Furthermore, the regulator provides a technical guideline including algorithm and the type of propagation model to be used by qualified GLSD operators in their implementation. Additionally, the regulator jointly coordinates the interference management function with the operators.
Specifically, this is attributable to the fact that private operators must strictly enforce the set-out regulatory limits calculated by the regulator in their GLSD implementation. Furthermore, the tight coupling framework allows more efficient monitoring of possible interference by WSD to incumbents as this function is collectively carried out with private GLSD operators.
The framework gives the regulator the ability to switch off noncompliant secondary GLSDs. Disadvantages of this approach are as follows: i Complexity : the requirement to have a reference GLSD to perform baseline calculations to determine TVWS availability and the corresponding WSD transmit power limits translates to added investment and running costs on the overall framework implementation to the regulator.
Additionally, this means that the regulator must possess expert personnel to run and maintain such a complex infrastructure. Such complexity and costs render this approach less feasible to regulators from the developing world who often are plagued by weak institutional capacity [ 19 ].
Figure 3 illustrates this further. However, the regulator furnishes private GLSD operators with raw technical information required to calculate the protection parameters of the incumbent receivers.
These include, but are not limited to, the location of the incumbent transmitter, antenna height, transmitting power levels, pattern, and technical details of the type of the approved WSDs. Furthermore, the regulator provides technical guidelines including the algorithm and type of propagation model to be used by approved GLSD operators in their implementation.
The regulator independently monitors possible interference that might be caused by the WSDs to the incumbent services. The loose coupling DSM framework has many advantages, chief among which are the following: i Simplicity : once the regulator has provided the relevant technical information about incumbent networks and the framework guideline to the qualified private GLSD operators, there is no requirement for a regulator-controlled reference GLSD to perform baseline calculations for determining TVWS availability and corresponding WSD transmit power limits.
As such, there is no ambiguity about how operators can implement the DSM framework. This lightly applied DSM policy enforcement is particularly suitable for deployment in the developing world environment, where weak government institutional-frameworks are prevalent coupled with a lack of institutional capacity. The key disadvantage is as follows: i Reduced capability to enforce and monitor ruleset implementation : the main drawback of this regime is reduced ability for the regulator to enforce and monitor the ruleset implementation.
This is largely attributable to absence of a reference GLSD. Spectral emission masks are used to define the maximum permitted out-of-band OOB emissions for operation of secondary systems such as WSDs in the RF band of interest [ 29 ]. To ensure the protection of terrestrial broadcast TV receivers from potential harmful interference that might be generated by WSDs, spectrum regulators are required to prescribe WSD emission requirements with respect to cochannel and adjacent channels specifically for various channel bandwidths.
Figure 4 a depicts a typical WSD emission mask. Protection ratios PRs are defined as the difference of primary system signal power and the secondary system at the primary system receiving antenna point of failure [ 30 ]. In contrast, blocking masks define the level at which a receiver rejects unwanted OOB emissions before the point of failure.
Figure 4 b depicts a WSD-primary system protection ratio. Radio propagation and channel models are crucial components of the regulatory framework. They are used for performance evaluation of the behavioural patterns of complex wireless systems reflecting actual on-the-ground conditions [ 31 ]. Regulators are expected to prescribe preferred radio propagation model s for each reference planning geometry of spectrum sharing scenario. The following are commonly used coexistence calculation methodologies also known as Algorithms utilised in geolocation based DSM frameworks [ 32 ]:.
HAAT is height above average terrain of the antenna. CINR is the carrier to interference noise ratio. Typically, this is a Minimum Coupling Loss MCL based methodology that largely relies on rigid rules of separation distance vectors to each grade of terrestrial broadcast TV contour in order to determine the availability of TVWS channels [ 9 , 21 ].
The separation distance vector calculations are performed using statistical curves of wanted and interference field strengths, respectively. Algorithm 1 describes key parts of the vectorised approach. This is basically an enhanced MCL-based methodology; the approach compares the received signal power level within a small geographical area of interest against the minimum CINR threshold to determine if a channel is occupied [ 18 , 33 ]. The process is repeated across all small areas. Algorithm 2 further describes the CNIR threshold approach.
This is a statistical approach that utilises a Monte Carlo MC simulations methodology to determine the degradation in location probability of a DTT receiver in small geographical coverage areas pixels. Any presence of a WSD interfering signal within a pixel reduces the location probability of an incumbent receiver, [ 34 — 36 ]. This degradation is subsequently used to calculate the availability of TV white space channels.
Algorithm 3 describes the main parts of the degradation of location probability approach. Table 1 lists the building blocks of a DSM framework. The TVWS framework by the Federal Communications Commission FCC , the regulator of the USA, is meant to allow opportunistic access to the unused spectrum in the TV bands by unlicensed wireless devices in order to increase the availability of broadband services particularly in rural and underserved areas [ 12 , 20 ].
This could be achieved while protecting television and other services that operate in the TV bands. TVWS spectrum has superior propagation characteristics that allow signals to reach farther and penetrate human made and natural structures. Moreover, the FCC believes that opportunistic exploitation of TVWS could potentially enable many other innovative applications such as real-time video streaming in home networks and the deployment of sensors to monitor wide-area power and water grids.
The GLSD technical rules are outlined in [ 12 , 20 ]. The TVWS networks are required to operate without causing harmful interference to receivers of incumbent networks and to accept interference to their receivers. This is achievable through the use of GLSDs to be operated by designated administrators. We categorise the approach as loose coupling LC.
The framework utilises nonprioritised access, license-exempt spectrum assignment approach. The framework allows an unlimited number of GLSD administrators. The framework requires certified GLSD administrators to utilise the prescribed algorithm to perform necessary calculations for protecting incumbent services.
The framework prescribes an algorithmic guideline for performing the necessary calculation required to protect incumbent services. Fundamentally, the algorithm follows a vectorised approach by utilising the provided table of separation contour distances and their corresponding transmit power levels that WSDs could use in the vicinity of incumbent service areas.
Coverage contour distances are calculated using the and statistical curves for analogue and digital TV broadcasting technologies, respectively. Separation contour distances are calculated using the statistical curves. Separation contours for protecting different incumbent services are illustrated in Figure 5. Extract from the FCC calculated separation distance contours is illustrated in Table 2 [ 20 ]. Entities wishing to become a designated GLSD administrator are required to undergo a day public trial as part of the qualification process.
Such capabilities include the following: i Providing protection to all incumbents as required by the framework, including protecting primary services located in the border areas of neighbouring countries. Moreover, the framework allows operation of spectrum sensing WSDs. Categorisation of devices is further illustrated in Figure 6. Description of Figure 6 is as follows: i Table 3 illustrates this further.
Tests include, but are not limited to, i maximum conducting power output of WSD; ii power spectral density of WSD; iii adjacent channel power of WSD; iv radiated spurious emission beyond TV bands; and v AC power line conducted emission limits. The above tests are performed by an accredited service provider recognised by the regulator. However, the framework does not mention any specific communication protocol to be used. Moreover, such layer of interaction must enforce the following security measures: i Prevention of unauthorised access to the system.
The framework does not clearly define the primary responsibilities of the GLSD administrator within the interference management protocol. The approach is categorised as tight coupling TC. The framework utilises the nonprioritised access, license-exempt spectrum assignment approach. The framework allows multiple GLSD providers. Moreover, qualified providers are required to perform coexistence calculations with respect to the protection of PMSEs, including incorporating periodic updates in the baseline dataset received from Ofcom.
The Ofcom framework utilises the degradation of location probability methodology Algorithm 3. In this approach, there are no separation contour distances to limit WSDs from operating close to primary services.
The chief benefit of this algorithm is the provision allowing WSDs to operate at higher EIRPs in areas where there is strong primary service field strength. Key steps of the Ofcom approach are depicted in Figure 7. This results in the degradation of the location probability map with respect to DTT self-interference.
Candidate GLSD providers must demonstrate the capability to implement framework rules to the satisfaction of Ofcom. Such capabilities include the following: i Correct implementation of the algorithms provided by Ofcom. There is no provision for WSD capable of autonomous sensing. Additionally, both categories of WSDs are grouped into two types: i Type A : this is a fixed WSD which may has an in-built, dedicated, or external antenna.
There is no consideration for compensation of possible WSD antenna polarisation discrimination. However, there is no prescription of any preferred communication protocol to be used. This is largely made possible through a White Space Information Platform WSIP interface that allows interference management teams to automatically instruct master WSD to reduce or completely cease transmission.
Additionally, Ofcom possesses the capability to remove a noncomplying GLSD from a device discoverable web-list. This section highlights TVWS frameworks proposed by other national regulators and nongovernmental entities. These frameworks have minor variations from the ones discussed above. However, there are minor variations related to the protection of Remote Rural Broadband System RRBS stations that were historically licensed to provide broadband services in rural areas utilising the unused TV channels.
The DSA alliance proposes the use of Algorithm 2 i. Further, the proposal considers the use of point-to-point Longley-Rice radio propagation model in the calculations.
The MCDA is an umbrella term for approaches and techniques used for solving or evaluating complex multistakeholder decision-making problems with multicriteria or multiobjectives and could potentially include qualitative or quantitative aspects.
The evaluation approach of DSM frameworks includes the following key steps: i Identifying the problem to be addressed. The DSM framework building blocks listed in Table 1 were identified as evaluation criteria. We asked a group of 25 respondents that included Small and Medium Enterprises SMEs ICT entrepreneurs, senior telecommunications engineers, and policy experts to provide weights 1 to 7 on each of the listed criterion with 1 being the highest weight and 7 the lowest.
The average weights are used in this evaluation. The criteria normalisation is obtained as follows: where is the criteria weight. This evaluation utilises multiple objectives across different disciplines, including regulatory, policy, technical, and socioeconomic.
We align each criterion with the relevant objective. Based on the in-depth description of each alternative i. A complete list of inputs for evaluation model is provided in Table 4 , for which the mathematical function could be to minimise or maximise the various options.
Consider an evaluation scenario where there are criteria with variable with preference function and assigned weights. We derive the pairwise preference comparison function for over as follows: where is the preference index. The comparison is conducted among preference functions characterised by their flow types, namely, i the entering flow, ii the leaving flow, and iii the net flow [ 44 ].
The entering flow which is used to measure the weakness of action relative to other actions, this is given by where is the entering preference index. Similarly the leaving flow which is used to measure the strength of action is given by where is the leaving preference index. The net flow is determined as the balance of the between the entering flow and the leaving flow as follows: Hence, the equilibrium of 4 and 5 can be put into a compact form as follows:.
A positive preference flow value translates to a strongly preferred option, while negative flow value suggests a weaker preferred option. Figure 9 presents a sensitivity analysis with respect to weights during the decision-making process. Hence, the results suggest that this decision largely gravitates around the following criteria that are close to each other: coexistence algorithm and interference management.
Figure 10 depicts a typical interference management protocol for the DSM framework. The protocol details eight key steps that must be observed by stakeholders in order to mitigate any potential interference to the primary network caused by the secondary network. Sustainable DSM Framework.
We define a sustainable DSM framework as one that promotes efficient utilisation of the RF spectrum to achieve socioeconomic development objectives in resource constrained environments relevant to the context of developing countries. We finally propose a sustainable DSM framework relevant to the context of developing countries by i introducing new features that are not found in either of the evaluated frameworks and ii borrowing salient features from the two evaluated DSM frameworks i.
We propose the tight-coupled framework approach used by Ofcom to empower the national regulator with a firm control of the process. We prefer the lightly managed license-exempt approach used by both the Ofcom and FCC. Notably, Stucke [ 45 ] proposed a four-level spectrum assignment regime that would include time-dependant spectrum usage fee.
However, we argue that this approach is not suitable for promoting new entrants and growth of SMEs, as these often fall into the previously disadvantaged population in developing countries. We prefer the simpler approach used by the FCC. We propose a robust interference management protocol relevant to the context of the developing countries see Figure This approach provides sufficient protection to the primary users in both grade B and grade C coverage contours.
For example, viewers in marginal areas who cannot receive grade B quality can still be protected under grade C contours. In developing countries, the majority of rural TV viewers are located in fringe reception areas and make do with fairly poor reception quality or do their best to improve their reception by raising their mast height beyond the norm. We further modify the FCC approach by allowing operation of fixed WSD adjacent to an active TV channel; we have validated this proposal in [ 22 ], which was duly acknowledged by the FCC in their recent proposed rule-making [ 12 ].
The Ofcom approach, despite it robustness, is not preferred because there is a lack of reliable national dwelling address system that corresponds with the location TV license holders. In many developing countries it is normal to find several TV license holders living in one house. This problem could inhibit the process of identifying the location of TV receivers to be protected.
Additionally, this approach involves massive countrywide pixel-by-pixel calculations which requires higher computing resources, which thus increases operational costs. However, we adopt incumbent receiver protection ratios used by Ofcom since they harmonise with ITU region 1 to which Africa belongs. This article has proposed an efficient approach to enable formulation of technical spectrum management regulatory policy. Finally, the authors proposed a sustainable DSM framework that utilises a simplified lightly managed license-exempt approach which is critical to allow new entrants and spur the creation of knowledge-based industries in the context of developing countries.
The proposed approach is suitable for the formulation of technical regulatory frameworks for enabling futuristic radio technologies such as those envisaged in 5G networks.
The authors declare that there are no conflicts of interest regarding the publication of this article. This is an open access article distributed under the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Article of the Year Award: Outstanding research contributions of , as selected by our Chief Editors.
Read the winning articles. Journal overview. Special Issues. Academic Editor: Paolo Bellavista. Received 29 Oct Revised 12 Feb Accepted 01 Mar Published 01 Jun Abstract National regulatory authorities NRAs in developing countries need an accelerated means to formulate technical regulations for the telecommunications sector. More Filters. Development of direct method of direction finding with two-dimensional correlative processing of spatial signal.
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