JP4680113B2 - Radio transmission apparatus and radio transmission method - Google Patents

Description

  The present invention relates to a radio transmission apparatus and a radio transmission method, and more particularly to a technique for adaptively forming a transmission beam using an array antenna.

  An array antenna composed of a plurality of antenna elements is used to control the amplitude and phase of each transmission signal distributed and input to each antenna element (a transmission array that is a weight of a transmission wave transmitted from each antenna element). Research and development of a transmission beam control technique capable of adaptively forming an arbitrary transmission beam pattern by giving a weight) has been actively conducted. This technology not only can form a beam with high gain directivity, but also has a feature that it can form a null that cancels the transmission signal in another direction. By assigning beam patterns orthogonal to each other to multiple mobile stations, a beam is formed for each mobile station (referred to as an undesired station hereinafter) and a null is formed. Can communicate at the same time.

  By applying such transmission beam control technology to cellular system base station equipment, it is possible to use “space”, which is a dimension independent of time and frequency, for multiple access of communications, so that frequency utilization efficiency can be improved. There are great expectations for improvement. For example, an FDD / SDMA cellular system that realizes space division multiple access (SDMA) that performs beam multiplexing using a transmission beam control technique in a frequency division duplex (FDD) cellular system is proposed. Has been.

In order to realize the transmission beam control as described above, information on the propagation path characteristics (downlink space vector) between each antenna element of the array antenna and the receiving antenna of the mobile station is acquired on the base station side that performs the control. It is necessary to keep it. There are roughly the following two methods. One is a method of performing feedback control at the base station using a downlink space vector obtained on the mobile station side. In this method, since a communication line (uplink) is used for feedback control, there is a problem that transmission efficiency is lowered as a whole. Another method is based on the premise that an array antenna having a high correlation of transmission signals between antenna elements is used, and the relative level (amplitude) and relative phase between the antenna elements in the state where the array antenna is configured. There is a method in which the antenna radiation characteristic (array antenna characteristic) is estimated or measured in advance and held, and the array antenna characteristic corresponding to the direction of the mobile station estimated in the arrival direction in the uplink is substituted as a downlink space vector. (For example, refer nonpatent literature 1). In this method, it is not necessary to perform feedback control, and transmission beam control can be realized only by processing in the base station.
Liang Ying-Chang et al., Downlink channel covariance matrix (DCCM) estimation and its application in wireless DS-CDMA systems, “IEEE Journal on Selected Areas in Commun.”, February 2001, Vol. 19, No. 2, p. 222-232

  However, in the latter method, conventionally, only the array antenna characteristic in the horizontal plane is used, and the same array antenna characteristic is used in the vertical plane (the depression direction of the radio wave transmitted from the base station). . If all the antenna elements are ideal and the characteristics in the vertical plane direction are the same, the array antenna characteristics will be the same in the vertical plane and no problem will occur. However, an actual array antenna has a vertical error between antenna elements due to manufacturing errors. Since the radiation characteristics in the direction vary, the array antenna characteristics in the vertical plane have a deviation. In this case, even if the transmission beam control is performed in the same horizontal plane and the beam and the null are correctly formed, the mobile station to which the null is directed actually exists in different vertical plane directions (that is, directions having different depression angles). In such a case, a situation may occur in which the transmission beam pattern does not have a null value in that direction. For this reason, the accuracy of transmission beam control for such a mobile station is degraded, and the effect of SDMA is reduced.

  In particular, since the antenna for the base station of the cellular system directs directivity in the cell edge direction (direction in which the depression angle is almost horizontal) on the vertical plane, the gain is low in the direction near the base station (direction in which the depression angle is large). As a result, the transmission beam pattern is distorted for users near the base station, and the SDMA effect cannot be obtained sufficiently. As a specific example, FIG. 6 shows the vertical plane radiation characteristics of the antenna elements constituting the base station array antenna. The horizontal axis represents the direction of the vertical plane (a depression angle) viewed from the base station, where 0 degree is a direction parallel to the ground and the positive direction is the depression angle (downward angle). Further, the directivity is formed corresponding to the +5 degree direction corresponding to the cell edge direction, but the direction of +30 degrees or more in the vicinity of the base station has a low gain of −40 dB or less compared to the directivity direction. .

  The present invention has been made in view of the above points, and an object thereof is to provide a radio transmission apparatus and a radio transmission method capable of forming a transmission beam pattern in which both the horizontal plane direction and the vertical plane direction are optimized. .

  The present invention has been made to solve the above problems, and the invention according to claim 1 is directed to the amplitude and phase of a transmission wave transmitted from each antenna element by an array antenna composed of a plurality of antenna elements. In a horizontal plane that estimates a direction in a horizontal plane where the mobile station is located based on a received signal received from the mobile station in a radio transmission apparatus that adaptively forms a beam by controlling the radio and performs radio communication with the mobile station An estimation unit, a vertical plane direction estimation unit that estimates a direction in a vertical plane where the mobile station is located based on a received signal received from the mobile station, and a horizontal plane in which the mobile station may exist for each antenna element and An array antenna characteristic storage unit for storing data relating to downlink radiation characteristics in an arbitrary direction in the vertical plane; and the estimated direction in the horizontal plane and the vertical plane of the mobile station Based on the radiation characteristic data, a weight of a transmission wave for each antenna element for transmitting a transmission beam adaptively formed toward a plurality of mobile stations having different directions in a horizontal plane is calculated as a transmission array weight. A transmission beam control unit; and a transmission beam forming unit that controls the amplitude and phase according to the calculated transmission array weights and adaptively forms a transmission beam in the array antenna, the transmission beam control unit comprising: A transmission array weight which maximizes the gain of the transmission beam with respect to the direction of the desired station and minimizes the gain of the transmission beam with respect to the direction of the undesired station whose direction in the vertical plane differs from that of the desired station. The wireless transmission device is characterized by calculating.

  According to a second aspect of the present invention, in the wireless transmission device according to the first aspect, a transmission wave centered around a direction in the horizontal plane of the estimated mobile station based on a received signal received from the mobile station. A spatial angular spread estimating unit for estimating a spatial angular spread of the mobile station, wherein the transmission beam control unit determines a transmission array weight, a direction in a horizontal plane and a vertical plane of the estimated mobile station, the radiation characteristic data, and the The calculation is based on the estimated spatial angular spread.

  According to a third aspect of the present invention, an array antenna composed of a plurality of antenna elements controls the amplitude and phase of a transmission wave transmitted from each antenna element to adaptively form a beam, In the wireless transmission method for performing wireless communication, a procedure for estimating the direction in the horizontal plane where the mobile station is located based on the received signal received from the mobile station, and the mobile station based on the received signal received from the mobile station An array antenna characteristic storage unit for storing a procedure for estimating a direction in a vertical plane, and data regarding downlink radiation characteristics in an arbitrary direction in a horizontal plane and a vertical plane in which a mobile station may exist for each antenna element The procedure for extracting the radiation characteristic data of the estimated mobile station direction, the direction in the horizontal plane and the vertical plane of the estimated mobile station and the extracted Based on the radiation characteristics data, a transmission wave weight is calculated as a transmission array weight for each antenna element for transmitting transmission beams adaptively formed to a plurality of mobile stations having different directions in a horizontal plane. And a step of controlling the amplitude and phase in accordance with the calculated transmission array weight and adaptively forming a transmission beam in the array antenna, and by means of the calculated transmission array weight, A radio transmission method characterized in that a gain of a transmission beam with respect to a direction is maximized, and a gain of the transmission beam with respect to a direction of an undesired station having a different direction in a vertical plane from the desired station is minimized.

  According to a fourth aspect of the present invention, there is provided a radio transmission method according to the third aspect, wherein a transmission wave centered on a direction in the horizontal plane of the estimated mobile station based on a received signal received from the mobile station. In the calculation of the transmission array weight, based on the estimated direction in the horizontal and vertical planes of the mobile station, the radiation characteristic data, and the estimated spatial angular spread. And calculating.

  According to the present invention, radiation characteristic data for the horizontal plane direction and the vertical plane direction is provided, and the transmission array weight is calculated based on the radiation characteristic data and the direction estimation value of the horizontal plane and the vertical plane. Transmit beam control in which the transmit beam pattern is optimized simultaneously with respect to the direction is possible. Therefore, even when the beam is not uniform in the vertical plane direction, effective SDMA can be realized.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
<< First Embodiment >>
FIG. 1 is a functional block diagram showing a configuration of a wireless transmission device 1 according to the first embodiment of the present invention. In the figure, the wireless transmission device 1 includes a horizontal plane direction estimation unit 11 that estimates the direction of the mobile station in the horizontal plane with reference to the position of the array antenna 16, and a vertical plane direction that similarly estimates the direction of the mobile station in the vertical plane. An estimation unit 12, an array antenna characteristic storage unit 13 for storing previously estimated or measured array antenna characteristics, and a plurality of mobile stations using each estimated value and array antenna characteristics in the horizontal and vertical plane directions of the mobile station A transmission beam control unit 14 for calculating a transmission array weight for controlling a transmission beam pattern in a horizontal plane, and each antenna element 17 by multiplying each mobile station (first user to k-th user) by the transmission signal weight of the modulated transmission signal. -1 to 17-N transmission beam forming units 15-1 to 15-k for controlling the amplitude and phase of transmission waves, and weighted by transmission array weights And an array antenna 16 which radiates the transmission signal. The array antenna 16 has a configuration in which N antenna elements 17-1 to 17-N are arranged in an array on a horizontal plane.

  The horizontal plane direction estimation unit 11 estimates the direction of the mobile station in the horizontal plane with reference to the position of the array antenna 16 using the received signal received from the mobile station on the uplink. As the estimation method, a conventionally used method such as a beamformer method, a MUSIC method, or an ESPRIT method based on a signal received by an array antenna 16 of a horizontal plane array type is applied.

The vertical plane direction estimation unit 12 estimates a direction (a depression angle) in the vertical plane of the mobile station with reference to the position of the array antenna 16 using a received signal received from the mobile station on the uplink. As an estimation method, for example, the distance h from the base station (array antenna 16) is estimated from the signal attenuation using the RSSI (Received Signal Strength Indicator) of the uplink, and the height h of the array antenna 16 known in advance is known. The value of the arc tangent tan ⁻¹ (h / d) obtained using is used as the above depression angle. Similarly to the horizontal plane direction estimation unit 11, by using an array antenna of a vertical plane array type in which antenna elements are arranged on a vertical plane, a beamformer method based on a received signal, a MUSIC method, an ESPRIT method, etc. It can also be applied.

  The array antenna characteristic storage unit 13 stores antenna radiation characteristics (array antenna characteristics) estimated or measured in advance with respect to the downlink frequency for each of the antenna elements 17-1 to 17-N constituting the array antenna 16. . This characteristic indicates the radiation characteristic of each antenna element in each of the horizontal plane direction and the vertical plane direction. The array antenna 16 of the present embodiment is of a horizontal plane array type in which N antenna elements 17-1 to 17-N are arranged in a horizontal plane, and the array antenna characteristics have a horizontal plane direction θ and a vertical plane direction φ as variables. It is expressed by the following equation as a vector function V (θ, φ).

Here, ν _n (θ, φ) is a radiation characteristic of the n-th antenna element in the state in which the array antenna 16 is configured, and is a complex function composed of amplitude and phase information.

The transmission beam control unit 14 weights transmission signals from the antenna elements 17-1 to 17-N to each of a plurality of mobile stations (first user to k-th user) existing in the horizontal plane. Is calculated. The transmission array weight for the k-th user uses the horizontal plane direction estimation value θ ^(k) , the vertical plane direction estimation value φ ^(k) , and the array antenna characteristics V (θ ^(k) , φ ^(k) ) of the mobile station. Thus, the transmission array weight vector W ^(k) is calculated by the following equation.

Here, H represents a complex transpose conjugate of a vector, N ₀ is noise power, and I is an N × N unit matrix.

The transmission beam forming unit 15 distributes the modulated transmission signal s ^(k) (t) having the time t as a variable to the number N of antenna elements for each mobile station that performs simultaneous transmission by SDMA and transmits the transmission array weight vector W to each of them. The components of ^(k) are integrated and a transmission signal vector S ^(k) (t) expressed by the following equation is output.

  To the array antenna 16, the components of the transmission signal vectors of the mobile stations that are simultaneously transmitted and output from the transmission beam forming unit 15 are added for each antenna element and input. Each antenna element 17-1 to 17-N transmits a transmission wave on which a transmission signal to each mobile station is superimposed according to this input. The signal S (t) transmitted from the array antenna 16 under transmission beam control in this way is expressed by the following equation.

  As described above, according to this embodiment, the wireless transmission device 1 including the horizontal plane array arrangement type array antenna 16 maintains the array antenna characteristics as a function of both the horizontal plane direction and the vertical plane direction. The transmission array weight is calculated from the antenna characteristics and the direction estimation values of the horizontal and vertical planes. As a result, it is possible to perform transmission beam control in which the transmission beam pattern is optimized simultaneously in the horizontal plane direction and the vertical plane direction. Therefore, even when the beam is not uniform in the vertical plane direction, effective SDMA is realized.

<< Second Embodiment >>
Next, a second embodiment of the present invention will be described. The present embodiment relates to a radio transmission apparatus that performs transmission beam control using spatial angular spread estimation.
FIG. 2 is a functional block diagram showing the configuration of the wireless transmission device 2 according to the present embodiment. In the figure, each component of the horizontal plane direction estimating unit 11, the vertical plane direction estimating unit 12, the array antenna characteristic storage unit 13, the transmission beam forming unit 15, the array antenna 16, and the antenna elements 17-1 to 17-N is as follows. It is the same as that shown in FIG.

  The spatial angle spread estimation unit 18 uses the received signal received from the mobile station on the uplink to statistically measure the radio wave centered on the estimated direction in the horizontal plane of the mobile station with respect to the position of the array antenna 16. Estimate the standard deviation of the spatial extent. As an estimation method, a conventionally used spatial angular spread estimation method for obtaining a standard deviation of spatial spread by approximating a spatial angular spread model based on a signal received by an array antenna 16 of a horizontal plane array type is used. Shall apply.

The transmission beam control unit 14 of the wireless transmission device 2 uses the spatial angular spread σ ^(k) of the k-th user estimated by the spatial angular spread estimation unit 18 and uses this transmission array weight vector W ^(k) for the k-th user. Is calculated according to the following equation.

Here, eig (X) represents an eigenvector corresponding to the maximum eigenvalue obtained by eigenvalue decomposition of the matrix X. A (θ, σ, θ ^(l) ) is a distribution function of the spatial angular spread for the downlink l-th user used in the spatial angular spread estimation unit 18, and centered on the user direction θ ^(l). A function having the spatial angular spread σ as a standard deviation and the direction θ as a variable. When normal distribution is used, it is expressed by the following equation.

Next, an embodiment of the present invention will be described with reference to FIGS.
FIG. 3 is a system model showing the arrangement of the base station array antenna 16 constituting the radio transmission apparatus according to the present invention and the two mobile stations 20 (user A and user B) existing in the cell. . In the figure, the direction of the mobile station in the vertical plane is α degrees for user A and β degrees for user B. Although not shown in the figure, the direction of each mobile station in the horizontal plane is 90 degrees for user A and 270 degrees for user B. Furthermore, it is assumed that the array antenna characteristics V (θ, α) and V (θ, β) in the vertical direction α and the vertical direction β of the array antenna 16 are different characteristics.

(1) Transmit beam control by array antenna characteristic V (θ) considering only horizontal plane For comparison, an example of transmit beam control using array antenna characteristic V (θ) having only the horizontal plane direction θ as a variable for comparison. Indicates. Here, the array antenna characteristic in the vertical direction α is used. FIG. 4 shows a transmission beam pattern in this case. FIG. 4A shows a transmission beam pattern formed in the vertical direction α, and FIG. 4B shows a transmission beam pattern formed in the vertical direction β. .

  In the vertical direction α (FIG. 4A), the transmission beam pattern of the user B forms a null at 90 degrees in the horizontal direction where the user A exists, so that inter-beam interference is greatly suppressed. On the other hand, in the vertical direction β (FIG. 4B), since the null formation of the transmission beam pattern of the user A is distorted at 270 degrees in the horizontal direction where the user B exists, inter-beam interference is sufficiently suppressed. Not.

  In the transmission beam control based on the array antenna characteristic V (θ), an optimal beam and null are formed in a specific vertical direction (here, the vertical direction α), so that the vertical direction α (actually 270 degrees in the horizontal direction) In this direction, there is no user B), and the transmission beam pattern of user A forms a null (FIG. 4A).

(2) Transmit beam control based on array antenna characteristics V (θ, φ) considering vertical plane Next, an embodiment of transmit beam control according to the present invention will be described. FIG. 5 shows a transmission beam pattern when transmission beam control is performed using array antenna characteristics V (θ, φ) having the horizontal plane direction θ and the vertical plane direction φ as variables, and FIG. 5A shows the vertical direction. The transmission beam pattern formed in α and FIG. 5B show the transmission beam pattern formed in the vertical direction β.

  In the vertical direction α (FIG. 5A), since the transmission beam pattern of the user B forms a null at 90 degrees in the horizontal direction where the user A exists, inter-beam interference is greatly suppressed. Also, in the vertical direction β (FIG. 5B), the transmission beam pattern of the user A forms a null in the horizontal direction 270 degrees where the user B exists, and the beam between the user B is also between the beams. Interference is suppressed.

  4A and 4B, or FIGS. 5A and 5B, the transmission beam patterns of each user are different in the vertical directions α and β. As described above, even when the transmission beam is non-uniform in the vertical direction, SDMA can be realized by transmission beam control by using the wireless transmission device of the present invention.

  As described above, the embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the scope of the present invention. Can do.

It is a functional block diagram which shows the structure of the radio | wireless transmitter by the 1st Embodiment of this invention. It is a functional block diagram which shows the structure of the radio | wireless transmission apparatus by the 2nd Embodiment of this invention. 2 is a system model including a wireless transmission device and a mobile station in an embodiment of the present invention. It is an example of the transmission beam pattern by the conventional transmission beam control. It is an example of the transmission beam pattern in the Example of this invention. The vertical plane radiation characteristic of an antenna element is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 ... Wireless transmitter 11 ... Horizontal surface direction estimation part 12 ... Vertical surface direction estimation part 13 ... Array antenna characteristic memory | storage part 14 ... Transmission beam control part 15-1 to 15-k ... Transmission beam formation part 16 ... Array antenna 17 -1 to 17-N antenna element 18 spatial angle spread estimation unit 20 mobile station

Claims (4)

An array antenna composed of a plurality of antenna elements arrayed on a horizontal plane controls the amplitude and phase of the transmission wave transmitted from each antenna element to adaptively form a beam and perform wireless communication with a mobile station In the wireless transmission device,
A horizontal plane direction estimation unit that estimates a direction in a horizontal plane where the mobile station is located based on a received signal received from the mobile station;
A vertical plane direction estimation unit that estimates a direction in a vertical plane where the mobile station is located based on a received signal received from the mobile station;
Each the antenna element, the array antenna characteristic storage section for storing the radiation characteristics data representing the amplitude and phase of the radiation wave from the antenna element to any direction in the horizontal plane and the vertical plane in which the mobile station may be present When,
Based on the estimated directions in the horizontal and vertical planes of the mobile station and the radiation characteristic data, to transmit a transmission beam adaptively formed to a plurality of mobile stations having different directions in the horizontal plane A transmission beam control unit that calculates a weight of a transmission wave for each of the antenna elements as a transmission array weight;
A transmission beam forming unit that controls the amplitude and phase according to the calculated transmission array weight, and that adaptively forms a transmission beam in the array antenna;
With
The transmission beam control unit includes:
Calculates the transmit array weight that maximizes the gain of the transmit beam with respect to the direction of the desired station and minimizes the gain of this transmit beam with respect to the direction of the undesired station that has a different direction in the vertical plane from the desired station A wireless transmitter characterized by: A spatial angle spread estimation unit for estimating a spatial angle spread of a transmission wave centered on a direction in a horizontal plane of the estimated mobile station based on a received signal received from the mobile station;
The transmission beam control unit calculates a transmission array weight based on the estimated direction in a horizontal plane and a vertical plane of the mobile station, the radiation characteristic data, and the estimated spatial angular spread. The wireless transmission device according to claim 1. An array antenna composed of a plurality of antenna elements arrayed on a horizontal plane controls the amplitude and phase of the transmission wave transmitted from each antenna element to adaptively form a beam and perform wireless communication with a mobile station In the wireless transmission method,
A procedure for estimating a direction in a horizontal plane where the mobile station is located based on a received signal received from the mobile station;
Estimating a direction in a vertical plane where the mobile station is located based on a received signal received from the mobile station;
From array antenna characteristic storage section for storing the radiation characteristics data representing the amplitude and phase of the radiation wave from the antenna element to any direction of the respective antenna elements in the horizontal plane and the vertical plane in which the mobile station may be present for Taking out the estimated radiation characteristic data of the mobile station direction;
Based on the estimated directions in the horizontal plane and vertical plane of the mobile station and the extracted radiation characteristic data, transmission beams adaptively formed for a plurality of mobile stations having different directions in the horizontal plane are generated. A procedure for calculating a weight of a transmission wave for each antenna element for transmission as a transmission array weight;
Performing the amplitude and phase control according to the calculated transmit array weight, and adaptively forming a transmit beam in the array antenna;
With
The calculated transmit array weight maximizes the gain of the transmit beam with respect to the direction of the desired station, and minimizes the gain of this transmit beam with respect to the direction of the undesired station that differs in the direction in the vertical plane from the desired station. A wireless transmission method characterized by the above. Based on a received signal received from the mobile station, comprising estimating a spatial angular spread of a transmission wave centered on a direction in a horizontal plane of the estimated mobile station,
The calculation of the transmission array weight is performed based on the estimated directions in the horizontal and vertical planes of the mobile station, the radiation characteristic data, and the estimated spatial angular spread. 4. The wireless transmission method according to 3.

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