JPH10303764A - Spread spectrum receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide with a simple configuration a spread spectrum(SS) receiver capable of eliminating noise included in a signal. SOLUTION: A reception signal is converted into a base-band SS signal at a down converter 1 and given to a spread demodulation section 2. Furthermore, the signal is given also to a synchronization detection section 3, where synchronization is acquired. Then the detected demodulation spread code is compared with a threshold level at a waveform-processing section 4, and if the threshold level is exceeded, it is regarded as information and an information detection signal is outputted. A spread coding section 5 is synchronized by the information detection signal, and a clock signal is fed to the spread demodulation section 2. The SS signal is spread and demodulated based thereon. Then the spread demodulation signal is fed to a D/A converter circuit 20 and also to a noise elimination circuit 7, where a high-level noise is eliminated. The analog spread demodulation signal, from which the noise component is eliminated, is converted into a digital signal at an A/D converter circuit 21, and QPSK demodulation processing is conduced by an information demodulation section 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum receiving apparatus, and more particularly to noise reduction of an intermittently transmitted spread spectrum signal.

[0002]

2. Description of the Related Art In a spread spectrum (hereinafter abbreviated as SS) communication system, a transmitting side uses a spread code sequence such as a pseudo-noise code (hereinafter abbreviated as a PN code) to convert a transmitted digital signal into a digital signal. A signal having an extremely wide bandwidth compared to the original data is generated, converted into an RF signal, and transmitted.

[0003] On the receiving side, despreading (spreading demodulation) is performed using the same demodulation spreading code as that on the transmitting side to correlate with the received signal.
To convert the received signal into a narrow band signal having a bandwidth corresponding to the original data. Then perform normal data demodulation,
Play back the original data.

[0004] At this time, if the clock frequency and code phase of the demodulation spread code do not completely match the received signal, the correlation output decreases, and the S / N deteriorates. Therefore, a synchronization circuit for synchronizing the received signal with the demodulation spread code is necessary and important.

FIG. 2 shows an SS receiver provided with such a synchronization circuit.

In FIG. 2, a received SS signal is converted by a down converter 1 into a baseband SS signal.
The signal is input to the spread demodulation unit 2. Further, the baseband SS signal is also input to the synchronization detection unit 3, and the synchronization detection unit 3 performs synchronization acquisition. As shown in FIG. 8, the synchronization detecting section 3 is constituted by a digital matched filter.

The following description is based on the assumption that the input SS signal is a 4-bit signal.

In FIG. 8, a digital matched filter includes three shift registers 3 which are delayed by one clock.
1, four multipliers 32 for multiplying the input signal and the signal delayed by each shift register 31, and each multiplier 32
And an adder 33 that simply adds the output from the adder 33. And in the digital matched filter, P
Pattern matching with the N sequence is performed, and a demodulation spreading code synchronized with the information signal included in the timing signal at which the pattern matching output reaches a peak is detected.

Next, the detected demodulation spread code is compared with a threshold value in the waveform processing unit 4. If the demodulation spread code exceeds the threshold value, it is regarded as information and an information detection signal is output. The spread code unit 5 is synchronized with the information detection signal, and a clock signal is supplied to the spread demodulation unit 2.

The spread demodulation unit 2 performs spread demodulation of the SS signal based on the clock signal.

[0011]

The receiving performance of the SS communication system depends on the performance of synchronization acquisition and the accuracy of spread demodulation. Further, the accuracy at the time of information demodulation depends on the signal-to-noise ratio (S / N ratio) of the spread demodulated signal. On the other hand, in the above-described configuration, although synchronization acquisition, which is a feature of the SS communication system, is performed, no measures have been taken for improving the S / N ratio for the spread-demodulated signal. This is because the spread-demodulated signal is a digital signal, but the digital signal is generally distributed over a wide band, and it is difficult to insert a narrow-band filter for removing noise.

The present invention has been made in view of the above-mentioned drawbacks, and has as its object to provide an SS receiver capable of satisfactorily removing noise contained in a spread demodulated signal with a simple configuration.

[0013]

SUMMARY OF THE INVENTION The present invention provides a receiving section for receiving a signal transmitted by a spread spectrum system (hereinafter abbreviated as SS system), and a spread demodulation for demodulating a signal received from the receiving section. Unit, a synchronization detection unit that receives a reception signal from the reception unit and performs synchronization detection, and a spread code unit that creates a demodulation signal based on a detection output from the synchronization detection unit,
A D / A converter for converting a demodulated signal from the spread demodulator into an analog signal; a noise remover for removing a noise component included in the analog demodulated signal; and a signal from which the noise component has been removed is converted to a digital signal. And an A / D conversion unit.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
The receiving device will be described.

In FIG. 1, a received SS signal is converted by a down converter 1 into a baseband SS signal.
The signal is input to the spread demodulation unit 2. Further, the baseband SS signal is also input to the synchronization detection unit 3, and the synchronization detection unit 3 performs synchronization acquisition. As shown in FIG. 8, the synchronization detecting section 3 is constituted by a digital matched filter.

In the following, the input SS signal will be described as a 4-bit signal.

In FIG. 8, the digital matched filter has three shift registers 3 which are delayed by one clock.
1, four multipliers 32 for multiplying the input signal and the signal delayed by each shift register 31, and each multiplier 32
And an adder 33 that simply adds the output from the adder 33. And in the digital matched filter, P
Demodulation synchronized with the information signal included in the timing signal that performs pattern matching with the N-sequence and peaks the pattern matching output (in FIG. 8, a timing signal is generated every four clocks because it is one cycle with four clocks). Detecting the spreading code for use.

Next, the detected demodulation spread code is compared with a threshold value in the waveform processing unit 4. If the demodulation spread code exceeds the threshold value, it is regarded as information and an information detection signal is output. The spread code unit 5 is synchronized with the information detection signal, and a clock signal is supplied to the spread demodulation unit 2.

The spread demodulation unit 2 performs spread demodulation of the SS signal based on the clock signal.

Next, the spread-demodulated signal is supplied to a D / A converter 20, where it is converted from a digital signal to an analog signal. This analog demodulated signal is supplied to a noise removal circuit 7.
And the noise is removed.

The configuration and operation of the noise elimination circuit will be described below with reference to FIGS.

FIG. 3 shows a first embodiment of a noise elimination circuit used in the SS receiver of the present invention, and FIG. 6 shows a specific circuit configuration of an amplifier circuit constituting the noise elimination circuit.

In FIG. 3, the input signal containing noise is
Bandpass filters having different passbands (hereinafter referred to as B
Abbreviated as PF. ) The signals separated into the respective bands by 11 to 1n and including the noise components in the respective bands are output to the respective amplifier circuits 91.
To 9n.

Each of the amplifying circuits 91 to 9n processes the input signal and the noise component of the passed band so that the component having a relatively large amplitude has a large gain and the component having a small amplitude has a small gain. As a result, a noise component having a small amplitude is removed.

Hereinafter, the configuration and operation of the amplifier circuits 91 to 9n will be described.

The amplifier circuits 91 to 9n have the configuration shown in FIG. The input signal is input to the plus terminal of the operational amplifier OP1 via the coupling capacitor C0. And
The output of the operational amplifier OP1 is input to the plus terminal of the operational amplifier OP2. The output of the operational amplifier OP2 is a resistor R1,
The resistance is divided by R2, and negatively fed back to the minus terminal of the operational amplifier OP1. Here, when the potential at the point A is smaller than the forward voltage Vf of the diode, the diode D0,
D1 becomes non-conductive and is not output. When the potential at the point A is higher than Vf, one of the diodes D0 and D1 conducts, and the output terminal substantially receives the input signal (R1 +
R2) / R1 times the output signal is obtained.

Accordingly, as shown in FIG. 7, a noise component having a small amplitude (specifically, (R1 / (R1 + R
2)) The signal up to × Vf) is not output, and the signal component beyond that is amplified approximately (R1 + R2) / R1 times and output. Therefore, the noise component removal range can be changed by changing the resistance values of the resistors R1 and R2 in the amplifier circuit of FIG.

By the way, when the pass bandwidths of the respective BPFs 11 to 1n are substantially the same as shown in FIG.
As shown in FIG. 3C, the group delay characteristic input to 0 is such that the delay time increases as the frequency increases.

Therefore, in the first embodiment, by providing the equalizer 10, the group delay characteristic of the signal passing through each BPF is corrected so that the characteristic becomes flat.

FIG. 4 shows a second embodiment of the noise elimination circuit of the present invention.

FIG. 4 differs from FIG. 3 in that BPFs 11 to 1n having different pass bandwidths are provided as shown in FIG. 4B in place of the equalizer 10 for correcting the group delay characteristic, and the group delay characteristic is made flat. This is a working example.

FIG. 5 shows a third embodiment of the noise elimination circuit of the present invention.

FIG. 5 differs from FIG. 4 in that BPFs 11 to 1n having different pass bandwidths are replaced by secondary phase shift circuits (BPFs 11 to 1n) having the same pass bandwidth and amplifying circuits 91 to 9n. This is an example in which APFs 111 to 11n are provided, and the group delay characteristics are flattened by the APFs 111 to 11n.

In the noise removing circuit 7 configured as described above, the SS signal passes through only a specific or several BPFs. On the other hand, since the noise components are distributed over a wide band, the level of the noise components passing through each BPF is low. Therefore, when attention is paid to the noise of the pass frequency component of each BPF, even a relatively high-level noise has a sufficiently low level with respect to the SS signal. Therefore, of the noise components output from the noise removal circuit 7, the noise components passing through the same BPF as the SS signal remain as they are, but the noise components passing through the other BPFs are removed. As a result, when supplied to the information demodulation unit 6 described later, the high-level noise component detected by the conventional circuit has a sufficiently small value that the noise component is not detected by the information demodulation unit 6.

Then, in the information demodulation unit 6, if the signal is transmitted by the digital modulation method on the transmission side, for example, the QPSK modulation method, the QPSK demodulation processing is performed.

[0036]

According to the present invention, high-level noise generated when an SS signal is received can be sufficiently removed with a simple configuration. As a result, demodulation processing in SS system reception can be performed with high accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram showing a spread spectrum receiver according to the present invention.

FIG. 2 is a diagram illustrating a conventional spread spectrum receiving apparatus.

FIG. 3 is a diagram showing a first embodiment of a noise elimination circuit used in the spread spectrum receiver according to the present invention.

FIG. 4 is a diagram showing a second embodiment of the noise elimination circuit used in the spread spectrum receiver of the present invention.

FIG. 5 is a diagram showing a third embodiment of the noise elimination circuit used in the spread spectrum receiver of the present invention.

FIG. 6 is a diagram illustrating an amplifier circuit of the noise removal circuit in FIG. 5;

FIG. 7 is a diagram showing input / output characteristics of the amplifier circuit in FIG. 6;

FIG. 8 is a diagram showing a digital matched filter used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Down converter 2 Spreading demodulation part 3 Synchronization detection part 4 Waveform processing part 5 Spreading code part 6 Information demodulation part 7 Noise removal circuit 20 D / A conversion circuit 21 A / D conversion circuit

Claims (4)

[Claims] 1. A receiving unit for receiving a signal transmitted by a spread spectrum system (hereinafter abbreviated as an SS system), a spread demodulation unit for demodulating a signal received from the receiving unit, and a signal from the receiving unit. A synchronization detection unit that receives a reception signal and performs synchronization detection, a spread code unit that creates a demodulation signal based on a detection output from the synchronization detection unit, and a D that converts a demodulation signal from the spread demodulation unit into an analog signal. / A converter, a noise remover for removing a noise component included in the analog demodulated signal, and an A / D converter for converting the signal from which the noise component has been removed into a digital signal. Spread spectrum receiver. 2. A receiving section for receiving a signal transmitted by a spread spectrum method (hereinafter abbreviated as an SS method), a spread demodulation section for demodulating a signal received from the receiving section, and a signal from the receiving section. A synchronization detection unit that receives a reception signal and performs synchronization detection, a spread code unit that creates a demodulation signal based on a detection output from the synchronization detection unit, and a D that converts a demodulation signal from the spread demodulation unit into an analog signal. An A / D converter, a noise remover for removing a noise component included in the analog demodulated signal, and an A / D converter for converting the signal from which the noise component has been removed into a digital signal. , A plurality of pass band filters separated by different pass bands, and a signal having passed through the plurality of band pass filters has a large gain for a signal having a larger amplitude than a certain value, and has a smaller amplitude than a certain value. A spread spectrum receiver comprising: a plurality of gain control circuits for controlling a small gain of a small signal; and a first combining circuit for combining signals subjected to gain control by the plurality of gain control circuits. apparatus. 3. A receiving section for receiving a signal transmitted by a spread spectrum system (hereinafter abbreviated as SS system), a spread demodulation section for demodulating a signal received from the receiving section, and a signal from the receiving section. A synchronization detection unit that receives a reception signal and performs synchronization detection, a spread code unit that creates a demodulation signal based on a detection output from the synchronization detection unit, and a D that converts a demodulation signal from the spread demodulation unit into an analog signal. An A / D converter, a noise remover for removing a noise component included in the analog demodulated signal, and an A / D converter for converting the signal from which the noise component has been removed into a digital signal. Receives a received signal, separates the received signal in different passbands, and has a plurality of bandpass filters having substantially equal delay times due to the respective group delay characteristics, and an amplitude of a signal passed through the plurality of bandpass filters. A plurality of gain control circuits that increase the gain for a signal larger than a certain value and decrease the gain for a signal whose amplitude is smaller than a certain value, and are controlled by the plurality of gain control circuits. And a first combining circuit for combining the received signals. 4. Each of the plurality of pass band filters constituting the noise removing unit has a pass band width such that delay times due to group delay characteristics of the respective band pass filters become substantially equal. The spread spectrum receiving apparatus according to claim 3, wherein: