JP4106612B2 - Direct spread spectrum spread signal transmitter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a direct spread spectrum spread signal transmission apparatus, and more particularly to a spread modulation means in a transmission system.
[0002]
[Prior art]
The direct sequence spread spectrum (hereinafter referred to as DS-SS) method directly multiplies a data signal by a code sequence that is sufficiently wider than the bandwidth of the data signal, thereby reducing the bandwidth of the data signal. This is a technique for converting to a wide transmission signal. As a result, the power of the original data signal is spread over a wide band, so that the power density is low. Also, it is known as a communication system that is resistant to noise and interference waves by despreading the spread spectrum signal during demodulation.
[0003]
The basic configuration of the DS-SS system is to first modulate a data signal to be transmitted by a predetermined modulation system (primary modulation) and then perform spread spectrum modulation (secondary modulation) by a spreading code sequence.
Conventionally, for example, a “spread spectrum communication device” as disclosed in JP-A-5-122193 has been proposed. This is because the value of each point of parallel data of 2 bits or more obtained from a parallel output of a carrier wave oscillator, a primary modulator that modulates this output with a transmission signal, and two or more binary pseudo noise sources is represented by BPSK ( A first logic device that assigns three types of modulation states obtained by adding “no signal” to two types of phase states (Binary Phase Shift Keying), a secondary modulation device that modulates an output signal in the assigned modulation state, The values of each point of parallel data of 2 bits or more obtained from the parallel output of the transmission circuit, the reception circuit, and two or more binary pseudo noise sources are transmitted to the two types of phase states of BPSK as “none”. A second logic device that is assigned to three types of modulation states plus a signal, a secondary demodulator that remodulates the received signal in the assigned modulation state, a local oscillator, and a demodulator 1 for demodulating the received signal with this output Next demodulator Thus, it is possible to obtain the effects of suppression of the perspective problem, generation of codes suitable for CDMA, etc., and improvement of autocorrelation.
[0004]
In the DS-SS system, when the data signal to be transmitted is a digital signal, a system in which primary modulation is omitted and the data signal and the code sequence are directly multiplied and the carrier wave is modulated by this signal is often seen. Such a spread spectrum system is described in detail in, for example, “Mitsuo Yokoyama, Spread Spectrum Communication System, Science and Technology Publishers, May 1988”.
[0005]
FIG. 7 is a functional block diagram showing a configuration example of a conventional direct spread spectrum spread signal transmitter.
The transmission apparatus shown in this example multiplies a data signal to be transmitted, which is a digital signal, and a code signal output from a code generator 10 that generates a code sequence having a sufficiently wider bandwidth than the data signal. 20, a modulation unit 30 that BPSK modulates the multiplied signal output from the multiplier 20, and a digital / analog that converts the modulated signal output from the modulation unit 30 from a digital signal to an analog signal A converter (hereinafter referred to as D / A) 40 is provided, and an analog signal output from the D / A 40 is transmitted as a DS-SS transmission signal.
The modulation unit 30 stores sampling data of a predetermined frequency in advance, generates a carrier wave based on the sampling data, and outputs the carrier wave from the carrier generator 31 from the multiplier 20. A broadband modulator 32 that performs BPSK modulation with the multiplied signal and outputs the result.
[0006]
FIG. 8 is a diagram showing signal waveform examples in each part of the conventional direct spread spectrum spread signal transmitter shown in FIG. 7, and the circle numbers (1) to (4) in both figures correspond.
That is, the waveform (1) shown in FIG. 8 is an example of a data signal to be transmitted and is a binary digital signal. Here, positive logic is set to +1, negative logic is set to -1, and the same applies to other digital waveforms. A waveform (2) in the figure is an example of a code signal generated by the code generator 10, and is a binary digital signal. A waveform (3) in the figure is a multiplication signal output from the multiplier 20. Waveform (4) in the figure is an example of a transmission signal output from D / A 40, and is an analog signal subjected to phase modulation. Thus, a DS-SS transmission signal like the above-mentioned waveform (4) is output from a conventional direct spread spectrum spread signal transmission apparatus.
[Problems to be solved by the invention]
[0007]
However, the conventional direct spread spectrum spread signal transmitter described above has the following problems. In other words, when the signal (waveform (3)) resulting from the multiplication of the data signal and the code signal changes (+ 1 → −1 or vice versa), the phase of the carrier wave is changed by 180 °, so that the transmission signal is out of phase. As a result, side lobes outside the band of the code sequence are generated. The frequency spectrum of the DS-SS transmission signal is as shown in FIG.
FIG. 9 is a diagram illustrating a frequency spectrum of a BPSK-modulated transmission signal output from a conventional transmission apparatus, where the horizontal axis indicates the frequency band and the vertical axis indicates the power level.
In this figure, the large peak at the center is the main band component (main lobe) of the code string, and the peaks located on both sides are side lobes.
[0008]
Usually, transmission of unnecessary out-of-band components is suppressed, but this is generally dealt with by inserting a filter in the transmission stage, and the filter used for this is a high performance with steep passband characteristics. This is a factor that causes an increase in cost as a transmission apparatus.
[0009]
The present invention has been made to solve such problems, and provides a direct spread spectrum spread signal transmitter capable of reducing the transmission level of side lobes without using an expensive filter. For the purpose.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the direct spread spectrum spread signal transmission apparatus according to the first aspect of the present invention multiplies a predetermined code signal from a code sequence generator by a data signal of digital information to be transmitted. A direct spread spectrum spread signal transmission apparatus comprising: a multiplication unit; and a wideband modulator that performs BPSK (Binary-Phase Shift Keying) modulation on a data signal multiplied by a code signal by a carrier wave generated by a carrier wave generator, In the carrier wave generator, data of two kinds of carrier waves having the same frequency and different levels are sampled and stored in advance, a data signal multiplied by the code, a signal obtained by delaying the data signal by one chip, And a determination unit that selects carrier data output from the carrier generator based on the multiplication result of the second multiplication unit. In addition, a transmission signal in which the level at the phase change point is smaller than the level at other points is output.
[0011]
The direct spread spectrum spread signal transmitter according to claim 2 of the present invention is the direct spread spectrum spread signal transmitter according to claim 1, wherein the two types of carrier data stored in the carrier generator are used. , When one carrier peak level is 1, the other carrier peak level is 1 / √2.
[0012]
The direct spread spectrum spread signal transmitter according to claim 3 of the present invention is the direct spread spectrum spread signal transmitter according to claim 1 or 2, wherein the determination unit is a code signal 1 chip. Each time interval, the multiplication result of the current value and the value one chip before is sequentially held, and the selection of the carrier wave to be output from the carrier wave generator is determined by the combination of the held values.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on the illustrated embodiment.
FIG. 1 is a functional block diagram showing an embodiment of a direct spread spectrum spread signal transmitter according to the present invention. It should be noted that the same functional blocks as those shown as the conventional example in FIG.
The transmission apparatus shown in this example includes a multiplier 20 that multiplies a code signal output from the code generator 10 and a data signal to be transmitted, and a predetermined frequency based on the multiplied signal output from the multiplier 20. A modulation unit 50 that performs BPSK modulation on a carrier wave and a digital / analog converter (D / A) 40 that converts a digital signal output from the modulation unit 50 into an analog signal are configured.
[0014]
Further, the modulation unit 50 has the following functional blocks therein. That is, the first delay unit 1, the second delay unit 2, and the multiplier 3 that receive the output from the multiplier 20, and the carrier signal determination unit 4 that receives the output of the multiplier 3, A carrier wave generator 5 that receives the output of the carrier wave signal determination unit 4 and a broadband modulator 6 that receives the output of the carrier wave generator 5 and the output of the first delay device 1 are provided. The output of the second delay device 2 is connected to the other input of the multiplier 3.
[0015]
Here, two types of carrier data stored in the carrier generator 5 which is a characteristic point of the present invention will be described with reference to FIG.
FIG. 2 is a diagram illustrating a waveform example of sampling data stored in the carrier wave generator in the direct spread spectrum spread signal transmission apparatus according to the present invention. The carrier data shown in this example is two types of carrier data having the same frequency and different levels. If the peak level of one carrier data a having a high level is ± 1, the carrier having the other level is low. The data b has a peak level of ± 1 / √2. That is, carrier data of the same frequency having a relative level difference is stored.
[0016]
Next, FIG. 3 is a diagram showing signal waveform examples in each part of the direct spread spectrum spread signal transmission apparatus according to the present invention, and the circle numbers (1) to (5) in FIG. Corresponds to the round numbers listed inside.
Returning to FIG. 1, the function of the direct spread spectrum spread signal transmitter according to the present invention will be described.
The direct spread spectrum spread signal transmitter shown in this figure functions as follows. That is, the multiplier 20 multiplies the data signal to be transmitted (waveform 1) and the code signal (waveform 2) output from the code generator 10 that generates a code sequence having a sufficiently wider bandwidth than the data signal. The signal (waveform 3) is divided into three and supplied to the first delay device 1, the second delay device 2, and the second multiplier 3, respectively. Here, both the delay amounts of the first delay device 1 and the second delay device 2 are shown as one chip (the width of the 1-bit code signal), but the delay amount of the first delay device 1 is actually described later. It is also necessary to consider delays such as carrier signal determination processing to be performed. That is, the first delay device 1 and the second delay device 2 output a signal (waveform 4) delayed by 1 chip. The second multiplier 3 outputs a signal (waveform 5) obtained by multiplying the multiplied signal (waveform 3) and the signal delayed by 1 chip (waveform 4).
[0017]
The carrier wave signal determination unit 4 determines which of the signals stored in the carrier wave generator 5 in the subsequent stage is output based on the signal (waveform 5) from the second multiplier 3. That is, the signal (waveform 5) from the second multiplier 3 indicates whether or not a state change (+ 1 → −1 or vice versa) has occurred for the multiplied data signal from the multiplier 20. In (waveform 5), “+” indicates no change, and “−” indicates change.
[0018]
Next, FIG. 4 is a diagram illustrating a configuration example of the carrier signal determination unit. The carrier signal determination unit 4 shown in this example refers to a holder 7 that holds a value of 2 bits for a signal (waveform 5) output from the second multiplier 3, and a value that the holder 7 holds. And a selection determination unit 8 for determining which carrier is to be selected by the carrier generator 5.
The combination of 2 bits sequentially held as “current value” and “1 chip before” in the holder 7 of the carrier wave signal determination unit 4 includes (+, +), (+, −), (−, +), Since there are four types (-,-), the selection determination unit 8 outputs selection information to the carrier wave generator 5 according to the determination criterion associated in advance. In this figure, in the case of (+, +), it is selected and determined to output a carrier wave as shown in (a), and in the case of (+, −), it is selected and determined to output a carrier wave as shown in (b). In the case of (−, +), selection determination is made to output a carrier wave as in (c), and in the case of (−, −), selection determination is made to output a carrier wave as in (d).
[0019]
The carrier data (a) to (d) described above are output from the carrier generator 5. The carrier data will be described in more detail. Here, carrier wave data for one wavelength is associated with one chip, and an example of level values is set for every 45 degrees of carrier wave phase.
That is, when the combination of the holding values of the holder 7 is (+, +) and the sign of the multiplication result of the data signal and the code signal does not change continuously, the data output from the carrier generator is ( 0, + 1 / √2, + 1, + 1 / √2,0, −1 / √2, −1, −1 / √2,0), which is a level stored in the carrier wave generator 5 Only the higher carrier wave data a.
[0020]
Further, when the combination of the holding values of the holder 7 is (+, −) and the sign of the multiplication result of the data signal and the code signal is 1 chip before, there is a change and there is no change at present, the carrier generator The data output from is one cycle of (0, + 1 / √2, +1, + 1 / √2, 0, −1/2, −1 / √2, −1/2, 0), The first half period is composed of carrier data a having a higher level, and the second half period is composed of carrier data b having a lower level.
[0021]
Further, when the combination of the holding values of the holder 7 is (−, +), and the sign of the multiplication result of the data signal and the code signal is not changed one chip before and there is a change at present, the carrier generator Is one cycle of (0, +1/2, + 1 / √2, +1/2, 0, -1 / √2, -1, -1 / √2, 0), The first half cycle is composed of carrier data b having a lower level, and the second half cycle is composed of carrier data a having a higher level.
[0022]
When the combination of the holding values of the holder 7 is (−, −) and the sign of the multiplication result of the data signal and the code signal changes continuously, the data output from the carrier generator is ( 0, +1/2, + 1 / √2, +1/2, 0, -1/2, -1 / √2, -1/2, 0), which is stored in the carrier wave generator 5 Only the lower carrier wave data b.
[0023]
In this way, using the carrier wave output from the carrier wave generator 5, the wideband modulation unit 6 performs BPSK modulation on the signal from the first delay unit 1 and outputs the result to the D / A converter 40 at the next stage. Thus, a signal obtained by converting a digital signal into an analog signal is transmitted.
FIG. 5 is obtained by adding a carrier output (waveform 6) from the carrier generator 5 and a transmission output (waveform 7) from the D / A converter 40 to the one shown in FIG. is there. In addition, in the waveform 7, in order to clearly indicate the phase change point and the carrier wave level, a signal input to the wideband modulator 6 is also shown.
[0024]
That is, as shown in the waveform 7, it is possible to obtain a DS-SS transmission signal to which the low-level carrier data b is assigned for the first half of the phase change point. The frequency spectrum of the DS-SS transmission signal is as shown in FIG.
FIG. 6 is a diagram showing a frequency spectrum of a BPSK-modulated transmission signal output from the direct spread spectrum spread signal transmission apparatus according to the present invention. Comparing the one shown in this figure with the one shown in FIG. 9 as the conventional example, the level of the main lobe portion is the same, but the level of the side lobe portion is that shown in FIG. 6 according to the present invention. It is a low level. In this way, at the point where the sign of the multiplication result of the data signal and the code signal changes, by generating a carrier wave so as to suppress the carrier wave immediately before the change and immediately after the change, the side generated when the phase of BPSK modulation changes The power level of the lobe can be reduced.
[0025]
In the embodiment of the present invention described above, an example in which one wavelength carrier wave is associated with one chip is shown. However, the present invention is not limited to this example, and practically, for example, A plurality of wavelengths having the same frequency are associated with each chip, and a carrier generator 5 is used which assigns low-level carrier data at the data change point in BPSK modulation, that is, the first half of the phase change point. It goes without saying that it should be done.
[0026]
In order to further suppress the side lobe of the DS-SS transmission signal, a filter may be inserted into the output of the D / A converter 40 in the transmission apparatus. Even in this case, since the power level of the side lobe of the DS-SS transmission signal is reduced as compared with the conventional one, it is not necessary to obtain high performance for the filter, and it is possible to reduce the cost of the transmission apparatus. Can be avoided.
[0027]
As described above, the direct spread spectrum spread signal transmission apparatus according to the present invention stores two carrier data having the same frequency and different levels in the carrier generator 5, and the carrier signal determination unit 4 includes the multiplier 20. Based on the result of multiplication by the second multiplier 3 of the multiplication result of the data signal and the code signal output from the signal signal and the multiplication result of the data signal delayed by one chip by the second delay unit 2 and the code signal. Since the carrier wave signal corresponding to the change in the signal state is selected and the carrier wave output from the carrier wave generator 5 is selected, the output signal subjected to the BPSK modulation by the broadband modulator 6 is Therefore, the carrier level of the first half of the phase change point is small, and the electric power that appears in the side lobe in the frequency spectrum of the DS-SS transmission signal It is possible to obtain a small DS-SS transmission system.
[0028]
【The invention's effect】
As described above, in the direct spread spectrum spread signal transmitting apparatus according to the present invention, the data carrier generator samples and stores data of two types of carrier waves having the same frequency and different levels in advance. A second multiplier that multiplies the multiplied data signal by a signal delayed by one chip of the data signal, and selects carrier wave data to be output from the carrier generator based on a multiplication result of the second multiplier And a function to output a DS-SS transmission signal having a level at the phase change point smaller than the level at other points, so that an expensive filter is used for the sidelobe transmission level. It is possible to realize a direct spread spectrum spread signal transmitter that can be reduced without any problem.
[Brief description of the drawings]
FIG. 1 is a functional block diagram illustrating a configuration example of a direct spread spectrum spread signal transmission apparatus according to the present invention.
FIG. 2 is a diagram showing a waveform example of carrier wave data stored in a carrier wave generator in the direct spread spectrum spread signal transmission apparatus according to the present invention.
FIG. 3 is a diagram showing an example of a signal waveform in each part of the direct spread spectrum spread signal transmitter according to the present invention.
FIG. 4 is a diagram illustrating a configuration example of a carrier signal determination unit used in a direct spread spectrum spread signal transmission apparatus according to the present invention.
5 is a diagram showing an example of signal waveforms in each part of the transmission apparatus according to the present invention, in which a waveform 6 and a waveform 7 are further added to those in FIG.
FIG. 6 is a diagram showing an example of a frequency spectrum of a transmission signal subjected to BPSK modulation output from a direct spread spectrum spread signal transmission apparatus according to the present invention.
FIG. 7 is a functional block diagram showing a configuration example of a conventional direct spread spectrum spread signal transmitter.
8 is a diagram illustrating an example of a signal waveform in each unit of the transmission device illustrated in FIG.
FIG. 9 is a diagram illustrating an example of a frequency spectrum of a transmission signal subjected to BPSK modulation output from a conventional transmission apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... 1st delay device 2 ... 2nd delay device 3 ... 2nd multiplier 4 ... Carrier wave signal determination part 5 ... Carrier wave generator 6 ... Broadband modulator 7 ... Operation / display section 8 ... Ticket sales section 9 ... Public line 10 ... Code generator 20 ... Multiplier (first multiplier)
30 ... Modulator 31 ... Carrier wave generator 32 ... Broadband modulator 40 ... Digital / analog converter (D / A)
50: Modulation section

Claims (3)

A multiplier for multiplying a predetermined code signal from the code sequence generator by a data signal of digital information to be transmitted;
A direct spread spectrum spread signal transmitter comprising: a wideband modulator that modulates a BPSK (Binary-Phase Shift Keying) data signal multiplied by a code signal by a carrier wave generated by a carrier generator;
In the carrier wave generator, data of two types of carrier waves having the same frequency and different levels are sampled and stored in advance,
A second multiplier that multiplies the data signal multiplied by the code and the signal delayed by one chip of the data signal;
An apparatus for transmitting a direct spread spectrum spread signal, comprising: a determination unit that selects carrier wave data output from the carrier wave generator based on a multiplication result of the second multiplication unit. The two types of carrier data stored in the carrier generator are set to a level ratio in which one carrier peak level is 1 and the other carrier peak level is 1 / √2. Item 5. A direct-spread spectrum spread signal transmitter according to Item 1. The determination unit sequentially holds a multiplication result of a current value and a value one chip before for each section of the code signal, and performs selection determination of a carrier wave to be output from the carrier wave generator by a combination of the held values. 3. The direct spread spectrum spread signal transmission apparatus according to claim 1, wherein the direct spread spectrum spread signal transmission apparatus is configured as described above.

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