For many satellite operator interference represents a serious problem for network operations. Several hundreds of events are recorded per year and this number is likely to grow with the increase in traffic and the number of unattended stations.
Therefore, the proposed system will be designed to support the satellite communications market in terms of rapidly detecting an interferer and geo-locating the offending emitter's position on the earth together with other useful information about the interferer, such as indications on the antenna size (by comparing the signal level on the interfered satellite and the adjacent satellite).
In order to make optimum use of the ILS, the geographical position information will be complemented with careful exploitation of the SIECAMS earth station and carrier database. The system will integrate the SIECAMS interference detection technology with state-of-the-art geo-location techniques on a common signal acquisition and processing platform.
The result will be a seamless, all-in-one interference location solution with dramatic improvement in system affordability and capability. Because ILS is based on common signal acquisition equipment, it can also be used for spectrum monitoring and interference detection purpose. Therefore, the planned enhancement of Siecams will fully support spectrum monitoring, interference detection and sophisticated geo-location functions in a single system.
Currently available transmitter location systems are limited in detection performance with weak signals and/or signals suffering non-linear distortion from transponder saturation. For this purpose, the proposed development will provide significant improvements by supporting dedicated demodulation techniques and signal post linearization concepts based upon these techniques.
In addition, the proposed project shall deal with the requirements for locating the source of frequency agile interferences
Development and integration of a tracking system into SIECAMS Automatic. User initiated determination of satellite ephemeris data. Development and integration of an interference location system into SIECAMS Manual and 'one-button-transfer-mode' determination of the localization of:
- Digital carriers
- Hidden carrier interference
- Frequency agile traffic
Use of SIECAMS for regular monitoring and detection of interferences (Signal under Carrier, Spurious Detection).
Current systems suffer in case a satellite transponder is operated in its non-linear range (saturated). The SIECAMS ILS means a significant improvement by applying signal linearization and adaptive filter techniques before processing the data in terms of cross-correlation.
Together with the additional features provided by SIECAMS XPDM (cross polarization discrimination measurements) the system provides higher localisation accuracy of interferences.
The investigation of several techniques showed that the method utilizing the time difference of arrival (TDOA) and frequency difference of arrival (FDOA) technique provides the most efficient, reliable and feasible way to determine the interference location. Therefore, the proposed system will investigate TDOA and FDOA of the signal transmitted from the source of interference and retransmitted via two satellites to a receiving station (see Figure below).
The signals are retransmitted by the satellites along two independent signal paths to the receiving station. E.g. one satellite lies in the main beam of the source antenna radiation pattern and the other in a sidelobe. Although the power level of the signal passed via the adjacent satellite is considerable lower (according the antenna radiation pattern) the ILS system needs to receive the interfering signal from at least one adjacent satellite.
The two signal path lengths are normally unequal which results in arrival times at the receiver differing by the TDOA value. FDOA is due to satellite motion relative to earth and to one another, which Doppler shifts the signal frequencies. Two measurements of TDOA or FDOA at different times, or one of each at one or more times, provides two lines of position (LOP) on the earth's surface which intersect at the position of the source of interference to be located.
The Figure below illustrates the signal propagation between earth-based transmitters, satellite relays and the interference location system.
The satellite is assumed to be the conventional type which passes the signal to a transponder that performs frequency conversion, amplification and filtering before retransmitting the signal to the earth. This type
For each phase of the development process a review is defined in order to verify the results of the phase concerning technical aspects, quality assurance aspects and project control aspects.
Following is an overview of the review meetings and review dates as actually planned for this project:
|BDR||Baseline Design Review||28-Mar-07||Siemens|
|MTR||Mid Term Review||25-Jun-07||Siemens|
- Tracking system finalized,
- Baseline version of ILS finished.
Planned next tasks:
- Automatic reference carrier selection,
- Signal linearization.