System and method for large scale multiple input multiple output communications

1. A method for communicating using a large scale multiple input multiple output (MIMO) antenna array, the method comprising:

determining, by a transmitting device, angular domain channel estimates of the large scale MIMO antenna array in accordance with antenna domain channel estimates of the large scale MIMO antenna array;

identifying, by the transmitting device, significant beams of the large scale MIMO antenna array by maximizing the angular domain channel estimates; and

transmitting, by the transmitting device, to at least one receiving device utilizing the significant beams as identified.

2. The method of claim 1 , wherein the angular domain channel estimates are a superposition of the antenna domain channel estimates.

3. The method of claim 2 , wherein the angular domain channel estimates are expressible as

h

^

k

⁡

(

α

,

β

,

τ

)

=

1

M

·

∑

m

=

1

M

⁢

∑

n

F

=

1

N

C

⁢

steering

m

⁡

(

f

UL

+

n

F

·

Δ

⁢

⁢

f

,

α

,

β

,

τ

)

·

h

^

m

,

Where: M is a number of receive antennas;

N C is a number of subcarriers;

steering m is a steering vector associated with a precoding vector that orient a beam towards a specified direction;

ĥ m are the antenna domain channel estimates, expressible as

h

^

m

=

1

N

REF

·

∑

n

T

=

1

N

REF

⁢

ref

k

*

⁡

(

n

F

,

n

T

)

·

y

m

⁡

(

n

F

,

n

T

)

;

N REF is a length of a reference or pilot sequence;

n T is a time index;

ref k *(n F ,n T ) is a reference or pilot sequence at time n T and in subcarrier n T ; and

y m (n F ,n T ) is a signal received by antenna m at time n T and in subcarrier n T .

4. The method of claim 1 , wherein identifying the significant beams comprises searching for beams with amplitudes that exceed a first threshold.

5. The method of claim 4 , wherein searching for the beams comprises:

performing a coarse resolution search to identify first amplitudes that exceed a second threshold; and

performing a precise resolution search near the first amplitudes to identify the significant beams that exceed the first threshold.

6. The method of claim 4 , wherein searching for the beams comprises:

performing a peak gradient search for each beam parameter.

7. The method of claim 1 , wherein communicating with at least one receiving device comprises:

beamforming a transmission with beam parameters of a significant beam oriented towards the at least one receiving device; and

transmitting the beamformed transmission towards the at least one receiving device.

8. A non-transitory computer-readable medium storing programming for execution by a processor, the programming including instructions to:

determine angular domain channel estimates of a large scale multiple input multiple output (MIMO) antenna array in accordance with antenna domain channel estimates of the large scale MIMO antenna array;

identify significant beams of the large scale MIMO antenna array by maximizing the angular domain channel estimates; and

transmit to at least one receiving device utilizing the significant beams as identified.

9. The non-transitory computer-readable medium of claim 8 , wherein the programming includes instructions to perform a coarse resolution search to identify first amplitudes that exceed a first threshold, and perform a precise resolution search near the first amplitudes to identify the significant beams that exceed a second threshold, wherein the second threshold is greater than the first threshold.

10. The non-transitory computer-readable medium of claim 8 , wherein the programming includes instructions to perform a peak gradient search for each beam parameter.

11. The non-transitory computer-readable medium of claim 8 , wherein the programming includes instructions to beamform a transmission with beam parameters of a significant beam oriented towards the at least one receiving device, and transmit the beamformed transmission towards the at least one receiving device.

12. A large scale multiple input multiple output (MIMO) communications device comprising:

an antenna array;

a processor; and

a computer readable storage medium storing programming for execution by the processor, the programming including instructions configuring the large scale MIMO communications device to:

determine angular domain channel estimates of a large scale MIMO antenna array in accordance with antenna domain channel estimates of the large scale MIMO antenna array,

identify significant beams of the large scale MIMO antenna array by maximizing the angular domain channel estimates, and

transmit to at least one receiving device utilizing the significant beams as identified.

13. The large scale MIMO communications device of claim 12 , wherein the programming includes instructions to perform a coarse resolution search to identify first amplitudes that exceed a first threshold, and perform a precise resolution search near the first amplitudes to identify the significant beams that exceed a second threshold, wherein the second threshold is greater than the first threshold.

14. The large scale MIMO communications device of claim 12 , wherein the programming includes instructions to perform a peak gradient search for each beam parameter.

15. A method for decoding received signals, the method comprising:

transforming, by a receiving device, antenna domain received signals into angular domain received signals;

selecting, by the receiving device, antenna beams with an average energy levels exceeding a specified threshold out of available antenna beams of the receiving device;

updating, by the receiving device, a received signal vector in accordance with the selected antenna beams;

determining, by the receiving device, angular domain channel estimates and an angular domain noise covariance matrix in accordance with the updated received signal vector; and

decoding, by the receiving device, the updated received signal vector utilizing an interference rejection combining (IRC) algorithm.

16. The method of claim 15 , wherein transforming the antenna domain received signals into angular domain received signals comprises:

multiplying the antenna domain received signal with a Hermitian of a steering matrix, expressible as

Y AngularDomain =W H ·Y AntennaDomain ,

Where: Y AntennaDomain is a samples vector of the receiver in the antenna domain;

Y AngularDomain is a samples vector of the receiver in the angular domain;

W H is the Hermitian of a steering matrix W with dimension M by S, wherein individual elements w m,s are expressible as

w

m

,

s

=

steering

m

⁡

(

α

s

,

β

s

)

=

1

M

·

exp

⁡

(

j

·

2

·

π

·

f

·

(

x

m

·

cos

⁡

(

α

)

·

cos

⁡

(

β

)

+

y

m

⁢

cos

⁡

(

α

)

·

sin

⁡

(

β

)

+

z

m

·

sin

⁡

(

α

)

c

)

)

;

M is a number of antennas; and

S is a number of antenna beams.

17. The method of claim 15 , wherein selecting the antenna beams with the average energy levels exceeding the specified threshold comprises:

determining an average energy level for each of the available antenna beams;

determining a total average energy level for all of the available antenna beams; and

selecting the antenna beams with an associated average energy level that is greater than the total average energy level times the specified threshold.

18. The method of claim 17 , wherein decoding the updated received signal vector comprises evaluating

H′ AngularDomain H ·inv( R′ YY AngularDomain )· Y′ AngularDomain

Where: H′ AngularDomain H is the Hermitian of the angular domain channel estimates;

R′ YY AngularDomain is the angular domain noise covariance matrix; and

Y′ AngularDomain is the updated received signal vector.

19. A non-transitory computer-readable medium storing programming for execution by a processor, the programming including instructions to:

transform antenna domain received signals into angular domain received signals;

select antenna beams with an average energy levels exceeding a specified threshold out of available antenna beams of a receiving device;

update a received signal vector in accordance with the selected antenna beams;

determine angular domain channel estimates and an angular domain noise covariance matrix in accordance with the updated received signal vector; and

decode the updated received signal vector utilizing an interference rejection combining (IRC) algorithm.

20. The non-transitory computer-readable medium of claim 19 , wherein the programming includes instructions to multiply the antenna domain received signal with a Hermitian of a steering matrix, expressible as

Y AngularDomain =W H ·Y AntennaDomain ,

Where: Y AntennaDomain is a samples vector of the receiver in the antenna domain;

Y AngularDomain is a samples vector of the receiver in the angular domain;

W H is the Hermitian of a steering matrix W with dimension M by S, wherein individual elements w m,s are expressible as

w

m

,

s

=

steering

m

⁡

(

α

s

,

β

s

)

=

1

M

·

exp

⁡

(

j

·

2

·

π

·

f

·

(

x

m

·

cos

⁡

(

α

)

·

cos

⁡

(

β

)

+

y

m

⁢

cos

⁡

(

α

)

·

sin

⁡

(

β

)

+

z

m

·

sin

⁡

(

α

)

c

)

)

;

M is a number of antennas; and

S is a number of antenna beams.

21. The non-transitory computer-readable medium of claim 19 , wherein the programming includes instructions to determine an average energy level for each of the available antenna beams, determine a total average energy level for all of the available antenna beams, and select the antenna beams with an associated average energy level that is greater than the total average energy level times the specified threshold.

22. The non-transitory computer-readable medium of claim 19 , wherein the programming includes instructions to evaluate

H′ AngularDomain H ·inv( R′ YY AngularDomain )· Y′ AngularDomain

Where: H′ AngularDomain H is the Hermitian of the angular domain channel estimates;

R′ YY AngularDomain is the angular domain noise covariance matrix; and

Y′ AngularDomain is the updated received signal vector.