapters.

Throughout the measurements there was no movement in the rooms when recording the data except in the ICU.

3.1. Operating room L4 (K6 234)

The positions of transmitter and receiver antennas are shown in Figure 5. The first TX-antenna position was TX01. RX-antenna was in position RX01. Then the RX-antenna carriage was moved to position RX02.

Finally, the TX-antenna was placed to position TX02. Now there is a concrete wall between the transmitter and the receiver (non line-of-sight).

The measurement system rack was placed in the room K6 223.

The main building material of the room is concrete. The height of the ceilings varies as can be seen from Figure 5. There are some chromium plated working tables in this room. The washing machines in the next rooms are also chromium plated.


L4

6020

6685

TX01

1130

1120

TX02

2965

1434

6685

2760

RX012190

1045

4712

1435

1430

3933

RX02

Operating Table

3110

2574

Room Height2599

Room Height5539

Room Height3178

3178

5539

Cross-Section

Operating Room-16.6.2004-

Figure 5. Layout of the operating room and the used antenna positions.


3.2. X-ray examination room (N4 111)

The second room where the measurements were carried out was X-ray examination room. To eliminate unintentional X-ray radiation, there are thick lead walls in this room. There are also two leaded windows whose locations can be seen in Figure 6. TX-antenna was placed in the position TX01. The positions of the antennas are shown in Figure 6. There were two receiver carriage positions for the soundings inside a room. The last position of the RX-antenna carriage (RX03) was placed to the corridor. Because of lack of time only four sweeps per position were taken.

TX01TX01RX01RX01

RX02RX02

RX03RX03

11363641

1042 1840 2688

514

Room Height3219

7025 5805

1134

4559

2747

51271780 1030

1370

50502654

2055

17,5°

16,0°

Leaded Window Leaded Window

X-ray Examination Room (1/2)-17.6.2004-

909

Figure 6. Layout of the X-ray examination room and the used antenna positions.


3.3. Intensive care unit 2 (N5 223)

In the intensive care unit 2, there was an empty bed for the RX-antenna carriage which made the measurements much easier. In the room, the movement was heavy and therefore the channel was very dynamic. The sounding was started from the positions TX01 and RX01 (see Figure 7). Next, TX-antenna was moved closer to RX, to position TX02. After that, 2 x 2 grid was created for RX-antenna and TX-antenna was moved to the position TX03. In positions RX03A-D 50, sweeps per positions were measured.

13735

9417

Room Height 2538

2210

2161

TX03TX03

TX01TX01

40605265

RX02RX02

RX01RX01

TX02TX024129

4410

3384

1720

1351

21943144

2144

700200

200

A

BC

D

Intensive Care Unit 2 (1/2)-18.6.2004-

22,3°

zoom

Figure 7. Layout of the intensive care unit 2 and the used antenna positions.

4. PRELIMINARY RESULTS

The recorded data was stored in a polar format, i.e., in complex numbers. Data from each position was saved in a different file as described in Appendix 2. The name of the data file consists of the measurement day and a running number which corresponds to the measurement location.

Firstly in the post-processing, the raw *.dat -format data is converted into *.mat for Matlab, and then inverse Fourier transformed to time domain for the analysis. The time domain data contains impulse responses of the measured radio channels. The following figures present typical impulse responses from operation room (Figure 8), x-ray examination room (Figure 9 and Figure 10) and intensive care unit 2 (Figure 11). It must be noted that Figure 10 represents an environment where the link between the TX and the RX is blocked by a thick leaded window (cf. link TX01–RX03 in Figure 6). The figures are generated by the VNA itself through its time-domain module.


Figure 8. An absolute valued impulse response from the operating room.

Figure 9. An absolute valued impulse response from the x-ray examination room.


Figure 10. An absolute valued impulse response outside the x-ray examination room.

Figure 11. An absolute valued impulse response from the intensive care unit 2.


4.1. Channel characteristics

It is evident from figures 8–11 that the delay spread is different in different rooms. RMS delay spread, mean excess delay and number of paths within 10 dB of the peak are obtained from the measurement data. RMS delay spread is a time domain parameter which is typically used to give an idea of the channel’s characteristic. It is calculated from the power delay profile (PDP), as [3]

∑

∑

=

=

−−

= L

kk

L

kkk

th

tht

1

2

1

22Am

RMS

)(

)()ττ(τ , (2)

where

h(tk) is the sampled impulse response of the channel,

tk is delay at time k,

L is the number of delay samples and

∑

∑

=

=

−

=L

kk

L

kkk

th

tht

1

2

1

22A

m

)(

)()τ(τ , (3)

presents the mean excess delay of the radio channel.

The time domain parameters are obtained from the PDPs by taking into account the thresholds presented in Figure 12 for the line-of-sight (LOS) link.

Figure 12. Typical PDP in LOS channel in the operating room.


Channel characteristics extracted from the measurement data are listed in Table 2. The measurement positions mentioned in the table are defined in Appendix 1 in more details.

Table 2. Preliminary channel characteristics

Channel Characteristics

Operating Room X-ray Examination Room

Intensive Care Unit 2

Measurement position 1 2 3 4 5 6 7 8 9

τm [ns] 24.2 26.4 31.0 27.0 28.5 40.2 42.1 24.2 62.9τRMS [ns] 9.2 10.9 10.4 14.1 15.0 15.5 13.9 12.1 16.9NP10 dB 13 18 19 13 16 41 9 9 58 NP85 % 29 42 60 50 56 75 38 38 169

4.2. Path Loss

In this campaign, path loss was studied in the all measured environments. Path losses are calculated by averaging the transfer functions over the frequency band as a function of distance, as [4]

−= ∑

=

1601

1

2i10 ),(

16011log10)(

ifdHdPL , (4)

where H(fi) is the measured channel transfer function.

Averaging over the frequencies can be account for the fact that the total path loss for UWB signal is relatively insensitive to frequency. In addition, the focus is to investigate the path loss relative to the total received power over the measured band. Figures 13–15 depict the path losses in the different measured cases. The path loss exponent is calculated from the slope of the linear regression line, which is shown in the path loss figures. All path loss cases are combined in Figure 16. The path losses presented in Figures 13–15 prove that an indoor UWB LOS radio channel can have a path loss exponent below the case of free space loss, i.e., two. This can be explained by the fact that the UWB indoor radio channel is very multipath rich from signals reflected from the walls. In addition, path loss in X-ray examination room proves smaller path loss exponent value compared to other rooms, since thick concrete walls and leaded windows keep the signal inside the room what strengthen the received signal level.


Figure 13. Path loss in operating room (Pos 2).

Figure 14. Path loss in X-ray examination room (Pos 5).


Figure 15. Path loss in intensive care unit (Pos 8).

Figure 16. Path loss of the positions Pos 2, Pos 5 and Pos 8 together.


5. CONCLUSIONS

This document studies UWB radio channel behaviour in hospital environment. The measurements were carried out in three various rooms at the Oulu University Hospital. The used frequency domain measurement system was based on the vector network analyser. The reference measurements in an anechoic chamber were taken into account in the data post-processing.

Channel characteristics including RMS delay spread, mean excess delay, number of paths within 10 dB of the peak, number of paths within 85 % of the captured energy were extracted from the data as a preliminary result and presented in Chapter 4.

The final channel models will be embedded to the document when the data post-processing is ready.


6. REFERENCES

[1] Agilent 8720E Family, Microwave Vector Network Analyzers, Data sheet. Agilent Technologies, 35 p.

[2] Technical Manual for Conical Monopole Antenna CMA-118/A 1.0-18.0 GHz. 5 p. [3] H. Hashemi (1993) “The Indoor Radio Propagation Channel,” Proceedings of the IEEE,

Vol. 81, Issue: 7, p. 943-968. [4] S.S. Ghassemzadeh, L.J. Greenstein, A. Kavčić, T. Sveinsson and V. Tarokh (2003)

“An Empirical Indoor Path Loss Model for Ultra-Wideband Channels,” KICS Journal of Communications and Networks, Vol. 5, No. 4, p. 303–308.


7. APPENDICES

Appendix 1 – Transfer functions of the used amplifier and cables

Appendix 2 – Measurement campaign at the Oulu University Hospital

Appendix 3 – The disposition of equipment in the X-ray examination room

Appendix 4 – The disposition of equipment in the intensive care unit 2

UNIVERSITY OF OULU Centre for Wireless Communications 04.08.2004

Transfer functions of the amplifier and the cables APPENDIX 1

Gain of the amplifier

Loss of the TX cable

Loss of the RX cable


Measurement campaign at the Oulu University Hospital APPENDIX 2

Meas.

Date

Meas.

Room

Running

Pos.

Number

Meas.

Positions

Saved Data

File

Additional

comments

16.6.2004 Operating Room 1 TX01,RX01 160604_01.dat

2 TX01,RX02 160604_02.dat

3 TX02,RX02 160604_03.dat

17.6.2004 X-ray Examination Room

4 TX01,RX01 170604_01.dat

5 TX01,RX02 170604_02.dat

6 TX01,RX03 170604_03.dat Only 4 sweeps per position

18.6.2004 Intensive Care Unit 2 7 TX01,RX01 180604_01.dat

8 TX02,RX01 180604_02.dat

9 TX03,RX02A 180604_03A.dat RX: 2 x 2 grid, 50 sweeps per position

9 TX03,RX02B 180604_03B.dat

9 TX03,RX02C 180604_03C.dat

9 TX03,RX02D 180604_03D.dat


The disposition of equipment in the X-ray examination room APPENDIX 3

1224

224214361938

3625

2827741

1660

803

15613876

Operating Table

= Metallic Closet

= Hanging Machine

= Machine

X-ray Examination Room (2/2)-17.6.2004-

1000


The disposition of equipment in the intensive care unit 2 APPENDIX 4

Control Room

= Bedpatient

Left 14:30

Arrived 13:20Left 13:00

= Medicine Cart

= Hanging Computer

Intensive Care Unit 2 (2/2)-18.6.2004-

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Project Title: Concepts for Ultra Wideband Radio Systems (CUBS) Distribution: CUBS ... · 2005-02-09 · Project Title: Concepts for Ultra Wideband Radio Systems (CUBS) Distribution: