Method of grouping users for opportunistic downlink in multiuser, multiple-input-multiple-output wireless communication

1. A method implemented in a base station having a plurality of antennas, comprising:

associating, at the base station, users with different first pre-coding matrices based on information provided by the users and received by the base station using the plurality of antennas, wherein each pre-coding matrix can be associated with a predetermined number of users;

combining users associated with the first pre-coding matrices into a first user group when each of the first pre-coding matrices is associated with less than the predetermined number of users; and

associating users in the first user group with a second pre-coding matrix that is at a higher level in a code tree than the first pre-coding matrices, wherein pre-coding matrices at higher levels in the code tree are connected to pre-coding matrices at lower levels of the code tree by branches.

2. The method of claim 1 , wherein associating the users with the first pre-coding matrices comprises:

receiving, from each of the users, information indicating at least one preferred first pre-coding matrix from the first pre-coding matrices; and

associating the users with the first pre-coding matrices based on the information indicating said at least one preferred first pre-coding matrix.

3. The method of claim 2 , wherein associating the users with the first pre-coding matrices comprises:

receiving, from the users, information indicative of at least one channel condition of at least one channel of air interfaces between the base station and the users; and

associating the users with the first pre-coding matrices based on the information indicating said at least one channel condition.

4. The method of claim 3 , wherein associating the users with the first pre-coding matrices comprises associating each user with a column of a first pre-coding matrix.

5. The method of claim 1 , comprising transmitting information to the plurality of users concurrently using the first or second pre-coding matrices.

6. The method of claim 1 , wherein associating users in the first user group with said at least one second pre-coding matrix comprises associating users in the first user group with at least one second pre-coding matrix that so the first pre-coding matrices correspond to a finer angular resolution than said at least one second pre-coding matrix.

7. A method implemented in a base station having a plurality of antennas, comprising:

associating a plurality of users with a plurality of first pre-coding matrices based on information provided by the plurality of users;

determining whether at least one of the plurality of first pre-coding matrices is incomplete, wherein determining whether at least one of the plurality of first pre-coding matrices is incomplete comprises determining that at least one of the plurality of first pre-coding matrices is incomplete when the number of users associated with said at least one first pre-coding matrix is less than the number of antennas included in the base station; and

associating users with at least one second pre-coding matrix when at least one first pre-coding matrix is incomplete, the users being associated with said at least one incomplete first pre-coding matrix, and said at least one second pre-coding matrix being formed based on said at least one incomplete first pre-coding matrix.

8. A method implemented in a base station having a plurality of antennas, comprising:

associating, at the base station, users with first pre-coding matrices based on information provided by the users and received by the base station using the plurality of antennas;

determining that the first pre-coding matrices are incompletely associated with users when less than a threshold fraction of the columns of the first pre-coding matrices has been associated with a user;

combining users associated with the first pre-coding matrices into a first user group when the first pre-coding matrices are incompletely associated with users; and

associating users in the first user group with a second pre-coding matrix that is associated with the first pre-coding matrices.

9. A method implemented in a base station having a plurality of antennas, comprising:

associating a plurality of users with a plurality of first pre-coding matrices based on information provided by the plurality of users;

determining that more than one of the plurality of first pre-coding matrices is incomplete;

associating users with at least one second pre-coding matrix when more than one first pre-coding matrix is incomplete, the users being associated with said more than one incomplete first pre-coding matrix, and said at least one second pre-coding matrix being formed based on said more than one incomplete first pre-coding matrix; and

selecting a plurality of said more than one incomplete first pre-coding matrices based on a distance metric indicative of at least one distance between the plurality of said more than one incomplete first pre-coding matrices.

10. The method of claim 9 , wherein associating users with said at least one second pre-coding matrix comprises associating users with at least one second pre-coding matrix that is part of an upper level of a tree structure, and wherein the plurality of incomplete first pre-coding matrices is part of a lower level of the tree structure.

11. The method of claim 9 , comprising forming said at least one second pre-coding matrix based on the selected plurality of incomplete first pre-coding matrices.

12. The method of claim 11 , comprising providing, to the plurality of users, information indicative of at least one of the second pre-coding matrices or the first pre-coding matrices.

13. A method implemented in a base station having a plurality of antennas, comprising:

associating, at the base station, users with different first pre-coding matrices based on information provided by the users and received by the base station using the plurality of antennas;

combining users associated with the first pre-coding matrices into a first user group when the different first pre-coding matrices are incompletely associated with users; and

associating users in the first user group with a second pre-coding matrix that is at a higher level in a code tree than the first pre-coding matrices so that the second pre-coding matrix is more complete than the first pre-coding matrices, and

wherein said at least one second pre-coding matrix comprises a plurality of second pre-coding matrices, and comprising:

determining whether at least one of the plurality of second pre-coding matrices is incomplete;

forming a second user group by grouping users associated with said at least one incomplete second pre-coding matrix with users associated with another second pre-coding matrix; and

associating users in the second user group with at least one third pre-coding matrix when said at least one second pre-coding matrix is incomplete, said at least one third pre-coding matrix being at a higher level in the code tree than said at least one second pre-coding matrix and said another second pre-coding matrix.

14. A method implemented in a base station having a plurality of antennas, comprising:

associating, at the base station, users with different first pre-coding matrices based on information provided by the users and received by the base station using the plurality of antennas;

combining users associated with the first pre-coding matrices into a first user group when the different first pre-coding matrices are incompletely associated with users; and

associating users in the first user group with a second pre-coding matrix that is at a higher level in a code tree than the first pre-coding matrices so that the second pre-coding matrix is more complete than the first pre-coding matrices, wherein associating users in the first user group with said at least one second pre-coding matrix comprises associating users in the first user group with at least one second pre-coding matrix that so the first pre-coding matrices correspond to a finer angular resolution than said at least one second pre-coding matrix, and wherein associating users in the first user group with said at least one second pre-coding matrix comprises associating users in the first user group with said at least one second pre-coding matrix using a distance metric that indicates an angle difference between main lobe directions of antenna patterns corresponding to the first and second pre-coding matrices.

15. A method implemented in a base station having a plurality of antennas, comprising:

associating, at the base station, users with first pre-coding matrices based on information provided by the users and received by the base station using the plurality of antennas, wherein each pre-coding matrix can be associated with a predetermined number of users; and

consolidating the users associated with the first pre-coding matrices into a first user group assigned to a second pre-coding matrix when the first pre-coding matrices are associated with less than the predetermined number of users.

16. The method of claim 15 , wherein consolidating the users comprises assigning the users to a second pre-coding matrix that is selected based on a distance metric indicative of at least one distance between the first pre-coding matrices and the second pre-coding matrix.