CN102404033B - Antenna array calibration method and device in Orthogonal Frequency Division Multiplexing (OFDM) system - Google Patents

Abstract

The invention relates to antenna array calibration method and device in an Orthogonal Frequency Division Multiplexing (OFDM) system. The method disclosed by the invention comprises a pre-calibration step and a periodical calibration step to antennas, wherein the pre-calibration step is mainly used for acquiring compensation coefficients in a transmission direction and a reception direction of antenna units with respect to an antenna calibration unit; and the periodical calibration step performs transmission calibration and reception calibration to each antenna unit in quasi real-time according to a preset period. The method and the device disclosed by the invention can realize real-time and high-precision calibration of consistency of phases of a reception channel and a transmission channel of a Long Term Evolution (LTE) system, through common compensation to time delay and the phases through a Building Baseband Unit (BBU) and a Radio Remote Unit (RRU), can guarantee high consistency of phases of an air interface sending signal and a BBU reception signal of an antenna array, and is particularly suitable for a communication system which has high demand on consistency of antennas, for example, a Time Division Duplex (TDD)-LTE, etc..

Description

Antenna array calibration method and apparatus in a kind of ofdm system

Technical field

The present invention relates to wireless communication technology, particularly relate to the antenna array calibration method and apparatus in a kind of ofdm system.

Background technology

In LTE system (Long Term Evolution is called for short LTE), in order to increase cell coverage area, reduce the interference in community and between the user of minizone and increase edge, community user's throughput, in base station, (eNodeB) side has been introduced form-giving array antennas beams technology.Form-giving array antennas beams refers to by multiple antenna elements and forms aerial array according to certain geometrical shape, by regulating the weighted amplitude of each array signal and phase place to change the antenna pattern of array, the signal power maximum that desired user is received, the interference minimum that simultaneously makes narrow beam range of exposures unexpected user in addition be subject to.The prerequisite of form-giving array antennas beams technology application is that delay and the first phase between array antenna has consistency.

Because the signal sending on different antennae array often passes through different IF processing units and radio-frequency transmissions passage, can cause the signal of different passage transmittings to there is different amplitudes and phase difference.In addition, antenna, feeder line and the radio-frequency channel that is made up of analogue device are along with the variation of the environment such as device aging, temperature and humidity, and each passage often has different amplitudes and phase place variation characteristic.In order to guarantee accuracy and the reliability of shaped-beam direction, need to calibrate to each aerial array passage the amplitude between assurance aerial array and the consistency of phase preserving height.In addition, in LTE, adopt the key technology such as OFDM (OFDM) and MIMO (multiple-input and multiple-output), if physical antenna number is more than logical antenna ports number, in the time realizing logical antenna ports to the mapping of physical antenna port, the consistency that need to carry out amplitude and phase place to the different physical antenna being shone upon by same logic port is calibrated.

One class is carried out aerial array in time domain in the application for a patent for invention of method of real time calibration (as application number 200810068090.2,200810148076.3 etc.), disclose the method that multiple use calibrating sequence pair array antenna carries out real time calibration, this calibrating sequence is generated by cyclic shift by the basic sequence with good circulation autocorrelation performance.The calibrating sequence of a fixed level of calibration link transmitting, receiver obtains the calibration factor of aerial array to be calibrated by carrying out to received signal the channel estimating of time domain, it compensation is given to aerial array and reached the object of calibration.These class methods now well apply to the TD-SCDMA system of single carrier frequency and carrier aggregation.

An other class is carried out in the patent of invention of method of real time calibration (as application number 200910134214.7 at frequency domain pair array antenna, CN101854323.A, CN10106492.B etc.), disclosing antithetical phrase carrier frequency point in ofdm system divides into groups, determine the frequency domain calibration pilot signal of transmitting antenna according to grouping, transmitting terminal is according to pilot tone signal acquisition time domain integral calibration pilot signal and utilize time domain integral calibration pilot signal structure time domain to transmit to send to receiving terminal, and receiving terminal is determined transmitting terminal penalty coefficient according to the frequency domain response of all subcarriers.In the patent of invention of the method that a class pair array antenna is calibrated in addition (as application number 200810044412.x), the evolution of method one is disclosed, the thought of utilizing frequency division or code to divide, combine the frequency domain response of estimating each transmitting antenna at receiving terminal, then compensate the difference of each transmitting antenna frequency domain response, thereby realize the pre-calibration of each transmitting antenna electric channel.The application scenarios that these two class methods are expected is the multicarrier system of OFDM.

TD-SCDMA is a kind of single-carrier system, and antenna calibration error is no more than positive and negative 1/8 chip and just can meets antenna shaped-beam direction and be less than 5 degree and must ask.The LTE system of 20MHz has 1200 subcarriers, each subcarrier spacing 15KHz, any small time delay presents very large phase difference in different sub carrier, if be less than 5 degree by array antenna shaped-beam deflection error on requirement subcarrier conventionally, the calibration error of aerial array will be less than 1/32 sampling interval Ts, obviously the precision of said method estimation time delay cannot meet the demand of LTE system, and this will have a strong impact on accuracy and the validity of LTE system wave beam forming direction.Time delay and the phase equalization of multiple physical antenna arrays that in LTE system, the application of MIMO is also shone upon same logic port have in addition proposed high requirement.

Summary of the invention

The object of the invention is to avoid above the deficiencies in the prior art that the method and apparatus of the antenna array calibration in a kind of ofdm system is provided, to solve the precision of the array antenna calibration existing in LTE system and the complexity issue of calibration steps.

Operation principle of the present invention is that the calibration of aerial array is divided into two steps: pre-calibration and periodic calibration, and also referred to as initialization of calibration and real time calibration.Pre-calibration is mainly used in obtaining the penalty coefficient of antenna element relative calibration antenna element at transmit direction and receive direction; Periodic calibration is according to the predefined cycle, quasi real time each antenna element is carried out transmitting calibration and receives calibration.Wherein, pre-calibration comprises thick calibration and the essence calibration of many array antennas time delay.Periodic calibration just can be carried out after only having pre-calibration to complete.Specifically be achieved in that, after base station preheating completes, pair array antenna carries out pre-calibration; After pre-calibration completes, trigger periodic antenna calibration the non-interrupting service in the situation that with cycle of setting by operation maintenance center (OMC).Pre-calibration comprises the antenna calibration of transmission channel and the antenna calibration of receive path.For non-interrupting service in periodic calibration, all calibrations are all carried out at the GP of TDD-LTE (Guard Period) time slot.

The calibration of aerial array relates to radio frequency unit RRU (Remote RF Unit) and the baseband control unit (Base Band Unit) in wireless communication system, they both can be connected and be supported remote radio by transmission means such as optical fiber or cables, also can directly connect.Before calibration, the sequence x with good their cross correlation of a certain length of BBU structure _u(n), for example ZC sequence, its length is no more than the sub-carrier number of ofdm system to be calibrated, for example, in the LTE of 20MHz system, be 1024.Be mapped to by certain criterion on the subcarrier of system, be FFT and be transformed into time domain, insert the front and back CP of certain length, protect interval for the baseband signal of antenna calibration through being no more than GP after receiving or send out the delay of passage.

Concrete technical scheme of the present invention is as follows:

A method for antenna calibration in ofdm system, the method comprises the steps:

The calibrating sequence signal of step 1:BBU structure time-frequency domain;

Step 2:RRU and BBU preheating and array antenna receive after the pre-calibration command request from operating console OMC or system default configuration file, and RRU is according to being transmitting calibration or receiving calibration is switched to corresponding receipts or sending alignment state by the state of RRU; BBU receives calibrating signal, extract effective subcarrier, utilize local sequence and receiving sequence spectrum correlation to obtain the coarse delay of the sampling interval Ts level of respective antenna unit, antenna is received or sent out the relatively maximum poor RRU that informs of antenna delay that receives or send out passage of passage, RRU compensates respectively the relative time delay of each passage;

Step 3:RRU adjusts to each antenna receiving signal moment at the maximum delay place of receiving or sending out passage.BBU is transformed into frequency domain by calibrating signal through FFT, extracts after effective subcarrier, is transformed into time domain through DFT, is transformed into frequency domain after time domain noise reduction, calculate that each antenna is received or originating party to the phase shift theta of effective subcarrier k _k, the criterion based on least mean-square error is to θ _kcarry out linear fit, estimate time delay Δ t and the first phase θ of each array antenna decimal times Ts by following formula _ini.

${\mathrm{\Δ\θ}}_k=\frac{L\·\underset{k\∈K}{\mathrm{\Σ}}(k\·{\mathrm{\θ}}_k)-\underset{k\∈K}{\mathrm{\Σ}}{\mathrm{\θ}}_k\·\underset{k\∈K}{\mathrm{\Σ}}k}{L\·\underset{k\∈K}{\mathrm{\Σ}}{k}^2-{\left(\underset{k\∈K}{\mathrm{\Σ}}k\right)}^2}$

${\mathrm{\θ}}_{\mathrm{ini}}=\frac{\underset{k\∈K}{\mathrm{\Σ}}(k\·{\mathrm{\θ}}_k)\·\underset{k\∈K}{\mathrm{\Σ}}k-\underset{k\∈K}{\mathrm{\Σ}}{\mathrm{\θ}}_k\·\underset{k\∈K}{\mathrm{\Σ}}{k}^2}{{\left(\underset{k\∈K}{\mathrm{\Σ}}k\right)}^2-L\·\underset{k\∈K}{\mathrm{\Σ}}{k}^2}$

wherein L is the sub-carrier number of including linear fit in, and K is subcarrier collection.

Receive passage and send out passage the time delay Δ t and the first phase θ that calculate respectively decimal times Ts _ini, to receiving passage and sending out passage and calibrate respectively.

Step 4: first phase θ _iniwith time delay lower than the RRU if sampling interval frequency domain compensation at BBU, the time delay at RRU if sampling interval compensates at RRU intermediate frequency;

Step 5: system completes after phase alignment, carries out amplitude calibration based on subband.System bandwidth is divided into some subbands, calibrating signal the reserved part subcarrier of each subband mapping different antennae.Based on preserved sub-carrier do noise estimate, by receive calibrating signal time domain noise reduction process after, on frequency domain, do channel estimating, by the Amplitude Compensation of different sub-band on subband amplitude corresponding to antenna maximum transmission power.Receive passage and send out passage and do respectively amplitude calibration;

Step 6: when given antenna is received after periodic calibration order, first judge whether to carry out pre-calibration, if do not have, first early warning, then carry out pre-calibration by step 2～5, carry out periodic calibration, the time delay to decimal times Ts in this periodic calibration and the calibration of first phase are the same with the calibration steps of the time delay to decimal times Ts and first phase in pre-calibration again.

Calibrating sequence signal in described step 1 is the certain length sequence x with good their cross correlation _u(n), this length is no more than effective sub-carrier number of ofdm system to be calibrated.

Antenna calibration signal in described step 1 sends or receives at GP free timeslot.

In described step 3, transceiver channel is calibrated respectively.When passage is received in calibration, boresight antenna sending alignment signal, array antenna is close alignment signal simultaneously; When passage is sent out in calibration, aerial array while or successively sending alignment signal, boresight antenna close alignment signal.

In described step 4, aerial array time delay and phase difference compensate at RRU and BBU simultaneously, the delay inequality at RRU compensation if sampling interval, and BBU compensation is lower than remaining delay inequality and the first phase at if sampling interval.

In step 6, in periodic calibration, get the phase shift theta of the frequency response of all or part of subcarrier _kcarry out time delay and estimate Δ t, sending out in the calibration of passage, can be staggered between array antenna by sending calibrating sequence, all passages of joint calibration, also can calibrate respectively single antenna respectively successively.

A kind of antenna calibration device, this device comprises: the calibrating signal generation module of BBU, calibration link Transmit enable and the control module of RRU, the calibration time delay of BBU and phase calculation module, the timing compensating module of RRU, the amplitude of BBU and phase compensation block.

The calibrating signal generation module of BBU, for generation and the structure of calibrating signal;

Calibration link Transmit enable and the control module of RRU, for RRU receive or sending alignment order after, the transmitted signal of boresight antenna is coupled to uplink receiving channel, or the transmitted signal of array antenna is coupled on boresight antenna by transmission channel;

The calibration time delay of BBU and phase calculation module, for the calculating of the thick time delay of transceiver channel integral multiple Ts and decimal times Ts essence delay and aerial array first phase;

RRU timing compensating module, for the delay at RRU compensation if sampling interval;

BBU amplitude and phase compensation block, residual retardance and first phase for BBU compensation lower than if sampling interval.

The invention has the advantages that:

1. the present invention can carry out the calibration of real-time high-precision to the consistency of the receive path of LTE system and transmission channel phase place, the common compensation to time delay and phase place by BBU and RRU, can guarantee that the aerial array transmitted signal of eating dishes without rice or wine is consistent with BBU phase of received signal height.Be particularly useful for TDD-LTE etc. to the higher communication system of antenna consistency needs.

2. this calibration steps of the present invention not only should be in RRU and the direct-connected system of BBU, also can be applied to the system that optical fiber between BBU and RRU or cable zoom out;

3. this calibration steps of the present invention is not only applied to wave beam forming characteristic, is also applied to multiple-input and multiple-output mimo system and carries out array antenna calibration;

4. this calibration steps of the present invention is not only applied to the ofdm system of single carrier, is also applicable to the ofdm system of carrier aggregation.

Accompanying drawing explanation

Fig. 1 is the schematic flow sheet of the calibration steps of array antenna of the present invention;

Fig. 2 is the schematic diagram of the frame structure of antenna calibration signal of the present invention;

Fig. 3 be in the embodiment of the present invention one when down going channel amplitude calibration calibrating signal at the mapping graph of subband;

Fig. 4 is array antenna calibrated channel control schematic diagram in the embodiment of the present invention one.

Embodiment

In order more clearly to illustrate object of the present invention, technical scheme and advantage, referring to the accompanying drawing embodiment that develops simultaneously, the present invention is described in further detail.

Main thought of the present invention is to utilize ZC sequence or other to have the sequence of good autocorrelation performance, the thick time delay that utilizes known local sequence and receiving sequence to carry out correlation estimation to go out array antenna at frequency domain, the calibrating signal of reception is done to FFT after time domain noise reduction and be transformed into frequency domain, calculate the phase shift of each subcarrier of transmitting or receive path, the essence of finally utilizing minimum mean square error criterion linear fit to go out this array antenna postpones and first phase.Wherein FFT/IFFT used calculates DFT association processing unit that can multiplex baseband digital signal processor, makes to calculate simple and effective.

Embodiment mono-

Fig. 1 is the calibration steps of array antenna of the present invention and the schematic flow sheet that device is applied in TDD-LTE system.Before calibration, construct a ZC sequence that length is 1024, 0≤n≤1023, u is ZC sequence index.Calibrating sequence can also use m sequence or other to have the sequence of good autocorrelation characteristic.By x _u(n) be mapped to system subcarrier x (k),

According to the calibrating signal that produces time domain shown in Fig. 2, front and back CP takes fully to cover possible maximum delay value, and for example 256.Can also be according to system, thick step estimates and receives the time delay that signal transmits relatively, adjusts according to this time of reception that receives signal.In order better to explain the present invention, we choose conventional LTE configuration, 20M bandwidth, and eight aerial arrays, the baseband signal sample rate of 30.72M is example.

From transmission channel pre-calibration, four aspects of the periodic calibration of receive path pre-calibration and transmitting, receive path describe respectively calibration process in detail below.

The calibration of transmission channel in A, pre-calibration

Step 101: base station obtains to be sent out after passage pre-calibration order, and each control unit of RRU is switched to

Sending alignment state, BBU sends calibrating signal at GP time slot successively by each array antenna;

Step 102: after the calibrating signal that base station sends by boresight antenna successively receiving array antenna, the delay of calculating each antenna calibration signal by following method a is antenna sequence number, general a=1 ..., 8.

In GP, get and receive signal and be 2048 IFFT and obtain y (k) and extract effective subcarrier y _n(k), k=1 ..., 1024, the ZC sequence of dot product frequency domain $z_u\left(k\right)=\mathrm{ifft}\left(y_u\left(k\right)\right)\·\mathrm{ifft}\left(x_u^{*}\left(k\right)\right);$ k＝1，...，1024

By z _u(k) be transformed into time domain z _u(n)=IDFT{z _u(k) }, n=1 ..., 1024

In search time domain | z _u(n) | maximum n corresponding to peak value, records the time delay nT of all antennas _sand find out maximum sky wire delay, and antenna array unit is fed back to RRU with respect to the difference of the maximum delay of aerial array, RRU postpones the transmitting of immediately adjusting respective antenna, and the delay of all antenna elements is dressed to the antenna of maximum delay.

Step 103: boresight antenna is adjusted the acceptance point of boresight antenna signal according to the maximum delay of antenna transmission passage, the acceptance point error of each like this array antenna is just at a sampling interval Ts.

Step 104: base station has been adjusted after the acceptance point of boresight antenna signal, the time domain of the same antenna is received to signal and be transformed into frequency domain, extracting effective subcarrier is converted to time domain and does the phase place that is converted to again the effective subcarrier of frequency-domain calculations after noise reduction process, carry out minimum Mean Square Error Linear matching based on sub-carrier phase again, estimate delay and the first phase of the decimal times Ts of each antenna transmission passage.

The signal of supposing frequency domain transmission is s=[s ₀, s ₁..., s _m/2-1, 0 ... 0, s _n-m/2+1, s _n], wherein N is sub-carrier number 2048, and M is effective sub-carrier number 1200, and L is CP length, and Ts is the sampling interval.

Suppose that in time domain, receiving signal indication is:

X=[x _n-L..., x _n-1..., x _n-1, x ₀, x ₁..., x _n-1, x ₀..., x _l-1]+n, n is white noise, d is time delay;

At effective subcarrier of the reception signal of frequency domain be:

$r_k=\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}{x}_n\exp (-j\×\frac{2\mathrm{\π}}{N}\×n\×k),k\∈[0,M/2-1]\∪[N-M/2+1,N]$

The channel response of supposing subcarrier on frequency domain is H _k, time delay Δ t, H _kcan be expressed as

$H_k=r_k/s_k-n_k/s_k=\left|H_k\right|\·e^{j{\mathrm{\θ}}_k}$

The phase place of its sub-carriers is n _kfor white noise, for first phase.

The phase difference that each subcarrier is estimated is

${\mathrm{\&theta;}}_k=\left\{\begin{array}{cc}\mathrm{\&phi;}\left(r_k^{\&prime;}{s}_k^{*}\right)& 0\&le;k<M\\ \mathrm{\&phi;}\left(r_k^{\&prime;}{s}_{M-k}^{*}\right)& N-M/2+1\&le;k<N\end{array}\right.$

Delay and the first phase estimated by minimum Mean Square Error Linear fitting criterion are expressed as

${\mathrm{\&Delta;\&theta;}}_k=\frac{L\&CenterDot;\underset{k\&Element;K}{\mathrm{\&Sigma;}}(k\&CenterDot;{\mathrm{\&theta;}}_k)-\underset{k\&Element;K}{\mathrm{\&Sigma;}}{\mathrm{\&theta;}}_k\&CenterDot;\underset{k\&Element;K}{\mathrm{\&Sigma;}}k}{L\&CenterDot;\underset{k\&Element;K}{\mathrm{\&Sigma;}}{k}^2-{\left(\underset{k\&Element;K}{\mathrm{\&Sigma;}}k\right)}^2}$

${\mathrm{\&theta;}}_{\mathrm{ini}}=\frac{\underset{k\&Element;K}{\mathrm{\&Sigma;}}(k\&CenterDot;{\mathrm{\&theta;}}_k)\&CenterDot;\underset{k\&Element;K}{\mathrm{\&Sigma;}}k-\underset{k\&Element;K}{\mathrm{\&Sigma;}}{\mathrm{\&theta;}}_k\&CenterDot;\underset{k\&Element;K}{\mathrm{\&Sigma;}}{k}^2}{{\left(\underset{k\&Element;K}{\mathrm{\&Sigma;}}k\right)}^2-L\&CenterDot;\underset{k\&Element;K}{\mathrm{\&Sigma;}}{k}^2}$

wherein L is the sub-carrier number of including linear fit in, and K is subcarrier sequence number collection.

Step 105: adjustment is postponed to send to RRU, adjust the time delay of the Ts time delay of integral multiple and the little several times of maximum possible by regulating the buffer of RRU IF processing unit, for example, Sampling Rate is six times of baseband signal sample rate, compensate at intermediate frequency higher than 1/6Ts, lower than the delay δ of 1/6Ts _tbe multiplied by phase factor in base band compensate, wherein k is subcarrier sequence number, δ ₁for residual retardance.

Step 106: suppose that the calibrating signal that antenna a frequency domain receives is r _a(k), 12 subcarriers of each subband, the calibrating signal of 8 antennas is mapped to respectively front 8 subcarriers of each subband, and rear 4 tone reservations do noise and estimate.Channel estimating based on least mean-square error is

$H_a\left(k\right)=\frac{r_a\left(k\right)}{x_u^{\&prime;}\left(k\right)},k=a,a+12,a+24,...,a+12*99;a=\mathrm{1,2},...8$

The noise power of antenna a is $P_{\mathrm{noise},a}=\mathrm{mean}(\underset{k=\mathrm{nullsubcarriers}}{\mathrm{\&Sigma;}}{H}_a\left(k\right)*H_a{\left(k\right)}^H);$

The signal power of antenna a is $P_{\mathrm{average},a}=\mathrm{mean}(\underset{k=\mathrm{validsubcarriers}}{\mathrm{\&Sigma;}}{H}_a\left(k\right)*H_a{\left(k\right)}^H);$ By channel estimation in frequency domain H _a(k) be transformed into time domain h _a(n) do noise reduction process,

h _a(n)＝IDFT(H _a(k))

H ' _a(n)=h _a(n), work as h _a(n)>=T _threshold* P _noisetime; H ' _a(n)=0, works as h _a(n) < T _threshold* P _noisetime;

Estimate h ' based on the time domain channel after noise reduction _a(n) calculate amplitude compensating factor A ' _{comp, a},

$A_{\mathrm{comp},a}^{\&prime;}=h_a^{\&prime;}\left(n\right)/\sqrt{P_{\mathrm{average},a}}.$

By A ' _{comp, a}zero padding is FFT and is converted the Amplitude Compensation coefficient that is transformed into frequency domain acquisition full bandwidth

A _comp，a(k)＝DFT([A′ _comp，a，zeros(1，1200-sizeof(A′ _comp，a))])，k＝1，2，...，1200。

BBU will use A _{comp, a}go the amplitude of boresight antenna a at frequency domain.

So far, completed the pre-calibration of transmission channel.

In step 101, structure is sent out the method for the calibrating signal of passage, can be also, and N passage sends orthogonal ZC sequence simultaneously, and the signal Combined Treatment in the lump that boresight antenna sends N passage calculates the coarse delay of all passages in a frame.In step 101, the method for the calibrating signal of a structure passage can also be, N passage sends the ZC sequence that same sequence produces through different time shifts, boresight antenna, to doing relevant treatment from the receive channel of N passage, calculates the coarse delay of each transmission channel in a frame simultaneously.In step 101, the method for the calibrating signal of a structure passage can be also, sequence is divided into N equal portions by antenna number, frequency division multiplexing sends at N transmission channel simultaneously, boresight antenna receives after the transmitted signal of N passage, extracts transmitting of different passages carry out the estimation of time delay and first phase at frequency domain.Suppose eight aerial arrays, the LTE system of 20MHz is carried out antenna calibration, as shown in Figure 3, and to sending out when calibrate, n the frequency domain calibrating signal of sending out passage is mapped on n+12*m subcarrier of antenna calibration signal frequency domain, m=1,2 ..., 100 is n the subcarrier sequence number of sending out passage antenna, n gets 1～8, all the other 4 tone reservations in every 12 subcarriers, the calibrating signal of not shining upon any passage.

The calibration of receive path in B, pre-calibration

Step 201: base station obtains receives after the accurate order of passage pre-calibration, and each control unit of RRU is switched to close alignment state, and base station sends calibrating signal at GP time slot by boresight antenna;

Step 202: base station each array antenna received boresight antenna signal.Receive the estimation of the thick time delay of passage with the mode of the thick calibration of sendaisle, the difference of the thick time delay of each receive path being received relatively to passage maximum delay reports RRU, RRU according to the upper debit of the poor adjustment of each receipts channel delay RRU to IF processing unit, make each receipts passage debit to the delay delay of receiving passage to maximum dress.

Step 203: boresight antenna is adjusted the acceptance point of boresight antenna signal according to the maximum delay of antenna transmission passage, the receive time delay error of each like this array antenna is just at a positive and negative sampling interval Ts.

Step 204: base station has been adjusted after the acceptance point of array antenna signal, through the same method of smart delay estimation in the sending alignment that coexists, estimate sheet antenna is received delay and the first phase of the decimal times Ts of passage.

Step 205: adjustment is postponed to send to RRU, by regulating RRU debit to adjust the time delay of the Ts time delay of integral multiple and the little several times of maximum possible to the sequential of IF processing unit, for example, Sampling Rate is six times of baseband signal sample rate, compensate at intermediate frequency higher than 1/6Ts, lower than the delay δ of 1/6Ts _tbe multiplied by phase factor in base band compensate, wherein k is subcarrier sequence number, δ _tfor residual retardance.

Step 206: similar calibrate of antenna amplitude calibration of receiving passage.

So far, completed the pre-calibration of receive path.

The calibration of transmission channel in C, periodic calibration

Complete after array antenna pre-calibration, carrying out the calibration of periodic array antenna according to the configuration of oam center (OMC).Only have the successful antenna element of initialization of calibration, whenever can carry out periodic calibration to it, guaranteed that like this periodic calibration can carry out all available antenna unit.

Step 301:BBU obtains after the transmission channel period regulation order of given antenna, and the control unit of this antenna is switched to transmitting calibration state by RRU, and BBU sends calibrating signal at GP time slot by each array antenna;

The calibrating signal that step 302:BBU sends by boresight antenna receiving array antenna, carries out the estimation of day wire delay and first phase by the method for times Ts delay estimation of the smart decimal in antenna pre-calibration, and compensates in RRU and baseband processing unit.

So far the calibration of the transmission channel of given antenna in execution cycle property calibration.

The calibration of receive path in D, periodic calibration

Step 401:BBU obtains after the receive path period regulation order of given antenna, and the control unit of this antenna is switched to close alignment state by RRU, and BBU sends calibrating signal at GP time slot by boresight antenna;

After the each array antenna received calibrating signal of step 402:BBU, carry out the estimation of day wire delay and first phase by the method for times Ts delay estimation of the smart decimal in antenna pre-calibration, and compensation respectively in RRU and baseband processing unit.

So far, in the calibration of execution cycle property, the calibration of the receive path of given antenna, also finishes the calibration of the present embodiment array antenna.

The present invention also comprises a kind of antenna calibration device, is illustrated in figure 4 the embodiment of the present invention one alignment device at array antenna calibrated channel control schematic diagram.This calibrating installation comprises the calibrating signal generation module of BBU, for generation and the structure of calibrating signal; Calibration link Transmit enable and the control module of RRU, for RRU receive or sending alignment order after, the transmitted signal of boresight antenna is coupled to uplink receiving channel, or the transmitted signal of array antenna is coupled on boresight antenna by transmission channel; The calibration time delay of BBU and phase calculation module, for the calculating of the thick time delay of transceiver channel integral multiple Ts and decimal times Ts essence delay and aerial array first phase; RRU timing compensating module, for the delay at RRU compensation if sampling interval; BBU amplitude and phase compensation block, residual retardance and first phase for BBU compensation lower than if sampling interval.

The foregoing is only the preferred embodiments of the present invention, be not intended to limit protection scope of the present invention, all any modifications of doing within the spirit and principles in the present invention, be equal to replace and improve, within all should being included in protection scope of the present invention.

Claims (7)

1. a method for antenna calibration in ofdm system, is characterized in that: the method is as follows:

Pre-calibration:

The calibrating sequence signal of step 1:BBU structure time-frequency domain;

Step 2:RRU and BBU preheating and array antenna receive after the pre-calibration command request from operating console OMC or system default configuration file, and RRU is according to being transmitting calibration or receiving calibration is switched to corresponding receipts or sending alignment state by the state of RRU; BBU receives the antenna calibration signal from GP time slot, extract effective subcarrier, utilize local sequence and receiving sequence spectrum correlation to obtain the coarse delay of the sampling interval Ts level of respective antenna unit, antenna is received to passage or send out the relatively maximum poor RRU of informing of antenna delay that receives passage or send out passage of passage, RRU compensates respectively the relative time delay of each passage;

Step 3:RRU adjusts to each antenna receiving signal moment at the maximum delay place of receiving or sending out passage, BBU is transformed into frequency domain by calibrating signal through FFT, extract after effective subcarrier, be transformed into time domain through DFT, after time domain noise reduction, be transformed into frequency domain, calculate that each antenna is received or originating party to the phase shift theta of effective subcarrier k _k, the criterion based on least mean-square error is to θ _kcarry out linear fit, by following formula estimate that each array antenna is received or originating party to time delay Δ t and the first phase θ of decimal times Ts _ini, wherein

$\mathrm{\&Delta;}{\mathrm{\&theta;}}_k=\frac{L\&CenterDot;\underset{k\&Element;K}{\mathrm{\&Sigma;}}(k\&CenterDot;{\mathrm{\&theta;}}_k)-\underset{k\&Element;K}{\mathrm{\&Sigma;}}{\mathrm{\&theta;}}_k\&CenterDot;\underset{k\&Element;K}{\mathrm{\&Sigma;}}k}{L\&CenterDot;\underset{k\&Element;K}{\mathrm{\&Sigma;}}{k}^2-{\left(\underset{k\&Element;K}{\mathrm{\&Sigma;}}k\right)}^2}$

${\mathrm{\&theta;}}_{\mathrm{ini}}=\frac{\underset{k\&Element;K}{\mathrm{\&Sigma;}}(k\&CenterDot;{\mathrm{\&theta;}}_k)\&CenterDot;\underset{k\&Element;K}{\mathrm{\&Sigma;}}k-\underset{k\&Element;K}{\mathrm{\&Sigma;}}{\mathrm{\&theta;}}_k\&CenterDot;\underset{k\&Element;K}{\mathrm{\&Sigma;}}{k}^2}{{\left(\underset{k\&Element;K}{\mathrm{\&Sigma;}}k\right)}^2-L\&CenterDot;\underset{k\&Element;K}{\mathrm{\&Sigma;}}{k}^2}$

l is the sub-carrier number of including linear fit in, and K is subcarrier collection; Receive passage and send out passage the time delay Δ t and the first phase θ that calculate respectively decimal times Ts _ini, to receiving passage and sending out passage and calibrate respectively;

Step 4: first phase θ _iniwith time delay lower than the RRU if sampling interval frequency domain compensation at BBU, the time delay at RRU if sampling interval compensates at RRU intermediate frequency;

Step 5: system completes after phase alignment, carries out amplitude calibration based on subband; System bandwidth is divided into some subbands, calibrating signal the reserved part subcarrier of each subband mapping different antennae; Based on preserved sub-carrier do noise estimate, by receive calibrating signal time domain noise reduction process after, on frequency domain, do channel estimating, by the Amplitude Compensation of different sub-band on subband amplitude corresponding to antenna maximum transmission power; Receive passage and send out passage and do respectively amplitude calibration;

Periodic calibration:

Step 6: when given antenna is received after periodic calibration order, first judge whether to carry out pre-calibration, if do not have, first early warning, then carry out pre-calibration by step 2～5, carry out periodic calibration, the time delay to decimal times Ts in this periodic calibration and the calibration of first phase are the same with the calibration steps of the time delay to decimal times Ts and first phase in pre-calibration again.

2. the method for antenna calibration in a kind of ofdm system according to claim 1, is characterized in that, the calibrating sequence signal in described step 1 is the certain length sequence x with good their cross correlation _u(n), this length is no more than effective sub-carrier number of ofdm system to be calibrated.

3. the method for antenna calibration in a kind of ofdm system according to claim 1, is characterized in that, the calibrating sequence signal in step 1 sends or receives at GP free timeslot.

4. the method for antenna calibration in a kind of ofdm system according to claim 1, is characterized in that, in step 3, transceiver channel is calibrated respectively, when passage is received in calibration, and boresight antenna sending alignment signal, array antenna is close alignment signal simultaneously; When passage is sent out in calibration, aerial array while or successively sending alignment signal, boresight antenna close alignment signal.

5. the method for antenna calibration in a kind of ofdm system according to claim 1, it is characterized in that, in step 4, aerial array time delay and phase difference compensate at RRU and BBU simultaneously, the delay inequality at RRU compensation if sampling interval, BBU compensation is lower than remaining delay inequality and the first phase at if sampling interval.

6. the method for antenna calibration in a kind of ofdm system according to claim 1, is characterized in that, in step 6, gets the phase shift theta of the frequency response of all or part of subcarrier in periodic calibration _kcarry out time delay and estimate Δ t, sending out in the calibration of passage, can be staggered between array antenna by sending calibrating sequence, all passages of joint calibration, also can calibrate respectively single antenna respectively successively.

7. the method for antenna calibration in a kind of ofdm system according to claim 1, is characterized in that, in this calibration steps, the time-frequency domain of signal is changed, calculating is relevant, time domain noise reduction has adopted FFT computing.