Over-the air test

1. An apparatus comprising:

a signal processing unity; and

at least one calibration antenna placable in at least two positions in a test zone in an over-the-air chamber including over-the-air antennas, the at least one calibration antenna, at each position, being configured to receive calibration transmission from the over-the-air antennas via undesired interactions between the calibration transmission and structures associated with the over-the-air chamber, and the signal processing unit being configured to receive signals from the at least one calibration antenna of the at least two positions in response to a reception of the calibration transmission, form a chamber model with the undesired interactions based on the received signals, and store the chamber model for a cancellation of effects of the undesired interactions by a predistortion of a radio frequency transmission from the over-the-air antennas in the over-the-air chamber; and

wherein the signal processing unit is configured to form a distortion electric field by a convolution of a measured chamber model and a frequency response of a desired radio channel to be emulated, an inversion of the distortion electric field, a formation of a frequency response based on an inverted distortion electric field, and a combination of the frequency response of the desired radio channel to be emulated and the frequency response associated with the inverted distortion electric field for a cancellation of effects of the undesired interactions during emulation.

2. The apparatus of claim 1 , wherein the signal processing unit is configured to iterate the chamber model by a formation and a storage of a next chamber model in response to a calibration transmission predistorted based on a present chamber model.

3. The apparatus of claim 1 , wherein the signal processing unit is configured to combine antenna-specific distortion electric fields of the over-the-air antennas for forming the distortion electric field.

4. The apparatus of claim 3 , wherein the signal processing unit is configured to form an antenna-specific distortion field for each over-the-air antenna by a weighting operation between a measured chamber model of an over-the-air antenna and an element which belongs to a frequency response of a desired radio channel to be emulated and to a corresponding over-the-air antenna.

5. The apparatus of claim 1 , wherein the signal processing unit is configured to process the signals and form and store the chamber model as a function of an over-the-air antenna and a direction of the reception of the at least one calibration antenna.

6. The apparatus of claim 5 , wherein the signal processing unit is configured to additionally process the signals and form and store the chamber model as a function of a frequency and a direction of polarization.

7. The apparatus of claim 1 , wherein the signal processing unit is configured to separate the signals associated with a calibration transmission of different over-the-air antennas from each other based on a time division or a code division.

8. An emulation system comprising:

a radio channel generator having a radio channel model predistorted based on a predetermined chamber model;

a plurality of over-the-air antennas;

an emulator coupled to the radio channel generator to receive weights of the radio channel model predistorted based on the chamber model; and

a transmitter coupled to the emulator for feeding a communication signal to the emulator, the emulator being configured to weight the communication signal with the radio channel model predistorted based on the chamber model, the over-the-air antennas being configured to receive the weighted communication signal for a transmission to a device under test, wherein the radio channel generator is configured to form the weights by a formation of a distortion electric field by a convolution of a measured chamber model and a frequency response of the radio channel to be emulated, an inversion of the distortion electric field, a formation of a frequency response of the inversion of the distortion electric field, and a combination of the frequency response of the radio channel to be emulated and the frequency response of the inversion of the distortion electric field.

9. The emulation system of claim 8 , wherein the radio channel generator comprises a radio channel model predistorted based on the chamber model.

10. The emulation system of claim 8 , wherein the radio channel generator comprises a radio channel model predistorted based on a chamber model formed by a simulation.

11. A method comprising:

placing at least one calibration antenna in at least two positions in a test zone in an over-the-air chamber including over-the-air antennas;

receiving, by the at least one calibration antenna, calibration transmission of the over-the-air antennas via interactions between the calibration transmission and structures associated with the over-the-air chamber at each position; and

forming, by a signal processing, a chamber model with the interactions based on received signals,

storing, in a memory, the chamber model for a cancellation of effects of undesired interactions by a predistortion of a radio frequency transmission from the over-the-air antennas in the over-the-air chamber;

forming a distortion electric field by convoluting the chamber model with a frequency response of a desired radio channel to be emulated;

inverting the distortion electric field;

forming a frequency response based on the inverted distortion electric field; and

combining the frequency response of the desired radio channel to be emulated with the frequency response associated with the inverted distortion electric field for a cancellation of effects of the undesired interactions during emulation.

12. The method of claim 11 , the method further comprising iterating the chamber model by forming and storing a next chamber model in response to a calibration transmission predistorted based on a present chamber model.

13. The method of claim 11 , further comprising combining antenna-specific distortion electric fields of the over-the-air antennas for forming the distortion electric field.

14. The method of claim 13 , further comprising forming an antenna-specific distortion field for each over-the-air antenna by weighting the measured chamber model of an over-the-air antenna with an element which belongs to a frequency response of a desired radio channel to be emulated and to a corresponding over-the-air antenna.

15. The method of claim 11 , the method further comprising:

processing the signals; and

forming and storing the chamber model as a function of an over-the-air antenna and a direction of receptions of the at least one calibration antenna.

16. The method of claim 11 , the method further comprising processing the signals and forming and storing the chamber model as a function of a frequency and a polarization.

17. The method of claim 11 , the method further comprising separating the signals associated with a calibration transmission of different over-the-air antennas from each other based on a time division or a code division.

18. A method of performing radio channel emulation in an over-the-air chamber, the method comprising:

weighting a communication signal in an emulator with a radio channel model distorted based on a predetermined chamber model; and

feeding the weighted communication signal to over-the-air antennas for transmission to a device under test, wherein weights are formed for the weighting by:

forming a distortion electric field by convoluting the chamber model with a frequency response of a desired radio channel to be emulated;

inverting the distortion electric field;

forming a frequency response based on the inverted distortion electric field; and

combining the frequency response of the desired radio channel to be emulated with the frequency response associated with the inverted distortion electric field for a cancellation of effects of undesired interactions during emulation.

19. The method of claim 18 , the method further comprising weighting the communication signal in the emulator with the radio channel model distorted based on the chamber model.

20. The method of claim 18 , the method further comprising weighting the communication signal in the emulator with the radio channel model distorted based on a chamber model formed by a simulation.

21. The method of claim 18 , the method further comprising weighting the communication signal as a function of the over-the-air antenna and a direction of receptions of the at least one calibration antenna.

22. The method of claim 18 , the method further comprising weighting the communication signal as a function of a frequency and a polarization.

23. A measurement arrangement comprising:

at least one calibration antenna placable in at least two positions in a test zone in an over-the-air chamber including over-the-air antennas;

at least one processor; and

a memory including a computer program code, the memory and the computer program code configured to, with the at least one processor, cause the measurement arrangement to at least:

transmit, by the over-the-air antennas, calibration transmission;

receive, by the at least one calibration antenna at each position, the calibration transmission of the over-the-air antennas via interactions between the calibration transmission and structures associated with the over-the-air chamber;

form and to store a chamber model with the interactions in a chamber model memory based on the received signals for a cancellation of effects of undesired interactions by a predistortion of a radio frequency transmission from the over-the-air antennas in the over-the-air chamber;

form a distortion electric field by convoluting the chamber model with a frequency response of a desired radio channel to be emulated;

invert the distortion electric field;

form a frequency response based on the inverted distortion electric field; and

combine the frequency response of the desired radio channel to be emulated with the frequency response associated with the inverted distortion electric field for a cancellation of effects of the undesired interactions during emulation.