WF40 MANET waveform
MESIT Defence’s offerings including the WF40 MANET waveform which can handle data at rates of up to 240kbps. (MESIT Defence)

This headline encapsulates the importance of waveforms for tactical radios. Each task that a radio executes must be performed in a certain way. This article aims to demystify the oft-baffling domain of the tactical radio waveform.

The late tactical communications expert and defence journalist Adam Baddeley once told your correspondent that tactical radios were interesting, but their waveforms were even more so. In a moment of conspicuous ignorance, your correspondent was forced to admit that they did not actually know what a waveform was, nor why they were so integral to tactical communications. This conversation sparked an unwavering desire to understand both Mr. Baddeley’s fascination, and the waveform’s critical role. The first port-of-call in this quest to understand what constitutes a waveform was the Oxford English Dictionary (OED). This noble custodian of the English language defined a waveform as “a curve showing the shape of a wave at a given time.” Eliminating only a scintilla of ignorance, this definition left much to understand. Seeking further clarification, Merriam-Webster’s respected English Dictionary placed some more flesh on the bones, stating that a waveform is “usually a graphic representation of the shape of a wave that indicates its characteristics (as frequency and amplitude).” While the latter definition provided some further insight vis-à-vis the OED, it remained insufficient to satisfy curiosity. With layperson’s sources such as dictionaries exhausted, the only available recourse was to confer with tactical radio experts to answer the above conundrum.

Raison d’Etre

Michael Fraebel, director of operational marketing at Rohde and Schwarz’s secure communications division articulated to Armada that a waveform: “encompasses the entire set of radio functions that occur from the user input (when the user speaks into the radio, or when they use it for transmitting data) to the output of that action as radio frequency energy.” Thus the waveform turns the intentions of the user into a transmission. Expanding on Mr. Fraebel’s definition, Ondrej Sohajek, the chief executive officer of MESIT Defence stated that the clearest way to understand a waveform is to contemplate one’s own cellphone: “Tactical radio hardware is not unlike a smartphone. An entire population using smartphones is like a battlefield full of soldiers, where different applications running on the smartphones (or as online service coming from the internet) give the people the desired functionality (for their devices).” Mr. Sohajek continued that: “Without any additional application running on a smartphone you can make a voice call or send a text, which is sufficient for certain people, however most people need more. Using additional applications you can exchange emails, files, pictures and videos to be played offline. Other people want to stream video, which requires different applications or services.”

A written statement supplied to Armada by Elbit Systems further expanded some of the above explanations, adding that a tactical radio waveform is like a specific language with each waveform having its own characteristics in terms of encryption, data capability (how many kilobits/megabits per second of information the waveform can carry) and the frequencies over which it is transmitted.” Communications security is another important waveform characteristic. A written statement supplied by Barrett Communications argued that: “Tactical waveforms provide an assured means to link and transfer digital information such as files and pictures,” in additional to enabling voice traffic. For this to be achieved, the statement continues that “Tactical waveforms are typically those waveforms which exhibit characteristics of low probability of detection and interception by a third party.”

Examples

Some examples maybe instructive: The United States armed forces, and several allied nations around the world use the Single Channel Ground and Airborne Radio System (SINCGARS) waveform. This can handle voice and data traffic between radios equipped with the necessary software to receive and transmit this waveform. It operates in a frequency range of 30 megahertz (MHz) to 87.975MHz and can use either a single frequency within this waveband or ‘hop’ across frequencies in this waveband at a rate of 111 hops-per-second rendering it all but impossible for the eavesdropper or jammer to know where in this waveband the transmission will next hop and thus interfere with the transmission. The SINCGARS waveform is utilised for communications between ground units, and between ground units and aircraft. Meanwhile, US and allied nations also employ the HAVE QUICK-I/II waveform. Inhabiting the 225MHz to 400MHz waveband, it is primarily intended for communications between aircraft and also for ground-to-air/air-to-ground communications.

WF40 MANET waveform
MESIT Defence’s offerings including the WF40 MANET waveform which can handle data at rates of up to 240kbps. (MESIT Defence)
Elbit’s PNR-1000
Elbit’s PNR-1000, also a member of the firm’s E-Lynx family, can accommodate the company’s ESRW (Elbit Soldier Radio Waveform), capable of carrying hundreds of kilobits-per-second of data. (Elbit)

So why are different waveforms such as SINCGARS and HAVE QUICK-I/II used? Elbit emphasises that this is because: “each waveform has its own advantages and disadvantages,” as there is no ‘one size fits all’ for every military communications requirement. The firm’s statement continues that Ultra High Frequency (UHF: 300MHz to three gigahertz) radio communications will provide high data rates, but might be limited in geographical range. Very High Frequency (VHF: 30MHz to 300MHz) transmissions will have comparatively smaller data rates than UHF, but might be able to achieve longer geographical ranges, and also to work in environments which are saturated with other VHF transmission crowding the electromagnetic spectrum as their communications occupy a narrower part of the waveband. This is important as the military is not the only user of the VHF waveband. They must share it with television broadcasting, which uses VHF transmissions, as does two-way land mobile radio such as that equipping taxis or emergency vehicles: “Different waveforms are optimised to be very good at certain things,” observed Jeffrey Kroon, director of product management for radio products and innovations at Harris. For example: “VHF is good at handling basic data, while handling megabits of data is the preserve of UHF.” High Frequency transmissions, meanwhile, can reach intercontinental ranges thanks to their ability to ‘bounce’ off the ionosphere; an area of the atmosphere residing at between 40.5 nautical miles/nm (75 kilometres/km) to 540nm (1000km) altitude. The ionosphere acts as a naturally-occurring ‘satellite dish’ across which transmissions can skip to reach intercontinental ranges unlike V/UHF transmissions that can be restricted to line-of-sight ranges. Nonetheless, HF communications are hampered by the amount of data that they can accommodate. For example, open sources state that data rates of 19.2 kilobits-per-second (kbps) are achievable using HF communications, whereas data rates in the realm of megabits-per-second are achievable using UHF. Moreover, the integrity of HF radio transmissions is affected by solar radiation levels and meteorology which can cause interference.

Design

AN/PRC-154 Rifleman radio
The AN/PRC-154 Rifleman radio, jointly produced by General Dynamics and Thales, contains the SRW developed by Harris for the US armed forces. (Thales)

Therefore, the frequency choice for the waveform’s intended task; the encryption and communications security it will employ alongside the bandwidth available to the waveform plus the intended geographical range the waveform is to serve become key considerations in waveform design, Elbit’s statement continued. The waveform’s intended user becomes another imperative in the waveform’s design, according to Mr. Kroon: “In the air, aircraft move a lot faster than vehicles on the ground. Some work well with fast moving aircraft, and some do not work so well.” He continued that: “if you optimise one waveform for ground-to-ground communications, it might not work so well for ground-to-air communications.” This explains the differences between the SINCGARS and HAVEQUICK-I/II waveforms discussed above, designed as they are for different applications. For example, the SYNAPS V/UHF tactical radio range which Thales launched in 2016 includes several waveforms optimised for their intended task: namely the Manoeuvre waveform for ground-to-ground voice and data communications, and the Airborne waveform for air-to-ground/ground-to-air voice and data communications.

When tactical radio engineers are contemplating a new waveform, Mr. Kroon added, several questions will be asked such as the users expected velocities; the circa 59 kilometres-per-hour (37 miles-per-hour) on road top speed of a BAE Systems’ FV4034 Challenger-2 main battle tank, or the Mach 2.2 (2400km/h) maximum speed of a Panavia Tornado-GR4 fighter, for example? Air communications are instructive in this regard. Mr. Fraebel stated that, because of the high speed of an airborne platform, those waveforms which are used for such communications must have Dopplar Shift Compensation. In layperson’s terms the Dopplar Shift, also known as the Dopplar Effect, is the change in frequency for an observer vis-à-vis a moving object. A traditional means of explanation is the phenomena witnessed by static person hearing a police car driving past: As the police car approaches the person, the sound frequency of the car’s siren appears to increase in tone, and then decreases in tone once the car has driven past them. In air platforms, this can mean that the shift in frequency between a transmitted and received radio signals can see a Dopplar Shift which can be considerable given the high speeds of the aircraft.

Elbit’s MCTR-7200
Elbit’s MCTR-7200 tactical radio family, part of the firm’s E-Lynx radio range, uses the firm’s Multi-band Channel Waveform platforms. These support MANET and also include robust protection against jamming. (Elbit)

Mr. Kroon added that other pertinent questions will include the quantity of data that the waveform will need to handle. This is particularly important if the waveform will need to transmit images or streaming video, both of which are traditionally ‘data heavy’. Other aspects needing to be satisfied will include the size of the network that the waveform will serve both in terms of users and physical area. Additional criteria will include the waveform’s required level of encryption. Designing a waveform, Mr. Sohjek asseverated, is one of the most taxing elements of realising a waveform: “The hardest part is figuring out the right design considerations. There are not always enough requirements available, or the deployment context is not stabilised when the waveform is being defined.” He continued that so-called MANET (Mobile Ad Hoc Networking) waveforms provide an instructive example of the challenges faced by waveform developers. Put simply, MANET networks serve to reduce the line-of-sight disadvantage inherent in V/UHF communications (see above). While a transmission across UHF from the ground-to-the-air and back can have a comparatively long range as, for instance, it is easier to see a long distance from the top of the Eiffel Tower, when being used for ground-to-ground communications their range can be restricted to the visible distance, which on clear, flat ground can be restricted to the horizon, although shortened further if undulating terrain or vehicles stand in the way.

MANET offers one means by which this disadvantage can be mitigated. MANET enables each radio to behave as a transmitter across which a transmission can ‘skip’ to arrive at its destination. A deployed division may be separated by tens of kilometres, yet MANET transmissions can reach from one side of this division to the other by using MANET. An analogy is a frog crossing a pond: The frog cannot reach the other side of the pond in one jump, but can reach the other side by jumping from one lily pad to the next. The crucial aspect of waveform designs for MANET networks is the “maximum number of active nodes” in a network, remarked Mr. Sohjek. These nodes are analogous to the lily pads discussed above. The more nodes on a MANET network, the larger the network can be and the more users and larger geographical range it can cover.

PRC-2090 HF tactical radio
Barrett Communications’ PRC-2090 HF tactical radio employs the firm’s waveforms which can enable voice, messaging and high speed data transmission. (Barrett Communications)

Increasingly, interoperability is a prerequisite in waveform designs. Multinational operations have been a hallmark of military activity since the start of the 21st Century, as well as before, note the US-led multinational coalitions which performed combat operations in Afghanistan and Iraq. In a written statement supplied to Armada, Rafael Advanced Defence Systems which provide both wideband and narrowband waveforms for their BNET tactical radio family, stated that: “modern battlefields are comprised of coalition forces and large arrays of users that need to have the ability to communicate.” To this end, new waveforms are in the offing that will progressively facilitate this. Commencing in 2010, the ESSOR programme is managed by OCCAR (Organisation Conjointe de Coopération en Matière d’Armement/Joint Armament Control Organisation); a European intergovernmental organisation managing collaborative defence programmes involving Belgium, France, Germany, Italy, Spain and the United Kingdom. The ESSOR (European Secure Software Defined Radio) initiative aims to develop a high data rate wideband networking waveform for software defined radios which can be made available to the participating nations of Finland, France, Italy, Poland, Spain and Sweden. This aims to improve interoperability by providing a waveform for use with tactical radios across the participating nations, and other third party countries. ESSOR waveforms are expected to become available in the circa 2020 timeframe.

As the ESSOR initiative shows, waveform technological development is by no means static with work ongoing to develop tomorrow’s tactical radio waveforms. Arguably, one of the most vexing challenges faced by tactical radio experts is ensuring that their waveforms can operate in the most efficient way possible in an increasingly crowded electromagnetic environment: “Waveform technology is constrained by the limits of bandwidth,” articulated Barrett Communications’ statement. The HF and V/UHF bands inhabited by tactical radios are not their exclusive preserve. Tactical radios must inhabit their respective parts of the spectrum in a neighbourly fashion (i.e. not provoking interference) with other military and non-military users alike. For example, military and civilian radar can use both respective VHF and UHF frequencies in the 133-144/216-225MHz and 420-450/890-942MHz wavebands. Likewise, UHF satellite communications use a frequency range of 240-270MHz. As noted above, other VHF occupants include television broadcasting and two-way land mobile radio systems, alongside amateur radio, air traffic control radio and maritime communications. UHF, meanwhile, is employed for TV broadcasting and includes the frequencies used by the satellite-based Global Positioning System, domestic wi-fi and even cordless telephones. Like VHF and UHF, HF is also used for radar, in addition to shortwave radio broadcasting and amateur radio, to list just three users.

Thus the room for manoeuvre vis-à-vis tactical radio within these three wavebands is restricted in terms of growth. To further complicate matters, the military is under pressure to vacate parts of the radio spectrum to allow this to be auctioned off by governments for civilian use. For example, in June 2010, the administration of US President Barack Obama announced plans to make available up to 500MHz of radio spectrum occupied by the US military and federal agencies by 2020. Mr. Obama’s initiative formed an intrinsic element of the ‘Connecting America’ National Broadband Plan to greatly extend internet coverage across the country. Illustrative of the appetite for spectrum encouraged by the proliferation of smartphones amongst the US population, figures produced by AT&T Mobility, an American company providing wireless communications, stated that usage of the firm’s data network had increased by 8000 percent between 2007 and 2010. That tomorrow’s waveforms will require frequency flexibility is therefore a sine qua non, to ensure that they can perform their core functions, while adopting new capabilities like those inherent in waveforms such as ESSOR (see above), all the while in an increasingly spectrum-constrained environment.

by Thomas Withington