M. S. Duhan , DDG(E) , Doordarshan
"While flexibility in the use of spectrum rights is desirable it is up to the government to decide the degree of flexibility., "
Radio waves were discovered over 150 years ago and it is almost taken for granted now. James Clerk Maxwell showedin theoretical and mathematical form in 1864 that electromagnetic waves could propagate through free space. In 1888 Heinrich Rudolf Hertz was able to conclusively prove transmitted airborne electromagnetic waves in an experiment confirming Maxwell's theory of electromagnetism. Electromagnetic waves are those waves in which electric and magnetic field vectors change sinusoidally and are perpendicular to each other as well as at right angles to the direction of propagation of wave. Maxwell's equations govern all of electricity and magnetism.
The real progress in radio transmission started in 20th century. Radio waves have many usesthe category is divided into many subcategories, including microwaves and electromagnetic waves used for AM and FM radio, cellular telephones, and television. Radio waves are used to transmit television and radio programs. Television uses higher frequencies than radio. The radio frequency spectrum is a very precious resource which must be managed to ensure efficient and equitable access for the services which use it. In India, radio frequencies are confined between 9kHz and 3000 GHz and are being used for 40 different types of services like fixed communication, mobile communication, broadcasting, radio navigation, radiolocation, fixed and mobile satellite service, aeronautical satellite service, radio navigational satellite service etc. Frequency bands are not allocated to any wireless user or service provider. It is the individual frequency, which is assigned by the administration for a radio station under specified conditions.
Regulations & Procedures
The regulations and procedures promulgated and adopted by the national spectrum management authority include steps for legal appeal of some decisions and cover areas such as procedures for obtaining and renewing a license, technical standards, equipment authorization procedures, channeling plans, and operational requirements. A spectrum management organization is guided by national policies, ensuring that its regulations conform to national objectives as set forth in domestic law and do not conflict with international regulations. It addresses international and domestic components, ensures interference-free access to the radio frequency spectrum for as many users and as many uses as is possible, andis a large revenue generator.
The Indian Telegraph Act 1885 and the Indian Wireless Telegraphy Act 1933 and related rules and procedures provide the legal basis for spectrum management. The National Frequency Allocation Plan (NFAP) 1981, and subsequent revisions or amendments, derived from the table of frequency allocations of the Radio Regulations, in consultation with the national users through the forum of Standing Advisory Committee on Radio Frequency Allocations (SACFA), provide the basis for assignment of frequencies. The Wireless Planning and Coordination (WPC) wing of the ministry of communication is the radio regulatory agency responsible for radio frequency spectrum management, including licensing. While flexibility in the use of spectrum rights is desirable it is up to the government to decide the degree of flexibility. Under Section 11 Sub-section 1 Clause (a) (viii) of TRAI Act, the TRAI may make recommendations to DoT. The International Telegraph Union is a specialized agency of the United Nations, responsible for issues concerning information and
communication technologies the International Telecommunication Union (ITU) has divided all countries into three regions. India is located in ITU Region 3.
RF Spectrum and Limitations
The limitation of the radio frequency spectrum is mainly due to the propagation characteristics of different types of radio waves, availability of technology and equipment for different types of radio frequency spectrum applications and the suitability of frequency bands for specific applications. The National Table of Frequency Allocations(NFAP) is based on the international table of frequency allocations and forms the basis for development and manufacturing of wireless equipment and spectrum utilization in the country. The frequencies from the top end of the AM band to the bottom of the VHF television band, shortwave range, is a historical term. Short wave radio is radio transmission using shortwave frequencies, generally 1.6–30 MHz, just above the medium wave band. Shortwave radio is used for long distance communication by means of skywave or skip propagation, in which the radio waves are reflected or refracted back to Earth from the ionosphere, allowing communication around the curve of the Earth.
Propagation at Medium Frequency wavelengths, (MW), rangesfrom 531–1,611 kHz in ITU regions 1 and 3, with 9 kHz spacing. At MW wavelengths they can over hills, and cover a radius of several hundred miles from the transmitter, with longer distances over water and damp earth. The ground conductivity is the most important factor in the transmitter's coverage area in ground wave propagation. Frequency Modulation (FM) provides high-fidelity sound over broadcast radio. Throughout the world, the FM broadcast usually falls in 87.5 to 108.0 MHz. Digital radios are now becoming popular due to their higher data capacity and spectral efficiency.
Television has four bands - VHF band I, VHF band III, UHF band IV, and UHF band V. WRC-07 identified 698-790 MHz band/portions of UHF band V for IMT. For Doordarshan total available spectrum in band I (2 channels), band III (8 channels), band IV (14 channels), and band V (limited to 8 channels) is only 248 MHz , which may be used for analogue and digital TV.
Planning begins with understanding the user requirement, which answers what service the user expects in time, space, and service. In space, the requirement defines precisely which geographic areas are to be covered; in service, the specification may define the call types to be supported, the service for packet transmission or the data throughput; and, in time defines the way the user expects the network to evolve. The specification normally includes performance parameters such as path availability, confidence in achieving a particular connectivity, limits to intra-network interference for given spectrum blocks and the like.
The various planning objectives include avoid or minimize interference and disruption to existing radio & television reception and other services, identify the technology; analogue or digital, type of standard, fixed or mobile, indoor or outdoor services channels, SFN/MFN, location and time variations, minimum cost to viewers and broadcasters and suitability for existing transmission facility. No propagation model is perfect. The network planner must examine the confidence with whichpredictions are being made and make an assessment.
Field Strength Requirement
In AM the field-strength limited contour is defined by a field strength of at least 66dBV/m for commercial radio services andat least 76dBV/m for community radio services measured 1.5 meters above ground. The interference-limited contour is defined by a co-channel protection ratio of 27 dB, and an adjacent channel (9 kHz separation) protection ratio of 3 dB; for synchronous services a co-channel protection ratio of 7 dBs is used.