MANET or Mobile Ad Hoc Networking is the glue that holds tactical military communications together. It has revolutionised the tactical radio domain since its introduction, and holds further promise as the technology develops in the future.
To most people, the word Manet is more usually associated with Édouard Manet, the French artist who lived between 1832 and 1883, and was pivotal in the transition from the realism school to impressionism. In the military domain, he shares his name with an acronym which has been similarly revolutionary, transforming the way that troops communicate on the battlefield.
MANET essentially refers to a wireless communications network which is able to configure itself as a formation of deployed forces, and accompanying air and sea platforms, move around the battlefield and support these troops. Civilian cell phone networks operate wirelessly, but they are dependent on fixed transmitters, often atop of buildings or high elevations, which receive the transmissions from a cell phone and transmit these to another tower until they reach their intended destination. As cell phones provide full duplex communications (people can talk and listen at the same time as they would in a normal conversation) cell phone networks handle transmission and reception of communications between phones simultaneously.
MANET tactical communications networks differ in that the Very High Frequency (VHF: 30-300 Megahertz/MHz) and Ultra High Frequency (UHF: 300MHz to three gigahertz) radios which comprise these networks not only enable the reception and transmission of voice, data and imagery traffic, much like a civilian cell phone, but also act in a similar fashion to a cell phone tower as a ‘router’. The router helps to carry radio traffic to and from its intended destination. For example, a V/UHF radio in a vehicle may perform a voice transmission back to a headquarters several miles away. The radio communications leave the vehicle’s radio, find the nearest V/UHF radio in the network, and ‘skip’ from this radio to another radio in the network, and so on, until the transmissions reach their intended destination—a process which occurs at the speed of light, 1080 million kilometres-per-hour (671 million miles-per-hour).
Mobile Ad Hoc Networking has some key attractions for military communications in terms of logistics, manoeuvrability and survivability. Firstly, as the radios build and maintain the network there is no need to move large numbers of fixed transmitters into theatre to established a fixed network in a similar fashion to cell phone communications; this reduces time to establish the network, and the accompanying cost in terms of finance and human capital. Secondly, a fixed network will only maintain integrity as long as all of the users operate within range of the fixed transmitters; MANET has the advantage that, because its accompanying radios are also its routers, it moves with the forces who are using the network. In land manoeuvres this is especially important where speed and drive play a vital role in manoeuvring into a position of advantage regarding one’s adversary. Thirdly, the fact that the MANET radios also act as routers, means that there is no single point of failure for the communications network: a vehicle carrying a radio may be incapacitated or destroyed by hostile action, but this will not mean that the entire network ceases to operate.
A related benefit concerns traffic volume. In terms of radio engineering, V/UHF radios can typically handle large quantities of voice, data and imagery traffic, in the order of several hundred kilobits-per-second (kbps) compared to High Frequency (HF: three to 30MHz) which may only carry tens of kilobits-per-second, but this attribute comes with a cost: V/UHF radios are limited by a line-of-sight range. Across flat terrain, at zero altitude, this is typically a range of around 4.7 kilometres (2.9 miles) for a person standing on the ground holding the radio. If the radio waves do not hit another radio within that distance, they will continue moving in a straight line (although rising in altitude relative to the Earth’s curved surface, eventually moving into space). HF radios have the advantage that they can offer intercontinental ranges as they ‘bounce’ their transmissions off the ionosphere; a layer of the atmosphere typically at an altitude of 60km (37 miles) to 1000km (620 miles). Yet these ranges come at the cost of bandwidth, and HF communications often lack the ability to carry the data- and imagery-heavy communications of their V/UHF counterparts (see above). Ultimately, HF gives you range, but V/UHF gives you bandwidth. How does this affect MANET? For ground troops V/UHF is preferable as it allows high bandwidth communications, while enabling troops and vehicles to use radios which do not require especially large antennae, preserving the ability of troops and vehicles to move in a relatively unhindered fashion.
Nevertheless, battles are not always performed on flat expanses of land. As such, terrain can impede V/UHF communications by simply ‘getting in the way’ of radio transmissions. The ability of MANET communications to ‘skip’ across several radios which act as routers to reach their intended recipient allow communications to avoid natural obstacles such as mountains. If a mountain is between two radios trying to communicate, then the radio’s transmissions skip from one router to another around the mountain until they reach their destination. Such a capability was particularly important during US-led combat operations in Afghanistan from 2001 where that country’s rugged topography would have otherwise impeded tactical communications. Away from the Hindu Kush, the ‘urban canyons’ of cities such as Fallujah or Tikrit in Iraq posed similar problems for military communications, as buildings, floors and concrete walls could act as obstacles to V/UHF communications, hence the importance of MANET to provide a means by which radio transmissions could ‘skip’ from one radio to another to provide communications.
Certainly, MANET has brought great benefits to land forces communications, particularly during manoeuvres, but it remains a work in progress, and the consensus in the tactical communications community following recent US-led operations in Afghanistan and Iraq is that there is room for improvement. “MANET has existed for over ten years, but we are having problems using it. Even the US military is having problems using it,” remarks Haidong Wang, director of product management at US tactical radio specialists TrellisWare. He explains that, “most existing MANET capabilities have limitations such as scalability. How does the network perform as the network changes from a static environment (i.e. when troops or formations are stationary) to a moving environment (when those same units are advancing to contact with the enemy)?” Other challenges, Mr. Wang notes, includes a MANET network’s ability to host new nodes (the technical terms for the transceivers which also act as routers along with behaving as radios) as they enter the network. Each of these nodes occupies some radio bandwidth. As noted above, V/UHF uses a portion of the electromagnetic spectrum from 30MHz to three gigahertz. This may sound like a lot, but spectrum is a finite resource. Today’s battlefield has more than its fair share of users who demand radio spectrum to operate, from troops, to Unmanned Aerial Vehicles, inhabited military aircraft, radars and satellite communications. This is not to mention civilian users such as the emergency services, paramilitary forces, civilians with cell phones and satellite television providers, for example. The Afghan and Iraqi theatres have illustrated that today’s and tomorrow’s conflicts may well be performed in theatres where, to an extent, civilian ‘life goes on’ regardless of military activity. Therefore, adversely disrupting civilian communications via military bandwidth demands may not be conducive to prevailing in the all-important ‘battle for hearts and minds’ so integral to counter-insurgency operations.
Given the finite nature of the spectrum, military users may want to occupy all the available space, but may in reality only be free to use a portion of it, due to the considerations outlined above. Therefore, armies deploying into theatre have to think about, “how many nodes can you accommodate on each megahertz?” asks Mr. Wang. Such considerations mean that MANET networks require “very complex planning,” he continues. Moreover, each theatre may have several small MANET networks used by each formation of troops, for example, and “these need to be stitched together into a very large network. Once you have 300 people, all of whom want to use the network, how will you deal with this? A single radio channel can be narrowed in terms of the number of hertz it uses, but how much do you want to narrow the channel, as this can degrade performance?”
Mr. Wang’s observations chime with those of Ondrej Sohajek, chief technology officer of Czech Republic tactical radio experts MESIT Defence (formally DICOM): “The number of network users is one of the most sensitive parameters. There is a myth that the more network users, the better the MANET performance. This comes primarily from a logical assumption that particular network nodes in dense networks work more efficiently for each other’s advantage re-broadcasting the data and that there are more communication paths available and higher redundancy, plus the increased stability of the network and longer communication ranges as a result.” The truth is that another rebroadcast is nothing else than usage (blocking) of the same communication channel for a specific time and shared transmission capacity is adequately reduced. Mr. Sohajek continues that, as far as the capabilities of MANET communications are concerned, “It is important to remember a few dogmas, like the definitiveness of frequency spectrum, physical properties of radio signal propagation and the consequences of the fact that we are working with a shared media; radio channels with finite capacity.”
Development is another challenge in realising MANET techniques and systems. Mr. Sohajek states that the deployed MANETs are typically extremely complex in their composition. “Methods used in contemporary MANET networks are usually very complex which is why it is extremely difficult to verify them in conditions of real deployment.” Such networks can have an “infinite number of possible layouts,” composing different environmental or topographical conditions to traffic usage or network size. Therefore, as Mr. Sohajek continues, accurately replicating the ‘real world conditions’ in which a MANET may be deployed is nigh-on impossible.
Nevertheless, the software world comes to the aid of MANET developers. “Verification against simulated models is increasingly used because the verification of a network ‘in action’ is practically impossible,” Mr. Sohajek observes. Yet, as well as offering the developer a potentially greatly-expanded range of scenarios against which they can test their MANET architecture, it also potentially reduces development and testing costs, compared to having to evaluate every possible scenario with an actual army formation.
As Mr. Wang explains above, the challenges faced by MANET networks are clear and present. How can they be overcome? “The answer is to ensure that your network is scalable,” he argues. TrellisWare’s approach employs a concept which the company calls the Barrage Relay Network (BRN). Mr. Wang says that the BRN approach gets the nodes discussed above to collaborate with one another. Currently, MANET radios ascertain which path, via ‘skips’ is best to move radio traffic from A to B across several nodes. Mr. Wang states that this approach is analogous to the game of ‘Chinese Whispers/Telephone’ in which one person has a phrase which they say to another, who then says it to another until it reaches the end of the line and the recipient and originator of the phrase compare their two phrases to see how they have changed in the transmission. The BRN technique is equivalent to the person telling everyone in the game of their phrase simultaneously. Mr. Wang continues that the firm is already using this approach for its tactical radios such as its TW-400 Cub, TW-225 CheetahNet Mini, TW-600 Ocelot and TSM Ghost and their accompanying waveforms (see below).
Like TrellisWare, waveforms are at the core of how Thales addresses the challenges posed in ensuring workable, robust MANET networks. For the uninitiated a waveform is essentially a software algorithm which tasks a soldier’s radio to behave in a particular fashion to communicate in a particular way. It can be thought of as similar to a civilian smartphone software application or ‘app’. An app essentially tells a cell phone to behave in a particular way to achieve a particular task. For example, a satellite navigation programme tells the phone to listen for satellite transmissions from a Global Positioning System satellite to enable the user to find their location or their direction. Waveforms are being used to address some of the challenges which Mr. Wang discusses above, such as the quantity of nodes which can be accommodated on a single network.
This challenge is being addressed by the European Secure Software-Defined Radio (ESSOR) initiative. Several European countries principally Finland, France, Italy, Poland Spain and Sweden are involved in the ESSOR initiative which is under the auspices of the OCCAR (Organisation Conjointe de Coopération en Matière d’Armement/Joint Organisation for Cooperation in Armaments). Europe-wide organisation which manages multinational European defence programmes. ESSOR aims to realise a suite of HF and VHF waveforms which can handle high data rate transmissions, which can also carry simultaneous voice, data and position information. However, in terms of meeting the node challenge, ESSOR is envisaged to be able to accommodate up to 150 nodes on a specific network, according to a written statement provided to Armada by Thales. This statement continued that development of the ESSOR waveform has now been completed, and testing has commenced, with interoperability evaluations between different radios completed towards the end of 2015. It is envisaged that ESSOR could be rolled out across the radios of the participating nations from circa 2020.
The ability to provide wideband communications across mobile ad hoc networks is also at the heart of the WF40 wideband networking V/UHF waveform developed by MESIT Defence. The WF40 can handle data rates of several hundred kilobits-per-second, typically supporting transmission which can hop between seven routers to reach its recipient.
Managing a large number of nodes on a network, and knitting these networks together, is a challenge which Thales recognises. The company continues that ensuring the full connectivity of soldiers on the battlefield not only via their radios, but also increasingly via their all-important battle management systems which give cartographic information, situational awareness, and timely information and orders, is intrinsic to prevailing against one’s adversary. “Transformation cannot be achieved through dedicated bubbles with a limited number of users. MANET waveforms (must) be designed to insure tactical radio network deployment with a large number of users and applications.”
Radio engineers thus have their work cut out. The demand for MANET in the future is unlikely to diminish and will only increase. However, initiatives such as the ESSOR waveform discussed above, plus so-called ‘Cognitive Radio’ techniques which, put simply, employ software which automatically configures a radio change its behaviour to ensure its optimum performance. For example, the radio may detect that a particular segment of the spectrum is heavily congested and thus move its transmissions to another part of the spectrum to ensure that data transmission and reception is not adversely affected. Cognitive Radio could help to address some of the challenges which MANET techniques face today. Lessons from recent combat operations will be digested and incorporated into future tactical radio hardware and software. MANET may have changed battlefield communications beyond recognition, but it is still far from becoming a panacea. It has revolutionised the battlefield, but like most revolutions it has so far failed to create a utopia.