34 results about "Quaternary phase shift keying" patented technology

The invention provides a remote underwater acoustic communication method based on soft-demodulation soft-decoding joint iteration. The method comprises the following steps that: a transmitting end performs low density parity check (LDPC) coding on a binary information sequence which is sent by a signal source, performs quaternary phase shift keying (QPSK) modulation and Gray mapping, maps code elements to one of four positions in a constellation diagram by taking two code elements as a group, performs Walsh-m composite sequence spectrum spreading to obtain a signal to be transmitted, and converts a digital signal to be transmitted into an underwater acoustic signal; and an underwater acoustic transducer at a receiving end converts the received underwater acoustic signal, de-spreads by using a composite sequence which is the same as that of the transmitting end to obtain a receiving signal, performs self-adaptation decision feedback equalization to obtain an amplitude fading complex signal, performs soft-demodulation soft-decoding joint iteration on the signal, stops joint iteration after set iteration frequency is reached, performs belief propagation (BP) decoding on an LDPC decoder and outputs a bit value to a sink. By the method provided by the invention, the reliability of remote underwater acoustic communication is improved. The method is applicable to the remote underwater acoustic communication.

A method and apparatus for providing an asymmetrical backwards compatible communications signal that is capable of being decoded by QPSK and OQPSK receivers as well as PSK and QAM receivers is provided. The invention comprises a timing error accumulator coupled to a first bit stream. The first bit stream includes content that is common to the QPSK/OQPSK receiver and to the PSK/QAM receiver. A phase error accumulator is coupled to a second bit stream and adjusts the phase of symbols in the second bit stream. A phase and timing error compensator is coupled to the phase error accumulator and the timing error accumulator and adjusts the first and second bit streams received from the phase error accumulator and the timing error accumulator in order to reduce timing and phase errors. A higher order modulator coupled to the phase and timing error compensator is also provided. The higher order modulator processes the first and second bit streams to provide the asymmetrical backwards compatible signal.

The invention relates to a quaternary phase-shift keying signal tracking method and device, which are applied to a GNSS (Global Navigation Satellite System) receiver. Under the combined tracking mode of in-phase and orthogonal dicode channels, the method comprises the following steps of: carrying out correlation operation respectively with corresponding local PRN (Pseudo-Random Noise) codes on an in-phase (I) code channel signal and an orthogonal (Q) code channel signal after down-conversion, and outputting the integral results of the I code channel signal and the Q code channel signal; respectively carrying out identification on the integral results of the I code channel signal and the Q code channel signal in at least one tracking loop so as to obtain identification results; and carrying out mathematic operation on the identification results of the I code channel signal and the Q code channel signal in the same tracking loop so as to obtain a synthesized identification result. In the tracking loop, the corresponding devices comprise an I code channel identifier, a Q code channel identifier and a synthetic identifier. According to the quaternary phase-shift keying signal tracking method and device, the noise intensity of the tracking loops such as DLL (Dynamic Link Library), PLL (Phase Locked Loop) and FLL (Fixed Loss Loop) is obviously reduced.

A 2ⁿ-QAM (e.g. 16-QAM) optical modulator comprising cascaded I-Q modulators. The first I-Q modulator applies 2^n-2 (e.g. 4) QAM to an optical signal, having a constellation diagram with the 2^n-2 (e.g., 4) constellation points located in quadrant I. The second I-Q modulator subsequently applies a quaternary phase-shift keying (QPSK) modulation scheme to the optical signal, thereby rotating the constellation points of the 2^n-2-QAM modulation scheme to quadrants II, III and IV, to produce a 2ⁿ-QAM modulation constellation diagram. The rotation causes the 2ⁿ-QAM modulator to inherently apply four quadrant differential encoding to the optical signal. A method of 2ⁿ-QAM optical modulation is also provided and optical signal transmission apparatus comprising the 2ⁿ-QAM optical modulator.

The invention discloses a digital modulation method, a digital transmission device and equipment. The digital modulation method comprises the following steps: implementing symbol mapping on the source data of each sub-channel to obtain quaternary phase shift keying (QPSK) symbols; grouping the QPSK symbols and performing discrete Fourier transform (DFT) to obtain frequency domain signals; implementing low-pass filtering and frequency reuse processing on the frequency domain signals of each sub-channel; implementing inverse Fourier transform on the frequency domain signals that are subjected to frequency reuse to obtain an OFDM symbol, and then transmitting the OFDM symbol after adding the OFDM symbol into a cyclic prefix (CP). According to the digital modulation method, the digital transmission device and equipment disclosed by the invention, the frequency domain signals obtained by implementing DFT on each sub-channel are separately subjected to low-pass filtering, and thus the bandwidth of modulation signals subjected to frequency domain reuse becomes narrower, the crosstalk damages caused by multiplexing multiple sub-bands can also be reduced, and the spectrum efficiency can be increased.

A modulation and demodulation method of a wave form synergy signal based on a frequency domain and a fractional Fourier domain orthogonal basis function relates to a signal modulation and demodulation method, and aims at solving the problem that a modulation and demodulation method of an existing quaternary phase shift keying (QPSK) signal is low in efficiency. Modulation and demodulation are achieved by a way of wave form synergy of a chirp signal and a sine and cosine signal, and therefore the modulation and demodulation method of the wave form synergy signal based on the frequency domain and the fractional Fourier domain orthogonal basis function is a novel modulation and demodulation method. In addition, two branches of chirp signals are respectively added to an I branch and a Q branch modulated by the existing QPSK signal and are used as carrier waves to respectively modulate one branch of baseband signal, so that existing two-way modulation is added up to four-way modulation, and at the demodulation end, filter waves are combined and matched by using a frequency domain template and a fraction domain template, and eight integrators are designed, and finally filtering results are combined so as to judge the information bit. The modulation and demodulation method is appropriate for the wireless communication field.

A method implemented in a transmission apparatus used in an optical fiber communications system for a polarization switched differential quaternary phase-shift keying (DQPSK) signal is disclosed. The method comprises splitting data into two or more data streams, inputting said two or more data streams to 1-bit DQPSK precoders to perform 1-bit DQPSK precoding, and multiplexing inphase outputs of the 1-bit DQPSK precoders to generate a first output; and multiplexing quadrature outputs of the 1-bit DQPSK precoders to generate a second output. Other methods, apparatuses, and systems also are disclosed.