Methods and apparatus for antenna calibration

1. A method in a Radio Base Station (RBS) for inter-transceiver antenna calibration, the method comprising:

collecting a first phase difference between a first signal and a first reception signal and a second phase difference between a second signal and a second reception signal,

wherein the first signal is transmitted through a reference transmission path of a first transceiver and received through a reference reception path of a second transceiver as the first reception signal, and

wherein the second signal is transmitted through a reference transmission path of the second transceiver and received through a reference reception path of the first transceiver as the second reception signal;

determining an inter-loop phase response difference between a first reference path loop of the first transceiver and a second reference path loop of the second transceiver by subtracting the second phase difference from the first phase difference,

wherein the first reference path loop consists of the reference transmission path and the reference reception path of the first transceiver, and

wherein the second reference path loop consists of the reference transmission path and the reference reception path of the second transceiver; and

compensating for the inter-loop phase response difference.

2. The method of claim 1 , wherein the first signal and the second signal are transmitted on a plurality of subcarriers, and wherein compensating for the inter-loop phase response difference comprises:

determining, for each subcarrier, a frequency component (φ k ) of the inter-loop phase response difference;

determining, based on the determined frequency components for the plurality of subcarriers, an inter-loop delay difference (Δt est ) and an inter-loop initial phase difference (φ ini _ est ) between the first reference path loop of the first transceiver and the second reference path loop of the second transceiver; and

compensating for the inter-loop delay difference (Δt est ) and the inter-loop initial phase difference (φ ini _ est ).

3. The method of claim 2 , wherein the inter-loop delay difference (Δt est ) and the inter-loop initial phase difference (φ ini _ est ) are determined according to one of the following polynomial fitting algorithms:

standard least squares polynomial fitting,

weighted least squares polynomial fitting,

constrained least squares polynomial fitting, and

robust least squares polynomial fitting.

4. The method of claim 3 , wherein, according to the standard least squares polynomial fitting, the inter-loop delay difference (Δt est ) is determined as

Δ

⁢

⁢

t

est

=

L

·

∑

k

∈

K

⁢

(

k

·

φ

k

)

-

∑

k

∈

K

⁢

φ

k

·

∑

k

∈

K

⁢

k

L

·

∑

k

∈

K

⁢

k

2

-

(

∑

k

∈

K

⁢

k

)

2

*

N

2

⁢

π

,

where K denotes a subcarrier set consisting of the plurality of subcarriers on which the first and the second signals are transmitted, L denotes a number of the plurality of subcarriers and N denotes a total number of subcarriers used by the RBS for wireless communications.

5. The method of claim 3 , wherein, according to the standard least squares polynomial fitting, the inter-loop initial phase difference (φ ini _ est ) is determined as

φ

ini

⁢

_

⁢

est

=

∑

k

∈

K

⁢

(

k

·

φ

k

)

·

∑

k

∈

K

⁢

k

-

∑

k

∈

K

⁢

φ

k

·

∑

k

∈

K

⁢

k

2

(

∑

k

∈

K

⁢

k

)

2

-

L

·

∑

k

∈

K

⁢

k

2

,

where K denotes a subcarrier set consisting of the plurality of subcarriers on which the first and the second signals are transmitted, L denotes a number of the plurality of subcarriers and N denotes a total number of subcarriers used by the RBS for wireless communications.

6. An apparatus for inter-transceiver antenna calibration in a Radio Base Station (RBS) comprising a memory and a processor, wherein the memory stores machine-readable program code that, when executed by the processor, causes the apparatus to:

collect a first phase difference between a first signal and a first reception signal and a second phase difference between a second signal and a second reception signal,

wherein the first signal is transmitted through a reference transmission path of a first transceiver and received through a reference reception path of a second transceiver as the first reception signal, and

wherein the second signal is transmitted through a reference transmission path of the second transceiver and received through a reference reception path of the first transceiver as the second reception signal;

determine an inter-loop phase response difference between a first reference path loop of the first transceiver and a second reference path loop of the second transceiver by subtracting the second phase difference from the first phase difference,

wherein the first reference path loop consists of the reference transmission path and the reference reception path of the first transceiver, and

wherein the second reference path loop consists of the reference transmission path and the reference reception path of the second transceiver; and

compensate for the inter-loop phase response difference.

7. The apparatus according to claim 6 , wherein the first signal and the second signal are transmitted on a plurality of subcarriers, and wherein the apparatus is operative to compensate for the inter-loop phase response difference by:

determining, for each subcarrier, a frequency component (φ k ) of the inter-loop phase response difference;

determining, based on the determined frequency components for the plurality of subcarriers, an inter-loop delay difference (Δt est ) and an inter-loop initial phase difference (φ ini _ est ) between the first reference path loop of the first transceiver and the second reference path loop of the second transceiver; and

compensating for the inter-loop delay difference (Δt est ) and the inter-loop initial phase difference (φ ini _ est ).

8. The apparatus according to claim 7 , wherein the inter-loop delay difference (Δt est ) and the inter-loop initial phase difference (φ ini _ est ) are determined according to one of the following polynomial fitting algorithms:

standard least squares polynomial fitting,

weighted least squares polynomial fitting,

constrained least squares polynomial fitting, and

robust least squares polynomial fitting.

9. The apparatus according to claim 8 , wherein, according to the standard least squares polynomial fitting, the inter-loop delay difference (Δt est ) is determined as

Δ

⁢

⁢

t

est

=

L

·

∑

k

∈

K

⁢

(

k

·

φ

k

)

-

∑

k

∈

K

⁢

φ

k

·

∑

k

∈

K

⁢

k

L

·

∑

k

∈

K

⁢

k

2

-

(

∑

k

∈

K

⁢

k

)

2

*

N

2

⁢

π

,

where K denotes a subcarrier set consisting of the plurality of subcarriers on which the first and the second signals are transmitted, L denotes a number of the plurality of subcarriers and N denotes a total number of subcarriers used by the RBS for wireless communications.

10. The apparatus according to claim 8 , wherein, according to the standard least squares polynomial fitting, the inter-loop initial phase difference (φ ini _ est ) is determined as

φ

ini

⁢

_

⁢

est

=

∑

k

∈

K

⁢

(

k

·

φ

k

)

·

∑

k

∈

K

⁢

k

-

∑

k

∈

K

⁢

φ

k

·

∑

k

∈

K

⁢

k

2

(

∑

k

∈

K

⁢

k

)

2

-

L

·

∑

k

∈

K

⁢

k

2

,

where K denotes a subcarrier set consisting of the plurality of subcarriers on which the first and the second signals are transmitted, L denotes a number of the plurality of subcarriers and N denotes a total number of subcarriers used by the RBS for wireless communications.

11. An apparatus for inner-transceiver antenna calibration in a Radio Base Station (RBS) comprising a memory and a processor, wherein the memory stores machine-readable program code that, when executed by the processor, causes the apparatus to:

collect, for each of one or more transmission paths, a first phase difference between a first signal and a first reception signal and, for each of one or more reception paths, a second phase difference between a second signal and a second reception signal,

wherein the first signal is transmitted through each of the one or more transmission paths and received through a calibration reception path of the transceiver as the first reception signal, and

wherein the second signal is transmitted through a calibration transmission path of the transceiver and received through each of the one or more reception paths as the second reception signal;

determine, for each of one or more working path loops, each working path loop consisting of a corresponding pair of transmission and reception paths, a relative loop-back phase response difference by subtracting the second phase difference from the first phase difference, wherein the relative loop-back phase response difference is a loop-back phase response difference of the working path loop minus a loop-back phase response difference of a calibration path loop consisting of the calibration transmission path and the calibration reception path; and

compensate for an inconsistency among the relative loop-back phase response differences of the one or more working path loops.

12. The apparatus according to claim 11 , wherein the first signal and the second signal are transmitted on a plurality of subcarriers, and the apparatus is operative to compensate for the relative loop-back phase response differences among the one or more working path loops by:

determining, for each working path loop, a relative loop-back delay difference and a relative loop-back initial phase difference by:

for each subcarrier, determining a frequency component of the relative loop-back phase response difference of the working path loop; and

determining, based on the determined frequency components for the plurality of subcarriers, the relative loop-back delay difference and the relative loop-back initial phase difference of the working path loop; and

compensating for an inconsistency among the relative loop-back delay differences of the one or more working path loops and an inconsistency among the relative loop-back initial phase differences of the one or more working path loops.