JPH04328921A - Parallel spread spectrum modulator-demodulator - Google Patents

Abstract

PURPOSE:To realize the parallel spread spectrum modulator-demodulator in which trade-off between an information speed and an inter-code interference is remarkably improved and high speed processing is attained while providing the effect onto an interference wave, a disturbing wave and noise or the like. CONSTITUTION:A modulation section 10 gives an information signal d(t) such as a data to a serial/parallel converter 2 from an input terminal I1, in which the signal is converted into sets of low speed information d1(t), d2(t), d3(t) and the sets of information d1(t)-d3(t) are fed to multipliers 11-13 being components of a parallel spread spectrum SS modulation section. Then the sets of information d1(t)-d3(t) are added (3) and a resulting composite SS modulation signal is outputted. On the other hand, a demodulation section 40 applies demodulation by inverse spread to a signal resulting from a reception input signal subject to elimination of a high frequency interrupt signal component for a main lobe band of the spread code or over. Then N sets of low speed processing data obtained in this way are subject to parallel/serial conversion to obtain the original information. Then the low speed coding data is subject to parallel/serial conversion through an inter-code interference noise circuit of N sets of inverse spread demodulation section of the demodulation section 40.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a parallel spread spectrum modulation and demodulation device, and in particular, it introduces an intersymbol interference suppression technique to a parallel SS (spread spectrum) system to eliminate the trade-off between information rate and intersymbol interference. This invention relates to a parallel spread spectrum modulation demodulation device that has been greatly improved and enables higher speeds.

0002

[Technical Background] In various fields that handle information, how to increase the amount of information within set limits is an eternal theme. It is no exaggeration to say that the progress and direction of technology in recent years is represented by highly efficient coding technology and modulation/demodulation technology.
As can be seen in the application of re Amplitude Modulation (orthogonal amplitude modulation) to mobile communications, it can be said that research and development of technology to increase transmission speed within a defined frequency band is common. One of the promising communication methods in this field is spread spectrum (hereinafter referred to as “Spread Spectrum”).
There is a modulation/demodulation method (also referred to as "SS").

[0003] The SS modulation and demodulation method is such that on the modulation side, an information signal, etc. is spread-modulated using a wideband noise-like spreading code.
This method spreads over a very wide frequency band and despreads on the demodulation side using a spreading code equivalent to the spreading code used on the modulation side. The SS communication method, which communicates using such a modulation and demodulation method, has extremely high confidentiality, is resistant to external interference, noise, and intentional interference, can coexist with conventional systems, can transmit with very low power, and is Since it has many features such as being able to multiplex within the same frequency band by changing the noise code, it is currently being applied not only to communication equipment but also to various fields, and is beginning to be applied to consumer equipment.

0004

[Prior Art] SS modulation and demodulation systems, including SS communication systems, are resistant to jamming, narrowband interference, and transmission path fluctuations, but on transmission paths with limited bandwidth, the frequency band of the data to be transmitted is limited. It has the property of being spread over a very wide band for transmission. If the spreading ratio is used to take advantage of this characteristic, the disadvantage is that the data rate will be low relative to the band occupied by the transmitted signal. Therefore, in an attempt to improve the data speed without impairing the advantages of the SS method as much as possible, a parallel data communication system based on the SS method, which takes advantage of the code division property, which is another feature of the SS method, has been developed, for example, for electronic information. Journal of the Institute of Communication Studies (IEICE) August
, 4, 5 '89, etc. Furthermore, parallel data communication systems using the M-ary SS method are being developed as countermeasures against the fact that the number of parallel channels increases as data speeds increase, and performance deteriorates due to interference caused by cross-correlation between sequences. , is featured in the same magazine.

[0005] Here, the principle of a parallel data communication system based on the SS method will be briefly explained. First, on the transmission (modulation) side, communication data is converted from serial to parallel (serial-parallel) to multiple channels. (channel) into lower-speed data, and divide this into lower-speed data for all channels. After synchronizing the data of each ch. Each signal is spread using a PN sequence and transmitted. on the other hand,
On the receiving side, each channel. Demodulate the data each time, parallel → serial (
The final received data is obtained through parallel-to-serial) conversion. In such a parallel data communication system, an orthogonal spreading code is used because the cross-correlation value can be reduced as a spreading code, and as a result, the number of parallel data can be increased.

[0006]

[Problem to be Solved by the Invention] However, this method is effective when the transmission frequency band of the SS signal is wide and there is no transmission loss of the SS signal, but if the transmission frequency band is limited, , the orthogonality of the orthogonal spreading code will be impaired, the cross-correlation value will increase {that is, the inter-symbol interference noise in the despreading output will increase},
As a result, problems arise such as the number of parallel data cannot be increased very much.

[0007] In addition, in such a system, the process gain in the conventional SS method can be expected to suppress interference waves and noise that enter the transmission process, but the performance needs to be improved to further enhance the suppression effect. I don't have it. Therefore, while further increasing the suppression effect against interference etc., it is necessary to trade this suppression effect with information speed.
There has been a strong desire for the emergence of a parallel SS communication system (SS modulation/demodulation device) that can improve the off (compatibility) problem.

[0008]

[Means for Solving the Problems] The parallel spread spectrum modulation demodulation device of the present invention obtains N pieces of slowed-down data obtained by serial/parallel converting an information signal, and converts each of these N pieces of slowed-down data into A spread spectrum modulation unit configured to perform spread spectrum modulation using N different spreading codes, add the obtained N spread spectrum modulation signals, and output the resultant result as a composite spread spectrum modulation signal, and a composite spread spectrum modulation signal. The input signal is transmitted through an input filter that removes high-frequency interference signal components above the main lobe band of the spreading code, and then supplied to N demodulation circuits. A parallel spread spectrum demodulator configured to perform parallel/serial conversion on N slowed data obtained by performing demodulation by despreading using spreading codes equivalent to the respective codes to obtain the original information signal. In a spread spectrum modulation demodulation device, each of the N despreading demodulators constituting the spread spectrum demodulator is provided with an independent intersymbol interference noise suppression means, and after the intersymbol interference noise is reduced by this suppression means, each despread demodulated signals in parallel/
The above problem was solved by serially converting the signal to obtain the original information signal.

[0009]

[Example] Parallel spread spectrum modulation demodulation device of the present invention (
An embodiment (hereinafter also referred to as "parallel SS modulation and demodulation device") will be described with reference to the drawings. FIG. 1 is a block diagram of a parallel SS modulation and demodulation apparatus 1 according to the present invention, in which 10 is a modulation section and 40 is a demodulation section. In the figure, 2 is a serial/parallel converter, 3 is an adder, 4 to 9 are spreading code generation circuits (PNG), 11 to 22 are multipliers, 24 and 25 to 2
7 is an input filter and an equalization filter (usually LPF) for the transfer function HL (s), 37 to 39 are reciprocal circuits, 2
8 to 30 are LCF (low cut filter, high pass filter)
, 31 to 33 are HCFs (high cut filters, low pass filters), 41 to 43 are equalizer circuits, 44 to 46 are subtracters, 34 to 36 are LPFs (low pass filters), 47 to 49 are waveform shaping circuits, 50 is a parallel/serial converter. The characteristics of the equalizer circuits 41 to 43 may be, for example, the same as those disclosed in Japanese Patent Application No. 2-253689, which is the applicant's earlier application.

Next, the functions and operations of the parallel SS modulation and demodulation apparatus 1 of the present invention will be explained with reference to the spectrum diagram shown in FIG. First, in the modulation section 10, the input terminal In
1 supplies the information signal d(t) such as data to the serial/parallel converter 2 to obtain the speed reduction information d1(t), d2(t),
d3(t). Converted speed reduction information d1(t
) to d3(t) are multipliers 1 constituting each SS modulation section.
1 to 13. On the other hand, input terminals In2, ~In
4, the clock signal C(t) is PNG4 to PNG6 respectively.
These PNG4-6 are supplied with different spreading codes P1(t)-P3(t) based on this clock signal.
) (usually a pseudo-noise code), and each multiplier 11
~13 is supplied to the other input terminal.

Multipliers 11 to 13 each receive speed reduction information d.
1(t) to d3(t) spreading codes P1(t) to P3(t
), SS signal SS is
1(t) {see Figure 2(A)}, SS2(t), SS3(
t), that is, P1(t)d1(t) to P3(t)d3(t
) is generated. These three SS signals are added and combined in adder 3, and the summed SS signal Sm(t) {Figure 2(B)
reference} and is output from, for example, an antenna (not shown) via the output terminal Out1. Therefore, the added SS signal Sm(t) is calculated by the following formula: Sm(t)=P1(t)d1(t)+P2(t)d
2(t)+P3(t)d3(t) …………………
(1) It is expressed as:

Next, the functions and operations of the demodulator 40 will be explained with reference to the frequency spectrum diagram of FIG. 2. Note that since the configuration and operating principle of each despreading demodulator from the multipliers 14, 17, 20 to the waveform shaping circuits 47, 48, 49 are the same, one despreading demodulation unit from the multiplier 14 to the waveform shaping circuit 47 This section will mainly be explained. however,
The spreading codes generated by PNG7 to PNG9 are different from each other, and PNG
The spreading codes of NG7, 8, and 9 are P1(t) and P2(t
), P3(t) {that is, the same as the spreading codes generated by PNG4, 5, and 6, respectively}.

The added SS signal Sm(t) is supplied from the input terminal In5 of the demodulator 40 to the input filter 24, where noise components in unnecessary frequency bands {frequency components other than the main lobe of the spread signal}, etc. are removed. After that, it is transmitted to each despreading demodulator. At that time, part of the information of the added SS signal Sm(t) is lost in the input filter 24, and Sm'(t)
becomes. That is, it is expressed as. That is, P1'(t)*
d1(t), P2'(t)*d2(t), P3'(t)
*d3(t) is the loss information, and the added SS signal S
m'(t) is multiplier 14, 17, and 2 for despreading.
0.

On the other hand, the spreading codes P1(t) to P3(t) generated in PNGs 7 to 9 based on the clock signals C(t) from the input terminals In6 to In8 are the spreading codes P1(t) during modulation, respectively. ) to P3(t) at the same time and with the same code. The spreading code P1(t) is an equalization filter 2 having the same transfer function as the input filter 24.
5, P1(t)-P1'(
t) and is supplied to the reciprocal circuit 37 and the multiplier 15. Then, from the reciprocal circuit 37, 1/{P1(t)-
P1'(t)} is output and supplied to multipliers 14 and 16 for despreading. Therefore, the output SD1(t) of the multiplier 14 is as follows. In this equation, the first term on the right side is the demodulated speed reduction information d1(t), and the second term is the spread signal component that cannot be synchronized with other SS signals {see Figure 2 (C)} .

The despreading output SD1(t) is supplied to the subtracter 44 and also to the LCF 28 for information removal, where the despreading output SD1(t) and the spread information included in this frequency band are supplied to the LCF 28 for information removal. A portion of the component is removed as shown by curve a in FIG. 2(D). The removed component is U(t)
Then, the output S1(t) of the LCF 28 is as follows. The filter output S1(t) is outputted by the multiplier 15
The above corrected spreading code P1(t)-P1'(t)
An output S2(t) as shown in the following equation is obtained.

[0016] This multiplication output S2(t) has a spectrum as shown in Fig. 2(E), in which curves b and c
, d are respectively {P2(t)-P2'(t)}d2(t),
{P3(t)-P3'(t)}d3(t), and {P1
(t)-P1'(t)}U(t) (the broken line represents a negative component). This multiplication output S2(t
) is supplied to the next stage HCF31, HCF31 becomes as shown in Figure 2.
As can be seen from (F), the filter has a cutoff frequency above the main lobe of the SS frequency band, so
As a result, the above signal components b, c, and d are respectively shown in FIG. 2(F).
e, f, g, and when expressed in a mathematical formula, it becomes.

The HCF output S3(t) is sent to the multiplier 16
Here, multiplication with the reciprocal spreading code 1/{P1(t)-P1'(t)} from the reciprocal circuit 37 is performed, and S4(t) is obtained as the output {Fig. 2(
G) Reference}. Expressing this mathematically, the third term on the right side of the seventh equation is an undesired signal component, and if G(t) is set to 1, this third term can be set to 0.

That is, in equation 10, the spreading code P1(
t) is 1, the component P1'(t) removed by the equalization filter 25 is 0.2, HCF3
If the component P1''(t) removed by 1 is 0.3, the total value is 0.375, and G(t) is 2
．． Multiplying by 67 gives G(t) = 1. The equalizer circuit 41 at the next stage has the function of setting the value of G(t) to 1, so the output S5(t) of the equalizer circuit 41 is S5(
t)=[{P2(t)-P2'(t)}d2(t)-V
1(t)]/{P1(t)-P1'(t)}+[{P3
(t)-P3'(t)}d3(t)-V2(t)]/{
P1(t)-P1'(t)}...(11). In short, some of the diffused components are lost as U(t) due to the LCF28, which is a filter for information removal, but G(t)
= 1, U(t) = 0, which means that the lost diffuse component is generated as shown in Figure 2 (H), which is lower than the low cutoff frequency fc of the LCF 28 for information removal. This equalizer circuit 41 has a characteristic of increasing the frequency band by 2.67 times, so that G(t)=1. In addition, V1(t) in the 11th equation
and V2(t) are the diffuse components shown in Equations 8 and 9, respectively, and their power spectra are very small as shown by the broken line k in Figure 2 (H), so they are omitted for approximation. It's okay.

According to the above operating principle, the equalizer circuit 4
The output S5(t) of 1 is as follows. That is, this is the same value as the second term on the right side of the third equation, and by supplying this to the subtracter 44 at the next stage and subtracting it from the despread demodulation output SD1(t), the spread component is As a result, only the speed reduction information d1(t) is obtained. This subtraction output actually includes noise outside the information frequency band, as shown by the broken line l in Figure 2 (I), so this unnecessary noise component l is removed by the next stage LPF 34. ing. Then, after shaping the waveform as a logic signal in the waveform shaping circuit 47 at the next stage, it is supplied to the parallel/serial converter 50, where the speed reduction information d2 (
t) and d3(t) in time series to restore the original demodulated information data d(t), and output the output terminal Out2.
In other words, it outputs more.

Note that, as mentioned above, the multipliers 17 and 20
The basic operation of each despreading demodulator from the multiplier 14 to the waveform shaping circuit 48 and 49, respectively, is as follows.
Since the principle of operation is the same as that of No. 7, the explanation thereof will be omitted. In addition, in the above explanation, the number N of speed reduction data is set to 3, but if the number of spread demodulators of the modulator 10 and the number of despread demodulators of the demodulator 40 are equal, the number N is not limited to 3, but other numbers can be used. A number is also fine.

[0021]

[Effects of the Invention] As described above, the parallel spread spectrum modulation demodulation device of the present invention has the effect of suppressing interference waves, jamming waves, noise, etc., while making a trade-off between information speed and intersymbol interference. Parallel SS that can significantly improve speed and speed up
A modulation/demodulation device can be realized. This enables a wide range of applications for demodulating SS communication devices, and has the excellent feature of contributing to the spread and development of in-vehicle radio telephones, cordless telephones, etc., for example.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of a parallel spread spectrum modulation and demodulation device of the present invention.

FIG. 2 is a signal spectrum diagram for explaining the operation of the parallel SS modulation and demodulation device of the present invention.

[Explanation of symbols]

1 Parallel spread spectrum modulation demodulation device 2 Serial/parallel converter 3 Adders 4 to 9 Spreading code generation circuit (PNG) 11 to 22
Multiplier 24 Input filters 25 to 27 Equalization filters 28 to 30 LCF (low cut filter) 31 to 3
3 HCF (high cut filter) 34~36L
PF (low pass filter) 37-39 Reciprocal circuits 44-46 Subtracters 41-43 Equalizer circuits 47-49 Waveform shaping circuit 50 Parallel/serial converter.

Claims (2)

[Claims] Claim 1: Obtaining N pieces of slowed-down data (N is an integer of 2 or more) by serial/parallel converting information signals such as data, and each of the N pieces of slowed-down data obtained is different from each other. Spread spectrum modulation is performed using N spreading codes, and the obtained N
a spread spectrum modulation section configured to add up the spread spectrum modulation signals and output the resultant spread spectrum modulation signal as a composite spread spectrum modulation signal;
The input signal is transmitted through an input filter that removes high-frequency interference signal components above the main lobe band of the spreading code, and then supplied to N demodulation circuits, and each signal is combined with the spreading code used during modulation. Parallel spread spectrum modulation comprising a spread spectrum demodulator configured to perform parallel/serial conversion of N slowed data obtained by demodulating by despreading using an equivalent spreading code to obtain the original information signal. The demodulator is provided with independent inter-symbol interference noise suppression means for each of the N despreading demodulators constituting the spread spectrum demodulation section, and after the inter-symbol interference noise is reduced by the suppression means, each of the N 1. A parallel spread spectrum modulation demodulation device, characterized in that it is configured to perform parallel/serial conversion on despread demodulated signals to obtain an original information signal. 2. As an intersymbol interference noise suppression means in a plurality of despreading demodulation units constituting a spread spectrum demodulation unit,
The reciprocal of the corrected spreading code obtained by transmitting the spreading code for despreading to an equalizing filter having a transfer function substantially equal to that of the input filter and the spreading code signal from the spreading code generating circuit through the equalizing filter is taken. a reciprocal circuit; a first multiplier that performs despreading by multiplying the output signal of the input filter by the output of the reciprocal circuit; and a low-cut filter that removes demodulated information signal components from the output signal of the multiplier. , a second multiplier that multiplies the output of the low-cut filter by the corrected spreading code, a high-cut filter that removes high frequency components from the output of the second multiplier, and a reciprocal of the output of the high-cut filter. a third multiplier that multiplies the output of the circuit; and correcting the spectrum of the spread interference signal obtained by the third multiplier so that it is approximately equal to the spectrum of the spread interference signal in the output of the first multiplier. an equalizer circuit, a subtracter that performs subtraction between the output of the equalizer circuit and the output of the first multiplier, and a low-pass filter that removes high frequency components higher than the demodulated information signal from the output of the subtracter. 2. A parallel spread spectrum modulation demodulation device according to claim 1, characterized in that said parallel spread spectrum modulation demodulation device comprises: