S.N. Eliseev – Dr. Sci. (Eng.), professor, head of department of radio communication, broadcasting and television, Volga state university of telecommunications and informatics. E-mail: firstname.lastname@example.org
M.A. Khairullin – leading Engineer, JSC «Concern «Automation».E-mail: email@example.com
Warning system by its nature is imposed system, that is not to create a separate channel of communication lines, and is used to transfer the existing communication network and deliver messages to alert. Characteristics of the message flow have pronounced unevenness and transmitted at peak load used in primary communications networks.
The main indicators of the quality of work systems alert emergency situations:
reliable message delivery notification, which is determined by the probability of crossing warning messages
timely message delivery notification defined permissible value of time delay warning messages in systems emergency alert
One of the requirements to the Emergency Alert is a warning system of unauthorized emergency warning and unauthorized or inadvertent disconnection, which along with the authorization message alert each link, transmitting or relaying messages warning messages should take notice of not less than two sources.
Considering the circumstances open the possibility of building an information service broadcasting systems, in which messages are transmitted simultaneously on several radio channels alert radio emitting at different frequencies.
Such a transfer method may be called a parallel transmission, and can be used to improve the reliability of receiving alert messages when dubbing for transmission over different channels, and to increase the transmission rate when the paging message via the data parallelizing.
In this paper we consider a variant of systems Emergency Alert in which information is transmitted through two parallel channels broadcasting range 88–108 MHz (t.e. FM range).
Broadcasting information service system is implemented in accordance with the principles of frequency division multiplexing low-frequency channel that broadcasts a comprehensive program of basic stereo audio broadcasting, placing OFDM signal broadcasting information service system integrated stereo program above the basic sound broadcasting in the frequency band 62–94 kHz. This OFDM signal is transmitted with a level equal to the level of a few percent of the integrated program of basic stereo audio broadcasting. This occurs when a data rate decrease is compensated by introducing a hybrid modulation in two stages: Initially the signal modulated OFDM subcarriers by law multifrequency (MFSK), and then differential-phase (DPSK) modulation. In our case, the possibility of parallel transmission using a compromise way: information data stream from the encoder «0» is duplicated and transmitted through two channels broadcasting systems information service broadcast at different frequencies in the form of characters MFSK, are accepted methods of finger and then used as carriers demodulation information streams are independently encoded by the encoder of «1» and encoder «2».
For clarity, the principles of the system are illustrated in Example MFSK for M = 4, variant known as double frequency telegraphy.