CN104618080B

CN104618080B - Channel calibration method for extensive multiple-input and multiple-output tdd systems

Info

Publication number: CN104618080B
Application number: CN201510047935.XA
Authority: CN
Inventors: 粟欣; 容丽萍; 曾捷; 刘强; 许希斌; 王京
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2015-01-30
Filing date: 2015-01-30
Publication date: 2017-12-26
Anticipated expiration: 2035-01-30
Also published as: CN104618080A

Abstract

The present invention relates to a kind of channel calibration method for extensive multiple-input and multiple-output tdd systems, belong to wireless communications relay channel calibration technical field, this method includes：Extensive multi-input multi-output system is divided into three subsystems, three subsystems include a single-input single-output system, two single-input multiple outputs；The up-downgoing channel for calibrating three subsystems respectively draws channel calibration coefficient.Then the calibration factor of whole multi-input multi-output system is drawn according to the channel calibration coefficient of three subsystems, the more accurately downlink channel condition information of whole system is drawn further according to uplink channel status information.This method can reduce the feedback of channel condition information, power system capacity is improved compared to general conventional method, and reduce system and send the power that pilot tone is consumed.

Description

Channel calibration method for large-scale multiple-input multiple-output time division duplex system

Technical Field

The invention belongs to the technical field of wireless communication relay channel calibration, and particularly relates to a method for calibrating a downlink channel from a multi-antenna base station to a multi-antenna relay in the TDD-LS-MIMO (time division duplex-least square-error multiple input multiple output) in the field of wireless communication

Background

With the increasing of mobile terminals, the traffic of downlink data is also increasing, and a Multiple Input Multiple Output (MIMO) system can increase channel capacity, thereby drawing extensive attention in the industry and academia. MIMO has two duplex modes, one is Frequency Division Duplex (FDD) and the other is Time Division Duplex (TDD). Frequency Division Duplex (FDD) is a duplex mode widely used at present, and is mainly characterized in that uplink and downlink channels work in different frequency bands, however, in the MIMO system, the pilot overhead of Frequency Division Duplex (FDD) is too large when estimating the downlink channel state. And a Time Division Duplex (TDD) mode is adopted, and because the uplink and downlink channels work in the same frequency band, the uplink and downlink channels have reciprocity, and the state information of the downlink channel can be estimated according to the state information of the uplink channel. However, the reciprocity of the channel is damaged due to the imperfection of the receiving device caused by the uplink and downlink transmission, and the state information of the downlink channel cannot be accurately estimated by using the state information of the uplink channel. Therefore, the uplink and downlink channels need to be calibrated to satisfy reciprocity. The conventional channel calibration technology is to obtain the uplink and downlink channel state information respectively, and then perform calibration to obtain the relationship between the uplink and downlink channels, which is inefficient and requires a large amount of downlink channel state information to be fed back to the base station.

Disclosure of Invention

The invention aims to promote the application of a time division duplex large-scale multiple-input multiple-output technology in the field of wireless communication, and provides a channel calibration method for a large-scale multiple-input multiple-output time division duplex system.

The invention provides a channel calibration method for a large-scale multi-input multi-output time division duplex system, which is characterized by comprising the step of dividing the large-scale multi-input multi-output system into three subsystems, wherein the three subsystems comprise a single-input single-output system (SISO) and two single-input multi-output Systems (SIMO). And respectively calibrating the uplink and downlink channels of the three subsystems to obtain channel calibration coefficients. Then, the calibration coefficient of the whole multiple input multiple output system (MIMO) is obtained according to the channel calibration coefficients of the three subsystems, and the more accurate downlink channel state information of the whole system is obtained according to the uplink channel state information.

The invention specifically comprises the following steps:

1) determining a reference channel, a reference antenna, and dividing the subsystem: dividing a large-scale base station and a user multi-input multi-output system a into three subsystems, wherein a user B end sends an uplink pilot signal, and a base station A end sends a pilot signal according to the B endEstimating uplink channel state information by using frequency signals, selecting a channel with the highest channel gain as a reference channel, using antennas at two ends of the reference channel as reference antennas, and setting M antennas at the A end as A₁～A_MThe reference antenna selected by the base station A is A₁，A₂～A_M，A_i∈ C (i 2, 3.. M) represents other antennas of a, the base station a sends information containing reference antennas to the base station B, and the B end has N antennas which are respectively B₁～B_NThen the base station B selects the reference antenna as B according to the information sent by the base station A₁，B₂～B_N(B_j∈ D (j 2, 3.., N)) represents the other antenna of B, antenna a₁And an antenna B₁Form a single-input single-output SISO system b, a reference antenna A₁And an antenna A₂～A_MForming a single-input multi-output sub SIMO system c, an antenna B₁And an antenna B₂～B_NForming another single-input multi-output sub SIMO system d;

2) estimating β channel calibration coefficients for system b_b: estimating uplink and downlink channel state information of a SISO system b, and obtaining the estimation result according to a formula (3): g_b＝H_b·β_b(4)，

Wherein,multiple estimation of G_b,H_bGenerating a total least squares problem, solving the least squares problem, and finding the calibration coefficients β_b；

3) Estimating β channel calibration coefficients for system b_c：A₁And A₂～A_MSIMO system c composed of obtaining uplink and downlink channel state information G of SIMO system c_c,H_cObtained according to equation (3):

G_c＝β_c·H_c(5)

wherein,multiple estimation of G_c,H_cGenerating M-1 total least squares problems, solving the least squares problem, and finding the calibration coefficients β_c：diag(β_c) Is β_cA main diagonal element;

4) estimating β channel calibration coefficients for system b_d: obtained by B₁，B₂～B_NComposed SIMO system d, obtaining the status information G of the up and down channels of the SIMO system d_d,H_dG is obtained from the formula (3)_d＝β_d·H_d(6)

WhereinMultiple estimation of G_d,H_dGenerating N-1 total least squares, solving the least squares problem, and finding the calibration coefficients β_d：diag(β_d) Is β_dA main diagonal element;

5) calculating β calibration coefficients for massive MIMO system a_aComprises the following steps:

from steps 2),3),4) it is possible to derive β_b,β_c,β_cContaining β_aAll of the information of (1), therefore β_aBy β_b,β_c,β_cIs represented as follows:

6) estimating downlink channel state information of the massive multiple-input multiple-output system a according to formula (8):

[G]_mn＝[H]_mn·[β_a]_mn(8)

[G]_mnfor downlink channel state information of the nth channel, [ H ]]_mnFor the uplink channel state information of the mn-th channel,

[β_a]_mnand if the channel calibration coefficient is the channel calibration coefficient of the nth channel, estimating the state information of the downlink channel according to the uplink channel information.

The method can reduce the feedback of the channel state information, improve the system capacity to a certain extent compared with the common traditional method, and reduce the power consumed by the system for sending the pilot frequency.

Drawings

FIG. 1 is a schematic diagram of a system model of the present invention.

FIG. 2 is a schematic diagram of an equivalent circuit of the system of the present invention.

FIG. 3 is a block diagram of a method of the present invention.

Detailed Description

The channel calibration method for the large-scale MIMO TDD system provided by the invention is further explained in the structural drawings and the embodiment as follows:

the present invention divides the mimo system of large-scale base station and user into three subsystems, as shown in fig. 1: the large-scale multiple-input multiple-output system a (MIMO) is divided into three subsystems including a single-input single-output system b (SISO), two single-input multiple-output systems c and d (SIMO). The transmitting end is represented by base station a and the receiving end by user B. The A end is provided with M antennae A₁～A_M，A₁To selectFixed reference antenna, A₂～A_M(A_i∈ C (i 2, 3.. M)) represents the other antenna of a, and the B end has N antennas, respectively B₁～B_N，B₁For the selected reference antenna, B₂～B_N(B_j∈ D (j 2, 3.., N)) represents the other antenna of B₁～A_MAnd B₁～B_NConstituting the entire MIMO system, reference antenna A₁And a reference antenna B₁The constituent single-input single-output sub-SISO systems are denoted by system b, reference antenna A₁And an antenna A₂～A_MThe SIMO system with one single input and multiple outputs is represented by system c, and antenna B₁And an antenna B₂～B_NThe constituent single-input multiple-output sub-SIMO systems are denoted by system d.

The principle of the invention is as follows:

the equivalent circuit of the above system is shown in fig. 2: t is_AEquivalent filter for A-terminal transmission circuit, T_BEquivalent filter for B-terminal transmission circuit, R_AEquivalent filters for A-terminal receiving circuits, R_BAnd C is an ideal electromagnetic channel.

Setting: the downlink channel state information is: g ═ R_B·C·T_A(1)，

The uplink channel state information is: h ═ R_A·C^T·T_B(2)。

Due to T_A，T_B，R_A，R_BIs that the uplink channel state information H is not equal to the downlink channel state information G, i.e. G ≠ H, and for estimating G using H, the channel needs to be calibrated, i.e. G

By eliminating C in the formulae (1) and (2): g ═ P_B·H·P_A(3)，

WhereinAnd T, regardless of the crosstalk problem between the antennas_A，T_B，R_A，R_BIs a diagonal matrix.

The invention relates to a channel calibration method for a large-scale multiple-input multiple-output time division duplex system, which is characterized by comprising the following specific steps of:

1) determining a reference channel, a reference antenna, and dividing the subsystem: user B sends up pilot signal, base station A estimates up channel state information according to B sent pilot signal, selects one channel with highest channel gain as reference channel, the antennas at two ends of reference channel are used as reference antenna, the reference antenna selected by base station A is set as A₁If the base station A sends the information containing the reference antenna to the base station B, the base station B selects the reference antenna as B according to the information sent by the base station A₁Antenna A₁And an antenna B₁Forming a single-input single-output SISO system b;

Wherein,multiple estimation of G_b,H_bThen a total least squares problem is generated, the least squares problem is solved, and the calibration coefficients β are obtained_b；

3) Estimating the channel calibration coefficients β for subsystem c_c：A₁And A₂～A_MSIMO system c composed of obtaining uplink and downlink channel state information G of SIMO system c_c,H_cFrom equation (3), we can obtain: g_c＝β_c·H_c(5)

Wherein,(because there is no antenna between them)Problem of crosstalk, so P_CAlso diagonal matrix, system c is decomposed into M-1 SISO systems) estimate G multiple times_c,H_cThen M-1 total least squares problems can be generated, and the least squares problem solved to find the calibration coefficients β_c，diag(β_c) Is β_cMain diagonal element, then

4) Estimating β channel calibration coefficients for subsystem d_d: obtained by B₁，B₂～B_NComposed SIMO system d, obtaining the status information G of the up and down channels of the SIMO system d_d,H_dG is obtained from the formula (3)_d＝β_d·H_d(6)

Wherein(since there is no crosstalk problem between the antennas, P_DAlso diagonal, so system d can be decomposed into N-1 SISO systems) estimate G multiple times_d,H_dThen N-1 total least squares problems can be generated, and the calibration coefficients β can be found by solving the least squares problem_d。diag(β_d) Is β_dThe main diagonal elements are the elements of the main diagonal,

5) calculate calibration coefficients β for the entire System a_aComprises the following steps:

from steps 2),3),4) it is possible to derive β_b,β_c,β_cContaining β_aAll of the information of (1), therefore β_aCan be used as β_b,β_c,β_cIs represented as follows:

6) estimating the downlink channel state information of the system a according to the formula (8):

[G]_mn＝[H]_mn·[β_a]_mn(8)

[G]_mnfor downlink channel state information of the nth channel, [ H ]]_mnFor the uplink channel status information of the mn-th channel, [ β ]_a]_mnFor the channel calibration coefficients of the mn-th channel, the downlink channel state information can be estimated according to the uplink channel information, (since the coherence time of the antenna transmitting circuit and the receiving circuit is longer than that of the electromagnetic channel, the channel can be calibrated for a plurality of times within the coherence time of the antenna transmitting circuit and the receiving circuit, and the downlink channel state information for a plurality of times can be estimated according to the formula (8).

Examples

In a specific embodiment of the method of the present invention, an a-side antenna M is 128, and a B-side antenna N is 16;

the method comprises the following specific steps:

1) user B sends up pilot signal, base station A estimates up channel state information according to pilot signal sent by B, selects one channel with highest channel gain as reference channel, and the antennas at two ends of reference channel are used as reference antenna, then base station A can select reference antenna A₁If base station A sends information containing reference antenna to base station B, then base station B can select reference antenna B according to information sent by base station A₁Antenna A₁And an antenna B₁System b.

2. Estimating uplink and downlink channel state information G of SISO system b_b,H_bFrom equation (3), we can obtain: g_b＝H_b·β_b(4)，

Wherein,multiple estimation of G_b,H_bThen a total least squares problem can be generated, and the least squares problem solved to find the channel calibration coefficients β for system b_b；

3)A₁And A₂～A₁₂₈SIMO system c composed of obtaining uplink and downlink channel state information G of SIMO system c_c,H_cFrom equation (3), we can obtain: g_c＝β_c·H_c(5)

Wherein,(since there is no crosstalk problem between the antennas, P_CAlso diagonal matrix, system c is decomposed into 127 SISO systems) estimate G multiple times_c,H_cThen 127 total least squares problems can be generated, and the channel calibration coefficients β of system b can be found by solving the least squares problem_c，diag(β_c) Is β_cMain diagonal element, then

4) Obtained by B₁，B₂～B_NComposed SIMO system d, obtaining the status information G of the up and down channels of the SIMO system d_d,H_dG is obtained from the formula (3)_d＝β_d·H_d(6)

Wherein(since there is no crosstalk problem between the antennas, P_DAlso diagonal matrix, so system d can be decomposed into 15 SISO systems) estimate G multiple times_d,H_dThen 15 total least squares problems can be generated and solved to find the system bChannel calibration coefficients β_d。diag(β_d) Is β_dThe main diagonal elements are the elements of the main diagonal,

5) the calibration coefficients for system a were calculated as:

the result of steps 2,3 and 4 is that β is_b,β_c,β_cContaining β_aAll of the information of (1), therefore β_aCan be used as β_b,β_c,β_cIs represented as follows:

6) based on [ G]_mn＝[H]_mn·[β_a]_mn(8)

[G]_mnFor downlink channel state information of the nth channel, [ H ]]_mnFor the uplink channel status information of the mn-th channel, [ β ]_a]_mnFor the channel calibration coefficient of the mn-th channel, the downlink channel state information can be estimated according to the uplink channel information, (since the coherence time of the antenna transmitting circuit and the receiving circuit is longer than that of the electromagnetic channel, the channel can be calibrated for many times within the coherence time of the antenna transmitting circuit and the receiving circuit, and the downlink channel state information for many times can be estimated according to the formula (8).

Claims

1. A channel calibration method for a large-scale multiple-input multiple-output time division duplex system is characterized by comprising the steps of dividing the large-scale multiple-input multiple-output system into three subsystems, wherein the three subsystems comprise a single-input single-output system and two single-input multiple-output systems; calibrating uplink and downlink channels of the three subsystems respectively to obtain channel calibration coefficients; then, obtaining the calibration coefficient of the whole multi-input multi-output system according to the channel calibration coefficients of the three subsystems, and obtaining the accurate downlink channel state information of the whole system according to the uplink channel state information;

the method specifically comprises the following steps:

1) determining a reference channel, a reference antenna, and dividing the subsystem: dividing a multi-input multi-output system a of a large-scale base station and a user into three subsystems, wherein a user B end sends an uplink pilot signal, a base station A end estimates uplink channel state information according to the pilot signal sent by the B end, one channel with the highest channel gain is selected as a reference channel, antennas at two ends of the reference channel are used as reference antennas, and the A end is provided with M antennas which are respectively A₁～A_MThe reference antenna selected by the base station A is A₁，A₂～A_M，A_i∈ C, i is 2,3, M represents other antennas of the base station A, C represents a set formed by other antennas of the base station A, the base station A sends information containing reference antennas to the base station B, and N antennas at the B end are respectively B₁～B_NThen the base station B selects the reference antenna as B according to the information sent by the base station A₁，B₂～B_N，B_j∈ D, j 2,3, N, for other antennas of base station B, D for the set of other antennas of base station B, antenna a₁And an antenna B₁Form a single-input single-output SISO system b, a reference antenna A₁And an antenna A₂～A_MForming a single input multiple output sub SIMO system c and a reference antenna B₁And an antenna B₂～B_NForming another single-input multi-output sub SIMO system d;

2) estimating β channel calibration coefficients for system b_b: estimating uplink and downlink channel state information of SISO system b according to formula G ═ P_B·H·P_A(3) Wherein G is downlink channel state information, H is uplink channel state information, T_Aequivalent filter for A-terminal transmission circuit, T_BEquivalent filter for B-terminal transmission circuit, R_AEquivalent filters for A-terminal receiving circuits, R_BIs terminated by BAn equivalent filter of the receiving circuit, and T without considering the problem of crosstalk between the antennas_A，T_B，R_A，R_BIs a diagonal matrix;

obtaining: g_b＝H_b·β_b(4)，

Wherein G is_b,H_bFor estimating the downlink and uplink channel state information of SISO system b,multiple estimation of G_b,H_bGenerating a total least squares problem, solving the least squares problem, and finding the calibration coefficients β_b；

3) Estimating β channel calibration coefficients for system c_c：A₁And A₂～A_MSIMO system c composed of obtaining downlink and uplink channel state information G of SIMO system c_c,H_cAccording to the formula G ═ P_B·H·P_A(3) Obtaining:

G_c＝β_c·H_c(5)

4) estimating β channel calibration coefficients for system d_d: obtained by B₁，B₂～B_NComposed SIMO system d, obtaining the status information G of the downlink and uplink channels of the SIMO system d_d,H_dG is obtained from the formula (3)_d＝β_d·H_d(6)，

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[G]_mn＝[H]_mn·[β_a]_mn(8)