TECHNICAL FIELD

This application is related to wireless communications.

BACKGROUND

Discontinuous reception (DRX) operation in a release 8 (R8) long term evolution (LTE) system is defined by the medium access control (MAC) third generation partnership project (3GPP) specification. This functionality consists of a set of rules that define when, (i.e., in which subframes), a network (i.e., an evolved Node-B (eNB)) may send control information consisting of downlink (DL) assignments and/or uplink (UL) grants (i.e., shared channel dynamic allocations) to a wireless transmit/receive unit (WTRU) using a physical DL control channel (PDCCH). The eNB DL assignments and/or UL grants, received by the WTRU on the PDCCH, signal to the WTRU the existence of DL and/or UL shared channel transmission opportunities. The period of time during which the WTRU monitors the PDCCH for this control information is referred to as the “active time”. The WTRU may turn off its receiver circuitry on a condition that the PDCCH and other DL physical channels need not be monitored, thus resulting in battery savings.

In order to further improve achievable throughput and coverage of LTE-based radio access systems, and in order to meet the international mobile telecommunications (IMT)-advanced requirements of 1 Gbps and 500 Mbps in the DL and UL directions, respectively, LTE-advanced (LTE-A) is currently under study in the 3GPP standardization body. One improvement proposed for LTE-A is carrier aggregation and support of a flexible bandwidth arrangement in order to allow DL and UL transmission bandwidths to exceed 20 MHz in R8 LTE, (e.g., 40-100 MHz).

To support carrier aggregation, it has been proposed that control information carrying a DL assignment pertaining to a given component carrier (CC), (over PDCCH), be transmitted over a different DL CC than the one that contains the data, (e.g., the physical DL shared channel (PDSCH)). Such an arrangement may be advantageous to the system operator for allowing flexibility in the configuration of control channels and thus maximizing capacity. For instance, it allows the transmission of all PDCCHs from a single CC.

In R8, a time relationship is established based on PDSCH data being immediately transmitted in a subframe (i.e., transmission timing interval (TTI)) of a radio frame after a PDCCH containing a corresponding DL assignment is transmitted in the same subframe. It would be beneficial to maintain this time relationship for the scenario where PDSCH data and a corresponding PDCCH DL assignment are transmitted on different CCs. However, this scenario potentially requires a higher battery consumption, since two CCs, (the one containing a PDCCH and the one containing a PDSCH), have to be monitored for a potential DL reception. Thus, efficient DRX methods need to be defined to minimize battery consumption.

On the other hand, if the PDSCH data is not transmitted in the same subframe as the PDCCH containing the corresponding DL assignment, higher battery efficiency may be achieved, since it is known in advance whether a CC needs to be monitored or not for PDSCH. However, breaking the time relationship creates issues that need to be addressed. If a delay between the PDCCH DL assignment and the PDSCH reception is to be introduced, it is necessary for new procedures to be defined for the WTRU to determine how to find the PDSCH over a period of time.

SUMMARY

A method and apparatus are described for operating a wireless transmit/receive unit (WTRU) in a discontinuous reception (DRX) mode employing carrier aggregation. In one scenario, a physical downlink (DL) shared channel (PDSCH) is received on a DL component carrier (CC) of a particular serving cell during a cell-specific active time, whereby the DL CC is associated with an uplink (UL) CC. Then, a physical DL control channel (PDCCH) is monitored for DL assignments for the particular serving cell, and UL grants for the UL CC, during the cell-specific active time. In another scenario, a first subset of CCs is configured for PDCCH reception, and a second subset of the CCs is not configured for PDCCH reception. DRX is applied to at least one CC in the second subset based on a PDCCH active time of at least one of the CCs in the first subset.

