Distributed MIMO and/or transmit diversity in a cloud-ran system
One embodiment is directed to a system that implements a downlink transmission mode that precodes sequences of symbols using a precoder matrix selected from a codebook. Linear transformations are performed on the sequences of precoded symbols using a distribution matrix. The distribution matrix is configured so that each of a plurality of precoder matrices provides perfect steering of transmit power to a corresponding one of a plurality of disjoint subsets of the antenna ports used for the downlink transmission mode. Also, the distribution matrix can be configured so that at least one precoder matrix provides peak power at all of the antenna ports used for the downlink transmission mode.
1. A method of reusing a resource element to transmit user data to a plurality of items of user equipment using a downlink transmission mode that uses multiple antenna ports, wherein the downlink transmission mode precodes sequences of symbols using a precoder matrix selected from a codebook, wherein the precoding produces sequences of precoded symbols, the method comprising:
performing linear transformations on the sequences of precoded symbols using a distribution matrix, wherein the distribution matrix is configured so that each of a plurality of precoder matrices provides perfect steering of transmit power to a corresponding one of a plurality of disjoint subsets of the antenna ports used for the downlink transmission mode;
determining if the resource element can be reused to transmit user data to the plurality of items of user equipment; and
when the resource element can be reused, reusing the resource element to transmit user data to the plurality of items of user equipment by:
assigning a respective simulcast group to each of the plurality of items of user equipment that uses a respective one of the plurality of disjoint subsets of antenna ports; and
transmitting user data to each of the items of user equipment using a respective precoder matrix that provides perfect steering to the respective subset of antenna ports in the respective simulcast group for that item of user equipment.
2. The method of claim 1 , further comprising:
when the resource element can be reused, transmitting user data at a first power level that is less than a second power level at which reference signals are transmitted to the items of user equipment.
3. The method of claim 1 , wherein the distribution matrix is configured so that at least one precoder matrix provides peak power at all of the antenna ports used for the downlink transmission mode; and
wherein the method further comprises, when the resource element cannot be reused, using the resource element to transmit user data to one of the items of user equipment by:
assigning to said one of the items of user equipment that a simulcast group that uses all of the antenna ports for the downlink transmission mode; and
transmitting user data to said one of the items of user equipment using said at least one precoder matrix that provides perfect steering to all of the antenna ports.
4. The method of claim 1 , further comprising:
when the resource element cannot be reused, transmitting user data to said one of the items of user equipment at a power level that is used to transmit reference signals to the items of user equipment.
5. The method of claim 1 , wherein the distribution matrix is configured to be unitary and to have, for each column of the distribution matrix, a non-zero gain for a corresponding entry associated with each antenna port.
6. The method of claim 1 , wherein the method is implemented using a controller and a plurality of radio points communicatively coupled to the controller, each radio point associated with at least one antenna.
7. The method of claim 6 , wherein performing the linear transformation on the sequences of precoded symbols using the distribution matrix comprises performing the linear transformation on the sequences of precoded symbols using the distribution matrix by the controller.
8. The method of claim 6 , wherein performing the linear transformation on the sequences of precoded symbols using the distribution matrix comprises performing the linear transformation on the sequences of precoded symbols using the distribution matrix at one or more of the radio points.
9. A system to provide wireless service to user equipment, the system comprising:
a controller communicatively coupled to a core network of a wireless service provider;
a plurality of radio points to transmit and receive radio frequency signals to and from the user equipment, each of the radio points associated with at least one antenna and located remote from the controller, wherein the plurality of radio points is communicatively coupled to the controller; and
wherein the controller and plurality of radio points implement a base station for a radio access network;
wherein the system is configured to reuse a resource element in order to transmit user data to a plurality of items of user equipment using a downlink transmission mode that uses multiple antenna ports;
wherein the system is configured to implement a downlink transmission mode that precodes sequences of symbols using a precoder matrix selected from a codebook, wherein the precoding produces sequences of precoded symbols;
wherein the system is configured to perform linear transformations on the sequences of precoded symbols using a distribution matrix, wherein the distribution matrix is configured so that each of a plurality of precoder matrices provides perfect steering of transmit power to a corresponding one of a plurality of disjoint subsets of the antenna ports used for the downlink transmission mode;
wherein the system is configured to determine if the resource element can be reused to transmit user data to the plurality of items of user equipment; and
wherein the system is configured to, when the resource element can be reused, reuse the resource element to transmit user data to the plurality of items of user equipment by:
assigning a respective simulcast group to each of the plurality of items of user equipment that uses a respective one of the plurality of disjoint subsets of antenna ports; and
transmitting user data to each of the items of user equipment using a respective precoder matrix that provides perfect steering to the respective subset of antenna ports in the respective simulcast group for that item of user equipment.
10. The system of claim 9 , wherein the system is configured to, when the resource element can be reused, transmit user data at a first power level that is less than a second power level at which reference signals are transmitted to the items of user equipment.
11. The system of claim 9 , wherein the distribution matrix is configured so that at least one precoder matrix provides peak power at all of the antenna ports used for the downlink transmission mode; and
wherein the system is configured to, when the resource element cannot be reused, use the resource element to transmit user data to one of the items of user equipment by:
assigning to said one of the items of user equipment that a simulcast group that uses all of the antenna ports for the downlink transmission mode; and
transmitting user data to said one of the items of user equipment using said at least one precoder matrix that provides perfect steering to all of the antenna ports.
12. The system of claim 9 , wherein the system is configured to, when the resource element cannot be reused, transmit user data to said one of the items of user equipment at a power level that is used to transmit reference signals to the items of user equipment.
13. The system of claim 9 , wherein the distribution matrix is configured to be unitary and to have, for each column of the distribution matrix, a non-zero gain for a corresponding entry associated with each antenna port.
14. The system of claim 9 , wherein the controller is communicatively coupled to the radio points using a switched ETHERNET network.
15. The system of claim 9 , wherein the controller is configured to perform the linear transformation on the sequences of precoded symbols using the distribution matrix by the controller.
16. The system of claim 9 , wherein one or more of the radio points are configured to perform the linear transformation on the sequences of precoded symbols using the distribution matrix at one or more of the radio points.
17. The system of claim 9 , wherein the downlink transmission mode comprises a multiple-antenna Long-Term Evolution (LTE) downlink transmission mode.
18. The system of claim 9 , wherein the downlink transmission mode uses four antenna ports, and wherein each of the plurality of disjoint subsets of antenna ports comprises two antenna ports.
19. The system of claim 18 , wherein each radio point is associated with either two antenna ports or one antenna port.
20. The system of claim 9 , wherein the system is configured to not use the distribution matrix for some at least one other downlink transmission mode.