<< Future wars, which are likely to be fought in the electromagnetic spectrum, can only be won by those who can best control and manage the spectrum >>
The demand for the frequency spectrum was never so large and this demand will continue to grow manifold in the times to come. Not only are the number of equipments increasing, the services which require the frequency spectrum are also growing. Some of the radio emissions are: communication and noncommunication services including safety services like aeronautical, maritime, radio navigation, radiolocation, radio astronomy, radio ranging, meteorological, broadcasting, satellite broadcasting, fixed-satellite, mobile-satellite, space services, etc. In accordance with international regulations, all frequency bands are shared amongst different types of radio emission services for a variety of applications and technologies by different countries. Neither do the electromagnetic (EM) waves restrict themselves to be available for a certain service nor are they limited by international boundaries. Hence, willingly or unwillingly, the spectrum must be shared.
The basic tools of radio frequency sharing require application of principles of time-sharing, technical sharing and geographical sharing. No user, no service and no country can work in isolation. It is a collective spectrum management exercise and radio regulatory mechanism which alone can ensure the interference free operation of various emitter and receptor networks. Individual frequencies are assigned to users or service providers and not frequency bands. No wireless user or service provider, be it government or private, has ownership claim on any part of the spectrum, only frequency assignments are made in particular frequency bands, as per national and international plans and regulations, for operation of radio networks owned by any agency.
National coordination, sharing, co-existence and protection are key elements of spectrum management process. Electromagnetic compatibility (EMC) is solution for efficient and economical utilisation of radio frequency spectrum. 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.
Military and the spectrum
The ever growing demand of frequency resource for civilian and commercial use is shrinking the share of electromagnetic spectrum of the defence services in the country. The density of civilian and commercial emitters is spatially increasing very rapidly in the battlespace along land and sea borders. Modernisation of defence services has also resulted in increased use of electromagnetic spectrum. Future conflicts will have more joint military operations than in the past and therefore will result in use of more number of frequencies in the same battlespace for command and control, coordination, logistics, weapon and surveillance systems.
Military operations rely heavily on radio equipment using the limited spectrum resources to achieve and maintain information superiority. In joint operations, frequency requirements may well exceed the amount of spectrum available in the battlespace of interest. Also, the EMC characteristics may negatively impact the way in which the limited available spectrum can be used. This may further reduce the spectrum available for use. As a result, efficient use and control of the available spectrum is critical for the success of military operations. The government is also diverting some of the defence spectrum for civil use. This imposes more constraints on the defence forces to optimally use the available spectrum resources. Therefore, new methods have to be found to optimally exploit and manage the available spectrum.
Figure 1: Concept of EMS
Electromagnetic Battlespace (EMBS)
Electromagnetic Space (EMS) is defined as the real-time spectral density at each point in the geographic area. There are three dimensions to the EMS: –
- Geographic location
- Spectral density
EMBS is the battlefield subset of EMS. EMBS is the space in which the electromagnetic spectrum war is fought. In a more elaborate definition, EMBS can be defined as the real-time spectral density at each geographic point in the battlespace.
Management of EMBS is the combination of administrative and technical procedures to ensure efficient operation of communication equipment and without causing or experiencing unwanted interference. The main function of the management of EMBS is to allow electronic system to function smoothly in their planned location without causing or experiencing unacceptable interference. This check that has to be performed on any electronic equipment designed to operate in an already occupied environment is referred to as the electromagnetic compatibility measures.
A key factor that will determine optimal use is frequency reuse. This can only be undertaken if interference free conditions can be ensured. To ensure interference free conditions, it is imperative to consider the interference and susceptibility characteristics of all equipments which have to be deployed in the EMBS. All emissions will need to be modelled into the EMBS and all receptors will need to consider the spectral density at their point of deployment and the effect of the spectral density before choosing a frequency for operation. Automation of the frequency assignment is obvious. Consideration of the EMI/ EMC characteristics of the equipment will be mandatory. Spectral density at all geographic points of interest will need to be monitored/ calculated/ interpolated and considered for all decision making. It will also be essential to compare the computed/interpolated spectral density with the one which is being monitored to detect unauthorised transmissions.
System for Management of the EMBS (SMEMBS)
The SMEMBS would help in optimising the planning and utilisation of spectral resources across space and time in an intense, dynamic and mobile battle environment. Some of the functionalities of the SMEMBS would be:
- To maximise the spectrum efficiency and minimise interference using techniques of frequency reuse
- To automate the request for demand and assignment of frequencies in the entire spectrum range from field user level to respective headquarters
- To calculate the possibility of interference by comparing spectral density at the point with the susceptibility of the equipment. Sources of interference such as polarisation, orientation, coverage contour, harmonics etc will all need to be compared
- To operate on a real-time basis
- To segment both laterally (geographic location) and vertically (frequency spectrum) for easier storage in the database and computation
- To capture the electromagnetic characteristics of all equipments (communication and noncommunication) of various services and populate databases for later use and authentication
- To simulate the effects of allotment of particular frequency spot to the same equipment or other equipments in the battlespace based on operating frequency, equipment and antennae characteristics, propagation models, terrain and environmental models
- To support various propagation models such as Free Space, Hata, Cost-Hata, Sky-wave, ground wave, shoot and bounce algo, microwave model, satellite model and radar
- To develop a geo-spectral database depending on existing and required frequency assignments
- To store information about authorised emitters in the central database and compare the generated spectral density at a location to that monitored by the spectrum monitoring system.
- To present the direction finding bearings and measured signal spectra from surveillance receivers online in a spectrum viewer display
- Spectrum Management System coverage tool should generate coverage of the detected transmitters found through direction finding. This coverage data should also be sent back to the Map Viewer software
- To back-up system with regular updates to operate on fail-safe mechanism
- Engineering and analysis module to help test/ analyse a link before actual deployment
- Report generation to provide end user with a record of the operation results for analysis
- Login module to grant access rights and privileges to only authorised personnel
SMEMBS is built on a GIS platform and is based on a Linux platform. The terrain and location characteristics are the most important parameters while conducting a propagation analysis for an emitter. The choice of the operating system is to further facilitate the near realtime operation.
As is the general definition, GIS is a system designed to capture, store, manipulate, analyse, manage, and present all types of geographical data. SMEMBS takes this information from the GIS storage and uses it to analyse and predict the effects of electromagnetic propagation. It is with the help of the information from GIS that SMEMBS is able to predict the effect in a real-time and accurate manner. Apart from the GIS in-built modules that are available for use, SMEMBS has its own modules. These are used to glide through the frequency assignment process in a smooth way. SMEMBS can analyse all files that are supported by Quantum-GIS.
Figure 2: Simulation of the EMBS
As of today, SMEMBS is in its evolving stage. It provides effective solutions for frequency assignment and is capable of making the frequency based operations function without a hitch. As we move towards a life with increasing dependence on frequency, interference-free-frequencyassignment will be a mandate and thus SMEMBS would be a must-have tool in every corner of the world.