Over-the-air test

1. A system for emulating an over-the-air channel for communicating with a device under test, the system comprising:

an anechoic chamber having N A primary probes and N B secondary probes where N A >N B ;

a dividing module for dividing N A primary impulse responses {μ n A } into N B subsets; and

a defining module for defining N B secondary impulse responses {v n B } in terms of the primary impulse responses {μ n A } and a set of N B complex sequences {λ n B },

wherein the primary probes are downlink probes, the primary impulse responses are downlink impulse responses, the secondary probes are uplink probes and the secondary impulse responses are uplink impulse responses, or the primary probes are uplink probes, the primary impulse responses are uplink impulse responses, the secondary probes are downlink probes and the secondary impulse responses are downlink impulse responses, and

wherein the anechoic chamber is arranged to:

emulate downlink transmission to the device under test by forming a beam with at least one of the downlink probes based on a primary channel model h A or a secondary channel model h B , and

emulate uplink transmission from the device under test by capturing a signal from the device under test with at least one of the uplink probes and artificially fading the signal based on the secondary channel model h B or the primary channel model h A , respectively.

2. The system according to claim 1 , wherein the defining module is arranged to define an n B th secondary impulse response v n B in terms of the primary impulse responses {μ n A } belonging to an n B th subset and an n B th complex sequence λ n B .

3. The system according to claim 1 , further comprising a setting module for setting a correlation between the primary channel model h A =Σ n A √{square root over (g n A )}·μ n A of the over-the-air channel and the secondary channel model h B =Σ n B √{square root over (w n B )}·v n B of the over-the-air channel to a predetermined value.

4. The system according to claim 3 , wherein the defining module is arranged to define an n B th secondary impulse response v n B based on the correlation having been set to the predetermined value.

5. The system according to claim 4 , wherein the setting module is arranged to determine, based on having set the correlation to the predetermined value, a coefficient c n B for building the n B th secondary impulse response v n B from the primary impulse responses {μ n A }belonging to an n B th subset and an n B th complex sequence λ n B .

6. The system according to claim 5 , wherein coefficients {c n B }, including the coefficient c n B , are in dependence on secondary weights {w n B }, primary weights {g n A }, and how the primary impulse responses are divided into N B subsets.

7. The system according to claim 3 , wherein the communicating is by time-division duplexing and the predetermined value is one.

8. The system according to claim 3 , wherein the communicating is by frequency-division duplexing and the predetermined value is between zero and one.

9. The system according to claim 1 , wherein the N B complex sequences {λ n B } are independent and identically distributed.

10. The system according to claim 1 , wherein the subsets are of equal size.

11. The system according to claim 1 , wherein the subsets are of unequal sizes.

12. The system according to claim 1 , wherein the over-the-air channel has a uniform power angular spectrum.

13. The system according to claim 1 , wherein the over-the-air channel comprises a Laplacian shaped spatial cluster.

14. A method of emulating an over-the-air channel for communicating with a device under test in an anechoic chamber having N A primary probes and N B secondary probes where N A >N B , the method comprising:

dividing N A primary impulse responses {μ n A } into N B subsets;

defining N B secondary impulse responses {v n B } in terms of the primary impulse responses {μ n A } and a set of N B complex sequences {μ n A }, wherein the primary probes are downlink probes, the primary impulse responses are downlink impulse responses, the secondary probes are uplink probes and the secondary impulse responses are uplink impulse responses, or the primary probes are uplink probes, the primary impulse responses are uplink impulse responses, the secondary probes are downlink probes and the secondary impulse responses are downlink impulse responses;

emulating downlink transmission to the device under test by forming a beam with at least one of the downlink probes based on a primary channel model h A or a secondary channel model h B ; and

emulating uplink transmission from the device under test by capturing a signal from the device under test with at least one of the uplink probes and artificially fading the signal based on the secondary channel model h B or the primary channel model h A , respectively.

15. The method according to claim 14 , further comprising defining an n B th secondary impulse response v n B in terms of the primary responses {μ n A } belonging to an n B th subset and an n B th complex sequence λ n B .

16. The method according to claim 14 , further comprising setting a correlation between the primary channel model h A =Σ n A √{square root over (g n A ·)}μ n A of the over-the-air channel and the secondary channel model h B =Σ n B √{square root over (w n B ·)}v n B of the over-the-air channel to a predetermined value.

17. The method according to claim 16 , further comprising defining an n B th secondary impulse response v n B based on the correlation having been set to the predetermined value.

18. The method according to claim 17 , further comprising determining, based on having set the correlation to the predetermined value, a coefficient c n B for building the n B th secondary impulse response v n B from the primary impulse responses {μ n A } belonging to an n B th subset and an n B th complex sequence λ n B .