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THE WHITE SPACE: STATE OF ART
ICTP – White Space Technologies - Trieste 3 -14 March 2014
Summary
1- Wireless services: need for additional spectrum
2 - Defining the “White Space”
3 - The license for primary services
4 - License-exempt for secondary services
5 – Evaluating TVWS demand
6 - Sensing devices to find idle spectrum
6.1 Cognitive Radio
6.2 Geo-location database
7 - Standards for sensing devices
7.1 Wireless Regional Area Networks (WRAN).
7.2 Machine-to Machine communication (M2M)
8. Exploring value of spectrum
9 - Optimizing spectrum management
10 - The long-term ICT strategies
11. ICT statistics and forecast
12 – Planning future availability of TVWS
13 – Trend of TVWS applications
14. Conclusions
Abstract
Since 2005, Administrations and Providers, in the telecom sector,are carrying out studies and tests with the objective of accessingunused broadcast band (TV White Space) to route wireless services suffering network shortage.The potential demand to access the TV White Spaces varies as a function of: population density,of TV coverage, of TV operation and of the level of development of national ICT infrastructure.
The availability of TV spectrum, in terms of time and location, is tested by sensing devices(Cognitive Radio, Geo-location Database) whose standards are defined by national regulation and whose costs add up to the basic cost of transmission mean. Access to TV band is permitted under licence (primary services) or under licence-exempt (secondary services).
The economic value of spectrum is the reference basis when fixing the prices for the use of TV band. Starting from basic costs, economic strategies, subject to national social and economic constraints, should be developed to meet market expectation, to provide affordability, to face competition, to possibly decide economic return.
In the long term, the potential future implementation of TVWhite Space depends by some technical (transition to digital TV, ICT expansion), regulatory (spectrum allocation), and economical (reduce digital gap)factors. The availability of TVWS is subject to some risks as a function of TV expansion broadcast. An unexpected evolution in TV sector (increase operation, expand coverage) might suddenly reduce band usable by TVWS.To forecast future availability of TV White appears, at present, a little difficult.
1- Wirelessservices: need for additional spectrum
When market for telecommunication services is expanding and an increasing number of users are applying for connection, the dedicated national network is expected to gradually saturate: especially in developing regions the transmission means assigned to services is, actually, a finite resource. In absence of significant implementation of national network, an intensive demand of access can drive the whole system to unbalance.
Because of that,Administrations and Providers started looking for alternative network solutions:in particular the attention was turned to recover part of TV spectrum to route partof wireless service demand. The TV spectrum, considered available,includeseither the frequency band imposed between TV channels (guard band) and the spectrum which turns free (unused spectrum)whenTVbroadcast movesfrom analogue to digital technology. The concept of reallocation of unused TV band was, so far,quite successful: the chance of satisfyingadditional wireless demand and the opportunity of optimizing utilization of TV spectrum,stimulated the interest to use the UHF resource and raised the expectationof its availability in the long-term.
Studies and experiments started in the year 2005 to analyze the constraints and the problems concerning the coexistence of TV signals and wireless services over the same band. The first practical study (2007) was related to the potential interference among services. Special cognitive devices (white space devices) were designed to detect the presence of unused TV band, following a CEPT Study (2008).The first experiments did not give positive results, but a Coalition ofeight companies([1]) succeeded(2009) to deliver internet access to US consumers via TV available frequencies.Experiments in USA and Europe have finalized the use ofGeo-location Sensing Systemto ensure the protection of DTT (Digital Terrestrial Television) services. The test became operational in 2013: ten installations located on University campus in Cape Town delivered broadband internet services to ten primary and secondary schools within a 10 km radius.
2- Defining the “White Space”
According to ITU Report “Digital Dividend: insights for spectrum decisions”, the portions of spectrum left unused by TV broadcasting is defined as “TV White Space” (TVWS) and is referred to as the unoccupied portions of spectrum in the television frequency bands (mainly VHF and UHF).From operational and administrative point of view, a first main hierarchical separation can be stated between TV Broadcasting and the wireless services routed over TVWS: the first one is a “primary service” and has access priority to TV band, the other one is a “secondary service” and access TV band only when TV broadcast band is, temporarily or definitely, off-line.
Consequently, when using White Space,secondary services are subjected to the constraint of avoiding interference with TV broadcastingwhich has priority as primary service:in particular, the European Conference of Postal and Telecommunications (CEPT), carried out extensive studies to check,in the band 470-790 MHz,the co-existence between services allocated on TVWS and the TV broadcast, when they are operating in the same frequency band.
3- The license for primary services
Television broadcasting is considered a public service. As such, it should have the right of exclusive use when accessing dedicated TV band. The relevant license should include the necessary regulation in order to ensure priority to TV broadcast as primary service.
The incumbent radio services authorized for operation on a given frequency band, include:
- Terrestrial Broadcasting Service
- Program Making and Special Events (PMSE)
- Radio Astronomy Service (RAS) in the 608-614 MHz band
- Aeronautical Radio Navigation Service (ARNS) in the 645-790 MHz band
- Mobile Service(MS) below 470 MH and above 790 MHz
Different mechanisms for licensing spectrum at national level have been used as part of national spectrum management frameworks (channels utilization), which define the rights and the obligations of spectrum users and provide a framework for user responsibility. Whether licenses involve property rights, they can assure more flexibility for commercial mobile services requiring high QoS (Quality of Service). Licensing options allow different levels of flexibility:
1. Fixed-term licences under periodic review;
2. Revolving licences with automatic renewal;
3. Perpetual licences with provision for recovery.
In practice, the characteristics of the spectrum to be licensed play a significant role in determining its licence duration and security of ownership. Users should have the certainty that the duration in time stated by licence is respected:government re-appropriation, restructuring or re-organization of spectrum should not affect the length in time assigned. And this in the interest of provider (market trade) and to the benefit of users (trust to Provider).
Some details are given in Annex 1.
4- License-exempt forsecondary services
No license is necessary to secondary services for the use of additional spectrum, but strict rules are necessary to regulate the allocation of wireless services into the new available band. The full availability of analogue TV band is obtained once the transition from the analogue TV service to the digital TV service is completed and the “switch-off” of the analogue service is carried out. Only then, the vacated TV bands can be deployed for use to the secondary services, whose nature (bidirectional) is not compatible with the TV broadcasting service (unidirectional). If both services were to operate in the same frequency band, harmful interference would occur, rendering both services useless.
Access to spectrum is either open to all users or to a group of users who access that spectrum in common.The simplification of administrative requirement for spectrum use, stated by licence-exempt, together with the technological implementation of TV network and withservice innovation, lowers barriers to market entry and stimulate TV network expansion.
Licence-exempt spectrum use is,at present, permitted in two forms. The first one involves low power transmissions, where interference is limited by strict power constraints and by regulatory equipment approval. This allows low-power users to co-exist in bands simultaneously used for higher power emissions. The second one involves spectrum use in bands allocated for licence-exempt use like industrial, scientific and medical (2,4GHz; 5 GHz) bands. Most regulators require users of these bands to be subject to certain restrictions, such as output power limits or communication protocols aimed at minimizing interference.
5–EvaluatingTVWSdemand
The growth of advanced consumer mobile applications has considerably increased the usage of bandwidth either in dedicated mobile network and license-exempt available TV spectrum.Spectrum demand variesby different regions. It depends, mainly, on population density, on national income, andon the level of expansion of broadband fixed networks(ICT).
In urban markets, where developed infrastructures exist, the demand for new mobile products is high and it might be difficult to fully satisfy the consumers’ application, using TVWS, unless an efficient form of spectrum utilizationexists. In case of bandwidth shortage, thetechnical choices toovercomethe problem would be to explore forms of dynamic spectrum access as toachieve maximum spectrum efficiency.
In developingmarkets,the main existingproblem is the national “digital divide”.When the level of fixed broadband infrastructure is not sufficiently widespread to adequately satisfy most of the connectivity demand, the use of TVWS might help meetnational demand for wireless broadband communication especially in peripheral areas.Even in these cases, in many urban centres, with high concentration of population,the growing demand and the intensive applicationscreate, again, bandwidth bottlenecks which reduce the TVWS availability.
In the rural areas there is a lack of connectivity: the population is sparsely distributed, theconsumption and the need for connection is low,the geographic coverage may not be sufficient. The implementation of fixed line infrastructure in these areasis capital-intensive:so that therelevant low economic returnwould discourage Providers. A wireless alternative is a more viable choice; the alternatives can include wireless networks in lower frequency bands (below 1 GHz).
6 - Sensing devicestofind idle spectrum
Sensing devices have the objective tohelp achieving maximum spectrum efficiency by exploring forms of dynamic spectrum access (mainly: cognitive radio, geo-location database), as well as by checkingalternative tests for spectrum sharing.
When, the deployment of TVWS services involves large number of sensing devices distributed in different regions(with different purposes), more attention must be paid to determine the levels of interference and avoid its negative impact on TVWS bandwidth availability. To this extent, the CEPT (ECC Report 159) emphasizes the need for more studies to understand the impact of TVWS sensing devices in the bands adjacent to 470-790 MHz which will require careful attention especially in cross-border situations.
6.1 Cognitive Radio
Cognitive Radio (ITU-R Report SM.2152) is a radio system employing technology that allows the system to obtain knowledge of its operational and geographical environment. In particular, a cognitive radio is a software radio whose control capacity lets provide an intelligent process to access unused band. The empty spectrum is detected autonomously, the destinations of calls is stored and, as last step,their routingis arranged by available carriers.
When implementing real sensing process, CR users cannot distinguish between primary signals and other user signals, so that the hole detection may become more difficult;moreover, sensing and transmission cannot be performed at the same time:in consequence, during the sensing time, all the CR users have to stop transmitting.Efficient spectrum sensing is essential in CR so it is important to find the optimal sensing technique with the optimal sensing period and observation time that maximizes the efficiency maintaining a given interference level.
When there are many CR users that may access the same frequency bands at the same time and location, a CR user needs to coordinate its access with other users. The spectrum availability changes over time and over space and, in consequence, a dynamic inter-cell spectrum sharing is needed in a CR network. The spectrum sharing technique should maximize the cell capacity, minimize interference to neighbour users and protect primary users.
6.2 Geo-location database
Geo-location databases are an alternative to sensing techniques in Cognitive Radio. They offer a practical solution to monitor capabilities and primary transmissions. A secondary user has access to a database system to get information about the primary users in a given area. The secondary user interact with the database to know which frequencies are free in a certain time and in a certain location and determine the transmission power they are allowed to use.
To offer the White Space distribution over the frequency bands, the geo-location database needs some parameters and information such as primary user’s frequency of operation, transmitted power, size and type of transmit antenna, etc. these parameters are provided to the database system by primary users. Although the database systems solve the problems of location uncertainties, fading effect and detection errors of sensing techniques, they have the trade off of synchronizing and updating the database appropriately.
A more precise reuse of spectrum is possible thanks to database systems and the US FCC has presented it as the main tool to detect white spaces. In Europe on the other hand, a use of both a database system and sensing techniques has been proposed.
It facilitates the spectrum sharing collaboration among regulators, broadcasters and TV White Space industry. Although the geo-location database had been introduced by the TV White Space industry, the collaboration assumes that also broadcasters and wireless microphones participate in contributing information to the database and benefit by doing so.
7 - Standards for sensing devices
The research of alternative forms of spectrum utilizationcould drive, in recent years, to new devices and to the definition of their structure. They are intended to face the increasing demand for wireless connectivity as part of the evolution of ICTs in the “Digital Information Era”.Providing access to efficient ICT infrastructure has become a mainobjective worldwide, especially considering the important role that ICT play in the word society.
7.1 Wireless Regional Area Networks (WRAN).
The WRAN includes standards for low-power devices able to deliver broadband connectivity mainly in rural areas:their operation does not produce interferenceon TV primary bands. Such development has taken place under the IEEE 802.22 standards which suggestthe specific rules for devices operating in TVWS. One of the objectives of this technical standard concerns interference protection of the incumbent television broadcasting service.
Protection of interference to TV broadcasting service is, as well, provided to other authorized radio transmitters which operate in the band, such as wireless microphones, used when attending events or local and public meetings. An important aim of this standard is based upon the development of cognitive radio technology for implementing non-interfering spectrum use in a shared-spectrum environment.
The WRAN devices would be available either in fixed and mobile modes; in order to prevent interference to the TV service, a database assignment process has been proposed for operation.
This database assignment approach adopted in the US (FCC), consists of a geo-location capability of devices operating in TVWS.
7.2 Machine-to Machinecommunication (M2M)
Also referred as M2M communication, it consists of very low-power radio transmitters used for low-data rate industrial and commercial applications such as monitoring, tracking, metering and control (smart machines). They are intended for operation under a license-exempt framework, always under a non interference basis. Recently, in the United Kingdom (Special Interest Group = SIG), open specification for M2M devices, for operation in TVWS, has been agreed as a preliminary stage. This group released, in April 2013, a specification for low-data rates M2M devices to operate in the terrestrial television bands, transmitting data over idle TV frequency channels in geographical areas where TVWS is available. As the use of M2M devices grows, and more applications are requested, it is expected that numbers of M2M devices deployed will grow exponentially especially considering the higher coverage ranges offered by the terrestrial television frequency bands.
8. Exploring value of spectrum
Increased traffic on wireless networks increases the demand for the spectrum on which these wireless broadband services run. As a consequence, advanced wireless networks are taking more significant placein many national economies, increasing the need to assess the value of spectrum accessed.Considering the economic scenario (competition, market affordability), within whichtechnology for Broadband Wireless Access (BWA) is expanding, there arises the need for regulators to find, at least, a viable estimate of spectrum valuation.
The perceived value of a spectrum licence comes, mainly, from the comparison between the economic evaluation of market demand (potential revenue) and network investment. To balance demand and spectrum supply, regulators should rely on pure economic models, letting market forces play a larger role in spectrum management.
Therefore most valuation models involve a calculation of cost associated with network infrastructure, including equipment and construction costs, as well as cost of capital and labour (management and maintenance). Some of these costs can be known or, at least well estimated, through benchmarking and survey of existing equipment market. Such cost calculations are made on a forward-looking, incremental basis, as to account for ongoing costs.
Opportunity cost. The opportunity cost is defined (New Oxford American Dictionary) as “the loss of potential gain from other alternative when one alternative is chosen”. That is: it is assumed to be the best choice among several exclusive alternatives. Essentially, the opportunity cost is the amount that a potential buyer would have to confront before giving up or change alternative.
For example, for a user of a point-to-point fixed service band, a possible real alternative to the use of original band would be either to moveto more efficient system or to relocate to higher frequencies.