Method for calibrating smart antenna array systems in real time

• US 20060009162A1
• Filed: 06/23/2005
• Published: 01/12/2006
• Est. Priority Date: 12/25/2002
• Status: Active Grant

• Current Assignee: Datang Mobile Communications Equipment Company Limited (China Information Communication Technology Group Co. Ltd.)
• Original Assignee: Datang Mobile Communications Equipment Company Limited (China Information Communication Technology Group Co. Ltd.)
• Inventors: Li, Feng, Tan, Zhe
• Granted Patent: US 7,102,569 B2
• Time in Patent Office: Days
• US Class Current: 455/67.110
• CPC Class Codes: H01Q 3/267 Phased-array testing or checking devices

Abstract

Transmitting and receiving compensation coefficients of each antenna element relative to a calibration antenna element are obtained in the pre-calibration of a smart antenna. After the antenna array is installed, in transmitting calibration, amplitude and phase response of each transmitting link is computed according to the calibration signals received by the calibration link and, together with the transmitting compensation coefficient obtained in the pre-calibration, the compensation coefficient of each transmitting link is computed to compensate the downlink data of a base station. In receiving calibration, the amplitude and phase response of each receiving link is computed based on the signals received by the receiving links and, together with the receiving compensation coefficient obtained in pre-calibration, the compensation coefficient of each receiving link is computed to compensate the uplink data of the base station. The calibration signal of each antenna element is generated by a periodic cycling shift of a basic calibration sequence.

Claims

1. A method for calibrating smart antenna array systems in real time, comprising:

pre-calibrating each antenna element of a smart antenna array to obtain a transmitting compensation coefficient c_k^TX and a receiving compensation coefficient c_k^RX of each antenna element relative to a calibration antenna element;

performing a transmitting calibration procedure comprised of transmitting calibration signals simultaneously over a plurality of transmitting links to form a combined signal such that a calibration link receives the combined signal;

performing a receiving calibration procedure comprised of transmitting a receiving calibration signal over the calibration link such that a plurality of receiving links receive the receiving calibration signal simultaneously; and

processing the combined signal received by the calibration link and the receiving calibration signal received by the receiving links, respectively, with a baseband signal processor to obtain compensation coefficients of each transmitting link and each receiving link of the smart antenna array, wherein;

A. the transmitting and receiving calibration signal for each antenna element is generated by a periodic cycling shift of a basic calibration sequence such that each calibration signal is a calibration sequence with good anti-white-noise characteristics;

B. in the transmitting calibration procedure, the baseband signal processor first computing an amplitude and phase response of each transmitting link on the basis of the combined signal received by the calibration link, then computing the compensation coefficient of each transmitting link on the basis of the amplitude and phase response of each transmitting link and the transmitting compensation coefficients c_k^TX obtained in the pre-calibration for compensating downlink data of the base station; and

C. in the receiving calibration procedure, the baseband signal processor first computing an amplitude and phase response of each receiving link on the basis of the received receiving calibration signal of each receiving link, then computing the compensation coefficient of each receiving link on the basis of the amplitude and phase response of each receiving link and the receiving compensation coefficients C_k^RX obtained in the pre-calibration for compensating uplink data of the base station.

2. The method according to claim 1, wherein said pre-calibrating each antenna element of a smart antenna array to obtain a transmitting compensation coefficient c_k^TX and a receiving compensation coefficient C_k^RX of each antenna element relative to a calibration antenna element comprises:

connecting one end of a network vector analyzer to the calibration antenna element and the other end of the network vector analyzer to each antenna element one by one;

in the transmitting pre-calibration, the k^th antenna element transmitting a fixed level data signal sequentially, the calibration antenna element receiving the signal, then obtaining the transmitting compensation coefficient C_k^TX between each antenna element and the calibration antenna element; and

in the receiving pre-calibration, the calibration antenna element transmitting a fixed level data signal, the k^th antenna elements receiving the signal, then obtaining the receiving compensation coefficients C_k^RX between the calibration antenna element and each antenna element, wherein k=1, . . . . N, and N is the number of the antenna elements in the antenna array.

3. The method according to claim 1, wherein generating the transmitting and receiving calibration signal for each antenna element by a periodic cycling shift of a basic calibration sequence further comprises:

taking a binary sequence m_p with a length P as the basic calibration sequence;

performing a phase equalization to the sequence m_p to generate a complex vector of calibration sequence m_p;

expanding the m_p periodically to obtain a new periodical complex vector m;

obtaining a calibration vector for each antenna element from the m;

generating said transmitting and receiving calibration signal for each antenna element from the calibration vector for each antenna element.

4. The method according to claim 3, wherein said P is selected as a power of 2.

5. The method according to claim 1, wherein said transmitting calibration procedure and receiving calibration procedure, in steps B and C, are periodically performed in the idle gap of a mobile communication system.

6. The method according to claim 1, wherein, in a TD-SCDMA system, said transmitting calibration procedure and receiving calibration procedure, in steps B and C, are periodically performed in the guard period between an uplink pilot time-slot and a downlink pilot time-slot in a frame.

7. The method according to claim 1, wherein computing the compensation coefficient of each transmitting link in the transmitting calibration procedure in said step B further comprises:

b1. obtaining a complex vector of the combined signal received by the calibration link R=(r₁, r₂, . . . r₁), where l=P+2×

(w−

1), P=w×

N represents the length of said basic calibration sequence, N is the number of antenna elements of the smart antenna array, and w is a window length in a channel estimation of each transmitting link;

b2. intercepting from the complex vector a section R_p=(r₁,r₂, . . . , r_p) with a length equal to that of the basic calibration sequence P;

b3. computing a Channel Impulse Response sequence with a length P using the formula CIR=(c₁,c₂, . . . ,c_p)=ifft(fft(R_p•

S)), where S is a constant vector;

computing a Channel Impulse Response sequence with a length P using the formula CIR^k=(c₁^k,c₂^k, . . . ,c_p^k)=fft(fft(R_p^k•

S)), where k=1 . . . N, and S is a constant vector;

b4. computing an interpolation function of a peak value between the channel estimation results c<sub>w×

(k−

1)+1</sub>˜

c_work of a k^th transmitting link;

CIR_k=f max(c<sub>w×

(k−

1)+1</sub>, . . . ,c_work), and obtaining the amplitude and phase response of the k^th link including a path between a transmitter and the antenna element of the calibration link, k=1, . . . N;

b5. multiplying CIR_k with the transmitting compensation coefficient C_k^TX of the k^th link obtained in the pre-calibration, obtaining the amplitude and phase response of the k^th link including the path between the transmitter and the antenna element thereof;

CIR_k=CIR_k×

c_k^TX, k=1 . . . N;

b6. computing the mean power of a transmitting link with the following formula;

$\mathrm{Mean\_power}=\left(\underset{k=1}{\overset{N}{\sum <br><br>}}<br><br>{\left(\mathrm{abs}<br><br>\left({\mathrm{CIR}}_k^{\mathrm{\prime <br><br>}}\right)\right)}^2\right)/N;<br><br>$

b7. computing the transmitting compensation coefficient of each transmitting link with the following formula;

Corr_factor^k=sqrt(Mean_power)/CIR′

_k, where sqrt ( ) represents a square root function.

8. The method according to claim 7, wherein said Step b2 is performed by intercepting a part of the basic calibration sequence as expressed by the following formula R_p=(r_w−

1,r_w, . . . , r<sub>w+p−

2</sub>).

9. The method according to claim 7, wherein the constant vector S in Step b3 is computed by the formula:

S=1./fft(m_P)=1, /fft(m₁,m₂, . . . ,m_P) where the complex vector of the calibration sequence, m_P=(m₁,m₂, . . . ,m_P), is generated by a phase equalization to the basic calibration sequence m_P=(m₁,m₂, . . . ,m_P), the element of the sequence m_i=(j)<sup>i−

1</sup>·

m_i, i=1, . . . P, P=w×

N represents the length of said basic calibration sequence, N is the number of antenna elements of the smart antenna array, and w is the window length in channel estimation of each transmitting link.

10. The method according to claim 1, wherein computing the compensation coefficient of each receiving link in the receiving calibration in said step C, further comprises:

c1. obtaining a complex vector sequence of the signal received by each receiving link R^k=(r₁^k, r₂^k, . . . r₁^k) where l=P+2×

(w−

1), k=1, . . . N, P=w×

N represents the length of the basic calibration sequence, N is the number of antenna elements of the smart antenna array, and w is the window length of channel estimation of each receiving link;

c2. intercepting from the basic calibration sequence a section with a length equals to that of the basic calibration sequence P, R_P^k=(r₁^k,r₂^k, . . . ,r_p^k) k=1, . . . N;

c3. obtaining a Channel Impulse Response sequence with a length P by the formula CIR^k=(c₁^k,c₂^k, . . . ,c_p^k)=ifft(fft(R_p^k•

S)), where k=1, . . . N and S is a constant vector;

c4. computing an interpolation function of a peak value between the channel estimation results c₁^k˜

c_work^k of a k^th receiving link with CIR_k=f max(c₁^k,c₂^k . . . ,c_p^k), obtaining an amplitude and phase response of the k^th receiving link including a path between an antenna element of the calibration link and an RF receiver, k=1, . . . N;

c5. multiplying CIR_k with the receiving compensation coefficient c_k^RX of the k^th link obtained in the pre-calibration, obtaining the amplitude and phase response of the k^th receiving link including the path between the antenna element and the RF receiver, CIR′

_k=CIR_k×

c_k^RX k=1, . . . N;

c6. computing the mean power of a receiving link with the formula;

$\mathrm{Mean\_power}=\left(\underset{k=1}{\overset{N}{\sum <br><br>}}<br><br>{\left(\mathrm{abs}<br><br>\left({\mathrm{CIR}}_k^{\mathrm{\prime <br><br>}}\right)\right)}^2\right)/N;<br><br>$

and

c7. computing a receiving compensation coefficient of each receiving link with the formula;

Corr_factor^k=sqrt(Mean_power)/CIR_k, where k=1, . . . N and sqrt( ) represents a square root function.

11. The method according to claim 10, wherein said step c2 is performed by intercepting a part of the basic calibration sequence as expressed by the formula R^k_p=(r_w−

1^k,r_w^k, . . . , r<sub>w+p−

2</sub>^k), k=1, . . . N.

12. The method according to claim 10, wherein said constant vector S in said step c3 is computed with the formula:

S=1./fft(m_P)=1./fft(m₁,m₂, . . . ,m_P) where the complex vector of the calibration sequence m_P=(m₁,m₂, . . . ,m_P) is generated by a phase equalization to the basic calibration sequence m_P=(m₁,m₂, . . . ,m_P), the element of the sequence m_i=(j)<sup>i−

1</sup>·

m_i, i=1, . . . P, P=w×

N represents the length of the basic calibration sequence, N is the number of the antenna elements of the smart antenna array, and w is the window length of channel estimation of each receiving link.

13. A method for generating a calibration sequence signal for the real-time calibration of a smart antenna array by a periodic cycling shift of a basic calibration sequence, comprising the steps of:

a1. providing a binary sequence mp with the length P as the basic calibration sequence, m_P=(m₁, m₂, . . . ,m_P), where P=w×

N, N is the number of antenna elements of a smart antenna array, and w is the window length of channel estimation of each transmitting or receiving link;

a2. performing a phase equalization to the sequence m_p, generating a complex vector of the calibration sequence m_p, m_P=(m₁,m₂, . . . ,_P), where elements of the sequence m_i=(j)<sup>i−

1</sup>·

m_i, i=1, . . . P, and j is the square root of −

1;

a3. expanding m_p periodically and obtaining a new periodical complex vector m, m=(m₁,m₂, . . . ,m_imax)=(m₂,m₃, . . . ,m_p,m₁,m₂, . . . ,m_p);

a4. obtaining a calibration sequence vector with a length Lm=P+w−

1 for each antenna element from the periodical complex vector m, m^(k)=(m₁^(k),m₂^(k), . . . ,m_Lm^(k)), k=1, . . . N, an element of the calibration sequence vector m_i^(k)=m<sub>i+(N−

k)W</sub>, i=1, . . . . Lm and k=1, . . . N; and

a5. generating a calibration sequence signal with a fixed power from the calibration sequence vector on the basis of a calibration requirement.