Spread spectrum communications system

- Pitway Corporation

A spread spectrum communication system for direct sequence transmission of digital information having a modulation format which is particularly suitable for indoor communication within residential, office and industrial structures. The modulation format combines BPSK or MSK spreading with FM carrier modulation by data bits and a carrier frequency shift whose magnitude is related to both a chip rate and a spreading sequence length. The carrier, chip clock and data clock are all synchronous and the sequence length is an integral submultiple of the bit length. The system reduces the frequency error between the transmitter chip clock and the receiver chip clock to permit the elimination of a code phase tracking loop in the receiver to reduce the receiver complexity. The receiver has an extended dynamic range which makes possible the reception of very strong signal without an automatic gain control loop (AGC) as well as reducing the time needed for code phase acquisition. The transmission system is highly resistant to CW jamming and short distance multipath effects.

Latest Pitway Corporation Patents:

Skip to:  ·  Claims  ·  References Cited  · Patent History  ·  Patent History

Claims

1. A method of transmitting digital data, comprising the steps of:

a) generating a radio frequency carrier;
b) modulating the frequency of said carrier by data bits assembled in data packets of predetermined format;
c) spreading said carrier during a transmission time, which a predetermined PN sequence having a period Ts related to a bit time Tb
where
N being an integer >1 Ts is a pseudo noise (PN) sequence period;

2. The method according to claim 1, further comprising the steps of:

d) receiving the transmitted data; and
e) multiplying said transmitted spread carrier in a receiver by a locally generated predetermined PN sequence, for collapsing the bandwidth of the received spread carrier when the local PN sequence phase in agreement with the sequence phase imposed on the received spread carrier thereby spreading any jamming signals which are received along with the desired transmitted signal into many components separated by 1/Ts intervals and reduced in amplitude by the spreading function.

3. The method according to claim 1, wherein step c) generates spectral components of the spread carrier that are separated by a frequency interval greater than 1/Ts.

5. The method according to claim 4, wherein the data frequency is synchronously derived from said one frequency source.

6. The method according to claim 1, wherein said predetermined data packet format comprises a preamble period during which said carrier frequency is equal to a nominal frequency and a data period during which the carrier frequency is modulated by said data bits.

7. A transmitter for transmitting digital data comprising:

a) carrier frequency generator means for generating a carrier frequency signal;
b) modulator means for modulating said carrier by data bits;
c) pseudo random sequence generator means for generating a predetermined PN sequence;
d) carrier spread means for spreading power of said carrier frequency by said pseudo noise sequence, said spread carrier generating spectral components separated by a frequency interval greater than 1/Ts where Ts is a pseudo noise (PN) sequence period.

8. The transmitter according to claim 7 wherein Ts is related to the bit time Tb where

9. The transmitter according to claim 7 further including a phase lock loop means for deriving said first carrier frequency from a crystal reference oscillator.

12. The transmitter according to claim 7 wherein said transmitter further includes means for generating said formated data packet for modulating said carrier frequency, said data packet comprising a preamble period during which the carrier frequency is equal to a nominal value and data period during which the carrier frequency is deviated according to the corresponding data bit values.

13. A receiver for a spread spectrum signal comprising:

a) a wide band receiving means for receiving a spread carrier radio signal for generating a spread carrier electric signal;
b) means for generating a predetermined PN (pseudo noise) sequence;
c) multiplying means coupled to said receiving means and said generating means for multiplying said spread carrier electrical signal by said predetermined PN sequence, for collapsing a bandwidth of the received spread carrier when the local PN sequence phase is in agreement with the sequence phase imposed on the received spread carrier by a transmitter means, thereby spreading any jamming signals which are received along with the transmitted spread signal into many components separated by 1/Ts intervals and reduced in amplitude by the spreading function;
d) narrow band FM receiver means coupled to an output of said multiplying means for recovering data and having a bandwidth less than 1/(2*Ts) where Ts is at period of said PN sequence.

16. The receiver according to claim 14 wherein each of said receiver means further includes means for automatic frequency control (AFC) and means for activating said AFC upon synchronization of a phase of said PN sequence with a phase of the PN sequence modulating said receiver signal.

17. The receiver according to claim 13 wherein each of said receiver means further includes signal strength indicator means to detect power of said received signal.

18. A system for transmitting and receiving digital data, comprising:

a) means for generating a radio frequency carrier;
b) means for modulating the frequency of said carrier by data bits assembled in data packets of predetermined format;
c) means for spreading said carrier at said first and said second frequency, during a transmission time, by a predetermined PN sequence having a period Ts related to a bit time Tb
where
N being an integer>1 Ts is a PN (pseudo noise) sequence period;
d) means for receiving the transmitted data; and
e) means for multiplying said transmitted spread carrier in said receiver means by a locally generated predetermined PN sequence, for collapsing the bandwidth of the received spread carrier when the local PN sequence phase in agreement with the sequence phase imposed on the received spread carrier;
f) narrow band FM receiver means coupled to an output of said multiplying means for recovering data and having a bandwidth less than 1/(2*Ts).

19. The system according to claim 18, wherein said means for spreading said carrier generates spectral components of the spread carrier that are separated by a frequency interval greater than 1/Ts.

21. The system according to claim 20, wherein the data frequency is synchronously derived from said one frequency source.

23. The system according to claim 18, wherein said predetermined data packet format comprises a preamble period during which said carrier frequency is equal to a nominal frequency and a data period during which the carrier frequency is modulated by said data bits.

Referenced Cited
U.S. Patent Documents
2341649 February 1944 Peterson
2354827 August 1944 Peterson
2539797 January 1951 Smith
2624834 January 1953 Atwood
2636115 April 1953 Peterson et al.
3164773 January 1965 Daniel
3728529 April 1973 Kartchner et al.
3761817 September 1973 Kaltschmidt et al.
3805192 April 1974 Ocnaschek et al.
3947769 March 30, 1976 Rousos et al.
3953798 April 27, 1976 Sjostrand et al.
4206462 June 3, 1980 Rabow et al.
4355399 October 19, 1982 Timor
4583231 April 15, 1986 Puckette
4774715 September 27, 1988 Messenger
5121407 June 9, 1992 Partyka et al.
Foreign Patent Documents
0131458 January 1985 EPX
0199410 October 1986 EPX
2450727 November 1979 DDX
Other references
  • J. Fischer et al, "Wide-Band Packet Radio for Muiltipath Environments"; IEEE Trans. on Comms.; vol. 36, No. 5; May 1988; pp. 564-576. A. Saleh et al, "A Statistical Model for Indoor Multipath Propagation"; IEEE Journ. on Selected Areas in Comms.; vol. SAC-5, No. 2; Feb. 1987; pp. 128-137. S. Patsiokas et al, "Propagation of Radio Signals Inside Buildings At 150, 450, and 850 MHz"; IEEE, 1986. R. Murray et al, "815 MHz Radio Attenuation Measured Within a Commercial Building"; IEEE, 1986, pp. 209-212. S. Alexander, "Characterizing Building for Propagation at 900 MHZ"; Electronics Letters; Sep. 29, 1983; vol. 19, No. 2; p. 860. D. Devasirvatham, "A Comparison of Time Delay Spread and Signal Level Measurements within Two Dissimilar Office Buildings"; IEEE Trans. on Antis and Prop.; vol. AP-35; No. 3; Mar. 1987; pp. 319-324. S. Alexander, "Radio Propagation Within Buildings at 900 MHz"; Electronics Letters; Oct. 14, 1982; vol. 18, No. 21; pp. 913-914. Jee Journal of Electronic Engineering, vol. 25, No. 25, Jul. 1988, Tokyo JP "Weak Signal Transceiver Uses Asynchronous Spread Spectrum Communication Method", pp. 102-104.
Patent History
Patent number: RE35650
Type: Grant
Filed: Jun 15, 1995
Date of Patent: Nov 4, 1997
Assignee: Pitway Corporation (Syosset, NY)
Inventors: Andrzej Partyka (Bediminster, NJ), Lee F. Crowley (Farmingville, NY)
Primary Examiner: Bernarr E. Gregory
Law Firm: Ladas & Parry
Application Number: 8/490,955
Classifications
Current U.S. Class: 375/206; Automatic Frequency Control (375/344); Plural Carrier Frequencies (380/34)
International Classification: H04L 2730;