NTIA Technical Report TR-11-480 

In-Building Radio Enhancement 

Systems for Public Safety 

Robert J. Achatz 

Roger A. Dalke 

John J. Lemmon

NTIA Technical Report TR-11-480 

In-Building Radio Enhancement 

Systems for Public Safety 

Robert J. Achatz 

Roger A. Dalke 

John J. Lemmon

U.S. DEPARTMENT OF COMMERCE 

September 2011

iii

7BDISCLAIMER 

Certain commercial equipment 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 the best available 

for this purpose. 

v

CONTENTS 

Page 

FIGURES .................................................................................................................................vii

TABLES ....................................................................................................................................ix

ACRONYMS .............................................................................................................................. x

EXECUTIVE SUMMARY ........................................................................................................ xi

1 1BINTRODUCTION ................................................................................................................... 1

2 2BIBRES TECHNOLOGY .......................................................................................................... 6

2.1 8BBDA ............................................................................................................................... 6

2.2 9BDistribution Network ...................................................................................................... 9

2.3 10BAntennas ....................................................................................................................... 11

2.4 1BDesign, Installation, Testing, and Commissioning ......................................................... 12

2.5 12BExamples ...................................................................................................................... 14

2.6 13BLink Power Budgets...................................................................................................... 17

3 3BCOMMON PROBLEMS AND THEIR SOLUTIONS ........................................................... 18

3.1 14BFeedback ...................................................................................................................... 18

3.2 15BGain Reduction ............................................................................................................. 20

3.3 16BNoise Transmission ...................................................................................................... 21

3.4 17BDelay ............................................................................................................................ 22

3.5 18BRadio-Wave Propagation .............................................................................................. 23

3.6 19BCost .............................................................................................................................. 26

4 4BCONCLUSION ..................................................................................................................... 27

5 5BACKNOWLEDGEMENTS ................................................................................................... 29

6 6BREFERENCES ...................................................................................................................... 30

APPENDIX A: Tables .............................................................................................................. 35

A.1 Building Material Attenuation....................................................................................... 35

A.2 High-Site Building Attenuation..................................................................................... 35

A.3 Low-Site Building Attenuation ..................................................................................... 36

A.4 Narrowband Public Safety Mobile Radio Frequency Bands .......................................... 36

A.5 Donor Antenna Characteristics ..................................................................................... 36

A.6 References .................................................................................................................... 37

APPENDIX B: Radio-Wave Propagation .................................................................................. 38

B.1 Ideal Radio Wave Propagation Path Loss Models ......................................................... 38

B.2 Practical Path Loss Models ........................................................................................... 40

B.3 Propagation Into Buildings ............................................................................................ 41

B.4 Propagation Inside Buildings ........................................................................................ 42
vi 

B.5 Availability ................................................................................................................... 42

B.6 Site-specific Propagation Models .................................................................................. 44

B.7 Multipath Fading .......................................................................................................... 45

B.8 References .................................................................................................................... 45

APPENDIX C: Calculations ...................................................................................................... 47

C.1 Required Power ............................................................................................................ 48

C.2 Link Budgets ................................................................................................................ 50

C.3 Effects of AGC ............................................................................................................. 55

C.4 Distance Needed to Prevent Repeater Receiver Desensitization..................................... 58

C.5 References .................................................................................................................... 60

APPENDIX D: BDA Measurements ......................................................................................... 61
vii 

FIGURES 

Page 

Figure 1. Signal transmission into building is represented as arrows. Narrowing arrow 

widths correspond to diminishing signal power caused by construction 

material attenuation.................................................................................................... 2

Figure 2. In-building communications using the repeater system. ................................................ 4

Figure 3. In-building communications using direct communications............................................ 4

Figure 4. In-building communications using a mobile repeater system. ....................................... 5

Figure 5. In-building communications using an IBRES. .............................................................. 5

Figure 6. Class A, Class B, and custom BDA filtering. Solid lines represent the user’s 

channels. Dashed lines represent channels from another system. Rectangles 

over the channels represent the BDA filter bandwidth. The Class A BDA 

amplifies only one of the user’s channels. The Class B BDA amplifies all 

channels indiscriminately. The custom filtered BDA amplifies any 

combination of channels. As configured, this would be classified as Class B. ............ 8

Figure 7. BDA showing front panel with donor antenna socket, distribution network 

socket, A/C power plug, and power indicator light. .................................................... 8

Figure 8. BDA functional block diagram. .................................................................................... 9

Figure 9. Coaxial cable cross-section (left) and profile (right). .................................................... 9

Figure 10. Optical cable. ........................................................................................................... 10

Figure 11. Twisted-pair cable. ................................................................................................... 10

Figure 12. Yagi antenna. ........................................................................................................... 11

Figure 13. Omnidirectional antenna. .......................................................................................... 12

Figure 14. Leaky coax, cross section (left) and profile (right). Periodic holes are present 

on the flattened side. ................................................................................................ 12

Figure 15. Floor plan gridded for coverage test.......................................................................... 14

Figure 16. IBRES implemented with coaxial (COAX) cable in a building with a small 

number of floors. ..................................................................................................... 15

Figure 17. IBRES implemented with coaxial (COAX) cable, fiber-optic (FO) cable, and 

corresponding CIUs in a building with a large number of floors. .............................. 16

Figure 18. IBRES implemented with coaxial (COAX) cable, fiber-optic (FO) cable, and 

twisted-pair (TP) cables and corresponding CIUs in a building with a large 

number of floors. ..................................................................................................... 17
viii 

Figure 19. Insufficient isolation between the BDA output and its input causes feedback. 

Feedback, labeled S, can occur in both the portable and repeater transmit 

frequency ranges. The feedback signal in the portable radio transmit 

frequency range, SP, is transmitted to the repeater. The repeater frequency 

shifts SP to SR, which is retransmitted throughout the entire system. ......................... 19

Figure 20. Strong signal from another system is received by public safety IBRES causing 

gain reduction. ......................................................................................................... 21

Figure 21. IBRES is transmitting noise into another system’s repeater. ..................................... 22

Figure 22. Performance degradation due to reception of delayed IBRES signal. ........................ 23

Figure 23. Radio coverage prediction using a path loss model. The circles surrounding 

the antennas represent the antenna’s radio coverage area. ......................................... 24

Figure 24. Radio coverage prediction using a site-specific radio-wave propagation model. 

Differing colors represent various received signal power levels................................ 25

Figure 25. Public safety communication system BDA shares a neutral host system with 

two cellular system BTSs. The main and remote interface units include signal 

conditioning (SC), combiner/splitter (C/S), fiber optic interface (FOI) 

functions. The management (M) function in the main interface unit allows 

system performance to be monitored over the Internet. ............................................ 27

Figure C-1. Schematic representation of scenario used for calculations in this Appendix. .......... 47

Figure C-2. IBRES model parameters ....................................................................................... 52

Figure C-3. Distribution network used in this example .............................................................. 53

Figure D-1. Measurement test fixture used to perform BDA measurements. .............................. 61

Figure D-2. BDA output spectrum with 45.5 dB FLM showing amplified noise, but no 

feedback. ................................................................................................................. 65

Figure D-3. BDA output spectrum with 15.5 and 0.5 dB FLM showing distortion. .................... 65

Figure D-4. BDA output spectrum with -0.5 dB FLM showing oscillation. ............................... 66

Figure D-5. BDA output spectrum with -0.5 dB FLM showing oscillation regardless of 

AGC setting. ............................................................................................................ 66
ix

TABLES 

Table 1. Results for buildings with and without the IBRES ....................................................... 18

Table A-1. Construction material attenuation ............................................................................ 35

Table A-2. High- site building attenuation at 850 MHz ............................................................. 35

Table A-3. Low-site building attenuation .................................................................................. 36

Table A-4. Narrowband public safety mobile radio frequency bands ......................................... 36

Table A-5. Representative characteristics of several types of donor antenna ..............................37

Table B-1. Path loss parameters for office building furnished with 5 ft. (1.5 m) tall office 

partitions .................................................................................................................. 42

Table B-2. Parameter t for the most common percent availabilities, %A .................................... 44

Table C-1. Required power when measured with a dipole antenna ............................................ 49

Table C-2. Minimum power for portable radio operated outside building .................................. 50

Table C-3. Power required by a portable radio operated inside building without an IBRES ....... 51

Table C-4. Power provided to the portable radio operated inside building without an 

IBRES ..................................................................................................................... 51

Table C-5. Mean outdoor path loss ............................................................................................ 52

Table C-6. Optimum BDA Gain ................................................................................................ 54

Table C-7. IBRES Gain ............................................................................................................. 54

Table C-8. Power required by a portable radio operated inside building with an IBRES ............ 54

Table C-9. Power provided to the portable radio operated inside building with an IBRES ......... 54

Table C-10. Power required by repeater .................................................................................... 55

Table C-11. Power received by repeater antenna ....................................................................... 55

Table C-12. Gain and indoor channel power for various numbers of channels with equal 

input power. ............................................................................................................. 57

Table C-13. Maximum 

n  th

channel power allowed without activating the AGC.................... 58

Table C-14. Noise power at the BDA output. ............................................................................ 59

Table C-15. Other system receiver noise power. ........................................................................ 60

Table D-1. BDA Specifications supplied by manufacturer ......................................................... 62

Table D-2. Spectrum analyzer settings. ..................................................................................... 62

Table D-3. Results for cable assembly loss, BDA gain, and maximum power output 

measurements. ......................................................................................................... 63
x

Table D-4. BDA Spectrum measurement results with AGC turned off....................................... 64

Table D-5. Noise power for 45.5 dB FLM trace in Figure D-2...................................................64

ACRONYMS 

AGC Automatic gain control 

BDA Bi-directional amplifier 

BTS Base transceiver station 

CIU Cable interface unit 

COAX Coaxial cable 

DAQ Delivered audio quality 

dB Decibel 

dBd Decibels relative to a dipole antenna 

dBi Decibels relative to an isotropic antenna 

dBm Decibels relative to a milliwatt 

IBRES In building radio enhancement system 

ICC International Code Council 

INR Interference to noise power ratio 

FCC Federal Communications Commission 

FLM Frequency loop margin 

FO Fiber optic cable 

FOI Fiber optic interface 

MGC Manual gain control 

NFPA National Fire Protection Association 

NPSAC National Public Safety Radio Advisory Committee 

NPSTC National Public Safety Telecommunications Council 

P25 Project 25 

SNR Signal to noise power ratio 

TP Twisted pair cable 
xi 

EXECUTIVE SUMMARY 

The purpose of public safety radio is to provide reliable communications over a jurisdiction. 

Industry standards recommend that 97 percent of a jurisdiction area have radio coverage. 

Unfortunately, because of building attenuation, this availability ends once public safety 

professionals enter buildings within the jurisdiction where a significant amount of their work 

lies. 

Building attenuation varies widely with the variety of construction materials, how the materials 

are used architecturally, the location of the building, type of building, and position within the 

building. It is particularly high in the lower floors of buildings in urban areas. 

A number of approaches have been used to overcome building attenuation such as reducing 

repeater coverage areas, enabling portable radios to bypass the repeater and talk directly to each 

other, and using mobile repeaters. However, the most reliable approach is to use an in-building 

radio enhancement system (IBRES). 

IBRESs circumvent building attenuation by guiding the signal between indoor and outdoor 

antennas over a robustly designed distribution network. Loss of radio coverage is virtually 

eliminated by the judicious placement of the indoor antennas. These systems are typically 

designed to provide coverage greater than 90 percent in most areas of the building and 95 percent 

in critical areas such as lobbies, stairs, and elevators. 

The technology used in today’s IBRESs has been developed over a long period of time. 

Considerable strides in its development were made in the 1950s for communications in mining 

and transportation tunnels and again in the 1980s for the burgeoning cellular phone industry. A 

renewed interest has developed in the past decade for the continued expansion of the cellular 

phone industry, proliferation of wireless local area networks, and our Nation’s resolve to provide 

public safety professionals with the best possible radio systems. 

Although this is a mature technology, it is not without problems. Firefighters have noted that 

IBRESs are vulnerable to both fire and fire-fighting operations. IBRES designers are confronted 

with a difficult and often unpredictable in-building radio wave propagation environment. 

Building owners would like to reduce installation and maintenance costs. In addition, the bidirectional amplifier (BDA) used in the IBRES to overcome losses in the radio wave propagation 

paths and distribution network can create a number of problems if not used properly. Most 

notably, it can cause radio interference by introducing intermodulation, feedback, noise, and 

delay. 

This report is intended to be used by public safety professionals tasked with assisting building 

owners to fulfill IBRES requirements mandated by their jurisdiction. The information used in 

writing this report was collected through interviews with public safety professionals, designers, 

installers, and equipment manufacturers. The report has two sections. The first section describes 

current IBRES technology and the second section discusses the problems described above and 

common methods that mitigate them. 
xii 

Appendices provide building attenuation tables, radio-wave propagation theory, link budget 

calculations, and BDA measurements necessary to understand results cited in the main body of 

the report. The link budget calculations demonstrate the utility of the IBRES by comparing 

received power in buildings with and without an IBRES against the power required for reliable 

operation. They also show how noise transmitted by an IBRES can desensitize another system’s 

repeater several hundred meters away. The BDA measurements show spectrum of a BDA 

experiencing feedback. Sufficient detail is provided to allow the reader to replicate the 

measurements using ordinary radio laboratory equipment. 
IN BUILDING RADIO ENHANCEMENT SYSTEMS FOR PUBLIC SAFETY 

Robert J. Achatz, Roger A. Dalke, and John J. Lemmon 

Reliable public safety communications between system repeaters outside a building and portable 

radios inside a building is often not possible due to building attenuation. To circumvent this 

problem, increasing numbers of municipalities are requiring building owners to provide inbuilding radio enhancement systems (IBRESs) for public safety communications. This report is 

intended to be used by public safety communications professionals who are tasked with assisting 

building owners to fulfill this requirement. The main body describes IBRES technology, 

problems endemic to it, and solutions to these problems. Appendices provide detailed data tables, 

theory, calculations, and measurements that support assertions made in the main body. 

Keywords: Bi-directional amplifiers; building attenuation; distributed antenna system; inbuilding radio enhancement system; land mobile radio; link budget; public safety 

radio; radio-wave propagation 

1 1BINTRODUCTION 

The purpose of public safety radio is to provide reliable communications over a jurisdiction. 

Industry standards recommend that 97 percent of a jurisdiction area have radio coverage [1]. 

Unfortunately, because of building attenuation, this availability ends once public safety 

professionals enter buildings within the jurisdiction, where a significant amount of their work 

lies. 

Understanding building attenuation begins by studying how construction materials attenuate the 

radio signal. As shown in Figure 1, construction material attenuation decreases the power of a 

signal each time it passes through a wall. The magnitude of this attenuation depends on the 

frequency of the radio wave, the type of material, and the angle of incidence. Construction 

material attenuation has been comprehensively evaluated by the National Institute of Standards 

and Technology (NIST) through laboratory measurements [2] and [3]. These measurements 

show that at 800 MHz, a commonly used public safety frequency, a radio wave striking a 

concrete wall “head on” (i.e., at a 0-degree angle of incidence) can be attenuated by up to 30 dB 

(i.e. to 0.1 percent of its initial power). Examples for other materials are provided in Appendix 

A. Increasing the angle of incidence attenuates the signal even more. For example, a radio wave 

striking the same wall at a 70-degree angle of incidence is attenuated by 40 dB (i.e. to 0.01 

percent of its initial power) [4]. 
2

Figure 1. Signal transmission into building is represented as arrows. Narrowing arrow widths 

correspond to diminishing signal power caused by construction material attenuation. 

But building attenuation, the ratio of the signal power inside the building to the signal power 

outside the building, is more complex than the construction material attenuation described above. 

The building’s surroundings, the variety of materials, and how they are used architecturally 

contribute to the complexity of building attenuation. This complexity causes building attenuation 

to vary widely with building location (i.e., urban or suburban), building type (i.e., office or 

warehouse), and position within the building. Radio system engineers address this variability by 

characterizing building attenuation statistically in terms of its mean and standard deviation [5], 

[6]. 

We now consider some common approaches public safety organizations use to overcome 

building attenuation [7]. For the purposes of this discussion, the public safety radio system signal 

is assumed to originate from a simulcast radio repeater system that operates in the 800 MHz 

National Public Safety Advisory Committee (NPSAC) band with full-duplex, narrow-bandwidth 

signals. With simulcast systems, repeaters strategically located throughout the metropolitan area 

receive the relatively weak signal from mobile and portable radios on one frequency, f1, and 

retransmit it over the entire metropolitan area on another, f2. Channel bandwidths can be 25, 12.5, 

or 6.25 kHz wide—which are all narrow in comparison to the 800 MHz carrier frequency.1 A 

table of state and local narrowband public safety mobile radio frequency bands is provided in 

Appendix A. 

 

1

 In 2013, the maximum channel bandwidth will be 12.5 kHz. 

Repeater Exterior Wall Interior Wall

Stairs

Portable
3

Figure 2 illustrates how in-building communications are provided by the repeater system. By 

design, the system overcomes building attenuation by reducing the coverage areas of repeaters in 

urban areas where it is expected to be highest. With smaller coverage areas, portable radio power 

normally budgeted to overcome loss due to distance can be used to overcome loss due to 

building attenuation. 

A number of researchers have comprehensively measured building attenuation for this high-site 

scenario, in which a repeater antenna is mounted high above ground level and radiates over a 

large portion of a metropolitan area [6], [8], [9]. Analysis of the measurements showed that 

building attenuation was high and widely variable in urban areas in the lower floors of buildings. 

As an example, building attenuation at 850 MHz on the first floor of a building in an urban area 

was found to have a mean of 18 dB and a standard deviation of 8 dB. Other examples of these 

measurements are provided in Appendix A. The high mean attenuation and wide variability in 

this scenario is likely to cause loss of radio coverage. 

Another strategy for overcoming building attenuation is to use direct or simplex communications 

between radios at the incident site as shown in Figure 3. With direct communications, everyone 

transmits and receives on an additional frequency, f3, not used by the repeater system. If two 

radios are unable to connect due to an obstruction within the building, they may be able connect 

to other radios free of the obstruction. This diversity reduces the likelihood that anyone will be 

completely cut off from radio communications. 

Since direct communications are performed at a frequency that is not used by the repeater 

system, interactions with those outside the incident site (such as dispatch) are not possible. To 

circumvent this, direct communications is replaced by mobile repeater communications, shown 

in Figure 4, as soon as a vehicle with a mobile repeater arrives at the incident site. In this mode, 

the portable radios operate in full duplex with a pair of frequencies, f4 and f5, not used by the 

repeater system. The mobile repeater converts these frequencies to those used by the repeater 

system. In other words, signals received on f4 are transmitted to the repeater on f1 and signals 

received on f2 are transmitted to the portable radio on f5. 

NIST has performed comprehensive measurements of building attenuation for this low-site 

scenario, where a repeater antenna is mounted low and radiates into a nearby building [10], [11]. 

These measurements also found high and widely variable amounts of attenuation in several 

different types of buildings. For example, attenuation at 867 MHz in an office building had a 

mean of 38 dB with a standard deviation of 14 dB. Other examples of these measurements are 

provided in Appendix A. As in the previous scenario, there is likely to be loss of radio coverage. 

The most reliable strategy for overcoming building attenuation, which is the subject of this 

report, is to use an in-building radio enhancement system (IBRES) [12]. The IBRES, shown in 

Figure 5, distributes a radio signal more uniformly throughout the building by providing alternate 

guided paths. 

Outside the building, a donor antenna establishes a link with the donor repeater site. Inside the 

building, a distribution network guides signals to and from indoor antennas located throughout 

the building. Between the donor antenna and the distribution network, a bi-directional amplifier 
4

(BDA) provides signal amplification necessary to overcome distribution network and radio-wave 

propagation losses. 

Figure 2. In-building communications using the repeater system. 

Figure 3. In-building communications using direct communications. 

Repeater

Incident

Dispatch Site

Mobile

Portable

f1

f2

f

1

f

2

f

1

f

2

f

1

f

2

f2

f1

f1

f2

Fixed

Repeater

Incident

Dispatch Site

Mobile

Portable

f1

f3

f3

f3

f3

f2

f1

f2

Fixed
5

Figure 4. In-building communications using a mobile repeater system. 

Figure 5. In-building communications using an IBRES. 

Repeater

Incident

Dispatch Site

Mobile

Mobile Repeater Portable

f1

f4

f5

f4

f5

f5

f4

f2

f1

f2

f1

f2

Fixed

Repeater

Dispatch

Donor Antenna

Incident

Public

Safety

Site IBRES

Mobile

Indoor Antenna

Distribution Network

f1

f1

f2

f2

f2

f1

f2

f1

f2

f1

f1

f2

Fixed

BDA

Portable

1
6

IBRESs have none of the deficiencies of the first two approaches. Loss of radio coverage can be 

virtually eliminated by the judicious placement of indoor antennas and no new frequencies are 

needed to maintain communications with those outside the incident site. Because of these 

advantages, more and more municipalities are requiring buildings to have IBRESs for public 

safety communications. This strategy is completely different from the others because the 

equipment is provided by the building owner rather than the public safety organization. This 

report is intended to be used by public safety communications professionals tasked with assisting 

building owners to fulfill this requirement. 

The information used in writing this report was collected through interviews with public safety 

professionals, designers, installers, and equipment manufacturers as well as through the more 

traditional literature search. The report has two sections. The first section describes current 

IBRES technology and the second section discusses problems endemic to the IBRES and 

common methods for mitigating them. Appendices provide details necessary to understand 

results cited in the main body of the report. 

2 2BIBRES TECHNOLOGY 

The technology used in today’s IBRESs has been developed over a long period of time. 

Considerable strides in its development were made in the 1950s for communications in mining 

and transportation tunnels [13] and again in the 1980s for the burgeoning cellular phone industry 

[14]. A renewed interest has developed in the past decade due to the continued expansion of the 

cellular phone industry, proliferation of wireless local area networks, and our Nation’s resolve to 

provide public safety professionals with the best possible radio systems [15]. 

This section provides an overview of today’s IBRES technology. It is organized in terms of the 

IBRES components introduced previously: the BDA, the distribution network, and the antennas. 

The section culminates with examples of IBRESs and link budget analysis results that 

demonstrate their utility. 

2.1 BDA 8B

The purpose of the BDA is to amplify signals to overcome distribution network and radio-wave 

propagation losses. Signals from the donor antenna are amplified for transmission by the indoor 

antenna and signals from the indoor antenna are amplified for transmission by the donor antenna. 

Unlike repeaters, BDAs do not shift frequencies. Signals are transmitted on the same frequencies 

at which they were received. 

Signal amplification and retransmission is highly regulated by the Federal Communications 

Commission (FCC) because of its interference potential. The FCC controls this interference 

potential through regulations and a certification process [16]. 

One consequence of signal amplification is intermodulation. Intermodulation creates interfering 

signals at frequencies that are sums and differences of input signal frequencies and their 

harmonics. These signals can affect channels across the entire BDA bandwidth. Intermodulation 

can be caused by non-linear amplification due to excessively high input powers and BDA gains. 

Intermodulation is mitigated by careful control of BDA gain. 
7

BDA gain is set, by manual gain control (MGC) or by computer, to a level that assures optimal 

performance during normal operating conditions. The amount of gain needed is dependent on the 

input power of all the signals in the BDA bandwidth and the output power required for reliable 

service. In general, gain is set to as low a level as possible. Automatic gain control (AGC) limits 

output power to a level that minimizes intermodulation by introducing attenuation when higher 

than normal input powers are experienced. The higher input powers may be due to strong signals 

from mobile radios outside the building or a larger number of channels being used during an 

incident. 

Another consequence of signal amplification is the possibility of amplifying another system’s 

channels and causing interference in that system. The FCC separates BDAs into two classes by 

whether or not they can avoid this. Class A BDAs avoid this by being able to filter and 

selectively amplify a specific channel. Class B BDAs do not have this capability. In many cases, 

Class B BDAs filter and amplify an entire band of channels. The FCC restricts the use of Class B 

BDAs to closed spaces such as in tunnels and buildings to reduce this source of interference 

potential. In the IBRES industry, Class A and Class B BDAs are referred to as narrowband and 

broadband BDAs, respectively. 

While Class A BDAs have the least interference potential, their implementation is typically more 

complicated than that of Class B BDAs. This complexity is due to the need to shift the signal to a 

lower intermediate frequency to achieve narrow filter bandwidths [17]. 

In the past, BDA signal processing operations such as filtering and frequency shifting were 

implemented solely in hardware. With the advent of modern digital signal processors, some 

manufacturers have chosen to perform these signal processing tasks with software algorithms. 

With this approach, the BDA can operate as Class A or Class B depending on the circumstances. 

Custom channel filtering and gain configurations can be implemented with software that can be 

updated over a radio link. This is clearly advantageous when channel assignments need to be 

changed. 

Figure 6 illustrates three BDA filtering schemes. It is important to note that the choice of BDA 

class and implementation must be evaluated in the context of the radio environment in which the 

BDA will be operating. As an example, the added complexity of a Class A BDA may be 

unnecessary if there are no other system’s signals in the BDA bandwidth. 
8

Figure 6. Class A, Class B, and custom BDA filtering. Solid lines represent the user’s channels. 

Dashed lines represent channels from another system. Rectangles over the channels represent the 

BDA filter bandwidth. The Class A BDA amplifies only one of the user’s channels. The Class B 

BDA amplifies all channels indiscriminately. The custom filtered BDA amplifies any 

combination of channels. As configured, this would be classified as Class B. 

Figure 7 shows a BDA and Figure 8 is a functional block diagram of its operation showing 

filtering and gain control. Alarm circuits notify the system operator when events that affect 

operation occur. These events would include line-power loss, low battery power, amplification 

problems, and donor antenna malfunction. 

Figure 7. BDA showing front panel with donor antenna socket, distribution network socket, A/C 

power plug, and power indicator light. 
9

Figure 8. BDA functional block diagram. 

2.2 Distribution Network 9B

The distribution network consists of the cables and associated components needed to guide the 

signals between the BDA and the indoor antennas throughout the building. Cable types include 

coaxial (Figure 9), optical (Figure 10), and twisted-pair (Figure 11). These cables all have 

different characteristics that are exploited in a number of ways. Cable components enable signal 

splitting, combining, coupling, attenuation, and amplification. 

Figure 9. Coaxial cable cross-section (left) and profile (right). 

Alarm

MGC AGC

Filter

Duplexer

Amp.

Amp.

Amp.

Duplexer

Amp. Filter

Power

Measurement

Power

Measurement

Gain Control

Attenuator

Attenuator

Distribution

Network

Donor

Antenna

x x

x x

AGC MGC

Gain Control

Outer Layer

Shield

Conductor

Insulator
10

Figure 10. Optical cable. 

Figure 11. Twisted-pair cable. 

The most significant difference between coaxial cable and the others is that coaxial cable can 

carry narrowband public safety signals at the same frequency at which they were transmitted 

over the air. In other words, the over-the-air transmission frequencies are within the coaxial cable 

frequency range. Fiber-optic and twisted-pair cables require cable interference units (CIU) to 

shift over-the-air transmission frequencies to cable frequency ranges. While the CIUs are an 

extra expense, they are often used advantageously to monitor and report system status. 

Coaxial cable is composed of a center conductor, an insulator, a corrugated metal shield, and a 

protective outer layer. The most common type used for public safety bands is fairly rigid and 

1⁄2 in. (12.7 mm) in diameter. Typical losses for an air-insulated 1⁄2-inch cable are approximately 

0.4 to 4.0 dB per 100 feet (30.5 meters) over the frequency range of 30 MHz to 2 GHz. 

Extremely long lengths of coaxial cable need periodic, in-line amplification. However, because 

in-line amplifiers introduce noise, the number of amplifiers that can be used is limited. 

Fiber-optic cable is composed of thin light-carrying fibers and layers needed for strength and 

protection. A 4-fiber cable is flexible and approximately 1∕6 in. (4.24 mm) in diameter. Fiberoptic cable transmits monochromatic 1310 and 1550 nm wavelength light corresponding to 229 

and 193.5 THz frequencies, respectively, which are well above those used by public safety. CIUs 

are needed to modulate the signal to and from the fiber-optic frequency range [18], [19]. The 

Fibers

Outer Layer

Strength Layer

Tube

Insulation

Copper

Conductor

Outer Layer
11

main advantages of fiber-optic cable are its extremely low loss and its wide bandwidth. Fiber 

optics are also immune to interference from RF signals. Loss is approximately 1 and 0.4 dB per 

mile (1.8 km) for 1310 and 1550 nm wavelength cables, respectively. CIUs with 2 GHz 

bandwidths are available. Fiber-optic cable is commonly used over the long distances needed to 

distribute the signals within large buildings or between buildings. 

Twisted-pair cable is composed of twisted wire pairs wrapped in a protective layer. Both 

shielded and unshielded types are available. A cable with four twisted wire pairs is flexible and 

approximately 1∕6 in. (4.24 mm) in diameter. Twisted-pair cable is classified by a category 

identifier. Category 5e and 6 twisted-pair cable is used to transmit up to 125 MHz and 250 MHz, 

respectively. CIUs are needed to shift the signal to and from the cable frequency range. Category 

5e cable has losses of 0.6 to 7 dB per 100 feet (30.5 meters) from 1 to 125 MHz. Its flexibility 

makes it easier to install than coax and, in many cases, twisted-pair cable has already been 

installed for computer networking. If computer networks are already using the cable, the CIU 

merely needs to shift the over-the-air transmission frequencies to cable frequencies not used by 

the computer network.

2.3 10BAntennas 

The donor antenna is typically a directional antenna whose beam is pointed directly at the 

repeater site. The directionality reduces the chances of interference with other systems as well as 

feedback from its own indoor antennas. Typical directional antenna designs include the Yagi, 

corner reflector, parabolic reflector, and panel. 

The IBRES designer takes the antenna’s gain, beam-width, and front-to-back ratio characteristics 

into consideration when choosing the donor antenna type. The most commonly used donor 

antenna is the Yagi depicted in Figure 12. The other antennas are chosen when there is a need for 

more gain to compensate for a weak signal, a narrower beamwidth to attenuate signals that are 

close in bearing, or a higher front-to-back ratio to provide more attenuation of signals out of the 

main beamwidth. Representative characteristics of each antenna type are provided in Appendix 

A. 

Figure 12. Yagi antenna. 

Indoor antennas are either discrete or continuous. The discrete antenna is typically an 

omnidirectional, short monopole antenna on a ground plane. These elements are shown mounted 
12

in a typical plastic housing in Figure 13. This antenna has a 360-degree azimuthal beamwidth. 

Hung from the ceiling, this antenna creates a circular coverage area. 

Figure 13. Omnidirectional antenna. 

Narrower beamwidth discrete antennas are used when it is necessary to avoid radiating in certain 

directions. For example, panel antennas with beamwidths less than 90 degrees can be used to 

avoid radiating towards exterior wall areas with low attenuation, such as windows and doors. 

Figure 14. Leaky coax, cross section (left) and profile (right). Periodic holes are present on the 

flattened side. 

The continuous antenna is commonly referred to as leaky coax. Leaky coax has a 360-degree 

lateral beamwidth. Hung from the ceiling, it creates a linear coverage area wherever the cable is 

run. The properties of leaky coax have been studied extensively [20], [21], [22], [23] and many 

types are manufactured. A commonly used type, shown in Figure 14, looks remarkably like the 

coaxial cable shown previously. The difference is the presence of periodic holes in the 

corrugated metal shield. 

The main disadvantage of leaky coax is its high coupling loss, i.e., the ratio of the power 

received by a standard antenna a fixed lateral distance away from the cable and the power in the 

cable. Measurements made 2 meters away show coupling losses in excess of 70 dB at 500 MHz. 

In spite of this disadvantage, leaky coax is commonly used in long, narrow areas such as 

stairwells and elevator shafts. 

2.4 1BDesign, Installation, Testing, and Commissioning 

The design, installation, testing, and commissioning of IBRESs are complex processes best left 

to experienced professionals. These professionals are guided by a number of organizations 

including, but not limited to, the National Public Safety Telecommunications Council (NPSTC), 

the Federal Communications Commission (FCC), the International Code Council (ICC), and the 

National Fire Protection Association (NFPA). 

Ground Plane

Monopole Antenna

Coaxial Cable Outer Layer

Shield

Conductor

Hole

Insulator
13

The NPSTC develops telecommunication policy on behalf of public safety organizations and 

companies that manufacture public safety telecommunications equipment. Among their 

publications is a report outlining best practices for the design and installation of IBRESs [24]. 

The FCC issues regulations to minimize interference in other radio systems. 

Local authorities adopt into law building codes that specify how IBRESs are to be designed and 

installed. These codes are based on consensus standards developed by the ICC [25], [26] and the 

NFPA [27], [28]. Although these standards could be adopted in whole, they are generally 

amended to fit local circumstances [29]. 

Despite the fact that standards vary among municipalities, some general statements can be made 

in their regard. For example, codes usually only require public safety IBRESs in the areas of 

large buildings that do not have adequate coverage from outside. Existing buildings are often 

excluded unless they undergo renovation. Whether the building is new or is being renovated, 

building owners are free to wait until the construction is finished before determining whether an 

IBRES is necessary. However, provisions for installing the IBRES, such as vertical cable risers, 

are often required. If the IBRES is needed, the certificate of occupancy can be delayed until it is 

commissioned. The fire marshal reviewing the building plans prior to construction may 

recommend installing the IBRES during construction to avoid delays. 

Firefighters have noted that IBRESs are vulnerable to both fire and fire-fighting operations [30]. 

IBRES designers readily acknowledge that cables and antennas directly exposed to flame will 

quickly become useless. However, when fighting fires it is also important that communications 

be possible in other parts of the building that are not on fire. Consequently, many municipalities 

are adopting codes for minimizing the effect of the fire on IBRES operation in other parts of the 

building. For example, some municipalities require that active electronics such as BDAs, CIUs, 

and uninterruptable power supplies be enclosed by water-resistant NEMA-4 cabinets and fireprotected rooms. In addition, some municipalities require that cables running through the 

building to remote locations be able to withstand some degree of water and fire exposure. 

Finally, BDAs and CIUs are vulnerable to power outages. Most municipal codes require that 

they be connected to battery backup systems capable of supplying power for an extended period 

of time. 

Prior to design, it is highly recommended that a radio spectrum survey be performed. Results 

from the survey are used to determine the best donor repeater site and whether signals from other 

systems will need to be mitigated. 

IBRESs are often designed with the aid of graphical computer-aided design software. The 

software uses building architectural design information and specifications for various IBRES 

components including BDAs, cables, cable components, CIUs, and antennas. These components 

can be interactively located while designing the system. Once the system has been designed, the 

software can be used to calculate transmitted powers and radio coverage. Bills of material, 

installation labor, and cost reports can also be generated. 

Municipalities often require that the IBRES be installed by certified technicians. Certification is 

typically acquired through the equipment manufacturers. Once installed, the IBRES is inspected 
14

for code compliance. If it passes, the system is commissioned by the municipality. Once 

commissioned, the IBRES is periodically tested. 

Radio system coverage tests are part of the code compliance inspection. Coverage tests are 

similar to channel performance criterion (CPC) tests developed by the Telecommunications 

Industry Association [31]. The coverage test divides each building floor into a rectangular grid 

pattern as shown in Figure 15. To pass the coverage test, the building must have a specified 

percentage of cells with coverage, i.e., covered area availability. In most cases, this percentage 

equals or exceeds 90 percent. For critical areas, such as exit stairs, this percentage equals or 

exceeds 95 percent. 

Figure 15. Floor plan gridded for coverage test. 

In many municipalities, the cells of the grid are deemed to have coverage if the signal meets or 

exceeds a minimum power level. In others, a more stringent subjective speech quality metric 

called delivered audio quality (DAQ) is used. The scale ranges from 1 to 5, with 1 being 

unintelligible to 5 being perfect. Public safety radio uses a DAQ of 3.4, which corresponds to 

speech that is understandable and rarely needs repetition. 

2.5 12BExamples 

The components described above are used to build IBRESs in a number of ways [32], [33], [34]. 

Figures 16-18 show how IBRESs are implemented in buildings with small and large numbers of 

floors. In all three examples, the donor antenna is mounted on the roof so that it points at the 

donor repeater station. After passing through the building exterior, the antenna cable is 
15

connected to the BDA. All of the buildings have stairwells on the right and one floor below 

ground level. 

Figure 16 depicts an IBRES in a building with a small number of floors. The distribution 

network is composed of coaxial cable alone. The floor area is serviced by discrete antennas and 

the stairway uses leaky coax. Figure 17 depicts an IBRES in a building with a larger number of 

floors. Coaxial cable loss is too high for the long distances needed to distribute the signal 

between floors. Hence, optical cable and fiber-optic/coaxial (FO/COAX) CIUs are needed. 

Figure 18 depicts a system where the coaxial cable is replaced by twisted-pair cable. This 

requires additional twisted-pair/coaxial (TP/COAX) CIUs. 

The IBRES in Figure 16 is considered passive because it has neither signal amplifiers nor CIUs 

in the distribution network. The other two IBRESs with CIUs are referred to as active. In 

addition to buildings with large numbers of floors, active IBRESs are often used in buildings 

with large areas, such as shopping malls or convention centers. 

Figure 16. IBRES implemented with coaxial (COAX) cable in a building with a small number of 

floors. 
16

Figure 17. IBRES implemented with coaxial (COAX) cable, fiber-optic (FO) cable, and 

corresponding CIUs in a building with a large number of floors. 
17

Figure 18. IBRES implemented with coaxial (COAX) cable, fiber-optic (FO) cable, and twistedpair (TP) cables and corresponding CIUs in a building with a large number of floors. 

2.6 13BLink Power Budgets 

This section analyzes the utility of an IBRES with an example that compares the power received 

by a portable radio operated at ground level inside a building with and without an IBRES. The 

portable radio is assumed to be an analog frequency-modulated public safety portable radio 

operating in the 800 MHz NPSAC band with 12.5 kHz channel spacing. The IBRES is assumed 

to be similar to the one illustrated in Figure 16. 

The methodology used in this section is straightforward. We first calculate the minimum power 

required outside the building, 

Preq OUT ,

, to achieve a 3.4 DAQ with 97 percent covered area 

availability performance level. We then calculate the power inside the building, 

P

r

, and compare 

that to the minimum power required inside the building, 

Preq IN,

, to achieve a 3.4 DAQ with 90 

percent covered area availability performance level. If 

P

r

 is greater than or equal to 

Preq IN,

 the 

link meets the performance level objective. 

It is important to note that links not meeting the objective may still “work”. For example, the link 

may be operating with a DAQ of 3.0, which means that greater effort is needed to understand 

speech and more repetition is required. 
18

The powers 

Preq OUT ,

, Preq IN,, and 

P

r

 are calculated with link power budgets. Detailed 

explanations of the propagation phenomenon involved and link power budget calculations are 

provided in Appendices B and C, respectively. It is important to note that these calculations 

assume high losses of a hip-mounted portable radio antenna and are expressed in terms of power 

received by a dipole antenna commonly used for conformance tests. Results for this example are 

provided in Table 1. These results clearly show that the performance objective can only be met if 

the building is equipped with an IBRES. 

Table 1. Results for buildings with and without the IBRES 

P

r

Preq IN,

Performance Objective Met

Without IBRES -91.0 -74.0 No

With IBRES -78.2 -78.2 Yes

There are two reasons for the effectiveness of the IBRES. First, the donor antenna is typically 

mounted on the roof, which provides relief from attenuation by nearby buildings or urban clutter. 

Second, there are a number of ways to increase gain and decrease losses when designing the 

IBRES. For example, if more gain is needed a designer can install high-gain BDAs or antennas. 

If less loss is needed the designer can reduce indoor antenna spacing. 

3 3BCOMMON PROBLEMS AND THEIR SOLUTIONS 

This section focuses on problems commonly found in IBRESs. These problems include 

feedback, gain reduction, noise transmission, delay, complex radio-wave propagation, and cost. 

The problems are described, specific examples are identified, and solutions are discussed. Two 

other problems commonly found in IBRESs, intermodulation and vulnerability to fire and 

firefighting operations, are not discussed in this section as they were addressed in Sections 2.1 

and 2.4, respectively. 

3.1 14BFeedback 

BDAs receive on the same frequency as they transmit. This leaves IBRESs vulnerable to the 

effects of unwanted signals created by feedback. Feedback occurs when there is insufficient 

isolation between the BDA output and its input [35], [36]. The path the signal takes from the 

output of the BDA to its input is referred to as the feedback loop, and it consists of the 

distribution network, indoor antenna, propagation path, donor antenna, and cable between the 

donor antenna and BDA input. 

Feedback can cause either oscillation or distortion. Oscillation occurs when the BDA gain equals 

or exceeds feedback loop attenuation, resulting in either a non-existent or negative feedback loop 

margin (FLM). Distortion occurs when BDA gain is less than feedback loop attenuation. The 

FLM is positive, which prevents oscillation, but it is not large enough to protect the signal from 

interfering with itself. Spectrum measurements showing the effects of oscillation and distortion 

are described in Appendix D. 
19

Feedback signals can occur in both the portable radio and repeater transmit frequency ranges. 

Both signals are transmitted from the donor and indoor antennas. However, only the signal in the 

portable radio transmit frequency range can be received by the repeater and cause outages 

throughout the system when retransmitted. 

Feedback outages are rarely caused by high-quality BDAs deployed in well-designed, correctly 

installed, and properly-maintained IBRESs. They are more commonly due to substandard BDAs 

installed in an ad hoc fashion. For example, substandard BDAs have caused feedback when 

installed in vehicles where it is difficult to obtain sufficient isolation. These outages can put 

civilians and public safety professionals at risk and be difficult to correct [37]. 

Figure 19. Insufficient isolation between the BDA output and its input causes feedback. 

Feedback, labeled S, can occur in both the portable and repeater transmit frequency ranges. The 

feedback signal in the portable radio transmit frequency range, SP, is transmitted to the repeater. 

The repeater frequency shifts SP to SR, which is retransmitted throughout the entire system. 

Example: A BDA oscillates when the door to a building is opened. 

Solution: Opening the door reduces propagation loss between the indoor and outdoor antenna. 

The FLM can be increased by decreasing BDA gain, increasing the separation between indoor 

and donor antennas, relocating the indoor antenna away from the door, using a directional indoor 

antenna to point the signal away from the door, or adding attenuation to the distribution network 

prior to the indoor antenna. 

Repeater

Incident

Site

Low

Building

Attenuation Dispatch

Mobile

SR

S

SR

S

S

P

SR

Fixed

BDA

Portable
20

Example: A windstorm knocks a roof-mounted donor antenna over, leaving it pointed directly at 

an indoor antenna. 

Solution: The BDA can be designed to detect oscillations and reduce gain when present. If 

oscillations persist, the BDA can turn off amplification and activate an alarm. As shown in 

Appendix D, a BDA with AGC can still oscillate. Hence, the gain reduction required for 

oscillation mitigation must be addressed in addition to the gain reduction used by AGC. 

3.2 15BGain Reduction 

Class B BDAs amplify all signals within their bandwidth. Once AGC is engaged, the addition of 

more channels reduces gain and channel output power. At some point, it is possible to have so 

many channels that some may no longer be received at powers that can meet the performancelevel objective. A strong signal can also aggravate this situation, as shown in Figure 20. 

Consider the example of the building with an IBRES in Section 2.6 and Appendix C. It would 

take approximately 114 channels to drive 

P

r

 below

Preq IN,

. Far fewer channels can be driven 

below 

Preq IN,

 if there is a strong channel. For example, seven channels can be driven below

Preq IN,

if one of the channels is allowed to increase its power to more than -52.6 dBm outdoors or -57.8 

dBm indoors. 

Example: A strong undesired signal from another system causes the other signals to go below the 

received power threshold. 

Solution: Minimize BDA gain to avoid engaging AGC. Reduce the undesired signal power by 

pointing the donor antenna to a repeater in another direction. If this is not possible, reduce the 

undesired signal power by additional filtering. 
21

Figure 20. Strong signal from another system is received by public safety IBRES causing gain 

reduction. 

3.3 16BNoise Transmission 

BDAs amplify and transmit the noise the IBRES generates F1F

2

 through the donor antenna. The 

transmitted noise power can cause repeater receiver desensitization. Desensitization can occur 

over significant distances. For example, an IBRES uplink can desensitize another system’s 

repeater operating at a 3.4 DAQ to a 3.0 DAQ as far away as 1447 feet (441 meters). Calculation 

details are provided in Appendix C. 

Example: Another system’s repeater is being desensitized by noise transmitted from a nearby 

public safety IBRES using a Class B BDA. 

Solution: Reduce BDA gain as much as possible, attenuate the noise in the other system’s 

channels by filtering, and point the donor antenna toward a public safety repeater in another 

direction. 

Example: A public safety repeater is being desensitized because a number of public safety 

IBRES donor antennas from different buildings are pointed at it.

 

2

 In addition, a BDA amplifies the natural and man-made noise in the environment, which is 

substantial in the VHF band. 

Public

Safety

Repeater

Public

Safety

Repeater

Public

Safety

Repeater

Other

System

Public

Safety

IBRES

BDA
22

Solution: Reduce BDA gain as much as possible, point donor antennas at other public safety 

repeaters, and reduce the number of BDAs by connecting distribution networks in different 

buildings together. 

Figure 21. IBRES is transmitting noise into another system’s repeater. 

3.4 17BDelay 

Narrow bandwidth filters and long runs of fiber-optic cables can introduce significant delays in 

the signal. Radio system performance can be degraded when signals delayed by the IBRES are 

combined with signals that did not go through the IBRES. Tests have shown that radios can 

tolerate this delay if there is a sufficient difference in power between delayed and undelayed 

signals[17]. More delay can be tolerated with larger differences in power levels. For example, 

Phase 1 P25 analog FM and digital C4FM radios operating in a 12.5 kHz bandwidth can tolerate 

a 40 μs delay with a 6 dB difference, but only 33 μs with 0 dB. 

Example: An indoor antenna is placed near a window. The signal from the repeater enters the 

building through the window and interferes with the signal from the indoor antenna.

Solution: Larger differences in signal power can be obtained by increasing the power to the 

indoor antenna. To ensure that the increased power does not cause problems to a radio outside 

the building, the indoor antenna must be moved away from windows and doors. Directional 

panel antennas are also useful for increasing the power difference. The directional antenna 

should be mounted on the wall between the indoor coverage area and the repeater site [38]. 

Public

Safety

Repeater

Public

Safety

Repeater

Public

Safety

Repeater

Other

System

Public

Safety

IBRES

BDA
23

If the delay is caused by narrow bandwidth filters and the problem persists after increasing the 

difference in signal powers, then the delay must be reduced by widening the filter bandwidth. A 

12.5 kHz channel filter has a minimum of 1∕12,500 s or 80 μs of delay. Increasing the bandwidth to 

200 kHz can decrease this minimum to 1∕200,000 s or 5 μs.

Figure 22. Performance degradation due to reception of delayed IBRES signal. 

3.5 18BRadio-Wave Propagation 

Building walls, floors, and furnishings create complex radio-wave propagation conditions that 

make radio coverage difficult to predict and test. 

Example: Indoor antenna location is usually determined by the judgment of an experienced RF 

engineer using a path loss model [39]. An example of this prediction is shown in Figure 23. The 

approach is prone to error because the model predicts path loss for a generic type of building, for 

example, an office or warehouse. Specific architectural details of the actual building are not 

considered. Appendix B contains a description of some commonly used path loss models. 

Solution: Measure coverage after installation and add additional antennas if necessary. Another 

solution is to “saturate” the building with antennas spaced closer than what the path loss model 

recommends. Research has shown that a saturated design is less dependent on the floor plan and 

antenna location [40]. 

Repeater

Mobile

f2

f2

f2

f2

f2

BDA

Low

Building

Attenuation
24

Figure 23. Radio coverage prediction using a path loss model. The circles surrounding the 

antennas represent the antenna’s radio coverage area. 

Finally, the designer can use site-specific models that consider the effect of the building’s 

architectural details on radio-wave propagation. An example of such a prediction is shown in 

Figure 24. Although error cannot be eliminated, it can be reduced. Advanced algorithms are 

being developed for site-specific models to determine the optimal antenna location [41], [42], 

[43], [44]. Appendix B contains supplemental material on site-specific modeling methods. 
25

Figure 24. Radio coverage prediction using a site-specific radio-wave propagation model. 

Differing colors represent various received signal power levels. 

Example: IBRES coverage tests require that a building be divided into a grid pattern and that a 

certain percentage of the grid cells have powers that equal or exceed a minimum level. However, 

multipath fading can cause the signal power to fluctuate over small changes in position within 

the cell making it hard to assign a power level. 

Solution: Measure grid cell signal power by averaging (in watts) a number of power 

measurements collected over a small area within the cell. NFPA code specifies the number of 

measurements that must be made over an x-shaped pattern. This guarantees statistical confidence 

in the average power estimate. As an example, averaging 50 power samples over 40 wavelengths 

produces an average power estimate that is accurate to within 1 dB with a 90-percent confidence 

level. At 800 MHz, 40 wavelengths equal a distance of 49.2 feet (15 meters) [45]. 

Example: Multipath delay can cause poor speech quality even when the specified received signal 

strength is met. 

Solution: Measure signal quality in terms of delivered audio quality (DAQ) in addition to 

received signal strength. 
26

3.6 19BCost 

Issue: Designing, installing, and maintaining public safety IBRESs increases the costs of 

constructing, remodeling, and operating a building. 

Solution: IBRESs are now being installed in buildings to distribute cellular, WLAN, telemetry, 

and building automation signals. These systems are referred to as neutral host systems because 

they are not owned by the telecommunications services provider [46]. 

Adding public safety communications to the neutral host system can reduce the cost of 

designing, installing, and maintaining public safety IBRESs [47]. Continued interest in providing 

public safety communications with state-of-the-art wideband communication capability over 

commercial cellular carrier networks also makes this approach attractive [48], [49], [50]. 

Figure 25 shows how public safety communications can be added to a neutral host system. This 

configuration has a public safety BDA and cellular system base transceiver stations (BTS). The 

public safety BDA is connected to a donor antenna pointed at a repeater. The BTS can be 

connected by radio link or cable to the cellular master-switching station. The units use signal 

conditioning (SC) circuits, which independently control BDA and BTS signal powers so that 

intermodulation in the fiber optic interface (FOI) is minimal. 

The disadvantage of adding public safety communications to a neutral host system is losing 

control over system modifications or maintenance which, if done poorly, can severely degrade 

system performance [12]. This disadvantage can be overcome by monitoring system 

performance information over the Internet. 
27

Figure 25. Public safety communication system BDA shares a neutral host system with two 

cellular system BTSs. The main and remote interface units include signal conditioning (SC), 

combiner/splitter (C/S), fiber optic interface (FOI) functions. The management (M) function in 

the main interface unit allows system performance to be monitored over the Internet. 

4 4BCONCLUSION 

IBRES technology is a mature art that was refined in response to a myriad of challenges over the 

past several decades. When designed, installed, and maintained by experienced professionals, 

these systems are considered reliable. As a testament to IBRES reliability, many municipalities 

across the United States are requiring buildings to have IBRESs for public safety 

communications. 

Link budget calculations in the Appendices below show how installing an IBRES provided 

reliable communications in a building which, without the IBRES, was unable to meet 

performance objectives. There are two reasons for the effectiveness of the IBRES. First, the 

donor antenna is typically mounted on the roof, which provides relief from attenuation by nearby 

buildings or urban clutter. Second, there are a number of ways to increase gain and decrease 

losses when designing the IBRES. For example, if more gain is needed a designer can install a 

PS

BDA

roof

main

remote FO

coax

FOI

C / S

SC SC SC

C / S

ceiling

BTS

SCSC

C / S

F O I

M

SC

BTS
28

higher gain BDA or antenna. If less loss is needed the designer can reduce indoor antenna 

spacing. 

IBRES technology has a number of common problems, but none have proven to be 

insurmountable. These problems, listed in the order discussed, include intermodulation, 

vulnerability to fire and fire-fighting operations, feedback, gain reduction, noise transmission, 

delay, complex radio-wave propagation, and cost. 

Of these problems, the most commonly encountered are feedback, gain reduction, and noise 

transmission. In general, an experienced professional can mitigate these problems with simple 

measures such as reducing BDA gain, repointing the donor antenna towards a different repeater, 

choosing a different donor antenna, relocating the indoor antenna, using a directional indoor 

antenna, or filtering. 

These problems are also being addressed through telecommunications policy. For example, in a 

number of cases, these problems were due to public safety radio systems with high-site land 

mobile radio architectures sharing the same band as systems with low-site cellular radio system 

architectures [51]. The FCC mitigated these problems by moving the two types of radio systems 

into separate frequency bands [52]. In addition, the FCC is working diligently to eliminate 

harmful interference caused by substandard BDAs [37]. 
29

5 5BACKNOWLEDGEMENTS 

The authors would like to thank the Department of Homeland Security’s Office for 

Interoperability and Compatibility (DHS/OIC), Mr. Dereck Orr, Program Manager; and Mr. Jeff 

Bratcher, Technical Manager of the Public Safety Communications Research (PSCR) program 

for support of this work. The PSCR program is a joint effort of the National Institute of 

Standards and Technology Office of Law Enforcement Standards (NIST/OLES) and the National 

Telecommunications and Information Administration’s Institute for Telecommunication 

Sciences (NTIA/ITS). 

The authors would also like to thank Frank Sanders, Division Chief for the NTIA/ITS Theory 

Division, and Dr. Robert Johnk of NTIA/ITS for developing the project; Frank Sanders for 

conducting bi-directional amplifier measurements; John Vanderau of NTIA/ITS for his diligent 

review of the calculations in Appendix C; Al Romero, Visual Information Specialist at the 

National Oceanic and Atmospheric Administration (NOAA), for creating the figures; and Kristen 

Davis at NTIA/ITS for preparing the document for publication. 

Special thanks are given to Myron Kissinger of the City and County of Denver (Colorado), 

Electronic Engineering Bureau, and to Gabrielle Sharkey and George Gallie of Triple C 

Communications (Englewood, Colorado) for sharing their expertise and serving as reviewers for 

this report. 

Finally, the authors would also like to thank all the public safety professionals, system designers, 

installers, and equipment manufacturer representatives who took the time to answer our 

questions. 
30

6 6BREFERENCES 

[1] Telecommunication Industry Association, TIA Telecommunications Systems Bulletin: 

Wireless communications systems, Performance in noise and interference limited 

situations, Part 1: Recommended methods for technology-independent modeling, TSB88.1-C., Feb. 2008, Table D-6, “Estimated Area Coverage Reliability,” p. 166. 

[2] W.C. Stone, “Electromagnetic Signal Attenuation in Construction Materials,” NIST 

Construction and Automation Program Report No. 3, NISTIR 6055, Oct. 1997. 

[3] C.A. Grosvenor, R.T. Johnk, J. Baker-Jarvis, M.D. Janezic, and B. Riddle, “Time-domain 

free field measurements of the relative permittivity of building materials,” IEEE Trans. on 

Instrumentation and Measurement, Vol. 58, No. 7, July 2009. 

[4] D. Pena, R. Feick, H. D. Hristov, and W. Grote, “Measurement and modeling of 

propagation losses in brick and concrete walls for the 900 MHz band,” IEEE Trans. On 

Antennas and Propagation, Vol. 51, No. 1, Jan. 2003, pp. 31–39. 

[5] D. Molkdar, “Review on radio propagation into and within buildings,” Microwaves, 

Antennas and Propagation, IEE Proceedings H, Vol. 138, No. 1, pp. 61–73, Feb. 1991. 

[6] L.P. Rice, “Radio transmission into buildings at 35 and 150 mc,” Bell System Technical 

Journal, Vol. 38, No. 1, Jan. 1959, pp. 197–210. 

[7] Chapter 5.1.7 ”Coverage” in R.I. Desourdis, Jr., D.I. Smith, W.D. Speiquits, R.J. Dewey, 

J.R. DiSalvo, Emerging Public Safety Wireless Communications Systems, Boston, MA: 

Artech House, 2002. 

[8] E.H. Walker, “Penetration of radio signals into buildings in the cellular radio 

environment,” Bell System Technical Journal, Vol. 62, No. 9, Nov. 1983, pp. 2719–2734. 

[9] J.M. Durante, “Building penetration loss at 900 MHz,” in Proc. of the 1973 Vehicular 

Technology Conference, Dec. 1973, pp. 81–87. 

[10] C.L. Holloway, W.F. Young, G. Koepke, K.A. Remley, D. Camell, and Y. Becquet, 

“Attenuation of radio wave signals coupled into twelve large building structures,” NIST 

Tech. Note 1545, Aug. 2008. 

[11] W.F. Young, K.A. Remley, J. Ladbury, C.L. Holloway, C. Grosvenor, G. Koepke, D. 

Camell, S. Floris, W. Numan, and A. Garuti, “Measurements to support public safety 

communications: Attenuation and variability of 750 MHz radio wave signals in four large 

building structures,” NIST Tech. Note 1552, Aug. 2009. 

[12] J. Daniel, “In-building communications,” Mission Critical Communications, Mar. 2004. 
31

[13] D.J.R. Martin, “Leaky-feeder radio communication: a historical review,” in Proc. of the 

1984 Vehicular Technology Conference, Pittsburgh, Pennsylvania, 1984, pp. 25–31. 

[14] A.A.M. Saleh, A.J. Rustako, Jr., and R.S. Roman, “Distributed antennas for indoor radio 

communications,” IEEE Trans. on Comm., Vol. COM-35, No. 12, Dec. 1987, pp. 1245–

1251. 

[15] National Commission on Terrorists Attacks upon the United States, “Heroism and Horror,” 

Chapter 9 in 9/11 Commission Report: Final Report of the National Commission on 

Terrorists Attacks upon the United States, Washington, D.C.: U.S. Government Printing 

Office, 2004, http://www.gpoaccess.gov/911/pdf/fullreport.pdf. 

[16] 47 CFR Part 90 (2010) Private Land Mobile Radio Service, 47 CFR § 90.7 (2010) 

Definitions, 47 CFR § 90.203 (2010) Certification required, 47 CFR § 90.210 (2010) 

Emission masks, and 47 CFR § 90.219 (2010) Use of signal booster. 

[17] G. Grimes, “Providing robust in-building coverage in public safety wireless networks,” 

Appendix C in Best Practices for In-Building Communications, S. Overby, (Chair), 

National Public Safety Telecommunications Council In-building Working Group, 

www.npstc.org, Nov. 12, 2007. 

[18] I. Frigyes, Application of optical communication methods in wireless communications, in 

Proc. of SBMO International Microwave Conf., Brazil, 1993, pp. 691–696. 

[19] I. Frigyes, I. Havermajaer, B.G. Molnar, A. Seeds, F. Som, Noise and loss characteristics of 

microwave direct modulated optical links, in Proc. of the 27th European Microwave Conf., 

1997, pp. 309–317. 

[20] D.J. Cree and L.J. Giles, “Practical performance of radiating cables,” The Radio and 

Electronic Engineer, Vol. 45, No. 5, May 1975, pp. 215–223. 

[21] S. Okada, T. Kishimoto, K. Akagawa, Y. Nakahara, K. Mikoshiba, F. Horiguchi, and K. 

Okamoto, “Leaky coaxial cable for communication in high speed railway transportation,” 

The Radio and Electronic Engineer, Vol. 45, No. 5, May 1975, pp. 224–228. 

[22] Y.P. Zhang, “Indoor radiated-mode leaky feeder propagation at 2.0 GHz,” IEEE Trans. on 

Veh. Tech., Vol. 50, No. 2, Mar. 2001, pp. 536–545. 

[23] J.M. Jacobsmeyer, “Leaky Cables are a good thing,” Urgent Communications, Oct. 2005, 

http://preview.mrtmag.com/mag/radio_leaky_cables_good/. 

[24] S. Overby, (Chair), “Best practices for in-building communications,” National Public 

Safety Telecommunications Council In-building Working Group, www.npstc.org, Nov. 12, 

2007. 

[25] International Code Council, “Emergency responder radio coverage,” Section 510 in 

International Fire Code, 2009 Edition. 
32

[26] International Code Council, “Emergency responder radio coverage,” Appendix J in 

International Fire Code, 2009 Edition. 

[27] J. Jacobsmeyer, “The X Factor”, Urgent Communications, Sep. 10, 2010, pp. 28–31. 

[28] National Fire Protection Association, “In-building Public Safety Radio Enhancement 

Systems,” Annex O in NFPA-1 2009 Edition. 

[29] “Public Safety in-building/in-tunnel ordinances and their benefits to interoperability,” 

Public Safety Wireless Network Program Report, Nov. 2002. 

[30] M. Worrell and A. MacFarlane, “Phoenix fire department radio system safety project, Final 

report, version 1.7,” City of Phoenix Fire Department Report, Oct. 8, 2004. 

[31] Telecommunication Industry Association, “Performance confirmation,” Section 5 in TIA 

Telecommunications Systems Bulletin: Wireless communications systems, Performance in 

noise and interference limited situations, Part 3: Performance Verification, TSB-88.3-C.

[32] S. Scheinert, “In-building cellular: Why it is a Wi-Fi alternative: Part 1,” Wireless Net 

Design Line, http://www.eetimes.com/design/communications-design/4012637/Inbuilding-cellular-Why-it-is-a-Wi-Fi-alternative?pageNumber=0, Sep. 12, 2006. 

[33] S. Scheinert, “In-building cellular: Why it is a Wi-Fi alternative: Part 2,” Wireless Net 

Design Line, http://www.eetimes.com/design/communications-design/4012637/Inbuilding-cellular-Why-it-is-a-Wi-Fi-alternative?pageNumber=1, Sep. 19, 2006. 

[34] J. Spindler, “InFocus: Passive, active, and hybrid solutions for in-building wireless,” 

Connected Planet Online, http://connectedplanetonline.com, Mar. 28, 2006. 

[35] J. Daniel, “Introduction to in-building wireless signal distribution for public safety,” 

Appendix B in Best Practices for In-Building Communications, S. Overby, (Chair), 

National Public Safety Telecommunications Council In-building Working Group, 

www.npstc.org, Nov. 12, 2007. 

[36] S. Blum, “Dual band, in-building wireless networks”, Mobile Radio Technology, Apr. 1, 

2001, pp. 52–55. 

[37] Federal Communications Commission, “Wireless telecommunications bureau seeks 

comment on petitions regarding the use of signal boosters and other signal amplification 

techniques used with wireless services,” Public Notice, 25 FCC Rcd. 68 (2010). 

[38] J. Daniels, “Optimizing 16 dB capture effect to overcome Class A ‘channelized’ signal 

booster group delay problems with public safety communication systems,” Jul. 30, 2008, 

http://rfsolutions.com/16dB.pdf. 

[39] M.A. Panjwani, A.L. Abbott, and T.S. Rappaport, “Interactive computation of coverage 

regions for wireless communication in multi-floored indoor environments,” IEEE Journal 

on Selected Areas in Communications, Vol.14, No. 3, Apr. 1996, pp. 420–430. 
33

[40] G. Zhou, H. Tang, and K.Y. Lau, “In-building radio distribution using a “saturated” 

distributed antenna architecture—Universal radio-power and delay-spread statistics,” in 

Proc. of IEEE Int. Conf. on Comm., Jun. 1999, pp. 29–35. 

[41] J. He, A.A. Verstak, L.T. Watson, C.A. Stinson, N. Ramakrishnan, C.A. Shaffer, T.S. 

Rappaport, C.R. Anderson, K.K. Bae, J. Jiang, and W.H. Tranter, “Globally optimal 

transmitter placement for indoor wireless communications systems,” IEEE Trans. on 

Wireless Communications, Vol. 3, No. 6, pp. 1906–1911, Nov. 2004. 

[42] T. Fruhwirth and P. Brisset, “Optimal planning of digital cordless telecommunications 

systems,” in Proc. of PACT 1997: Third Int’l Conf. Practical Application of Constraint 

Technology, Los Alamitos, Calif.: IEEE Computer Soc. Press, pp. 165–176, 1997. 

[43] S.J. Fortune et al., “WISE Design of Indoor Wireless Systems: Practical Computation and 

Optimization,” IEEE Computational Science & Eng., Vol. 2, No. 1, pp. 58–68, Spring 

1995.

[44] D. Stametelos and A. Ephremides, “Spectral efficiency and optimal base placement for 

indoor wireless networks,” IEEE J. Selected Areas in Comm., Vol. 14, No. 4, pp. 651–661, 

May 1996. 

[45] W.C.Y. Lee, “Path loss over flat terrain,” in Mobile Communications Engineering, New 

York: McGraw-Hill, 1982, pp. 87–114. 

[46] Infinigy Networks, “An Introduction to Neutral Host Distributed Antenna Systems,” 

http://www.infinigy.com/PDF/InfinigyNeutralHostWhitepaper.pdf. 

[47] In-Building Wireless Alliance, Convergence of buildings, communications, and public 

safety,” 2006 PRTM Whitepaper, http://www.ibwalliance.org/documents/Wireless 

Convergence whitepaper_June06.pdf. 

[48] Public Safety Trust, “A brief history of public safety communications,” 

http://www.psst.org/history.jsp, Aug. 25, 2009. 

[49] D. Jackson, “The FCC places its bet,” Urgent Communications, Apr. 10, 2010, pp. 32–39. 

[50] R. Blom, P. de Bruin, J. Eman, M. Folke, H. Hannu, M. Naslund, M. Stalnacke, and P. 

Synnergren, “Public safety communications using commercial cellular technologies,” in 

Proc. of the Second International Conf. on Next Generation Mobile Applications, Services, 

and Technologies, pp. 291–295. 

[51] “Avoiding Interference between Public Safety Wireless Communications Systems and 

Commercial Wireless Communications Systems at 800 MHz, a Best Practices Guide,” Dec. 

2000, http://www.safecomprogram.gov/NR/rdonlyres/CC79A5A3-2A2A-42CB-90DB00CECA812F44/0/Avoiding_Interference_Between.pdf. 

[52] Federal Communications Commission, “Improving Public Safety Communications in the 

800 MHz Band,” Report and Order, 19 FCC Rcd. 14969 (2004). 
34

Further Reading 

[1] P. Frazier, R. Hooper, B. Orgen, N. Hankin, J. Williams, “Structure Communications 

Issues,” Chapter IV in Current Status, Knowledge Gaps, and Research Needs Pertaining to 

Firefighter Radio Communication Systems, September 2003, Prepared for National 

Institute for Occupational Safety and Health, Morgantown, W.V. by Tri Data Corporation, 

Arlington, Virginia. 
35

APPENDIX A: TABLES 

A.1 Building Material Attenuation 

Table A-1 contains a list of typical construction materials and their corresponding attenuation at 

800 MHz and 0-degree angle of incidence. Variations are due to differences in thickness, 

density, or composition of the material samples. Values in this table are derived from [A-1]. 

Table A-1. Construction material attenuation 

Construction Material Attenuation (dB)

Drywall 0.2

Plywood 0.3 – 1.1

Glass (non-metalized) 0.5 – 2.75

Wood 2.2 – 5.4

Brick 3.0 – 5.5

Brick/Masonry-block 10.1

Brick/Concrete-wall 13.0 - 23.0

Masonry block 11.0 – 27.0

Concrete wall (Type 1) 11.0 – 35.0

Reinforced concrete wall 25.0 – 29.0

A.2 High-Site Building Attenuation 

Table A-2 contains a list of building attenuation statistics where the outside antenna is mounted 

high above the ground. The attenuation is the ratio of average power in the streets surrounding 

the building to the average power measured over a small distance inside the building. The test 

signals were radiated by seven advanced mobile phone system (AMPS) cellular radio sites, 

operating at 850 MHz, spaced approximately 15 miles (24 km) apart throughout a metropolitan 

area. The inside antenna was omnidirectional. Values are derived from [A-2]. 

Table A-2. High- site building attenuation at 850 MHz 

Environment Floor No. of Bldgs. Mean (dB) Standard Deviation(dB)

Urban 1 3 18.0 7.7

Suburban 1 10 13.1 9.5

All 1 13 14.2 9.3

2 8 10.6 8.5

3 6 6.8 9.8

4 4 -0.8 10.7

5 3 2.9 9.2
36

A.3 Low-Site Building Attenuation 

Table A-3 contains a list of building attenuation statistics where the outside antenna is mounted 

low near the ground. Attenuation is the ratio of the average power measured outside the building 

on the wall nearest the transmitter to the average power measured over a small distance inside 

the building. The outside antenna is directional and mounted approximately 13 feet (4 meters) 

off the ground. The inside antenna is omnidirectional. Values are derived from [A-3]. 

Table A-3. Low-site building attenuation 

Building Frequency (MHz) Mean (dB)

Standard 

Deviation (dB)

Apartment building, New Orleans, LA 902 34.2 13.8

Apartment building Boulder, CO 908 27.0 10.9

Office, Phoenix, AZ 867 37.9 13.5

Office, Gaithersburg, MD 902 57.7 14.1

Office, Silver Spring, MD 902 70.4 10.5

Hotel, Colorado Springs, CO 902 34.1 18.8

Shopping Mall, Bethesda, MD 902 44.6 6.3

Convention Center, Washington, DC 902 61.8 14.5

A.4 Narrowband Public Safety Mobile Radio Frequency Bands 

Table A-4 contains a list of frequency bands for narrowband radios used by state and local public 

safety agencies [A-4]. Mobile and base frequencies are not always specified for the 150 and 450 

MHz bands. The 800 MHz interleaved band has both public safety and non-public safety 

licensees. The 800 MHz National Public Safety Advisory Committee (NPSAC) band is licensed 

solely by public safety agencies. 

Table A-4. Narrowband public safety mobile radio frequency bands 

Band Mobile Transmit (MHz) Base Transmit (MHz)

150 MHz - VHF High 150-162 Same

450 MHz - UHF 450-470 Same

700 MHz 799-805 769-775

800 MHz - NPSAC 806-809 851-854

800 MHz - Interleaved 809-816 854-861

A.5 Donor Antenna Characteristics 

Table A-5 lists four commonly used donor antenna types and their characteristics. Gain in dBi is 

obtained by adding 2.15 dB to the dBd value shown. 
37

Table A-5. Representative characteristics of several types of donor antenna 

Antenna type

Freq.

(MHz)

Bandwidth

(MHz)

Gain

(dBd)

Beam width (deg) F/B

(dB)

Dim.

H V (in)

Yagi (6-element) 806-866 60 9 42 40 16 28" L

Corner reflector 806-960 90 8.5 45 56 23

68" W

38" H

18" D

Parabolic 806-896 90 16 12 24 25

68" W

36" H

18" D

Panel 806-900 94 14.5 102 7 20

95" H

8" W

6" D

A.6 References 

[A-1] W.C. Stone, “Electromagnetic Signal Attenuation in Construction Materials,” NIST 

Construction and Automation Program Report No. 3, NISTIR 6055, Oct. 1997. 

[A-2] E.H. Walker, “Penetration of radio signals into buildings in the cellular radio 

environment,” Bell System Technical Journal, Vol. 62, No. 9, Nov. 1983, pp. 2719–2734. 

[A-3] C.L. Holloway, W.F. Young, G. Koepke, K.A. Remley, D. Camell, and Y. Becquet, 

“Attenuation of radio wave signals coupled into twelve large building structures,” NIST 

Tech. Note 1545, Aug. 2008. 

[A-4] 47 CFR Part 90 (2010) Private Land Mobile Radio Service, Subpart B, Public Safety 

Radio Pool. 
38

APPENDIX B: RADIO-WAVE PROPAGATION 

Variable names are consistent within the Appendix. Unless otherwise stated, upper case variables 

are the decibel equivalents of their corresponding lower-case variables and logarithms are 

base 10. 

B.1 Ideal Radio Wave Propagation Path Loss Models 

Radio propagation models are often used to determine how much signal attenuation or loss there 

is between antennas. These models are based on the fundamental definition that loss, l, is the 

ratio of transmitted and received powers, i.e. 

t

r

p

l

p

 , (B-1) 

where pt is power at the input to the transmitting antenna and pr is the output of the receiving 

antenna. 

For free-space propagation, where transmit and receive antennas are far removed from any 

obstruction, the received power is 

2

4

t

r t

g

p p a

 d

 , (B-2) 

where gt is the transmitting antenna gain, d is the distance between transmitter and receiver, and 

a is the effective area of the receiving antenna which captures the radiated field. The effective 

area is 

2

4

r

g

a





 , (B-3) 

where gr is the receiving antenna gain and λ is wavelength. Substituting (B-3) into (B-2) we 

obtain 

2

4

t r

r t

g g

p p

 d





     

. (B-4) 

Rearranging terms we find that 

2

1 4

t r

d

l

g g





 

    

. (B-5) 
39

Basic transmission path loss is often used to express path loss independent of antenna gains 

p t r l lg g 

(B-6) 

yielding the expression 

t t r

r

p

p g g

p

l

 , (B-7) 

or in decibels 

    ( ) P P G G dBmL r t t r p

. (B-8) 

Hence, free-space loss is

2

4

















 d

l

p

. (B-9) 

In land mobile and cellular radio systems, loss is invariably influenced by reflections off the 

earth’s surface. Because of this, their path loss cannot be predicted by free-space loss. However, 

assuming that the distance between transmit and receive antennas is small compared to the 

curvature of the earth, and large compared to the height of the antennas, their path loss can be 

predicted by plane earth loss 

2

2

2

4 1 2

 

2 2 4sin λsin

 

  

 

   

   

 

     

           

       

       

p

r t r t

d d l

h h h h

d d

, (B-10)

where ht is height of transmitter antenna and hr is height of receiver antenna. This function 

produces a scalloping pattern when  increases. In other words, alternately increases and 

decreases with height because of interference from the ground reflected wave. If the angle 

created by 

2 r t h h

d





 is small, i.e. ≤ 0.3 radians, then 

2 2 sin r t r t h h h h

d d

 

 

 

    

 and 

2

2

p

t r

d

l

h h

 

     . (B-11)

 

Plane earth loss at small angles differs from free-space loss in that it increases by the 4th power 

of distance instead of the 2nd power. This means plane earth loss increases by 12 dB each time 

distance is doubled as compared to 6 dB for free-space loss. 
40

B.2 Practical Path Loss Models 

The propagation of signals used by narrowband land mobile and cellular radio systems is very 

complex [B-1]. Its complexity is due to the myriad of interactions a radio wave has with the 

cluttered environment. In the outdoors, the clutter includes building exteriors, terrain, and 

vegetation. Indoors, the wave interacts with the building’s walls, floors, and furnishings. Because 

of clutter, propagation loss cannot be accurately predicted with ideal free-space and plane-earth 

loss. 

From a physical perspective, these interactions can be explained by electromagnetic 

transmission, reflection, and diffraction phenomena. From a radio engineering perspective, they 

are characterized by shadowing and multipath fading. Shadowing attenuates mean radio signal 

power and is caused by obstructions in the radio wave path. It is characterized by , which like 

free-space and plane-earth loss, depends on the distance between antennas. 

Multipath enhances and diminishes instantaneous radio signal power and is caused by scattering 

off nearby objects in the vicinity of the antennas. The effects of multipath are readily noticed 

with small changes in position [B-2]. The instantaneous power fluctuations created by multipath 

have no effect on mean radio signal power or path loss. When measuring path loss, the 

fluctuations are removed by averaging instantaneous power measurements (in watts) over a small 

area.

As mentioned previously, path loss due to shadowing is dependent on distance. However, even at 

the same distance, path loss has been found to vary with large changes in position—a 

phenomenon called path loss variability, or shadow fading. This occurs because large changes in 

position also mean a change in the characteristics of the obstructions in the radio wave path and a 

corresponding effect on path loss. Because of its variability, path loss is considered a nonstationary random process 

p p p l m x  , (B-12)

where mp is the mean path loss and xp is the random variable that characterizes path loss 

variability. The corresponding expression in decibels is

  ( ) L M X dB p p p

. (B-13) 

The mean has two components. The first component is a reference distance and accounts for the 

part of the path, out to a distance d0, which experiences free-space loss. However, after that 

distance, losses can increase with a path loss exponent, n, which only needs to be greater than 0. 

2

0

0

4

n

p

d d

m

d





   

       

(B-14)

The variable Xp is often characterized as a zero-mean, Gaussian or normally distributed random 

variable with standard deviation, σ [B-3]. It is important to note that both n and σ are 
41

environmentally dependent. As an example, we do not expect office buildings, warehouses, 

suburban areas, and urban areas to have the same n and σ. 

The complete expression for path loss is 

2

0

0

4

n

p p

d d

l x

d





   

       

, (B-15) 

which in decibels is 

4

20log 10 log ( ) 



   

    

   

o

p

p

o

d d

L n X dB

d

. (B-16) 

B.3 Propagation Into Buildings 

For propagation into buildings, the path loss is extended to include building attenuation. Like 

path loss above, building attenuation varies with large changes in position and is considered a 

non-stationary random process characterized by 

BLD BLDBLD

 xml

, (B-17)

where mBLD is the mean building attenuation and xBLD is the building attenuation variability. 

The total path loss is 

p OUT OUT BLD BLD l m x m x  , (B-18)

where mOUT and xOUT are the mean and variability of the path loss outside the building, 

respectively. Let 

p

x

= 

OUT BLD x x

or

X p

= 

X X OUT BLD 

. Assuming building attenuation 

variability is independent of outside variability, zero-mean, and Gaussian distributed in decibels, 

the standard deviation of 

X p

is 

2 2      ( ) OUT BLD dB . (B-19)

The complete expression is 

2

0

0

4

n

p BLD p

d d

l m x

d





   

       

, (B-20)

which in decibels is 
42 4

20log 10 log ( ) o

p BLD p

o

d d

L n M X dB

d





   

            . (B-21) 

B.4 Propagation Inside Buildings 

A number of methods are used to increase the accuracy and precision of indoor path loss 

predictions. For example, if antennas will be installed on each floor of a multistory building, then 

n and σ should be derived from measurements performed on the same floor instead of with 

measurements that may have included paths between floors. 

Another more site-specific approach is to replace Mp terms with free-space loss over the entire 

distance, and the sum of the losses of the walls the signal is known to pass though along the 

direct path, i.e., 

4

20 ( ) 



 

       p  i p

i

d

L log A X dB

(B-22) 

where Ai is the attenuation of the i-th wall [B-4]. 

Examples of differences between these approaches are shown in Table B-1 [B-4]. These 

measurements were taken at 900 MHz in a five-floor, two-wing, office building divided by 5 ft. 

(1.5 m) tall plastic office partitions. The first row represents parameters derived from 

measurements between any two points in the entire building. The second row restricts 

measurements to those acquired on the same floor. The third row predicts the mean path loss by 

summing wall attenuation, as in (B-22), assuming 1.39 dB loss through the office partitions and 

2.38 dB loss through masonry block walls. Clearly, the use of wall attenuation decreases σ. 

Table B-1. Path loss parameters for office building furnished with 5 ft. (1.5 m) tall office 

partitions 

Measurement Area n σ

Entire building 3.54 12.8

Same floor 3.27 11.2

Summing wall attenuation 2.0 4.1

B.5 Availability 

Because of path loss variability, radio link designers using path loss models can only quantify the 

chances that the power will exceed a required value. This is referred to as availability. 

Availability is defined as 

A Pr P P     r req

, (B-23) 
43

where Pr{}represents the probability of its argument, P

r

 is the received power in dB and 

P

req

 is 

the required value. 

Beginning with the link budget equation 

    ( ) P P G G L dBm r t t r p

, (B-24) 

we can rewrite the expression for availability as 

A Pr L P G G P       p t t t req 

(B-25) 

or 

A Pr L P G G P       1  p t t r req . (B-26) 

As mentioned earlier, is Gaussian distributed with mean and standard deviation so

 

1

P G G P M t t r req p A Q



       

   

   

, (B-27)

where 

Q{}

 is the Q function2.F2F2F

3

Thus, for a link to meet its performance objective, the condition 

P G G M P t dBm t t r p req      ( ) 

(B-28) 

must be met, where is the availability factor defined by 

  1

t Q A 1  

(B-29)

and the product 

t

is the shadow-fading margin. 

Land mobile radio evaluates availability in two ways. The expression 

 { 

( ) } (B-30)

is referred to as contour availability. This is the availability at a specific location on the 

circumference of a circle with radius R. The transmitter is at the center of the circle. The 

expression 

 

3 {

 

 

} { } ∫ 

 

 

 

 

 

 and its inverse is 

 { { }} 

 

 

, where 

and are the mean and standard deviation of the random variable . 
44

 

 ∫∫ { 

( ) }

 

 

 (B-31)

is referred to as covered area availability. This is the average availability over the circular area. 

Contour and covered area availabilities can be related to one another through the path loss model 

 and parameters [B-5]. 

For public safety, 97 percent covered area availability is often required for outdoor applications 

and 90 percent is required indoors, except in critical areas such as exit stairs where 95 percent or 

more is required. Table B-2 lists t for the most common percent availabilities. 

Table B-2. Parameter t for the most common percent availabilities, %A 

%A 84.13 90.0 95.0 97.0 97.7

t 1.0 1.28 1.64 1.88 2.0

B.6 Site-specific Propagation Models 

Site-specific models calculate the power at any point in a building from detailed information 

such as floor layout and building material electrical properties. Site-specific models can be very 

helpful for positioning antennas inside the building. Ray tracing and dominant-path are two 

commonly used site-specific models. 

Ray tracing sums continuous-wave signals launched over the antenna beamwidth [B-6]. It is 

based on physical principles and depends on knowing the exact locations and electrical 

characteristics of the building’s walls, floors, and ceilings. The signals or “rays” arrive delayed 

and attenuated due to interactions with the building’s walls and floors. Furnishings are generally 

not considered. Enhanced versions include effects of diffraction. The rays can be summed with 

or without phase information. If they are summed with phase, the results include multipath 

fading effects. Although ray tracing is computationally burdensome for in-building propagation 

analysis, it is not prohibitively so with current computer technology. Comparison of ray tracing 

results to measurements within a building showed a 1.6 dB mean error with a 6.8 dB standard 

deviation. 

The dominant path method reduces computational burden by dramatically reducing the number 

of rays or paths used to predict field strength [B-7], [B-8]. This approach is based on empirical 

evidence, which shows that most energy arriving at a location comes from a small number of 

paths. The dominant path is obtained using an algorithm that selects the path with the least 

attenuation from a tree diagram depicting the spatial relationships between rooms within the 

building. Field strength is then predicted by feeding a number of characteristics of the dominant 

path into a neural network algorithm that has been previously trained with measured data from 

similar buildings. Accuracy of the dominant path method is increased if the neural network is 

also trained with measurements from the specific building. Comparison of the dominant path 

method to measurements within a building showed a 7.7 dB mean error with an 8.0 dB standard 

deviation when no measurements from the building were used in training. This mean error was 
45

reduced to 0.2 dB and the standard deviation to 3.5 dB when measurements from the building 

were used in training. 

B.7 Multipath Fading 

Although multipath fading has no effect on path loss, this is not to say it has no effect on radio 

performance. In fact, the low instantaneous signal powers caused by multipath fading do 

momentarily diminish audio quality. One way to compensate for multipath fading is to add a 

multipath fading margin to the SNR required for a radio operating in AWGN. 

Determination of the margin depends on knowing the statistical distribution of the instantaneous 

power fluctuations. Worst-case multipath fading is typically characterized by Rayleigh 

distributed amplitudes. This is a reasonable assumption when the radios operate in a narrow 

bandwidth, with omnidirectional antennas, and in or around nearby objects that scatter the radio 

signal into a number of rays. In addition, this assumption is well supported by measurements in 

outdoor [B-9] as well as indoor [B-10], [B-11] environments. 

B.8 References 

[B-1] T.S. Rappaport, Wireless Communications Principles and Practice, Upper Saddle River, 

N.J., Prentice Hall, Inc., 1996, pp. 126–131. 

[B-2] H. Hashemi, “The indoor radio propagation channel,” Proc. of the IEEE, Vol. 81, No. 7, 

July 1993, pp. 943–968. 

[B-3] T.S. Rappaport, “Radio-wave propagation for emerging wireless personal 

communications systems,” IEEE Antennas and Propagation Magazine, Vol. 35, No. 5, 

October 1994, pp. 14–24. 

[B-4] S.Y. Seidel and T.S. Rappaport, “914 MHz path loss prediction models for indoor 

wireless communications in multi-floored buildings,” IEEE Trans. On Veh. Tech., Vol. 

40, No. 2, Feb. 1992, pp. 207–217. 

[B-5] Douglas O. Reudink, “Properties of Mobile Radio Propagation Above 400 MHz,” IEEE 

Trans. on Veh. Tech., Vol. VT-23, No. 4, Nov. 1974, pp. 143-159. 

[B-6] S.Y. Seidel and T.S. Rappaport, “A ray tracing technique to predict path loss and delay 

spread inside buildings,” in Proc. of the 1992 IEEE Global Telecommunications Conf., 

pp. 649–653, 1992. 

[B-7] G. Wolfle and F. M. Landstorfer, “Field strength prediction in indoor environments with 

neural networks,” in Proc. of the 1997 IEEE Vehicular Technology Conf., pp. 82–86, 

1997. 

[B-8] G. Wolfle and F. M. Landstorfer, “Dominant paths for the field strength prediction,” in 

Proc. of the 1998 IEEE Vehicular Technology Conf., pp. 552–556, 1998. 
46

[B-9] W.R. Young, Jr., “Comparison of Mobile Radio Transmission at 150, 450, 900, and 3700 

Mc,” The Bell System Technical Journal, Nov. 1952, pp. 1068–1085. 

[B-10] F. Lotse, J. Berg, R. Bownds, “Indoor propagation measurements at 900 MHz,” in Proc. 

of the 1992 Vehicular Technology Conference, Denver, CO, May 1992, pp. 629–632. 

[B-11] V. Nikolopoulos, S. Stavrou, and S.R. Saunders, “Narrowband fading analysis of indoor 

distributed antenna systems,” IEEE Antennas and Propagation Letters, Vol. 2, 2003, pp. 

89–92. 
47

APPENDIX C: CALCULATIONS 

This Appendix contains calculations that compare how well a portable radio operates in a 

building without and with an IBRES as in Section 2.6, demonstrate how automatic gain control 

(AGC) can cause gain reduction as in Section 3.2, and demonstrate how noise transmitted by 

BDA can degrade the performance of another systems repeater as in Section 3.3. 

Figure C-1. Schematic representation of scenario used for calculations in this Appendix. 

Figure C-1 depicts the scenario used in this Appendix which is composed of a repeater and a 

building located on the edge of the repeater coverage area. The repeater has a circular coverage 

area with radius . The path loss from the repeater to the edge of the coverage area is . 

For calculations without the IBRES, building attenuation is 

LBLD

. The portable radio is assumed 

to be on the first floor. The exact location on the first floor is not important. 

For calculations with the IBRES, the building has a donor antenna, BDA, distribution network, 

and indoor antenna. The path loss from the repeater to the donor antenna is 

Lfs

. The indoor 

antenna has a circular coverage area with radius

IN d

. The portable radio is assumed to be at the 

edge of the indoor antenna coverage area. The path loss from the indoor antenna to the edge of 

its coverage area where the portable radio is operated is . 

Outdoor, building, and indoor propagation parameters are derived from measurements. In all 

cases propagation loss is composed of a mean and variable, shadow fading component as 

described in Appendix B 

L M X dB   ( ), (C-1)
48

where M is the mean and X is the variable component characterized by 

 . 

The outdoor propagation parameters are derived from measurements of a 900 MHz cellular 

system [C-2] where M is computed from n = 3.0 and

0 d

 = 1 km, and 



 is 8.9 dB. The building 

attenuation parameters are derived from measurements of urban high-rise buildings on the first 

floor [C-3] where M is 18 dB and 



 is 8 dB. The indoor propagation parameters are derived 

from measurements of an office environment at 914 MHz [C-7] where M is computed from n = 

3.3 and 

0 d

= 1 m, and 



is 11.2 dB. 

The calculations assume an analog frequency modulated (FM) public safety portable radio 

operated in the 800 MHz National Public Safety Advisory Committee (NPSAC) band in a 12.5 

kHz channel. The portable radio has a quarter-wave whip antenna and is mounted on the hip. The 

repeater is equipped with a stacked dipole antenna and a tower top amplifier. 

Transmitter powers and receiver noise figures are referred to the antenna terminals. Received 

powers are reported in terms of the power received by an unobstructed dipole antenna. Variable 

names are consistent within the Appendix. Unless otherwise stated, upper case variables are the 

decibel equivalents of their corresponding lower-case variables and logarithms are base 10. 

C.1 Required Power 

This section calculates the amount of power, 

P

req

, required to achieve our desired delivered audio 

quality (DAQ) performance level. It is a worst-case estimate in that it assumes high antenna loss 

associated with a hip-mounted portable radio with a quarter-wave whip antenna. The carrier to 

noise ratio (CNR) is that needed to achieve the desired performance level in a Rayleigh fading 

channel. Shadow fading is not taken into account. 

This worst-case estimate is expressed in terms of the power received by an unobstructed 

vertically-polarized, half-wave dipole antenna by 

t t d

req

p

p g g

p

l

 , (C-2)

where 

t

p

 is the transmitted power, 

t

g

 is the transmitter antenna gain, 

d g

 is the dipole antenna 

gain, and 

p

l

 is the path loss. Dipole antennas are commonly used for conformance tests. 

The CNR after reception by the antenna and detection filtering is 

req

a

p

l n

  , (C-3)

where 

a

l

 is the antenna loss relative to

d g

 and 

n

is the noise power in the detection filter 

bandwidth. The loss includes body absorption, depolarization and antenna pattern irregularities. 

The noise power is 
49

0 eq port n kT b f 

, (C-4)

where 

k

 is Boltzman’s constant, 

T0

 is the ambient temperature in Kelvin, 

eq b

 is the detection 

filter equivalent noise bandwidth, and 

port f

 is the noise factor. 

Solving for 

req p

we find that 

req eq port a 0 p kT b f l  

(C-5)

or in decibels 

0 Ψ ( ) P kT B F L dBm req

     eq port a

. (C-6) 

Table C-1 shows that -87.7 dBm is needed when measured with the dipole antenna. 

Table C-1. Required power when measured with a dipole antenna 

Value (C-6) Notes

0

kT

-174.0 

dBm/Hz -174.0

B

eq

38.9 dB-Hz 38.9 7.8 kHz ENBW

Fport

6.0 dB 6.0

Ψ 26.0 dB 26.0 DAQ 3.4, Rayleigh fading

L

a

15.4 dB 15.4 Relative to dipole antenna

P

req -87.7 dBm Dipole antenna

The factors 

B

eq

,, and 

L

a

 were derived from[C-1]. The factor 

B

eq

 is from Table 5, 

“Intermediate Frequency Filter Specifications for Simulating Receiver.” The factor 



is from 

Table A-1, “Projected Channel Protection Criteria (CPC) Requirements for Different Delivered 

Audio Qualities (DAQ).” The target DAQ, commonly used for public safety radio design, is 

from Table 2, “Delivered Audio Quality.” The factor 

L

a

 is from Table D-5, “Median Portable 

Antenna Loss Outside and Inside Vehicle.” 

In some municipalities radio power measurements are made with the handheld portable radio. In 

general the loss of a portable radio with an unobstructed quarter-wave whip antenna is 5 dB 

compared to the dipole antenna. The corresponding received signal strength is -92.7 dBm. 
50

C.2 Link Budgets 

C.2.1 Portable Radio Operated Outside Building 

The portable radio operating outside a building requires 

,

 ( ) P P t dBm req OUT req OUT   , (C-7) 

where 

 OUT

 is the standard deviation of the outdoor path loss variability in dB, t is the contour 

availability factor, and 

 OUT t

 is the outdoor shadow-fading margin. As shown in Table C-2, 

Preq OUT ,

 is -73.0 dBm assuming 

 OUT

 is 8.9 dB, the contour availability corresponding to 97 

percent covered availability is 95 percent, 

t

 is 1.65, and the shadow fade margin is 14.7 dB. 

Table C-2. Minimum power for portable radio operated outside building 

Value (C-7) Notes

P

req -87.7 dBm -87.7 Dipole antenna

 OUT t

14.7 dB 14.7

Preq OUT , -73.0 dBm Dipole antenna

C.2.2 Portable Radio Operated Inside Building Without an IBRES 

A portable radio operating inside a building without an IBRES requires 

,

 ( ) P P t dBm req IN req   , (C-8) 

where 

2 2 ( )      OUT BLD dB

(C-9) 

and 

 BLD

 is the building path-loss variability standard deviation. 

The power received in the building is 

,

 ( ) P P M dBm r req OUT BLD  , (C-10) 

where 

MBLD

 is the mean building attenuation. 

As shown in Table C-3 and Table C-4,

P P r req IN 

,

. Consequently, the link does not meet the 

performance level objective. The calculations assume

 BLD

is 8 dB, 

MBLD

is 18 dB, the contour 

availability corresponding to 90 percent covered availability is 83 percent, 

t

 is 0.96, and the 

shadow fade margin is 13.7 dB. 
51

Table C-3. Power required by a portable radio operated inside building without an IBRES 

Value (C-8) Notes

P

req -87.7 dBm -87.7 Dipole antenna

t

13.7 dB 13.7

Preq IN, -74.0 dBm Dipole antenna

Table C-4. Power provided to the portable radio operated inside building without an IBRES 

Value (C-10) Notes

Preq OUT , -73.00 dBm -73.00 Dipole antenna

MBLD

18.0 dB -18.0

P

r

-91.0 dBm Dipole antenna

C.2.3 Portable Radio Operated Inside Building With an IBRES 

A portable radio operating inside a building with an IBRES requires 

,

 ( ) P P t dBm req IN req IN   . (C-11) 

The power received in the building is 

, ,

    ( ) P P G G M dBm r req OUT C IBRES p IN

(C-12) 

where 

Gc

is the clutter gain, 

GIBRES

is the IBRES gain, and is the mean indoor path loss. 

Clutter gain is 

,

  ( ) G M L dB C p OUT fs

(C-13) 

The mean outdoor path loss is 

, , ,

    ( ) Mp out t REP REP d req OUT P G G P dB

(C-14) 

where 

Pt REP ,

 is the repeater power, is the repeater antenna gain, and is the dipole gain. 

Using the values in Table C-5, is 123.3 dB. This path loss corresponds to a distance of 

12.4 km when the path loss exponent,

n , is 3 and the reference distance, , is 1 km . The at 

this distance is 112.4 dB. Consequently  is 10.9 dB. This estimate is considerably more 

conservative than one that uses a flat-earth reference [C-4]. 
52

Table C-5. Mean outdoor path loss 

Value (C-14) Notes

Pt REP ,

43.0 dBm 43.0 20 watts at antenna terminals

GREP

5.15 dBi 5.15 40 degree elevation beamwidth, 

omnidirectional antenna

Gd

2.15 dBi 2.15

Preq OUT , -73.0 dBm 73.0 Dipole

M p out ,

123.3 dB

The IBRES gain is composed of three elements, i.e. 

 ( ) G G G L dB IBRES      BDA

, (C-15) 

where 

G

is the IBRES gain before the BDA due primarily to the donor antenna, and 

L

 is the 

IBRES loss after the BDA primarily due to the distribution network. Locations of these IBRES 

model parameters are depicted in Figure C-2. 

Figure C-2. IBRES model parameters 
53

The BDA gain, 

GBDA

, can vary from 

GBDA max mgc ,  L

to

GBDA max ,

 where 

L

mgc

 is the manual gain 

control attenuation. The effective BDA gain, 

 , is the amount of gain in dB after both manual 

and automatic gain control has been applied and can vary from 

G L BDA agc  to

GBDA

 where 

L

agc

is the automatic gain control attenuation. The gain factor corresponding to 



is



. The 

maximum amount of power the BDA can supply is 

PBDA max ,

dB. 

The optimal BDA gain is that needed for 

P P r req IN

,

 when the power outside is 

Preq OUT ,

. 

Combining (C-12) and (C-15) and solving for 

, , , ,

( ) G P L M P G BDA opt req IN         p IN req OUT c G dB

(C-16) 

Gain is computed for the IBRES in our example, which consists of a Yagi donor antenna, BDA, 

and coaxial distribution network similar to the one shown in Figure 16. The Yagi donor antenna 

is connected to a BDA through 25 feet of cable. The 

GBDA max ,

 is 80 dB, 

L

mgc max ,

is 30 dB, 

L

agc max ,

is 30 dB, and 

PBDA max ,

 is 30 dBm. 

The distribution network, shown in Figure C-3, is designed with guidance from [C-5] and [C-6]. 

The network is composed of coaxial cable and directional couplers. The cable has losses of 2 dB 

per 100 feet. Directional coupler loss is shown in the figure. Starting with the antenna closest to 

the vertical cable, the signal is attenuated 17.0, 17.8, and 16.8 dB by the distribution network. 

We will use the highest attenuation in our calculations. 

Figure C-3. Distribution network used in this example 

Mean indoor path loss, 

M p IN,

, at the edge of the 62.5 foot radius coverage area is 72.8 dB 

when the path loss exponent, , is 3.3 and the reference distance, , is 1 m. 

The 

GBDA opt ,

and 

GIBRES

are given in Table C-6 and Table C-7. As shown in Table C-8 

 is -78.2 dBm assuming 

 IN

 is 11.2 dB, the contour availability corresponding to 90 

percent covered area availability is 80 percent, is 0.85, and the shadow fade margin is 9.5 dB. 

As shown in Table C-9, and the IBRES meets its performance level objective. 

100 100

Directional

Coupler

100

1.8dB 1dB

1dB

7dB

50

4.8dB 7dB

BDA
54

Table C-6. Optimum BDA Gain 

Value (C-16) Notes

Preq IN, -78.2 dBm -78.2

Distribution network 

loss 17.8 dB

Indoor antenna gain 3.0 dB

L

14.8 dB 14.8

M p IN,

72.8 dB 72.8

Preq OUT , -73.0 dBm 73.0

GC

10.9 dB -10.9

Donor antenna gain 11.1 dB

Rooftop cable loss 0.5 dB

G

10.6 dB -10.6

GBDA opt ,

60.9 dB

Table C-7. IBRES Gain 

Value (C-15) Notes

G

10.6 dB 10.6

GBDA

60.9 dB 60.9

L

14.8 dB -14.8

GIBRES

56.7 dB downlink

Table C-8. Power required by a portable radio operated inside building with an IBRES 

Value (C-11) Notes

P

req -87.7 dBm -87.7 Dipole antenna

IN  t

9.5 dB 9.5

Preq IN, -78.2 dBm Dipole antenna

Table C-9. Power provided to the portable radio operated inside building with an IBRES 

Value (C-12) Notes

Preq OUT , -73.0 dBm -73.0 Dipole antenna

GC

10.9 dB 10.9

GIBRES

56.7 dB 56.7 downlink

 72.8 dB -72.8

 

-78.2 dBm Dipole antenna
55

The corresponding uplink link budget needed later in repeater desensitization calculations is 

, , ,

        ( ) P P G t M G L G dBm r REP t PORT PORT IN p IN IBRES fs REP

(C-17) 

where is the power received by the repeater antenna, is the power transmitted by 

the portable radio, is the portable antenna gain, and is the repeater antenna gain. 

Tables C-9 and C-10 show how this link budget can be satisfied. The repeater is assumed to have 

a tower top amplifier and a system noise figure equivalent to the portable noise figure. 

Consequently, the optimal BDA gain is that needed to achieve -103.1 dBm at the output of the 

repeater antenna. is 69.1 dB in the uplink, making 64.9 dB. 

Table C-10. Power required by repeater 

Value Notes

 

-174.0 dBm/Hz -174.0

 38.9 dB-Hz 38.9 7.8 kHz ENBW

 6.0 dB 6.0 

 26.0 dB 26.0 DAQ 3.4, Rayleigh fading

 -103.1 dBm

Table C-11. Power received by repeater antenna 

Value (C-17) Notes

 34.8 dBm 34.8 3 watts

 -13.25 dBi -13.25 Hip-mounted, quarter-wave whip

 9.5 dB -9.5 

 72.8 dB -72.8 62.5 feet coverage radius

 64.9 dB 64.9 uplink

 112.4 dB -112.4 12.4 km

 5.15 dBi 5.15 Omnidirectional, 40 degree vertical beamwidth

 -103.1 dBm

C.3 Effects of AGC 

Class B BDA ACG reduces gain when activated. The reduction in gain can potentially cause the 

received signal power to fall below what is required. In this section, we show two examples of 

how this might occur in the IBRES downlink. These examples are highly idealized in that they 

assume that channels can be evenly powered and always in use. 

Channel powers outside the building at street level and inside the building are 

POUT

 and

PIN

, 

respectively. The relationship between these powers is 
56

,

 Γ   ( ) P P G G L M dBm IN OUT c         p IN

 (C-18) 

where  is the clutter gain, is the IBRES gain before the BDA, is the BDA gain after both 

manual and automatic gain control have been applied, is the IBRES loss after the BDA, and 

 is the mean indoor path loss. 

In the first example, we show how increasing the number of channels can cause the received 

signal to fall below 

Preq IN,

 when AGC is activated. Assume there are 

n

 equal power channels 

that have outdoor powers equal to 

Preq OUT ,

. 

The power at the input to the BDA is 

,

 ( ) P P G G N dBm       req OUT c

 (C-19) 

where ( ). 

If then the AGC is not activated 

,

  ( ) G dB BDA opt

(C-20) 

and 

, , ,

( ) P P G G G M dBm IN req OUT c         BDA opt L p IN

. (C-21) 

If then the AGC is activated 

,

Γ ( )  

BDA max P P dB

(C-22) 

and 

, ,

( ) P P L M N dBm IN BDA max

     p IN

. (C-23) 

The maximum number of channels the BDA can provide is

 ( )⁄ . (C-24)
57

For the example in C.2.3 where 

 30 dBm

 -73.0 dB

 -78.2 dB

 10.9 dB

 10.6 dB

 60.9 dB

 14.8 dB

 72.8 dB

  is 114.8. If is 32 then = -36.45 dBm, , the AGC is not 

activated, = 60.9 dB, and = -78.2 dBm. If n is 128 then = -30.4 dBm, 

 , the AGC is activated, = 60.4 dB, and = -78.7 dBm which is less than . 

Table C-11 summarizes these results for a range of .

Table C-12. Gain and indoor channel power for various numbers of channels with equal input 

power. 

n (dB) (dBm) AGC state

1 60.9 -78.2 Off

2 60.9 -78.2 Off

4 60.9 -78.2 Off

8 60.9 -78.2 Off

16 60.9 -78.2 Off

32 60.9 -78.2 Off

64 60.9 -78.2 Off

114 60.9 -78.2 Off

128 60.4 -78.7 Activated

In the second example we show how one strong channel can drive the remaining channels below 

Preq IN,

 when 

n

 is less than 

c

n

. Suppose 

n 1

 channels operate outside the building at 

Preq OUT ,

 as 

in the previous example, but the n-th channel power is allowed to vary. Also, assume that the 

n 1

 channels operate inside the building at 

Preq IN,

, AGC attenuation is not activated, and 

 .

The power of the n-th channel inside the building is 

 ( ( ) ) ( ) (C-25)

and the corresponding power outside the building is 
58

 ( ). (C-26)

Any additional power would activate the AGC, decrease BDA gain, and cause the other n-1 

channels to fall below . Table C-13 shows the maximum n-th channel power allowed 

without activating the AGC. These results were calculated with the same parameters used in the 

previous example. They show a strong channel can drive the other equally powered channels 

below with fewer than  channels. 

Table C-13. Maximum 

n  th

channel power allowed without activating the AGC. 

n (dBm) (dBm)

2 -52.4 -57.6

4 -52.5 -57.7

8 -52.6 -57.8

16 -53.0 -58.2

32 -53.7 -58.9

64 -55.8 -61.0

114 -70.4 -75.6

C.4 Distance Needed to Prevent Repeater Receiver Desensitization 

This calculation determines the distance needed to separate another system’s antenna from the 

IBRES donor antenna to protect the other system’s receiver from noise desensitization. The 

estimate is worst-case because the propagation path from the donor antenna to the other system’s 

antenna is assumed to be line of sight. 

We start with the equation for calculating free-space loss between the other system’s antenna and 

the IBRES donor antenna 

 

 

 

 

 

 

(

 

 

)

 

(C-27)

where

t

p

is the transmitted IBRES noise power in the channel bandwidth at the BDA output,

i

p

is the interfering noise power in the same bandwidth received by the other system, 

t

g

 is the 

donor antenna gain, 

r

g

is the other system’s antenna gain, 

d

is the distance between the two 

antennas, and 



 is the wavelength. 

Rearranging terms, 

4

t

t r

i

p

d g g

p





 (C-28) 

or
59

20log /4  

20 1 0

G G P P t r t i

d

     

 . (C-29) 

In decibels 

0     ( ) P kT B F G dBm t BDA BDA

, (C-30) 

where 

0

kT

 is the thermal noise floor, 

FBDA

is the BDA noise figure, 

GBDA

 is the BDA gain, and 

B

is the channel bandwidth. 

Pi

 is computed from 

  ( ) P N INR dBm i

, (C-31) 

where 

0    ( ) N kT B F dBm os

, (C-32) 

10log 1 ( ) snr INR dB

sinr

 

     

,

 

(C-33) 

and is the other system noise figure. 

We have chosen an

SINR

of 23 dB which would correspond to a 3.0 DAQ for the 12.5 kHz 

analog portable radio we are analyzing. The DAQ degradation from 3.4 at 26 dB to 3.0 at 23 dB 

would be noticeable to the user. At a DAQ of 3.4, repetitions are rarely needed. However, at a 

DAQ of 3.0, occasional repetitions are necessary. 

For our example, 

Pt

 is -61.5dBm as shown in the table below. 

SNR

 is 26 dB, 

SINR

 is 23 dB, 

INR

is 0 dB, and 

Pi

 is -129.1 dBm, as is also shown in the table below. Finally, 

Gt

 is 11.15 dBi, 

Gr

 is 5.15 dBi, and the distance is 1447.2 ft. (441.0 m). 

Table C-14. Noise power at the BDA output. 

Value (C-30) Notes

0

kT -174.0 dB/Hz -174.0 

B

38.9 dB-Hz 38.9 7.8 kHz ENBW

FBDA

5.0 dB 5.0 

GBDA

69.12 dB 69.12 

0.5 dB -0.5 Cable loss

Pt

-61.5 dBm
60

Table C-15. Other system receiver noise power. 

Value (C-31) and (C-32) Notes

0

kT -174.0 dBm/Hz -174.0 

B

38.9 dB-Hz 38.9 7.8 kHz ENBW

 6.0 dB 6.0 

INR

0 dB 0 

Pi

-129.1 dBm

C.5 References 

[C-1] Telecommunication Industry Association, TIA Telecommunications Systems Bulletin: 

Wireless communications systems, Performance in noise and interference limited 

situations, Part 1: Recommended methods for technology-independent modeling, TSB88.1-C.

[C-2] S.Y. Seidel, T.S. Rappaport, S. Jain, M.L. Lord, R. Singh, “Path loss, scattering, and 

multipath delay statistics in four European cities for digital cellular and microcellular 

radiotelephone,” IEEE Trans. on Veh. Tech., Vol. 40, No. 4., Nov. 1991, pp. 721–730. 

[C-3] E.H. Walker, “Penetration of radio signals into buildings in the cellular radio 

environment,” Bell System Technical Journal, Vol. 62, No. 9, Nov. 1983, pp. 2719–2734. 

[C-4] G.B. Rowe and A.G. Williamson, “Mobile radio propagation in Aukland at 851 MHz,” 

Electronic Letters, Vol. 22, No. 22, Oct. 23, 1986, pp. 1154–1155. 

[C-5] Bird Technologies, How to properly design an In-building DAS, Part: 1, http://www.birdtechnologies.com/resources/white_papers/How-to-Properly-Design-an_In-BuildingDistributed-Antenna-System_Pt.1.pdf 

[C-6] Bird Technologies, How to properly design an In-building DAS, Part: 1, http://www.birdtechnologies.com/resources/white_papers/How-to-Properly-Design-an_In-BuildingDistributed-Antenna-System_Pt.2.pdf 

[C-7] S.Y. Seidel and T.S. Rappaport, “914 MHz path loss prediction models for indoor 

wireless communications in multi-floored buildings,” IEEE Trans. on Veh. Tech., Vol. 

40, No. 2, Feb. 1992, pp. 207–217. 
61

APPENDIX D: BDA MEASUREMENTS 

BDA gain, output power, feedback, and noise measurements are described in this Appendix. 

Unless otherwise stated, uppercase variable names are in decibels. 

The measurement test fixture is shown in Figure D-1. Principle components of the test fixture are 

a continuous wave (CW) signal generator, BDA, and spectrum analyzer (SA). These components 

are connected together by various cable assemblies. 

The cable assembly connecting the signal generator to the BDA input, A to B, includes a power 

combiner and has loss . The cable assembly connecting the spectrum analyzer to the BDA 

output, C to D, includes a 20 dB directional coupler and has loss . The cable assembly 

comprising the feedback loop path, C to B, includes a 20 dB directional coupler, variable 

attenuator, and power combiner. The variable attenuation, , can be adjusted from 0 to 132 dB 

in 1 dB steps. The feedback loop has loss when is set to 0 dB. 

Specifications for the BDA are listed in Table D-1. The BDA amplifies both uplink and 

downlink signals. It does not matter which link is used for these measurements. The BDA has 

manual gain control (MGC) and automatic gain control (AGC). The BDA did not have a 

specialized oscillation detection and mitigation function. AGC prevents the signal from 

exceeding the BDA’s FCC-certified maximum power output. For these measurements, MGC 

was set to its minimum 0 dB value and AGC was turned off unless otherwise noted. 

Spectrum analyzer settings are given in Table D-2. Reference level and attenuation are given 

with the spectrum measurement descriptions. The SA is tuned to the middle of the BDA 

bandwidth. The span is set wider than the BDA bandwidth. Video averaging is used to obtain a 

reliable noise power estimate. 

Figure D-1. Measurement test fixture used to perform BDA measurements. 

B D A

A B C

D

Signal

Generator

Directional

Coupler

Power

Combiner

x x

Variable

Attenuator

Spectrum

Analyzer
62

Table D-1. BDA Specifications supplied by manufacturer. 

Parameter Specification Notes

Frequency range (MHz) 806-824 uplink

851-869 downlink

Power output (dBm) 24 +/- 1 

Gain (dB) 60 Minimum gain at minimum 

attenuation

Gain flatness (dB) +/- 1.5 Maximum deviation from mean gain

Manual gain control (dB) 15

Automatic gain control (dB) 30 Activated at maximum output

Noise figure (dB) 6 At maximum gain

VSWR In/Out 1.5:1 Maximum

3

rd order intermodulation 

distortion (dBc) 50 Typical. Two 20 dBm tones.

3

rd order intercept point (dBm) 45 Typical. Two 20 dBm tones.

Table D-2. Spectrum analyzer settings. 

Setting Value

Frequency 860 MHz

Span 30 MHz

Resolution bandwidth 300 kHz

Video bandwidth 300 kHz

Video averaging On

Detection sample

Sweep time 50 ms

Points per trace 601 

1 dB compression point -5 dBm

A number of measurements were made with this test fixture. Measurement details are provided 

below. 

First, the cable assembly losses 

LAB

, LCB, and 

LCD

 were measured. The cabling assemblies were 

temporarily detached from the measurement fixture. The power supplied by the CW signal 

generator, 

P1

, was measured by connecting a cable directly to the spectrum analyzer. Next, the 

power through the cable assembly, 

P2

, was measured by disconnecting the cable from the SA 

and reestablishing the circuit through the cable assembly. The cable assembly loss is 

1 2 L P P   . Equation Chapter 4 Section 1(D-1)

Second, the BDA gain, 

GBDA

, was measured. The variable attenuator was set to maximum 

attenuation to eliminate feedback. Using the same methodology as measuring the cable assembly 

loss above 
63     2 1     G P L P L BDA CD AB . (D-2) 

Third, the maximum BDA output power, 

P

max

, was measured. The variable attenuator was set to 

maximum attenuation to eliminate feedback. The power out of the CW signal generator was 

increased from a level where the BDA maximum output power light was off until it turned on,

 . The maximum output power is 

2,   P P L max max CD

(D-3) 

Results for these tests are summarized in Table D-3. 

Table D-3. Results for cable assembly loss, BDA gain, and maximum power output 

measurements. 

LAB

5.5 dB

LCB

10.8 dB

LCD

21.6 dB

GBDA

64.3 dB

P

max

22.5 dBm

Fourth, the BDA output spectrum was measured. For this measurement, the signal generator was 

turned off. Feedback between the output of the BDA and its input causes two conditions: 

oscillation and distortion. These conditions are caused by an inadequate feedback loop margin 

(FLM) defined by 

FLM L G  

FL BDA

, (D-4) 

where 

  L L L FL VA CB

. (D-5) 

Table D-3, Figure D-2, Figure D-3, Figure D-4, and Figure D-5 show results of laboratory BDA 

output spectrum measurements with various amounts of FLM. Measurements for Figures D-2 

and D-3 used -10 dBm reference level and 0 dB attenuation SA settings. Measurements for 

Figures D-4 and D-5 are much higher power and used a 10 dBm reference level and 20 dB of 

attenuation SA settings and an additional 3 dB attenuator at the SA input. Power was corrected 

for Figures D-2 and D-3 with 

 (D-6)

Power was corrected for Figures D-4 and D-5 by 

 (D-7)
64

Table D-4. BDA Spectrum measurement results with AGC turned off. 

LVA

(dB)

LCB

(dB)

LFL

(dB)

GBDA

(dB)

FLM

(dB) Spectral Characteristic

53.0 10.8 63.8 64.3 -0.5 Oscillation

54.0 10.8 64.8 64.3 0.5 Distortion

69.0 10.8 79.8 64.3 15.5 Distortion

99.0 10.8 109.8 64.3 45.5 Filtered noise

Figure D-2 shows the spectrum when the FLM is 45.5 dB. The BDA bandwidth is filled with 

amplified noise across the BDA bandwidth. Table D-5 shows how the power of this noise is 

calculated. 

Table D-5. Noise power for 45.5 dB FLM trace in Figure D-2. 

Value Calculation

0

kT -174.0 dBm/Hz -174.0 dBm/Hz

Noise figure 6.0 dB 6.0

BDA gain 64.3 dB 64.3 

Resolution bandwidth 54.7 dB 54.7 

Error due to envelope detection, logarithmic 

amplification, and Gaussian filter response -2.5 dB -2.5 

Noise power -51.5 dBm/300 KHz

Figure D-3 shows the spectrum when the FLM is 15.5 and 0.5 dB. The noise at the BDA input is 

distorted in a way that produces ripple in the spectra. Distortion occurs when the FLM is positive 

but not large enough stop the signal at the BDA input from interfering with itself. The ripple peaks 

are spaced approximately 5 MHz apart. The 15.5 dB FLM peaks have much less power than those 

in the 0.5 dB FLM case; 15 dB is often recommended as a minimal amount of FLM. The shift in 

frequency between curves is most likely due to the different paths through the variable attenuator. 

Figure D-4 shows the spectrum when the FLM is -0.5 dB. This spectrum has a spike, the power 

of which exceeds 1 watt. The ripple observed in the distorted measurements is also present. The 

measurement noise floor has risen due to the increased SA attenuation. 

All the previous measurements were conducted with AGC off. We repeated the spectrum 

measurements with AGC on to see what effect the AGC has. The AGC had no effect in the 

distorted and undistorted cases shown in Figure D-2 and Figure D-3. Figure D-5 is the exact 

same oscillating BDA measurement as in Figure D-4 except that the AGC is turned on. The 

figure shows that the AGC only limits the maximum power. It does not stop oscillation. 
65

Figure D-2. BDA output spectrum with 45.5 dB FLM showing amplified noise, but no feedback. 

Figure D-3. BDA output spectrum with 15.5 and 0.5 dB FLM showing distortion. 
66

Figure D-4. BDA output spectrum with -0.5 dB FLM showing oscillation. 

Figure D-5. BDA output spectrum with -0.5 dB FLM showing oscillation regardless of AGC 

setting.
FORM NTIA-29 U.S. DEPARTMENT OF COMMERCE

(4-80) NAT’L. TELECOMMUNICATIONS AND INFORMATION ADMINISTRATION

BIBLIOGRAPHIC DATA SHEET

1. PUBLICATION NO.

TR-11-480

2. Government Accession No. 3. Recipient’s Accession No.

4. TITLE AND SUBTITLE

In-Building Radio Enhancement Systems for Public Safety

5. Publication Date

September 2011

6. Performing Organization 

Code

ITS.T

7. AUTHOR(S)

Robert J. Achatz, Roger A. Dalke, John J. Lemmon

9. Project/Task/Work Unit 

No.

6513000-343

8. PERFORMING ORGANIZATION NAME AND ADDRESS

Institute for Telecommunication Sciences

National Telecommunications & Information Administration

U.S. Department of Commerce

325 Broadway

Boulder, CO 80305

10. Contract/Grant No.

11. Sponsoring Organization Name and Address 12. Type of Report and 

Period Covered

14. SUPPLEMENTARY NOTES

15. ABSTRACT (A 200-word or less factual summary of most significant information. If document 

includes a significant bibliography or literature survey, mention it here.)

Reliable public safety communications between system repeaters outside of a building and portable radios inside 

of a building is often not possible due to building attenuation. To circumvent this problem, increasing numbers of 

municipalities are requiring building owners to provide in-building radio enhancement systems (IBRES). The 

report is intended to be used by public safety communications professionals who are tasked with assisting 

building owners fulfill this requirement. The main body describes IBRES technology, problems endemic to it, 

solutions to these problems, and its future challenges. Appendices provide detailed tables, theory, calculations, 

and measurements that support assertions made in the main body.

16. Key Words (Alphabetical order, separated by semicolons)

bi-directional amplifiers; building attenuation; distributed antenna system; in-building radio enhancement system; 

land mobile radio; link budget; public safety radio; radio-wave propagation

17. AVAILABILITY STATEMENT

UNLIMITED.

FOR OFFICIAL DISTRIBUTION.

18. Security Class. (This report)

Unclassified

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 84

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