147 results about "Doppler spread" patented technology

Methods and systems in a wireless receiver for enabling the reception of input signals at varied power levels in the presence of co-channel interference utilizing combinations of space-time adaptive processing (STAP), interference cancellation multi-user detection (MUD), and combined STAP / MUD techniques. In MUD, code, timing, and possibly channel information of multiple users are jointly used to better detect each individual user. The novel combination of adaptive signal reconstruction techniques with interference cancellation MUD techniques provides accurate temporal cancellation of interference with minimal interference residuals. Additional methods and systems extend adaptive signal reconstruction techniques to take Doppler spread into account. STAP techniques permit a wireless receiver to exploit multiple antenna elements to form beams in the direction of the desired signal and nulls in the direction of the interfering signals. The combined STAP-MUD methods and systems increase the probability of successful user detection by taking advantage of the benefits of each reception method. An additional method and system utilizes STAP techniques in the case where no pilot signal is available. This method compares the outputs of various hypothesized STAP solutions.

The invention discloses a self-adapting channel estimating method applied to 3GPP LTE system. The method comprises the following steps: (1) the LS (least square) channel estimating value at a pilot tone is computed according to reference signals in a receiving data field; (2) interpolation in the time domain is performed according to current frame pilot tone channel estimated value data and reserved delay frame pilot tone channel estimated value data, and a pilot matrix encrypted is obtained through computing; (3) channel delay spread is estimated according to LS estimation value at the pilot tone, then radio frequency channel filtering coefficient is selected according to the delay spread, and the frequency domain estimation value is computed; and (4) channel Doppler spread is estimated according to the LS estimation value at the pilot tone, then time domain filtering coefficient is selected according to the Doppler spread, and the time domain channel estimation value is computed. The self-adapting channel estimating method provided by the invention has a self-adapting capability to channel characteristics, reduces the occupancy rate and working consumption of hardware resource, improves the estimating speed and reduces computation delay of an estimator.

A synchronization of a pilot assisted channel estimation orthogonal frequency division multiplexing can be achieved by receiving a signal containing pilot symbols, providing an initial time and frequency synchronization to the signal, phase rotating the signal across time, transforming the signal with a fast Fourier transformation, phase rotating the signal across frequency, extracting the pilot symbols and generating a channel estimator. The phase rotating across time and the phase rotating across frequency are controlled by a phase rotation controller in accordance with the channel estimator. The initial time and frequency synchronization synchronizes the signal such that intercarrier interference effects and intersymbol interference effects are negligible. The signal may include plural carrier frequencies each having an arrival timing offset and a frequency offset. The signal may also include delay spread or Doppler spread. The phase rotation controller measures a phase different between the channel estimator at times k and k+Δk, where k is time and Δk is a symbol period and measures a phase difference between the channel estimator at frequencies n and n+Δn, where n is tone frequency and Δn is a frequency spacing between adjacent tones.

An exemplary fast Fourier transform (FFT) numerology for an orthogonal frequency division multiple access (OFDMA) downlink transmission system is described. The exemplary FFT numerology reduces the FFT sampling rate for a given transmission bandwidth, thereby increasing the battery life of a UE. The FFT numerology increases robustness against Doppler spread, phase noise, and frequency offset, enabling operation in channels with high delay spread, such as occurs in mountainous regions. The described numerology might provide the following without altering standard sub-frame duration: increased intercarrier spacing; reduced FFT sampling frequency across the transmission bandwidths; reduced FFT size across all transmission bandwidths; increased number of OFDM symbols per sub-frame; and / or increased cyclic prefix length choices.

Method and apparatus for improving the detection and discrimination of slow moving or stationary range-Doppler spread objects on or in close proximity to the ground (or sea surface). Invention detects, discriminates and separates radar returns from interference including ground clutter discretes via a coherent process for separating target returns from the myriad of received signals. Thus the method and apparatus improves the probability of detecting and declaring the presence or absence of an object at the same time that the probability of false declaration decreases. The method and apparatus may be applied to the processing of any over resolved object, including airborne radar.

A method for estimating Doppler spread in mobile wireless communication devices, for example in CDMA or W-CDMA cellular communication systems, with improved noise immunity. The Doppler spread estimation is based on an estimated value of an autocorrelation or autocovariance at a first lag (210) and at a second lag (220), the magnitude of which is greater than the first lag. A first ratio is determined (250) between a first difference (230) and a second difference (240). The estimated Doppler spread is generally proportional to a square root (260) of the first ratio, and is scaled (270) by a multiplicative factor that depends on whether the estimated function is an autocorrelation or autocovariance function.

Methods and systems in a wireless receiver for enabling the reception of input signals at varied power levels in the presence of co-channel interference utilizing combinations of space-time adaptive processing (STAP), interference cancellation multi-user detection (MUD), and combined STAP / MUD techniques. In MUD, code, timing, and possibly channel information of multiple users are jointly used to better detect each individual user. The novel combination of adaptive signal reconstruction techniques with interference cancellation MUD techniques provides accurate temporal cancellation of interference with minimal interference residuals. Additional methods and systems extend adaptive signal reconstruction techniques to take Doppler spread into account. STAP techniques permit a wireless receiver to exploit multiple antenna elements to form beams in the direction of the desired signal and nulls in the direction of the interfering signals. The combined STAP-MUD methods and systems increase the probability of successful user detection by taking advantage of the benefits of each reception method. An additional method and system utilizes STAP techniques in the case where no pilot signal is available. This method compares the outputs of various hypothesized STAP solutions.

The invention discloses a bistatic MIMO radar high-speed movement target parameter estimation method based on dual-frequency transmission. Echo signals of high-speed high-mobility targets are received through a receiving array of bistatic MIMO radar, and the echo signals of the receiving array are divided according to different carrier frequencies; conjugate multiplication is conducted on the two routes of echo data obtained through division, and whole cycle integration is conducted in a rapid time domain; Fourier conversion is conducted on the integrated data in a slow time domain, and each target speed is estimated; high-speed target matching filtering functions are set up; matching filtering is conducted on the echo signals of the receiving array to form a virtual array; the transmission angle of each target and the receiving angle of the target are estimated. The range walk of the high-speed targets is corrected according to the characteristic of the echo signals of the dual-frequency transmission MIMO radar, the problem that the parameter estimation performance is influenced by unstable factors such as Doppler spread and RCS rapid fluctuation is solved, and MIMO radar parameter estimation under the high-speed high-mobility targets is achieved.

The invention provides a phase-coherent accumulation detection method applied to a three-order maneuvering target, belonging to the technical field of radar signals. The method comprises the followingsteps: carrying out fast-time frequency domain pulse compression on an echo signal, and carrying out three-order Keystone conversion so as to correct three-order range migration of a target; carryingout frequency shift mutual correlation and scale Fourier transform, so as to obtain a defined speed value; eliminating first-order range walk by virtue of the cooperation of a fast-time frequency domain matched filtering equation constructed by the defined speed, combining an accelerated speed with a jerk of the searched target by virtue of a two-dimensional matched filtering equation, and compensating and eliminating second-order range walk and Doppler spreading effect of the target; and detecting the phase-coherent accumulation of the energy of the target by virtue of slow time fast Fouriertransform. According to the method, phase-coherent accumulation is realized by virtue of the range and phase information of the target echo to eliminate the range migration and the Doppler migrationeffect of the three-order maneuvering target, so that the detection performance of radar can be remarkably improved, and the practicability is strong.

The invention relates to a symbol synchronization and Doppler compensation method for a mobile orthogonal frequency division multiplexing (OFDM) underwater sound communication signal. The method comprises the following steps of: obtaining rough estimation of a first OFMD symbol start position according to a frame header signal, extracting a symbol, then obtaining Doppler expansion rough estimation of the symbol according to a frequency measurement simple-frequency signal in the symbol, converting the symbol to a frequency domain according to Chirp-z conversion, searching a precise start moment and a Doppler expansion amount of the symbol by taking a pilot of the frequency domain and a relevant value of a local pilot as cost functions, presuming the start position of the next symbol according to the start position of the current symbol, extracting the next symbol, and repeating the operations till the end of a frame of signal. According to the Doppler measurement and compensation method, based on the Chirp-z conversion, the measurement and compensation precision is high; the Chirp-z conversion is implemented according to fast Fourier transformation (FFT); the practicability is high; according to the Doppler expansion search method which is in a manner that large step length is superior to small step length, so that the search efficiency is high; a Doppler measurement range is not limited; and the method can be used for constant-speed motion and variable-speed motion.

A system and method for controlling clutter Doppler spread in a bistatic radar system is developed resulting in enhanced detection of low-Doppler targets or improved SAR mode performance. In an illustrative embodiment, a bistatic radar system (10) includes a transmitter (12) for transmitting electromagnetic energy (106) towards a target (16), a receiver (14) adapted to receive the electromagnetic energy (116) reflected from the target (16), and a processor (122) for optimizing a parameter or parameters of the system such that the directional derivative of the bistatic Doppler field along the isorange contour is near a desired value. The parameters to be optimized may include the transmitter velocity vector, the receiver velocity vector, or the receiver azimuth flight direction. The desired value is the minimal absolute value of the directional derivative in order to minimize the clutter Doppler spread, or the maximum absolute value of the directional derivative in order to maximize the clutter Doppler spread.

The invention discloses a method for processing Doppler expansion of underwater sound high-speed OFDM communication. The method relates to a Doppler estimation and compensation module, a channel estimation module based on compression sensing and a part fast Fourier transform demodulation module, wherein the key portion is the part fast Fourier transform demodulation module and output of the other two modules serves as input of the part fast Fourier transform demodulation module. According to the method for processing Doppler expansion of underwater sound high-speed OFDM communication, a traditional OFDM demodulation method is modified, part Fourier transform is firstly adopted to serve as a demodulation method and part of Doppler expansion can be eliminated in the process of demodulation; due to the fact that Doppler expansion is processed for twice, influence on signals by Doppler expansion can be reduced to a lower range and the method is particularly high in adaptation to a rapidly-changed underwater sound channel. Therefore, the high processing performance of Doppler expansion is achieved.

A Doppler spread value of a channel in an Orthogonal Frequency Division Multiplexing (OFDM) system is estimated, wherein the channel comprises a plurality of carrier frequencies. Estimating involves selecting a set of two or more carrier frequencies from the plurality of carrier frequencies. A Doppler spread value is estimated for each of the selected carrier frequencies. An estimate of the Doppler spread value of the channel is produced by combining the estimated Doppler spread values of each of the selected carrier frequencies. For example, the Doppler spread value of the channel may be estimated by averaging the estimated Doppler spread values of each of the selected carrier frequencies.

A method for correlating scattered pilot locations in a sequence of OFDM symbols in a multi-carrier transmission system, and includes mapping pilot locations comprising pilot symbols having predetermined known values, wherein the pilot symbols are positioned among data subcarriers in time and frequency dimensions consisting of received pilot symbols and having a predetermined position pattern in the time and frequency dimensions, wherein the predetermined position pattern comprises a finite number of sub-position patterns each corresponding to positions of the pilot symbols; estimating a Doppler spread in a frequency spectrum between the transmitter and the receiver in the multi-carrier transmission system; estimating a channel length of a set of channel paths received at the receiver; and the receiver automatically selecting one of a plurality of predetermined methods of correlating the scattered pilot locations in the sequence of OFDM symbols based only on the estimating processes.

Method and apparatus for improving the detection and discrimination of slow moving or stationary range-Doppler spread objects on or in close proximity to the ground (or sea surface). Invention detects, discriminates and separates radar returns from interference including ground clutter discretes via a coherent process for separating target returns from the myriad of received signals. Thus the method and apparatus improves the probability of detecting and declaring the presence or absence of an object at the same time that the probability of false declaration decreases. The method and apparatus may be applied to the processing of any over resolved object, including airborne radar.

An airborne wind profiling portable radar (AWiPPR) system comprising a mobile airborne platform including one or more navigation units configured to produce navigation data including at least the position and orientation of the mobile airborne platform. A radar unit is mounted and positioned to the mobile airborne platform, the radar unit is configured to transmit a wide-band frequency modulated continuous wave radar signal in a downward direction from the mobile airborne platform towards the ground and configured to continuously receive a reflected signal from a plurality of clear air scatters (CAS) targets or volumetric targets and output radar data. An inertial measurement unit (IMU) in communication with the one or more navigation units and the radar unit is configured to receive the navigation data and determine the position and orientation of the radar at a specific point in time and output IMU data. A data acquisition unit in communication with the radar unit and the is configured to receive and time align radar data and the IMU data for each reflected signal from each of the plurality of CAS targets or volumetric targets to provide an antenna pointing direction for each received reflected signal. The data acquisition unit is configured to process the time aligned radar data and IMU data to determine a distance and a Doppler velocity of each of the plurality of CAS targets or volumetric targets, provide a range, a velocity, and an antenna pointing direction for each of the plurality of CAS targets or volumetric targets, and calculate a vector wind velocity using the range, the velocity, and the antenna pointing direction for each of the plurality of CAS targets or volumetric scatters targets, The data acquisition unit may be configured to further correct the range, the velocity, and / or the antenna pointing direction of each of the plurality of CAS targets or volumetric targets to accommodate for a motion shift in data produced by one or more on a relative motion and orientation of the mobile airborne platform, a Doppler spread in the range, the velocity and / or the antenna pointing direction, and a ground echo.

The invention discloses a passive time-reversal underwater acoustic communication method based on indirect channel function tracking. The method comprises the following steps: firstly, using a training sequence which receives a signal to estimate a channel time delay, namely a Doppler spread function; analyzing the Doppler extension phenomenon to implement indirect channel function modeling, then carrying out Doppler compensation on the received signal of each array element, carrying out time reversal processing on channel estimation obtained by an indirect channel function estimated by the training sequence and the signal compensated by Doppler, estimating and tracking the indirect channel function by using a Kalman / extended Kalman filter, judging whether a Doppler compensation factor and the channel estimation are updated or not according to a normalized amplitude of the estimated indirect channel function, and finally, recovering a transmitted symbol from the signal processed by time-reversal by utilizing a decision feedback equalizer which is less than ten orders. The method uses the tracking for the indirect channel function to confront the performance reduction of passive time-reversal communication caused by environment time-varying, thereby realizing the high-speed and stable uplink underwater acoustic communication in a rapidly changing environment of an underwater acoustic channel.

The invention discloses an arrival angle estimation method based on a single antenna and belongs to the field of communication. The estimation method comprises selecting N measuring points located on the same straight line within a selected target range, enabling the interval between adjacent measuring points to be not larger than half of the length of a carrier, performing channel detection on the N measuring points by using a single antenna channel detection system, and obtaining channel time domain impact responses and corresponding receiving gains of the measuring points; adjusting the channel time domain impact responses according to the receiving gains, performing Fourier transform in spatial domains according to the adjusted channel time domain impact responses and calculating Doppler spread spectrums; extracting effective paths from the Doppler spread spectrums to obtain Doppler shifts corresponding to the effective paths, and calculating corresponding arrival angles according to the Doppler shifts. According to the estimation method, hardware costs and the realization complexity are low, and the estimation method is applied to rail transit environments as well as other wireless communication and positioning scenes.

A method and device for reporting antenna calibration information and determining antenna calibration factor are provided by the present invention. When reporting the antenna calibration information, a user equipment (UE) estimates the downlink equivalent baseband channel from a plurality of antennas of the base station to the UE; according to the equivalent baseband channel, determines the amplitude response and delay value to be reported, and then reports the amplitude response and delay value to the base station. When determining the antenna calibration factor, according to the uplink signal sent by the UE on the base station-directed time-frequency resources, the base station determines the amplitude response and the delay value; according to the amplitude response and delay value reported by the UE and according to the amplitude response and delay value determined by the uplink signal, the base station calculates the antenna calibration factor. Because the UE pre-processing process is added, the sensitivity degrees to the channel estimation error and to the channel Doppler extension are reduced.

The invention discloses a low-complexity underwater acoustic channel estimation algorithm based on orthogonal matching pursuit, and relates to a low-complexity underwater acoustic channel estimation algorithm based on orthogonal matching pursuit. Firstly, ignoring a Doppler spread factor, and establishing a solution space required by a PSO algorithm on a time delay dimension; secondly, optimizingan inertia weight coefficient in a PSO algorithm, and searching a most matched atom set in a solution space, namely, an initially estimated path delay set; thirdly, expanding the initially estimated path delay set, and establishing a solution space required by the PSO algorithm again in combination with a Doppler spread factor; and finally, searching the most matched atom set by adopting a PSO algorithm to obtain an underwater acoustic channel impulse response estimation value. An inner product storage index table is established in the process of searching the most matched atoms twice, so thatrepeated calculation of the inner product is avoided, and the searching speed is increased. On the basis of an existing OMP algorithm, a two-step estimation method is adopted, the number of times ofinner product calculation can be reduced, and the complexity of the existing OMP algorithm is effectively reduced.

A method uses LAS code to construct low interference window expanding frequency code, in which, the non-cyclic self-related and non-cyclic inter-related sequences of the low interference window expanding frequency code are less than the predetermined values in the vicinity of zero-offset, and the LAS code comprises compound LA code and LS code. The method includes the following steps: step one: choose two or more LS expanding frequency codes Cln and Csn with zero interference windows of [-W, W]; step two: combine the said expanding frequency codes Cln and Csn chosen from the first step, remove the protective interval on the side or in the center of the low interference expanding frequency code Cn, and obtain the low interference window expanding frequency code Cn. The low interference window expanding frequency code of the invention is used for OFDM communication system, and processes frequency domain expanding frequency modulation in the OFDM frequency domain, and it can reduce ICI interference due to frequency shift or Doppler expansion.

The invention provides a high-speed stealth target detection method of the polynomial Hough Fourier transform, and aims at solving the problems in distance walk and Doppler expansion in accumulated detection of a high-speed maneuvering stealth target. The detection method comprises that polynomial models of relatively high resolution are established, energy accumulation of a parameter space is realized by the polynomial Hough Fourier transform, polynomial models of higher resolution are established according to a parameter corresponding to the maximal energy value of the parameter space, polynomial Hough Fourier transform of high resolution is then carried out in small areas and so on till the requirement for compensation precision is met, and thus, coherent accumulation detection for the high-speed maneuvering stealth target is realized. The searching train of thought is approached layer by layer via the multiple resolution levels of the polynomial models, accumulation detection for the target is realized by the provided polynomial Hough Fourier transform, and compared with multi-dimension parameter search in a large range in a traditional method, the computational complexity, the memory amount and the complex degree can be substantially decreased, and convenience is provided for engineering.

The invention discloses a method and a device for detecting the speed of a mobile terminal. The method comprises the following steps of: performing noise estimation according to received network side data to obtain noise estimation values; performing channel estimation according to the received network side data and extracting a channel estimation value at a reference signal from obtained channelestimation values; determining an instantaneous maximum Doppler spread value according to the noise estimation values and the channel estimation value at the reference signal; and computing the speedof the mobile terminal according to the maximum Doppler spread value. In the method and the device, the more accurate speed of the mobile terminal can be detected in an orthogonal frequency division multiplexing (OFDM) system.

An apparatus and a method for estimating a Doppler frequency in a mobile communication system are provided. The apparatus includes an estimator for temporarily estimating a maximum Doppler frequency based on channel values sampled according to a first period in a frame, a detector for calculating at least one correlation value between at least one channel value additionally sampled in the frame and at least one channel value sampled over the first period, and for determining whether aliasing occurs based on the correlation value, and a determiner for determining a final maximum Doppler frequency according to the occurrence or non-occurrence of the aliasing.

The invention discloses an underwater acoustic OFDM communication method based on Dual-Zadoff. The invention relates to a signal synchronization method of a Chu sequence, which relates to the field ofunderwater acoustic OFDM communication, comprising a transmitter and a receiver, wherein the transmitter sends a preamble with a length of 2N, and the preamble is composed of two Dual codes with thesame length of N; ZC sequence in series, Dual-ZC sequence is composed of two ZC sequences with N length, same parameter setting and g (0 (g (N)) frequency difference. The receiver can simultaneously complete signal synchronization, Doppler spread estimation, channel estimation and other tasks through the corresponding receiving steps.

An exemplary fast Fourier transform (FFT) numerology for an orthogonal frequency division multiple access (OFDMA) downlink transmission system is described. The exemplary FFT numerology reduces the FFT sampling rate for a given transmission bandwidth, thereby increasing the battery life of a UE. The FFT numerology increases robustness against Doppler spread, phase noise, and frequency offset, enabling operation in channels with high delay spread, such as occurs in mountainous regions. The described numerology might provide the following without altering standard sub-frame duration: increased intercarrier spacing; reduced FFT sampling frequency across the transmission bandwidths; reduced FFT size across all transmission bandwidths; increased number of OFDM symbols per sub-frame; and / or increased cyclic prefix length choices.

The invention relates to a hypersonic speed target detecting method for polynomial Radon-polynomial Fourier transform, and belongs to the technical field of radar signal processing and detecting. The method comprises the steps that N periodic signals to be accumulated are sampled, a slow time-fast time target observed value is extracted, and pulse compression is performed on the sampled signals separately; initialization parameters of polynomial Radon-polynomial Fourier transform are determined; search, compensation and accumulation are performed in a parameter space through polynomial Radon-polynomial Fourier transform to obtain a range-Doppler distribution diagram subjected to phase-coherent accumulation; constant false-alarm detection and target motion parameter estimation are performed on the range-Doppler distribution diagram. According to the method, model building is performed on target motion through polynomial, range walk and Doppler spread of the signals are compensated through parameter search of the polynomial, and therefore effective accumulation detection on a high-speed high-mobility target can be achieved under a low signal-to-noise ratio background; in addition, effective search on the multi-dimensional parameter space is achieved in a multi-resolution search mode, and therefore the search real-time performance is improved.

The invention discloses a high-frequency sky-ground wave MIMO radar realization method, and provides an effective solution for the problems of multipath and multi-mode effect and clutter Doppler expansion and the like for a sky-ground wave over-the-horizon radar. A radar system is formed by a plurality of sky wave transmitting stations and a plurality of ground wave receiving stations. Each transmitting station and each receiving station are formed by a plurality of antenna units, so that coexistence of distributed and intensive MIMO radars is realized, and spatial resolution is improved, and multi-angle observation can be realized. By allocating different frequency bands or phases to transmitting subunits, a multiplexed orthogonal effect of transmitting signals is realized. The receiving stations realize pulse compression through frequency mixing and filtering, so that separation of multipath orthogonal signals is realized. The multi-angle observation enlarges detection range and improves detection precision; and MIMO virtual array elements enable the sky-ground wave MIMO radar system to have flexible wave beam formation capability, and influence from different-spatial-orientation multipath and multi-mode effect and clutter expansion due to ionosphere contamination in the sky-ground wave radar can be eliminated properly.