Detection of the Frequency Hopping Spread Spectrum Signal Sources and Estimation of Their Number by Direction Finding Data

Analysis of the radio environment in a wide frequency band carried out by radio monitoring systems, including correlation-interferometric direction finders, involves, among other things, the detection of the frequencyhopping spread spectrum signals and the estimation of the number of sources that generate them. During the estimation, a complicating factor is that the receiving equipment operates, as a rule, in a panoramic mode, and the receiving paths of the monitoring system are sequentially retuned into adjacent frequency subbands, cyclically changing the tuning frequency within a wide frequency range. As a result, the data that one receives from the antenna pairs of the direction finding system and that are required for determining the directions to the radio sources are very fragmentary and chaotic. Whether these data can be used efficiently depends greatly on the possibility of grouping their pieces as belonging to one or several sources. Therefore, when collecting direction finding data, it is necessary to determine how many signal sources are currently operating in the analyzed frequency band. In the current study, a fast algorithm for estimating the number of transmitters exchanging information by the frequency-hopping spread spectrum signals is introduced. The algorithm does not have a very high angular resolution, but its advantages are that it requires neither a priori information on the radio emission parameters nor a detailed description of the design of the antenna system used. It is also characterized by low computational complexity. The performance of the algorithm is confirmed by the results of its full-scale tests