Radiofrequency transmission system

An opportunistic radiofrequency transmission system comprising:

• means of scanning a predetermined frequency range and determining an unoccupied frequency band in the predetermined frequency range that relates to a predefined communication standard;
• means of producing at least one digital signal quantised on N bits according to said communication standard and at a lower frequency than said unoccupied frequency and;
• for each of said at least one digital signal, digital processing means comprising:
• filtering means of a sigma-delta type capable of producing, on basis of a digital input signal quantised on N bits at said lower frequency, a digital output signal quantised on M bits at said lower frequency, where M is less than N;
• downstream from the sigma-delta type filtering means, means of repetition over-sampling capable of producing, on the basis of a digital input signal quantised on M bits and sampled at said lower frequency, an output signal quantised on M bits and sampled at L times the second frequency by inserting L−1 zeros between each sample of the digital input signal, thereby generating a signal at said unoccupied frequency band, where L is an integer and is an oversampling factor selected based on the unoccupied frequency band, and
• downstream from the means of repetition over-sampling, convolution means capable of convoluting the digital input signal quantised on M bits and sampled at L times said lower frequency with a sequence having a length equal to L or 2L samples, quantised on M bits and rotating at L times said lower frequency;
• digital-to-analogue conversion means capable of converting the convoluted digital output signal into an analogue signal;
• and
• analogue filtering means capable of filtering said analogue signal so as to select a narrow frequency band which includes said frequency in said unoccupied frequency band.