RF modem utilizing saw resonator and correlator and communications transceiver constructed therefrom

• US 6,535,545 B1
• Filed: 10/15/1999
• Issued: 03/18/2003
• Est. Priority Date: 10/15/1999
• Status: Expired due to Fees

• Current Assignee: Vishay Intertechnology Incorporated
• Original Assignee: RF Waves, Ltd.
• Inventors: Ben-Bassat, David, Lerner, Moshe
• Primary Examiner(s): CORRIELUS, JEAN B
• Application Number:
  US09/419,824
• Time in Patent Office: 1,250 Days
• Field of Search: 375/130,140-143,146,147,150,151,153,219,222
• US Class Current: 375/142
• CPC Class Codes: H04B 1/70712 with demodulation by means of convolvers, e.g. of the SAW type SAW convolvers in general G06G7/195
• CPC Class Codes: H04B 1/7093 Matched filter type
• CPC Class Codes: H04L 25/03834 using pulse shaping
• CPC Class Codes: H04L 25/06 Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection
• CPC Class Codes: H04L 25/4902 Pulse width modulation; Pulse position modulation
• CPC Class Codes: H04L 27/02 Amplitude-modulated carrier systems, e.g. using on-off keying; Single sideband or vestigial sideband modulation H04L27/32 takes precedence
• CPC Class Codes: H04L 7/043 Pseudo-noise [PN] codes variable during transmission synchronisation of spread spectrum receivers H04B1/69

Abstract

A bidirectional direct sequence spread spectrum half-duplex RF modem which can be applied to transmit and receive numerous types of analog and digital pulse modulation. The modem incorporates two different SAW devices fabricated on a single monolithic substrate. A first SAW device is used as a resonator in the oscillator circuit while a second SAW device is used as the correlator for transmit and receive operations. The RF modem operates as an analog or digital pulse transmitter and receiver and is adapted to be generic and versatile enough to be used in many different types of data communication systems, such as OOK, PWM and PPM. The RF modem can be used as the physical (PHY) layer in a layered communication system such as the ISO OSI communication stack. In an alternative embodiment, the transmission bit rate is increased using a plurality of correlators wherein each is configured with a unique function (i.e., code) that is orthogonal with all other functions.

Claims

1. A direct sequence spread spectrum radio frequency (RF) modem, comprising:

an oscillator having a resonator and adapted to generate an oscillator signal, the center frequency of said oscillator determined by the center frequency of said resonator;

switching means for gating said oscillator signal in accordance with input data to be transmitted so as to generate a series of pulses;

spreading means for spreading the pulses output of said switching means with a spreading code sequence waveform so as to generate a spread spectrum transmission signal;

means for transmitting said spread spectrum transmission signal;

means for receiving said spread spectrum transmission signal;

correlator means adapted to de-spread said spread spectrum transmission signal in accordance with said code sequence so as to generate a correlator signal;

detection means for detecting an envelope of said correlator signal so as to generate a detection signal; and

decision means for applying a threshold to said detection signal so as to generate an output data signal therefrom.

2. The modem according to claim 1, wherein said resonator comprises a surface acoustic wave (SAW) resonator.

3. The modem according to claim 1, wherein said switching means comprises a plurality of switches coupled in series and operative to provide a high level of electrical isolation.

4. The modem according to claim 3, wherein said plurality of switches comprises a plurality of Field Effect Transistor (FET) switches.

5. The modem according to claim 1, wherein said spreading means comprises a surface acoustic wave (SAW) matched filter/correlator.

6. The modem according to claim 1, wherein said spreading code sequence comprises a Barker code series sequence.

7. The modem according to claim 6, wherein said Barker code series sequence comprises a 13-chip Barker sequence {1, 1, 1, 1, 1, −

1, −

1, 1, 1, −

1, 1, −

1, 1}.

8. The modem according to claim 1, wherein said means for transmitting comprises:

an output amplifier for amplifying said spread spectrum transmission signal; and

an antenna coupled to the output of said output amplifier.

9. The modem according to claim 1, wherein said means for receiving comprises:

an antenna adapted to receive said spread spectrum transmission signal;

a band pass filter coupled-to said antenna; and

a low noise amplifier coupled to the output of said band pass filter.

10. The modem according to claim 1, wherein said correlator means comprises a surface acoustic wave (SAW) matched filter/correlator.

11. The modem according to claim 10, wherein said SAW matched filter/correlator is configured with a Barker code series sequence.

12. The modem according to claim 11, wherein said Barker code series sequence comprises a 13-chip Barker sequence {1, 1, 1, 1, 1, −

1, −

1, 1, 1, −

1, 1, −

1, 1}.

13. The modem according to claim 1, wherein said spreading means and said correlator means share a surface acoustic wave (SAW) correlator adapted to be used half duplex for transmission and receiving.

14. The modem according to claim 1, wherein:

said resonator means comprises a surface acoustic wave (SAW) resonator;

said spreading means and said correlator means share a surface acoustic wave (SAW) correlator adapted to be used half duplex for transmission and receiving; and

wherein said SAW resonator and said SAW correlator are constructed on the same monolithic substrate.

15. The modem according to claim 1, wherein said detection means comprises:

a slow peak detector adapted to generate a slowly varying reference signal; and

a fast peak detector adapted to track the envelope of said correlator signal and to generate said detection signal therefrom.

16. The modem according to claim 1, wherein said decision means is adapted to generate a binary output signal in accordance with said detection signal applied against said threshold.

17. The modem according to claim 16, wherein said detection means is adapted to generate said threshold dynamically in accordance with said correlator signal.

18. A method of modulating and demodulating a direct sequence spread spectrum signal, said method comprising the steps of:

generating an oscillator signal utilizing a resonator wherein the frequency of oscillation is determined by the center frequency of said resonator;

gating said oscillator signal in accordance with input data to be transmitted so as to generate a series of pulses;

spreading said pulses utilizing a spreading code sequence waveform so as to generate a spread spectrum transmission signal;

transmitting said spread spectrum transmission signal;

receiving said spread spectrum transmission signal;

de-spreading said spread spectrum transmission signal in accordance with said code sequence so as to generate a correlator signal;

detecting an envelope of said correlator signal so as to generate a detection signal; and

applying a threshold to said detection signal so as to generate an output data signal therefrom.

19. A direct sequence spread spectrum radio frequency (RF) modem, comprising:

an oscillator having a resonator and adapted to generate an oscillator signal, the center frequency of said oscillator determined by the center frequency of said resonator;

a plurality of N transmit/receive circuits, each said transmit/receive circuit comprising;

switching means for gating said oscillator signal in accordance with input data to be transmitted so as to generate a series of pulses;

spreading means for spreading the pulses output of said switching means with a spreading code sequence waveform so as to generate a spread spectrum transmission signal;

correlator means adapted to de-spread a spread spectrum receive signal in accordance with said code sequence so as to generate a correlator signal;

detection means for detecting an envelope of said correlator signal so as to generate a detection signal; and

decision means for applying a threshold to said detection signal so as to generate an output data signal therefrom;

wherein the correlator in each transmit/receive circuit is configured with a unique function substantially orthogonal to functions in other correlators;

means for combining and transmitting the N spread spectrum transmission signals generated by said N transmit/receive circuits as a combined spread spectrum transmission signal;

means for receiving and splitting said combined spread spectrum transmission signal into N spread spectrum receive signals; and

wherein N is a positive integer.

20. The modem according to claim 19, wherein said resonator comprises a surface acoustic wave (SAW) resonator.

21. The modem according to claim 19, wherein said switching means comprises a plurality of switches coupled in series and operative to provide a high level of electrical isolation.

22. The modem according to claim 21, wherein said plurality of switches comprises a plurality of Field Effect Transistor (FET) switches.

23. The modem according to claim 19, wherein said spreading means comprises a surface acoustic wave (SAW) matched filter/correlator.

24. The modem according to claim 19, wherein said spreading code sequence comprises a Barker code series sequence.

25. The modem according to claim 19, wherein said spreading code sequence comprises a linear FM code.

26. The modem according to claim 19, wherein said means for transmitting comprises:

an output amplifier for amplifying said combined spread spectrum transmission signal; and

an antenna coupled to the output of said output amplifier.

27. The modem according to claim 19, wherein said means for receiving comprises:

an antenna adapted to receive said spread spectrum transmission signal;

a band pass filter coupled to said antenna; and

a low noise amplifier coupled to the output of said band pass filter.

28. The modem according to claim 19, wherein said correlator means comprises a surface acoustic wave (SAW) matched filter/correlator.

29. The modem according to claim 28, wherein said SAW matched filter/correlator is configured with a Barker code series sequence.

30. The modem according to claim 19, wherein said spreading means and said correlator means in each transmit/receive circuit share a surface acoustic wave (SAW) correlator adapted to be used half duplex for transmission and receiving.

31. The modem according to claim 19, wherein:

said resonator means comprises a surface acoustic wave (SAW) resonator;

each said spreading means and each said N correlator means share a surface acoustic wave (SAW) correlator adapted to be used half duplex for transmission and receiving; and

wherein said SAW resonator and said N SAW correlators are constructed on the same monolithic substrate.

32. The modem according to claim 19, wherein said detection means comprises:

a slow peak detector adapted to generate a slowly varying reference signal; and

a fast peak detector adapted to track the envelope of said correlator signal and to generate said detection signal therefrom.

33. The modem according to claim 19, wherein said decision means is adapted to generate a binary output signal in accordance with said detection signal applied against said threshold.

34. The modem according to claim 33, wherein said detection means is adapted to generate said threshold dynamically in accordance with said correlator signal.

35. The modem according to claim 19, wherein said means for combining the N spread spectrum transmission signals comprises an RF power combiner splitter.

36. The modem according to claim 19, wherein said means for splitting said combined spread spectrum signal comprises an RF power combiner splitter.

37. A method of modulating and demodulating N direct sequence spread spectrum signals, each direct sequence spread spectrum signal associated with one of N channels, said method comprising the steps of:

generating N oscillator signals utilizing a resonator wherein the frequency of oscillation is determined by the center frequency of said resonator;

for each channel;

gating each oscillator signal in accordance with input data for the N^th channel to be transmitted so as to generate a series of pulses;

spreading said pulses utilizing a spreading code sequence waveform so as to generate a spread spectrum transmission signal, said spreading code sequence waveform for the N^th channel substantially orthogonal with the spreading code sequence waveforms of all other channels;

de-spreading a spread spectrum transmission receive signal in accordance with said code sequence so as to generate a correlator signal;

detecting an envelope of said correlator signal so as to generate a detection signal;

applying a threshold to said detection signal so as to generate an output data signal for the N^th channel therefrom;

combining and transmitting the N spread spectrum transmission signals as a combined spread spectrum transmission signal;

receiving and splitting said combined spread spectrum transmission signal into N spread spectrum receive signals; and

wherein N is a positive integer.