PROCEDURE AND DEVICE FOR TRANSMITTING INFORMATION BY RADIO

Abstract: The invention concerns a procedure for transmitting one middle channel, a first side channel and a second side channel in a radio system. According to the invention, the middle channel is transmitted as a frequency-modulated (FM) radio signal modulated by a suitable frequency, a signal symmetrically amplitude-modulated (AM) with respect to the mid-frequency of the middle channel is generated, a first amplitude-modulated single side band (LSB) is formed from the amplitude-modulated signal, a second amplitude-modulated single side band (USB) is formed from the amplitude-modulated signal, the first single side band (LSB) is modulated by the information in the first side channel, thus forming two side bands for the first single side band, the second single side band (USB) is modulated by the information in the second side channel, thus forming two side bands for the second single side band, the frequency-modulated (FM) signal, the first single side band (SSB) and the second single side band (SSB) are combined in a combiner so that all three channels are transmitted simultaneously.

Description: PROCEDURE AND DEVICE FOR TRANSMITTING INFORMATION BY RADIO FIELD OF THE INVENTION The present invention relates to a procedure as defined in the preamble of claim 1 and to a transmitter unit as defined in the preamble of claim 7 for transmitting one middle channel, a first side channel and a second side channel in a radio system. BACKGROUND OF THE INVENTION Electronic location and tracking refers to systems which can be used to locate and, if necessary, to follow a desired object as it moves, with a desired accuracy and in desired geographic extent by using radio technical methods. An application in which location service is a desired property is the national safety service network called SafeNet. The principal functions of SafeNet are transfer and routing of su- pervision information, adaptation of different safety systems and networks for integrated utilisation and establishment of a simple user interface to provide access to different telecommunication services needed in the safety sector. SafeNet has been designed to provide standard interfaces for the commonest object- under-surveillance systems and to combine in the same service network the telecommunication services needed by the operative functional units. The radio communication must be encrypted and it must be able to pro- vide a sufficient data transmission capacity for SafeNet properties. BRIEF DESCRIPTION OF THE INVENTION The object of the present invention is to make it possible to achieve the above-mentioned prop- erties. A specific object of the invention is to disclose a new type of procedure for transmitting information by radio and a new type of apparatus for implementing the transmission of information. As for the features characteristic of the present invention, reference is made to the claims. The procedure of the invention concerns the transmission of one middle channel, a first side channel and a second side channel in a radio system. The radio system comprises a channel transmitter unit and a channel receiver unit, which have been fitted to function at a plurality of radio frequencies. In the procedure of the invention, the width of the middle channel frequency band is defined and the widths of the side channel frequency bands are so defined that they are equal to or smaller than the width of the middle channel frequency band. The middle channel is transmitted as a frequency-modulated (FM) radio signal, modulated by a suitable frequency. A signal sym- metrically amplitude-modulated (AM) with respect to the mid-frequency of the middle channel is generated, in other words, the frequency of the carrier wave of the amplitude-modulated signal is substantially the same as the mid-frequency of the middle channel. From the amplitude-modulated signal, a first amplitude-modulated single side band is produced by suppressing the middle wave and the upper single side band by taking a sample of the middle wave and the upper single side band and reversing the phase of the sample and summing it with the original amplitude- modulated signal. A second amplitude-modulated single side band is formed from the amplitude-modulated signal in a corresponding manner, by suppressing the middle wave and the lower single side band by taking a sample of the middle wave and the lower single side band and reversing the phase of the sample and summing it with the original amplitude-modulated signal. The first single side band is modulated by the information in the first side channel, thus forming two side bands for " the first single side band. The second single side band is modulated by the informa- tion in the second side channel, thus forming two side bands for the second single side band. The frequency- modulated signal, the first single side band and the second single side band are combined in a combiner so that all three channels are transmitted simultane- ously. In a preferred embodiment of the invention, the first and the second single side bands are transmitted substantially in phase with each other. The middle channel is transmitted substantially in oppo- site phase relative to the single side bands. In a preferred embodiment of the invention, an analogue signal is transmitted in the middle channel and a digital signal is transmitted in a side band. In a preferred embodiment of the invention, the carrier frequency used on reception is either the frequency-modulated signal, the first single side band or the second single side band. In a preferred embodiment of the invention, a key code for the middle channel is transmitted in a single side band, said key code allowing an encrypted message to be decrypted. Moreover, the invention relates to a transmitter unit for the transmission of one middle chan- nel, a first single side band and a second single side band in a radio system. The radio system comprises a channel transmitter unit and a channel receiver unit, which have been fitted to function at a plurality of suitable radio frequencies. The transmitter unit co - prises means for generating a suitable transmission frequency and means for modulating the middle channel into -a frequency-modulated form. The transmitter unit also comprises means for generating an amplitude- modulated signal so that the carrier wave is at the mid-frequency of the middle channel. Thus, the carrier waves of the amplitude-modulated and frequency- modulated signals are substantially at the same frequency. The transmitter unit comprises means for forming a first and a second single side band from the amplitude-modulated signal, means for modulating the first single side band by a first side channel, means for modulating the second single side band by a second side channel, and means for combining the first single side band, the second single side band and the middle channel and transmitting them simultaneously. In a preferred embodiment of the invention, the means for forming a single side band comprise means by which a carrier wave to be suppressed and a single side band are substantially reversed in phase and summed with an amplitude-modulated signal. The transmitter unit preferably comprises means for phas- ing the first and the second single side bands so as to make them substantially cophasal. The transmitter unit preferably comprises means for phasing the middle channel so as to make it substantially opposite in phase with respect to the single side bands. The invention provides the advantage of achieving three information channels combined in a single signal, thereby obviating interference between signals. The invention can be used to implement an encryption function especially as needed in SafeNet ap- plications, the side channels being modulated by the encryption keys. The invention is easy to implement using existing components, and the actions required in the procedure are relatively simple. DETAILED DESCRIPTION OF THE INVENTION In the following, the invention will be described by the aid of a few examples of its embodi- ments with reference to the attached drawing, which presents a diagram representing an embodiment of the invention. Fig. 1 is a diagrammatic representation of the operation of a transmitter unit as provided by the invention. The transmitter unit comprises an oscillator 1, which generates a suitable carrier frequency for a frequency modulator 2 and a single side band generator 3. The carrier is modulated in the frequency modulator 2 by the middle channel information 7 to produce a frequency-modulated signal (FM, Frequency Modulation) . The single side band generator 3 comprises an amplitude modulator which produces an amplitude- modulated signal from the carrier frequency and a suitable clock frequency 8. The amplitude-modulated signal thus produced is in the frequency plane substantially symmetrical with respect to the carrier frequency. From the amplitude-modulated signal, two separate single side bands are formed. A single side band (SSB) is formed by suppressing the middle carrier wave and the second side band. The suppression is implemented by reversing the phase of a sample taken from the signal and summing it with the original sig- nal, with the result that they cancel each other. The first single side band LSB (Lower Side Band) separated from the amplitude-modulated signal is taken to modulator 4 and the second single side band USB (Upper Side Band) is taken to modulator 5. The first single side band LSB is modulated by the information 10 in the first side channel in modulator 4 and the second single side band USB is modulated by the information 9 in the second side channel in modulator 5. When the single side band is modulated by the side channel information, two side bands are formed for the single side band. The middle channel FM, the first single side band LSB and the second single side band USB are taken to a combiner 6. The combiner 6 phases the three signals in an appropriate manner and removes any extra modulation results so that the three signals can be transmitted simultaneously. The characteristics of the combiner 6 include a large attenuation between all three input ports, a small attenuation out from the input ports and a large return loss for all input ports. The combiner 6 phases the two single side bands USB, LSB so that they are substantially in phase with each other and in opposite phase relative to the single side bands USB, LSB of the frequency-modulated signal FM. The signal 11 to be sent to the preamplifier and antenna thus consists of the frequency- modulated signal FM transmitted in the centre and the first single side band LSB and the second single side band USB, transmitted at similar distances from it in the frequency plane. For reception, any one of the three signals can be used as a carrier wave. As the difference between the signal frequencies is known, one signal can be used as a basis for determining the frequencies of the other two signals. The invention is applicable for use in several frequency ranges. The signals are preferably transmitted in a 25 Hz frequency band divided into five 5-Hz bands. In this case, the order of the frequency bands from a lower frequency to a higher frequency is as follows: 5-Hz buffer band for adjacent band interference, first single side band LSB, frequency-modulated middle channel, second single side band USB and second 5-Hz buffer band for adjacent band interference. The apparatus of the invention can be implemented e.g. using standard Gilbert Cells. These can be connected as an oscillator, mixer, summer, separator or amplifier. The circuit to be used preferably contains integrated components for the phasing functions, e.g. capacitive or inductive components. In the implementation of the invention, it is necessary to con- sider the slight inaccuracy resulting from component tolerances, which, however, can be eliminated via calibration. The invention is not restricted to the examples of its embodiments described above, but many variations are possible within the scope of the inventive idea defined in the claims.

Claims: CLAIMS 1. Procedure _ for transmitting one middle channel, a first side channel and a second side channel in a radio system, said radio system comprising a channel transmitter unit and a channel receiver unit, which have been fitted to function at a plurality of radio frequencies, characteri sed in that - the width of the middle channel frequency band is defined, - the widths of the side channel frequency bands are defined to be equal to or smaller than the width of the middle channel frequency band, - the middle channel is transmitted as a frequency-modulated (FM) radio signal, modulated by a suitable frequency, - a signal symmetrically amplitude-modulated (AM) with respect to the mid-frequency of the middle channel is generated, - from the amplitude-modulated signal, a first amplitude-modulated single side band (LSB) is formed by suppressing the middle wave and the upper single side band by taking a sample of the middle wave and the upper single side band and reversing the phase of the sample and summing it with the original amplitude- modulated signal, - a second amplitude-modulated single side band (USB) is formed from the amplitude-modulated signal by suppressing the middle wave and the lower single side band by taking a sample of the middle wave and the lower single side band and reversing the phase of the sample and summing it with the original amplitude- modulated signal, - the first single side band (LSB) is modulated by the information in the first side channel, thus forming two side bands for the first single side band, - the second single side band (USB) is modulated by the information in the second side channel, thus forming two side bands for the second single side band, - the frequency-modulated (FM) signal, the first single side band (SSB) and the second single side band (SSB) are combined in a combiner so that all three channels are transmitted simultaneously. 2. Procedure as defined in claim 1, characteri sed in that the first (LSB) and the second (USB) single side bands are transmitted substan- tially in phase with each other. 3. Procedure as defined in claim 2, characterised in that the middle channel (FM) is transmitted substantially in opposite phase relative to the single side bands (LSB, USB) . 4. Procedure as defined in any one of the preceding claims 1 - 3, characteri sed in that an analogue signal is transmitted in the middle channel (FM) while a digital signal is transmitted in the side channel. 5. Procedure as defined in any one of the preceding claims 1 - 4, characteri sed in that the carrier wave frequency used on reception is either the frequency-modulated signal (FM) , the first single side band (LSB) or the second single side band (USB) . 6. Procedure as defined in any one of the preceding claims 1 - 5, characteri sed in that a key code for the middle channel (FM) is transmitted on a single side band, said key code allowing an encrypted message to be decrypted. 7. Transmitter unit for transmitting one middle channel, a first side channel and a second side channel in a radio system, said radio system comprising a channel transmitter unit and a channel receiver unit, which have been fitted to function at a plurality of radio frequencies, characteri sed in that 'the transmitter unit comprises means (1) for gen- erating a suitable frequency, means (2) for modulating the middle channel into a frequency-modulated (FM) form, means (3) for generating an amplitude-modulated (AM) signal so that the carrier wave is at the mid- frequency of the middle channel, means (3) for forming a first and a second single side band from the amplitude-modulated signal, means (4) for modulating the first single side band by the first side channel (10), means (5) for modulating the second single side band by the second side channel (9), means for combining the first single side band (LSB) , the second single side band (USB) and the middle channel (FM) and transmitting them simultaneously. 8. Transmitter unit as defined in claim 7, characterised in that the means (3) for forming a single side band comprise means for rendering the carrier wave to be suppressed and the single side band substantially opposite to each other in phase and summing them with the amplitude-modulated signal. 9. Transmitter unit as defined in claim 8, characterised in that the transmitter unit comprises means (6) for phasing the first and the second single side bands so as to make them substantially cophasal. 10. Transmitter unit as defined in claim 9, characterised in that the transmitter unit comprises means (9) for phasing the middle channel so as to make it substantially opposite in phase to the single side bands.

Inventors: LUOMA ARI-MATTI, LUOMA, ARI-MATTI
Applicants: LUOMA ARI MATTI, SONERA OYJ, LUOMA, ARI-MATTI
Application year: 1999
Main classification: H04L27
IPC codes: H04B1, H04J9, H04K1