JP2847687B2 - Digital filter for modulator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital filter for a modulator that inputs transmission data composed of digital data and outputs a complex envelope waveform in a digital modulator.

2. Description of the Related Art In recent years, with the digitization of electronic devices, as a digital modulator, a transmission data is passed through a digital filter to generate a complex envelope waveform, and after D / A conversion, this is input to an analog quadrature amplitude modulator. A configuration in which a modulated waveform is obtained by using the same is often used.

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

The digital filter includes a control circuit 404 and a storage device 405. The control circuit 404 includes a shift register 401, an m-value counter 402, and a frequency dividing circuit 403.

The shift register 401 stores one of the input data before modulation.
Unit, ie, transmission data consisting of 2 bits per symbol
406 and the number of symbols that can be transmitted per unit time, that is, a clock 407 having a frequency equal to the symbol rate, are input, and n symbols (a _{k + n} , a _{k + n−1} ,... A _{k + 1} ) are input. Are sequentially output. Also, the counter 402
Receives a clock 409 having a frequency that is m times as high as the clock 407 and outputs a count value 410. The frequency divider 403 receives the clock 407, divides the frequency by two, and outputs the result as group identification information 411. I do.

The storage device 405 outputs the real component 412 and the imaginary component 413 of the sample value of the complex envelope waveform by using the transmission data sequence 408, the group identification information 411, and the count value 410 as inputs.

By the way, when the code point arrangement of the π / 4 shift QPSK is represented on a complex plane, the code points are divided into two groups A and B, as shown in FIG. , And the code points of the groups A and B are used alternately. Then, the transmission data 406, in which one symbol is composed of two bits, input to the shift register 401, corresponds to the code point of the modulation scheme.

The transmission data 406 (a _i , (i = 1, 2,...)) Is input to the shift register 401, and in accordance with the clock 407, a transmission data sequence 408 (a _{k + 1} ,. , a
_{k + n} , (k = 0, 1, 2,...)) are output.

A counter 402 having an m value (m = 2 ^b , b is a positive integer) counts 410 bits (c, (c = 0, 1) consisting of b bits specifying a time point within one symbol length according to the clock 409. ,
.., M-1)) are sequentially output.

The clock 407 input to the shift register 401 is input to the frequency dividing circuit 403 at the same time, frequency-divided by two, and output as group identification information 411.

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

The storage device 405 stores real number components Y ₁₁ ,..., Y _1m of m sample values in the central portion of one symbol length of the complex envelope waveform corresponding to the phase change determined by the transmission data sequence 408 and the group identification information 411. and imaginary component Y _Q1, ..., Y _Qm is stored, it is sequentially output in accordance with the count value 410.

Here, the transmission data sequence 408 and the group identification information 411
The relationship between the real component and the imaginary component of the sample value and the complex envelope waveform will be described in detail below.

As shown in FIG. 6 (a), starting from the group A as shown in FIG. 6 (a) depending on which of the groups A and B in FIG. 5 the initial code points belong to a certain transmission data sequence 408 as shown in FIG. 6 (a). A code point sequence and two code point sequences starting from the group B as shown in FIG. The phase change corresponding to each code point sequence is as shown in FIG. 6 (b) or (f), and the real component and the imaginary component of the complex envelope waveform corresponding to these phase changes are the sixth component, respectively.
It is obtained as shown in FIG.

M at the center of one symbol length of this complex envelope waveform
Real components Y ₁₁ , ..., Y _1m and imaginary components Y _Q1 ,
.., Y _Qm are obtained as shown in FIG. 6 (d) or (h), and are stored in advance at addresses corresponding to the transmission data sequence 408, the group identification information 411, and the count value 410.

Here, the group identification information 411 is used for discriminating the groups A and B, and the sample value of FIG. 6D is assigned to the address where the group identification information 411 corresponds to 0, and the address where the group identification information 411 corresponds to 1 In FIG. 6 (h).

Since the group identification information 411 alternates between 0 and 1 for each symbol, the code points of the complex envelope waveform output from the storage device 405 alternate between groups A and B.

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

However, in the above configuration, the storage device 405
Since (2 × n + b + 1) bits are used in the read address space of (1), a storage capacity for storing 2 ^{(2n + b + 1)} sample values is required. For example, when a roll-off filter or the like is realized with high accuracy, the value is usually n = 6, b = 3 (m = 8), and a large storage capacity for storing about 65,000 sample values is required. This is necessary and disadvantageous in reducing the size and cost of the apparatus.

The present inventor has proposed a π / 4 shift QPSK modulation scheme and a π / 2 shift BP
Most modulation schemes such as the SK modulation scheme use one of the modulation schemes.
The convolution output of the complex envelope waveform of the symbol and the waveform shaping filter is line-symmetric with respect to the center of one symbol length,
It has been found that by reading out the complex envelope waveform data of one code point sequence in the reverse direction, it is possible to read out the complex envelope waveform of another code point sequence.

An object of the present invention is to provide a digital filter for a modulator based on such knowledge, which can reduce the storage capacity of a storage device necessary for storing a complex envelope waveform by half.

Means for Solving the Problems In order to solve the above problems, the digital filter for a modulator of the present invention uses two different types of phase groups alternately for transmission data input at a fixed symbol rate. A modulator digital filter that outputs a sample value of a complex envelope waveform obtained by modulating, a shift register that outputs, in parallel, a transmission data sequence that is a sequence of the latest n pieces of input transmission data, 1
A counter that outputs a count value that is incremented from zero at a frequency of m times the symbol rate in parallel with a binary number each time transmission data is input, and a time inversion that is a clock signal obtained by dividing the symbol rate by 2 A frequency divider for outputting information, an operation of outputting the transmission data sequence output from the shift register as it is in accordance with the time reversal information, and outputting the n transmission data constituting the transmission data sequence in a reversed order. A sequence inversion circuit that alternately performs an operation, and a bit that alternately performs an operation of outputting the count value output from the counter as it is in accordance with the time inversion information and an operation of logically inverting and outputting each bit of the count value. An inverting circuit, and values output from the order inverting circuit and the bit inverting circuit are stored in advance as read addresses. A storage device for outputting a sample value of the complex envelope waveform, the sample value of the complex envelope waveform corresponding to the transmission data sequence starting from the phase modulation using one of the two types of phase groups. Is stored.

Operation In the above configuration, for a certain transmission data sequence,
The complex envelope waveform of one group among the two types of complex envelope waveforms different depending on the group to which the initial code point belongs is stored, and the complex envelope waveform of the one group is read out in a temporally reverse direction. As a result, a 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 specifically described with reference to FIGS. 1 to 3. FIG.

This digital filter for a modulator is a digital filter for a π / 4 shift QPSK modulator, and as shown in FIG. 1, a control circuit 104, a time inverting circuit 107, and a storage device 108.
And are provided.

The control circuit 104 inputs the transmission data 109 in which one symbol is composed of 2 bits and the clock 110 having a frequency equal to the symbol rate of the modulation scheme, and transmits a transmission data sequence 111 (a) composed of the past n transmission data 109. _{k + n} , a _{k + n-1} ,…, a
_{k + 1} ), the shift register 101, and the clock 110
Input clock 112 of m times frequency and count value 113
(C, (c = 1, 2,...)) And a frequency dividing circuit 103 which receives the clock 110 as an input, divides the frequency by 2 and outputs it as time inversion information 114. The configuration is the same as that of the control circuit 404 of the conventional example.

The time inversion circuit 107 receives the transmission data sequence 111 and the time inversion information 114 and outputs a transmission data sequence 115. The order inversion circuit 105 outputs the count value 113 and the time inversion information 114, and outputs the count value 116. And a bit inversion circuit 106.

The storage circuit 108 includes a transmission data sequence 115 output from the order inversion circuit 105 and a count value 11 output from the bit inversion circuit 106.
It is configured to output a real component 117 and an imaginary component 118 of the sample value of the complex envelope waveform with 6 (c ′) as an input.

The transmission data 109 input to the shift register 101
(A _i , (i = 1, 2,...)) Correspond to the code points of the modulation scheme.

In the above configuration, the transmission data 109 input to the control circuit 104 is input to the shift register 101,
A transmission data sequence 111 (a _{k + 1} ,..., A _{k + n} (k = 0, 1, 2,...)) Consisting of the past n transmission data 109 is output according to 110. Here, for the n code point sequences, n must be an even number so that the group to which the initial code point belongs and the group to which the final code point belongs are different.

The counter 102 having an m value (m = 2 ^b , b is a positive integer) counts 113 bits (c, (c = 0, 1) consisting of b bits designating a time point within one symbol length according to the clock 112. ,
.., M-1)) are sequentially output.

The clock 110 is input to the frequency dividing circuit 103, frequency-divided by two, and output as time inversion information 114.

The transmission data sequence 111, count value 113, and time inversion information 114 output from the control circuit 104 are input to the time inversion circuit 107.

The transmission data sequence 111 (a _{k + 1} ,..., A _{k + n} , (k = 0, 1, 2,
..)) And the time inversion information 114 are sequentially input to the inversion circuit 105, and a ′ _i = a _i (when the time inversion information 114 is 0) a ′ _i = a _{n−i + 1} (when the time inversion information 114 is 1) The transmission data sequence 115 (a ′ _{k + 1} ,..., A ′) obtained by the conversion of (i = 1, 2,..., N)
_{k + n} (k = 0, 1, 2, ...) is output.

The count value 113 (c, (c = 0, 1,..., M−1)) and the time inversion information 114 are input to the bit inversion circuit 106. When the time inversion information 114 is 0, the count value 113 is used as it is in the bit inversion circuit. When the time inversion information 114 is 1, a bit inversion output c ′ (= m−1−c) of the count value 113 is output as the count value 116 from the 106.

The transmission data sequence 115 and the count value 116 output from the time inversion circuit 107 are input to the address of the storage device 108,
According to this, the real component 117 of the sample value of the complex envelope waveform,
And the imaginary component 118 are output.

Next, the sample values of the complex envelope waveform stored in the storage device 108 will be described in detail with reference to FIG.

Assuming that the initial code point belongs to the group A in FIG. 5 for a certain transmission data sequence as shown in FIG. 2 (a), a phase change as shown in FIG. 2 (b) is obtained. Correspondingly, a real component and an imaginary component of the complex envelope waveform as shown in FIG. 2 (c) are obtained.

M at the center of one symbol length of this complex envelope waveform
Real components Y ₁₁ , ..., Y _1m and imaginary components Y _Q1 ,
.., Y _Qm are obtained as shown in FIG. 2 (d), and are stored in addresses 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 the B group is not stored.

Next, the operation of the time inversion circuit will be described in detail with reference to FIG.

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

In the time inversion circuit, when the group to which the initial code point given by the time inversion information 114 belongs is A, the transmission data sequence 111 and the count value 113 are output to the storage device as they are, and when the group is B, The following conversion is performed so that a desired waveform is obtained, and output to a storage device.

When it is desired to obtain a complex envelope waveform whose initial code points correspond to the code point sequence belonging to the B group of the code point arrangement of FIG. 5 as shown in FIG. 3 (a), first, the order of the transmission data sequence is inverted. A transmission data sequence as shown in FIG.
Give to 108.

At this time, the real components Y _I1 ,..., Y _Im and the imaginary components of the sample values of the complex envelope waveform as shown in FIG. Y _Q1 ,..., Y _Qm are stored, and by sequentially reading them out with the bit-reversed count value 106, a real number component as shown in FIG.
Y _Im, ..., Y _I1 and imaginary components Y _Qm, ..., Y _Q1 is obtained as the output. This corresponds to the complex envelope waveform of the code point sequence in FIG. A desired waveform is obtained as described above.

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

Note that, in order to be able to read out in the reverse direction in terms of time, the convolution output of the complex envelope waveform of one symbol of the modulation method and the waveform shaping filter must be line-symmetric with respect to the center of one symbol length. is necessary. For most modulation schemes (including π / 4 shift QPSK and π / 2 shift BPSK), this condition is satisfied.

In addition, since the complex envelope waveform is smoothly connected without error, for example, as shown in FIG. 2 (d), the positions of the m sample points are shifted to the boundary line between the central symbols of the n code point sequences. Desirably, it is symmetrical.

As described above, according to the present embodiment, since n transmission data sequences 115 and the count value 116 composed of b bits are input to the waveform storage device 108 as addresses, the address space is (2 × n + b) bits. Become.

Therefore, the address given to the storage device can be reduced by one bit as compared with the conventional modulator digital filter, and the required storage capacity can be reduced by half.

As described above, according to the present invention, a read address output from a control circuit according to transmission data is input to a time inversion circuit, and a read address time-inverted according to time inversion information output from the control circuit is stored in a storage device. To reduce the storage capacity of the storage device required to store the complex envelope waveform of the modulation method by half. Thus, a compact and low power consumption digital filter for a modulator can be configured.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a digital filter for a modulator according to an embodiment of the present invention. FIG. 2 is an explanatory diagram showing a method of calculating a complex envelope waveform stored in the storage device of FIG. FIG. 4 is an explanatory diagram showing the operation of the time inverting circuit shown in FIG. 1, FIG. 4 is a block diagram showing the configuration of a conventional digital filter for a modulator, FIG. 5 is a code point arrangement diagram of π / 4 shift QPSK, and FIG. FIG. 7 is an explanatory diagram showing a method of calculating a complex envelope waveform stored in the storage device of FIG. 104 a control circuit, 107 a time reversing circuit, 108 a storage device.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) H04L 27/00-27/38

Claims (1)

(57) [Claims] A digital filter for a modulator for outputting a sample value of a complex envelope waveform obtained by performing phase modulation on transmission data input at a constant symbol rate by using two different types of phase groups alternately. A shift register for outputting in parallel a transmission data sequence which is an arrangement of the latest n pieces of transmission data that have been input, and each time one piece of transmission data is input, at a frequency that is m times the symbol rate. A counter that outputs a count value that is incremented from zero in parallel in a binary number; a frequency divider that outputs time inversion information that is a clock signal obtained by dividing the symbol rate by two; an output from the shift register according to the time inversion information Operation of outputting the transmitted transmission data sequence as it is and inverting the order of n transmission data constituting the transmission data sequence An order inversion circuit that alternately performs an operation of outputting the count value output from the counter according to the time inversion information, and an operation of logically inverting and outputting each bit of the count value according to the time inversion information. A bit inversion circuit that performs the alternation, and a storage device that outputs a sample value of a complex envelope waveform that is stored in advance as a read address using the value output from the order inversion circuit and the bit inversion circuit. Is a digital filter for a modulator, wherein only sample values of a complex envelope waveform corresponding to a transmission data sequence starting from phase modulation using one of the two types of phase groups are stored.