Apparatus and method for low complexity spatial division multiple access in a millimeter wave mobile communication system

1. For use in a wireless communication network, a transmitter comprising:

a baseband precoder configured to precode a plurality of input signals;

a plurality of Radio frequency (RF) chains;

an array of sub-array antennas, wherein each

of the plurality of RF chains configured to apply a phase shift and beamforming weight to one of the plurality of input signals,

wherein each of the plurality of RF chains is coupled to a respective sub-array antenna of the array of sub-array antennas,

wherein the baseband precoder and the plurality of RF chains are configured to apply a gain based on a direction of transmission of each of the plurality of input signals, and

wherein the transmitter is configured to apply a plurality of RF beamforming weights and a plurality of digital beamforming weights to provide a plurality of signals to a plurality of users.

2. The transmitter as set forth in claim 1 , wherein the baseband precoder comprises a digital precoder configured to apply a digital beamforming weight to the signal.

3. The transmitter as set forth in claim 1 , wherein the baseband precoder provides a first precoded signal to a first RF chain coupled to a first antenna sub-array and a second precoded signal to a second RF chain coupled to a second antenna sub-array.

4. The transmitter as set forth in claim 1 , wherein the array of sub-array antennas comprises at least one of: a two-dimensional array and a linear array.

5. The transmitter as set forth in claim 1 , wherein the gain is a complex gain comprising a phase and amplitude.

6. For use in a wireless communication network, a transmitter comprising:

a baseband precoder configured to precode a plurality of input signals;

an array of sub-array antennas; and

a plurality of radio frequency (RF) chains configured to apply a plurality of phase shifts and a plurality of beamforming weight to the plurality of input signals, wherein each of the plurality of RF chains is coupled to a respective sub-array antenna of the array of sub-array antennas,

wherein the baseband precoder and the plurality of RF chains are configured to apply a gain based on a direction of transmission of each of the plurality of input signals,

wherein the transmitter is configured to apply a plurality of RF beamforming weights in a first direction using a first beam width and a plurality of digital beamforming weights in a second direction using a second beam width, and

wherein the RF beamforming configured to determines an RF beam shape,

wherein the digital beamforminq configured to have a digital beam shape within the RF beam shape determined by the RF beamforminq.

7. The transmitter as set forth in claim 6 , wherein the first direction and the second direction are a same direction.

8. The transmitter as set forth in claim 7 , wherein the signal is configured for a single user, and wherein the baseband precoder comprises a unitary precoding matrix and is configured to provide a same precoded signal to each of the RF chains to provide multiple streams of the precoded signal to the single user, wherein each stream is transmitted from a respective antenna sub-array of the array of sub-array antennas.

9. The transmitter as set forth in claim 6 , wherein the first direction is a same direction for each antenna sub-array and the second direction of a first antenna sub-array is different than the second direction of a second antenna sub-array.

10. For use in a wireless communication network, a method comprising:

preceding, by a baseband precoder, a plurality of input signals for spatial division multiple access (SDMA);

applying, by each of a plurality of radio frequency (RF) chains, a plurality of phase shifts and a plurality of beamforming weights to the plurality of input signals; and

transmitting the plurality of phase shifted and weighted input signals by an array of sub-array antennas,

wherein each of the plurality of RF chains is coupled to a respective sub-array antenna of the array of sub-array antennas,

wherein a gain applied to each of the plurality of input signals is based on a direction of transmission of each of the plurality of input signals, and

wherein a plurality of RF beamforming weights is applied and a plurality of digital beamforming weights is applied to provide a plurality of signals to a plurality of users.

11. The method as set forth in claim 10 , wherein the baseband precoder comprises a digital precoder and precoding further comprises applying a digital beamforming weight to the signal.

12. The method as set forth in claim 10 , wherein precoding further comprises providing a first precoded signal to a first RF chain coupled to a first antenna sub-array and a second precoded signal to a second RF chain coupled to a second antenna sub-array.

13. The method as set forth in claim 10 , wherein the array of sub-array antennas comprises at least one of: a two-dimensional array and a linear array.

14. The method as set forth in claim 10 , wherein the gain is a complex gain comprising a phase and amplitude.

15. For use in a wireless communication network, a method comprising:

precoding, by a baseband precoder, a plurality of input signals for spatial division multiple access (SDMA);

applying, by each of a plurality of radio frequency (RF) chains, a plurality of phase shifts and a plurality of beamforming weights to the plurality of the input signals; and

transmitting the plurality of the phase shifted and weighted signals by an array of sub-array antennas,

wherein each of the plurality of RF chains is coupled to a respective sub-array antenna of the array of sub-array antennas, wherein a gain applied to the signal is based on a direction of transmission of the signal, and

wherein a plurality of RF beamforming weights is applied in a first direction and a plurality of digital beamforming weights is applied in a second direction.

16. The method as set forth in claim 15 , wherein the first direction and the second direction are a same direction.

17. The method as set forth in claim 16 , wherein the signal comprises a signal for a single user and the baseband precoder comprises a unitary precoding matrix, and wherein precoding comprises providing a same precoded signal to each of the RF chains to provide multiple streams of the precoded signal to the single user, and wherein transmitting comprises transmitting each stream from a respective antenna sub-array of the array of sub-array antennas.

18. The method as set forth in claim 15 , wherein the first direction is a same direction for each antenna sub-array and the second direction of a first antenna sub-array is different than the second direction of a second antenna sub-array.