NTIA Report 96-333 

Testing and Evaluation of the 

Subcarrier Traffic Information Channel 

John F. Mastrangelo 

Wayne R. Rust 

U.S. DEPARTMENT OF COMMERCE 

Mickey Kantor, Secretary 

Larry Irving, Assistant Secretary 

for Communications and Information 

September 1996 

iii

PRODUCT DISCLAIMER 

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. 

v 

CONTENTS 

Page 

PRODUCT DISCLAIMER ........................................................................................................... iii 

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

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

2. STIC SYSTEM DESCRIPTION ...............................................................................................2 

3. LABORATORY EVALUATION .............................................................................................2 

 3.1 Laboratory Testing...............................................................................................................3 

 3.2 Laboratory Results...............................................................................................................4 

4. STIC FIELD TESTING AND EVALUATION ........................................................................6 

 4.1 STIC Installation..................................................................................................................6 

 4.2 Route Planning.....................................................................................................................9 

 4.3 STIC Field Evaluation .......................................................................................................11 

 

5. CONCLUSIONS......................................................................................................................37 

APPENDIX A: DATA COLLECTION SYSTEM.......................................................................41 

APPENDIX B: DATA-PROCESSING METHODOLOGY........................................................43 

APPENDIX C: CONVERSION OF RECEIVED SIGNAL POWER TO ELECTRIC FIELD 

 STRENGTH........................................................................................................47 

APPENDIX D: COMPARISON OF PREDICTED AND RECEIVED SIGNAL POWER 

 LEVELS..............................................................................................................49 

TESTING AND EVALUATION OF THE SUBCARRIER TRAFFIC 

INFORMATION CHANNEL 

John F. Mastrangelo and Wayne R. Rust∗

In support of the Federal Highway Administration of the United States Department 

of Transportation, the Institute for Telecommunication Sciences has completed a 

laboratory and field test program designed to independently evaluate the 

performance of an FM subcarrier-based traveler information broadcast system. This 

system was developed by the MITRE Corporation to investigate the use of FM 

subcarriers for the broadcast of traffic data to vehicles on highways. The testing and 

evaluation program measured the Subcarrier Traffic Information Channel (STIC) 

system performance both in the laboratory and when installed in the subcarrier 

channel of a commercial FM broadcast station. STIC performance was measured 

and evaluated in a variety of reception environments in order to assist in the future 

prediction of STIC coverage in areas of the United States that differ dramatically in 

terrain and population density. 

Key words: Advanced Traffic Information Systems (ATIS); FM broadcast subcarrier; Intelligent 

Transportation Systems (ITS); propagation measurements; propagation predictions; 

Subcarrier Traffic Information Channel (STIC) system 

1. INTRODUCTION 

The United States Department of Transportation (DOT) established the Intelligent Transportation 

System (ITS) program to use advanced computer, electronics, and communications technologies to 

improve the effectiveness of the nation’s highway system. The goals are to provide travel planning 

and management, traveler information, energy conservation, and advanced vehicle control to 

highway users. The Federal Highway Administration (FHWA) contracted the MITRE Corporation 

to investigate the use of FM subcarriers for the broadcast of traffic data to vehicles on highways to 

support ITS. In response to this contract, MITRE developed the Subcarrier Traffic Information 

Channel (STIC) waveform and prototype STIC system to evaluate the potential use of the existing 

FM broadcast infrastructure to broadcast traffic information. The National Telecommunications 

and Information Administration/Institute for Telecommunication Sciences (NTIA/ITS) was 

contracted by the FHWA to perform independent analysis and additional laboratory and field 

testing of the STIC system. NTIA/ITS measured the STIC system performance when installed in 

the subcarrier channel of a commercial FM broadcast station. STIC performance was evaluated in 

a variety of reception environments: urban high-rise, urban low-rise, rural mountain, and rural 

plains. 

 

∗

 The authors were formerly with the Institute for Telecommunication Sciences, National 

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

CO 80303-3328. 
2

2. STIC SYSTEM DESCRIPTION 

The STIC system is a proof-of-concept prototype developed by the MITRE Corporation under the 

sponsorship of the ITS program. The prototype is intended to demonstrate the ability to broadcast 

high-speed digital data using the existing commercial FM broadcast radio infrastructure. 

The STIC system is an FM subcarrier-based data transmission and reception system. It is designed 

to achieve reliable communications in the multipath and fading environment associated with very 

high frequency (VHF) mobile receivers. To achieve that end, the STIC system uses high levels of 

signal processing and error correction. The key characteristics of the waveform are: 

• 72.2-kHz center frequency, 

• 20-kHz bandwidth, 

• π/4 DQPSK with square root raised cosine filtering, 

• 1⁄2-rate convolutional code (mitigation of random errors), 

• Reed-Solomon (228,243) block code (mitigates burst errors and provides error detection), 

• convolutional interleaving (to randomize burst errors), and 

• 18.05-kbps channel data rate, >8-kbps information data rate. 

The prototype STIC system consists of a transmitter subsystem and receiver subsystem. The STIC 

transmitter subsystem consists of the STIC subcarrier generator and a personal computer (PC). The 

PC is used to control and configure the subcarrier generator and generate messages for 

transmission. The subcarrier generator is enclosed in a single rack-mounted chassis. It connects 

directly to the subcarrier input port of an FM broadcast exciter. The STIC receiver subsystem 

consists of an FM car stereo receiver (modified to demodulate the subcarrier signal), a Global 

Positioning System (GPS) antenna, the STIC receiver (which also functions as a GPS receiver), a 

hand-held data terminal, a data collection PC, and the STIC power supply and harness. 

3. LABORATORY EVALUATION 

The goals of the laboratory testing were to familiarize the NTIA/ITS engineers with the operation 

of the STIC system before embarking on the field-testing program, verify adjacent subcarrier and 

entertainment signal compatibility by measuring the occupancy bandwidth of the STIC signal, and 

determine the baseline performance under the best possible operating conditions in preparation for 

field testing. Extensive compatibility testing of the STIC waveform with an audio program or other 

subcarrier systems was not performed due to time and equipment constraints. The primary purpose 

of the STIC laboratory performance testing was to measure the system error rates vs. received 

signal power. Error performance for the STIC system consisted of three performance metrics: 

channel error rate (CER), bit error rate (BER), and packet error rate (PER). Each of these was 

measured and recorded for a range of received signal power levels. 
3

3.1 Laboratory Testing 

Laboratory testing was used to characterize the idealized system error performance (CER, BER, 

and PER) as a function of the received power level. The received power level is a metric closely 

associated with radio area coverage. The ultimate goal of the field test program was to predict 

STIC performance in different geographic environments (i.e., system coverage) by using either 

known or predicted received signal power levels. 

The STIC system can operate in message mode and BER mode. In message mode, the STIC 

transmits a user-specified message. This message can be generated via the keyboard, a previously 

stored file, a modem, or any other input device. The message mode was not used during the 

NTIA/ITS testing. In BER mode, the transmitter continuously sends a BER data pattern that is 

known by the receiver. By comparing the received BER data pattern with the stored BER data 

pattern, error rate information can be computed. The STIC prototype can also perform 

convolutional interleaving of the transmitted data. The convolutional interleaver can operate in one 

of four modes; denoted x1, x2, x4, or x8. Each mode corresponds to an interleaver depth. Two of 

the four modes, x1 and x2, were evaluated during laboratory testing. Error performance was 

divided into three categories: CER, which corresponds to the actual channel error rate; BER, which 

is post-error-correction bit error rate; and PER, which corresponds to the packet error rate. A 

packet with errors is defined as a packet containing one or more bit errors. A packet consists of 

1824 bits. The laboratory evaluation system is shown in Figure 1. 

Figure 1. Laboratory test configuration for error rate testing. 

In order to simulate the STIC subcarrier signal imposed onto a commercial FM carrier, the STIC 

signal was modulated using a Fluke 6062A synthesized RF signal generator. The signal generator 

carrier frequency was set to 100.5 MHz and the FM modulation sensitivity was adjusted for an 

injection level of 10% for the STIC signal. The carrier frequency was chosen for minimal 

commercial broadcast energy in the surrounding frequency band. Additionally, the laboratory 

testing was conducted in the NTIA/ITS screen room to minimize the reception of spurious RF
4

signals. The RF output of the signal generator was connected to a power divider. The output power 

of the RF generator was varied using a precision output attenuator contained in the generator. One 

output of the power divider was routed to a spectrum analyzer for signal power measurements and 

the other output was routed to the modified FM stereo receiver. The hand-held data terminal and 

data collection PC were connected to the STIC receiver. The hand-held data terminal was used to 

configure the STIC receiver and the PC was used to collect and store error information. Laboratory 

testing of the STIC system consisted of two parts: bandwidth occupancy and error rate testing. 

3.2 Laboratory Measurement Results 

3.2.1 Bandwidth Occupancy Measurements 

The STIC waveform was designed to be compatible with the entertainment signal, the 57-kHz 

Radio Broadcast Data System (RBDS) and the 92-kHz subcarrier channel. This required that the 

STIC signal power (when injected at 10%) be suppressed by at least 60 dB relative to the carrier 

level at 62 and 82 kHz. Examination of the STIC signal power spectrum (Figure 2) displayed in the 

Figure 2. STIC baseband power spectrum. 
5

spectrum analyzer plots supports this assertion, with a 6-dB bandwidth of 10 kHz and a 60-dB 

bandwidth of approximately 20 kHz. The out-of-band attenuation suggested that the STIC 

waveform did not interfere with the 57-kHz and 92-kHz subcarriers or the audio program. 

3.2.2 Error Rate Performance 

Error rate vs. received signal power was determined experimentally for three performance metrics 

and two system configurations. 

For the x2 interleaver configuration (Figure 3), channel errors began to appear at power levels less 

than approximately -84 dBm. For channel error rates less than 1x10-2, the error-correcting codes 

implemented in the STIC receiver worked well and corrected 100% of the channel errors. Note that 

for ease of plotting, error rates less than 1x10-6 were assigned the value 1x10-6. When the received 

signal power level was reduced to approximately -95 dBm and the corresponding CER increased to 

4x10-2, the post error-correction bit errors began to appear. The corresponding PER at this power 

level was approximately 1x10-3 and the post error-correction BER was 1x10-5. However, when the 

received power level decreased an additional 1 dB to -96 dBm, performance degraded 

dramatically. At -96 dBm and at a CER of roughly 5x10-2, the post error-correction BER jumped to 

5x10-3 and PER increased to 0.2. By decreasing the signal power an additional 1 dB to -97 dBm, 

the PER increased to effectively 1. 

Figure 3. CER, BER, and PER vs. received signal power for x2 interleaver. 

Behavior of the system in the x1 interleaver mode (Figure 4) was similar to the x2 mode with one 

exception. At signal levels of -96 dBm ± 0.5 dB, the STIC receiver would not maintain 

synchronization. The system would acquire the STIC signal, then immediately lose
6

synchronization. Increasing or decreasing the power level allowed the system to regain 

synchronization. At this signal level, switching to the x2 mode would allow the STIC receiver to 

acquire the signal and maintain synchronization. This behavior did not occur at any power level 

during the x2 testing. MITRE personnel suggested this behavior was the result of a STIC receiver 

program error. The direct effects of this error on STIC field performance are unknown. However, 

the minimum signal power encountered during the field testing was -84 dBm, significantly greater 

than the -95 dBm power level at which the malfunction occurred. 

Figure 4. CER, BER, and PER vs. received signal power for x1 interleaver. 

4. STIC FIELD TESTING AND EVALUATION

Once the laboratory testing of the STIC system was complete, a field test program was initiated. 

The primary goal of the field test program was to correlate the STIC performance with received 

signal level in a variety of reception environments. 

4.1 STIC Installation 

The following two subsections describe the installation and configuration of the STIC transmitter, 

STIC receiver, and signal power measurement system (Figure 5). 
7

Figure 5. STIC field test configuration. 

4.1.1 Transmitter 

A local FM radio station agreed to participate in the STIC field testing program. The STIC 

transmitter was installed at the transmitter site of KYGO-FM, a Denver-area commercial FM radio 

station broadcasting with an effective radiated power of 100 kW and at a frequency of 98.5 MHz. 

The KYGO transmitter is located roughly 25 miles west of Denver, Colorado (altitude 5,280 feet), 

at an altitude of 10,597 feet. The transmitter site provides an unobstructed path into much of the 

Denver metropolitan area and to the East. The STIC signal was injected into the broadcast signal at 

a 10% injection level. The subcarrier injection level was set at the transmitter site by momentarily 

interrupting the entertainment signal and measuring the total modulation on the transmitter’s 

modulation meter. No other subcarriers were carried by the station. The program format is countrywestern. 

The STIC system can operate using a variety of interleaver sizes. At the time of the STIC 

transmitter installation, NTIA/ITS and MITRE personnel decided to operate the STIC system in 

the default x1 mode. This mode was chosen because the transmitter site had encountered 

occasional power outages due to severe weather conditions and in the event of a power cycle, the 

STIC transmitter would automatically resume operation in the default x1 mode. The transmitter 

site is a considerable distance from Boulder, Colorado and there were no provisions at the 

transmitter location for remote configuration of the STIC system. 
8

4.1.2 Receiver 

In order to efficiently measure STIC performance over a wide geographical area, a mobile data 

collection system was employed. The data collection system consisted of a van with both the STIC 

receiver system and signal power measurement systems (Figure 6). GPS receivers were employed 

by both systems allowing the simultaneous collection of received signal power, STIC performance, 

time, and location. The STIC receiver was configured to utilize the x1 interleaver. Appendix A 

provides details of the measurement system and Appendix B details the data-processing 

methodology. 

Figure 6. Mobile data collection van. 

This report describes the STIC performance as a function of received signal power. In some cases, 

electric field strength is a more useful parameter with which to correlate system performance. 

Appendix C describes the procedure for conversion from received signal power to electric field. 

strength. 
9

4.2 Route Planning 

The metropolitan Denver area provides a wide variety of natural and man-made reception 

environments in which to evaluate the STIC performance. Denver, Colorado, is located on the 

plains of the American Mid-West, 20 miles east of the dramatic rise of the Rocky Mountains. Its 

location provides four areas in which the STIC system may operate. These areas were defined as: 

urban high-rise, deep canyons formed by long rows of high-rise buildings; urban low-rise, areas of 

significant numbers of buildings roughly 1 or 2 stories high; rural plains, great open areas typically 

devoid of significant structures or dramatic terrain features; and rural mountains, areas dominated 

by tall mountains and deep natural canyons. The two urban environments encompass typical urban 

and suburban areas while the two rural categories cover most rural environments. 

A series of driving routes was chosen to provide significant time in each environment and to define 

the boundaries of coverage by increasing the distance from the transmitter. The table below 

summarizes each environment, lists the number of miles over which data were collected, and 

provides a color key for each environment that corresponds to the map in Figure 7. 

Reception Environment Data and Map Color Key 

Environment Miles Map Key Characteristics 

Transmitter N/A Orange Mountain-top location. 

Urban High-Rise 16.4 Pink City streets, urban canyons, high-rise corridors. 

Urban Low-Rise 117.0 Yellow Significant man-made obstacles and obstructions, 

typically no greater than 2 stories tall. 

Rural Mountain 130.0 Green Deep canyons, rugged terrain, significant terrain 

shadowing. 

Rural Plains 330.0 Blue Few significant natural or man-made obstacles. 

Typically line-of-sight. 
10

Figure 7. Map of data collection routes. 
11

4.3 STIC Field Evaluation 

For each environment described above, several statistics of performance were computed and 

analyzed. In a dynamic signal environment, such as experienced by a mobile receiver, the received 

signal was likely to experience significant degradation and distortion as the mobile receiver 

changed location. In certain locations, the signal degradation will be so severe that the reception of 

any data was impossible. It was in these areas that the STIC system would lose synchronization 

with the transmitter and thereby lost the ability to receive message or BER data. When the receiver 

was moved to a location more favorable to signal reception, the STIC system would regain 

synchronization. However, the effect of losing synchronization extended beyond the period of 

degraded signal reception. Upon moving to a location more favorable to signal reception, the STIC 

system would re-establish synchronization after an initialization period of approximately 15 

seconds (for the x1 interleaver). During this resynchronization period, message or BER data were 

not being accepted and therefore the error rates (CER, BER, and PER) were assigned their 

maximum value. Discussions with MITRE personnel suggested that the STIC synchronization 

performance would have improved if the x2 interleaver were used instead of the x1. Due to time 

and equipment constraints it was not possible to repeat the field data collection procedure for the 

x2 interleaver but by filtering the field performance data to remove the data points corresponding 

to the STIC system “out of sync,” it was possible to evaluate an approximate upper bound on STIC 

synchronization performance. These figures are labeled as “SYNC Data” in the following sections. 

In the following sections, three sets of statistics are presented as a function of received signal 

power: mean error rate, median error rate, and percentile error rate. Additionally, mean and 

percentile error rates are presented in the “SYNC Data” form and several other statistics are 

computed and presented. No one statistical or performance measure can evaluate or quantify the 

performance of a complex communication system such as the STIC. Each statistical estimation of 

STIC performance provides unique insight into the system performance. 

4.3.1. Rural Plains Environment 

Data for the rural plains environment were collected over paths totaling 330 miles. These data were 

collected at distances between 25 and 103 miles from the transmitter and consisted of 4,127 signalpower and STIC error-rate measurement locations. The propagation environment was typically 

either line-of-sight or close to line-of-sight. Few significant geographical features or man-made 

obstacles were present. 

Figure 8 displays mean error rates vs. received signal power. The mean error rates for a specific 

signal power level were calculated by forming the arithmetic mean of channel, bit, and packet error 

rate measurements for a specific power level (± 2 dB) and placing them in the appropriate bin. 

Figure 9 displays the same data set with the out-of-sync errors removed. The removal of these data 

points produced an improvement of approximately 8 dB in STIC performance. 
12

Figure 8. Mean CER, BER, and PER vs. received signal power for rural plains environment. 

Figure 9. Mean CER, BER, and PER vs. received signal power (SYNC data) for rural plains 

environment. 

Figures 10, 11, and 12 show the STIC performance data using median and percentile error rates vs. 

signal power. Median and percentile error rates assist in illuminating the almost binary nature of 

STIC PER performance, where errors typically occur in bursts. 
13

Figure 10. Median CER, BER, and PER vs. received signal power for rural plains environment. 

Figure 11. Percentile packet error rates vs. received signal power for rural plains environment. 

Figure 13 displays mean error rates vs. distance from the transmitter. The error rates were 

computed in the same manner as the data in Figure 8 except that error rate measurements were 

sorted by distance instead of power level. It was interesting to note the dramatic decrease in STIC 

performance at the ranges of 33 miles, and 43 to 51 miles. Examining the scatter plot of signal 

power vs. distance (see Figure 17), there were instances of unusually low signal power at 33 miles,
14

a significant group in the range of 43 to 51 miles, another group in the range of 65 to 77 miles, and 

above 85 miles. These power levels (< -70 dBm) were consistent with high packet error rates 

shown in Figures 8 through 12. 

Figure 12. Percentile packet error rates vs. received signal power for rural plains environment. 

Figure 13. Mean error rates vs. distance from transmitter for rural plains environment. 
15

Figure 14 displays cumulative error rates vs. error rate for the three performance metrics and 

Figures 15 and 16 display the raw channel and packet error rate data in the form of scatter plots. It 

was from these scatter plots that the mean, median, and percentile error rate plots were generated. 

Figure 14. Cumulative error rates vs. error rate for rural plains environment. 

Figure 15. Channel error rates vs. received signal power for rural plains environment. 
16

Figure 16. Packet error rates vs. received signal power for rural plains environment. 

Figure 17 shows received signal power vs. distance to transmitter in the form of scatter plot. 

Figures 18 and 19 show the number of measurements used to construct each error rate estimate. 

Figure 17. Received signal power vs. distance from transmitter for rural plains environment. 
17

Figure 18. Measurement count vs. received signal power for rural plains environment. 

Figure 19. Measurement count vs. distance from transmitter for rural plains environment. 
18

4.3.2 Rural Mountain Environment 

Data for the rural mountain environment were collected over paths totaling 130 miles through the 

foothills and mountainous regions of the Rocky Mountains west and south of the Denver 

metropolitan area. The data were collected at distances between 2 and 48 miles from the 

transmitter and consisted of 1,726 signal-power and STIC error-rate measurements. 

Figures 20 through 28 reveal the generally poor performance of the STIC system in the rural 

mountain environment. Error performance was poor over a wide range of received power levels 

and distances from the transmitter. This was not surprising considering the severe multipath and 

shading imposed on the STIC receiver. The severity of the environment was apparent in the scatter 

plot of received power vs. distance from transmitter (Figure 29). Received power level spreads of 

60 dB or more for similar distances were common. 

Figure 20. Mean CER, BER, and PER vs. received signal power for rural mountain environment. 
19

Figure 21. Mean CER, BER, and PER vs. received signal power (SYNC data) for rural mountain 

environment. 

Figure 22. Median CER, BER, and PER vs. received signal power for rural mountain environment. 
20

Figure 23. Percentile CER, BER, and PER vs. received signal power for rural mountain 

environment. 

Figure 24. Percentile CER, BER, and PER vs. received signal power (SYNC data) for rural 

mountain environment. 

In Figure 25 (Mean Error Rates vs. Distance from Transmitter) there appeared to be an 

inconsistency in the STIC error rate performance. At distances between 25 and 34 miles from the
21

transmitter, the STIC system appeared to be operating error free. This inconsistency was explained 

by Figures 29 through 31 which show that very little data were collected at that distance. 

Figure 25. Mean CER, BER, and PER vs. distance from transmitter for rural mountain 

environment. 

Figure 26. Cumulative error rates vs. error rate for rural mountain environment. 
22

Figure 27. Channel error rates vs. received signal power for rural mountain environment. 

Figure 28. Packet error rates vs. received signal power for rural mountain environment. 
23

Figure 29. Received signal power vs. distance from transmitter for rural mountain environment. 

Figure 30. Measurement count vs. received signal power for rural mountain environment. 
24

Figure 31. Measurement count vs. distance from transmitter for rural mountain environment. 

4.3.3. Urban Low-rise Environment 

The urban low-rise environment was defined as geographical areas where some man-made or 

geographical obstacles were present. Typical scenarios were suburban areas and city streets 

populated by primarily 1- and 2-story buildings but lacking significant terrain features that would 

classify the areas as rural mountain or urban high-rise environments. A total of 117 miles were 

classified as urban low-rise, and ranged from 17 to 47 miles from the transmitter. The data set 

consisted of 1,474 signal-power and STIC error-rate measurements. 

Performance in the urban low-rise environment remained relatively constant over the range of -34 

to -62 dBm (Figure 32). Error rates rose dramatically at power levels of -66 dBm and below 

(Figures 32 through 36), as they did for the rural plains environment. Removing data points where 

the STIC was out of sync resulted in a significant improvement in error performance at power 

levels greater than -66 dBm. This indicated that the primary cause of STIC performance 

degradation was loss of STIC synchronization. Additional data is shown in Figures 37 through 39. 

During resynchronization (nominally 15 seconds) CER and BER were defined as 0.5 and PER was 

defined as 1. This was evident in the scatter plot of PER vs. signal power (Figure 40). A high 

proportion of data points on the PER = 1 line corresponded to the STIC system being out of 

synchronization. It was clear that these points dominate the error behavior of the system. It was 

also interesting that these out-of-sync periods were apparently not highly correlated with received 

signal power. 
25

Judging from Figure 37, STIC performance in the urban low-rise environment actually improved 

with increasing distance from the transmitter. Figure 37 shows packet errors occurring only at 

distances between 21 and 27 miles from the transmitter. This was likely due to the categorization 

of the data. Figure 7 shows that the shorter distance urban low-rise data were collected in an area 

contiguous with the longer distance rural mountain data. The scatter plot of received signal power 

vs. distance (Figure 41) shows a high variability in received signal power vs. distance in the range 

of 18 to 30 miles. This behavior was consistent with the rural mountain environment (Figure 29). 

Figure 41 suggests that perhaps the urban low-rise data in the range of 18 to 30 miles may be more 

accurately described as rural mountain environment. 

Other than the inconsistency in the short-distance urban low-rise data, the performance of the STIC 

system in the urban low-rise environment was very similar to the performance in the rural plains 

environment. 

Figure 32. Mean CER, BER, and PER vs. received signal power for urban low-rise environment. 
26

Figure 33. Mean CER, BER, and PER vs. received signal power (SYNC data) for urban low-rise 

environment. 

Figure 34. Median CER, BER, and PER vs. received signal power for urban low-rise environment. 
27

Figure 35. Percentile CER, BER, and PER vs. received signal power for urban low-rise 

environment. 

Figure 36. Percentile CER, BER, and PER vs. received signal power (SYNC data) for urban lowrise environment. 
28

Figure 37. Mean CER, BER, and PER vs. distance from transmitter for urban low-rise 

environment. 

Figure 38. Cumulative CER, BER, and PER vs. error rate for urban low-rise environment. 
29

Figure 39. Channel error rates vs. received signal power for urban low-rise environment 

Figure 40. Packet error rates vs. received signal power for urban low-rise environment. 
30

Figure 41. Received signal power vs. distance from transmitter for urban low-rise environment. 

Figure 42. Measurement count vs. received signal power for urban low-rise environment. 
31

Figure 43. Measurement count vs. distance from transmitter for urban low-rise environment. 

4.3.4 Urban High-rise Environment 

The urban high-rise environment data set was collected over paths totaling 16.4 miles and at 

distances between 25.5 and 26.5 miles from the transmitter. The data set consisted of 276 signalpower and STIC error-rate measurements. 

The urban high-rise environment data were collected on the streets of downtown Denver, Colorado 

in the deep canyons formed by the rows of tall buildings. These artificial canyon walls were 

typically 5 or more stories high and provided a severe multipath and fading environment for the 

STIC receiver. This section of downtown Denver was a reasonably square area, approximately 

one-half mile on each side. In order to maintain a consistent environment and not leave the 

boundaries of the high-rise sector, the measurement van was driven up and down adjacent streets, 

within the confines of the tall buildings. The path was then reversed, driving on the opposite side 

of the streets previously driven. When the high-rise area was traversed, the streets perpendicular to 

the first set were driven and the process was repeated. 

The Denver high-rise environment may not be typical of the reception environment of most highrise areas. A typical FM transmitter, located atop a tall building in a high-rise area, may present a 

much greater signal level than a transmitter located 26 miles away and produce significantly 

improved system performance. 
32

As expected, STIC performance degraded in the urban high-rise environment (Figures 43-53). 

Similar to the rural plains data, removal of the out-of-sync data resulted in an 8- to 10-dB 

improvement in STIC PER performance. Due to the very small (1 mile) distance over which the 

data were collected, error rate performance vs. distance plots were not included for this 

environment. 

Figure 44. Mean CER, BER, and PER vs. received signal power for urban high-rise environment. 

Figure 45. Mean CER, BER, and PER vs. received signal power (SYNC data) for urban high-rise 

environment. 
33

Figure 46. Median CER, BER, and PER vs. received signal power for urban high-rise 

environment. 

Figure 47. Percentile CER, BER, and PER vs. received signal power for urban high-rise 

environment. 
34

Figure 48. Percentile CER, BER, and PER vs. received signal power (SYNC data) for urban highrise environment. 

Figure 49. Cumulative CER, BER, and PER vs. received signal power for urban high-rise 

environment. 
35

Figure 50. Channel error rates vs. received signal power for urban high-rise environment. 

Figure 51. Packet error rates vs. received signal power for urban high-rise environment. 
36

Figure 52. Received signal power vs. distance from transmitter for urban high-rise environment. 

Figure 53. Measurement count vs. received signal power for urban high-rise environment. 
37

5. CONCLUSIONS 

Figures 54 through 57 compare mean and 95th percentile channel, bit, and packet error rates for the 

four environments including and excluding out-of-sync data. The STIC system performed most 

reliably in the rural plains environment and similarly in the urban low-rise environment. These two 

environments were relatively clear of significant natural or man-made obstacles. In these 

environments, STIC performance degradation was due to occasional severe signal shadowing by 

local geographic obstacles, such as hills or locally dense clusters of buildings. These encounters 

with severe signal shadowing often resulted in the STIC system losing synchronization. 

STIC performance was degraded by 15 to 20 dB when operated in the urban high-rise 

environment; performance degraded by 27 to 42 dB in the rural mountain environment. This 

performance degradation was with respect to the rural plains environment. In the rural mountain 

environment, the proximity of the receiver to the transmitter was not an issue, ranging from 2-48 

miles, but the signal power vs. distance scatter plot (Figure 29) shows that the effect of local terrain 

shadowing was significant. Proximity of receiver to transmitter may have been an issue in the 

analysis of the urban high-rise data. Figures 44 through 51 show a significant increase in STIC 

performance vs. received signal power when operated in the urban high-rise environment. As 

mentioned in Section 4.3.4, the Denver urban high-rise environment may not be typical of the 

reception environment of most high-rise areas. A typical FM transmitter, located atop a tall 

building in a high-rise sector, may present a greater signal level than a transmitter located 26 miles 

away and produce significantly improved system performance. 

The primary culprit in the degradation of STIC system performance in all environments was loss of 

synchronization. While it can be argued that the system was initializing during this period, it was 

also true that the system had to first lose synchronization before this resynchronization was 

necessary. During the resynchronization period (approximately 15 seconds), the STIC CER, BER, 

and PER were at a maximum and a significant performance reduction was inflicted. Discussions 

with MITRE personnel suggested that the STIC synchronization performance would have 

improved if the x2 interleaver was used instead of the x1 interleaver. 

Comparisons of measurements with predictions of received signal power were made using data 

from two paths for the STIC field test measurements. The results are shown in Figures D-1 and 

D-2 of Appendix D show that for these environments where the STIC system will be used, the 

NTIA/ITS Communication System Performance Model (CSPM) can be used for reliable coverage 

predictions. 
38

Figure 54. Mean packet error rates vs. received signal power for four environments. 

Figure 55. Mean packet error rates vs. received signal power for four environments (SYNC data). 
39

Figure 56. 95th percentile packet error rates vs. received signal power for four environments. 

Figure 57. 95th percentile PERs vs. received signal power for four environments (SYNC data). 

41 

APPENDIX A: DATA COLLECTION SYSTEM 

In order to efficiently measure STIC performance and received signal power over a wide 

geographical area, a mobile data collection system was employed. The data collection system 

consisted of a van with both the STIC receiver and FM signal power measurement. GPS receivers 

were employed by both systems allowing the simultaneous collection of signal power, STIC 

performance, time, and location. 

The STIC receiver and power measurement systems were installed in a van. The single FM 

antenna, shared between the STIC and FM power measurement systems, was a quarter wavelength 

monopole mounted on a 132-cm diameter circular ground plane. The antenna was set at a nominal 

height of 79 cm and adjusted for a minimum voltage standing wave ratio (VSWR) at 98.5 MHz. 

The VSWR was reduced to 1.5:1 by impedance matching the antenna. The antenna and ground 

plane were mounted on a roof rack about 13 cm above the roof of the van. The gain of the antenna 

was 1.5 dBi. The feed from the antenna was connected to an RF power splitter where it was routed 

to the FM stereo receiver (STIC system) antenna terminal and to the spectrum analyzer (FM signal 

power measurement system). Also mounted on the roof of the van were two GPS receiver 

antennas, one for each system. The STIC system has provisions for receiving and recording GPS 

data along with the error data. An additional GPS antenna and receiver were used with the signal 

power measurement system in order to continue the reception of GPS data while the STIC system 

was out of synchronization. They also were used to record an independent estimate of position. 

Each system employed a PC dedicated to system control, configuration, and data collection. The 

entire system was powered by a portable generator that was towed behind the van. 

A.1 Data Collection - STIC 

When operating in BER mode, the STIC transmitter continuously sends a pseudorandom noise 

(PN) data sequence. The receiver compares the incoming sequence to the transmitted sequence 

(stored internally at the receiver) and computes and stores system performance data. A system data 

record was stored every Ti/72 seconds where Ti was the interleaver time (5.76 seconds for the x1 

interleaver). A data record consists of the following fields: 

• time, 

• speed, 

• frame identification number, 

• channel error count, 

• packet count, 

• latitude, 

• heading, 

• synchronization value, 

• bit error count, 

• packet errors, 

• longitude, 

• synchronization flag, 

• byte count, 

• Viterbi errors, and 

• system parameter mask. 

For the purposes of the NTIA/ITS test program, not all of the fields are relevant. All were 

collected, however, in order to maintain compatibility with software routines that MITRE 

provided. The processing of this data is explained in Appendix B. 
42 

A.2 Data Collection - Signal Power 

The signal power data collection system consisted of an HP 8562A Spectrum Analyzer, Trimble 

PAC II GPS receiver, and a laptop PC. The spectrum analyzer was configured to operate in the 

detector sample mode, at a center frequency of 98.5 MHz, span of 0 Hz, resolution and video 

bandwidths of 300 kHz and a sweep time of 30 seconds. In this configuration, the spectrum 

analyzer displays and stores received power as a function of time in a 300-kHz bandwidth centered 

at 98.5 MHz. The sweep data were sampled and stored as a series of 601 data points. The 30-

second sweep time yields a 20-Hz sampling rate. The PC alternately collects time and location data 

from the GPS receiver and power measurements from the spectrum analyzer. The data collection 

PC first queries the spectrum analyzer for the current set of received power data. At the end of each 

30-second sweep, the data collection PC then queries the GPS receiver for the current time and 

location. These values are stored to the data collection hard disk. This cycle repeats continuously 

until a command was given to cease. At that time, the system continued to operate until the current 

sweep was finished and saved and a final GPS time and location estimate were received and stored. 

The received signal power data file format was as follows: 

data header, 

time, latitude, longitude, power[0], power[1], power[600], 

time, latitude, longitude, power[0], power[1], power[600], 

......... 

......... 

......... 

......... 

time, latitude, longitude, power[0], power[1], power[600], 

time, latitude, longitude. 
43 

APPENDIX B: DATA-PROCESSING METHODOLOGY 

Data collection was performed by two independent systems. However, the data files from each 

system ultimately needed to be combined in order to correlate received signal power to STIC 

performance. The STIC system collected GPS location, GPS time, and STIC performance data. 

The FM power measurement system collected GPS location, GPS time, and signal power as a 

function of time (and therefore location). The time resolution of each GPS system was 1 second. 

B.1 Signal Power Data Analysis 

The signal power measurement system consisted of an FM band antenna, GPS antenna and 

receiver, spectrum analyzer, and data collection PC. The spectrum analyzer was used to measure 

available signal power, the GPS receiver to determine position and time, and the PC to collect and 

store spectrum analyzer and GPS data. Data from the spectrum analyzer and GPS receiver were 

collected periodically and stored serially in a file. 

Each file entry consisted of a time, latitude and longitude reading from the GPS receiver followed 

by 601 power measurements from the spectrum analyzer. The 601 points corresponded to one full 

sweep from the analyzer, therefore a sweep time of 30 seconds yielded a power measurement 

every 0.05 seconds. Following guidelines recommended by Lee [1], the recommended procedure 

for measuring the local received power for a mobile radio system was to obtain a series of 

measurements over a path, from 20 to 40 wavelengths in length, sampling at least 36 times during 

this interval and finding the arithmetic mean of the 36-sample set. A 40-wavelength sampling 

interval was preferable. 

A spectrum analyzer sweep time of 30 seconds was chosen such that a single sweep would be 

appropriate over the expected range of receiver velocities of 5 to 60 mph. Averages were computed 

over intervals approaching 40 wavelengths whenever possible. Only when the average speed 

decreased to under 5 mph did the effective sampling interval begin to approach 20 wavelengths. 

Given the wavelength of the broadcast signal: 

3.05 meters

98.5 10

3 10

6

8

= ×

× λ =

and 

20× λ = 61 meters, 40× λ = 122 meters
44 

then the lowest vehicle speed at which the measurement system would traverse 20 wavelengths in 

a 30-second interval was: 

2.03 /sec 4.54 / . 30 sec

61

min meters ond miles hour

onds

meters V = = =

Lee also stated that at least 36 samples should be taken over the 20- to 40-wavelength interval. At a 

sampling rate of 20 samples/second, 36 samples were recorded in 1.8 seconds. The receiver 

velocity at which 40 wavelengths were traversed in 1.8 seconds is: 

67.8 /sec 151.5 / . 1.8 sec

122 max meters ond miles hour

onds

meters V = = =

This implied that our sampling rate and block length were sufficient for all vehicle speeds greater 

than 4.5 mph and less than 150 mph. 

As mentioned previously, data were recorded in 30-second blocks of data containing power levels 

in dBm with time, latitude, and longitude values at the beginning of each block. The time, latitude, 

and longitude values at the beginning of the next block were used as the end values for the 

previous block. When processing the data, the first value computed was the distance traversed 

during the 30-second scan in order to verify that the minimum 20-wavelength distance was 

traversed for the block. This was computed by determining the distance between the beginning and 

ending (latitude, longitude) pairs for the block and then converting that value to the number of 

wavelengths traversed. If the distance traveled for a block was less than 20 wavelengths, the data 

block was discarded. If the distance traveled for a block was more than 20 wavelengths, then the 

data block was divided into an integral number of sub-blocks using the following equation: 

1

40

tan

+⎥

⎦

⎥ ⎢

⎣

⎢

× − = wavelength

dis ce Nsub blocks

Each of these sub-blocks represented the spatial sampling of the local signal power taken over an 

interval of 20 to 40 wavelengths and have at least 36 samples per sub-block. The mean power 

value was then computed on each of the sub-blocks by computing the arithmetic mean on the 

logarithmic power levels (dBm) in the data [1]. Since time, latitude, and longitude information was 

only stored in blocks every 30 seconds and a typical sub-block was approximately 5 seconds in 

length, estimates of time, latitude, and longitude had to be made for each of the N sub-blocks to 

provide position information. This was performed by linearly interpolating between the time, 

latitude, and longitude measurements at the beginning and end of each measurement block and 

evaluating these functions at the center of each sub-block. The values of center time, center 

latitude, center longitude, and mean signal power in dBm were stored in a file to process either 

separately or in conjunction with the STIC error data. 
45 

B.2 STIC Data 

The STIC data collection system consisted of a specially modified FM stereo receiver, STIC 

receiver and laptop PC. As described in Appendix A, the STIC system recorded a data record 

every 80 milliseconds. 

The data in this file needed to be associated with the signal power data file in order to correlate 

error rates with signal power. Each signal power measurement was computed over a time interval 

between 4.5 and 30 seconds in length, depending on the velocity of the vehicle. Each entry in the 

signal power file consisted of start time, center time, stop time, center latitude, center longitude, 

and signal power. The start and stop times were used to select STIC data file entries that occurred 

during a particular signal power measurement interval. 

For each signal power measurement there was an associated start and stop time. The start and stop 

times were used to select entries from the STIC data file. These data were then used to compute 

CER, BER, and PER for the current signal power measurement. The error ratios were computed as 

follows: 

∑

∑

=

=

× × ×

= stop time

t start time

stop time

t start time

byte count

channel errors

CER

228

243 2 8

∑

∑

=

=

×

= stop time

t start time

stop time

t start time

byte count

bit errors

BER

8

∑

∑

=

= = stop time

t start time

stop time

t start time

packet count

packet errors

PER

Depending on the environment, the STIC system occasionally lost synchronization; i.e., became 

inoperable while the STIC system attempted to regain sync with the transmitter. During these 

times, no data were written to the data collection PC as there were no BER data being received by 

the STIC. During the time that the STIC system was out of sync, there were no data entries in the 

STIC data file. Therefore, during these times, the sums were not formed and the error rates were 

assigned default values of CER = BER = 0.5 and PER = 1. 
46 

These three error ratios were computed for each signal power measurement and stored to a new file 

now consisting of the following fields: 

• center time, 

• center latitude, 

• center longitude, 

• signal power, 

• CER, 

• BER, and 

• PER. 

This data file was used to develop a number of graphs. The type of plots generated for each 

environment (rural plains, rural mountain, urban low-rise, and urban high-rise) were: 

• mean error rates (CER, BER, PER) vs. signal power, 

• mean error rates (sync data only) vs. signal power, 

• median error rates vs. signal power, 

• percentile PER vs. signal power, 

• percentile PER (sync data only) vs. signal power, 

• mean error rates vs. distance from transmitter, 

• cumulative error rates vs. error rate, 

• scatter plot of CER vs. signal power, 

• scatter plot of PER vs. signal power, 

• received power vs. distance from transmitter, 

• measurement count vs. signal power, and 

• measurement count vs. distance from transmitter. 

Additional plots comparing the four environments were: 

• mean PER vs. signal power for four environments, 

• mean PER vs. signal power for four environments (sync data), 

• percentile PER vs. signal power for four environments, and 

• percentile PER vs. signal power for four environments (sync data). 

REFERENCES 

[1] W.C.Y. Lee, “Estimate of local average power of a mobile radio signal,” IEEE Trans. Veh. 

Technol., VT-34, No.1, pp. 22-27, Feb. 1985. 
47 

APPENDIX C: CONVERSION OF RECEIVED SIGNAL POWER TO 

ELECTRIC FIELD STRENGTH 

Throughout this report, STIC performance has been reported as a function of received signal 

power. In some cases, electric field strength is a more useful parameter with which to correlate 

system performance. Fortunately, received signal power can easily be converted to electric field 

strength. The pertinent components of the signal power measurement system are shown in the 

Figure C-1. 

Figure C-l. FM antenna system loss. 

The equation for converting received signal power to electric field strength is as follows: 

E(dBuV / m = received signal power (dBm) + 77.21 + 20 x log(f / 106

) 

 - antenna gain(dBi) + cable loss(dB) + divider loss(dB). 

Substituting the appropriate values yields: 

E(dBuV / m) = received signal power(dBm) + 77.21 + 39.87 -1.5 + 0.5 + 4.0 

 = received signal power(dBm) + 120.1 

49 

APPENDIX D: COMPARISON OF PREDICTED AND RECEIVED 

SIGNAL POWER LEVELS 

System performance predictions were made to compare with measured data of several paths 

collected for this report. The received signal power level versus distance data were collected and 

processed using the methods described in the previous appendices to determine the mean received 

signal power versus distance from the transmitter. The distance from the transmitter to the test 

vehicle was used (not the distance along the path), since none of the paths was actually a radial 

path from the transmitter. The measured data were available at increasing distances from the 

transmitter at approximately every 0.06 miles. The predictions were made to occur at these same 

points to compare directly with the measured data. The predictions were performed using the 

NTIA/ITS Communication System Performance Model (CSPM), a widely used and accepted 

model for performance of communication systems in the frequency range of 20 MHz to 20 GHz. 

Path locations at one-mile intervals of distance from the transmitter were selected for plotting. The 

final calculations for the predictions take into account the gain as a function of elevation angle of 

the receiver antenna on the test vehicle and the gain of the transmitter antenna at the radio station. 

The resulting data were plotted in Figures D-l and D-2 for the paths along Interstate 25 and 

Interstate 76, respectively. Considering that the CSPM prediction model does not openly account 

for losses due to vegetation or man-made structures, these figures show good agreement between 

actual measurements and predictions. Performance predictions can be made with confidence for 

other areas of the country where the coverage for the STIC system needs to be determined. 

Figure D-l. Measured and predicted mean received signal power for north-bound path (along 

Interstate 25). 
50 

Figure D-2. Measured and predicted mean received signal power for north-east bound path (along 

Interstate 76).