Itt Manufacturing Enterprises, Inc.

Itt Corporation

Itt Industries, Inc.

Meshnetworks, Inc.

Exelis Inc.

Donald John Rasmussen

Dennis D McCrady

Eric A Whitehill

Larry Koos

Daniel D Shearer, Iii

Michael Mayor

Charles A Simmons, Jr

Gregory Thomas Barnett

Daniel J Schwarz

Timothy P Dempsey

Delbert Todd Mulholland

A method of pulse shaping a spread signal of serially formatted in-phase (I) and quadrature (Q) waveforms, where each waveform includes a predetermined number of chips per symbol, includes (a) examining adjacent chips of the I and Q waveforms at a symbol boundary; and (b) determining that one of the I or Q waveforms, includes two adjacent first and second chips separated by a single chip period, where the first chip belongs to a previous symbol and the second chip belongs to a present symbol. If the chips are of the same value, the method extends a peak value between the first and second chips, and zeros the other waveform of the I or Q waveform during the extended duration. If the chips are of opposite values, then the method zeroes one of the chips and inserts a chip into the other waveform.

Phase mapping for QPSK/QBL-MSK waveform

Methods and apparatus for synchronization (SYNC) detection of a received serial offset quadrature pulse shaped waveform modulated by a symbol SYNC sequence are provided. The waveform is serially demodulated into a serial baseband signal and serially correlated with segments of the symbol SYNC sequence. Correlation strength estimates of each of the serially correlated output signal are computed and combined to detect a coarse SYNC. The serially correlated output signals are phase corrected based upon phase change conditions and the phase corrected signals are used to detect a fine SYNC.

Synchronization technique for serial modulated waveforms

A transmitter is configured to transmit a time of arrival (TOA) message to a receiver applying a quadrature multiple frequency ranging (QMFR) algorithm for separating multiple path signal components. The transmitter includes (1) a modulator for generating a quasi-band limited minimum shift keyed (QBL-MSK) signal, (2) a serial formatter for generating a serial QBL-MSK (SQBL-MSK) signal, and (3) a switch for disabling the serial formatter, during a time that the TOA message is being transmitted to the receiver. The receiver includes (1) a matched filter for separating a data packet with the TOA message into in-phase (I) and quadrature (Q) spreading sequences, (2) an even sample mapping section, coupled to the matched filter, for outputting the even samples of the I and Q spreading sequences, (3) an odd sample mapping section, coupled to the matched filter, for outputting the odd samples of the I and Q spreading sequences, and (4) sliding correlator banks for receiving the even samples of the I and Q spreading sequences and the odd samples of the I and Q spreading sequences and outputting despread even I and Q samples and despread odd I and Q samples to a QMFR algorithm for separating multiple path signal components.

QBL-MSK mapping for time of arrival (TOA) applications

Methods and apparatus for synchronization (SYNC) detection of a received serial offset quadrature pulse shaped waveform modulated by a symbol SYNC sequence are provided. The waveform is serially demodulated into a serial baseband signal and correlated in parallel with segments of the symbol SYNC sequence. Correlation strength estimates of each of the correlated output signals are computed and used to adjust a SYNC threshold level. The correlation strength estimates or the correlated output signals are combined and a peak is determined in the resulting signal. The peak in the resulting signal is compared to the SYNC threshold level to detect synchronization.

Adaptive synchronization enhancement technique for serial modulated waveforms

A technique for determining the time of arrival of a signal includes generating a spread spectrum signal with a number of code sectors, each including a periodic sequence of spread spectrum chips that corresponds to a predetermined correlation function. The periodic sequences of chips of the code sectors are shifted in time by differing amounts relative to a periodic time reference. Upon reception, the spread spectrum signal is periodically sampled, and the different code sectors produce different sampling points on the correlation function such that a number of time-shifted correlation functions results from time shifts of the code sectors. The time of arrival of the spread spectrum signal can be determined by curve fitting of the sampling points from the set of time-shifted correlation functions.

Methods and apparatus for improving signal timing accuracy

Methods and apparatus for determining carrier frequency error of a serial offset quadrature pulse shaped signal, such as a minimum shift keyed (MSK) signal, are disclosed. Carrier frequency error is determined by receiving a quadrature pulse shaped signal having a synchronization sequence, detecting synchronization of the quadrature pulse shaped signal, and storing a baseband inphase (I) signal and a baseband quadrature (Q) signal of the synchronization sequence while detecting synchronization. After detecting synchronization, segments of the stored baseband I and Q signals are read and correlated with a spreading sequence. Carrier frequency error is then estimated based on phase differences between each of the correlated segments.

Fast digital carrier frequency error estimation algorithm using synchronization sequence

A simplified timing correction method is provided for data despreading of serial offset quadrature pulse-shaped spread signals. The simplified timing correction algorithm is applied to a rake receiver for improved performance in a multi-path channel. Serial formatting of the spreading modulation waveform is selected to reduce the SYNC/serial probe correlation complexity. The method includes the steps of: (a) decimating serial inphase (I) and quadrature (Q) signals to form decimated I and Q even samples and decimated I and Q odd samples; (b) obtaining an autocorrelation profile of a spreading sequence used by the receiver; (c) detecting a synchronization starting point using the I and Q even samples; and (d) deciding to either move, or not move, the synchronization starting point, based on the autocorrelation profile obtained in step (b). Step (d) decides to move the synchronization starting point, and uses the I and Q odd samples for subsequent despreading of the I and Q signals. Step (d) also decides not to move the synchronization starting point, and uses the I and Q even samples for subsequent despreading of the I and Q signals.

Simplified timing correction for data despreading of serial offset quadrature pulse-shaped spread signals

A method of correcting phase error of a phase shift keyed (PSK) signal includes (a) receiving a signal modulated by a spreading sequence; (b) despreading the received signal using a receiver spreading sequence similar to the spreading sequence of step (a); (c) calculating a crosscorrelation profile between the receiver spreading sequence and the received signal; and (d) calculating an autocorrelation profile of the receiver spreading sequence to determine a spreading code property (SCP). The method also includes (e) estimating a timing error in alignment between the autocorrelation and the crosscorrelation profiles; and (f) correcting a phase error of the signal despread in step (c), by using the SCP and the estimated timing error.

Enhanced QPSK or DQPSK data demodulation for direct sequence spreading (DSS) system waveforms using orthogonal or near-orthogonal spreading sequences

Operational parameters for transmitting a signal over a communication channel of a network are selected by first determining RF conditions on the communication channel from a received signal transmitted over the communication channel. An initial set of parameter values is selected for transmitting the signal based on RF conditions determined from the received signal. The initial set of parameter values is used to identify other sets of parameter values as other potential candidates for transmitting the signal. The parameter values in the other sets of parameter values differ from parameter values in the initial set of parameter values by less than a predetermined amount. The expected performance of the candidate sets of parameter values is compared to determine which set of parameter values has the best expected performance among the candidate sets of parameter values. The signal is transmitted on the communication channel using the selected set of parameter values.

Methods and apparatus for organizing selection of operational parameters in a communication system

A system and method for enabling a transmitter employing signal spreading techniques to increase the data rate of the transmitted modulated signal without reducing the multi-path delay spread. Specifically, the system and method use concatenated spreading sequences to provide data modulated spread signals having increased data rates with extended multi-path delay spread. The system and method therefore removes the one-to-one relationship between the repetitive spreading code length and maximum multi-path delay spread of a data modulated spread signal, to thus increase the data rate for a given multi-path delay spread while preserving the autocorrelation and cross-correlation properties of the individual spreading sequences.

System and method employing concatenated spreading sequences to provide data modulated spread signals having increased data rates with extended multi-path delay spread

A modulator device is disclosed for a spread spectrum communication system which generates a modulated signal from incoming data. The device includes a QPSK portion for separating the incoming data into two data channels and for further spreading the two channels over a wide bandwidth according to a predetermined spreading code. A phase mapping element coupled to the QPSK portion for processing both channels in order to minimize spectral regrowth of the modulated signal by preventing the RF envelope deviation from going close to zero. Pulse shaping elements coupled to the phase mapping element for further processing each channel in order to improve the modulator spectral efficiency and minimize adjacent channel interference. A quad-mixer coupled to the pulse shaping elements for combining both channels into a recombined signal and for further modulating the recombined signal according to a predetermined carrier frequency.

QPSK/QBL-MSK waveform enhancement

Disclosed is a digital pulse shaping circuit for reducing undesirable frequency components in subsequent data modulated transmissions, which circuit can be easily manufactured as a monolithic integrated circuit. In a preferred embodiment, the pulse shaping circuit employs an edge detector circuit to detect data transitions of an incoming serial data stream. Upon a data edge detection, the edge detector provides a control signal to a digital counter to enable the counter to begin counting applied clock pulses and generate a linear count. The linear count is provided to a decoding circuit, which generates an output word as a nonlinear function of the value of the count. The decoded output word then drives a digital modulator which modulates an RF carrier to provide wireless data transmission with improved spectral efficiency.

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Fort Wayne, IN, United States of America

Donald John Rasmussen