Beamforming for hybrid antenna arrays

1. A wireless device, comprising:

a hybrid antenna array configured to receive a signal transmitted by another wireless device over a wireless channel; and

a transceiver configured to update analog radio frequency precoders of a hierarchical codebook based on magnitudes of multipath components of the wireless channel, and by:

selecting a first radio frequency precoder receiving a multipath component having a maximum magnitude;

selecting a second radio frequency precoder receiving a multipath component having a minimum magnitude; and

replacing each of the first and second radio frequency precoders with a radio frequency precoder that is one level higher in die hierarchical codebook than that of the first radio frequency precoder.

2. The wireless device of claim 1 , wherein the transceiver comprises:

radio frequency chains; and

variable phase-shifters or attenuators coupling the radio frequency chains with the respective antennas of the hybrid antenna array, and configured to update the analog radio frequency precoders.

3. The wireless device of claim 1 , wherein the received signal comprises pilot symbols.

4. The wireless device of claim 1 , wherein the transceiver is further configured to update the analog radio frequency precoders periodically to adjust to a varying wireless channel condition.

5. A wireless device, comprising:

a hybrid antenna array configured to receive a signal transmitted by another wireless device over a wireless channel; and

a transceiver configured to update analog radio frequency precoders of a hierarchical codebook based on magnitudes of multipath components of the wireless channel and to update a digital baseband precoder by conjugating the received signal, and normalizing a resulting vector to satisfy a power constraint.

6. The wireless device of claim 5 , wherein the transceiver is further configured to transmit a transmit signal based on the updated digital baseband precoder.

7. The wireless device of claim 6 , wherein if a signal-to-noise ratio of the received signal is greater than a predetermined threshold, the transmit signal is transmitted comprising data or pilots.

8. A wireless device, comprising:

a hybrid antenna array configured to receive a signal transmitted by another wireless device over a wireless channel; and

a transceiver configured to update analog radio frequency precoders of hierarchical codebook based on magnitude of multipath components of the wireless channel, to

detect a decrease in the magnitudes of the plurality of the multipath components of the wireless channel, and

to update the analog radio frequency precoders by replacing the analog radio frequency precoders to a level in the hierarchical codebook level that is lower.

9. A method of beamforming, comprising:

receiving, by a hybrid antenna array of a first wireless device, a signal transmitted by a second wireless device over a wireless channel; and

updating, by a transceiver of the first wireless device, analog radio frequency precoders of a hierarchical codebook based on magnitudes of multipath components of the wireless channel, wherein the updating of the analog radio frequency precoders comprises:

selecting a first radio frequency precoder receiving a multipath component having a maximum magnitude; and

selecting a second radio frequency precoder receiving a multipath component having a minimum magnitude; and

replacing each of the first and second radio frequency precoders with a radio frequency precoder that is one level higher in the hierarchical codebook than that of the first radio frequency precoder.

10. The method of claim 9 , wherein the updating of the analog radio frequency precoders comprises:

adjusting values of variable phase-shifters or attenuators, which couple radio frequency chains with respective antennas of the hybrid antenna array.

11. The method of claim 9 , further comprising:

initializing the analog radio frequency precoders to a level in the hierarchical codebook that is lowest.

12. The method of claim 9 , wherein the hierarchical codebook is a directional hierarchical codebook.

13. The method of claim 9 , wherein the received signal comprises pilot symbols.

14. The method of claim 9 , wherein the analog radio frequency precoders are updated periodically to adjust to a varying wireless channel condition.

15. The method of claim 14 , further comprising:

detecting a decrease in the magnitudes of the plurality of the multipath components of the wireless channel; and

updating the analog radio frequency precoders by replacing the analog radio frequency precoders to a level in the hierarchical codebook that is lowest.

16. A method of beamforming, comprising:

receiving, by a hybrid antenna array of a first wireless device, a signal transmitted by a second wireless device over a wireless channel;

updating, by a transceiver of the first wireless device, analog radio frequency precoders of a hierarchical codebook based on magnitudes of multipath components of the wireless channel; and

updating, by the transceiver, a digital baseband precoder by conjugating the received signal, and normalizing a resulting vector to satisfy a power constraint.

17. The method of claim 16 , further comprising:

initializing the digital baseband precoder randomly.

18. The method of claim 16 , further comprising:

initializing the analog radio frequency precoders or the digital baseband precoder based on Channel State Information (CSI); and

transmitting a transmit signal comprising pilot symbols and data based on the initialized analog radio frequency precoders or the initialized digital baseband precoder.

19. The method of claim 16 , wherein the analog radio frequency decoders or the digital precoder is initialized or updated periodically by an additional beamforming method.

20. The method of claim 16 , further comprising:

transmitting, by the first wireless device, a transmit signal based on the updated digital baseband precoder.

21. The method of claim 20 , further comprising:

repeating, by the second wireless device, the receiving step, the updating analog radio frequency precoders step, the updating the digital baseband precoder step, and the transmitting step.

22. The method of claim 21 , wherein the updating analog radio frequency precoders step or the updating the digital baseband precoder step is not performed for each repeated iteration.

23. The method of claim 20 , wherein if a signal-to-noise ratio of the received signal is greater than a predetermined threshold, the transmit signal is transmitted comprising data.