TVWS sharing in commercial, governmental and military sectors
The debate is largely over. TV White Spaces (TVWS) below 698 MHz are free and up for grabs whilst spectrum from 698 MHz to 806 MHz, commonly called ‘the 700 Megahertz band’ as licensed and is normally awarded through auctions. The arguments that radios cannot use white space without causing interference to licensed and reserved bands did not hold water even right from the beginning. Multi-radio coexistence is not a new-fangled idea. Both the Pentagon and the US Military have been using this technology successfully in national mission critical situations. Unlicensed sharing of military spectrum in the upper part of the 5 GHz band is working just fine. When in that band, it is mandatory and regulated for wireless device to dynamically scan for any operation in radar systems to avoid interference. If our Pentagon and servicemen are using this proven technology successfully, should there be any reason why it could not be replicated in the commercial world?
According to the New America Foundation, Wireless Future Program as far back as Jan of 07; working paper #16 reported as claiming that “…thru analysis and simulation it had shown that an occupied Digital TV (DTV) channel can be identified with practical certainty by an unlicensed device even if nearby roof mounted antennas are receiving the DTV signal at the threshold of visibility (TOV) and the unlicensed device sees the DTV signal with over 37 dB additional attenuation compared to the rooftop antennas. Once an occupied DTV channel has been identified, it can be avoided to prevent the possibility of co-channel interference (CCI). Additionally, adjacent DTV channels can also be avoided if necessary to prevent adjacent channel interference (ACI)…”.
Had the FCC auctioned off this TV White Space, it is estimated to have put $8 to $24 billion in its bank account (from public sources). By not doing so, the benefits are estimated to exceed this value range by leaps and bounds. The competitive nature of the commercial sector can now be fully exercised in a level playing field. Fixed, portable and mobile devices capable of legally consuming TV White Spaces are called TV Band Devices (TVBDs). They operate under FCC Part 15 of unlicensed electronic device to share this spectrum of airway.
Benefits in the free sharing of TVWS
Securities, Public Safety Agencies and Towns and Municipal Wireless Networks are known to have disparate and different radio network types. They have expectedly slower adaptation of next generation communication technologies and upgrades are done at different times based on local budgeting priorities. This creates major interoperability issues between agencies at times of emergencies and disasters even if wireless communication was never severed. The compromised and high cost connectivity of these networks are mostly using 2.4GHz band today and is making its usefulness at times; marginal. Indeed, for military and commercial use alike, free TV White Space spectrum sharing not only can lower connectivity cost significantly but have longer range and better penetration and propagation characteristics. It would be no surprise to see an avalanche of new use cases in applications like Advanced Metering Infrastructure (AMI) in Smart Grids, weather and volcanic activities monitoring, remote control of public utilities in meter reading, problem diagnostics, crime scene investigation (CSI), mesh networking and pretty much anything your imagination can come up with.
Department of Defense (DoD) and Department of Homeland Security (DHS) can certainly also benefit from the opening up of TV White Space and its emerging richer set of enabling technologies at a time when national security is constantly under threat and spectrum is in increasingly high demand. TV White Spaces provides more readily available spectrum for first responders, emergency personnel and the expected surge of usage by everyone else jamming traffic over the air at the same time. It is critical for DOD, DHS and the commercial industry folks to work together on the spectrum policy and standardization of protocols for seamless and secure multimedia wireless communications anywhere, anytime and in due time, with any radios in any device.
TVBD’s low cost access points and client devices are envisioned to be used for flexible spectrum access in large volumes and interference is expected to increase proportionally to the incoming floods of application traffic affecting quality of service in the next few years. Without serious spectrum optimization schemes and ways to meet the low power limits mandated by Part 15, the pendulum could very well swing to the other side of the equation driving up overhead and actual cost in exchange of using free spectrum. It is hard-pressed for me to imagine however, that the wireless industry will not be able to solve this and any other problems in its way in order to use this free resource to milk profits from all sorts of venues.
What we now have
In is common knowledge that the DoD Joint Tactical Radio System (JTRS) program has succeeded in harnessing networking adaptability and RF changeability technologies in the development of Mobile Ad hoc networks which are well suited for use between service branches in battlefields. Also, the Ground Mobile Radios (GMR) facilitate sharing of audio, video and other medias for troops on the move in combat situations where otherwise incompatible radios would not link up.
In October of 2008, DoD approved its first four-channel multiband vehicular radio system Falcon III AN/PRC-117G after exhaustive testing to obtain four major technical certifications. According to the news report, it allows access to secure IP data in standalone or Internet-connected network with on-air rates of up to 5 Mbps. DoD is well on its way to transition to the next-generation of Cognitive Radio (CR) which is in a nut shell a spectrum sensing technology for mobile units capable of forming self-configuring mesh networks in field operations. This technology is the fruit of joint development effort made by commercial, governmental and military individuals in the IETF wireless routing protocol study group called MANET (Mobile Ad hoc Network).
Reconfigurable wireless technology in Software-Defined Radio (SDR) and the sensing capabilities in Cognitive Radio (CR) are gearing up for the near future wide-spread and sure-to-be popular commercial and governmental deployments. The intelligence and planned broadband services with optimized spectrum usage can determine which communication channels are occupied, automatically switch to using unoccupied channels and to work seamlessly with other SDR/CR mobile devices. Public Safety and local and regional governmental agencies stand to gain the most, since they are always with limited resources to deal with anything from natural disaster to school shooting. These are use cases as untapped opportunities that intersect the commercial sector with the public safety and governmental agencies. The US military can also undoubtedly leverage the rapid development and the potential broad market testing of commercial products onto defense applications and vice versa.
How it works
According to The Federal Code Of Regulation (CFR) FCC Part 15 which quotes “<this partregulates intentional, unintentional, or incidental radiator that can be operated without an individual license…” does not have stringent provisions to limit interference between TVBDs or TVBDs and other FCC certified electronic devices operating in the same band. Nevertheless, both scenarios must work and work without a hitch. Currently, the 2.4 GHz band is let say, well utilized although not saturated but as TVBD devices gain momentum and flourish as anticipated, it would be hard-pressed to not bet on TV White Space sharing not having to face the same performance issues caused by interference from adjacent systems any less than what Bluetooth and WiFi have gone through.
In the Wireless industry, three main methods are discussed to solving the TV White Space interference problem. They are Control Signals, Positioning Systems and Cognitive Radio with sensing technology. Fixed and portable unlicensed TV band devices use these methods to guard against channel-coexistence interference and adjacent-channel interference. TVBD devices must include geo-positioning capability and be able to access an Internet database that will tell the device which white space channels it is permitted to operate on in its current location. Within this database stores licensed bands for regular TV, Medical Telemetry frequencies (e.g. used in heart/lung machines), reserved national and local frequencies for emergencies (e.g. FEMA) and registered consumer products (e.g. wireless microphones). Additionally, fixed TVBDs must have antennas mounted outdoors to ensure successful sensing of wireless microphones and other protected signals that have no records found in the location database; in near real-time.
Power control adaptability in TVBDs is mandatory so minimum power can be used at any given time to sustain a communication link. According to the FCC, fixed TVDB’s can operate at up to 4 Watts EIRP (effective isotropic radiated power). Personal/portable TVDBs are restricted to < 100 milliwatts of power except when they are occupying channels adjacent to protected frequencieswhere they are limited to 40 milliwatts. Fixed TVDB’s can operate between the channels 2 to 15 except 2, 4, and 37. Personal/Portable TVDB’s are restricted to any unoccupied channels between 21 and 51, except 37. Moreover, certain channels between 14 and 20 are restricted for use by land mobile operations (i.e. T-bands) and also strictly wireless microphone usage only between channels 21 and 51. This info is public knowledge and is widely available in the Internet.
Unlimited Use Cases
Multi-band, multi-mode and multi-protocol radios are an important part of the SDR/CR technologies with capabilities including Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC) and are in service in military systems today, according to military web sites. Slowly and surely, this technology is creeping into the commercial sector where the flood gate is ready to open up for a possible explosion of TVBD devices and a landslide of applications taking advantage of it. These applications acknowledge a single radio providing a broad range of functionalities from remote dog leashes to remote rocket ship control with traffic patterns usually highly bursty in nature. This is indeed the core technology of DoD’s JTRS program aimed at increasingly better versions of secure and seamless interoperable systems and equipments of different radio types making use of any available spectrum on the fly according to DFS-policy based cognitive radio algorithms.
FCC had made it clear that TVBDs using white space spectrum will be subjected to a barrage of careful testing and must be certified in its laboratory. This presents the wireless testing community a challenging and interesting problem when dealing with continuous unpredictable demand of power between different radios technologies for a multitude of different applications and provided with chunks of TV White Space at largely unpredictable time patterns. The geolocaton positioning, database access and frequency sensing capabilities would be the main testing targets expected to be done in extensive field tests on the ground, in the air and at sea.
It is arguably true that DoD, DHS, Public Safety Agencies even hospitals, malls and schools’ demand of spectrum usage is accelerating at a faster pace than commercial needs especially at times of crisis when the need to share the airways and the media (e.g. audio, video) is extremely high. These are very valid applications that can greatly benefit from making use of free frequencies effectively and on-the-fly. TVWS / TVBD devices can only be growing deeper into our consciousness before it becomes popular and all the enabling technologies in the works and ones yet to come are well-poised to assist.
Standards Work currently in Progress
The earliest working wireless networks that coexist in the same spectrum without causing harmful interference to each other are known to be WiFi and Bluetooth both operating in the 2.4 GHz frequency.
Now, IEEE P1900.2 is developing a Recommended Practice for Interference and Coexistence Analysis standard for any radio systems operating in either co-channel or adjacent channel.
IEEE 802.19 focuses on IEEE 802 radio systems coexistence issues in existing 802 standards and standards under development e.g. coexistence between 802.11y and 502.16h operating in the 3650 MHz band. Several Coexistence Assurance (CA) documents have been developed and are currently under review. This work complements the work of the P1900.2 study group.
IEEE 802.22 is developing a standard for a cognitive radio-based PHY/MAC/air-interface for use by TVBDs on a non-interfering basis in spectrum that is allocated to the TV Broadcast Service for wireless
Regional Area Networks (WRAN).
Conclusion
In closing, I would like to quote a remarkably suitable analogy made by Dr. Didier Bourse at the Wireless World Initiative, August 07 meeting at Brussels about a ‘Communication Cube’ as he coined the concept. It can be pictured as ‘…one side represents radio frequency, a second side represents the range of radio technologies available and a third side maps all the possible services…” He went on to say that today’s devices operate at only a few points within the cube. At any given time, our mobile device will use a given frequency (e.g.900 or 1800 MHz), a technology (e.g. GSM) and a service (e.g. Audio Call). In the not-so-far future, Bourse envisioned our potential use of the entire volume of the cube, selecting whatever frequency, technology and service is available to get whatever we want across efficiently.
That day should come hopefully, not from too far down the road.
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Citations, References and Bibliography
Facts mentioned on this article can be referenced at the FCC (Federal Communications Commission), IEEE (Institute of Electrical and Electronics Engineers) and the JPEO JTRS (Joint Program Executive Office, Joint Tactical Radio System) websites and other published documents
Full Scale TechnologiesAuthor: Mimi Tam (CTO)Page 1