CN110011707B - Multi-base station coordination system and channel correction method thereof - Google Patents

Multi-base station coordination system and channel correction method thereof Download PDF

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CN110011707B
CN110011707B CN201811555256.3A CN201811555256A CN110011707B CN 110011707 B CN110011707 B CN 110011707B CN 201811555256 A CN201811555256 A CN 201811555256A CN 110011707 B CN110011707 B CN 110011707B
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base station
uplink
channel
channel information
downlink
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CN110011707A (en
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蒋坤霖
陈家铭
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Sercomm Corp
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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
    • H04B7/0408—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas using two or more beams, i.e. beam diversity
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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Abstract

The invention provides a multi-base station coordination system and a channel correction method thereof. The system includes a reference device, a base station and a server. The reference device receives the beam-coded downlink reference signal from the base station via the directional beam. The base station receives the beam-coded uplink reference signal from the reference device via the pointing beam. The server receives the uplink channel information and the downlink channel information. The up channel information is generated based on an up reference signal, and the down channel information is generated based on a down reference signal. The server obtains a channel correction coefficient according to the uplink channel information and the downlink channel information. The channel correction factor is used to estimate the downlink channel. Therefore, the problem of the existing coordination system can be solved, and the method can be applied to multi-beam base stations.

Description

Multi-base station coordination system and channel correction method thereof
Technical Field
The invention relates to a multi-base-station coordination technology, in particular to a multi-base-station coordination system and a channel correction method thereof.
Background
Compared with the conventional fourth generation (4G) Long Term Evolution (LTE) system, the New Radio (NR) system of the fifth generation (5G) will use more antennas to improve the transmission efficiency. In theory and practical applications, it has been proved that multi-antenna systems can utilize Precoding (Precoding) and/or Beamforming (Beamforming) techniques to simultaneously enable multi-User Equipment (UE) to access radio resources, thereby increasing spectrum utilization efficiency. In addition, in recent years, it has been studied that if the number of antennas mounted on a base station is greater than four times the number of users, the spectrum use efficiency grows linearly as the number of users increases.
However, due to physical limitations, it is difficult for a general base station to carry a massive (dominant) antenna. Therefore, it is proposed that a plurality of base stations can be coordinated to transmit data to the ue together, so as to achieve the performance equivalent to a huge number of antennas. Such an architecture is referred to as a Multi-Cell Coordination (MCC) system. In the MCC system, all base stations are controlled by a Coordination Server (Coordination Server), and the Coordination Server can select the best transmission mode according to the user's situation. Since the Clock sources (Clock sources) of each base station in the MCC system are independent, there may be Carrier Frequency Offset (CFO) between base stations, which is the largest difference compared to massive antenna systems. In addition, other imperfect factors (e.g., Sampling Clock Offset (SCO) caused by CFO, Timing Offset (Timing Offset) caused by transmission delay, opposite linear phases of downlink and uplink channels caused by CFO, time varying effect of rf response, etc.) may also cause channel estimation inaccuracy, and Inter-Cell Interference (ICI) and Inter-User Interference (IUI) may be generated after precoding, thereby reducing system capacity. Therefore, the existing MCC system still needs to be improved.
Disclosure of Invention
In view of the above, the present invention provides a multi-base station coordination system and a channel calibration method thereof, which can solve the problems of the existing MCC system and can be applied to the multi-beam technology.
The multi-base station coordination system of the embodiment of the invention at least comprises but is not limited to a reference device, a base station and a server. The base station includes at least one antenna, and the antennas provide a directional beam. The base station performs a first pre-coding of the downlink reference signal to be transmitted via the directional beam, the first pre-coding being based on beam coding. The reference device receives downlink reference signals from the base station via the directional beam. The reference device performs a second precoding on the uplink reference signal to be transmitted via the directional beam, wherein the second precoding is based on the beam coding. The base station receives an uplink reference signal from the reference device via the directional beam. The server receives the uplink channel information from the base station and the downlink channel information from the reference device. The uplink channel information is generated based on the uplink reference signal and the second precoding, and the downlink channel information is generated based on the downlink reference signal and the first precoding. The server obtains a channel correction coefficient according to the uplink channel information and the downlink channel information. The channel correction factor is used to estimate the downlink channel.
On the other hand, the channel calibration method of the embodiment of the present invention at least includes, but is not limited to, the following steps. First precoding, by the base station, a downlink reference signal to be transmitted through the directional beam, the first precoding being based on beam coding. Downlink reference signals from the base station are received by the reference device via the pointing beam. The uplink reference signals to be transmitted via the directional beam are second precoded by the reference device, and the second precoding is based on beam coding. A directional beam is provided by a base station to receive uplink reference signals from a reference device. Uplink channel information from the base station and downlink channel information from the reference device are received by the server. The uplink channel information is generated based on the uplink reference signal and the second precoding, and the downlink channel information is generated based on the downlink reference signal and the first precoding. The server obtains a channel correction factor according to the uplink channel information and the downlink channel information, and the channel correction factor is used for estimating a downlink channel.
Based on the above, the multi-base station coordination system and the channel correction method thereof according to the embodiments of the present invention provide the corresponding channel correction coefficients for the channels corresponding to different beams in response to the multi-beam technology in the future 5G NR system. In addition, the reference device solves the problems of synchronization between base stations, time-varying effect of radio frequency response, frequency selective fading channel, and downlink channel state information acquisition, thereby achieving the efficiency of a massive antenna system.
In order to make the aforementioned and other features and advantages of the invention more comprehensible, embodiments accompanied with figures are described in detail below.
Drawings
FIG. 1 is a schematic diagram of a multi-base station coordination system according to an embodiment of the invention;
FIG. 2 is a flow chart of a channel calibration method according to an embodiment of the invention;
FIG. 3 is a transmission model between a base station and a reference device according to an embodiment of the present invention;
FIG. 4 is a flowchart of carrier frequency offset estimation according to an embodiment of the present invention;
FIG. 5 is a flow chart of coefficient normalization according to one embodiment of the invention;
fig. 6 is a flow chart of estimating an equivalent downlink channel according to an embodiment of the invention.
Description of the reference numerals
1: multi-base station coordination system
BS 1-BSj: base station
RA 1-RAr: reference device
CS: servo device
UE 1-UEm, UEu: user equipment
b 1-bh: pointing beam
UL _ RS _ R1, UL _ RS _ R2, UL _ RS _ R3, UL _ RS _ U1: uplink reference signal
DL _ RS _ R1, DL _ RS _ R2, DL _ RS _ R3, DL _ RS _ U1: downlink reference signal
S210 to S260, S410 to S430, S510 to S520, and S610 to S630: step (ii) of
PBS,(b,n),p、PUE,(r,k),p: precoding
αb,n、βr,k、αr,k、βb,n: radio frequency response
g(b,n)→(r,k)、g(r,k)→(b,n): aerial passage
θb,n、φr,k、θr,k、φb,n: initial phase
εb、ηr: carrier frequency
t、T0: time of day
Detailed Description
Fig. 1 is a schematic diagram of a multi-base station coordination system 1 according to an embodiment of the present invention. Referring to FIG. 1, the multi-base station coordination system 1 includes at least one or more base stations BS1 BSj, one or more reference devices RA1 RAr, a server CS, and one or more user equipments UE1 UEn. j. r and n are positive integers.
The Base stations BS1 BSj may have various embodiments, such as, but not limited to, Home Evolved Node B (HeNB), eNB, Advanced Base Station (ABS), Base Transceiver System (BTS), repeater (relay), repeater (repeater), and/or satellite-based communication Base Station. In the present embodiment, each BS1 BSj has one or more antennas that provide a plurality of directional beams b1 bh that point in a particular direction from b1 bh. For example, base station BSb (b is a positive integer from 1 to j) transmits wireless signals using different directional beams b 1-bh in sequence by a beam sweeping (beam sweeping) technique. h. j is a positive integer.
Various embodiments of the reference devices RA 1-RAr are possible, such as but not limited to a mobile device, a personal computer, or a base station in idle mode. The idle base station is a base station that is determined by the server CS to be currently not providing service or to have a load lower than a specific threshold. Server CS may also schedule base stations BS 1-BSj, taking turns with any idle one of base stations BS 1-BSj as reference devices RA 1-RAr. In the present embodiment, each of the reference devices RA 1-RAr has one or more antennas. r is a positive integer.
The server CS may be any type of computing device such as a server, a computer host, a workstation, or the like. In the present embodiment, the server CS is connected to the base stations BS1 BSj and the reference devices RA1 RAr by wire or wirelessly.
Various implementations of user Equipment UE 1-UEm are possible, including, but not limited to, Mobile stations, Advanced Mobile Stations (AMS), telephony devices, Customer Premises Equipment (CPE), wireless sensors, etc. User equipments UE 1-UEm may be served by any of base stations BS 1-BSj. m is a positive integer.
In the present embodiment, the base stations BS1 to BSj and the reference devices RA1 to RAr can be time-synchronized by using Global Positioning System (GPS) signals. Base stations BS1 BSj, reference devices RA1 RAr, and user equipments UE1 UEm have independent clock sources. That is, each device has its own carrier frequency. For example, the carrier frequency of base station BSb is εbAnd the carrier frequency of the reference device RAr is etar. In addition, base station BThe S1 BSj, the RA1 RAr, and the UE1 UEm may support fourth (4G), fifth (5G), or later generation mobile communication technologies, but the invention is not limited thereto.
To facilitate understanding of the operation process of the embodiment of the present invention, the operation process of the multi-base station coordination system 1 in the embodiment of the present invention will be described in detail below with reference to a plurality of embodiments. Hereinafter, the method according to the embodiment of the present invention will be described with reference to each device in the multi-base station coordination system 1. The flow of the method according to the embodiment of the present invention may be adjusted according to the implementation situation, and is not limited thereto. For convenience of description, one or more of the base stations BS 1-BSj, the reference apparatuses RA 1-RAr, and the user equipment UE 1-UEm will be referred to as an example, and the operations of the remaining apparatuses of the same type will be referred to the corresponding description and will not be described again.
Fig. 2 is a flowchart of a channel calibration method according to an embodiment of the invention. Referring to fig. 1 and 2, the base station BSb performs a first precoding on the DL _ RS _ R2 to be transmitted through the directional beam bp (p is a positive integer between 1 and h) (step S210). Specifically, the base station BSb may transmit different or the same downlink signals via a plurality of different directional beams b 1-bh. In order to identify and/or improve transmission efficiency, the bs BSb performs a first precoding on all or part of the downlink signals directed to the carriers b 1-bh based on beam coding. This beam coding may be based on a beam codebook (codebook), such as Precoding Matrix Indexes (PMIs), or other Precoding matrices. That is, the downlink signals directed to the carriers b1 to bh are precoded by the codewords, coefficients, or weights in the precoding matrix and then transmitted. It should be noted that the directional beam bp is taken as an example for the description of the present embodiment, and the description of the remaining directional beams will not be repeated.
The reference device RAr receives the DL _ RS _ R2 from the base station BSb via the directional beam bp (step S220). Specifically, after the base station BSb transmits the DL RS 2 at Time t (for example, in a Time Division Duplex (TDD) system), the reference device RAr may be assigned or self-determined to receive signals via the directional beam bp.
Fig. 3 shows a link model between a base station BSb and a reference device RAr according to an embodiment of the present invention. Suppose that the nth antenna of the base station BSb provides the directional beam bp and the kth antenna of the reference device RAr receives signals via the directional beam bp. The downlink reference signal DL _ RS _ R2 (from the base station BSb to the reference device RAr, i.e. via the downlink) is a training signal known to both the base station BSb and the reference device RAr. The reference device RAr can estimate the downlink channel information for this directional beam bp based on the downlink reference signal DL _ RS _ R2. The mathematical expression of this downstream channel is as follows:
Figure GDA0003017090630000051
(b, n) → (r, k) indicating transmission through the nth antenna of the kth base station (i.e., base station BSb) and reception through the kth antenna of the r-th reference device (i.e., reference device RAr); pBS,(b,n),pIs the first precoding of the base station BSb for the p-th beam (i.e., the directional beam bp); beta is ar,kIs the radio frequency response of the reference device RAr at the kth antenna receiving end; alpha is alphab,nThe radio frequency response of the base station BSb at the transmitting end of the nth antenna; g(b,n)→(r,k)Is an Air (Over-The-Air) channel (g if reciprocity (reciprocity) is present)(b,n)→(r,k)Can also be regarded as g(r,k)→(b,n))；θb,nIs the initial phase of the base station BSb at the transmitting end of the nth antenna; phi is ar,kIs the initial phase of the reference device RAr at the kth antenna receiving end; epsilonbThe carrier frequency of base station BSb; etarIs the carrier frequency of the reference device RAr;
Figure GDA0003017090630000061
is the estimated carrier frequency offset. The reference device RAr then sends the estimated downlink channel information for the directional beam bp to the server CS.
Notably, the aforementioned carrier frequency offset
Figure GDA0003017090630000062
May be estimated in advance or predetermined. How to estimate the carrier frequency offset will be described below
Figure GDA0003017090630000063
Fig. 4 is a flowchart of carrier frequency offset estimation according to an embodiment of the present invention. Referring to fig. 1 and 4, the base stations BSb, BSj and the reference device RAr are exemplified as follows. The reference apparatus RAr transmits uplink reference signals UL _ RS _ R2 and UL _ RS _ R3 to the base stations BSb and BSj, respectively (step S410). The base stations BSb and BSj respectively obtain two sets of corresponding uplink channel information based on the uplink reference signals UL _ RS _ R2 and UL _ RS _ R3 (step S420). The server CS obtains the (relative) carrier frequency offsets of the two base stations BSb, BSj based on the uplink channel information (step S430). In other words, the embodiment of the present invention uses the difference in carrier frequency offset between the two base stations BSb, BSj as the relative carrier frequency offset. Thereby, the base station BSb can obtain the uplink channel information shown in expression (1) based on the carrier frequency offset for itself. It should be noted that all the base stations BS 1-BSj can obtain their corresponding relative carrier frequency offsets based on the embodiment of fig. 4, which will not be described in detail below. In addition, the reference device RAr still needs to transmit the uplink reference signals UL _ RS _ R2 and UL _ RS _ R3 after the time D, and the server CS obtains the carrier frequency offset according to the channel variation between two time points.
Referring back to fig. 2, the reference device RAr performs a second precoding on the uplink reference signal UL _ RS _ R2 to be transmitted through the directional beam bp based on the beam coding (step S230). In the present embodiment, the second precoding may refer to the description of the first precoding, and may employ the same or different precoding matrices. Then, the reference device RAr is at time T + T0The uplink reference signal UL _ RS _ R2 is transmitted such that the base station BSb provides the directional beam bp to receive the uplink reference signal UL _ RS _ R2 from the reference device RAr (step S240). The uplink reference signal UL _ RS _ R2 (from the reference device RAr to the base station BSb, i.e., via the uplink) is a training signal known to both the base station BSb and the reference device RAr. And the base station BSb can estimate the uplink reference signal UL _ RS _ R2 based on the uplink reference signal UL _ RS _ R2And pointing to the uplink channel information of the beam bp.
The mathematical expression of this upstream channel is as follows:
Figure GDA0003017090630000071
(r, k) → (b, n) indicating transmission through the kth antenna of the reference device RAr and reception through the nth antenna of the base station BSb; pRA,(r,k),pIs a second precoding of the reference device RAr for the directional beam bp; beta is ab,nThe radio frequency response of the base station BSb at the receiving end of the nth antenna; alpha is alphar,kIs the radio frequency response of the reference device RAr at the k-th antenna transmitting end; g(r,k)→(b,n)Is an air channel (g if reciprocity is present)(r,k)→(b,n)Can also be regarded as g(b,n)→(r,k))；φb,nThe initial phase of the base station BSb at the receiving end of the nth antenna; thetar,kIs the initial phase of the reference device RAr at the k-th antenna transmission end; epsilonbThe carrier frequency of base station BSb; etarIs the carrier frequency of the reference device RAr;
Figure GDA0003017090630000072
is the estimated carrier frequency offset (which can be estimated with reference to the embodiment of fig. 4). The base station BSb then transmits the estimated up channel information for the directional beam bp to the server CS.
Referring back to fig. 2, the server CS then receives the uplink channel information (e.g., the formula (2)) from the base station BSb and the downlink channel information (e.g., the formula (1)) from the reference device RAr (step S250), and the server CS derives the channel correction coefficients according to the uplink channel information and the downlink channel information (step S260).
Specifically, the server CS uses the ratio of the uplink channel information and the downlink channel information corresponding to different time points as a correction coefficient:
Figure GDA0003017090630000073
wherein the channel correction coefficient c(b,n)→(r,k)(t+T0) Is formed by
Figure GDA0003017090630000074
And (4) causing the generation of the new medicament.
FIG. 5 is a flow chart of coefficient normalization according to an embodiment of the invention. Referring to fig. 1 and 5, the server CS obtains a second channel correction factor according to the uplink channel information and the downlink channel information (assumed to pass through the first antenna) between the BS1 and the reference device RAr via another directional beam b1 (step S510). The second channel correction factor can be generated as described above with reference to fig. 2, i.e., the reference device RAr estimates the downlink channel information for the directional beam b1 based on the downlink reference signal RL _ RS _ R1 from the base station BS1, the base station BS1 estimates the uplink channel information for the directional beam b1 based on the uplink reference signal UL _ RS _ R1 from the reference device RAr, and the server CS derives the second channel correction factor c based on the uplink/downlink channel information for the directional beam b1(1,1)→(r,1)(t+T0). The server CS then normalizes the channel correction coefficients obtained in step S260 according to the second channel correction coefficients (step S520):
Figure GDA0003017090630000081
c(1,1)→(r,1)(t+T0) Is the second channel correction factor, (1,1) → (r,1) representing transmission through the 1 st antenna of the 1 st base station (i.e., base station BS1) and reception through the 1 st antenna of the reference device RAr; pBS,(1,1),1Is the first precoding of the base station BSb for the 1 st beam (i.e., the directional beam b 1); beta is ar,1Is the radio frequency response of the reference device RAr at the receiving end of the 1 st antenna; alpha is alpha1,1Is the radio frequency response of base station BS1 at the transmit end of the 1 st antenna;
Figure GDA0003017090630000082
is the initial phase and base of the base station BSb at the transmitting end of the n-th antennaThe difference between the initial phase of BS1 at the transmitting end of the 1 st antenna and the sum of the difference between the initial phase of BS1 at the receiving end of the 1 st antenna and the initial phase of BS b at the transmitting end of the nth antenna (i.e.,
Figure GDA0003017090630000083
ε1the carrier frequency for base station BS 1;
Figure GDA0003017090630000084
is the estimated carrier frequency offset; pRA,(r,1),1Is the second precoding of the reference device RAr for the pointing beam b 1; beta is a1,1Is the radio frequency response of base station BS1 at the 1 st antenna receiving end; alpha is alphar,1Is the radio frequency response of the reference device RAr at the 1 st antenna transmit end.
It should be noted that, although the base station BS1, the first antenna and the directional beam b1 are taken as examples, in other embodiments, the server CS may select any combination of other base stations, other antennas and/or other directional beams as the normalization reference. It should be emphasized that the above description is only for the nth antenna and the directional beam bp of the base station BSb and the kth antenna of the reference apparatus RAr, and the above description is referred to the channel calibration coefficients for other base stations, other antennas, other directional beams and other reference apparatus combinations, which are not repeated herein.
It is noted that the above-mentioned channel calibration coefficients can be used to estimate the downlink channel between the base station BSb and the UE 1-UEm, as will be described later. Fig. 6 is a flowchart of estimating an equivalent downlink channel according to an embodiment of the invention. Referring to fig. 1 and 6, at time T + T1At this time, ue UEu (U is a positive integer from 1 to m) transmits UL _ RS _ U1 to BSb via the directional beam bp1 (step S610). The base station BSb depends on the uplink reference signal UL _ RS _ U1 and the (normalized) channel correction coefficient c'(b,n)→(r,k)(t+T0) Estimate the (equivalent) downlink channel via the directional beam bp (step S620):
Figure GDA0003017090630000091
ηuthe carrier frequency of the u-th user equipment (i.e., user equipment UEu),
Figure GDA0003017090630000092
are channel calibration coefficients calculated by the reference devices RA 1-RAr and the base stations BS 1-BSj. In other words, the server CS calculates the downlink channel information of the UE UEu using the channel calibration coefficients calculated by the reference devices RA 1-RAr and the base stations BS 1-BSj.
Furthermore, the downlink channel matrix for the directional beam bp can be represented as:
Figure GDA0003017090630000093
hBS1→UE1representing the channel vector from BS1 to UE1 (and so on),
Figure GDA0003017090630000094
for the matrix of channel correction coefficients, HCFO(t+T1) Is a matrix of carrier frequency offsets.
The bs BSb then performs a third precoding on the signal sent to the ue UEu according to the estimated downlink channel (step S630). This third precoding is based on, for example, forced Zero (Zero forcing), Minimum Mean-Square Error (MMSE), or other equalization algorithms. And at time T + T2The base station BSb serves the ue UEu with the downlink signal generated by the third precoding. It should be noted that the transmission behavior between the BSb and the ue UEu is taken as an example, and other combinations of BSb and ue can be referred to the above description and will not be described again.
In summary, the multi-base station coordination system and the channel calibration method thereof according to the embodiments of the present invention utilize the reference device to solve the problems of synchronization between base stations, time-varying effect of rf response, frequency selective fading channel, and downlink channel status information acquisition. In addition, the embodiments of the present invention further contemplate the application of multi-beam transmission, thereby enabling the application to 5G or later generation communication systems.
Although the present invention has been described with reference to the above embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (8)

1. A multi-base station coordination system comprising:
a base station comprising at least one antenna, wherein the at least one antenna provides a directional beam, the base station performing a first precoding on a downlink reference signal to be transmitted via the directional beam, wherein the first precoding is based on beam coding,
a reference device, wherein the reference device receives the downlink reference signals from the base station via the directional beam, the reference device performs a second precoding on uplink reference signals to be transmitted via the directional beam, wherein the second precoding is based on the beam coding, and the base station receives the uplink reference signals from the reference device via the directional beam;
a server for receiving uplink channel information from the base station and downlink channel information from the reference device, wherein the uplink channel information is generated based on the uplink reference signal and the second precoding, and the downlink channel information is generated based on the downlink reference signal and the first precoding, and the server obtains a channel correction coefficient according to the uplink channel information and the downlink channel information, wherein the channel correction coefficient is used for estimating a downlink channel; and
a second base station, wherein the server obtains a second channel calibration coefficient according to second uplink channel information and second downlink channel information between the second base station and the reference device via a second directional beam, the server normalizes the channel calibration coefficient according to the second channel calibration coefficient, and the base station estimates the downlink channel via the directional beam according to the normalized channel calibration coefficient, wherein the normalized channel calibration coefficient is a value obtained by dividing the channel calibration coefficient by the second channel calibration coefficient.
2. The multi-base station coordination system of claim 1, further comprising:
a user equipment transmitting a second uplink reference signal via the directional beam, wherein the base station estimates the downlink channel via the directional beam according to the second uplink reference signal and the channel correction factor, and the base station performs a third precoding on a signal transmitted to the user equipment according to the estimated downlink channel.
3. The multi-base station coordination system of claim 1, further comprising:
a third base station, wherein the reference device sends a third uplink reference signal to the base station and the second base station, the base station and the second base station respectively obtain two third uplink channel information based on the third uplink reference signal, and the server obtains a carrier frequency offset based on the two third uplink channel information, wherein the base station obtains the uplink channel information based on the carrier frequency offset and the uplink reference signal, and the reference device obtains the downlink channel information based on the carrier frequency offset and the downlink reference signal.
4. The multi-base station coordination system of claim 1, wherein the downlink channel information, and the uplink channel information are further related to initial phase, carrier frequency offset, and carrier frequency of the base stations and the reference devices at the transmitting end and the receiving end.
5. A method of channel correction, comprising:
performing, by a base station, first precoding on a downlink reference signal to be transmitted via a directional beam, wherein the first precoding is based on beam coding;
receiving, by a reference device, the downlink reference signal from the base station via the directional beam;
second precoding, by the reference device, uplink reference signals to be transmitted via the directional beam, wherein the second precoding is based on the beam coding;
providing, by the base station, the directional beam to receive the uplink reference signal from the reference device;
receiving, by a server, uplink channel information from the base station and downlink channel information from the reference device, wherein the uplink channel information is generated based on the uplink reference signal and the second precoding, and the downlink channel information is generated based on the downlink reference signal and the first precoding;
obtaining a channel correction coefficient by the server according to the uplink channel information and the downlink channel information, wherein the channel correction coefficient is used for estimating a downlink channel;
obtaining, by the server, a second channel correction factor according to second uplink channel information and second downlink channel information of a second directional beam between a second base station and the reference device;
normalizing the channel correction coefficient by the server according to the second channel correction coefficient; and
estimating, by the base station, the downlink channel through the directional beam according to a normalized channel correction factor, wherein the normalized channel correction factor is a value of the channel correction factor divided by the second channel correction factor.
6. The channel correction method of claim 5, wherein the step of deriving the channel correction coefficients is followed by further comprising:
transmitting, by the user equipment, a second uplink reference signal via the directional beam;
estimating, by the base station, the downlink channel via the directional beam according to the second uplink reference signal and the channel correction factor; and
and performing third pre-coding on the signal sent to the user equipment through the base station according to the estimated downlink channel.
7. The channel calibration method of claim 5, wherein the step of receiving the downlink reference signal from the base station further comprises:
transmitting a third uplink reference signal to the base station and a third base station respectively through the reference device;
obtaining, by the base station and the third base station, second third uplink channel information based on the third uplink reference signal, respectively; and
deriving, by the server, a carrier frequency offset based on the second and third uplink channel information, wherein the uplink channel information is derived based on the carrier frequency offset and the uplink reference signal, and the downlink channel information is derived based on the carrier frequency offset and the downlink reference signal.
8. The method of claim 5 wherein the downlink channel information and the uplink channel information are further related to initial phase of transmitter and receiver, carrier frequency offset, and carrier frequency of the base station and the reference device.
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CN102340338A (en) * 2011-10-21 2012-02-01 西安交通大学 Method for correcting array antenna channel of a base station in time division duplexing (TDD) mode
CN102511130A (en) * 2009-08-14 2012-06-20 诺基亚西门子通信公司 Improvements for coordinated multipoint transmission
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CN102511130A (en) * 2009-08-14 2012-06-20 诺基亚西门子通信公司 Improvements for coordinated multipoint transmission
CN102340338A (en) * 2011-10-21 2012-02-01 西安交通大学 Method for correcting array antenna channel of a base station in time division duplexing (TDD) mode
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