NTIA Report 98-352

ELECTROMAGNETIC COMPATIBILITY TESTING

OF A DEDICATED SHORT-RANGE

COMMUNICATION SYSTEM

Roger A. Dalke

Frank H. Sanders

Brent L. Bedford

U.S. Department of Commerce

William M. Daley, Secretary

Larry Irving, Assistant Secretary

for Communicating and Information

July 1998

iii

PREFACE

This work was sponsored by the Federal Highway Administration (FHWA), McLean, Virginia, under

the direction of J.A. Arnold, FHWA Contracting Officer Technical Representative.

Certain commercial companies, equipment, instruments, and materials are identified in this report 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 identified is necessarily the best

available for the purpose.
iv

CONTENTS

Page

PREFACE ................................................................ iii

EXECUTIVE SUMMARY .................................................... v

ABSTRACT ............................................................... 1

1. INTRODUCTION ........................................................ 1

1.1 Background ....................................................... 2

1.2 Approach ........................................................ 3

1.3 Experimental Configuration ........................................... 4

1.4 Calibration and DSRC System Performance Parameters ..................... 6

2. DSRC SYSTEM SOFTWARE DESCRIPTION .................................. 7

2.1 Automated Fee-Collection Mode ....................................... 7

2.2 Software Algorithm for the Tests ...................................... 8

3. MEASUREMENT RESULTS AND DATA ANALYSIS ........................... 9

3.1 System Performance Measurements ..................................... 9

3.2 Statistical Measurements of DSRC System Performance .................... 11

3.3 Frequency Offset Measurements ...................................... 13

3.4 Analysis of Measurements ........................................... 13

4.0 SUMMARY AND RECOMMENDATIONS .................................. 20

4.1 Summary ........................................................ 20

4.2 Recommendations for Enhanced DSRC Electromagnetic Compatibility ......... 21

4.3 Recommended Additional Analysis .................................... 22

5. REFERENCES ......................................................... 23

APPENDIX A: MEASURED WAIT TIME STATISTICS ........................... 24
v

EXECUTIVE SUMMARY

Dedicated short-range communication (DSRC) systems have been proposed for operation at locations

across the United States in the 5850- to 5925-MHZ band. This is part of a larger band, 5250-5925

MHZ (“5-GHz band”), that is currently allocated to radiolocation (radar) services. Deployment of

DSRC systems is contingent upon assurances that their operations will be electromagnetically

compatible with existing and future radar systems in the 5-GHz portion of the spectrum.

The Institute for Telecommunication Sciences performed a series of tests on a DSRC electronic toll

collection system to determine the extent to which electromagnetic compatibility problems may be

experienced when operated in proximity to various radar systems in the 5-GHz spectrum. During the

tests, simulated radar signals were coupled into the DSRC beacon receiver, both on the beacon

frequency (co-channel) and off the beacon frequency (off-channel). Radar signals were selected to

represent the range of parameters used by both existing radars and possible future radar designs.

Thresholds at which radar signals caused adverse impact on DSRC system operations were

determined for each set of radar signal parameters, and these thresholds were determined for both cochannel and off-channel radar interference. Statistical data sets were acquired to quantify the effects

of these interference thresholds. The measured interference thresholds for various combinations of

interference pulse widths and pulse repetition rates were used to compute minimum interference

power levels at which existing 5-GHz radars would be expected to produce interference to DSRC

systems at deployment locations in the United States. For each type of 5-GHz radar, the distance at

which the radar would be expected to cause interference to this type of DSRC system (coordination

distance) was determined for various conditions of electromagnetic isolation between the systems.

This analysis yielded the conclusion that, for typical coupling conditions, the DSRC system

coordination distances for most 5-GHz radars are often substantially less than 1 km, and usually do

not exceed several kilometers.

Only one type of radar—associated with U.S. test range facilities and used at approximately 15-20

locations in the United States for tracking rockets, aircraft, and balloons—appears to require larger

coordination distances. This occurs because this radar type can be tuned to co-channel frequencies

with DSRC systems. However, if the test range radars and the DSRC systems are not co-channel,

and if these tracking radars do not directly illuminate the DSRC locations, then the coordination

distances can become relatively short for this case, as well. The key to achieving electromagnetic

compatibility is coordination (e.g., frequency coordination) at these test range locations.

Based on these measurement and analysis results, no engineering modifications are recommended for

the type of DSRC system that was tested. It is recommended that DSRC systems deployed in close

proximity to various U.S. test range facilities perform coordination with those facilities to avoid cochannel operations and direct illumination by the test range radars identified in this report. Such

coordination should ensure electromagnetically compatible operations between such radars and the

deployed DSRC systems.
 The authors are with the Institute for Telecommunication Sciences, National Telecommunications 1

and Information Administration, U.S. Department of Commerce, Boulder, CO 80303.

ELECTROMAGNETIC COMPATIBILITY TESTING OF A

DEDICATED SHORT-RANGE COMMUNICATION SYSTEM

Roger A. Dalke, Frank H. Sanders, and Brent L. Bedford1

Dedicated short-range communication systems have been proposed for operation at

locations across the United States in the 5850- to 5925-MHz band. Various search

and tracking high-power radars operate at or near this frequency band and are a

source of potential interference. The successful operation of such digital

communication systems is dependent upon compatible operation and coexistence with

these radars. The Institute for Telecommunication Sciences has performed a series

of interference tests to determine the electromagnetic compatibility of DSRC systems

used for automatic toll collection and high-power 5-GHz radars. The methods used

to perform the tests and results are presented in this report.

Key words: dedicated short-range communications (DSRC) systems; high-power radars;

electromagnetic compatibility; interference; electronic toll collection; access control

systems

1. INTRODUCTION

This report describes the methodology and results of tests in which a dedicated short-range

communication (DSRC) system was tested by the Institute for Telecommunication Sciences (ITS)

for its response to high-power incident field strengths in the 5850- to 5925-MHz band, and also for

its response to strong signals in the radiolocation band between 5250 and 5850 MHz. The DSRC

system was tested to determine the interference thresholds at which performance was degraded, up

to and including total failure of the DSRC communications link. Physical burn-out of the DSRC

system under test was not performed.

Using the results of these tests in conjunction with previous measurements of emissions (in both

frequency-domain and time-domain) from high-power radars in the 5250- to 5925-MHz portion of

the spectrum (e.g., [1-4]), ITS engineers performed an analysis to determine the extent of

electromagnetic compatibility problems the DSRC device under test may encounter if it is deployed

in the United States in the proposed 5850- to 5925-MHz band. The results of the tests,

measurements, and electromagnetic compatibility analysis for this DSRC system, are presented in this

report.
2

1.1 Background

Wireless communication systems, called dedicated short-range communications (DSRC) systems,

have been designed for operation in highway environments. The purpose of the DSRC systems is to

enhance efficiency of highway travel by providing motorists with, for example, such services as

automated, wireless-interrogation stations that would collect tolls electronically as vehicles pass

through such stations without stopping. Anticipated deployment of such DSRC systems in the United

States has led to a search by system designers, spectrum engineers, and spectrum managers for

spectrum bands in which the devices may be deployed. Taking into account both technical and

administrative restrictions on the use of various portions of the spectrum, as well as the fact that

DSRC systems have already been designed to operate in particular spectrum bands in Europe, the

portion of the spectrum between 5850 and 5925 MHz has been identified as a likely band for DSRC

deployment in the United States. This band is part of a larger band (5250-5925 MHz) that is

allocated on a primary basis in the United States for radiolocation (radar) operations. An industrial,

scientific, and medical (ISM) band also has been established between 5725 and 5875 MHz.

As detailed in Section 3, the 5-GHz radiolocation band is occupied in the United States by highpower radar systems that present the potential for interference with DSRC devices in roadway

environments. These radars typically use transmitters that produce between 0.25 and 1 MW peak

power, with antennas that produce effective isotropic radiated power (EIRP) values that are 30-40dB

higher than transmitter output power. These radars operate with duty cycles (pulse width divided by

pulse repetition interval) that are on the order of 1:1000. The radar antennas typically scan across

any given point in space repetitively, approximately every 3-10 s, although shorter and longer

intervals do occur. Radar beams typically illuminate any given point (such as a typical DSRC station)

for about 20 ms during each beam-scan period. The radar antennas often keep the main-beam power

in the sky, with power levels somewhat lower than main-beam values being produced at ground level.

However, some 5-GHz radars, such as maritime navigation/surface search units, do directly illuminate

the ground, where DSRC systems may be located along highways.

ITS has measured electromagnetic emissions from various 5-GHz high-power radar systems and has

accumulated extensive data on important radar emissions parameters such as radiated power levels,

time waveforms, and antenna patterns. The interference testing and measurement strategy described

in this report were largely based on an analysis of this data. A review of the 5-GHz radar emission

data revealed the following important points:

1. field strengths are not likely to exceed +165 dBFV/m in the 5250- to 5925-MHz frequency range.

This represents the maximum level to which the 5-GHz DSRC systems need to be tested;

2. DSRC systems need to be tested under conditions that allow for strict control of the interference

frequency, incident power, pulse repetition rate, and pulse width. These variables cannot easily be

controlled at actual radar locations, where environmental conditions tend to interfere with efficient

testing programs; and hence,
3

3. the most effective method of determining DSRC electromagnetic compatibility with 5-GHz radar

signals is to acquire an operational DSRC system and operate it in the presence of interference signals

that simulate those produced by radars. This report describes the results of such a series of tests on

a DSRC system designed for electronic toll collection. 

1.2 Approach

The tests were performed at the ITS laboratory in Boulder, Colorado. The overall goal of the tests

was to determine:

1. the interference levels, for various interference modulations, at which co-channel interference

would occur; and 

2. the interference thresholds for off-frequency interference.

Interference modulations were both continuous-wave (CW) and pulsed. The interference pulse

parameter combinations used in the tests are shown in Table 1, below. The pulse parameters were

selected as representative of the parameters for 5-GHz radars in the United States and are described

in terms of pulse width and duty cycle. The related parameters pulse repetition frequency (PRF) and

pulse repetition interval (PRI) are given for reference.

Table 1. Radar Parameters Used for DSRC Interference Signal Testing

Radar Interference

Parameters

Pulse width Pulse width Pulse width

(PRF = 300 Hz, (PRF = 1 kHz, (PRF = 3 kHz,

PRI = 3.3 ms) PRI = 1 ms) PRI = 330 μs)

Duty cycle: -20 dB (1%) ---------- 10 μs 3.3 μs

Duty cycle: -30 dB (0.1%) 3.3 μs 1 μs 0.33 μs

Duty cycle: -40 dB (0.01%) 0.33 μs --------- ---------

For each interference signal modulation that was tested, the interference level was initially adjusted

to a very low amplitude, well below the DSRC beacon interference threshold. The amplitude was

then gradually increased, while the beacon was operating, until an adverse effect on beacon operation

was noted. Interference amplitude was increased beyond the level of minimal interference, first by

10 dB and then by 20 dB, to ascertain effects of increasing interference in excess of the minimum.

The interference thresholds (minimal adverse effect and 10 dB and 20 dB above the minimum) were

recorded for each interference modulation, for both co-channel and off-channel interference.

Subsequent to determining the set of interference thresholds, the beacon operations were monitored

for extended numbers of beacon/tag information exchanges at each interference threshold and each
 The beacon was only using the response from the upper channel during the tests, but future 2

expansion of beacon capabilities may result in the use of the second frequency.

 The tag is normally powered by a battery when used in a vehicle, but for purposes of these tests, 3

batteries were exhausted quickly, and marginal power from a battery near the end of its life could

adversely affect test results; therefore power was supplied via a BNC cable from a DC source.

4

beacon modulation. For each threshold, diagnostic histograms related to beacon performance

parameters were produced to obtain a quantitative measure of the adverse impact of interference on

the beacon at each threshold.

1.3 Experimental Configuration

The hardware configuration used for the DSRC testing is shown as a block diagram schematic in

Figure 1. The units under test, consisting of a DSRC roadside beacon unit and a DSRC tag, were

mounted on separate, telescoping masts that were, in turn, mounted at opposite corners of a metallic

vehicle rooftop that itself measured about 2 m by 2 m. The vehicle rooftop was 2.7 m above the

ground, and the two masts were elevated to a height of 1.5 m above the rooftop, equal to 4.2 m

above the ground. The vehicle was parked at an outdoor location during the tests. Thus, the DSRC

beacon and tag were effectively suspended in free space at a height of 4.2 m above the ground, with

a metallic plane 1.5 m below them, and stretching between them. 

An important consideration for this arrangement was that the measurements approximate to what

would be obtained if the DSRC system were operating in free space, i.e., the receiver was in the far

field and the effects of multipath were minimal. Since the largest dimension of the transmitting

antennas is about 15 cm, the physical separation between the beacon and tag was sufficient to

produce far field results. Given the relatively high directive gain of the beacon antenna and the height

of the beacon and tag above the roof of the measurement van, it was expected that the effects of

multipath would be negligible. For the short wavelengths used in this experiment (about 5 cm),

interference due to multipath would be apparent and vary significantly with small changes in the

relative positions of the transmitter and receiver. Such tests were performed by moving a calibrated

horn antenna to various locations between the beacon and tag. Significant fluctuations in the signal

strength that would accompany multipath were not observed.

The beacon transmitter and receiver were physically integrated into a single, weather-proof housing,

but are shown separately in Figure 1 for purposes of schematic clarity. During testing, the DSRC

beacon was operated from a laptop personal computer inside the van, via an RS-232 cable. DSRC

control software (described in Section 2) was used to control all beacon functions. The beacon

transmitted interrogations to the tag at a frequency of 5850 MHz. The tag would then, in normal

operation, respond to the beacon at two frequencies: 5848 MHz and 5852 MHz. The tag operated 2

autonomously, its only external connections being for power and the mast-mount. 3
Diagnostic

check on

RF signal

Pulse

input Pulse

generator

HP8661

signal

generator

RS-232

Beacon

transmitter

Laptop

computer

controller

Rx

Tx 2.8 m

2.8 m

RF power

combiner

Beacon

receiver Oscilloscope

Tag

LNA

GPIB

Separation

Separation

GPIB

Video

out to

oscilloscope

Spectrum

analyzer

Monitor

antenna

Control and data

collection computer

5

Figure 1. Block diagram of interference testing arrangement.

Since the major goal of the testing was to determine the thresholds at which DSRC performance was

adversely affected for various types of interfering signals, and because separate theoretical and

engineering considerations demonstrate that interference effects should be manifested as a result of

interference signals that are received at the beacon rather than at the tag, interference signals were

coupled into the beacon receiver. The signals were coupled via hardline, rather than via RF radiation,

so as to better control the amplitudes at which the interfering signals were injected into the beacon

receiver. To achieve this coupling, an RF power combiner was used between the beacon receiver

antenna and the beacon receiver, as shown in Figure 1.

Interference signals were generated by adjusting modulation parameters on a pulse-waveform

generator; that output was then routed to a modulation input on an HP-8661 signal generator. Pulse

parameters were verified by observing pulse generator outputs on an oscilloscope. RF spectrum

output from the signal generator was measured on a spectrum analyzer (Figure 1 and Section 3). The
6

signal generator was used to generate RF energy at the proper amplitudes and frequencies for the

tests. The interfering signal was coupled into the beacon receiver via a broadband combiner, along

with the desired signal from the beacon receiver antenna.

While tests were in progress, a monitoring antenna was mounted on the rooftop, to the side of the

beacon-to-tag propagation path. The monitor antenna output was connected to a spectrum analyzer,

and the spectrum analyzer’s detected video output was in turn monitored on an oscilloscope

(Figure 1). This monitor provided the capability to observe both the frequency-domain and timedomain emissions from the beacon and the tag during the tests. This monitoring proved to be a useful

diagnostic while tests were in progress, showing the effects of injected interference on the

transmissions between the beacon-tag pair. Data from the spectrum analyzer and the oscilloscope

were recorded via a GPIB bus interface to these instruments. These data served to document various

aspects of the testing effort.

1.4 Calibration and DSRC System Performance Parameters

The nature of these tests and measurements required that the amplitudes of both the interference

signals and the signals transmitted by the beacon and the tag be accurately measured. This required,

in turn, that all measurement system components be accurately calibrated for gains and losses.

Calibrations were performed in two ways: noise diode Y-factor calibration technique and injection

of CW signals into various components, such as RF cabling. Both techniques depend upon

measurement of the difference in power between two different system states. In the case of the noise

diode Y-factor technique, a noise source of accurately known and calibrated equivalent noise

temperature (in this case, a noise diode) is turned on at some point in the system (usually at the point

that an antenna is normally attached to an RF line) and the power that reaches a device at the other

end of the path (in this case, a spectrum analyzer) is measured. Then, the noise diode is turned off,

 and the power at the other end of the path is again measured. The difference between these two

measured values is called Y. Measurement of Y, together with knowledge of the noise

temperature of the noise source, makes possible the calculation of the system noise figure and the 

total gain through the system. For this set of tests, the noise diode calibration technique was used

to determine gain and noise figure of various test system paths as a function of frequency between

4 and 8 GHz.

Losses through RF cabling in the measurement system were determined by injecting a CW signal into

each cable and measuring the difference in RF power levels with and without the cable. A spectrum

analyzer was used to measure the power levels. The two calibration techniques (CW signal and noise

diode) were used to produce independent calibration results. No calibration difficulties were

encountered with the ITS measurement and test system, and the calibration data were used to

determine directly, among other parameters, the gain of the beacon antennas.

A desired calibration of the beacon receiver noise figure and front-end preselection roll-off proved

impossible to perform. These two parameters were not specified in the manufacturer’s

documentation, and at the time this report was written, this information was not available from the
7

manufacturer. In an effort to measure these parameters directly, the beacon receiver box was opened

to obtain access to the receiver front-end. The goal was to perform a noise diode calibration through

the front-end, thus yielding gain and noise figure of the receiver front-end as a function of RF

frequency. However, inspection of the opened receiver unit revealed that no mechanical connections

were available for such a calibration effort.

2. DSRC SYSTEM SOFTWARE DESCRIPTION

The DSRC system that was tested could not be operated under any sort of manual control; all DSRC

beacon operations were performed under the control of software, while the DSRC tag device

operated autonomously. All test results were obtained through outputs from the DSRC software

control program.

2.1 Automated Fee-Collection Mode

The beacon was operated in a mode called automated fee-collection (AFC) transaction. This mode

is used to collect identifying information from a tag as the tag passes through the beacon’s beam.

One transaction is composed of five separate messages, as listed in Table 2. The messages are:

Beacon Service Table (BST) - This message is transmitted by the beacon at regular time intervals

when the communication channel is error free. This regular interval may be disrupted when a tag is

in the beacon’s beam and certain messages are retransmitted.

Private Window Request (PrWRq) - This message is transmitted by the tag in response to a BST from

the beacon. The tag decodes the beacon’s identification number from the BST and responds with a

PrWRq if a transaction with that identification number has not occurred recently. Upon receiving a

PrWRq, the beacon will attempt to complete a transaction with the tag within a BST time interval.

Private Window Allocation (PrWA) - This message is transmitted by the beacon in response to a

PrWRq from a tag. This message defines three time windows. The tag may choose to respond in

any of the three windows.

Vehicle Service Table (VST) - This message is transmitted by the tag in response to a PrWA from the

beacon. This message contains information that identifies that particular tag to the beacon.

Release - This message is transmitted by the beacon in response to a VST from the tag. This message

closes the DSRC link. The tag knows that the beacon received its VST and the tag will not respond

to further BST’s for a set time limit.

The order of occurrence of messages to form a complete transaction is shown in Table 2 for an errorfree channel.
8

Table 2. Message Type as a Function of Transmitter Unit in the DSRC System

Transmitting Device Message Type

Beacon BST

Tag PrWRq

Beacon PrWA

Tag VST

Beacon Release

2.2 Software Algorithm for the Tests

The DSRC beacon has a serial port interface that allowed it to communicate with a computer using

a specific set of commands to which the beacon responded. Using these commands, a software

algorithm was developed to allow the computer to collect statistical information about the RF link.

The algorithm was designed to measure a parameter called the wait time. Wait time as used in this

report refers to the time interval starting with the transmission of the first beacon service table (BST)

when the tag is in the communication zone, and the successful reception of a VST by the beacon.

The wait time is effectively a measure of how long it takes for a beacon to collect a tag’s

identification information after the tag enters the beam of a beacon. The algorithm recorded the wait

time for a predefined number of trials. The results were stored in a file on the computer’s hard disk.

The algorithm consisted of a series of commands that are sent to the beacon from the computer in

a defined sequence. The first few commands set the beacon for measurements. First, a command was

sent that performed a soft-reset on the beacon firmware. The beacon assumed a well-defined, known

state with this command. Next, the beacon transmit frequency was tuned to 5.850 GHz, the

frequency used in these measurements. The beacon was instructed to send to the computer, via the

serial interface, each VST that was received by the beacon via the RF interface.

In normal operation, the tag is designed to remain silent for a period of time after successfully

completing a transaction. (At an operational DSRC station, this feature prevents the beacon from

recording the tag’s presence in a given location more than once as a vehicle passes a beacon.) In the

measurement setup, the tag remained in the beam of the beacon continuously and in normal operation,

the tag would respond once, then remain silent. For the tests, it was necessary to have the tag

respond repeatedly in this situation in order to measure the statistical behavior of the link; hence, a

software command was used to instruct the beacon to change its identification after each wait time

measurement. During a wait time measurement, the beacon identification was locked. After a

transaction was completed, and a wait time was obtained, the beacon was instructed to change its

identification. A 4-s delay was used before beginning the next measurement to ensure that the beacon

had time (nominally 3 s) to change its identification number before starting the wait time measurement

timer.
9

To start a wait time measurement, the beacon was commanded to send BST’s at a rate of 1 BST per

60 ms and the personal computer timer (DOS user timer) was started. This timer has a resolution of

approximately 55 ms. The computer waited for a VST to arrive (from the beacon) at the serial port

interface. The content of the received VST was compared to the expected content. If the contents

were identical, the timer was stopped, and the wait time was calculated and recorded. In an

interference-free environment, the wait time can be on the order of several ms to 20 ms, which is the

equivalent of zero on our time scale. Resolution of these short wait times is unimportant, since they

are an indication of normal operation. As the interference power level increases, the wait times

increase substantially, to values ranging from hundreds of milliseconds to seconds. Therefore, the

55-ms timer resolution is more than adequate to measure the wait times in the presence of

interference.

After a successful wait time measurement, the beacon was commanded to stop sending BST’s. The

beacon identification number was unlocked to allow this number to change. After a 4-s delay, the

next wait time measurement was initiated. The computer executed this loop for a user-defined

number of trials (usually about 500).

3. MEASUREMENT RESULTS AND DATA ANALYSIS

In this section, system performance measurements and statistical data obtained from interference

testing are presented. System performance measurements were made to determine the spectral

characteristics of the downlink and uplink signals and to estimate the sensitivity of the beacon receiver

in the absence of interference. Measurements of the time required for a successful transaction

between the beacon and tag in an interference-free channel were also performed and are included with

the statistical data given below. The measurement configuration shown in Figure 1 was used for all

of the results described in this section. Statistical measurements were made with the interference RF

frequency coincident with the tag RF frequency. Frequency offset measurements were also made to

determine interference power levels that effectively disrupt operations. In all cases, the DSRC system

was operated in the AFC mode.

3.1 System Performance Measurements

Figure 2 shows the beacon and tag spectra measured with a calibrated 10-dBi horn antenna located

1 m from and aimed at the beacon transmitter antenna. Note that the tag transmits two sidebands

offset from the beacon RF carrier by 2 MHz. Using this measurement configuration, we found that

the power delivered by the beacon to the transmit antenna was 16 dBm. This power level was

maintained for all measurements described in this section.

Figure 3 shows the power spectra measured at the beacon RF input terminal. This measurement was

made by direct connection to the input terminal using a power splitter while the DSRC system was

operating in AFC mode. The total power received at the beacon terminal was then obtained by

integrating the power spectrum and removing the gain (or losses) of the measurement system. The

measured power received from the tag at the beacon RF input terminal was !63 dBm.
-80

-70

-60

-50

-40

5847.5 5848.5 5849.5 5850.5 5851.5 5852.5

Frequency (MHz)

-100

-90

-80

-70

5851.5 5851.7 5851.9 5852.1 5852.3 5852.5

Frequency (MHz)

10

Figure 2. Beacon (center) and tag (± 2 MHZ) spectra measured with a 10-dB 

 horn antenna 1 m from and aimed at the beacon transmitter (30-kHz 

 resolution bandwidth).

Figure 3. Tag spectra measured at the beacon receiver RF input terminal (30-kHz 

 resolution bandwidth).
11

As noted in Section 1, the beacon construction precluded a quantitative measure of beacon receiver

sensitivity. A qualitative measurement of the beacon receiver sensitivity was obtained by connecting

attenuators to the beacon RF input. When the signal level at the beacon RF input terminal was

reduced to !79 dBm, there was a noticeable degradation in the system performance, and at !89 dBm,

the system completely failed to operate. This would indicate a system sensitivity of greater

than -79 dBm to achieve a bit error ratio of 10 .

!6

3.2 Statistical Measurements of DSRC System Performance

The primary goal of this measurement effort was to determine the effects of various C-band pulsed

radars on the operation of the DSRC system. When operating in AFC mode, the DSRC system

protocol allows for the retransmission of frames (e.g., the vehicle service table; VST) if a transaction

is not completed due to bit errors resulting from, for example, pulsed radar interference. In addition,

both the arrival time of the pulsed radar signal as well as its phase are random with respect to a

particular AFC mode transaction. As a consequence, the time it takes for a complete transaction in

the presence of radar interference, previously defined (Section 2.1) as wait time, is a random variable.

If the distribution of wait times is such that an unacceptably large percentage (to be determined) of

vehicles will traverse the communication zone before a successful transaction can be accomplished,

then clearly the DSRC system and the interferer are not compatible. Such a determination requires

a statistical characterization of the wait time random process. Using the measurement equipment

and methods described in the previous sections of this report, we measured the wait time statistics

based on several hundred (usually 500) independent trials for the pulsed radar parameters shown in

Table 1.

The wait time statistics in the absence of interference are presented in Figures 4 and 5. For the most

part, the wait time is less than the resolution of the measurement system or nominally 0 s, as would

be expected. The few wait times exceeding 0 s are most likely due to errors resulting from the

precision used in the floating point arithmetic. Measurement resolution and errors based on floating

point number precision while evident for the relatively short wait time observed in the absence of

interference, are expected to have an imperceptible effect on the statistics of the much longer wait

times resulting from interference.

The measured wait time statistics in the presence of interference are given in Appendix A in the form

of both histograms and cumulative distribution functions. In each case, statistics were obtained at

several levels of peak RF interference power. For each pulse parameter set, statistics were measured

at three interference power levels: the lowest power level where the wait time obviously starts to

increase relative to an interference-free channel, and two additional measurements at 10 and 20 dB

above this minimum. The percentage of trials that exceed a desired wait time can be evaluated

directly from the cumulative distribution plots.
0.01

0.1

1

10

100

0 2 4 6 8 10

Mean = .02 s

SD = .03 s

Mean = .02 s

SD = .03 s

Wait time (s)

Percent

0

1

2

3

0.1 1 10 100

Percent exceeding ordinate

12

Figure 4. Wait time histogram, no interference.

Figure 5. Wait time cumulative distribution, no interference.
13

3.3 Frequency Offset Measurements

The measurements described in the previous section can be considered to be worst case since the

interference center frequency is equal to the center frequency for the upper-side band of the tag. To

ascertain the DSRC system performance when the interferer is offset in frequency, several

measurements were made at various frequency offsets using a pulsed signal as well as a continuous

RF signal (CW). The results of these measurements are given in Table 3 below. 

The interference power levels given in Table 3 correspond to mean wait times that exceed tens of

seconds and for practical purposes completely disrupt effective communications. The CW interference

has a very narrow bandwidth and is expected to interfere through the mechanism of RF front-end

overload. It is interesting to note that while frequency offsets provide a margin in terms of allowable

interference levels, the interference still disrupts operation for both the pulsed interference and CW.

3.4 Analysis of Measurements 

Using the measurement results described above, the interference effects of typical pulsed radars

operating in-band or nearly in-band with respect to the DSRC system were analyzed. First, it was

necessary to estimate the maximum amount of time that might be allowed for a DSRC system

transaction (maximum allowable wait time). For a particular installation, this will be approximately

equal to the ratio of the length (along the roadway) of the communication zone and the speed of

vehicle. Using the measured statistics for wait time, the percentage of vehicles that may exceed the

maximum allowable wait time were estimated for various radar pulse parameters. The results are

presented in Table 4.

Table 3. Deleterious Peak Interference RF Power Levels as a Function of Frequency Offset

Frequency Offset (MHZ) CW (dBm) Pulse width 3.3 μs

1% Duty Cycle (dBm)

!300 !5 !15

!200 !10 !15

!100 !20 !10

!50 !20 !20

!20 !20 !35

0 !98 !91

The communication zone for DSRC systems is typically defined as the volume of space where a

reference bit error ratio (BER) of 10 can be achieved. In addition, it is required that the minimum !6

power incident on the tag (relative to a 0-dB receiver antenna) within the communication zone is
Wreceived'EIRP%Greceiver!Lfreespace

!A

Lfreespace'32.45%20log10FMHzDkm

Wreceived EIRP

Greceiver FMHz Dkm

14

(1)

!40 dBm [5]. Using this requirement, the upper bound or maximum length of a communication

zone along a roadway can be estimated using the following expression for the power received by the

tag:

where = !40 dBm is the power received by the tag, is the effective isotropic radiated

power, = 0 dB is the gain of the tag antenna, = 5850 MHZ, is the distance in km,

and A is the attenuation of the radio channel. Assuming a free space propagation path (A=0 dB) and

an effective isotropic radiated power of 32 dBm (16 dBm delivered to transmitter antenna plus 16 dB

antenna gain) the maximum length of the communication zone is about 16 m. Note that this

calculation assumes that the tag is in the main beam of the antenna when it is 16 m from the beacon

along the roadway. The length of the communication zone may be somewhat less for a particular

installation, however, 16 m should provide a reasonable upper bound.

Assuming that a vehicle travels for 16 m in the communication zone at a constant speed, Table 4

shows the peak RF interference power levels that resulted in wait times in excess of the maximum

allowable wait times for vehicle speeds of 96.6-32.2 km/hr (20-60 mph). The percentage of trials that

exceeded the maximum wait times are shown in parenthesis.

Table 4. Peak Pulsed Interference Power Levels Resulting in Wait Times that Exceed the Maximum

Allowable Wait Time as a Function of Vehicle Speed in the Communication Zone (PW = Pulse Width,

 DC = Duty Cycle)

 

Vehicle Max PW=1 ms PW=3.3 μs PW=10 μs PW=.33 μs PW=3.3 μs

Speed Allowable DC=0.1% DC=1% DC=1% DC=0.1% DC=0.1%

km/hr Wait Time PRF= PRF= PRF= PRF= PRF=

(mph) (s) 1 kHz* 3.03 kHz* 1 kHz* 3.03 kHz* 303 Hz*

96.6 0.6 !68 dBm !91 dBm !89 dBm !61 dBm !14 dBm

(60) (2%) (1%) (9%) (17 %) (1%)

80.5 0.72 !68 dBm !91 dBm !89 dBm !61 dBm !14 dBm

(50) (1%) (0.4%) (5%) (12.5 %) (0.8%)

64.4 0.89 !68 dBm !91 dBm !89 dBm !61 dBm !14 dBm

(40) (0.5%) (0.2%) (2.7%) (6 %) (0.4%)

48.3 1.19 !58 dBm !81 dBm !89 dBm !61 dBm not

(30) (3.3%) (43.5%) (0.8%) (2.6 %) measured

32.2 1.79 !58 dBm !81 dBm !89 dBm !61 dBm not

(20) (0.4%) (28.3%) (0.2%) (0.25 %) measured

 The percentage of trials exceeding the maximum are shown in parenthesis.

*
15

Typically, the radars operating at or near the proposed DSRC system center frequency have peak

(EIRP) in the range of 113-133 dBm. The worst case interference had a pulse width of 3.3 μs, a duty

cycle of 1%, and interferes with the DSRC system at power levels as low as !91 dBm at the beacon

receiver. For this case, at least 220-240 dB of isolation is required. The best case interference (on

frequency, from the Table 4) occurs for a pulse width of 3.3 μs and a duty cycle of 0.1% requiring

143-163 dB of isolation. It is clear that if the DSRC system and the interfering radar operate at about

the same RF frequency, the required isolation is quite significant.

In general, the required isolation can be achieved by a variety of techniques including the use of a

highly directive DSRC beacon receiver antenna, offsetting the operating frequencies of the radar and

DSRC system, and allowing sufficient physical separation between the DSRC system and radar to

achieve a specified basic transmission loss. It is estimated that 15 dB of isolation may be achieved

in cases where the DSRC system can be installed so that the radar is well out of the beacon receiver

antenna main beam. Also, when the DSRC system is well out of the main beam of the radar (e.g., due

to installation or rotation) it may be possible to obtain 25 dB of isolation. The most optimistic case

would then give 40 dB of isolation for antenna alignment. The measurement results for interference

as a function of frequency offset (Table 3) indicate that about 75-80 dB of additional isolation may

be achieved for offsets of a few hundred megahertz. This in combination with antenna sidelobe

attenuation and basic transmission loss for distances of several hundred meters may be sufficient to

allow effective operation of the DSRC system in most cases.

The required physical separation for the general ranges of best case (!143 to !163 dB of required

isolation) and worst case (!220 to !240 dB of required isolation) interference scenarios was

calculated for the following cases:

Case 1- isolation is achieved via physical separation only.

Case 2- isolation is achieved via physical separation and antenna alignment that provides an

 additional 40 dB of isolation.

Case 3- isolation is achieved via physical separation and frequency offset that provides 

approximately 80 dB of additional isolation.

Case 4- isolation is achieved via physical separation and frequency offset plus antenna

alignment that provides an additional 120 dB of attenuation.

The basic transmission loss as a function of distance was calculated using the ITS Irregular Terrain

Model [6] and is shown in Figure 6. The parameters used to determine the basic transmission loss

 are given in Table 5. The calculated separation distances are given in Table 6.
Wreceived'133%16!Lfreespace

!A'!91 (dBm)

Lb'Lfree space%A'240 (dB).

Lb

16

(2)

Table 5. ITM Parameters Used to Calculate Basic Transmission Loss

Parameter Value

Frequency 5850 MHZ

Antenna Heights 13 m (radar), 6.1 m (DSRC)

Polarization Vertical

Terrain Irregularity 90 m

Surface Refractivity 301 N-units (4/3 earth)

Climate Continental temperate

Electrical Ground Constants F = 0.001 S/m

, = 15 r

Time Reliability, Location 90%, 90%, 50%

Reliability, and Confidence Level

Table 6. Required Separation for Best Case and Worst Case Interference Pulses

Required Isolation Case 1 Required Case 2 Required Case 3 Required Case 4 Required

(dB) Separation (km) Separation (km) Separation (km) Separation (km)

!143 17 0.6 <0.1 <0.1 

!163 44 4 <0.1 <0.1 

!220 379 64 14 <0.4 

!240 621 203 40 <3.0 

For example, if the interfering radar transmits 3.3 μs pulses with a 1% duty cycle at an EIRP of

133 dBm (worst case interferer), the received interference power (at the beacon receiver) should not

exceed !91 dBm (from Table 4). Equation 1 can be used to calculate the basic transmission loss 

required to obtain !91 dBm:

From Figure 6, the required basic transmission loss is achieved at a distance of 621 km as given in

Table 6. If 40 dB of isolation is achieved by antenna alignment (Case 2), then 203 km of separation

is required to obtain a basic transmission loss of 200 dB.
0

100

200

300

0 200 400 600 800 1000

Basic transmission loss

Free space loss

Distance (km)

 The file of all United States Government frequency assignments. This file is updated monthly. 4

17

Figure 6. Basic transmission loss as a function of distance.

These results indicate that when the DSRC system and the radar antennas are aligned such that the

radar is viewed with the minimum directive gain for both antennas, and the center RF frequencies are

offset by a few hundred MHZ, the systems should be compatible at separation distances of 3 km or

more for the worst-case required isolation of 240 dB (EIRP = +133 dBm). If only 220 dB of

isolation is required (EIRP = + 113 dBm), then the systems should be compatible at separation

distances of 0.4 km or more. The condition for minimum directive gain should be realized for

rotating high-gain radar antennas with rotation rates of a few seconds, in which case the DSRC

system would be in the main beam for only about 20 ms.

In Table 7, we give the results of interference calculations for specific existing radars that may

potentially interfere with the operation of DSRC systems. This table shows specifically the radars that

can reasonably coexist with the DSRC system and those where additional efforts will be required to

improve compatibility. The radars and operating characteristics were taken from the Government

Master File, and should include all of the radars that may potentially interfere with the

4

implementation of DSRC systems in the 5850- to 5925-MHZ band.

In the first column, we give the specific radar identification, pulse parameters (pulse width in μs and

pulse repetition frequency; PRF), and the measured minimum interference power (MIP) for the pulse

parameters. These were matched as closely as possible to the measurement results (Table 4) to

estimate the MIP for that particular radar. In most cases, there is a range of possible pulse widths
18

and repetition frequencies resulting in large differences in the required isolation. In such cases, we

have shown the best and worst cases associated with possible pulse parameters for each radar.

In the following columns of Table 7, we give the results for each previously defined case and an

additional case (Case 5) where the DSRC system antenna sidelobe is in the main beam of the radar

antenna and the isolation due to antenna alignment is 15 dB. There are two table entries for all cases:

the required isolation for interference free operation, and the separation distance required to achieve

that isolation. For Case 3, there is an additional entry showing the value of )f that was used to

estimate the isolation due to frequency offset (from Table 3). The frequency offset used is the

minimum offset based on the radar RF frequency range and the proposed DSRC system RF frequency

range.

For most existing radars, Case 4 should be achievable. As discussed previously, maximum isolation

due to antenna alignment is likely for most rotating radars. Furthermore, installation of the DSRC

system so as to achieve maximum antenna alignment isolation should be possible in many cases. The

results show that for Case 4, the required separation distance is less than 1 km except for the test

radar which has a required separation distance of 2 km. Case 5 may occur when the DSRC system

is in the main beam of the radar for prolonged periods of time. This will occur, for example, if a

nonrotating radar happens to be pointed at the DSRC system antenna sidelobe. This case, while

somewhat unlikely, is possible and does significantly increase the required separation distance relative

to Case 4.

Cases 1 and 2 only occur when the DSRC system and the radar are co-channel resulting in quite large

required separation distances. These cases are only applicable to the FPS-16 and RIR-778C tracking

radars. A map showing their locations is given in Figure 7. For these radars, a significant decrease

in the required isolation is achieved when antenna alignment and frequency offset are possible (see

Case 4). In cases where maximum isolation due to antenna alignment and frequency offset are

difficult to achieve, coordination between the radar facility and DSRC system operations may be

required to ensure electromagnetic compatibility. Such efforts could include RF frequency

coordination and/or spatial masking.
19

Table 7. Required Separation Distances Between Specific Interfering Radars and the

DSRC System for Different Isolation Cases

Specific Radar Case 1: Isolation Case 2: Isolation Case 3: Isolation Case 4: Isolation Case 5: Isolation

by physical by physical by physical by physical by physical

separation only separation and separation and separation, separation,

40 dB from frequency offset frequency offset, frequency offset,

antenna alignment and 40 dB from and 15 dB from

antenna alignment antenna alignment

RIR-778C/FPS-16 348 km 61 km 20 km 0.8 km 8 km

1μs, 1 kHz )f=50 MHZ

MIP* =!68 dBm 217 dB 177 dB 146 dB 106 dB 131 dB

Test radar 505 km 140 km 32 km 2 km 14 km

10 μs, 1 kHz )f=180 MHZ

MIP =!89 dBm 231 dB 191 dB 155 dB 115 dB 140 dB

Test radar 34 km 2.2 km 0.05 km <0.001 km 0.008 km

3.3 μs, 303 Hz )f=180 MHZ

MIP =!14 dBm 156 dB 116 dB 80 dB 40 dB 65 dB

SPS-10 182 km 35 km 13 km 0.4 km 5 km

1 μs, 1 kHz )f=25 MHZ

MIP=!68 dBm 197 dB 157 dB 139 dB 99 dB 124 dB

SPS-10 17 km 0.6 km .08 km <0.001 km 0.015 km

3.3 μs, 303 Hz )f=25 MHZ

MIP=!14 dBm 143 dB 103 dB 85 dB 45 dB 70 dB

SPS-67 196 km 39 km 15 km 0.5 km 6 km

1 μs, 1 kHz )f=25 MHZ

MIP=!68 dBm 199 dB 159 dB 141 dB 101 dB 126 dB

SPS-67 147 km 28 km 10 km 0.2 km 3 km

.33 μs, 3.03 kHz )f=25 MHZ

MIP=!61 dBm 192 dB 152 dB 134 dB 94 dB 119 dB

WSR-74C 266 km 50 km 9 km 0.17 km 2.5 km

1 μs, 1 kHz )f=200 MHZ

MIP=!68 dBm 208 dB 168 dB 132 dB 92 dB 117 dB

WSR-74C 31 km 2 km 0.04 km <0.001 km 0.006 km

3.3 μs, 303 Hz )f=200 MHZ

MIP=!14 dBm 154 dB 114 dB 78 dB 38 dB 63 dB

*Minimum interference power (MIP).
Aberdeen

WallopsIs.

Coquina

Huntsville

CapeCanaveral

=Potentiallyco-channelradars

=OtherradarspossibilyrequiringEMCcoordination

Cape

San

Blas

Eglin

AFB

Ft.

Polk

Ft. Hood

Ft. Huachuca

OatmanMtn.

Ft.Bliss

WSMR

Kokee

Ft.Wingate

Green

River

Tonopah

EdwardsAFB

VandenburgAFB

Pt. Mugu

San

NicholasIs.

20

Figure 7. U.S. locations possibly requiring EMC coordination for DSRC deployment.

4.0 SUMMARY AND RECOMMENDATIONS

The tests and measurements performed on the DSRC system resulted in quantitative determinations

of the adverse impact that various C-band radar transmissions produce on beacon operations. These

adverse impacts were quantified as a function of both the interference amplitude and the interference

modulation parameters. This section summarizes the results of the tests, and also makes

recommendations to improve electromagnetic compatibility where required.

4.1 Summary

DSRC beacon operations were found to be significantly affected by co-channel radar signals that use

pulse widths and pulse repetition rates that are representative of actual 5-GHz radars, and that are

expected to be representative of radars that may operate in the 5-GHz band in the future. For cochannel operations between DSRC stations and radar stations, mitigation of adverse effects due to

radar signals may require separation distances of up to a few hundred kilometers to achieve the

necessary isolation. Our results further indicate that significant isolation can be achieved when the

RF frequencies are offset by more than 25 MHZ. When combined with the expected maximum
21

isolation achieved by antenna alignment (about 40 dB), we found that for all but one radar type, the

DSRC system and existing C-band radars should be compatible at distances of 1 km, (or less) with

the exceptional case requiring a 2-km separation. 

It is expected that for most radar installations, coordination with DSRC systems operations will allow

the required isolation resulting from frequency offset and antenna alignment to be achieved. Possible

modifications that can be used to enhance compatibility in the event that the required isolation cannot

otherwise be achieved are given below.

4.2 Recommendations for Enhanced DSRC Electromagnetic Compatibility

Taking into account the results of the DSRC tests and data analysis, we make the following

recommendations for design modifications to the DSRC to improve electromagnetic compatibility

with both current and future radiolocation operations in the 5-GHz portion of the spectrum:

1. The electromagnetic compatibility between DSRC stations and radar stations within the 5850- to

5925-MHZ spectrum band can be enhanced through the incorporation of modified DSRC

data-encoding schemes.

It was noted during the course of the tests and measurements that deleterious interference effects

were more pronounced when the duty cycle was increased, and that pulse repetition rate was

particularly important as an interference factor. This dependence implies that significantly improved

DSRC performance in the presence of radar interference may be achievable through the use of shorter

DSRC data packets, and possibly through the use of forward error correction (FEC) in the DSRC

coding scheme. Shorter DSRC data packets would reduce the probability of the loss of data bits due

to simultaneous occurrence with radar pulses. We believe that shorter data packets would have the

same effect as lower radar duty cycle. FEC should be useful in recovering individual bits that might

be lost due to radar pulse interference as well, but the effectiveness of both of these approaches is

beyond the scope of this report, and need to be studied separately.

2. Even with the suggested changes to the DSRC system protocol, there remains one possible

electromagnetic compatibility problem that cannot be solved by modifying the DSRC design: the case

in which a radar is co-channel to the DSRC receiver frequency, and the radar signal is received at

such a high amplitude that front-end overload occurs in the DSRC beacon receiver front-end. This

may happen if a DSRC station is within close proximity to a very high-power radar, such as an FPS16. In such a case, electromagnetic compatibility can only be achieved by installing a notch filter in

the DSRC front-end at the radar frequency (or a band-reject filter that is effective across the range

of selectable radar frequencies), or else by tuning the radar below 5850 MHZ (where the interference

will be mitigated by the DSRC 5250- to 5850-MHZ band-reject filter). At such locations, long-term

coordination will be required to ensure that the DSRC and radar frequencies do not coincide.

Locations in the United States where we anticipate that such coordination may be required are
22

Wallops Island, Patuxent Naval Air Test Center, Cape Canaveral Air Force Station, Eglin Air Force

Base, White Sands Missile Range, Edwards Air Force Base, China Lake Naval Weapons Center,

Vandenburg Air Force Base, and Point Mugu.

4.3 Recommended Additional Analysis

Our measurements indicate that there is a strong likelihood that DSRC system performance in the

presence of radar interference can be substantially improved through the use of data encoding

schemes. The tests and analysis that were performed were not adequate to make that determination

definitively. Further analysis needs to be performed to determine, quantitatively, to what extent

DSRC electromagnetic compatibility can be improved through the use of such a design modification,

and indeed what data encoding modifications would be most effective. Therefore, we recommend

that additional resources be devoted to determining engineering changes in DSRC data transfer

protocols that would effectively mitigate co-channel, pulsed interference from radar stations.
23

5. REFERENCES

[1] F.H. Sanders and V.S. Lawrence, “Broadband spectrum survey at Denver, Colorado,” NTIA 

 Report 95-321, Sep. 1995.

[2] F.H. Sanders, B.J. Ramsey, and V.S. Lawrence, “Broadband spectrum survey at San Diego, 

 California,” NTIA Report 97-334, Dec. 1995.

[3] F.H. Sanders, R.L. Hinkle, and B.J. Ramsey, “Analysis of electromagnetic compatibility 

 between radar stations and 4 GHz fixed-satellite earth stations,” NTIA Report 94-313, Jul. 

 1994.

[4] R.J. Matheson, J.D. Smiley, G.D. Falcon, and V.S. Lawrence, “Output tube emission 

 characteristics of operational radars,” NTIA Report 82-92, Jan. 1992.

[5] European Committee for Standardization (CEN), “Dedicated short-range communications 

 physical layer,” Predraft Standard, Dec. 1995.

[6] G.A. Hufford, A.G. Longley, and W.A. Kissick, “A guide to the use of the ITS Irregular 

 Terrain Model in the area prediction mode,” NTIA Report 82-100, Apr. 1982.
24

APPENDIX A: MEASURED WAIT TIME STATISTICS

The measured wait time statistics in the presence of interference are presented in this appendix. These

data are presented in Figures A-1 through A-30 in the form of both histograms and cumulative

distribution functions for the interference pulse parameters given in Table 1 of this report. In each

case, statistics were obtained at several levels of peak RF interference power. For each pulse

parameter set, statistics were typically measured at three interference power levels: the lowest power

level where the wait time obviously starts to increase relative to an interference-free channel, and two

additional measurements at 10 and 20 dB above this minimum. The percentage of trials that exceed

a desired wait time can be evaluated directly from the cumulative distribution plots.
0.01

0.1

1

10

100

0 2 4 6 8 10

Mean = .17 s

SD = .16 s

Wait time (s)

Percent

0

1

2

3

0.1 1 10 100

Percent exceeding ordinate

Wait time (s)

25

Figure A-1. Wait time histogram, interference pulse parameters: pulse 

width = 1 μs, pulse period = 1 ms, peak RF power = !68 dBm.

Figure A-2. Wait time cumulative distribution, pulse parameters: pulse 

width = 1 μs, pulse period = 1 ms, peak RF power = !68 dBm.
0.01

0.1

1

10

100

0 2 4 6 8 10

Mean = .36 s

SD = .35 s

Wait time (s)

Percent

0

1

2

3

0.1 1 10 100

Percent exceeding ordinate

Wait time (s)

26

Figure A-3. Wait time histogram, interference pulse parameters: pulse 

width = 1μs, pulse period = 1 ms, peak RF power = !58 dBm.

Figure A-4. Wait time cumulative distribution, pulse parameters: pulse 

width = 1μs, pulse period = 1 ms, peak RF power = !58 dBm.
0.01

0.1

1

10

100

0 2 4 6 8 10

Mean = .44 s

SD = .42 s

Wait time (s)

Percent

0

1

2

3

0.1 1 10 100

Percent exceeding ordinate

Wait time (s)

27

Figure A-5. Wait time histogram, interference pulse parameters: pulse 

width = 1μs, pulse period = 1 ms, peak RF power = !48 dBm.

Figure A-6. Wait time cumulative distribution, pulse parameters: pulse 

width = 1μs, pulse period = 1 ms, peak RF power = !48 dBm.
0.01

0.1

1

10

100

0 2 4 6 8 10

Mean = .25 s

SD = .24 s

Wait ime (s)

Percent

0

1

2

3

0.1 1 10 100

Percent exceeding ordinate

Wait time (s)

28

Figure A-7. Wait time histogram, interference pulse parameters: pulse 

width = 10μs, pulse period = 1 ms, peak RF power = !89 dBm.

Figure A-8. Wait time cumulative distribution, pulse parameters: pulse 

width = 10μs, pulse period = 1 ms, peak RF power = !89 dBm.
0.01

0.1

1

10

100

0 2 4 6 8 10

Mean = .69 s

SD = .63 s

Wait time (s)

Percent

0

1

2

3

4

5

0.1 1 10 100

Percent exceeding ordinate

Wait time (s)

29

Figure A-9. Wait time histogram, interference pulse parameters: pulse 

width = 10μs, pulse period = 1 ms, peak RF power = !79 dBm.

Figure A-10. Wait time cumulative distribution, pulse parameters: pulse 

width = 10μs, pulse period = 1 ms, peak RF power = !79 dBm.
0.01

0.1

1

10

100

0 2 4 6 8 10

Mean = 1.20 s

SD = 1.24 s

Wait time (s)

Percent

0

2

4

6

8

0.1 1 10 100

Percent exceeding ordinate

Wait time (s)

30

Figure A-11. Wait time histogram, interference pulse parameters: pulse 

width = 10μs, pulse period = 1 ms, peak RF power = !69 dBm.

Figure A-12. Wait time cumulative distribution, pulse parameters: pulse 

width = 10μs, pulse period = 1 ms, peak RF power = !69 dBm.
0.01

0.1

1

10

100

0 2 4 6 8 10

Mean = .10 s

SD = .11 s

Wait time (s)

Percent

0

1

2

3

0.1 1 10 100

Percent exceeding ordinate

Wait time (s)

31

Figure A-13. Wait time histogram, interference pulse parameters: pulse width = 

3.3 μs, pulse period = .330 ms, peak RF power = !91 dBm.

Figure A-14. Wait time cumulative distribution, pulse parameters: pulse width = 

3.3 μs, pulse period = .330 ms, peak RF power = !91 dBm.
0.01

0.1

1

10

100

0 2 4 6 8 10

Mean = 1.38 s

SD = 1.38 s

Wait time (s)

Percent

0

2

4

6

8

0.1 1 10 100

Percent exceeding ordinate

Wait time (s)

32

Figure A-15. Wait time histogram, interference pulse parameters: pulse width = 

3.3 μs, pulse period = .330 ms, peak RF power = !81 dBm.

Figure A-16. Wait time cumulative distribution, pulse parameters: pulse width = 

3.3 μs, pulse period = .330 ms, peak RF power = !81 dBm.
0.01

0.1

1

10

100

0 2 4 6 8 10

Mean = .11 s

SD = .11 s

Wait time (s)

Percent

0

1

2

3

0.1 1 10 100

Percent exceeding ordinate

Wait time (s)

33

Figure A-17. Wait time histogram, interference pulse parameters: pulse width = 

.33 μs, pulse period = .330 ms, peak RF power = !71 dBm.

Figure A-18. Wait time cumulative distribution, pulse parameters: pulse width = 

.33 μs, pulse period = .330 ms, peak RF power = !71 dBm.
0.01

0.1

1

10

100

0 2 4 6 8 10

Mean = .32 s

SD = .32 s

Wait time (s)

Percent

0

1

2

3

0.1 1 10 100

Percent exceeding ordinate

Wait time (s)

34

Figure A-19. Wait time histogram, interference pulse parameters: pulse width = 

.33 μs, pulse period = .330 ms, peak RF power = !61 dBm.

Figure A-20. Wait time cumulative distribution, pulse parameters: pulse width = 

.33 μs, pulse period = .330 ms, peak RF power = !61 dBm.
0.01

0.1

1

10

100

0 5 10 15 20 25

Mean = 3.58 s

SD = 3.59 s

Wait time (s)

Percent

0

10

20

30

0.1 1 10 100

Percent exceeding ordinate

Wait time (s)

35

Figure A-21. Wait time histogram, interference pulse parameters: pulse width = 

.33 μs, pulse period = .330 ms, peak RF power = !51 dBm.

Figure A-22. Wait time cumulative distribution, pulse parameters: pulse width = 

.33 μs, pulse period = .330 ms, peak RF power = !51 dBm.
0

1

2

3

0.1 1 10 100

Percent exceeding ordinate

Wait time (s)

0.01

0.1

1

10

100

0 2 4 6 8 10

Mean = .06 s

SD = .05 s

Wait time (s)

Percent

36

Figure A-24. Wait time cumulative distribution, pulse parameters: pulse width = 

3.3 μs, pulse period = 3.3 ms, peak RF power = !24 dBm.

Figure A-23. Wait time histogram, interference pulse parameters: pulse width = 

3.3 μs, pulse period = 3.3 ms, peak RF power = !24 dBm.
0.01

0.1

1

10

100

0 2 4 6 8 10

Mean = .13 s

SD = .14 s

Wait time (s)

Percent

0

1

2

3

0.1 1 10 100

Percent exceeding ordinate

Wait time (s)

37

Figure A-25. Wait time histogram, interference pulse parameters: pulse width = 

3.3 μs, pulse period = 3.3 ms, peak RF power = !14 dBm.

Figure A-26. Wait time cumulative distribution, pulse parameters: pulse width = 

3.3 μs, pulse period = 3.3 ms, peak RF power = !14 dBm.
0.01

0.1

1

10

100

0 2 4 6 8 10

Mean = .14 s

SD = .15 s

Wait time (s)

Percent

0

1

2

3

0.1 1 10 100

Percent exceeding ordinate

Wait time (s)

38

Figure A-27. Wait time histogram, interference pulse parameters: pulse width = 

3.3 μs, pulse period = 3.3 ms, peak RF power = !4 dBm.

Figure A-28. Wait time cumulative distribution, pulse parameters: pulse width = 

3.3 μs, pulse period = 3.3 ms, peak RF power = !4 dBm.
0.01

0.1

1

10

100

0 2 4 6 8 10

Mean = .12 s

SD = .11 s

Wait time (s)

Percent

0

1

2

3

0.1 1 10 100

Percent exceeding ordinate

Wait time (s)

39

Figure A-29. Wait time histogram, interference pulse parameters: pulse width = 

.33 μs, pulse period = 3.3 ms, peak RF power = !21 dBm.

Figure A-30. Wait time cumulative distribution, pulse parameters: pulse width = 

.33 μs, pulse period = 3.3 ms, peak RF power = !21 dBm.