335 results about "Spread spectrum communication systems" patented technology

The equalizer of the present invention operates on input multipath signal samples, preferably at chip or sub-chip resolution, to remove or substantially cancel the effects of one or more secondary signals from the main path signal. Using predetermined path information for one or more of the secondary path signals, including magnitude, phase, and time offset relative to the main path signal, the equalizer compensates input multipath signal samples by subtracting estimated secondary signal values from the input samples. For each input sample, the equalizer forms a sliced sample, where the sliced sample represents a nominal phase value defined by the modulation scheme used in the original chip or symbol transmission that is closest in value to the actual phase of the input sample. These sliced samples are held in a running buffer and used, in combination with the predetermined path information and scaling logic, to form the estimated secondary signal values for compensating the input samples.

A multiple access, spread-spectrum communication system processes a plurality of information signals received by a radio carrier station over telecommunication lines for simultaneous transmission over a radio frequency channel as a code-division-multiplexed signal to a group of subscriber units. The radio carrier station receives a call request signal that corresponds to a telecommunication line information signal, and a user identification signal that identifies a user to receive the call. The radio carrier station includes a plurality of CDMA modems, one of which provides a global pilot code signal. The modems provide message code signals synchronized to the global pilot signal. Each modem combines an information signal with a message code signal to provide a code division multiplexed signal. The RCS includes a system channel controller is coupled to receive a remote call. A radio frequency transmitter is connected to all of the modems to combine the code division multiplexed processed signals with the global pilot code signal to generate a code division multiplexed signal. The transmitter also modulates a carrier signal with the code division multiplexed signal and transmits the modulated carrier signal through a radio frequency communication channel to the subscriber units. Each subscriber unit includes a CDMA modem which is also synchronized to the global pilot signal. The CDMA modem despreads the code division multiplexed signal and provides a despread information signal to the user. The system includes a closed loop power control system for maintaining a minimum system transmit power level for the radio carrier station and the subscriber units, and system capacity management for maintaining a maximum number of active subscriber units for improved system performance.

A wireless spread spectrum communication system for transmitting data includes a plurality of end point transmitters and at least one receiver. The end point transmitters transmit data via a frequency hopped spread spectrum signal where the transmitting signal is sent without the benefit of frequency stabilization. The receiver is responsive to the frequency hopping spread spectrum signals and includes a correlator and a signal processor. The correlator samples at least a first portion of a preamble of the signal and correlates the portion of the preamble with a known preamble pattern to determine a probability of correlation. The signal processor applies a Fast Fourier Transform algorithm to the signal in response to the probability of correlation to track a narrowband frequency of the signal based on at least a second portion of the preamble and to decode data encoded within the signal subsequent to the preamble.

A method of performing antenna diversity in a wireless spread spectrum communication system is disclosed. A spread spectrum phase shift keyed (PSK) packet signal having data symbols formed from high rate mode chips is received in each of two respective spaced antenna of a spread spectrum receiver. The bit sync peak sample is determined within the packet signal for each antenna. Predetermined bit sync samples are subtracted a predetermined number of chips on either side of the bit sync peak sample from the peak for each antenna. The antenna having the higher value obtained in the subtracting step accomplished for each antenna is selected.

A petroleum well has an electronic module and a number of sensors which communicate with the surface using the tubing string and casing as conductors. Induction chokes at the surface and downhole electrically impede AC flow through the (tubing or casing if so configured) with the resulting voltage potential useful for power and communication. A high bandwidth, adaptable spread spectrum communications system is used to communicate between the downhole electronics module and a surface master spread spectrum modem. Downhole sensors, such as pressure, temperature, acoustic and seismic sensors accurately assess downhole physical conditions. In a preferred form, the electronics module and sensors are wireline insertable and retrievable into a side pocket mandrel in the tubing string. Permanent downhole sensors that can communicate with the surface allow such diverse applications as optimizing well and field performances, monitoring and assessing the geophysics of the fomrations around the well, assessing well and reservoir reserves, assessing reservoir conditions.

In a burst-mode, high-speed spread-spectrum communications system, faster convergence of a receiver's automatic gain control (AGC) circuit reduces the time required to bring a received signal within the operating range of an operation amplifier and other radio-frequency and digital sections of the receiving system. A gain control circuit includes a coarse-gain feedback loop and a fine-gain feedback loop to improve convergence speed and at the same time maintain the stability of the AGC circuit. The coarse-gain feedback loop quickly brings the received signal, using a large gain signal, to the desired operating range. The fine-gain feedback loop uses a smaller gain signal to gradually smooth the received signal to avoid saturation on the A/D converters.

Techniques to improve the acquisition process in a spread spectrum environment. The signals from different CDMA systems are spread with different sets of PN sequences, with the PN sequences in each set being uncorrelated to the PN sequences in the other sets. By using uncorrelated PN sequences, the likelihood of detecting a pilot signal from an undesired system is reduced or minimized, and the mean time to acquisition of the pilot signal from the desired system is improved. The mobile station can attempt to acquire the pilot signal by processing the received signal with a first set of PN sequences corresponding to a first hypothesis of the particular signal being acquired. If acquisition of the pilot signal fails, a second set of PN sequences corresponding to a second hypothesis is selected and used to process the received signal. The PN sequences in the second set are uncorrelated to the PN sequences in the first set. The PN sequences for the first set can be generated based on the characteristic polynomials defined by IS-95-A, and the PN sequences for the second set can be the reverse of the PN sequences for the first set.

A receiver for spread spectrum communication system receives a traffic channel and common control channel by a plurality of matched filters at least one of which is selectively available for the traffic or the common control channel. At the initial acquisition, a plurality of matched filters are used for receiving the common control channel. At the hand-over, a plurality of matched filters are used to receive traffic channels of the current base station and the base stations in the adjacent cells.

A method is provided for generating a coherent chaotic sequence spread spectrum communications system. The method includes phase modulating a carrier with information symbols. The method also includes generating a string of discrete time chaotic samples. The method further includes modulating the carrier in a chaotic manner using the string of discrete time chaotic samples. Each of the discrete time chaotic samples has a shorter sample time interval than the duration of the information symbols. The generating step includes selecting a plurality of polynomial equations. The generating step also includes using residue number system (RNS) arithmetic operations to respectively determine solutions for the polynomial equations. The solutions are iteratively computed and expressed as RNS residue values. The generating step further includes determining a series of digits in the weighted number system based on the RNS residue values. The method further includes synchronizing the chaos generated at the receiver with that generated at the transmitter without periodic transfer of state update information.

A data hopping device is provided with a hopping generation unit and a data selection unit, the hopping pattern generation unit generating a predetermined hopping pattern, and the data selection unit outputs a plurality of subcarrier transmission signals corresponding to respective subcarriers, by receiving transmission data and outputting only the data carried in the subcarrier designated by the hopping pattern as the subcarrier transmission signal, while maintaining the other subcarrier transmission signals at a zero output level. An inverse Fourier transform device subjects the entirety of subcarrier reception signals output from the data selection unit to inverse Fourier transform and outputs frequency-hopped spread-spectrum transmission signals.

A multiple access, spread-spectrum communication system processes a plurality of information signals received by a Radio Carrier Station (RCS) over telecommunication lines for simultaneous transmission over a radio frequency (RF) channel as a code-division-multiplexed (CDM) signal to a group of Subscriber Units (SUs). The RCS receives a call request signal that corresponds to a telecommunication line information signal, and a user identification signal that identifies a user to receive the call. The RCS includes a plurality of Code Division Multiple Access (CDMA) modems, one of which provides a global pilot code signal. The modems provide message code signals synchronized to the global pilot signal. Each modem combines an information signal with a message code signal to provide a CDM processed signal. The RCS includes a system channel controller is coupled to receive a remote call. An RF transmitter is connected to all of the modems to combine the CDM processed signals with the global pilot code signal to generate a CDM signal. The RF transmitter also modulates a carrier signal with the CDM signal and transmits the modulated carrier signal through an RF communication channel to the SUs. Each SU includes a CDMA modem which is also synchronized to the global pilot signal. The CDMA modem despreads the CDM signal and provides a despread information signal to the user. The system includes a closed loop power control system for maintaining a minimum system transmit power level for the RCS and the SUs, and system capacity management for maintaining a maximum number of active SUs for improved system performance.

A multiple access, spread-spectrum communication system processes a plurality of information signals received by a radio carrier station over telecommunication lines for simultaneous transmission over a radio frequency channel as a code-division-multiplexed signal to a group of subscriber units. The radio carrier station receives a call request signal that corresponds to a telecommunication line information signal, and a user identification signal that identifies a user to receive the call. The radio carrier station includes a plurality of CDMA modems, one of which provides a global pilot code signal. The modems provide message code signals synchronized to the global pilot signal. Each modem combines an information signal with a message code signal to provide a code division multiplexed signal. The RCS includes a system channel controller is coupled to receive a remote call. A radio frequency transmitter is connected to all of the modems to combine the code division multiplexed processed signals with the global pilot code signal to generate a code division multiplexed signal. The transmitter also modulates a carrier signal with the code division multiplexed signal and transmits the modulated carrier signal through a radio frequency communication channel to the subscriber units. Each subscriber unit includes a CDMA modem which is also synchronized to the global pilot signal. The CDMA modem despreads the code division multiplexed signal and provides a despread information signal to the user. The system includes a closed loop power control system for maintaining a minimum system transmit power level for the radio carrier station and the subscriber units, and system capacity management for maintaining a maximum number of active subscriber units for improved system performance.

An approach for utilizing a pilot scheme in a spread spectrum communication system (e.g., Multi Carrier Code Division Multiple Access (MC-CDMA)) is provided. A communications link includes a sub-bands and a single pilot channel that is designated for the sub-bands for channel estimation. Pilot symbols transmitted over the single pilot channel are used to determine a first channel estimate associated with a first one of the sub-bands, and a second channel estimate corresponding to a second one of the sub-bands is derived from the first channel estimate.

A system and method for maximizing channel utilization by efficiently allocating codes and frequencies based on estimated relative interference between subscriber units in a wireless communications network, such as an ad-hoc wireless communications network, in such a way as to minimize multiple access interference. The system and method perform the operations of collecting existing and proposed transmission information between nodes in the network, and calculating a respective interference factor for each existing transmission between certain nodes and each proposed transmission by a transmitting node. The interference factors can be calculated based on, for example, respective distances between certain nodes. The system and method then assign the communications channel configuration, including a frequency channel and code channel, to the transmitting node for communications to other nodes as designated by a minimum of the calculated respective interference factors.

According to one aspect, a spread spectrum communications system is capable of automatically adjusting transmission power level so as to optimize one or more aspects of the spread spectrum communication system performance. The spread spectrum communications system is comprised of a first spread spectrum transmitter, an associated first spread spectrum receiver, and a feedback communication system. The first spread spectrum transmitter is adapted to transmit a spread spectrum type signal. The first spread spectrum receiver is adapted to receive the spread spectrum type signal sent by the first spread spectrum transmitter and to subsequently generate transmission power level control information, which is conveyed to the first spread spectrum transmitter via a feedback communication system. The first spread spectrum transmitter is further adapted to receive and process transmission power level control information that is provided by the feedback communication system, and subsequently adjust transmission power in accordance with the received transmission power level control information.

A multiple access, spread-spectrum communication system processes a plurality of information signals received by a radio carrier station over telecommunication lines for simultaneous transmission over a radio frequency channel as a code-division-multiplexed signal to a group of subscriber units. The radio carrier station receives a call request signal that corresponds to a telecommunication line information signal, and a user identification signal that identifies a user to receive the call. The radio carrier station includes a plurality of CDMA modems, one of which provides a global pilot code signal. The modems provide message code signals synchronized to the global pilot signal. Each modem combines an information signal with a message code signal to provide a code division multiplexed signal. The RCS includes a system channel controller is coupled to receive a remote call. A radio frequency transmitter is connected to all of the modems to combine the code division multiplexed processed signals with the global pilot code signal to generate a code division multiplexed signal. The transmitter also modulates a carrier signal with the code division multiplexed signal and transmits the modulated carrier signal through a radio frequency communication channel to the subscriber units. Each subscriber unit includes a CDMA modem which is also synchronized to the global pilot signal. The CDMA modem despreads the code division multiplexed signal and provides a despread information signal to the user. The system includes a closed loop power control system for maintaining a minimum system transmit power level for the radio carrier station and the subscriber units, and system capacity management for maintaining a maximum number of active subscriber units for improved system performance.

The present invention is directed to signal cancellation in spread spectrum communication systems. In particular, the present invention provides method and apparatus for selectively canceling interfering signals, even where symbols to be canceled do not align with symbols associated with a desired signal path. Furthermore, the interference cancellation provided by embodiments of the present invention is capable of functioning to remove interference associated with channels utilizing a symbol length that is different than the symbol length of a desired signal path. In accordance with a further embodiment of the present invention, method and apparatus for efficiently calculating projections to enable signal cancellation are provided.

An improved spread spectrum communication system includes a transmitter and a receiver utilizing a pilot channel for the transmission of pure rather than modulated PN codes for code acquisition or tracking purposes with a lower bit error rate. The pilot signal is used to obtain initial system synchronization and phase tracking of the transmitted spread spectrum signal. At the transmitter side, a Walsh code generator, a Walsh modulator, a first PN code generator, a first band spreader, a second band spreader, finite impulse response filters, digital-analog converters, low-pass filters, an intermediate frequency mixer, a carrier mixer, a band-pass filter are used to transmit a spread spectrum signal. At the receiver side, a corresponding band-pass filter, a carrier mixer, an intermediate-frequency mixer, low-pass filters, analog-digital converters, a second PN code generator, an I channel despreader, a Q channel despreader, a PN code synchronization controller, a Walsh code generator, a first Walsh demodulator, a second Walsh demodulator, accumulator & dump circuits, a combiner, and a data decider are used to demodulate a received spread spectrum signal

Disclosed is a method of generating a detection signal for detecting energy in a spread-spectrum signal, comprising: de-spreading the spread-spectrum signal by applying a predetermined spreading code to obtain a sequence of de-spread signal symbols (202A-202D); accumulating a number of said signal symbols to obtain a single detection signal. The accumulation includes: obtaining a first and a second subset of said de-spread signal symbols, wherein the symbols of the first subset have values that are known to the receiver or at least known to be the same for all symbols of the first subset, and wherein the symbols of the second subset have unknown values; coherently accumulating the symbols of the first subset to obtain a first partial detection signal (203A, 203B, 203C); non-coherently accumulating the symbols of the second subset to obtain a second partial detection signal (204A, 204B, 204C); and combining the first and second partial detection signals to obtain the single detection signal (208).

A spread spectrum communications system is provided for reducing the number of required matched filters to simplify the configuration associated with the reception. In a spread spectrum transmitter, a plurality of spread channel signals are synthesized by shifting their respective phases by a time sufficiently shorter than one symbol period. In a spread spectrum receiver, a plurality of spread code sequences are set one by one at a tap of a single matched filter in one symbol period in a time division manner to recover transmitted data.

A novel and useful acquisition and synchronization mechanism for spread spectrum communication systems whereby a synchronization sequence comprising a plurality of known symbols spaced apart by predefined time delay intervals is transmitted as the start of packet signal. At the transmitter, a synchronization sequence is transmitted at the beginning of each packet. A synchronization sequence is generated which includes a plurality of symbols with predefined time gaps between each of the symbols. Multiple synchronization sequences may be generated wherein each sequence comprises a unique set of time delays or gaps between each of the symbols. Each set of unique time delays or gaps between symbols of a sequence is stored as a synchronization sequence gap template in memory. When required to generate a synchronization sequence, the sequence generator outputs the plurality of synchronization symbols and inserts a specific time delay between each of the symbols in accordance with the contents of the gap template for the particular synchronization sequence.

An embodiment of the present invention described in the specification and the drawings is an apparatus and method for code correlation in spread spectrum communication systems. The apparatus receives a data sequence, and offsets the data sequence with a fixed sub-chip delay. The data sequence and the offset data sequence are each despread with a locally generated code sequence. The despread results are summed and accumulated. The accumulated results may then be used to achieve a lower “miss” probability during code correlation.