BilSpect is an integrated spectrum engineering and planning software for the simulation, planning and analysis of radio spectrum from 10 kHz to 40 GHz. An engineer in the design and regulation area is faced with many challenges. The outdoor measurements are quite costly and is limited in trying out different what-if scenorios. Besides, the results are interfered and cluttered by today’s fully-utilized RF spectrum. Finally, outdoor measurements do not easily fit for an automated optimum frequency allocation algorithm.

Faced with such challenges, our engineers have developed BilSpect software to simulate the field strengths, to analyze the interference phenomena among different stations, and through full integration with a database management system, to allocate the available band in an efficient way. In order to facilitate the preparation of ITU regulation forms, an automated ITU report generation module is also provided. BilSpect is the tool that facilitates the functions that all operators, administrations and regulatory authorities have to execute.

Monitoring facilities and stations are the most important tools for the administrations to enforce the regulations, to identify unlicenced radiations and resolving intereference problems. The efficiency of the monitoring facilities is significantly improved if the monitoring is computer controlled and the results are viewed on a computer interface. For this purpose, a monitor support system has been included in the BilSpect.

It is also worth mentioning that, BilSpect spectrum engineering output interface is a commercial GIS, which provides fast and elegant visualizations which cannot be matched otherwise. BilSpect is composed of two systems. The first one is the spectrum engineering system and the second one is the monitoring support system. Below is a short description of BilSpect menu functions.

1. SPECTRUM ENGINEERING SYSTEM (SMS)
1.1. TECHNICAL ANALYSIS
This module provides the core functions such as propagation simulation, link analysis, digital Radio/TV broadcasting analysis, calculation of human exposure safety distance and auxiliary programs. Each of these are described briefly below.

1.1.1. PROPAGATION SIMULATION
Propagation Simulation sub-module allows three types of studies: Coverage area, point-to-point and odd azimuth. In all of these, the user is required to enter the parameters of the transmitter to be studied. These parameters can also be brought from the database. Multiple transmitters can be studied in batch form. Transmitter and receiver antenna patterns can be read from files. This allows antenna discrimination to be included in the analysis. Propagation and simulation parameters are then entered. Among those are the K-factor (for tropospheric diffraction), propagation simulation model, atmospheric and environmental parameters. Various propagation models can be employed for different frequency bands. These models range from the ground wave models for low frequencies to free space models for high frequencies. In the VHF and UHF bands, ITU propagation curves, Okumura–Hata, Walfish-Ikegami or ITU Rec. 529 and 1146 models can be readily employed. Diffraction correction to some of these models can also be chosen. Epstein–Peterson, Deygout and Vogler methods are available for the diffraction correction. The studies are done on a circular sector around the transmitter which is formed by radial paths. The result of the study is written to files defined by the user. Simulation studies can be viewed through the integrated GIS program. GIS menu options are already available for drawing contours corresponding to different signal levels, querying population inside the contours or for other typical GIS applications.

1.1.1.1 COVERAGE STUDY
Coverage Study program makes various analyses in a circular sectoral area for certain transmitter and receiver antenna patterns for a definite radius. The available analysis types are electrical field strength value, received power level, received voltage level, path loss and talk-back region studies. After the study is performed, the results can be viewed or examined graphically on the map background. An example of a coverage study is shown in Figure 1. In this figure, coverage areas of two stations are given without any interference assesment. In Figure 2, the interference effects of the Çamlıca station on the coverage area of Gazitepe station is taken into consideration and the actual coverage area (interference-free) of the Gazitepe station is given.




Figure 1: Coverage areas of the Çamlıca and Gazitepe analog TV stations operating in the UHF IV band in Marmara region of Turkey without interference considerations.




Figure 2: The actual coverage area of Gazitepe station obtained by considering the interference from Çamlıca station is determined as the inner region shown in white color.

1.1.1.2. POINT-TO-POINT STUDY
Point-to-Point Study program makes various analyses for a given receiver location using certain transmitter and receiver antenna radiation patterns. The available analysis types are electrical field strength value, received power level, received voltage level and path loss studies.

1.1.1.3 ODD AZIMUTH STUDY
Odd Azimuth Study program makes various analyses on a given azimuth through a desired distance by using a defined receiver antenna pattern. The available analysis types are electrical field strength value, received power level, received voltage level, path loss and talk-back region studies.

1.1.2. LINK ANALYSIS
Link Analysis is a program that can be used for performance evaluation and design of the microwave links with defined parameters. According to the given parameters, the link availability and the link outages are the main outputs. ITU documents are chosen as references in the calculations (ITU-Rec. P.530). By using the interface of the Link Analysis program, path profile can be observed and the link design can be made. To evaluate the link performance, the availability of the link and the time percentages that do not exceed defined enhancements are calculated. Investigated link parameters can be saved in a link file or the link files saved earlier can be re-analyzed. In addition, on a graph, the line of sight (LOS) path along the link is shown on the terrain profile. The first Fresnel zone is also depicted to illustrate the link blockage.

1.1.3. DIGITAL RADIO/TV BROADCASTING ANALYSIS
Digital Audio Broadcasting (T-DAB) and Digital Video Broadcasting (DVB-T) Analysis sub-module produces various simulation results by examining transmitter antenna network in a defined area. It can be used for planning of a Single Frequency Network (SFN) as well as planning of Multiple Frequency Networks (MFN). The study area can be defined as a rectangular region or in the case of T-DAB a region along a highway can also be defined. In order to perform an analysis, the propagation studies corresponding to the %1 and % 50 time percentage statistics for the stations in the region, have to be calculated using the propagation simulation sub-module.
The outputs of this program are the usable signal level, the interference signal level, the network gain, the protection margin, the coverage area and the coverage probability.
After the results are obtained, the GIS-Viewer is opened and the study results can be visualized on the screen. On these images, it is possible to draw contours of various values or multiple images with contours can be observed on the same screen. An example of a coverage study for a single frequency network in DVB is shown in Figure 3.




Figure 3: 48 dBuV/m usable field strength contour and the 95 % coverage probability contour for a single frequency network with seven transmitters in DVB-T.

1.1.4. HUMAN EXPOSURE SAFETY DISTANCE
The human exposure safety distance module evaluates the distance in which the radiated field of a given antenna is below the threshold value. The threshold values are taken from the standard defined by Turkish Standards Institute dated April 2, 1996 (TSE-ENV-50166) for the general population and for long time exposure. In order to make sure that the distance is the safest, the maximum value corresponding to the main beam direction is determined. It is accepted in here that the electric and magnetic fields are related with far field principle. So the safety distance has to be in the far field zone. For this reason if the calculated safety distance is not in far field zone, it is expanded to far field zone limits.

1.1.5. AUXILIARY PROGRAMS
1.1.5.1 ANTENNA PATTERN VIEWING PROGRAM
This program enables to observe the horizontal and vertical radiation patterns of the antennas whose pattern files are available.

1.1.5.2 ANGLE-DISTANCE /EFFECTIVE HEIGHT PROGRAM
Angle-Distance/Effective Height Program calculates the distance and azimuth values between any two points on earth, given the coordinates. It also calculates the coordinates of a point at a given azimuth and distance from another given coordinate. Another feature of this program is the calculation of the effective height and (terrain irregularity parameter defined in ITU Rec. P-370) values corresponding to a transmitter antenna location.

1.1.5.3. SIGNAL PLOTTING PROGRAM
Signal Plotting Program reads signal values from the file produced by the coverage study program and plots them with respect to distance away from the simulated transmitter.

1.1.5.4 COORDINATE CONVERSION PROGRAM
This program is used to convert the geographic coordinates defined by degrees, minutes and seconds into Universal Transverse Mercator (UTM) coordinates or vice versa.

1.2. INTERFERENCE ANALYSIS
> 1.2.1. FM RADIO-TV
This program examines if there is any interference between given sets of FM radio or TV transmitters. Namely, it defines whether or not an FM station is interfered by other FM stations or if it interferes other FM stations. The same analysis can be carried out for TV transmitters also. Results are written into an output file.

1.2.2. LAND MOBILE
It examines whether or not the land mobile stations are interfered by other land mobile stations. Analyses are made for all test points in the coverage area of land mobile stations to check if the protection ratio is satisfied or not. An output file containing the percentage of test points that have interference problem is produced.

1.2.3. FM RADIO-AERONAUTICAL SERVICES COMPATIBILITY
FM Radio-Aeronautical Services Compatibility program is based on the ITU Recommendation ITU-R 1009. In this document, a method is described to analyse whether the FM radio broadcasts cause interference with the aeronautical signals around the airports. The program is written in order to perform such an analysis on the computer.
In the analyses, two kinds of systems are considered. The first one is named as ILS (Instrument Landing System) and the second one as VOR (VHF Omnidirectional Radiocommunication ). ILS is a service formed for the airplanes to find the runway in landing and the coverage area is not only very limited compared with VOR but also depends on the direction of the runway. The coverage area of VOR is cylindrical in shape and it is wider and independent of the direction of the runway.
FM radio stations may cause interference to these services since they use neighbouring frequencies as the services do. In ITU-R 1009, four types of interferences are defined. They are called as A1, A2, B1 and B2. After the analysis, which kind of interference is caused by which FM station is written into an output file.
Program starts with finding the FM stations needed to be included in the analysis from the transmitter database for ILS or VOR. Afterwards, any interference in the coverage area of the aeronautical service is analysed. Finally, the results are written into an output file.<

1.2.4. INTERMODULATION ANALYSIS
This program is used to define the interference when some stations interfere some receivers in the case of intermodulation. When two or more transmitters seem to broadcast at a new frequency other than their original value, this situation is called intermodulation. Intermodulation can happen in two ways. A transmitter can be intermodulated with one or more than one co-sited transmitters and propagate the power at a new frequency. In the second case, two or more transmitters’ signals can be intermodulated at the receiver and act like a new frequency for the receiver. Both of these cases are included in the analysis.

1.2.5. DESENSITIZATION ANALYSIS
In the case of powerful transmitters, the sensitivity of the receivers may get lost in the regions close to the transmitters because of the high transmitted power levels. This situation is called desensitization. This program is written to define the region in which the receivers can not work appropriately because of the powerful transmitters. The program calculates the distance from high power transmitter(s) below which desensitization phenomena occurs and writes the results into an output file.

1.2.6. DATABASE SEARCH AND LIST
Database Search and List program queries the stations in the database according to given criteria and writes the technical and administrative parameters of these stations into an output file.

1.3. FREQUENCY ASSIGNMENT AND PLANNING
1.3.1. DETERMINING CANDIDATE FREQUENCY
Determining Candidate Frequency program is the first step of frequency assignment process. The goal of this program is to prepare detailed information to the Propagation Simulation sub-module for the FM Radio, TV and Land mobile services. Also, this program directly produces the list of interfered frequencies to be used by Frequency Selection program for aeronautical and microwave services.

1.3.2. FREQUENCY SELECTION
Frequency Selection program is the last step of frequency assignment process before the assigned frequency is recorded into the database. It extracts the interfered frequency values calculated by Determining Candidate Frequency program or Interference Analysis sub-modules, from the list including all candidate frequencies and presents the interference-free frequency list to the user. User may select one of these interference-free frequencies or leave the selection to the program. Also, the user can manually enter a frequency value which is not included in the list.

1.3.3. RECORDING TO DATABASE
Recording to Database program is the last step of frequency assignment process. It enables the user to save all of the data related to assigned frequency, station, transmitter, antenna and administrative data into the database tables. The interface of the program has different data grids for different database tables such as frequency, station, transmitter, antenna and administrative operation tables.

1.3.4. DATABASE FREQUENCY QUERY
Database Frequency Query program is used to query database frequency, administrative operation, station, transmitter and antenna tables according to the defined criteria.

1.3.5. FREQUENCY PLANNING
Frequency Planning sub-module is used to produce the frequency plans including more than one station in a local area or distributed throughout the country in the FM Radio and Analog TV services. It can manage frequency planning for a frequency band with existing or without existing transmitters. If the existing transmitters are to be taken into account, a database query is done first to extract the technical details of the existing stations necessary to perform the propagation simulations and interference analysis. Otherwise, only the technical parameters of new stations are passed to propagation simulation and interference anlaysis phases.
After the interference analysis is performed, frequency distribution part of this sub-module is run to display the interference analysis results in a tabular form of frequencies versus transmitters and to assign suitable frequencies to the new stations. The interface of the program shows the frequencies with or without interference in different colors for each station and it can give the source of interference for any transmitter-frequency pair. Additionally, when the user assigns a frequency to a new transmitter, its interference effects on the other transmitters are displayed in different color in a dynamic way. Frequency Distribution part of this sub-module is a useful tool to make trials of frequency assignments and finally determining the suitable frequencies for the new stations.

1.4. INTERNATIONAL COORDINATION
1.4.1. ITU NOTIFICATION FORMS
This program prepares the ITU Notification Forms for a given station. These ITU forms vary according to the service type, frequency band and the required information. So the user can select the required form for his or her notification purposes. These forms are used by ITU for the IFL (International Frequency List) registration and the determination of international coordination. ITU regulations require that these forms have to be filled and sent to ITU for a new station or a modified existing station. An example of the ITU forms ready for taking printout is shown in Figure 4.

1.4.2. REGISTRATION OF INTERNATIONAL CORRESPONDENCE
This program is a database interface for storage and retrieval of information required for coordination with neighbouring and ITU member countries. This interface is classified according to the service type and related data is entered by the user for each service type.<
1.4.3. COUNTRIES TO BE COORDINATED<
This program finds the countries to be coordinated for a new station or a modified existing station. This is basically a computation of limiting distance of the station according to given parameters. The countries inside the limiting distance are then determined and identified as the countries to be contacted for coordination of this station.

1.4.4. STATIONS TO BE COORDINATED
This program determines the stations near the international border areas according to given criteria. This information may be used by the administration for the international coordination purposes. It is noted that this is only a useful tool which gives the list of transmitters possibly needed to be coordinated. The results are written to a file and can be viewed on the map through GIS. The user can reach the details of any station by clicking the station symbol on the map. The results of a.n example study are shown in Figure 5.




Figure 4: A sample ITU Notification Form T11.




Figure 5: An illustration of the “Stations To Be Coordinated” program.

1.5. FREQUENCY ALLOCATION TABLES
This tool presents the international and national frequency allocation tables with all the footnotes and auxiliary information. Basically three tables are listed. They are ITU, CEPT and Turkish Telecommunications Authority allocation tables. There are various query options like given frequency, given frequency band or search through a keyword. User also has the option to modify the information or add new information to these database tables if national or international authorities declare changes. Finally, the user can take the printout.<

1.6. QUERY AND REPORTING
1.6.1. QUERY<
The query program retrieves the information from the database tables. The SQL statements are used to make all kinds of sophisticated querying. According to the given criteria, tables and fields are selected and then SQL statements are applied on these fields stored in the database.
1.6.2. REPORTING
This program is used for preparing reports in specific service types or specific frequency bands determined by the telecommunication authority. For the query processes that are frequently performed by the user, this program is used rather than the query program mentioned above. By this way, the user can reach the information required in an easy and fast manner.

2. MONITORING SUPPORT SYSTEM (MDS)
Monitoring Support System is the computer interface of the monitoring equipment. This system includes five menu items: monitoring visualization, pre-study for monitoring, monitoring recording, monitor query and triangulation.

2.1. MONITORING VISUALIZATION
Under this module, GIS windows are opened, and regional map details and transmitter search parameters are entered. The program searches the database and the stations conforming to the given criteria are marked with symbols on the map background. Clicking on the symbol gives the detailed information about the selected transmitter. An example is given in Figure 6.

2.2. PRE-STUDY FOR MONITORING
This module mainly concentrates on a single monitoring station. It has a facility to view the spectrum occupancy data obtained from the monitoring station. One other facility is the list of transmitters that can be monitored by the monitoring station. In this module, a database search is applied to the transmitters and path loss calculations are done and finally those transmitters with signal levels above the threshold are filtered and listed. The final program in this module is a database query for the licenced transmitters around the monitoring station.




Figure 6: Analog TV stations operating in the UHF IV band near İstanbul are shown by radiotower symbols on the map background.

2.3. MONITORING RECORDING
This module has a program to view the alarms generated by the monitoring stations. Another program in this module assings tasks to the monitoring stations. Tasks are given on a weakly basis. The tasks can also be examined and modified. There are three types of tasks; namely, monitoring of licenced stations, monitoring of unlicenced stations and monitoring of spectrum occupancy.

2.4. QUERY
The query module retrieves the information from the monitoring database tables. The SQL statements are used to make all kinds of sophisticated querying. According to the given criteria, tables and fields are selected and then SQL statements are applied on these fields stored in the database.

2.5. TRIANGULATION
Triangulation module helps the DF system by showing the triangle formed by the directions predicted by three DF antennas. This triangle corresponds to the most likely region in which the monitored transmitter is located. To help the user, a map backgraund is automatically brougth under the triangulation region on the GIS window. An example is given in Figure 7.




Figure 7: An example of Direction Finding (DF) measurement results produced by three monitoring stations in different locations.

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