Mitigating interferences for a multi-layer MIMO system augmented by radio distribution network

1. A wireless User Equipment (UE) receiving system comprising:

two or more beamformers, each beamformer having a plurality of tunable receiving antennas; and

a control module configured to:

carry out a periodic, non-continuous channel estimation on a plurality of desired signals and a plurality of undesired co-channel downlink signals which are transmitted from different base stations and received by said plurality of antennas; and

identify the undesired co-channel downlink signals having a strongest interference level,

wherein the control module is configured to select between two alternative weights tuning based on highest signal plus interference to noise ratio (SINR) by:

tuning said plurality of tunable receiving antennas so as to maximize a total average power of said desired signals; and

tuning said plurality of tunable receiving antennas so as to minimize a total average power of the identified undesired co-channel downlink signals having the strongest interference level.

2. The UE receiving system according to claim 1 , wherein the UE receiving system is a multiple inputs multiple outputs (MIMO) receiving system having number N channels, wherein each of the channels is associated with one of the beamformers and wherein the total number of said plurality of tunable receiving antennas is M=Σ j=1 N K j wherein K j is a number of tunable antennas for the j th beamformer, wherein M is greater than N.

3. The UE receiving system according to claim 2 , wherein the UE is configured to tune the receiving antennas of a beamformer with K antennas, wherein K may be different for each beamformer, by:

choosing for all beamformer antennas i (1 to K), amplitudes α i =1 and phases Φ i εA, wherein A is a finite set of discrete phases, so as to maximize the total average power of the desired signals;

choosing for all beamformer antennas i (1 to K), amplitudes α i =1 and phases Φ i εA so as to minimize the total average power of the undesired co-channel downlink signals having the strongest interference level;

comparing the measured SINR for both sets of phases, one set including the phases for a maximizing the total average power of the desired signals, and the other set including the phases for minimizing the total average power of the undesired signals; and

selecting the set of phases that yields the highest measured SINR.

4. The UE receiving system according to claim 3 , wherein for each beamformer the total average power of the desired signals is PWR Signal and defined as:

PWR Signal =W BF H H S W S W S H H S H W BF ,

wherein H S is a K×P signal channel matrix from the P transmit antennas to the beamformer's K receive antennas,

wherein W S is a P×U weight matrix applied to the signal by the transmitter, wherein U≦P, and

wherein W BF is a K×1 conjugate beamformer weight vector.

5. The UE receiving system according to claim 4 , wherein for each beamformer the total average power of the undesired co-channel downlink signals having the strongest interference level is PWR Interference and defined as:

PWR Interference =W BF H H I W I W I H H I H W BF ,

wherein H I is a K×L interference channel matrix from the L antennas of the strongest interfering base station to the beamformer's K receive antennas, and

wherein W I is an L×L weight matrix applied to the interference by the transmitter.

6. The UE receiving system according to claim 5 , wherein both phase and amplitude are selected by:

choosing for all beamformer antennas i (1 to K), amplitudes α i εB, wherein B is a finite set of discrete amplitudes, and phases Φ i εA, wherein A is a finite set of discrete phases, so as to maximize PWR Signal ;

choosing for all beamformer antennas i (1 to K), amplitudes α i εB and phases Φ i εA so as to minimize PWR interference ; and

comparing the measured SINR for both sets of best amplitudes and phases and decide for those that yield the highest measured SINR.

7. The UE receiving system according to claim 1 , wherein W x denotes the beamformer antenna weights selected for improving the desired signals, and W y denotes the beamformer antenna weights selected for reducing the strongest interference, and wherein the control module is further configured to measure and compare SINR for W x and W y ; wherein in a case that the SINR for W y is greater than the SINR for W x then W y is selected, wherein otherwise, W x is used temporarily or until it is determined that updated interference estimation may be available.

8. A wireless User Equipment (UE) receiving system comprising:

two or more beamformers, each beamformer having a plurality of tunable receiving antennas; and

a control module configured to:

carry out a periodic, non-continuous channel estimation on a plurality of desired and undesired co-channel downlink signals which are transmitted from different base stations and received by said plurality of antennas; and

determine the undesired co-channel downlink signals having a strongest interference level,

wherein the control module is configured to tune said plurality of tunable receiving antennas so as to maximize a ratio between a total average power of: said desired signals, and a combination of said undesired co-channel downlink signals having the strongest interference level and an internal noise of the UE receiving system.

9. The UE receiving system according to claim 8 , wherein the UE receiving system is a multiple inputs multiple outputs (MIMO) receiving system having number N channels, wherein each of the channels is associated with one of the beamformers and wherein the total number of said plurality of tunable receiving antennas is M=Σ j=1 N K j wherein K j is a number of tunable antennas for the jth beamformer, wherein M is greater than N.

10. The UE receiving system according to claim 9 , wherein for each beamformer the SINR is defined as

SINR

=

PWR

Signal

PWR

Interference

+

Noise

=

W

BF

H

⁢

H

S

⁢

W

S

⁢

W

S

H

⁢

H

S

H

⁢

W

BF

W

BF

H

⁡

[

H

I

⁢

W

I

⁢

W

I

H

⁢

H

I

H

+

C

]

⁢

W

BF

+

σ

n

2

and wherein the UE is configured to tune the receiving antennas of a beamformer with K antennas, wherein K may be different for each beamformer, by choosing for all beamformer antennas i (1 to K), amplitudes α i εB, wherein B is a finite set of discrete amplitudes, and phases Φ i εA, wherein A is a finite set of discrete phases, so as to maximize the SINR,

wherein H S is a K×P signal channel matrix from the P transmit antennas to the beamformer's K receive antennas,

wherein W S is a P×U weight matrix applied to the signal by the transmitter, wherein U≦P,

wherein W BF is a K×1 conjugate beamformer weight vector,

wherein H I is a K×L interference channel matrix from the L antennas of the strongest interfering base station to the beamformer's K receive antennas,

wherein W I is an L×L weight matrix applied to the interference by the transmitter,

wherein C is the covariance matrix of the external noise, and

wherein σ n 2 is the variance or power of the UE internal noise.

11. The UE receiving system according to claim 8 , wherein W x denotes the beamformer antenna weights selected for improving the desired signals, and W y denotes the beamformer antenna weights selected for maximizing the power ratio between the desired signals and strongest interference plus internal noise, and wherein the control module is further configured to measure and compare SINR for W x and W y ; wherein in a case that the SINR for W y is greater than the SINR for W x then W y is selected, wherein otherwise, W x is used temporarily or until it is determined that updated interference estimation is available.

12. A method comprising:

receiving wireless signals from a plurality of transmit antennas via beamformers with a plurality of tunable receiving antennas;

carrying out a periodic, non-continuous channel estimation on a plurality of desired and undesired co-channel downlink signals which are transmitted from different base stations and received by said plurality of tunable receiving antennas;

determining the undesired co-channel downlink signals having a strongest interference level, and

selecting based on highest SINR between:

(i) tuning said plurality of tunable receiving antennas so as to maximize a total average power of said desired signals; and

(ii) tuning said plurality of tunable receiving antennas so as to minimize a total average power of the determined undesired co-channel downlink signals having the strongest interference level.

13. The method according to claim 12 , wherein the tuning of the antennas of a beamformer with K antennas, wherein K may be different for each beamformer, is carried out by:

choosing, for all beamformer antennas i (1 to K), amplitudes α i εB, wherein B is a finite set of discrete amplitudes, and phases Φ i εA, wherein A is a finite set of discrete phases, so as to maximize the total average power of the desired signals;

choosing, for all beamformer antennas i (1 to K), amplitudes α i εB and phases Φ i εA, so as to minimize the total average power of the undesired co-channel downlink signals having the strongest interference level;

comparing the measured SINR for both sets of best amplitudes and phases; and

selecting the set of amplitudes and phases that yields the highest measured SINR.

14. A method comprising:

receiving wireless signals from a plurality of transmit antennas via beamformers with a plurality of tunable receiving antennas;

carrying out a periodic, non-continuous channel estimation to a plurality of desired and undesired co-channel downlink signals which are transmitted from different base stations and received by said plurality of tunable receiving antennas;

determining the undesired co-channel downlink signals having a strongest interference level; and

tuning said plurality of tunable receiving antennas so as to maximize a ratio between a total average power of a) said desired signals and b) a combination of said undesired co-channel downlink signals having the strongest interference level and an internal noise of the UE receiving system.

15. The method according to claim 14 , wherein for each beamformer the SINR is defined as

SINR

=

PWR

Signal

PWR

Interference

+

Noise

=

W

BF

H

⁢

H

S

⁢

W

S

⁢

W

S

H

⁢

H

S

H

⁢

W

BF

W

BF

H

⁡

[

H

I

⁢

W

I

⁢

W

I

H

⁢

H

I

H

+

C

]

⁢

W

BF

+

σ

n

2

and wherein said tuning is carried out for each beamformer by choosing for all beamformer antennas i (1 to K), amplitudes α i εB, wherein B is a finite set of discrete amplitudes, and phases Φ i εA, wherein A is a finite set of discrete phases, so as to maximize the SINR,

wherein H S is a K×P signal channel matrix from the P transmit antennas to the beamformer's K receive antennas,

wherein W S is a P×U weight matrix applied to the signal by the transmitter, wherein U≦P,

wherein W BF is a K×1 conjugate beamformer weight vector,

wherein H I is a K×L interference channel matrix from the L antennas of the strongest interfering base station to the beamformer's K receive antennas,

wherein W I is an L×L weight matrix applied to the interference by the transmitter,

wherein C is the covariance matrix of the external noise, and

wherein ρ n 2 is the variance or power of the UE internal noise.