Self-synchronous spread spectrum transmitter/receiver

• US 4,912,722 A
• Filed: 09/20/1988
• Issued: 03/27/1990
• Est. Priority Date: 09/20/1988
• Status: Expired due to Term

• Current Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation), Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: AT&T, Inc.
• Inventors: Carlin, James W.
• Primary Examiner(s): CANGIALOSI, SALVATORE A
• Application Number:
  US07/246,724
• Time in Patent Office: 553 Days
• Field of Search: 375/1, 380/21, 380/34
• US Class Current: 375/146
• CPC Class Codes: H04B 1/70718 with asynchronous demodulation, i.e. not requiring code synchronisation

Abstract

The present invention relates to a self-synchronous spread spectrum transmitter and an associated remote spread spectrum receiver which communicate with each other by the transmission of both (1) a spread spectrum Pseudo Noise Code (PNC) sequence signal, and (2) a combined PNC sequence plus the data information (PNC+data) signal. The two signals can be transmitted concurrently using either different frequency bands or on a quadrature carrier; or the two signals can be transmitted with a time offset between signals. At the receiver the PNC and the PN+data signals are separately recovered for the case of the concurrent transmission techniques, and directly mixed to despread the received signal and recover the data signal at baseband. For the time offset technique, the delay provided in one of the time offset signals is again introduced to the previously delayed signal, and the delayed and undelayed signal portions of the received combined signal are directly mixed and then low pass filtered to recover the data signal. Such techniques eliminate the necessity for providing PNC acquisition and tracking circuits in associated spread spectrum transmitter and receiver combinations.

Claims

1. A spread spectrum transmitter comprising:

a generator for generating a pseudo-noise code sequence;

combining means for combining the pseudo-noise code sequence from the generator and a data information signal provided as an input to the transmitter to generate a spread spectrum data information output signal;

a modulator/combiner for separately modulating each of (1) the spread spectrum data information output signal from the combining means and (2) the pseudo-noise code sequence from the generator to place both modulated signals into a predetermined synchronous multiplexing relationship to each other so that each signal is capable of being simultaneously received, separated and multiplied together to provide self-synchronous instantaneous despreading at a remote receiver, and combining the two modulated signals into a multiplexed modulator/combiner output signal; and

means for transmitting the multiplexed output signal from the modulator/combiner in an appropriate frequency band to a remote receiver.

2. A spread spectrum transmitter according to claim 1 wherein the predetermined multiplexing relationship is a frequency division multiplexed relationship and the modulator/combiner comprises:

modulating means for modulating a first predetermined carrier with the spread spectrum data information output signal from the combining means to generate a modulated spread spectrum data information output signal disposed in a first frequency band, and for separately modulating a second predetermined carrier with the pseudo-noise code sequence from the generator to generate a modulated pseudo-noise code sequence output signal in a second frequency band which does not overlap the first frequency band; and

a combiner for combining the modulated spread spectrum data information output signal and the modulated pseudo-noise code sequence output signal to generate the modulator/combiner frequency division multiplexed output signal.

3. A spread spectrum transmitter according to claim 2 wherein the modulating means of the modulator/combiner comprises:

generating means for generating both a first predetermined frequency output signal, and a second predetermined frequency output signal which includes a different frequency band from the first frequency output signal;

means for mixing the first and second predetermined frequency output signals from the generating means to produce (1) a first sideband signal corresponding to the first predetermined carrier, and (2) a second sideband signal corresponding to the second predetermined carrier signal;

mixing means for (1) mixing the first predetermined carrier with the spread spectrum data information output signal from the combining means to generate the modulated spread spectrum data information output signal, and (2) mixing the second predetermined carrier with the pseudo-noise code sequence from the generator to generate the modulated pseudo-noise code sequence output signal.

4. A spread spectrum transmitter according to claim 1 wherein the predetermined multiplexing relationship is a quadrature signal relationship, the modulator/combiner comprising:

carrier generating means for generating from a predetermined carrier a separate in-phase and quadrature carrier component;

mixing means for (1) mixing either one of the spread spctrum data information signal and the pseudo-noise code sequence with the in-phase carrier component to provide an in-phase output signal, and (2) mixing the other one of the spread spectrum data signal and the pseudo-noise code sequence with the quadrature carrier component to provide a quadrature output signal; and

a combiner for combining the in-phase and quadrature output signals from the mixing means to generate the multiplexed modulator/combiner output signal.

5. A spread spectrum transmitter according to claim 1 wherein the predetermined multiplexing relationship is a time division multiplexed relationship, the modulator/combiner comprising:

delay means for delaying only one of the spread spectrum data information output signal from the combining means and the pseudo-noise code sequence from the generator by a predetermined amount of time;

a generator for generating a predeterming carrier;

means for separately modulating the spread spectrum data information signal and the pseudo-noise code sequence signal, subsequent to a delay introduced to one of the signals by the delay means, to generate a modulated spread spectrum data information output signal and a modulated pseudo-noise code sequence output signal, respectively; and

a combiner for combining the modulated spread spectrum data information output signal and the modulated pseudo-noise code sequence output signal to generate the modulator/modulator output signal.

6. A spread spectrum transmitter according to claim 5 wherein

the predetermined amount of delay time provided by the delay means is equal to KT_Chip, where K is an integer and T_Chip is the chip rate associated with the pseudo-noise code sequence.

7. A method of transmitting signals from a transmitter in a spread spectrum communication system, the method comprising the steps of:

(a) generating a predetermined pseudo-noise code sequence signal;

(b) combining the pseudo-noise code sequence signal with a data information input signal received by the transmitter to generate a spread spectrum data information output signal;

(c) separately modulating each of (1) the spread spectrum data information output signal generated in step (b), and (2) the pseudo-noise code sequence signal generated in step (a) to generate a modulated spread spectrum data information output signal and a modulated pseudo-noise code sequence output signal, respectively, which signals are disposed in a predetermined synchronous multiplexing relationship with each other;

(d) combining the modulated spread spectrum data information signal and the modulated pseudo-noise code sequence signal from step (c) to generate a multiplexed output transmission signal wherein each modulated signal is capable of being simultaneous received at a remote receiver to provide self-synchronous instantaneous despreading at the remote receiver; and

(e) transmitting the multiplexed output transmission signal from step (d) to the remote receiver in an appropriate frequency band.

8. The method according to claim 7 wherein in performing step (c), performing the steps of:

(c1) modulating a first predetermined carrier with the spread spectrum data information signal to generate the modulated spread spectrum data information output signal disposed a first frequency band; and

(c2) modulating a second predetermined carrier with the pseudo-noise code sequence to generate the modulated pseudo-noise code sequence output signal disposed in a second frequency band which is different from the first frequency band.

9. The method according to claim 7 wherein in performing step (c), performing the steps of:

(c1) generating a first and a second sideband carrier signal of a predetermined carrier frequency;

(c2) modulating the first sideband carrier signal with the spread spectrum data information signal to generate the modulated spread spectrum data information output signal; and

(c3) modulating the second sideband carrier signal with the pseudo-noise code sequence to generate the modulated pseudo-noise code sequence output signal.

10. The method according to claim 7 wherein in performing step (c), performing the steps of:

(c1) generating an in-phase and a quadrature component of a predetermined carrier signal;

(c2) modulating one of the in-phase and quadrature components of the predetermined carrier signal with the spread spectrum data information signal to generate the modulated spread spectrum data information output signal; and

(c3) modulating the other one of the in-phase and quadrature components of the predetermined carrier signal, not used in step (c2), with the pseudo-noise code sequence signal to generate the modulated pseudo-noise code sequence output signal.

11. The method according to claim 7 wherein in performing step (c), performing the steps of:

(c1) delaying only one of the spread spectrum data information signal and the pseudo-noise code sequence by a predetermined amount of time; and

(c2) separately modulating a predetermined carrier with each of (1) the spread spectrum data information signal and (2) the pseudo-noise code sequence signal, subsequent to any delay imposed in one of the signals in step (c1), to provide the modulated spread spectrum data information output signal and the modulated pseudo-noise code sequence output signal, respectively.