US 5,359,625 A · Spread spectrum communication system particularly-suited for RF network communication

Abstract

Spread spectrum communication using direct sequences that approximate a swept frequency waveform in which successive square waves are formed by the chips making up the sequence, and in which the durations of the square waves extend over a plurality of chips, and in which the frequency of the square waves varies across at least a portion of the sequence. Information is encoded by varying the direction of the direct sequence, so that the sequence is transmitted as either a forward or a reverse frequency-swept sequence. The spectrum of the direct sequences is in a passband. The direct sequence biphase modulates a carrier (e.g., RF) to produce a spread-spectrum signal with two passbands centered about the frequency of the modulated carrier. Received signals are fed to a correlator having forward and reverse sequence outputs, the outputs of the correlator are independently tracked, and generally different sampling times are used for taking samples of the forward and reverse correlator outputs for purposes of making decoding decisions. The receiver uses a local oscillator for demodulation that is not synchronized with the local oscillator used for modulation in the transmitter. The overall phase of successive direct sequences is pseudorandomly varied to produce a more uniform spreading of energy across the frequency band. Dual level coding is used, in which a quality and value outputs from the lower level decoding are used to provide, in effect, a correlator for the higher level decoding. Both 0 and 90 degree matched filter sections are provided to make the correlator insensitive to phase shifts.

Claims57

Dependent claims

A method of transmitting data on a communication channel, comprising the steps of:

receiving a stream of digital signals for transmission on said communication channel, said digital signals having at least two possible values;
generating at least two different direct sequences each containing a plurality of chips, said chips being selected to approximate a swept frequency waveform in which successive square waves are formed by said chips, in which the durations of the square waves extend over a plurality of said chips, and in which the frequency of said square waves varies across at least a portion of said sequence;
encoding said digital signals by using different ones of said direct sequences to represent different values of said digital signals;
using said direct sequences to generate a direct sequence spread spectrum signal;
and
transmitting said spread spectrum signal across said channel.

3 more elements

A method of transmitting data on a communication channel, comprising the steps of:

receiving a stream of digital signals for transmission on said communication channel, said digital signals having at least two different values;
generating first and second spread spectrum signals, said first spread spectrum signal having the form of a frequency-swept spread spectrum signal in which frequency is swept in a first direction over at least a portion of said signal, and said second spread spectrum signal having the form of a frequency-swept spread spectrum signal in which frequency is swept in a second direction opposite the first direction over at least a portion of said signal;
encoding said digital signals by representing one said value of said digital signal using said first spread spectrum signal, and representing another said value of said digital signal using said second spread spectrum signal;
and
transmitting said spread spectrum signals across said channel.

2 more elements

Apparatus for transmitting data on a communication channel, comprising:

means for receiving a stream of digital signals for transmission on said communication channel, said digital signals having at least two different values;
means for generating first and second spread spectrum signals, said first spread spectrum signal having the form of a frequency-swept spread spectrum signal in which frequency is swept in a first direction over at least a portion of said signal, and said second spread spectrum signal having the form of a frequency-swept spread spectrum signal in which frequency is swept in a second direction opposite the first direction over at least a portion of said signal;
means for encoding said digital signals by representing one said value of said digital signal using said first spread spectrum signal, and representing another said value of said digital signal using said second spread spectrum signal;
and
means for transmitting said spread spectrum signals across said channel.

2 more elements

A method of receiving and decoding data that has been encoded and transmitted using forward and reverse swept frequency spread spectrum signals, so that the received signal consists of a succession of spread spectrum signals in which information is encoded as the difference in direction of sweep, so that different digital values are represented by different patterns of forward and reverse swept frequency signals, said method comprising the steps of:

receiving said stream of frequency swept spread spectrum signals;
passing said signals through a correlator having forward and reverse outputs, the forward output representing the correlation of a received signal to the forward swept spread spectrum signal, and the reverse output representing the correlation of a received signal to the reverse swept spread spectrum signal;
tracking the forward correlator output so that the forward correlator output is sampled at times when a received signal would be received if it was a forward swept signal;
tracking the reverse correlator output independently of the tracking of the forward correlator output so that the reverse correlator output is sampled at times when a received signal would be received if it was a reverse swept signal;
and
making decisions as to whether a received signal is a forward or reverse swept signal based on samples of the forward and reverse correlator outputs that are taken generally at different times.

3 more elements

Apparatus for receiving and decoding data that has been encoded and transmitted using forward and reverse swept frequency spread spectrum signals, so that the received signal consists a succession of spread spectrum signals in which information is encoded as the difference in direction of sweep, so that different digital values are represented by different patterns of forward and reverse swept frequency signals, said apparatus comprising:

means for receiving said stream of frequency swept spread spectrum signals;
means for passing said signals through a correlator having forward and reverse outputs, the forward output representing the correlation of a received signal to the forward swept spread spectrum signal, and the reverse output representing the correlation of a received signal to the reverse swept spread spectrum signal;
means for tracking the forward correlator output so that the forward correlator output is sampled at times when a received signal would be received if it was a forward swept signal;
means for tracking the reverse correlator output independently of the tracking of the forward correlator output so that the reverse correlator output is sampled at times when a received signal would be received if it was a reverse swept signal;
and
means for making decisions as to whether a received signal is a forward or reverse swept signal based on samples of the forward and reverse correlator outputs that are taken generally at different times.

3 more elements

A method of receiving and decoding data that has been encoded and transmitted using dual level spread spectrum modulation in which information is conveyed as superbits, and in which superbits are encoded as unique sequences of a plurality of subbits, each represented by a unique spread spectrum signal, said method comprising the steps of:

receiving a stream of spread spectrum signals;
passing said signals through a correlator configured to distinguish between said unique spread spectrum signals representing said subbits;
sampling the output of the correlator, and determining therefrom the values of a succession of subbits;
determining a quality indicator from the strength of the sampled correlator output used in determining the value of a subbit;
combining the value and quality indicators for a succession of subbits in decoding the superbits.

2 more elements

Apparatus for receiving and decoding data that has been encoded and transmitted using dual level spread spectrum modulation in which information is conveyed as superbits, and in which superbits are encoded as unique sequences of a plurality of subbits, each represented by a unique spread spectrum signal, said apparatus comprising:

means for receiving a stream of spread spectrum signals;
means for passing said signals through a correlator configured to distinguish between said unique spread spectrum signals representing said subbits;
means for sampling the output of the correlator, and determining therefrom the values of a succession of subbits;
means for determining a quality indicator from the strength of the sampled correlator output used in determining the value of a subbit;
means for combining the value and quality indicators for a succession of subbits in decoding the superbits.

2 more elements

Dependencies are inferred from the claim text.

Spread spectrum communication system particularly-suited for RF network communication

Life of this patent

Spread spectrum communication system particularly-suited for RF network communication

Life of this patent

Abstract

Claims57