JP2000307476A - Receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a receiver which actualizes by small-sized constitution removal of an interference signal from a received signal including a wide-band spread signal after spread modulation by a CDMA system and a narrow-band interference signal. SOLUTION: In the receiver, the received signal is distributed by a distributor 1 and outputted to an interference detection part 2 and an interference removal part 3. The interference detection part 2 detects the intensity of the received signal as a function of a frequency by an intensity detecting means 11 through, for example, fast Fourier transformation to detect the frequency at which the intensity detected by an interference frequency detecting means 12 is larger than a threshold value as an interference frequency. An interference removal part 3 constituting a removing means removes the signal component of the detected interference frequency from the received signal by local frequency oscillators L1 to Ln, notch filters F1 to Fn and mixers M1 to Mn and K1 to Kn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver for removing an interference signal from a reception signal including a wide-band spread signal and a narrow-band interference signal spread and modulated by the CDMA method, and more particularly to a receiver compared with the related art. The present invention relates to a receiver capable of removing an interference signal with a small configuration.

[0002]

2. Description of the Related Art For example, in a mobile communication system using the DS-CDMA system, multiplex communication between a plurality of mobile stations and a base station is realized by assigning different spreading codes to each mobile station. Specifically, while each mobile station spreads and modulates a signal to be transmitted with a spreading code assigned to itself, the base station reverses a received signal using a spreading code assigned to each mobile station. The signal from the desired mobile station is demodulated by spreading. Similarly, the mobile station demodulates a signal addressed to itself by despreading a received signal from the base station using a spreading code assigned to the mobile station.

FIG. 4 shows an example of a spread code sequence composed of, for example, a PN (pseudo noise signal) sequence. As shown in the figure, one unit (one symbol) of spread code is composed of a plurality of chip data (for example, a sequence of “1” values and “−1” values). By making the patterns different, a plurality of different spreading codes can be generated.

FIG. 1 shows the time width of one chip data (chip section Tc) and the time width of one symbol of a spread code (bit section T). Here, the time width of the spreading code for one symbol is determined by the transmission data (eg, “1” value and “0”) transmitted from the transmitter (eg, mobile station or base station) to the receiver (eg, base station or mobile station). Value). That is, the change speed of the chip data constituting the spread code is much faster than the switching speed (symbol switching speed) of the transmission data spread-modulated by the spread code. When the transmission data is spread-modulated using the above-described spreading code, a spread signal having a band much wider than the frequency band before the spread modulation is generated.

[0005] In the above-described radio communication, other narrowband signals (that is, other than the CDMA system) are mixed in the frequency band used for the communication against the intention, thereby causing interference. There are cases. If such an interference signal is larger than the degree of interference due to noise or the like assumed at the time of system design, for example, the reception quality at the receiver may be significantly deteriorated.

Also, for the purpose of effective use of the frequency band, for example, a system for communicating using a relatively wide frequency band such as a CDMA system and a system for communicating using a narrow band such as an FM (frequency modulation) system. It is also possible to realize multiplex communication by using Specifically, for example, it is possible in principle to multiplex a signal based on an analog communication system such as the FM system into a frequency band of a spread signal based on the CDMA system to effectively use the frequency band. However, if the CDMA receiver cannot remove the signal based on the FM method or the like from the received signal, the signal and the spread signal interfere with each other, so that bit errors increase and the reception quality is deteriorated.

FIG. 5 shows an example of the spectrum of a received signal including a wideband spread signal by the CDMA system and a narrowband FM modulated signal (FM interference wave) by the FM system, and the horizontal axis indicates the frequency. And the vertical axis indicates the spectrum intensity.

As described above, if an interference signal is intentionally or accidentally present in the frequency band of a spread signal by the CDMA system, the CDMA receiver suffers from a problem that the reception quality of the spread signal is degraded. Therefore, it is necessary to remove such an interference signal. In particular, when the level of the interference signal is very large, it may be impossible to normally demodulate the spread signal by the CDMA method.

FIG. 6 schematically shows an example of the configuration of an interference canceling device which has been studied in the past. This interference canceling device is provided, for example, in a receiver and has the above-mentioned narrow band. Is removed from the received signal. As a specific operation of the interference canceling apparatus shown in the figure, first, a wideband spread signal (desired signal) by the CDMA system is used.
A received signal including a received signal and a narrow-band interference signal based on the FM method or the like is input to a distributor 21, and the input received signal is output to an interference detector 22 and an interference remover (adaptive analog notch filter circuit) 23. You.

Next, in the interference detecting section 22, an interference signal in the received signal input from the distributor 21 is extracted by a plurality of band-pass filters B1 to Bj, and the interference signals extracted by the respective band-pass filters B1 to Bj are extracted. A control signal corresponding to the signal frequency (interference frequency) is output to each of the local frequency generators R1 to Rj described below. Then, the interference removing unit 23 converts the signal component of the interference frequency from the received signal input from the distributor 21 into a plurality of notch filters Z1.
ＺZj.

Here, the local frequency generators R1 to Rj and the mixers P1 to Pj, Q1 provided in the interference removing unit 23 are provided.
ＱQj are adjusted in accordance with the control signal from the interference detection unit 22 so that the signal components of the interference frequency are removed from the received signal by the notch filters Z1 to Zj. Also,
Band-pass filters B1 to Bj and notch filters Z1 to
The reason why a plurality of Zj and the like are provided is that, even when a plurality of interference signals of a plurality of different frequencies are mixed in the received signal, for example, the plurality of (here, j) interference signals are removed. This is to make it possible.

[0012]

However, an interference canceling device provided in a conventional receiver as shown in FIG. 6, for example, employs a configuration for removing an interference signal from a received signal using a band-pass filter. Therefore, there were the following problems. That is, in order to accurately remove, for example, a plurality of narrow-band interference signals from a wide-band received signal as in the case of receiving a spread signal by the CDMA system, a band having a very narrow pass-band width is required in consideration of frequency resolution. It is necessary to provide a large number of pass filters, which causes a problem that the hardware becomes large-scale and the cost increases. In addition,
When trying to remove an interference signal that accidentally mixes with a received signal, the frequency and the like of the interference signal are often unknown, and the above-described disadvantages are particularly noticeable.

SUMMARY OF THE INVENTION The present invention has been made to solve such a conventional problem. An interference signal is obtained from a received signal including a wide-band spread signal and a narrow-band interference signal spread and modulated by the CDMA system. It is an object of the present invention to provide a receiver that can achieve the elimination with a smaller configuration than the conventional configuration shown in FIG. 6, for example.

[0014]

To achieve the above object, a receiver according to the present invention provides a CDM as follows.
The interference signal is removed from a received signal including a wideband spread signal and a narrowband interference signal spread-modulated by the A method. That is, the intensity detecting means detects the intensity of the received signal with respect to the frequency by, for example, Fourier transform processing, detects the frequency at which the intensity detected by the interference frequency detecting means is equal to or more than a predetermined threshold as the interference frequency, and detects the interference detected by the removing means. The frequency signal component is removed from the received signal.

Therefore, according to the present invention, an interference signal can be removed from a received signal without providing a large number of bandpass filters. Therefore, for example, a conventional device having a large number of bandpass filters as shown in FIG. Compared to the configuration of
The size of the device can be reduced, and the cost of the device can be reduced.

The principle by which an interference signal can be removed from a received signal by the configuration of the present invention will be described. That is, an interference signal spread and modulated by the CDMA method is generally spread over a wide band at a relatively low signal strength (power density), while an interference signal by the FM method or the like appears as a narrow band peak at a relatively high signal strength. I do. For this reason, when the strength of the received signal with respect to the frequency is detected by the above-described strength detection means, the strength of the received signal becomes relatively high at the frequency of the interference signal.

Therefore, such a frequency is detected as an interference frequency by the above-described interference frequency detecting means, and the interference frequency signal component is removed from the received signal by the above-described removing means, thereby removing the interference signal from the received signal. be able to. In the configuration of the present invention, when removing the signal component of the interference frequency from the received signal, it may be possible to remove not only the component of the interference signal but also the component of the spread signal, but the band of the spread signal is removed. Since the band is wider than the band of the component, no particular problem occurs. Even in the configuration of the present invention, it is sufficiently possible to normally perform despreading of the spread signal after removing the interference signal.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment according to the present invention will be described with reference to the drawings. The main part of the receiver according to the present invention,
Since the configuration is such that the interference signal is removed from the received signal, in this example, the components will be described in detail, and illustration and description of other components of the receiver will be omitted. FIG. 1 shows a configuration example of a main part of a receiver according to the present invention,
That is, an example of the configuration of an interference canceller that is provided in the receiver of the present example and removes an interference signal from a received signal is shown.

Here, the receiver of this embodiment is, for example, a CDMA.
A transmitter that communicates with a transmitter that wirelessly transmits a wideband spread signal that has been spread-modulated by the method, receives a spread signal wirelessly transmitted from the transmitter, and receives a spread signal.
Do what you type. In this case, in this example, for example, while the spread signal transmitted from the transmitter propagates through the wireless transmission path and is received by the receiver, a narrow band interference signal by the FM method or the like is added to the spread signal. Suppose. That is, the signal received by the receiver of this example includes a CD
It is assumed that a wideband spread signal (desired signal) spread-modulated by the MA method and one or a plurality of narrowband interference signals are included.

A configuration example and an operation example of the interference canceling device provided in the receiver of this embodiment shown in FIG. 1 will be described. The interference canceling device shown in FIG.
And an interference detector 2 for detecting the frequency of the interference signal (interference frequency) included in the received signal, and an interference remover (adaptive analog notch filter circuit) 3 for removing the interference signal from the received signal. I have.

The distributor 1 inputs a signal received by the receiver, and converts the input received signal into an FFT operation unit 11 of an interference detection unit 2 described later and a mixer M of an interference removal unit 3 described later.
It has a function of distributing to 1 and outputting. Interference detector 2
Includes an FFT operation unit 11 that performs a Fourier transform process and an interference frequency detection unit 12 that detects the frequency of an interference signal.

The FFT operation unit 11 receives the received signal output from the distributor 1 and performs a Fourier transform process on the input received signal, thereby obtaining the power spectrum of the received signal (the intensity of the received signal with respect to the frequency). And calculate
It has a function of generating the power spectrum data.

Here, in this example, as a preferable mode,
By executing the above-described Fourier transform processing using an algorithm of fast Fourier transform (FFT), the amount of calculation is reduced and the processing speed is increased. Further, by using such an algorithm of the fast Fourier transform, it is possible to calculate the power spectrum of the received signal in real time, whereby, for example, the frequency of the interference signal included in the received signal fluctuates with time. In such a case, it is possible to respond in real time.

The power spectrum data generated by the FFT operation unit 11 is, for example, a frequency in the band of the received signal as a variable X, such as the spectrum shown in FIG. , Each frequency X
The data in which the frequency X and the strength Y of the received signal are associated with each other can be used as the variable Y with the strength of the received signal in the above. Further, the FFT operation unit 11 has a function of outputting the generated power spectrum data to the interference frequency detection unit 12.

In the present embodiment, the FFT operation unit 11 detects the power spectrum of the received signal to constitute an intensity detecting means for detecting the intensity of the received signal with respect to the frequency according to the present invention. In the present example, as a preferred embodiment, the strength of the received signal with respect to the frequency is detected by the Fourier transform process, but the strength of the received signal with respect to the frequency may be detected in another manner.

The interference frequency detecting unit 12 is an FFT calculating unit 1
Input the power spectrum data output from 1 and
It has a function of detecting the frequency (interference frequency) of the interference signal included in the received signal based on the input power spectrum data. Specifically, the interference frequency detection unit 12 of the present example detects at most n (n is an integer of 1 or more) frequencies at which the intensity of the received signal specified by the input power spectrum data has a peak, Then, by comparing the peak value of the intensity of the received signal with respect to each detected frequency with a predetermined threshold (threshold), the frequency at which the peak value of the intensity of the received signal is equal to or more than the threshold among the detected frequencies is determined. It has a function of detecting as an interference frequency.

In this embodiment, the average intensity of the spread signal included in the received signal is detected by the receiver, and a value higher than the average intensity of the spread signal is set to the predetermined value. It is set as a threshold. Setting such a threshold is preferable because only a signal having a higher value than the intensity of the spread signal included in the received signal, that is, a frequency of only the interference signal can be detected as the interference frequency.

In this embodiment, as described above, the interference frequency detector 12 detects a frequency at which the intensity of the received signal is equal to or higher than a predetermined threshold as an interference frequency, so that the detected intensity according to the present invention is equal to the predetermined threshold. Interference frequency detection means for detecting the above frequencies as interference frequencies is configured.

In this example, if (n + 1) or more interference signals of different frequencies are included in the received signal, the signal having the higher peak intensity of the received signal is prioritized as described above. After detecting n frequencies, it is determined whether or not the peak value of the detected n frequencies is equal to or greater than a predetermined threshold value. The reason for this is that in the present example, at most n This is because a configuration capable of removing the interference signals from the received signal is used. here,
The value of n is not particularly limited as long as it is 1 or more, and may be arbitrarily set according to the communication status of the receiver (for example, the number and strength of the interference signals included in the received signal). Also,
In the present invention, a configuration in which the upper limit (n described above) is not necessarily provided for the number of interference signals that can be removed from the received signal may not be used. For example, a configuration in which all the interference signals included in the received signal are removed Can also be used.

As the predetermined threshold, various values can be set as long as the frequency of the interference signal included in the received signal can be detected as the interference frequency. The setting method can be used. For example, as a preferred embodiment, the predetermined threshold value is higher than the intensity of the spread signal included in the received signal as in this example, and the peak of the received signal intensity at the frequency of the interference signal included in the received signal. It is better to set a lower value than the value.

If the spread signal can be normally despread even if the received signal contains a small amount of interference signal, the intensity of the interference signal allowed as described above (the reception sensitivity of the spread signal) ), The above-mentioned predetermined threshold value may be set somewhat higher. When such a threshold is set, the received signal strength of the frequency including only the spread signal or the received signal strength including the allowable degree of interference signal is less than the threshold, while the despreading of the spread signal is performed. The received signal strength of a frequency that includes an interference signal to the extent that the signal interferes with the received signal is equal to or higher than the threshold, so that only the frequency that includes such an unacceptable interference signal can be detected as the interference frequency.

The method of setting the predetermined threshold value is not limited to a method of setting the threshold value in advance, but a method of setting the threshold value in a feedback manner according to the result of the interference removal processing may be used. it can. Here, when the threshold value is set in advance, an arbitrary threshold value may be set as necessary in consideration of communication conditions such as the above-described spread signal reception sensitivity and the like.

When the threshold value is feedback-controlled, as an example, the threshold value can be feedback-controlled so as to increase the S / N ratio (signal-to-noise ratio) of the received signal after interference removal. That is, increasing the S / N ratio means reducing the ratio of the interference signal to the spread signal included in the reception signal after the interference removal.

The above-mentioned interference frequency detecting section 12 outputs a control signal corresponding to the interference frequency detected as described above to a local frequency generator L provided in the interference removing section 3 described later.
1 to Ln. Here, in the present example, n local frequency generators L1 to Ln are provided in correspondence with the detection of a maximum of n interference frequencies, and the interference frequency detection unit 12 responds to each interference frequency. The control signal is output to each of the local frequency generators L1 to Ln. The control signal will be described later.

FIG. 2 shows an example of the procedure of the processing performed by the FFT operation unit 11 and the interference frequency detection unit 12 described above. That is, as described above, when a received signal is input from the distributor 1, the FFT operation unit 11 performs a fast Fourier transform process on the received signal (step S1), and generates data of a power spectrum generated thereby. Is output to the interference frequency detector 12 (step S2).

The interference frequency detector 12 detects a maximum of n frequencies at which the intensity of the received signal (spectrum) has a peak by the processing of the peak detection loop, for example, by non-restoration extraction (step S3). The peak value (detected spectrum intensity) of each frequency is compared with a predetermined threshold value by the processing of the loop (step S4), and a control signal corresponding to the frequency (interference frequency) at which the peak value is equal to or higher than the threshold value is transmitted to the interference removal unit. (Adaptive analog notch filter circuit section) 3 (Step S5).

The interference elimination unit 3 includes one local frequency generator L1 to Ln, one notch filter F1 to Fn, and two mixers provided at input and output terminals of the notch filters F1 to Fn. There are provided n analog notch filter circuits composed of M1 to Mn and K1 to Kn connected in series. Here, since the configuration and operation of each adaptive analog notch filter circuit are the same, in this example, an adaptive analog notch filter circuit including a local frequency generator L1, a notch filter F1, a mixer M1, and a mixer K1 is used. The configuration example and the like will be described as a representative.

That is, the local frequency generator L1
It is connected to the above-mentioned interference frequency detection unit 12 by a signal line, receives a control signal output from the interference frequency detection unit 12, generates a signal having a frequency corresponding to the input control signal, and generates a mixer M1 and a mixer. It has the function of outputting to K1. The frequency of the signal generated by the local frequency generator L1 will be described later.

The mixer M1 provided at the input end of the notch filter F1 mixes the received signal input from the distributor 1 with the signal input from the local frequency generator L1, thereby reducing the frequency of the received signal as a whole. Shift to
It has a function of outputting the shifted received signal to the notch filter F1.

The notch filter F1 is, for example, a filter for attenuating only a signal of a specific frequency (notch frequency). To the mixer K1 provided at the output end.

Here, in this example, in order to realize the removal of the interference signal from the received signal, the frequency of the received signal is shifted by the above-mentioned mixer M1 so that the interference frequency detected by the interference frequency detecting section 12 ( That is, the adjustment is performed such that the frequency of the interference signal in the received signal) matches the notch frequency. In this example, a signal having a frequency that can realize such adjustment is output from the local frequency generator L1, and a signal having such a frequency is output from the local frequency generator L1. A control signal that can be generated is output from the interference frequency detection unit 12 described above. When considering the bandwidth of the interference signal, for example, it is preferable to match the center frequency of the interference signal with the notch frequency.

By performing the above-described adjustment, the notch filter F1 of this embodiment removes the interference signal from the received signal because the frequency of the interference signal in the input received signal matches the notch frequency. Can be. FIG. 3 conceptually shows an example of the interference removal processing performed by the notch filter F1, and as shown in FIG. 3, according to the transmission characteristics of the notch filter F1, the received signal before interference removal is performed. Are removed by the notch filter F1.

The mixer K1 provided at the output end of the notch filter F1 mixes the received signal after the interference removal input from the notch filter L1 with the signal input from the local frequency generator L1 to thereby mix the received signal. Is output in the opposite direction to the above-described mixer M1, and the received signal thus shifted back to the original frequency is output to the mixer M2 of the next-stage adaptive analog notch filter circuit. I have.

Here, the configuration example and the like of one adaptive analog filter circuit have been described above. However, in this example, since n adaptive analog filter circuits are provided, the maximum It is possible to remove n interference signals from the received signal. The received signal from which the interference signal has been removed as described above is output from the interference removal unit 3, and thereafter, the receiver performs processing such as despreading the spread signal included in the received signal. The received signal after the interference removal includes, for example, only a spread signal or mainly a spread signal.

In this example, the interference removing unit 3
The removal means for removing the signal component of the interference frequency detected from the received signal according to the present invention by removing the signal component of the interference frequency detected by the interference frequency detection unit 12 from the received signal.

With the above configuration and operation, the interference canceller provided in the receiver according to the present embodiment eliminates one or a plurality of narrow-band interference signals included in an input received signal from the received signal. Accordingly, the reception quality of the spread signal included in the received signal can be improved.

Therefore, in the receiver of this embodiment, one or a plurality of narrow-band interference signals can be accurately removed from the received signal without providing a large number of band-pass filters. Compared with the conventional configuration including a large number of bandpass filters, the size of the device can be reduced, and the cost of the device can be reduced. Further, in this example, when detecting the frequency (interference frequency) of the interference signal from the reception signal including the wideband spread signal and the narrowband interference signal, the Fourier transform processing is used to detect the strength of the reception signal with respect to the frequency. It is noted that it is effective to use, and the interference removal processing is executed using such a Fourier transform processing.

Here, in the receiver shown in the above embodiment,
The intensity detecting means, the interference frequency detecting means, and the removing means according to the present invention are configured by executing a control program by a processor in a hardware resource including, for example, a processor, a memory, and the like. Can be configured as an independent hardware circuit, for example. Further, the present invention can be understood as a computer-readable recording medium such as a floppy disk or a CD-ROM storing the above-described control program, and the control program is input from the recording medium to the computer and executed by the processor. Thereby, the processing according to the present invention can be performed.

The interference signal that can be removed by the receiver according to the present invention is not necessarily limited to the signal based on the FM system, and the present invention can remove various narrow-band signals as interference signals. It is something. Also,
The receiver according to the present invention can be applied to, for example, a base station or a mobile station (for example, a mobile phone terminal) that performs wireless communication according to the CDMA system. Not only can it be applied, but it can also be applied to an apparatus having both a transmission function and a reception function.

As an example, a receiver according to the present invention is a CDM
When the present invention is applied to a base station adopting the A method, the base station can be downsized, so that many base stations can be installed in a small space. Further, as another example, when the receiver according to the present invention is applied to a mobile phone terminal or the like employing the CDMA system, the mobile phone terminal or the like can be reduced in size, thereby improving user-friendliness. be able to.

The configuration of the receiver according to the present invention is not necessarily limited to the one described above. In short, the frequency at which the strength of the received signal is equal to or higher than a predetermined threshold is detected as the interference frequency and detected. Various configurations may be used as long as they remove the signal component of the interference frequency from the received signal.

[0052]

As described above, according to the receiver of the present invention, when the interference signal is removed from the reception signal including the wideband spread signal and the narrowband interference signal spread-modulated by the CDMA system, Since the intensity of the received signal with respect to the frequency is detected, the frequency at which the detected intensity is equal to or higher than the predetermined threshold is detected as the interference frequency, and the signal component of the detected interference frequency is removed from the received signal.
For example, as compared with the conventional configuration having a large number of bandpass filters as shown in FIG.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration example of a receiver according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a procedure of a process performed by an interference detection unit.

FIG. 3 is a diagram illustrating an example of an interference removal process using a notch filter.

FIG. 4 is a diagram illustrating an example of a spreading code sequence.

FIG. 5 is a diagram illustrating an example of a spectrum of a received signal including a wideband spread signal and a narrowband interference signal according to the CDMA method.

FIG. 6 is a diagram for explaining a configuration of an interference canceling device provided in a conventional receiver.

[Explanation of symbols]

1 ··· Distributor, 2 ··· Interference detection unit, 3 ··· Interference removal unit (adaptive analog notch filter circuit unit), 11 ·· FF
T calculation unit, 12 ... interference frequency detection unit, L1 to Ln
・ Local frequency generator, F1-Fn ・ ・ Notch filter, M1-Mn, K1-Kn ・ ・ Mixer,

Claims (1)

[Claims] 1. A receiver for removing an interference signal from a reception signal containing a wide-band spread signal and a narrow-band interference signal spread-modulated by the CDMA method, wherein the intensity detection means detects the strength of the reception signal with respect to the frequency. Interference frequency detecting means for detecting a frequency at which the detected intensity is equal to or higher than a predetermined threshold value as an interference frequency; and removing means for removing a signal component of the detected interference frequency from a received signal. Receiving machine.