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.

The present disclosure provides a transmission method comprising splitting a block of bits to be transmitted into a number of groups each consisting of k+2q bits, wherein k and q are natural numbers and each of the groups includes a subgroup consisting of k bits and two subgroups each consisting of q bits and performing 2.sup.q-ary QAM modulation on the subgroups of q bits from the groups of k+2q bits to obtain QAM symbols, respectively. The QAM symbols are processed so that two QAM symbols obtained from the two subgroups of q bits in each of the groups of k+2q bits are mapped onto at least two antennas as consecutive processed symbols. Through the use of 2.sup.k-ary FSK modulation, a frequency tone to which the two consecutive processed symbols are allocated is selected according to the subgroup of k bits from each of the groups of k+2q bits before transmission.

Various aspects described herein relate to distinguishing frequency shift keying (FSK) signals transmitted by each user of multiple users in a wireless communications system. One or more symbols for transmitting in an FSK-modulated signal can be obtained by a user. The one or more symbols can be encoded based on a tone location assignment corresponding to a unique spreading code associated with the user. Quadrature amplitude modulation (QAM) and/or phase-shift keying (PSK) can be performed over at least one tone associated with the encoded symbols. Each user can transmit the encoded symbols to a receiving entity, where the receiving entity can decode each symbol received from the plurality of users to produce a distinguishable symbol for each user based on the unique spreading codes associated with each user.

Various aspects described herein relate to distinguishing frequency shift keying (FSK) signals transmitted by each user of multiple users in a wireless communications system. One or more symbols for transmitting in an FSK-modulated signal can be obtained by a user. The one or more symbols can be encoded based on a tone location assignment corresponding to a unique spreading code associated with the user. Quadrature amplitude modulation (QAM) and/or phase-shift keying (PSK) can be performed over at least one tone associated with the encoded symbols. Each user can transmit the encoded symbols to a receiving entity, where the receiving entity can decode each symbol received from the plurality of users to produce a distinguishable symbol for each user based on the unique spreading codes associated with each user.

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.

Embodiments of the present invention provide a decoding method and apparatus. The method includes: acquiring a demodulation signal; acquiring a first decoding signal, where the first decoding signal is a signal fed back after the i.sup.th M-ary differential decoding processing is performed on the demodulation signal, and i is an integer greater than or equal to 0; and performing M-ary differential decoding processing on the demodulation signal according to the first decoding signal, to obtain a second decoding signal. The first decoding signal that is fed back is added and input to a decoder.

The present invention relates to a transmit diversity method for FQAM and an apparatus therefor. According to the present invention, a transmit diversity method for FQAM and apparatus therefor are provided, the transmit diversity method comprising the steps of: modulating data into at least one FQAM symbol; interleaving a plurality of tones constituting the at least one FQAM symbol such that tones having the same index are located in adjacent resources; and transmitting the at least one interleaved FQAM symbol through at least one transceving unit.

A communication method and apparatus are provided, to improve frequency shift keying (FSK) demodulation performance of a low-power device. After determining at least two orthogonal frequency division multiplexing (OFDM) subcarriers, a first device sends an FSK signal to a second device on the at least two OFDM subcarriers, and the second device demodulates the FSK signal. In this way, FSK transmission of a low-power receiver can be compatible with OFDM, so that the FSK demodulation performance can be improved.