JPH05227122A - Spread spectrum communication equipment - Google Patents

Abstract

PURPOSE:To reduce the influence of a disturbing wave by flattening each frequency spectrum of a spread spectrum modulation signal by using a spectrum flattening circuit consisting of only a passive element in spread spectrum communication equipment. CONSTITUTION:The level of each spectrum component in the prescribed spread band of a PN signal from a PN code generator 11 is extremely uniformalized by passing the PN signal through the spectrum flattening circuit 12 consisting of only the passive element, and it is outputted to a DBM 13. The PN signal is synthesized with a carrier signal from a carrier oscillator 14 at the DBM 13, and furthermore, it is band-limited at a BPF 15, and it is converted to the transmission of a flat spectrum whose side lobe is suppressed, and is transmitted from an antenna 17 via a power amplifier 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum communication device, and more particularly to an improvement for flattening each spectrum of frequencies of a transmission signal.

[0002]

2. Description of the Related Art Spread spectrum (hereinafter referred to as SS)
In communication, there is a demand for stronger anti-jamming performance. The transmission wave in SS communication has radio waves distributed within a predetermined diffusion band. That is, in SS communication, it is considered that a transmission wave at a certain frequency is diffused by a predetermined procedure. Therefore, it is desirable that the levels of the respective frequency components within the predetermined frequency band are as uniform as possible.

That is, as described above, the sum of all the components in the spread band (more accurately, the level integrated with respect to the frequency) is regarded as a transmission wave of one frequency, and thus, within the band. If the levels have variations, the interference margin in the entire band becomes small if the frequency components with small levels interfere.

For example, as shown in comparison with FIGS. 8 (a) and 8 (b), for two types of level distributions A and B in the band, the a (dB) level is placed at the frequency f _1. When an interfering wave to suppress occurs, the dynamic range is 3a in A.
Although it deteriorates to (dB), B only deteriorates to 4a (dB). That is, since the quality of the SS transmission wave as a whole is determined by the dynamic range of the part where the level is the lowest, it means that there is a part A'where the level is high, such as A. Nonetheless, it is desirable that the power distribution be as uniform as possible, as in B. According to the technique of MSK modulation, such a spectrum can be flattened.

FIG. 6 shows a conventional surface acoustic wave (SAW) MSK.
1 shows a schematic configuration of a transmitter using a filter. In the figure, 1 is a mixer, 2 is a carrier oscillator, 3 is a SAW M.
It is an SK filter. The baseband transmission data S ₁ and the carrier S ₂ are frequency-converted by the mixer 1 to be BP
The SK modulated wave signal S ₃ is output to the SAW MSK filter 3.

In this case, the input IDT spectrum is as shown in FIG. 7A, where T is the minimum chip period of the transmission data S ₁ and f ₁ is the center frequency of the BPSK modulated wave signal S ₃ , and f ₂ = f _{If 1} + 1 / 2T, then f ₁ -1 / T to f ₂
It has a band up to + 1 / T and the center frequency is fc.
Therefore, when the signal S ₃ passes through the input side transducer of the SAW MSK filter 3, it has a B spectrum. The transducer on the output side of the filter has the characteristic of C in FIG. 7, and the output of the SAWMSK filter 3 has the characteristic of D in FIG. 7 to flatten the spectrum.

[0007]

As described above, the conventional SAW MSK has been used to flatten the spectrum.
Since a special device such as a filter is required, the structure is complicated and expensive.

An object of the present invention is to obtain a uniform power density in the spread band of a spread spectrum communication device by using a spectrum flattening circuit composed of a simple combination of a capacitor and a resistor, resulting in interference. It is to be able to reduce the influence of the price at low cost.

[0009]

In order to achieve the above object, the present invention relates to a transmitting apparatus for spreading and distributing a frequency spectrum of a signal to be transmitted on a frequency axis by a predetermined algorithm, and A spectrum spreader comprising a receiver for demodulating each spectrum of frequencies of signals transmitted and received from a transmitter by despreading on the frequency axis by another algorithm having a predetermined relationship with the above predetermined algorithm. In the communication device,
The transmission device is characterized in that it has control means consisting of only passive elements for controlling each spectrum spread on the frequency axis so that the amplitude of the transmission signal becomes uniform in a predetermined frequency range. In the apparatus of the present invention, the control means may be a flattening circuit that operates so as to equalize the amplitude of each spectrum of the transmission signal within the predetermined frequency range. Further, the flattening circuit is
A parallel circuit section having a predetermined roll-off frequency and composed of a first resistor and a first capacitor; and a predetermined cut-off frequency higher than the predetermined roll-off frequency,
It can be configured by connecting in series a high-pass filter unit configured by a second resistor and a second capacitor.
Further, the first and second capacitors of the parallel circuit section and the high-pass filter section may be composed of a common capacitor element. The second resistance of the high pass filter section may be a load resistance of the flattening circuit.

[0010]

In the spread spectrum communication device of the present invention,
Each spectrum of the transmission signal spread on the frequency axis by the control means is controlled so that its amplitude is made uniform in a predetermined frequency range. Therefore, the influence of the interfering wave on the transmission signal can be reduced.

[0011]

Embodiments of the present invention shown in the drawings will be described below.
FIG. 1 shows a configuration example of a spectrum flattening circuit suitable for a spread spectrum communication apparatus of the present invention. In the figure,
R ₁ and R ₂ are resistors, C ₁ and C ₂ are capacitors, S is a signal source, r is an internal resistance of the signal source S, and C ₂ cuts a DC component. 1 can be rewritten as shown in FIG.

The frequency response characteristic of the circuit of FIG. 2 is shown in FIG. 3A, where ω _C is the cutoff frequency (the frequency at which 3 dB is increased) and ω _R is the roll-off frequency (the frequency at which 3 dB is decreased). Like This characteristic is shown in FIG.
Ω _C = 1 / R ₂ C ₁ shown in (b) and ω _R = shown in FIG.
It is a combination of the filter characteristics with 1 / R ₁ C ₁ . That is, the characteristic is a combination of the filter formed by the combination of R ₁ and C ₁ and the filter formed by the combination of R ₂ and C ₁ .

Therefore, when the input signal S ₄ from the signal source S is a spread spectrum signal, the output signal S ₅ is flattened as shown in FIG. 4 by appropriately selecting ω _C and ω _R. be able to. That is, although the level at the center frequency fc is slightly attenuated only by the portion a in FIG. 4 by the R ₁ C ₁ filter, the level can be raised for the higher frequency portion and the level is made uniform over the entire band. It becomes possible to do.

FIG. 5 shows the configuration of a transmitter of a spread spectrum communication apparatus to which the spectrum flattening circuit according to the present invention is applied. In the figure, 11 is a PN code generator, which is composed of a reference oscillator 11a and a PN modulator 11b. 12 is a spectrum flattening circuit as shown in FIG. 1, 13 is D
BM (Double Balanced Mixer),
14 is a carrier oscillator, 15 is a band pass filter (B
PF), 16 is a power amplifier, and 17 is a transmitting antenna.

From the PN code generator 11, the reference oscillator 1
The reference signal of frequency f ₀ generated in 1a is PN-modulated by the PN modulator 11b, and the PN signal is output. This PN
By passing through the spectrum flattening circuit 12, the signal is processed so that the level of each spectrum component within a predetermined spread band is made as uniform as possible.

Next, in the DBM 13, the flattened PN signal and the frequency f from the carrier oscillator 14 are used.
The carrier signal of ₁ is combined to generate a transmission signal. This transmission signal is band-limited by the BPF 5 and converted into a flat spectrum signal in which the side rope is suppressed, and the converted signal is power-amplified to a desired level by the power amplifier 16 and transmitted from the antenna 17.

In the circuit of FIG. 1, for example, the load resistance of the transmitter may be directly used as R ₂ , and in that case, the spectrum flattening circuit requires R ₁ and R _2. , C ₁ , only three passive elements are provided, and the spectrum flattening circuit can be realized with a very simple and inexpensive structure as compared with the conventional SAW MSK filter. The present invention is a DS using the above-mentioned DBM.
The present invention is not limited to the (Direct Sequence) type device, but can be applied to other types.

[0018]

As described above, according to the present invention, in the spread spectrum communication device, the influence of the interference wave on the spread modulation transmission signal can be reduced by the spread spectrum flattening circuit composed of the simple and inexpensive passive element. ..

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a spectrum flattening circuit according to the present invention.

FIG. 2 is a circuit diagram in which the circuit of FIG. 1 is simplified.

FIG. 3 is a characteristic diagram showing the frequency response of the circuit of FIG.

FIG. 4 is a characteristic diagram for explaining the flattening action of the circuit of FIG.

FIG. 5 is a block diagram showing a transmitter of a spread spectrum communication device to which a spectrum flattening circuit according to the present invention is applied.

FIG. 6 is a block diagram showing a transmitter using a SAW MSK filter.

FIG. 7 is a spectrum diagram of the filter of FIG.

FIG. 8 is a characteristic diagram showing the level of a transmission wave in SS communication.

[Explanation of symbols]

R ₁ and R ₂ resistors C ₁ and C ₂ capacitors 11 PN code generator 12 spectrum flattening circuit 13 DBM 14 carrier oscillator

Claims (6)

[Claims] 1. A transmission device that spreads and distributes a frequency spectrum of a signal to be transmitted on a frequency axis by a predetermined algorithm, and each spectrum of a frequency of a signal transmitted and received from the transmission device. In a spread spectrum communication device comprising a receiving device for demodulating by despreading on the frequency axis by another algorithm having a predetermined relationship with the above predetermined algorithm, wherein the transmitting device spreads on the frequency axis. A spread spectrum communication device, comprising: a control means composed of only passive elements for controlling each of the generated spectrums so that the amplitude of a transmission signal is made uniform in a predetermined frequency range. 2. The control means is a flattening circuit which operates to equalize the amplitude of each spectrum of the transmission signal within the predetermined frequency range.
The spread spectrum communication device described in. 3. The flattening circuit includes a parallel circuit section having a predetermined roll-off frequency and including a first resistor and a first capacitor, and a predetermined cut-off frequency higher than the predetermined roll-off frequency. 3. The spread spectrum communication device according to claim 2, wherein the second resistor and the high-pass filter unit configured by the second capacitor are connected in series. 4. The spread spectrum communication device according to claim 3, wherein the first and second capacitors of the parallel circuit unit and the high-pass filter unit are composed of a common capacitor element. 5. The spread spectrum communication device according to claim 3, wherein the second resistor of the high pass filter unit is a load resistor of the flattening circuit. 6. A signal having a spectrum of frequencies distributed and distributed on a frequency axis by a predetermined algorithm is transmitted, and the spectrum of each received transmission wave is set in a predetermined relationship with the predetermined algorithm. In a transmission device of a spread spectrum communication system that despreads and demodulates on the frequency axis by another algorithm having, the transmission device has a signal of each spectrum spread on the frequency axis with an amplitude in a predetermined frequency range. A spread-spectrum communication system transmitter, comprising control means composed of only passive elements for controlling to be uniform.