WO1990010982A1 - Systeme de communications a spectre etendu employant un signal de randomisation - Google Patents

Systeme de communications a spectre etendu employant un signal de randomisation Download PDF

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Publication number
WO1990010982A1
WO1990010982A1 PCT/US1990/000783 US9000783W WO9010982A1 WO 1990010982 A1 WO1990010982 A1 WO 1990010982A1 US 9000783 W US9000783 W US 9000783W WO 9010982 A1 WO9010982 A1 WO 9010982A1
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WO
WIPO (PCT)
Prior art keywords
signal
chip
frequencies
randomizing
range
Prior art date
Application number
PCT/US1990/000783
Other languages
English (en)
Inventor
Alan Pate
Original Assignee
Hillier Technologies Limited Partnership
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hillier Technologies Limited Partnership filed Critical Hillier Technologies Limited Partnership
Publication of WO1990010982A1 publication Critical patent/WO1990010982A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J13/00—Code division multiplex systems
    • H04J13/0007—Code type
    • H04J13/0022—PN, e.g. Kronecker
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J13/00—Code division multiplex systems
    • H04J13/10—Code generation

Definitions

  • the present invention relates to methods and apparatus for spread-spectrum information transmission.
  • a transmission signal such as a radio frequency carrier signal is simply modulated with the information to be transmitted. This modulation causes some spreading of the power in the carrier signal over a range of frequencies. However, the major portion of the power remains concentrated within relatively narrow bands of frequencies.
  • the power of the transmission signal is spread over a bandwidth greater than that required to carry the information.
  • the information to be transmitted is encoded according to one or more predetermined spreading or “chipping" codes so that each bit value in the series of information bit value to be sent is represented by a plurality of bit values, commonly referred to as "chip" values in a chip value signal.
  • chips are provided at a substantially higher chip frequency.
  • the transmission signal is modulated with the chip value signal, thereby impressing both the original information bits and the spreading code on the transmission signal.
  • the transmission signal is demodulated to recover a base band signal corresponding substantially to the chip value signal.
  • the chip value signal is then decoded by applying a despreading scheme inverse to the spreading scheme used in the transmitter, thereby recovering the original information bit signal.
  • Spread spectrum communication systems provide several significant benefits. They are distinctly less sensitive to interference such as that caused by random noise signals or by willful jamming. Further, such systems have substantial resistance to loss of information caused by multipath interference. Additionally, a receiver arranged to decode information based upon one code will provide substantial immunity against unwanted reception of information encoded according to a different code.
  • the '365 publication discloses one system in which wall-mounted light switches are not connected directly to the building wiring system. Instead, a small battery powered spread-spectrum transmitter is provided at each wall switch, and a corresponding receiver is provided at each lamp or other appliance to be controlled. Control signals are sent from the wall switch to the appliance via free space radio frequency communication. This markedly reduces the cost of system installation. In a system of this nature, the cost of the receivers and transmitters is significant.
  • the '365 publication therefore discloses particularly effective low-cost spreading and despreading devices, which, when coupled with radio frequency modulation and demodulation components, provide effective, low-cost spread-spectrum transmitters and receivers.
  • the direct sequence devices disclosed as preferred embodiments in the aforementioned publication can operate with spreading code sequences of substantially any length or number of chips per bit, the cost of the spreading and despreading components varies directly with the length of the spreading code sequence.
  • the most preferred embodiments disclosed in the this publication utilize a spreading code sequence of about 15 chips per bit. Such a spreading code sequence is markedly shorter than the typical spreading codes of 1000 or more chips per bit utilized in sophisticated, high-cost military and aerospace applications. Even with a relatively short, 15-bit code, the systems disclosed in the '365 publication provide sufficient immunity from interference and accidental reception of unwanted signals to permit their use in applications such as building electric power wiring controls and the like.
  • a transmitter for use in a spread spectrum communication system.
  • a transmitter according to this aspect of the present invention includes spreading code means for providing a spreading code and transmission means for providing a transmission signal and impressing both the information to be transmitted and the spreading code on the transmitted signal so that the information is carried by one or more active components of the transmission signal.
  • the transmitter further includes means for providing a randomizing signal varying in a substantially random manner with time within a randomizing signal range of frequencies substantially different from the frequency of any active, information- bearing component in the transmission signal.
  • the transmission means is arranged to impress the randomizing signal on the transmission signal along with the spreading code and the information.
  • the spreading code means includes means for encoding a series of information bits to be transmitted according to a predetermined spreading code to form a series of chip values wherein each information bit is represented by a plurality of chip values and providing a chip value signal including this series of chip values at a predetermined chip frequency.
  • the chip frequency component carries the information.
  • the randomizing signal range of frequencies is substantially different from the chip frequency.
  • the transmission means desirably includes means for modulating the transmission signal with the chip value signal and with the randomizing signal.
  • the transmission signal may be a radio frequency signal and the randomizing signal range of frequencies may be a range of frequencies substantially lower than the chip frequency, typically below about one-tenth of the chip frequency and preferably lower than about one fiftieth of the chip frequency.
  • the chip frequency may be between about 500 KHz and about 2 MHz, whereas the randomizing signal range of frequencies may be a range of frequencies below about 20 KHz.
  • the spreading code desirably is a relatively short sequence code, such that each information bit is represented by about 50 or fewer, more preferably about 30 or fewer and most preferably about 15 chips.
  • the added modulation introduced by the randomizing signal causes additional dispersion of the power in the transmitted signal over the frequency spectrum.
  • introduction of the randomizing signal provides a more uniform power distribution and effectively eliminates any remaining power concentrations or peaks within particular narrow frequency bands.
  • the randomizing signal can be introduced at the transmitter by very simple circuit elements which do not add appreciably to the cost of the transmitter.
  • the randomizing signal consists of frequencies substantially different from the frequencies carrying information in the transmission signal, and preferably differing from any active frequency by one or more orders of magnitude, the randomizing signal can be separated from the desired signal at the receiver by circuits which are also relatively simple and economical.
  • a further aspect of the present invention provides a receiver.
  • the receiver includes demodulation and despreading means for receiving and demodulating a transmitted signal carrying information and a predetermined spreading code and stripping out the spreading code.
  • the receiver further includes means for rejecting signals within a predetermined randomizing signal range of frequencies different from any active frequency carrying information in the transmitted signal.
  • the demodulation and despreading means includes means for providing a base band signal and the rejection means includes filter means for processing the base band signal so as to remove from the base band signal frequencies within a predetermined filtering range and thereby provide a processed base band signal, substantially devoid of components at frequencies within the filtering range.
  • the despreading means may include means for sampling the processed base band signal at a chip frequency substantially different from the frequencies in the filtering range, selecting sets of the samples and applying predetermined despreading codes to each such set to thereby derive information bit values from the sets.
  • the chip frequency applied in the receiver corresponds to the chip frequency used by the transmitter
  • the filtering range used at the receiver includes the randomizing signal range used by the transmitter. Because of the very substantial difference between the frequencies of the randomizing signal and the chip frequency the filter means used in the receiver need not be particularly precise or have a particularly sharp cutoff. Thus, simple, inexpensive filtering circuitry can be employed.
  • FIG. 1 is a block diagram of apparatus in accordance with one embodiment of the invention. BEST MODE FOR CARRYING OUT THE INVENTION
  • a transmitter 10 in accordance with one embodiment of the invention includes a source 12 of information to be transmitted.
  • Source 12 is arranged to provide the information to be transmitted as a series of binary values expressed as high and low voltages in the conventional manner.
  • Information source 12 may be arranged to accept information from an external source such as a data communications device, to generate information internally or both.
  • the information source 12 may include a switch, means for providing a set of one or more predetermined information bits to signify a "on" actuation of the switch and means for providing another set of one or more predetermined information bits to signify an "off" actuation of the switch.
  • information source 12 may provide information bits as an address intended to designate a particular receiver.
  • Information source 12 is arranged to provide the high and low values designating the information bits in a predetermined sequence and at a predetermined bit rate.
  • Information source 12 is linked to a spreading code generator 14.
  • the spreading code generator is arranged to provide a series of digital binary chip values, represented by high and low voltages on an output line 16.
  • Code generator 14 is arranged to produce one predetermined series of fifteen chip values in response to a binary "one" bit value from information source 12, and to produce a different series of fifteen chip values responsive to a binary "zero" bit value.
  • the spreading code generator 14 is arranged to provide a series of high and low voltages representing the successive chip values on line 16, which voltages constitute a chip value signal.
  • the spreading code generator is arranged to provide the successive chip values at the rate of approximately 1 MHz, i.e., 106 chip values per second.
  • the output of code generator 18 is connected to a low-pass shaping filter 18, which filter is arranged to suppress components at frequencies substantially above the 1 MHz chip frequency and thereby eliminate undesired harmonics of the chip frequency from the chip value signal.
  • a randomizing signal source 20 includes a random noise generator 22 and a low-pass filter 24 connected to the output of the random noise generator.
  • Filter 24 is arranged to eliminate those components of the signal from generator 22 leaving frequencies of about 20 KHz. Thus, the components passed through filter 24 will consist essentially of random signals in a predetermined frequency band from DC to about 20 KHz.
  • the outputs of filters 24 and 18 are connected to a summing amplifier 26 and the output of this summing amplifier is connected to an RF signal generation and modulation unit 30.
  • Unit 30 is arranged to generate a carrier signal of about 915 MHZ. Further, unit 30 is arranged to frequency modulate the carrier signal in accordance with the signal appearing at the output of the summing amplifier 26.
  • Unit 30 may include substantially conventional RF signal generation units and a substantially conventional modulation circuit such as a varactor controlled oscillator.
  • the output of unit 30 is connected to an RF amplification unit 32, which in turn is connected to an antenna 34.
  • a receiver 40 for use with transmitter 10 incorporates an antenna 42 connected to an amplification and demodulation unit 44.
  • Unit 44 may incorporate substantially conventional RF amplification, intermediate frequency generation, mixing and detection stages and the like, all arranged to demodulate an FM signal using a carrier frequency of 915 MHz and to provide a base band signal replicating the received signal but without the carrier signal component.
  • the output of amplification and demodulation unit 44 is connected to a high pass filter 46. Filter 46 is arranged to substantially suppress all signal components at frequencies below about 50 KHz and to pass the remaining higher frequency components.
  • Receiver 40 further includes a chip value recovery unit 48 arranged to convert an analog signal into a series of digital chip values by timing a series of one microsecond intervals and providing a binary one or zero value for each such interval depending upon whether the value of the analog signal is above or below a predetermined threshold during the interval.
  • chip recovery unit 48 operates at a frequency of about 1 MHz and provides a series of digital chip values at that frequency.
  • the receiver further includes a despreading unit 50 arranged to receive the chip values from chip recovery unit 48.
  • the despreading unit 50 desirably includes a 15 position shift register, means for clocking successive chip values into the register and means for testing the set of values contained in the register on any given cycle of the clocking means against the sets of chip values representing one and zero bit values.
  • the despreader 50 thus is arranged to take successive sets of chip values from recovery unit 48 and derive one and zero bit values from those sets which match the recovered one and zero bit values to an information output unit 52.
  • the information output 52 may incorporate devices for testing the received information and/or for actuating other devices based upon the received information. For example, where receiver 40 is employed in an addressable system incorporating a plurality of different receivers, unit 52 may be arranged to examine some of the received information bits against a predetermined address sequence and to take further action only if that address sequence appears and otherwise to reject the signal. Unit 52 may be arranged to treat the remaining bits as indicating some action to be taken, such as turning on or turning off a light linked to the receiver.
  • output unit 52 may be arranged to pass some or all of the received information bits to other devices.
  • Components such as information source 12, code generator 14, chip recovery unit 48 and despreader 50 may be of the types disclosed in the aforementioned International Patent Publication W0-88/06365.
  • analog components of the transmitter such as shaping filter 18, modulator 30, amplification unit 32 and antenna 34 be fabricated on a common printed circuit board.
  • elements of the printed circuit board rather than discrete components as the necessary capacitors, inductors and transmission lines in transmitter 10 to the greatest possible extent.
  • the antenna 42, amplification and demodulation unit 44 and high pass filter 46 of the receiver desirably are all fabricated -li ⁇ as elements of a unitary printed circuit board, using similar techniques.
  • information source 12 is operated to supply information bits and at a predetermined bit rate, and these bits are encoded by code generator 14 so as to provide a chip value signal incorporating the successive chip values in sequence.
  • Random signal generator 22 and low pass filter 24 are actuated to provide narrow band noise, incorporating frequencies varying in a substantially random manner with time within the range of about DC to about 20 KHz as a randomizing signal, thereby impressing the information, code and randomizing signals on the carrier.
  • the randomizing and chip value signals are combined in summing amplifier 26.
  • Unit 30 forms a carrier signal and frequency modulates the carrier signal with this combined signal.
  • the combined signal after amplification in unit 32 passes from antenna 34 through free space radiation to antenna 42.
  • the received signal is amplified and demodulated.
  • the resulting base band signal pass through the input of filter 46 incorporates the chip value signal formed by spreading code unit 14 and also the narrow band random noise signal from the random noise generator 22 and filter 24 of the transmitter.
  • Filter 46 substantially strips out the randomizing signal, leaving a processed base band signal which essentially corresponds to the chip value signal alone.
  • the chip recovery unit 48 provides a series of digital chip values, and the despreader 50 reconverts this series of digital values back into the original information supplied by unit 12.
  • carrier signal generator and modulator 30 need not be a frequency modulation unit, but instead may be arranged to provide a plitude modulation, phase modulation or the like, provided that the modulation unit somehow alters a characteristic of the carrier signal in accordance with the signal to be transmitted. Also, it is not essential to combine the randomizing signal with the chip value signal prior to modulation. Instead, the carrier signal can be separately modulated with these two signals.
  • the enhanced power dispersion provided by the randomizing signal is particularly useful with relatively short sequence codes, such as those wherein each information bit is represented by about 50 chips or less and more preferably about 30 chips or less.
  • the greatest possible difference between the chip frequency and the randomizing signal frequency range is desirable to permit effective suppression of the randomizing signal component in the received signal without appreciable loss of chip frequency signal components, even where a relatively inexpensive filter having imprecise cutoff characteristics is employed.
  • the ratio between the chip frequency and the maximum frequency in the randomizing signal range is about 10:1 or more and more preferably about 50:1 or more.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Transmitters (AREA)

Abstract

Un système de spectre étendu en séquence directe emploie un générateur (22) de signaux stochastiques. On ajoute (26) la sortie dudit générateur (22) de signaux stochastiques à des valeurs binaires (16) dénotant des signaux, puis on module (30) un signal porteur à l'aide de ce signal combiné. Le signal stochastique permet une dispersion améliorée de la puissance dudit signal porteur sur une large fréquence. Le récepteur (40) comporte un filtre (46) destiné à supprimer la composante de signal stochastique du signal reçu.
PCT/US1990/000783 1989-03-06 1990-02-12 Systeme de communications a spectre etendu employant un signal de randomisation WO1990010982A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US31952689A 1989-03-06 1989-03-06
US319,526 1989-03-06

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WO1990010982A1 true WO1990010982A1 (fr) 1990-09-20

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0484065A2 (fr) * 1990-11-02 1992-05-06 AT&T Corp. Système de communication à spectre étalé et à séquence directe à modulation de fréquence utilisé pour obtenir l'étalement du spectre

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3614316A (en) * 1964-05-20 1971-10-19 Us Navy Secure communication system
US4320514A (en) * 1980-06-09 1982-03-16 Bell Telephone Laboratories, Incorporated Spread spectrum FH-MFSK radio receiver
US4653068A (en) * 1984-10-19 1987-03-24 Itt Corporation Frequency hopping data communication system
US4752939A (en) * 1986-09-03 1988-06-21 Hughes Aircraft Company Hidden preamble for frequency hopped synchronization
US4864588A (en) * 1987-02-11 1989-09-05 Hillier Technologies Limited Partnership Remote control system, components and methods
US4866771A (en) * 1987-01-20 1989-09-12 The Analytic Sciences Corporation Signaling system

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3614316A (en) * 1964-05-20 1971-10-19 Us Navy Secure communication system
US4320514A (en) * 1980-06-09 1982-03-16 Bell Telephone Laboratories, Incorporated Spread spectrum FH-MFSK radio receiver
US4653068A (en) * 1984-10-19 1987-03-24 Itt Corporation Frequency hopping data communication system
US4752939A (en) * 1986-09-03 1988-06-21 Hughes Aircraft Company Hidden preamble for frequency hopped synchronization
US4866771A (en) * 1987-01-20 1989-09-12 The Analytic Sciences Corporation Signaling system
US4864588A (en) * 1987-02-11 1989-09-05 Hillier Technologies Limited Partnership Remote control system, components and methods

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0484065A2 (fr) * 1990-11-02 1992-05-06 AT&T Corp. Système de communication à spectre étalé et à séquence directe à modulation de fréquence utilisé pour obtenir l'étalement du spectre
EP0484065A3 (en) * 1990-11-02 1993-03-17 American Telephone And Telegraph Company Direct sequence spread spectrum (dss) communications system with frequency modulation utilized to achieve spectral spreading

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Publication number Publication date
AU5197490A (en) 1990-10-09

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