CN106160809B

CN106160809B - Mixed precoding method and device for multi-user multi-antenna system

Info

Publication number: CN106160809B
Application number: CN201510171123.6A
Authority: CN
Inventors: 吴克颖; 武露
Original assignee: Alcatel Lucent SAS
Current assignee: Alcatel Lucent SAS
Priority date: 2015-04-10
Filing date: 2015-04-10
Publication date: 2020-03-13
Anticipated expiration: 2035-04-10
Also published as: CN106160809A

Abstract

The invention relates to a multi-user multi-antenna systemA unified hybrid precoding method and apparatus thereof. According to one embodiment of the present invention, a method for hybrid analog/digital precoding for multi-user antenna systems includes assigning N_TThe root antenna is divided into L groups; digitally pre-encoding the K data streams into S data streams; configuring the phase shift network into L sub phase shift networks with signal isolation, wherein the L sub phase shift networks respectively correspond to the L groups of antennas; wherein the phase shifting network comprises S radio frequency links for receiving each of the S data streams, respectively, each of the L sub phase shifting networks further comprising at least one of the S radio frequency links; and mapping the output of each radio frequency link in each sub-phase shifting network to each antenna in the corresponding antenna group, wherein N is_TS, K, L is an integer greater than 1, NT is greater than or equal to S and greater than or equal to K, and S is greater than or equal to L. The invention can effectively balance the complexity and the performance of the multi-user antenna system.

Description

Mixed precoding method and device for multi-user multi-antenna system

Technical Field

The present invention relates to a multi-user multi-antenna system, and more particularly, to a hybrid analog/digital precoding method and apparatus for a multi-user multi-antenna system.

Background

In a multi-user antenna system, the hybrid precoding technique reduces the number of radio frequency paths by moving part of the spatial signal processing from the baseband side to the radio frequency front end, which can effectively reduce the cost, hardware complexity and power consumption caused by the arrangement of the radio frequency paths (RF paths). And theoretically, although the multiplexing gain is limited by the number of radio frequency paths, the hybrid precoding technique can still obtain the complete diversity gain and array gain through proper processing.

The analog precoding in hybrid precoding is implemented by means of an analog phase network. However, the existing hybrid precoding processing method and apparatus are difficult to achieve a good balance between the complexity of the analog phase shifting network and the precoding performance, one still uses the complex analog phase shifting network to achieve high performance, and the other cannot achieve good performance though the complexity of the analog phase shifting network is reduced.

Accordingly, there remains a need in the art for improvements to existing hybrid precoding techniques.

Disclosure of Invention

It is an object of the present invention to provide a hybrid analog/digital precoding method and apparatus for a multi-user multi-antenna system that combines implementation complexity and performance without biasing towards either extreme.

An embodiment of the present invention provides a system for multiple users for multiple daysMethod for hybrid precoding of a line system, comprising converting N_TThe root antenna is divided into L groups; digitally pre-encoding the K data streams into S data streams; configuring the phase shift network into L sub phase shift networks with signal isolation, wherein the L sub phase shift networks respectively correspond to the L groups of antennas; wherein the phase shifting network comprises S radio frequency links for receiving each of the S data streams, respectively, each of the L sub phase shifting networks further comprising at least one of the S radio frequency links; and mapping the output of each radio frequency link in each sub-phase shifting network to each antenna in the corresponding antenna group, wherein N is_TS, K, L is an integer greater than 1, N_TS is more than or equal to K and S is more than or equal to L.

In one embodiment, N_TGreater than 2. Performing wideband analog precoding in each of the sub phase-shifting networks, and performing narrowband digital precoding between the L sub phase-shifting networks; with C_lWideband analog precoding matrix representing the L (1-L) th group, B_wRepresenting the digital precoding matrix on the w-th subcarrier, the whole precoding process is represented as:

wherein y is_wIs a K x 1 vector, H, received by K user equipment antennas on the w-th subcarrier_wIs KxN on all user equipment antennas on the w-th subcarrier_TChannel vector, x_wIs a K x 1 data vector transmitted on the w-th subcarrier, and n_wIs additive white gaussian noise. C_lCan be formed by transmitting correlation matrix

The following calculation is carried out:

from

Extracting (N) corresponding to the l-th group of antennas_T/L)×(N_T/L) sub-matrix

Then execute

Singular Value Decomposition (Singular Value Decomposition) of (A) to obtain

Wherein U is_lIs a unitary matrix, Λ_lIs a diagonal matrix with diagonal elements arranged in descending order

Singular value of, C_l＝U_l(:,1:S/L)，U_l(1: S/L) represents a group represented by U_lThe first to S/L-th columns of (a).

In one embodiment, the wideband precoding employs an iterative greedy search method for users served by each sub-outphasing network, which includes:

in each iteration, accessing the L sub phase shift networks and adding at most one user equipment to a service user equipment list of each sub phase shift network; starting with p ═ 0 iterations, where arbitrary l.values are initialized

C_l0; wherein κ_lAn index set representing user equipments of the ith group of services; each iteration comprises L sub-iterations, and the qth sub-iteration of the pth iteration is denoted as the (p, q) th iteration if q is equal to 1 to L<L can be moved to the (p, q +1) th iteration, and when q is equal to L, the (p +1,1) th iteration can be moved; in the (p, q) th iteration, only κ in the previous iteration is modified_qAnd C_qWhile maintaining { κ_lL ≠ q } with { C_lL ≠ q } is unchanged; when no new user equipment is added to any of the L sub phase shift networks, the iteration stops.

The kappa chain_qAnd C_qIs modified by searching all the indexes k e v k_qThe upsilon represents a set of all user equipment in the cell; k belongs to upsilon and k for each user equipment_qRegenerating the corresponding κ_q∪ k of C_qAnd calculating the average capacity of the corresponding effective channel, and selecting a user equipment k with the maximum average capacity of the effective channel if corresponding to k_q∪ k has a capacity greater than corresponding k_qAdding k to k_q. In one embodiment, N is_TThe antennas are equally allocated to the L groups, and in another embodiment the NT antennas are unequally allocated to the L groups.

An embodiment of the present invention also provides a base station comprising NT antennas configured to be divided into L groups, a baseband precoder configured to digitally precode K data streams into S data streams, and a phase shifting network configured to comprise S radio frequency links that respectively receive each of the S data streams. The phase shift network is further configured to be L sub-phase shift networks respectively corresponding to the L groups of antennas, wherein NT, S, K and L are integers greater than 1, NT is greater than or equal to S and is greater than or equal to K, and S is greater than or equal to L. Each of the L sub phase shifting networks further comprises at least one of the S rf chains, an output of each rf chain in each sub phase shifting network is mapped to each antenna in a corresponding antenna group, and the L sub phase shifting networks are signal isolated from each other.

In one embodiment, each of the sub-phase shifting networks further comprises a power divider configured to divide the output of each rf link in each of the sub-phase shifting networks into multiple paths; a phase shifter configured to shift the phase of each output of the power divider; and a combiner configured to combine outputs of the phase shifters corresponding to the same antenna.

The hybrid precoding method and the hybrid precoding device provided by the embodiment of the invention can flexibly adjust the setting of the complexity and the performance of the system according to the specific requirements of the multi-user antenna system, thereby allowing the current multi-user multi-antenna system to select the most appropriate complexity and system performance.

Drawings

FIG. 1 is a diagram illustrating a structure of a typical hybrid precoding device;

FIG. 2 is a schematic diagram of another exemplary hybrid precoding device;

fig. 3 is a schematic structural diagram of a hybrid precoding device according to an embodiment of the present invention;

fig. 4 and 5 respectively illustrate different grouping methods when the planar antenna arrays of 8 by 8 are equally divided into 4 groups according to an embodiment of the present invention.

Detailed Description

In order that the spirit of the invention may be better understood, some preferred embodiments of the invention are described below.

In the hybrid precoding technique, analog precoding is usually implemented by using an analog phase shifting network, and the complexity of the phase shifting network depends on the specific architecture of the analog precoding processing device.

For example, fig. 1 is a schematic diagram of a typical hybrid precoding device 10. The hybrid precoding device 10 may be provided to a base station (not shown) having N antennas 12, N being an integer greater than 1. As shown in fig. 1, hybrid precoding device 10 includes a baseband precoder 14 and a phase shifting network 16. The phase shifting network 16 includes S radio frequency chains (RF chains) 160, where S is an integer greater than or equal to 1 and less than or equal to N. The output of each rf chain 160 is split by the power splitter 162, phase-shifted by the phase shifter 164, and mapped to all N antennas 12, and the received signals of all S rf chains 160 on each antenna 12 are added together by the combiner 166 for transmission. It can be seen that in the hybrid precoding device 10, the phase shift network 16 needs to arrange S × N rf paths 168 to realize full mapping of signals. The hybrid precoding device 10 trades the most complex hardware structure for optimal performance.

Fig. 2 is a schematic diagram illustrating the structure of another exemplary hybrid precoding device 20. The hybrid precoding device 20 may be disposed at a base station (not shown) having N antennas 22, N being an integer greater than 1. As shown in fig. 2, the hybrid precoding device 20 includes a baseband precoder 24 and a phase shift network 26. The phase shifting network 26 includes S rf chains 260, where S is an integer greater than or equal to 1 and less than or equal to N and N is set to be an integer multiple of S for simplicity. The N antennas 22 are divided into S groups. The output of each rf link 260 is split by a power splitter 262 into N/S signals, phase shifted by a phase shifter 264 and mapped to each antenna 22 for transmission. It can be seen that in the hybrid precoding device 20, the phase shift network 26 only needs to arrange N rf paths 268. The hybrid precoding device 20 has the simplest structure, but has poor performance.

The hybrid precoding method and the hybrid precoding device provided by the embodiment of the invention can flexibly adjust the relation between complexity and performance according to the system requirements, have the advantages of the two structures and reduce the defects of the two structures as far as possible. Simulation results show that compared with the prior art, the hybrid precoding technology provided by the embodiment of the invention only loses 4% of performance under the condition that the hardware complexity is reduced to half of the structure shown in FIG. 1; and only 12% of the performance is lost with the hardware complexity reduced to one fourth of the architecture shown in figure 1.

Fig. 3 is a schematic structural diagram of a hybrid precoding device 30 according to an embodiment of the present invention.

As shown in fig. 3, the hybrid precoding device 30 can be disposed on a base station (not shown) having N disposed thereon_T Root antenna 32, N_TIs an integer of 1 or more, preferably 2 or more. In this embodiment, the base station is set for simplicity to transmit downlink data for K single-antenna user equipments (not shown), where K is an integer greater than or equal to 1. In other embodiments, the user equipment may not be single antenna and does not affect the essence of the present invention.

The hybrid precoding device 30 includes a baseband precoder 34 and a phase shifting network 36. Phase shifting network 36 includes S radio frequency links 360, N_TS is more than or equal to K. Will N_TThe antennas 32 may be equally or unequally distributed into L groups, S ≧ L, with no handshaking between the antennas 32 of the groups. Accordingly, the phase shifting network 36 is further configured as L sub-phase shifting networks 360, each sub-phase shifting network 360 corresponding to a group of antennas 32. Similarly, sub-phase shifting network 360 has no signal communication therebetween. In this embodiment, N is set for simplicity_TS is an integral multiple of L to convert N to_TThe antenna 32 and the S radio frequency links 361 are divided into L groups, and N is arranged in each group_Ta/L antennas 32 and S/L RF links 361. For example, fig. 4 and 5 respectively illustrate different grouping methods when the planar antenna array of 8 x 8 is divided into 4 groups, each group having 16 days, according to an embodiment of the present inventionLine 32, different patterns representing different groupings. These different grouping methods are based on the number of antennas N_TAnd the number of packets L is determined without affecting the essence of the present invention. For the case of staggered antenna 32 positions within each group in fig. 5, an antenna mapper may be used to implement the design of each sub-phase shifting network 360 output corresponding to any antenna 32.

When the base station intends to transmit K data to K served user equipments, the K data streams are first processed by the digital precoding processor 34 of the baseband as S data streams, and the S data streams are respectively provided to the S rf links 361. Each sub-phase shift network 360 comprises S/L radio frequency links 361, S/L power dividers 363, and SN/L²Phase shifters 335 and S/L combiners 367. Within each sub-phase shifting network 360, the output of each RF link 361 is split by a power splitter 363 into N_Tthe/L split signals are phase-shifted by the phase shifter 365 to be provided to N corresponding to the sub-phase shifting network 360 respectively_TAnd L antennas. For a base station antenna 32, it receives signals provided by all S/L rf links 361 in the corresponding sub-phase shifting network 360, and these signals are superimposed by the combiner 367 and then transmitted to the user equipment by the antenna 32. That is, the present invention achieves the maximum performance requirements for the antennas 32 within each group. Meanwhile, because a grouping processing method is adopted, no signal communication exists between groups, the integral phase shifting network 36 is controlled in SN/L radio frequency paths, and the value of L can be far smaller than that of SN radio frequency paths in full mapping by controlling.

The embodiment of the present invention also provides a hybrid precoding method, which can be executed by the hybrid precoding device 30 shown in fig. 3. Spatial signal processing is divided into wideband analog precoding and narrowband digital precoding, where analog precoding is performed within each sub-phase shifting network 360 and digital precoding is performed jointly between the L sub-phase shifting networks 360.

In particular, for a compound having N_FFTFor the downlink of a massive mimo system with subcarriers, time division multiplexing is used so that the base station can obtain channel state information from uplink detection. Based on the foregoing settings, assume that the output of the l-th group is mapped to an index of (l-1) N_T/L+1～lN_TAn antenna of/L. h is_k,wN on w sub-carrier for k user equipment_TX 1-dimensional frequency domain channel vector. From the Kronecker channel model, one can obtain

Wherein

Is h_k,wIs constant over the entire bandwidth, and

is a random vector containing independent identically distributed (i.i.d.) elements.

The transmission periods, the user equipments served by each sub-phase shifting network 360 and the corresponding set of antennas 32 may be the same or different, depending on the scheduling result of the base station. With κ_lA set of indices representing user equipments served by the ith group (each sub-phase shifting network 360 and corresponding group of antennas 32),

(no repetition). K_lAnd K each represents K_lAnd the size of κ.

With C_lWideband analog precoding matrix, B, representing the l-th group_wRepresenting the digital precoding matrix on the w-th subcarrier, the whole precoding process is represented as:

wherein y is_wIs a K × 1 vector, H, received by K user equipments (user equipment antennas, for a single antenna user equipment, the number of user equipment antennas is equal to the number of user equipments, the same applies below) on the w-th subcarrier_wIs K N of K user equipments on w-th subcarrier_TChannel vector, x_wIs a K x 1 data vector transmitted on the w-th subcarrier, and n_wIs Additive White Gaussian Noise (AWGN).

Analog precoding matrix { C_lB and a digital precoding matrix B_wCan be obtained by mutually independent methods, as explained below

First for analog precoding, K of the l-th group_l×N_TThe channel matrix is represented as:

H_l,wthe transmit correlation matrix of (a) may be calculated as:

from

Then execute

Singular Value Decomposition (SVD) of

The singular value of (a).

The l-th group of analog precoding matrices C_lThe calculation is as follows:

C_l＝U_l(：，1：S/L) (6)

wherein U is_l(1: S/L) represents a group represented by U_lThe first to S/L-th columns of (a).

After obtaining the simulation precoding matrix { C_lAfter the calculation, a digital precoding matrix B of each subcarrier can be calculated based on (analog precoding) effective channels_w，

Wherein the precoding matrix is simulated

Is an active channel on the w-th subcarrier; and P is a diagonal matrix whose diagonal elements represent the average transmission power of K user equipments.

In order to maximize the system performance, the embodiment of the invention provides a group-by-group greedy search method for user equipment scheduling during wide simulation precoding.

All user equipment sets in the cell are expressed by upsilon, and the broadband precoding method of the embodiment of the invention adopts an iterative exhaustive search method for different groups, namely each sub phase-shifting network 360. In each iteration, all groups are accessed and at most one user device is added to its list of serving user devices for each group. Starting with p ═ 0 iterations, where arbitrary l.values are initialized

C_l0. Each iteration comprises L sub-iterations. Designating the qth (q 1-L) sub-iteration of the pth iteration as the (p, q) th iteration if q is greater than<L may be shifted to the (p, q +1) th iteration, and to the (p +1,1) th iteration when q ═ L. In the (p, q) th iteration, by modifying only κ in the previous iteration_qAnd C_qWhile maintaining { κ_lL ≠ q } with { C_lAnd l ≠ q } is unchanged, the effective channel capacity can be maximized by the broadband precoding method. Kappa_qAnd C_qIs modified by searching all the values with indices k e v k_qThe user equipment of (1). K belongs to upsilon and k for each user equipment_qThe wideband precoding method pair κ of the embodiment of the present invention_q∪ k, using equation (6), to regenerate C_qAnd calculates the average capacity of the corresponding effective channel. Then, the ue with the maximum average capacity of the active channels is set to k, if corresponding to k_q∪ k has a capacity greater than corresponding k_qAdding k to k_q. When no user equipment is added to any group, the iteration stops.

While the foregoing has been with reference to the disclosure of the present invention, it will be appreciated by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the protection scope of the present invention should not be limited to the disclosure of the embodiments, but should include various alternatives and modifications without departing from the invention, which are covered by the claims of the present patent application.

Claims

1. A method for hybrid analog/digital precoding for a multi-user multi-antenna system, the method comprising:

will N_TThe root antenna is divided into L groups;

digitally pre-encoding the K data streams into S data streams;

configuring a phase shift network into L sub phase shift networks with signal isolation, wherein the L sub phase shift networks respectively correspond to the L groups of antennas; wherein the phase shifting network comprises S radio frequency chains respectively receiving each of the S data streams, each of the L sub phase shifting networks further comprising at least one of the S radio frequency chains, wherein N_TS, K, L is an integer greater than 1, N_TS is more than or equal to K and S is more than or equal to L;

the output of each radio frequency link in each sub-phase shifting network is mapped to each antenna in the corresponding antenna group.

2. The method of claim 1, wherein N_TGreater than 2.

3. The method of claim 1, wherein wideband analog precoding is performed in each of the L sub phase-shifting networks, and narrowband digital precoding is performed between the L sub phase-shifting networks; with C_lWideband analog precoding matrix representing the L (1-L) th group, B_wRepresenting the digital precoding matrix on the w-th subcarrier, the whole precoding process is represented as:

wherein y is_wIs a Kx 1 vector, H, received by K user equipment antennas on the w-th subcarrier_wIs KxN on all user equipment antennas on the w-th subcarrier_TChannel vector, x_wIs a K x 1 data vector transmitted on the w-th sub-carrier, and n_wIs additive white gaussian noise.

4. The method of claim 3, wherein C_lBy transmitting correlation matrices

The following calculation is carried out:

from

Then execute

Singular Value Decomposition (Singular Value Decomposition) of (A) to obtain

Wherein U is_lIs a unitary matrix, Λ_lIs composed of

Medium diagonal matrix with diagonal elements in descending order

Singular value of, C_l＝U_l(:,1:S/L)，U_l(1: S/L) represents a group represented by U_lThe first to S/L-th columns of (a). .

5. The method of claim 3, wherein the wideband precoding uses an iterative greedy search method for users served by the each sub-outphasing network, comprising:

in each iteration, accessing the L sub phase shift networks and adding at most one user equipment to a corresponding service user equipment list for each sub phase shift network;

starting with p ═ 0 iterations, where arbitrary l.values are initialized

C_l0; wherein

An index set representing user equipments of the ith group of services;

each iteration comprises L sub-iterations, the qth sub-iteration of the pth iteration is marked as the (p, q) th iteration, if q is less than L, the iteration can be shifted to the (p, q +1) th iteration, and if q is equal to L, the iteration can be shifted to the (p +1,1) th iteration;

in the (p, q) th iteration, only those in the previous iteration are modified

And C_qTo maintain

And { C_lL ≠ q } is unchanged;

and when no new user equipment is added into any one of the L sub phase-shifting networks, the iteration is stopped.

6. The method of claim 5, wherein the

And C_qBy searching all the indexes

The user equipment of (1) is selected,

representing a set of all user equipments in a cell; for each user equipment

Regenerating correspondences

C of (A)_qAnd calculating the average capacity of the corresponding effective channel, and selecting a user equipment k with the maximum average capacity of the effective channel if corresponding to the maximum average capacity

Is greater than corresponding

Adding k to the volume of (1)

7. The method of claim 1, wherein said N is_TThe root antennas are equally distributed into L groups.

8. The method of claim 1, wherein said N is_TThe root antennas are non-equally allocated to the L groups.

9. A base station, comprising:

N_Ta root antenna configured to be divided into L groups;

a baseband precoder configured to digitally precode K data streams into S data streams;

a phase shifting network configured to include S radio frequency links that respectively receive each of the S data streams; and the phase shift network is further configured to have L sub-phase shift networks respectively corresponding to the L groups of antennas, wherein N is_TS, K, L is an integer greater than 1, N_TS is more than or equal to K and S is more than or equal to L;

wherein each of the L sub phase shifting networks further comprises at least one of the S radio frequency links, an output of each radio frequency link in each sub phase shifting network is mapped to each antenna in a corresponding antenna group, and the L sub phase shifting networks are signal isolated.

10. The base station of claim 9, wherein said N is divided_TThe root antennas are equally distributed into L groups.

11. The base station of claim 9, wherein said N is divided_TThe root antennas are non-equally allocated to the L groups.

12. The base station of claim 9, wherein N_TGreater than 2.

13. The base station of claim 9, wherein each of said sub phase shifting networks further comprises a power divider configured to divide the output of each rf link in said each sub phase shifting network into multiple paths; a phase shifter configured to shift the phase of each path of output of the power divider; and a combiner configured to combine outputs of the phase shifters corresponding to the same antenna.

14. A method for joint multi-user scheduling among networks having L sub-phase shifts, the method comprising:

in each iteration, accessing the L sub phase shift networks and adding at most one user equipment to a service user equipment list of each sub phase shift network;

starting with p ═ 0 iterations, where arbitrary l.values are initialized