US 5,963,586 A · Method and apparatus for parallel noncoherent correlation of a spread spectrum signal

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. The demodulating reference signal in the receiver may or may not be frequency or phase matched with the transmitter. In other embodiments, single bit or multi-bit digitization of the received spread spectrum signal for both I and Q signals (or real I, real Q, imaginary I, and imaginary Q signals) is carried out prior to correlation. In another embodiment, the transmitter differentially phase encodes the information to be transmitted, and the receiver decodes the phase encoded information by determining a quantized phase angle of the received signal.

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Claims14

Dependent claims

A method for despreading a received continuous phase modulated spread spectrum signal comprising the steps of:

dividing a received spread spectrum signal into a first signal and a second signal, said first and second signal being duplicates of one another,
demodulating said first signal into a real-I/imaginary-Q signal using a first non-coherent local reference signal,
demodulating said second signal into an imaginary-I/real-Q signal using a second non-coherent local reference signal having the same frequency as said first non-coherent local reference signal but phase offset therefrom by 90 degrees,
temporarily storing said real-I/imaginary-Q signal in a single first register,
temporarily storing said imaginary-I/real-Q signal in a single second register,
correlating the contents of said first register to generate a real I correlation signal and an imaginary Q correlation signal, said contents of said first register comprising odd and even chips, said odd chips being correlated with odd chips of a chip sequence and said even chips being correlated with inverses of even chips of said chip sequence,
correlating the contents of said second register to generate an imaginary I correlation signal and a real Q correlation signal, said contents of said second register comprising odd and even chips, said odd chips being correlated with odd chips of said chip sequence and said even chips being correlated with said even chips of said chip sequence, and
combining said real I correlation signal, said real Q correlation signal, said imaginary I correlation signal and said imaginary Q correlation signal into a final correlation signal.

5 more elements

A method for despreading a received continuous phase modulated spread spectrum signal comprising the steps of:

dividing a received spread spectrum signal into a first signal and a second signal, said first and second signal being duplicates of one another,
demodulating said first signal into a first demodulated signal using a first non-coherent local reference signal,
demodulating said second signal into a second demodulated signal using a second non-coherent local reference signal having the same frequency as said first non-coherent local reference signal but phase offset therefrom by 90 degrees,
temporarily storing said first demodulated signal in a single first register,
temporarily storing said second demodulated signal in a single second register,
correlating the contents of said first register, said contents comprising a plurality of chips, to generate a first correlation signal based on a correlation of odd chips of said first register with a plurality of odd chips of a chip sequence, and a second correlation signal based on a correlation of even chips of said first register with inverses of a plurality of even chips of said chip sequence,
correlating the contents of said second register, said contents comprising a plurality of chips, to generate a third correlation signal based on a correlation of odd chips of said second register with said odd chips of said chip sequence, and a fourth correlation signal based on a correlation of even chips of said second register with said even chips of said chip sequence, and
combining said first correlation signal, said second correlation signal, said third correlation signal and said fourth correlation signal into a final correlation signal.

5 more elements

An apparatus for despreading a received continuous phase modulated spread spectrum signal comprising:

a power divider having as an input a received spread spectrum signal and having as outputs a first signal and a second signal,
a first multiplier coupled to said first signal and a first local reference signal and having as an output a third signal, said first local reference signal differing in phase and small amounts of frequency from a carrier in said spread spectrum signal,
a second multiplier coupled to said second signal and a second local reference signal and having as an output a fourth signal, said second local reference signal phase offset from said first local reference signal by 90 degrees,
a first low pass filter coupled to said third signal and having as an output a first filtered signal,
a second low pass filter coupled to said fourth signal and having as an output a second filtered signal,
a first even/odd correlator receiving said first filtered signal and having as outputs a first correlation signal and a second correlation signal,
a second even/odd correlator receiving said second filtered signal and having as outputs a third correlation signal and a fourth correlation signal, and
means for combining said first correlation signal, said second correlation signal, said third correlation signal, and said fourth correlation signal into a final correlation signal,
said first even/odd correlator comprising
a single register having a first plurality of odd chip locations and a first plurality of even chip locations for receiving chips of said first filtered signal,
a plurality of odd chip multipliers, said odd chip locations of said first plurality of odd chip locations coupled to odd chip inputs of said plurality of odd chip multipliers for multiplication by odd chips of a chip sequence, said odd chip multipliers having first odd outputs;
a first summer having as first summer inputs said first odd outputs, and said first summer having as an output a first correlation signal,
a plurality of even chip multipliers, said even chip locations of said first plurality of even chip locations coupled to even chip inputs of said plurality of even chip multipliers for multiplication by inverses of even chips of said chip sequence, said even chip multipliers having first even chip outputs;
and
a second summer having as second summer inputs said even chip outputs, and said second summer having as an output a second correlation signal;
said second even/odd correlator comprising
a single register having a second plurality of odd chip locations and a second plurality of odd chip locations and a second plurality of even chip locations for receiving chips of said third filtered signal,
a second plurality of odd chip multipliers, said odd chip locations of said second plurality of odd chip locations coupled to odd chip inputs of said second plurality of odd chip multipliers for multiplication by said odd chips of said chip sequence, said odd chip multipliers having second odd chip outputs;
a third summer having as third summer inputs said second odd chip outputs, and said third summer having a third correlation signal as an output,
a second plurality of even chip multipliers, said even chip locations of said second plurality of even chip locations coupled to even chip inputs of said second plurality of even chip multipliers for multiplication by said even chips of said chip sequence, said even chip multipliers having second even chip outputs;
and
a fourth summer having as fourth summer inputs said second even chip outputs, and said fourth summer having a fourth correlation signal as an output.

19 more elements

An apparatus for despreading a received continuous phase modulated spread spectrum signal comprising:

a power divider having as an input a received spread spectrum signal and having as outputs a first signal and a second signal, said first signal and said second signal being duplicates of one another,
means for demodulating said first signal into a real-I/imaginary-Q signal, said means comprising a first non-coherent local reference signal,
means for demodulating said second signal into an imaginary-I/real-Q signal, said means comprising a second non-coherent local reference signal having the same frequency as said first non-coherent local reference signal but phase offset therefrom by 90 degrees,
a first even/odd correlator for correlating said real-I/imaginary-Q signal and generating a real I correlation signal and an imaginary Q correlation signal,
a second even/odd correlator for correlating said imaginary-I/real-Q signal and generating an imaginary I correlation signal and a real Q correlation signal,
means for combining said real I correlation signal, said real Q correlation signal, said imaginary I correlation signal, and said imaginary Q correlation signal into a final correlation signal,
said first even/odd correlator comprising
a single register having a first plurality of odd chip locations and a first plurality of even chip locations for receiving chips of said real I/imaginary Q signals,
a plurality of I multipliers, said odd chip locations of said first plurality of odd chip locations coupled to I inputs of said plurality of I multipliers for multiplication by odd chips of a chip sequence, said I multipliers having first I outputs;
a first I summer having as first I summer inputs said first I outputs, and said first I summer having a real I correlation signal as an output,
a plurality of Q multipliers, said even chip locations of said first plurality of even chip locations coupled to Q inputs of said plurality of Q multipliers for multiplication by inverses of even chips of said chip sequence, said Q multipliers having first Q outputs;
and
a first Q summer having as first Q summer inputs said first Q outputs, and said first Q summer having an imaginary Q correlation signal as an output;
said second even/odd correlator comprising
a single register having a second plurality of odd chip locations and a second plurality of odd chip locations and a second plurality of even chip locations for receiving chips of said imaginary I/real Q signals,
a second plurality of I multipliers, said odd chip locations of said second plurality of odd chip locations coupled to I inputs of said second plurality of I multipliers for multiplication by said odd chips of said chip sequence, said I multipliers having second I outputs;
a second I summer having as second I summer inputs said second I outputs, and said second I summer having an imaginary I correlation signal as an output,
a second plurality of Q multipliers, said even chip locations of said second plurality of even chip locations coupled to Q inputs of said second plurality of Q multipliers for multiplication by said even chips of said chip sequence, said Q multipliers having second Q outputs;
and
a second Q summer having as second Q summer inputs said second Q outputs, and said second Q summer having a real Q correlation signal as an output.

17 more elements

A method comprising the steps of:

generating a CPM signal having a carrier frequency w.sub.0,
transmitting said CPM signal,
receiving said CPM signal,
splitting said received CPM signal into a first received CPM signal and a second received CPM signal,
generating a local cosine waveform and a local sine waveform in said receiver, each of said waveforms having substantially the same frequency, w.sub.1, said w.sub.1 frequency offset from said transmitter carrier signal frequency w.sub.0 by a variable phase shift .THETA.,
modulating said first received CPM signal by said local cosine waveform to obtain a first product signal,
modulating said second received CPM signal by said local sine waveform to yield a second product signal,
low pass filtering said first product signal to provide a first filtered signal,
low pass filtering said second product signal to provide a second filtered signal,
inputting said first filtered signal into a first even/odd correlator, said first even/odd correlator comprising a single register for receiving said first filtered signal, said register thereby containing a plurality of even and odd chips of said first filtered signal,
inputting said second filtered signal into a second even/odd correlator, said second even/odd correlator comprising a single register for receiving said second filtered signal, said register thereby containing a plurality of even and odd chips of said second filtered signal,
correlating said first filtered signal in said first even/odd correlator to generate a Real I correlation signal and an Imaginary Q correlation signal, said odd chips of said first filtered signal being correlated with odd chips of a chip sequence and said even chips of said first filtered signal being correlated with inverses of even chips of said chip sequence,
correlating said second filtered signal in said second even/odd correlator to generate an Imaginary I correlation signal and a Real Q correlation signal, said odd chips of said second filtered signal being correlated with said odd chips of said chip sequence and said even chips of said second filtered signal being correlated with said even chips of said chip sequence,
summing said Real I correlation signal and said Real Q correlation signal to obtain a Real correlation signal,
summing said Imaginary I correlation signal and said Imaginary Q correlation signal to obtain an Imaginary correlation signal,
squaring each of said Real correlation and Imaginary correlation signals,
summing said squared Real and Imaginary correlation signals to obtain a unified correlation signal, and
computing a square root of said unified correlation signal.

15 more elements

Dependencies are inferred from the claim text.

Description28,711 words

Summary1,524 words

#The field of this invention relates to spread spectrum communication and, more particularly, to transmitting and receiving continuous phase modulated (CPM) signals such as spread spectrum signals.

#Spread spectrum is a type of signal modulation that spreads a signal to be transmitted over a bandwidth that substantially exceeds the data-transfer rate, hence the term "spread spectrum". In direct sequence spread spectrum, a data signal is modulated with a pseudo-random chip sequence; the encoded spread spectrum signal is transmitted to the receiver which despreads the signal. Several techniques are available for the transmitter to modulate the data signal, including biphase shift keying (BPSK) and continuous phase modulated (CPM) techniques. Minimum shift keying (MSK) is a known variation of CPM.

#In despreading a spread spectrum signal, the receiver produces a correlation pulse in response to the received spread spectrum signal when the received spread spectrum signal matches the chip sequence to a predetermined degree. Various techniques are available for correlating the received signal with the chip sequence, including those using surface acoustic wave (SAW) correlators, tapped delay line (TDL) correlators, serial correlators, and others.

Brief description of the drawings37 figures

#FIG. 1 is a block diagram of a spread spectrum communication transmitter and receiver as known in the art.

#FIG. 2 depicts a pattern of cells for use in spread spectrum communication.

#FIG. 3 is a graph of phase changes over time for an MSK signal.

Detailed description26,487 words

#FIG. 1 is a block diagram of a spread spectrum communication transmitter 101 and receiver 108 as known in the art.

#The spread spectrum transmitter 101 of FIG. 1 comprises an input port 102 for input data 103, a transmitter chip sequence generator 104, and a modulator 105. The transmitter 101 thereby transmits a spread spectrum signal 106 over a transmission channel 107. The transmission channel 107 may comprise an RF channel, but may also comprise other transmission media, such as modulated laser, ultrasound, or fluidic systems. The spread spectrum receiver 108 of FIG. 1 comprises a receiver chip sequence generator 110, a demodulator 111, and an output port 112 for generating output data 113. In the FIG. 1 system, a single chip sequence, which appears essentially random to others not knowing the spreading code upon which it is based, may be identically generated by both the transmitter generator 104 and the receiver generator 110. An extensive discussion of spread spectrum communication, spreading codes, and chip sequences may be found in R. Dixon, Spread Spectrum Systems with Commercial Applications (J. Wiley & Sons, 3d ed. 1994).

#FIG. 2 depicts a pattern of cells for use in spread spectrum communication.

Facts

Application

08/486,824Filed 7 Jun 1995 · continuation in part

Priority

9 Sep 1994

Granted

5 Oct 1999

Term ended

5 Oct 2016

Estimated · how

Pre-1995 term; greater of 17 years from grant or 20 years from filing when eligible. Maintenance-fee lapses, terminal disclaimers and statutory extensions have not been checked. The continuity chain may be incomplete; this is not an enforceability determination.

Classification12 codes

H04B 1/707
Spread spectrum techniques: using direct sequence modulation
H04B 1/708
With code phase acquisition: parallel implementation
H04J 13/10
Code division multiplex systems: code generation
H04L 27/2014
In which the phase change within each symbol period is constrained: in which the phase changes in a piecewise linear manner during each symbol…

Method and apparatus for parallel noncoherent correlation of a spread spectrum signal

Life of this patent

Method and apparatus for parallel noncoherent correlation of a spread spectrum signal

Life of this patent

Life of this patent

Abstract

Drawings

Drawings

Claims14

Description28,711 words

Drawings

Classification12 codes

Life of this patent

Description28,711 words