Verification of time telegrams in Long Wave Radio systems

Abstract

This paper describes a method to verify received time telegrams distributed by Long Wave Radio systems for the example of the radio ripple control technology .In the given approach, the time between two time telegrams is continuously measured and compared with the time difference calculated from the time information contained in the telegrams. In other words, physical and logical information is compared. The physical time difference is directly calculated using the carrier frequency of the transmission system (for example: DCF49 transmission system uses a carrier frequency of 129.1 kHz with FSK modulation). A counter is clocked using the received carrier frequency of the system. The physical time difference between the transmissions of two time telegrams can be derived from the number of carrier cycles. The logical time difference is given by the content of the time telegrams. The comparison of physical and logical time differences is continuously verified to detect time jumps, which may appear during the transmission of time telegrams. Therefore, manipulated or delayed time telegrams can be accurately identified. This method can be applied without changing the time distribution protocol and it can be adapted to other time distribution services.