Abstract: This invention discloses a digital wireless speaker system for use in consumer audio applications. A digital radio frequency transmitter is connected to an analog or digital audio source and a digital radio frequency receiver provides for reception of the transmitted audio information in remote locations. In addition, the digital receiver will be able to receive control information to implement such things as volume, tone controls, or other auxiliary information. This allows the user to listen to high quality audio in a variety of locations without the need of independent stereos or external wires. The system is based on digital circuitry to improve the performance of the system and provide for compact disc quality sound. The digital circuitry incorporates forward error correction techniques and interleaving to enable the system to account for errors in transmission and thus improve the overall performance of the system.

Abstract: A technique for modulating and demodulating CPM spread spectrum signals and variations of CPM spread spectrum signals. A transmitter divides a signal data stream into a plurality of data streams (such as I and Q data streams), independently modulates the I and Q data streams using CPM or a related technique, and superposes the plurality of resultants for transmission. A receiver receives the superposed spread spectrum signal and simultaneously attempts to correlate for a plurality of chip sequences (such as I and Q chip sequences), and interleaves the correlated I and Q data streams into a unified signal data stream. In one embodiment, the receiver separates the received spread spectrum signal into real and imaginary parts, attempts to correlate both real and imaginary parts for a plurality of chip sequences, and combines the real I, real Q, imaginary I, and imaginary Q signals into a unified signal data stream.

Abstract: A digital delay-locked loop (DLL) circuit of high synchronous maintaining precision, which is usually affected by the quantization error of signal digitization, is provided for a spread spectrum communications receiver for mobile communications system. Three correlation sections are provided for calculating the correlation values in the peak phase, in the phase leading the peak phase and in the phase lagging behind the peak phase respectively in a delay profile on the basis of a received signal. A control section calculates the difference of the correlation values between the value in the lagging phase and the value of the advancing phase, and determines the threshold value for controlling a spread code generation section.

Abstract: Methods for estimating the tracking error in estimated time of arrival of a composite incoming signal that contains a known, digital, spread spectrum signal S.sub.d (t) and that may contain one or more multipath signals whose source is the known signal. Some methods use linear, quadratic or other approximations for the measured correlation function AC(.tau.) for the early and late regions of the time shift variable .tau. (separated by a punctual value .tau.=t.sub.P). Other methods require only knowledge of the measured correlation function AC(.tau.) for one or two time shift values in the early region .tau.<t.sub.P.

Abstract: A method for RF communication between transceivers in a radio frequency identification system that improves range, decreases multipath errors and reduces the effect of outside RF source interference by employing spread spectrum techniques. By pulse amplitude modulating a spread spectrum carrier before transmission, the receiver can be designed for simple AM detection, suppressing the spread spectrum carrier and recovering the original data pulse code waveform. The data pulse code waveform has been further encrypted by a direct sequence pseudo-random pulse code. This additional conditioning prevents the original carrier frequency components from appearing in the broadcast power spectra and provides the basis for the clock and transmit carrier of the transceiver aboard an RFID tag. Other advantages include high resolution ranging, hiding transmissions from eavesdroppers, and selective addressing.

Abstract: Disclosed are methods and apparatus for use in a synchronous CDMA communications system (10) that employs orthogonal pn spreading codes. The methods are intended for synchronizing transmissions from a subscriber unit (SU 14) to a radio base unit (RBU 12), and include the steps of: (a) transmitting individual ones of a plurality of bursts from the SU to the RBU, each burst being transmitted with a different pn spreading code timing alignment; (b) receiving individual ones of the plurality of bursts with the RBU and determining a power estimate of each received burst; and (c) in response to a determined power estimate of one of the bursts exceeding a threshold, sending a message from the RBU to the SU. The message indicates that the SU is to use for subsequent transmissions the pn spreading code timing alignment that was employed when transmitting the burst that exceeded the threshold.

Abstract: A search method for acquisition of time synchronization between a spreading sequence of a receiver and a spreading sequence of a transmitter, the receiver receiving a spread signal and demodulating the signal using the spreading sequence of the receiver includes a test step consisting in measuring the energy of the demodulated signal by integrating the demodulated signal during a time interval Tobs.sub.i and comparing that energy with a threshold value to determine if the threshold value is exceeded, for a given hypothesis as to the time shift between the spreading sequences, and modifying the time shift hypothesis if the threshold value is not exceeded and incrementing the value of a counter. Steps a and b are repeated until the value of the counter reaches a predetermined value. When the predetermined value is reached, the time interval Tobs.sub.i is replaced with a time interval Tobs.sub.i+1, with Tobs.sub.i+1 =m.Tobs.sub.i and m>1, and the process resumes at step a replacing Tobs.sub.i with Tobs.sub.

Abstract: A method and apparatus is provided to facilitate coherent communication in a random access channel. In encoding, reference symbols are inserted into a stream of access channel message data symbols and appended to a synchronization message to form a reference coded access channel transmission. Subsequently, the access channel transmission is prepared for transmission over a communication channel by being spread with a spreading code. In decoding, a known synchronization sequence is correlated with a received communication signal to generate a correlation peak when a synchronization message is present. The received communication signal is despread with a spreading code to derive a stream of reference samples and data samples. A channel response is determined from the correlation peak and revised based on estimates derived from the stream of reference samples. Finally, an estimated data symbol is detected from the stream of data samples by utilizing the revised channel response.

Abstract: A frequency using method for minimizing a time for an initial synchronization between a mobile station and a base station in a mobile telecommunication system. The frequency using method includes the steps of inputting current time data; reading out an initial synchronization frequency from an internal memory; determining an initial synchronization hopping frequency and an initial synchronization hopping cycle according to a hopping pattern polynomial and the current time data; and sequentially searching for frequencies within a communication channel on a one-by-one basis according to the initial synchronization hopping frequency and the initial synchronization hopping cycle to produce a synchronized frequency to establish synchronization between the mobile station and the base station.

Abstract: A synchronizing method and circuit accurately and stably operates a direct spread spectrum multiple access communication system. A signal transmitted by modulating the spreading code with data at the transmission side is sampled by a signal of n times (n: 1 or larger integer) the clock speed of the spread spectrum signal at the reception side, and the correlation is detected by a digital matched filter. Consequently, the detection output in every sample in the symbol period is compared with the envelope detection output determined in every sampling period, and the sample positions for a specific number of determined samples are stored in the descending order of the output. The number of times of storage of large sample positions in the stored detection output is counted in every symbol period, and the position of the largest number of storage times is detected as the peak position. From this peak position, capturing or holding the symbol period, and setting of the reception window position results.

Abstract: A method and apparatus are disclosed for characterizing multipath-induced distortions in the autocorrelation function of a correlation receiver in order to reduce effects of these multipath-induced distortions on the accuracy of detecting the time of arrival of a received signal. The magnitude of the multipath-induced errors adversely affecting the shape of the autocorrelation function is estimated in real time, for example, through the use of secondary scanning correlators whose time base is independent of a typical receiver's detection-oriented correlators. This error is subtracted from the detection-oriented correlator's timing, thereby yielding a more accurate autocorrelation function.

Abstract: A receiver for pseudorandom noise (PRN) encoded signals consisting of a sampling circuit, multiple carrier and code synchronizing circuits, and multiple digital autocorrelators. The sampling circuit provides digital samples of a received composite signal to each of the several receiver channel circuits. The synchronizing circuits are preferably non-coherent, in the sense that they track any phase shifts in the received signal and adjust the frequency and phase of a locally generated carrier reference signal accordingly, even in the presence of Doppler or ionospheric distortion. The autocorrelators in each channel form a delay lock loop (DLL) which correlates the digital samples of the composite signal with locally generated PRN code values to produce a plurality of (early, late), or (punctual, early-minus-late) correlation signals.

Abstract: A novel and improved method of acquisition in a spread spectrum communication system is presented. In the present invention, a large window of PN chip offset hypotheses are searched and if an energy signal is found that might indicate the presence of the pilot signal having one of the chip offsets of the large search window, then a search of a subset of offset hypotheses, or small window, is searched.

Abstract: A digital audio broadcasting (DAB) system includes a radio-frequency (RF) transmitter and a corresponding RF receiver that includes a frame detection circuit for providing a frame synchronization signal. The latter is used to inhibit a Reed-Solomon decoder from correcting data in any frame for which there was no synchronization.

Abstract: A frequency acquisition and compensation device and method for direct sequence spread spectrum communications systems has an identification (ID) sequence in an acquisition frame which is received by a receiving station and an ID sequence stored in an ID register. A received acquisition frame is demodulated using dot product and cross product demodulation. An ID detector detects the ID sequence in the demodulated dot product, cross product, or inverse cross product acquisition frame. When the ID is detected by the dot product demodulator, the receive frame timing is adjusted to coincide with a time interval when the ID was detected. Also, when the ID sequence stored in the ID register matches either the dot product, cross product or inverted cross product of the received ID sequence, the system microcontroller updates the automatic frequency control value.

Abstract: A spread spectrum receiving apparatus comprises: a reproducing circuit to reproduce a carrier signal from a reception signal and a diffusion code; a demodulation circuit to demodulate the reception signal into a base band signal on the basis of the carrier signal reproduced by the reproducing circuit; and a judgment circuit to judge the reception data from the base band signal from the demodulation circuit. The reproducing circuit has an operation circuit to arithmetically operate the reception signal and the diffusion code and a detection circuit to detect a difference between the phases of an output of the operation circuit and an output of an oscillator. The oscillator oscillates at a carrier frequency in accordance with a phase difference detected by the detecting circuit.

Abstract: A modulator that modulates and encodes data using data symbols, interspersed with pilot symbols, for transmission to another modem, and a demodulator that decodes data symbols of a signal received from another modem. In the demodulator, a received signal is sampled at four times the symbol rate. The sampled signal is converted to quadrature signals and low-pass filtered to produce a complex baseband signal. Data symbols in the complex baseband signal are sampled in synchronization with the start of each symbol based on the pilot symbols that are interspersed in the signal. By processing the pilot symbols, full modem synchronization is maintained down to a very low signal-to-noise ratio, through noise bursts, or even when the data symbols representing data are replaced by predefined sequences of data symbols that convey the dots and dashes of Morse code identifying the station transmitting the modulated signal.

Abstract: A data demodulator circuit for spread spectrum communication, presenting improved demodulation characteristics by allowing the elimination of the influence of a carrier offset remaining after down converting, and the removal of the interference caused by pilot signals with different timing. In-phase axis receive signal and operate with their respective reception timing of pilots signal. Phase difference information is extracted from the input signals and the signals are delayed to insure that the extracted phase difference information is equivalent to the average phase revolution. The influence of the carrier offset is eliminated by use of the extracted phase difference information. A data demodulator with canceler removes an interference I.sub.DF of pilot signals with different timing originating from the outputs of an interference amount calculator.

Abstract: Analog signals representing individual digital values (.+-.1, .+-.3) pass through a telephone line to a receiver. These signals may be first provided in a pseudo random sequence. A linear echo canceller and a first adder eliminate, to an extent, echo signals resulting from second analog signals transmitted on the same telephone line by the receiver. A non-linear echo canceller and a second adder further reduce the echo signals and specifically reduce non-linear components in the echo signals. Adjustable signal delays achieve optimal performance of the linear and non-linear echo cancellers. An equalizer containing four (4) different modules then compensates for signal distortions introduced by the telephone line and minimizes the effect of noise in the telephone line. The equalizer modules are a digital gain control element, a feed forward digital filter and two (2) feedback digital filters. A detector module produces in one of several different ways at the receiver an estimate of the digital data (.+-.1, .+-.

Abstract: A spread spectrum communication apparatus receives a preamble signal or a postamble signal as a pilot signal, and applies a correlative demodulation by using a single spread signal to the pilot signal, and a correlative output obtained after the correlative demodulation is compared to a reference value. If the correlative output is equal to or greater than the reference value, then it is recognized as a preamble or postamble signal. In accordance with a trailing edge of the preamble signal or a leading edge of the postamble signal, a start point or an end point of information transmission can be recognized, respectively, in a lower level of a communication system without using a unique word in a data stream, thereby reducing overhead of an upper level protocol and improving data transmission efficiency.

Abstract: The present invention relates to an apparatus for providing a digital radio link between at least one fixed unit and at least one mobile unit wherein the apparatus comprises a small number of Rake fingers, one or more of which is assigned at any given to perform a searching operation. Whenever a searching Rake finger or fingers finds a path with higher energy than the current lowest Rake finger, the roles of the Rake finger are exchanged.

Abstract: A synchronizing method and circuit accurately and stably operates a direct spread spectrum multiple access communication system. A signal transmitted by modulating the spreading code with data at the transmission side is sampled by a signal of n times (n: 1 or larger integer) the clock speed of the spread spectrum signal at the reception side, and the correlation is detected by a digital matched filter. Consequently, the detection output in every sample in the symbol period is compared with the envelope detection output determined in every sampling period, and the sample positions for a specific number of determined samples are stored in the descending order of the output. The number of times of storage of large sample positions in the stored detection output is counted in every symbol period, and the position of the largest number of storage times is detected as the peak position. From this peak position, capturing or holding the symbol period and setting of the reception window position results.

Abstract: In a time diversity radio communications system, quadrature-modulated spread spectrum signals of different mutual time delay are combined into a code division multiplex signal and up-converted to a radio-frequency signal and transmitted. At a receive site, the signal is received by an antenna and down-converted to recover the code division multiplex signal. Quadrature-modulated component signals contained in the recovered code division multiplex signal are converted to baseband signals which are then time-aligned with each other. The time-aligned baseband signals are multiplied respectively by complex weighting factors and are combined together to produce an input signal for an adaptive equalizer. This input signal is also applied to an AGC amplifier where it is amplified and applied to correlation detectors where correlations between the amplified signal and the baseband signals are detected and the complex weighting factors are derived respectively from the correlations.

Abstract: A method is disclosed for synchronizing, in the presence of sign ambiguity, to a pseudo random maximal length sequence having a characteristic polynomial of order k with a coefficients vector A given by:A=?1 a.sub.1 a.sub.2 . . . a.sub.k-1 1!where each of the coefficients a.sub.1 to a.sub.k-1 is 1 for an intermediate tap location and otherwise is 0. A received symbol sequence is supplied to and shifted through a K=k+1 stage shift register with P intermediate taps in positions determined by a coefficients vector A.sub.in given by:A.sub.in =?1 a.sub.1 (a.sub.1 .sym.a.sub.2) (a.sub.2 .sym.a.sub.3) . . . (a.sub.k-2 .sym.a.sub.k-1) a.sub.k-1 1!where a.sub.1 and a.sub.k-1 are the inverse of a.sub.1 and a.sub.k-1 respectively and .sym. denotes a modulo-2 sum, whereby the shift register has P intermediate taps where P is a positive integer less than K. A respective correlation signal is recursively added at an input for the received symbol sequence and at each intermediate tap.

Abstract: A method of synchronizing to a pseudo random sequence, which can be generated by a linear feedback shift register having k stages and p intermediate taps, where k and p are positive integers and k>p, and a synchronization arrangement for carrying out the method are described. A received symbol sequence is supplied to a k-stage shift register with p intermediate taps in positions corresponding to the p taps of the linear feedback shift register. A respective correlation signal is recursively added at an input for the received symbol sequence and at each intermediate tap. Each correlation signal is produced by correlating at least two signals from said input, intermediate taps, and output other than the signal to which the respective correlation signal is added. The invention is particularly applicable to pilot synchronization in CDMA terminals.

Abstract: A digital audio broadcasting (DAB) system includes a radio-frequency (RF) transmitter and a corresponding RF receiver. The RF transmitter formats a DAB signal into a sequence of frames, each frame having a header comprising a predefined grouping of psuedo-random number sequences comprising 100 symbols. Of these 100 symbols, 86 symbols of the header are used for frame synchronization and channel sounding (for characterization of a communications channel), while the remaining 14 symbols are used for interleaver and data synchronization in an interleaved fashion.

Abstract: Methods for generating code sequences that have rapid acquisition properties and apparatus which implement the methods by processing spreading codes on in-phase and quadrature channels. A first method combines two or more short codes to produce a long code. This method may use many types of code sequences, one or more of which are rapid acquisition sequences of length L that have average acquisition phase searches r=log2L. Two or more separate code sequences are transmitted over the complex channels. If the sequences have different phases, an acquisition may be done by acquisition circuits in parallel over the different code sequences when the relative phase shift between the two or more code channels is known. When the received length L codes or the length L correlation codes used to find the phase of the received codes have a mutual phase delay of L/2, the average number of tests to find the code phase of the received code is L/4.

Abstract: In a spread spectrum multipoint-to-point communication system there is provided a novel frequency to phase converter, for automatically synchronizing the PN codes of the user transmitters/receiver with the receiver/transmitter in the central hub. The highly accurate frequency to phase converter generates a highly accurate phase error signal for synchronizing the multiuser network. The frequency to phase converter includes a serial adder and a series to parallel converter and a shift register which integrates the highly accurate phase error signal values and produces a highly accurate frequency value which is applied to the input of the resident processor in the central hub transmitter/receiver. The central hub transmitter/receiver calculates the clock offset for synchronizing each of the user receiver transmitters and generates a clock adjusting signal which is transmitted to the user receiver/transmitters.

Abstract: A receiver for pseudorandom noise (PRN) encoded signals consisting of a sampling circuit, multiple carrier and code synchronizing circuits, and multiple digital autocorrelators. The sampling circuit provides digital samples of a received composite signal to each of the several receiver channel circuits. The synchronizing circuits are preferably non-coherent, in the sense that they track any phase shifts in the received signal and adjust the frequency and phase of a locally generated carrier reference signal accordingly, even in the presence of Doppler or ionospheric distortion. The antocorrelators in each channel form a delay lock loop (DLL) which correlates the digital samples of the composite signal with locally generated PRN code values to produce a plurality of (early, late), or (punctual, early-minus-late) correlation signals.

Abstract: A process may be implemented which obtains a signal indicating a synchronization error between a pseudo-random signal sequence from a transmitter and a reference pseudo-random signal sequence from a receiver in a measuring device on the receiving end. In order to be able to detect a synchronization error as quickly and reliably as possible, successive sections (a, b, c) of a reference pseudo-random signal sequence (g'(n)) are each cross-correlated separately with the received pseudo-random signal sequence (g(n)), yielding partial cross-correlation functions (KKF.sub.a (n), KKF.sub.b (n) and KKF.sub.c (n)). The partial cross-correlation functions are added up to obtain a sum cross-correlation function (KKF.sub.s (n)). The sum cross-correlation function (KKF.sub.s (n)) is analyzed to detect the proper chronological occurrence of at least three maximums (m.sub.a, m.sub.b and m.sub.c). If the maximums (m.sub.a, m.sub.b and m.sub.

Abstract: An OCDMA spread spectrum communication system is provided with a PN encoded acquisition channel signal which is free of Radamacher functions. This provides a technique for very rapid acquisition of the PN code and data symbol timing; enables accurate PN chip time tracking with a minimum of power; enables accurate frequency tracking with a minimum of power; provides a technique for accurate signal power measurement at the receiver; enables the receiver to maintain code lock during deep fades; and penetrates into areas of high attenuation for paging or to alert user that he has a call waiting.

Abstract: A system for receiving, correlating and interpreting secured wireless transmissions, periodic or otherwise, including multiplexed receivers, robust correlator design, a state machine device for controlling the receivers and correlation function, and the ability to determine signal spatial diversity via switched antenna signal processing. The correlator is constructed to include a synchronization scheme adaptive to any variety of input signals from the coupled receiver tuned frequencies.

Abstract: A novel code division multiple access (CDMA) system and apparatus is provided which permits a plurality of encoded modulated data messages to be transmitted simultaneously on the same channel in one frequency band as a composite CDMA signal. An identification signal is generated and spread by a spreading signal having a duty cycle less than fifty percent to produce a combined signal which is transmitted to a receiver having a tapped delay with a plurality of taps each of which produce a replica of the received combined signal delayed by an odd multiple of the duty cycle of the spreading signal. Each of the replica signals is multiplied by a predetermined weighted value to produce weighted delayed signals and a controller responsive to the received combined signal, is employed for controlling individual weighted delayed signals which are then combined to suppress the spreading signal leaving the identification signal.

Abstract: A wireless telecommunications system (1) includes a central terminal (10) for transmitting and receiving radio frequency signals to and from a subscriber terminal (20). A downlink communication path is established from a transmitter (200) of the central terminal (10) to a receiver (202) of the subscriber terminal (20). A downlink signal (212) is transmitted from the transmitter (200) to the receiver (202) during setup and operation of the wireless telecommunications system (1). The downlink signal (212) includes an overhead channel (224) having a code synchronization signal (234). The code synchronization signal (234) is capable of adjusting a phase of a transmitter (204) in the subscriber terminal (20). A receiver (206) in the central terminal (10) monitors an uplink signal (214) transmitted by the transmitter (204) in the subscriber terminal and provides changes to the code synchronization signal (234) such that the transmitter (204) is synchronized to the receiver (206).

Abstract: A pulse-width modulating device comprises: a counter for generating a plurality of counter signals of n-bit, where n is an integer of 2 or more; a fundamental waveform generator for outputting a signal for the least significant bit of the count signal as the most significant bit of a fundamental waveform signal, obtaining a first product of inverted signals of all of the count signals for higher order bits than LSB, obtaining a second product of the first product and the count signal for a certain bit, carrying out this for every bit, and outputting n-bit fundamental waveform signals extending from the upper order bits to the lower order bits; and a pulse-width modulator for obtaining a product sum total for each bit of the n-bit data signal and each of the n-bit of fundamental waveform signals corresponding to the each bits of n-bit data and generating a pulse-width modulated signal, configured in such a manner that a pulse-width modulating signal having a pulse-width corresponding to the data signal and hav

Abstract: An apparatus and method for synchronizing a spread spectrum receiver comprises a preamble matched filter and a plurality of symbol code correlators for receiving and correlating to a received spread spectrum signal. The preamble matched filter is preferably non-coherent in nature and outputs a correlation signal including a correlation pulse of variable width. The pulse is converted to a square wave having a duration of a discrete number of chip periods. The correlation pulse is used as a timing reference for the symbol code correlators, which are also non-coherent in nature. A center seeking circuit provides an offset to the timing reference according to the width of the correlation pulse. In a preferred TDMA system, a timing window is used for a subsequent time frame for defining a period of time in which the correlation signal output from the preamble matched filter can yield a valid correlation pulse.

Abstract: An impulse radio communications system using one or more subcarriers to communicate information from an impulse radio transmitter to an impulse radio receiver. The impulse radio communication system is an ultrawide-band time domain system. The use of subcarriers provides impulse radio transmissions added channelization, smoothing and fidelity. Subcarriers of different frequencies or waveforms can be used to add channelization of impulse radio signals. Thus, an impulse radio link can communicate many independent channels simultaneously by employing different subcarriers for each channel. The impulse radio uses modulated subcarrier(s) for time positioning a periodic timing signal or a coded timing signal. Alternatively, the coded timing signal can be summed or mixed with the modulated subcarrier(s) and the resultant signal is used to time modulate the periodic timing signal. Direct digital modulation of data is another form of subcarrier modulation for impulse radio signals.

Abstract: Interference removal in spread spectrum signals, comprises the steps at a spread spectrum transmitter (10) of spreading information across a predetermined spectrum by phase modulating a repeating noise sequence (18), providing a spread spectrum signal and transmitting the spread spectrum signal. The method further comprises the steps at a receiver of receiving the spread spectrum signal along with interference (41) multiplying (42) the spread spectrum signal along with interference by a window function (44) providing a multiplied spread spectrum signal. The information is recovered by despreading the multiplied (48) spread spectrum signal using a reciprocal (50) of the spectrum of the repeating noise sequence to obtain a data spectrum with interference and subsequently normalize (52) to obtain a clean data spectrum. Alternatively the information can be recovered by substituting a corrupted magnitude spectrum with a prestored PN sequence magnitude spectrum (70) as shown by receiver (60).

Abstract: A direct-sequence spread spectrum communication system using a high power transmitter and a short spreading sequence which still satisfies FCC Rule 15.247 regarding power density. In addition to the spreading sequence, the carrier signal is modulated with a phase reversal sequence. Typically, each period of the phase reversal sequence has a duration equal to the total duration of the spreading sequence. The phase reversal sequence reduces the maximum power density of the signal, but is transparent to a receiver.

Abstract: A receiver and a method for controlling a receiver, the receiver being implemented on the RAKE principle and comprising a number of correlators (30a-30d) which are able to synchronize with a received signal. To effectively utilize the correlators of the receiver, the operation made of the correlators in the receiver is changed dynamically in the method of the invention between the received signal tracking and acquisition modes according to the need.

Abstract: The invention relates to a method and apparatus for synchronization of transmitters and receivers in digital transmission systems of the OFDM type. The system uses FFT technique to carry out the modulation and demodulation procedures. According to the invention, the transmitter sends synchronization frames with known frequencies and phase positions and with known time intervals in certain time slots. The receiver carries out a series of time-shifted FFT operations over the time position where the synchronization frame is calculated to be. For each operation, a cross-correlation is carried out in the frequency plane of the output signal with the known frequency function of the synchronization frame. The correlation maximum is detected, and this determines the time slot which contains the synchronization frame, whereupon this is used as time base for the following data frames.

Abstract: A spread spectrum communication apparatus for communication with a plurality of communication units includes a reception circuit, an automatic gain control circuit, a spread spectrum code detection circuit, and a synthesis circuit. The reception circuit receives signals of a frequency channel inclusive of a target communication unit. The automatic gain control circuit controls the signal intensity of the frequency channel received by the reception circuit to a constant level. The spread spectrum code detection circuit detects the signal intensity of the spread spectrum code of the target communication unit from an output signal of the automatic gain control circuit. The synthesis circuit combines the signal intensity which is based on a gain control signal of the automatic gain control means with a signal intensity as detected by the spread spectrum code detection circuit to find a reception intensity.

Abstract: A PN code acquisition system for Code Division Multiple Access (CDMA) Direct Sequence Spread Spectrum (DSSS) systems, with automatic decision threshold, is based on the combination of the Maximum Likelihood (ML) and Serial Search (SS) acquisition approaches. In contrast to the conventional SS acquisition system, the disclosed system adaptively estimates optimal threshold by exploiting the statistics of the signal and noise, and makes an optimal decision based on the threshold. The system estimates the threshold by employing ML estimation and applies the threshold as in SS acquisition and makes a decision by comparing the updated threshold with the current signal strength. Together with post detection verification logic, this approach will increase detection probability and reduce false alarm probability significantly. An optimum system parameter design approach and the advantages of this approach as compared to conventional approaches (ML or SS acquisition) are demonstrated.

Abstract: Analog signals representing individual digital values (.+-.1, .+-.3) pass through a telephone line to a receiver. These signals may be first provided in a pseudo random sequence. A linear echo canceller and a first adder eliminate, to an extent, echo signals resulting from second analog signals transmitted on the same telephone line by the receiver. A non-linear echo canceller and a second adder further reduce the echo signals and specifically reduce non-linear components in the echo signals. Adjustable signal delays achieve optimal performance of the linear and non-linear echo cancellers. An equalizer containing four (4) different modules then compensates for signal distortions introduced by the telephone line and minimizes the effect of noise in the telephone line. The equalizer modules are a digital gain control element, a feed forward digital filter and two (2) feedback digital filters. A detector module produces in one of several different ways at the receiver an estimate of the digital data (.+-.1, .+-.

Abstract: A CDMA communication system capable of operating at higher data rates with less bit errors and reduced cochannel interference facilitates coherent detection without the use of a pilot tracking signal. A transmitter in the communication system includes a coherence interval channel encoder, an orthogonal function encoder, such as a Walsh encoder, as well as a pseudo noise (PN) channel modulator. The channel encoder processes data sequences into sufficiently short encoded data blocks to minimize any phase shifts at a receiver in a high mobility environment due to a Doppler frequency shift. Depending on the application, several transmitters may be synchronized such that the corresponding transmitted information signals are orthogonal to one another.

Abstract: A system and method for adaptively sectorizing channel resources within a digital cellular communication system is disclosed herein. The system includes an antenna arrangement for providing at least first and second electromagnetic beams for receiving a first information signal transmitted by a specific one of a plurality of users, thereby generating first and second received signals. A first set of beam-forming signals are then generated from the first and second received signals. A demodulating receiver is provided for demodulating at least first and second beam-forming signals included within the first set of beam-forming signals, thereby producing first and second demodulated signals. The system further includes a tracking network for tracking multipath information signals, received from various positions and angles of incidence, based on comparison of the first and second demodulated signals.

Abstract: The desynchronizer stores information units corresponding to time slots of a PCM-stream (IN) in consecutive memory locations of a buffer memory (BM). The number of memory locations of this memory (BM) corresponds to the length of a subframe within which the desynchronizer substantially randomizes the order of the information units. This randomization is achieved by reading the stored information units in an order dictated by a permutation (A1) of the addresses of the memory locations. This permutation (A1) is substantially randomly selected from the limited number of possible permutations by a permutation device (PM) and is started simultaneously with the arrival of the first information unit of a subframe. In order to ensure that all information units are forwarded to the output stream (OUT) the mentioned permutation is repeated (A2) by a permutation repetition device (PRM) simultaneously with a new permutation (A1) corresponding to a next subframe.

Abstract: A multi-level correlation technique and apparatus for detecting symbol and data frame synchronization in high noise and multi-path environments, wherein received signals are correlated with known pseudorandom noise (PN) or other known codes at the base level and the base level correlation results are in turn correlated with PN or other known codes at the next higher level, such that the top level of correlation includes all lower levels of encoding in the complete synchronization pattern. In a two level implementation, the base level codes define symbols while the top level code defines the synchronization pattern in terms of the base level symbols. Correlation hardware is minimized while processing gain is maximized for enhancing low signal to noise levels over a long synchronization pattern. Additionally, precise ranging is facilitated because the top level correlation result covers the entire synchronization pattern.

Abstract: A wireless alarm system using spread spectrum transmitters, fast frequency shift keying, spread spectrum receivers and computer with a display. The spread spectrum transmitter includes an oscillator coupled to a microprocessor with chip code generation means, preamble register, address register and data register. The spread spectrum receiver acquires synchronization of the spread spectrum signal using a microprocessor coupled to the quieting, signal strength or baseband output of the receiver, with a two step algorithm. The steps comprise achieving a coarse lock and a fine lock to the spread spectrum signal.

Abstract: A digital radio communication system includes a receiver for receiving a signal stream that includes data frames, each frame including a data signal sequence and a synchronizing signal sequence. The communication system synchronizes the receiver by employing the signal stream. The receiver comprises: a sampling circuit for sampling symbol levels in the synchronizing signal sequence; cross correlation circuitry for comparing values derived from the sampled symbol levels with an expected set of values and producing an error value output; and correction circuitry that is responsive to the error output and produces a sample control output to the sample circuitry to alter the times of sampling of the symbol levels so as to reduce the error output and achieve time synchronization with the received synchronizing signal sequence. A further embodiment of the invention is described in relation to a CDMA receiving system.