JPH04170128A - Digital filter for modulator - Google Patents

Abstract

PURPOSE:To halve a storage capacity of a storage device, to reduce the cost and to miniaturize the filter by inputting a read address outputted from a control circuit to a time inversion circuit and inputting a read address subjected to time inversion to the storage device according to time inversion information outputted from the control circuit. CONSTITUTION:One group of a complex envelope waveform in two complex envelope waveforms different from groups belonging to an initial code point is stored in a storage device 108 with respect to a transmission data series and the one group of the complex envelope waveform is read in an opposite direction hourly. Thus, the other group of a complex envelope waveform is obtained. Thus, the storage capacity of the storage device 108 required to store the complex envelope waveform is halved, the filter is miniaturized and the reduction in cost is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a digital filter for a digital modulator that inputs transmission data consisting of digital data and outputs a complex envelope waveform.

BACKGROUND OF THE INVENTION In recent years, with the digitization of electronic equipment, digital modulators are used to pass transmission data through a digital filter to generate a complex envelope waveform, which is then input to an analog quadrature amplitude modulator after D/A conversion. A configuration in which a modulated waveform is obtained using

As a conventional digital filter for a modulator, there is, for example, a digital filter for a π/4 shift 1-QPSK modulator shown in FIG.

This digital filter is provided with a control circuit 404 and a storage device 405, and the control circuit 404 includes a shift register 401, an m-value counter 402, and a frequency dividing circuit 40.
3 is provided.

The shift register 401 stores 1 of the input data before modulation.
Input the transmission data 406 in which one symbol consists of 2 bits, and the clock 407 with a frequency equal to the number of symbols that can be sent in a unit time, that is, the symbol rate.
The counter 402 sequentially outputs a transmission data series 408 consisting of n-I+"' a k**). Also, the counter 402 inputs a clock 409 with a frequency m times the clock 407, outputs a count value 410, and divides the frequency. The circuit 403 manually generates the clock 407, divides the frequency by two, and outputs the divided frequency as group identification information 411.

The storage device 405 inputs the transmission data series 408, the group identification information 4411, and the count value 410, and outputs the real component 412 and the imaginary component 413 of the sample value of the complex envelope waveform.

By the way, when the code point arrangement of π/4 shift QPSK is expressed on a complex plane, as shown in Figure 5, the code points are divided into two groups ASB, and code points from the same group are not taken between adjacent symbols. The code points of the first, A, and B groups are used alternately. And shift register 40
Transmission data 406 in which one symbol inputted by 1 is composed of 2 bits almost corresponds to the code point of the modulation method.

Transmission data 406 (al, (i=1.2...)
) is input to the shift register 401, and the clock 407
Accordingly, the transmission data series 40 B (aI11+"'+ ah++
s+(k=0.1, 2...)) is output.

In addition, a counter 402 of m value (m=2b, b is a positive integer)
is a count value 410 (c,
(c −4, 1, −, m−1)) are output sequentially.

A clock 407 input to the shift register 401 is simultaneously input to a frequency dividing circuit 403, divided by two, and output as group identification information 411.

The transmission data series 408, count value 410, and group identification information 411 are input to the address of the storage device 405.

The storage device 405 stores the real components Y0 . ..., YI and imaginary component Y08.
. . , Y, , are stored and are sequentially output according to the count value 410.

Here, the transmission data series 408 and the group identification information 4
11, the real component and imaginary component of the sample value, and the complex envelope waveform are detailed as follows.

Depending on whether the initial code point belongs to group A or B in FIG. 5 for a certain transmission data series 408 as shown in FIG. 6(a), the initial code point starts from group A as shown in FIG. 6(a). There are two possible code point sequences starting from group B as shown in FIG. The phase changes corresponding to each code point sequence are shown in Figure 6(b) or (
The real component and imaginary component of the complex envelope waveform corresponding to these phase changes are obtained as shown in FIG. 6(C) or FIG. 6(g), respectively.

The real component Y11 of the m sample values of the central 1-symbol length portion of this complex envelope waveform. ..., Yll, and the imaginary component Y01. ..., Y0□ as shown in Figure 6(d) or (
h), and transmit data series 408.
, the group identification information 411 and the count value 410 are stored in advance at addresses corresponding to the group identification information 411 and the count value 410.

Here, the group identification information 411 is group A.

B, the sample value shown in FIG. 6(d) is assigned to the address where the group identification information 411 corresponds to 0, and the sample value shown in FIG. 6(h) is assigned to the address where the group identification information 411 corresponds to 1. Remember.

Since the group identification information 411 alternately takes values of 0 and 1 for each symbol, the code points of the complex envelope waveform output by the storage device 405 alternately take groups A and B.

In this way, a complex envelope waveform corresponding to the transmission data is obtained.

Problems to be Solved by the Invention However, in the above configuration, the storage device 405
Since (2Xn+b+1) focuses are used in the read address space of , a storage capacity for storing 2<2''+b''I) sample values is required. For example, when implementing a roll-off filter with high precision, normally n=6. b=3 (
m = 8), which requires a large amount of storage capacity to store approximately 65,000 sample values, which is a disadvantage in reducing the size and cost of the device. It had a point.

The present inventor has proposed that in most modulation schemes such as π/4 shift) QPSK modulation scheme, π/2 shift l-, and BPSK modulation scheme, the convolution output of the complex envelope waveform of one symbol of the modulation scheme and a waveform shaping filter is is symmetrical about the center of one symbol length, and by reading out the complex envelope waveform data of one code point series from the opposite direction, it is possible to read out the complex envelope waveform of another code point series. That's what I found out.

Based on this knowledge, it is an object of the present invention to provide a digital filter for a modulator that can halve the storage capacity of a storage device required to store complex envelope waveforms.

Means for Solving the Problems In order to solve the above-mentioned problems, the digital filter for a modulator of the present invention has the following objectives:
a control circuit that outputs a count value and time reversal information; a time reversal circuit that time inverts the transmission data series and the count value and outputs a read address according to the time reversal information output from the control circuit; The present invention is characterized in that it includes a storage device that outputs a complex envelope waveform stored in advance in accordance with the read address output from the inversion circuit.

Operation In the above configuration, for a given transmission data series, one of two complex envelope waveforms that differ depending on the group to which the initial code point belongs is stored, and the complex envelope waveform of one group is stored. By reading out the complex envelope waveform of one group from the temporally opposite direction, the complex envelope waveform of the other group is obtained.

Embodiment Hereinafter, a digital filter for a modulator according to an embodiment of the present invention will be explained in detail with reference to FIGS. 1 to 3.

This modulator digital filter is π/4 shift QPS
This is a digital filter for a K modulator, and as shown in FIG. 1, it includes a control circuit 104, a time reversal circuit 107, and a storage device 108.

The control circuit 104 inputs transmission data 109 in which one symbol consists of 2 bits and a clock 110 having a frequency equal to the symbol rate of the modulation method, and generates a transmission data series 111 (ak+
ll+ all+I'l-1,-"+ ak+1)
The shift register 01 outputs the clock 110, and the clock 110
The m-value counter 02 inputs a clock 112 with a frequency m times m and outputs a count value 113 (c, (c・1,2...)), and the clock 110 is input and the frequency is divided by 2. The control circuit 40 of the conventional example described above is equipped with a frequency divider circuit 103 that outputs the time-reversed information as time-reversed information 114.
It is configured in the same way as 4.

A time reversal circuit 107 inputs a transmission data series 111 and time reversal information 114 and outputs a transmission data series 115, and an order reversal circuit 105 receives a count value 113 and time reversal information 114 and outputs a count value 116. The bit inversion circuit 1.6 is also provided.

The storage circuit 108 inputs the transmission data series 115 output from the order inversion circuit 105 and the count value 116 (C'') output from the bit inversion circuit 1.6, and stores the real component 117 and imaginary component of the sample value of the complex envelope waveform. 118.

Note that transmission data 1 input to the shift register 101
09 (az, (i·1, 2...)) corresponds to the code point of the modulation method.

In the above configuration, the transmission data 109 input to the control circuit 104 is input to the shift register 101, and according to the clock 110, a transmission data series 111 (ah-+, "・,
ah411(k=0.1,2.・”)) is output.Here, in order to make the group to which the initial code point belongs and the group to which the final code point belongs different for the n code point series, , n must be even numbers.

In addition, a counter 102 of m value (m=2b, b is a positive integer)
is determined according to the clock 112, ■ count value 113 (c,
(c=0.1..., m=1)) are output sequentially.

Clock 110 is input to frequency divider circuit 103, frequency-divided by two, and output as time-reversed information 114.

Transmission data series 111 output from control circuit 104,
The count value 113 and time reversal information 114 are input to the time reversal circuit 107.

The above transmission data series 111 (ak+1+"'+
ak+n+(k=0.1.2...)) and time reversal information 114 are sequentially input to the inversion circuit 105, and Jl't! 5 (when time reversal information 114 is 0)
a' i = ay1- i 41 (time reversal information 11
4 is 1) (i=1.2...,n) Transmission data sequence 115 obtained by converting (+1 to a')
+++, output 411 (k=o, 1, 2.-)) to a'.

Count value 113 (c, (c=0.1.-, m-
1)) and the time reversal information 114 are input to the bit reversal circuit 106, and when the time reversal information 114 is 0, the count value 113 is output as is from the bit reversal circuit 106 as the count value 116, and when the time reversal information 114 is 1, the count value 113 is outputted as the count value 116. Focus inversion output c' (=
m-1-c) is output as a count value 116.

Transmission data series 11 output from time reversal circuit 107
5 and the count value 116 are input to the address of the storage device 108, and accordingly, the real component 117 and the imaginary component 118 of the sample value of the complex envelope waveform are output.

Next, the sample values of the complex envelope waveform to be stored in the storage device 108 will be explained in detail using FIG. 2.

Assuming that the initial code point belongs to group A in FIG. 5 for a certain transmission data series as shown in FIG. 2(a), FIG. 2(b)
) to obtain the phase change shown in ).

Correspondingly, the real component and imaginary component of the complex envelope waveform as shown in FIG. 2(C) are determined.

The real component Y, ..., Yl, and the imaginary component Y, ..., Y, of the m sample values of the central 1-symbol length part of this complex envelope waveform are expressed as second As shown in Figure (d), each is obtained and stored in an address corresponding to the transmission data series. The difference from the conventional example is that the complex envelope waveform when the initial code point belongs to group B is not stored.

Next, the operation of the time reversal circuit will be explained in detail using FIG.

As described above, the storage device 108 stores only the complex envelope waveform when the initial code point of the transmission data series given as the address belongs to group A of the code point arrangement in FIG.

In the time reversal circuit, if the group to which the initial code point given by the time reversal information @114 belongs is A, the transmission data series 111 and the count value 113 are output to the storage device as they are; , performs the following conversion to obtain the desired waveform and outputs it to the storage device.

When it is desired to obtain a complex envelope waveform corresponding to a code point sequence whose initial code points belong to group B of the code point arrangement shown in Fig. 5, as shown in Fig. 3(a), first, the order of the transmitted data sequence is The transmission data sequence as shown in FIG. 3(b) is inverted and stored in the storage device 1.
Give it to 08.

At this time, the storage device 108 stores the real components Y, ..., Yl of the sample values of the complex envelope waveform as shown in FIG. 3(d) corresponding to the phase changes in FIG. 3(c). and imaginary component Y
01. . . , Y, 1 are stored, and by sequentially reading them with the bit-inverted count value 106, the real number components Y111+ . . . , Yl as shown in FIG. 3(e) are stored.
l and imaginary components Y, . . . , Yol are obtained as outputs. This corresponds to the complex envelope waveform of the code point sequence shown in FIG. 3(a). A desired waveform is obtained in the above manner.

As described above, in this embodiment, the waveform when the initial code point belongs to group B is obtained by reading out the waveform when the initial code point belongs to group A in the reverse direction in time.

Note that in order to be able to read from the reverse direction in time, the convolution output of the complex envelope waveform of one symbol of the modulation method and the waveform shaping filter must be axisymmetric with respect to the center of the one symbol length. is necessary. This condition is satisfied in most modulation methods (including π/4 shift QPSK and π/2 shift BPSK).

In addition, in order for the complex envelope waveforms to be connected smoothly and without errors, the positions of m sample points should be aligned with the boundary line between the central symbols of the n code point series, as shown in Figure 2(d), for example. It is desirable that it be symmetrical.

As described above, according to this embodiment, the count value 116 consisting of n transmission data sequences 115 and b bits is input to the waveform storage device 108 as an address, so the address space becomes (2Xn+b) bits.

Therefore, compared to conventional digital filters for modulators, the address given to the storage device can be reduced by 1 bit, and the required storage capacity can be reduced to 1/2. - Effects of the Invention As described above, the present invention inputs a read address output from a control circuit according to transmission data to a time reversal circuit, and stores the read address time-reversed according to time reversal information output from the control circuit. By having a configuration in which the complex envelope waveform is obtained by inputting it to the device, the storage capacity of the storage device required to store the complex envelope waveform of the modulation method can be reduced to 1/2, resulting in a low It is possible to construct a digital filter for a modulator that is small in price and has low power consumption.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a digital filter for a modulator in an embodiment of the present invention, FIG. 2 is an explanatory diagram showing a calculation method for a complex envelope waveform stored in the storage device of FIG. Figure 4 is an explanatory diagram showing the operation of the time reversal circuit in Figure 1, Figure 4 is a block diagram showing the configuration of a conventional digital filter for a modulator, Figure 5 is a code point arrangement diagram of π/4 shift) QPSK, FIG. 6 is an explanatory diagram showing a method of calculating a complex envelope waveform to be stored in the storage device of FIG. 4. 104... Control circuit, 107... Time reversal circuit, 6th ABA BA BAB (b) o %ruru... %ruH<--s4ru
Le %le YQ1...Yqm BAB AS ABA

Claims (1)

[Claims] (1) A control circuit that outputs a transmission data series, a count value, and time reversal information according to the transmission data, and a read address by time reversing the transmission data series and the count value according to the time reversal information output from the control circuit. A digital filter for a modulator, comprising: a time reversal circuit that outputs a time reversal circuit; and a storage device that outputs a complex envelope waveform stored in advance in accordance with the read address output from the time reversal circuit.