156 results about "Generalized frequency division multiplexing" patented technology

Channel estimation techniques are provided for a receiver of a wireless communication system using orthogonal frequency division multiplexing (OFDM), including legacy 802.11a and various extended rate systems. Training signals are received from one or more receive antennas. An estimated channel impulse response is computed from the received training signals by reference to a training sequence. The estimated channel impulse response is truncated in the time domain based on channel power and noise data. Channel response tracking techniques may also be implemented to correct for variations in channel response over the transmission time of a packet.

Embodiments are provided for pre-cancelling signal interference in Generalized Frequency Division Multiplexing (GFDM). Signal interference is pre-cancelled, at a transmitter, so that clean pilots are observed at a receiver and hence used for channel estimation. Using a Pilot-Interference Cancellation (Pilot-IC) method, interference is pre-cancelled at only pilot symbols. Alternatively, interference is simultaneously pre-cancelled at all symbols using a Transmitter IC (Tx-IC) method. The embodiments also include scattering the pilots over frequency and time resources to estimate channels which are frequency selective and time-variant. The channel estimates at the receiver are then used for single-tap channel equalization at time-frequency grid data points, where no assumption of time-invariant channels is required.

The invention provides an orthogonal frequency division multiplexing passive optical network system, which modulates an uplink data stream by using orthogonal frequency division multiplexing (OFDM) on the basis of not increasing hardware cost and media access control (MAC) complexity. The system adopts OFDM modulation for both uplink transmission and downlink transmission. In the OFDM modulation of uplink data, the positions and bandwidths of frequency bands allocated to each optical network unit and used for bearing valid uplink data in the whole converged OFDM frequency band are variable. Different frequency bands are allocated to uplink channels of different optical nodes, so that the frequency bands allocated to all the ONUs in the system and used for bearing the valid uplink data are positioned at different positions of the whole OFDM frequency spectrum, and are not overlapped with one another. An uplink transmission module can perform adaptive source configuration, dynamically allocate the number of sub-carriers according to the traffic of a user and regulate the bandwidths of the frequency bands used for bearing the valid uplink data.

The embodiment of the invention provides an information transmission method and device, an electronic device and a storage medium. The information transmission method comprises the steps of determining at least a polarization code transmission channel of a GFDM (Generalized Frequency Division Multiplexing) system based on a two-step channel polarization transformation method; determining reliability of each polarization transmission channel; obtaining a to-be-transmitted information vector, coding the information vector through a coding method and modulating the coded information vector through a preset signal modulation method to obtain the sent information vector; selecting a target polarization code transmission channel which has the byte number as same as that of the sent information vector and has high reliability from the at least one polarization code transmission channel; and transmitting the sent information vector to a receiving end through the target polarization code transmission channel. According to the embodiment of the invention, the information transmission method which combines the polarization code and the GFDM system can improve the information transmission performance of the GFDM system.

Aspects of the disclosure relate to methods and apparatus of wireless communication to support frequency division multiplexing (FDM) of multiple waveforms. The methods and apparatus schedule FDM symbols where the scheduling of the FDM symbols is selectively based on one or more waveform parameters during a time interval when the FDM symbols are transmitted. The FDM symbols are then transmitted over the time interval. Further aspects also include the reception of the FDM symbols in a receiver where the waveform parameters are applied for decoding based on the waveform parameters.

A new diversity scheme for orthogonal frequency division multiplexing/multi-input multi-output (OFDM/MIMO) systems. The new diversity scheme, i.e., turbo layered space-frequency coded OFDM (TLSFC-OFDM), uses the turbo principle with space hopping (SH). The TLSFC-OFDM system uses a successive interference cancellation (SIC) algorithm to reduce the number of iterations. As a result, this scheme reduces computational complexity. Simulation results show that the SIC-based TLSFC-OFDM system outperforms a conventional OFDM/Horizontal Bell Labs Layered Space-Time (H-BLAST) system using a horizontal coding scheme.

The invention provides a data domain based frequency offset estimation and correction method and system. The method includes S1, subjecting signals received by an IEEE802.11 MIMO-OFDM (multiple input multiple output-orthogonal frequency division multiplexing) system antenna to analog-digital conversion to obtain a high-throughput mixed-format preamble short training sequence; S2, using the high-throughput mixed-format preamble short training sequence to estimate a signal-to-noise ratio to obtain a correlation coefficient Rho; S3, subjecting the high-throughput mixed-format preamble short training sequence to symbol timing coarse synchronization and coarse frequency offset estimation and correction, and subjecting an obtained signal to removal of high-throughput preambles to obtain OFDM signal sequences of a high-throughput data domain; S4, through the correlation coefficient Rho, subjecting the OFDM signal sequences of the high-throughput data domain to symbol timing fine synchronization so as to obtain a frequency offset estimated value, and according to the frequency offset estimated value, subjecting symbols of each OFDM signal sequence to frequency offset compensation so as to finish a frequency offset estimation and correction process.

Disclosed is a physical layer encryption/decryption method based on ONU (optical network unit) end time-varying keys in an OFDM-PON (orthogonal frequency division multiplexing-passive optical network) in the field of safety communication. Up data of each ONU are uploaded to an OLT (optical line terminal) to serve as a key and subjected to exclusive or operation with down data detected on the OLT to obtain encrypted data, so that the down data are encrypted, the encrypted data are downloaded to each corresponding ONU through down subcarriers, and then each ONU performs decryption according to locally stored up data to obtain decrypted down data. The keys vary along with the up data in real time, and encryption reliability is further realized, so that the safety feature of an OFDM-PON system is effectively improved.

The invention discloses an orthogonal frequency division multiplexing (OFDM) frequency domain interpolation pilot frequency-based cyclostationary feature spectrum sensing method. The invention mainly aims to solve the problems that the performance of the traditional sensing technology is limited by the length of a cyclic prefix, and the performance is lowered by the random variation of a pilot frequency phase. The OFDM frequency domain interpolation pilot frequency-based cyclostationary feature spectrum sensing method comprises the following implementation steps of (1) transforming a time domain signal into a frequency domain signal by performing fast Fourier transformation on the time domain signal received by a receiving end; (2) calculating a spectral correlation function of the frequency domain signal by utilizing a time domain smoothness periodogram method; (3) selecting feature points from the spectral correlation function; (4) constructing corresponding test statistics by utilizing the selected feature points according to the channel condition; and (5) comparing the test statistics with corresponding sensing judgment thresholds so as to judge whether a master user signal exists in a channel to be sensed or not, and giving the reliability tolerance of the master user signal. The OFDM frequency domain interpolation pilot frequency-based cyclostationary feature spectrum sensing method disclosed by the invention does not depend on the length of the OFDM symbol cyclic prefix, is good in detection performance under the low-signal to noise ratio fading channel condition, and can be widely applied to various broadband wireless OFDM communication systems.

The invention discloses an estimation method for a signal interference noise ratio in an orthogonal frequency division multiplexing (OFDM) system. Through obtaining a period self-correlation function of a received signal on a receiving end of the OFDM system, the energy distribution rule of a transmission signal, a radio frequency interference signal and the period self-correlation function of Gauss white noise is analyzed, the signal power can be effectively separated from the noise-added interference power by selecting an appropriate delay variable and a circulating frequency, and then according to the definition of the signal interference noise ratio, a signal interference noise ratio value during a signal transmission process is effectively estimated. By the adoption of the estimation method, the calculation complexity is low, the estimation precision is high, aiming to the situation that current frequency spectrum resource is gradually deficient, the utilization rate of a frequency band can be well increased, and under the environment of more serious radio frequency interference, performance of the communication system can be effectively improved.

An OFDM (orthogonal frequency division multiplexing) transmitter includes an inverse fast Fourier transform circuit, which, in operation, generates, based on digital input data, a complex time-varying digital signal having real and imaginary components; and a multiplexer adapted to generate a time-multiplexed digital signal by time-multiplexing one or more of the real components with one or more of the imaginary components.

The invention relates to the field of communications, in particular to an orthogonal frequency division multiplexing (OFDM) anti-interference synchronization method under a complex multipath channel with strong interference signals. According to the method, an existing OFDM synchronization scheme is not suitable for a strong-interference complex multipath environment any more, and thus the OFDM anti-interference synchronization method under the complex multipath channel is designed. The method includes the specific steps that a sequence C(k), c(k) and [x(k) and x(k)] is generated; a sliding correlation value is solved; timing synchronization is conducted; frequency offset estimation is carried out. Compared with an existing synchronization method, by the adoption of the scheme, the OFDM symbol timing and frequency estimation accuracy under the complex multipath environment can be improved, and the anti-interference performance of the system is improved.

The invention provides a sideband information transmission method of SLM (selective mapping method) and PTS partial transmit sequences) in a OFDM (orthogonal frequency division multiplexing) system reduce peak-to-average power ratio (PAPR) technology. In the sideband information transmission method, the linearity property of IFFT (inverse fast Fourier transform) is used, that is, sideband information and data information are respectively combined into a sideband symbol and a data symbol in a frequency domain; in the data symbol, the position for transmitting data is used for storing data, theposition for transmitting the sideband is set to zero, a data position in the sideband symbol is set to zero, and a sideband position is used for storing the sideband information. After the data symbol and the sideband symbol are respectively subject to IFFT, the data symbol and the sideband symbol are added in the time domain to obtain final time domain information; and a receiving end can extract the sideband information from the known sideband position when the received data is subject to FFT (fast Fourier transform). The sideband information transmission method does not cause the problem of PAPR (peak-to-average power ratio) regeneration if applied to the SLM method, but the sideband information transmission causes parts of peak value to regenerate if applied to the PTS method. The sideband information transmission method can used to preferably lower the PAPR on the premise of guaranteeing error rate performance.

The invention belongs to the technical field of optical fiber communication and optical network transmission, and particularly relates to a noise diffusion suppression method based on RF pilot frequency in a high-speed optical DFT-S OFDM modulation system. The method mainly comprises adding an RF pilot frequency component in a DFT-S OFDM modulation signal; equalizing signals by use of the RF pilot frequency according to the characteristic of the component similar to the modulation signal that is distorted in the transmission link; and realizing nonlinear compensation and phase noise compensation at the same time. The noise diffusion suppression method provided by the invention can lower nonlinear distortion and phase noise in the DFT-S OFDM system so as to suppress the noise diffusion caused by inverse Fourier transform during DFT-S OFDM modulation, thereby improving the resistance to linear distortion and phase noise and improving the transmission performance of the system.

The invention discloses a method for suppressing the peak-to-average ratio of orthogonal frequency division multiplexing (OFDM) signals. The method includes the following steps that: (1) inputted serial data signals are converted into parallel signals at a signal transmitting end, so that a parallel signal sequence can be obtained; (2) the obtained parallel signal sequence is multiplied by a constructed precoding matrix, so that a peak-to-average ratio-suppressed precoded signals can be obtained; (3) a cyclic prefix is added to the precoded signals, companding processing is performed through using a segmented exponential companding function, so that the peak-to-average ratio of the companded signals can be further suppressed; and (4) parallel-to-serial conversion is performed on the companded signal sequence at the signal transmitting end, so that orthogonal frequency division multiplexing (OFDM) transmission signals can be obtained. The method of the invention is low in complexity, can significantly reduce the signal-to-average ratio of the signals without decreasing the bit error rate of the received signals, and can improve the performance of a communication system.

The invention discloses a signal peak-to-average ratio reduction method for an orthogonal frequency division multiplexing (OFDM) system. A peak-to-average ratio is reduced by combining a constellation extension method and null sub-carriers. Regulation is performed on data sub-carriers according to constellation extension rules. Frequency domain filtering is performed on the null sub-carriers. In the method, amplitude-prelimited signal noises are processed to generate a peak cancellation vector in ways of regulating data on the data sub-carriers according to the constellation extension rules, performing a frequency domain filtering operation on the null sub-carriers, reserving noises of a null sub-carrier part and zero-setting the noises of a data sub-carrier part to completely transfer the noises to areas of the null sub-carriers and constellation extension without influencing judgment in a constellation diagram of a receiver to further reduce the peak-to-average ratio of a signal. By the method, the peak-to-average ratio of the OFDM signal can be effectively reduced, and iteration times can be reduced.

The invention discloses a modulation method for reducing a peak-to-average power ratio of an orthogonal frequency division multiplexing-visible light communication (OFDM-VLC) system. According to the modulation method provided by the invention, through performing specific peak clipping and mapping treatments on visible light vector signals, the peak-to-average power ratio of the OFDM-VLC system can be effectively reduced, and meanwhile the bit error rate performance of the system can also be improved.

The invention discloses an estimation method for a plurality of Doppler frequency offsets of an OFDM (orthogonal frequency division multiplexing) system in a high-speed mobile environment. The estimation method comprises the following steps that: a mobile relay terminal is set on a high-speed mobile vehicle and used for forwarding communication data between a base station and a mobile station, at the time, transmission routes with a limited number exist between the base station and the mobile relay terminal, and each route corresponds to different Doppler frequency offsets; and a plurality of Doppler frequency offsets between the base station and the mobile station on the vehicle are obtained by analysing the plurality of Doppler frequency offsets between the base station and the mobile relay terminal. With the adoption of the method disclosed by the invention, estimation for the plurality of Doppler frequency offsets in the high-speed mobile environment is realized. Moreover, the greater a sub-carrier number Nc is, the smaller a mean square error under the same signal-to-noise ratio is, namely, the more accurate the estimation for the frequency offsets is. Because in the case that Nb is given, increase for the Nc is increase for Na essentially, and the Na is equal to the fast beat number of a signal, the accuracy of estimation for a covariance matrix Rd can be improved via the increase for the Nc, thus the estimation for the frequency offsets is more accurate.

The invention discloses a union resource distributing method of an improved-type multi-user OFDM (orthogonal frequency division multiplexing) DF (decoding forwarding) system, wherein a relay station assist information source with a DF (decoding-forwarding) mechanism communicates with a plurality of users; the union resource distribution of the system is realized through a dual-time-clearance transmission mode, comprising system subcarrier matching, subcarrier pair-user distribution as well as subcarrier power distribution; based on the analysis of channel state information by a pivot control unit, the system working mode switching is realized; and when a certain subcarrier of the system is in the idle mode, an idle subcarrier of an information source second time clearance is allowed to be transmitted additionally. Compared with the traditional OFDM based multi-user relay cooperative system, the method provided by the invention effectively overcomes the defect that a relay subcarrier of the traditional OFDM system can not be fully utilized at the second time clearance and obviously improves the frequency spectrum frequency.