Introduction of Dynamic Spectrum Access Technology in ... - IEEE Xplore

2013 IEEE Military Communications Conference

Introduction of Dynamic Spectrum Access technology in NATO Europe tactical communications (Invited Paper) Bart Scheers CISS Department Royal Military Academy (RMA) Brussels, Belgium [email protected] Abstract—To facilitate the introduction of Dynamic Spectrum Access (DSA) technology and associated dynamic spectrum management (DSM) procedures in military tactical radio communication, a roadmap was presented to NATO CaP3 military session in Oct 2012. The main objective of the roadmap was to create a dedicated band for cognitive radio, in the hope that this would take away uncertainties about spectrum regulations and be a sufficient incentive for military communication industry to start investing and developing products. This paper describes the proposed roadmap and formulates the critics of the NATO spectrum managers (CaP3) on this proposition. Taking into account the remarks of CaP3, a possible way ahead is described. The most promising idea is to create a Military dual-priority band that would take into account the existing saturation of the VHF/UHF band, and meanwhile create a clear spectrum access model for future DSA systems.

In this paper we will first motivate and present a DSM roadmap that was presented to the NATO frequency managers during a CaP3 military session meeting in October 2012. A key-point in this roadmap was the creation of a dedicated band for cognitive systems in the UHF band. In section 4 we will formulate the critics of NATO CaP3 on the proposed roadmap. In the last section we will discuss some possible scenarios for the introduction of cognitive radios and DSM in NATO tactical communications in the VHF/UHF band. II.

The term cognitive radio (CR) was coined by Joe Mitola in 1999. Since then, a lot of research has been done in this area. However, CR technology has to date not been adopted in the military tactical communications. No military off-the-shelf VHF/UHF tactical radio systems, integrating DSA or other cognitive features, are available on the market. Looking to the effort that military communication industry is putting into the R&D of those systems, this should not be surprising.

Keywords—Dynamic Spectrum Access Roadmap; NATO tactical radio communications; Military dual-priority band;

I.

I NTRODUCTION

Military tactical networks are being required to support a greater number of services than ever before. In addition, the bandwidth requirements associated with many of the new services are also rapidly increasing. The combination of these two factors means that we are nearing a time when there will be insufficient spectrum to support the services required for future military operations. Today’s military operations are also typically undertaken by multiple nations cooperating in a coalition force. The spectrum and frequency planning activities associated with the deployment are extremely complex [1], [2]. Both of the aforementioned problems, spectrum scarcity and deployment burden, will be driving factors to introduce cognitive radio technology in the military communications domain.

The technical challenges in tactical DSA systems are huge and it is fair to say that today the CR technology is not mature enough to cope with these challenges, despite the fact that the technology is being or will be adopted in some civil communication standards like IEEE802.22 and IEEE802.11af [5]. The fundamental difference between civil and military tactical systems is that the latter needs to operate in an uncontrolled and unpredictable EM environment, far more hostile and dynamic in nature. Further, tactical systems can not rely on an existing infrastructure. At the moment it is not yet clear for researchers and developers what will be the best design choices for such cognitive tactical radio network, leaving a lot of questions unanswered. Will an overlay waveform perform better than an underlay waveform? Can we use a cognitive signalling channel or not? If a cognitive signalling channel is used, how to implement it so that it will be robust enough? What about vulnerabilities against cognitive jamming? What will be the most appropriate CR network architecture: centralised or distributed, cooperative or non-cooperative? What will be the best spectrum awareness method: beacons, database, sensing or a combination of the previous? How will two different cognitive managers react if their networks need to co-exist in the same area? How can

However, a decade after its inception, no military offthe-shelf cognitive system is available on the market yet. So somehow, industry needs an incentive to continue or even to accelerate the development in this domain. On the other hand, military end-users would like to have some control over the introduction of this new and often unknown technology in their tactical communication systems. Therefore a clear and realistic roadmap is needed where military users can develop trust in, and experience with, these novel technologies in manageable steps and limit risk to existing operational capabilities. 978-0-7695-5124-1/13 $31.00 © 2013 IEEE DOI 10.1109/MILCOM.2013.131

T HE D EADLOCK IN THE DEVELOPMENT OF TACTICAL DSA SYSTEMS

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we prevent a network of being greedy? It is clear that a huge effort in research is still needed. The reality however is that the development of cognitive tactical radio systems is trapped in a kind of deadlock. To understand this deadlock, we have to look from the perspective of the three actors: the military end-users, the spectrum regulator and the military communication industry. Military end-users are generally no early adopters for new technologies. Further, they are quite risk averse. If by any chance there exist a possibility that a DSA system could interfere with an operation-critical legacy system, they will never allow the use of such DSA system in a shared-use spectrum access model. Until today, nobody can guarantee this non-interference. In summary, the military end-user is waiting for the technology and the systems to become more mature. Today’s military spectrum management is based on static frequency allocation [1]. Within the NATO Europe military frequency bands, there is no specific allocation for dynamic frequency access. Hence the use of frequency opportunities or white spaces in the military spectrum is currently not allowed and it is not clear that it will be in the near future. NATO considers CR and DSA as a technology rather than as a service or system and has therefore refrained from making frequency allocations, necessitating further negotiations and lobbying to overcome this hurdle. This situation is a source of uncertainty about future regulations regarding these types of systems.

Fig. 1.

A. The First Step - A Dedicated Band for CR Systems We propose the introduction of a band exclusively dedicated to CRs within the military allocation. All cognitive devices would operate within this band and all existing legacy systems would operate outside this dedicated band that is governed by current spectrum management procedures. Initially, we would expect only a limited number of CRs within a coalition force and the bandwidth requirement for this CRonly band would be small in comparison to that required to support the legacy systems of the coalition.

From the military industry point of view the situation is obvious. On one hand they don’t see a clear market and on the other hand there is an uncertainty about regulations, resulting in an atmosphere that is not optimal for investing in development.

We propose that the CR-only band would be managed under a commons DSA model [4] where all CR users would be considered equal and no traditional spectrum management procedures, such as channel assignment, would be required leading to a reduced pre-operation preparation time. Separate CR networks would be able to coexist within the same band by autonomously and cooperatively or non-cooperatively selecting different operating channels within the band (i.e. channels with the least interference).

In summary, everybody is waiting for the other actors to take a first step, resulting in a deadlock. III.

A DSM ROADMAP TO BREAK THE DEADLOCK

In order to break this deadlock, a roadmap has been proposed [2]. The roadmap is a result of multiple discussions within the NATO STO Research and Task Group IST077 on the use of Cognitive Radio in NATO [3] and the work done within the EDA CORASMA project 1 .

This CR-only band may be utilized by military users at all levels of the military hierarchy. However, it may be best to initially target the technology at the lower priority echelons (group - section - platoon) and for particular applications, e.g. tactical radio networks for voice and data. The number of lower echelon networks and the number of radio operators involved are significant, hence the benefits brought DSM in terms of spectrum management, spectrum reuse and deployment burden will be the highest here. Given this, the most appropriate frequency band to create this dedicated military band for CR is obvious the NATO-harmonized UHF I band I (225-400 MHz), due to its ideal propagation characteristics for limited range tactical radio systems. Currently, most of these low echelon tactical radio systems are also deployed in this band. From a technical point of view, and taking into account the possible applications, we think that at least a band of 5 to 10 MHz should be defined. Other possible candidate frequency bands are the military UHF band II (790-960 MHz), the military UHF band III (1350-2690 MHz) and the SHF band (44005000 MHz), where cognitive systems for short range wireless networks could be envisaged.

This DSM roadmap, starts from the present day, with no cognitive radios, and with each increment takes a step further into the future with an increasing exposure to DSM in terms of number of devices, spectrum access complexity and freedom in operating spectrum. The DSM roadmap is designed such that military users may develop trust in and experience with the technology in an incremental fashion, and limit risk to existing operational capabilities. The roadmap is presented in figure 1. In this section, we will mainly focus on the first step in the roadmap. As mentioned previously, it is imperative that this first step involves minimal risk to existing legacy operations and allows military end-users the opportunity to build trust in and evaluate CR technology. 1 CORASMA

DSM roadmap

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easily extended and integrate more complex spectrum access models with civilian and/or military primary users.

If CRs demonstrate success at this lower level, they are more likely to gain acceptance and be more widely adopted across all layers of the military hierarchy.

In summary, in light of the advantages described above, the introduction and use of a dedicated band for CR seems to be by far the most appropriate first step in the road-map towards the introduction of cognitive radio in the military, for both the end-users and the military industry point of view. The question is if this first step is acceptable for the spectrum managers?

The choice of a dedicated band for CR systems as a first step in the road-map has some important advantages. 1) No risk for interference with legacy systems: Military end-users are generally conservative and risk averse. The use of a cognitive system in a shared-use spectrum access mode that could degrade a legacy communication system would not be acceptable. The use of a dedicated band for cognitive systems eliminates this risk.

If this first step proves to be successful, the following steps can be implemented to overcome spectrum scarcity and alleviate current deployment burdens.

2) Relaxation of system requirements: From a technical point of view, a dedicated band based on the managed commons model will relax system requirements for CR systems. The primary reason for this statement is that the cognitive band will lack primary users, placing less severe constraints on CR sensing and decision making functions to gather and process spectrum information to adapt its behaviour. Cognitive systems would thus only need to address interference from other cognitive systems and jammers, which can be expected to be less time-critical compared to more challenging channel evacuation requirements.

B. The Next Steps In the second step, we propose to extend the military CR footprint by allowing military CR systems to operate as secondary users within limited civilian bands (taking advantage of white spaces in time and space). The terrestrial television and radio UHF/VHF bands are a likely first candidate due to the ideal propagation characteristics for tactical radio systems, the relatively stable channel availability and the maturity of the commercial IEEE 802.22 standard. Within these television and radio bands, the military CR systems would operate on a non-interfering secondary user basis under a spectrum overlay model.

3) Familiarity: The concept of a license free band such as the current 2.4 GHz ISM band, is not new for most military end-users and the introduction of a license free military band for CR is likely to be regarded not as a revolution, but as a case where military procedures catch up to the less restrictive procedures used in the civilian world.

In a third step we propose to build on the experience developed in the second step. We propose that military CR systems would also be allowed to coexist with legacy systems in limited military bands. The legacy systems would be designated as primary users. The CRs would operate on a non-interfering secondary user basis. This will allow military CR systems to take advantage of white spaces in time and space left fallow by military legacy systems. In the proposed third step there is an increase in risk of interference to existing military operations. However, with the experience of the previous steps in the roadmap and only allowing a limited spectrum overlap (between military legacy and CR systems), this risk may be easily managed.

4) Compatibility with current NATO spectrum management procedures: In NATO, the civil/military spectrum Capability Panel 3 (CaP3) is responsible for the harmonization of radio frequency use among NATO allies (see section 4.1). The military part of the CaP3 panel manages the harmonized military spectrum by allocating bands to applications or services, such as wide-band land systems or satellite broadcast services. As such, the proposed first step would be compatible with established administrative spectrum management procedures where CaP3 would allocate one or multiple bands exclusively for CR systems.

In this final step we propose that military spectrum will be managed under a highly flexible and dynamically variable combination of the uncontrolled commons, managed commons, dynamic exclusive-use and overlay DSA model types controlled using DSM policies. We also propose the continual and extensive use of civil spectrum bands on a secondary use basis. A CR network will be provided DSM policies which identify where in spectrum it will be allowed to operate and the associated operating conditions, which it must adhere to. Such allocations may include multiple bands each managed under a different DSA model type.

5) Incentives for research and development: One of the main obstacles in the technological development of military CR is the deadlock created by the general lack of confidence in the technology. As long as there is no clear sign from the military end-user showing an interest in the technology and thus establishing a potential market, the military communications industry will be hesitant to invest in the development of military CR systems. On the other hand, as long as there are no military off-the-shelf CR products, which can prove the concept and clearly demonstrate key CR benefits, the military end-user will remain skeptical towards the technology. The creation of a dedicated band for CR systems can end this deadlock and be an incentive for the industry to start investing and developing products, comparable to what happened in the civil 2.4 GHz ISM band.

IV.

NATO C A P3

AND THEIR COMMENTS ON THE ROADMAP

The previously described DSM roadmap was presented to the NATO CaP3 military session on their meeting of Oct 2012 in NATO Headquarters Brussels. The briefing had two main goals. First to brief the panel about the possible impact of DSM on the existing military spectrum management and operational frequency allocation procedures and secondly to lay a baseline for discussion, how CR and associated DSM procedures can

6) Extensibility: As mentioned previously, an important motivation for this first step is gaining trust. Once the concept of CR proves to work in this dedicated band, the band can be

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CaP 3 has two main responsibilities. Firstly it has to provide sufficient spectrum resources to ensure that NATO military forces have enough spectrum access to fulfil their mission and secondly it has to harmonise military use of radio frequencies among NATO allies.

be introduced in the Military. More specific, we asked CaP3 to investigate the possibility to implement as soon as possible (horizon 2018-2020) the first step of the roadmap. During the briefing, we particularly asked for a 5 to 10 MHz band in the NATO-harmonized UHF I band (225-400 MHz), as this band is the most appropriate for the targeted applications and as CaP3 is responsible for the management of this band in NATO Europe.

So it must be clear that the implementation of step 1 of the roadmap imperatively needs to go through CaP3.

Before going into the details of the comments on the roadmap, we will first give some insight in the NATO procedures concerning the coordination of military frequencies.

B. The CaP3 answer In the discussed following the presentation of the roadmap it was clear that:

A. NATO CaP3 Although a nation retain sovereign rights over its use of the radio spectrum, the nation needs to ratify the NATO Joint Civil/Military Frequency Agreement (NJFA) if it wants to become a NATO member state. the ”NATO Joint Civil/Military Frequency Agreement (NJFA)” is a document constituting the joint agreement between the civil and military authorities of the NATO nations on the use of the radio spectrum for military purposes required by NATO forces or in support of NATO. In other words, the NJFA sets out military spectrum requirements which NATO nations agree to accept by reflecting such needs in their national frequency allocation table.

•

CaP3 understands the problem concerning the deadlock in the development of DSM systems and the uncertainty industry has to face.

•

CaP3 also agreed that a step by step approach in the roadmap is a good approach to keep control over the smooth introduction of these kinds of systems in military communications.

However, the defining of a dedicated band for CR systems in an harmonized NATO band, especially in the UHF I band is just not realistic. During the discussion, the following points were raised.

The management and the coordination of this ’NATO’ spectrum is carried out by a specialised civil and military NATO body, called the Capability Panel 3 (CaP3). CaP3 resorts under the NATO Consultation, Command and Control Board (C3B), as shown in figure 2. Unlike the other Capability Panels of the board, CaP3 is not on the advisor level, but is a decision making authority as delegated by the C3B. It is also important to notice that changes to the NJFA can only be initiated through CaP3.

•

Harmonized NATO bands are already saturated and no green space is available. Hence it is impossible to free a 5 - 10 MHz band for this purpose, without compromising the necessary spectrum resources of other applications and systems.

•

NATO does not allocate nor reserve frequency bands to systems in a too early stage of development. CaP3 agreed that reserving 5 to 10 MHz of the NATO UHF band for a technology which will still take many years to be operational is not a suitable way forward and would set a bad precedent.

•

Concerning the deadlock in the development of DSA systems, it is not up to CaP3, but to the industry to take the risk, despite the uncertainty in regulation.

The only positive point in the discussion was that CaP3 is aware of the benefits that DSM can bring to the military operations, and as such is not opposed to the introduction of CR technology. They clearly stated that the discussion will be reopened from the moment there is a fully operational system. Fig. 2.

C3B structure

V.

D IFFERENT SCENARIOS TO INTRODUCE DSA IN M ILITARY C OMMUNICATIONS

The first step in the roadmap presented in figure 1 is clearly unacceptable for the NATO frequency managers. The question is then ’what next’? How will the development of DSA systems evolve and how can the introduction of DSA systems in military communications be controlled? For this we see some possible scenarios.

CaP3 has two sessions, a military session and a mixed military/civil session. The CaP3 is chaired by a Military CoChairman (from the Spectrum and C3 Infrastructure Branch, SC3IB) and a national Military Co-Chairman (MoD/NARFA) for the military sessions or a national Civil Co-Chairman (national civil spectrum authorities) for the Civ/Mil session.

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A. Natural evolution

space left in its harmonized bands. As a consequence, an already existing band should be re-assigned. This could be, for example, one of the UHF I bands that is currently assigned to ’wideband mobile land systems’. The radio systems already using this band, can still continue doing so, but now as a Priority User. A priority user can access the band on preassigned static frequencies, without sensing or any kind of spectrum negotiation. In other words, this first service, the Priority Access service, is meant for legacy tactical communication systems and future interference tolerant tactical communication systems without DSA capabilities. The military dualpriority band shall also host a second service, the Cognitive Access service, which will be opened to systems with DSA capabilities and no pre-assigned frequencies. These systems can opportunistically access the band on a secondary user bases, according to certain policies. These policies can e.g. be a limitation on the maximum transmit power and bandwidth, a power detection threshold for sensing, etc. in order to protect the priority users operating in the first service.

The first scenario is that no further actions to facilitate the introduction of DSA systems in military communications are undertaken from the regulator nor from the enduser side. In this case we aspect that new developments or industrial products will gradually embrace cognitive features, like spectrum sensing and interference avoiding, mainly to enhance the capabilities of the system, to make them more robust and of course for product marketing. Actually, this process is already ongoing. A nice example is the MUOS UHF satellite communication system [6] in which the 5MHz wide uplink carriers are dynamically notched to avoid narrowband interferers. A critical part however will be the dynamic spectrum access. Military end-users will always stay sceptical about this. The acceptance of DSA will mainly depend on the evolution in civil radio communication technologies. As such, this scenario is not too bad, the only drawback is that the end-user and the CaP3 will have very limited control over the evolution and that the introduction of DSA will take longer than necessary.

The military dual-priority band sets out a clear spectrum access strategy and can be a nice compromise between the arguments brought up by CaP3 on the dedicated band of the initial roadmap. In a first time, the native legacy systems can continue using this band as priority users, which will avoid an escalation of saturation in the harmonized UHF band. In a near future, before the introduction of real DSA capable systems, the legacy systems can gradually be upgraded to more robust tactical systems with no DSA capabilities, still under the priority access model. In a far future, DSA systems can then be introduced in this band, using the cognitive access service.

B. A dedicated band at national level A second scenario is that a dedicated CR band, from the first step in the roadmap, is implemented on a national bases. In the NJFA, it is foreseen that the management of certain subbands within the NATO UHF I band is brought back under the responsibility of the national military frequency managers or NARFA’s (National Allied Radio Frequency Agencies). An idea could then be that interested NATO member states implement a dedicated CR band on a national bases.

The majority of the advantages of the first step of the roadmap as represented in section 3 are still valid. The interference between DSA systems and non-DSA systems can not be totally excluded, but will be limited and controllable. As we are dealing with interference tolerant priority users, and not with primary users, the system requirements of the DSA systems can be relaxed. Limited interference, defined in the spectrum access policies, is allowed. Allocating such a band is compatible with the NATO spectrum management procedures and the band can be easily extended. An important issue is also that by defining a dual-priority band, the NATO frequency managers will give an unmistakable message to the military communication industry that DSA systems will be allowed in NATO harmonized band.

This solution would not be advisable, as we are convinced that there is a need for harmonization within NATO Europe. C. A military dual-priority band at NATO level A last scenario would be to reintroduce the roadmap as presented in figure 1, but replace in the first step the dedicated CR band by a military dual-priority band at NATO level. This dual priority band is inspired on the Pluralistic Licensing (PL) concept, jointly developed within COST-TERRA and ICTACROPOLIS 2 [7], [8]. In the Pluralistic Licensing concept, a fresh block of spectrum is assigned to CR purpose. In this band, 2 services are defined, with different priorities. For the first service, the Primary User service, there is no need to use cognitive access, i.e. no sensing, nor opportunistic spectrum access. However, the use of this service goes with a certain fee. The second service, the Secondary User service, can be used at reduced cost or even at no fee. In this service, a CR access is required. The major difference between the PL access model and the classical Primary/Secondary user access model is that in the first model, the prioritized users are from the start aware that they will operate in a mixed band where CR are allowed, and hence that they can experience limited interference by them.

VI.

Despite the benefits cognitive technology and DSA can bring to tactical military communication systems, the necessary military research and development in this domain is slowed down by a lack of confidence in the technology from the end-user and the lack of a clear regulatory framework concerning DSA. To facilitate the introduction of these promising systems and to offer an incentive to the military communication industry, a roadmap was presented to the CaP3 military session. The creation of a dedicated band for CR systems, which constituted the first step in this roadmap, although well motivated, was unacceptable for Cap3. The saturation of the popular harmonized NATO frequency band is too important to allocate frequency band for non-existing systems. So other solutions needs to be worked out. One promising solution,

The military dual-priority band is based on the PL concept with some minor adjustments. First of all, NATO has no green 2 FP7

C ONCLUSION

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is to stick to the roadmap, but to replace in the first step the dedicated band for CR systems by a military dual-priority band at NATO level. This dual-priority band would accommodate two types of services, a priority service, meant for interference tolerant systems with static frequency allocation (without DSA capabilities), having priority in the spectrum access mechanism and a CR service for DSA systems. The major advantage of this approach is that this band can be introduced without jeopardising spectrum availability of existing systems. If NATO Europe could re-assign one of the harmonized UHF I bands for wideband mobile systems to a dual-priority band, this could be a realistic first step towards the introduction of DSA in tactical communications and an incentive to military communication industry to accelerate the investment effort in this technology. R EFERENCES [1]

[2]

[3]

[4]

[5]

[6] [7]

[8]

Combined Communications and Electronics Board, Guide to Spectrum Management in Military Operations, ACP 190(D). Available through http://jcs.dtic.mil/j6/cceb/acps/acp190/ACP190D Feb 13.pdf, February 2013. B. Scheers, A. Mahoney, and H. kermark, A Realistic Roadmap for the Introduction of Dynamic Spectrum Management in Military Tactical Radio Communication. Military Communications and Information Systems Conference (MCC’2012), Gdask, poland, October 2012. Cognitive Radio in NATO. ISBN 978-92-837-0183-5, available through http://ftp.rta.nato.int/publiC/PubFullText/RTO/TR/RTO-TR-IST077/$-RTO-TR-IST-077-Pre-Release-ALL.pdf, reference RTO-TR-IST077, January 2013. Q. Zhao, and B. Sadler, A Survey of Dynamic Spectrum Access: Signal Processing, Networking, and Regulatory Policy. IEEE Signal Processing Magazine: Special Issue on Resource-Constrained SignalProcessing, Communications, and Networking, May 2007. Demian Lekomtcev, and Roman Marlek Comparison of 802.11af and 802.22 standards physical layer and cognitive functionality. elektrorevue, vol. 3, No. 2, pp. 12-18, June 2012. John D. Oetting, Tao Jen, Satellite SpotlightUnderstanding + Using MUOS. MilsatMagazine, pp. 72-82, April 2013. O. Holland, L. De Nardis, K. Nolan, A. Medeisis, P. Anker, L. Minervini, F. Velez, M. Matinmikko, J. Sydor, Pluralistic Licensing. IEEE DySPAN 2012, Bellevue, WA, USA, October 2012. Advanced coexistence technologies for radio optimisation in licensed and unlicensed spectrum(ACROPOLIS), Document Number D17.1. ICTACROPOLIS Deliverable D17.1, March 2012.

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