JPH06141019A - Spread spectrum communication system - Google Patents

Abstract

PURPOSE:To obtain an interference elimination system capable of eliminating an interference wave independently of the kind, the nature, or the number of the wave when the interference wave exists in either a USB or LSB in a communication zone. CONSTITUTION:A reception signal is divided into an LSB component and a USB component by an HPF 503 and an LPF 504, and they are supplied to power detection circuits 514, 515, respectively, and respective power level is detected, and is compared at a comparator 516. A reference signal is also divided into the LSB component and the USB component by an HPF 508 and an LPF 509. Selection circuits 505, 507 are controlled by the output of the comparator 516, and either or both the LSB component and the USB component are selected corresponding to power level difference, and correlation is taken by a correlator 506.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interference canceling method suitable for a spread spectrum communication system, and more specifically, it relates to a narrow band interference signal in a lower side band (LSB) or an upper side band of a communication band. The present invention relates to a method for easily removing this interference wave when present in either (USB) and giving interference to spread spectrum communication.

[0002]

2. Description of the Related Art In a conventional interference wave elimination method in a spread spectrum communication system, an interference wave is removed by tuning a narrow band band rejection filter (BRF) to the narrow band interference wave. ing. In this case, a control circuit for matching the center frequency of the BRF with the center frequency of the interference wave is required as shown in FIG.

However, an interference wave whose center frequency fluctuates,
In order to remove an interference wave whose frequency hops, it is necessary to detect the interference wave at high speed and match the center frequency of the filter.

The above-mentioned conventional system will be described in more detail. The configuration is such that the first frequency conversion circuit 101 and the first power detection circuit 107 to which the received signal is input and the interference wave are removed as shown in FIG. BRF 102 and a second frequency conversion circuit 103 for controlling the voltage controlled oscillator VCO (Voltage Cont.
The output of the rolled oscillator 110 is input. The output of the second frequency conversion circuit is input to the intermediate frequency amplification circuit 104, and the output of the intermediate frequency amplification circuit 104 is input to the correlation circuit 106 and the second power detection circuit 108. First
The outputs of the second power detection circuits 107 and 108 are input to the control circuit 109, and the control circuit 109 outputs the VCO 11
Control the oscillation frequency of zero.

In this system, the received signal including the interference wave of the intermediate frequency whose center frequency is fs is frequency-converted by the first frequency conversion circuit 101. At this time, the center frequency of the interference wave is fi, the oscillation frequency of the VCO 110 is fo, and
The center frequency of the RF 102 is fr, the lower limit frequency of the band is fl, and the upper limit frequency is fu. At first, fr = fl
-Fo. The center frequency of the signal that has passed through the BRF becomes fs again by the second frequency conversion circuit 103 and is input to the correlator 106 and the power detection circuit 108.

The power detection circuits 107 and 108 detect the power at this time, and this data is input to the control circuit 109. The operation of the control circuit 109 will be described with reference to the flowchart of FIG. In the control circuit 109, first, the VCO 110
The oscillation frequency is set to fr + fo = fl (step S1).

At this time, it is compared whether or not the power level difference between the power detection circuits 107 and 108 is larger than the power level difference previously stored in the memory in the control circuit 109 (steps S2 and S3). At this time, if the difference between the newly measured power levels is large, the difference between the power level and fr
The frequency of + fo is stored (step S4). But,
If the newly measured power level difference is smaller than the stored power level difference, the stored value is retained.

Next, it is checked whether fu = fr + fo (step S5). When fu ≠ fr + fo, V
The oscillation frequency of the CO 110 is changed upward by half the band of the BPF (step S6). Then, the difference in power level is measured and the same operation is repeated (the level difference is checked from the lower limit of the band toward the higher direction).

If fu = fr + fo, then VCO
The oscillation frequency of 110 is controlled to be the stored frequency (step S7). Then, the power level difference is measured (step S8), and it is checked whether or not the power level difference is smaller than the specified value (step S9).
If it is larger than the specified value, the measurement of the power level difference is continued, and if it is smaller than the specified value, it returns to the initial state.

[0010]

However, in order to remove the interference wave by this conventional method, it is necessary to search the entire communication band, and the search speed at that time is determined by the bandwidth of the BPF. . Therefore, it is difficult to track and remove the interference when the interference wave is hopping or sweeping. There is a need).
Further, it is difficult to remove the interference wave when the interference band is wider than the BPF band or when there are a plurality of interference waves.

An object of the present invention is to divide the communication band into two, so that at least the communication band of USB or L
It is an object of the present invention to provide an interference canceling method capable of canceling an interference wave regardless of the type, property, or number of the interference wave when the interference wave exists in only one of the SBs.

[0012]

In order to achieve the above object, the spread spectrum communication system of the present invention is a signal that is DSB modulated with data to be transmitted and further spread spectrum modulated with a desired type of signal. And a pair of filters for receiving the signal transmitted from the transmitter and demodulating the data, the pair of filters separating the received signal into an LSB component signal and a USB component signal. Means for generating a signal modulated with the desired type of code corresponding to the received signal, and a means for separating the signal modulated with the desired type of code into LSB component and USB component signals A pair of filters, means for determining whether the difference between the power levels of the LSB component and the USB component separated after the reception is less than a predetermined value, and the determination means When it is determined that the power level difference is less than or equal to a predetermined value, it is determined that the corresponding components of the signals separated by the pair of filters and another pair of filters are simultaneously correlated and the power level difference exceeds the predetermined value. And a receiver including a correlating means for correlating only the component having the smaller level among the signals separated by the pair and another pair of filters. .

[0013]

When the power level difference between the LSB component and the USB component is less than or equal to a predetermined value, the corresponding signal components from each filter are correlated with each other. Correlation is performed only by the signal components.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show an embodiment of a transmitting circuit and a receiving circuit of a spread spectrum communication system adopting an interference canceling method of the present invention.

In FIG. 1, a modulation circuit 201 modulates a high frequency carrier generated by an oscillation circuit 203 with data. The modulation circuit 202 spread-modulates the high-frequency modulated data signal with the PN code generated by the PN code generation circuit 204 and transmits the data signal. When the center frequency of the transmission signal is fc, the transmission signal may be a DSB signal as shown in FIG. 3A or a combined SSB signal as shown in FIG. 2B.

Further, in FIG. 2, it is assumed that the received signal is converted to the intermediate frequency of the center frequency fs. The intermediate frequency signal of the center frequency fs is a band pass filter BPF.
It is input into 501. Then, the intermediate frequency amplifier circuit 502
And is input to the low pass filter LPF 504 and the high pass filter HPF 503. LPF504
Of the power detection circuit 515 and the selection circuit 505, and the output of the HPF 503 is output to the power detection circuit 514.
And the other input of the selection circuit 505, respectively.
The output of the selection circuit 505 is connected to one input of the correlator 507.

On the other hand, the high frequency carrier generated by the oscillator circuit 513 is supplied to one input of the modulation circuit 511, and the reference PN code generated by the reference PN code generation circuit 512 is supplied to the other input of the modulation circuit 511. To be done. Then, the modulation circuit 511 performs spread modulation. At this time,
The output signal of the modulation circuit 511 is a DSB as shown in FIG.
The SSB signal combined with the signal may be used, but the same method as the transmission signal is preferable.

Then, this signal is band-limited by the BPF 510 and then input to the LPF 509 and the HPF 508. The output of the LPF 509 is supplied to one input of the selection circuit 507, and the output of the HPF 508 is supplied to the other input of the selection circuit 507. The output of the selection circuit 507 is supplied to the other input of the correlator 506.

The correlator 506 correlates the received signal with the reference signal and outputs it to the data demodulation circuit. By the way, the output of the power detection circuit 515 is supplied to one input of the comparison circuit 516, and the output of the power detection circuit 514 is supplied to the other input of the comparison circuit 516. Comparison circuit 516
Then, the input power levels are compared, and the selection circuits 505 and 507 are controlled according to the result. In this method, the bands of the LPFs 504 and 509 and the HPFs 503 and 508 are set so as to divide the communication band into two, as shown in FIG.

In FIG. 2, when there is no interference signal, there is almost no difference between the power levels detected by the power detection circuits 515 and 514. In this case, the signal from the comparison circuit 516 controls the selection circuits 505 and 507 so as to select both the output of the LPF 504 and the output of the HPF 503 and both the output of the LPF 509 and the output of the HPF 508. If the interference wave exists in the LSB or the USB, the power levels detected by the power detection circuits 515 and 514 are different from each other. If this power level difference is larger than the specified value, it means that the interference wave exists in either band, and the level is suppressed, so the comparison circuit 5
16 controls the selection circuits 505 and 507 so as to select the output of the filter having the higher power level. This makes it possible to remove the interference wave regardless of the type, nature, and number of the interference wave by removing the band in which the interference wave exists and taking the correlation in the band that is not affected by the interference wave.

FIG. 5 shows a more specific embodiment of the present invention. In the block diagram of FIG.
An electric wave that has been SB-modulated and further modulated with a predetermined PN code at 202 is transmitted. Then, the received signal is frequency-converted and input to the BPF 701 as an intermediate frequency signal.
The output of the BPF 701 is distributed to the HPF 703 and the LPF.
It is input to 704 and divided into USB and LSB components. The output of the HPF 703 is supplied to one input of the selection circuit 705 and the power detection circuit 719. Also, LPF70
The output of No. 4 is supplied to the other input of the selection circuit 705 and the power detection circuit 720. The output of the selection circuit 705 is supplied to one input of the correlator 706.

On the other hand, the output of the oscillation circuit 713 is supplied to one input of the modulation circuit 711, and the output of the reference PN code generation circuit 712 is supplied to the other input of the modulation circuit 711. Then, the reference signal spread-modulated by the modulation circuit 711 is band-limited by the BPF 710, then divided, input to the HPF 708 and the LPF 709, and divided into USB and LSB signal components. The output of the HPF 708 is supplied to one input of the selection circuit 707, and the output of the LPF 709 is supplied to the other input of the selection circuit 707.
The output of the selection circuit 707 is supplied to the other input of the correlator 706. The correlator 706 calculates the correlation between the received signal and the reference signal and outputs it as a correlation signal. The correlation signal is input to the data demodulation circuit.

The power detection circuit 719 is composed of, for example, an envelope detection circuit 714 and an integration circuit 716, and the power detection circuit 720 is composed of an envelope detection circuit 715 and an integration circuit 717. Power detection circuits 719 and 7
Reference numeral 20 denotes an envelope detection circuit 714 and 71 for the input signal.
After performing envelope detection at 5, the integration circuits 716 and 717 perform integration to obtain the power levels of the LSB and USB components. The output of the power detection circuit 719 is supplied to one input of the comparison / control circuit 718, and the output of the power detection circuit 720 is compared.
It is supplied to the other input of the control circuit 718. The comparison control circuit 718 compares the power levels of the two input signals and controls the selection circuits 705 and 707.

This operation will be described with reference to the flowchart of FIG. In the power detection circuits 719 and 720, US
The respective power levels of B and LSB are obtained (step S11). The power level comparison / control circuit 718 compares whether or not the power level difference between the LSB and the USB is a specified value or more (step S12). If there is no difference, the comparison / control circuit 718 causes the selection circuits 705 and 7 to operate.
07 is controlled so that both LSB and USB are selected (step S13).

If there is a difference greater than the specified value, L
It is compared whether the power level of USB is higher than that of SB (step S14). If the LSB is larger, the comparison / control circuit 718 switches the selection circuits 705 and 707 to US.
Control is performed so that only B is selected (step S15).
If the USB is larger, the comparison / control circuit 71
8 controls the selection circuits 705 and 707 so as to select only the LSB (step S16). By repeating this operation and removing the sideband in which the interference wave exists, correlation demodulation without the influence of the interference wave can be realized. Although the operation in the IF stage is described in the embodiment, the operation is not limited to this, and the same operation can be performed in the RF stage.

[0026]

As described above, according to the present invention, the interference wave can be efficiently removed by the extremely simple structure and control, and the interference removal which has less influence on the correlation demodulation performance is eliminated. The method can be realized and is extremely useful in practice.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a receiving circuit according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram of a transmission signal spectrum used in the present invention.

FIG. 4 is a characteristic explanatory diagram of a filter used in the present invention.

FIG. 5 is a block diagram showing a more specific embodiment of the present invention.

FIG. 6 is a flowchart for explaining the operation of the embodiment of FIG.

FIG. 7 is a block diagram showing an interference wave removing method of a conventional spread spectrum receiver.

8 is a flowchart for explaining the operation of the method of FIG.

[Explanation of symbols]

 503, 508 HPF 504, 509 LPF 505, 507 Selection circuit 506 Correlation circuit 511 Modulation circuit 512 Reference PN code generation circuit 513 Oscillation circuit 514, 515 Power detection circuit 516 Comparison circuit

Claims (1)

[Claims] 1. A transmitter that transmits a signal that is DSB-modulated with data to be transmitted and is further spread-spectrum-modulated with a desired type of signal, and receiving a signal transmitted from the transmitter, A receiver for demodulating data, comprising a pair of filters for separating the received signal into an LSB component signal and a USB component signal, and a signal modulated with the desired type code corresponding to the received signal. Means for generating a signal, another pair of filters for separating the signal modulated by the desired type of code into LSB component and USB component signals, and power levels of the LSB component and USB component separated after the reception Means for determining whether the difference in power levels is less than or equal to a predetermined value, and when the power level difference is determined to be less than or equal to a predetermined value by the determination means, the pair and another pair of filters Of the signals separated by the filter, while simultaneously taking a correlation between corresponding components, when it is determined that the power level difference exceeds a predetermined value, among the signals separated by the pair and another pair of filters, A spread spectrum communication system, comprising: a receiver including a correlating unit that correlates only components having a smaller level.