Physical Uplink Shared Channel Demodulation Reference Signal Design for Uplink Coordinated Transmission in Type II Relay

1. A method for an access node to perform channel estimation, comprising: when a user equipment (UE) and at least one relay node are present in a cell with the access node, the access node receiving a first demodulation reference signal (DMRS) from the UE in a resource block containing both data and control information and receiving a second DMRS from the at least one relay node in a resource block containing only the data and the second DMRS, wherein the DMRS from the UE is orthogonal to the DMRS from the at least one relay node; the access node performing a first channel estimation based on the DMRS that was transmitted by the UE; the access node performing a second channel estimation based on the DMRS that was transmitted by the at least one relay node; the access node adding the first channel estimation to the second channel estimation to derive a combined channel estimation; the access node using the first channel estimation to demodulate the control information received from only the UE; and the access node using the combined channel estimation to demodulate the data received from both the UE and the at least one relay node.

3. The method of claim 2 , wherein the delta value is one of: preconfigured in at least one relay node; and wirelessly transmitted to at least one relay node.

4. The method of claim 1 , wherein, when a plurality of relay nodes are present in the cell, the access node receives the same DMRS signal from the plurality of relay nodes that is orthogonal to the DMRS received from the UE.

5. The method of claim 1 , wherein, when a plurality of relay nodes are present in the cell, the DMRS signals that the access node receives from the plurality of relay nodes have different cyclic shifts relative to one another and to the DMRS received from the UE, and the access node performs a separate channel estimation for each of the plurality of relay nodes based on the DMRS signal that the access node receives from each of the plurality of relay nodes.

6. The method of claim 1 , wherein, when a plurality of relay nodes are present in the cell, the access node receives the DMRS from the UE in a first subset of a set of resource elements available to the UE and the relay nodes, and the access node receives the DMRS from all of the relay nodes in a second subset of the set of resource elements available to the UE and the relay nodes, and the access node performs a separate channel estimation for each of the plurality of relay nodes based on the DMRS signal that the access node receives from each of the plurality of relay nodes, the first subset and the second subset being different, and resource blocks containing the first subset and the second subset being transmitted synchronously, and DMRS received from the relay nodes is orthogonal to the DMRS received from each other relay node.

7. The method of claim 1 , wherein the control information is received via a physical uplink control channel.

8. The method of claim 7 , wherein the data is received via a physical uplink shared channel.

9. An access node, comprising: a processor configured such that, when a user equipment (UE) and at least one relay node are present in a cell with the access node, the access node receives a first demodulation reference signal (DMRS) from the UE in a resource block containing both data and control information and receives a second DMRS from the at least one relay node in a resource block containing only the data and the second DMRS, wherein the DMRS from the UE is orthogonal to the DMRS from the at least one relay node, the access node performs a first channel estimation based on the DMRS that was transmitted by the UE, the access node performs a second channel estimation based on the DMRS that was transmitted by the at least one relay node, the access node adds the first channel estimation to the second channel estimation to derive a combined channel estimation, the access node uses the first channel estimation to demodulate the control information received from only the UE, and the access node uses the combined channel estimation to demodulate the data received from both the UE and the at least one relay node.

11. The access node of claim 10 , wherein the delta value is one of: preconfigured in the at least one relay node; and wirelessly transmitted to the at least one relay node.

12. The access node of claim 9 , wherein, when a plurality of relay nodes are present in the cell, the access node receives the same DMRS signal from the plurality of relay nodes that is orthogonal to the DMRS received from the UE.

13. The access node of claim 9 , wherein, when a plurality of relay nodes are present in the cell, the DMRS signals that the access node receives from the plurality of relay nodes have different cyclic shifts relative to one another and to the DMRS received from the UE, and the access node performs a separate channel estimation for each of the plurality of relay nodes based on the DMRS signal that the access node receives from each of the plurality of relay nodes.

14. The access node of claim 9 , wherein, when a plurality of relay nodes are present in the cell, the access node receives the DMRS from the UE in a first subset of a set of resource elements available to the UE and the relay nodes, and the access node receives the DMRS from all of the relay nodes in a second subset of the set of resource elements available to the UE and the relay nodes, and the access node performs a separate channel estimation for each of the plurality of relay nodes based on the DMRS signal that the access node receives from each of the plurality of relay nodes, the first subset and the second subset being different, and resource blocks containing the first subset and the second subset being transmitted synchronously, and DMRS received from the relay nodes is orthogonal to the DMRS received from each other relay node.

15. The access node of claim 9 , wherein the control information is received via a physical uplink control channel.

16. The access node of claim 15 , wherein the data is received via a physical uplink shared channel.