Systems and methods for improved uplink coverage
Systems and method are specified to improve the reception of UL transmission, for example in power or coverage limited situations. A WTRU may modify procedures to increase the available signal energy for reception at an eNB and/or to make more efficient use of the available signal energy at the receiver for processing UL transmissions. Example methods for increasing UL link coverage may include modifying HARQ timing (e.g., shorter HARQ), using longer TTIs, use of dedicated PUSCH allocations, use of new PUSCH modulations, enhanced reference signal design, UL macro diversity reception for PUSCH, utilizing protocol reduction techniques, ensuring in-order packet delivery, and/or utilizing a configuration for coverage limited/power limited modes of operation. The proposed methods may be applied individually or in any combination.
1. A method implemented by a wireless transmit receive unit (WTRU) for performing transmission time interval (TTI) bundling, the method comprising:
receiving a radio resource control (RRC) message, the RRC message indicating that the WTRU is to perform TTI bundling, wherein the RRC message indicates which of a plurality of hybrid automatic repeat request (HARQ) configurations are to be used when performing TTI bundling, wherein a first HARQ configuration is associated with a shorter time period between the WTRU receiving HARQ feedback for a bundled transmission and the WTRU performing a HARQ retransmission for the bundled transmission than a second HARQ configuration;
performing a first bundled transmission, wherein the first bundled transmission is associated with a bundle size of four subframes;
receiving first hybrid automatic repeat request (HARQ) feedback for the first bundled transmission, wherein the first HARQ feedback comprises a negative acknowledgement (NACK), wherein HARQ feedback for a bundled transmission is received four subframes after completion of the bundled transmission for each of the first and second HARQ configurations; and
transmitting a first bundled retransmission, wherein the first bundled retransmission is associated with a bundle size of four subframes and is transmitted a determined number of subframes after receiving the first HARQ feedback, wherein the determined number of subframes is shorter for the first HARQ configuration than for the second HARQ configuration.
2. The method as in claim 1 , wherein the first HARQ configuration corresponds to a coverage limited mode of operation.
3. The method as in claim 1 , wherein a number of active HARQ processes is dependent on whether the WTRU is operating according to the first HARQ configuration or the second HARQ configuration.
4. The method as in claim 3 , wherein the first HARQ configuration is associated with fewer active HARQ processes than the second HARQ configuration.
5. The method as in claim 1 , further comprising receiving a TTI bundling reconfiguration, wherein the TTI bundling reconfiguration changes the HARQ configuration to be used for performing subsequent bundled transmissions.
6. A wireless transmit receive unit (WTRU) comprising a processor configured, at least in part, to:
receive a radio resource control (RRC) message, the RRC message indicating that the WTRU is to perform transmission time interval (TTI) bundling, wherein the RRC message indicates which of a plurality of hybrid automatic repeat request (HARQ) configurations are to be used when performing TTI bundling, wherein a first HARQ configuration is associated with a shorter time period between the WTRU receiving HARQ feedback for a bundled transmission and the WTRU performing a HARQ retransmission for the bundled transmission than a second HARQ configuration;
perform a first bundled transmission, wherein the first bundled transmission is associated with a bundle size of four subframes;
receive first hybrid automatic repeat request (HARQ) feedback for the first bundled transmission, wherein the first HARQ feedback comprises a negative acknowledgement (NACK), wherein HARQ feedback for a bundled transmission is received four subframes after completion of the bundled transmission for each of the first and second HARQ configurations; and
transmit a first bundled retransmission, wherein the first bundled retransmission is associated with a bundle size of four subframes and is transmitted a determined number of subframes after receiving the first HARQ feedback, wherein the determined number of subframes is shorter for the first HARQ configuration than for the second HARQ configuration.
7. The WTRU as in claim 6 , wherein the first HARQ configuration corresponds to a coverage limited mode of operation.
8. The WTRU as in claim 6 , wherein a number of active HARQ processes is dependent on whether the WTRU is operating according to the first HARQ configuration or the second HARQ configuration.
9. The WTRU as in claim 8 , wherein the first HARQ configuration is associated with fewer active HARQ processes than the second HARQ configuration.
10. The WTRU as in claim 6 , wherein the processor is further configured to receive a TTI bundling reconfiguration, wherein the TTI bundling reconfiguration changes the HARQ configuration to be used for performing subsequent bundled transmissions.
11. An evolved Node B (eNB) comprising a processor configured, at least in part, to:
transmit a radio resource control (RRC) message to a wireless transmit receive unit (WTRU), the RRC message indicating that the WTRU is to perform transmission time interval (TTI) bundling, wherein the RRC message indicates which of a plurality of hybrid automatic repeat request (HARQ) configurations are to be used when performing TTI bundling, wherein a first HARQ configuration is associated with a shorter time period between the WTRU receiving HARQ feedback for a bundled transmission and the WTRU performing a HARQ retransmission for the bundled transmission than a second HARQ configuration;
receive a first bundled transmission, wherein the first bundled transmission is associated with a bundle size of four subframes;
transmit first hybrid automatic repeat request (HARQ) feedback for the first bundled transmission, wherein the first HARQ feedback comprises a negative acknowledgement (NACK), and HARQ feedback for a bundled transmission is transmitted four subframes after completion of the bundled transmission for each of the first and second HARQ configurations; and
receive a first bundled retransmission, wherein the first bundled retransmission is associated with a bundle size of four subframes and is transmitted a determined number of subframes after receiving the first HARQ feedback, wherein the determined number of subframes is shorter for the first HARQ configuration than for the second HARQ configuration.
12. The eNB as in claim 11 , wherein the first HARQ configuration corresponds to a coverage limited mode of operation.
13. The eNB as in claim 11 , wherein a number of active HARQ processes is dependent on whether the WTRU is operating according to the first HARQ configuration or the second HARQ configuration.