KR20080058870A - Interference cancellation apparatus for ics microwave repeaters - Google Patents

Abstract

An interference cancellation apparatus of ICS(Interference Cancellation System) microwave repeaters is provided to implement a filter coefficient easily by having a lattice-based structure. An ICS algorithm unit(32) detects a reception side signal including an original signal and an interference signal and an output side signal and calculates a weight vector through correlation of the reception side signal and the output side signal. An FIR(Finite Impulse Response) filter(33) generates an interference cancellation signal by applying the weight vector. A subtracting unit(31) subtracts the interference cancellation signal from the reception side signal to generate a post subtraction removal signal. The FIR filter unit has a lattice-based structure.

Description

Interference elimination device of ICS repeater {INTERFERENCE CANCELLATION APPARATUS FOR ICS MICROWAVE REPEATERS}

1 is a block diagram of a general ICS repeater.

2 is a conventional structure of a FIR filter applied to the ICS repeater of FIG.

3 is a block diagram of an ICS repeater according to an embodiment of the present invention.

4 is a structure of the FIR filter of FIG.

5 is a flowchart illustrating an interference cancellation method performed in the ICS repeater of FIG. 3.

6 and 7 are graphs comparing interference cancellation performance in the ICS repeater to which the prior art and the technique according to the present invention are applied by comparing the output level of the ERROR signal in the ICS repeater to which the FIR filter of FIGS. 2 and 4 is applied.

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

300: interference elimination device

31: Subtraction

32: weight factor calculation unit

33: FIR filter unit

S: original signal I: interference signal

R: Received signal ^ S: Output signal

^ I: Interference cancellation signal Err: Signal after interference cancellation

W: Weight Factor

The present invention relates to an interference cancellation method and apparatus for a wireless repeater for mobile communication.

In general, it is intended to satisfy the service quality of mobile communication in the area by constructing a repeater in the area covering the radio shade area or the burden of the installation cost of the base station.

The repeater is divided into a wired repeater connected to the base station by wires such as an optical cable and a wireless repeater connected to the base station by wireless.

The wired repeater can maintain good call quality because wired communication is performed between the repeater and the base station. However, the wired repeater is more expensive than the wireless repeater.

On the contrary, since the wireless repeater performs wireless communication between the repeater and the base station, the call quality is lower than that of the wired repeater, but the installation and operation costs are low.

Such a wireless repeater may be more appropriately applied than an expensive wired repeater when the area covered by the repeater is small due to the electromagnetic shielding effect of the structure such as the basement inside the building.

However, if the wireless repeater is installed in an open area, not inside the building, the transmission signal through the transmitting antenna of the wireless repeater is fed back to the receiving antenna and mixed with the original receiving signal, resulting in signal interference or oscillation. Not only do not provide services, but in the worst case will cause base station failure. Due to this problem, the wireless repeater has been used only in limited places such as the basement inside the building as described above.

However, the advantages of the wireless repeater that the installation and operation cost is cheaper than the wired repeater is still attractive, and technology has been introduced to remove the interference of the feedback signal, thus eliminating the interference of the feedback signal. The wireless repeater to which the present technology is applied is called an interference cancellation system (ICS) repeater.

Conventional interference elimination techniques include techniques using the analog method disclosed in Korean Laid-Open Patent Publication No. 2003-0017171, techniques using the digital method described in Korean Laid-Open Patent Publication No. 2003-0060186, analog methods, and There is a method in which a digital method is mixed, and the present invention relates to an interference cancellation technique using a digital method.

Hereinafter, an example of an interference cancellation technique using a general digital method will be described with reference to FIG. 1.

The ICS algorithm unit detects a reception side signal (R, R = S (original signal) + I (interference signal)) received through the reception antenna 11 at the front end of the subtractor 21, and detects the transmission antenna 12. The output side signal (^ S) to be transmitted through is detected at the front end of the transmitting antenna (12). The interference position is derived from the correlation between the received signal R and the output signal ^ S, and a weight factor (W) is calculated to remove the interference using the ICS algorithm. Subsequently, the weight factor calculation unit 22 applies the calculated weight factor W to the FIR filter 23 shown in FIG. 2, and the FIR filter 23 generates the interference elimination signal ^ I. Next, the generated interference elimination signal ^ I is input to the subtractor 21. The subtractor 21 adds the interference cancellation signal ^ I input from the FIR filter 23 to the reception signal R input from the reception antenna 11 side.

However, the FIR filter 23 having the structure shown in FIG. 2 applied to the conventional ICS repeater as described above has the following problems.

First, in the adaptive signal processing method, since the initial convergence of the algorithm is slow, a long convergence period (time) is required when the interference channel environment changes.

Second, a large number of bits must be allocated to digitally implement a FIR filter coefficient having a wide dynamic range.

Third, if proper isolation is not obtained due to a change in convergence section or channel, oscillation may occur, which may cause damage to a base station or a terminal.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a technique in which a FIR filter is replaced with a lattice structure, that is, a lattice-based structure.

In order to achieve the above object, an interference cancellation apparatus for an ICS repeater according to the present invention includes a reception side signal (a signal from the reception antenna side) and an output side signal (transmission) in which an original signal S and an interference signal I are mixed. An ICS algorithm unit for detecting a signal going to the antenna side and calculating a weight factor (W) through correlation between the reception side signal and the output side signal; A FIR filter unit generating an interference cancellation signal (^ I) by applying a weight factor calculated by the weight factor calculator; And a subtraction unit which subtracts the interference elimination signal (^ I) generated by the interference elimination signal generator from the reception side signal to generate a subtracted elimination signal (Err). It includes, wherein the FIR filter portion is characterized in that the lattice-based structure (Lattice-based structure).

The present invention also includes an ICS repeater to which the interference canceling device is applied.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention as described above will be described in detail.

Figure 3 is a perspective view of the main portion of the ICS repeater to which the interference cancellation device 300 according to an embodiment of the present invention is applied.

As illustrated in FIG. 3, the interference canceling apparatus 300 according to the exemplary embodiment of the present invention includes a subtracting unit 31, a weight factor calculating unit 32, an FIR filter unit 33, and the like.

The subtraction unit 31 is a reception side signal (R, R = S + I, hereinafter referred to as a 'receive signal') in which the original signal S and the interference signal I received through the reception antenna 11 are mixed. Generates an interference canceled signal Err obtained by subtracting the interference canceled signal ^ I input from the interference canceled signal generator 33.

The weight factor calculation unit 32 detects the reception signal R coming through the reception antenna 11 and the transmission side signal (^ S, hereinafter referred to as a 'transmission signal') to be transmitted through the transmission antenna 12, and then the ICS. A weight factor (W) is calculated by using a correlation between the received signal R and the output signal ^ S.

As shown in detail in FIG. 4, the FIR filter part includes a lattice structure, that is, a filter having a lattice-based structure, and applies the weight factor W calculated by the weight factor calculator 32 to remove the interference signal. (^ I) is generated and provided to the subtraction unit 31.

The interference cancellation method performed by the interference cancellation apparatus 300 configured as described above will be described with reference to the flowchart of FIG.

1.Signal Detection <S501>

The reception signal R and the output signal ^ S are detected.

2. Weight factor calculation <S502>

The weight factor calculation unit 32 calculates the weight factor W in real time through a correlation between the reception signal R and the output signal ^ S using the ICS algorithm.

3. Generate interference cancellation signal <S503>

The FIR filter unit 33 applies the weight factor W calculated by the weight factor calculation unit 32 to the output signal ^ S detected at the front end of the transmission antenna 12 to apply the interference cancellation signal ^ I. Create That is, the output signal ^ S input to the FIR filter unit 33 and the weight factor W are multiplied and added to generate the interference cancellation signal ^ I, and then output to the subtractor 31.

4. Signal generation after interference cancellation <S504>

The subtractor 31 subtracts the interference cancellation signal ^ I input from the FIR filter 33 from the reception signal R received through the reception antenna 11 in real time, thereby removing the interference signal from the reception signal R. Generate (Err).

6 and 7 are performance comparison graphs based on a comparison of an output level of an error signal output from a subtractor when the conventional FIR filter of FIG. 2 and the FIR filter of FIG. 4 are applied.

Fig. 6 shows the performance comparison in the case of floating point calculation (without the decimal point or other values), and in Fig. 6, Lattice compared to the technique in which the RLS / NLMS algorithm is applied to the conventional structure (transversal filter application structure). When the FIR filter is applied, the output ratio of the error signal is lowered and the initial convergence section is shortened. For reference, Lat1, Lat2, and Lat3 mean that the signal processing algorithm is different from the hardware structure as shown in FIG. 4, and in any case, it can be seen that it has better performance than the conventional structure.

Fig. 7 shows the performance comparison in the case of operation with 14 bits, and it can be seen that even in this case, it has better performance than the conventional structure.

For reference, in Figs. 6 and 7, the X axis is an axis relating to time (or number of samples), and the Y axis is an axis of an error signal.

As described above, the detailed description of the present invention has been made by the embodiments with reference to the accompanying drawings. However, since the above-described embodiments have only been described with reference to preferred examples of the present invention, the present invention is limited to the above embodiments. It should not be understood that the scope of the present invention is to be understood by the claims and equivalent concepts described below.

As described in detail above, the present invention has the following effects.

First, as shown in FIG. 6 and FIG. 7, when the Lattice structure filter is applied, the initial convergence section is short, and thus it is adaptable in a fast channel environment, thereby ensuring stability in field operation.

Second, since it is a lattice structure, it is easy to implement filter coefficients.

Claims (2)

The receiver side signal (the signal from the receiving antenna side) and the output side signal (the signal going to the transmitting antenna side) mixed with the original signal S and the interference signal I are detected, and the correlation between the receiving side signal and the output side signal is detected. An ICS algorithm unit for calculating a weight factor (W); A FIR filter unit generating an interference cancellation signal (^ I) by applying a weight factor calculated by the weight factor calculator; And A subtraction unit which subtracts the interference elimination signal (^ I) generated by the interference elimination signal generator from the reception side signal to generate a subtracted elimination signal (Err); Including; The interference cancellation device of the ICS repeater, characterized in that the FIR filter unit has a lattice-based structure. ICS repeater, characterized in that the interference elimination device of claim 1.

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