CN109167618B - FDD large-scale MIMO downlink channel reconstruction and multi-user transmission method - Google Patents
FDD large-scale MIMO downlink channel reconstruction and multi-user transmission method Download PDFInfo
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- CN109167618B CN109167618B CN201810728817.9A CN201810728817A CN109167618B CN 109167618 B CN109167618 B CN 109167618B CN 201810728817 A CN201810728817 A CN 201810728817A CN 109167618 B CN109167618 B CN 109167618B
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- H04L5/00—Arrangements affording multiple use of the transmission path
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- H04B7/0413—MIMO systems
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- 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
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- 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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- H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
- H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
- H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
- H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
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- H04B7/0626—Channel coefficients, e.g. channel state information [CSI]
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Abstract
The invention discloses a downlink channel reconstruction and multi-user transmission method for an FDD large-scale MIMO system, which comprises the following steps: the user sends the up pilot frequency to the base station, the pilot frequency is orthogonal among users, the base station extracts the direction angle and time delay of all propagation paths in each user channel; the base station uses the estimated direction angle information to select and schedule users; the base station sends downlink sparse pilot frequency, the selected users estimate downlink gain of each propagation path according to the received pilot frequency and feed back the downlink gain to the base station, and the base station reconstructs a downlink channel for each selected user; and the base station designs a precoding matrix by utilizing the reconstructed downlink channel for downlink multi-user data transmission. The invention breaks through the bottleneck of multi-user channel reconstruction of an FDD large-scale MIMO system with lower overhead, and realizes the downlink multi-user interference-free data transmission with high throughput.
Description
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a downlink channel reconstruction and multi-user transmission method for an FDD large-scale MIMO system.
Background
Multiple Input Multiple Output (MIMO) technology has been regarded as a key means for improving spectrum efficiency since the fourth generation (4G) mobile communication systems. A plurality of antennas are erected at the base station end, so that the space dimensionality is developed, the space utilization rate is enhanced in the modes of space division multiplexing and the like, and the frequency spectrum efficiency is improved. With the explosive increase of the user demand for mobile communication services, in order to meet the user demand, the industry has proposed a concept of massive MIMO in the early stage of research of the fifth generation (5G) mobile communication. The base station end is configured with a large-scale antenna array, so that the spatial degree of freedom is excavated to the maximum extent, and tens of users can be served with the same frequency at the same time. The massive MIMO technology is widely considered as a key technology in the field of 5G and future mobile communication, and has extremely strong commercial value.
However, the introduction of massive MIMO presents new challenges for systems operating in Frequency Division Duplex (FDD) mode. The acquisition of channel state information (CSI-T) at the transmitting end of the downlink is an important prerequisite to guarantee the space division performance. In order to obtain high-dimensional CSI-T, if pilot frequencies completely orthogonal in time-frequency domain are adopted at different antenna ports, hundreds of completely orthogonal pilot frequency patterns cannot be designed under the limitation of time-frequency resource networks, coherence time and related bandwidth. For FDD massive MIMO systems, therefore, the industry generally follows the codebook-based CSI-T acquisition method in 4G, and a set of spatial directional codebooks are preset for each user to select. However, this method is suitable for a channel environment with extremely strong sparsity in space, and is not suitable for an FDD low-frequency rich scattering scene specified by a 5G protocol. In addition, the industry also explores a great deal of CSI-T methods based on compressed sensing, and the compressed sensing also presupposes channel sparsity and has high requirements on the computing processing capacity of a mobile phone end, so that the compressed sensing cannot be realized in reality. Therefore, the acquisition of CSI-T in FDD massive MIMO systems has been one of the long-standing challenges in the industry.
In an FDD large-scale MIMO system, when a CSI-T acquisition method based on a codebook or based on compressed sensing is adopted, a user end feeds back the information to a base station after calculating a codebook number or a spatial sampling direction of a channel propagation path, and the base station can acquire only coarse spatial CSI-T rather than fine spatial CSI-T. For downlink multi-user transmission, the coarse spatial CSI-T cannot well achieve spatial multi-user interference cancellation, which causes interference leakage and rapid decrease of transmission efficiency. The base station must select a group of users completely avoided spatially to avoid the generation of interference as much as possible, which also puts higher requirements on the user scheduling policy. Therefore, on the premise of inaccurate CSI-T acquisition, the effect of user interference cancellation in FDD massive MIMO systems is also lost.
In summary, how to obtain the downlink multi-user CSI-T with higher accuracy with smaller pilot frequency and feedback overhead and how to ensure that the multi-user transmission performance is not lost due to the existence of interference become a challenge to the solution of the FDD massive MIMO system.
Disclosure of Invention
The purpose of the invention is as follows: in order to overcome the defects in the prior art, the method for reconstructing the downlink channel and transmitting the multiple users for the FDD large-scale MIMO system is provided, the bottleneck of acquiring the downlink CSI-T of the FDD large-scale MIMO system is broken through, the downlink multi-user channel with higher accuracy is reconstructed with lower pilot frequency and feedback overhead, and the method for transmitting the downlink multi-users without interference is provided by combining the characteristics of the system.
The technical scheme is as follows: in order to achieve the purpose, the invention specifically adopts the following technical scheme to solve the technical problems:
a downlink channel reconstruction and multi-user transmission method for an FDD large-scale MIMO system comprises the following steps:
1) the user sends the up pilot frequency to the base station, the pilot frequency is orthogonal among users, the base station extracts the direction angle and time delay of all propagation paths in each user channel;
2) the base station uses the estimated direction angle information to select and schedule users;
3) the base station sends downlink sparse pilot frequency, the selected users estimate downlink gain of each propagation path according to the received pilot frequency and feed back the downlink gain to the base station, and the base station reconstructs a downlink channel for each selected user;
4) and the base station designs a precoding matrix by utilizing the reconstructed downlink channel for downlink multi-user data transmission.
Further, the step 2 comprises the following steps:
2.1) the base station presets a group of sample direction angles, wherein the sample direction angles are a group of samples of the space direction and uniformly cover the whole space range;
2.2) for each direction angle extracted in the step 1, the base station normalizes the direction angle to the direction angle of the sample closest to the direction angle and marks the direction angle of the sample; for the same user channel, if two different extracted direction angles are normalized to the same sample direction angle, normalizing the latter extracted direction angle to the first nearest sample direction angle which is not selected by the user temporarily, and marking the sample direction angle;
2.3) counting the weights of all marked sample direction angles, wherein the weight of each sample direction angle is equal to the number of users covering the sample direction angle;
2.4) put these direction angles into the selected set of sample direction angles, and put all users into the selected set of users
Further, the base station in step 2 determines whether the number of the sample direction angles in the selected sample direction angle set exceeds a threshold, if so, deletes the first sample direction angle with the smallest weight from the selected sample direction angle set, deletes the user covering the sample direction angle from the selected user set, and updates the selected sample direction angle set and the selected user set; the above process is repeated until the number of sample direction angles in the selected set of sample direction angles does not exceed the threshold.
Further, the step 3 specifically includes the following steps:
3.1) the base station sends downlink sparse pilot frequency, the downlink pilot frequency is modulated to the sample direction angle in the selected sample direction angle set in sequence by adopting the beam forming technology, and the pilot frequencies corresponding to different sample direction angles are orthogonal;
3.2) for each user in the selected user set, only receiving the downlink pilot frequency corresponding to the covered sample direction angle, estimating the downlink gain of each propagation path in the channel by using the downlink pilot frequency, and feeding back the downlink gain to the base station;
3.3) for each user in the selected user set, the base station reconstructs a downlink channel for the user according to the uplink estimated direction angle, the uplink estimated time delay and the downlink gain obtained by feedback.
Further, in step 4, the base station designs a precoding matrix with multi-user interference suppression capability by using the reconstructed downlink channel, and the precoding matrix is applied to the downlink data transmission process, and the base station serves the users in the selected user set in a space division multiple access manner.
Has the advantages that: compared with the prior art, the invention adopting the technical scheme has the following technical effects:
1. the method presets a group of sample direction angles, normalizes the extracted direction angles to the sample direction angles, is equivalent to unifying the space directions of different users to the same group of space bases, changes the downlink pilot frequency from the special pilot frequency designed for a certain user into the common pilot frequency shared by all the users, and saves the downlink pilot frequency overhead.
2. After the downlink multi-user CSI-T is reconstructed, the method can directly utilize the high-accuracy CSI-T to design a downlink precoding method, perform space division multiple access transmission on all users with the reconstructed channel, eliminate the interference among the users and realize the maximum mining of the space freedom degree of the large-scale MIMO.
Drawings
Fig. 1 is a schematic diagram of a method for calculating a sample direction angle weight and a deletion user criterion in an embodiment of the present invention.
Detailed Description
The invention provides a downlink channel reconstruction and multi-user transmission method for an FDD large-scale MIMO system, which specifically comprises the following steps:
1) the user sends the up pilot frequency to the base station, the pilot frequency is orthogonal among users, the base station extracts the direction angle and time delay of all propagation paths in each user channel;
2) the base station uses the estimated direction angle information to select and schedule users, and the method specifically comprises the following steps:
2.1) the base station presets a group of sample direction angles, wherein the sample direction angles are a group of samples of the space direction and uniformly cover the whole space range;
2.2) for each direction angle extracted in the step 1, the base station normalizes the direction angle to the direction angle of the sample closest to the direction angle and marks the direction angle of the sample; for the same user channel, if two different extracted direction angles are normalized to the same sample direction angle, normalizing the latter extracted direction angle to the first nearest sample direction angle which is not selected by the user temporarily, and marking the sample direction angle;
2.3) counting the weights of all marked sample direction angles, wherein the weight of each sample direction angle is equal to the number of users covering the sample direction angle;
2.4) put these direction angles into the selected sample direction angle set and put all users into the selected user set;
2.5) the base station judges whether the number of the sample direction angles in the selected sample direction angle set exceeds a threshold, if so, the base station deletes the first sample direction angle with the minimum weight from the selected sample direction angle set, deletes the user covering the sample direction angle from the selected user set, and updates the selected sample direction angle set and the selected user set; the above process is repeated until the number of sample direction angles in the selected set of sample direction angles does not exceed the threshold.
3) The base station sends downlink sparse pilot frequency, the selected users estimate downlink gain of each propagation path according to the received pilot frequency and feed back the downlink gain to the base station, and the base station reconstructs a downlink channel for each selected user, which specifically comprises the following steps:
3.1) the base station sends downlink sparse pilot frequency, the downlink pilot frequency is modulated to the sample direction angle in the selected sample direction angle set in sequence by adopting the beam forming technology, and the pilot frequencies corresponding to different sample direction angles are orthogonal;
3.2) for each user in the selected user set, only receiving the downlink pilot frequency corresponding to the covered sample direction angle, estimating the downlink gain of each propagation path in the channel by using the downlink pilot frequency, and feeding back the downlink gain to the base station;
3.3) for each user in the selected user set, the base station reconstructs a downlink channel for the user according to the uplink estimated direction angle, the uplink estimated time delay and the downlink gain obtained by feedback.
4) And the base station designs a precoding matrix by utilizing the reconstructed downlink channel for downlink multi-user data transmission. The base station designs a pre-coding matrix with multi-user interference suppression capability by utilizing the reconstructed downlink channel, the pre-coding matrix is applied to the downlink data transmission process, and the base station serves the users in the selected user set in a space division multiple access mode.
In order to verify that the method of the present invention can provide a downlink channel reconstruction and multi-user transmission method for an FDD massive MIMO system, the following further explains the technical scheme of the present invention by a specific embodiment with reference to the accompanying drawings:
in an FDD massive MIMO system, the base station is located at the center of a cell, and a massive antenna array is erected, with the number of antenna elements being M, typically of the order of 102、103. The K users are uniformly and randomly distributed in the cell, and each user adopts single antenna configuration. The embodiment selects among K users, reconstructs the downlink channel of the selected user, and performs downlink interference-free transmission design for the selected user, including the following steps:
the method comprises the following steps: each user sends an uplink pilot frequency, the uplink pilot frequencies of different users are orthogonal to each other, and for a user K, K is 1k,lAnd the direction angle thetak,lWherein L1k，LkThe number of propagation paths in the user k channel.
Step two: the base station defines a set of sample direction angles
For user k, the base station will θk,l,l＝1,...,LkNormalized to the nearest sample orientation angle, respectively, and labeled, e.g. thetak,l+1Nearest sample orientation angle and θk,lNormalized to the same sample direction angle, then θ will bek,l+1Normalizing to another nearest sample orientation angle and marking the sample orientation angle. After the direction angles of all users are normalized, the base station puts all marked sample direction angles into a selected sample direction angle set phi, counts the weight of each sample direction angle in the phi, the weight of each sample direction angle and the like and the number of users marking the sample direction angle, as shown in figure 1,
the weight of (a) is 1,
with a weight of 2, and then put all users into the selected user set Ψ. And the base station counts the number of the direction angles of the samples in phi and judges whether the number exceeds a threshold. If the threshold is exceeded, the first sample direction angle with the smallest weight in Φ is deleted, as in FIG. 1
The user that marked the sample azimuth, e.g., user 4 in fig. 1, is also deleted from Ψ, and Φ and Ψ are updated. Judging whether the number of the sample direction angles in phi exceeds a threshold, if so, repeating the process until the number T of the sample direction angles in phi does not exceed the threshold, and at the moment, the user in psi is k1,...,
。
Step three: the base station sends T downlink sparse pilots, each pilot is orthogonal, and pilot 1 to pilot T point to sample direction angle 1 to sample direction angle T in phi respectively. For users in Ψ
Only receiving the pilot frequency corresponding to the marked sample direction angle, and estimating the downlink gain of each propagation path in the channel according to the pilot frequency
l＝1,...,
And feeds back the gain value to the base station. For the user
Base station utilization
Reestablish its downlink channel
Step four: base station utilizes reconstructed downlink multi-user channel
Computing zero-forcing precoding matrix W-H with multi-user interference suppression capabilityH(HHH)-1The method is used in the downlink multi-user space division multiple access data transmission process.
Claims (5)
1. A downlink channel reconstruction and multi-user transmission method for FDD large-scale MIMO system is characterized in that: the method comprises the following steps:
1) the user sends the up pilot frequency to the base station, the pilot frequency is orthogonal among users, the base station extracts the direction angle and time delay of all propagation paths in each user channel;
2) the base station uses the estimated direction angle information to select and schedule users;
3) the base station sends downlink sparse pilot frequency, the selected users estimate downlink gain of each propagation path according to the received pilot frequency and feed back the downlink gain to the base station, and the base station reconstructs a downlink channel for each selected user;
4) the base station designs a pre-coding matrix by utilizing the reconstructed downlink channel for downlink multi-user data transmission;
the step 2) comprises the following steps:
2.1) the base station presets a group of sample direction angles, wherein the sample direction angles are a group of samples of the space direction and uniformly cover the whole space range;
2.2) for each direction angle extracted in the step 1, the base station normalizes the direction angle to the direction angle of the sample closest to the direction angle and marks the direction angle of the sample;
2.3) counting the weights of all marked sample direction angles, wherein the weight of each sample direction angle is equal to the number of users covering the sample direction angle;
2.4) put these direction angles into the selected sample direction angle set and put all users into the selected user set.
2. The method according to claim 1, wherein the method for downlink channel reconstruction and multi-user transmission for FDD massive MIMO system comprises: the step 2.2) is specifically as follows: for the same user channel, if two different extracted direction angles are normalized to the same sample direction angle, the latter extracted direction angle is normalized to the nearest first sample direction angle which is not selected by the user temporarily, and the sample direction angle is marked.
3. The method according to claim 1, wherein the method for downlink channel reconstruction and multi-user transmission for FDD massive MIMO system comprises: in the step 2.4), the specific process for the selected sample direction angle set and the selected user set is as follows:
the base station judges whether the number of the sample direction angles in the selected sample direction angle set exceeds a threshold, if so, the base station deletes the first sample direction angle with the minimum weight from the selected sample direction angle set, deletes the user covering the sample direction angle from the selected user set, and updates the selected sample direction angle set and the selected user set; the above process is repeated until the number of sample direction angles in the selected set of sample direction angles does not exceed the threshold.
4. The method according to claim 1, wherein the method for downlink channel reconstruction and multi-user transmission for FDD massive MIMO system comprises: the step 3) specifically comprises the following steps:
3.1) the base station sends downlink sparse pilot frequency, the downlink pilot frequency is modulated to the sample direction angle in the selected sample direction angle set in sequence by adopting the beam forming technology, and the pilot frequencies corresponding to different sample direction angles are orthogonal;
3.2) for each user in the selected user set, only receiving the downlink pilot frequency corresponding to the covered sample direction angle, estimating the downlink gain of each propagation path in the channel by using the downlink pilot frequency, and feeding back the downlink gain to the base station;
3.3) for each user in the selected user set, the base station reconstructs a downlink channel for the user according to the uplink estimated direction angle, the uplink estimated time delay and the downlink gain obtained by feedback.
5. The method according to claim 1, wherein the method for downlink channel reconstruction and multi-user transmission for FDD massive MIMO system comprises: and 4) designing a precoding matrix with multi-user interference suppression capability by the base station by using the reconstructed downlink channel in the step 4), wherein the precoding matrix is applied to a downlink data transmission process, and the base station serves the users in the selected user set in a space division multiple access manner.
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