Reciprocity calibration coefficient tracking method for time division duplex multi-node cooperation system

Abstract

This application discloses a reciprocity calibration coefficient tracking method for a time-division duplex multi-node cooperative system. The method involves remote radio units (RFUs) transmitting calibration signals to each other, and a base station calculating initial calibration coefficients from the received calibration signals. A terminal sends uplink sounding reference signals to multiple RRUs, and the base station calculates the uplink channel state information between the terminal and the RRUs at two adjacent time intervals. Based on the uplink channel state information, the phase offset of the terminal's antenna within the time slots of two adjacent time intervals is calculated, and the calibration coefficients of each antenna of the RRUs are updated based on the phase difference between the two adjacent time intervals. By tracking the phase change of the calibration coefficients through changes in the uplink channel phase, the overhead of the calibration reference signal is reduced. Multiple uplink channel information is used to smooth channel phase changes, increasing the accuracy of channel phase change estimation, thereby accurately tracking the calibration coefficient phase and ensuring downlink precoding performance.

Description

Technical Field

[0001] This application relates to the field of wireless communication transmission technology, and in particular to a method for tracking reciprocity calibration coefficients in a time-division duplex multi-node cooperative system. Background Technology

[0002] In Time Division Duplex (TDD) mode, based on the reciprocity of uplink and downlink channels, the downlink channel can be estimated from the uplink channel, thus enabling coherent downlink transmission. This reciprocity-based coherent downlink transmission is widely used in Massive Multiple-Input-Multiple-Output (MIMO), Coordinated Multi-Point (CoMP), Coherent Joint Transmission (CJT) in Multiple Transmission and Reception Point (Multi-TRP) systems, and Cell-free massive MIMO, a key technology in current 6G.

[0003] However, due to the mismatch in RF gain between the transceiver antennas, the overall channel is not reciprocal, thus requiring reciprocity calibration. For multi-node cooperative transmission systems, since the remote radio units (RRUs) on the base station side are distributed, the reciprocity calibration of the base station antennas requires each RRU antenna to send and receive calibration reference signals to estimate the bidirectional channel between the RRU antennas and then calculate the RRU antenna calibration coefficients. This process is called calibration mode.

[0004] After obtaining the calibration coefficients at the base station, the uplink channel is estimated by the user equipment (UE) sending uplink sounding reference signals (SRS) to each RRU. The base station then uses the uplink channel and the RRU antenna calibration coefficients to calculate the precoding matrix and performs downlink coherent transmission.

[0005] However, in a distributed RRU deployment system, because each RRU does not share a common local oscillator, there is a local oscillator frequency deviation between RRUs. Therefore, the phase of the reciprocity calibration coefficients of the RRU antennas will drift over time. Furthermore, due to the jitter of the local oscillator frequency, the phase of the calibration coefficients does not change linearly, increasing the difficulty of phase tracking. Entering calibration mode before each downlink transmission would result in significant overhead for calibrating the pilots. If the calibration coefficients are not updated before each downlink transmission, the orthogonality of the downlink precoding matrix will be destroyed, affecting downlink transmission performance. In reality, the RF gain does not change for a considerable period, so the amplitude of the calibration coefficients does not change during this time; only the phase shifts over time due to the local oscillator frequency offset. Summary of the Invention

[0006] This application provides a reciprocity calibration coefficient tracking method for a time-division duplex multi-node cooperative system to solve problems such as large calibration reference signal overhead and inaccurate estimation of channel phase change in related technologies.

[0007] This application provides a method for tracking reciprocity calibration coefficients in a time-division duplex multi-node cooperative system. The time-division duplex multi-node cooperative system consists of multiple remote radio units, at least one terminal, and a base station. The method includes the following steps:

[0008] The multiple remote wireless units send calibration signals to each other, and the base station calculates the calibration signals received by the multiple remote wireless units to obtain the initial calibration coefficients.

[0009] The terminal sends uplink sounding reference signals to the plurality of remote radio units, and the base station calculates the uplink channel state information between the terminal and the plurality of remote radio units at two adjacent times.

[0010] The phase offset of the terminal's antenna in two adjacent time slots is calculated based on the uplink channel state information, and the calibration coefficients of each antenna of the remote wireless unit are updated based on the phase difference between the two adjacent time slots.

[0011] Optionally, in one embodiment of this application, the time-division duplex multi-node cooperative system includes Q terminals and P remote wireless units. Each terminal is configured with K antennas, and each remote wireless unit is configured with L antennas. Using the Lth antenna of the Pth remote wireless unit as a reference antenna, t is calculated. i The uplink channel state information between the terminal and the plurality of remote radio units within the time slot is calculated as follows:

[0012] t iAt any given time, the base station, based on the uplink sounding reference signal sent by the terminal, obtains the channel gain between the k-th antenna of the q-th terminal and the l-th antenna of the p-th RRU through channel estimation.

[0013]

[0014] p=1,…,P l=1,…,L q=1,…,Q k=1,…,K

[0015] Among them, b r,p,l Let u be the RF receive gain of the l-th antenna on the p-th remote wireless unit. t,q,k h is the RF transmit gain of the k-th antenna on the q-th terminal. p,l,q,k (t i ) represents the distance t between the l-th antenna on the p-th remote wireless unit and the k-th antenna on the q-th terminal. i Time slot air channel, Δf p,q (t i )=f q (t i )-f p (t i ) for t i The local oscillator frequency difference between the p-th remote wireless unit and the q-th terminal in time slot.

[0016] Optionally, in one embodiment of this application, when the L antenna channels of each remote wireless unit are not implemented using a common local oscillator, the step of calculating the antenna of the terminal at t based on the uplink channel state information is... i The phase offset within a time slot is calculated as follows:

[0017] Based on all the antennas of the terminal, calculate at t i The phase shift caused by frequency offset in the time slot is:

[0018]

[0019] Among them, G P,L,q,k (t i ) is the t-th i-1 The channel gain between the k-th antenna of the q-th terminal and the L-th antenna of the P-th RRU at time q is given by angle[·].

[0020] Optionally, in one embodiment of this application, when the L antenna channels of each remote wireless unit are implemented using a common local oscillator, the phase offset of all antennas on the same remote wireless unit is the same, i.e., θ p,l (t i )=θ p (t i), l=1,…,L, the antenna of the terminal is calculated based on the uplink channel state information at t i The phase offset within a time slot is calculated as follows:

[0021]

[0022] Among them, G P,L,q,k (t i ) is the t-th i-1 The channel gain between the k-th antenna of the q-th terminal and the L-th antenna of the P-th RRU at time q is given by angle[·].

[0023] Optionally, in one embodiment of this application, updating the calibration coefficients of each antenna of the remote wireless unit based on the phase difference between two adjacent times includes:

[0024] According to t i Phase difference θ between time slot uplink channels p,l (t i ) and t i-1 Phase difference θ between time slot uplink channels p,l (t i-1 ), update t i Calibration coefficient c of each antenna in the time slot remote radio unit p,l (t i ):

[0025]

[0026] Among them, c p,l (t i-1 ) for t i-1 The calibration coefficient of the time slot.

[0027] Optionally, in one embodiment of this application, when any terminal in the time-division duplex multi-node cooperative system continuously transmits uplink probe reference signals, only the initial calibration coefficient is calculated to track the calibration coefficient of the remote radio unit; when any terminal in the time-division duplex multi-node cooperative system does not continuously transmit uplink probe reference signals, the initial calibration coefficient of the remote radio unit is calculated before the next time the terminal transmits the uplink probe reference signal.

[0028] The reciprocity calibration coefficient tracking method for a time-division duplex multi-node cooperative system in this application estimates the phase offset of the inter-antenna channel of the remote radio unit by using the phase offset value of adjacent time slots of the uplink channel to track the antenna calibration coefficient of the remote radio unit. The base station only needs to transmit and receive calibration pilots and estimate the calibration channel and calibration coefficients during the initial calibration phase, significantly reducing calibration pilot overhead and computational overhead. By utilizing the principle of common local oscillator frequencies for different antennas of the same device and taking advantage of the good consistency among channels within the remote radio unit, the estimated phase offset values ​​of adjacent time slots of the uplink channel are averaged and smoothed, improving the accuracy of phase offset estimation.

[0029] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0030] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0031] Figure 1 This is a flowchart of a reciprocity calibration coefficient tracking method for a time-division duplex multi-node cooperative system according to an embodiment of this application;

[0032] Figure 2 This is a schematic diagram illustrating the execution process of the reciprocity calibration coefficient tracking method for a time-division duplex multi-node cooperative system according to an embodiment of this application.

[0033] Figure 3 This is a performance gain diagram of the reciprocity calibration coefficient phase tracking method according to an embodiment of this application. Detailed Implementation

[0034] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0035] In time-division duplex systems, the non-reciprocity of transmit and receive channels leads to non-reciprocity of uplink and downlink channels. In particular, when remote radio units (RRUs) in the system typically employ non-local oscillator implementations, the frequency differences between RRUs cause phase variations in calibration coefficients, severely degrading downlink precoding performance. This invention tracks the phase changes of calibration coefficients by varying the uplink channel phase, significantly reducing calibration reference signal overhead. Simultaneously, this invention utilizes multiple uplink channel information to smooth channel phase changes, resulting in more accurate estimates of channel phase changes and more precise tracking of the calibration coefficient phase, thereby ensuring downlink precoding performance.

[0036] Figure 1 This is a flowchart of a reciprocity calibration coefficient tracking method for a time-division duplex multi-node cooperative system according to an embodiment of this application.

[0037] like Figure 1 As shown, the time-division duplex multi-node cooperative system consists of multiple remote radio units (RRUs), one or more terminals (UEs), and base stations (BSs). The system has Q UEs, each configured with K antennas, and P RRUs, each configured with L antennas. The process of obtaining calibration coefficients is divided into two stages: initial calibration and phase tracking of calibration coefficients.

[0038] The reciprocity calibration coefficient tracking method for a time-division duplex multi-node cooperative system includes the following steps:

[0039] In step S101, multiple remote wireless units send calibration signals to each other, and the base station calculates the calibration signals received by the multiple remote wireless units to obtain the initial calibration coefficients.

[0040] Initial calibration coefficient calculation steps: Multiple RRUs send calibration signals to each other, and the RRUs send the received calibration signals to the BS. The BS then calculates the initial calibration coefficients.

[0041] In the initial calibration phase, self-calibration between RRUs is employed. The calibration coefficient vector estimation method can employ traditional reference antenna calibration or RRU group calibration methods. Using the Lth antenna of the Pth RRU (antenna number denoted as (P,L)) as the reference antenna, the initial calibration coefficient of the lth antenna of the pth RRU (antenna number denoted as (p,l)) is denoted as c. p,l (t0).

[0042] In step S102, the terminal sends uplink sounding reference signals to multiple remote radio units, and the base station calculates the uplink channel state information between the terminal and the multiple remote radio units at two adjacent times.

[0043] Optionally, in one embodiment of this application, t is calculated using the Lth antenna of the Pth remote wireless unit as the reference antenna. i The calculation method for uplink channel state information between the terminal and multiple remote radio units within a time slot is as follows:

[0044] t i At time t, based on the uplink sounding reference signal sent by the terminal, the base station obtains the channel gain between the k-th antenna of the q-th terminal and the l-th antenna of the p-th RRU through channel estimation:

[0045]

[0046] p=1,…,P l=1,…,L q=1,…,Q k=1,…,K

[0047] Among them, b r,p,l Let u be the RF receive gain of the l-th antenna on the p-th remote wireless unit. t,q,k h is the RF transmit gain of the k-th antenna on the q-th terminal. p,l,q,k (t i ) represents the distance t between the l-th antenna on the p-th remote wireless unit and the k-th antenna on the q-th terminal. i Time slot air channel, Δf p,q (t i )=f q (t i )-f p (t i ) for t i The local oscillator frequency difference between the p-th remote wireless unit and the q-th terminal in time slot.

[0048] In step S103, the phase offset of the terminal's antenna in two adjacent time slots is calculated based on the uplink channel state information, and the calibration coefficients of each antenna of the remote wireless unit are updated based on the phase difference between the two adjacent time slots.

[0049] Optionally, in one embodiment of this application, the BS calculates the phase difference between the channel gain of each UE and the (P,L)-th antenna based on the channel between the UE and each antenna: taking the k-th antenna of the q-th terminal as an example, the phase difference between its channel gain to the (p,L)-th antenna and its channel gain to the reference antenna (P,L) is: angle[G p,l,q,k (t i )]-angle[G P,L,q,k (t i Based on the antennas of all terminals, it can be obtained that at t i The phase shift caused by frequency offset in the time slot is:

[0050]

[0051] Here, angle(·) represents calculating the phase angle.

[0052] According to t i Phase difference θ between time slot uplink channels p,l (t i ) and t i-1 Phase difference θ between time slot uplink channels p,l (t i-1 ), update t i Calibration coefficients for each antenna:

[0053]

[0054] Where p = 1, ... P, l = 1, ... L.

[0055] When the L antenna channels of each RRU are implemented using a common local oscillator, they exhibit good consistency. It can be assumed that the phase difference of the L antennas of the p-th RRU is the same, i.e.: θ p,l (t i )=θ p (t i ), l=1,…,L. Considering the phase offset between all L antennas on RRUp where antenna (p,l) is located and all L antennas on RRUP where the reference antenna (P,L) is located, the channel between RRUp and RRUP at time t is obtained. i The phase shift caused by the frequency difference in the time slot is:

[0056]

[0057] The calibration coefficients of each antenna can be updated according to the following formula:

[0058]

[0059] In the embodiments of this application, when there are terminals continuously sending uplink probe signals in the system, only initial calibration is needed to track the calibration coefficient of the RRU. When there are terminals not continuously sending uplink probe signals in the system, initial calibration is required before the next time the terminal sends an uplink probe.

[0060] In the embodiments of this application, in order to obtain better continuous tracking performance, a reference terminal that transmits uplink SRS can be deployed in the system for RRU calibration phase tracking.

[0061] In the embodiments of this application, in order to obtain better continuous tracking performance, the base station system can select the uplink probe channel of a low-speed or stationary terminal for the calibration phase tracking of the RRU.

[0062] The reciprocity calibration coefficient tracking method of the time-division duplex multi-node cooperative system of this application will be described in detail below through specific embodiments.

[0063] Suppose the system has P Remote Assist Units (RRUs), each equipped with L antennas, and Q User Equipments (UEs), each equipped with K antennas. Uplink communication is achieved by the UEs transmitting SRS (Search and Redirect Channel Response), and each RRU receives this data and estimates the uplink channel matrix G. UL The uplink channel from the k-th antenna on the q-th UE to the l-th antenna on the p-th RRU at the base station can be modeled as follows:

[0064]

[0065] p=1,…,P l=1,…,L q=1,…,Q k=1,…,K

[0066] Where b r,p,l u represents the RF receive gain of the l-th antenna on the p-th RRU at the base station side. t,q,k h represents the RF transmit gain of the k-th antenna on the q-th UE side; p,l,q,k (t i ) represents the distance t between these two antennas. i The time-slotted air channel contains both large-scale and small-scale fading. When the air channel is in a slowly varying state, it can be considered... Δf p,q (t i )=f q (t i )-f p (t i ) is t i The local oscillator frequency difference between the p-th RRU and the q-th UE in time slot.

[0067] In the initial calibration mode, the RRU antennas transmit and receive calibration pilots to estimate the bidirectional calibration channel matrix. The elements of the bidirectional calibration channel can be modeled as follows:

[0068]

[0069]

[0070] m, n∈{1,…,P}k, l=1,…,L, if m=n then k≠l

[0071] Among them, b r,m,k b represents the RF receive gain of the k-th antenna on the m-th RRU at the base station side. t,n,l b represents the RF transmit gain of the l-th antenna on the n-th RRU at the base station side. r,n,l ,b t,m,k Similarly; h m,k,n,l (ti ) is the distance between these two antennas at t i The time-slot air channel contains both large-scale and small-scale fading, and according to reciprocity, h m,k,n,l (t i ) = h m,k,n,l (t i Furthermore, when the air channel is in a slowly varying state, h can be considered... m,k,n,l (t i ) = h m,k,n,l (t i-1 );Δf m,n (t i )=f n (t i )-f m (t i ) is t i The difference in local oscillator frequency between the nth RRU and the mth RRU in time slot.

[0072] like Figure 2 As shown, in the initial calibration coefficient estimation stage, each antenna on the base station side transmits and receives calibration signals to each other. After estimating the bidirectional channel between RRU antennas, the calibration coefficient vector estimation method can adopt traditional reference antenna calibration or RRU group calibration methods. Regardless of the air interface calibration method, the obtained calibration coefficients are relative values ​​of the reference antenna calibration coefficients.

[0073] If the RRU grouping calibration method is used, then the RRUs are divided into... Two groups of RRUs transmit and receive calibration pilots to each other, estimating the inter-group bidirectional calibration channel matrix. for Number of antenna groups for Number of antennas in a group. And establish the following TLS optimization model:

[0074]

[0075] st||c cal || 2 =1

[0076] in, They are The diagonal array formed by the calibration coefficients of the RRU antennas is represented by diag[·], which is the diagonalization symbol. It is the calibration vector for all RRU antennas.

[0077] This model can be simplified to the following model:

[0078]

[0079] st||ccal || 2 =1

[0080] in:

[0081]

[0082]

[0083]

[0084]

[0085]

[0086] The ⊙ symbol represents element-wise matrix multiplication, and diag[diag(·)] refers to taking the diagonal elements of the matrix to form a diagonal matrix. The final initial calibration vector is c(t0) = c cal c cal The solution is the eigenvector corresponding to the smallest eigenvalue of the matrix Φ.

[0087] During the calibration coefficient phase tracking stage

[0088] If the calculated initial calibration coefficients are taken with the (P,L)th antenna on the base station side as a reference (i.e., c... P,L =1), for the (p,l)th antenna, without considering channel noise, its t i The calibration coefficient of a time slot can be expressed as:

[0089]

[0090] in It can be denoted as c p,l (t0).

[0091] Due to the frequency difference between RRUp and RRUP:

[0092] Δf p,P (t i )=f P (t i )-f p (t i )

[0093] The uplink frequency difference between RRUp,P and the same UEq is:

[0094] Δf p,q (t i )=f q (t i )-f p (t i )

[0095] Δf P,q (t i )=f q (t i )-f P (t i )

[0096] The frequency difference information between RRUp and P can be obtained from the frequency difference information in the uplink channel, that is:

[0097] Δf p,P (t i )=Δf p,q (t i )-Δf P,q (t i )

[0098] Since the frequency difference is not constant, updating the phase information of the calibration channel by estimating the frequency difference between RRUs will introduce significant errors and cannot adapt to changes in the frequency difference. However, according to the frequency difference relationship in the above formula, if the phase information of the calibration channel is directly tracked using the phase change information of the uplink channel, thereby tracking the phase of the calibration coefficients, the problem of frequency difference jitter can be avoided. Therefore, the phase of the calibration coefficients can be updated through the following steps:

[0099] Step 1: Through t i The phase difference between uplink channels in time slots is used to indirectly calculate t. i The channel phase difference between each antenna on the time-slot base station side and the reference antenna (P,L). When the L antenna channels of each RRU are implemented using a common local oscillator, exhibiting good consistency, the phase offset between all L antennas on the RRUp where the (p,l) antenna is located and all L antennas on the RRUP where the reference antenna (P,L) is located can be comprehensively considered. This allows us to calculate the channel phase difference between RRUp and RRUP at time t. i The phase shift caused by the frequency difference in the time slot is:

[0100]

[0101] Where L is the number of antennas on each RRU, Q is the number of UEs, and K is the number of antennas on each UE. Furthermore, the phase offset of all L antennas on the same RRU p is θ. p (t i ),Right now:

[0102]

[0103] If the L antenna channels of each RRU are not implemented using a common local oscillator, they will not have good consistency. Therefore, the channel between antenna (p,l) and reference antenna (P,L) at time t... i The phase shift caused by the frequency difference in the time slot is:

[0104]

[0105] Step 2: Update the (p,l) antenna at t i Time slot calibration factor:

[0106]

[0107] After updating all antennas on the base station side according to the above steps, t is formed. i The calibration vector c(t) of the time slot i ).

[0108] After updating the calibration coefficients of each antenna in the remote radio unit, downlink precoding is performed based on the updated calibration coefficients. A typical method is to... i Uplink channel matrix for time slot estimation Multiply by the calibration coefficient matrix C(t) i )=diag[c(t i The inverse of )]:

[0109]

[0110] Then use the calibrated uplink channel. Calculate the precoding matrix.

[0111] like Figure 3 As shown, a performance gain diagram of the reciprocity calibration coefficient tracking method is presented. "Real-time calibration coefficients" refers to the process where, before each downlink transmission, the base station-side RRUs exchange calibration pilots to estimate the calibration channel and solve for updated calibration coefficients used in downlink precoding. "Calibration coefficient 5ms / 10ms delay" refers to the fact that each updated calibration coefficient is used for downlink precoding 5ms / 10ms later. It can be seen that without real-time updates to the calibration coefficients, downlink performance will be significantly reduced. Meanwhile, the calibration coefficient tracking method proposed in this invention achieves near-optimal performance, i.e., "real-time calibration coefficient" performance. However, the proposed tracking method only requires the base station-side RRUs to exchange calibration pilots during the initial calibration phase to estimate the calibration channel and solve for updated calibration coefficients, greatly reducing calibration pilot overhead and computational overhead.

[0112] The reciprocity calibration coefficient tracking method for a time-division duplex multi-node cooperative system proposed in this application first performs initial calibration coefficient estimation, and then tracks the phase offset of the RRU based on two consecutive adjacent SRS channel estimates of the terminal. This significantly reduces the overhead of calibrating the reference pilot. Simultaneously, by utilizing the good consistency among the channels within the RRU, channel phase changes are smoothed, resulting in more accurate estimates of channel phase changes and thus more precise tracking of the calibration coefficient phase, thereby ensuring downlink precoding performance.

[0113] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0114] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "N" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0115] Any process or method described in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or N executable instructions for implementing custom logic functions or processes, and the scope of the preferred embodiments of this application includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as should be understood by those skilled in the art to which embodiments of this application pertain.

Claims

1. A method for tracking reciprocity calibration coefficients in a time-division duplex multi-node cooperative system, wherein the time-division duplex multi-node cooperative system comprises multiple remote radio units, at least one terminal, and a base station, characterized in that, The method includes the following steps: The multiple remote wireless units send calibration signals to each other, and the base station calculates the calibration signals received by the multiple remote wireless units to obtain the initial calibration coefficients. The terminal sends uplink sounding reference signals to the plurality of remote radio units, and the base station calculates the uplink channel state information between the terminal and the plurality of remote radio units at two adjacent times. The phase offset of the terminal's antenna in two adjacent time slots is calculated based on the uplink channel state information, and the calibration coefficients of each antenna of the remote wireless unit are updated based on the phase difference between the two adjacent time slots. When the L antenna channels of each remote wireless unit are not implemented using a common local oscillator, the calculation of the terminal's antenna based on the uplink channel state information... The phase offset within a time slot is calculated as follows: Based on all the antennas of the terminal, calculate in The phase shift caused by frequency offset in the time slot is: in, For the first At time q, the base station, based on the uplink sounding reference signal sent by the terminal, estimates the relationship between the k-th antenna and the q-th antenna of the terminal through channel estimation. Channel gain between the l-th antenna of each RRU For the first The channel gain between the k-th antenna of the q-th terminal and the L-th antenna of the P-th RRU at time q. This indicates a search for the phase angle; When the L antenna channels of each remote radio unit are implemented using a common local oscillator, the phase offset of all antennas on the same remote radio unit is the same, that is... The step of calculating the antenna of the terminal based on the uplink channel state information. The phase offset within a time slot is calculated as follows: in, For the first The channel gain between the k-th antenna of the q-th terminal and the L-th antenna of the P-th RRU at time q; The step of updating the calibration coefficients of each antenna of the far-end wireless unit based on the phase difference between two adjacent times includes: according to Phase difference between time slot uplink channels as well as Phase difference between time slot uplink channels ,renew Calibration coefficients of each antenna in the time-slot remote radio unit : in, for The calibration coefficient of the time slot.

2. The method according to claim 1, characterized in that, The time-division duplex multi-node cooperative system includes Q terminals and P remote wireless units. Each terminal is equipped with K antennas, and each remote wireless unit is equipped with L antennas. Using the Lth antenna of the Pth remote wireless unit as a reference antenna, the calculation... The uplink channel state information between the terminal and the plurality of remote radio units within the time slot is calculated as follows: No. At time q, the base station, based on the uplink sounding reference signal sent by the terminal, obtains the relationship between the k-th antenna and the q-th antenna of the q-th terminal through channel estimation. The channel gain between the l-th antennas of the RRUs is: in, For the first On the first remote wireless unit The RF receiving gain of the root antenna, For the first On the first terminal The RF transmit gain of the root antenna, For the first On the first remote wireless unit root antenna and the first On the first terminal Between the antennas Time slot air channel, for Time slot number The first remote wireless unit and the first The difference in local oscillator frequency between each terminal.

3. The method according to claim 1, characterized in that, When any terminal in the time-division duplex multi-node cooperative system continuously transmits uplink probe reference signals, only the initial calibration coefficient is calculated to track the calibration coefficient of the remote radio unit; when any terminal in the time-division duplex multi-node cooperative system does not continuously transmit uplink probe reference signals, the initial calibration coefficient of the remote radio unit is calculated before the next time the terminal transmits the uplink probe reference signal.

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