JPH0586098B2 - - Google Patents

Description

[Detailed description of the invention] Technical field of invention The present invention relates to a wireless communication system.

Background of the Technology In a wireless communication system in which data is transmitted wirelessly from a transmitting system and the data is demodulated and reproduced in a receiving system, digital modulation based on the data is applied to a carrier wave. As this digital modulation, various methods have been put into practical use. Among these, the present invention particularly focuses on multilevel quadrature amplitude modulation (QAM).
Modulation). A QAM wireless communication system modulates the phase and amplitude components of a carrier wave for data to be transmitted, and schematically arranges a large number of modulation points corresponding to the data on a plane and transmits the data. be. Therefore, a large amount of data can be transmitted at once, and the transmission capacity of the wireless transmission path can be significantly increased.

Conventional technology and issues A large number of modulation points are formed in the QAM method (as described above), and the number of modulation points can be 16, 32, or 64.
values, ranging from 128 values, etc. One of the important functions of the receiving system in this case is regeneration of a reference carrier wave for coherent detection. This recovered carrier wave is used to demodulate the original data. Normally, the 16-value QAM method is mainly used among the multi-value QAM methods, but in this case, the reference carrier wave is regenerated using a four-phase phase keying (PSK) method. A similar method is used. That is, so-called multiplication methods (2 multiplication, 4 multiplication, etc.) in which a carrier wave regeneration circuit is provided with a phase selection control function are well known.

When using the conventional carrier wave recovery circuit as described above, problems such as suppression of jitter in the recovered carrier wave become noticeable when the number of values becomes 16. Moreover, 32 values, 64 values,
When the value becomes 128, it becomes almost impossible for this type of carrier wave recovery circuit to recover a reference carrier wave for practical synchronous detection. Therefore, it is desirable to realize a wireless communication system using a new method different from the conventional one, and to put into practical use a QAM wireless communication system that can be fully applied to multi-value orthogonal modulation of 32 or more values.

Purpose of the Invention In view of the above-mentioned circumstances, the present invention provides multi-valued
The purpose of this study is to propose a wireless communication system that can be put to practical use even if it is QAM.

Structure of the Invention In order to achieve the above object, the present invention transmits a modulated wave obtained by modulating a carrier wave having a frequency of ₀ with a digital signal having a predetermined clock frequency _CL to a receiving system. In a wireless communication system that receives a modulated wave, extracts the carrier wave therefrom, and reproduces the digital signal using the extracted carrier wave, in the transmission system, the frequency is set on the signal spectrum of the modulated wave. ₀ and 1/N (N is an integer of 2 or more) of the clock frequency _CL ( ₀ +
1/N・_CL ) and a first carrier wave regeneration signal and a second carrier wave regeneration signal having a frequency ( ₀ − 1/N・_CL ) corresponding to the difference thereof, respectively, to form the modulated wave; In the receiving system, the first carrier wave regeneration signal (frequency is ₀ + 1/N) _CL and the second carrier wave recovery signal (frequency is ₀ - 1/N _CL ) are applied to a modulator to obtain the frequency The present invention is characterized in that the carrier wave of ₀ and the signal of the clock frequency _CL are extracted and the digital signal is reproduced.

Embodiments of the Invention FIG. 1 is a diagram showing a general signal spectrum of a modulated wave transmitted from a transmission system. In this figure, the horizontal axis is frequency and the vertical axis is power W. As mentioned above, it is difficult to extract the carrier wave with multilevel modulated waves. Therefore, attempts have already been made to insert a carrier wave regeneration signal into a modulated wave in advance in the transmission system to facilitate carrier wave extraction in the reception system and to simplify the reproduction of digital signals. Such a carrier recovery signal is usually inserted at the zero point of the signal spectrum. In the figure, the frequency ( ₀ + _CL ) or ( ₀
− _CL ) is the zero point. Here, ₀ is the frequency of the carrier wave in the transmission system, and _CL is the clock frequency of the digital signal that modulates the carrier wave. In the figure, the carrier wave regeneration signal is placed at the zero point of frequency ( ₀ + _CL ).
The state with C _r inserted is shown. By inserting the carrier wave regeneration signal C _r at the zero point in this way, it does not give any noise or interference to the data signal, and the signal C _r itself does not receive interference from the data signal, so it is a so-called S/ N becomes good. It is well known that the above zero points appear periodically with a so-called Nyquist rate.

However, inserting the carrier wave regeneration signal C _r at the above zero point, that is, the zero point appearing in the Nyquist rate, is not suitable for a commercial communication system. This is because the signal spectrum is restricted by the Radio Law, etc., and the carrier regeneration signal C _r cannot be transmitted to the receiving system with sufficient power.

FIG. 2 is a diagram showing a signal spectrum when band limitation is applied to the transmission signal of FIG. 1. In this figure, hatched areas indicate areas to which band restrictions have been applied according to the Radio Law and the like. As a result of such band limitation, the carrier wave regeneration signal C _r to be transmitted is masked and disappears.

Therefore, in the present invention, the carrier wave regeneration signal C _r is forcibly pushed into the signal component within the band limit. Inserting the carrier wave regeneration signal C _r into the signal component in this way is inherently disadvantageous from the viewpoint of S/N and is not a good idea. However, in the multilevel QAM system, even if some signal degradation is allowed, it is preferable to simplify the hardware required for inserting a carrier wave recovery signal in the transmission system and for carrier wave recovery in the reception system, and this is According to the method of the invention, this can be simplified (described later).
FIG. 3 is a diagram showing a signal spectrum for explaining the present invention. In this figure, C _r1 is the first carrier wave regeneration signal that is forcibly inserted into the signal component. Also, a second carrier wave reproduction signal C _r2 is also inserted at the same time. The frequencies of these carrier wave regeneration signals C _r1 and C _r2 may be selected anywhere in principle, but these frequencies are determined according to certain rules, especially in order to simplify the hardware in the receiving system (described later). That is, for C _r1 , it is ( ₀ + 1/ _N.CL ) (N is an integer of 2 or more), and for C _r2 , it is ( ₀ - 1/ _N.CL ). ₀ is the frequency of the carrier wave mentioned above, _CL
is also the clock frequency mentioned above. In Figure 3, N
=2 is shown as an example.

FIG. 4 is a block diagram showing an example of the configuration of a transmission system for realizing the system of the present invention. In the transmission system S, 45 is a 1/N frequency divider for generating the 1/N· _CL . Now, since we are taking N=2 as an example, it works as a 1/2 frequency divider. First, the digital signal D to be transmitted is processed in the data processing section 41 and becomes an analog signal S _A. This data processing section 41 is, for example, a serial/parallel converter, a digital/
Consists of analog converters, etc. A clock signal (frequency _CL ) for this data processing is supplied from a clock generator 44.

The analog signal S _A is input to the modulator 42 and modulates a carrier wave (frequency ₀ ). This carrier wave is given to the modulator 42 from a carrier wave generator 47. In this way, the output from the modulator 42 passes through the hybrid circuit 43 and becomes the modulated wave S _put to be transmitted to the receiving system.
becomes. Furthermore, first and second carrier wave regeneration signals C _r1 ( ₀ + 1/N・_CL ) and C _r2 ( ₀ −1
/N・_CL ). The clock signal ( _CL ) from the clock generator 44 is converted into a frequency-divided signal (1/N・_CL ) by the 1/N frequency divider 45, and this is converted into a carrier wave ( ₀ ) by the modulator 46 from the carrier wave generator 47. and the first and second carrier wave regeneration signals
C _r1 , C _r2 (frequency is ( ₀ + 1/N・_CL ) and ( ₀
−1/N)) _CL・) is obtained and inserted onto the signal spectrum via the hybrid circuit 43. In this way, the modulated wave S _put containing C _r1 and C _r2 is transmitted to the receiving system.

FIG. 5 is a block diagram showing an example of the configuration of a receiving system for implementing the system of the present invention. In the receiving system R, the modulated wave S _put in Fig. 4 is transmitted through a transmission path (not shown).
is received as a modulated wave S _io . The received modulated wave S _io is applied to a bandpass filter 51 on the one hand, and a first carrier recovery signal C _r1 having a frequency ( ₀ +1/N· _CL ) is extracted. On the other hand, it is applied to the bandpass filter 52 to extract a second carrier wave regeneration signal C _r2 having a frequency of ( ₀ -1/N· _CL ). When these C _r1 and C _r2 are applied to the modulator 53, a signal with a frequency of ₂₀ and a signal with a frequency of 2/N· _CL are obtained, which are selectively extracted by bandpass filters 54 and 56, respectively. . Furthermore, the frequency ₂₀ signal is divided into 1/2 by the 1/2 frequency divider 57.
The frequency is divided by 2 to reproduce the original carrier wave ( ₀ ), and the 2/N multiplier 55 multiplies the signal with the frequency 2/N _CL by 2/N to reproduce the original clock signal CL. In this case, in this example where N is selected to be 2, the signal is multiplied by 2/2, and this 2/N multiplier 55 is virtually unnecessary and is most advantageous for simplifying the receiving system. Also, N is an even number of 4 or more (N=4,
6, 8...), the configuration of the 2/N multiplier 55 becomes simple. Note that the clock signal is a signal necessary for reproducing the original digital signal D as digital data.

On the other hand, the carrier wave ( ₀ ) from the 1/2 frequency divider 57 and the received modulated wave S _io are both applied to the detector 58 to perform synchronous detection, but as shown in FIG. Since C _r1 and C _r2 are forcibly superimposed on the originally existing information components, when viewed on the time axis, the output signal S _B has a clock frequency of N
Since the frequency-divided offset is included, it is not the final demodulated data, and the carrier wave regeneration signals C _r1 and C _r2 fluctuate with an offset frequency (1/N· _CL ). In order to cancel this fluctuation, a signal having a frequency of 1/N _CL is differentially added to the signal S _B.

For this purpose, a signal with a frequency of 1/N· _CL from the 1/2 frequency divider 59 is applied to a subtracter 60, and the difference with the signal S _B is calculated to obtain demodulated data S _C.

FIG. 6 is a diagram showing a signal spectrum for clarifying the operation of the circuit (transmission system) shown in FIG. 4. Referring to this figure, when the carrier wave ( ₀ ) from the carrier wave generator 47 is modulated in the modulator 42 by the analog signal S _A from the data processing section 41 in FIG. 4, the output from the modulator 42 is The signal spectrum of ₀ is as shown in column (1) of Figure 6.
Appears in a band centered on . Note that _SA shown on the left side of column (1) is the signal spectrum of the analog signal _SA . Next, the clock signal ( _CL ) from the clock generator 44, the frequency-divided signal (1/N・CL) obtained by dividing this by the 1/N frequency divider 45, and the frequency-divided signal (1/N・_CL ) from the clock signal (CL) from the clock generator 44, A first carrier wave regeneration signal C _r1 obtained by multiplying the carrier wave ( ₀ ) by the _modulator 46
( ₀ + 1/N· _CL ) and the second carrier regeneration signal C _r2 ( ₀ −1/N· _CL ) each have a signal spectrum shown in column (2) of FIG. Therefore, the signal spectrum of the band centered on ₀ in column (1) of FIG. 6 and the signal spectrum of C _r1 and C _r2 in column (2) of FIG. When synthesized in , the signal spectrum shown in column (3) of FIG. 6 is obtained.

FIG. 7 is a signal spectrum for clarifying the operation of the circuit (receiving system) shown in FIG. 5. Referring to this figure, the first carrier wave regeneration signal C _r1 ( ₀ +
1/N・_CL ), the second carrier wave regeneration signal C _r2 ( ₀ −1/N・_CL ) from the bandpass filter 52, and these C _r1 and C _r2 are multiplied by the modulator 53, and then The output (2/N・_CL ) extracted by the band-pass filter 54 and the output (2 ₀ ) extracted by the band-pass filter 56 each correspond to the signal spectrum shown in column (1) of FIG. have Furthermore, the output (CL) and output ( ₀ ) obtained by passing the above output (2/N・_CL ) and output (2 0 ) through the ₂ /N multiplier 55 and 1/2 frequency divider ₅₇ , respectively, in FIG. and the output (1/N・_CL ) obtained by dividing the above output (2/N・_CL ) by the 1/2 frequency divider 59 are the signals shown in column (2) of FIG. It has a spectrum. Then, the recovered carrier wave ( ₀ ) obtained by the 1/2 frequency divider 57 and the received modulated wave
S _io and the output signal S _B obtained by demodulating this S _io with the recovered carrier wave ( ₀ ) in the detector 58 are respectively
It has a signal spectrum shown in column (3) of the figure. In this case, the received modulated wave S _io fluctuates with the offset frequency (1/N· _CL ) of the carrier recovery signals C _r1 and C _r2 within the band.

Column (3) in FIG. 7 shows the signal spectra of these offset frequency components as C _r1 and C _r2 . The subtracter 60 shown in FIG. 5 cancels this out.

FIG. 8 is a waveform diagram for clarifying the operation of the subtracter 60 in FIG. 5. Since the received modulated wave S _io includes the offset frequency components of C _r1 and C _r2 as described above, the output signal from the detector 58 in FIG.
S _B should originally change in a smooth “1” and “0” pattern as shown by the solid lines S _B and S _B ′ in column (1) of Fig. 8, but in reality, the output signal S _B ″ is the dotted line. A distorted output signal that looks like the output signal S _B of the solid line is connected is demodulated. This is because the level of the signal with the component of the offset frequency (1/N・_CL ) periodically changes from the output signal S _B This is because the level of the output signal S B '' is shifted by, for example, the level Δa and changed to the output signal S _B ″. Therefore, the signal having the component of the offset frequency (1/N・_CL ) is reproduced by the 1/2 frequency divider 59 in FIG. 5, and as shown in column (2) of FIG. Obtain a signal that changes at a frequency of /N・_CL . Since the signal in column (2) is synchronized with the dotted output signal S _B '' shown in column (1) in Figure 8, the level of the signal in column (2) is almost equal to the level Δa above. After adjusting as shown in the figure, the subtracter 60 differentially adjusts
Add it to the signal in column (1) (S _B +S _B ″). As a result, the output signal shown by the dotted line in column (1) in Figure 8
S _B '' is corrected to the output signal S _B ' shown by the solid line, and a distortion-free output signal (S _B +S _B ') is obtained. This becomes the demodulated data S _C in FIG. 5.

Effects of the Invention As explained above, according to the present invention, the hardware required for inserting a carrier wave regeneration signal in the transmitting system and regenerating the carrier wave in the receiving system is greatly simplified, and it can be applied to multilevel QAM communication systems. The effect is extremely large.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a general signal spectrum of a modulated wave transmitted from a transmission system, Fig. 2 is a diagram showing a case where band limitation is added to the signal spectrum of Fig. 1, and Fig. 3 is a diagram showing the case where the signal spectrum of the present invention is FIG. 4 is a diagram showing a signal spectrum for explanation; FIG. 4 is a block diagram showing an example of the configuration of a transmission system for realizing the method of the present invention;
FIG. 5 is a block diagram showing an example of the configuration of a receiving system for realizing the method of the present invention, FIG. 6 is a diagram showing a signal spectrum to clarify the operation of the circuit in FIG. 4, and FIG. FIG. 5 is a diagram showing a signal spectrum to clarify the operation of the circuit in FIG. 5, and FIG. 8 is a waveform diagram to clarify the operation of the subtracter in FIG. 42, 46...Modulator, 44...Clock generator, 45...1/N frequency divider, 47...Carrier wave generator, 51, 52, 54, 56...Band pass filter, 53...Modulator , 55... N/2 multiplier, 57, 59... Frequency divider, 58... Detector, 60... Subtractor, D... Digital signal, S _put ... Modulating wave, S _io
... Received modulated wave, _SC ... demodulated data, CL ... clock signal, C _r1 , C _r2 ... first and second carrier wave regeneration signals, S ... transmission system, R ... reception system.

Claims (1)

[Claims] 1. In the transmission system, a carrier wave having a frequency of ₀ ,
A modulated wave phase-modulated with a digital signal having a predetermined clock frequency _CL is transmitted to a receiving system, the receiving system receives the modulated wave, extracts the carrier wave from this, and uses the extracted carrier wave. In the wireless communication system for reproducing the digital signal, in the transmission system, the frequency ₀ and the clock frequency are included on the signal spectrum of the modulated wave.
A first carrier wave having a frequency ( ₀ + 1/N・_CL ) corresponding to the sum of 1/N of CL (N is an integer of 2 or more) and a frequency _{( 0} −1/N・_CL ) corresponding to the difference thereof. A reproduction signal and a second carrier reproduction signal are further inserted to form the modulated wave, and the receiving system receives the first carrier reproduction signal (frequency is ₀ + 1/N・_CL ) and the second carrier wave. A reproduction signal (with a frequency of ₀ - 1/N・_CL ) is applied to a modulator to obtain a carrier wave with a frequency of ₀ , a signal with a clock frequency _CL , and a signal with a frequency of 1/N・_CL . After the received modulated wave is detected by a wave detector, the difference between the signal of the frequency 1/N・_CL and its detection output is taken as demodulated data, and the clock frequency is determined from the demodulated data.
A wireless communication system characterized in that the digital signal is reproduced using _{a CL} signal. 2 In the transmission system, the clock frequency
The output from the clock generator that generates _{the CL} signal is divided by 1/N to obtain a signal with the frequency 1/N・_CL , and the output from the carrier wave generator that generates the carrier wave with the frequency ₀ and the frequency 1/N are divided by 1/N. Add the N・_CL signal to the modulator to obtain the frequency ₀ +1/N・_CL and the frequency ₀ −1/N.
- The wireless communication system according to claim 1, wherein the first and second carrier wave regeneration signals of _CL are respectively obtained and inserted into the modulated wave phase-modulated with the digital signal. 3 When the integer N is N=2, the first and second modulated waves received in the receiving system are
Extract each carrier wave regeneration signal and calculate the frequency.
₂₀ and a second signal with a clock frequency _CL , the first signal is further applied to a 1/2 divider to obtain the carrier wave with a frequency of ₀ , and the second signal with a clock frequency CL is obtained.
is applied to a 1/2 frequency divider to obtain a third signal with a frequency of 1/2・_CL , and after detecting the received modulated wave using the carrier wave, the third signal and its detection output are 3. The wireless communication system according to claim 2, wherein the demodulated data is obtained by calculating the difference between the two. 4 When the integer N is an even number of N=4 or more, the first modulated wave received in the receiving system
and a second carrier wave regeneration signal to obtain a first signal with a frequency of ₂₀ and a second signal with a frequency of 2/N・_CL , and convert these first and second signals into 1/ 2 frequency divider and N/2 multiplier to obtain the carrier wave of frequency ₀ and the clock signal of frequency _CL , and after the modulated wave received by the carrier wave is detected by a wave detector, the third 3. The wireless communication system according to claim 2, wherein the demodulated data is obtained by calculating the difference between the signal and its detected output.