Enhanced PHICH transmission for LTE-advanced

1. A method for communication in a wireless telecommunication system, the method comprising:

monitoring, by a user equipment (UE), both a physical hybrid automatic repeat request (HARQ) indicator channel (PHICH) and an enhanced PHICH (E-PHICH) transmitted by a network element; and

determining, by the UE, whether the PHICH or the E-PHICH is being used to assign resources, wherein the UE determines whether the PHICH or the E-PHICH is being used based on a number of PHICH groups and a number of E-PHICH groups, wherein the number of PHICH groups is indicated in a physical broadcast channel (PBCH), and wherein the number of E-PHICH groups is indicated via one of higher layer signaling or in unused bits within the PBCH.

2. The method of claim 1 , further comprising:

comparing, by the UE, the number of PHICH groups with the number of E-PHICH groups; and

determining, by the UE, that the E-PHICH is being used to assign resources if the number of PHICH groups is greater than or equal to the number of E-PHICH groups.

3. The method of claim 1 , further comprising determining, by the UE, whether the PHICH or the E-PHICH is being used depending on whether a physical uplink shared channel (PUSCH) physical resource block (PRB) index and a demodulation reference signal (DMRS) value satisfy certain criteria.

4. The method of claim 1 , further comprising monitoring, by the UE, both the PHICH and the E-PHICH in a downlink subframe.

5. The method of claim 1 , further comprising monitoring, by the UE, only the E-PHICH in a downlink subframe where the PHICH is not monitored.

6. The method of claim 1 , further comprising receiving, by the UE, UE-specific radio resource control (RRC) signaling from the network element that directs the UE to receive an acknowledgement/negative acknowledgement (ACK/NACK) only via the E-PHICH, wherein the UE-specific RRC signaling carries resource allocation information for the E-PHICH, and wherein the UE-specific RRC signaling triggers the UE to receive a downlink control channel via an enhanced physical downlink control channel (E-PDCCH).

7. The method of claim 1 , further comprising:

receiving, by the UE, UE-specific radio resource control (RRC) signaling from the network element that directs the UE to stop monitoring the E-PHICH; and

monitoring, by the UE, only the PHICH in response to receiving the UE-specific RRC signaling.

8. A user equipment (UE) comprising:

at least one memory device; and

a processor configured to execute instructions stored on the at least one memory device such that when executed, the UE:

monitors both a physical hybrid automatic repeat request (HARQ) indicator channel (PHICH) and an enhanced PHICH (E-PHICH) transmitted by a network element;

determines whether the PHICH or the E-PHICH is being used to assign resources; and

monitors only the PHICH or the E-PHICH in response to receiving signaling that directs the UE to stop monitoring the E-PHICH or the PHICH, respectively.

9. The UE of claim 8 , wherein the UE determines whether the PHICH or the E-PHICH is being used based at least on a physical uplink shared channel (PUSCH) physical resource block (PRB) index.

10. The UE of claim 9 , wherein all PHICH and E-PHICH resources are jointly mapped to the PUSCH PRB index.

11. The UE of claim 8 , wherein the PHICH is used when an uplink downlink control information (DCI) grant is transmitted on a physical downlink control channel (PDCCH), and wherein the E-PHICH is used when the uplink DCI grant is transmitted on an enhanced PDCCH (E-PDCCH).

12. The UE of claim 11 , wherein:

when the uplink DCI grant is transmitted on the PDCCH, the UE calculates a PHICH group index using the following formula:

n PHICH group =( I PRB _ RA lowest _ index +n DMRS )mod N PHICH group +I PHICH N PHICH group ;

and

n PHICH seq =(└ I PRB _ RA lowest _ index /N PHICH group ┘+n DMRS )mod2 N SF PHICH

when the uplink DCI grant is transmitted on the E-PDCCH, the UE calculates the PHICH group index using the following formula:

n E-PHICH group =( I PRB _ RA lowest _ index +n DMRS )mod N E-PHICH group +I PHICH N E-PHICH group

n E-PHICH seq =(└ I PRB _ RA lowest _ index /N E-PHICH group ┘+n DMRS )mod 2 N SF PHICH .

13. The UE of claim 8 , wherein, when the UE is configured to decode the E-PHICH, the UE derives an E-PHICH group number and a sequence index using the following formula:

n E-PHICH group =( I PRB _ RA lowest _ index +n DMRS )mod N E-PHICH group +I PHICH N E-PHICH group

n E-PHICH seq =(└ I PRB _ RA lowest _ index /N E-PHICH group ┘+n DMRS )mod 2 N E-SF PHICH .

14. The UE of claim 8 , wherein the UE monitors a downlink acknowledgement/negative acknowledgement (ACK/NACK) response only via the PHICH in a legacy control region when the UE initially attaches to the network element.

15. The UE of claim 8 , wherein a resource set of the E-PHICH in a subframe relates to a variable sent to a plurality of UEs by the network element.

16. The UE of claim 15 , wherein a first value of the variable indicates that the resource set resides in a first slot of a subframe only, and a second value of the variable indicates that the resource set spans a first slot and a second slot of a subframe.

17. The UE of claim 8 , wherein the PHICH is used to carry a HARQ-ACK response when a related uplink downlink control information (DCI) grant is transmitted on a physical downlink control channel (PDCCH), and the E-PHICH is used to carry the HARQ-ACK response when a related uplink DCI grant is transmitted on an enhanced PDCCH (E-PDCCH).

18. The UE of claim 8 , wherein a resource set of the E-PHICH is defined independently of a resource set of the PHICH.

19. The UE of claim 8 , wherein:

when the network element adds the second component carrier to the UE as a secondary cell, the UE starts to receive HARQ-ACK responses related to uplink data transmission on the second component carrier via a downlink channel of the second component carrier, wherein the network element configures the E-PHICH on the second component carrier before the second component carrier is added as a secondary cell; and

when the network element removes the second component carrier from the UE's secondary cell list, the UE switches to receiving HARQ-ACK response uplink data transmission on the second component carrier via a downlink channel of the first component carrier.

20. A non-transitory computer medium storing computer readable instructions executable by a processor to implement a method for communication in a wireless telecommunication system, the method comprising:

monitoring, by a user equipment (UE), both a physical hybrid automatic repeat request (HARQ) indicator channel (PHICH) and an enhanced PHICH (E-PHICH) transmitted by a network element;

determining, by the UE, whether the PHICH or the E-PHICH is being used to assign resources; and

monitoring, by the UE, only the PHICH or the E-PHICH in response to receiving signaling that directs the UE to stop monitoring the E-PHICH or the PHICH, respectively.