WO2016203311A1 - Method of implementing beam tracing in a millimeter wave communication-based communication system - Google Patents

Method of implementing beam tracing in a millimeter wave communication-based communication system Download PDF

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Publication number
WO2016203311A1
WO2016203311A1 PCT/IB2016/000955 IB2016000955W WO2016203311A1 WO 2016203311 A1 WO2016203311 A1 WO 2016203311A1 IB 2016000955 W IB2016000955 W IB 2016000955W WO 2016203311 A1 WO2016203311 A1 WO 2016203311A1
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Prior art keywords
channel capacity
precoding
amplitude vector
user equipment
precoding matrixes
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French (fr)
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Huan Sun
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Alcatel Lucent SAS
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Alcatel Lucent SAS
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Classifications

    • 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
    • H04B7/0413—MIMO systems
    • H04B7/0417—Feedback systems
    • 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
    • H04B7/0413—MIMO systems
    • H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
    • 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
    • H04B7/0413—MIMO systems
    • H04B7/0452—Multi-user MIMO systems
    • 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]
    • 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

Definitions

  • the present invention generally relates to mobile communication technology, and particularly to a method and an apparatus of implementing beam tracing in a millimeter wave communication-based communication system.
  • Millimeter Wave Communication has been regarded as one of the key technologies in the 5G wireless network, which is expected to support Gigabit level data transmission.
  • MMC Millimeter Wave Communication
  • Beam based transmission solution can significantly improve the channel quality and realize the high data rate transmission. But this transmission has some limitations:
  • the size of the code book is limited, and thus it is hard to realize the steering beam transmission by a single channel quality indicator (CQI) feedback.
  • CQI channel quality indicator
  • one beam tracing solution which is based on multiple CQI feedbacks, is proposed and it can be used to realize the steering beam transmission in MMC networks.
  • BT-MCQI beam based transmission-multiple CQI
  • multiple mobile user equipments can be supported with a high data rate in 5G MMC networks.
  • a method in a user equipment in a millimeter wave communication-based communication system, of assisting a base station to implement beam tracing, the method comprising: traversing all precoding matrixes to calculate a channel capacity for a beam; selecting n precoding matrixes from the precoding matrixes, wherein the channel capacity calculated by using the n precoding matrixes is the top n maximum channel capacity in all the calculated channel capacity; determining an amplitude vector, the amplitude vector consisting of n channel performance indicators corresponding to the top n maximum channel capacity respectively; and sending n precoding matrix indicators corresponding to the n precoding matrixes and the amplitude vector to the base station.
  • the amplitude vector is determined by the following equation:
  • ⁇ ⁇ is a quotient between a channel performance indicator corresponding to the n th maximum channel capacity and a channel performance indicator corresponding to the maximum channel capacity.
  • the channel performance indicator includes: signal to noise ratio, signal to interference plus noise ratio or signal to noise and distortion ratio.
  • n equals to 2 or 3.
  • the column number of the precoding matrix corresponds to the number of rank in the communication system.
  • a method in a base station in a millimeter wave communication-based communication system, of implementing beam tracing, the method comprising: a. receiving n precoding matrix indicators and an amplitude vector from a user equipment, wherein the amplitude vector consists of n channel performance indicators, which correspond to n channel capacity respectively, the n channel capacity is the top n maximum channel capacity in all the calculated channel capacity obtained by the user equipment after traversing all precoding matrixes in order to calculate a channel capacity for a beam; b. determining a first precoding matrix based on n precoding matrixes respectively corresponding to the n precoding matrix indicators and the amplitude vector; and c. sending data to the user equipment by using the first precoding matrix.
  • the amplitude vector is
  • ⁇ is a quotient between a channel performance indicator corresponding to the n th maximum channel capacity calculated by the user equipment and a channel performance indicator corresponding to the maximum channel capacity calculated by the user equipment, after the user equipment traverses all precoding matrixes in order to calculate a channel capacity for a beam.
  • step b further includes:
  • W (n) is the n th precoding matrix, and I is a unit matrix with rank m;
  • m corresponds to the number of the rank in the communication system.
  • an apparatus in a user equipment in a millimeter wave communication -based communication system, of assisting a base station to implement beam tracing, the apparatus comprising: calculating unit, for traversing all precoding matrixes to calculate a channel capacity for a beam; selecting unit, for selecting n precoding matrixes from the precoding matrixes, wherein the channel capacity calculated by using the n precoding matrixes is the top n maximum channel capacity in all the calculated channel capacity; determining unit, for determining an amplitude vector, the amplitude vector consisting of n channel performance indicators corresponding to the top n maximum channel capacity respectively; and sending unit, for sending n precoding matrix indicators corresponding to the n precoding matrixes and the amplitude vector to the base station.
  • an apparatus in a base station in a millimeter wave communication-based communication system, of implementing beam tracing, the apparatus comprising: receiving unit, for receiving n precoding matrix indicators and an amplitude vector from a user equipment, wherein the amplitude vector consists of n channel performance indicators, which correspond to n channel capacity respectively, the n channel capacity is the top n maximum channel capacity in all the calculated channel capacity obtained by the user equipment after traversing all precoding matrixes in order to calculate a channel capacity for a beam; determining unit, for determining a first precoding matrix based on n precoding matrixes respectively corresponding to n precoding matrix indicators and the amplitude vector; and sending unit, for sending data to the user equipment by using the first precoding matrix.
  • Figure 1 shows a beam gain illustration according to one embodiment of the present invention
  • Figure 2 shows an optimized steering beam according to one embodiment of the present invention
  • Figure 3 shows a flowchart of a method of implementing beam tracing according to one embodiment of the present invention
  • Figure 4 shows an apparatus diagram at a user equipment side for implementing beam tracing according to one embodiment of the present invention.
  • Figure 5 shows an apparatus diagram at a base station side for implementing beam tracing according to one embodiment of the present invention.
  • the basic idea of the present invention is in that: in BT-MCQI, a user equipment feeds back multiple CQIs to a base station simultaneously in one time slot, which include multiple PMIs (Precoding Matrix Indicator) and an amplitude vector, for example. Those parameters are utilized to optimize the transmit beam, such that the transmit beam can align/trace the user equipment accurately.
  • the proposed invention has the following features for example:
  • Optimized beam can better match the propagation channel to realize the steering beam transmission, and achieve higher performance gain.
  • Figure 1 shows a beam gain illustration according to one embodiment of the present invention.
  • a transmit beam group is used to over all the cell area.
  • k beams are designed to cover the whole cell area. Those k beams can change dynamically.
  • UE user equipment
  • the antenna gain of UE subject from the m-th beam is a m
  • the antenna gain of the n-th beam is a n .
  • a UE will feedback a PMI to the base station. Then, the base station will determine the MSC level to be used and etc. therefrom. However, if the UE moves from the m-th beam to the n-th beam, the achieved beam gain of the m-th beam is continuous decreasing. This will degrade the system performance. Even if the UE is not moving, it cannot get the greatest beam gain due to the limited code book size. Thus, in order to overcome those potential problems and improve the system performance, multiple CQIs would be designed to be feed back to the base station to optimize the transmit beam.
  • Figure 3 shows a flowchart of a method of implementing beam tracing according to one embodiment of the present invention.
  • a UE traverses all precoding matrixes to calculate a channel capacity for a beam.
  • the UE will use all the precoding matrixes in the code book to calculate a channel capacity for beam i.
  • the channel capacity can be calculated by using equation 1 :
  • matrix H z is the channel matrix
  • matrix I is a unit matrix
  • W is the precoding matrix
  • step S302 the UE selects n precoding matrixes from all the precoding matrixes, wherein the channel capacity calculated by using the n precoding matrixes is the top n maximum channel capacity in all the calculated channel capacity.
  • n is an integer greater than 1.
  • n 2 or
  • the column number of the used precoding matrix corresponds to the number of rank in the communication system. For example, when rank is 1, that is, when one stream is transmitted, one column is selected as a precoding matrix. When rank is 2, that is, when two streams are transmitted, a group of two columns is selected as a precoding matrix.
  • the UE determines the precoding matrixes W (1) and W (2) , which are associated with the m-th beam and the n-th beam in Fig.l , respectively.
  • the channel capacity c (1) and c (2) are the channel capacity of the m-th beam and the channel capacity of the n-th beam respectively.
  • step S303 the UE determines an amplitude vector.
  • This amplitude vector is used to provide the power indication for the base station, such that the base station can determine the direction divergence of the UE, whether the UE diverges to the m-th beam or diverges to the n-th beam, for example.
  • the UE will derive the corresponding n channel performance indicators from the top n maximum channel capacity obtained in the last step, and construct the amplitude vector with those n channel performance indicators.
  • the channel performance indicator includes: signal to noise ratio, signal to interference plus noise ratio or signal to noise and distortion ratio.
  • the amplitude vector is determined by equation 2:
  • ⁇ [l, ...., ⁇ ⁇ ] ( 2 ) wherein ⁇ is a quotient between a channel performance indicator corresponding to the n th maximum channel capacity and a channel performance indicator corresponding to the maximum channel capacity.
  • x is the quotient between a channel performance indicator corresponding to the 2 maximum channel capacity and a channel performance indicator corresponding to the maximum channel capacity.
  • c (1) and c (2) in the equation are the maximum channel capacity and the 2 nd maximum channel capacity determined above.
  • the amplitude vector can be determined by other ways.
  • step S304 the UE sends n PMIs corresponding to the n precoding matrixes and the amplitude vector to the base station.
  • n equals to 2
  • ⁇ can be sent instead of sending the amplitude vector.
  • step S305 the base station determines a first precoding matrix based on n precoding matrixes respectively corresponding to n PMIs and the amplitude vector. That is, in this step, the base station will determine a new precoding matrix.
  • W (1) to W (n) correspond to a I s procoding matrix to a n precoding matrix, respectively.
  • W (n) is a n precoding matrix
  • the n precoding matrixes in equation 5 form a new matrix
  • I is a unit matrix with rank m.
  • ⁇ _ ⁇ ⁇ I when rank is 1 , ⁇ _ ⁇ ⁇ I will be a value. When rank is 2, ⁇ _ ⁇ ⁇ I will be a matrix with 2x2.
  • the first m vertical vectors are extracted from the matrix V as the first precoding matrix, wherein m corresponds to the number of rank in the communication system. For example, when rank is 1, that is, when one stream is transmitted, the first vertical vector is selected as the first precoding matrix. When rank is 2, that is, when two streams are transmitted, the first two vertical vectors are selected as the first precoding matrix.
  • equation 5 is transformed as:
  • primary vectors can be extracted by channel singular value decomposition still according to equation 6.
  • a first vector group is extracted from the matrix V . Since the number of the column depends on the number of rank in the communication system, the first column vector would be thereby extracted.
  • This step achieves the optimization for the transmit beam, as shown in Fig.2.
  • a new beam would be generated, as shown in the oblique line area.
  • step S306 the base station sends data to the UE by using the first precoding matrix.
  • the optimized beam can be steered to the UE better, and the channel quality and system performance is enhanced.
  • Figure 4 shows an apparatus diagram at a user equipment side for implementing beam tracing according to one embodiment of the present invention.
  • the apparatus 40 includes a calculating unit 401, a selecting unit 402, a determining unit 403 and a sending unit 404.
  • the calculating unit 401 is configured for traversing all precoding matrixes to calculate a channel capacity for a beam.
  • the selecting unit 402 is configured for selecting n precoding matrixes from the precoding matrixes, wherein the channel capacity calculated by using the n precoding matrixes is the top n maximum channel capacity in all the calculated channel capacity.
  • the determining unit 403 is configured for determining an amplitude vector, the amplitude vector consisting of n channel performance indicators corresponding to the top n maximum channel capacity respectively.
  • the sending unit 404 is configured for sending n precoding matrix indicators corresponding to the n precoding matrixes and the amplitude vector to the base station.
  • Figure 5 shows an apparatus diagram at a base station side for implementing beam tracing according to one embodiment of the present invention.
  • the apparatus 50 includes a receiving unit 501, a determining unit 502 and a sending unit 503.
  • the receiving unit 501 is configured for receiving n precoding matrix indicators and an amplitude vector from a user equipment, wherein the amplitude vector consists of n channel performance indicators, which correspond to n channel capacity respectively, the n channel capacity is the top n maximum channel capacity in all the calculated channel capacity obtained by the user equipment after traversing all precoding matrixes in order to calculate a channel capacity for a beam.
  • the determining unit 502 is configured for determining a first precoding matrix based on n precoding matrixes respectively corresponding to n precoding matrix indicators and the amplitude vector.
  • the sending unit 503 is configured for sending data to the user equipment by using the first precoding matrix.
  • the smoothly beam tracing indicates that the stable beam gain can be achieved and a more stable transmission rate is ensured, and the user experience is enhanced.
  • This solution according to the present invention can also be applied for the channel measurement based on pre-coded CSR-RS.
  • the PMIs and the amplitude vector are feedback to the base station for beam optimization.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Mathematical Physics (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

The present invention provides a method and an apparatus of implementing beam tracing in a millimeter wave communication-based communication system. According an embodiment of the present invention, the method comprises: traversing ail precoding matrixes to calculate a channel capacity for a beam; selecting n precoding matrixes from the precoding matrixes, wherein the channel capacity calculated by using the n precoding matrixes is the top n maximum channel capacity in ail the calculated channel capacity; determining an amplitude vector, the amplitude vector consists of n channel performance indicators corresponding to the top n maximum channel capacity respectively; and sending n precoding matrix indicators corresponding to the n precoding matrixes and the amplitude vector to the base station. Through the present invention, multiple mobile user equipments can be supported with a high data rate in 5 G MMC networks.

Description

Method of Implementing Beam Tracing in a Millimeter Wave
Communication-based Communication System
Field of the invention
The present invention generally relates to mobile communication technology, and particularly to a method and an apparatus of implementing beam tracing in a millimeter wave communication-based communication system.
Background of the invention
Millimeter Wave Communication (MMC) has been regarded as one of the key technologies in the 5G wireless network, which is expected to support Gigabit level data transmission. However, there is a big challenge in the propagation channel quality of millimeter wave due to the severe propagation loss. Fortunately, a compact antennal array can be well utilized in the MMC as the wave length is shorter than that in 4G networks.
Beam based transmission solution can significantly improve the channel quality and realize the high data rate transmission. But this transmission has some limitations:
1. This is more suitable for quasi-static transmission scenario. For a high mobility user, the performance will be degraded due to that the user may move out the coverage of the transmission beam.
2. The size of the code book is limited, and thus it is hard to realize the steering beam transmission by a single channel quality indicator (CQI) feedback.
Thus, it is necessary to design one fast beam-tracing solution to guarantee the beam-based high date transmission in 5G MMC networks. Summary of the invention
In view of the above technical problem, one beam tracing solution, which is based on multiple CQI feedbacks, is proposed and it can be used to realize the steering beam transmission in MMC networks. Herein, it is referred as BT-MCQI (beam based transmission-multiple CQI). Through the present invention, multiple mobile user equipments can be supported with a high data rate in 5G MMC networks.
According to a first aspect of the present invention, it is provided a method, in a user equipment in a millimeter wave communication-based communication system, of assisting a base station to implement beam tracing, the method comprising: traversing all precoding matrixes to calculate a channel capacity for a beam; selecting n precoding matrixes from the precoding matrixes, wherein the channel capacity calculated by using the n precoding matrixes is the top n maximum channel capacity in all the calculated channel capacity; determining an amplitude vector, the amplitude vector consisting of n channel performance indicators corresponding to the top n maximum channel capacity respectively; and sending n precoding matrix indicators corresponding to the n precoding matrixes and the amplitude vector to the base station.
Advantageously, the amplitude vector is determined by the following equation:
Figure imgf000003_0001
wherein αη is a quotient between a channel performance indicator corresponding to the nth maximum channel capacity and a channel performance indicator corresponding to the maximum channel capacity.
Advantageously, the channel performance indicator includes: signal to noise ratio, signal to interference plus noise ratio or signal to noise and distortion ratio. Advantageously, n equals to 2 or 3.
Advantageously, the column number of the precoding matrix corresponds to the number of rank in the communication system.
According to a second aspect of the present invention, it is provided a method, in a base station in a millimeter wave communication-based communication system, of implementing beam tracing, the method comprising: a. receiving n precoding matrix indicators and an amplitude vector from a user equipment, wherein the amplitude vector consists of n channel performance indicators, which correspond to n channel capacity respectively, the n channel capacity is the top n maximum channel capacity in all the calculated channel capacity obtained by the user equipment after traversing all precoding matrixes in order to calculate a channel capacity for a beam; b. determining a first precoding matrix based on n precoding matrixes respectively corresponding to the n precoding matrix indicators and the amplitude vector; and c. sending data to the user equipment by using the first precoding matrix.
Advantageously, the amplitude vector is
Figure imgf000004_0001
wherein ηΛ is a quotient between a channel performance indicator corresponding to the nth maximum channel capacity calculated by the user equipment and a channel performance indicator corresponding to the maximum channel capacity calculated by the user equipment, after the user equipment traverses all precoding matrixes in order to calculate a channel capacity for a beam.
Advantageously, the step b further includes:
bl . determining matrix H by the following equation:
Figure imgf000004_0002
■J wherein W(n) is the nth precoding matrix, and I is a unit matrix with rank m;
b2. decomposing the matrix H by singular value decomposition:
H = VA\H ; and
b3. extracting the first m vertical vectors from the matrix V as the first precoding matrix;
wherein m corresponds to the number of the rank in the communication system.
According to a third aspect of the present invention, it is provided an apparatus, in a user equipment in a millimeter wave communication -based communication system, of assisting a base station to implement beam tracing, the apparatus comprising: calculating unit, for traversing all precoding matrixes to calculate a channel capacity for a beam; selecting unit, for selecting n precoding matrixes from the precoding matrixes, wherein the channel capacity calculated by using the n precoding matrixes is the top n maximum channel capacity in all the calculated channel capacity; determining unit, for determining an amplitude vector, the amplitude vector consisting of n channel performance indicators corresponding to the top n maximum channel capacity respectively; and sending unit, for sending n precoding matrix indicators corresponding to the n precoding matrixes and the amplitude vector to the base station.
According to a fourth aspect of the present invention, it is provided an apparatus, in a base station in a millimeter wave communication-based communication system, of implementing beam tracing, the apparatus comprising: receiving unit, for receiving n precoding matrix indicators and an amplitude vector from a user equipment, wherein the amplitude vector consists of n channel performance indicators, which correspond to n channel capacity respectively, the n channel capacity is the top n maximum channel capacity in all the calculated channel capacity obtained by the user equipment after traversing all precoding matrixes in order to calculate a channel capacity for a beam; determining unit, for determining a first precoding matrix based on n precoding matrixes respectively corresponding to n precoding matrix indicators and the amplitude vector; and sending unit, for sending data to the user equipment by using the first precoding matrix.
Brief description of drawings
Other features, objects and advantages of the invention will become more apparent upon review of the following detailed description of non-limiting embodiments taken with reference to the drawings in which:
Figure 1 shows a beam gain illustration according to one embodiment of the present invention;
Figure 2 shows an optimized steering beam according to one embodiment of the present invention;
Figure 3 shows a flowchart of a method of implementing beam tracing according to one embodiment of the present invention;
Figure 4 shows an apparatus diagram at a user equipment side for implementing beam tracing according to one embodiment of the present invention; and
Figure 5 shows an apparatus diagram at a base station side for implementing beam tracing according to one embodiment of the present invention.
In the drawings, identical or like reference numerals denote identical or corresponding components or features throughout the different figures.
Detailed description of embodiments
The basic idea of the present invention is in that: in BT-MCQI, a user equipment feeds back multiple CQIs to a base station simultaneously in one time slot, which include multiple PMIs (Precoding Matrix Indicator) and an amplitude vector, for example. Those parameters are utilized to optimize the transmit beam, such that the transmit beam can align/trace the user equipment accurately. The proposed invention has the following features for example:
1. Optimized beam can better match the propagation channel to realize the steering beam transmission, and achieve higher performance gain.
2. Realizing a more smoothly beam tracing and offering stable user specific services, such as offering data transmission with a stable rate for the specified user equipment.
3. Relaxing the requirement of the feedback period, and reducing the system overhead.
In the following, the embodiments of BT-MCQI will be described in detail with reference to scenario Figs. 1 and 2 in combination with the method flowchart in Fig.3.
Figure 1 shows a beam gain illustration according to one embodiment of the present invention. As shown in Fig.l , to improve the channel quality, a transmit beam group is used to over all the cell area. For example, in Fig. l , k beams are designed to cover the whole cell area. Those k beams can change dynamically. In Fig.l , there is one user equipment (UE) associated with the m-th beam. The antenna gain of UE subject from the m-th beam is am, and the antenna gain of the n-th beam is an.
In a traditional system, a UE will feedback a PMI to the base station. Then, the base station will determine the MSC level to be used and etc. therefrom. However, if the UE moves from the m-th beam to the n-th beam, the achieved beam gain of the m-th beam is continuous decreasing. This will degrade the system performance. Even if the UE is not moving, it cannot get the greatest beam gain due to the limited code book size. Thus, in order to overcome those potential problems and improve the system performance, multiple CQIs would be designed to be feed back to the base station to optimize the transmit beam.
Figure 3 shows a flowchart of a method of implementing beam tracing according to one embodiment of the present invention.
As shown in step S301 in Fig.3, a UE traverses all precoding matrixes to calculate a channel capacity for a beam. Herein, the UE will use all the precoding matrixes in the code book to calculate a channel capacity for beam i.
For exemplary illustration, in an embodiment of the present invention, the channel capacity can be calculated by using equation 1 :
Figure imgf000008_0001
w ere n s t e num er o t e su carr ers n t s eam, matrix Hz is the channel matrix, matrix I is a unit matrix, and W; is the precoding matrix.
In step S302, the UE selects n precoding matrixes from all the precoding matrixes, wherein the channel capacity calculated by using the n precoding matrixes is the top n maximum channel capacity in all the calculated channel capacity. Herein, n is an integer greater than 1.
In an advantageous embodiment of the present invention, n is 2 or
3.
Herein, the column number of the used precoding matrix corresponds to the number of rank in the communication system. For example, when rank is 1, that is, when one stream is transmitted, one column is selected as a precoding matrix. When rank is 2, that is, when two streams are transmitted, a group of two columns is selected as a precoding matrix.
In this step, based on the criterion of maximum channel capacity, multiple precoding matrixes are selected according to the descend order of the achievable channel capacity. Herein, the illustration would be given for the exemplary situation, where a transmit beam is optimized based on two CQIs feedback (i.e. n equals 2). Thus, two precoding matrixes W(1) and W(2) , which can achieve the greatest channel capacity c (1) and the second greatest channel capacity c (2) respectively, are selected. In fact, in this step, the UE determines the precoding matrixes W(1) and W(2) , which are associated with the m-th beam and the n-th beam in Fig.l , respectively. The channel capacity c (1) and c (2) are the channel capacity of the m-th beam and the channel capacity of the n-th beam respectively.
In step S303, the UE determines an amplitude vector. This amplitude vector is used to provide the power indication for the base station, such that the base station can determine the direction divergence of the UE, whether the UE diverges to the m-th beam or diverges to the n-th beam, for example.
In this step, the UE will derive the corresponding n channel performance indicators from the top n maximum channel capacity obtained in the last step, and construct the amplitude vector with those n channel performance indicators.
Herein, the channel performance indicator includes: signal to noise ratio, signal to interference plus noise ratio or signal to noise and distortion ratio.
Advantageously, the amplitude vector is determined by equation 2:
a = [l, ....,αηΛ] ( 2 ) wherein ηΛ is a quotient between a channel performance indicator corresponding to the nth maximum channel capacity and a channel performance indicator corresponding to the maximum channel capacity.
The following detail illus ld still be based on n equals 2:
Figure imgf000009_0001
x is the quotient between a channel performance indicator corresponding to the 2 maximum channel capacity and a channel performance indicator corresponding to the maximum channel capacity.
When the channel performance indicator is the signal to noise ratio, γ can be de a =
Figure imgf000010_0001
c(1) and c (2) in the equation are the maximum channel capacity and the 2nd maximum channel capacity determined above.
It is appreciated for those skilled in the art that the above embodiment is only exemplary. In a different criterion, the amplitude vector can be determined by other ways.
In step S304, the UE sends n PMIs corresponding to the n precoding matrixes and the amplitude vector to the base station. When n equals to 2, γ can be sent instead of sending the amplitude vector.
In step S305, the base station determines a first precoding matrix based on n precoding matrixes respectively corresponding to n PMIs and the amplitude vector. That is, in this step, the base station will determine a new precoding matrix.
This can be determined by using a general function shown in equation 4 for example:
W = MWC(w(1)....W(„),a1 αηΛ ) (4)
W(1) to W(n) correspond to a I s procoding matrix to a n precoding matrix, respectively.
Similarly, when n equals to 2, the following general function can be used:
Figure imgf000010_0002
The following will give an example for the above general function. It should be appreciated for those skilled in the art that the following embodiment is only exemplary, but not limited.
Firstly, the matrix H is determined by using equation 5:
Figure imgf000011_0001
wherein, as described above, W(n) is a n precoding matrix, and the n precoding matrixes in equation 5 form a new matrix, I is a unit matrix with rank m.
For example, when rank is 1 , η_γ■ I will be a value. When rank is 2, η_γ■ I will be a matrix with 2x2.
Then, the matrix H is decomposed by singular value decomposition:
H = UAVfl (6)
Then, the first m vertical vectors are extracted from the matrix V as the first precoding matrix, wherein m corresponds to the number of rank in the communication system. For example, when rank is 1, that is, when one stream is transmitted, the first vertical vector is selected as the first precoding matrix. When rank is 2, that is, when two streams are transmitted, the first two vertical vectors are selected as the first precoding matrix.
The following illustration is based on n equals 2 and rank is 1, for example. In this situation, equation 5 is transformed as:
Figure imgf000011_0002
Then, primary vectors can be extracted by channel singular value decomposition still according to equation 6. Similarly, a first vector group is extracted from the matrix V . Since the number of the column depends on the number of rank in the communication system, the first column vector would be thereby extracted.
This step achieves the optimization for the transmit beam, as shown in Fig.2. By using this new precoding matrix, a new beam would be generated, as shown in the oblique line area.
When n=2, this means that a new beam is derived according to the m-th beam and the n-th beam.
In step S306, the base station sends data to the UE by using the first precoding matrix. As shown in Figs.l and 2, it is clearly shown that the optimized beam can be steered to the UE better, and the channel quality and system performance is enhanced.
Figure 4 shows an apparatus diagram at a user equipment side for implementing beam tracing according to one embodiment of the present invention.
As shown in Fig. 4, the apparatus 40 includes a calculating unit 401, a selecting unit 402, a determining unit 403 and a sending unit 404.
The calculating unit 401 is configured for traversing all precoding matrixes to calculate a channel capacity for a beam.
The selecting unit 402 is configured for selecting n precoding matrixes from the precoding matrixes, wherein the channel capacity calculated by using the n precoding matrixes is the top n maximum channel capacity in all the calculated channel capacity.
The determining unit 403 is configured for determining an amplitude vector, the amplitude vector consisting of n channel performance indicators corresponding to the top n maximum channel capacity respectively.
The sending unit 404 is configured for sending n precoding matrix indicators corresponding to the n precoding matrixes and the amplitude vector to the base station.
Figure 5 shows an apparatus diagram at a base station side for implementing beam tracing according to one embodiment of the present invention.
As shown in Fig. 5, the apparatus 50 includes a receiving unit 501, a determining unit 502 and a sending unit 503.
The receiving unit 501 is configured for receiving n precoding matrix indicators and an amplitude vector from a user equipment, wherein the amplitude vector consists of n channel performance indicators, which correspond to n channel capacity respectively, the n channel capacity is the top n maximum channel capacity in all the calculated channel capacity obtained by the user equipment after traversing all precoding matrixes in order to calculate a channel capacity for a beam.
The determining unit 502 is configured for determining a first precoding matrix based on n precoding matrixes respectively corresponding to n precoding matrix indicators and the amplitude vector.
The sending unit 503 is configured for sending data to the user equipment by using the first precoding matrix.
From the above analysis, the smoothly beam tracing is realized instead of the previous discrete beam tracing based on codebook in the prior art. Thereby, a more accurate steering beam can be implemented for data transmission.
1. Due to the optimized beam aligns its bore sight direction to user as more possible, this ensures the user locates in the center area of the beam coverage and needs more time (T0) to move out the beam coverage. Given the speed, the larger value of T0, the longer period of CQI feedback can be accepted. This means the system overhead can be significantly reduced.
2. The smoothly beam tracing indicates that the stable beam gain can be achieved and a more stable transmission rate is ensured, and the user experience is enhanced.
This solution according to the present invention can also be applied for the channel measurement based on pre-coded CSR-RS. The PMIs and the amplitude vector are feedback to the base station for beam optimization.
It shall be appreciated that the foregoing embodiments are merely illustrative but will not limit the invention. Any technical solutions without departing from the spirit of the invention shall fall into the scope of invention, including that different technical features, methods appearing in different embodiments are used to combine to advantage. Further, any reference numerals in the claims cannot be recognized as limiting the related claims; the term "comprise" will not preclude another apparatus or step which does not appear in other claims or the description.

Claims

1. A method, in a user equipment in a millimeter wave communication-based communication system, of assisting a base station to implement beam tracing, the method comprising:
traversing all precoding matrixes to calculate a channel capacity for a beam;
selecting n precoding matrixes from the precoding matrixes, wherein the channel capacity calculated by using the n precoding matrixes is the top n maximum channel capacity in all the calculated channel capacity;
determining an amplitude vector, the amplitude vector consisting of n channel performance indicators corresponding to the top n maximum channel capacity respectively; and
sending n precoding matrix indicators corresponding to the n precoding matrixes and the amplitude vector to the base station.
2. The method according claim 1 , wherein the amplitude vector is determined by the following equation:
a = [l, <¾, ...., «„.! ] ;
wherein η is a quotient between a channel performance indicator corresponding to the nth maximum channel capacity and a channel performance indicator corresponding to the maximum channel capacity.
3. The method according to claim 1 or 2, wherein the channel performance indicator includes: signal to noise ratio, signal to interference plus noise ratio or signal to noise and distortion ratio.
4. The method according to claim 1, wherein n equals to 2 or 3.
5. The method according to claim 1 , wherein the column number of the precoding matrix corresponds to the number of rank in the communication system.
6. A method, in a base station in a millimeter wave communication-based communication system, of implementing beam tracing, the method comprising: a. receiving n precoding matrix indicators and an amplitude vector from a user equipment, wherein the amplitude vector consists of n channel performance indicators, which correspond to n channel capacity respectively, the n channel capacity is the top n maximum channel capacity in all the calculated channel capacity obtained by the user equipment after traversing all precoding matrixes in order to calculate a channel capacity for a beam; b. determining a first precoding matrix based on n precoding matrixes respectively corresponding to the n precoding matrix indicators and the amplitude vector; and
c. sending data to the user equipment by using the first precoding matrix.
7. The method according to claim 6, wherein the amplitude vector is
a = [l, <¾, ...., «„.! ] ;
wherein η is a quotient between a channel performance indicator corresponding to the nth maximum channel capacity calculated by the user equipment and a channel performance indicator corresponding to the maximum channel capacity calculated by the user equipment, after the user equipment traverses all precoding matrixes in order to calculate a channel capacity for a beam.
8. The method according to claim 7, wherein the step b further includes:
bl . determining matrix H by the following equation:
Figure imgf000016_0001
wherein W(n) is the nth precoding matrix, and I is a unit matrix with rank m;
b2. decomposing the matrix H by singular value decomposition:
H = UAVfl ; and b3. extracting the first m vertical vectors from the matrix V as the first precoding matrix;
wherein m corresponds to the number of the rank in the communication system.
9. The method according to claim 7, wherein the channel performance indicator includes: signal to noise ratio, signal to interference plus noise ratio or signal to noise and distortion ratio.
10. The method according to claim 6, wherein n equals to 2 or 3.
11. An apparatus, in a user equipment in a millimeter wave communication-based communication system, of assisting a base station to implement beam tracing, the apparatus comprising:
calculating unit, for traversing all precoding matrixes to calculate a channel capacity for a beam;
selecting unit, for selecting n precoding matrixes from the precoding matrixes, wherein the channel capacity calculated by using the n precoding matrixes is the top n maximum channel capacity in all the calculated channel capacity;
determining unit, for determining an amplitude vector, the amplitude vector consisting of n channel performance indicators corresponding to the top n maximum channel capacity respectively; and
sending unit, for sending n precoding matrix indicators corresponding to the n precoding matrixes and the amplitude vector to the base station.
12. An apparatus, in a base station in a millimeter wave communication-based communication system, of implementing beam tracing, the apparatus comprising:
receiving unit, for receiving n precoding matrix indicators and an amplitude vector from a user equipment, wherein the amplitude vector consists of n channel performance indicators, which correspond to n channel capacity respectively, the n channel capacity is the top n maximum channel capacity in all the calculated channel capacity obtained by the user equipment after traversing all precoding matrixes in order to calculate a channel capacity for a beam;
determining unit, for determining a first precoding matrix based on n precoding matrixes respectively corresponding to n precoding matrix indicators and the amplitude vector; and
sending unit, for sending data to the user equipment by using the first precoding matrix.
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