1. Spectrum Management Process:

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1 SPECTRUM Abstract Radio Frequency (RF) spectrum is a scarce limited natural resource. It is part of the electromagnetic spectrum, arbitrarily up to about 3000 GHz, beyond which are infra-red rays, seven colours of white light, ultra-violet rays, x-rays, gammarays and cosmic rays. Radio waves are governed by laws of physics and travel in a straight line with the speed of light. Radio waves cannot be confined to national boundaries or specific areas and are susceptible to harmful interference. Propagation of radio waves has different characteristics in different frequency bands and is influenced by different phenomenon, including inter-alia, cosmic noise, man made radio noise, geographical terrain and climatic conditions. Like any other natural resource, it cannot be owned but can only be shared amongst various countries, services, users, technologies etc. While, prima-facie, the spectrum may appear to be quite in abundance, in practical terms it is extremely limited because of availability of technologies, propagational and operational constraints and enormous requirements for variety of applications. Wireless is being used so predominantly, now a days, that there is hardly any walk of life, which does not use radiocommunication in one form or the other. It includes maritime, aeronautical, broadcasting, transport, oil & electricity sectors, public utility services, health & environment, public telecommunication services, internet, e-commerce, and so on and so forth. To cater for the gigantic demand on the spectrum, the world-over, it is essential that the spectrum be used efficiently, economically, rationally and optimally Regulation of radio is the mechanism, entirely different from regulation of other activities or the term 'regulation' in general parlance. It is predominantly governed by the scientific features and physical laws of nature. Spectrum can neither be created, nor destroyed. It is the use of spectrum, which can be regulated so as to multiply its usage by technological means, taking into account natural phenomenon of its capabilities and its constraints. An evaluation of the interference threat to and from a new station is an integral part of radio regulatory mechanism requiring an in-depth analysis of technical characteristics of the station and its environment. More are the number of stations, more is the pollution of electromagnetic environment; more are the types of services and applications, more are the complexities of co-existence; more are the diverse technologies, more are the problems of regulation. Situation is somewhat 1

2 analogous to road traffic. More is the number and variety of vehicles on the road, more is the chaos and the need and complexity of regulation. 1. Spectrum Management Process: 1.1 Management of spectrum is the combination of administrative and technical procedures with legal connotations necessary to ensure efficient operation of radiocommunication services without causing harmful interference. Efficient and effective spectrum management, therefore, needs to be the art and science of carefully planning spectrum allocation in a coordinated manner without compromising national interests and efficiently assigning frequencies for the benefit of users at large with minimum scope of harmful interference. In fact, radiocommunication networks are like global society necessitating appropriate discipline. 1.2 There are forty different types of radiocommunication services, including safety services like aeronautical, maritime, radionavigation, radiolocation, radio astronomy, meteorological, broadcasting, satellite broadcasting, fixed, fixedsatellite, mobile, mobile-satellite, space services, etc. In accordance with international treaties, all the frequency bands are shared amongst different types of radiocommunication services for variety of applications and technologies by different countries. The basic tools of radio frequency sharing require application of principles of time sharing, technical sharing and geographical sharing. No user can work in isolation, no service can work in isolation and no country can work in isolation. It is a collective spectrum management exercise and technical regulatory mechanism which alone can ensure the interference free operation of various networks. It is the individual frequency, which is assigned to a user or a service provider and not a frequency band. No service provider, be it a government or private, has ownership claim on any part of the frequency band, only frequency assignments are made in a particular frequency band, as per national and international plans and regulations, for operation of radio networks owned by an agency. Spectrum management and radio regulatory mechanism have multi-dimensional facets. 1.3 National and international coordination, sharing, coexistence and protection are key elements of spectrum management process. Spectrum management and radio regulatory process is techno-legal in character. Moreover, international and national aspects of radio regulatory process are completely inter-linked. Radio regulatory process has multifarious activities, which include, among others, interaction with ITU, with Administrations of other countries, national and international frequency planning and coordination, 2

3 formulation of legislation, rules and regulations, implementation of national and international rules, formulation of channeling plans, etc. Non-optimum utilisation of the radio frequency spectrum and the satellite orbits results in waste of these vital natural resources. It is, therefore, essential that these limited natural resources must be utilised efficiently, economically, rationally and optimally. 1.4 Electromagnetic compatibility (EMC) is consensus solution for efficient and economical utilisation of radio frequency spectrum. Society's increasing use of radio-based technologies for various telecommunication applications, and the tremendous opportunities provided by these technologies for socio-economic development, highlight importance of the electromagnetic compatibility among various radiocommunication systems. Advances in technology have made it practicable to implement new sharing schemes that offer possibilities for increasing the efficiency of spectrum sharing and frequency utilisation. 2. Frequency assignment process: 2.1 The international Radio Regulations of the ITU define the assignment of a radio frequency or radio frequency channel as authorisation given by an administration for a radio station to use a radio frequency or radio frequency channel with specified parameters and under specific conditions. Frequency assignment process, therefore, involves examination of requirements for spectrum/ frequencies from national as well as international radio regulatory procedures. 2.2 Whenever a person wishes to establish and operate a wireless station, application is required to be made in appropriate proforma with associated technical details. The application, as and when received, is processed and examined with respect to government policies and guidelines in consultation with concerned Ministries and Departments. In case of service providers, these applications are processed after obtaining recommendations of the concerned administrative Ministries. Further, the assignment of frequency and effective utilization of the same is being ensured in an objective, transparent and nondiscriminatory manner ensuring no objection from concerned administrative Ministries, as appropriate, wherever, policies issues are in their respective domain. Application are also processed for technical examination/ evaluation in accordance with international Radio Regulations and national regulations as well as coordination with other wireless networks, nationally and internationally, as the case may be, for establishing electromagnetic compatibility and for assessing availability of spectrum. 3

4 2.3 It may be borne in mind that same frequency is repeated several times within the country as well as by different countries depending on electromagnetic analysis for coexistence. Further, a particular frequency can be assigned to one user for one type of services and the same frequency can be assigned to another user for different type of services and for different type of application. Electromagnetic compatibility depends on many associated technical parameters of the frequency assigned. Even the same frequency can be assigned to different types of services in the same area of operation if electromagnetic compatibility is established. Frequency assignment for one type of service has impact on other types of services in the same frequency band as well as in different frequency bands, based on technical parameters of different networks. For instance, if a frequency is assigned for broadcasting, it may have impact on assignment of Fixed Service or Radiolocation Service using the same or nearby frequency bands. Further, frequency assignment also depends on geographical topography and terrain, climatic variations, rainfall, etc. 3. Spectrum Allocation Radio spectrum has traditionally been managed by governments. The Administrations world over have their own National Radio Spectrum Regulatory Authority like FCC & NTIA in USA and Ofcom in UK etc and it international level, it is managed by International Telecom Union (ITU). All over the world, three spectrum management models exist command and control (static model), exclusive use model, and unlicensed use (open sharing model). The increased demand for and use of traditional wireless services and applications have strained the spectrum management regime. The problems are compounded by the increasingly varied demands for radio spectrum because of:- the desire to transmit a larger quantity and a greater variety of information; the need for more diverse types of communications systems to meet specialized needs; the rapid overall changes in the technology and the marketplace; Therefore, Flexible Spectrum Allocation would need to be developed for increasing the spectrum utilization efficiency by opening the licensed spectrum band to secondary users besides primary users, limiting the interference experienced by the primary users. Hybrid of exclusive use model and open sharing model of spectrum management models provides a view for spectrum 4

5 sharing between primary & secondary users. There are two approaches for such sharing. Now day s the role of the spectrum regulators are becoming more difficult as to accommodating the new services in already crowded frequency slots. Regulators have to make a balance between facilitating the rapid development of innovative services and protecting existing services and users of spectrum. There is a need to move towards more flexible systems. DSA is one of tool which provides flexible spectrum management, which can accommodate new services with protection to existing services. There are so many issues which need to be addressed before implementation of DSA like management of Interference between primary and secondary users is major concern associated with DSA. A policy should be made in such a way that secondary users should have complete freedom and at the same time interest of the primary user should also be protected. Technical neutrality and humanization is also major concerns of the regulators. Besides these, there are other issues like use of software in cognitive radio system, to what extent change in parameters of secondary users can be permitted to change to avoid the interference, hidden node problems etc. would also be taken care of by the regulators. 4. Future Wireless Technologies and Dynamic Spectrum Access (DSA) Advancement in wireless technology has stimulated the demand for more radio spectrum from every corner and this demand is going to accelerate in future. Being a limited natural resource, the role of spectrum regulator becomes more difficult as to fulfill the demand of spectrum many new technology like BWA, WiMAX and 4G etc. and at the same time to provide interference free environment for their efficient roll out. The existing practice of spectrum regulation has resulted in vastly underutilized spectrum band not only in remote areas but also in dense urban areas. Studies have shown considerable parts of the spectrum, allocated to specific services, are practically not used for significant period of time, meaning thereby that utilization of spectrum is relatively low not just by frequency domain but also across the spatial and temporal domain. This shows that existing static approach of spectrum management model is not efficient to cater the present and future requirement of spectrum for new wireless applications. Worldwide, spectrum regulators are looking for alternative method of managing spectrum, which give a much more efficient and flexible utilization of spectrum. The solution lies with dynamic management of spectrum, which allows spectrum sharing among the various wireless technologies. Spectrum sharing is not new a phenomenon. The unlicensed 2.4 GHz frequency band in which Wi-Fi and Bluetooth technology operates is one of the best examples of spectrum sharing. Such kind of sharing is also known as horizontal sharing. This has put tremendous pressure on spectrum regulator to delicensed other bands also as spectrum utilization of the licensed band is 5

6 relatively low. It is possible to open licensed band for secondary usage with some conditions like operation of secondary user would not interfere with the primary user. This type of sharing is known as the vertical sharing. Secondary users can access the spectrum, meant for primary user, through Dynamic Spectrum Access (DSA) technology, a new phenomenon in wireless communication. The key characteristic of DSA is their ability to exploit knowledge of their electromagnetic environment to adapt their operation and access to spectrum. The concept of dynamic spectrum access has emerged as a way to dramatically improve spectrum utilization. The basic idea behind DSA is that a device first senses the spectrum it wishes to use and characterizes the presence, if any, of primary users. Based on that information, and regulatory policies, the device identifies communication opportunities ( holes ) in frequency, time, or even code and transmits using those opportunities in a manner that limits the interference perceived by primary users. Opportunistic spectrum access allows dramatically higher spectrum utilization. It also enables near-zero deployment time through radios that can opportunistically retarget their services to a new portion of the spectrum as needed with obvious and significant impact on both civilian and military communications. Dynamic spectrum access is also referred to as opportunistic spectrum access, and is normally considered as part of the larger concept of cognitive radios. 4.1 The basic idea behind the dynamic spectrum access is that the device first senses the spectrum and characterizes the presence, if any, of primary users as well as other cognitive radios. Based on that information, and regulatory policies applicable to that spectrum, the device identifies spectrum opportunities (frequency, time, space and code), and transmits in a manner that avoids (according to policy) creating interference that would be noticed by primary users, while attempting to limit (in accordance with spectrum etiquette) interference with other unlicensed devices operating in its vicinity. While conceptually simple, the realisation of opportunistic and autonomous spectrum access is highly challenging. There are several issues like sensing over a wide frequency band, identifying the presence of primary users and determining the nature of opportunities, coordinating the use of these opportunities with other nodes and adherence to existing regulatory policies are linked with DSA, which need to be solved before implementation. 6

7 4.2 Major Benefits of Dynamic Spectrum Access More efficient use of spectrum The main reason for the development of dynamic spectrum access techniques is to provide more efficient use of spectrum, which is essentially a finite, but reusable, resource. With static model of spectrum management provides efficient use of spectrum during busy hour, but inefficiently at all other times. Dynamic spectrum access would enable spectrum to be used for other services during periods of low utilisation, increasing efficiency. This efficiency could also be extended to creating greater device convergence, allowing multiple services to coexist in the same devices, as well as in the same spectrum. Faster access to spectrum Lowering barriers to entry by making spectrum available to users who need it as quickly as possible is an important ingredient for wireless innovation. It is difficult with static approach to meet the demand for access to spectrum, particularly where spectrum has already been assigned to users. Dynamic spectrum access attempts to bypass much of the delays here by carrying out its own spectrum management. Greater Innovation and Competition Efficient use of and faster access to spectrum, are both important to help encourage wireless innovation. This in turn results in faster time to market for innovative new wireless services. An environment that supports innovation ultimately contributes to a healthy competitive environment with a greater choice of services for end users. 5. Cognitive radio: The key enabling technology of Dynamic Spectrum Access is Cognitive Radio (CR). CR technique provides the capability to use the spectrum in opportunistic manner. Cognitive radios, built upon software radio platform, are expected to operate at frequencies that were originally licensed to primary users, in addition to available frequencies in unlicensed bands. Cognitive Radio continuously performs spectrum sensing over a large range of frequency spectrum, 7

8 dynamically identifies unused spectrum, and then operates in this spectrum at times when it is not used by the primary user. The wireless LAN IEEE TM can be referred to cognitive radio based system as it operates with a listen before talk spectrum access and with dynamically changing frequency and transmission power. Therefore, dynamic spectrum access is inherent property of cognitive radio. Overlay spectrum sharing: Under this approach does not impose severe restrictions on the transmission power of secondary users, but rather on when and where they may transmit. Spectrum is shared explicitly in one of three ways; Opportunistic, where spectrum is used whenever the licensee does not use it; Cooperative, where frequencies are allocated centrally based on real-time negotiation with the licensee; and Mixed, where sharing is cooperative when possible and opportunistically. The cognitive radio opportunity can be categorized into four different classes. First class belongs to spectrum that is assigned but rarely utilized within a specific geographic region. The second class belongs to fixed signals, such as television transmission where the spectrum appears to be fully utilized, but because of the predictable nature of the signal, time based opportunities are available for cognitive radio based secondary users. The third category belongs to those spectral regions that are infrequently utilized, where the cognitive radio must be capable in detecting incumbent transmissions when they occur, and also strong in ceasing transmissions immediately, or moving the transmissions to other unoccupied channel. Military and civilian government bands are examples of this class. The last category is those regions where the spectrum is relatively well-utilized, but still has some capacity available, especially in certain period of the day. In this case, the cognitive radio capabilities will be highly capable to insure that the radios do not interfere with incumbent spectrum users, and still deliver value as a communications medium. 5.1 Cognition and DSA Solution of these problems is lies with cognitive radio based system. The secondary users must have cognitive capability as CR techniques provide the capability to use or share the spectrum in an opportunistic manner and at the same time network in which secondary users are allowed to access, must be Dynamic Spectrum Access or NeXt Generation (xg) Network (DAPRA, a research agency of USA). The xg network will provide high bandwidth to users by using dynamic spectrum access techniques. There are two basic problems lies with Dynamic Spectrum Access i.e. spectrum opportunity identification and its exploitation and regulatory policy. The opportunistic identification gives an idea about how to identify spectrum hole or vacant channel and spectrum exploitation provides view how to use this vacant 8

9 channel or spectrum hole for transmission. The regulatory policy defines the basic etiquettes for secondary users to ensure compatibility with legacy systems. 6. Potential Challenges for Dynamic Spectrum Access Interference and Quality of Service The biggest concern over the introduction of dynamic spectrum access systems is an increased level of interference. The operation of dynamic spectrum access relies on being able to detect and avoid the transmissions of other wireless systems. The ability to do this in a reliable way in real-time can be a source of concern for existing spectrum users and managers. Interference scenarios such as the hidden node problem are important here. In some cases an increased level of interference will still enable services to function, but at a lower quality of service. Instances of interference in a dynamic spectrum environment are likely to be more difficult for spectrum managers identify, trace and resolve than in a traditional method of spectrum management. The Hidden Node Problem This is important in the case of a dynamic spectrum access system attempting to operate on a shared basis with other services. While the dynamic spectrum access device will listen to determine whether any other device is using the same frequencies at that time, it may not be able to identify all transmissions in its area or nearby areas due to the hidden node problem. Under certain circumstances the presence of a device will not be detected by another system seeking to use the same spectrum. The undetected device is known as a hidden node and it is likely to experience interference with the other system. Regulatory compliance While dynamic spectrum access systems will be designed to avoid interference there may still be a possibility that interference may occur. In such instances it would be difficult to determine the source of interference due to the way in which the spectrum is used (i.e. not in a command and control manner). Global ICT Standardization Forum for India contact@gisfi.org 9