136results about How to "Frequency synchronization" patented technology

The invention relates to an IEEE 1588 based accurate clock synchronization protocol system and a synchronization method thereof, belonging to the technical field of network information transmission. By adopting the invention, a main clock carries an accurate timestamp while sending a synchronization message, and a follow message is not required to be sent, thus greatly reducing communication bandwidth required for realizing clock synchronization. Meanwhile a frequency adjustable clock counter is constructed, and clock synchronization algorithm is combined, so as to realize frequency compensation function and achieve high accuracy clock synchronization requirement.

The present invention discloses a method for modulating digital television ground broadcasting transmitter based on insertion training sequence and LDPC code, wherein the method comprises the following steps: 1) forming an FFT coded data block with the input bit flow through LDPC coding; 2) switching the FFT coded data block to a time domain discrete coded data sample block through IFFT; 3) forming a complex training sequence discrete sample block with a mode that a training sequence is used as a real part sequence and an operational indicator sequence is used as an imaginary part sequence; 4) continuously repeating the complex training sequence for four times to form a time domain insertion training sequence discrete sample block; 5) directly overlapping the time domain discrete coded data sample block with the time domain insertion training sequence discrete sample block for forming a time domain insertion training sequence coded data block; 6) inserting a circulating prefix into the time domain insertion training sequence coded data block for forming a signal frame; 7) forming a signal frame pulse with a square-root raised cosine roll-off filter; and 8) upconverting the baseband signal to the carrier.

The invention discloses a space frequency modulation method for digital TV terrestrial broadcasting transmitter based on embedding training sequence and LDPC coding comprising: 1) coding input bit stream by LDPC and forming coding data block on frequency domain; 2) then demodulating by space-frequency coder and regulating time for synchronization; 3) converting data block after space-frequency modulation to time domain discrete data sample value block via IFFT; 4) training sequence serving as real part, service index sequence serving as imaginary part sequence, constituting discrete sample value block of plural training sequence; 5) repeating continuously the plural training sequence four times to form discrete sample value block of time domain embedded training sequence; 6) superposing the space-frequency modulated time domain discrete data sample value block and time domain embedding training sequence discrete sample value block to form space-frequency modulated time domain embedded training sequence data block; 7) inserting cyclic prefix as protective interval and forming signal frame; 8) pulse shaping to signal frame using square root raised consine roll-off filter; 9) up-converting base band to carrier.

The invention discloses a method for transmitting a digital mobile broadcast signal, which is a transmission proposal of time domain and frequency domain mixing. The method for transmitting a digital mobile broadcast signal disclosed by the invention has the advantages of low peak-to-average power ratio, short synchronization time, fading noise influence resistance, controllable multi-service etc.

The invention discloses a method for unidirectionally synchronizing transmission time frequency. Through utilization of the method, the high-precision time frequency synchronization problem between amaster station and a secondary station can be effectively solved. The method is realized by the following technical scheme that the master station and the secondary station realize inter-station relative distance high-precision measurement through satellite navigation relative positioning; the master station measures surrounding parameters through utilization of a meteorograph, precisely evaluatestransmission path atmosphere delay, takes own rubidium clock as a reference clock, generates a spread spectrum distance measurement signal through a spread spectrum distance measurement signal moduleand transmits the spread spectrum distance measurement signal to the secondary station through a transmitting radio frequency front end and an antenna; and the secondary station captures and tracks the spread spectrum distance measurement signal and sends a code frequency control word output by a code loop filter to a direct digital synthesizer DDS, phase detection is carried out on an output sinusoidal wave signal and a constant temperature crystal oscillator of a phase-lock loop of the secondary station, and frequency synchronization of the constant temperature crystal oscillator of the secondary station and the rubidium clock of the master station is realized through application of a high-precision reference clock output by the constant temperature crystal oscillator.

The invention discloses a micro-grid frequency synchronization anti-attack coordinated control method. The frequency of a micro grid is controlled by using a specially designed control rate, and any constant attack on a controller can be completely eliminated on the premise of ensuring system frequency synchronization. The control rate is obtained by carrying out integral operation on the basis ofa traditional distributed control method and subtracting a corresponding frequency state quantity, and the purpose of eliminating constant value attacks exerted by the controller is achieved. The convergence of the control method is strictly proved through the final value theorem. Compared with an existing constant value attack resisting method, a complex evaluation mechanism does not need to beestablished to evaluate the credibility of neighbor node information, an additional communication network is not needed to assist in attack elimination, and the influence of constant value attacks onthe system can be completely eliminated.

The invention discloses an anti-interference transmission method for a digital broadcast wireless signal. The method is a time domain / frequency domain combined transmission scheme. The anti-interference transmission method has the advantages of low peak-to-average power ratio, short synchronization time, anti-interference performance, multi-service controllability and the like.

The invention discloses a robust transmission method for digital broadcasting wireless signals, which is a time domain and frequency domain hybrid transmission scheme. The method has the advantages of low peak-to-average power ratio, short synchronous time, robustness, controllability in multiple services and the like.