JPS598444A - Spread spectrum receiver - Google Patents

Abstract

PURPOSE:To improve probability of synchronism detection, by providing a means for controlling a local oscillating frequency in follow up to a frequency fluctuation of a carrier of an input signal to an input section of a receiver to make the intermediate frequency after frequency conversion constant and improving the ability for removing interference. CONSTITUTION:A receiving signal Vi is converted interms of frequency on a voltage Vl from a VCO26 by a frequency converter 2 and supplied to an inverse spread modulator 4. The modulator 4 performs the inverse spread modulation with a local reference signal from a local reference code generator 5 to supply a part of the signal of inverse spread modulation to a narrow band pass filter 6 and other is supplied to a limiter 22. A signal Vm having the amplitude limited by the limiter 22 and an output signal Vs of an IF oscillator 24 oscillated in a prescribed frequency fs are compared in terms of phase by a phase detector 23 and the frequency of the signal fs is made equal to the center frequency IF of the pass band of the filter 6. When fmnot equal to fs, a signal proportional to fm-f3 is generated at an output of the detector 23 to control the VCO26 via an LPF25, thereby making the IF after frequency conversion constant and improving the ability of interference.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spread spectrum receiver, and more particularly, to a spread spectrum receiver, which uses a carrier wave modulated with a pseudo noise code and an information signal.
The present invention relates to a receiving device that receives the information signal by completely demodulating the modulated signal using the same code as the pseudo-noise code.

In spread spectrum communication, the spectrum of the transmission wave is spread, and it is possible to communicate without band restrictions and with low power density, and because of its characteristics such as maintaining confidentiality, it is suitable for mobile communication, data communication, personal communication, etc. Although applicable to a variety of applications, there are also many problems to be solved.

In particular, in a receiving device, it is essential to synchronize the pseudo-noise code of the transmitter with the local reference code of the receiving device, and in the configuration of the synchronization control circuit, the frequency of the carrier wave included in the transmitted signal is not stable. This makes it impossible to accurately demodulate the desired signal from the received waves. On the other hand, in a transmitter, if you try to increase the stability of the oscillator for generating pseudo-noise codes or carrier wave generation, you will need a constant temperature device and many other circuit devices to stabilize the frequency, which will increase the size of the transmitter. , resulting in high power consumption and therefore high cost. This poses a serious obstacle in the practical application of spread spectrum communications. In other words, when used for mobile communication or measurement, it is necessary to make the transmitter completely smaller and lower power consumption, but if these requirements are to be met, it is not realistic to use an oscillator with a stable frequency. Not on point.

Conventionally, in order to solve these problems, a plurality of narrow band pass filters with different center frequencies were provided in parallel in the synchronization circuit of the receiving device, and a majority logic circuit was used to select a signal from one of the plurality of filters. is known. However, this configuration complicates the device and increases cost. Furthermore, since the configuration of the reference carrier wave forwarding circuit must have a wide pull-in frequency width and high stability against temperature and noise, the advantages of replacing existing narrowband communication systems are diminished.

Therefore, an object of the present invention is to realize a spread spectrum receiving device that stably performs full demodulation with a simple device even when the carrier wave included in the input signal or the frequency of the local oscillator necessary for frequency conversion of the receiving device fluctuates. That is,
Realization of a complete receiving device that improves interference rejection ability, shortens code synchronization time, improves synchronization detection probability, does not require processing to increase the number of band-pass filters, and narrows the frequency width of the reference carrier decay circuit. It is to be.

In order to achieve the above object, the present invention provides a spread spectrum receiver, in which means is provided at the input section of the receiver to control the local oscillation frequency by following the frequency fluctuation of the carrier wave of the input signal, and the intermediate frequency after frequency conversion is is always kept constant, and is made to be -t with respect to the center frequency of the narrow band pass filter placed after it.

According to the above configuration of the present invention, the frequency-converted intermediate frequency is stabilized, so that the required bandwidth of the bandpass filter can be realized as a very narrow band approximately equal to the bandwidth of the information signal. Therefore, the signal-to-noise ratio can be improved, and therefore, interference such as unwanted waves can be effectively eliminated. In addition, code synchronization acquisition time can be shortened and synchronization errors can be greatly improved. Furthermore, since the receiving device according to the present invention is effective against frequency fluctuations of carrier waves,
Since the transmitting device in spread spectrum communication does not require any special circuit or device for frequency stabilization, it is possible to significantly reduce the size and cost of the device, and the present invention is an effective means for putting spectrum communication into practical use. All that is offered. Furthermore, since the carrier wave regeneration circuit can be designed with emphasis on the signal-to-noise ratio and steady-state phase error in the loop gain and loop delay time, the degree of freedom in design is increased compared to the conventional circuit.

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 1 is a block diagram showing the configuration of an embodiment of a spread spectrum receiver according to the present invention. This embodiment includes a code synchronization circuit for obtaining a synchronization determination signal Vue and a reference carrier wave Vue.
Although only a circuit for obtaining "r, V't'c" and a circuit for obtaining an information signal V1 are shown, they are not shown because they are not directly necessary for explaining the present invention.

The received signal VI received by the antenna is sent to the frequency converter (mixing circuit) 2 by a voltage-controlled crystal oscillator (local oscillator).
It is mixed with the 26 signals Vt (which may be an ordinary frequency variable oscillator (for example, a voltage controlled oscillator)) and frequency-converted.

The frequency-converted signal is passed through a despreading modulator, that is, a correlator 4, and a local reference code generator (in this case, from the PNN code generator side used 5) that generates a code identical to the pseudo-noise code of the desired wave in the received signal. is despread modulated with a local reference code.

A part of the despread modulated signal is passed through a narrow band pass filter 6,
The other part is added to limiter 22.

Signal ■m whose amplitude is limited by IJ transmitter 22 (frequency f
m) and the output signal Vs of the intermediate frequency oscillator (reference signal source) 24 that oscillates at a constant frequency f- are detected by the phase detector 23.
and the phase is compared.

f- is equal to the center frequency fIF' of the passband of the filter 6. Here, in the case of an fm
The oscillation frequency ft of is controlled so that fm=f-.

The output signal of filter 6 passes through intermediate frequency amplifier 7 and phase detectors 8 and 9 . voltage controlled oscillator 20
multiplied by the regenerated carrier wave from Phase detectors 8 and 9
The outputs of are added by an adder 15 through integrators 10 and 11 and absolute value circuits 13 and 14, respectively. A synchronous footfall circuit 16 compares the output of the adder 15 with a threshold level, determines the magnitude relationship between these signals, and issues a command signal for search mode or tracking mode.

A portion of the output of the integrating circuit 10 is applied to a discriminator 12 to reproduce the information signal Vl. A portion of the output of the integrating circuit 11 is applied to the voltage controlled oscillator 20 of the reference carrier regeneration loop via a sampling and holding circuit 17, a polarity inverting amplifier circuit 18 and a loop filter 19. The circuit on the right side of the intermediate frequency amplifier 7 in FIG. 1 is constructed in the same manner as conventionally known circuits, and a detailed explanation of its operation will be omitted. According to the above embodiment, since the automatic frequency control circuit is disposed at the input section of the spread spectrum receiver, that is, at the section that converts the input signal into an intermediate frequency signal, the filter 6 Since a signal with a frequency equal to the center frequency fry is always input to the filter, the pass band of the filter can be matched to the band of the information signal, and the interference rejection ability can be maximized. Furthermore, since the frequency is controlled to be constant before the filter 6, the control sensitivity of the voltage controlled oscillator 20 of the reference carrier recovery loop may be extremely small.

Therefore, a voltage-controlled crystal oscillator with high stability (eg, frequency stability of about 10-6) can be used as the oscillator 20. Moreover, the carrier wave tM can be easily generated in an extremely short period of time.

FIG. 2 shows another embodiment of the spread spectrum receiver according to the present invention. In this figure, the parts denoted by the same numbers as in FIG. 1 have the same structural functions as those in FIG. 1, so the explanation will be omitted. In this embodiment, the output signal '(rlJ) of the frequency converter 2 is inputted to the rlJ transmitter 22 to control the oscillation frequency ft'k of the voltage-controlled crystal oscillator 26. 4 before despreading, the amplitude change of the signal Vl is small.Therefore, the limiter 22 is unnecessary or may have a small dynamic range.

Further, an integrator and a sampling hold circuit may be inserted between the phase detector 23 and the low-pass filter 25. Furthermore, a bandpass filter that allows the frequency (fI-ft) component to pass may be inserted before the limiter 22.

As can be seen from the above description, in the device of the present invention, by automatically controlling the frequency at the input section of the receiving device, the intermediate frequency after frequency conversion always matches the center frequency of the narrowband bandpass filter. (1) The ability to eliminate interference can be maximized, and the characteristics of the spread spectrum communication system can be maximized.

(2) Since the pull-in frequency width of the carrier wave regeneration circuit may be extremely narrow, the carrier wave regeneration circuit is simple and carrier wave regeneration is also facilitated.

(3) Code synchronization time is also shortened, and synchronization detection probability is further improved.

(4) There is almost no need to consider fluctuations in the input carrier frequency when determining the loop gain and pull-in frequency width of the carrier regeneration circuit. For this purpose, we can design the entire loop gain and loop delay time with emphasis on the signal-to-noise ratio and the steady phase difference of 8 points.
The degree of freedom in design is increased compared to the conventional method, and even if the input carrier frequency fluctuates widely, carrier wave regeneration can be performed easily. Therefore, the transmitter does not need to consider frequency stability, and can be made smaller and consume less power.

[Brief explanation of the drawing]

Both FIG. 1 and FIG. 2 show the configuration of an embodiment of a spread spectrum receiving apparatus according to the present invention.

Claims (1)

[Claims] 1. A carrier wave modulated with a pseudo-noise code and an information signal is used as a received signal, and after the received signal is frequency-converted, an information signal is demodulated from a signal subjected to despread modulation using a local reference code. In the spread spectrum receiver, the circuit that performs the frequency conversion includes a variable frequency local oscillator, a mixing circuit that mixes the output of the local oscillator and the received signal, a reference signal source that generates a reference frequency, and a frequency of the reference signal source. and a control circuit that controls the entire oscillation frequency of the local oscillator so that the intermediate frequency after frequency conversion matches the center frequency of the bandpass filter using the frequency comparison signal of the frequency-converted signal. Features a spread spectrum receiver. 2. The spread spectrum receiving device according to claim 1, wherein the frequency-converted signal to be compared with the frequency of the reference signal is extracted from the signal on which the output of the mixing circuit has been subjected to despread modulation. 3. In the apparatus according to item 1, the spread spectrum is configured such that the frequency-converted signal to be compared with the frequency of the reference signal is extracted from the signal before being subjected to despread modulation at the output of the mixing circuit. Receiving device. 4. In the apparatus described in item 1, the control circuit includes a limiter that limits the amplitude of the frequency-converted signal, and a phase detector whose output is the output of the limiter and the output of the reference signal source.
A spread spectrum receiver comprising a low-pass filter that extracts low frequency components from the output of the phase detector, and a circuit that controls the entire oscillation frequency of the local oscillator using the output of the low-pass filter.