Reciprocity calibration for multiple-input multiple-output systems

1. A method for reciprocity calibration of a multiple-input multiple-output (MIMO) system, the method comprising:

receiving, by a base station, a first set of pilot symbols by receivers (RXes) of the base station based on a first pilot symbol transmitted from a transmitter (TX) of at least one reference antenna, wherein each of the first set of pilot symbols is received as an r i,0 pilot symbol by an individual antenna of the RXes of the base station, where index “i” denotes individual antenna “i” of the base station, and index “0” denotes the at least one reference antenna;

transmitting, by the base station, a second pilot symbol by TXes of the base station, wherein the transmitted second pilot symbol is received by an RX of the at least one reference antenna as a second set of r 0,i pilot symbols;

calculating non-reciprocity compensation factors based on the first set of pilot symbols and the second set of pilot symbols as

r

i

,

0

r

0

,

i

,

 and

applying the non-reciprocity compensation factors to payload data.

2. The method of claim 1 wherein the at least one reference antenna is one of the antennas of the base station.

3. The method of claim 1 wherein the at least one reference antenna is an antenna at a user equipment (UE) side.

4. The method of claim 1 wherein the at least one reference antenna is a dedicated auxiliary (AUX) antenna.

5. The method of claim 1 , wherein the non-reciprocity compensation factors are applied to payload data of the base station.

6. The method of claim 5 wherein the non-reciprocity compensation factors are applied as, r M =H DL C T WS, wherein r M denotes received symbols by the antennas of the base station, H DL denotes an observed transfer function, C T denotes a matrix combination of the non-reciprocity compensation factors, and WS denotes a beamformed payload data.

7. The method of claim 1 wherein the first pilot symbol transmitted by the TX of the at least one reference antenna is outside of a frequency bandwidth of a payload data.

8. The method of claim 1 wherein the first pilot symbol transmitted by the TX of the at least one reference antenna has a power spectral density that is generally comparable to that of symbols of a payload data.

9. The method of claim 1 , further comprising transmitting a payload data from the TXes of the base station to RXes of a user equipment (UE) side, wherein the first pilot symbol and the data payload are transmitted within same time domain and within different frequency bandwidths.

10. The method of claim 9 wherein the pilot symbol and the payload data are within same frequency bandwidth.

11. The method of claim 10 wherein transmitting the payload data pauses while transmitting the first pilot symbol.

12. The method of claim 1 , further comprising transmitting a payload data from the TXes of the base station to RXes of a user equipment (UE) side, wherein transmitting the payload data pauses when the first pilot symbol is transmitted.

13. A multiple-input multiple-output (MIMO) system for wireless signals, comprising:

a reference TX and at least one reference antenna, the reference TX and the at least one reference antenna configured to transmit a first pilot symbol;

a base station comprising a plurality of base station antennas, wherein the plurality of base stations antennas and antennas of a user equipment (UE) side are configured to exchange the wireless signals, and wherein RXes of the plurality of base station antennas are configured to receive a first set of pilot symbols based on the first pilot symbol transmitted from the reference TX and the at least one reference antenna, wherein each pilot symbol of the first set of pilot symbols is received as the r i,0 pilot symbol of the RX of individual antenna “i” of the base station, and wherein TXes of the plurality of base station antennas are configured to transmit a second pilot symbol, and wherein an RX of the at least one reference antenna is configured to receive a second set of pilot symbols, wherein each pilot symbol of the second set of symbols is received as the r 0,i pilot symbol of the RX of the at least one reference antenna, wherein index “i” denotes individual antenna “i”of the base station, and index “0” denotes the at least one reference antenna;

wherein the (MIMO) system is configured to calculate non-reciprocity compensation factors based on the first set of pilot symbols and the second set of pilot symbols as

r

i

,

0

r

0

,

i

;

 and

wherein the non-reciprocity compensation factors are applied to payload data.

14. The system of claim 13 wherein the at least one reference antenna is one of the antennas of the base station.

15. The system of claim 13 wherein the at least one reference antenna is an antenna of the user equipment (UE) side.

16. The system of claim 13 wherein the at least one reference antenna is a dedicated auxiliary (AUX) antenna.

17. The system of claim 13 wherein the computing module is further configured to apply the non-reciprocity compensation factors as r M =H DL C T WS, wherein r M denotes received symbols by the antennas of the base station H DL denotes an observed transfer function, C T denotes a matrix combination of the non-reciprocity compensation factors, and WS denotes a beamformed payload data.

18. The system of claim 13 wherein the first pilot symbol transmitted by the TX of the at least one reference antenna is outside of a frequency bandwidth of a payload data.

19. The system of claim 13 wherein the first pilot symbol transmitted by the TX of the at least one reference antenna and a payload data are within same frequency bandwidth.

20. The system of claim 13 wherein the first pilot symbol transmitted by the TX of the at least one reference antenna has a power spectral density that is generally comparable to that of symbols of a payload data.