MXPA97003504A

MXPA97003504A - Extend spectrum modulator

Info

Publication number: MXPA97003504A
Application number: MXPA/A/1997/003504A
Authority: MX
Inventors: Nara Yoshikazu
Original assignee: Nara Yoshikazu
Priority date: 1996-05-16
Filing date: 1997-05-13
Publication date: 1998-04-01

Abstract

The present invention relates to a system and method for producing a modulated information signal, limited in the band. A generator of the modulation signal is described, which provides a limited modulation signal in the band having a predetermined bandwidth and characteristic cut. A modulator system and method is described for producing a modulated information signal, limited in the band by combining an information signal with the limited modulation signal in the band. A generator of the modulation signal and method is described, which generates a limited modulation signal in the band as a series of values of the modulation signal at periodic intervals. An additional modulation signal generator is described which provides a limited modulation signal in the band by generating frequencies and combining them at appropriate amplitudes and phases to synthesize a limited modulation signal in the band. An additional modulation signal generator is described for generating a limited modulation signal in the band by generating a time domain signal having a predetermined frequency spectrum and by sequentially outputting a digital representation of that domain signal in time.

Description

EXTENDED SPECTRUM MODULATOR Field of the Invention The present invention relates to an extended spectrum modulator for use in an extended spectrum transmitter and more specifically to an extended spectrum modulator to produce a limited output in the band without requiring a pass filter. of band.

BACKGROUND OF THE INVENTION An example of the construction of an extended spectrum modulator of the prior art is shown in Figure 1 (a). This extended spectrum modulator of the prior art includes a diffusion signal generator 33, which supplies a broadcast signal to a multiplier 31. The multiplier receives the broadcast signal and an information signal 100 and combines them to form an output modular. A bandpass filter receives the modulated output of the multiplier and has the function of limiting the bandwidth of the signal before the transmission of the 1 10 diffusion modulation signal to reduce as much as possible, the interference coupled on an adjacent frequency channel which could be used by other transmitters and communication systems. The operations of the extended spectrum modulator described above will now be described. An information signal 100 having a limited bandwidth, as shown in Fig. 1 (b) is received at the multiplier input 31 of the spread spectrum modulator. The generator Ref. 24669 33 of the broadcast signal generates a periodic broadcast signal which has a very broad frequency spectrum as shown in Figure 1 (c). As illustrated in Figure 1 (c), the frequency spectrum of the diffusion signal can be expressed as the sum of the discrete line spectra, which correspond to the sine wave signals in the time domain. As a result of multiplying the information signal 100 by the diffusion signal, a modulated output signal is produced, which has a very broad frequency spectrum as illustrated in Figure 1 (d). The modulated output is input to the bandpass filter 32, which then limits its bandwidth, to output a modulated signal having a frequency spectrum as illustrated in 1 (e), f denotes the frequency in these figures. Figure 2 illustrates an example of the construction of a transmitter of the prior art containing an extended spectrum modulator of the prior art of the type as illustrated in Figure 1. The prior art transmitter incorporates a microphone 41 to convert a voice signal 200 to an analog electrical signal, an encoder 42 for converting the analog signal to a digital information signal and an extended spectrum modulator 43 of the type as illustrated in Figure 1, coupled to receive the digital information signal. The digital information signal is received at the input to the multiplier 48 of the spread spectrum modulator 43. The generator 50 of the broadcast signal generates a periodic broadcast signal. The modulated output is introduced to the bandpass filter 49. A frequency converter 44 and an additional bandpass filter 45 are coupled to the output of the spread spectrum modulator 43 to respectively convert the modulated signal to the transmission frequency and limit its transmission bandwidth. An amplifier 46 is used to amplify the output of the bandpass filter 46. The antenna 47 is used to transmit the output signal of the amplifier 46 on air waves. The operation of the transmitter of the prior art will now be described.

The microphone 41 converts a speech signal 200 to an analog electrical signal and enters it into the encoder 42. The encoder 42 converts the analog signal to a digital signal and, depending on the case, can be used to digitally process or compress the signal. Then the encoder 42 outputs the resulting digital signal to the spread spectrum modulator 43 for modulation thereof. After modulation, the frequency converter 44 shifts, in a manner as illustrated in FIG. 2 (b), the baseband output of the spread spectrum modulator 43 to a wireless transmission frequency, which results in a modulated transmission signal which has a frequency spectrum as shown in Figure 1 (e), except that it is shifted to the transmission frequency. ? f denotes the frequency shift in Figure 2 (b). While a frequency spectrum of the negatively shifted signal appears in Figure 2 (b), only the positive portion of the frequency spectrum is transmitted. The bandpass filter 49, used in the spread spectrum modulator 43 does not generally have a characteristic sharp cut which would eliminate the signal components which are outside the assigned transmission bandwidth. Accordingly, the prior art transmitter incorporates an additional bandpass filter 45 to eliminate the frequency components at the output of the frequency converter 44 which is outside the assigned transmission band. In this way, the level of interference coupled between the signals transmitted at adjacent frequencies can be maintained within acceptable limits. The extended spectrum modulator of the prior art and the transmitter, which are illustrated in FIGS. 1 and 2, depend on bandpass filters to minimize the interference coupled to the adjacent signal frequencies. Since the frequency spectrum of the input signal to the bandpass filter 32 has a shape as illustrated in FIG. 1 (d) and the frequency spectrum of the output signal must have a shape as shown in FIG. Figure 1 (e), bandpass filters 32 and 45 should have sharp cutting characteristics. In order to implement a bandpass filter in physical components which has an acute cutoff characteristic, the scale of the physical components must be increased. On the other hand, if such a bandpass filter is to be implemented in programming elements, the amount of calculation must be increased beyond acceptable limits. As a result, with the transmitter and modulator of the prior art, a design point must be reached either with the results in the unsatisfactory coupling of the interference on the adjacent channels or in the modulator systems which require bulky physical filter elements , expensive and / or additional processing power to appropriately limit the signals for transmission in the band. Further, in the spread spectrum transmitters of the prior art, because the built-in bandpass filter 32 of the spread spectrum modulator 43 has unsatisfactory cutting characteristics, an additional bandpass filter 45 must be provided to reduce the interference coupled to adjacent frequency channels within acceptable limits. It is therefore an object of the present invention to provide an extended spectrum modulator which does not require a band pass filter, while eliminating coupled interference over an adjacent signal frequency. It is a further object of the invention to provide an extended spectrum modulator which allows a reduction in the scale of the physical elements and / or the amount of calculation of the programming elements. Still another object of the invention is to provide an extended spectrum modulator for incorporation into an extended spectrum transmitter which produces a modulated signal output that is free of interference components that can be coupled over the adjacent signal frequencies, in such a manner that the extended spectrum transmitter does not require a bandpass filter.

BRIEF DESCRIPTION OF THE INVENTION In order to solve the above problems associated with the spread spectrum modulators and transmitters of the prior art, the present invention provides an extended spectrum modulator having a diffusion signal generator, which generates a signal of limited diffusion in the band, used to modulate the information signal. By modulation with a limited diffusion signal in the band, a limited modulated signal is produced directly in the band, thereby eliminating the need for a subsequent limitation step in the band, which would require a bandpass filter that have a sharp cutting characteristic. At the same time, the filtering requirement of the subsequent bandpass of the signal, after conversion to the transmission frequency is also eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 (a) shows a block diagram and schematic of an extended spectrum modulator of the prior art. Figure 1 (b) illustrates a frequency spectrum of an information signal before modulation. Figure 1 (c) illustrates a frequency spectrum of an extended spectrum modulation signal used to modulate an information signal. Figure 1 (d) shows a frequency spectrum of an extended spectrum modulated signal before the subsequent limitation in the band.

Figure 1 (e) shows a frequency spectrum of an extended spectrum modulated signal after limitation in the band. Figure 2 (a) shows a block diagram and schematic of an extended spectrum transmitter of the prior art. Figure 2 (b) illustrates a shift in the frequency spectrum, carried out by a frequency converter of a baseband to a wireless transmission frequency band. Figure 3 (a) illustrates a block diagram and schematic of an extended spectrum modulator constructed in accordance with the present invention. Figure 3 (b) illustrates a frequency spectrum of an extended spectrum modulation signal limited in the band. Figure 4 is a schematic block diagram of an extended spectrum transmitter constructed in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of an extended spectrum modulator, constructed in accordance with the present invention will now be described with reference to Figures 3 and 4. Figure 3 (a) illustrates the interconnection of the elements of the spectrum modulator. extended according to the present invention. The spread spectrum modulator incorporates an extended spectrum modulation signal generator 12, to provide an extended spectrum modulation signal limited in the band to a multiplier 11. The multiplier 11 is used to combine the limited modulation signal in the band and an information signal 100 for producing an output signal 120 of limited spectrum in the band which does not require additional bandpass filtering before transmission. The extended spectrum modulated output signal 120, limited in the band, is encoded according to a broadcast code and can be demodulated in a receiver by using the same broadcast code as the broadcast code used in the modulation process. The generator 12 of the diffusion signal incorporates a memory 13 and a direction counter 14. The address counter 14 is used to provide a destination designation signal to sequentially recover the values of the stored modulation signal from the memory 13 which represent the spread spectrum modulated signal limited in the band. The generator 12 of the broadcast signal sequentially outputs the values of the modulation signal stored at periodic intervals according to the address designation signal. The address counter 14 provides a designation signal of address according to the following. A synchronization (or clock) signal 130 is provided to the address counter 14 of a synchronization input. The address counter 14 maintains a count which is proportionally related to the number of synchronization cycles or clock cycles which have elapsed. The address designation signal is based on the count thus obtained. The address counter 14 continues with the count increment in proportional relation to the synchronization signal 130 until the address counter 14 has passed through all the values of the modulation signal stored in the memory 13. At that time the counter 14 of address restores the count and begins to recover the values of the modulation signal stored from the beginning again. This process is repeated again during each subsequent cycle of the extended spectrum modulation signal. The limited spectrum modulated signal in the band is prepared according to the following principles. As described above in relation to the extended spectrum modulator and transmitter of the prior art, the extended spectrum modulation signal of the prior art is a periodic signal, such as a periodic diffusion coding signal. As is well known, any periodic signal can be represented as a Fourier series of sine waves at defined amplitudes and phases. Accordingly, the frequency spectrum of the periodic spread spectrum modulation signal can be expressed as a sum of the line spectra (sine wave signals), as shown in Figure 1 (c). By the principles described in the foregoing, the broadband extended spectrum modulation signal, which is emitted from the diffusion signal generator 33 of the prior art, can be synthesized by generating a series of sine waves which have the same frequencies such as those observed in the frequency spectrum (Figure 1 (c)) of the broadband extended spectrum modulation signal and by combining those sine waves at the appropriate amplitudes and phases to synthesize the modulation signal. In a similar manner, an extended spectrum modulation signal, limited in band, having a frequency spectrum characterized by a predetermined bandwidth and characteristic cut can be synthesized by generating a series of sine waves which have the same frequencies as those observed in the limited frequency spectrum in the band (Figure 3 (b)) of the limited modulation signal in the band and then combine those sine waves at the appropriate amplitudes and phases. Accordingly, the values of the modulation signal which are used in the extended spectrum modulator of the present invention for combination with the information signal are prepared according to one embodiment of the invention by synthesizing the limited frequency spectrum in the band of the same, having a predetermined bandwidth and characteristic cut and then digitally converting and storing the values of the modulation signal of the limited modulation signal in the resulting band in the memory 13. In this embodiment of this invention, the limited band diffusion signal generator 12, of the spread spectrum modulator, is constructed with a memory 13 and a direction counter 14, which provides a direction designation signal, based on the counting of the synchronization, to address the memory. However, one skilled in the art will recognize how to build and operate a limited diffusion signal generator in the band, to incorporate it into an extended spectrum modulator of the present invention which synthesizes and emits a limited diffusion signal in the band in real time, according to the principles described above. An alternative way to realize a limited spectrum modulation signal in the band, which is appropriate for the stored generation methods and in real time, is carried out by means of mathematical manipulations of the frequency spectrum of a modulation signal. broad band. As described above, it is well known that each time domain signal, periodic, can be represented as a series of sine waves at defined amplitudes and phases. Such a representation of the signal by the sine wave series is also referred to as a spectral representation. The spectral representation of a signal can be manipulated by means of mathematical calculations carried out by micro-coding, programming elements or by physical elements. Thus, a modulation signal, limited in the band, which has a limited frequency spectrum in the band, characterized by a predetermined bandwidth and characteristic cut, can be made according to a mathematical calculation method by: first determining the frequency spectrum of a broadband modulation signal (eg, the frequency spectrum as shown in Figure 1 (c)); truncating that broadband frequency spectrum to obtain the limited frequency spectrum in the band of the limited modulation signal in the band (eg, such as the frequency spectrum shown in Figure 3 (b)); and then transform the limited frequency spectrum in the band by additional calculations to a periodic modulation signal, domain in time, having the predetermined bandwidth and characteristic cutoff. After being generated, the limited modulation signal in the band is then combined to a multiplier 11 with an information signal to modulate that information signal, as in the case of a real-time mode of the invention. Alternatively, the limited modulation signal in the band can be converted to a digital representation for storage in a memory 13 and then combined with an information signal at periodic intervals, as described above. In the following, one embodiment of an extended spectrum transmitter constructed in accordance with the present invention will be described with reference to Figure 4. As shown, the construction of the spread spectrum transmitter according to the present invention differs from the spectrum transmitter extended from the prior art by having an extended spectrum modulator 23 limited in the band and by not incorporating an additional bandpass filter 45 at the output of the frequency converter 24. The transmitter incorporates a microphone 21 for converting a speech signal 200 to an analog electrical signal, an encoder 22 for converting the analog signal to a digital information signal and an extended-spectrum modulator 23 of the type illustrated in Figure 3 and coupled to receive the digital information signal. A frequency converter 24 and an amplifier 25 are coupled to the output of the spread spectrum modulator 23. The antenna 26 is used to transmit the output signal of the amplifier 25 on the air waves. The spread spectrum modulator 23 incorporates an extended spectrum modulation signal generator 30 to provide an extended spectrum modulation signal limited in the band to a multiplier 27. The generator 30 of the diffusion signal incorporates a memory 28 and a counter 29 of address. A synchronization signal 140 is provided to the address counter 29. The operations of the spread spectrum transmitter according to the present invention will now be described. Since the frequency spectrum of the output of the spread spectrum modulation signal of the generator 30 of the broadcast signal is limited to the allocated bandwidth, the output of the modulated signal of the multiplier 28 does not contain interference components to be coupled over an adjacent frequency channel. Accordingly, even after the conversion of the modulated signal to the transmission frequency by the frequency converter 24, the signal converted to the frequency does not contain interference components outside the assigned transmission band. In this way, the need for an additional bandpass filter 45, after the frequency converter 24, is eliminated. Thus, the spread spectrum transmitter according to the present invention is used to transmit the limited modulated signals in the band, without requiring expensive physical bandpass filter elements or a calculation amount of the excessive programming elements. While the invention has been described in detail herein in accordance with certain preferred embodiments thereof, many modifications and changes thereto can be made by those skilled in the art. Therefore, it is proposed that the appended claims cover all such modifications and changes that are presented within the true spirit and scope of the invention.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, it is claimed as property, what is contained in the following Numeration 11, 27, 31, 48 Multiplier 12, 30, 33, 50 Broadcast signal generator 13, 28 Memory 14, 29 Address counter 21, 49 Microphone 22, 42 Encoder 23, 43 Extended spectrum modulator 24, 44 Frequency converter 25, 46 Amplifier 26, 47 Antenna 32, 45, 49 Bandpass filter 100 Information signal 110, 120 Broadcast modulation signal 130, 140 Clock or synchronization signal 00 Analogue voice signal

Claims

Claims 1. A modulator for modulating an information signal to produce a modulated information signal, limited in the band, characterized in that it comprises: generating means for generating a limited modulation signal in the band having a predetermined bandwidth and cutting characteristic; and means for combining the information signal with the modulation signal to produce the limited modulated information signal in the band.
2. The modulator according to claim 1, characterized in that the generating means include: means for generating frequencies necessary to synthesize the limited modulation signal in the band; and means for combining the generated frequencies at appropriate amplitudes and phases to synthesize the limited modulation signal in the band.
3. The modulator according to claim 1, characterized in that the generating means provide a series of modulation signal values at periodic intervals representative of the limited modulation signal in the band.
4. The modulator according to claim 1, characterized in that the modulation signal is a broadcast code signal for use in the production of an extended spectrum modulated information signal.
5. The modulator according to claim 3, characterized in that the generating means further include: means for storing the series of values of the modulation signal; and means for sequentially recovering, at periodic intervals, the values of the modulation signal.
6. The modulator according to claim 5, characterized in that the modulation signal is a broadcast code signal for use in the production of an extended spectrum modulated information signal.
7. A generator of the modulation signal for providing a limited modulation signal in the band having a predetermined bandwidth and characteristic cut, characterized in that it comprises: generation means for generating the frequencies necessary to synthesize a frequency spectrum of the signal of limited modulation in the band; and means for combining the generated frequencies at appropriate amplitudes and phases to synthesize the limited modulation signal in the band.
8. The generator of the modulation signal according to claim 7, characterized in that the modulation signal is a broadcast code signal for use in the production of an extended spectrum modulated information signal.
9. A generator of the modulation signal for generating a periodic modulation signal having a predetermined frequency spectrum for use in the modulation of a digital information signal, characterized in that it comprises: means for generating a domain signal in time that has a frequency spectrum predetermined; and means for sequentially outputting a digital representation of the domain signal in time to generate the periodic modulation signal.
10. The generator of the modulation signal according to claim 9, characterized in that it also includes: means for storing a digital representation of the domain signal in time; and means to sequentially recover the digital representation.
11. A method for modulating an information signal to produce a limited modulated information signal in the band, characterized in that it comprises the steps of: generating a limited modulation signal in the band having a predetermined bandwidth and characteristic cut; and combining the information signal with the modulation signal to produce the limited modulated information signal in the band.
12. The method according to claim 1, characterized in that the modulation signal is a broadcast code signal for use in the production of an extended spectrum modulated information signal.
13. The method according to claim 1, characterized in that the generation step includes: generating the frequencies necessary to synthesize a frequency spectrum of the limited modulation signal in the band having a predetermined bandwidth and characteristic cut; and combining the generated frequencies at appropriate amplitudes and phases to synthesize the limited modulation signal in the band.
14. The method according to claim 11, characterized in that the generation step includes. providing a series of values of the modulation signal at periodic intervals representative of a modulation signal having the predetermined bandwidth and characteristic cut.
15. The method according to claim 14, characterized in that the step of providing a series of values includes storing the series of modulation values; and sequentially recovering, at periodic intervals, the values of the modulation signal.
16. A method for generating a time domain, periodic modulation signal, having a frequency spectrum limited in the band from a wideband modulation signal, for use in the modulation of a digital information signal, the The frequency spectrum limited in the band is characterized by a predetermined bandwidth and characteristic cut, and the method is also characterized in that it comprises the steps of: determining the frequency spectrum of the broadband modulation signal; truncate the frequency spectrum of the broadband modulation signal to obtain the frequency spectrum limited in the band; and transform the frequency-limited spectrum in the band to the domain modulation signal in time, periodic.