KR20050087177A - Apparatus and method for control of smart antenna - Google Patents

Abstract

The present invention relates to a smart antenna control apparatus and method for efficiently using a smart antenna used to increase the capacity of the base station, when the position tracking for the terminal is not accurately performed, a beam having a wide null (null) By controlling the smart antenna to form a reduction effect due to interference, if the location tracking for the terminal is precisely controlled by controlling the smart antenna to form a beam having a narrow null (Signal to Interfere Ratio, SIR) Increasing can minimize the effect of the Angle of Arrival (AOA) estimation error on the system, while optimizing the system for the communication environment.

Description

Smart antenna control device and method {APPARATUS AND METHOD FOR CONTROL OF SMART ANTENNA}

The present invention relates to a smart antenna used in a mobile communication system, and more particularly, to an apparatus and method for controlling a smart antenna such that the smart antenna is less affected by AOA (Angle Of Arrival) estimation error.

In the current mobile communication system, capacity increase of the base station is required due to factors such as increase of subscribers and implementation of additional data service in addition to voice service. A system using a smart antenna is being used as one method of increasing base station capacity to satisfy such a demand.

In the Code Division Multiple Access (CDMA) mobile communication environment, the most fundamental cause of limiting subscriber capacity is interference caused by signals of other subscribers. All signals generated in the same cell become interference waves that interfere with communication of subscribers in a call, which is a structural signal environment of CDMA. The smart antenna realizes increased capacity by reducing interference caused by signals occurring for calls of these other subscribers. The base station uses smart antennas to increase capacity by sending strong power to any subscriber on the call and weak power to other subscribers to improve the Signal to Interferer Ratio (SIR).

The base station uses a direction tracking algorithm to estimate the direction of the desired and undesired subscribers, and based on this estimate, forms a high gain beam in the direction of any subscriber to provide the call. In other subscriber directions, the smart antenna is controlled to form a low gain beam. Directional tracking algorithms that can be used include ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques), MUSIC (MUltiple Signal Identification and Classification), and CAPON. have.

The base station may form a beam having a desired shape by applying appropriate weighting to each element of the smart antenna. Additionally, spatial filters in unwanted directions create nulls at certain angles of the beam pattern, resulting in greater signal-to-interference ratios. Can be increased.

As described above, the principle of the smart antenna is to determine the location of the subscribers from the received signal by using an array antenna and to give a direct weight to each antenna element to form a beam having directivity. Therefore, it is very important to know the direction of the subscriber in the smart antenna algorithm. However, in reality, the base station does not accurately determine the location of the subscriber due to a communication environment such as a subscriber moving at high speed or an angular spread caused by a scatterer around it. . An error that occurs when the subscriber's location is estimated is referred to as an Angle Of Arrival (AOA) estimation error. In general, smart antenna patterns formed to reduce interference are sensitive to AOA estimation errors because they have sharp characteristics with respect to the interference direction. The problem caused by this will be described with reference to FIG.

1 is a diagram illustrating a mobile communication environment.

Terminal 1 (100-1) and terminal 2 (100-2) shown in Figure 1 is a device that the subscriber uses to provide a communication service. The base transceiver system (BTS) 120 performs signal transmission and reception with the terminal 100 to provide a communication service to the terminal 100. The antenna of the BTS 120 forms a beam of high gain in the direction in which the terminal (for example, terminal 1) 100-1, which is the communication target, is located, and the other terminal (for example, terminal 2) 100 By forming a beam of low gain in the direction in which -2) is located, it is a smart antenna that reduces the interference generated in the terminal 2 (100-2) due to the communication of the terminal 1 (100-1). However, the aforementioned AOA estimation error is particularly severe in urban areas where there are many buildings that can be scattered around as shown in FIG. 1. As a result, current smart antennas perform well in large plains, but they do not work in urban areas where more capacity is needed.

Therefore, in order to overcome the above problems and to efficiently use the smart antenna even in a poor communication environment, there is a need for a smart antenna control apparatus and method capable of controlling the smart antenna to be less affected by the AOA estimation error.

An object of the present invention is to provide a smart antenna control apparatus and method to be less affected by the error of the Angle Of Arrival (AOA) estimation.

Another object of the present invention is to provide a smart antenna control apparatus and method for enabling the smart antenna to operate adaptively in a communication environment.

The present invention allows the smart antenna to form a beam of a pattern having a wide null so that the smart antenna is less affected by the AOA estimation error.

In addition, the present invention allows the smart antenna to selectively form a beam of a pattern having a narrow null or a pattern of a pattern having a wide null in accordance with the conditions, such as communication environment in order to enable the adaptive operation in the communication environment. .

Such a device of the present invention is a device for controlling the smart antenna in a base station of a mobile communication system that provides a communication service to at least one terminal by using a smart antenna, receiving the signal received from the terminal AOA ( AOA estimator for estimating an angle of arrival, and an AOA estimation value from the AOA estimator to determine a beam pattern formation condition according to a communication environment of the terminal to determine a beam pattern to be generated by the smart antenna. A determination unit, a weight vector calculator for calculating a weight vector for allowing the smart antenna to generate the beam of the determined pattern, and a control signal for generating a beam of the pattern according to the calculated weight vector value; Smart antenna control device including a beam forming unit for outputting to the smart antenna.

In addition, the method of the present invention, in the method for controlling the smart antenna in the base station of the mobile communication system that provides a communication service to at least one terminal using a smart antenna, receiving the uplink signal received from the terminal A first step of estimating AOA (Angle Of Arrival), a second step of determining a beam pattern to be generated by the smart antenna by receiving the AOA estimation value and determining a beam pattern forming condition according to a communication environment of the terminal; And a third process of calculating a weight vector allowing the smart antenna to generate the beam of the determined pattern, and a fourth process of generating a beam of a pattern satisfying the weight vector through the smart antenna. Antenna control method.

As described above, the present invention is one of the initial processes of the call setup process between the BTS 120 and the terminal 100, and is generally made before the call setup is completed and the call is started. In addition, transmission of a signal for carrying out the present invention is generally performed through a pilot channel.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

2 is a diagram illustrating a BTS providing a communication service to a terminal using a smart antenna.

The terminal 100 performs signal transmission and reception for communication with the smart antenna 110 which is a type of array antenna. The BTS 120 includes an RF (Radio Frequency) unit 200, an IF (Intermediate Frequency) unit 210, and a channel card 220. The RF unit 200 and the IF unit 210 convert the signal received from the channel card 220 into a signal that can be transmitted to the terminal 100 through the smart antenna 110, or through the smart antenna 110 The signal received from the terminal 100 is converted into a signal that can be processed by the channel card 220. The channel card 220 includes a modem, a digital signaling processor (DSP), and the like, and performs signal processing for providing a communication service to the terminal 100.

3 is a block diagram showing a configuration of a channel card of a BTS for controlling a smart antenna in accordance with the present invention.

3 shows only the components necessary to carry out the invention. The AOA estimator 300 of FIG. 3 receives a signal received from the terminal 100 and performs an AOA estimation and AOA selection process. In this case, the AOA selection process is the AOA of the terminal (for example, terminal 1) 100-1 to which the estimated AOA is to provide communication, or the interference of the terminal (for example, terminal 2) 100-2. It is the process of determining whether it is AOA.

The communication environment determiner 310 determines a beam pattern to be formed through the smart antenna 110 according to the communication environment of the region where the BTS 120 is currently located. That is, the communication environment determination unit 310 determines whether the current communication environment is a communication environment capable of estimating high accuracy AOA, and if the high accuracy AOA can be estimated, a beam pattern having a narrow null. If a high accuracy AOA cannot be estimated, a beam pattern having a wide null is formed. If the null is widened in the beam pattern, the effect of reducing interference is generated, and thus, the effect due to the AOA estimation error can be reduced when the correct AOA cannot be estimated.

Here, conditions for estimating high accuracy AOA may include an AOA's Angular Spread (AS) and a speed of the interfering terminal 100-2. When the AS of the signal in the direction of the interference, ie, the signal due to the terminal 100-2 that is the interference is large or the speed is high, the accuracy of the AOA estimation is lowered and the AOA estimation error is increased. Therefore, the communication environment determination unit 310 detects the AS and the speed of the interference direction signal, and forms a beam having a wide null in the corresponding direction when the signal has a large AS or a high speed characteristic.

The weight vector calculator 320 calculates a weight vector for forming a beam having a desired shape through the smart antenna 110. The beam forming unit 330 generates a control signal for allowing the smart antenna 110 to form a beam according to the weight vector calculated by the weight vector calculator 330 and outputs the control signal to the smart antenna 110.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Hereinafter, two embodiments of the present invention to be applied to a time division duplex (TDD) system and a case to be applied to a frequency division duplex (FDD) system will be described. Unlike a TDD system in which the uplink and downlink carrier frequencies have the same carrier frequency, the FDD system has a different carrier frequency in the uplink and downlink, so that the beam pattern calculated from the uplink signal is compared to the downlink. In order to apply, it is necessary to correct according to the frequency change.

First, an embodiment of applying the present invention to a TDD system will be described.

FIG. 4 is a flowchart according to an embodiment of the present invention, and illustrates an operation when the present invention is applied to a TDD (Time Division Duplex) communication system.

In the flow chart of FIG. 4, steps 400 to 404 are processes for obtaining information necessary for nulling by analyzing an array signal received in the uplink.

The AOA estimator 300 receiving the array signal received in the uplink in operation 400 estimates the AOA for the terminal 100 using the received signal in operation 402. AOA estimation is a well known problem in the field of signal processing. Commonly used methods are ESPRIT and Unitary ESPRIT, which are subspace approaches, and Capon's algorithm is an example of a method using beamforming technology. Capon's algorithm will be described with reference to the following equation.

The AOA estimator 300 selects the AOA in step 404 after performing the AOA estimation in step 402. The AOA selection process is a process of distinguishing whether the AOAs estimated in step 402 are AOAs of a desired terminal 100-1 or AOA of an interfering terminal 100-2. At this time, all AOA information of the desired terminal 100-1 is preferably used for the final beam forming. In actual implementation, it is common to use only the strongest one among the various directions of the desired terminal 100-1, but having one or more of the above-mentioned direction information (AOA) can quickly switch to the largest signal among the signals that change over time. There is this. If there are more interferences than the number of antenna arrays, it is desirable to consider only those effects that are large.

In operations 406 through 412, the communication environment determination unit 310 determines whether to form a beam having a pattern having a narrow null in the interference direction by using the information obtained in operations 400 through 404. Determine whether to form a pattern. Examples of consideration criteria in this case include the AS and the speed of the terminal 100-2 that interferes with each other. If the AS of the terminal 100-2 is large or the speed is high, a wide null is formed. In operation 406, the communication environment determination unit 310 determines whether the AS of the terminal 100-2 is large, and if the AS is large, selects a wide null in operation 412. If it is determined in step 406 that the AS of the terminal 100-2 is not large, the communication environment determination unit 310 determines whether the speed of the terminal 100-2 is high in step 408, and determines whether the terminal 100-2 is fast. If the speed is high, a wide null is selected in step 412. If the AS of the terminal 100-2 is not large and the speed is not fast, the communication environment determination unit 310 selects a narrow null in step 410. The determination at this time may be made by determining a predetermined reference value in advance and comparing the measured value with that value. Meanwhile, in the present embodiment, both conditions of AS and speed of the terminal 100-2 are taken into consideration, and a wide null is selected even if only one of them is satisfied, but only one of them depends on the communication environment and system. May be considered as a criterion, or a wide null may be selected only if both conditions are met.

Step 414 is a beam forming process according to the selected null shape, which may be performed by the weight vector calculating unit 320 and the beam forming unit 330 of FIG. 3. The weight vector calculator 320 calculates a weight vector for forming a beam pattern having the selected null. The beam forming unit 330 generates a control signal based on the calculated weight vector and outputs the control signal to the smart antenna 110 so that the smart antenna 110 can form a beam having a required shape.

On the other hand, it will be described with reference to the equations used to perform the process of AOA estimation, beam forming, etc. of the present invention as shown in FIG.

The AOA estimator 300 shown in FIG. 3 (which may be implemented with an array processor, for example) estimates AOAs from M array antenna output samples X (M × 1 vector). In general, the configuration of the M arrays can be any arbitrary, but is described with an example using a Uniform Linear Array (ULA) to facilitate the description of the present invention. Direction of the terminal 100-1 in which the AOAs are desired ( Direction of the terminal 100-2 that interferes with ), And the beamforming weight vector w (M × 1) is obtained using a beamforming algorithm that optimizes the Signal to Noise and Interference Ratio (SNIR). At this time, the signals received from the various interference directions are analyzed to form a beam pattern having a wide null proposed in the present invention in a direction in which AS is large or a fast moving speed, and in other directions, a narrow and deep null. . With the calculated weight vector w, the subscriber signal s is Is estimated.

Algorithms for calculating complex antenna weights include a minimum variation beamformer (MVB) and a general optimal beamformer (GOB), but in this embodiment, a modified capon's beamformer modified from a capon's beamformer is used. In the basic Capon's beamformer, the weight vector is calculated as in Equation 1 below.

In Equation 1, a is a vector for adjusting subscriber AOA as ULA, and is determined as in Equation 2 below.

In Equation 2, d is the distance between the antenna elements, Is the uplink (reverse) wavelength length. Using a weight vector made from a basic Capon's beamformer, the beam shape forms sharp nulls in the direction of interference. Thus, Equations 1 and 2 are used to generate nulls in the interference direction where AS is small and slow.

Next, a description will be given of the beam pattern synthesis that makes the null non-sharp and flat for a particular direction. For explanation, a well-known covariance matrix (M × M matrix) of an input signal, represented by Equation 3 below, may be expressed as Equation 4 below instead of a value based on AOA estimation. .

Where A is a matrix for adjusting the estimated values of the interference AOA for the terminal 100-1, is a noise power, and I is an identity matrix. The matrix A may be expressed as in Equation 5 below.

On the other hand, in order to null certain AOAs of interference, the existing weight vector w must satisfy the following Equation 6.

The method proposed in the present invention limits the order of derivatives as shown in Equation 7 below to increase the width of the null generated by the condition that satisfies Equation 6.

Where N is the degree of null to be. In consideration of an array steering vector, Equation 6 may be expressed as Equation 8 below.

Applying Equation 9 to Equation 8, the modified covariance matrix proposed in the present invention is expressed as Equation 10 below.

That is, the weight vector having a wider null proposed in the present invention, Equation 1 may be expressed as Equation 11 below using Equation 10 instead of Equation 2 with respect to Equation 1 below.

Using Equation 11, a beam pattern having a wide null in the interference direction can be formed. That is, the weight vector of the final equation (11), Is applied to the uplink beamformer to generate the uplink beam pattern. In the TDD system, since the uplink carrier frequency and the downlink carrier frequency are the same, Equation 11 can be applied to the downlink to form a beam having a desired shape.

Next, an embodiment in which the present invention is applied to an FDD system in which an uplink carrier frequency and a downlink carrier frequency are different from each other will be described.

FIG. 5 is a flowchart according to another embodiment of the present invention and illustrates an operation when the present invention is applied to a frequency division duplex (FDD) communication system.

In the case of the FDD system, if the weight vector obtained in the uplink is applied to the downlink due to the difference between the carrier frequency of the uplink and the carrier frequency of the downlink, the smart antenna 110 beams having a shape different from the required beam pattern. Will generate To compensate for this difference, the BTS 120 of the FDD system requires a carrier frequency calibration process for a weight vector for forming a beam pattern of a downlink. In this regard, the embodiment illustrated in FIG. 5 will be described.

Since steps 500 through 504 of FIG. 5 are the same as steps 400 through 404 of FIG. 4, a separate description thereof will be omitted. In addition, since steps 508 to 516 of FIG. 5 are the same as steps 406 to 414 of FIG. 4, description thereof will be omitted.

In the FDD system, in order to apply the beam pattern formed by using the information obtained in the uplink to the downlink due to the difference between the uplink carrier frequency and the downlink carrier frequency, the difference between the uplink carrier frequency and the downlink carrier frequency is considered. A calibrated beam pattern must be formed. The carrier frequency calculation of step 506 shown in FIG. 5 is a process of calibrating the beam pattern in consideration of the difference in the carrier frequency in the FDD system. This is expressed as an equation.

Carrier frequency difference mentioned above May be expressed as in Equation 12 below.

here Are the downlink carrier frequency and the uplink carrier frequency, respectively.

There are several possible carrier frequency calibration methods using the present invention. In the present invention, the receiving antenna weights generated in the uplink As an example, a method of calculating the transmit antenna weight using the rotated value will be described. At this time, the rotate value is represented by the following equation (13).

The transmit antenna weight after calibrating the carrier frequency using this value may be expressed as in Equation 14 below.

In equation (14) Is J term of the In the FDD system, a beam pattern having a desired null for the downlink may be formed by calculating a weight vector corrected by considering the carrier frequency difference using Equation (14).

Next, the result of implementing the present invention as described above will be described with reference to the drawings.

6 to 9 are diagrams showing an application result according to embodiments of the present invention, and show a comparison between a beam pattern generating a narrow null and a beam pattern generating a wide null.

6 is a power beam pattern for ULA with eight elements in the uplink.

AOA of the terminal 100 is 0 degrees and AOA of interference exists in two directions of 60 degrees and -40 degrees. In FIG. 6, the solid line is a beam pattern generated when the narrow null using Equation 1 is selected, and the dotted lines 1 (---) and the dotted line 2 (-·-·-) are wide nulls using Equation 11. Are beam patterns generated when the selection is made. In particular, the dotted line 1 is a beam pattern measured by null order 1 (N = 1) in Equation 11, and the dotted line 2 (-·-·-) is 2 (N = 2) in Equation 11 It is a beam pattern measured by.

7 shows a downlink power pattern after performing carrier frequency calibration in an FDD system.

In this case, the weight vector of the solid line is the result of applying angular correction according to Equation 12 to the uplink result calculated using Equation 1, and the dotted lines 1 and the dotted line 2 are uplink calculated using Equation 11. It is the result of applying each correction by Equation 12 to the result.

8 and 9 show noise power in the uplink The effect on the power beam pattern is experimental. All environments in FIGS. 8 and 9 are the same as in FIG. 6. FIG. 8 is a simulation result of setting the noise power to 0.5 when the signal power is 1, and FIG. 9 is a result of simulating the noise power to 0.00001 when the signal power is 1.

As can be seen from the measurement results shown in Figs. 6 to 9, applying the present invention makes it possible to generate a wide null at a desired position. As a result, a system using a smart antenna is less affected by interference in a communication environment with a large AOA estimation error.

In addition, when the AOA estimation error commonly used in the AOA estimation used in the smart antenna technology is large, the null formation of the interference direction is further widened so that the system is less affected by the AOA estimation error, and the AOA estimation error is small. In this case, the narrow null enables the system to achieve the signal-to-noise ratio optimized for the subscriber's environment.

By using the present invention, it is possible to control the smart antenna to be less affected by the AOA estimation error that occurs according to the communication environment. In addition, when the AOA estimation error occurs large and small, it is possible to select and generate different nulls so that the smart antenna can be implemented to obtain an optimized signal-to-noise ratio for the subscriber's environment. Through this, smart antennas can be effectively used in the outlying areas as well as in urban areas where AOA estimation errors are large.

1 illustrates a mobile communication environment.

2 is a diagram illustrating a base station providing a communication service to a terminal using a smart antenna.

3 is a block diagram showing the configuration of a channel card of a base station for controlling a smart antenna in accordance with the present invention;

4 is a flowchart according to an embodiment of the present invention, illustrating an operation when the present invention is applied to a TDD (Time Division Duplex) communication system.

FIG. 5 is a flowchart according to another embodiment of the present invention, illustrating an operation when the present invention is applied to a frequency division duplex (FDD) communication system. FIG.

6 to 9 illustrate beam patterns according to the prior art and beam patterns according to the present invention;

Claims (10)

An apparatus for controlling the smart antenna in a base station of a mobile communication system that provides a communication service to at least one terminal using a smart antenna, An AOA estimator for estimating AOA (Angle Of Arrival) by receiving an uplink signal received from the terminal; A communication environment determination unit which receives an AOA estimation value from the AOA estimator and determines a beam pattern formation condition according to a communication environment of the terminal to determine a beam pattern to be generated by the smart antenna; A weight vector calculator configured to calculate a weight vector allowing the smart antenna to generate the beam of the determined pattern; And a beam forming unit configured to generate a control signal for generating a beam of a pattern according to the calculated weight vector value, and output the generated control signal to the smart antenna. The smart antenna control apparatus of claim 1, wherein the beam pattern forming condition is an Angular Spread (AS) and a speed of an AOA. The method according to claim 2, wherein the communication environment determiner determines that the smart antenna generates a beam according to the first beam pattern when the AS of the AOA is large, and the smart antenna according to the second beam pattern when the AS of the AOA is small. Smart antenna control device for determining to generate a beam. The method of claim 3, wherein the communication environment determiner determines that the smart antenna generates a beam according to the first beam pattern when the speed of the AOA is high, and the smart antenna according to the second beam pattern when the AS of the AOA is small. Smart antenna control device for determining to generate a beam. The method of claim 3 or 4, wherein the weight vector calculation unit forms a first beam pattern using the following equation, only, , d is the distance between the smart antenna elements, lambda_UP is the uplink wavelength length. Smart antenna control device to form a second beam pattern using the following equation. only, , d is the distance between the smart antenna elements, lambda_UP is the uplink wavelength length. The smart antenna control apparatus of claim 1, wherein if the mobile communication base station is a base station of a time division duplex (TDD) scheme, the weight vector calculator calculates the same weight vector for beam pattern generation of uplink and downlink. The method of claim 1, wherein if the base station is a base station of a frequency division duplex (FDD) scheme, the weight vector calculator uses the following equation to calculate a weight vector for generating an uplink beam pattern, only, , d is the distance between the smart antenna elements, lambda_UP is the uplink wavelength length. Smart antenna control device using the following equation to correct the difference between the uplink carrier frequency and the downlink carrier frequency to calculate the weight vector for generating the downlink beam pattern. only, A method of controlling the smart antenna in a base station of a mobile communication system that provides a communication service to at least one terminal using a smart antenna, A first step of estimating AOA (Angle Of Arrival) by receiving an uplink signal received from the terminal; A second process of determining the beam pattern to be generated by the smart antenna by determining the beam pattern formation condition according to the communication environment of the terminal by receiving the AOA estimate value; A third process of calculating a weight vector allowing the smart antenna to generate the beam of the determined pattern; And a fourth process of generating a beam having a pattern satisfying the weight vector through the smart antenna. The method of claim 8, wherein the second process, Comparing the AS of the AOA with a predetermined reference value and determining to form a first beam pattern when the AS of the AOA is larger than a predetermined reference value; And comparing the speed of the AOA with a predetermined reference value and determining to form a first beam pattern when the speed of the AOA is faster than a predetermined reference value. The method of claim 9, wherein if the base station is a base station of the FDD scheme, the third process, Calculating a weight vector for forming a beam pattern of the uplink using the following equation; only, , d is the distance between the smart antenna elements, Is the uplink wavelength length. And calculating a weight vector for forming a beam pattern of the downlink, wherein a difference between the carrier frequency of the uplink and the carrier frequency of the downlink is corrected by using the following equation. only,