NTIA Report 94-309

Impulse Response Measurements

in the 1850-1990 MHz Band

in Large Outdoor Cells

J.A. Wepman

J.R. Hoffman

L.H. Loew

u.s. DEPARTMENT OF COMMERCE

Ronald H. Brown, Secretary

Larry Irving, Assistant Secretary

for Communications and Information

JUNE 1994

Product Disclaimer

Certain commercial equipment, instruments, or materials are identified in this paper to specify

adequately the technical aspects of the reported results. In no case does such identification imply

recommendation or endorsement by the National Telecommunications and Information

Administration, nor does it imply that the material or equipment id~ntified is necessarily the best

available for the purpose.

111

CONTENTS

Page

FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. vi

TABLES ...........................".................... Vlll

ABSTRACT 1

1. INTRODUCTION 1

2. MEASUREMENT SYSTEM 3

2.1 Transmitter 3

2.2 Receiver "..................... 3

3. MEASUREMENT PROCEDURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 9

4. MEASUREMENT LOCATIONS 13

5. DATA ANALYSIS METHODS AND RESULTS 17

5.1 Delay Statistics 18

5.2 Effects of Spatial Diversity 26

5.3 Multipath Power Statistics 26

5.4 Number of Paths, Path Arrival Time, and Path Power Statistics 29

5.5 Correlation Bandwidth 41

6. SUMMARY AND CONCLUSIONS 46

7. REFERENCES 48

v
FIGURES

Page

Figure 2.1. Photograph of the measurement system transmitter van 4

Figure 2.2. Photograph of the measurement system receiver van . . . . . . . . . . . . .. 5

Figure 2.3. Block diagram of the measurement system transmitter . . . . . . . . . . . .. 6

Figure 2.4. Block diagram of the measurement system receiver . . . . . . . . . . . . . .. 7

Figure 3.1. Example calibration power delay profile 10

Figure 4.1. Measurement routes in the flat rural cell 14

Figure 4.2. Measurement routes in the hilly rural cell 15

Figure 4.3. Measurement routes in the urban high-rise cell 16

Figure 5.1. Histograms of maximum delay (a), mean delay (b), and RMS delay spread

(c) for the flat rural cell using a threshold 20 dB below the peak in each

APDP 20

Figure 5.2. Histograms of maximum delay (a), mean delay (b), and RMS delay spread

(c) for the hilly rural cell using a threshold 20 dB below the peak in each

APDP 21

Figure 5.3. Histograms of maximum delay (a), mean delay (b), and RMS delay spread

(c) for the urban high-rise cell using a threshold 20 dB below the peak in

each APDP 22

Figure 5.4. Cumulative distributions of maximum delay (a), mean delay (b), and RMS

delay spread (c) for the flat rural cell using a threshold 20 dB below the

peak in each APDP 23

Figure 5.5. Cumulative distributions of maximum delay (a), mean delay (b), and RMS

delay spread (c) for the hilly rural cell using a threshold 20 dB below the

peak in each APDP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Figure 5.6. Cumulative distributions of maximum delay (a), mean delay (b), and RMS

delay spread (c) for the urban high-rise cell using a threshold 20 dB below

the peak in each APDP 25

Figure 5.7. Effects of spatial diversity in the flat rural (a), hilly rural (b), and urban

high-rise (c) cells 27

VI
FIGURES (cont'd)

Page

Figure 5.8. Average and standard deviation of power (a), peak power (b), and

threshold statistics (c) for the flat rural cell . . . . . . . . . . . . . . . . . . . . 30

Figure 5.9. Average and standard deviation of power (a), peak power (b), and

threshold statistics (c) for the hilly rural cell 31

Figure 5.10. Average and standard deviation of power (a), peak power (b), and

threshold statistics (c) for the urban high-rise cell 32

Figure 5.11. Cumulative distributions of the number of significant paths for different

thresholds for the flat rural (a), hilly rural (b), and urban high-rise (c)

cells 34

Figure 5.12. Histograms (a-b) and cumulative distributions (c) of correlation bandwidth

for the flat rural cell 42

Figure 5.13. Histograms (a-b) and cumulative distributions (c) of correlation bandwidth

for the hilly rural cell 43

Figure 5.14. Histograms (a-b) and cumulative distributions (c) of correlation bandwidth

for the urban high-rise cell 44

Vll
TABLES

Page

Table 5.1. Mean (p.) and Standard Deviation (0") of Path Arrival Time (in p.s) and

Path Power (in dB) Using a -20 dB Threshold for Each Individual Path for

APDPs Having a Total of n Paths in the Flat Rural Cell 35

Table 5.2. Mean (p.) and Standard Deviation (0") of Path Arrival Time (in p.s) and'

Path Power (in dB) Using a -20 dB Threshold for Each Individual Path for

APDPs Having a Total of n Paths in the Hilly Rural Cell 36

Table 5.3. Mean (p.) and Standard Deviation (0") of Path Arrival Time (in p.s) and

Path Power (in dB) Using a -20 dB Threshold for Each Individual Path for

APDPs Having a Total of n Paths in the Urban High-Rise Cell 37

Table 5.4. Mean (p.) and Standard Deviation (0") of Path Arrival Time (in p.s) and

Path Power (in dB) Using a -10 dB Threshold for Each Individual Path for

APDPs Having a Total of n Paths in the Flat Rural Cell 38

Table 5.5. Mean (p.) and Standard Deviation (0") of Path Arrival Time (in p.s) and

Path Power (in dB) Using a -10 dB Threshold for Each Individual Path for

APDPs Having a Total of n Paths in the Hilly Rural Cell . . . . . . . . . . . 39

Table 5.6. Mean (p.) and Standard Deviation (0") of Path Arrival Time (in p.s) and

Path Power (in dB) Using a -10 dB Threshold for Each Individual Path for

APDPs Having a Total of n Paths in the Urban High-Rise Cell 40

V111
IMPULSE RESPONSE MEASUREMENTS IN THE. 1850-1990 MHz BAND IN LARGE

OUTDOOR CELLS

Jeffery A. Wepman, J. Randy Hoffman, and Lynette H. Loew·

Mobile impulse response measurements were taken in the 1850-1990 MHz band

in three different macrocellular (cell radii of5 km) environments: flat rural, hilly

rural, and urban high-rise. Spatial diversity with a 15-wavelength separation was

employed by using a dual-channel receiver. All antennas were omnidirectional

and venically polarized. The data were analyzed to provide delay statistics,'

spatial diversity statistics; multipath power statistics; number of paths, path

arrival time, and path powerstatistics; and correlation bandwidth statistics. The

urban high-rise cell showed more multipath components (out to 4 or 5 p.s in

delay) than the rural cells. Very long delays (greater than 10 p.s), while not seen

often, were seen more frequently in the rural cells than in the urban high-rise

cell. Parameters to help design a tapped delay model ofthe radio channel in the

different environments are given.

Key words: arrival time, channel model, coherence bandwidth, correlation bandwidth,

impulse response, multipath, power delay profiles, RMS delay spread, spatial

diversity, tapped delay model, wideband measurements

1. INTRODUCTION

The impulse response of the radio propagation channel is of great importance in the design,

development, 'and planning of radio systems since it completely describes the radio propagation

channel. Once the impulse response of a channel is known, the actual received signal can be

determined given a specific transmitted signal by convolving the transmitted signal with the

impulse response. Modelling of the impulse response has been and will continue to be an

important effort, as will be hardware and software simulation utilizing impulse responses.

Additionally, there have been many attempts made throughout the years to correlate the

performance of radio systems through a propagation channel using analytical methods with

measured impulse responses. Impulse response measurements are therefore needed to support

the ongoing channel modelling and simulation efforts as well as to support analytical methods

required in the development of new telecommunication services such as Personal Communication

Services (PCS) and advanced cellular mobile systems. This paper addresses this need by

discussing a set of impulse response measurements taken in the 1850-1990 MHz band.··

• The authors are with the Institute for Telecommunication Sciences, National

Telecommunications and Information Administration, U.S. Department of Commerce, Boulder,

CO 80303

•• Funding for these measurements was provided by Telesis Technologies Laboratory, Inc.
The impulse response measurements presented in this paper were taken in three different cell

environments in the Denver, Colorado, area. These environments included a flat rural cell, a

hilly rural cell, and an urban high-rise cell. The measurements within each cell were made

using a fixed-location receiver placed at the center oi the cell and a mobile transmitter installed

in a measurement van. All of the measurements were made within a 5-km radius of the center

of each cell, using omnidirectional, vertically polarized transmit and receive antennas. Impulse

response data were collected as the transmitter van travelled along predetermined routes within

each cell. The data were analyzed to provide delay statistics; spatial diversity statistics;

multipath power statistics; number of paths, path arrival time, and path power statistics; and

correlation bandwidth statistics.

2
2. MEASUREMENT SYSTEM

The impulse response measurements presented in this report were taken using the Digital

Impulse Response Measurement System (patent pending) developed jointly by the Institute for

Telecommunication Sciences and Telesis Technologies Laboratory, Inc. This system is

comprised of a separate transmitter and a dual-channel receiver employing spatial diversity. The

transmitter was installed in a mini-van and utilized a well-regulated diesel generator mounted on

a trailer to provide AC power. Figure 2.1 shows a photograph of the transmitter van. For the

measurements in both of the rural cells, the receiver was mounted in a large van and kept at a

fixed location. The antennas were mounted on a telescoping mast 8.7 m aboveground. A

photograph of the receiver van is shown in Figure 2.2. In the urban high-rise cell, the receiver

was located on the rooftop of a building approximately 103 m aboveground in the center of the

high-rise district in downtown Denver. The building height was typical for the buildings in this

area. The height of the ground above average terrain at the receiver site out 5 km in radius was

-4 m, +12 m, and -8 m in the flat rural, hilly rural, and urban high-rise cells, respectively.

These heights do not include the antenna mast heights in the rural cells or the building height

in the urban high-rise cell.

2.1 Transmitter

A block diagram of the transmitter is shown in Figure 2.3. The pseudo-random noise (PN) code

generator produces a 511-bit maximal-length code and is clocked at a 10 Mbit/s rate by a

rubidium frequency standard. The PN code is then level-shifted to eliminate the DC component

and amplitude clamped. A low-pass filter with a cutoff frequency of 10 MHz is used to

attenuate spectral components above the first null. This PN code is used to modulate an RF

carrier in the 1850-1990 MHz band producing a binary phase-shift keyed (BPSK) signal. This

signal is bandpass filtered, amplified to the appropriate level, and transmitted through a

vertically polarized, omnidirectional, biconical antenna with a gain of 0 dBi. The power level

is set to provide 50 W effective isotropically radiated power (EIRP).

2.2 Receiver

Figure 2.4 shows the receiver block diagram. A personal computer is used to control the

measurement system receiver via a GPIB bus. The spectrum analyzers and digital oscilloscope

are all under GPIB control. A vertically polarized, omnidirectional, biconical antenna with a

gain of 0 dBi is used for each channel to receive the transmitted signal. The spatial separation

between the antenna for Channel 1 and the antenna for Channel 2 is 15 wavelengths at the center

of the 1850-1990 MHz band. The received signal is first bandpass filtered to eliminate

undesired signals and then amplified using .low-noise amplifiers to minimize the system noise

figure. After filtering and amplification, the BPSK signal is downconverted to IF using portable

spectrum analyzers and an additional double-balanced mixer stage. The IF signal is then lowpass filtered to eliminate the local oscillator frequency from the additional mixer stage. After

this, video amplifiers are used to boost the signal level before it is digitized by the digital

oscilloscope. A rubidium frequency standard is used to phase lock the spectrum analyzers and

the signal generators. The divide-by-511 counter is clocked by the lO-MHz output from the

3
4
Figure 2.2. Photograph of the measurement system receiver van.

5
0'\

Ball Efratom

FRT Rubidium

Oscillator

llAini-Circuits

ZFSC-2-1W

10 dB

Ext

Ref

Power Amp

MPE PAS-49-

0-1725/2025

Fluke 6062A

Signal

Generator

Figure 2.3. Block diagram of the measurement system transmitter.

EllA Systems

A6533

Biconical

Antenna

Narda 3002-30

Directional Coupler

20 dB

Calibration

Port
Personal

Computer

GPIB Bus

Ext

Clk

Ext

Trig

1

Lecroy

9450A

Digital

Oscilloscope

27 dB

27 dB

Com linear

CLC 501

Mini-Circuits

ZFM-2000

Mini-Circuits

ZFM-2000

Mini-Circuits Comlinear

SLP-70 CLC 501

Pwr

Div

RF

Out

Mini-Circuits

ZFL-2AD

Ext

Ref

HP 8662A

Signal

Generator I

Mini-Circuits

ZFL-2AD

Ext

Ref

Tecom

201093-1v

HP 8563A

Spectrum

Analyzer

HE 2463- Mini-Circuits

1920M-50 ZHL-1724HLN Ext Ref

I

Pwr

Div

• I I

-.l Tecom

r 201093-1v

~Ref

HP 8563

Spectrum

I Analyzer

HE 2463- Mini-Circuits

1920M-50 ZHL-1724HLN

Ball Efratom r--------1. Pwr

MRT Rubidium L I Div

Oscillator

Ext Ref

HP 8662A

Signal

Generator

Figure 2.4. Block diagram of the measurement system receiver.
rubidium frequency standard. The output of this counter produces a pulse train used for

externally triggering the digital oscilloscope. The pulses (lOO-ns pulse width) occur at the start

of every PN code word transmitted. Synchronization between the PN code word and this pulse

train is accomplished by circuitry that resets both the PN code generator in the transmitter and

the'divide-by-511 counter in the receiver simultaneously. This synchronization provides absolute

time measurement capability to the Digital Impulse Response Measurement System. The

absolute time capability has a resolution determined by the relative frequency drift between the

transmitter and receiver frequency standards.

After the signal is digitized by the oscilloscope, the digitized IF signal is then transferred over

the GPIB bus to the computer and stored on the hard disk. The in-phase and quadrature phase

components, as well as the impulse responses, are derived in software; this processing can be

performed either immediately after the raw data has been taken or at a later date.

8
3. MEASUREMENT PROCEDURE

The calibration, system verification, and setup procedures described here were performed in

each cell every morning before measurements began. Measurements were made during the

daytime from approximately 8 AM to 5 PM. Before calibration began, the transmitter and

receiver equipment were warmed up for one-half hour. The rubidium frequency standards were

warmed up for at least 24 hours prior to calibration. The output power of the transmitter into

a 50-ohm load was measured and recorded using a directional coupler and a power meter.

Three primary calibration procedures were performed: frequency calibration, amplitude

calibration, and absolute time calibration.

The frequency calibration procedure consisted of tuning the rubidium frequency standard located

in the receiver so that its frequency matched that of the rubidium frequency standard located in

the transmitter. This was accomplished by connecting the 5-MHz outputs of each frequency

standard to a gain/phase meter and adjusting the frequency of the receiver's frequency standard

to minimize the change in the phase difference over time between the two frequency standards.

Frequency calibration was performed and highly stable rubidium frequency standards were used

for three primary reasons. First, it was necessary to ensure that the in-phase and quadrature

phase components for an individual impulse response did not rotate appreciably during data

collection. Secondly, the sampling clock had to be accurate enough to ensure that the correct

number of samples were taken within the 511-bit PN code word. If this condition is not met,

the correlation noise floor increases, thereby decreasing the interval of discrimination (ID). The

ID is the amplitude difference between the correlation peak and the peak of the noise in the

power delay profile (PDP). The PDP is the magnitude squared of the measured complex

impulse response. Finally, the absolute time capability required that the PN code generator in

the transmitter and divide-by-511 board in the receiver remained synchronized as closely as

possible for the entire duration of the measurements" Therefore, the rubidium frequency

standards were used to clock both the PN code generator and the divide-by-511 board.

The second type of system calibration that was performed was a receiver amplitude calibration.

This entailed connecting the transmitter directly to the receiver via a coaxial cable, with a

variable attenuator inserted between the transmitter and receiver to control the amplitude of the

signal input into the receiver. A complete amplitude calibration was performed after

configuration of the measurement system before the actual measurements commenced. The

complete amplitude calibration provided a series of PDPs at varying RF input power levels to

the receiver for both receiver channels. The RF input power was decreased in lO-dB steps from

the receiver's 0.5-dB compression point until the signal-to-noise ratio was so low that no PDP

could be obtained.

An example of these calibration PDPs for a high-level input signal into the receiver (-48 dBm)

is shown in Figure 3.1. From this PDP, the ID is seen to be approximately 51 dB. This

approaches the theoretical limit of a 9-bit PN code generator given by 20*loglo (2n-l) = 54 dB

where n = 9. From the calibration PDPs, it is noted that as the RF input power into the

receiver qecreases to roughly -60 dBm, the ID does not decrease. As the RF input power into

the receiver decreases below -60 dBm, the ID decreases due to system noise. Processing gain

is the difference between the output and input signal-to-noise ratios of a system [1]. The

processing gain from a 9-bit PN code generator is given as lO*loglo (2n-l) = 27 dB. This

9
j :

r- ....

j ........ ,

.... ..........

....... . , ...... ..................

- ........ ...... ......

.........

:/\f\/""'\f ,/I A 0, ,0 1\ ~MrA,rv ,1\f'.J' A

,

V W

',.

I I ,

60

50

--CD

'0 40 ........

Q)

'0

::J

.'!: 30

Q.

E

< 20 Q)

>'.0:;

co

Q5 10

a:

0

-10

-10 -8 -6 -4 -2 o 2 4 6 8 10

Time (microseconds)

Figure 3.1. Example calibration power delay profile.

means that when the RF input power into the receiver is equal to the system noise of the

receiver, the correlation peak will be 30 dB above the average noise level. This occurs when

the RF input power is approximately -91 dBm. The presence of multipath even further reduces

the ID.

The complete amplitude calibration is important since it allows verification of the proper

operation of the measurement system, provides a relationship between the received signal power

and the PDP, and allows approximate determination of the receiver noise figure from the PDP.

Every morning before measurements were made, an abbreviated amplitude calibration was

performed. This procedure was identical to the complete amplitude calibration procedure except

that the RF input power to the receiver was limited to one high and one low level. The PDPs

obtained using these input power levels into the receiver were then compared to the

corresponding PDPs generated in the complete calibration procedure. The results of this

comparison showed whether the measurement system was operating properly.

The absolute time calibration was then performed. This procedure required a reset cable to be

connected between the transmitter and receiver. A single switch then reset both the PN code

generator in the transmitter and the divide-by-511 board in the receiver simultaneously. This

ensured that the PN code and the external trigger pulse to the digital oscilloscope were

synchronized within a few nanoseconds. The reset cable was then disconnected. With the

transmitter still connected to the receiver via the coaxial cable and attenuator, data were captured

at a high-level RF input signal into the receiver. The PDP was obtained and the time that the

peak of the PDP occurred was recorded. If there was no delay through the transmitter and

10
receiver systems and the cable connecting the two, the peak of the PDP would occur at time

zero. Due to delays through the filters and other components in the transmitter and receiver,

however, the peak received signal occurred at about 300 ns.

After all of the calibration procedures were completed, the radio frequency spectrum was

observed to determine the potential interfering signals in or near the measurement frequency

band. The transmitter was disconnected and turned off while the receiver inputs were connected

to the receive antennas. The antennas were mounted on the top of the telescoping mast for the

rural sites and on top of the building in the urban high-rise cell. The receiver spectrum

analyzers were set up in sweep mode to observe and display frequencies from 1850 to

1990 MHz. Interfering signals at several different frequencies were seen within the band in all

of the cells. The center frequency of the measurement system was set such that any interference

from or to existing services would be avoided.

An over-the-air test, which was primarily qualitative in nature, was then performed to test the

proper functioning of the entire transmitter/receiver measurement system including the antennas

and antenna feed cables. For this test, the transmitter was separated from the receiver by

approximately 0.15 lan. The transmitter was turned on and the received signals on both

channels were checked for proper frequency and amplitude. Data were captured for both

channels and the corresponding PDPs were compared to expected results to determine if the

entire system was operating properly. The transmitter was kept operating while the rest of the

setup procedures were performed and was not turned off until the measurements in that cell were

completed for the day.

The transmitter van was moved to the beginning of the first route selected for measurement

within the cell. The data acquisition and control software was activated at the receiver to

prepare the measurement system for data collection. First, under computer control, the receiver

hardware was initialized. Based upon the received signal levels, the amplitude sensitivity of both

channels of the digital oscilloscope was automatically set by an autoscaling procedure. The

sensitivity of each channel was set independently. The system operator had the option of

overriding the automatic amplitude sensitivity settings and entering those desired. The system

operator was then prompted for information to be stored in the data file header. This

information included the cell number and description; the route number within the cell; and the

transmit antenna type, polarization, and height.

After these setup procedures, the data acquisition was initiated and the transmitter van began

travelling along the selected route. A rapid succession of 10 PDPs was taken at intervals of

approximately 0.7 s as the transmitter van was moving. Within this succession of PDPs a time

interval of255.5 J.l.s (5 times the PN code word duration) was used between the beginning of one

impulse and the beginning of the next. Spatial distance between each PDP within the succession

of 10 ranged from approximately 0.17 to 0.63 cm. The spatial distance between each succession

of 10 PDPs ranged from 4.66 to 17.26 m. When the transmitter had to stop along the

measurement routes, the data collection was suspended. The control software monitored signal

levels on both channels and if either signal level was too low or too high for adequate

digitization, an alarm would sound and the corresponding data on both channels would not be

recorded. If the signal levels were persistently too low or too high, the measurement van was

stopped and the autoscale procedure was executed again before restarting data acquisition. Data

11
of appropriate signal level were stored on the computer hard disk. Periodically, while data were

not being collected, the previously recorded data would be spot checked by looking at randomly

chosen PDPs. After all of the data had been acquired for the day, the data were checked by

looking at selected PDPs taken that day. Assured that the data were sound, the data were

backed up onto optical disk.

12
4. MEASUREMENT LOCATIONS

The measurements were taken in three different cell environments: flat rural, hilly rural, and

urban high-rise. The flat rural area consisted primarily of open spaces and farmland. The

receiver was located at the center of the cell along Route 256 east of the intersection with Road

35 between the towns of Gilcrest and La Salle, Colorado. This site was approximately 45 kIn

east of the foothills of the Rocky Mountains. Throughout most of the cell, the elevation varied

by only about 30 m. There were some small hills in the far southeast corner of the cell with

elevations up to 80 m above the receiver site. Figure 4.1 shows a map of this cell; the

measurement routes followed by the transmitter are marked on this map.

The hilly rural area consisted primarily of open space areas with some valleys and rolling hills.

The receiver was located at the U.S. Department of Energy Wind Site off of Highway 128

between Boulder and Golden, Colorado. The elevation varied by about 300 m throughout this

cell. The foothills of the Rocky Mountains were approximately 5 km west of the receiver site.

A map of this cell showing the measurement routes taken by the transmitter van is shown in

Figure 4.2.

Figure 4.3 shows a map of the urban high-rise cell, with the routes marked where the transmitter

van travelled. The receiver was located on the top of a building 103 m aboveground at

410 1']th St. in the center of the high-rise district in Denver, Colorado. This area consists of

closely spaced buildings with heights typically ranging from 25 to 35 stories. The elevation of

the terrain throughout this cell varied by about 85 m.

13
2 kilometers

\l End Route

Marker

o Begin Route

Marker

MAP FROM DELORME'S MAPEXPERT, FREEPORT, MAINE.

/

------_/ ROUTE7»

..•.......

r

j/~"",,,-/- ,/~:/;;~ ../' ..- ..'

e / 'j.?? - ~\~ ./ v.~~---- "----r'i:--\l-_-_-_-_-_-_-_-_-_-_-_-_-_-_--I, _- I I

_---- I _- I

---- ( --

I

I

I

I

I

I

I

I

I

I

I

.....•

N

f

............

® 1992 DeLorme Mapping

/---------------~

/ ROUTE 5 » I I I

I I I I ,

I I I

6 I ROUTE 1»1 0 O---------------l r----------------- ------~ 1I========Q256!)==i='+=======~'-----------t---zF----~------h-------------.l._--------I

I

I

I

I

I

I

I

I

I

I

o

Gilcrest<> 60

Figure 4.1. Measurement routes in the flat rural cell.

14
Dillon Road

12

_4

"- "-"- "- "-,,-

"- "-

"-,,- ROUTE '1 »

,~--------------

93

(>

Eldorado Springs

N

f

MAP FROM DELORME'S MAPEXPERT, FREEPORT, MAINE.

2kilometers

@ 1992 DeLonne Mapping

US Dept

ofEnc:rgy

(>

L<yden

72

w'"

V

V

o Begin Route

Marker

\7 End Route

Marker

Figure 4.2. Measurement routes in the hilly rural cell.

15
o Begin Route

Marker

\l End Route Marker

Colfax Ave.

17th Ave.

DENVER

57 / /

/

~'f!" //

4# ///

/

/ / /

/ /

/

/

/

/

/ /

/ /

/

/ /

/

/

//.,'1

/~'IJ /&/ 20th Ave.

---------------------------------. From Quebec St. «ROUTE 1 To

7.5 km --------->. Quebec

St.

o/

/

/ /

/

/ /

/

/

~. //

<;I;~ ///

/ /

/

/

/ / /

/ /

/

/

/ /

/

/ /

/

/~... /~& /11'

/~~-----------------------~ «ROUTE 5 /

I

I

I

I

I

1\

1\

UJ '"

...

=>

o

It:

--------------------------v ROUTE 4 »

To Hwy76

f

]

...

1

A/ I // I / I

/ I

/ I / I / I

I

N

500 meters

+

@ 1992 DeLonne Mapping

--------- To Wadsworth Blvd.

To

Wadsworth «------- 7.5km----------->-j.1 . 1••---------------- I

1

] &';

V'J §

r

To I Evans I

Ave. :

MAP FROM DELORME'S MAPEXPERT, FREEPORT, MAINE.

Figure 4.3. Measurement routes in the urban high-rise cell.

16
5. DATA ANALYSIS METHODS AND RESULTS

This section provides a detailed explanation of how the data were analyzed, along with a

presentation of the results. The general types of analyses presented may be classified as delay

statistics, number of paths and arrival time statistics, multipath power statistics, correlation

bandwidth statistics, and spatial diversity statistics. The statistics were formed from data taken

in each cell separately. All statistics were computed using the data from Channel 1 only, except

for the spatial diversity statistics which inherently rely on the data from both channels. All of

the raw data were taken utilizing the absolute time circuitry. Synchronization was lost for the

data taken in the urban high-rise cell, so that set of data does not have the absolute time

information. The results of the data analysis presented in this paper did not make use of the

absolute time information so that previously written analysis software could be used. All of the

statistics were computed from averaged PDPs (APDPs). Therefore, the first step in the data

analysis process, common to all of the statistics, was to develop the APDPs.

An APDP was calculated from each succession of 10 PDPs according to the following

procedure. Initially, the total signal power was determined for each of the 10 PDPs and the

PDP with the greatest total power was identified. Any of the 10 PDPs with a total power 10 dB

or more below the PDP with the greatest total power was tagged as invalid and excluded from

processing. Therefore, a set of valid PDPs within the succession of 10 PDPs consisted of one

to ten PDPs. Usually, there were 10 PDPs within a set of valid PDPs.

In order to compute an APDP, alignment in time between all valid PDPs (within a succession

of 10 PDPs) was required. Alignment was accomplished by performing cross correlations

between consecutive valid PDPs. The second valid PDP was aligned with the first valid PDP

by shifting the second one in time according to the results of the correlation. Each subsequent

valid PDP was then aligned with the previous (aligned) valid PDP. Once aligned, all of the

valid PDPs (within the succession of 10 PDPs) were averaged together to give an APDP. This

type of alignment was utilized to obtain average values of power for signals with the same delay

time.

The received signal levels obtained in the measurements tended to be relatively low in some

locations due to the long distances between the transmitter and receiver, limited transmitter

power as required by the experimental license, and shadow fading. Due to these relatively low

signal levels and the presence of multipath, an ID of only 20 dB could be guaranteed from

APDPs taken in these locations. Because of this and also to treat APDPs of varying IDs on an

equivalent basis, only delayed signals within 20 dB of the peak value in the APDP were counted

as significant for the computations. The APDPs were used as the basis for computing all of the

statistics.

To ensure that noise was not included in the statistical computations, an APDP was only

considered valid (for inclusion. in the statistics) ifits ID was 23 dB or greater. This assured that

samples of the APDP up to 20 dB below the peak received signal would be actual delayed

signals and not noise (by providing a 3-dB buffer between the peak of the noise and the region

where the amplitude of delayed signals was considered significant). Ifthe APDP had an ID less

than 23 dB, this APDP, as well as the APDP that was computed from PDPs taken

simultaneously on the other channel, were not counted in the statistics. This was done so that

every APDP from one channel had a corresponding APDP (computed from PDPs taken

simultaneously on the other channel) as required for the spatial diversity processing.

17
Alignment in time between each APDP was then addressed. All of the valid APDPs (Le., those

APDPs having at least one sample 23 dB or more above the peak noise value and having the

corresponding APDP on the other channel also meet this criterion) were then shifted in time

such that the first perceptible received copy of the transmitted signal was set to zero time. After

this alignment procedure, the APDPs were ready to be utilized in the statistical computations.

Note that when the term APDP is used in the rest of this paper, that it implies a valid and

aligned APDP.

In the discussion of the various different statistics that follows, the number of valid APDPs

within each cell should be kept in mind. The flat rural cell had 3220 valid APDPs, the hilly

rural cell had 1341 valid APDPs, and the urban high-rise cell had 3813 valid APDPs. The

relatively low number of valid APDPs in the hilly rural cell is indicative of the terrain. In many

locations within the cell, the signal level was too low to guarantee a sufficient ID. This was

probably due to shadow fading caused by the hills.

5.1 Delay Statistics

The three types of delay statistics that were analyzed were maximum delay, average delay', and

RMS delay spread. Each of these parameters IS a single number that is used to descnbe an

entire APDP. Therefore, these parameters are useful in statistically describing a set of many

impulses. For the computation of these parameters, since delayed signals within 20 dB of the

peak value in the APDP are the only ones counted as significant, samples within each APDP that

are more than 20 dB below the maximum signal level are set to zero.

The maximum delay p is found for each APDP by finding the delay time between the first and

last perceptible reception of the transmitted signal in the APDP. The average delay d.(in s) is

the average of the power-weighted delays (with respect to the time-of-arrival of the first

perceptible reception of the transmitted signal) in the APDP. This average delay is given

as [2-4]

d = N

LP(TJ

k=l

where N is the number of sample data points in the APDP, Tk is the time delay (in s) of the Ieh

sample in the APDP relative to the time of occurrence of the first perceptible reception of the

transmitted signal, and P(TJ is the value of the APDP at a time delay of Tk.

While the average delay is the average of the power-weighted delays in the APDP, RMS delay

spread is the standard deviation of the power-weighted delays [5]. The RMS delay spread is

computed for each APDP by [2-4]

s =

1

N 2

L (Tk - d)2 P(TJ

k=l

18
For each cell, a histogram and cumulative distribution of the maximum delay, average delay,

and RMS delay spread are computed.

Figures 5.la-5.3a show the histograms for the maximum delay for the flat rural, hilly rural, and

urban high-rise cells, respectively. These histograms show the number of APDPs having

maximum delay values that fall within 0.5-/-,s bins. The flat rural cell has a distribution such

that maximum delays less than 1 /-,S occur most frequently. As the maximum delay increases

beyond 1 /-'S, the number of APDPs per bin decreases rapidly. The hilly rural cell has a similar

distribution with maximum delays less than 0.5 /-,S occurring most frequently. The distribution

of maximum delays is much wider for the urban high-rise cell (than in the rural cells) with

maximum delays occurring most frequently around 3 to 4 /-,S.

Figures 5. 1(b-c)-5.3(b-c) show the histograms for the mean delay and RMS delay spread for the

flat rural, hilly rural, and urban high-rise cells, respectively. These histograms show the number

of APDPs having mean and RMS delay spread values that fall within O.l-/-,s bins. The

distributions between the two rural cells for both mean delay and RMS delay spread are

relatively similar. Mean delays between 0.1 and 0.2 /-,S occur most frequently in both of the

rural cells. As the mean delay increases above 0.2/-,s, the number of APDPs per bin decreases

rapidly. RMS delay spread values of up to 0.2 /-'S occur most frequently in the flat rural cell,

whereas in the hilly rural cell, RMS delay spread values of up to O.l/-,s occur most frequently.

The mean delays in the urban high-rise cell show a wide and fairly even distribution from 0.1

to 1.4 /-,S before slowly tapering off. The RMS delay spread distribution shows a more or less

bell shaped distribution with the maximum number of APDPs having values from 0.6 to 0.9 /-'s.

The cumulative distributions of maximum delay, mean delay, and RMS delay spread are given

for the flat rural, hilly rural, and urban high-rise cells in Figures 5.4-5.6, respectively. By

comparing the cumulative distributions from both rural cells, it is evident that the probability of

exceeding the maximum delay, mean delay, and RMS delay spread is slightly lower for the flat

rural cell than for the hilly rural cell. This suggests that there was slightly more multipath

present during the measurements in the hilly rural cell than in the flat rural cell.

The cumulative distribution of maximum delay for the urban high-rise cell shows a much higher

probability of exceeding maximum delay values than in the rural cells in the range up to about

5 /-,S (Figures 5.4a-5.6a). As an example, the probability of exceeding a maximum delay of 4 /-,s

is about 0.45 for the urban high-rise cell and only 0.12 for the flat rural cell. Beyond 10 /-'s,

the cumulative distribution of maximum delay for the urban high-rise cell shows a lower

probability of exceeding the maximum delay values than in the rural cells. This suggests that

very long delays (greater than 10 /-,s), while not seen often, were seen more frequently in the

rural cells than in the urban high-rise cell.

Compare the cumulative distribution of mean delay between the urban high-rise cell and the rural

cells (Figures 5.4b-5.6b). Up. to 1.5 /-'S, the probability of exceeding the mean delay is much

greater for the urban high-rise cell than for the rural cells. Similarly, the cumulative distribution

of RMS delay spread shows a higher probability of exceeding RMS delay spread values (up to

1 /-,s) in the urban high-rise cell than in the rural cells (Figures 5.4c-5.6c). The histograms and

cumulative distributions of maximum delay, mean delay, and RMS delay spread indicate that,

although very long delays are seen more frequently in the rural cells, there are significantly

more delayed signals (out to 5 or 6 /-,s) with higher power in the urban high-rise cell than in the

rural cells.

19
I

. ; ; ...............

: I

.

I '------ , r-

.

i

;

I

.......

! ...........

...... :

F=-

i : ;

- : .

i

. : :

, I I ,

II)

CD 2500 ii!

0

...

Q.

>- 2000 <0

G)

C

...

CD 1500

0

Q.

"t:l 1000 CD

Cl

<0

...

CD 500

-

0

....

II)

2500 ;;::

0

...

Q.

2000

...

CD 1500

0

Q.

i 1000

Cl

<0

...

CD

> 500 «

'0

....

II)

2500 ;;::

0

...

Q.

2000

G)

C

...

CD 1500

0

Q.

"t:l 1000 CD

Cl

<0

... 500

-0

....

o

o

o

2

0.5

0.5

4 6 8 10 12 14

Maximum Delay, p (microseconds)

(a)

1~ 2 ~5

Mean Delay, d (microseconds)

(b)

1.5 2 2.5

RMS Delay Spread, S (microseconds)

(c)

3

3

16

3.5

3.5

18 20

4

4

Figure 5.1. Histograms ofmaximum delay (a), mean delay (b), and RMS delay spread (c)

for the flat rural cell using a threshold 20 dB below the peak in each APDP.

20
1000

e 900

a. 800 1-- ........

>-

700

I 600 F=

500 f-..

a.

i 400 f-.....

C) 300 I-- ................ tU...

CD 200 f-. I '0 100 4-,.

0 2 4

... , , .

6 8 10 12 14

Maximum Delay, p (microseconds)

(a)

16 18 20

j 1000

;;::::

0 900 ...

a. 800 >- tU

700

... 600

0 500

a.

i 400

e 300

200

'0 100

r0 0.5 1 1.5 2 2.5 3 3.5 4

Mean Delay, d (microseconds)

(b)

lB 1000

0 900 ...

a. 800

ECD 700

C

... 600 I--. ...........

CD

500 I-- 0

a.

"0 400 f-.....

CD

C) 300 e

CD 200

'---J - 100 0

0 0.5 1.5 2 2.5 3 3.5 4

RMS Delay Spread, S (microseconds)

(c)

Figure 5.2. Histograms ofmaximum delay (a), mean delay (b), and RMS delay spread (c)

for the hilly rural cell using a threshold 20 dB below the peak in each APDP.

21
m 1000

900 ...

e. 800 >-

700

I 600

500

Q.

i 400

0) 300 e

G) 200

'5 100

..

I

r--L

I I

tr i '----.

L r--n

0 2 4 6 8 10 12 14 16 18 20

Maximum Delay, p (microseconds)

(a)

j 1000

;;:::

0 900 ...

Q. 800

700 f- ..........

... 600 f- G)

500 f--........

0

Q.

i 400 f- ...

0) 300 as... ~I:- I

i 200 l-

---, '5 100 '-.,

... 0 0.5 1 1.5 2 2.5 3 3.5 4

Mean Delay, d (microseconds)

(b)

o 0.5 3 3.5 4

300 1,

200 f-~""""""""""""""""""""""""'" ~I + , , , ,

100 I:-J 1--

1000

900

800

700

600

500 ,

400 I I

,J '--

1.5 2 2.5

RMS Delay Spread, S (microseconds)

(c)

Figure 5.3. Histograms ofmaximum delay (a), mean delay (b), andRMS delay spread (c)

for the urban high-rise cell using a threshold 20 dB below the peak in each

APDP.

22
0.9

co

I/J 0.8 I/J ·0

I/J 0.7

.0

00( 0.6

1\

a. 0.5

0.4

:0

co 0.3 .0

0

"- 0.2 Do

0.1

\

r-\

r~

r

o

o 2 4 6 8 10 12 14

Maximum Delay, p (microseconds)

(a)

16 18 20

1-\

\

'" i

f- "---

0.9

co

I/J 0.8 I/J ·0

I/J 0.7

.0

00( 0.6

1\

"0 0.5

0.4

:0

co 0.3

.0

0

"- 0.2 Do

0.1

o

o 0.5 1.5 2 ~5

Mean Delay, d (microseconds)

(b)

3 3.5 4

O.f 3 3.5 4

\

\

"'" "------t-----.. -'i

o

o 1~ 2 ~5

RMS Delay Spread, S (microseconds)

(c)

Figure 5.4. Cumulative distributions of maximum delay (a), mean delay (b), and RMS

delay spread (c) for the flat rural cell using a threshold 20 dB below the

peak in each APDP.

0.9

co

I/J 0.8 I/J ·0

I/J 0.7

.0

00( 0.6

1\

(J) 0.5

>- :!: 0.4

:0

co 0.3 .0

0

"- 0.2 Do

0.1

23
0.9

co

l/l 0.8 l/l

'0

l/l 0.7

.0« 0.6

A

0. 0.5

0.4

:0

co 0.3 .0

0

... 0.2 ll.

0.1

••••

•

\

-.....,.. :--- ---....'---

o

o 2 4 6 8 10 12 14

Maximum Delay, p (microseconds)

(a)

16 18 20

0.9

co

la 0.8

'0

l/l 0.7

.0« 0.6

A

"0 0.5

0.4

:0

co 0.3 .0

0 0.2 ...

ll.

0.1

•

.

..

...... ...................... . ....

-

'------------- o

o 0.5 1~ 2 ~5

Mean Delay, d (microseconds)

(b)

3 3.5 4

0.5 3 3.5 4

..............

•

"" • .................

.

---------- • i - •

.

, o

o 1.5 2 2.5

RMS Delay Spread, S (microseconds)

(c)

Figure 5.5. Cumulative distributions of maximum delay (a), mean delay (b), and RMS

delay spread (c) for the hilly rural cell using a threshold 20 dB below the

peak in each APDP.

0.9

co

l/l 0.8 l/l

'0 0.7

« 0.6

A

(J) 0.5

>- 0.4

:0

co 0.3 .0

0

... 0.2 ll.

0.1

24
0.91~_.,,-<.:i······································· ; + ; .

16 18 20

0.8 1-..................;"\\.

0.7 '\

o~

0.5 1- ,..................... .."'.;..... , ; ;.... + ; , ;.. \

0.4 1--............... +............................... '\:'\ +............ ;......................... +........................... ;

0.3 1--............... +................................ + ,,"".................. , ;............... +................ , ,

0.2 \- , ;... "'''''-c;~ ;

0.1 \- + , + :;::"".~:±____..+_ + ; + ,····················· ·.. ··1

OL... ........i. .......--.......J.. --L.---..---........L... ...i...-....:=::::=±:====i _........L -L....o....- ...J

o 2 4 6 8 10 12 14

Maximum Delay, p (microseconds)

(a)

'\

- ........

'"

""

----

0.6

0.9

0.8

0.7

A

"0 0.5

0.4

:cjg 0.3

e 0.2 Q.

0.1

a

a 0.5 1 1.5 2 ~5

Mean Delay, d (microseconds)

(b)

3 3.5 4

0.5 3 3.5 4

0.7 ,'\. f- "\ ,; , + ; ,. ;............................................ 1

0.6 1-- ; \\ +................................ ; +............................ , !................................ ,............................................... I

0.5 I- \

0.4 f- "\ ,.............................. .;........................................... + , +.... ·1

0.3 1-- ; \'\i. +.............. +................ ,.............................. ;............................................... !............................... I

02 1--..................................; ~~, ; , , " ;............................... I

0.1 1-- ;.......................................... , ,,"'---..................;....................................... ; ;.................................... •. ,............................. I

oL...._.. .....L....o....-..................J..- ....o....-.:::r:===ool==----.i.-----...i- .........i----............J

o 1.5 2 ~5

RMS Delay Spread, S (microseconds)

(c)

Figure 5.6. Cumulative distributions of maximum delay (a), mean delay (b), and RMS

delay spread (c) for the urban high-rise cell using a threshold 20 dB below

the peak in each APDP.

25
In the hilly rural cell, the cumulative distributions of maximum delay, mean delay, and RMS

delay spread show higher probabilities of exceeding large delay values than in the other cells.

The cumulative distribution of maximum delay shows a higher probability of exceeding delays

6 p,s or more than in the other cells. This tends to indicate that there were more signals with

delays greater than 6 p,s received in the hilly rural cell compared to the other cells. This may

have been due to reflections off of the foothills of the Rocky Mountains nearby.

5.2 Effects of Spatial Diversity

The measurements were taken to allow the effects of spatial diversity to be analyzed. Spatial

diversity was accomplished by transmitting one BPSK PN code sequence and receiving this code

on two identical receive channels. These two receive channels had antennas that were spaced

15 wavelengths apart. The effects of spatial diversity can be determined in many ways. Only

one of these methods is presented here. The method presented is based on RMS delay spread

values of the APDPs from both channels. This method compares the cumulative distributions

of RMS delay spread for Channell, for Channel 2, and for the lowest RMS delay spread

between both channels (hereafter called the diversity combination). The lowest RMS delay

spread is found by first taking the RMS delay spread of each pair of APDPs computed from

simultaneously taken PDPs on both channels (one on Channell and one on Channel 2). The

RMS delay spread that is the lowest between the two channels is then chosen. This process is

repeated for all pairs of APDPs for each cell and the cumulative distribution for each cell is then

formed.

Figure 5.7 shows the cumulative distributions ofRMS delayspread for the flat rural, hilly rural,

and urban high-rise cells. For each cell, the cumulative distributions of RMS delay spread are

shown for Channell, Channel 2, and the diversity combination of the two channels. Within

each cell, observe that the cumulative distributions for Channell and Channel 2, separately, are

nearly identical. This result is to be expected since the cumulative distribution for Channell

or Channel 2 is a statistical description of the RMS delay spread behavior in an entire cell over

a large number ofsamples. Therefore, regardless of how the RMS delay spread values compare

between a given APDP on Channell and the corresponding APDP formed from PDPs taken

simultaneously on Channel 2, the cumulative distributions for each channel separately within a

given cell should be quite similar. The cumulative distribution for the diversity combination

shows a lower probability of exceeding an RMS delay spread value in all three cells than for

Channell or Channel 2 separately. This result is most pronounced in the urban high-rise cell.

Some improvement is obtained (where improvement is measured as a lower cumulative

distribution of RMS delay spread) by using spatial diversity and the diversity combination

technique of selecting the lowest RMS delay spread from both channels for every received

impulse response. These results suggest that the wideband signals seen on each channel are

indeed uncorrelated to some degree. If these signals were correlated, one would expect to see

no difference in the cumulative distributions of RMS delay spread between Channell, Channel

2, and the diversity combination of the two channels.

5.3 Multipath Power Statistics

The multipath power statistics provide statistical information about the signal amplitude for every

delay time for all of the APDPs in a given cell. These statistics include, as a function of delay

time: average multipath power, standard deviation of multipath power, peak multipath power,

26
0.5 1 3 3.5 4

...............+ ; + + + ,. I-Channel 1

H- j f·····..·· ..·· ···..·..·········..·..··+····..········..···.. ·· + + + I --·Channel 2 .. 0.8

' ,Diversity 0.7 c·····....··..···..··········· ,

0.6 1+ ; "......................................... .,.......................................... ,........................................ +.......................................... ,.......................................... ..

0.5 ~' , "....................................... c.......................................... +.......................................... +.......................................... ,..................................... .,.......................................... I

\I":\\

0.4 \\"

03 \ \',

. \,~.

~:~ :··.,.,.;..•."'.~.~'C.~,.,O.·~":ii,.. ;;..;..;..;..:..:.. 0·· ;---'-"-·· ·.··· ·· 'i·, ·· ··..·· ·· ·· · ; ;;·..~··.··~ ;.•;+;;;.................. ,.......................................... t ·..· ········ , ,... I

a

a

0.9 1+- f· ···..· ···..· f · ·· · + · ·· ·+ · ·· ·c··............................, I-Channel 1

1+- f··· ·· ·..· ·· · f· · ·t · · , ; , I ···Channel 2 . 0.8 • . ...... DiverSity 0.7 tt ··..· ·· T· ·· ·· · ····.. ;............................................ . ···..· ··········..···· ·· ·r ..· ····..···· ···· L_---,-_--=---.J

0.6 1-+- , ,.......................................... c · ··..··· c ·.. · ···..· ······ ···· +......................................... ,......................................... • .. ·..·..······ ·········· ·· ···1

0.5

0.4 '.•

0.3 I- •••"";;.~, , .

..... ~:~ I- ,.,•••.~~..:..~.:.. :.~..:; ,..p;-:, ..~.,....,.~ ; ; ': ; ..;.; ; ; ; ; ; ; ..; ..; ..; ..;· ; ;;·:1t ::.. :;..;..; ;..;..;;..... t ··,······ ··..·..··· ·.............. , ··..··..··· ······· · ··1

••••••••••• , ••••:. - ••• ••••••••••• n ••••••••••••

o

a 0.5 1 1~ 2 ~5

RMS Delay Spread, S (microseconds)

(b)

3 3.5 4

,.... ..,~., . ~~ 101 II II;;;, 2 . ~~IOI II lei

\~:~ ,I wILY

[...,\

1-. ...............................

...••.. \

i """'\ I- ... .. ........

....... \

\ ... \

...... .'-......::--.-

0.9

51 0.8 .!!l

0

(/) 0.7

.0« 0.6

A

(J) 0.5

0.4

:0

co 0.3 .0

0

... 0.2 D.

0.1

o

o 0.5 1~ 2 ~5

RMS Delay Spread, S (microseconds)

(c)

3 3.5 4

Figure 5.7. Effects of spatial diversity in the flat rural (a), hilly rural (b), and urban

high-rise (c) cells.

27
and probability of multipath power exceeding a threshold. Each of these types of statistics will

be described in this section.

All of the multipath power statistics, like the delay statistics, are computed from the APDPs.

For computation ofthe delay statistics, the delay values are computed for each APDP separately,

then the statistics are developed. The amplitude relationship between the APDPs is not

important for the computation of the delay statistics. For computation of multipath power

statistics, however, the amplitude relationship between APDPs is Important. Therefore, some

type of amplitude normalization of the APDPs is required. Each APDP is normalized by

shifting the entire APDP in power such that the peak sample in the APDP is set to 0 dB. This

allows APDPs of varying total power to be treated on an equivalent basis.

The average multipath power shows the average power of a delayed signal at a given delay time

for the data in each cell. Average multipath power as a function of delay time is computed as

where M is the total number of normalized APDPs for a given cell, Tk is the time delay of the

kth sample in the APDP relative to the time of occurrence of the first perceptible reception of

the transmitted signal (i.e., relative to time zero), and Pj(TJ is the value of the i

th APDP at a

time delay of Tk' The peak value in the plots of average multipath power vs delay time will

usually be less than 0 dB. This is because the APDPs are aligned in tIme according to the first

perceptible reception of the transmitted signal, not according to the peak sample in the APDP.

The standard deviation of multipath power shows the standard deviation of a delayed signal's

power at a given delay time for the data in each cell. The standard deviation of multIpath power

as a function of delay time is given as

The peak multipath power shows the largest signal power that was observed at a given delay

time for the data in each cell. Peak multipath power is computed by finding the largest signal

power at each delay time in all of the normalized APDPs for the data in each cell.

Since each individual APDP is normalized so that the peak received multipath signal is set to

odB, and since the first perceptible received copy of the signal is aligned to zero time, many

of the values on the peak multIpath plots up to 3 p,s are 0 dB. This happens because the peak

received multipath signal frequently occurs some time after the first perceptible received signal.

This occurs when a received copy of the signal with the greatest power follows a route between

the transmitter and receiver that is longer than the first received signal (as is often the case

during non-line-of-sight transmitter/receiver orientation). In the graphs of average multipath

power vs delay, the power normalization and time alignment result in having all points on the

graph lie somewhere below 0 dB.

The last type of multipath power statistic is the probability of multipath power exceeding a

threshold. For the data in each cell, these statistics are computed by finding the probability that

a delayed signal's power will be greater than a given threshold for each delay time. The

computation is performed for each delay time by finding the number of normalized APDPs for

the data in a given cell in which the delayed signal power exceeds the threshold. This number

28
is then divided by the total number of normalized APDPs in that cell. Four different threshold

levels are used: -5, -10, -15, and -20 dB, where 0 dB represents the power of the peak sample

in each normalized APDP.

The average multipath power and the associated standard deviation vs delay time are shown in

Figures 5.8a-5.lOa for the flat rural, hilly rural, and urban high-rise cells, respectively. The

average multipath power curves for the two rural cells are similar, with both having a narrow

peak close to 0 dB that rapidly decreases to -20 dB at about 0.5 p.s of delay. The average

multipath power is much higher for every delay time out to about 3 p.s in the urban high-rise cell

as compared to the rural cells. The standard deviation curves tend to follow the average power

curves until the average power curves drop down to -20 dB.

Figures 5.8b-5.lOb show the peak multipath power vs delay time for the flat rural, hilly rural,

and urban high-rise cells, respectively. Note that in all cells there is a general tendency as the

delays get longer in time for the peak amplitudes to decrease. The hilly rural cell shows the

highest and the urban high-rise cell shows the lowest peak amplitudes for delay times greater

than 15 p.s. The urban high-rise cell has the highest peak amplitudes for delay times up to about

3 p.s. The standard deviation curves (Figures 5.8a-5.lOa) have peaks that correspond to large

amplitudes in the peak multipath power curves.

The threshold statistics vs delay time are displayed in Figures 5.8c-5.lOc for the flat rural, hilly

rural, and urban high-rise cells, respectively. For each graph, the top curve represents the

probability of the normalized multipath power exceeding -20 dB. The second, third, and fourth

curves from the top represent the probability of the normalized multipath power exceeding -15,

-10, and -5 dB, respectively. The urban high-rise cell shows a much higher percentage of

APDPs that are above threshold than the rural cells. For example, in the urban high-rise cell,

64% of the APDPs have delayed signals above the -20 dB threshold at a delay time of 1 p.s.

In the flat rural cell, only 5% of the APDPs have delayed signals above the -20 dB threshold

at a delay time of 1 p.s. As the threshold level is increased, the percentage of APDPs above

threshold decreases. As an example of this, consider the urban high-rise cell. At a delay time

of2 p.s, 41 %, 18%, 7%, and 1% of the APDPs have signals above the -20, -15, -10, and -5 dB

thresholds, respectively.

The multipath power statistics show again that the urban high-rise cell has by far more multipath

components above threshold than the rural cells (out to 4 or 5 P.s in delay). These statistics also

show that the peak (normalized) multipath power for very long delays (greater than 15 p.s) is the

highest in the hilly rural cell and the lowest in the urban high-rise cell.

5.4 Number of Paths, Path Arrival Time, and Path Power Statistics

The goal of the presentation of the statistics in this section is to provide information to assist in

the development of impulse response models (primarily tapped delay models) of the radio

channel. The first type of statistic presented is a cumulative distribution of the number of paths

that exceed a threshold. This statistic is generated for each cell by first determining the number

of paths that exceed a threshold (within a l00-ns resolution) in a single APDP. This process is

repeated for all of the APDPs within each cell and cumulative distributions showing the

probability of meeting or exceeding a number of paths are developed for each cell. Four

different threshold levels are used: -20, -10, -5, and -3 dB (where the peak sample in each

APDP is 0 dB). For the -20 dB threshold, a path is identified in one of two ways. First, iffour

consecutive samples in the APDP (spaced 25 ns apart) are all above the -20 dB threshold and

29
-Average ..............

···,Std. Deviation ...............

·

··:,

-.

~:

t:: ...

:: \ t. ,~ ~~ . ;

0

-2

-4 ... -6

Q. -8

jca -10 J;!~

as -12 E...

0 -14 Z

-16

-18

-20

o 2 4 6 8 10 12

Time (microseconds)

(a)

14 16 18 20

:~

M

II.

IV ........................

,....

n

IJII

n 1.1. II

IJ

id II I

'I ~I ! 1~V

...

! II/'Ill ~I ! II~I

0

-2

-4 ...

; -6

0

Q. -8

ica -10

~~ -12 E...

0 -14 Z

-16

-18

-20

o 2 4 6 8 10 12

Time (microseconds)

(b)

14 16 18 20

3 4 5 6

Time (microseconds)

(c)

2

Top Curve: -20 dB Threshold

2nd from Top: -15 dB Threshold

3rd from Top: -10 dB Threshold

Bottom Curve: -5 dB Threshold

\ _ \V\ ..

\ ,,\ i

~'--'- - , o

o

100

>- 90

.!!'O

~O 80

... j 70 CD ... ~..r:::

01- 60 Q. CD

&E 50

f!< 40

~! 30

_0

0'" 20

~Q. 10

Figure 5.8. Average and standard deviation of power (a), peak power (b), and

threshold statistics (c) for the flat rural cell.

30
i .

I- ,.... , ......... -Average I···········

···,Std. Deviation ...

i • I- :

.

.~

I~~ •

.

;:

: I i i

;~::1i : i •

.....................

:

A i'~ "= f~~\ ;r~~; , ,Ii; , • .

0

-2

-4 .... -6

0

Q. -8

,,-

G)£D -10 .t::I~

a; -12 E...

0 -14 Z

-16

-18

-20

o 2 4 6 8 10 12

Time (microseconds)

(a)

14 16 18 20

18 20

....... 1M

16

1.I

14

~I

v

,

8 10 12

Time (microseconds)

(b)

,

6

.

4

....... l

j

'IAU'..1··· .........j n,

t- : " '1IHI~IlII~llIlAnV/\11 H)fh~\ JJHI"A"'A'"'ft'········:·······~·'w·\I~:JU ········Il~ ~Wll.i.tt"t!'H·······,··········III·············II:lrA··············.....,..................... I

, V' v III II'

0

~.~ ....... -2

-4 '-- ...... " J .... -6 .......'l :

Q. -8 ~:

iiD -10 ~~as -12 E....

0 -14

Z

-16 f-

·18

-20

0 2

i Top Curve: -20 dB Threshold • i ..........

...... 2nd from Top: -15 dB Threshold

3rd from Top: ·10 dB Threshold

•

Bottom Curve: -5 dB Threshold

: i I .......

•

f

•

\~,~ i , i

100

>- 90

~"~o 80

.... "i

G)G) 70 .... 0-'= 60 0.1-

G)

&.8 50

e< 40

~~ 30

_00 .... 20

,#Q.

10

o

o 2 3

Time (microseconds)

(c)

4 5 6

Figure 5.9. Average and standard deviation of power (a), peak power (b), and

threshold statistics (c) for the hilly rural cell.

31
-Average ••.•..•......

···,Std. Deviation .............

\\

. \;"""

.-~~.-:~ "i1~

'-v--., .~~ ,

V\ ;,;.

\1\'" · . ,; · I I I I

· .. .

0

-2

-4 ... -8

Q. -8

'im ·10

~~ -12

0 ·14 Z

-16

-18

-20

o 2 4 6 8 10 12

Time (microseconds)

(a)

14 16 18 20

Or---"""'"llllr."'lr~-_-_--_--_--_--_--_--_-----'

J :-~•.••.•••••-~••••••••-~':~-' ••••'.'.'••••••••'.~••.•.•••~,..•.•...........•••.1··········· ·HHHrltftlt It················ 11 ,n~.. :.."~' :"".-"," ,' ,............... t

i m -10 1- , ,IH··I·I..········ " ·•.• \I.tl···\···11

~~ I~~W ~z15 ~~: ~I--- !............... . ;. + I········ . ~t~.L I.llltiHHUull··.······· 'I+lI··· .. ····t······ linlf··············· , !............... t

......... \I IV I

·16 I- .

-18 1-............ ·+········································4····· ····· ; ;....................... ,.' , " l.'u,lll·,~······················_; 1'1"................ 1

-20 L......._...............................l......o- __.............__..__.. """""""'IJI....................... ,_1.. " :11-....... 11.............. 1

o 2 4 6 8 10 12 14 16 18 20

Time (microseconds)

(b)

3 4 5 6

Time (microseconds)

(c)

2

f:"'

,

Top Curve: -20 dB Threshold ~11 I~ 2nd from Top: -15 dB Threshold

3rd from Top: -10 dB Threshold

l~~/"\..-.... Bottom Curve: -5 dB Threshold ...

~.

"~••••••"'~'" ....................................

'--./

...~~.. ...........

'V~

---. -.......L.... ____ j~ -'-----.~ .

i '""---.

o

o

100

90

_"0

~o 80

... ! 70 41) ...

~J:

o~ 60

Q.4I)

i~ 50

e< 40

~I 30 ee== _0

0'" 20

'#.Q.

10

Figure 5.10. Average and standard deviation of power (a), peak power (b), and

threshold statistics (c) for the urban high-rise cell.

32
are continually increasing in power, a path is identified.. Second, if a sample in the APDP is

of higher power than the next sample, a path is identified. Once a path is identified, three

samples (spaced 25 ns apart) are skipped and the search for a new path begins on the next

sample (i.e., on the fourth sample from the sample where the last path was identified). Skipping

three samples before beginning to look for a new path ensures that no more than one path is

identified within the resolution of the measurement system (100 ns). Identification of paths for

the other threshold levels begins with the paths that were identified for the-20 dB threshold.

Each of these paths is tested to see if it can still be counted as a path for the new threshold level.

The cumulative distributions of the number of paths are shown in Figure 5.11 for the flat rural

(a), hilly rural (b), and urban high-rise (c) cells. All four thresholds are shown on each graph.

The top curve represents the cumulative distribution using the -20 dB threshold, the second and

third curves from the top represent the cumulative distributions for the -10 and -5 dB thresholds,

respectively, and the bottom curve represents the cumulative distribution for the -3 dB threshold.

Note that in the rural cells, the curves for the -5 and -3 dB thresholds are nearly identical. The

probability of having APDPs with 2 or more paths is less than 0.09 in both of these cells for

these threshold levels. Both of the rural cells show a somewhat higher probability of having

APDPs with 2 or more paths when using the -10 dB threshold. There is a probability of about

0.26 and 0.20 of having APDPs with 2 or more paths in the flat rural and hilly rural cells,

respectively. The curves for the -20 dB threshold show a much greater probability of meeting

or exceeding a given number of paths than for the other threshold levels in all of the cells. In

the flat rural cell, about 10% of the APDPs have 8 or more paths. About 10% of the APDPs

have 13 or more paths in the hilly rural cell while about 10% of the APDPs have 33 or more

paths in the urban high-rise cell. The urban high-rise cell shows a greater probability of meeting

or exceeding a given number of paths than the rural cells for all threshold levels.

These results give an idea of the number of required taps that may be needed to model the

impulse response of the radio channel (within a 100-ns resolution) in different environments in

the 1850-1990 MHz band. The urban high-rise cell would, of course, require the largest number

of taps. Note that the number of paths is quite dependent on the chosen threshold level; as the

threshold level is set increasingly further below the peak of the APDPs, the number of paths

Increases.

The second set of statistics computed here are the path arrival time and path power statistics.

These statistics give a description of the time-of-arrival and power of each path that exceeds a

threshold for all APDPs within a cell that have n paths (where n varies from 1 to 10). The

results are displayed in a table where the mean and standard deviation of the arrival time and

power for each individual path are presented. Arrival time is relative to the time-of-occurrence

of the first path in each APDP. The mean and standard deviation of power are shown in dB

with respect to the peak value in the normalized APDPs. Recall that the peak value in the

normalized APDPs is set to 0 dB. Tables 5.1-5.3 show the time-of-arrival and path power

statistics using a -20 dB threshold for the flat rural, hilly rural, and urban high-rise cells,

respectively. Tables 5.4-5.6 show the corresponding tables using the -10 dB threshold. These

tables are organized so that each column represents all of the APDPs within a cell that have n

paths where n varies from 1 to 10. Each row represents a specific individual path for APDPs

having a total of n paths.

For an example of the use of these tables, consider Table 5.1. Choose the column with 3 paths

(n=3). The number ofAPDPs having 3 paths was 765 out of a total number of 3220 APDPs

taken in this cell. The first path always occurs at zero time therefore its mean and standard

deviation of arrival time are both zero. The mean power is -0.1 dB with a standard deviation

33
\"1 Top Culve: ·20 dB Threshold I-- ...

\ ,

2nd from Top: -10 dB Threshold

1--.. \ 3rd from Top: -5 dB Threshold

f- ........ \

Bottom ClIve: -3 dB Threshold

I--.m \ .

1--..... \

\ . ......

1--......

:1\\

~""- ---..r--

1

0.9

0.8

'0 0.7

0.6 AI

c::: 0.5

iii 0.4

.D

.8 0.3

0

... n. 0.2

0.1

o

o 5 10 15 20 25

Number of Paths, n

(a)

30 35 40 45

35 40 45

0.9 f-C'I..\ . . 1 -: Top Curve: -20 dB Threshold

0.8 f-\\m ,................................................... ,......... , ,.......................... 2nd from Top: -10 dB Threshold

! :::-\1.' ,......................... f , ,................. , l:tt:C::~: ~~:~= 0.5:\ ! .

~~ _ ..\"., .... , , , , , ; ,............ . .

.8n. e 0.2 - ...1\ ""- + , , ,................................ , .

0.1 -~"-t---.. : .

o

o 5 10 15 20 25 30

Number of Paths, n

(b)

--- ~! IJTop Culve: -20 dB Threshold

2nd from Top: ·10 dB Threshold

! 3rd from Top: -5 dB Threshold ........""- Bottom ClIve: -3 dB Threshold

"" ...................

,

"'" ,

I-- '~

1--.... ..................... ""- "~"'-- ---- --- . .....

,

0.9

J

0.8

0.7

0.6 AI

c::: 0.5

.~ 0.4

.8 0.3

n.e 0.2

0.1

o

o 5 10 15 20 25

Number of Paths, n

(c)

30 35 40 45

Figure 5.11. Cumulative distributions of the number of significant paths for different

thresholds for the flat rural (a), hilly rural (b), and urban high-rise (c) cells.

34
Table 5.1. Mean (,t) and Standard Deviation (u) of Path Arrival Time (in its) and Path Power (in dB) Using a -20 dB

Threshold for Each Individual Path for APDPs Having a Total of n Paths in the Flat Rural Cell

0=1 0=2 0=3

Total Number of Paths 0 in APOP

0=4 0=5 0=6 0=7 0=8 0=9 0=10

w

VI

Number of

APOPs Having

o Paths*

Path #

Time

pqW~t

2

3

4

5

6

7

8

9

10

183 1058 765 410 236 130 102 60 64 45

(1

0.86

HQ;~

1.76

H'VQ

4.21

AHW9

~e total oumber of APOPs in the flat rural cell was 3220.
Table 5.2. Mean (It) and Standard Deviation (00) of Path Arrival Time (in its) and Path Power (in dB) Using a -20 dB

Threshold for Each Individual Path for APDPs Having a Total of n Paths in the Hilly Rural Cell

/l q

19

n = 10

0.001 0.00

q

60 43

n=7 n = 8 n = 9

29 24 20

/l q /l q /l q

0.001 0.00 0.001 0.00 0.001 0.00

--,---- _. _ .. _ ...1'1'71 -""._1 .,,,, .. AI::'" :-::::::1::::"2:.[:< :>"1::0 ",t.'> L ,:,::::>,."

124

Total Number of Paths n in APDP

n=4 n=5 n=6

/l ql/l ql/l ql/l ql/l

0.00 0.00

0.0 _.-. ~·-I·· ..- •., ""'.~"-I _.-." '.C-''C+', ...'..'.'."-."" ,.-.~. -.-

q /l

1

Path #

n = 1 n=2 n=3 • . Number of

APDPs Having I 70 I 595 I 201

n Paths*

2

Tinle

Po~erll?

0.14

44.6

Time

3

Power-8.0

1.40

W

0'1 Tinle

4 .. Power I ...

Time

5 Power

7

Time 4.33 3.10 3.69 2.35 I '~

4.47 4.15 2.72

L· ..JlJ.O. 44.4 }13.8

8

9

10

"The total number of APDPs in the hilly rural cell was 1341.
Table 5.3. Mean (p.) and Standard Deviation (u) of Path Arrival Time (in p.s) and Path Power (in dB) Using a -20 dB

Threshold for Each Individual Path for APDPs Having a Total of n Paths in the Urban High-Rise Cell

Total Number of Paths n in APDP

n=4 n=5 n=6

w

-....J

n = 1 n = 2 n=3 = = = Number of

APDPs Having. 4 • 24 • 52

n Paths*

Path # I • u (J • u (J • u (J

2

3

4

5

6

7

8

9

10

69 140 93

n = 7

108

n = 8

93

n = 9

137

n = 10

106

(J

"The total number of APDPs in the urban high-rise cell was 3813.
Table 5.4. Mean (,.t) and Standard Deviation (u) of Path Arrival Time (in p.s) and Path Power (in dB) Using a -10 dB

Threshold for Each Individual Path for APDPs Having a Total of n Paths in the Flat Rural Cell

Total Number of Paths n in APDP

n=4 n=5 n=6 n = 7 n = 8 n=9 n = 10

*The total number of APDPs in the flat rural cell was 3220.

51 18 7 4 2 3 4

(J
Table 5.5. Mean CIt) and Standard Deviation (u) of Path Arrival Time (in p.s) and Path Power (in dB) Using a -10 dB

Threshold for Each Individual Path for APDPs Having a Total of n Paths in the Hilly Rural Cell

Total Number of Paths n in APDP

n=4 n=5 n=6

W

\0

n = 1 n=2 n=3 = Number of

APDPs Having' 1065 • 139 • 41

n Paths*

Path # I • u. (1 • u. (1 • u. (1

2

3

4

5

6

7

8

9

10

~e total number of APDPs in the hilly rural cell was 1341.

29 18 22

n=7

10

n = 8

9

n=9

7

n = 10

o

(1
Table 5.6. Mean (,L) and Standard Deviation (u) of Path Arrival Time (in p.s) and Path Power (in dB) Using a -10 dB

Threshold for Each Individual Path for APDPs Having a Total of n Paths in the Urban High-Rise Cell

Total Number of Paths n in APDP

n=4 n=5 n=6

o

n = 1 n=2 n=3

Number of

APDPs Having. 545 • 438 • 333

n Paths*

Path # I • u C1 • U C1 • U C1

2

3

4

5

6

7

8

9

10

318 293 264

n=7

215

n = 8

224

n=9

208

n = 10

173

C1

*The total number of APDPs in the urban high-rise cell was 3813.
of -12.3 dB. The mean arrival time of the second path is 0.14 J.Ls with a standard deviation of

0.21 J.Ls. The corresponding mean power is -12.2 dB with a standard deviation of -10.6 dB.

Values for these parameters are found in a similar manner for the third path.

The cumulative distributions of the number of paths give an indication of how helpful the timeof-arrival and path power information will be in the design of impulse response models. For

the -20 dB threshold, about 95%, 89%, and 22% of the APDPs had a maximum of 10 paths in

the flat rural, hilly rural, and urban high-rise cells, respectively. This shows that using a -20 dB

threshold, 10 paths can adequately represent most of the APDPs in the rural cells but not in the

urban high-rise cell. Hence, the time-of-arrival and path power information using the -20 dB

threshold should be quite helpful in the design of impulse response models for cells similar to

the rural cells in this study. For the -10 dB threshold, almost 100% of the APDPs in the rural

cells and about 79% of the APDPs in the urban high-rise cell had a maximum of 10 paths. This

shows that using a -10 dB threshold, 10 paths can adequately represent most of the APDPs in

all of the cells. The information shown in Tables 5.4-5.6 should therefore be quite helpful in

the design of impulse response models for cells similar to those used in this study.

5.5 Correlation Bandwidth

The correlation bandwidth (sometimes called coherence bandwidth) is the bandwidth in which

the spectral components of the transmitted signal are affected in a similar way [6]. In order to

find the correlation bandwidth, the autocorrelation of the frequency transfer function of the

channel must be determined. An easy way to obtain this autocorrelation is by taking the Fourier

transform of Ih(t) 1

2

, the magnitude squared of the complex impulse response of the channel [7].

Since the APDPs are digitized, bandlimited approximations to Ih(t) 12, they may be used to

obtain approximations to the autocorrelation of the frequency transfer function.

The procedure to compute correlation bandwidth therefore begins by taking the discrete Fourier

transform of each APDP. The magnitude of this quantity is given as IG(jfJI and represents an

approximation to the magnitude of the autocorrelation of the frequency transfer function of the

channel. Note that ft is the frequency of the I<:1h point along the spectrum and ranges from 0 to

20 MHz. The discrete Fourier transform is then taken of a PDP generated from the

measurement system with the transmitter and receiver connected via a coaxial cable and

attenuator as in the amplitude calibration setup. The magnitude of this quantity is given as

IF(jfJ I. The effects of the measurement system are removed by dividing IG(jfJ I by

IF(jfJ I [4]. The resulting magnitude spectrum is then used to determine the 90%, 77%, 63%,

and 50% correlation bandwidths (BcO.9' BcO.

77 , BcO.63 , and Bco.s) by finding the frequencies at

which the magnitude is 90%, 77%, 63 %, and 50% of the peak value, respectively. For the data.

in each cell, histograms of BcO.

9 and Bco.

s are then computed. Cumulative distributions of BcO•9,

BCo.77' BCo.63' and Bco.s are also computed.

The histograms for both the 50% and 90% correlation bandwidths show the number of APDPs

having correlation bandwidth values that fall within O.5-MHz bins. Figures 5. 12a-5.14a show

the histograms for Bco.

s for the flat rural cell, hilly rural cell, and urban high-rise cell,

respectively. Both of the rural cells show a similar distribution of Bco.

s. The distributions in

these cells are quite spread out, with Bco.

s values occurring most frequently in the 15 to 16 MHz

range. The distribution in the urban high-rise cell is dramatically different. This distribution

is substantially narrower, with Bco.

s values occurring most frequently between 0.5 and 1 MHz.

41
: ,

....... , .......

!

,

c--'

~!

h --'

,

600

"- D.. 500

>.

400

I 300

D..

I 200

"-CD

100

'0

.. o 2 4 8 8 10 12

50% Correlation Bandwidth (MHz)

(a)

14 16 18

r- ,

U :

1- ........

'--

1-... ........ -

Ls-J I

~I- : ,

.I 600

;;::

e

D.. 500

400

I 300

i

C) 200

t!

100

'0

.. . 0 2 4 6 8 10 12

90% Correlation Bandwidth (MHz)

(b)

14 16 18

0.9

·1 0.8

0.7

0.6 V

0.5

0.4

:5 0.3 .8

0.2

0.1

_...•.......

/ .....-- - --- ------ -- / ------- _......... i/

/ / ,/ / :

L / / /~ .

.....

1-7// / / ,

TopQrve: CooeIamn BW

/ i~ ______v

------ 2nd fran Top: T7'Yo Carelamn BW

~::; -- ---- ~dlromTop: m Carelation BW ..................................._. IloItan Qrve: 5ll% Correlation BW ...

i~

o 2 4 8 8 10 12

Correlation Bandwidth, Be (MHZ)

(e)

14 16 18

Figure 5.12. Histograms (a-b) and cumulative distributions (c) of, correlation bandwidth

for the flat rural cell.

42
I

:

:

i

,

i

i

i , ---e-

, .

.......... : i

- i

:

- i

.

"I I -

h-. ,

lfi 600

ii:

0

...

Q. 500

>- as

400

0 300

Q.

i

OJ 200

as

...

CD

100

'l5

=tI:

II) 600 CD

0...

Q. 500

>- as

400

...

CD

300 0

Q.

i

OJ 200

as

... 100 -<

-0

=tI:

o

o

2

2

4

4

6 8 10 12

50% Correlation Bandwidth (MHz)

(a)

6 8 10 12

90% Correlation Bandwidth (MHz)

(b)

14

14

16

16

18

18

0.9

as

II)

II) 0.8

'0

II) 0.7 .Q

-< 0.6 V

0.5

0.4

:0 0.3 as

.Q

...

0 0.2

Q.

0.1

I--

--- • ---- ---- I- ..--

1-- .... / .--/ / •

·7 i/ /

/ /

i Y ,

/ / / I--

I-- / •

/ / /

6----- ~/ ./ Top Qrve: 00% CarelalKln BW

• - ---------- ---..----- i !r00l Top: mCooelalkln BW >~-- ..... . ~d from Top: 63% Cooelalion BW •

V : Bottom Qrve: 50% Correlatkx1 BW ; , I

o 2 4 6 8 10 12

Correlation Bandwidth, Be (MHz)

(e)

14 16 18

Figure 5.13. Histograms (a-b) and cumulative distributions (c) of correlation bandwidth

for the hilly rural cell.

43
i

,

.

!

c--

-

_.

_.

I/) 3500 Q)

i3... 3000 a.

>.

CO 2500

2000

a. 1500

1J

Q)

Cl

CO 1000 ...

Q)

500

-

0

....

I/) 3500

:;::

0

... 3000 a.

G) 2500

0

...

Q) 2000

0

a. 1500

1J

Q)

Cl

CO 1000 ...

500

'5

....

o

o

2

2

4

4

6 8 10 12

50% Correlation Bandwidth (MHz)

(a)

6 8 10 12

90% Correlation Bandwidth (MHz)

(b)

14

14

16

16

18

18

0.9

CO

I/)

I/) 0.8

'0

I/) 0.7 .tJ

< 0.6 V

0 0.5 en

0.4

:0

CO 0.3

.tJ

...

0 0.2

a.

0.1

-~

------------ --- -- e------ ---

//--- //

?

I

Top Curve: 00% Coo~IKln BW

2OO!r00l Top: Tl% Coo~lion BW

3rd from Top: 63% Cooelation BW

BoItom ClIVe: 5ll% Correation BW

o 2 4 6 8 10 12

Correlation Bandwidth, Be (MHz)

(e)

14 16 18

Figure 5.14. Histograms (a-b) and cumulative distributions (c) of correlation bandwidth

for the urban high-rise cell.

44
Figures 5. 12b-5.14b show the histograms for BcO.

9 for the flat rural cell, hilly rural cell, and

urban high-rise cell, respectively. The two rural cells again show a somewhat similar

distribution, with a narrow peak: occurring at BcO•

9 values of 0.5 or 1 MHz and then a more

spread-out second peak: occurring at BCO.9 values around 4 or 5 MHz. Again the urban high-rise

cell shows a vastly different distribution. Here, a very narrow single peak: occurs in the

distribution at BcO•

9 values up to 0.5 MHz.

Figures 5. 12c-5.14c present the correlation bandwidth statistics as cumulative distributions of

BcO.

9, BCO.77 , BcO.63 , and BCO.5 for the flat rural cell, hilly rural cell, and urban high-rise cell,

respectively. These plots show, for all of the APDPs in a cell, the probability of correlation

bandwidth being less than a given correlation bandwidth value. Note the large difference

between BcO.

5 and BcO•

9 in all of the cells, particularly in the rural cells. As an example, in the

flat rural cell, the probability of &0.5 being less than 4 MHz is about 0.09 while the probability

of BcO.

9 being less than 4 MHz is about 0.7. The cumulative distributions of correlation

bandwidth for the rural cells are roughly similar. For the urban high-rise cell, probabilities of

correlation bandwidth being less than the abscissa are much higher than in the rural cells. The

difference in the correlation bandwidth statistics between the rural cells and the urban high-rise

cell tends to indicate that significantly more multipath is present in the urban high-rise

environment.

45
6. SUMMARY AND CONCLUSIONS

This paper discusses an impulse response measurement experiment consisting of measurements

taken in the 1850-1990 MHz band within three different cell environments in the Denver,

Colorado, area. These environments included a flat rural cell, a hilly rural cell, and an urban

high-rise cell. The measurements within each cell were made using a fixed-location receiver

placed at the center of the cell and a mobile transmitter installed in a measurement van. A

single binary phase-shift keyed (BPSK) PN code sequence was transmitted and a dual-channel

receiver employing spatial diversity was used to receive the transmitted signal. The separation

of the receive antennas was set for 15 wavelengths at the center of the 1850-1990 MHz band.

In the rural cells, the receiver was located in a large measurement van and kept at a fixed

location. The receive antennas were mounted on a telescoping mast 8.7 m aboveground. In the

urban high-rise cell, the receiver antennas were located on the rooftop of a building 103 m

aboveground in the center of the high-rise district in downtown Denver. The building height

was typical for the buildings in this area. All of the measurements were made within a 5-km

radius ofthe center of each cell. The measurements were taken using omnidirectional, vertically

polarized transmit and receive antennas in all of the cells. Impulse response data were collected

as the transmitter van travelled along predetermined routes within each cell. A rapid succession

of 10 impulse responses was taken at intervals of approximately 0.7 s while the transmitter van

was moving. Within this succession of 10 impulse responses, a time interval of 255.5 p.s (5

times the PN code word duration) was used between the beginning of one impulse and the

beginning of the next. This allowed for averaging of 10 impulses to reduce the noise floor. The

data were analyzed to provide delay statistics; spatial diversity statistics; multipath power

statistics; number of paths, path arrival time, and path power statistics; and correlation

bandwidth statistics.

Three types of delay statistics were presented: maximum delay, average delay, and RMS delay

spread. From these statistics, several conclusions were suggested. Slightly more multipath was

seen in the hilly rural cell than in the flat rural cell. Very long delays (greater than 10 p.s),

while not seen often, were seen more frequently in the rural cells than in the urban high-rise

cell. Although very long delays were seen more often in the rural cells, there were many more

delayed signals (out to 5 or 6 p.s) with higher power in the urban high-rise cell than in the rural

cells. More signals with long delays (greater than 6 p.s) were seen in the hilly rural cell than

in the other cells.

The effects of spatial diversity were analyzed by comparing the cumulative distribution of RMS

delay spread between Channell, Channel 2, and the diversity combination of both channels.

The results of this analysis showed some, although not a large, decrease in RMS delay spread

values using diversity combination. These results suggest that the wideband signals seen on each

channel were indeed uncorrelated to some degree.

The multipath power statistics provided statistical information about the signal amplitude

variation for every delay time for all of the APDPs in a given cell. These statistics included,

as a function of delay time: average multipath power, standard deviation of multipath power,

peak multipath power, and probability of multipath power exceeding a threshold. The results

of these analyses agreed very well with those from the delay statistics. The urban high-rise cell

had many more multipath components above threshold than the rural cells, out to 4 or 5 p.s in

delay. The peak (normalized) multipath power was also seen to be the highest for delays greater

than 15 p.s in the hilly rural cell and the lowest in the urban high-rise cell.

46
The goal of the presentation of the number of paths, path arrival time, and path power statistics

was to provide information to assist in the development of impulse response models (primarily

tapped delay models) of the radio propagation channel. The results provide an idea of the

number of required taps that may be needed to model the impulse response of the radio channel

(within a loo-ns resolution) in several different environments in the 1850-1990 MHz band. The

results clearly showed that the urban high-rise cell would require a far greater number of taps

than the rural cells for the -20 and -10 dB thresholds. It should be noted that these results, and

the rest of the results of the data analyses presented in this paper, are quite dependent on the

threshold level used in processing. As expected, processing with lower threshold levels (Le.,

those set further below the peak in the APDP) showed more paths. Mean and standard deviation

of the arrival time and path power of each individual path were presented for APDPs having a

total of up to 10 paths. For a threshold of -20 dB, it was found that 10 paths can adequately

represent most (89% or more) of the APDPs in each of the rural cells. In the urban high-rise

cell, for a -20 dB threshold, 10 paths are not adequate to represent most of the APDPs. For a

threshold of -10 dB, most (79% or more) of the APDPs in each of the cells can be adequately

represented with 10 paths.

The results of the correlation bandwidth statistics show only small differences in the cumulative

distributions of correlation bandwidth between the rural cells. The urban high-rise cell shows

much smaller correlation bandwidth values than in the rural cells. This indicates that

significantly more multipath was seen in the urban high-rise cell than in the other cells;

consistent with the findings in the other forms of data analyses presented here.

Finally, it should be noted that these impulse response measurements were made with a system

having a 20 MHz bandwidth. The results are expected to be different for measurements taken

with systems having different bandwidths.

47
7. REFERENCES

[1] R.C. Dixon, Spread Spectrum Systems, New York: John Wiley & Sons, Inc., 1976,

pp.7.

[2] D.C. Cox, "Delay doppler characteristics of multipath propagation at 910 MHz in a

suburban mobile radio environment," IEEE Trans. on Antennas and Propagation, AP-20,

No.5, pp. 625-635, September 1972.

[3] D.C. Cox, "Time- and frequency-domain characterizations of multipath propagation at

910 MHz in a suburban mobile-radio environment," Radio Science, Vol. 7, No. 12, pp.

1069-1077, December 1972.

[4] D.C. Cox and R.P. Leek, "Correlation bandwidth and delay spread multipath

propagation statistics for 910 MHz urban mobile radio channels," IEEE Trans.

Communications, COM-23, No. 11, pp. 1271-1280, November 1975.

[5] D.M.J. Devasirvatham, "Multipath time delay spread in the digital portable radio

environment," IEEE Communications Magazine, Vol. 25, No.6, pp. 13-21, June 1987.

[6] R.C.V. Macario, Personal and Mobile Radio Systems, London, U.K.: Peter Peregrinus,

Ltd., 1991, pp. 31-32.

[7] CCIR, "Propagation data and prediction methods for the terrestrial land mobile service

using the frequency range 30 MHz to 3 GHz," CCIR Report 567-4, International Radio

Consultive Committee, International Telecommunications Union, Geneva, Switzerland,

1990.

48
FORM NTIA-29

(4-80)

U.S. DEPARTMENT OF COMMERCE NAT'L. TELECOMMUNICATIONS AND INFORMATION ADMINISTRATION

BIBLIOGRAPHIC DATA SHEET

1. PUBLICATION NO.

NTIA Report 94-309

2. Gov't Accession No. 3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Impulse Response Measurements in the 1850-1990 MHz

Band in Large Outdoor Cells

7. AUTHOR(S)

J.A. Wepman, J.R. Hoffman, L.H. Loew

8. PERFORMING ORGANIZATION NAME AND ADDRESS

Nat'l Telecommunications & Information Administra.tion

Institute for Telecommunication Sciences

325 Broadway

Boulder, CO 80303

11. Sponsoring Organization Name and Address

14. SUPPLEMENTARY NOTES

5. Publication Date

6. Performing Organization Code

ITS.S3

9. ProjecVTaskiWork Unit No.

10. ContracVGrant No.

12. Type of Report and Period Covered

13.

15. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature

survey, mention It here.)

Mobile imp~lse response measurements were taken in the 1850-1990 MHz band

in three different macrocellular (cell radii of 5 km) environments: flat

rural, hilly rural, and urban high-rise. Spatial diversity with a 15-

wavelength separation was employed by using a dual-channel receiver. All

antennas were omnidirectional and vertically polarized. The data were

analyzed to provide delay statistics; spatial diversity statistics;

multipath power statistics; number of pathS, path arrival time, and path

power statistics; and correlation bandwidth statistics. The urban highrise cell showed more multipath components (out of .4 or 5 ~s in delay)

than the rural cells. Very long delays (greater than 10 ~s), while not

seen often, were seen more frequently in the rural cells than in the urban

high-rise cell. Parameters to help design a tapped delay model of the

radio channel in the different environments are given.

16. Key Words (Alphabetical order, separated by semicolons)

arrival time, channel model, coherence bandwidth, correlation bandwidth,

impulse response, multipath, power delay profiles, RMS delay spread,

spatial diversity, tapped delay model, wideband measurements.

17. AVAILABILITY STATEMENT

Q!I UNLIMITED.

o FOR OFFICIAL DISTRIBUTION.

18. Security Class. (This report)

UNCLAS

19. Security Class. (This page)

UNCLAS

20. Number of pages

49

2.1. Price: