KR20060071321A - Method for selecting switched beam using pilot signal and system thereof - Google Patents

Abstract

The present invention relates to a switched beam selection method and system for providing a maximum received power to a terminal.

The number of switched beams that a base station can use is finite and the value of the weight vector for these switched beamformings is predefined. In the present invention, the mobile terminal measures a channel value for each transmit antenna using a pilot signal designed to distinguish the transmit antennas, and uses a switched beam that provides a maximum signal-to-noise ratio using the measured channel value and previously known weight vectors. To judge. The terminal informs the base station of the selected beam by using a feedback channel, and the base station transmits the traffic using the switched beam requested by the terminal.

Switched beam, sector beam, weight vector, feedback channel

Description

Switched beam selection system using pilot signal and its method {METHOD FOR SELECTING SWITCHED BEAM USING PILOT SIGNAL AND SYSTEM THEREOF}

1 is a schematic diagram for explaining the operation of the switched beam.

2 is a diagram illustrating a configuration of a base station for forming a sector beam according to the present invention.

3 is a diagram illustrating a configuration of a base station for forming switched beamforming according to the present invention.

4 is a diagram illustrating a pilot structure according to an embodiment of the present invention in a single carrier transmission method.

5 is a diagram illustrating a pilot structure according to an embodiment of the present invention in a multi-carrier scheme.

6 is a block diagram showing the configuration of a base station system according to an embodiment of the present invention.

7 is a block diagram illustrating a configuration of a mobile terminal according to an embodiment of the present invention.

8 is a flowchart illustrating a switched beam selection method according to an embodiment of the present invention.

The present invention relates to a switched beam selection method and a system using a plurality of antennas.

More particularly, the present invention relates to a method and system for enabling the selection of switched beams that are effective with low errors and low computation of a plurality of antennas.

1 is a schematic diagram for explaining the operation of the switched beam.

Switched beam technology is one of smart antenna technologies, and provides a directional beam in the direction of the mobile terminal by giving different weights to the plurality of antenna elements in order to provide the maximum received power to the mobile terminal.

The base station 100 includes a plurality of antenna elements 101, 102, 103 for each sector. Meanwhile, the mobile subscriber station 200 transmits and receives traffic data with the base station 100 while moving in a sector.

As described above, in order to provide the optimum reception power to the subscriber station, if the antenna elements 101, 102 and 103 of the base station are provided with different weights, the beams emitted from the antennas may be optimally directed toward the subscriber station. Form.

Here, the weight vector for the antenna element according to the direction of beamforming is defined as a predetermined number and is selected for the proper beamforming direction.

Therefore, when the switched beamforming technique described above uses a directional beam that is narrower than a sector antenna, beamforming gain and co-chnnel interference can be reduced, thereby improving system performance.

Meanwhile, in the related art, in the switched beamforming technique using a plurality of antennas, a base station prepares several beamforming weight vectors, and uses the uplink signal transmitted from the subscriber station to direct the uplink signal to the base station. Measure

The base station determines the most suitable switched beam for the terminal with reference to the measured direction of arrival (DOA) and transmits user traffic using the same.

However, in the conventional switched beamforming, in order for the base station to continuously measure the angle of arrival of a signal transmitted by a specific terminal, an uplink signal of the same terminal is required to support the same. In order to measure the angle of arrival, an intermittent but continuous uplink signal is required, which wastes resources. In addition, a procedure for allocating an uplink resource to a corresponding terminal should be defined so that the base station can measure the angle of arrival.

Furthermore, since the main body of the switched beam selection for the beamforming direction is the base station, the load of the base station is increased, and a considerable length of uplink signal is required for each terminal for accurate arrival angle measurement, and in case of FDD, an uplink frequency band and a downlink frequency Since the bands are spaced apart, when the angle of arrival measured using the uplink signal is used for downlink switched beam selection, an error due to frequency separation occurs.

The technical problem to be achieved by the present invention is to provide a switched beam selection method and system that the terminal is the main body of the switched beam selection, reducing the load of the base station and can reduce the error due to the frequency separation.

Another object of the present invention is to provide a switched beam selection method and system for enabling beam selection to provide a maximum signal-to-noise ratio (SNR) using a downlink common pilot signal.

In order to solve this problem, according to an aspect of the present invention, there is provided a switched beam selection method of a subscriber station located in a sector area of a base station equipped with a smart antenna system for forming a switched beam with a plurality of transmit antennas. First, a mobile terminal is generated to identify a plurality of antennas, receives a pilot signal transmitted from the base station through a sector beam, and estimates a channel for each transmit antenna using a pilot signal. The received signal-to-noise ratio is calculated based on the respective weight vector using the channel estimate obtained through channel estimation and a plurality of weight vectors preset for the formation of the switched beam, and the maximum value of the calculated plurality of received signal-to-noise ratios. Detects a weight vector corresponding to. The mobile terminal transmits an identifier corresponding to the detected weight vector to the base station.

According to another feature of the present invention, there is provided a base station system having a smart antenna system for forming a switched beam with a plurality of transmit antennas to provide a switched beam to a subscriber station. The base station system includes a plurality of transmit antennas, a pilot signal generator, a switched beam controller, a switched beam identifier receiver, and a base station controller, wherein the plurality of transmit antennas provide a directional beam that is narrower than the sector beam. The pilot signal generator generates a pilot signal so that a plurality of transmit antennas can be identified, the switched beam controller generates a switched beam providing the directional beam according to a predetermined weight vector, and the switched beam identifier receiver transmits from the subscriber station. And an identifier of the switched beam to be switched, the identifier of the weight vector selected by the subscriber station. The base station controller transmits a pilot signal through a sector beam, and controls the switched beam controller to generate a switched beam based on the switched beam identifier information received by the switched beam identifier receiver.

According to another feature of the invention, there is provided a terminal for selecting a switched beam transmitted by a base station equipped with a smart antenna system for forming a switched beam with a plurality of transmit antennas. The terminal includes a channel estimator, a weight vector storage unit, a signal-to-noise ratio calculator and a weight vector determiner. The channel estimator estimates a channel for each of the plurality of transmit antennas of the base station using the received pilot signal, and the weight vector storage unit stores a plurality of weight vectors for forming a sector beam and a switched beam having a narrower orientation than the sector beam. do. The signal-to-noise ratio calculation unit calculates a received signal-to-noise ratio using a channel estimate and the weighted vectors of the plurality of switched beams, and the weight-vector determination unit determines the maximum of the signal-to-noise ratios calculated by the signal-to-noise ratio calculation unit. A weight vector is determined and an identifier of the determined weight vector is informed to the base station.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

In addition, when a part is said to "include" a certain component, which means that it may further include other components, except to exclude other components unless otherwise stated.

Now, a switched beam selection method and system thereof according to an embodiment of the present invention will be described in detail with reference to the drawings.

2 is a diagram illustrating a configuration of a base station for forming a sector beam to be applied in the present invention.

The transmit antenna of the base station shown in FIG. 2 is provided with weights to form beams in all directions in the sector cell.

The base station transmit antenna elements T1, T2 through TN are weighted vectors for forming the sector beams in order to form and radiate signals common to all mobile terminals in the sector in all directions. Womni, N) is set and operated.

The receiving antenna R of the subscriber station receives the sector beam formed on the basis of the above-described weight vector radiated omnidirectionally through the channel from each antenna element according to its position.

3 is a diagram illustrating a configuration of a base station for forming switched beamforming according to the present invention.

The transmit antenna of the base station shown in FIG. 3 is provided with antenna weights for switched beamforming with a narrower orientation than the sector beam.

The base station transmit antenna elements T1, T2 through TN are k weight vectors Wk predetermined for each base station transmit antenna elements T1, T2 through TN in order to be able to radiate a beam having directivity to a specific terminal. , 1 .... Wki, N).

The weight vector for forming the sector beam and the weight vector for switched beamforming may be represented by Equation 1 below.

The number of weight vectors is limited by the beamforming direction. When the subscriber station and the base station share an identifier for a specific weight vector, the base station is assigned to the terminal according to the identifier of the weight vector selected by the corresponding terminal. It is possible to provide a directional beam.

Meanwhile, the pilot signals provided to all terminals in the sector are transmitted using the sector beam shown in FIG. 2 without using beamforming, and the weight vector for forming the sector beam is a value known to the base station and the terminals. Accordingly, the subscriber station can continuously estimate the channel using the common pilot signal transmitted by the base station. Assuming that the number of transmitting antennas of the base station is N and the number of receiving antennas of the terminal is 1, the channel estimation result performed by the terminal is 1 × N, which is given by Equation 2.

Therefore, the channel estimation result obtained by removing the weight of the sector beam is shown in Equation 3 below.

Here, h _i means a channel between the i th transmit antenna element and the subscriber station. Meanwhile, since the k weights W _k for forming the switched beams are a predetermined value, the subscriber station can select the switched beam that provides the highest received power by using the channel estimation result.

That is, the received signal of the mobile subscriber station formed at the antenna element N and the index k of the downlink switched beam may be expressed as Equation 4.

Where r is a received signal, x is a transmitted signal, and n is noise.

Equation 5 below represents an instantaneous signal to noise ratio (instantaneous SNR) of the subscriber station.

That is, by using the channel estimate and the predetermined beamforming weight vector, the subscriber station can select a beam having the maximum average signal-to-noise ratio or instantaneous signal-to-noise ratio using Equations 6 and 7 below.

Equation 6 is to find a weight vector for switched beamforming when the average signal-to-noise ratio is maximum, and Equation 7 is to obtain a weight vector when the instantaneous signal-to-noise ratio is maximum.

값을 구하기 위해서는 송신 안테나의 구분이 필요하며, 본 발명 의 실시예에서는 이를 위하여 파일롯 신호를 이용한다.Meanwhile,

In order to obtain a value, it is necessary to distinguish transmission antennas, and an exemplary embodiment of the present invention uses a pilot signal.

4 is a diagram illustrating a pilot configuration according to an embodiment of the present invention when a single carrier transmission scheme is used.

As shown in FIG. 4, each antenna element T1, T2, T3, TN transmits a pilot for beam selection so that time does not overlap. That is, while the antenna element T1 transmits the pilot, the other antenna element does not transmit the pilot.

Thus, the terminal can obtain a channel estimate for each antenna element.

5 is a diagram illustrating a pilot structure according to an embodiment of the present invention when the multi-carrier method is used.

When a multi-carrier scheme such as an orthogonal frequency division multiplexing (OFDM) scheme is used, all base station antenna elements transmit the same data at the same time. Here, in order for the subscriber station to select a beam number, the base station uses M subcarriers (f1, f2, f3 .... fM) of a specific position of the downlink signal. The base station uses N orthogonal codes or random codes of length M to distinguish the transmitting antenna elements.

In the OFDM signal illustrated in FIG. 5, adjacent M subcarriers may transmit different Walsh codes according to transmission antenna elements. The antenna element T1 transmits Walsh code # 1 having a length of M using adjacent M subcarriers, and the antenna element TN transmits Walsh code #N having a length of M using adjacent M subcarriers.

Here, when M has a large size, more accurate channel estimation is possible. The channel estimate related to the transmit antenna k may be calculated as shown in Equation 8 below.

Here, the meaning of the subscript is as follows.

k 1... Integer between N (send antenna number)

i 1... Integer that exists between M (number of adjacent subcarriers used to distinguish transmission antennas)

k번째 송신안테나 구분을 위한 직교 코드의 i번째 값

i value of the orthogonal code for identifying the kth transmit antenna

송신안테나 구분을 위해 할당된 i번째 부반송파 수신 신호

I-th subcarrier received signal allocated to transmit antenna

6 is a block diagram showing the configuration of a base station system according to an embodiment of the present invention.

The base station 100 according to the embodiment of the present invention includes a base station controller 110, a digital signal transceiver 120, an analog transceiver 130, a pilot signal generator 140, a switched beam controller 150, and a switched beam. An identifier receiver 160 is included.

The base station identifier also includes a plurality of antenna elements T1, T2... TN and a receiving antenna R for transmission. Although the transmitting antenna or the receiving antenna is shown as a separate component in the figure, it may be implemented as a single antenna to implement a transmission and reception function together.

The digital signal transceiver 120 codes source data into a transmission digital signal and decodes a reception digital signal in accordance with a communication scheme and a policy.

The analog signal transceiver 130 modulates the digital signal to an analog signal or demodulates the received analog signal according to a communication scheme and policy.

The pilot signal generator 140 generates a pilot signal to be transmitted as a sector beam. As described above, in the case of a single carrier, the pilot signal may be arranged such that each of the transmitting antenna elements T1, T2,... TN does not overlap each other in time so that the UE receives the pilot signal from which antenna element. Do it. In addition, in the OFDM multi-carrier scheme, a UE transmits a neighboring M subcarrier using a Walsh code or a random code corresponding to each antenna element, thereby identifying which antenna element a pilot signal is received from.

The switched beam controller 150 determines whether the beam is transmitted through the plurality of transmission antenna elements T1, T2... TN, and a weight vector. As described above, the weight vector includes a weight vector for sector beam forming and a weight vector for directional beamforming.

The switched beam identifier receiver 160 receives the switched beam identifier fed back by the terminal to the reception antenna R, and notifies the base station controller 110. Here, the switched beam identifier is weight vector information regarding the switched beam that provides the maximum received power to the terminal by the channel estimation and the maximum signal-to-noise ratio calculation.

The base station controller 110 controls a series of operations of the digital signal transceiver 120 and the analog signal transceiver 130, and uses the weight vector fed back through the switched beam identifier receiver 160 to switch the switched beam controller 150. Control for optimal directional beamforming.

7 is a block diagram showing the configuration of a receiving terminal according to an embodiment of the present invention.

The mobile terminal 200 includes a channel estimator 210, a weight vector storage unit 220, an SNR calculator 230, a weight vector determination unit 250, and a terminal controller 240.

The channel estimator 210 estimates a channel from each base station antenna element by using a pilot signal received from the receiving antenna Ra. The pilot signal is transmitted to the terminal through the omni-directional sector beam, and the terminal obtains a channel estimate for each antenna element using the weight vector value of the sector beam stored in the weight vector storage unit 220.

The SNR calculator 230 calculates the received signal-to-noise ratio as shown in Equations 6 and 7 by using the channel estimate. Here, the weight vector storage unit stores a weight vector W _k corresponding to the switched beam, and the weight vector is a value already known to the base station and the subscriber station.

When the SNR calculator 230 determines the maximum signal-to-noise ratio using the estimated channel and the weight vector Wk, the terminal controller 240 transmits the corresponding weight vector to the weight vector determiner 250. The weight vector determiner 250 transmits an identifier of the weight vector corresponding to the weight vector, that is, a switched beam identifier, to the base station through the transmission antenna Ta.

As in the system described above, in the embodiment of the present invention, the weight vector of the switched beam is determined and fed back by the subscriber station, so that the base station performs an operation for measuring an angle of arrival of the uplink signal or calculating a weight vector suitable thereto. I never do that.

8 is a flowchart illustrating a switched beam selection method according to an embodiment of the present invention.

In step S100, the transmitting antenna of the base station transmits a transmitting antenna pilot signal to the receiving terminal to identify the transmitting antenna element. The pilot signal is transmitted on a single carrier or on a multicarrier so that the transmitting antenna can identify with the weight vector of the sector beam. In the case of single carrier transmission, the pilot signal may be transmitted so that the antenna element can be identified in time. In the case of multi-carrier transmission, a pilot signal may be transmitted to adjacent subcarriers so that an antenna element can be identified in a Walsh code or a random code.

The terminal receiving the pilot signal performs channel estimation using the pilot signal (S120). As described above, since the pilot channel is transmitted through the omni-directional sector beam, an estimate of the channel can be obtained by considering the weight vector of the sector beam. Algorithms for channel estimation using pilot signals have already been introduced, and those skilled in the art can select one of channel estimation algorithms according to a communication method.

In step S130, it is determined whether channel estimation from all transmission antenna elements is completed, and the channel estimation is repeated until pilot signals from all transmission antenna elements are received.

Once the estimates for the channels from all transmit antenna elements are calculated, a plurality of weight vectors preset for the channel estimates and switched beamforming are applied to Equation 6 to signal each of the plurality of switched beamforming weight vectors. To noise ratio is measured (S140). Since the weight vector for the switched beamforming used for measuring the signal-to-noise ratio is a value previously known to the base station and the subscriber station, the subscriber station may measure the signal-to-noise ratio using the weight vector of the switched beam.

In step S150, the maximum value of the measured signal-to-noise ratios for each switched beamforming weight vector is determined, a weight vector corresponding to the maximum signal-to-noise ratio is detected, and the identifier thereof is combined with the terminal identifier. Notify the base station. That is, the subscriber station feeds back the weight vector value providing the maximum received power to the base station, so that the subscriber station becomes the subject of the switch beam selection.

Since the number of weight vectors of the switched beams is limited, it can be represented as an identifier of a relatively small bit and transmitted.

The base station receiving the identifier of the weight vector selects the switched beam corresponding to the weight identifier, and performs directional beamforming on the subscriber station until the next feedback period (S160).

The embodiments of the present invention described above are not implemented only through the apparatus and the method, but may be implemented through a program for realizing a function corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded. Implementation may be easily implemented by those skilled in the art from the description of the above-described embodiments.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

According to the above-described configuration of the present invention, the subscriber station is the main body to select the switched beam, the uplink resources for the angle of arrival and the computational load of the base station is reduced.

In addition, an effect of selecting an optimal switched beam may be expected by eliminating an error caused by separation of uplink and downlink frequency bands.

In addition, since the downlink common pilot signal is used, the base station can reduce uplink radio resources for the angle of arrival measurement, and the terminal can select an optimal switched beam that provides the maximum reception power.

Claims (12)

In the switched beam selection method of the subscriber station located in the sector area of the base station equipped with a smart antenna system for forming a switched beam with a plurality of transmitting antennas, Receiving a pilot signal generated to identify the plurality of antennas and transmitted from the base station via a sector beam; Estimating a channel for each transmit antenna using the pilot signal; Calculating a received signal-to-noise ratio based on each weight vector using channel estimates obtained through the channel estimation and a plurality of weight vectors preset for forming a switched beam; Detecting a weight vector corresponding to a maximum value of the calculated plurality of received signal-to-noise ratios; And Transmitting an identifier corresponding to the detected weight vector to the base station Switched beam selection method comprising a. The method of claim 1, If the base station is operated in a single carrier transmission scheme, And the pilot signal for each transmit antenna is transmitted at different times for each transmit antenna. The method of claim 1, If the base station is operated in a multi-carrier transmission scheme And the pilot signal for each transmit antenna is transmitted by differently assigning codes to transmit subcarriers for each transmit antenna. The method of claim 3, And a code assigned to each transmit antenna is a Walsh code or a random code. The method of claim 1, The channel estimation step is Removing the effect of an omni-directional weight vector assigned to the sector beam. A base station system having a smart antenna system for forming a switched beam with a plurality of transmitting antennas to provide a switched beam to a subscriber station, A plurality of transmit antennas for providing directional beams narrower than sector beams; A pilot signal generator configured to generate a pilot signal to identify the plurality of transmit antennas; A switched beam controller for generating a switched beam providing the directional beam according to a predetermined weight vector; A switched beam identifier receiver configured to receive an identifier of a switched beam transmitted from the subscriber station-an identifier of a weight vector selected by the subscriber station; And A base station controller for transmitting the pilot signal through a sector beam and controlling the switched beam controller to generate a switched beam based on the switched beam identifier information received by the switched beam identifier receiver; Base station system comprising a. The method of claim 6, A digital transceiver for coding / decoding a digital signal; And And an analog signal transceiver for analog-modulating the digital signal or demodulating the received analog signal. The method of claim 7, wherein The digital transceiver and the analog transceiver unit employs an orthogonal frequency division multiplexing scheme, The pilot signal is a base station system in which a code for identifying a transmitting antenna is allocated to an adjacent subcarrier and transmitted. The method of claim 7, wherein The digital transceiver unit and the analog transceiver unit uses a single carrier scheme, the pilot signal is a base station system to be transmitted is assigned a time interval for identifying the transmit antenna. A terminal for selecting a switched beam transmitted by a base station equipped with a smart antenna system for forming a switched beam with a plurality of transmission antennas, A channel estimating unit estimating a channel for each of the plurality of transmitting antennas of the base station using the received pilot signal; A weight vector storage unit for storing a sector beam and a plurality of weight vectors for forming a switched beam having directivity narrower than that of the sector beam; A signal-to-noise ratio calculation unit configured to calculate a received signal-to-noise ratio using the channel estimate and the weight vector of the plurality of switched beams; And A weight vector determiner for determining a weight vector of the switched beam used for the maximum value of the calculated signal-to-noise ratio, and notifying the base station of the identifier of the determined weight vector. Terminal comprising a. The method of claim 10, The channel estimator removes the influence of the weight vector of the sector beam from the channel estimate by using the weight vector of the sector beam stored in the weight vector. The method of claim 10, The identifier information of the weight vector of the switched beam is shared with the base station.

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