چكيده به لاتين
Today’s railway transport control technologies have achieved more proficiency by employing communication-based Railway Intelligent Transportation Systems. In such technology, train locating system should have enough accuracy to detect intersection points in all conditions, in a manner that control system can determine train location besides coordinates and inform the driver. European Train Control System (ETCS) is known as one of mentioned types of technology. In ETCS, information is exchange between train and command center via wired or wireless communication channel, whose security against possible attacks is of prominent importance. Such attacks can be classified as telegram faking, displacement and jamming which are cited as examples of system vulnerabilities. The main contribution of this study is to propose a framework to employ a Direct Sequence Spread Spectrum (DSSS) method over the channel between balise and BTM as a countermeasure against jamming attacks. The aim of using DSSS is to reduce the jamming signal level after the de-spreading process. The analysis of this study is performed based upon mathematical relations and computer simulation verifications. The main figure of merit of this study is Bit Error Rate (BER), which is a function of signal to noise ratio, jammer power and spreading chip-rate. The proper value of chip-rate is derived based on train speed, telegram length and bandwidth. The simulations are designed to plot the BER performance against Signal to Jammer ratio (SJR). It is shown that how the proposed DSSS can lead to a significantly better error performance, compared with a regular system without DSSS in the presence of a wideband jammer. The results of the proposed scheme are also compared with Frequency Hopping Spread Spectrum (FHSS) techniques, and it is shown that for any given BER value, the phase-shift keying of the proposed DSSS requires half the power consumption of FHSS systems in previous related works, while the hardware implementation of the scheme is less complicated.
