US8532647B2 - Method and apparatus for determining downlink beamforming vectors in hierarchical cell communication system - Google Patents
Method and apparatus for determining downlink beamforming vectors in hierarchical cell communication system Download PDFInfo
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- US8532647B2 US8532647B2 US13/236,333 US201113236333A US8532647B2 US 8532647 B2 US8532647 B2 US 8532647B2 US 201113236333 A US201113236333 A US 201113236333A US 8532647 B2 US8532647 B2 US 8532647B2
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
- H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
- H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
- H04B7/0617—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal for beam forming
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
- H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
- H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
- H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
- H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
- H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
- H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
- H04B7/0621—Feedback content
- H04B7/0632—Channel quality parameters, e.g. channel quality indicator [CQI]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
- H04W16/24—Cell structures
- H04W16/32—Hierarchical cell structures
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W84/00—Network topologies
- H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
- H04W84/04—Large scale networks; Deep hierarchical networks
- H04W84/042—Public Land Mobile systems, e.g. cellular systems
- H04W84/045—Public Land Mobile systems, e.g. cellular systems using private Base Stations, e.g. femto Base Stations, home Node B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
- H04W88/08—Access point devices
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
- H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
- H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
- H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
- H04B7/0636—Feedback format
- H04B7/0639—Using selective indices, e.g. of a codebook, e.g. pre-distortion matrix index [PMI] or for beam selection
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
- H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
- H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
- H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
- H04B7/0658—Feedback reduction
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W28/00—Network traffic management; Network resource management
- H04W28/02—Traffic management, e.g. flow control or congestion control
- H04W28/04—Error control
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W48/00—Access restriction; Network selection; Access point selection
- H04W48/16—Discovering, processing access restriction or access information
Definitions
- the following description relates to a hierarchical cell communication system, and more particularly, to a method and apparatus for determining a downlink transmit beamforming vector and a downlink receive beamforming vector for wireless communication.
- a hierarchical cell environment indicates an environment in which small cells formed by small base stations within a macro cell are constructed as a self-organizing network form.
- Examples of a small cell include a relay cell, a femto cell, a pico cell, a cell by home node-B (HNB), a cell by home enhanced node-B (HeNB), a cell by remote radio head (RRH), and the like.
- the hierarchical cell environment enables the total system capacity to increase.
- a quality of service (QoS) for a user may deteriorate because of interference between a macro base station and a small base station. Accordingly, there is a desire to effectively manage interference between a macro cell and a small cell.
- a communication method of a macro base station including obtaining information associated with a first small effective channel formed between a first small terminal corresponding to a first small base station and a macro base station, obtaining information associated with a second small effective channel formed between a second small terminal corresponding to a second small base station and the macro base station, and determining a transmit beamforming vector of the macro base station based on information associated with the first small effective channel and information associated with the second small effective channel, wherein a receive beamforming vector of each of the at least one macro terminal is determined based on the transmit beamforming vector of the first small base station and the transmit beamforming vector of the second small base station.
- the determining may comprise determining the transmit beamforming vector of the macro base station based on information associated with the first small effective channel and information associated with the second small effective channel, such that interference from the macro base station is nulled in each of the first small terminal and the second small terminal.
- the communication method may further comprise receiving information associated with a first macro effective channel formed between a first macro terminal and the macro base station, and information associated with a second macro effective channel formed between a second macro terminal and the macro base station, wherein the first macro effective channel is associated with a receive beamforming vector of the first macro terminal and the second macro effective channel is associated with a receive beamforming vector of the second macro terminal, and the determining may comprise determining the transmit beamforming vector of the macro base station based on information associated with the first macro effective channel and information associated with the second macro effective channel, such that interference from the macro base station caused by a signal for the second macro terminal is nulled in the first macro terminal and such that interference from the macro base station caused by a signal for the first macro terminal is nulled in the second macro terminal.
- the communication method may further comprise obtaining information associated with an effective channel that is formed between a neighboring macro terminal corresponding to a neighboring macro base station and the macro base station, wherein the effective channel is associated with a receive beamforming vector of the neighboring macro terminal, and the determining may comprise determining the transmit beamforming vector of the macro base station based on information associated with the effective channel formed between the macro base station and the neighboring macro terminal, such that interference from the macro base station to the neighboring macro terminal is nulled in the neighboring macro terminal.
- the receive beamforming vector of each of the at least one macro terminal may be determined based on the transmit beamforming vector of the first small base station and the transmit beamforming vector of the second small base station, such that interference from the first small base station and the second small base station is nulled in each of the at least one macro terminal.
- the communication method may further comprise receiving information associated with channels formed between each of the first small base station and the second small base station and each of the at least one macro terminal, and transferring, to the first small base station and the second small base station, information associated with the channels formed between each of the first small base station and the second small base station and each of the at least one macro terminal.
- a communication method of a macro terminal corresponding to a macro base station including feeding back information associated with a first interference channel formed between a first small base station and the macro terminal, and a second interference channel formed between a second small base station and the macro terminal, determining a receive beamforming vector of the macro terminal based on a transmit beamforming vector of the first small base station and a transmit beamforming vector of the second small base station, calculating an effective channel formed between the macro base station and the macro terminal based on the receive beamforming vector of the macro terminal, and feeding back, to the macro base station, information associated with the effective channel formed between the macro base station and the macro terminal.
- the feeding back may comprise feeding back information in which information associated with the first interference channel and information associated with the second interference channel are combined.
- the feeding back may comprise feeding back, to the macro base station, information associated with the first interference channel and the second interference channel such that information associated with the first interference channel and the second interference channel are transferred to the first small base station and the second small base station.
- the communication method may further comprise receiving information associated with the transmit beamforming vector of the first small base station and information associated with the transmit beamforming vector of the second small base station, wherein the transmit beamforming vector of the first small base station and the transmit beamforming vector of the second small base station are determined such that interference from the first small base station and interference from the second small base station are aligned in the macro terminal.
- the determining may comprise determining the receive beamforming vector of the macro terminal such that interference from the first small base station is cancelled in the macro terminal based on the transmit beamforming vector of the first small base station and the first interference channel, and such that interference from the second small base station is cancelled in the macro terminal based on the transmit beamforming vector of the second small base station and the second interference channel.
- the determining may comprise determining the receive beamforming vector of the macro terminal to be orthogonal with respect to a direction of the interference from the first small base station and a direction of the interference from the second small base station.
- a macro base station including a receiver to obtain information associated with a first small effective channel formed between a first small terminal corresponding to a first small base station and a macro base station, and to obtain information associated with a second small effective channel formed between a second small terminal corresponding to a second small base station and the macro base station, and a transmit beamforming vector determining unit to determine a transmit beamforming vector of the macro base station based on information associated with the first small effective channel and information associated with the second small effective channel, wherein a receive beamforming vector of each of the at least one macro terminal is determined based on the transmit beamforming vector of the first small base station and the transmit beamforming vector of the second small base station.
- the transmit beamforming vector determining unit may be configured to determine the transmit beamforming vector of the macro base station based on information associated with the first small effective channel and information associated with the second small effective channel, such that interference from the macro base station is nulled in each of the first small terminal and the second small terminal.
- the receiver may be configured to receive information associated with a first macro effective channel formed between the first macro terminal and the macro base station, and information associated with a second macro effective channel formed between the second macro terminal and the macro base station, the first macro effective channel is associated with a receive beamforming vector of the first macro terminal and the second macro effective channel is associated with a receive beamforming vector of the second macro terminal, and the transmit beamforming vector determining unit may be configured to determine the transmit beamforming vector of the macro base station based on information associated with the first macro effective channel and information associated with the second macro effective channel, such that interference from the macro base station occurring due to a signal for the second macro terminal is nulled in the first macro terminal and such that interference from the macro base station occurring due to a signal for the first macro terminal is nulled in the second macro terminal.
- the receiver may be configured to obtain information associated with an effective channel formed between a neighboring macro terminal corresponding to a neighboring macro base station and the macro base station, and the effective channel is associated with a receive beamforming vector of the neighboring macro terminal
- the transmit beamforming vector determining unit may be configured to determine the transmit beamforming vector of the macro base station based on information associated with the effective channel formed between the macro base station and the neighboring macro terminal, such that interference from the macro base station to the neighboring macro terminal is nulled in the neighboring macro terminal.
- the receive beamforming vector of each of the at least one macro terminal may be determined based on the transmit beamforming vector of the first small base station and the transmit beamforming vector of the second small base station, such that interference from the first small base station and the second small base station is nulled in each of the at least one macro terminal.
- the receiver may be configured to receive information associated with channels formed between each of the first small base station and the second small base station and each of the at least one macro terminal
- the macro base station may further comprise a transfer unit to transfer, to the first small base station and the second small base station, information associated with the channels formed between each of the first small base station and the second small base station and each of the at least one macro terminal.
- a communication method of a targeted small terminal corresponding to a targeted small base station including obtaining information associated with an effective channel from a macro base station to the targeted small terminal based on a transmit beamforming vector of the macro base station, and information associated with a channel from a neighboring small base station to the targeted small terminal, determining a transmit beamforming vector of the neighboring small base station such that interference from the macro base station and interference from the neighboring small base station are aligned in the targeted small terminal, and determining a receive beamforming vector of the targeted small terminal such that interference from the macro base station is nulled in the targeted small terminal.
- the determining of the transmit beamforming vector of the neighboring small base station may comprise determining the transmit beamforming vector of the neighboring small base station based on the same codebook as a codebook used to generate the transmit beamforming vector of the macro base station, and the determining of the receive beamforming vector of the targeted small base station may comprise determining the receive beamforming vector of the targeted small terminal based on the same codebook as the codebook used to generate the transmit beamforming vector of the macro base station.
- FIG. 1 is a diagram illustrating an example of a hierarchical cell communication system.
- FIG. 2 is a diagram illustrating an example of a hierarchical cell communication system that performs a method of determining a transmit beamforming vector and a receive beamforming vector.
- FIG. 3 is a diagram illustrating an example of a hierarchical cell communication system in which at least two macro cells perform a method of determining a transmit beamforming vector and a receive beamforming vector.
- FIG. 4 is a flowchart illustrating an example of a communication method of a macro base station.
- FIG. 5 is a flowchart illustrating an example of a communication method of a macro terminal.
- FIG. 6 is a diagram illustrating an example of a macro base station.
- FIG. 7 is a diagram illustrating an example of a macro terminal.
- FIG. 8 is a diagram illustrating an example of a hierarchical cell communication system in which interference from pico base stations to a macro terminal is weak.
- FIG. 9 is a diagram illustrating an example of a signal transmission process of a hierarchical cell communication system in which interference from pico base stations to a macro terminal is weak.
- Various aspects relate to a method of generating transmit beamforming vectors and receive beamforming vectors that are capable of achieving a communication performance similar to a method of feeding backing full channel information.
- a relatively smaller amount of feedback information associated with a channel in a hierarchical cell communication environment is fed back.
- a small cell may include a relay cell, a femto cell, a pico cell, a cell by home node-B (HNB), a cell by home enhanced node-B (HeNB), a cell by remote radio head (RRH), and the like.
- HNB home node-B
- HeNB home enhanced node-B
- RRH remote radio head
- FIG. 1 illustrates an example of a hierarchical cell communication system.
- one or more small cells may be located within the coverage of a macro base station (i.e. within the coverage of a macro cell).
- a macro base station i.e. within the coverage of a macro cell.
- two small cells are within the macro cell.
- the macro cell may operate as a multi-user multiple-input multiple-output (MU-MIMO) communication system that simultaneously serves one or more macro terminals.
- the macro cell serves two macro terminals, a first macro terminal and a second macro terminal.
- the macro base station may have one or more antennas, for example, two antennas, four antennas, six antennas, eight antennas, or more antennas.
- the macro base station includes four antennas.
- the two small cells may operate as a single-user multiple-input multiple-output (SU-MIMO) communication system in which small base stations, for example, a first small base station and a second small base station serve single small terminals, for example, a first small terminal and a second small terminal, respectively.
- a small base station may have one or more antennas, for example, one antenna, two antennas, four antennas, for more.
- each of the first small base station and the second small base station may have two antennas. Because a small cell is generally manufactured with relatively smaller costs, a number of antennas installed in a small base station may be less than a number of antennas installed in a macro base station.
- each of the terminals for example, each of macro terminals and small terminals, have two antennas. Accordingly, each of the terminals may have a two-dimensional (2D) signal space. For example, each terminal may receive a single stream from a base station serving each respective terminal using a single signal space, and may align inter-cell interference and intra cell interference using another signal space. By doing so, each of the terminals may completely receive a single stream.
- 2D two-dimensional
- a signal transmitted from each base station for each terminal may be expressed by Equation 1.
- x i ⁇ square root over ( p i ) ⁇ v i s i [Equation 1]
- the first small terminal, the first macro terminal, the second macro terminal, and the second small terminal correspond to index 1, 2, 3, and 4, respectively.
- s i corresponds to a transmission stream
- p i corresponds to a transmit power of a data stream.
- a signal received by each terminal may be expressed as follows. Initially, a signal y 1 received by the first small terminal may be expressed by Equation 2.
- a signal y 2 received by the first macro terminal and a signal y 3 received by the second macro terminal may be expressed by Equation 3.
- a signal y 4 received by the second small terminal may be expressed by Equation 4.
- Equation 4 H ij corresponds to a channel matrix between a j th base station and an i th terminal, and n i corresponds to additive white Gaussian noise (AWGN) added to the i th terminal.
- AWGN additive white Gaussian noise
- each of the terminals may obtain an effective signal using a receive beamforming vector u i H of each of the terminals.
- a process of determining transmit beamforming vectors and receive beamforming vectors of a macro cell and small cells in a system model of FIG. 1 is further described herein.
- each small base station may receive information that is associated with interference channels from each small base station to each macro terminal.
- the first small base station may receive combined information that is associated with interference channels of macro terminals, instead of receiving information H 21 , H 23 , H 33 , and H 31 associated with all the interference channels from the small base stations to the macro terminals.
- the first small base station may receive (H 21 ) ⁇ 1 H 23 from the first macro terminal, and may receive (H 33 ) ⁇ 1 H 31 from the second macro terminal.
- the second small base station may receive (H 21 ) ⁇ 1 H 23 and (H 33 ) ⁇ 1 H 31 .
- the feedback information may be transferred from the macro terminals to the first small base station and the second base station via the macro base station.
- the first small base station and the second small base station may determine a transmit beamforming vector v 1 of the first small base station and a transmit beamforming vector v 2 of the second small base station such that interference from the first small base station and interference from the second small base station are aligned in each macro terminal.
- Equation 5 may be arranged to Equation 6.
- a transmit beamforming vector v 4 of the second small base station may be determined according to Equation 7.
- Equation 7 may be used to calculate an eigenvector of a 2 ⁇ 2 matrix. If the 2 ⁇ 2 matrix includes independent columns, two eigenvectors may exist.
- Equation 8 a transmit beamforming vector v 1 of the first small base station
- an eigenvector with relatively great gain in an aspect of a sum throughput may be determined as v 4 .
- any of two eigenvectors may be selected as v 4 .
- the terminals may determine receive beamforming vectors u 1 , u 2 , u 3 , and u 4 of the terminals based on interference that occurs due to transmit beamforming vector of the small base stations. Because the transmit beamforming vectors of the small base stations are already determined, each of the terminals may determine a receive beamforming vector u i H to cancel or otherwise reduce interference based on the transmit beamforming vectors of the small base stations and interference channel information.
- the first macro terminal may determine u 2 as (H 21 v 1 ) ⁇ that is in an orthogonal direction with respect to H 21 v 1 in which interference from the first small base station and interference from the second small base station are aligned.
- the second macro terminal may also determine u 3 using the same method.
- the first small terminal may determine u 1 as (H 13 v 4 ) ⁇ that is in an orthogonal direction with respect to H 13 v 4 that is a direction of interference from the second small base station.
- the second small terminal may also determine u 4 using the same method.
- MMSE minimum mean square error
- each of the terminals may calculate an effective channel from a macro base station to each terminal, based on a receive beamforming vector of each terminal.
- each of the terminals may feed back, to the macro base station, information that is associated with the effective channel.
- each terminal may feed back H i2 .
- H i2 corresponds to a 2 ⁇ 4 matrix.
- each terminal may feed back, to the macro base station, w i H H i2 information associated with an effective channel from the macro base station based on the receive beamforming vector of each terminal.
- H i2 corresponds to a 1 ⁇ 4 matrix. Accordingly, it is possible to significantly decrease a feedback overhead.
- the macro base station may determine transmit beamforming vectors v 2 and v 3 of the macro base station.
- the macro base station may determine the transmit beamforming vectors based on the receive beamforming vectors of each macro terminal. For example, the macro base station may determine the transmit beamforming vectors of the macro base station such that effective channels from the macro base station to each small terminal may be nulled in each macro terminal, and such that an effective channel from the macro base station to another macro terminal may be nulled in each macro terminal.
- the transmit beamforming vector of the macro base station may be determined based on an amount of noise instead of being determined such that the effective channels may be nulled.
- Equation 9 may be arranged to Equation 10.
- the macro base station may determine the transmit beamforming vectors of the macro base station using the method described with reference to FIG. 1 .
- a method of determining transmit beamforming vectors and receive beamforming vectors such that each terminal may receive each single stream is described.
- An example of an amount of channel information to be fed back with respect to a degree of freedom (DOF) is shown in Table 1.
- IA indicates interference aligning.
- a hierarchical interference alignment method may be classified into hierarchical IA 1 and hierarchical IA 2.
- hierarchical IA 1 corresponds to a method that does not feed back interference channel information from small base stations to macro base stations.
- Hierarchical IA 2 corresponds to a method that calculates an eigenvector of Equation 7 based on interference channel information from the small base stations to the macro base stations.
- Hierarchical IA 1 may achieve a performance that is proximate to a case in which full channel information is fed back based on a relatively small amount of feedback.
- FIG. 2 illustrates an example of a hierarchical cell communication system that performs a method of determining a transmit beamforming vector and a receive beamforming vector.
- a macro base station may service an outdoor terminal.
- a pico base station within a pico cell may service an indoor terminal.
- FIG. 3 illustrates an example of a hierarchical cell communication system in which at least two macro cells perform a method of determining a transmit beamforming vector and a receive beamforming vector.
- a method of determining a transmit beamforming vector and a receive beamforming vector may be applicable to a case in which at least two macro base stations are present.
- a macro base station may determine a transmit beamforming vector of the macro base station such that an effective channel from the macro base station to a neighboring outdoor terminal that is served by a neighboring macro base station is nulled.
- FIG. 4 illustrates an example of a communication method of a macro base station.
- the macro base station receives information associated with channels formed between each of a first small base station included in a first small cell and a second small base station included in a second small cell, and each of at least one macro terminals that are served by the macro base station.
- the macro base station transfers, to the first small base station and the second small base station, information that is associated with the channels that are formed between each of the first small base station and the second small base station and each of the at least one macro terminal, so that a transmit beamforming vector of the first small base station and a transmit beamforming vector of the second small base station may be determined.
- the macro base station obtains information associated with a first small effective channel formed between a first small terminal corresponding to a first small base station and a macro base station, and information associated with a second small effective channel formed between a second small terminal corresponding to a second small base station and a macro base station.
- the macro base station may obtain the information associated with the first small effective channel and the information associated with the second small effective channel, from the first small terminal and the second small terminal, respectively.
- each of the terminals may feed back, to the macro base station, information that is associated with the effective channel.”
- the macro base station may obtain the information from the small terminals via the small base stations, respectively.
- the small terminals transmit the information to the corresponding small base stations.
- the macro base station may obtain the information from the small terminals via the macro terminals.
- the small terminals transmit the information to the macro terminals.
- the first small effective channel may be associated with a receive beamforming vector of the first small terminal and the second small effective channel may be associated with a receive beamforming vector of the second small base station.
- the receive beamforming vector of each of the at least one macro terminal may be determined based on the transmit beamforming vector of the first small base station and the transmit beamforming vector of the second small base station.
- the macro base station determines a transmit beamforming vector of the macro base station based on information that is associated with the first small effective channel and information that is associated with the second small effective channel.
- the macro base station may determine the transmit beamforming vector such that interference from the macro base station may be nulled in each of the first small terminal and the second small terminal.
- the macro base station may determine the transmit beamforming vector of the macro base station based on the information associated with the first macro effective channel and information associated with the second macro effective channel such that interference from the macro base station that occurs due to a signal for the second macro terminal may be nulled in the first macro terminal and such that interference from the macro base station occurring due to a signal for the first macro terminal may be nulled in the second macro terminal.
- the macro base station may determine the transmit beamforming vector of the macro base station based on the information associated with the effective channel formed between the macro base station and the neighboring macro terminal such that interference from the macro base station to the neighboring macro terminal may be nulled in the neighboring macro terminal.
- FIG. 5 illustrates an example of a communication method of a macro terminal.
- the macro terminal feeds back information associated with a first interference channel that is formed between a first small base station and the macro terminal, and a second interference channel that is formed between a second small base station and the macro terminal.
- the macro terminal may feed back information in which information associated with the first interference channel and information associated with the second interference channel are combined.
- the feedback may be performed via the macro base station, or may be performed directly with respect to the first small base station and the second small base station.
- the macro terminal may receive information that is associated with the transmit beamforming vector of the first small base station and information associated with the transmit beamforming vector of the second small base station.
- the macro base station may transmit, to the macro terminal, the information that is associated with the transmit beamforming vector of the first small base station and information associated with the transmit beamforming vector of the second small base station.
- the small base stations transmit information associated with their transmit beamforming vector, respectively.
- the first small base station may transmit, to the macro terminal, the information that is associated with the transmit beamforming vector of the first small base station
- the second small base station may transmit, to the macro terminal, the information that is associated with the transmit beamforming vector of the second small base station.
- the macro terminal determines a receive beamforming vector of the macro terminal based on information that is associated with the transmit beamforming vector of the first small base station and information that is associated with the transmit beamforming vector of the second small base station. For example, the macro terminal may determine the receive beamforming vector of the macro terminal such that interference from the first small base station may be cancelled in the macro terminal based on the transmit beamforming vector of the first small base station and the first interference channel, and such that interference from the second small base station may be cancelled in the macro terminal based on the transmit beamforming vector of the second small base station and the second interference channel. In this example, the macro terminal may determine the receive beamforming vector of the macro terminal to be orthogonal with respect to a direction of the interference from the first small base station and a direction of the interference from the second small base station.
- the macro terminal calculates an effective channel formed between the macro base station and the macro terminal based on the receive beamforming vector of the macro terminal.
- the macro terminal feeds back, to the macro base station, information that is associated with the effective channel formed between the macro base station and the macro terminal before the transmit beamforming vector of the macro base station is determined.
- FIG. 6 illustrates an example of a macro base station.
- the macro base station includes a receiver 610 , a transfer unit 620 , a transmit beamforming vector determining unit 630 , and a precoder 640 .
- the receiver 610 may obtain information that is associated with a first small effective channel that is formed between a first small terminal corresponding to a first small base station and a macro base station, and information that is associated with a second small effective channel that is formed between a second small terminal corresponding to a second small base station and a macro base station.
- the first macro effective channel may be associated with a receive beamforming vector of the first macro terminal
- the second macro effective channel may be associated with a receive beamforming vector of the second macro terminal.
- the receiver 610 may receive information that is associated with channels that are formed between each of the first small base station and the second small base station, and each of the at least one macro terminal.
- the transfer unit 620 may transfer, to the first small base station and the second small base station, information that is associated with the channels that are formed between each of the first small base station and the second small base station and each of the at least one macro terminal.
- the first small base station and the second small base station may use the information to determine the transmit beamforming vector of the first small base station and the transmit beamforming vector of the second small base station, respectively.
- the transmit beamforming vector determining unit 630 may determine a transmit beamforming vector of the macro base station based on information that is associated with the first small effective channel and information that is associated with the second small effective channel.
- the precoder 640 may perform precoding using the transmit beamforming vector of the macro base station which is determined by the transmit beamforming vector determining unit 630 .
- FIG. 7 illustrates an example of a macro terminal.
- the macro terminal includes a receiver 710 , a channel estimator 720 , a feedback unit 730 , a receive beamforming vector determining unit 740 , and an effective channel calculator 750 .
- the receiver 710 may receive a pilot from a first small base station and a second small base station.
- the receiver 710 may receive a demodulation reference signal (DM-RS) based on a transmit beamforming vector of each of the first small base station and the second small base station.
- DM-RS demodulation reference signal
- the channel estimator 720 may estimate a channel from each of the first small base station, the second small base station, and a macro base station, to the macro terminal. That is, the channel estimator 720 may estimate a channel formed between the first small base station and the macro terminal, may estimate a channel formed between the second small base station and the macro terminal, and may estimate a channel formed between the macro base station and the macro terminal. The channel estimator 720 may estimate an effective channel from each of the first small base station, the second small base station, and the macro base station, to the macro terminal, based on the receive beamforming vector of the macro terminal. The channel estimator 720 may estimate the effective channel from each of the first small base station and the second small base station based on the transmit beamforming vector of each of the first small base station and the second small base station.
- the feedback unit 730 may feed back, to the macro base station, information that is associated with a first interference channel that is formed between the first small base station and the macro terminal, and a second interference channel formed between the second small base station and the macro terminal.
- the feedback unit 730 may feed back, to the macro base station, information that is associated with the effective channel formed between the macro base station and the macro terminal before the transmit beamforming vector of the macro base station is determined.
- the receive beamforming vector determining unit 740 may determine the receive beamforming vector of the macro terminal.
- the effective channel calculator 750 may calculate the effective channel that is formed between the macro base station and the macro terminal based on the receive beamforming vector of the macro terminal.
- a macro base station, a macro terminal, and a communication method of the macro base station and the macro terminal are described herein. Descriptions made herein with reference to FIG. 1 through FIG. 3 are applicable to the macro base station, the macro terminal, and the communication methods of the macro base station and the macro terminal that are described with reference to FIGS. 4 through 7 . Thus, further descriptions are omitted here.
- FIG. 8 illustrates an example of a hierarchical cell communication system in which interference from pico base stations to a macro terminal is weak.
- a first pico cell and a second pico cell are present within a macro cell.
- a first pico base station included in the first pico cell serves a first pico terminal.
- a second pico base station included in the second pico serves a second pico terminal.
- interference from the first pico base station and the second base station to the macro terminal may be weak.
- a method of determining a beamforming vector in the above hierarchical cell communication system is further described with reference to FIG. 9 .
- FIG. 9 illustrates an example of a signal transmission process of a hierarchical cell communication system in which interference from pico base stations to a macro terminal is weak.
- the macro terminal receives relatively small interference from a first pico base station and a second pico base station.
- the above assumption may be realized when cooperative scheduling is performed such that the same frequency resource as pico cells may be assigned to the macro terminal that receives a relatively small amount of interference from the pico cells.
- the macro terminal may not receive interference and thus, may operate like communication performed in a unit cell.
- a signal transmitted by each base station for each terminal may be expressed by Equation 11.
- x i ⁇ square root over ( p i ) ⁇ v i s i [Equation 11]
- a principle of symbols used for the description of FIG. 9 is similar to the symbols used for the description of FIG. 1 .
- a signal y 1 pico received by the first pico terminal, a signal y 2 macro received by the macro terminal, and a signal y 3 pico received by the second pico terminal may be expressed by Equation 12, Equation 13, and Equation 14, respectively.
- Each terminal may obtain an effective signal based on a receive beamforming vector u i H of each terminal.
- a macro base station may schedule the pico cells and a macro terminal that is not receiving interference from the pico cells among macro terminals.
- the macro terminal may measure a channel from the macro base station to the macro terminal, and may determine an optimal transmit beamforming vector v 2 and a receive beamforming vector u 2 in a unit cell aspect.
- the optimal transmit beamforming vector and the receive beamforming vector in a capacity aspect may be determined according to Equation 15.
- v 2 v 1 [ 22 ]
- u 2 u 1 [ 22 ] ⁇ ⁇ ⁇
- the macro terminal may feed back the transmit beamforming vector v 2 of the macro base station to the macro base station via an uplink channel.
- the macro terminal may feed back the transmit beamforming vector v 2 of the macro base station to the macro base station using a preferred matrix index (PMI) such as a method of using a unit cell codebook.
- PMI preferred matrix index
- the macro base station may transmit information that is associated with the transmit beamforming vector v 2 of the macro base station to a first pico terminal and a second pico terminal.
- the macro base station may transmit a v 2 precoded DM-RS to the first pico terminal and the second pico terminal, or may feed forward, to the first pico base station and the second pico base station via an X2 interface, information that is associated with v 2 and information that is associated with an interference channel from the macro base station to each of the first pico terminal and the second pico terminal.
- each of the first pico terminal and the second pico terminal may recognize a signal space in which effective interference from the macro base station is received.
- the first pico terminal may determine a transmit beamforming vector v 3 of the second pico base station and a receive beamforming vector u 1 of the first pico terminal that are capable of cancelling interference that is received at the first pico terminal, such that interference may be aligned in the corresponding signal space.
- the second pico terminal may also determine v 1 and u 3 using the same method.
- the pico terminal may determine a transmit beamforming vector v j of a neighboring pico base station and the receive beamforming vector u i of the pico terminal as shown in Equation 16.
- a zero-forcing scheme is used as an example to completely cancel interference. It should also be appreciated that a receive beamforming vector may be determined based on interference or noise.
- the first pico terminal may transmit the transmit beamforming vector of the second pico base station using an uplink resource of the first pico terminal.
- the second pico terminal may transmit the transmit beamforming vector of the first pico base station using an uplink resource of the second pico terminal.
- the first pico terminal and the second pico terminal may also directly transmit the transmit beamforming vector of the neighboring pico base station to the neighboring pico base station using an uplink coordinated multi-point (CoMP) scheme.
- CoMP coordinated multi-point
- the above method may satisfy an interference alignment condition at the pico terminal while the macro cell uses the optimal transmit beamforming vector and the receive beamforming vector. For example, if a mobility of the macro terminal is great, or if the macro cell does not use the optimal transmit beamforming vector and the receive beamforming vector, the transmit beamforming vector of the macro base station may be arbitrarily determined. Other beamforming vectors of all the base stations and terminals may be determined by repeating fourth through sixth operations. In this example, all the base stations and terminals may use the same codebook.
- a hierarchical IA technology may have a relatively high DOF gain compared to a time division multiple access (TDMA) and a combined form of the TDMA and a CoMP.
- TDMA time division multiple access
- CoMP channel state information at the transmitter
- the hierarchical IA technology may achieve the same DOF with a significantly small amount of channel information feedback.
- the terminal device described herein may refer to mobile devices such as a cellular phone, a personal digital assistant (PDA), a digital camera, a portable game console, an MP3 player, a portable/personal multimedia player (PMP), a handheld e-book, a portable lab-top personal computer (PC), a global positioning system (GPS) navigation, and devices such as a desktop PC, a high definition television (HDTV), an optical disc player, a setup box, and the like, capable of wireless communication or network communication consistent with that disclosed herein.
- mobile devices such as a cellular phone, a personal digital assistant (PDA), a digital camera, a portable game console, an MP3 player, a portable/personal multimedia player (PMP), a handheld e-book, a portable lab-top personal computer (PC), a global positioning system (GPS) navigation, and devices such as a desktop PC, a high definition television (HDTV), an optical disc player, a setup box, and the like, capable of wireless communication or network communication consistent with that disclosed herein
- a computing system or a computer may include a microprocessor that is electrically connected with a bus, a user interface, and a memory controller. It may further include a flash memory device. The flash memory device may store N-bit data via the memory controller. The N-bit data is processed or will be processed by the microprocessor and N may be 1 or an integer greater than 1. Where the computing system or computer is a mobile apparatus, a battery may be additionally provided to supply operation voltage of the computing system or computer.
- the computing system or computer may further include an application chipset, a camera image processor (CIS), a mobile Dynamic Random Access Memory (DRAM), and the like.
- the memory controller and the flash memory device may constitute a solid state drive/disk (SSD) that uses a non-volatile memory to store data.
- SSD solid state drive/disk
- the processes, functions, methods and/or software described herein may be recorded, stored, or fixed in one or more computer-readable storage media that includes program instructions to be implemented by a computer to cause a processor to execute or perform the program instructions.
- the media may also include, alone or in combination with the program instructions, data files, data structures, and the like.
- the media and program instructions may be those specially designed and constructed, or they may be of the kind well-known and available to those having skill in the computer software arts.
- Examples of computer-readable media include magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD ROM disks and DVDs; magneto-optical media such as optical disks; and hardware devices that are specially configured to store and perform program instructions, such as read-only memory (ROM), random access memory (RAM), flash memory, and the like.
- Examples of program instructions include both machine code, such as produced by a compiler, and files containing higher level code that may be executed by the computer using an interpreter.
- the described hardware devices may be configured to act as one or more software modules that are recorded, stored, or fixed in one or more computer-readable storage media, in order to perform the operations and methods described above, or vice versa.
- a computer-readable storage medium may be distributed among computer systems connected through a network and non-transitory computer-readable codes or program instructions may be stored and executed in a decentralized manner.
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Abstract
Description
x i=√{square root over (p i)}v i s i [Equation 1]
H 21 v 1 =αH 23 v 4
H 31 v 1 =βH 33 v 4 [Equation 5]
∴v 1=ρ(H 21)−1 H 23 v 4 [Equation 8]
v i=null([u 1 H H 12 u 4 H H 42 u j H H j2]) [Equation 9]
-
- null(A) is the vector in null space of A with unit norm
TABLE 1 | |||
Number of feedback | |||
DOF | information | ||
TDMA | 8/3 | (2 × 2): two | ||
(Existing) | (2 × 4): two | |||
|
4 | (2 × 2): two | ||
(Example) | (1 × 4): four | |||
|
4 | (2 × 2): four | ||
(Example) | (1 × 4): four | |||
IA | 4 | (2 × 2): eight | ||
(Existing) | (2 × 4): four | |||
x i=√{square root over (p i)}v i s i [Equation 11]
TABLE 2 | |||
number of feedback | |||
DOF | information | ||
TDMA(existing) | 2 | (2 × 2): three | ||
TDMA + CoMP | 2 | (2 × 2): three | ||
Hierarchical IA | 3 | (2 × 1): three | ||
(Max-SINR/ZF) | ||||
Iterative IS(existing) | 3 | (2 × 2): six | ||
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KR1020100094295A KR20120032777A (en) | 2010-09-29 | 2010-09-29 | Method and apparatus for determining downlink beamforming vectors in hierarchical cell communication system |
KR10-2010-0094295 | 2010-09-29 |
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