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Radio System Selection Strategies


The procurement and implementation of public safety radio systems has grown in cost and complexity as radio systems have evolved over the past 70 years. As the value of radio communications has proven itself over time, both private and public sectors have sought solutions to handle more users - each with ever increasing coverage and reliability objectives. Such growth exploded during the 1970-80s with the advent of reasonable hand-carried portable radios.

The complexity of today’s radio technology is such that user agencies/owners often seek guidance from those having real world experience in the design, implementation, testing, and maintenance of these advanced solutions. Yet, the owner is the one who makes the final decision in procurement. Theirs is a truly difficult job.

What follows is information that could help make this “once in a career” decision a bit less difficult. Of course, ours is not an exhaustive treatise on the state of public safety radio communications as that job is best shouldered by those retained to determine operational user needs and expectations. This paper is designed to coach those who have undertaken procurement steps, have received vendor proposals and are now in the process of evaluating and assessing solutions as offered. Our goal is to provide focus on those aspects of a radio system procurement that are critically important to agency users and, in the end, help you peel the layers back and bring light to what some might call Unknown Unknowns. Let’s begin.

Coverage

The single-most important aspect of any public safety radio system is coverage. And coverage is principally a function of the number of infrastructure tower sites, site geographic placement, site-to-site backhaul connectivity, and the radio technology employed at those sites. In the United States, public safety radio systems are aggregated into the following frequency bands: VHF (150-170MHz); UHF (450-512MHz) and 700/800MHz.

Each of these three spectrum allotments have unique signal propagation characteristics. As the frequency increases, free-space propagation losses increase by 6db as frequency doubles. So, UHF experiences 6db more propagation loss than VHF. 700/800MHz, correspondingly, sustains 12db additional free space loss as compared to VHF. A person having just a fundamental understanding of radio technology might assume that a VHF radio system would provide universally better coverage than either UHF or 700/800MHz solutions, but depending upon intended use that could be a grossly inaccurate assessment. Here’s why.

Noise Floor

The ability of a radio system to detect weak incoming radio signals, as is often the case from those operating hand-carried portable radio equipment, is limited by the intrinsic electrical nose floor resident at each tower site. Noise power density is inversely proportional to operating frequency, so systems

operable at VHF would typically encounter a higher noise level than those operable at UHF and significantly higher than those operable at 800MHz. As an example, if a tower site receiver system can potentially detect a signal as low as -120dBm but the actual noise floor is, say -110dBm, then the incoming signal must overcome that 10dB difference merely to be heard. Or stated another way, the receiver site is desensitized by a factor of 10dB. Thus, the incoming signal would have to be 10 times higher than normal to be detected by the tower site.

A site’s noise floor directly impacts coverage potential and must always be considered in a radio system’s design. Obviously, this consideration is far more acute for VHF radio systems as compared to 700/800MHz as at those higher frequencies the noise floor is usually extremely low. An inexperienced radio system designer might easily overstate VHF coverage via predictive modelling tools when knowledge of actual noise floor conditions at design sites is unknown or ignored. That ignorance results in costly redesign work, ineffective delivered radio coverage, and highly disgruntled radio users.

User Coverage Expectations

The service area needed by clients is highly understood/defined in order to select the most appropriate coverage solution. For example, a petrochemical pipeline operation might require on/off road radio coverage over areas that can encompass thousand square miles. In that instance a VHF radio system based on mobile operations is a good, time-proven solution. This works because the tower sites would likely be located in rural areas and well away from electrical noise producing sources. In that case, the tower sites would function with little degradation weak incoming radio signals.

Yet, if building portable unit coverage is the principal requirement (which is typical for municipal public safety operations) then use of 700/800MHz or even UHF would provide material coverage advantages. Sure, the propagation losses at higher frequencies are a consideration, but these are offset by use of higher gain tower site antennas (higher gain can be achieved due to size reduction as frequency is increased) and tower-top mounted receiver preamplifiers that overcome transmission line losses.

The likely question you may have is: “If tower-mounted preamplifiers can improve UHF or 700/800MHz system performance then can that technology also be applied to VHF?” The short answer is “No”. The reason has to do not so much with technology but the FCC’s frequency planning/channel assignment process applied to VHF operations.

When radio spectrum was first allocated to users by the FCC, the VHF band was first. During the 1940s-50s, all such operations were simplex…meaning that user-to-tower/tower-to-field communications were confined to a single radio channel. In the 1960s radio manufacturers had begun to field hand-carried portable radio devices and, due to their low transmitted power levels, a means to extend their rather limited range was developed using two actual channels and a new device termed repeater station.

The repeater station was located at the normal tower site where a distant filed unit would transmit to the tower site on one channel and receive on the other. The repeater station would simultaneously

rebroadcast all incoming traffic on its outbound channel. This is termed duplex operation since two actual radio channels are used to sustain communications rather than just one. The net effect of duplex operation was that field portable radios would gain the same talk-out coverage range as the repeater station with its optimally placed antenna and higher radiated power…but only if the low power field unit(s) could be detected by the repeater’s receive channel.

Today, most county and all municipal public safety agencies utilize portable radio devices. It is these low-powered units that set the design goals for talk-in (field unit-to-repeater/base station) tower sites. Further, these low-power units directly influence both the number, placement and configuration of radio tower sites as it is these sites that provide measurable coverage potential. Of course, Police/Fire and EMS operations routinely occur within building structures. The size, density and materials used to construct buildings present additional propagation losses that must be overcome by the tower placement/antenna system design in order to maintain reliable radio coverage. This is a key design element in any portable-based radio system and one that must be well understood by the system’s designer(s).

Adding further complication to the in-building design process is how the users intend to operate their equipment and related ergonomic requirements. When a portable radio is operated at hip-level using remote speaker/microphones, then the design must include high body losses for both the talk-in/talk-out instances. Yet, if no speaker/mic used, then the designer must consider high body loss for receive (talk-out) since the antenna is at hip-level, but a lesser loss when the radio is brought to head level when talking back to the distant tower site(s).

A related consideration involves the antenna installed on the portable unit, itself. Radio size has become a major consideration for public safety agencies and so the trend Today is the use of small, compact ¼ wavelength antennas. At 700/800MHz such an antenna is around 4 inches in length. While longer ½ wave antennas might provide better performance, they are an operational nuisance…plus it seems functionally inconsistent to field a radio package whose antenna is twice as long (if not longer) than the radio itself. A far better solution (and one popular with end users) is to field the smaller ¼ wave portable radio antenna and then accommodate portable radio inefficiencies at the tower-site configuration end of things.

Spectrum

Radio frequency spectrum is the “real estate” needed to construct radio communication systems. The VHF/UHF radio spectrum Today is highly congested and so is principally employed for regional and statewide radio systems as a means for achieving the greatest mobile unit coverage for the least cost. That said, most new radio systems for counties and municipal areas are constructed using 700/800MHz spectrum for the following reasons:

  • Large numbers of channels available for assignment consideration as compared to either VHF or UHF.

  • Supports trunked radio operations with minimal co-adjacent channel interference.

  • Lowest intrinsic noise floor as compared to other bands.

  • Allows use of tower-top preamplifiers for improved portable unit support.

  • Provides superior in-building coverage with fewer dead spots via use of receiver voting and transmitter simulcast technologies.

  • Allows for use of small portable unit antennas.

Statewide radio systems have been constructed using all 700/800MHz technology, especially in areas where large numbers of populous cities/counties exist. Yet, mixed-band radio systems have become popular where the coverage region includes large expanses of rural undeveloped areas. This integration of discrete frequency bands has become common place as manufacturers now market user portable and mobile radio products that are no longer restricted to merely one frequency band.

When reviewing vendor responses to RFP procurement specifications, an important aspect to consider and question: Is the radio system as described by the vendor’s proposed design licensable and constructable within the allotted time frame? In the case of 700/800MHz system designs, these each must first be reviewed and approved by the State’s Regional Planning Committee or RPC. The Committee then looks to the number of radio devices being procured and verifies that that number complies with FCC per-channel capacity and project completion requirements. Finally, the technical aspects of the design – principally those aspects involving coverage and FCC required co-channel/adjacent channel protection levels – are confirmed and modified by the vendor where necessary.

Where radio systems are proposed for construction in either the VHF or UHF spectrum, proceed with extreme caution. In either of those bands, the FCC offers no interference protection except for cases of intentional harmful interference. Even then, resolution of intentional interference cases by the FCC is a slow, difficult, and expensive proposition. And also, VHF radio systems are highly susceptible to receiver noise degradation at infrastructure tower sites. A VHF project’s procurement specification should always include a requirement for vendors to conduct noise floor evaluations of all infrastructure sites included within their proposed solution and, more importantly, to include those result findings within modelled coverage predictions.

It is important to question the placement of tower sites and the radiation patterns of antenna systems included in the design as these affect coverage reliability not only within the required service area but also their potential to cause outside area interference to others. Be especially cautious whenever a change in antenna pattern, antenna height or site placement is required as these could diminish or degrade the coverage necessary for the radio system to be accepted by its many user agencies.

Be suspicious of proposed tower site locations near county jurisdictional boundaries. Keep in mind, the construction of trunked radio sites is an expensive proposition, often nearing $1,000,000 per location. Is it the best use of funding resources to locate sites in areas where as much as half of the coverage potential from one or more towers must be eliminated (using highly directional antennas) to protect a next-door neighbor? Other alternatives may exist that make for better utility of tower sites.

Acceptance of design changes automatically implies the owner’s acceptance of potentially degraded coverage from that originally proposed. If such a design change is necessary to gain FCC licensing, first

secure a revised set of coverage maps from the vendor that depicts coverage with the new design and identification of areas that are predicted to have coverage that is diminished from what was originally proposed. Failing to understand the pros/cons of any site location change can result in costly project change orders and completion delays as the project unfolds.

Predicted Coverage Results

A critical and, frankly, the most important set of components within a vendor’s proposed radio system solution must include:

  • The design’s predicted coverage, inclusive of service area covered in square miles.

  • The guaranteed percentage of reliability implied by the supplied coverage maps.

  • The statistical accuracy of the design, in the form of a percentage of confidence.

  • The Delivered Audio Quality, as defined by TSB-88 () for mobile, portable on-street, and portable on-hip user radio configurations.

  • In-building coverage maps for loss factors of 6dB, 10dB, 15dB and 20dB.

  • Technical parameters1 used in developing the coverage predictions.

  • Time Delay Interference mapping for all simulcast transmission solutions.

When evaluating supplied coverage maps, cautiously inspect and consider the language used to define each map submittal. For example, an RFP technical specification may require 95% service area coverage. A responding vendor’s supplied map(s) may indicate “95% coverage” and thereby imply RFP compliance… but often that 95% applies only to the areas indicated as ‘covered’ on the map. Further, that “covered” area might be well below the user’s actual service area. So if the covered portion is indicated in, say, the color green, then all areas NOT covered in green would not guaranteed as covered --- and within those green areas as much as 5% could fail a project’s acceptance coverage test.

Vendors playing games with numbers is not so uncommon. For example, a county requiring a new radio system might have a jurisdictional service areas of 500 square miles. A vendor’s set of coverage maps could indicate ‘95% coverage’ but only for its predicted area of 420 square miles…which would be far below the county’s actual requirement. Perhaps an honest engineering mistake or a subtle attempt to lowball the project’s cost?

Here's another angle to consider. If a vendor’s supplied coverage maps are inclusive of the required service area, yet the statistical confidence of the model’s prediction is only 85% and not 95% or greater, then how much stock can be reasonably placed in a claimed 95% covered area submittal? Not much.

While it is important to understand the coverage provided by a design, from these examples it is far more important to understand what specific areas are likely to have degraded or no coverage. If the vendor’s predicted coverage is below what was required by the project’s procurement specifications, then the design should be graded down or, in cases where coverage is grossly underserved, rejected as unresponsive.

Here's an important sanity check to consider: Proposed coverage solutions by responsive vendors should correlate to conceptual solutions developed by the owner’s consultant during the needs assessment/solutions project phase.

Consultants utilize propagation modelling tools that, like for vendors, conform to approved Industry practice and process (EIA/TIA TSB-88). If a vendor’s submitted proposal solution include many more or many fewer sites than predicted by the consultant’s team, then a rigorous examination, inclusive of the consultant’s independent modelling of the vendor’s design while using approved gain/loss factors, should be undertaken as a ‘design sanity’ check.

System Reliability

As one owner once eloquently stated: When the situation is at its worst, one’s radio system takes center stage”. Hurricanes and ice storms routinely wreak widespread havoc on electric utility services and commercial cellular/telecommunication services. Yet, public safety radio systems are expected to work under those harsh environmental and crushing mutual aid capacity situations. System reliability must be designed into each design. Doing so results in both added infrastructure complexity and higher cost but is the public’s expectation.

The best procurement specifications call for the following:

  • Towers, antennas, and related appurtenances must minimally comply with EIA-222’s requirements for mission-critical/life safety radio services. For coastal regions susceptible to hurricanes, a wind survivability rating of 150MPH should be the design minimum.

  • Utilization of DC power systems with battery plants sized for 8-hours of uninterrupted operation.

  • Utilization of standby electrical generators, ideally configured for either natural gas or propane fuels. Diesel fuel is appropriate for manned facilities but must be properly maintained to eliminate the potential for fuel contamination.

  • Installation of ice shields, as necessary to protect microwave antennas, transmission lines and ground-located equipment.

  • Shelters, generators and fuel tanks should be elevated in accordance with FEMA flood elevation maps plus a 2-foot added contingency.

  • Equipment shelters should be configured with dual HVAC equipment and also an auxiliary fresh-air fan system.

  • Utilization of loop-protected, monitored hot standby microwave linkages for tower site connectivity. NEVER rely on commercial wired or wireless broadband connectivity services as a primary site linkage medium.

  • 11GHz linkages are appropriate only for path segments less than 5 linear miles. 6GHz linkages longer than 14 linear miles (particularly those near to large bodies of water) should employ antenna space diversity, frequency diversity, or both.

  • 40db flat fade margin for all microwave path segments. In combination with adaptive modulation such a design affords the best possible protection against atmospheric signal fading.

  • Cloud-based control and interoperable communications are potential system/network failure points. Keep in mind: loss of commercial broadband connectivity means a very bad day for cloud computing.

  • Geo-distributed trunking and simulcast control equipment allows for continued radio system availability should one or more radio sites sustain catastrophic failures.

  • System loading should never exceed 50% utilization during normal operations. The added “headroom” is necessary as during emergencies many more radios than normal will likely become operable on one’s radio system.

  • Queuing should rarely occur. Best practice for a public safety radio system is for a call blocking rate of no greater than 0.5% with call conversion to occur within 1.5 seconds.

A rigorous maintenance program for all elements of a radio system’s infrastructure is required and should be part of the procurement strategy. More importantly, whenever outside maintenance services are part of a procurement, it is essential that the work performed be reviewed by an independent party to ensure both the quality and effectiveness of the work. All maintenance service agreements should include adequate response time targets and, more importantly, financial penalties if a vendor’s response is contrary to their contracted agreement. Paying maintenance invoices absent proper oversight risks both waste of fiscal resources and is recipe for an unscheduled system failure.

User Equipment

In today’s landscape of Project-25 technology from multiple vendors, the industry has adopted a means to verify the features, functionality and operability of user radio devices, meaning portable and mobile radio equipment. The equipment provided by Today’s manufacturers is rigorously tested upon first development/introduction to the marketplace and as new software features are released during its life cycle – all to ensure that user radios can operate on any Project-25 trunked radio system.

The major differences between user radios today principally involve ergonomics, non-P25 recognized features, and talkgroup/channel capacity. Electrical parameters such as receiver sensitivity, power output, stability, etc. --- those that impact one’s ability to communicate with radio tower sites --- are on equal footing, across all major manufacturers. The realities of competition are always at play and help to level the field.

Most public safety agencies are sensitive to the size of radio devices. So, the trend is toward smaller radio packages and smaller antennas. Thus, coverage become a function of tower site placement, the number of infrastructure tower sites, and the types of transmit/receive antenna systems deployed. While ergonomic features are always an important consideration in user radios, coverage and capacity is provided by the system’s infrastructure – not the user radios – and remains the absolute most important consideration.

Many user agencies question the need for mobile radios if the radio system’s infrastructure is designed to support low-power portables. Yet, mobile radios continue to be deployed for one important reason: officer safety. A police or fire user might lose or damage a portable radio in the course of work, but can still communicate and request assistance if a vehicular-mounted mobile unit is available. Resist calls from administration leaders to save money through eliminating mobile radios…your success here could save someone’s life.

Owner vs. Vendor Responsibilities

Many county and municipal radio procurements are “turnkey’, meaning the successful vendor/contractor bears responsibility for the functionality, operability and installation of the project. This turnkey responsibility extends to materials and work provided by subcontractors or suppliers working under the Contractor’s project umbrella. If the Contractor failed to include materials or costs to complete some aspect of its project, that cost is borne by the Contractor, not the owner.

Projects of this sort place added risk on the Contractor, which is why the costs of such projects are typically higher than if the owner was to shoulder some of the burden. From a project management perspective the turnkey approach minimizes the risk of improper coordination across subcontractors and should (if, again, proper oversight is maintained) result in an accurate, expeditious project completion.

When evaluating proposal submittals, it is important to review the proposer’s delineation of owner versus contractor responsibilities. Simply because a proposer claims to accept turnkey responsibilities, some will attempt to dilute some by gradually shifting pre-requisite tasks onto the owner. If this occurs, the evaluation team should consider those task transitions as proposal exceptions -- and downgrade them accordingly. Keep in mind, exceptions taken by proposers are undertaken to enhance their profitability…but that could easily result in a substandard project result for the owner. Further, such exceptions have the silent potential of degrading competing proposals as submitted by others. Those competitors may be seemingly more costly as each is merely providing many if not all of the services (while absorbing all the performance risk) required by the owner’s procurement’s specification.

A ‘low-ball’ proposal whereby tasks or services are reflected back onto the owner saves the owner nothing. More often, the net result is a conga line of Contractor-initiated costly change order requests – usually for items/tasks that would be routinely shouldered by a project’s Contractor. The fundamental principal behind a turnkey project specification is to eliminate Contractor-initiated change orders. In fact, change orders necessary within a turnkey project should be only for those additive materials, equipment, and services not originally required by the owner.

Interoperability

The process of agency interoperability within an owner’s trunked radio system has never been easier. Today’s user radios, even for the lowest tiered models, have sufficient flexibility to include cross agency/wide area talkgroups for special events and emergency situations. The process of providing interoperability with outside-area districts is more complex and costly.

Most states now operate trunked radio networks, and it is these that can be leveraged to provide outside area interoperable communications. Where the owner’s and the state’s radio technology are via a single-same vendor, the process becomes one of P25 core sharing and operations-based mutual aid agreements. Where the radio systems involve disparate vendors, then the P25 standard allows for Core-to-Core connectivity through Inter-RF Sub System Interconnectivity technology or ISSI.

ISSI allows for provisioned radio users to operate on one another’s radio systems and still retain connectivity with home dispatch resources. Yet, ISSI connectivity requires core linkages via leased Ethernet broadband carriers or by privately owned microwave/fiber facilities. In addition, interfaces are needed at each vendor’s core to support the ISSI gateway connection. And, all of these resources require operational maintenance and management for continued, reliable operations 24/7/365.

A new service offered by at least one vendor is a “cloud based” ISSI subscription service. Here, the ISSI component is resident with the vendor and connectivity is likewise provided as a hosted service. The cloud ISSI service has the advantage of its management and maintenance being provided as a turnkey package. The disadvantage is that cloud services are an ongoing expense and, with respect to reliability, are functional only if its broadband connectivity component remains operational – unlikely during hurricanes or ice storms where commercial services of that type are frequently disrupted for extended periods.

Keep in mind, not all features within a trunked radio network/system’s portfolio map across ISSI gateways. For example, emergency activation features on one may not be fully available on an ISSI-linked configuration. And, due to gateway capacity limitations, not all talksgroups can or should be mapped via ISSI. In fact, a well-designed interoperable solution should be layered and include:

  • Shared across-agency talkgroups.

  • Integrated P25 base station gateways.

  • Console patching features.

  • Regionalization within groups of counties, where appropriate.

  • Leverage of state wide-area radio network resources, where feasible.

Closing Thoughts

Clearly, there are many potential traps one might encounter while selecting a new public safety radio system. Those cited here are merely the one’s I’ve uncovered in my 40+ year career. The good news is the system engineers and technicians assigned to contracted projects are a generally sincere lot and want to do a good job – for both their employer and customer. You see, their technical acumen is viewed through a different lens - in direct proportion to the number of deployed systems that fly through a Customer’s project acceptance test structure, intact and on-time. Yet, a vendor’s sales and project capture team’s success and value is assessed far differently: WINS – skins on the wall.

The capture team’s job is to get the vendor’s solution through the owner’s evaluation process and into contract negotiations. Getting to that point is a combination of meeting and exceeding client objectives and requirements where practical, but with perhaps a bit of creative writing and ambiguity when necessary to obscure a proposal’s shortcomings.

Let’s revisit that receiver noise floor example again to reinforce how just one overlooked or underappreciated aspect of a proposal submittal can become a costly owner headache. As the owner evaluates coverage maps, if the vendor neglected to consider the adverse effect of noise on the radio system’s ability to detect weak signals, the net result is the submitted maps are worthless.

In the example’s case, that 10db noise level means the incoming signal from portable units must be made 10 times higher than depicted by the map for the predicted coverage to be accurate. Sadly, a 3-watt portable radio cannot be made to transmit 30 watts to overcome that pesky 10dB noise hurdle. The example’s maps would depict a condition that doesn’t correlate to owner needs since too few tower sites will have been included. When too few tower sites are provided in a design, then obviously the corresponding cost proposal will be dramatically lower than that from one who’s design appropriates offsets the noise degradation.

Keep in mind, when a project award is made to an errant vendor, two others are damaged: The owner and the Unsuccessful vendor who faithfully addressed the owner’s performance expectations and produced a sound, well-designed solution. To make sure that error doesn’t become yours to correct with much grief and cost, proceed cautiously and take time to dig into the details of each proposal response submittal. Caution is, indeed, necessary since sales capture teams are an inventive bunch and continually work to optimize win themes and proposal strategies. For you, those are the new Unknown Unknowns!

NOTICE: This document and its content, dated February 3, 2023, are the copywrite property of Central Electronics, LLC. All rights reserved. You may not, without our expressed permission, distribute or commercially exploit the content or publish/link same on any other website or electronic media.

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