ETSI EP BRAN 3ERI084A30 March1998

page 1

Source: Jonas Medbo, Jan-Erik Berg, Ericsson Radio Systems AB,

and Henrik Andersson, Ericsson Microwave Systems AB

Title: Measured Radiowave Propagation Characteristics at 5 GHz fortypical HIPERLAN/2 Scenarios

Agenda Item:

Document for: Decision

Discussion X

Information X

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1 Introduction

An adequate characterization of radio wave propagation in representative envi-ronments is essential for the design of radio communication systems. For thispurpose there are two possibilities — either physical simulations, using e.g. raytracing techniques, or direct measurements. Simulations are either too heavyregarding the computational complexity or not sufficiently reliable. Therefore,measurements are indispensable.

In order to improve the characterization of the HIPERLAN/2 radio channel,wideband measurements have been performed at 5 GHz. The focus has been onpropagation in large open indoor environments since only few such measure-ments have been found in the literature. Also one typical office environment hasbeen included. For comparison, a few measurement points were also chosen atan outdoor location.

For the office environment, the range of measured delay spreads (typically 20ns, max 80 ns) is in agreement with literature [1, 2, 3, 4]. Moreover, the mea-sured path loss is also in agreement with a suggested model. A maximum delayspread of about 105ns was measured in the large open space indoor and outdoorenvironments.

2 Measurement technique

A network analyzer (HP8722) with a power amplifier at the transmitter and alow noise amplifier at the receiver was used. The receiver cable was 5m and thetransmitter cable 25m and, thus, the maximum distance was 30m. Two halfwavedipole antennas (2 dBi gain) were used. The amplitude and phase was measuredat 201 equidistant frequencies between 5.14 and 5.3 GHz. The measuring timefor all 201 points was about 20 seconds.

3 Analysis

Power delay profiles were obtained by applying a Hanning window and an IFFTto the measured frequency domain data.

At three locations, data was taken at 101 equidistant points on a 1.5m sectionmaking up a virtual array. By applying an FFT, this data was transformed to theDoppler frequency domain. This data was also used to determine average powerdelay profiles and the fading statistics.

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4 Measurement locations

The measurement data was collected at 5 different locations:

A The sixth floor of a typical Swedish office building (12x40m) withsmall offices at both sides of a long corridor. Outer walls, floorand ceiling were made of reinforced concrete. Inner walls con-sisted of double plasterboards with glass-wool in between (Fig.2).

B A large open space staff canteen (30x40m). The two outer wallsconsisted mainly of metallized windows. The ceiling was metal(at 3.67m height) with a suspended light material inner ceiling (at2.67m height) and the floor reinforced concrete (Fig. 3).

C A large glass covered pedestrian street (10x104m) between two 6storey buildings.

D A large open indoor shopping area (20x120m, 20m height) withone long side consisting of metallized window and the otherlong side of small shops and restaurants (Fig. 1).

E A park (90x90m) surrounded by multi storey (about 6 floors)office buildings.

Figure 1. Drawing of location D. The transmitter was placed at Tx. Measurements were made atpoints marked with x.

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Figure 2. Drawing of location A. The virtual array section is marked by an arrow and was mea-sured with the transmitter at Tx2. Measurements were made at scattered points marked with x and

the transmitter at Tx1.

Except for location B, the measurements were performed with people in motionin the vicinity of the antennas introducing noise at some level. However, thismotion was not allowed closer than 10m to the antennas. At the large open loca-tions the measurements were performed with line of sight (LOS), non line ofsight (NLOS) and obstructed line of sight (OLOS, person in front of receiver)conditions.

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Figure 3. Drawing of location B. The virtual array section is marked by an arrow and was mea-sured with the transmitter at Tx1. Measurements were made at points marked with x and the trans-

mitter at Tx1 and Tx2.

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Figure 4. Drawing of location C. The virtual array section is marked by an arrow and was mea-sured with the receiver at Rx.

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Figure 5. Drawing of location E. The transmitter positions are marked with x and the receiver withRx. There are buildings (black) surrounding a park.

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5 Results

5.1 Channel parameters

A number of channel characteristics can be determined from the three virtualarray sections at location A, B and C respectively. At location A the transmitterwas located in one office and the receiver in another office, 7m away, with threeinner walls in between. The measurements at locations B and C were performedwith line of sight conditions and a distance, between the receiver and the trans-mitter, of 15m and 20m respectively.

5.1.1 Power delay profiles

Typical instantaneous power delay profiles for large and small delay spread atlocations A and E are shown in Fig. 6. Here, instantaneous means no averagingin time or space has been performed. The profiles are very similar, having whatlooks like an

Figure 6. Typical power delay profiles from a) location A; and b) location E. The solid lines corre-spond to small delay spreads and the dashed lines to large delay spreads.

exponential decay and, for the small delay spread profiles, a spike at zero delay.

From the three virtual array measurements, average profiles and fading statisticscan be determined (Figs. 7, 8 and 9). The shape of the average profiles is wellapproximated by an exponentially decaying part and an optional spike at zero

0 200 400 600 800 1000−200

−150

−100

−50

Delay [ns]

Rel

ativ

e po

wer

[dB

]

a)

0 200 400 600 800 1000−200

−150

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−50

Delay [ns]

Rel

ativ

e po

wer

[dB

]

b)

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delay. Moreover, the fitted Ricean K factor is essentially less than 2 for all dis-crete delay times except for the LOS spike for which K was 4 and 12 (for 10nsbin size according to the equivalent noise bandwidth definition [6]) for locationB and C respectively. It should be noticed that a strong dependence of K on theresolution in time is expected. Assuming a constant average level of multi-pathunder the Ricean spike gives the relation

, (5.1)

where Tbin is the time resolution.

For locations B and C, the Doppler spectrum (Figs. 7-9 b) and e)) is essentiallyclassical with a spike corresponding to the direct path. The corresponding directpath spike is attenuated and broadened for location A. This can be explained as adirective spreading and attenuation of the direct ray during wall passage.

Figure 7. Power delay, Doppler and frequency data from virtual array measurement at location A.The power in linear gray scale is shown in a) and c) in the position/delay and position/frequency

plane respectively. In b) is shown the field amplitude in the delay/Doppler plane. The average powerdelay profile is shown in d) and the average Doppler profile in e). The corresponding Doppler filtered

profiles are indicated in gray. In f) is shown the average power, using the unfiltered measured fre-

K T bin( ) K 1( ) T bin⁄=

Position x [m]

Del

ay [n

s]

a)

0 0.5 1 1.50

50

100

150

200

250

Nor

mal

ized

Dop

pler

freq

uenc

y

Delay [ns]

b)

0 50 100 150 200 250

−1

−0.5

0

0.5

1

Position x [m]

Fre

quen

cy [G

Hz]

c)

0 0.5 1 1.55.14

5.16

5.18

5.2

5.22

5.24

5.26

5.28

5.3

Ave

rage

pow

er [d

B]

Delay [ns]

← K = 6

d)

0 500 1000−60

−50

−40

−30

−20

−10

0

10

Ave

rage

pow

er [d

B]

Normalized Doppler frequency

e)

−2 −1 0 1 2−40

−30

−20

−10

0

10

Ave

rage

pow

er [d

B]

Position x [m]

f)

0 0.5 1 1.5−10

−5

0

5

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quency response (5.14-5.3 GHz), versus position.

An artificial obstruction of the line of sight path can be achieved by Doppler fil-tering as indicated in Figs. 7-9. Doing so, the zero delay spike in the powerdelay profiles disappears. At location A, the power delay profile is essentiallyunaffected by the artificial obstruction which is logical since the Doppler spec-trum indicates that the power is received more or less uniformly in all direc-tions.

Figure 8. Same as Fig. 7 for location B.

Position x [m]

Del

ay [n

s]

a)

0 0.5 1 1.50

50

100

150

200

250

Nor

mal

ized

Dop

pler

freq

uenc

y

Delay [ns]

b)

0 50 100 150 200 250

−1

−0.5

0

0.5

1

Position x [m]

Fre

quen

cy [G

Hz]

c)

0 0.5 1 1.55.14

5.16

5.18

5.2

5.22

5.24

5.26

5.28

5.3

Ave

rage

pow

er [d

B]

Delay [ns]

← K = 4d)

0 500 1000−60

−50

−40

−30

−20

−10

0

10

Ave

rage

pow

er [d

B]

Normalized Doppler frequency

e)

−2 −1 0 1 2−40

−30

−20

−10

0

10

Ave

rage

pow

er [d

B]

Position x [m]

f)

0 0.5 1 1.5−10

−5

0

5

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Figure 9. Same as Fig. 7 for location C.

Position x [m]

Del

ay [n

s]

a)

0 0.5 1 1.50

50

100

150

200

250

Nor

mal

ized

Dop

pler

freq

uenc

y

Delay [ns]

b)

0 50 100 150 200 250

−1

−0.5

0

0.5

1

Position x [m]

Fre

quen

cy [G

Hz]

c)

0 0.5 1 1.55.14

5.16

5.18

5.2

5.22

5.24

5.26

5.28

5.3

Ave

rage

pow

er [d

B]

Delay [ns]

← K = 12

← K = 2

d)

0 500 1000−60

−50

−40

−30

−20

−10

0

10

Ave

rage

pow

er [d

B]

Normalized Doppler frequency

e)

−2 −1 0 1 2−40

−30

−20

−10

0

10

Ave

rage

pow

er [d

B]

Position x [m]

f)

0 0.5 1 1.5−10

−5

0

5

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5.1.1 RMS delay spreads

For each power delay profile, the rms delay spread was calculated discardingdata at delays larger than 1100ns and 30dB below the peak power. In Fig. 10 isshown the rms delay spread versus path loss for all measurement points. Thefollowing definition of path loss, L (dB units),

, (5.2)

where Pt and Pr is the transmitted and received power (dBm) respectively, andGt and Gr are the corresponding antenna gains (dBi), have been used.

Figure 10. Path loss versus rms delay spread for all measurement locations. The three gray clusterscorrespond to the three virtual array measurements. Circles correspond to location A. Squares cor-

respond to the large open indoor locations and the stars to the outdoor location.

The maximum observed delay spread was about 105ns for one NLOS outdoorand one NLOS indoor measuring point.

L Pt Pr– Gt Gr+ +=

0 20 40 60 80 100 12045

50

55

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65

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80

85

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95

100

Delay spread, rms [ns]

Pat

h lo

ss [d

B]

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Cumulative probability distributions are shown in Fig. 11 for the three virtualarrays and also for scattered points in the office location, A. The median delayspread is 20ns in the office environment and less than 60ns in the large openspace environments. Removing the direct path by Doppler filtering (See Figs. 7-9) implies an increase of delay spread to about 75ns at locations B and C, whileit is essentially unchanged at location A since the direct path is strongly attenu-ated by the passage through walls.

Figure 11. Cumulative delay spread distributions. a), b) and c) correspond to the virtual arraydata from locations B, C and A respectively. d) corresponds to scattered measurements at location A.

The dashed lines correspond to artificial obstruction of the direct path by Doppler filtering.

0 20 40 60 80 1000

25

50

75

100

a)

Delay spread, rms [ns]

Cum

ulat

ive

dist

ribut

ion

[%]

0 20 40 60 80 1000

25

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75

100

b)

Delay spread, rms [ns]

Cum

ulat

ive

dist

ribut

ion

[%]

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100

c)

Delay spread, rms [ns]

Cum

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dist

ribut

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[%]

0 20 40 60 80 1000

25

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100

d)

Delay spread, rms [ns]

Cum

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dist

ribut

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[%]

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For comparison purpose, virtual array data was also simulated. A simple chan-nel model was used. The average power was assumed to decline exponentiallyand all taps were assumed to be rayleigh fading. The average delay spread wasset to 20ns, 80ns and 110ns. It can be concluded from Fig. 12 that an averagedelay spread of 110ns will result in a probability of about 1% that, due to thefast fading of the taps, the observed instantaneous delay spread is larger than130ns. This means that for modeling purpose, the local average (or median)delay spread, and not the instantaneous, is the relevant parameter. Maximumdelay spreads of about 130ns have been reported from other measurements [5,1, 2] including very large open space indoor environments indicating that amaximum average of 110ns might be realistic. However, for outdoor environ-ments the statistical significance of the present measurement is quite low.

Figure 12. Cumulative delay spread distributions for simulated virtual array data. The three linescorrespond to average rms delay spreads of 20ns, 80ns and 110ns. An exponentially decaying model

with rayleigh fading taps was used. The spread of each distribution is purely statistical due to thefast fading.

0 20 40 60 80 100 1200

10

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30

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Delay spread, rms [ns]

Cum

ulat

ive

dist

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[%]

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5.2 Directive antennas

Some measurements were performed with directive antennas (7 dBi patchantenna with 90 deg. lobe width at 3dB attenuation) to indicate their potentialadvantages. In Fig. 13 is shown that a reduction in delay spread in the order of20ns might be realistic for large open environments. However, in order to assessthis gain substantially more measurement data is required

Figure 13. Path loss versus delay spread. Open symbols correspond to measurements with omniantenna at both transmitter and receiver. Black symbols correspond to measurements with direc-tional antenna at the transmitter and omni at the receiver where the direction giving the highest

received power is selected. Data from the same measuring point is connected with a line. Circles cor-respond to LOS, triangle to OLOS and squares to NLOS conditions. Virtual array data is indicated

in gray as a reference.

0 20 40 60 80 100 12045

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80

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100

Delay spread, rms [ns]

Pat

h lo

ss [d

B]

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5.3 Path loss model

For office environments a linear (in dB scale) path loss model was suggested in[3]. For this model it is assumed that the loss consists of the free space loss anda linear loss per meter (α dB/m):

, (5.3)

where d is the distance between the transmitter and the receiver.

This model has been compared with the present measurements for α=0.5dB/m.As seen in Fig. 14 the data fits well to the model. A large scale fading margin ofonly 7dB was required.

Figure 14. Path loss versus distance. The circles correspond to measurement points at location A.The curved line corresponds to the suggested model for office environments with α = 0.5 dB/m wherethe dashed line corresponds to a margin of 7 dB at 30m. The straight lines correspond to exponent

models (n=2 gives free space loss). The three circles close to the line with n=1 are from measurementsin a corridor.

L d( ) LFS d( ) αd+=

100

101

40

50

60

70

80

90

100

110

Pat

h lo

ss [d

B]

Distance [m]

n=1

n=2

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6 Conclusions

Wideband propagation measurements have been performed at 5 GHz at fourindoor environments and one outdoor location. The results indicate that a typi-cal average power delay profile consists of a component for which the powerdeclines exponentially with time and, for LOS conditions, a spike at zero delay.The fading at discrete delays follows rayleigh statistics except for the LOS spikewhich has a Ricean K factor in the range 5 to 15 (for 10ns resolution). This typeof fading statistics imply that individual paths are, in general, not resolvedwithin the resolution (10ns) of the present measurements. The measured Dop-pler spectrum is consistent with the classical (Jake’s) type with a LOS spike.

These measurements, and others found in literature, indicate that the range oftypical delay spreads for indoor environments is between 10ns and 110ns.

More measurements are still needed in order to improve the statistical signifi-cance — in particular concerning typical outdoor scenarios, and the advantageof directive antennas.

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References[1] D. A. Hawbaker, ‘‘Indoor Wide Band Radio Wave Propagation Mea-

surements and Models at 1.3 and 4.0 GHz’’, Master of Science ThesisMPRG-TR-91-05, Virginia Polytechnic Institute & State University,May 1991.

[2] R. van Nee, ‘‘Delay Spread Requirements for Wireless Networks in the2.4 GHz and 5 GHz Bands’’, Standards Working Group IEEE P802.11doc. 97/125. Nov. 1997.

[3] J. Medbo, ‘‘Radio Wave Propagation Characteristics at 5 GHz withModeling Suggestions for HIPERLAN/2’’, ETSI BRAN 3ERI074A,Jan. 1998.

[4] C. Bergljung, P. Karlsson and F. Malmström, ‘‘Indoor PropagationCharacteristics in the 5 GHz Band’’, ETSI BRAN 3TRS072B, Jan.1998.

[5] D.M.J. Devasirvatham, C. Banerjee, M.J. Krain & D.A. Rappaport,‘‘Multi-Frequency Radiowave Propagation Measurements in the Porta-ble Radio Environment’’, in Proc. Second IEEE Int. Symp. Personal,Indoor and Mobile Radio Commun., London, England, Sept. 1991, pp.98-103., COST 231 TD(90)14

[6] F. J. Harris, ‘‘On the Use of Windows for Harmonic Analysis wth theDiscrete Fourier Transform’’, Proc. of the IEEE, vol. 66, no. 1, Jan.1978. pps. 51-83.