CA2253043A1 - Electromagnetic communication system and method - Google Patents

Abstract

A single or multi-user communications system that utilizes coherent signals to enhance the system performance over conventional radio frequency schemes while reducing cost and complexity. The design allows direct conversion of radio frequencies into baseband components for processing and provides a high level of rejection for signals that are not related to a known or controlled slew rate between the transmitter and receiver timing oscillators. The system can be designed to take advantage of broadband techniques that further increase its reliability and permit a high user density within a given area.

Description

ELECTROMAGNETIC COMMUNICATION SYSTEM AND METHQD
BACKGROT.7ND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to electromagnetic wired and wireless communication systems.
PRIOR ART
Currently available communication systems fall into two categories; narrow bandwidth relative to the information contained in the signal (AM, FM, PM, etc.) and wide bandwidth relative to the information contained in the signal (spread spectrum). The narrow band system design requirements are less demanding than that of the wideband, but these systems are susceptible to interference on or near their operating frequencies and thus the performance of these systems is largely dependent on their operating environment.
Another characteristic of narrowband signals is the relatively small number of systems that can operate simultaneously in an area.
Further narrowing the bandwidth of these systems decreases the likelihood of interference and increases the number of users in a given area but reduces the amount of information that can be transferred in a given time interval. Wide bandwidth systems (spread spectrum) are less susceptible to interference, allow more information to be contained in the signal, and permit more users in an area but suffer from complex design criteria and high cost.
These drawbacks limit the applications in which wideband systems can be applied even though performance can be greatly enhanced over narrow band designs.
sg~in 1 Current wideband techniques such as direct sequence and frequency hopping occupy a small bandwidth at any instant in time and many different frequencies over a longer time period. The complexity of these wideband designs is due in part to the synchronization of the transmitted signal to the receiver so that the receiver knows where in the frequency spectrum and at what time to look for the transmitted signal. Time division multiple access uses a single frequency but the time synchronization problem remains. Prior art consists mainly of high-end design techniques including digital signal processors, high speed digital circuitry, and high speed analog techniques to accomplish the necessary encoding/decoding and correlation requirements.
Sampling techniques are also well known in the art and are widely used in measurement systems, particularly in high-bandwidth digitizing oscilloscopes.
SUMMARY OF THE INVENTION
In one aspect of the present invention there is provided a method of receiving a modulated signal, comprising the steps of:
A. sampling the modulated signal at a sampling rate to produce one or more samples; and B. generating an equivalent signal from the one or more samples, wherein the equivalent signal is substantially identical in information content to an information signal used to generate the modulated signal.
In another aspect of the present invention there is provided a receiver, comprising: a sampler for sampling, at a sampling rate, a modulated signal to produce one or more samples; and an sg~in 2 integrator coupled to the sampler for holding the samples to generate an equivalent signal from the samples, wherein the equivalent signal is substantially identical in information content to an information signal used to generate the modulated signal.
In yet another aspect of the present invention there is provided a method of transmitting information between a transmitter and a receiver comprising the steps of transmitting a first series of signals each having a known period from the transmitter at a known first repetition rate; sampling by the receiver the signal level of each signal in the first series of signals and for a known time interval, the sampling of the first series of signals being at a second repetition rate that is a rate different from the first repetition rate by a known amount; and generating by the receiver an output signal indicative of the signal levels sampled and having a period longer than the known period of a transmitted signal.
In still another aspect of the invention there is provided a communication system comprising a transmitter means for transmitting a first series of signals of known period at a known first repetition rate, a receiver means for receiving the first series of signals, the receiver means including sampling means for sampling the signal of the level of each signal first series of signals for a known time interval at a known second repetition rate, the second repetition rate being different from the first repetition rate by a known amount as established by the receiver means. The receiver means includes first circuit means for generating a first receiver output signal indicative of the signal SBi~ 3 levels sampled and having a period longer than one signal of the first series of signals. The transmitter means includes an oscillator for generating an oscillator output signal at the first repetition rate, switch means for receiving the oscillator output signal and for selectively passing the oscillator output signal, waveform generating means for receiving the oscillator output signal for generating a waveform generator output signal having a time domain and frequency domain established by the waveform generating means.
Other aspects will be determined from the following description of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The novel features which are believed to be characteristic of this invention are set forth with particularity in the appended claims . The invention itself , however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in which:
FIG. 1 is a simplified block diagram of an amplitude and pulse width modulated transmitter in accord with the present invention;
FIG. 2 is a simplified schematic of the transmitter of FIG.
1;
FIG. 3 illustrates waveforms present at different points in the transmitter of FIGS. 1 and 2;
FIG. 4 is an enlarged diagram of a single cycle pulse output Sgii~ 4 signal of the transmitter of FIGS. 1 and 2;
FIG. 5 is a diagram illustrating the frequency spectrum of the pulse of FIG. 4;
FIG. 6 is a simplified block diagram of a receiver in accord with the present invention;
FIG. 7 illustrates waveforms present at different points in the receiver of FIG. 6;
FIGS. 8-10 are simplified schematic diagrams illustrating the various circuits employed in the receiver of FIG. 6;
FIGS. 11-14 illustrate time and frequency domain diagrams of alternative transmitter output waveforms;
FIGS. 15-16 illustrate differential receivers in accord with the present invention; and FIGS. 17 and 18 illustrate time and frequency domains for a narrow bandwidth/constant carrier signal in accord with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENT OF THE INVENTION
INTRODUCTION
The present invention involves a single or multi-user communications system that utilizes coherent signals to enhance the system performance over conventional radio frequency schemes while reducing cost and complexity. The design allows direct conversion of radio frequencies into baseband components for processing and provides a high level of rejection for signals that are not related to a known or controlled slew rate between the transmitter and ssi~ 5 receiver timing oscillators. The system can be designed to take advantage of broadband techniques that further increase its reliability and permit a high user density within a given area.
The technique employed allows the system to be configured as a separate transmitter-receiver pair or a transceiver. The invention addresses the several deficiencies found in conventional systems as discussed hereinabove.
The basic obj ectives of the present system is to provide a new communication technique that can be applied to both narrow and wide band systems. In its most robust form, all of the advantages of wide band communications are an inherent part of the system and the invention does not require complicated and costly circuitry as found in conventional wide band designs. The communications system utilizes coherent signals to send and receive information and consists of a transmitter and a receiver in its simplest form. The receiver contains circuitry to turn its radio frequency input on and off in a known relationship in time to the transmitted signal.
This is accomplished by allowing the transmitter timing oscillator and the receiver timing oscillator to operate at different but known frequencies to create a known slew rate between the oscillators. If the slew rate is small compared to the timing oscillator frequencies, the transmitted waveform will appear stable in time, i.e., coherent (moving at the known slew rate) to the receiver's switched input. The transmitted waveform is the only waveform that will appear stable in time to the receiver and thus the receiver's input can be averaged to achieve the desired level sg~in 6 filtering of unwanted signals. This methodology makes the system extremely selective without complicated filters and complex encoding and decoding schemes and allows the direct conversion of radio frequency energy from an antenna or cable to baseband frequencies with a minimum number of standard components further reducing cost and complexity. The transmitted waveform can be a constant carrier (narrowband), a controlled pulse (wideband and ultra-wideband) or a combination of both such as a dampened sinusoidal wave and or any arbitrary periodic waveform thus the system can be designed to meet virtually any bandwidth requirement .
Simple standard modulation and demodulation techniques such as AM
and Pulse Width Modulation can be easily applied to the system.
Depending on the system requirements such as the rate of information transfer, the process gain, and the intended use, there are multiple preferred embodiments of the invention. The embodiment discussed herein will be the amplitude and pulse width modulated system. It is one of the simplest implementations of the technology and has many common components with the subsequent systems. An amplitude modulated transmitter consists of a Transmitter Timing Oscillator, a Multiplier, a Waveform Generator, and an Optional Amplifier. The Transmitter Timing Oscillator frequency can be determined by a number of resonate circuits including an inductor and capacitor, a ceramic resonator, a SAW
resonator, or a crystal. The output waveform is sinusoidal, although a squarewave oscillator would produce identical system performance .
ggm 7 The Multiplier component multiplies the Transmitter Timing Oscillator output signal by a 0 or 1 or other constants, K1 and K2, to switch the oscillator output on and off to the Waveform Generator. In this embodiment, the information input can be digital data or analog data in the form of pulse width modulation.
The Multiplier allows the Transmitter Timing Oscillator output to be present at the Waveform Generator input when the information input is above a predetermined value. In this state the transmitter will produce an output waveform. When the information input is below a predetermined value, there is no input to the Waveform Generator and thus there will be no transmitter output waveform. The output of the Waveform Generator determines the system's bandwidth in the frequency domain and consequently the number of users, process gain immunity to interference and overall reliability, the level of emissions on any given frequency, and the antenna or cable requirements. The Waveform Generator in this example creates a one cycle pulse output which produces an ultra-wideband signal in the frequency domain. An optional power Amplifier stage boosts the output of the Waveform Generator to a desired power level.
With reference now to the drawings, the amplitude and pulse width modulated transmitter in accord with the present invention is depicted at numeral 10 in FIGS . 1 and 2 . The Transmitter Timing Oscillator 11 is a crystal-controlled oscillator operating at a frequency of 25 Mhz. Multiplier 12 includes a two-input NAND gate 16 controlling the gating of oscillator 11 output to Waveform sg~in 8 Generator 13. Waveform Generator 13 produces a pulse output as depicted at 20 in FIGS. 3 and 4, which produces a frequency spectrum 23 in FIG. 5. Amplifier 14 is optional. The transmitter output is applied to antenna or cable 15, which as understood in the art, may be of various designs as appropriate in the circumstances.
FIGS. 3-5 illustrate the various signals present in transmitter 10. The output of transmitter 10 at "A" may be either a sinusoidal or squarewave signal 17 that is provided as one input 10 into NAND gate 16. Gate 16 also receives an information signal 18 at "B" which, in the embodiment shown, is digital in form. The output 19 of Multiplier 12 can be either sinusoidal or squarewave depending upon the original signal 17. Waveform Generator 13 provides an output of a single cycle impulse signal 20. The single cycle impulse 21 varies in voltage around a static level and is created at 40 nanoseconds intervals. In the illustrated embodiment, the frequency of transmitter 11 is 25 Mhz and accordingly, one cycle pulses of 1.0 Ghz are transmitted every 40 nanoseconds during the total time interval that gate 16 is °'on" and passes the output of transmitter oscillator 11.
FIG. 6 shows the preferred embodiment receiver block diagram to recover the amplitude or pulse width modulated information and consists of a Receiver Timing Oscillator 29, Waveform Generator 28, RF Switch Fixed or Variable Integrator 27, Decode Circuit 31, two optional Amplifier/Filter stages 26 and 30, and antenna or cable input 25. The frequency of the Receiver Timing Oscillator 29 can sgi~ 9 be determined by a number of resonate circuits including an inductor and capacitor, a ceramic resonator, a SAW resonator, or a crystal. As in the case of the transmitter, the oscillator 29 shown here is a crystal oscillator (see FIG. 9). The output waveform is a squarewave, although a sinewave oscillator would produce identical system performance. The squarewave timing oscillator output is shown as A in FIG. 7. The Receiver Timing Oscillator 29 is designed to operate within a range of frequencies that creates a known range of slew rates relative to the Transmitter Timing Oscillator 11. In this embodiment, the Transmitter Timing Oscillator 11 frequency is 25 Mhz and the Receiver Timing Oscillator 29 outputs between 25.0003 Mhz and 25.0012 Mhz which creates a +300 to +1200 Hz slew rate.
The Receiver Timing Oscillator 29 a.s connected to the Waveform Generator 28 which shapes the oscillator signal into the appropriate output to control the amount of time that the RF switch 27 is on and off. The on-time of the RF switch 27 should be less than 1/2 of a cycle (1/10 of a cycle is preferred) or in the case of a single pulse, no wider than the pulse width of the transmitted waveform or the signal gain of the system will be reduced.
Examples are illustrated in Table 1. Therefore the output of the Waveform Generator 28 is a pulse of the appropriate width that occurs once per cycle of the Receiver Timing Oscillator 29. The output of the waveform Generator is shown as B in FIG. 7.
The RF Switch/Integrator 27 samples the RF signal 35 shown as C in FIG. 7 when the Waveform Generator output 34 is below a sgi;~ 10 predetermined value. When the Waveform Generator output 34 is above a predetermined value, the RF Switch 27 becomes a high impedance node and allows the Integrator to hold the last RF signal sample 35 until the next cycle of the Waveform Generator 28 output .
The Integrator section of 27 is designed to charge the Integrator quickly (fast attack) and discharge the Integrator at a controlled rate (slow decay). This embodiment provides excellent unwanted signal rejection and is a major factor in determining the baseband frequency response of the system. The sense of the switch control is arbitrary depending on the actual hardware implementation.
In the preferred embodiment of the present invention, the gating or sampling rate of the receiver 24 is 300 hz higher than the 25 Mhz transmission rate from the transmitter 10.
Alternatively, the sampling rate could be less than the transmission rate. The difference in repetition rates between the transmitter 10 and receiver 24, the "slew rate", is 300 hz and results in a controlled drift of the sampling pulses over the transmitted pulse which thus appears "stable" in time to the receiver 24. With reference now to FIGS. 3 and 7, an example is illustrated for a simple case of an output signal 36 (FIG. 7, "D") that is constructed of four samples from four RF input pulses 35 for ease of explanation. As can be clearly seen, by sampling the RF pulses 35 passed when the transmitter information signal 18 (FIG. 3) is above a predetermined threshold the signal 36 is a replica of a signal 35 but mapped into a different time base. In the case of this example, the new time base has a period four times longer than the real time signal. The use of an optional Transmit ed WaveFOrm Gain Limit on-time Preferred on-time Single 1 nanosecond pulse 1 nanosecond 100 picoseconds 1 GigaHertz 1,2,3 etc. cycle output 500 picoseconds 50 picoseconds GigaHertz 1,2,3 etc. cycle output 50 picoseconds 5 picoseconds Table 1 Units:
s = 1 ps = 1x10-12 ns = 1x10'9 ~.s = 1x10'6 Mhz = 1x106 Khz = 1x103 Receiver Timing Oscillator Frequency = 25.0003 Mhz Transmitter Timing Oscillator Frequency = 25 Mhz period =
Transmitter Timing Oscillator Frequency period = 40 ns slew rate = -Receiver Timing Oscillator Frequency - Transmitter Timing Oscillator Frequency slew rate = 0.003 s slew rate time base multiplier = seconds per nanosecond 2 0 period time base multiplier = 8.333x104 Example 1:
1 nanosecond translates into 83.33 microseconds time base = (1 ns) x time base multiplier time base = 83.333 ~s Example 2:
2 Gigahertz translates into 24 Kilohertz 2 Gigahertz=500 picosecond period time base = (500 ps) x time base multiplier time base = 41.667 ~s frequency =
time base frequency = 24 Khz Table 2 Sgi~ 12 amplifier/filter 30 results in a further refinement of the signal 36 which is present at "E" as signal 37.
Decode Circuitry 31 extracts the information contained in the transmitted signal and includes a Rectifier that rectifies signal 36/37 to provide signal 38 at "G" in FIG. 7. The Variable Threshold Generator circuitry in circuit 31 provides a DC threshold signal level 39 for signal 37 that is used to determine a high (transmitter output on) or low (transmitter output off) and is shown at "H". The final output signal 40 at "F" is created by an output voltage comparator in circuit 31 that combines signals 38 and 39 such that when the signal 38 is a higher voltage than signal 39, the information output signal goes high. Accordingly, signal 40 represents, for example, a digital "1" that is now time-based to a 1:4 expansion of the period of an original signal 35. While this illustration provides a 4:1 reduction in frequency, it is sometimes desired to provide a reduction of more than 50,000:1;
100,000:1 or greater as is achieved in the preferred embodiment.
This results in a shift directly from RF input frequency to low frequency baseband without the requirement of expensive intermediate circuitry that would have to be used if only a 4:1 conversion was used as a first stage. Table 2 provides information as to the time base conversion and includes examples.
In the illustrated preferred embodiment, the signal 40 at "F"
has a period of 83.33 usec, a frequency of 12 Khz and it is produced once every 3.3 msec for a 300hz slew rate. Stated another way, the system is converting a 1 gigahertz transmitted signal into sgi~ 13 an 83.33 microsecond signal.
Accordingly, the series of RF pulses 21 that are transmitted during the presence of an "on" signal at the information input gate 16 are used to reconstruct the information input signal 18 by sampling the series of pulses at the receiver 24. The system is designed to provide an adequate number of RF inputs 35 to allow for signal reconstruction of information input signal 18 as output signal 40 at the receiver.
An optional Amplifier/Filter stage or stages 26 and 30 may be included to provide additional receiver sensitivity, bandwidth control or signal conditioning for the Decode Circuitry 31.
Choosing an appropriate time base multiplier will result in a signal at the output of the Integrator 27 that can be amplified and filtered with operational amplifiers rather than RF amplifiers with a resultant simplification of the design process. The signal 37 at "E" illustrates the use of Amplifier/Filter 30 (FIG. 8). The optional RF amplifier 26 shown as the first stage of the receiver should be included in the design when increased sensitivity and/or additional filtering is required. The simplified receiver schematic is shown in FIGS. 8-10.
FIGS. 11-14 illustrate different pulse output signals 41 and 43 and their respective frequency domain at 42 and 44. As can be seen from FIGS. 11 and 12, the half-cycle signal 41 generates a spectrum less subject to interference than the single cycle of FIG.
4 and the 10-cycle pulse of FIG. 13. The various outputs determine the system' s immunity to interference, the number of users in a given area, and the cable and antenna requirements. FIGS. 4 and illustrate the preferred embodiment pulse output.
FIGS. 15 and 16 show differential receiver designs. The theory of operation is identical to the non-differential receiver of FIG. 6 except that the differential technique provides an increased signal to noise ratio by means of common mode rejection.
Any signal impressed in phase at both inputs on the differential receiver will be attenuated by the differential amplifier shown in FIGS. 15 and 16 and conversely any signal that produces a phase difference between the receiver inputs will be amplified.
FIGS. 17 and 18 illustrate the time and frequency domains of a narrow band/constant carrier signal in contrast to the ultra-wide band signals used in the illustrated preferred embodiment.
V~lhile the invention has been described with respect to certain specific embodiments, it will be appreciated that many modifications and changes may be made by those skilled in the art without departing from the spirit of the invention. It is intended, therefore, by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.
Sgi~ 15

Claims (25)

1. A method of transmitting information between a transmitter and a receiver of an electromagnetic communication system comprising the steps of:
A. transmitting a first series of signals each having a known period from the transmitter at a known first repetition rate;
B. sampling by the receiver the signal level of each signal in the first series of signals and for a known time interval, the sampling of the first series of signals being at a second repetition rate that is a rate different from the first repetition rate by a known amount; and C. generating by the receiver an equivalent signal indicative of the transmitted first series of signals sampled in step B and having a period longer than the known period of a transmitted signal.

2. A communication system comprising a transmitter means for transmitting a first series of signals of known period at a known first repetition rate, a receiver means for receiving said first series of signals, said receiver means including sampling means for sampling the signal level of each signal of said first series of signals for a known time interval at a known second repetition rate, said second repetition rate being different from said first repetition rate by a known amount as established by said receiver means, said receiver means including first circuit means for generating a first receiver output signal indicative of the signal levels sampled and having a period longer than one signal of said first series of signals.

3. The communication system as defined in Claim 2 wherein said transmitter means includes an oscillator for generating an oscillator output signal at said first repetition rate, switch means for receiving said oscillator output signal and for selectively passing said oscillator output signal, waveform generating means for receiving said oscillator output signal for generating a waveform generator output signal having a time domain and frequency domain established by said waveform generating means.

4. The method of Claim 1 wherein step B includes the step of:
D. sampling by the receiver each signal for a known time interval equal to or less than one-half the period of the signal.

5. The method of Claim 1 wherein step B includes the step of:
D. sampling by the receiver each signal for a known time interval of approximately one-tenth the period of the signal.

6. The method of Claim 1 wherein step A includes the step of:
D. providing amplitude or pulse width modulation of the first series of signals by selectively controlling the transmission of the first series of signals.

7. The method of Claim 6 wherein step D includes the step of:
E. selectively controlling the transmission of the first series of pulses by selectively blocking or passing the first series of signals with an information signal.

8. The method of Claim 7 wherein step C includes the step of:
8. generating an output signal that is an equivalent signal and a replica of the information signal of step E.

9. The communication system as defined in Claim 3 wherein said transmitter means includes information input signal generating means for providing an information input signal to said switch means, said switch means selectively passing said oscillator output signal in response to said information input signal.

10. The communication system as defined in Claim 2 wherein said sampling means includes sampling control means to provide that the duration of sampling of said signal level of each said signal is equal to or less than one-half the period of said signal.

11. The communication system as defined in Claim 10 wherein said sampling control means provides for said duration of sampling to be approximately one-tenth the period of said signal.

12. The communication system as defined in Claim 9 wherein said first circuit means includes integrator circuit means for providing that said first receiver output signal is a replica of said information input signal.

13. The communication system as defined in Claim 3 wherein said transmitter means includes an amplitude or pulse width modulated transmitter circuit means.

14. The communication system as defined in Claim 2 wherein said first repetition rate is 25 Mhz and said second repetition rate is in a range of 25.003 - 25.0012 Mhz.

15. The communication system as defined in Claim 3 wherein said waveform generator output signal is an ultra-wideband signal.

16. The method of Claim 1 wherein the generated equivalent signal of step C has a period greater than the known period of a transmitted signal on an order of magnitude of thousands.

17. The method of Claim 8 wherein the generated equivalent signal of step C has a period greater than the known period of a transmitted signal on an order of magnitude of thousands.

18. The communication system of Claim 2 wherein said first receiver output signal has a period greater than the known period of said first series of signals on an order of magnitude of thousands.

19. The communication system of Claim 12 wherein said first receiver output signal has a period greater than the known period of said first series of signals on an order of magnitude of thousands.

20. The method of Claim 1 wherein the second repetition rate differs from the first repetition rate by 0.003 to 0.0012 Mhz.

21. A method of receiving a modulated signal, comprising the steps of:
A. sampling the modulated signal at a sampling rate to produce one or more samples; and B. generating an equivalent signal from said one or more samples, wherein said equivalent signal is substantially identical in information content to an information signal used to generate the modulated signal.

22. The method of claim 21, further comprising the following step that is performed before step A:
generating a train of pulses for sampling, wherein each of said pulses has a substantially identical pulse width, wherein said pulses are used to generate said samples.

23. A receiver, comprising:
a sampler for sampling, at a sampling rate, a modulated signal to produce one or more samples; and an integrator coupled to said sampler for holding said samples to generate an equivalent signal from said samples, wherein said equivalent signal is substantially identical in information content to an information signal used to generate the modulated signal.

24. The receiver of claim 23, wherein said sampler comprises:
a timing oscillator;
a waveform generator, wherein said waveform generator comprises a waveform generator input coupled to said timing oscillator and a waveform generator output; and a switch coupled to said waveform generator output;
wherein a train of pulses is output from said waveform generator output, said train of pulses being at said sampling rate;
wherein said switch uses said train of pulses to generate samples at said sampling rate.

25. A method of receiving an electromagnetic signal, comprising the steps of:
A. receiving a first series of signals each having a known period at a known first repetition rate;
B. sampling the signal level of each signal in the first series of signals for a known time interval, the sampling of the first series of signals being at a second repetition rate that is a rate different from the first repetition rate by a known amount;
and C. generating an equivalent signal indicative of the first series of signals sampled in step B and having a period longer than the known period of a transmitted signal.