Abstract: A method of encoding a plurality of data signals is disclosed. The method includes selecting a set of M ultrasonic frequencies, wherein each of the M ultrasonic frequencies differs from an adjacent frequency by at least a first frequency spacing, and wherein M is a positive integer. An encoder receives the plurality of data signals. Each of the plurality of data signals is encoded by a respective set of Q of the M ultrasonic frequencies, wherein Q is a positive integer less than M. A minimum frequency separation between any pair of the Q ultrasonic frequencies of any respective set is greater than the first frequency spacing.

Abstract: An ultrasonic communication circuit is disclosed. The circuit includes an ultrasonic transmitter arranged to transmit a training signal having a frequency to a remote transceiver over an ultrasonic communication channel. An ultrasonic receiver is arranged to receive information from the remote transceiver in response to the training signal. The ultrasonic transmitter is arranged to transmit a data signal to the remote transceiver. The data signal has a duty cycle determined by the information.

Abstract: An ultrasonic communication circuit is disclosed. The circuit includes an ultrasonic transmitter arranged to transmit a training signal having a frequency to a remote transceiver over an ultrasonic communication channel. An ultrasonic receiver is arranged to receive information from the remote transceiver in response to the training signal. The ultrasonic transmitter is arranged to transmit a data signal to the remote transceiver. The data signal has a duty cycle determined by the information.

Abstract: A method of encoding a plurality of data signals is disclosed. The method includes selecting a set of M ultrasonic frequencies, wherein each of the M ultrasonic frequencies differs from an adjacent frequency by at least a first frequency spacing, and wherein M is a positive integer. An encoder receives the plurality of data signals. Each of the plurality of data signals is encoded by a respective set of Q of the M ultrasonic frequencies, wherein Q is a positive integer less than M. A minimum frequency separation between any pair of the Q ultrasonic frequencies of any respective set is greater than the first frequency spacing.

Abstract: A method of encoding a data signal is disclosed. The method includes selecting a set of M ultrasonic frequencies, wherein each of the M ultrasonic frequencies differs from an adjacent frequency by at least a first frequency spacing, and wherein M is a positive integer. The method further includes forming a trellis matrix and encoding the data signal with the trellis matrix to form a set of Q of the M ultrasonic frequencies, wherein Q is a positive integer less than M, and wherein a minimum frequency separation between any pair of the Q frequencies of the set is greater than the first frequency spacing.