# US 8,542,763 B2 · Systems and methods to coordinate transmissions in distributed wireless systems via user clustering

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- Number: US 8,542,763 B2
- Document ID: US8542763B2
- Status: Granted
- Kind: B2
- Application number: 12/917,257
- Filed: 2010-11-01
- Published: 2011-02-24
- Granted: 2013-09-24
- Earliest claimed: 2004-04-02
- Assignees: Rearden, LLC
- Applicants: Antonio Forenza; Erik Lindskog; Stephen G. Perlman
- Inventors: Antonio Forenza; Erik Lindskog; Stephen G. Perlman
- Web page: https://patentgrep.com/patent/US8542763B2

## CPC

- H04B 7/0456: Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
- H04B 7/022: Site diversity; Macro-diversity (using two or more spaced independent antennas H04B7/04)
- H04B 7/024: Co-operative use of antennas of several sites, e.g. in co-ordinated multipoint or co-operative multiple-input multiple-output [MIMO] systems
- H04B 7/0434: {using multiple eigenmodes}
- H04B 7/046: {taking physical layer constraints into account}
- H04B 7/0469: {taking special antenna structures, e.g. cross polarized antennas into account}
- H04B 7/0626: {Channel coefficients, e.g. channel state information [CSI]}
- H04L 5/0048: {Allocation of pilot signals, i.e. of signals known to the receiver (allocation of control signalling H04L5/0053; use of control signalling H04L5/0091)}
- H04L 25/0232: {by interpolation between sounding signals}
- H04W 24/02: Arrangements for optimising operational condition
- H04W 24/08: Testing, {supervising or monitoring} using real traffic
- H04B 7/0452: Multi-user MIMO systems
- H04B: TRANSMISSION
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)

## Abstract

Systems and methods are described for coordinating transmissions in distributed wireless systems via user clustering. For example, a method according to one embodiment of the invention comprises: measuring link quality between a target user and a plurality of distributed-input distributed-output (DIDO) distributed antennas of base transceiver stations (BTSs); using the link quality measurements to define a user cluster; measuring channel state information (CSI) between each user and each DIDO antenna within a defined user cluster; and precoding data transmissions between each DIDO antenna and each user within the user cluster based on the measured CSI.

## Claims

### Claim 1

A method implemented within a multiuser (MU) multiple antenna system (MU-MAS) comprising:
measuring link quality between a target user and a plurality of MU-MAS distributed antennas of base transceiver stations (BTSs);
using the link quality measurements to define a user cluster;
measuring channel state information (CSI) between each user and each MU-MAS antenna within a defined user cluster; and
precoding data transmissions between the MU-MAS antennas within the user cluster and the users reachable by those MU-MAS antennas based on the measured CSI.

### Claim 2 (depends on 1)

The method as in claim 1 wherein the link quality is measured as a signal-to-noise ratio (SNR) or signal-to-interference-plus-noise ratio (SINR).

### Claim 3 (depends on 2)

The method as in claim 2 wherein the MU-MAS antennas or the users transmit training signals and the users or the MU-MAS antennas estimate the received signal quality based on that training.

### Claim 4 (depends on 1)

The method as in claim 1 wherein using the link quality measurements to define a user cluster comprises identifying a subset of the MU-MAS antennas having non-zero link-quality metrics to the target user.

### Claim 5 (depends on 1)

The method as in claim 1 further comprising:
implementing MU-MAS precoding with inter-MU-MAS-cluster interference (IMCI) cancellation at the BTSs in an interfering MU-MAS cluster to avoid RF interference at the target user if the target user is located within a zone in which the target user is transmitting and receiving data streams to and from the antennas in user cluster and is also detecting radio frequency (RF) signals transmitted from the antennas in the interfering MU-MAS cluster.

### Claim 6 (depends on 5)

The method as in claim 5 wherein the antennas in the interfering MU-MAS cluster transmit radio frequency (RF) signals to create locations in space with zero RF energy, including the space occupied by the user target.

### Claim 7 (depends on 6)

The method as in claim 6 wherein M distributed transmitting antennas create up to (M−1) points of zero RF energy.

### Claim 8 (depends on 6)

The method as in claim 6 wherein the locations of zero RF energy are receivers, the transmitting antennas are aware of the channel state information between the transmitters and the receivers, and the transmitters utilize the channel state information to determine the interfering signals to be simultaneously transmitted.

### Claim 9 (depends on 8)

The method as in claim 8 using block diagonalization precoding.

### Claim 10 (depends on 6)

The method as in claim 6 wherein the locations with zero RF energy correspond to the location of the users and MU-MAS precoding is used to create points of zero RF energy to the users.

### Claim 11 (depends on 1)

The method as in claim 1 wherein once the user clusters are selected, the CSI from all transmitters within the user-cluster to every user is made available to all BTSs within the user cluster.

### Claim 12 (depends on 11)

The method as in claim 11 wherein the CSI information is shared across all BTSs via a base station network (BSN).

### Claim 13 (depends on 12)

The method as in claim 12 wherein UL/DL channel reciprocity is exploited to derive the CSI from training over the UL channel for TDD systems.

### Claim 14 (depends on 12)

The method as in claim 12 wherein feedback channels from all users to the BTSs are employed in in FDD systems.

### Claim 15 (depends on 14)

The method as in claim 14 wherein, to reduce the amount of feedback, only the CSI corresponding to the non-zero entries of the link-quality matrix are fed back.

### Claim 16 (depends on 1)

The method as in claim 1 wherein singular value decomposition (SVD) of the effective channel matrix {tilde over (H)}k is computed and the precoding weight wk for the target user k is defined as the right sigular vector corresponding to the null subspace of {tilde over (H)}k.

### Claim 17 (depends on 1)

The method as in claim 1 wherein if the number of transmitters is greater than the number of users, and the SVD decomposes the effective channel matrix as {tilde over (H)}k=VkΣkUkH, the MU-MAS precoding weight for user k is given by
wk=Uo(UoH·hkT)
where Uo is the matrix with columns being the singular vectors of the null subspace of {tilde over (H)}k.

### Claim 18

A system for coordinating transmissions in a MU-MAS comprising:
a plurality of wireless users;
a plurality of base transceiver stations (BTSs) having a plurality of MU-MAS antennas for establishing multiple concurrent communication channels with the plurality of users;
wherein either the BTSs and/or the wireless users measure link quality of the communication channels therebetween and use the link quality measurements to define a user cluster;
the BTSs and/or the wireless users further measuring channel state information (CSI) between each user and each MU-MAS antenna within a defined user cluster and precoding data transmissions between the MU-MAS antennas within the user cluster and the users reachable by those MU-MAS antennas based on the measured CSI.

### Claim 19 (depends on 18)

The system as in claim 18 wherein the link quality is measured as a signal-to-noise ratio (SNR) or signal-to-interference-plus-noise ratio (SINR).

### Claim 20 (depends on 19)

The system as in claim 19 wherein the MU-MAS antennas transmit training signals and the users estimate the received signal quality based on that training.

### Claim 21 (depends on 18)

The system as in claim 18 wherein using the link quality measurements to define a user cluster comprises identifying a subset of the antennas having non-zero link-quality metrics to the target user.

### Claim 22 (depends on 18)

The system as in claim 18 wherein the BTSs implement MU-MAS precoding with inter-MU-MAS-cluster interference (IMCI) cancellation in an interfering MU-MAS cluster to avoid RF interference at the target user if the target user is located within a zone in which the target user is transmitting and receiving data streams to and from the antennas in user cluster and is also detecting radio frequency (RF) signals transmitted from the antennas in the interfering MU-MAS cluster.

### Claim 23 (depends on 22)

The system as in claim 22 wherein the antennas in the interfering MU-MAS cluster transmit radio frequency (RF) signals to create locations in space with zero RF energy, including the space occupied by the user target.

### Claim 24 (depends on 23)

The system as in claim 23 wherein M distributed transmitting antennas create up to (M−1) points of zero RF energy.

### Claim 25 (depends on 23)

The system as in claim 23 wherein the locations of zero RF energy are receivers, the transmitting antennas are aware of the channel state information between the transmitters and the receivers, and the transmitters utilize the channel state information to determine the interfering signals to be simultaneously transmitted.

### Claim 26 (depends on 25)

The system as in claim 25 using block diagonalization precoding.

### Claim 27 (depends on 23)

The system as in claim 23 wherein the locations with zero RF energy correspond to the location of MU-MAS the users and MU-MAS precoding is used to create points of zero RF energy to the users.

### Claim 28 (depends on 18)

The system as in claim 18 wherein once the user clusters are selected, the CSI from all transmitters within the user-cluster to every user is made available to all BTSs within the user cluster.

### Claim 29 (depends on 28)

The system as in claim 28 wherein the CSI information is shared across all BTSs via a base station network (BSN).

### Claim 30 (depends on 29)

The system as in claim 29 wherein UL/DL channel reciprocity is exploited to derive the CSI from training over the UL channel for TDD systems.

### Claim 31 (depends on 29)

The system as in claim 29wherein feedback channels from all users to the BTSs are employed in In FDD systems.

### Claim 32 (depends on 31)

The system as in claim 31 wherein, to reduce the amount of feedback, only the CSI corresponding to the non-zero entries of the link-quality matrix are fed back.

### Claim 33 (depends on 18)

The system as in claim 18 wherein singular value decomposition (SVD) of the effective channel matrix {tilde over (H)}k is computed and the precoding weight wk for the target user k is defined as the right sigular vector corresponding to the null subspace of {tilde over (H)}k.

### Claim 34 (depends on 18)

The system as in claim 18 wherein if the number of transmitters is greater than the number of users, and the SVD decomposes the effective channel matrix as {tilde over (H)}k=VkΣkUkH, the MU-MAS precoding weight for user k is given by
wk=Uo(UoH·hkT)
where Uo is the matrix with columns being the singular vectors of the null subspace of {tilde over (H)}k.