Once firmly rooted in its analog origins, critical communications is now steadily evolving to provide enhanced situational awareness. The latest public safety and military communications (MilCom) radios are more versatile and reliable, supporting ad-hoc networks to improve or enable connectivity. With higher-data-rate capabilities, critical communications solutions can send and receive high-resolution images, videos, and other types of data-intensive content. At the same time, they provide higher-quality voice communications while maintaining security. To ensure communications and interoperability, they still can support analog communications as a failsafe. These myriad capabilities are possible through the ongoing adoption of new technologies, ranging from digital public safety standards and modulation formats, to technologies like wireless local area networking (WLAN) and Long Term Evolution (LTE).
Public Safety Standards
In the public safety arena, this trend is evident as land mobile radio (LMR) evolves to digital standards. Examples include the Association of Public Safety Communications Officials (APCO) Project 25 (P25), Terrestrial Trunked Radio (TETRA), and Digital Mobile Radio (DMR). APCO P25, which originated in the U.S., allows public safety and other LMR systems, such as those used by utilities, to move to two-way digital communications. Beyond the integration of voice and data, the standards comprising APCO P25 aim to enable the production of equipment that is interoperable, compatible, and spectrally efficient. P25 has two phases that are non-compatible but Phase 2 radios and networks can revert to Phase 1 operation if needed. Both phases use a 12.5-kHz channel bandwidth but employ different channel access methods. Phase 1 leverages frequency division multiple access, while Phase 2 relies on two-slot time division multiple access (TDMA).
TETRA is the European version of a digital trunked mobile radio standard. For traditional professional mobile radio user organizations, it offers a scalable architecture that can provide local-area through wide-area coverage. TETRA features high-level voice encryption and rapid call setup for group calls over a wide area. With direct-mode operation, it permits back-to-back radio communication that is independent of the network. Trunked-mode operation can also be employed so that TETRA mobile radios operate with TETRA network infrastructure. Key to TETRA is its use of TDMA to maximize spectral efficiency with the allocation of four user channels on a single radio carrier with 25-kHz spacing between those carriers.
TETRA continues to evolve with the development of new standards including TETRA Release 2, which features TETRA Enhanced Data Service (TEDS). TEDS enables wideband, high-speed data communications services. It utilizes different RF channel bandwidths (25, 50, 100, and 150 kHz) and data rates for flexible use of professional mobile radio-frequency bands.
Another open standard, DMR, provides voice, data, and related services. Considered more of a business-critical than mission-critical solution, DMR leverages two-slot TDMA technology to add control features and double the capacity of an existing 12.5-kHz channel. The system enables two calls on the same channel independently, providing twice the system channel capacity as a standard two-way analog radio system. In the future, it will satisfy requirements for 6.25 kHz to meet U.S. Federal Communications Commission (FCC) certification rules demanding such operation. DMR systems promise audio quality improvements by converting voice data to digital data. The systems use signal processing algorithms to help minimize distortion and provide intelligent audio capable of adjusting volume in response to the noise level in the environment.
LTE and WLAN Adoption Rises
Leveraging the research and development done in the commercial world is a pragmatic approach to enable multi-format radios for critical communications quickly. The LTE architecture, which is all Internet Protocol, offers both low latency and high resilience. These features pave the way for interoperability in both voice and data applications; however, LTE’s lower 1 W transmit power translates into higher-density radio sites.
The Third Generation Partnership Project (3GPP) sets global standards for LTE and other cellular telecommunications. To support MilCom and public safety radios, 3GPP Release 12 focused on mission-critical applications. Release 13 added support for mission-critical push-to-talk and a range of features to support emergency users such as first responders. Release 14 introduced mission-critical data and video features into the standard, along with additional performance features. The U.S. has allocated spectrum in the 700-MHz band specifically for LTE, with the goal of providing large-scale coverage and superior propagation to penetrate structures. FirstNet public safety radios, which are LTE-time division duplexing (TDD) capable, are an example of LTE implementation.
Unlike LTE, WLAN technology offers easy deployment with fewer infrastructure demands. As a result, ad-hoc military and public safety networks worldwide already leverage WLAN technology. “Ad hoc” refers to the fact that they do not use an existing wireless infrastructure. Nodes forward data to each other based on aspects like connectivity and the employed routing algorithm. These networks do not rely on a central node and can be formed rapidly, which makes them attractive for emergency scenarios and military conflict zones.
In the U.S., for example, the FCC has allocated 50 MHz of spectrum in the 4.9-GHz band for fixed and mobile public safety services. At such frequencies, this spectrum will likely be used for short-range communications. Broadband applications supported in the U.S. band include mesh networks, hotspots, ad-hoc mobile networks, voice over IP, video surveillance, and backhaul. These capabilities enable fast and easy data sharing of potentially critical information in large video, image, and other file formats.
Leveraging Digital Modulation Formats
Key to these communications approaches is their use of modulation to move from analog to digital formats. Modulation enables multiline communications by changing the carrier wave’s characteristics to those of a different wave, referred to as the modulating signal. Digital signal processing – which converts analog information into digital data by altering the carrier-wave characteristics such as phase, amplitude, or frequency – is at the heart of digital modulation.
The three basic forms of digital modulation are amplitude shift keying, frequency shift keying, and phase shift keying. Quadrature amplitude modulation (QAM) and quadrature phase shift keying (QPSK) are complex modulation formats built upon these basic digital modulation formats. QAM and QPSK provide more efficient bandwidth usage and security for voice communication on the battlefield. Digitizing long-distance analog signals provides clearer, more accurate, and more secure military communications. Advances leveraged from complex modulation technology have enabled many recent advances in tactical communications.
Public safety and military agencies will take an increasingly diverse approach to update their radio communications systems, adding WLAN, LTE, and other technologies to augment capabilities and increase data sharing. Key to these systems is interoperability with both older and newer systems, allowing different units to communicate as needed. While infrastructure varies from smaller ad-hoc networks to more complex rollouts, all critical communications systems must meet requirements for performance, interoperability, and security.
Radio manufacturers must test these versatile radios for compliance with industry standards, such as LTE and WLAN, in addition to frequency checks that ensure correct radio operation and frequency precision. Among other performance indicators tested are power output and receive signal strength, which ultimately defines the range, audio clarity, volume, and more in the field. Complete testing of radio and network parameters and leveraging trusted critical communications solutions is key to securing the world, whether the scene is a local accident or a military zone.
This article was written by Nancy Friedrich, Industry Solutions Marketing, Keysight Technologies, Santa Rosa, CA. For more information, visit here .