Harmonic-frequency communication system with improved diversity scheme

Abstract: According to this invention, a modulator (11a) modulates a carrier serving as a fundamental wave with data to be transmitted, thereby to generate a modulated output including at least the fundamental wave and double wave thereof. A transmitting antenna (12) radiates electromagnetic waves into the air, and the electromagnetic waves include the fundamental wave and the double wave included in the modulated output generated by the modulator (11a). A receiving antenna (14) receives the electromagnetic waves including the fundamental wave and the double wave radiated from the transmitting antenna (12). A diversity section (17) generates an output having a diversity effect on the basis of the fundamental wave and the double wave included in the electromagnetic waves received by the receiving antenna (14). A demodulator demodulates the output having the diversity effect and generated by the diversity section (17), thereby to output data corresponding to the data to be transmitted.

Description: The present invention generally relates to a harmonic-frequency communication system with an improved diversity scheme for performing data communication using the fundamental and harmonic-frequency waves of electromagnetic waves generated from the output of a transmission side. In a radio communication system, the fundamental wave of electromagnetic waves is generally used. Such a communication system is suppressed by interference waves generated near the communication system. In order to solve this problem, there is provided a frequency diversity scheme in which data communication is performed by superposing the same data on a plurality of carriers. The United States Patent US-A-1,954,185 discloses a method of transmitting signals on short radio waves to prevent the problem of fading. The same signal is sent on several transmission channels by modulating a carrier wave with frequencies including a fundamental wave and its harmonics. A receiver is adapted to separate the received waves into the same frequency relationship as the fundamental and harmonic waves. The German Patent DE-C-86 93 61 discloses a method for multiple wireless transmission at different frequencies. The method is characterized in that the receiver automatically selects the received signal having the highest amplitude. The United States Patent US-A-2,955,199 discloses a receiving system comprising a single frequency oscillator having an output median frequency between the frequencies of the two received diversity signals. A heterodyne arrangement is provided to produce two intermediate signals and to detect a phase difference between the two intermediate signals. The phase difference is used to control the oscillator frequency such that the phase relation between the intermediate signals is within a predetermined phase for maximum additive combination thereof. The United States Patent US-A-4,584,716 discloses an automatic dual diversity receiver. The radio receiver is capable of receiving signals at at least two different frequencies simultaneously. A heterodyne frequency is selected midway between the received frequencies and an intermediate frequency is selected at a frequency equal to one half of the difference of the frequencies received. Fig. 8 is a block diagram showing a further conventional diversity scheme. Data D1 is input to first and second transmitting sections 1 and 2. The first transmitting section 1 modulates the data D1 and superposes it on a first carrier. The second transmitting section 2 modulates the data D1 and superposes it on a second carrier. As a result, the data D1 is radiated in the air as electromagnetic waves by a transmitting antenna 4 via an antenna combining equipment 3. The radiated electromagnetic waves travel in the air and are received by a receiving antenna 6. The received electromagnetic waves are input to a first receiving section 7 for the first carrier and to a second receiving section 8 for the second carrier, so that data are demodulated from the carriers and output. The quality levels of demodulated data are compared by some method, and the data of better quality is selected by a switch 9 and output therefrom as data D2. In the conventional communication system, however, the following drawback is present. That is, in addition to the antenna combining equipment, a plurality of transmitting sections are required for transmitting the plurality of carriers, thereby complicating the arrangement of the communication system. It is, therefore, an object of the present invention to provide a harmonic frequency communication system with an improved diversity scheme which uses fundamental and harmonic-frequency waves, which can achieve radio communication well protected against interference waves and fading, and which does not require a plurality of transmitting and receiving sections to simplify a transmitting section and decrease the size of the system. According to the present invention, there is provided a harmonic-frequency communication system as defined in claim 1 and 4. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a block diagram showing an arrangement of a harmonic-frequency communication system; Fig. 2 is a block diagram showing an arrangement of a harmonic-frequency communication system; Fig. 3 is a block diagram showing a harmonic-frequency communication system according to an embodiment of the present invention; Fig. 4 is a view showing a relationship between the frequency spectra of the transmitting and receiving sections in Fig. 3; Figs. 5, 6, and 7 are block diagrams respectively showing different practical embodiments of a harmonic-frequency communication system; and Fig. 8 is a view for explaining an arrangement of a communication system with a conventional frequency diversity scheme. Fig. 1 is a block diagram showing a harmonic-frequency communication system which does not fall under the claims of the present invention. That is, a fundamental wave f and a double wave 2f thereof are used as a plurality of carriers. In Fig. 1, data D3 is input to a transmitting section 11, modulated and amplified therein, and radiated as electromagnetic waves from a transmitting antenna 12. A fundamental wave and a double wave are radiated as the electromagnetic waves. The radiated electromagnetic waves travel in the air, and they are received by a receiving antenna 14 and input to a fundamental-wave receiving section 15 and a double-wave-receiving section 16. The fundamental-wave receiving section 15 demodulates data from the fundamental wave and outputs the data. The double-wave receiving section 16 demodulates data from the double wave and outputs the data. A switch SW serving as a diversity section 17 compares the demodulated data output from the fundamental-wave receiving section 15 and the double-wave receiving section 16 by some method and selectively outputs one data of better quality as data D4. Fig. 2 is a block diagram showing another harmonic-frequency communication system which does not fall under the claims of the present invention. That is, a fundamental wave f and a double wave 2f thereof are used as a plurality of carriers. In Fig. 2, data D5 is input to a transmitting section 21, modulated and amplified therein, and radiated as electromagnetic waves from a transmitting antenna 22. A fundamental wave and a double wave are radiated as the electromagnetic waves. The radiated electromagnetic waves travel in the air, and they are received by a receiving antenna 24 and input to a fundamental-wave receiving section 25 and a double-wave receiving section 26. The fundamental-wave receiving section 25 demodulates data from the fundamental wave and outputs the data. The double-wave receiving section 26 demodulates data from the double wave and outputs the data. After the demodulated data output from the fundamental-wave receiving section 25 and the double-wave receiving section 26 are weighted with predetermined weighting coefficients W1 and W2 by weighting circuits 27 and 28 included in a diversity section 17, respectively, the demodulated data are added to each other by an adder 29 so as to be output as data D6 having a diversity effect. Fig. 3 is a block diagram showing a harmonic-frequency communication system according to an embodiment of the present invention. Fig. 4 is a relationship between the frequency spectra of the harmonic-frequency communication system of this embodiment. According to this embodiment, a fundamental wave f 1 and a double wave f 2 thereof are used as a plurality of carriers. In Fig. 3, data D7 is input to a receiving section 31, modulated and amplified therein, and radiated as electromagnetic waves from a transmitting antenna 32. A fundamental wave and a double wave are radiated as the electromagnetic waves. The radiated electromagnetic waves travel in the air, and they are received by a receiving antenna 34 and input to a mixer 37 through an amplifier 35. The mixer 37 included in a diversity section 17 produces a signal having a frequency f 1 +F LO and a signal having a frequency f 2 -F LO from the fundamental wave f 1 , the double wave f 2 , and a signal f LO generated by a generator 36. At this time, the frequency of the signal f LO generated by the generator 36 is set to satisfy condition f 1 +f LO = f 2 -f LO . An output signal f I from the mixer 37 is produced by synthesizing the signal having the frequency f 1 +f LO and the signal having the frequency f 2 -f LO , and the output signal f 1 has a diversity effect. The output signal f I from the mixer 37 is demodulated by a demodulation section 38 to be output as data D8. In the above embodiment, a series of harmonic waves each having a frequency higher than that of a triple harmonic wave in addition to the fundamental wave and the double wave thereof are simultaneously output from the transmitting sections 11, 21, and 31. However, since these harmonic waves have low levels enough to be negligible, the harmonic wave can be removed by the frequency selecting function of each of the receiving sections. In this case, a band-pass filter or the like for removing a harmonic component having a frequency higher than that of a triple wave may be arranged in each of the transmitting sections. Several practical arrangements will be described below with reference to the accompanying drawings. In Fig. 5, a modulator 11a of the transmitting section 11 is constituted as a BPSK modulator having an oscillator for oscillating a carrier (a fundamental wave) of a predetermined frequency, a mixer, and a double-wave selection amplifier. In this modulator 11a, a modulated output is produced such that data D3 from a data source and the carrier from the built-in oscillator are mixed by the built-in mixer, and the double wave is amplified by the built-in double-wave selection amplifier at the same level of the fundamental wave, thereby outputting a fundamental (modulated) wave f and double (modulated) wave 2f. The electromagnetic waves including the fundamental wave f and the double wave 2f are radiated into the air from the transmitting antenna 12 connected to the output terminal of the modulator 11a. The electromagnetic waves including the fundamental wave f and the double wave 2f travel in the air, and they are received by the received antenna 14. Thereafter, the electromagnetic waves are branched into two signals, and the signals are guided to both the stationary contacts of the switch SW through a fundamental-wave band-pass filter 15a of the fundamental receiving section 15, a double-wave band-pass filter 16a of the double-wave receiving section 16, a fundamental-wave demodulator 15b, and a double-wave demodulator 16b. The switch SW included in the diversity section 17 selects one modulated output of better quality (in this case, the output has a higher level) in response to a control signal output from a comparator 17a for comparing the levels of the outputs from the fundamental-wave demodulator 15b and the double-wave demodulator 16b, thereby outputting the output as demodulated data D4 from a movable contact. Fig. 6 shows the second embodiment of the present invention. The arrangement and function of a path up to the fundamental-wave band-pass filter 15a and the double-wave band-pass filter 16a are the same as those of the first practical arrangement shown in Fig. 5. In this embodiment, after the fundamental wave f and the double wave 2f passing through the band-pass filters 15a and 16a are converted into signals each having an intermediate frequency (1.5f) between the frequencies of these waves, respectively, the signals are guided to both the stationary contacts of the switch SW. In this case, the SW included in the diversity section 17 selects one 1.5f converted output of better quality (in this case, the output has a higher level) in response to a control signal output from a level detector 17c for detecting and comparing the input or output levels of the frequency converters 15c and 16c, thereby outputting the 1.5f output of better quality to a 1.5f demodulator 18a. This 1.5f demodulator 18a demodulates the 1.5f signal and outputs it as the data D4. That is, the same effect as described above can be obtained by only one demodulator. Fig. 7 shows the third embodiment of the invention. In this embodiment, outputs f and 2f (in this case, f = 21.4 MHz, 2f = 42.8 MHz) from the same modulator 11a of the transmitting section as that of Fig. 5 are guided to a frequency converter 11b, and the outputs f and 2f are converted by a local oscillation signal having a predetermined frequency (in this case, 267.9 MHz) into transmission waves respectively having predetermined frequencies (in this case, f' = 289.3 MHz, 2f' = 310.7 MHz). These transmission waves are transmitted from the transmitting antenna 12. The receiving section 16 for receiving the transmission waves including the two frequency-converted waves at the receiving antenna 14 are branched and input to band-pass filters 15d and 16d respectively having predetermined frequency characteristics (in this case, 310.7 MHz and 289.3 MHz). The outputs passing through the band-pass filters 15d and 16d are frequency-converted twice by first and second frequency converters 15e and 16e having frequency converting units, respectively. At this time, since both the first frequency conversion operations are performed using a local oscillation signal having a frequency of 267.9 MHz, the outputs are converted into signals having frequencies of 42.8 MHz ( f ) and 21.4 MHz (2f), respectively. In the second conversion operations, a local oscillation signal having a frequency of 42.345 MHz is used in the converter 15e, and a local oscillation signal having a frequency of 21.855 MHz is used in the converter 16e. Therefore, signals each having a frequency of 0.455 MHz are output from both the converters 15e and 16e and supplied to both the stationary contacts of the switch SW. The SW included in the diversity section 17 selects one converted output (0.455 MHz) of better quality (in this case, the output has a higher level) in response to a control signal from a level detector 17d for detecting the input or output levels of the frequency converters 15e and 16e and converting the levels, and outputs the output to a demodulator 18b. This demodulator 18b demodulates the signal having a frequency of 0.455 MHz to output the data D4. In order to obtain a diversity effect, one wave of better quality is not necessarily selected from a fundamental wave and a harmonic wave (especially a double wave) thereof by a receiving section. Both the waves may be synthesized with each other to obtain the diversity effect. More specifically, when the fundamental wave and the harmonic wave are synthesized in phase, the diversity effect can be further increased. Note that the frequencies described in the second and third embodiments represent only examples, and frequencies falling within a range on a MHz order to a GHz order can be applied.

Claims: A harmonic-frequency communication system, comprising: a transmitting section (11) including: modulation means (11a) for modulating a carrier comprising harmonic waves with data to be transmitted, said modulation means (11a) adapted to generate a modulated output including at least the fundamental frequency wave (f 1 ) and double frequency wave (f 2 ); transmitting antenna means (12) for radiating electromagnetic waves into the air, the electromagnetic waves including the fundamental frequency wave (f 1 ) and the double frequency wave (f 2 ) of the modulated output; a receiving section (15) including: receiving antenna means (14) for receiving the electromagnetic waves including the fundamental frequency wave (f 1 ) and the double frequency wave (f 2 ) radiated from said transmitting antenna means (12); diversity means (17) for processing the fundamental frequency wave (f 1 ) and the double frequency wave (f 2 ) received by said receiving antenna means (14); and demodulation means (38) for demodulating the processed signal output from said diversity means (17), thereby outputting data which is the same as the data to be transmitted, characterized in that said diversity means (17) includes: an oscillator (36) for oscillating a local oscillation signal at a frequency f LO when the fundamental frequency wave and the double frequency wave have frequencies f 1 and f 2 respectively; and a mixer (37) for mixing the fundamental frequency wave and the double frequency wave with the local oscillation signal to output a synthesized signal of mixed signals respectively having frequencies f 1 + f LO and f 2 - f LO , where the frequency f LO is set to satisfy condition f 1 + f LO = f 2 - f LO' . A system according to Claim 1, wherein said modulation means (11a) includes means for causing the double frequency wave to have the same amplitude level as that of the fundamental frequency wave. A system according to Claim 1, wherein said diversity means (17) includes means for substantially selecting one wave of better quality from the fundamental frequency wave and the double frequency wave. A harmonic-frequency communication system, comprising: a transmitting section (11) including: modulation means (11a) for modulating a carrier comprising harmonic waves with data to be transmitted, said modulation means (11a) adapted to generate a modulated output including at least the fundamental frequency wave (f 1 ) and a double frequency wave (f 2 ) ; and transmitting antenna means (12) for radiating electromagnetic waves into the air, the electromagnetic waves including the fundamental frequency wave (f 1 ) and the double frequency wave (f 2 ) of the modulated output; and a receiving section (15) including: receiving antenna means (14) for receiving the electromagnetic waves including the fundamental frequency wave (f 1 ) and the double frequency wave (f 2 ) radiated from said transmitting antenna means (12); and diversity means (17) for processing the fundamental frequency wave and the double frequency wave, characterized in that said diversity means (17) includes: a first band-pass filter (15a) for filtering the fundamental frequency wave; a second band-pass filter (16a) for filtering the double frequency wave; first and second frequency converters (15c, 16c) for converting outputs from said first and second band-pass filters (15a, 16a) into outputs having the same frequency which is an intermediate frequency of the fundamental and double frequency waves; a level detector (17c) for detecting and comparing signal levels from the outputs or inputs of said first and second frequency converters (15c, 16c) to generate a control signal; switching means (SW) for selecting any one output of outputs from said first and second frequency converters (15c, 16c) in accordance with the control signal from said level detector (17c), and demodulation means (18a) for demodulating the output selected by said diversity means (17), thereby outputting data which is the same as the data to be transmitted. A system according to Claim 4, further comprising: frequency converting means (11b) for converting the fundamental frequency wave and the double frequency wave included in the modulated output generated by said modulation means (11a) into first and second signals each having a predetermined frequency higher than that of the fundamental and double frequency waves; said transmitting antenna means (12) adapted to radiate the first and second signals converted by said frequency converting means (11b); and said receiving antenna means (14) adapted to receive the first and second signals, and said diversity means (17) adapted to process the first and second signals in place of said fundamental frequency wave and said double frequency wave. A system according to Claim 4 or 5, wherein said modulation means (11a) includes means for causing the double frequency wave to have the same amplitude level as that of the fundamental frequency wave. A system according to Claim 4 or 5, wherein said diversity means (17) includes means for substantially selecting one wave of better quality from the fundamental frequency wave and the double frequency wave. A system according to Claim 4 or 5, wherein each of said first and second frequency converters (15e, 16e) includes means for performing a first conversion operation to obtain signals respectively having frequencies equal to the fundamental frequency wave and the double frequency wave according to the outputs from said first and second band-pass filters (15d, 16d) and performing a second conversion operation to obtain signals having the same frequency according to the signals obtained by the first conversion operation.

Inventors: NAGASAWA ZENICHIROU, TAKAGI TASUKU, NAGASAWA, ZENICHIROU, TAKAGI, TASUKU, Nagasawa, Zenichirou, c/o Semicond. Res. Found.
Applicants: SMALL POWER COMMUNICATION SYST, SMALL POWER COMMUNICATION SYSTEMS RESEARCH LABORATORIES CO., LTD.
Application year: 1992
Main classification: H04B7
IPC codes: H04L27, H04B7