JPS6346619B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides multi-channel pulse amplitude modulation (hereinafter referred to as
It is abbreviated as PAM. ) Related to orthogonal multiplex signal transmission equipment that increases information transmission efficiency by orthogonally multiplexing signals, especially multiple complex baseband
The present invention relates to a digital processing type transmitter that performs quadrature amplitude (hereinafter abbreviated as QAM) modulation and orthogonal multiplexing of a PAM signal through digital processing.

As this type of transmitting device, a "digital processing type transmitting signal device for orthogonal multiplexed signals" has already been proposed in Patent Application No. 104609 of 1972 (Japanese Unexamined Patent Publication No. 54-37520). However, in this digital processing transmitter for orthogonal multiplexed signals, it is necessary to perform N-point inverse Fourier transform every T/2 seconds, even though there is only N/2-point complex data as input (where T is for each PAM is the clock period of the signal,
N/T is the sampling frequency. ) Furthermore, it is necessary to provide switching control units for every T/2 seconds at various locations, which has the disadvantage of complicating the hardware design.

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks, it is an object of the present invention to provide a digital processing type transmitting device for orthogonal multiplexed signals, which allows the use of an N/2-point inverse Fourier transformer and reduces the number of switching control units every T/second. It is something.

The present invention will be explained below using the drawings.

Figure 1 is a block diagram showing the transmission/reception system of orthogonal multiplexed QAM signals, where 1 ₀ , 1 ₁ , ..., 1 _2L-1 are 2L PAMs synchronized with each other with a clock period of T seconds.
Input terminals where signals are input, 2 ₀ , 2 ₁ , ..., 2 _L-
1 is L T/2 second delay circuits, 3 ₀ , 3 ₁ , ...,
3 _2L-1 has 2L transmit baseband filters 4 ₀ ,
4 ₁ , ..., 4 _2L-1 is a 2L modulator, 5 is a multiplexing circuit that adds all the outputs of each modulation and sends it to the transmission path, 6 is a transmission path, 7 ₀ , 7 ₁ , ..., 7 _2L-1 is 2L demodulators, 8 ₀ , 8 ₁ , ..., 8 _2L-1 is 2L reception baseband filters, 9 ₀ , 9 ₁ ..., 9 _L-1 is L T /2 second delay circuit, 10 ₀ , 10 ₁ , ...,
10 _L-1 are L T-second delay circuits, 11 ₀ , 11 ₁ ,
..., 11 _2L-1 is an output terminal from which 2L PAM signals are output.

In Figure 1, the R-th input terminal (R is 0R<L
)1 _R and (L+R)th input terminal
1 _L+R respectively the Rth PAM signal and the (L+
It is assumed that the R)th PAM signal is input.
The R-th PAM signal is delayed by T/2 seconds at _2R , is band-limited and waveform-shaped at transmission baseband filter _3R , and then reaches modulator _4R .

On the other hand, the (L+R)th PAM signal is band-limited and waveform-shaped by the transmission baseband filter 3 _L+R as it is, and then reaches the modulator 4 _L+R . In the modulators 4 _R and 4 _L+R , the in-phase carrier cos2πf _R t of frequency f _R and the orthogonal carrier sin2πf _R t of frequency f R are input as modulation carriers, and both modulation outputs are added in the multiplexing circuit 5 to obtain the center frequency f _R becomes R
The second QAM signal is formed.

Here, the frequency of the carrier used in each modulator is f _R - f _R-1 = T ^-1 for R, which is 1RL-1.
The modulators 4 ₀ , 4 ₁ , ..., 4 _L-
The carrier in _{No. 1} has cosine waves and sine waves arranged alternately.

It is already well known that an orthogonally multiplexed QAM signal is output from the multiplexing circuit 5 by such a modulation operation on the transmitting side. The orthogonal multiplexed QAM signal output from the multiplexing circuit 5 is transmitted to the receiving side via the transmission line 6. On the receiving side, a conversion completely opposite to that on the transmitting side is performed, and the output terminals 11 ₀ , 11 ₁ , . . .
11 Each PAM signal corresponding to _2L-1 is obtained. Here, the transmission baseband filters 3 ₀ , 3 ₁ , ...,
3 _2L-1 and reception baseband filters 8 ₀ , 8 ₁ ,
......, 8 _2L-1 all have the same frequency response G (ω) and its 3 dB lower band (referred to as one-sided effective band) 1/2T
Assume that it is a Hertzian low-pass filter, and G ² (ω)
is a normal Nyquist filter that reduces by 6 dB at 1/2 T hertz, then the output terminal 11 on the receiving side
It is known that a PAM signal without intersymbol interference or interchannel interference can be obtained at an appropriate sampling point for ₀ , 11 ₁ , . . . , 11 _2L-1 .

Let us consider that the signal processing operations of the transmitting section from the input terminals 1 ₀ , 1 ₁ , . . . , 1 _2L-1 in FIG. 1 to the output of the multiplexing circuit 5 are all performed by digital processing. That is, each of the plurality of PAM signals is made into a sample value series with a sampling frequency of 1/T hertz, and a sample value series with a sampling frequency f _s hertz corresponding to the output of the multiplexing circuit 5 is generated. This sampling frequency f _s must be set to a certain high frequency so as not to cause interference due to aliasing in the signal spectrum after multiplexing.

f _s to further facilitate subsequent digital processing.
must be selected as an integral multiple of 1/T. Also, the first
In order to provide a delay difference of T/2 seconds at 2 ₀ , 2 ₁ , . . . , 2 _L-1, etc. in the figure, f _s needs to be an even multiple of 1/T.

Here, it is assumed that a frequency N times 1/T is selected as f _s . However, it is assumed that N is an even number and larger than the number of input PAM channels, 2L. The PAM signal sample value sequence every T seconds that is now input to input terminal 1 _{R is}
( ^ZN ). However, z=e ^j2 〓 ^f/fs .

Furthermore, if the transmitting baseband filter is z-transformed and expressed as G(z), the output of the transmitting baseband filter 3 _R is U _R (z) for R which is 0RL-1.
and the output of transmitting baseband filter 3 _R+L V _R
(z) are each expressed by the following equations.

U _R (Z)=X _R (Z ^N )G(Z)Z ^N/2 ……(1) V _R (Z)=X _R+L (Z ^N )G(Z) ……(2) (1 ), U _R (Z) and V _R (Z) given by equation (2) are modulated by cos2πf _R t and sin2πf _R t, respectively, if R is an even number, and then added to form the R-th QAM signal, If R is an odd number, sin2πf _R t and cos2πf _R
t and then summed to form the Rth QAM signal.

Therefore, the sample value series Y(Z) of the transmitted output is expressed as follows.

Y(Z)= 〓 〓 ^R=0,2u

Claims (1)

[Claims] 1. 2Ls synchronized with each other with a clock cycle of T seconds
A signal processing process in which L complex carriers with frequencies f ₀ , f ₁ , ..., f _L-1 are orthogonally modulated using baseband data (where L is a positive integer) and the outputs are orthogonally multiplexed is N. /T Hertz (where N is an even number and N≧2L), the parameter γ, which is the fractional part of the product f ₀ T of the above T and the minimum carrier frequency f ₀ , is set to 0.5. In the orthogonal multiplexed signal digital processing transmitter,
Selectively T/ to the first 2L baseband data
A 2-second delay is added and complexization is performed to obtain the complex signal group a ₁ ,
A preprocessing circuit that outputs a ₂ , ..., a _L and the complex signal group a ₁ , a ₂ , ..., a _L and (N/2-L) dummy signals are input, and the processing time is T/2 seconds. An offset Fourier inverse transformer that performs an N/2 point offset Fourier inverse transform for each N/2 point offset Fourier inverse transformer, and an N An orthogonal multiplexed signal comprising a polyphase circuit composed of /2 complex band filters, and obtaining an orthogonal multiplexed signal by time-division multiplexing N/2 real part outputs of the polyphase circuit. Digital processing type transmitter. 2 2L synchronized with each other with a clock period of T seconds
The signal processing process that orthogonally modulates L complex carriers using baseband data of 30000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 form 2000 3000 30000 form orthogonal form, orthogonal multiplexed form, using baseband data of In a transmitting device that performs digital processing at a _sampling rate _of ..., a _L and a preprocessing circuit that outputs b ₁ , b ₂ , ..., b _L , and the complex signal group a ₁ , a ₂ , ...
..., a _L and (N/2-L) dummy signals as input and performs N/2-point offset Fourier inverse transform every T/2 seconds, and the complex signal a second offset Fourier inverse transformer having the same configuration as the first offset Fourier inverse transformer, which inputs groups b ₁ , b ₂ , ..., b _L and (N/2-L) dummy signals; and a first polyphase circuit connected to the first offset Fourier inverse transformer and comprising N/2 complex bandpass filters having an effective bandwidth of 1/T Hertz and differing only in linear phase gradient in steps. , a second polyphase circuit connected to the second offset Fourier inverse transformer and having the same configuration as the first polyphase circuit, and a real part output of N/2 of the first polyphase circuit as the real part. After applying a desired frequency offset to the N/2 complex signals obtained by using the N/2 imaginary part outputs of the second polyphase circuit as the imaginary part, only the real part of the output is extracted. 1. A digital processing type transmission device for orthogonal multiplexed signals, comprising a processing circuit, and obtaining an orthogonal multiplexed signal by time-division multiplexing N/2 real signals obtained as outputs of the post-processing circuit.