KR20010086533A - Apparatus for removing interference signal in receiving path - Google Patents

Abstract

PURPOSE: An apparatus for canceling an interference signal of a receiving path is provided to cancel the interference signal of the receiving path using a simple structure by removing the interference signal of a BTS(Base Transceiver System) using a DSP(Digital Signaling Processor). CONSTITUTION: A receiving RF(Radio Frequency) block including a receiving band pass filter(BPF)(120), a low noise amplifier(130), a demodulation mixer(140), a low pass filter(LPF)(150), and an A/D converter(160) processes an RF signal of a receiving path as a baseband frequency signal and converts the baseband frequency signal into digital signal. A DSP(170) receives the digital signal of the baseband frequency outputted from the receiving RF block, obtains a level, a phase, and a frequency of a receiving interference signal, and outputs variables of the obtained values, respectively. A PLL(Phase Locked Loop)(180) controls an oscillated voltage using each variable to the receiving interference signal outputted from the DSP(170) and outputs a signal in which the level and frequency is same to the receiving interference signal and the phase is inverse. An RF combiner(110) combines the signal outputted from the PLL(180) with the RF signal of the receiving path.

Description

Apparatus for removing interference signal in receiving path

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication system, and more particularly, to an interference signal removing apparatus of a reception path for removing interference signals of a reception path at a base station of a CDMA system.

In general, mobile communication systems aim to provide high quality communication services to as many users as possible without increasing complexity.

However, in multi-user spread-band communication, multiple access interference and other narrow-band interferences are the major factors that degrade the system performance.

As an example, since the CDMA system currently adopts a single user signal detection scheme, signals of other users belonging to the same base station system are treated as interference. Therefore, as the number of other users sharing the same frequency increases, the interference that is multiplexed increases, thereby increasing the bit error rate of the received signal, thereby degrading system performance.

In order to reduce such interference, a plurality of receiving array antennas are used in a base station system.

1 is a diagram illustrating a part of a configuration of a base station system including a conventional interference signal removing apparatus.

Referring to FIG. 1, a base station system for removing interference signals includes receiving array antennas 11 and 12 that receive signals in respective paths, and high frequency signals received through corresponding reception antennas 11 or 12 as intermediate frequency signals. Received high frequency blocks 20 and 30 for down-frequency processing, and receiving the received signal from the received high frequency blocks (20, 30) is composed of a digital processor 40 for removing the interference signal of each path.

Each of the received high frequency blocks 20 and 30 has a reception bandpass filter (BPF-1 to BPF-N) 21 and 31, an amplifier 22 and 32, a demodulation mixer 23 and 33, and a low pass. Filter (LPF-1 to LPF-N) 24 and 34 and digital converters (A / D converters) 25 and 35, respectively, and the digital processing unit 40 is provided from the receiving high frequency blocks 20 and 30. A delay unit (Z ^-1 ) (41, 42) for delaying the received signals of each route by a given control amount in time and varying the magnitude of the signal output from the delay units (41, 42) by a given control amount. Variable amplifiers 43 and 44, and an interference cancellation processing unit 45 for removing interference signals from the received signal of each path using an interference signal cancellation algorithm.

Operation according to the above configuration is as follows.

The received signal including the interference signal is input through the reception array antennas 11 and 12 once.

The received signal of each input path is input to the digital processor 40 via the respective received high frequency blocks 20 and 30.

At this time, the interference cancellation processor 45 included in the digital processor 40 estimates and reproduces another user signal in a specific path, and removes it from the received signal of the path. Such interference cancellation is performed by the interference cancellation processor 45 providing the control signals for phase adjustment to the delay units 41 and 42 and the control signals for amplitude adjustment to the variable amplifiers 43 and 44.

In particular, in the interference cancellation processing unit 45, the phase (that is, time delay) and magnitude of each received signal so that the radiation patterns of the reception array antennas 11 and 12 become null-points in the direction in which interference occurs. Algorithm to adjust is used.

As described above, the base station system includes a plurality of receiving array antennas 11 and 12, and receiving high frequency blocks 20 and 30 for each antenna and path to remove the interference signal. And a processing unit 45.

This conventional device structure is expensive to implement, there is a problem that the implementation is also difficult.

SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus for removing interference signals of a reception path having a simpler device structure while more efficiently removing reception interference signals of a reception path.

In order to achieve the above object, there is provided an apparatus for removing interference signal of a reception path according to an embodiment of the present invention. A digital signal processor (DSP) which receives the digital signal of the baseband frequency output from the receiving high frequency block, obtains the magnitude, phase and frequency of the received interference signal, and outputs each variable for the obtained values; A phase control loop (PLL) for outputting a signal having the same magnitude and frequency and opposite in phase with the received interference signal by controlling the oscillation voltage by using variables for the received interference signal output from the digital signal processor. ) A circuit, a signal output from the phase control loop circuit and a high frequency of the reception path It consists of a frequency combiner for combining the call.

Preferably, the digital signal processing processor (DSP) fast Fourier transforms (FFT) the digital signal input from the received high frequency block to remove the received interference signal (G (r)). The product of the received interference signal magnitude (A) is obtained, and the deviation frequency (Δf) of the received interference signal is obtained.

In addition, the digital signal processing processor (DSP) is such that the normal received CDMA signal of the downlinked baseband frequency is "C_I (f, t)" and the baseband frequency signal processed downlink by the received high frequency block is " The baseband frequency after the Fast Fourier Transform (FFT) when G (r) -C_I (f, t) + A.G (r) -cos [Δf · t + (Φ + Φ (r)] The signal multiplied by " cos (Δf · t) " and integrated for " 1 / Δf " time to obtain the phase [phi] of the received interference signal.

1 is a view showing a part of the configuration of a base station system including a conventional interference signal removal apparatus.

2 is a view showing a part of the configuration of the base station system including the interference signal canceller according to the present invention.

* Description of the symbols for the main parts of the drawings *

100: receiving array antenna 110: RF combiner

120: reception bandpass filter (BPF) 130: low noise amplifier

140: demodulation mixer 150: low pass filter (LPF)

160: digital converter (A / D converter) 170: digital signal processing processor

180: Phase Locked Loop Circuit

Hereinafter, a preferred embodiment of an interference signal removing apparatus of a reception path according to the present invention will be described with reference to the accompanying drawings.

In the present invention, unlike the conventional method of removing the interference signal from the received signal of a specific path by referring to the received signal of each path, the interference signal having a narrow-band characteristic of a single tone type is simple without multiple reception paths. Remove with structure.

The device configuration and operation according to this are as follows.

2 is a diagram illustrating a part of a configuration of a base station system including an interference signal removing device according to the present invention.

The base station system shown in FIG. 2 has a configuration suitable for removing interference signals having narrowband characteristics in the form of a single tone.

A base station system for interference signal cancellation according to the present invention basically includes a reception array antenna 100, a reception bandpass filter (BPF) 120, a low noise amplifier 130, and a demodulation mixer 140. A low pass filter (LPF) 150, a digital converter (A / D converter) 160, a digital signal processor (hereinafter, abbreviated as DSP) 170, and a phase control loop. (Phase Locked Loop; hereinafter abbreviated as PLL) A circuit 180 and a high frequency combiner (RF combiner) (110).

In the above configuration, the reception bandpass filter (BPF) 120, the low noise amplifier 130, the demodulation mixer 140, the lowpass filter (LPF) 150, and the digital converter (A / The D converter 160 forms a reception high frequency block for down-frequency processing the received high frequency signal into a baseband frequency signal and converting the received high frequency signal into a digital signal.

The interference signal removing procedure according to the present invention according to the above configuration is as follows.

First, a variable A representing an interference signal, a variable Φ representing a phase, and another shift frequency Δf are obtained to generate a signal having the same but inverse phase with respect to the magnitude and frequency of the received interference signal. The interference signal is eliminated by combining the generated reverse phase signal with the CDMA signal of the reception path.

The process of obtaining the magnitude A, the phase Φ, and the shift frequency Δf of the interference signal is as follows.

The input signal r (t) of the center frequency f_ _rf received through the receive antenna array 100 of the base station system are: (1).

r (t) = C (f, t) + _Acos (f_ _itf t + Φ)

In Equation 1, C (f, t) is a normal received CDMA signal, and “A · cos ( _{f_itf} · t + Φ)” is an interference signal having narrow-band characteristics in the form of a single tone. In addition, A is the magnitude of the interference signal, Φ is the phase of the interference signal. In addition, the center frequency of the interference signal (f_ _itf ) is _expressed by the following equation (2).

f_ _itf = f_ _rf + Δf

At this time, the shift frequency Δf of the interference signal is limited as shown in Equation 3 below to limit the interference signal coming into the normal CDMA signal band.

△△ f ｜ <600㎑

At this time f_ _rf of the above formula 2 is a value already known to the center frequency of the received CDMA signal, △ f is unknown. In addition, the power density of the interference signal is higher than the power density of the normal CDMA signal under the condition shown in Equation 4 below.

C ( _{f_itf} , t)

Thereafter, the input signal r (t) of Equation 1 is a reception bandpass filter (BPF) 120, a low noise amplifier 130, a demodulation mixer 140, and a lowpass filter (LPF) 150. By passing through, the baseband signal b (t) shown in Equation 5 is obtained.

b (t) = G (r) -C_I (f, t) + A-G (r) -cos [Δf · t + (Φ + Φ (r)]

= G (r) · C_I (f, t) + A · G (r) · [cos (Δf · t) cos (Φ + Φ (r)) − sin (Δf · t) sin (Φ + Φ (r))]

In Equation 5, G (r) is a gain of each reception path, and Φ (r) is a phase change of each reception path. These are known values.

In Equation 5, "C_I (f, t)" is a baseband CDMA signal, and "A.G (r) .cos [Δf.t + (Φ + Φ (r)]" is a baseband interference signal. to be.

Subsequently, b (t) of Equation 5 is converted into a digital signal by the digital converter (A / D converter) 160 and input to the DSP 170.

The signal processing procedure in the DSP 170 is as follows.

The digital signal input to the DSP 170 first undergoes a Fast Fourier Transform (FFT). Variables of the interference signal which can be known by fast Fourier transforming (FFT) the input digital signal are "A.G (r)" and "Δf". That is, it is possible to know the product of the magnitude of the interference signal and the reception path gain to remove the interference signal, and the shift frequency of the interference signal.

The phase? Of the next interference signal is obtained by multiplying b (t) in Equation 5 by "cos (Δf · t)" and integrating it for "1 / Δf" time. Equation 6 below is a process of obtaining the phase Φ of the interference signal.

∫b (t) · cos (Δf · t) dt

= ∫ [G (r) · C_I (f, t) + A · G (r) · [cos (Δf · t) cos (Φ + Φ (r)) −

sin (Δf · t) sin (Φ + Φ (r))] cos (Δf · t) dt

A · G (r) · cos (Φ + Φ (r)) ∫ [cos ² (Δf · t)] dt

= [A, G (r), cosΦ (r)] / (2Δf)

In the above equation 6, the unknown index Φ is calculated by the following equation.

Φ = cos ^-1 [(2Δf / (A · G (r)) · ∫b (t) · cos (Δf · t) dt)]-Φ (r)

After all it is the magnitude A, the frequency of the interference signal "f_ _rf + △ f" and Φ the phase of the interference signal obtained by the signal processing procedure of the DSP (170).

Thereafter, the PLL circuit 180 extracts a variable for the interference signal obtained from the DSP 170, and controls the oscillated voltage using the single-tone signal " S_r (t) " Generates.

S_r (t) = -A and _{sin [(f_ rf + △ f} ) and t + Φ]

Since the single tone signal "S_r (t)" generated in the PLL circuit 180 is input to the frequency combiner 110, the interference signal of the single tone form that is eventually applied from the outside by the signal combination of the frequency combiner 110 is Removed.

As described above, the interference signal cancellation apparatus of the reception path according to the present invention has the following effects.

In the conventional base station system, interference signal cancellation is performed by using a plurality of receiving array antennas, receiving high frequency blocks for each antenna and path, and performing complex signal processing. The interference signal can be eliminated.

Therefore, the cost is reduced and the implementation is easy.

Claims (3)

A receiving high frequency block which down-frequency processes the high frequency signal of the reception path into a signal of the baseband frequency, converts the signal into a digital signal, and outputs the digital signal; A digital signal processor (DSP) which receives the digital signal of the baseband frequency output from the receiving high frequency block, obtains the magnitude, phase, and frequency of the received interference signal, and outputs respective variables for the obtained values; A phase control loop (PLL) for outputting a signal having the same magnitude and frequency and opposite in phase with the received interference signal by controlling the oscillation voltage by using variables for the received interference signal output from the digital signal processor. A) a circuit; And a frequency combiner for combining the signal output from the phase control loop circuit and the high frequency signal of the reception path. The method of claim 1, wherein the digital signal processing processor (DSP) performs a Fast Fourier Transform (FFT) of the digital signal input from the received high frequency block, and thus, the gain G (r) of the reception path to remove the received interference signal. )) And the product of the received interference signal magnitude (A), and the deviation frequency (Δf) of the received interference signal to obtain the interference signal cancellation apparatus of the reception path. 3. The digital signal processing processor (DSP) according to claim 2, wherein the digital signal processing processor (DSP) has a normal received CDMA signal of the down-band processed baseband frequency is " C_I (f, t) " When the band frequency signal is " G (r) · C_I (f, t) + A · G (r) · cos [Δf · t + (Φ + Φ (r)] ”, the past Fourier transform (FFT) Then, the baseband frequency signal is multiplied by "cos (Δf · t)" and integrated for "1 / Δf" time to obtain the phase Φ of the received interference signal. Device.