The present invention relates to an array antenna transmitter/receiver which suppresses interference with another user by control of antenna directivity and, more particularly, to a multi-beam antenna transmitter/receiver, transmitting/receiving method, and transmission beam selection method which select transmission/reception directivity from a plurality of fixed directional patterns (multi beams).
In a cellular mobile communication system and the like, it has been examined to apply a method of forming a directional pattern (beam) which increases the transmission/reception gain in a desired signal direction and decreases it in another direction by using an array antenna transmitter/receiver including a plurality of antenna elements for the purpose of a higher-speed, higher-quality signal and a larger subscriber capacity. One of such methods is a multi-beam method of selecting a transmission/reception beam from a plurality of fixed directional patterns (multi beams).
As disclosed in, e.g., “Multi-Beam Antenna System for Radio Base Station” (Japanese Patent Laid-Open No. 11-266228), a multi-beam antenna transmitter/receiver of this type selects and receives a reception beam having a delay path excellent in reception quality from a plurality of fixed reception beams in reception. In transmission, the multi-beam antenna transmitter/receiver selects and transmits a transmission beam in the same direction as that of a path delay/reception beam number pair excellent in reception quality from path delay/reception beam number pairs selected upon reception.
FIG. 7 is a block diagram showing an example of a conventional multi-beam antenna transmitter/receiver. The conventional multi-beam antenna transmitter/receiver comprises a reception array antenna 201, an antenna 1 radio reception unit 2031 to antenna N radio reception unit 203N corresponding to reception antenna elements 2021 to 202N, a reception beam 1 formation unit 2041 to reception beam M formation unit 204M (to be also referred to as reception beam formation units 204), a user 1 demodulation block 2051 to user L demodulation block 205L (to be also referred to as user demodulation blocks 205), a user 1 modulation unit 2111 to user L modulation unit 211L, a user 1 transmission beam switching circuit 2121 to user L transmission beam switching circuit 212L, a transmission beam 1 formation unit 2131 to transmission beam J formation unit 213J, an antenna 1 radio transmission unit 2141 to antenna K radio transmission unit 214K corresponding to transmission antenna elements 2161 to 216K, and a transmission array antenna 215.
The reception array antenna 201 is formed from the N reception antenna elements 2021 to 202N. Each of the reception antenna elements 2021 to 202N is free from any limitation on the horizontal and vertical directivities, and has, for example, omnidirectivity or dipole. The N reception antenna elements 2021 to 202N are arranged close to each other so as to correlate the reception signals of the antenna elements with each other. The reception array antenna 201 is not limited in the number of reception antenna elements and their layout as far as the N reception antenna elements 2021 to 202N are arranged close to each other. An example of the layout is a circular layout or linear layout at the half-wavelength interval of the carrier.
Signals received by the N reception antenna elements 2021 to 202N contain desired user signal components, interference signal components, and thermal noise. Each of the desired user signal component and interference signal component contains multipath components. In general, these signal components (desired user signal component and interference signal component) arrive from different directions. Thus, pairs of path delays and reception beam numbers (path delays/reception beam numbers) of desired user signals exist.
Each of the antenna 1 radio reception unit 2031 to antenna N radio reception unit 203N comprises a low-noise amplifier, bandpass filter, mixer, local oscillator, AGC (Auto Gain Controller), quadrature detector, low-pass filter, analog/digital converter, and the like. The antenna 1 radio reception unit 2031 will be taken as an example. The antenna 1 radio reception unit 2031 receives an output from the reception antenna element 2021, performs reception processes such as amplification of an input signal, frequency conversion from the radio band to the baseband, quadrature detection, and analog/digital conversion, and outputs the resultant signal to the reception beam 1 formation unit 2041 to reception beam M formation unit 204M.
The reception beam 1 formation unit 2041 to reception beam M formation unit 204M receive outputs from the antenna 1 radio reception unit 2031 to antenna N radio reception unit 203N, form fixed reception beams different between the respective reception beam formation units for the input signals, and output the beams to the user 1 demodulation block 2051 to user L demodulation block 205L. The number of fixed reception beams, the shape of the fixed reception beam, and the fixed reception beam formation method are not specifically limited. An example of the shape of the fixed reception beam is a quadrature multi-beam, and an example of the fixed reception beam formation method is a method of multiplying input signals by a fixed complex beam weight by digital calculation and calculating the sum.(digital beam forming). In FIG. 7, the reception beam 1 formation unit 2041 to reception beam M formation unit 204M are arranged on the output side of the antenna 1 radio reception unit 2031 to antenna N radio reception unit 203N, and form beams for digital signals of the baseband. A beam formation method in the radio band such as Butler matrix can also be adopted.
The reception beam 1 formation unit 2041 to reception beam M formation unit 204M form fixed reception beams different between the respective reception beam formation units 204 for input signals containing the components of all user signals (user 1 signal to user L signal) and the multipath components of the user signals, and demultiplex the input signals in respective arrival directions.
Each of the user 1 demodulation block 2051 to user L demodulation block 205L is formed from a reception beam 1 path detection unit 2061 to reception beam M path detection unit 206M, a path delay/reception beam selection unit 207, a transmission beam selection unit 209, and a demodulation unit 210.
The user 1 demodulation block 2051 to user L demodulation block 205L output user 1 reception data to user L reception data (user reception data) in correspondence with respective users. Since the user demodulation blocks 205 have the same function, the user 1 demodulation block 2051 will be exemplified.
The user 1 demodulation block 2051 receives outputs from the reception beam 1 formation unit 2041 to reception beam M formation unit 204M, and outputs a user 1 transmission beam number and user 1 reception data.
The reception beam 1 path detection unit 2061 to reception beam M path detection unit 206M receive outputs from the reception beam 1 formation unit 2041 to reception beam M formation unit 204M, detect the path delays of user signals in the input signals, measure the reception qualities of the user signals at the detected path delays, and output reception quality information to the path delay/reception beam selection unit 207. Input signals and the user 1 signal to user L signal are multiplexed, and the multipath components of the user signals by propagation delays are also multiplexed.
The reception beam 1 path detection unit 2061 to reception beam M path detection unit 206M can also detect paths and measure the reception qualities of user signals at the detected path delays by using only a known symbol (pilot symbol or the like) of the user signal.
The path delay/reception beam selection unit 207 receives pieces of reception quality information of user signals corresponding to path delays/reception beam numbers as outputs from the reception beam 1 path detection unit 2061 to reception beam M path detection unit 206M. The path delay/reception beam selection unit 207 selects a path delay/reception beam number pair used for demodulation on the basis of the reception quality of the user signal, and outputs reception quality information of a user signal corresponding to the selected path delay/reception beam number to the transmission beam selection unit 209 and demodulation unit 210.
The transmission beam selection unit 209 receives the reception quality information of the user signal corresponding to the path delay/reception beam number as an output from the path delay/reception beam selection unit 207, and outputs the number of a transmission beam in the same direction as that of a reception beam having the delay path excellent in reception quality to the user 1 transmission beam switching circuit 2121.
The number of selected transmission beams is generally smaller than the number of path delay/reception beam number pairs used for demodulation. In many cases, the number of transmission beams is 1 in order to reduce interference with another user by transmission of a plurality of beams.
The demodulation unit 210 receives the reception quality information of the user signal corresponding to the path delay/reception beam number as an output from the path delay/reception beam selection unit 207, performs a demodulation process on the basis of the input path delay/reception beam number, and outputs user 1 reception data.
The user 1 modulation unit 2111 to user L modulation unit 211L respectively receive user 1 transmission data to user L transmission data (user transmission data), perform a modulation process, and output the modulated signals to the user 1 transmission beam switching circuit 2121 to user L transmission beam switching circuit 212L.
The user 1 transmission beam switching circuit 2121 to user L transmission beam switching circuit 212L receive the user 1 transmission beam number to user L transmission beam number as outputs from the transmission beam selection units 209 for respective users, and the modulated user signals as outputs from the user 1 modulation unit 2111 to user L modulation unit 211L. The user 1 transmission beam switching circuit 2121 to user L transmission beam switching circuit 212L select transmission beam formation units corresponding to the transmission beam numbers for the users from the transmission beam 1 formation unit 2131 to transmission beam J formation unit 213J, and output the modulated user signals to the selected transmission beam formation units.
The transmission beam 1 formation unit 2131 to transmission beam J formation unit 213J receive outputs from the user 1 transmission beam switching circuit 2121 to user L transmission beam switching circuit 212L, form fixed transmission beams different between the transmission beam 1 formation unit 2131 and transmission beam J formation unit 213J for the input signals, and output the fixed transmission beams to the antenna 1 radio transmission unit 2141 to antenna K radio transmission unit 214K. The number of fixed transmission beams, the shape of the fixed transmission beam, and the fixed transmission beam formation method are not specifically limited. An example of the shape of the fixed transmission beam is a quadrature multi-beam, and an example of the fixed transmission beam formation method is a method of multiplying input signals by a fixed complex beam weight by digital calculation (digital beam forming). In FIG. 7, the transmission beam 1 formation unit 2131 to reception beam J formation unit 213J are arranged on the input side of the antenna 1 radio transmission unit 2141 to antenna K radio transmission unit 214K, and form beams for digital signals of the baseband. A beam formation method in the radio band such as Butler matrix can also be adopted.
Each of the antenna 1 radio transmission unit 2141 to antenna K radio transmission unit 214K comprises an amplifier, bandpass filter, mixer, local oscillator, quadrature modulation, low-pass filter, digital/analog converter, and the like. The antenna 1 radio transmission unit 2141 will be exemplified. The antenna 1 radio transmission unit 2141 receives outputs from the transmission beam 1 formation unit 2131 to transmission beam J formation unit 213J, performs reception processes such as digital/analog conversion of an input signal, quadrature modulation, frequency conversion from the baseband to the radio band, and amplification of a signal, and outputs the resultant signal to the transmission antenna element 2161.
The transmission array antenna 215 is formed from the K transmission antenna elements 2161 to 216K. Each of the transmission antenna elements 2161 to 216K is free from any limitation on the horizontal and vertical directivities, and has, for example, omnidirectivity or dipole. The K transmission antenna elements 2161 to 216K are arranged close to each other so as to correlate the transmission signals of the antenna elements with each other. The transmission array antenna 215 is not limited in the layout as far as the K reception antenna elements 2161 to 216K are arranged close to each other. An example of the layout is a circular layout or linear layout at the half-wavelength interval of the carrier.
The K transmission antenna elements 2161 to 216K receive and transmit signals in which user signals (user 1 signal to user L signal) by transmission beams as outputs from the antenna 1 radio transmission unit 2141 to antenna K radio transmission unit 214K are multiplexed.
The conventional multi-beam transmitter/receiver shown in FIG. 7 selects and receives a reception beam having a delay path excellent in reception quality from a plurality of fixed reception beams in reception. In transmission, the multi-beam transmitter/receiver selects and transmits a transmission beam in the same direction as that of a path delay/reception beam number pair excellent in reception quality from path delay/reception beam number pairs selected upon reception. With this process, the multi-beam transmitter/receiver can form a beam which increases the transmission/reception gain in a desired signal direction and decreases it in another direction.
A problem of the conventional multi-beam antenna transmitter/receiver as shown in FIG. 7 is deterioration of the transmission characteristic. This is because a transmission beam in the same direction as that of a path delay/reception beam number pair excellent in reception quality is selected from path delay/reception beam number pairs selected upon reception, and a transmission beam optimum in the multipath environment cannot be selected. In the multipath environment, the user signal component contains a plurality of multipath components. These signal components generally arrive from different directions, and each reception beam contains a plurality of multipath components.
The conventional multi-beam antenna transmitter/receiver selects a transmission beam in the same direction as that of a path delay/reception beam number pair excellent in reception quality from path delay/reception beam number pairs selected upon reception. When the overall reception qualities of reception beams are compared, a reception beam different from a selected reception beam may exhibit a higher overall reception quality. The overall reception quality is prepared by calculating (e.g., adding) some or all of the reception qualities of multipath components (path delays) contained in a reception beam. An optimum transmission beam is a transmission beam in a direction in which the transmission beam coincides with (is identical to) or is close to a reception beam excellent in overall reception quality. The conventional multi-beam antenna transmitter/receiver cannot select any transmission beam optimum in the multipath environment.
This will be expatiated with reference to numerical values, but the present invention is not limited to these values.
Assume that the path delay/reception beam selection unit 207 selects two upper pairs (pair a and pair b) from the following four path delay/reception beam number pairs.
Reception quality of pair a (path delay a/reception beam 1):10
Reception quality of pair b (path delay b/reception beam 2):8
Reception quality of pair c (path delay c/reception beam 2):5
Reception quality of pair d (path delay d/reception beam 1):1
At this time, if the transmission beam selection unit 209 selects one transmission beam, the conventional multi-beam antenna transmitter/receiver shown in FIG. 7 compares the reception qualities of pairs a and b (10>8), and selects a transmission beam in the same direction as reception beam 1. However, reception beam 2 has a higher overall reception quality obtained by calculating reception qualities for each reception beam (overall reception quality of reception beam 1=10+1< overall reception quality of reception beam 2=8+5). The conventional multi-beam antenna transmitter/receiver cannot select an actually optimum transmission beam.