A mechanism to communicate in a secure manner between locomotives of a train consist is disclosed. Controllers on locomotives generate data packets and encode them according to one of a plurality of modulation schemes and transmit the encoded data packets according to one of a plurality of frequencies. The frequencies and/or modulation schemes used to transmit data are changed periodically by the transmitting controller in a sequence. The receiving controller is aware of the current frequency and/or modulation scheme being used and can, therefore, decode the transmitted data. Since the transmission frequency and/or modulation scheme is not known by a malicious actor, the data communications between the controllers is secure. The sequence of frequencies and/or modulation schemes may be communicated between the two controllers during a handshaking procedure to set up communications. Clocks of the communicating controllers may be synchronized to enable the frequency and/or modulation hopping scheme.

A receiver for spread spectrum signals comprising a first part for preprocessing and digitizing a received signal, and a second part for tracking the digitized signal comprising a carrier loop and a code loop. The code loop comprises a generator for a reference receiver signal for correlation with the received signal and the code loop is configured to modify the reference signal to shape a correlation function between the received signal and the reference receiver signal. The first part is adapted to multiply the received spread spectrum signal with a first analog spectral offsetting signal provided for down-converting the received signal to an intermediate frequency and a sub-carrier frequency, selected from a set of sub-carrier frequencies, such that the received signal is down-converted and spectrally offset in the analog domain during a time interval covering at least one chip of a spreading code of the received signal.

A method for processing a data packet before transmission over a radio communications network as a succession of waveforms transmitted at positions defined by hopping codes, which are time positions or frequency positions. The packet is transmitted over a communications channel of the network by a transmitter node to a destination node. The method includes the following steps performed for each bit of the data packet to be transmitted, referred to as the current bit: calculating a hopping code at least as a function of the value of the current bit and of an encryption key generated by a pseudo-random generator, the encryption key having size greater than the maximum size of a data packet transmitted over the channel; and causing a waveform to be transmitted at the position defined by the calculated hopping code, the transmitted waveform being identical regardless of the value of the current bit.

Embodiments of the present disclosure are directed to systems and methods for avoiding or mitigating co-channel interference between terrestrial and satellite radio access networks (RANs). The systems and methods comprise one or more terrestrial base stations and one or more satellite base stations, each configured to transmit signals across overlapping frequency bands. The system further comprises applying an orthogonal spread spectrum code to the signals transmitted by the satellite base station, while the terrestrial base station transmits without such coding.