Radar White Spaces

Regulation of secondary access to TV bands, the so-called TV White Spaces, are already in place in the United States and are expected to be finalized in the UK this year. Due to their attractive sub-Gigahertz frequency range TVWS offer important opportunities for applications which are range-limited, and this is currently being exploited for  example  for broadband wireless access to  "not-spots" and rural communities.  On the other hand  TVWS spectrum consists of  8 MHZ non-contiguous channels, and its availability varies greatly with location making it less suitable to support bandwidth-intensive applications like wireless distribution of HDTV and multimedia inside the homes. Moreover, in February 2012 the International Telecommunication Union (ITU) has brought forward a decision to clear a larger portion  of   Digital Terrestrial TV (DTT) broadcasting band for mobile services in Europe, Africa and part of the Middle East.  The release of this “Second Digital Dividend” is planned by 2015. Since TVWS spectrum are spatially unused portions of DTT spectrum, clearing more DTT spectrum for mobile broadband ma have an  impact on the availability of TVWS spectrum.

Radar bands are a good candidate for cognitive radio access because their operations is in many cases predictable in time and space and because they operate in large portion of spectrums “sweet-spot”, e.g. in the US over 1.7   GHz of spectrum from 225 MHz to 3.7 involves radar and radio navigation infrastructure. 

Especially, the S (2.7-3.4 GHz) and C (5.255-5.870) bands are attractive because these bands are close to  the ISM 2.4 GHz and 2.6 GHz 4G band for which both  WiFi and LTE  devices exist today that could be easily reused in radar bands, and this would reduce barriers to markets due to low-cost implementation and the economy of scale. The L (960-1215) MHz radar spectrum is of interest because, due to the lower frequency range, it can offer good coverag. It could be used   to support wireless connectivity for future M2M applications, such as smart grids and connectivity to vehicles.  

In addition to civilian radar bands, cognitive radio technology could also be used for sharing of the Military  radar spectrum.  In the UK the Ministry of Defence (MoD) is seeking to release and share spectrum to raise revenue and reduce £155 M/annum spectrum fee. A report by PA consultancy, which was commissioned by Ofcom has identified important opportunities for sharing of MoD spectrum using cognitive radio technology.

The 5150 MHz to 5350 MHz and 5470 MHz to 5725 MHz radar bands are already open to secondary access by IEEE 802.11 WLAN devices which use Dynamic Frequency Selection (DFS) to protect radars from harmful interference. However, secondary access to these bands somewhat “pre-dates” recent advance in cognitive radio technology. In particular it solely relies on the use of sensing-techniques, and do not incorporate the idea of using Gelocation databases, which is becoming the regulators’ preferred  method  for incumbent protection and white space detection. Furthermore, 802.11 operation in radar bands  is best-effort, as it could be interrupted upon detection of radar signals, and therefore do not satisfy QoS requirements.

Some recent papers that explore using Radar White Spaces

Adressing the spectrum needs of smart grids and other M2M: Can cognitive radio help? (2)

Although a cognitive radio solution looks very promissing, especially for non mission and life-critical M2M communications, e.g. metering and monitoring data, applications that involve tightly coupled monitoring and control loops may require  very high reliability and  very low latency (e.g. ~milisecond for safety-of-life ITS applications, or some applications in smart grids, such as phasor monitoring) which initially seem unachievable using  opportunistically acquired spectrum.

Two issues arise

-1. M2M communication using cognitive radio is interuptable (this can happen when a primary system shows up in the band)

2. Even if this problem coul be fixed, e.g. because primary sytems spectral occupancy is predictable in space and time (e.g. using a geolocation database approach), then theres is the issue of interference due to other cognitive radios/secondary users operating in the band.

There is, in my view, no straighforward solution here. One option could be that a particular bands is exclusively used/dedicated  for secondary use of mission/life/safety critical M2M use, similiar to the recent approach that is being adopted for the MBABN (Medical Body Area Networks) in the United States, and is then managed using a database approach.  Another, more amitious approach woul be to rely on the ability of cognitive radios to switch channel/spectrum quickly and intelligently in  a way that QoS is maintined despite intermitency in spectrum availabilit, previous work on channel switching in IEEE 802.22 networks (mainly simulations though) suggest this is possible, at least to satisfy QoS requirements of human-driven traffic.   A final option is that M2M sytems would rely on a mix of licensed, license-exempt and opportunitically acquired spectrum. 

See also my forthcoming paper in  the IEEE Network

• Cognitive machine-to-machine communications: Visions and potentials  for the smart grid, with Yan Zhang, Maziar Nekovee et al. 

Adressing the spectrum needs of smart grids and other M2M: Can cognitive radio help? (1)

There is currently some interesting debate going on in Europe  on spectrum requirements for wireless communications of future smart grids, intelligent transportation, health monitoring and other Machine-to-Machine communication use cases. See for example

• Results of the Digital Assembly workshop on: Spectrum for Wireless Innovation in Europe,   Chaired by Catherine Trautmann, MEP, Brussels, 17 June 2011
•  Public Consultation Document On Use Of Spectrum For More Efficient Energy Production and Distribution , The EC, 24 January 2012.

Cellular networks are simply too expensive an option for smart grids, use too much power on the transceiver or do not offer ubiquitous coverage. Today’s deployments also pose important technical challenges in  managing large amounts of disparate M2M devices, QoS guarantee  and interoperability. An alternative to the cellular are the so-called capillary networks created by  short-range wireless (SRW) technologies  that connect machines directly to the fixed Internet. This greatly reduces both the cost and complexity in managing and operating M2M services, and for this reason is becoming defacto choice in applications such smart metering and health monitoring.  Important shortcomings of this alternative are limited coverage and little support for mobile M2M applications.  Furthermore, the massive adaptation   of WiFi-based communication devices is rapidly depleting the ISM (Industrial, Scientific and Medical) spectrum bands where most SRW technologies currently operate, and this is creating real concerns about the long-term sustainability of this alternative.

For smart grid  services to achieve their full potential there is  need for radio spectrum both below 1 GHz (to achieve universal connectivity at low cost) and above 1 GHz (to relieve congestion and achieve scalability).  This dual need  is especially acute  when it comes to M2M communications  for smart grids and  ITS which require  universal coverage  in order to  connect millions of  meters, vehicles etc to service-side monitoring  and control systems. This need could be met rapidly and in a cost and spectrum-efficient manner through innovative use of cognitive radio, which enables dynamic and flexible access to potentially large portions of already licensed but unused spectrum in TV and other bands for smart grid communications. Furthermore, the use of cognitive radio’s interoperability features will enable operators to provide “horizontal” M2M solutions for a range of applications, as opposed to the currently available vertical solutions. 

Some recent pictures from meetings and travels

QUASAR Workshop on Regulatory Aspects of Cognitive Radio/TVWS,

London, November 2011 

                                        Seminar at Shanghai University on mathematical modelling of rumour spreading  in 

                                                  social networks, July 2012 

                                            COST-TERRA meeting on cognitive radio, Lisbon, January 2012

Co-existence and spectrum sharing in White Spaces

One of the "hot" topics/question that came up at the IEEE Comm. Society meeting that was held in Washington DC on 19 September was the co-existence issues in TVWS (i.e. how spectrum should be shared among white space devices). The situation here is more complicated that it is the case for the licence-exempt access to, e.g., the ISM band because

-different access technologies may have to share TVWS spectrum among each other (e.g. 802.11.19. 802.11af, but also perhaps LTE, new standard for M2M etc)

-unlike the ISM bands where regulators have imposed low EIRP limits (100 mW in Europe, up to 4W in USA) to make possible efficient spatial sharing, in the case of TVWS we may see a mix of high and low-power use.

The main challenge is how to ensure fair (and also ideally efficient) sharing in TVWS between these heterogeneous users. The csma/ca-type listen-before-talk mechanism (these are sometimes called politness protocls or spectrum etiquettes) used in WiFi and Bluetoth are one option. This may work fine when sharing happens exclusively among  802.11-type systems but won't work if 4G technologies like LTE are also using these bands, since these technologies have very sophisticated mechanism for intra-system sharing but currently lack mechanism for sharing with other access technologies. Another issue with csma-ca type approaches is that because they are distributed a valuable portion of bandwidth is wasted for signalling. Also these mechanisms are ultimately aimed at best effort because they scarify QoS for fairness.

One possible short-tem solution to this problem is to use an additional layer in geolocation databases (GDB) that manage sharing between heterogeneous systems. This should be possible because GDB’s have access to information on location and type of devices. 

One potential problem, at least in the United States, with this approach is that the FCC does not seem to have mandated devices to report back to GDB provider the frequency and transmission power they are using. Another potential problem here is what happens to a database approach if sensing-only devices are also allowed in TVWS. More thoughts later on these and other issues of sharing.

Forthcoming publications and events

I am working on a couple of book chapters for a forthcoming book on cognitive communications, to be published begin 2012

-Regulatory, policy and economics of cognitive radio for secondary spectrum access

-Cognitive radio networks in TV White Spaces


I am/was involved in the following recent/forthcoming meetings

IEEE 2011 Communication Socitey Workshop on Dynamic Spectrum Access: Collaboartion between technical, regulatory and business community, 19 September 2011, Washington DC, USA (panel)


ETSI Business Innovation Summit: The Wireless Network of The Future, 4th-5th October 2011, London, UK (panel)


IEEE 2011 International Symposium on Information and Communication Technology: Green and Cognitive Communications for the Future, October 12-14, Hangzhou, China (steering committee)

some of my recent papers and lectures on vehicular (adhoc) networks for intelligent transport systems

Papers
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Universalities of Performance Parameters in WiFi-based Vehicular Adhoc Networks, IEEE Communication Letters, 2011
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5955146

Reducing congestion in obstructed highways with traffic data dissemination using vehicular networks EURASIP Journal on Advances in Signal Processing, 169503 ( 2010).
http://delivery.acm.org/10.1145/1930000/1928489/p1-hewer.pdf?ip=193.113.57.161&CFID=39329285&CFTOKEN=61896482&__acm__=1314118699_eeacaa5b6e4637a081fd244de6b4fc0e

Converging time synchronization algorithm for highly dynamic vehicular adhoc networks, IEEE CSNDP2010, Newcastle, UK, May 2010
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5580393

Epidemic algorithms for reliable and efficient information dissemination in vehicular adhoc networks, IET Intelligent Transport Systems, 3, 104 (2009)
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5071780

Quantifying performance requirement of vehicle-to-vehicle communication protocols for rear-end collision avoidance, IEEE VTC, May 2009, Barcelona, Spain
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5073822

Lectures
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Vehicular Communications and Networks,
Lecture notes presented at the ESF School on wireless technologies in emergeing spectrum bands, Brno University of Technology, Czech Republic, May 2010
http://www.radio.feec.vutbr.cz/kosy/soubory/maziar/Nekovee_lecture_2_fulltext.pdf