JP2006196978A - Beam control apparatus, array antenna system, and wireless device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To alleviate deviation in a SINR time variation characteristics among mobile stations when the number of antenna elements of an array antenna of base stations is small and sufficiently ensure an instantaneous variation amount in the SINR time variation characteristics. <P>SOLUTION: The beam control apparatus includes: a phase control variable arithmetic means for calculating a phase control variable given to a signal transmitted from an antenna element 11a-2; and an angular velocity fluctuation function arithmetic means for calculating an angular velocity variation on the basis of an angular velocity fluctuation function, and the angular velocity fluctuation function arithmetic means is provided with a beam control section 15 for calculating a variation amount per unit time of the phase control variable on the basis of an angular velocity resulting from summating the angular velocity variation to a fixed angular velocity. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a beam control apparatus, an array antenna system, and a radio apparatus.

  Conventionally, in a packet-switched mobile communication system using time division multiple access, in the downlink from the base station to the mobile station, the state of the radio propagation path that is independent for each mobile station is observed, and based on the propagation path condition By performing scheduling and adaptive channel allocation, transmission efficiency per base station is improved. In this scheduling method, a time slot is allocated to a mobile station having the best channel state. Also, the adaptive channel allocation method realizes a transmission rate suitable for the channel state by adaptively changing the transmission method (modulation method or coding rate) according to the channel state.

  In the scheduling method and the adaptive channel allocation method described above, the state of the radio propagation path between the base station and the mobile station is used, and the propagation path state is SINR (Signal to Interference plus Noise power Ratio) in the mobile station. Is done. This SINR is the ratio of the power of the signal received from the undesired base station and the noise power to the power of the signal received by the mobile station from the desired base station. The SINR instantaneously varies independently for each mobile station. This is because multipath fading occurs when a mobile station moves or an object around the mobile station moves, and as a result, the received signal from each base station varies instantaneously for each mobile station. The cause is. In particular, when out-cell interference from an undesired base station is dominant with respect to SINR fluctuation, there is a case where SINR is improved stochastically due to instantaneous reduction of out-of-cell interference. For this reason, transmission with high transmission efficiency is possible by the above-described scheduling and adaptive channel assignment.

  On the other hand, if the mobile station or an object around the mobile station is stationary or moving at a low speed and the instantaneous fluctuation of the propagation path due to multipath fading does not occur sufficiently, the SINR is as described above. Since no improvement cases occur, improvement in transmission efficiency cannot be expected. In particular, when the mobile station is stationary near the cell edge away from the base station, the average SINR is constantly low when the transmission power and antenna radiation pattern of the base station are fixed. Even if a slot is allocated, only a transmission channel with a low transmission rate is provided by adaptive channel allocation. As a result, transmission throughput bias occurs for each mobile station depending on the distance and position from the base station. Note that the average SINR is a steady propagation path characteristic depending on the location consisting of the transmission power and antenna radiation pattern of the base station, distance attenuation depending on the distance from the base station, and shadowing depending on the buildings around the mobile station. , Etc.

For this reason, for example, Non-Patent Document 1 discloses a conventional technique related to beam control for actively varying the average SINR of each mobile station over time. In this prior art, the base station is provided with an array antenna having a plurality of antenna elements and a beam control function, and by adding a variation amount varying at different fixed angular velocities to the phase amount of the signal transmitted from each antenna element. , Artificially fading. The fixed angular velocity corresponding to each antenna element is selected at random. FIG. 7 is a conceptual diagram for explaining a conventional beam control method. As shown in FIG. 7, the mobile station is in the vicinity of the boundary between the cell of the communication base station (desired base station) with which the mobile station is communicating and the cell of the interference base station (undesired base station) with which the mobile station is not communicating. At this time, each base station can periodically change the radiation pattern of the array antenna by periodically changing the weighting factor of the array antenna. Thereby, since the radiation patterns of the communication base station and the interference base station change, the received power from each base station changes in the mobile station, and the SINR of the mobile station changes.
P. Viswanath, DHC Tse, and R. Laroia, “Opportunistic Beamforming using Dumb Antennas,” IEEE Trans. Inform. Theory, vol. 48, pp. 1277-1294, June 2002.

  However, in the above-described prior art, when the number of antenna elements of the array antenna of the base station is small (generally in the case of 5 elements or less), the instantaneous fluctuation of SINR is biased depending on the position of the mobile station, so that the transmission throughput is not improved Will occur. FIG. 8 is a graph of a simulation result showing SINR time variation characteristics for each mobile station when the conventional beam control method is used. As this simulation condition, as shown in FIG. 9, seven base stations 100a and 100b and three mobile stations 200A, 200B, and 200C are arranged. The base station 100a is a desired base station, and the base station 100b is an undesired base station. The number of antenna elements of the array antenna that the base station has is two. In FIG. 8, the SINR time variation characteristics of the three mobile stations 200A, 200B, and 200C are shown by solid-line waveforms A, B, and C, respectively. In FIG. 8, a broken line waveform W is a SINR time variation characteristic in the case of no beam control. As shown in FIG. 8, in the conventional beam control method, the SINR of the mobile station can be improved stochastically, but the phase amount of the signal radiated from each antenna element is changed using a fixed angular velocity. The SINR time variation characteristics of each mobile station have periodicity and are biased among the mobile stations. In the example of FIG. 8, the SINR temporal variation characteristic of the mobile station 200A has a sufficiently large instantaneous variation amount, but the instantaneous variation amount is not sufficient for the mobile stations 200B and 200C.

  The present invention has been made in view of such circumstances, and the object of the present invention is to provide each movement of the SINR time variation characteristics when the number of antenna elements of the array antenna of the base station is small (generally when the number is 5 or less). An object of the present invention is to provide a beam control apparatus, an array antenna system, and a radio apparatus capable of reducing the deviation between stations and sufficiently securing the instantaneous fluctuation amount of the SINR time fluctuation characteristic.

  In order to solve the above problems, a beam control apparatus according to the present invention is a beam control apparatus for controlling a radiation pattern of an array antenna having a plurality of antenna elements. A phase control amount calculating means for calculating, and an angular velocity fluctuation function calculating means for calculating an angular velocity fluctuation function using an angular velocity fluctuation function, wherein the phase control amount calculating means calculates the angular velocity from the angular velocity obtained by adding the angular velocity fluctuation to a fixed angular velocity. A variation amount per unit time of the phase control amount is calculated.

  An array antenna system according to the present invention includes an array antenna having a plurality of antenna elements, the beam control apparatus according to claim 1, and a signal transmitted from the antenna element based on a phase control amount obtained by the beam control apparatus. And a phase shifter for adjusting the phase amount.

  A radio apparatus according to the present invention is a radio apparatus that performs time slot scheduling and adaptive channel allocation based on a state of a radio propagation path, and includes the array antenna system according to claim 2.

  According to the present invention, since the phase difference between signals transmitted by the antenna elements of the base station varies with the angular velocity fluctuation function with reference to the fixed angular velocity, the SINR temporal variation characteristic of each mobile station has periodicity. It will not be. Thereby, when the number of antenna elements of the array antenna is small (generally 5 elements or less), it is possible to reduce the deviation of the SINR time variation characteristics between the mobile stations, and to reduce the instantaneous variation amount of the SINR time variation characteristics. It can be secured sufficiently. As a result, transmission throughput can be improved for all mobile stations without depending on the position of the mobile station.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of an array antenna system 10 according to an embodiment of the present invention. In FIG. 1, the array antenna unit 11 has two antenna elements 11a-1 and 11a-2. The beam forming unit 12 includes a distributor 13 and a phase shifter 14. The distributor 13 distributes the input transmission signal to the antenna elements 11a-1 and 11a-2 at the time of transmission, and synthesizes and outputs the reception signals of the antenna elements 11a-1 and 11a-2 at the time of reception. The phase shifter 14 can arbitrarily adjust the phase amount of the transmission signal. Then, the phase shifter 14 gives the phase control amount θ (t) received from the beam control unit 15 to the transmission signal of the antenna element 11a-2. Thereby, the phase difference between the signals transmitted by the antenna elements 11a-1 and 11a-2 is controlled to θ (t). The beam control unit 15 calculates and outputs the phase control amount θ (t).

The beam control unit 15 calculates the phase control amount θ (t) by the equation (1).
θ (0) = θ _Initial
θ (t) = θ (t−Δt) + (ω _Const + Δω (t−Δt)) × Δt
(1)
However,
t is the time,
θ _Initial is the initial phase value [rad],
Δt is the beam control period [s],
ω _Const is a fixed angular velocity (however, any value in the range of −π to π [rad / s]),
Δω (t) is the angular velocity fluctuation function [rad / s],
It is.

As shown in the above equation (1), the phase control amount θ (t) fluctuates at an angular velocity obtained by adding the angular velocity fluctuation amount determined by the angular velocity fluctuation function Δω (t) to the fixed angular velocity ω _Const . As a result, the phase difference θ (t) between the signals transmitted by the antenna elements 11a-1 and 11a-2 varies with the angular velocity fluctuation function Δω (t) with the fixed angular velocity ω _Const as a reference. However, the phase change amount of the fixed angular velocity ω _Const and the angular velocity fluctuation function Δω (t) per time slot is assumed to be sufficiently small.

  The angular velocity fluctuation function Δω (t) is a random function having an average of 0 during the angular velocity fluctuation period T [s]. An example of the angular velocity fluctuation function Δω (t) is shown below.

(Example 1)
Δω (t) = α × ω _Const × sin (2 × π × t / T) (2)
Where α is a coefficient of variation (however, any value in the range of 0 to 1).

(Example 2)
Δω (t) = α × ω _Const × PN (t, T) (3)
However, PN (t, T) is a pseudo-random sequence of length T / Δt and element {−1, 1}, and its cycle is an angular velocity fluctuation cycle T.

Next, the control procedure of the beam control unit 15 shown in FIG. 1 will be described with reference to FIG. FIG. 2 is a control flowchart of the beam controller 15 shown in FIG.
In FIG. 2, first, the beam controller 15 performs initial setting (S1). Specifically, initial setting of the initial phase value θ _Initial , the fixed angular velocity ω _Const and the angular velocity fluctuation function Δω (t) is performed. Next, the initial value θ (0) of the phase control amount of the phase shifter 14 is set to the initial phase value θ _Initial (S2).

  Next, time t = t + Δt is set (S3), and the value (angular velocity fluctuation) of the angular velocity fluctuation function Δω (t) is calculated (S4). Next, the phase control amount θ (t) is calculated using the value of the angular velocity fluctuation function Δω (t) (S5). Next, the calculation result of the phase control amount θ (t) is output to the phase shifter 14 (S6). Thereafter, the above steps S3 to S6 are repeated.

  FIG. 3 is a graph of simulation results showing SINR time variation characteristics for each mobile station when the beam control method according to the present embodiment is used. The simulation conditions are the same as in the case of FIG. 8 according to the conventional beam control method. In FIG. 3, SINR time variation characteristics obtained by the beam control method according to the present embodiment of the three mobile stations 200A, 200B, and 200C shown in FIG. 9 are indicated by solid-line waveforms A, B, and C, respectively. ing. In FIG. 3, a broken line waveform W is the SINR time variation characteristic when there is no beam control.

  As is clear from the comparison between FIG. 3 and FIG. 8, according to the beam control method according to the present embodiment, the deviation of the SINR time variation characteristics between the mobile stations is reduced, and the instantaneous variation amount of the SINR time variation characteristics is further reduced. Is sufficiently secured.

  Further, FIG. 4 shows simulation results of transmission throughput characteristics of the mobile stations 200A, 200B, and 200C (corresponding to UserNumbers 1, 2, and 3 in the same order). As a simulation condition, the scheduling method uses a scheduling algorithm based on proportional fairness. As shown in FIG. 4, in the conventional beam control method, the transmission throughput of the mobile station 200A (UserNumber1) is prominent and the difference between the mobile stations is about three times. However, according to the beam control method of this embodiment, the mobile station 200A (UserNumber1) The disparity between stations is suppressed to about twice.

  As described above, according to the present embodiment, the phase difference between the signals transmitted by the respective antenna elements varies according to the angular velocity fluctuation function with reference to the fixed angular velocity, so that the SINR temporal variation characteristic of each mobile station is periodic. It will not have. As a result, when the number of antenna elements of the array antenna is small (in this embodiment, the minimum two elements), it is possible to reduce the deviation of the SINR time variation characteristics between the mobile stations, and the SINR time variation characteristics. Sufficient instantaneous fluctuation can be secured. As a result, transmission throughput can be improved for all mobile stations without depending on the position of the mobile station.

The number of antenna elements of the array antenna may be three or more. In this case, the phase control amount θ (t) can be obtained as “N−1” relative phase vectors with respect to N antenna elements with reference to one antenna element. Each relative phase vector is calculated from an independent fixed angular velocity and angular velocity fluctuation function. FIG. 5 shows a configuration of the array antenna system 10 having N (three or more elements) antenna elements. In FIG. 5, the beam controller 15 applies relative phase vectors θ ₁ (t) and θ ₂ (t, respectively, to phase shifters 14 provided corresponding to the antenna elements 11a-2, 3,. ), Θ ₃ (t),..., Θ _N−1 (t) are output.

  FIG. 6 is an example of a base station (wireless device) 100 according to the present embodiment. A base station 100 shown in FIG. 6 is a base station of a packet-switched mobile communication system using time division multiple access. In the downlink from the base station 100 to the mobile station 200, based on the state of the radio propagation path, Time slot scheduling and adaptive channel assignment. Also, the mobile station 200 measures SINR indicating the state of the downlink radio propagation path, and notifies the base station 100 of the SINR of the measurement result.

  In FIG. 6, a base station 100 includes an array antenna system 10 according to the present embodiment, and the array antenna system 10 transmits and receives radio sections between mobile stations 200. The basic configurations of base station 100 and mobile station 200 other than array antenna system 10 shown in FIG.

  According to this embodiment, the beam pattern radiated from the base station 100 by the array antenna system 10 changes according to the angular velocity fluctuation function with reference to the fixed angular velocity. Thereby, each base station 100 can artificially generate sufficient fading independently. In each mobile station, the radiation patterns of the communication base station (desired base station) and the interference base station (undesired base station) change independently, and the received signal from each base station varies instantaneously independently. Therefore, SINR instantaneously varies independently for each mobile station. As a result, the base station 100 can perform transmission with high transmission efficiency by performing scheduling and adaptive channel allocation according to the SINR of each mobile station.

The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design changes and the like within a scope not departing from the gist of the present invention.
For example, the present invention is applicable to a mobile communication system such as a time division multiple access packet switched cellular system and a wireless LAN system using a scheduling function and an adaptive channel assignment function. For example, it can be applied to a cdma2000 1xEV-DO system, a W-CDMA HSDPA system, or the like.

It is a block diagram which shows the structure of the array antenna system 10 which concerns on one Embodiment of this invention. It is a control flowchart of the beam control part 15 shown in FIG. It is a graph of the simulation result which shows the SINR time fluctuation characteristic according to mobile station at the time of using the beam control method concerning one embodiment of the present invention. It is a graph of the simulation result which shows the transmission throughput characteristic according to mobile station at the time of using the beam control method which concerns on one Embodiment of this invention. It is a block diagram which shows the structure of the array antenna system 10 which concerns on other embodiment of this invention. It is a block which shows the structure of one Example of the base station (radio | wireless apparatus) 100 which concerns on one Embodiment of this invention. It is a conceptual diagram for demonstrating the conventional beam control method. It is a graph of the simulation result which shows the SINR time fluctuation characteristic for every mobile station at the time of using the conventional beam control method. It is a figure which shows simulation conditions.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Array antenna system, 11 ... Array antenna part, 11a ... Antenna element, 12 ... Beam forming part, 13 ... Divider, 14 ... Phase shifter, 15 ... Beam control part, 100 ... Base station, 200 ... Mobile station.

Claims (3)

In a beam control apparatus for controlling a radiation pattern of an array antenna having a plurality of antenna elements,
Phase control amount calculation means for calculating a phase control amount to be given to a signal transmitted from the antenna element;
An angular velocity fluctuation function calculating means for calculating an angular velocity fluctuation amount by an angular velocity fluctuation function;
The beam control apparatus, wherein the phase control amount calculating means calculates a variation amount per unit time of the phase control amount from an angular velocity obtained by adding the angular velocity variation to a fixed angular velocity. An array antenna having a plurality of antenna elements;
A beam control device according to claim 1;
A phase shifter that adjusts a phase amount of a signal transmitted from the antenna element based on a phase control amount obtained by the beam control device;
An array antenna system comprising: In a radio apparatus that performs time slot scheduling and adaptive channel assignment based on the state of a radio channel,
A radio apparatus comprising the array antenna system according to claim 2.

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