98 results about "Direct sequence spread spectrum communications" patented technology

A spread-spectrum preamble synchronization peak detection system performs multiple statistical tests based on instant and time-averaged channel condition measurements to identify the synchronization peak. In a normalized peak-to-average test, a peak-to-average ratio measurement is normalized by a signal-to-noise ratio measurement to form a new statistical measure which effectively eliminates the impact of the wide dynamic range of the signal-to-noise ratio of the received samples. A transition SNR test is used to eliminate potential false alarms caused by spurious PARN peaks during the transition period at the onset of preamble arrival. Code-phase aligned time-averaging is used to estimate the signal and noise levels over a sliding window. The code-phase alignment of samples effectively separates signal and noise samples in the averaging process, and resulting in more accurate signal and noise measurements. In estimating noise levels, the system takes multi-path interference into account by excluding both the peak signal and the side-lobe signals caused by multi-path wireless channels, resulting in more accurate estimation of noise level.

A RAKE receiver which is employed in a direct sequence spread spectrum communication system, and which can effectively receive multipath signals. A path searcher measures the amplitude of each path, selects N paths with larger amplitudes in descending order of magnitude, where N is the number of despreaders, and assigns the despreaders to the selected paths to despread the signals of the paths. This assignment of the despreaders to the paths is carried out such that a path with a large amplitude and a path with a small amplitude are assigned to adjacent despreaders and are input to the same pre-detection combiner. The outputs of the despreaders are combined by the pre-detection combiners, and detected by detectors whose outputs are RAKE combined by a post-detection combiner.

Methods, systems and devices are described for a direct-sequence spread-spectrum communication scheme that increases the number of users by utilizing a plurality of closely spaced orthogonal carriers that produce overlapping spectra. A method includes overlapping a plurality of direct-sequence spread-spectrum signals using carrier frequencies that are orthogonally spaced relative to a bit rate. The methods, systems and devices provide advantages because they can accommodate an increase in the number of normalized users and can optimize the loading of users across multiple frequency channels.

Multipath delay estimation of a direct sequence spread spectrum (DS-SS) signal transmitted in a multipath fading channel is accomplished by measuring the envelope of the signal to determine a new delay estimate. Delay estimates are also obtained in ray strength order, by subtracting out the influence of the stronger rays on the weaker ones. This subtraction approach can be performed iteratively, allowing further refinement of the delay estimates. Delay estimates can also be determined by minimizing the mean square error (MSE) between a measured correlation function and a modeled correlation function. The minimum mean square error (MMSE) approach can performed iteratively, to further refine the delay estimates. Maximum likelihood (ML) delay estimates can also be obtained by exploiting side information regarding the transmit and receive pulse shapes.

The present invention provides a new baseband integrated circuit (IC) architecture for direct sequence spread spectrum (DSSS) communication receivers. The baseband IC has a single set of baseband correlators serving all channels in succession. No complex parallel channel hardware is required. A single on-chip code Numerically Controlled Oscillator (NCO) drives a pseudorandom number (PN) sequence generator, generates all code sampling frequencies, and is capable of self-correct through feedback from an off-chip processor. A carrier NCO generates corrected local frequencies. These on-chip NCOs generate all the necessary clocks. This architecture advantageously reduces the total hardware necessary for the receiver and the baseband IC thus can be realized with a minimal number of gate count. The invention can accommodate any number of channels in a navigational system such as the Global Positioning System (GPS), GLONASS, WAAS, LAAS, etc. The number of channels can be increased by increasing the circuit clock speed.

The invention discloses a fully-digital direct sequence spread spectrum communication system and a rapid pseudo code capturing method thereof. A digital signal is processed by using an FPGA (Field Programmable Gate Array) which comprises a pseudo code capturing module, a sampling signal of an ADC (Analog To Digital Converter) is subjected to frequency mixing with a signal of a local carrier NCO (Numerically Controlled Oscillator) and filtered to obtain a baseband signal, residual carrier Doppler frequency is eliminated from the baseband signal by adopting a differential multiplying mode, thus the phase deviation of a receiving signal and a local pseudo code is further obtained through an FFT (Fast Fourier Transform) algorithm without scanning on a carrier frequency domain; and when the phase deviation of the pseudo code is obtained, a local pseudo code phase is modified and is subjected to correlation degree of dissociation with the receiving signal, and the carrier Doppler frequency is figured out by using the FFT algorithm, and is compensated to a carrier NCO and a pseudo code NCO, thus carrier frequency capturing and pseudo code capturing are realized.

The invention relates to a Doppler domain and delay domain two-dimension acquiring method and device and belongs to the technical field of direct sequence frequency expansion communication. According to the invention, FFT conversion and circumferential shift are performed on direct expansion frequency guide signals and multiplication with FFT conversion sequence of a local fake code is implemented. After IFFT conversion, a matching filtering result of carrier Doppler compensation is obtained. Then an interpolation fitting method is used for adjusting the sampling rate of the filtering result, so that code Doppler compensation is realized. The output result of interpolation fitting is subjected to non-related accumulation and threshold judgment and carrier frequency deviation and fake code phase of the direct expansion frequency guide signals are obtained. Compared with the prior art, the acquiring method based on combined compensation of carrier Doppler and code Doppler is used, shortcomings of a tradition acquiring method in highly dynamic environments with large fake code lengths and weak signals are overcome. Related peak walk is corrected through the interpolation fitting method, so that platform effect in non-related accumulation is avoided and the acquiring performance is improved substantially. .

A system and method for communicating information signals using spread spectrum communication techniques. PN sequences are constructed that provide orthogonality between the users so that mutual interference will be reduced, allowing higher capacity and better link performance. With orthogonal PN codes, the cross-correlation is zero over a predetermined time interval, resulting in no interference between the orthogonal codes, provided only that the code time frames are time aligned with each other. In an exemplary embodiment, signals are communicated between a cell-site and mobile units using direct sequence spread spectrum communication signals. In the cell-to-mobile link, pilot, sync, paging and voice channels are defined. Information communicated on the cell-to-mobile link channels are, in general, encoded, interleaved, bi-phase shift key (BPSK) modulated with orthogonal covering of each BPSK symbol along with quadrature phase shift key (QPSK) spreading of the covered symbols. In the mobile-to-cell link, access and voice channels are defined. Information communicated on the mobile-to-cell link channels are, in general, encoded, interleaved, orthogonal signaling along with QPSK spreading.

A multi-channel direct sequence spread-spectrum communication system with the capability of automatic rate detection consists of a plurality of signal channels and a plurality of data channels. During signaling period, only the signaling channels corresponding to the desired symbol repetition and the data channels corresponding to the highest index among the indexes of all active data channels will be allowed to transmit. During data transmission period, only the active data channels will be allowed to transmit. Receiver will use the information provided in preamble signal and mid-amble signal to obtain the number of symbol repetition, the set of active data channels and etc, and to set up initial synchronization.

A method and apparatus for estimating signal quality in a direct sequence spread spectrum communication system such as a digital cordless telephone. The method and apparatus beneficially uses data that already available from a window-tracking function used to maintain a demodulation window around the correlation data coming from the system's matched filters. The window-tracking function outputs an in-window peak value and out-window peak value for each bit interval. The signal quality is rapidly and effectively estimated by accumulating the difference between the in-window peak correlation value and the out-window peak correlation value over a period time, preferably for one frame.

The invention provides a method for eliminating time-domain narrowband interference of a direct sequence spread spectrum communication system, which comprises the following steps of: 1) dividing received spread spectrum signals into two paths of same signals, wherein one path of signals are delayed and then output to an interference estimating module, and the other path of signals are taken as reference signals; 2) estimating interference signals in the first path of the spread spectrum signals by a transverse filter with unequal interval taps through a time-domain arithmetic, and outputting the interference signals; and 3) subtracting the interference signals from the reference signals, and obtaining the spread spectrum signals of which the narrowband interference is eliminated. In addition, the invention also provides a device for eliminating the time-domain narrowband interference of the direct sequence spread spectrum communication system. The method and the device have the advantages of little computation workload, no need of complicated hardware structure and easy digitalization. The transverse filter with the unequal interval taps can adapt to estimating more types of narrowband interference, and solves the problems of complicated realization of variable tap intervals and poor system continuous work performance at the same time.

The invention discloses a signal detection and estimation method based on a multi-dimensional characteristic neural network, and relates to the technical fields of artificial neural networks and direct sequence spread spectrum (DSSS) communication. According to the method, the presence of a DSSS signal is detected by using a correlation function accumulation method, and the estimation of a PN (Pseudo-Noise) code is finished, namely, a direct spread signal spread spectrum code is detected under the situation of low signal-to-noise ratio based on a multi-dimensional characteristic neural network method. The method comprises the following steps: extracting the multi-dimensional characteristics of a signal (comprising the period of the PN code, the width of a code element, the starting and stopping moments of the synchronization of the PN code and an information code, and the like); periodically segmenting the signal; inputting the segmented signals into the neural network in batches for training; and training and converging the segmented signals through the neural network to detect a spread spectrum sequence. Through adoption of the method, a signal can be detected from noise and a PN sequence of the signal can be estimated in non-cooperative communication through an artificial neural network; and moreover, the network can quickly converge to a sequence or a reverse sequence thereof under the situation of low signal-to-noise ratio.

The present invention provides a new baseband integrated circuit (IC) architecture for direct sequence spread spectrum (DSSS) communication receivers. The baseband IC has a single set of baseband correlators serving all channels in succession. No complex parallel channel hardware is required. A single on-chip code Numerically Controlled Oscillator (NCO) drives a pseudorandom number (PN) sequence generator, generates all code sampling frequencies, and is capable of self-correct through feedback from an off-chip processor. A carrier NCO generates corrected local frequencies. These on-chip NCOs generate all the necessary clocks. This architecture advantageously reduces the total hardware necessary for the receiver and the baseband IC thus can be realized with a minimal number of gate count. The invention can accommodate any number of channels in a navigational system such as the Global Positioning System (GPS), GLONASS, WAAS, LAAS, etc. The number of channels can be increased by increasing the circuit clock speed.

The invention disloss a spectrum monitoring system and method for an airspace anti-black-flight unmanned aerial vehicle. The spectrum monitoring system comprises an unmanned aerial vehicle platform, aremote control telemetry module, spectrum monitoring equipment and a processing display upper computer, and the airborne spectrum monitoring equipment is composed of a radio frequency module, a control processing module, a GPS module, a direct sequence spread spectrum communication module and the like. The method includes: guiding spectrum monitoring to a space domain; carrying frequency spectrummonitoring equipment on a legal flight unmanned aerial vehicle, patrolling in a monitoring area according to a certain track, searching for a black flight unmanned aerial vehicle as a task, and monitoring and identifying a frequency hopping signal of a remote measurement and remote control channel of the black flight unmanned aerial vehicle in an electromagnetic frequency spectrum domain by utilizing a frequency spectrum monitoring technology, thereby detecting the black flight unmanned aerial vehicle. The black fly signal extraction and recognition algorithm is good in extraction effect, high in recognition efficiency and small in calculated amount; and the direct sequence spread spectrum communication module has extremely low power spectrum density, so that the stable operation in a complex electromagnetic environment is ensured, and the monitoring of a remote control telemetry signal of the black flight unmanned aerial vehicle is not influenced.

The invention provides a data transmission system between noncontact double super satellite cabins and an operation method thereof. The integrated responder of a measurement and control subsystem supports measurement and control to the ground and measurement and control to the relay through different frequencies, and a load cabin and a platform cabin adopt the working mode of different pseudo-codes. The data integrated processor of a data transmission subsystem receives the high speed data of camera load, and the data are wirelessly transmitted to the platform cabin in real time to perform data transmission or the data are stored and arranged back to the platform cabin from a storage device and then data transmission is performed according to the situation of whether the satellite is within the border or the visual arc segment of the relay satellite. The inter-satellite communication responder adopts the modulation mode of an inter-satellite non-coherent direct sequence spread spectrum communication system and works in the S-band and the duplex mode, and the inter-satellite communication responder between the two cabins adopts the mode of different bands and different codes. The load cabin and the platform cabin communicate in a noncontact manner so that the problems of interference and fluttering caused by vibration of large flexible structures and moving parts can be solved, and the inter-satellite communication efficiency and the communication efficiency to the ground and the relay can be enhanced.

This invention discloses a signal test method for direct sequence frequency-spread communication including: computing the correlation values of received signals and local pilot signals in a test period, computing the average value and searching for the maximum value of said correlation values, if the ratio of the computed maximum value and the average value is greater than the preset effective threshold value, then the received signals are effective. This invention also discloses a signal test device, which can test effective signals accurately with fixed threshold values in a big S / N ratio sphere.

A digital transceiver operative for direct sequence spread spectrum communications is described, a master counter associated with a zero offset pseudorandom noise (PN) sequence; a slave counter associated with a demodulating finger; and a counter output of said master counter coupled to a counter input of said slave counter.

Disclosed is a direct sequence spread spectrum communication system which resists the multiple access interference and relates to the direct sequence spread spectrum wireless communication field, aiming at solving the problems that the multiple access interference is high and the new user can not receive the correct information. A multiple access interference computation module (11) is added to the transmitter of the direct sequence spread spectrum communication system in the prior art for figuring out the initial phase value; the computed initial phase value is transmitted to a first initial phase generator (12); the first initial phase generator (12) is used for generating the initial phase, receiving the initial phase parameter computed by the multiple access interference computation module (11) and sending the initial parameter to a first carrier generator (13); a second initial phase generator (17) is added to the receiver of the direct sequence spread spectrum communication system in the prior art for generating the initial phase parameter the same as the initial phase parameter generated by the first initial phase generator in the transmitter and sending the initial phase parameter to a second carrier generator (18). Compared with the direct sequence spread spectrum communication in the prior art, the direct sequence spread spectrum communication system which resists the multiple access interference improves the system capacity; the implementation method is simple and effective.

A sleep control system and method are provided that permit a reference clock and the direct sequence spread spectrum (DSSS) modem in a mobile station receiver to be turned off and turned back on at arbitrary points in time while still maintaining accurate base station system time. Accurate timing is made possible through a number of techniques including precise initial calibration using a rising edge / falling edge averaging system, determining the sleep clock and reference clock frequencies, and the determination of the frequency drift of the sleep clock that occurred during the previous sleep interval.

The invention discloses a low signal-to-noise ratio short frame burst communication open loop demodulation method and a low signal-to-noise ratio short frame burst communication open loop demodulationdevice, and belongs to the technical field of direct sequence spread spectrum demodulation technologies. According to the method, a segmented data processing mode is used for firstly demodulating dispreading data, then performing supply-zero FFT to estimate a frequency offset variation rate and frequency offset and perform compensation. A method of exhaustion is used for accurately estimating andcompensating each frequency offset, the polarity of a frame header is used for performing defuzzification on the phase, to complete correct demodulation of the data. Compared with the prior art, themethod and the device provided by the invention overcome the disadvantages that traditional phase-locked loop coherent demodulation devices are fuzzy in phase and slow in convergence speed, the frequency offset and the frequency offset variation rate can be quickly searched and compensated, the phase discrimination and phase correction can be completed, the short time is ensured, and a direct sequence spreading signal can be normally demodulated under the condition of a low signal-to-noise ratio.

The invention relates to a per-survivor processing based iterative equalization method applied to direct-sequence spread-spectrum communication, belongs to a joint equalization and decoding method adaptable to quick time-varying channels and can effectively track the time-varying channels without insertion of extra training data. Compared with the conventional direct-sequence spread-spectrum communication signal processing method, the method can realize flexible regulation of the spread spectrum ratio and can track varying of the channels adaptively without extra training data overhead. In the method, direct-sequence spread-spectrum symbols are taken as processing units of a receiver, a 'per-survivor channel estimation method' is utilized in an iterative equalization detector, and the channel estimation is updated adaptively according to size of the 'channel estimation matching index'; the detector adopts a soft-input and soft-output detection algorithm, a subsequent decoder adopts a soft-input and soft-output iterative decoding algorithm, and soft information is exchanged between the detector and the decoder, thus, the optional solution is approached by means iteration.

The invention discloses an interference detection and suppression optimization method. The method comprises the steps of frequency domain transformation, interference detection, interference suppression and time domain transformation. Background noise estimation and self-adaptive determination of an interference detection threshold are carried out on the converted frequency domain digital signal in the interference detection, so that the detection accuracy of the interference signal is improved, and the reduction of signal-to-noise ratio loss possibly caused by interference suppression due toinaccurate detection threshold setting is facilitated. The method is high in universality, and is particularly suitable for interference signal detection in direct sequence spread spectrum communication.

The present invention provides a system and a method for capturing spread-spectrum signals and is applied to the field of direct sequence spread-spectrum communication. The system comprises a satellite navigation time-service module, a trigger logical module, a clock error measurement module and a Doppler calculation module. The satellite navigation time-service module outputs the location, the speed and the time information of a carrier, wherein the time information contains the coordinated universal time and the pulse per second. The trigger logical module receives the coordinated universal time and the pulse per second output by the satellite navigation time-service module, and generates a trigger signal to trigger and generate a spread-spectrum code with the coordinated universal time as a time reference and the pulse per second as an input signal. The clock error measurement module receives the pulse per second output by the satellite navigation time-service module, and then calculates the clock error. The Doppler calculation module receives the location, the speed and the time information output by the satellite navigation time-service module, and calculates the Doppler deviation caused by the relative movement of the carrier. Based on the time-service function of a satellite navigation system, spread-spectrum signals can be quickly captured, while no large amount of hardware resources is occupied. Meanwhile, the communication efficiency is high. The method and the system are particularly advantageous to bursty communications that are shorter in communication time.

A spread-spectrum preamble synchronization peak detection system performs multiple statistical tests based on instant and time-averaged channel condition measurements to identify the synchronization peak. In a normalized peak-to-average test, a peak-to-average ratio measurement is normalized by a signal-to-noise ratio measurement to form a new statistical measure which effectively eliminates the impact of the wide dynamic range of the signal-to-noise ratio of the received samples. A transition SNR test is used to eliminate potential false alarms caused by spurious PARN peaks during the transition period at the onset of preamble arrival. Code-phase aligned time-averaging is used to estimate the signal and noise levels over a sliding window. The code-phase alignment of samples effectively separates signal and noise samples in the averaging process, and resulting in more accurate signal and noise measurements. In estimating noise levels, the system takes multi-path interference into account by excluding both the peak signal and the side-lobe signals caused by multi-path wireless channels, resulting in more accurate estimation of noise level.

The invention provides a quick chirp modulation interference detection and suppression method for a direct-sequence spread-spectrum communication system. By taking full advantage of the characteristic that the data spectrum transmitted in a channel is similar to that of white noise in the direct-sequence spread-spectrum communication system, it is determined that a transient energy spectrum has high peak value and a time-frequency energy distribution plane must have obvious peak value lines due to the inference of a chirp modulation signal. The method comprises: at the receiving terminal of the direct-sequence spread-spectrum communication system, selecting several energy spectrum peak value points at different time on the time-frequency plane; roughly estimating a chirp constant and a rotation angle alpha of fractional order Fourier transform according to a linear rule; performing the fractional order Fourier transform (p=2alpha / pi) according to parameters; if an obvious peak value is detected, performing accurate search by using an iterative process, and performing wave-eliminating processing in a fractional order Fourier transform domain to suppress chirp modulation interference; and outputting the denoised signal to a subsequent processing process.

The invention relates to a maximum absolute value cumulative mean and grid comparison-based adaptive bit cutting method, which is mainly applied to a direct sequence spread spectrum communication system and belongs to the field of communication signal processing. The method comprises the following steps of: segmenting a to-be-processed continuous signal; solving an absolute value of each segment of data, finding the maximum absolute value out and solving the cumulative mean value of the maximum absolute value, wherein the calculation method can save a large number of resources; designing a grid comparator according to to-be-cut bit and judging the cumulative mean value by the grid comparator to obtain a bit cutting mode; and cutting the bit of the data, splicing and transmitting to next stage for processing. In the method, the maximum absolute value of each segment of data does not need to be stored, so that a large number of resources are saved, the amount of calculation is reduced to a certain extent by solving the cumulative mean value by an approximate method, the sensitivity and the accuracy of bit cutting can be effectively improved by using the grid comparator, and the method can be suitable for various data types and can meet the requirements of real-time processing of communication systems.

Multipath delay estimation of a direct sequence spread spectrum (DS-SS) signal transmitted in a multipath fading channel is accomplished by measuring the envelope of the signal to determine a new delay estimate. Delay estimates are also obtained in ray strength order, by subtracting out the influence of the stronger rays on the weaker ones. This subtraction approach can be performed iteratively, allowing further refinement of the delay estimates. Delay estimates can also be determined by minimizing the mean square error (MSE) between a measured correlation function and a modeled correlation function. The minimum mean square error (MMSE) approach can performed iteratively, to further refine the delay estimates. Maximum likelihood (ML) delay estimates can also be obtained by exploiting side information regarding the transmit and receive pulse shapes.

A chip synchronization method by direct sequence spread spectrum based parallel dispreading is completed by a parallel dispreading system based on the direct sequence spread spectrum. The parallel dispreading system comprises a computer, an AD (analog-to-digital converter), a correlator and a sequence generator. Received parallel data in each channel and pseudo-random code sequences in each group extracted according to set extraction rate are subjected to correlated traversal processing, and current chip offset is judged according to correlated peak values of processed results so that chip synchronization is achieved by means of adjustment. By the chip synchronization method, chip synchronization is achieved quickly and conveniently, a computing method is simple and efficient, and difficulty in synchronization by parallel dispreading in direct sequence spread spectrum communication is overcome.

The invention discloses a weighted score Fourier transform-based variable parameter spread spectrum sequence low-detection probability signal emitting and receiving method, relating to the field of communication and solving the problem of poor interception and capture resisting capacity of the existing direct sequence spread spectrum communication system. A signal emitting process of the weighted score Fourier transform-based variable parameter spread spectrum sequence low-detection probability signal emitting and receiving method comprises the steps of: carrying out digital baseband mapping, spread spectrum and serial / parallel conversion on data of a data source and then dividing a signal into M segments; and respectively carrying out weighted score Fourier transform, then synthesizing one section of signal and carrying out parallel / serial transform, digital carrier modulation, digital / analog conversion, filter and up-conversion and then sending the signal to a channel. A signal receiving method of the weighted score Fourier transform-based variable parameter spread spectrum sequence low-detection probability signal emitting and receiving method comprises the steps of: carrying out down conversion, filter, analog / digital conversion, digital carrier demodulation and serial / parallel conversion on the received signal, and dividing the signal into M segments, respectively carrying out weighted score Fourier transform and merging into one section of decrypted signal; and then carrying out parallel / serial conversion, dispreading and digital baseband demapping and then outputting. The weighted score Fourier transform-based variable parameter spread spectrum sequence low-detection probability signal emitting and receiving method is suitable for wireless communication.