CN107911153B - FDD system-oriented downlink channel reconstruction method based on uplink CSI - Google Patents
FDD system-oriented downlink channel reconstruction method based on uplink CSI Download PDFInfo
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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
- H04B7/0413—MIMO systems
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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
- H04B7/0413—MIMO systems
- H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
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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
- H04B7/0621—Feedback content
- H04B7/0626—Channel coefficients, e.g. channel state information [CSI]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/003—Arrangements for allocating sub-channels of the transmission path
- H04L5/0048—Allocation of pilot signals, i.e. of signals known to the receiver
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Abstract
The invention discloses a downlink channel reconstruction method based on uplink Channel State Information (CSI) facing a Frequency Division Duplex (FDD) system.A base station firstly estimates the uplink CSI by using an uplink detection signal, wherein the uplink CSI comprises the gain, the direction angle and the time delay of one or more propagation paths, then sends downlink sparse pilot frequency, or sends the downlink pilot frequency in the direction of the estimated one or more propagation paths by using the reciprocity of the uplink angle and the downlink angle, user equipment re-estimates and feeds back the gain of each propagation path by using the downlink pilot frequency, and finally the base station reconstructs the downlink channel by using the direction angle and the time delay of each propagation path estimated by the uplink and the gain of each propagation path re-estimated and fed back by the user equipment. The invention provides a reconstruction method of FDD system downlink CSI, and particularly solves the problem of acquisition of FDD large-scale MIMO system downlink CSI.
Description
Technical Field
The invention relates to a downlink channel reconstruction method based on uplink Channel State Information (CSI) for a Frequency Division Duplex (FDD) system, in particular to a downlink channel reconstruction method based on uplink CSI for a FDD large-scale multiple-input multiple-output (MIMO) system.
Background
The large-scale MIMO is one of important technologies of fifth-generation mobile communication, and the large-scale antenna array is configured at the base station, so that the spatial degree of freedom can be greatly improved, the space division multiple access dimensionality is improved, and thermal noise and fast fading are smoothed. In order to obtain high-dimensional CSI and control the overhead of pilot frequency and control channel, a large-scale MIMO system usually adopts a pilot frequency multiplexing mode, and non-orthogonal pilot frequency is adopted between adjacent cells, so that the pilot frequency pollution is serious. And because the coherence time of the channel is limited, how to complete channel estimation under limited training resources needs to be researched and explored. Therefore, the acquisition of CSI becomes one of the difficulties of massive MIMO systems.
Currently commercially available duplex modes include Time Division Duplex (TDD) and FDD. Part of large-scale MIMO systems adopt a TDD transmission mode, and after uplink channel estimation is finished by means of uplink detection signals, uplink channel estimation results are directly applied to a downlink by utilizing reciprocity between uplink and downlink channels. However, most wireless communication systems adopt FDD transmission mode, where channel reciprocity does not exist, and the uplink channel estimated by the uplink sounding procedure cannot be applied to the downlink. Because the pilot frequency overhead and the feedback overhead required by downlink channel estimation are both in proportion to the number of antennas, in order to ensure the amount of time-frequency resources required by data service, the actual system will strictly control the overhead of pilot frequency and feedback, so that a large-scale MIMO base station working in an FDD mode can only obtain a small amount of downlink CSI. In addition, the downlink channel estimation is completed by the user equipment, the calculation and processing capabilities of the user equipment are limited, and the estimation accuracy of the high-dimensional channel is limited. Therefore, CSI acquisition for FDD massive MIMO systems becomes a bottleneck.
Initial research has been conducted on CSI acquisition for an FDD massive MIMO system, and a currently widely adopted strategy is to acquire a channel correlation matrix for downlink transmission, however, this method requires a large overhead, and is difficult in information acquisition and poor in downlink transmission performance. In addition, according to a research result, the gains, the direction angles and the time delays of the uplink and downlink propagation paths are completely equal, and the downlink channel can be directly reconstructed only by using the uplink estimation result, so that a downlink training process is not needed, but the actual channel measurement result shows that the error of the reconstruction result of the downlink channel without downlink training is large, and the requirement of an actual system cannot be met.
In summary, how to obtain FDD massive MIMO downlink CSI with high availability with low overhead becomes a challenge to be overcome in the fifth generation of mobile communications.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a downlink channel reconstruction method based on uplink CSI for an FDD system, which breaks through the bottleneck of acquiring the downlink CSI of the FDD large-scale MIMO system, realizes the reconstruction of the downlink channel of the FDD large-scale MIMO system by utilizing the reciprocity of uplink and downlink angle information and with smaller downlink pilot frequency overhead and feedback overhead, and simultaneously ensures the availability of the reconstructed channel.
The invention adopts the following technical scheme for solving the technical problems:
the invention provides a downlink channel reconstruction method based on uplink CSI for an FDD system.A base station in a frequency division duplex FDD wireless transmission system estimates the state information CSI of an uplink channel, re-estimates and feeds back partial CSI by utilizing reciprocity of uplink and downlink angles and sending downlink pilot frequency, and reconstructs the downlink channel by utilizing the estimated uplink CSI and the downlink re-estimated and fed back CSI; the method specifically comprises the following steps:
step 2, the base station sends downlink pilot frequency, the user equipment re-estimates downlink CSI by using the received downlink pilot frequency, and feeds back the re-estimated downlink CSI to the base station through an uplink;
and 3, the base station reconstructs a downlink channel by using the uplink CSI estimated in the step 1 and the downlink CSI reestimated and fed back by the user equipment in the step 2.
As a further optimization scheme of the present invention, the uplink CSI estimated by the base station in step 1 is information of one or more propagation paths, and the estimated number of propagation paths is L, which satisfies that L is greater than or equal to 1.
As a further optimization of the present invention, the information of the propagation path includes the gain, the direction angle and the time delay of the propagation path.
As a further optimization scheme of the present invention, in step 2, the base station sends downlink pilot frequency, including sparse pilot frequency or pilot frequency sent at the direction angle estimated in step 1.
As a further optimization scheme of the invention, the sparse pilot frequency comprises a frequency domain sparse interpolation pilot frequency and a time domain sparse interpolation pilot frequency.
As a further optimization scheme of the present invention, the pilots transmitted at the direction angles estimated in step 1 include beamformed or precoded pilots.
As a further optimization scheme of the present invention, the downlink CSI re-estimated and fed back by the user equipment in step 2 includes the gain of the propagation path estimated by the base station in step 1.
As a further optimization scheme of the present invention, after receiving the CSI re-estimated and fed back by the ue in step 3, the base station replaces the corresponding uplink CSI estimated by the base station in step 1 with the downlink CSI re-estimated by the ue when reconstructing the downlink channel.
As a further optimization scheme of the present invention, the CSI used by the base station to reconstruct the downlink channel in step 3 includes: in step 1, the base station estimates the direction angle and the time delay of the propagation path, and in step 2, the user equipment re-estimates and feeds back the gain of the propagation path.
As a further optimization scheme of the present invention, the base station can reconstruct a downlink channel for a plurality of user equipments, and the form of sending the downlink pilot frequency includes: a) sparse pilot frequency; b) the pilot frequency sent in the direction angle estimated in the step 1 is distinguished in a frequency division mode by the pilot frequency sent to different user equipment; c) the pilots sent in the direction angle estimated in step 1 are distinguished in a time division manner from the pilots sent to different user equipments.
Compared with the prior art, the invention adopting the technical scheme has the following technical effects:
1) according to the method, by utilizing reciprocity of uplink and downlink angles, after the uplink angular domain information is estimated, the downlink channel can be reconstructed only by sending a small amount of downlink pilot frequency, re-estimating the gain of a propagation path and feeding back, so that the pilot frequency and feedback overhead is effectively reduced, and the problem of acquiring the downlink CSI of the FDD large-scale MIMO system is solved;
2) after estimating CSI in the uplink, the method utilizes a small amount of downlink training and feedback resources to correct the gain of the downlink, ensures the accuracy of the downlink channel reconstruction of the FDD large-scale MIMO system, and greatly improves the availability of the reconstructed channel.
Drawings
FIG. 1 is a flow chart of an embodiment of the present invention.
Fig. 2 is an LTE uplink sounding signal pattern.
Fig. 3 is a frequency domain sparse pilot pattern for downlink transmission.
Fig. 4 shows directional pilots transmitted in beamforming or precoding.
Detailed Description
The technical scheme of the invention is further explained in detail by combining the attached drawings:
the invention relates to a downlink channel reconstruction method based on uplink Channel State Information (CSI) facing a Frequency Division Duplex (FDD) system, which is characterized in that in the FDD wireless transmission system, a base station estimates the uplink CSI, then uses reciprocity of uplink and downlink angles to enable user equipment to re-estimate and feed back partial CSI by sending a small amount of downlink pilot frequency, and reconstructs the downlink channel by using the estimated uplink CSI and the estimated downlink re-estimated and fed back CSI. The method specifically comprises the following steps:
(1) the user equipment sends an uplink detection signal, and the base station estimates uplink CSI by using the received uplink detection signal. The uplink CSI estimated by the base station is information of one or more propagation paths, the estimated number of the propagation paths is L, and L is more than or equal to 1. For L propagation paths estimated by the base station, the information to be estimated for each propagation path includes but is not limited to: gain, azimuth angle and delay of the propagation path.
(2) And the user equipment re-estimates part of downlink CSI by using the received downlink pilot frequency and feeds back the re-estimated downlink CSI to the base station through an uplink. The small number of downlink pilots transmitted by the base station includes, but is not limited to, the following forms: sparse pilots, or pilots transmitted at the direction angles estimated in step (1). The sparse pilot includes, but is not limited to, the following implementation forms: a frequency domain sparse interpolation pilot frequency and a time domain sparse interpolation pilot frequency; the pilots transmitted at the L direction angles estimated in step (1) include, but are not limited to, the following implementation forms: beamformed or precoded pilots. The partial CSI re-estimated and fed back by the user equipment includes, but is not limited to: and (3) the gains of the L propagation paths estimated in the step (1).
(3) And the base station reconstructs the downlink channel by using the estimated uplink CSI and the downlink CSI reestimated and fed back by the user equipment. And (3) after receiving the part of CSI re-estimated and fed back by the user equipment, the base station replaces the corresponding uplink CSI estimated in the step (1) with the re-estimated downlink CSI when reconstructing the downlink channel. The CSI used by the base station to reconstruct the downlink channel includes but is not limited to: the direction angle and the time delay of the L propagation paths estimated in the uplink, and the gains of the L propagation paths reestimated and fed back in the downlink.
In the method of the present invention, the base station can reconstruct the downlink channel for a plurality of user equipments: the number L of propagation paths corresponding to each user equipment may not be equal; the form of sending the downlink pilot includes but is not limited to: a) sparse pilot frequency, b) pilot frequency sent in the direction angle estimated in the step (1), the pilot frequency sent to different user equipment is distinguished in a frequency division mode, c) the pilot frequency sent in the direction angle estimated in the step (1), the pilot frequency sent to different user equipment is distinguished in a time division mode.
The technical scheme of the invention is further explained by the following specific embodiments:
in an FDD massive MIMO system, the number of base station antennas is M, typically of the order of 102、103The user equipment adopts a single antenna configuration. For downlink data transmission, the base station needs to acquire downlink CSI and reconstruct a downlink channel hDL. This embodiment will be on hDLThe reconstruction is performed, as shown in fig. 1, comprising the steps of:
the method comprises the following steps: the user equipment transmits an uplink sounding signal, and adopts an LTE uplink sounding signal pattern, as shown by a shaded part in figure 2, to perform comb-shaped transmission on the last OFDM symbol of the specified time slot of the system, and a signal model received by the base station at the moment is
y＝hULs+n,
Wherein y ∈ CM×1For uplink sounding signals received by the base station, hUL∈CM×1Is an uplink channel between a base station and user equipment, s is an uplink detection signal sent by the user equipment, and n belongs to CM×1For noise, the uplink channel has the following expression:
wherein L is the number of propagation paths, gUL,lFor the up gain of the l path, fULFor the uplink carrier frequency, τlFor the delay of the l-th path, a (-) is the base station antenna array response, θlIs the direction angle of the l-th path, wherelAnd thetalThe carrier frequency is irrelevant, and the device has uplink and downlink reciprocity;
step two: the base station processes and calculates the received signal y by using the received uplink detection signal and adopting a compressed sensing algorithm and the like to obtain
Of a single propagation path
Group parameter estimation, each group parameter estimation comprising
Estimated uplink based on reciprocity
Is equally effective in downlink, but the gain is
The method has no reciprocity between uplink and downlink, so that the gain of the downlink is also required to be estimated;
step three: the base station sends down-going frequency domain sparse pilot frequency, such as comb-shaped pilot frequency with sparse interpolation as shown by the shaded part in fig. 3, or in the direction of the propagation path estimated in step two in a pre-coding manner, i.e. in the direction of the angle
The pilot frequency is sent upwards, as shown in fig. 4, the pilot frequency is sent out by the base station after obtaining the directivity through precoding;
step four: user equipment utilizes downlink pilot frequency to recalculate downlink frequency band
Of a single propagation path
A gain value, get
Step five: downlink frequency band to be re-estimated by user equipment
Of a single propagation path
A gain value, i.e.
Feeding back to the base station;
step six: base station using uplink estimation
Direction angle, time delay and downlink reestimation of strip propagation path and feedback
Gain values of strip propagation paths, i.e.
And (3) reconstructing a downlink channel:
wherein f isDLIs a downlink carrier frequency.
The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can understand that the modifications or substitutions within the technical scope of the present invention are included in the scope of the present invention, and therefore, the scope of the present invention should be subject to the protection scope of the claims.
Claims (7)
1. A downlink channel reconstruction method based on uplink CSI for an FDD system is characterized in that in a frequency division duplex FDD wireless transmission system, after estimating uplink channel state information CSI, a base station re-estimates and feeds back partial CSI by utilizing reciprocity of uplink and downlink angles and sending downlink pilot frequency, and reconstructs a downlink channel by utilizing the estimated uplink CSI and the downlink re-estimated and fed back CSI; the method specifically comprises the following steps:
step 1, user equipment sends an uplink detection signal, and a base station estimates uplink CSI by using the received uplink detection signal; the uplink CSI is information of one or more propagation paths, the estimated number of the propagation paths is L, L is more than or equal to 1, and the information of the propagation paths comprises gain, direction angle and time delay of the propagation paths;
step 2, the base station sends downlink pilot frequency, the user equipment re-estimates downlink CSI by using the received downlink pilot frequency, and feeds back the re-estimated downlink CSI to the base station through an uplink; wherein, the downlink CSI comprises the gain of the propagation path estimated by the base station in the step 1;
and 3, the base station reconstructs a downlink channel by using the uplink CSI estimated in the step 1 and the downlink CSI reestimated and fed back by the user equipment in the step 2.
2. The method of claim 1, wherein the base station sends downlink pilots in step 2, the downlink pilots include sparse pilots or pilots sent at the direction angle estimated in step 1.
3. The method of claim 2, wherein the sparse pilot comprises a frequency-domain sparse interpolated pilot and a time-domain sparse interpolated pilot.
4. The method of claim 2, wherein the pilots transmitted at the direction angles estimated in step 1 include beamformed or precoded pilots.
5. The method for reconstructing the downlink channel based on the uplink CSI for the FDD system according to claim 1, wherein the downlink CSI re-estimated by the user equipment replaces the corresponding uplink CSI estimated by the base station in step 1 when the base station reconstructs the downlink channel after receiving the CSI re-estimated and fed back by the user equipment in step 3.
6. The method of claim 1, wherein the CSI used by the base station to reconstruct the downlink channel in step 3 comprises: in step 1, the base station estimates the direction angle and the time delay of the propagation path, and in step 2, the user equipment re-estimates and feeds back the gain of the propagation path.
7. The method of claim 1, wherein the base station is capable of reconstructing downlink channels for a plurality of user equipments, and the sending the downlink pilot comprises: a) sparse pilot frequency; b) the pilot frequency sent in the direction angle estimated in the step 1 is distinguished in a frequency division mode by the pilot frequency sent to different user equipment; c) the pilots sent in the direction angle estimated in step 1 are distinguished in a time division manner from the pilots sent to different user equipments.
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| CN108712243B (en) * | 2018-05-21 | 2020-10-16 | 东南大学 | Multi-carrier channel reconstruction method for carrier aggregation system |
| CN109167618B (en) * | 2018-07-05 | 2021-03-26 | 东南大学 | FDD large-scale MIMO downlink channel reconstruction and multi-user transmission method |
| CN109327918B (en) * | 2018-11-19 | 2021-09-28 | 东南大学 | Low-overhead FDD large-scale MIMO downlink channel reconstruction method |
| CN111356171A (en) * | 2018-12-21 | 2020-06-30 | 华为技术有限公司 | Configuration method for reporting Channel State Information (CSI) and communication device |
| CN110430147B (en) * | 2019-07-15 | 2021-12-14 | 东南大学 | Channel tracking method for FDD system |
| WO2021016858A1 (en) * | 2019-07-30 | 2021-02-04 | 北京小米移动软件有限公司 | Information sending and receiving methods and apparatuses, sending device and receiving device |
| CN112422245B (en) * | 2019-08-23 | 2022-04-22 | 华为技术有限公司 | Method and device for sending and receiving indication |
| WO2021062806A1 (en) * | 2019-09-30 | 2021-04-08 | 华为技术有限公司 | Channel measurement method and communication device |
| CN113746509B (en) * | 2020-05-28 | 2022-11-01 | 维沃移动通信有限公司 | Channel information processing method, device, terminal, network side equipment and medium |
| CN113572506B (en) * | 2021-06-01 | 2022-09-16 | 南京泰通科技股份有限公司 | High-speed rail multi-TRP wireless communication method based on FDD precoding |
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