In a digital world, analog still has its benefits

Digital-based communications systems for emergency responders offer significant advances over traditional analog voice radios, including better security, interoperability enhancements and the ability to share more information than just voice, such as photos, video, GPS locations, compass and maps. However, there are still some functions where analog voice—a 100-year-old technology—outshines the best digital systems available today, such as analog point-to-point communicators that do not require repeater towers. Or, when a signal is weak or noisy analog communications can be intelligible when Project 25 (P25) digital radios would not be.

Let’s explore the benefits of each technology and how emergency responders can leverage the benefits of both. What must public safety agencies do to cope with the simultaneous existence of analog and digital technologies? How can you best navigate the increasingly rapid evolution of its tools?

Intelligibility Scores[1]

25 kHz Analog FM

12.5 kHz Analog FM

P25 Full Rate
(7,200 bits/sec)

P25 Full Rate With Enhanced Vocoder
(7,200 bits/sec)

0.881

0.886

0.826

0.800

 

Analog has a large installed base

Until the rollout of P25 digital Land Mobile Radios (LMR) in the United States, all public safety personnel used analog radios. This installed base is already paid for and, given the durability of existing units, could last a decade or more.

Analog voice is highly intelligible

Analog voice using 25 kHz of bandwidth is the gold standard for voice clarity against which public safety measures P25 and will measure broadband LTE when it comes online. The National Institute of Standards (NIST) is responsible for drafting the standards for broadband voice that will be transmitted over the recently approved national Long-Term Evolution (LTE) fourth generation (4G) cellular network in the 700 MHz D-Block that was recently dedicated to public safety. NIST compared the digital voice encoders (Vocoders) used by P25 LMR with analog voice and reported the results presented in the table below.

Intelligibility Scores

P25 digital voice had an intelligibility rating of 0.826, and surprisingly P25 using the “enhanced” Vocoder scored even worse with an intelligibility score of 0.800. These scores were noticeably below standard 25 kHz analog voice, which had a voice quality of 0.881. Beginning Jan. 1, 2013, public safety licensees will be required by Federal Communications Commission (FCC) regulations to halve their bandwidth to 12.5 kHz. Public safety’s concern that going to narrowband would reduce intelligibility proved unfounded, as the intelligibility of narrowband analog voice is indistinguishable from full bandwidth analog voice with an intelligibility score of 0.886.

In urban and suburban locations where there exists a congestion of radios, narrowband waivers may be difficult to obtain from the FCC. However, in rural areas where spectrum is less congested, waivers of the narrowband requirements can reasonably be expected to be easier to obtain, and will allow the continued use of existing 25 kHz analog LMR.

When two or more speakers step on one another using analog LMR, listeners hear the conflict and can sort it out. When there is contention between speakers on P25 systems, only one speaker is heard. Because P25 cannot determine which transmission deserves priority, critical messages can easily be unheard if they are initiated while someone else is already speaking, and the speaker receives no indication that his/her transmission did not go through.

Voice latency is low with analog voice

Analog voice systems have no delay in setting up connections since analog radios tuned to the same frequency instantly connect. This compares to a 1.3-second call setup time for P25. Moreover, the latency in ongoing point-to-point analog connections is less than 0.1 seconds, whereas P25 latencies are 0.5 seconds or greater. The setup and ongoing latencies for broadband voice will not be known until the voice over LTE standard (VoLTE) is fully defined. However, they are expected to be comparable to P25.

Analog LMR is easy to use

Analog LMR radios have volume and channel controls and a push-to-talk button. All can be accessed easily, even by fire fighters wearing gloves. There is typically no need to look at the radio. P25 radios have useful capabilities like encryption and channel trunking that enhance security and enable interoperable talk groups to communicate with other agencies. Inevitably, these features add complexity to operating P25 LMR.

Analog voice requires agencies to be on separate frequencies

Early analog LMR system used amplitude modulation (AM) signals, which work identically to AM radio stations. For several decades, analog LMR has used standard frequency modulation (FM), because it is less susceptible to noise interference. Because FM is extremely simple, incompatibility between the analog LMR equipment provided by different vendors hasn’t been much of an issue.

The biggest “incompatibility” issue with analog LMR has been that the only way to keep nearby agencies from interfering with each other, precisely because their LMR could hear other agencies transmitting on the same frequency, was to use different frequencies. Consequently, agencies that did not have multi-band radios capable of transmitting on other agencies’ frequencies could not communicate by LMR with personnel from the other agency.

Public safety organizations, led by the Association of Public-Safety Communications Officials (APCO), developed the P25 digital voice standard to facilitate inter-agency communication. However, even after 22 years of development, compliance with the standard does not guarantee that equipment from different manufacturers will be able to communicate. Consequently, NIST and the National Telecommunications and Information Administration (NTIA) have created the Project 25 Compliance Assessment Program (P25CAP) to test P25
device compatibility.

Public safety agencies have been strongly encouraged to purchase equipment that has passed P25CAP compatibility testing. Still, many agencies choose to purchase incompatible equipment, many times because it costs less or has more useful features than certified P25 equipment. Organizations are most concerned that the units are compatible within the agency, and compatibility with the equipment of other agencies is not always considered sufficiently important to justify paying compatible P25 equipment’s premium cost. Some agencies, like volunteer fire departments, simply cannot afford equipment that would be compatible with surrounding agencies.

Analog LMR is far less expensive than P25

Even the smallest public safety organization can expect to spend tens of thousands of dollars converting to P25, because when infrastructure and lifetime operating and maintenance costs are added, the cost per P25 radio exceeds $10,000. That puts the wholesale replacement of analog LMR subscriber units and infrastructure beyond the reach of many smaller state and local public safety organizations.

Faced with a choice of no cash outlay to stay with existing analog systems versus the considerable investment to convert to P25, which in many ways is outperformed by analog voice, many organizations have delayed the conversion. Consequently, organizations that have made the jump to digital have no choice but to retain analog capabilities.

Making it all work together

The pace of evolution in public safety communication and information systems continues to accelerate. During the 20th century, field personnel relied on analog LMR and land-based telephone systems to communicate with one another and with their dispatchers and commanders. No new communications tools were added for 80 years until public safety started using commercial cell phones. Less than a decade later, digital cellular services were added to PCs in vehicles and P25 LMR systems rolled out. A couple of years later, smartphones allowed access to data services by personnel on foot.

Paradoxically, even though P25 voice technology was created to enhance interoperability, in the short-run the coexistence of multiple generations of voice and data systems actually makes interoperability more complex. As organizations move forward with broadband voice, they should remember that there will inevitably be times when they will need to communicate with other agencies who are a generation or two behind them in technology.

Therefore, when selecting equipment, public safety organizations must not only look at their own internal communications needs, but also the equipment and capabilities of the other agencies with which they are likely to interact. Critically important, interactions with the other agencies must be reviewed in the context of the Concept of Operations (ConOps) to understand the likely use cases. For example, if it is necessary to have low-latency reliable tactical communications between personnel in the field, the radios must support direct-mode talk-around between agencies. Questions such as what are acceptable latencies for mission critical voice can only be answered in the context of well defined ConOps.

To make things even more complicated, the pace of change continues to increase. To avoid obsolescence of equipment in only a few years, public safety organizations should consider tomorrow’s ConOps when making today’s purchasing decisions. The addition of broadband LTE for both voice and data will revolutionize the way public safety personnel communicate with each other and with the public. As next generation 911 systems come online, field personnel will be able to easily speak with the emergency caller and have a complete call history, GPS locations and other information to allow them to perform their job more effectively and more safely. Command and control systems and situational awareness systems will augment voice.

Most public safety organizations are too small to realistically analyze the complex internal and external interactions that have been or will become necessary. Consequently, organizations like APCO, and government agencies such as NIST and the NTIA are becoming increasingly important to ensure public safety has the tools it needs to communicate and coordinate. For them to do their job effectively, requirements and good ideas must bubble up from public safety organizations. Make
yourself heard!

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