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In-Building Radio Signal Enhancement System for Public Safety


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The following document is a guide to help understand in-building public safety radio signal enhancement systems in detail. This article is broken into several sections, but there are primarily three key points. These points are:

  1. The basic functionality of the Public Safety Radio Enhancement System including IBRES Technology and how that works within the public safety sector.
  2. Design and installation considerations.
  3. General problem and solution section.

Please note that each of above three key areas is divided into sub-sections and each section should be amply considered to understand the totality of the potential of the Public Safety Radio Enhancement System. Factors may vary slightly based on Authority Having Jurisdiction (AHJ) because local regulations vary for local in-building radio enhancement system installers of various counties, cities, and states across USA.

Acronyms you should know.

To reduce the amount of reading, standard Acronyms have been used throughout this document. The following list can be used for reference to such acronyms. Please familiarize yourself with these to dive right in.

  • AGC - Automatic gain control.
  • BDA - Bi-directional amplifier.
  • BTS - Base transceiver station.
  • CIU - Cable interface unit.
  • COAX - Coaxial cable.
  • DAQ - Diverted audio quality.
  • dB - Decibel.
  • dBd - Decibel relative to a dipole antenna.
  • dBi - Decibel relative to an isotropic antenna.
  • dBm - Decibel 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.

If additional acronyms are used in this text, they will be explained alongside the acronym being used.

Public Safety Radio Enhancement System including IBRES Technology.

The following is general information about in building public safety radio enhancement systems.

IBRES systems are primarily designed to address fluctuations in the reception, downloading, and uploading of communicative signals within a government or other public works building. As the standard for such communications mandates that 97% of the area under a sector's jurisdiction have coverage, maximizing the radio's efficiency is crucial to meeting these standards. Yet, in many situations public buildings find themselves at a loss. This can be the result of materials used in the construction of the building, the location of the building in relationship to other buildings, other radio frequencies in the area, or poor equipment.

When using an IBRES system, the owner/public building addresses the main issue, the reduction of force and effect of the signal. This is done by threading the signal along a specific path. Think of it as having a garden maze. Where most would have to walk around the maze to get to the exit, the IBRES system takes the person and places them on top of the maze, making the easiest and clearest access from point A to point B. Specifically, the IBRES uses both indoor and outdoor antennas to send the signal through a network, thus covering between 90 and 95% of a jurisdiction.

What does IBRES accomplish?

IBRES system helps to circumvent attenuation caused by exterior factors. This system is different from other options which are available. In that, it has none of the typical negatives which are offered by other options. Specifically, the loss of radio coverage is low to non-existent. Because the IBRES system is more reliable, many municipal courts have mandated that IBRES systems be in place in public safety facilities to maximize the potential for communications. However, for the sake of clarity, the other two options will be discussed below.

Option 1: The Higher Site.

Some facilities have opted to using repeater antennas located at higher ground throughout the jurisdiction. The repeater can span a large metropolitan area. On the surface this may seem to be a viable solution to weak or radio frequencies. Yet, one will find that such an option tends to reduce the overall dBm. In testing by the NIST, it was shown that there could be a fluctuation of as much as 8 dB. Additionally, using the high site repeater method does not allow for ample signal strength in lower levels and basements. Thus, a secondary method of amplification of the radio signal would be necessary.

Option 2: Direct and/or Simplex communications.

Primarily, this method uses direct communications between private radios and communication equipment on dedicated frequencies. This does allow for communications within the facility without the need for a repeater. However, the main problem which arises from the direct frequency method is that public safety communications outside of the building do not have the communication. The probability of a total lack of communication between various persons, especially in relation to outdoor and indoor radio signal strength is high.

Keep in mind that the radio frequencies are typically established on some small portable devices. And while the repeaters may be ample for the small coverage area, the loss of signal strength will tend to shift based upon where the person is within the building. Secondly, as stated previously, communications between the outside and inside may become lower or non-existent.

NIST, after performing several comprehensive measurement testing on various buildings with various repeater and attenuation reducing methodologies, has determined that IBRES system is the best means of circumventing the attenuation without the fluctuation which is mentioned in the two prior options. This is greatly due to the BDA, which provides the needed amplification radio wave losses.

The reliability of IBRES.

IBRES systems have nearly 70 years of development in the technology. It has been suggested that the technology may even pre-date the 1950s. The main contributions to the technology include the improvements made for miners as well as the 1980s upgrade to the technology, a need brought on about by the development and wider popularity of cellphones. It can be deduced that with the ever-evolving technology surrounding Smartphones, that the IBRES system will be fine-tuned and updated as technology progresses. BDA, because it is a key point of IBRES, therefore is updated alongside it.

BDA Explained.

Like all boosting options, the main purpose of the BDA is to amplify the signals in an area to allow for optimized radio communications between various parties. BDAs differ from repeaters in that they do not shift frequencies, requiring those using the radio to shift the frequencies/channels as well. Instead, the BDA transmits the frequencies on the same transmission. This is accomplished by sending the signal from the indoor antenna to the donor antenna.

BDA is based upon MGC. Yet, as more technology becomes automated, there's a chance that the gain set can be regulated and manipulated by computer. The BDA's intent is to optimize the gain based upon the input of all of the signals. Usually, BDA equipment is set to the lowest setting by default. However, based upon the radio signal needs, the signal amplification, gain, and other factors may need to be adjusted. AGC may be used for the output of power and where other considerations to the loss of value are concerned.

BDAs are, per the FCC, considered to fall into two categories. These categories are either Class A or Class B. There is an option for a customized channel, but such an option should only be attempted by someone who knows what he/she is doing.

  • Class A - does not cause interference with other systems amplification by filtering and amplifying a specific channel. It is a way in which to hone in on a selected frequency without causing harm to surrounding areas using IBRES/BDA amplification techniques.
  • Class B - amplifies an entire selection of signals. By increasing the band, there is a chance that the surrounding area, especially if the area is running upon the same band settings, may experience interferences.
  • Custom Channels - Usually based upon customized software algorithms. Dependent upon the type of software, the equipment, as well as the algorithm written, it may be possible to have the band amplification while retaining the properties of Class A (meaning that there is no interference with surrounding bands/channels which use BDA). Again, this is not considered to be one of the two classifications of the FCC, but rather a hybrid of the two classes. When using Custom channel settings, you will need to check for approval with not only the FCC but also with any network service provider associated with the radios or other communication equipment.

Please note that there's a chance when using BDA/ IBRES systems that you use will have some variation in intermodulation. This could cause some relay discrepancies with public safety radio enhancement. For the best results with your IBRES, try to minimize the non-linear amplification from BDA gains. Remember that the FCC regulates signal amplification and repeaters/ retransmissions. Therefore, it is imperative that you have an FCC licensed professional conduct the install of your equipment. Should you have any questions about FCC compliance, contact the FCC directly.

Of course, for the BDA to be effective, the correct cables and antenna must be used. This next section will focus on the three types of cables which are often used in amplifiers, repeaters, and IBRES amplifying equipment.

Cables/ Distribution Network of the Public Safety Enhancement System.

Responsible for the distribution networking of antenna to the enhancement system are the cables. These cables are the tie between the BDA and the interior antenna components. Each antenna, within the location, must have the appropriate cable connection in order to maximize the functionality of the Public Enhancement System. Cable components allow for the coupling, splitting, merging, and the enhancement of signals.

Generally, a COAX cable is used for any connections between the BDA and antennas. The main factor for this is that the COAX cable can transmit on a narrower bandwidth than the other cable options while still operating at a frequency that allows for maximum strength. Yet, there are times when other cable types can be used or should be utilized. Therefore, an explanation of the three main cables is show below:

  • COAX cable - Coaxial cables are universal in their use. They are made of a central conductor wire that is insulated and protected by copper meshing. Entire wire is then protected with rubber. As with most wiring, there're a few different guages. The most common COAX for public enhancement systems is the 12.7mm or ½ inch wire. When connecting the COAX cable, installers should try to minimize the overall length of the connection between the antennas, as the average loss is around 4dB per 100 feet. Note that even though an in-line amplifier can be used, due to the FCC regulations as well as the overall construction of the COAX cable, such inline signal amplifiers may be limited in signal strength enhancement. If not slightly more, they may definitely compensate for signal loss due to extensive cabling through interiors of the building.
  • Fiber-optic Cable - A bit different from the COAX cable, the fiber optic cable is made of light fibers used in layer to build strength within the wire housing. The FO provides more flexibility than the COAX cable, but this is not necessarily a benefit. Because the fibers are so thin, excessive bending could cause the fibers to break, thereby reducing the overall performance of the wire and increasing noise. Typical FO cables used with Public Enhancement Systems for Public service are 4.34 mm or 1/6” diameter. The main advantage of the FO cable is that there's low loss in the bandwidth. They do not see the same interference as other cables when it comes to RF. Typically, FO cables are used in facilities which require a substantial length of cable, allowing for distribution of the signal to large areas or multiple buildings. The multiple wires in the FO cable allow for flexibility, but it also makes the wire more susceptible to breakage. 
  • Twisted-pair cable - As the name suggests, the twisted pair cable is a pair of cables which are interwoven. In most designs, the TP cables are wrapped in a protective layer. Since there's a protected layer on its exterior, you can find both a shielded and unshielded wire. Shielded, of course, would have the protection around the wires inside of the protective layer, while unshielded would not. Identifying the proper cable is based upon a category identifier. Based upon the category (for example Category 6 TP can be used to transmit 125-250 MHz), as well as the length, the frequency may be able to amplify reception. Note that TP wires cannot be used by computer networks already using a cable. Generally, the TP is used for computer networks over an air-transmission network.


Perhaps the main core of the public safety enhancement system are its antennae. Depending upon the type of antenna that you get, amplification will vary. There're a few different antennas available. Those installing an antenna should pay attention to the direction, the cable, and other requirements of IBRES system. Each part builds off of the other. Here's a brief overviews of one type of exterior antenna:

Exterior antenna.

A Yagi antenna is an exterior antenna which is used for directional transmission of signal. The Yagi Antenna is the main source of compensation for weak signals. It is this antenna which is placed using the higher ground option or the multiple placement method mentioned earlier. When placing an external antenna, the IBRES designer will consider the gain, beam-width, front-to-back ratio as well as the other donor antennas in the area.

Though there's ability to install such antennas on buildings and in jurisdictions independently, it is more commonly found that these types of antenna are used alongside power lines and poles. This placement, especially for governmental services allows for a continuity in the equipment layout. The length of the "prongs" is dependent upon the model type and the amount of gain needed for the area. Other types of exterior antennas include omnidirectional antennas which are simply referred to, as "omni antenna".

Interior Antennas.

To have a functional public safety enhancement system, you need to have both an external antenna as well as an interior antenna. Both of these must be connected using COAX cable or the correct appropriate wiring. Generally, interior antennas used for such systems are Omnidirectional antennas. Antennas are made of the COAX cable connection, the ground plane, and the monopole antenna. The main reason behind the omni-directional antenna is that the antenna can broadcast at a 360 degree azimuthal beamwidth.

Such interior antennas referred to, as "dome antennas" are usually mounted on the ceiling. As such, the materials of the ceiling space should be considered as these can influence the amount of gain that the antenna is allowed to transmit/produce. Additionally, when mounting an interior antenna, it will need to be in a place where the signal can relate back to the exterior antennas with minimal obstacles (in other words it would not be beneficial to try to hide the antenna behind signage, exit signs, etc.). Although there're multiple components within the omni-directional antenna, many times the unit will be enclosed like a dome.

Design and Installation Considerations.

FCC regulations state that a licensed FCC installer must perform the installation of any non plug-in-play (non-commercial grade) signal boosters. Additionally, boosters, enhancement systems, and repeaters must be registered with the correct parties, mainly with any network providers and nearby networks from which the signals may be dependent upon. FCC operators and installers must adhere to the standards and guidelines set forth by the NPSTC, FCC, ICC, and NFPA as well as local building and zoning ordinances.

National Public Safety Telecommunications Council (NPSTC) standards are slightly different from the other regulating parties. NPSTC specifically focuses on telecommunication policies which are focused on the public safety sector. These policies are oriented to the organizations and the companies which produce the equipment and the enhancers needed to maximize radio signal strength. For those seeking to enhance the communications within their building, sector, or jurisdiction, it is strongly recommended that the CEO, COO, or communication representative read the latest publication from the NPSTC for standards and suggestions concerning IBRES systems.

While the FCC and the NPSTC, as well as other global regulation authorities, have the last say on policy, local governments can also make legislation for IBRES systems. Such regulations could determine whether existing public buildings are "grandfathered" into current policy, or if the buildings will need to undergo a communications renovation. Additionally, local governance will determine if outside of the building needs to have an IBRES system or enhancement equipment present or if only the interior and critical areas should have such.

Does your public safety building require IBRES?

IBRES enhancement equipment is not mandated on all facilities, but all buildings can benefit from such. It is the responsibility of the public service to know the standards of the local government to determine whether an IBRES system is needed. Please note that IBRES are not a universal fix for public safety enhancement systems. For example, firefighters may note that the wiring in the IBRES systems is susceptible to heat. This in turn drastically reduces the longevity of life on the devices being used. Therefore Plenum cables and wires can be used throughout the system, not only through Plenum spaces and pathways. And while many jurisdictions still require the IBRES system for firefighters, others have opted to using communication devices which are less susceptible to heat.

Common design features of an IBRES system.

IBRES systems have BDAs and CIUs, typically. These two elements are vulnerable to power outages. Therefore, most of the designs for the IBRES systems use a primary external power or have a back up battery to minimize the risk for loss of communications due to power outages. Municipalities may have codes and standards to minimize the impact of power outages on IBRES systems. When trying to determine the layout of your IBRES system, it is crucial that you have a spectrum survey performed, that you measure the gains and other existing information, and that you take into account the materials, frequencies, and other influences of the area.

Due to the advancements in technology, designs for IBRES systems are made using CAD software such as iBwave which is an In-building wireless network design planning and deployment solution. Analytics as well as sustainability testing within computer-aided programs allow for a level of pre-fabrication testing to be performed. Furthermore, the CAD software can help to test the interactivity between components of the IBRES design.

Installation requirements.

Most local as well as state codes and standards for public safety enhancement systems for public safety locations require that a certified technician install the equipment. But where and how are these technicians certified? Generally, the certifications come from the equipment manufacturers. Note that these are the manufacturers and not the distributors. Even when the IBRES equipment is installed, it must be inspected by a regulation party to ensure that it is compliance with code.

To gain compliance, a radio system coverage test must be performed on the IBRES system. This test is like CPC test used by other telecommunications networks. Yet, it varies in the way in which things are conducted. Cells must be present on floors, coverage is based upon the cells and coverage availability, additionally the coverage must reach a certain percentage. As stated at the beginning of the document, most requirements would place the percentage at 90% for non-crucial interior areas and 95% for places of high importance.

While there are several factors which contribute to the compliance of the IBRES system, or lack thereof, the number of floors, the materials, as well as the COAX connection between the Yagi Antenna and omni-directional antenna (and other equipment) will be the key factors. The more floors, the more COAX cable will be needed and the more apt the probability for dB loss. In-line amplifiers would help compensate for attenuation due to extensive network of cabling to distribute interior antennae. Nevertheless, if the building has multiple interior antennas, connected properly, the attenuation may be reduced.

Common Problems and Troubleshooting.

Feedback or Oscillation.

Feedback can occur on IBRES systems which have BDAs. Because BDAs transmit what they input, there is a high probability that any feedback which is obtained on the channel/band, will be replicated in with the BDA based IBRES. Unchecked feedback can quickly become a communication nightmare. As feedback can cause oscillation or distortion, it is imperative to have the FLM in the positive.

Due to the portable radio's main functionality, the retransmission of the signal may vary. Though it is rare that feedback will cause outages on BDAs deployed correctly, there's a minimal margin of such. Typically, however, if there is an outage due to the BDAs on the IBRES system, they are due to substandard equipment and should be replaced. Another solution is to conduct another signal test and reposition the interior antennas.

Opening the doors near the indoor and outdoor antenna may also help with communications. However, this may not be a feasible solution, especially in public safety buildings where security is a primary function (such as police stations).

Gain reduction.

If a system has a Class B BDA, there's a risk that the signals which are broadcast with have too much gain. As the Class B BDAs transmit all signals within the bandwidth/channel, it is quite possible that there would be too much amplification to the signals, basically causing a communications overload. Also, if too many channels are amplified, the needed gain may not occur. To fix this situation, try to avoid engaging the AGC. The easiest way to keep the AGC from engaging is to either (A) switch the BDAs to a class A, which makes it possible to focus on a dedicated frequency (though not without its issues, see above) or (B) to move the antenna in another direction and manually filter the signal for optimal performance.

Noise Transmissions.

If a system is experiencing noise transmission, it is generally caused by an outside antenna rather than inside antenna. However, if the interior antenna is improperly mounted, or if the antenna is mounted to a conductive material, it could result in noise transmissions. When noise transmissions are a result of the IBRES donor antenna, desensitization can occur. To fix noise, try to reduce the gain as much as possible. This can be done through filtering the channels, switching the channels, and by repositioning the outside antenna. Should you have other public service IBRES systems in the area, point the antenna away from that system for the best results.


Delays on an IBRES system are the result of poor cables relating the signals from antenna exterior to the antenna interior. Typically, the result of a delay is due to improper type of cable. For example, a COAX cable could be used instead of a fiber-optic cable. If the correct cable is used, it could be the result of a damaged wire. For example, if a fiber-optic cable has been used, one of the layers may have become damaged or crimped, therefore causing the delay. The solution is to increase the power to the indoor antenna. This may be accomplished by re-wiring the connection, by ampling the power safely (ask the equipment provider which power options are safe for the radios and public service equipment). Also, consider using a directional antenna mounted on the wall between the external and interior antennas, making sure that the antenna is on the repeater, booster, site.

Radio-Wave Propagation.

Radio waves are unpredictable due to both interior and the exterior elements. Building materials, other buildings, trees, other frequencies, furniture, and vehicles can all factor into the radio waves behavior. It is therefore paramount to your equipment that you measure the coverage after the installation of your IBRES system. Keep in mind that the more interior antennas that your building has, the more apt the building and the public equipment will have of maximum communication signals. Floorplan locations help, but abundance in the antennas has proven to be more beneficial in radio-wave propagation evenly throughout the building.

Closing Remarks.

IBRES systems can help to increase the amplification of radio waves and signals within the public sector. These systems may be mandated by the local municipals. If not, public service buildings should strongly consider such an enhancement system to increase the communications and the functionality of their public safety sector. While the systems may seem to be simplistic in nature, much designing and technological thought has been given to the optimization of public safety communications.

When considering an IBRES system always check with both the local as well as the state ordinances for regulations. Additionally, contact the FCC should you have any concerns about installation and use of an IBRES system.

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