User selection for MU-MIMO
A method is disclosed of selecting users for multi user multiple-input multiple-output (MU-MIMO) communication from an initial set of potential users. The method comprises repeating the following steps in successive iterations until a stopping criterion is met: determining a channel correlation metric for each user in the set of potential users, reducing the set of potential users by exclusion of a user based on the channel correlation metric, and calculating a performance metric of the set of potential users. The method also comprises selecting users corresponding to one of the sets of potential users, wherein the selection is based on a comparison of the calculated performance metrics of the sets of potential users. The channel correlation metric for a user may comprise one or more of: a channel filter norm for the user, a channel norm for the user, a channel gain for the user, pair-wise correlations between the user and one or more other users of the set of potential users, and a channel eigenvalue for the user. The performance metric may comprise one or more of: a sum-rate, a per-user-rate, an average error rate, a maximum error rate, a per-user error rate, and a sum-correlation. Corresponding apparatus, network node and computer program product are also disclosed.
1 . A method of selecting users for multi user multiple-input multiple-output (MU-MIMO) communication, the method comprising:
determining a first channel correlation metric for each user in a first set of potential users;
reducing the first set of potential users by exclusion of a user based on the determined channel correlation metrics, thereby producing a second set of potential users, which is a subset of the first set of potential users;
calculating a performance metric for the second set of potential users; and
selecting users for the MU-MIMO communication based on the calculated performance metric for the second set of potential users.
2 . The method of claim 1 , wherein
the method further comprises calculating a performance metric for the first set of potential users, and
selecting users for the MU-MIMO communication based on the calculated performance for the second set of potential users comprises selecting users for the MU-MIMO communication based on: i) the calculated performance for the first set of potential users and ii) the calculated performance for the second set of potential users.
3 . The method of claim 1 , wherein
the first channel correlation metric for a user comprises:
a channel filter norm for the user;
a channel norm for the user;
a channel gain;
pair-wise correlations between the user and one or more other users of the first set of potential users; and/or
a channel eigenvalue for the user.
4 . The method of claim 1 , wherein
exclusion of a user based on the determined channel correlation metrics comprises:
excluding a user associated with the highest channel filter norm among the users in the first set of potential users;
excluding a user associated with the lowest channel norm among the users in the first set of potential users;
excluding a user associated with the lowest channel gain among the users in the first set of potential users;
excluding a user associated with the highest pair-wise correlation among the users in the first set of potential users; and/or
excluding a user associated with the lowest eigenvalue among the users in the first set of potential users.
5 . The method of claim 1 , wherein
the performance metric for the second set of potential users comprises: a sum-rate, a per-user-rate, an average error rate, a maximum error rate, a per-user error rate, and/or a sum-correlation.
6 . The method of claim 1 , wherein
users are selected for the MU-MIMO communication based on: a highest sum-rate, a highest per-user-rate, a lowest average error rate, a lowest maximum error rate, a lowest per-user error rate, and/or a lowest sum-correlation.
7 . The method of claim 1 , wherein the method is repeated in successive iterations until a stopping criterion is met; and
the stopping criterion comprises that a maximum number of iterations have been performed.
8 . The method of claim 1 , wherein a user corresponds to a single-antenna user device, a multi-antenna user device, or an antenna of a multi-antenna user device.
9 . The method of claim 1 , wherein the MU-MIMO applies max-min power control.
10 . The method of claim 1 , wherein the method comprises a first collection of successive iterations of the method starting from the first set of potential users and a second collection of successive iterations of the method starting from the first set of potential users, wherein a criterion for exclusion of a user differs in the first and second collections.
11 . A computer program product comprising a non-transitory computer readable medium, having thereon a computer program comprising program instructions, the computer program being loadable into a data processing unit and configured to cause execution of the method of claim 1 when the computer program is run by the data processing unit.
12 . The method of claim 1 , wherein
exclusion of a user based on the determined channel correlation metrics comprises:
excluding a user associated with the highest channel filter norm among the users in the first set of potential users;
excluding a user associated with the lowest channel norm among the users in the first set of potential users;
excluding a user associated with the lowest channel gain among the users in the first set of potential users; and/or
excluding a user associated with the highest pair-wise correlation among the users in the first set of potential users.
13 . The method of claim 1 , wherein
the method further comprises calculating a performance metric for the first set of potential users,
selecting the users for the MU-MIMO communication based on the calculated performance metric for the second set of potential users comprises selecting a set of users from a plurality of sets of users,
the plurality of sets of users comprises the first set of potential users and the second set of potential users,
the selection of the set of users from the plurality of sets of users is based on i) the calculated performance metric for the first set of potential users and ii) the calculated performance metric for the second set of potential users, and
selecting the users for the MU-MIMO communication comprises comparing the calculated performance metric for the first set of potential users with the calculated performance metric for the second set of potential users.
14 . An apparatus for selecting users for multi user multiple-input multiple-output (MU-MIMO) communication, the apparatus comprising controlling circuitry configured to perform a method comprising:
determining a first channel correlation metric for each user in a first set of potential users;
reducing the first set of potential users by exclusion of a user based on the determined channel correlation metrics, thereby producing a second set of potential users, which is a subset of the first set of potential users; and
calculating a performance metric for the second set of potential users; and
selecting users for the MU-MIMO communication based on the calculated performance metric for the second set of potential users.
15 . The apparatus of claim 14 , wherein
the method further comprises calculating a performance metric for the first set of potential users, and
selecting users for the MU-MIMO communication based on the calculated performance for the second set of potential users comprises selecting users for the MU-MIMO communication based on: i) the calculated performance for the first set of potential users and ii) the calculated performance for the second set of potential users.
16 . The apparatus of claim 14 , wherein the first channel correlation metric for a user comprises:
a channel filter norm for the user;
a channel norm for the user;
a channel gain for the user;
pair-wise correlations between the user and one or more other users of the first set of potential users; and/or
a channel eigenvalue for the user.
17 . The apparatus of claim 14 , wherein exclusion of a user based on the determined channel correlation metrics comprises:
exclusion of a user associated with the highest channel filter norm among the users in the first set of potential users;
exclusion of a user associated with the lowest channel norm among the users in the first set of potential users;
excluding a user associated with the lowest channel gain among the users in the first set of users;
exclusion of a user associated with the highest pair-wise correlation among the users in the first set of users; and/or
exclusion of a user associated with the lowest eigenvalue among the users in the first set of potential users.
18 . The apparatus of claim 14 , wherein the performance metric for the second set of potential users comprises: a sum-rate, a per-user-rate, an average error rate, a maximum error rate, a per-user error rate, and/or a sum-correlation.
19 . The apparatus of claim 14 , wherein for the MU-MIMO communication based on: a highest sum-rate, a highest per-user-rate, a lowest average error rate, a lowest maximum error rate, a lowest per-user error rate, and/or a lowest sum-correlation.
20 . The apparatus of claim 14 , wherein the method is repeated in successive iterations until a stopping criterion is met; and
the stopping criterion comprises that a maximum number of iterations have been performed.