Method and apparatus for signaling the release of a persistent resource

A method and apparatus for signaling the release of a persistent resource in long term evolution (LTE) are disclosed. An indication of the release of a downlink (DL) persistent resource is received by a wireless transmit receive unit (WTRU) from an evolved Node-B (eNB) via a physical downlink control channel (PDCCH). A positive acknowledgement (ACK) is transmitted by the WTRU which denotes that the indication has been received. The PDCCH or a medium access control (MAC) CE may be used by the eNB to signal the indication. At least one bit may be added to contents of the PDCCH to signal whether the PDCCH is for DL persistent or dynamic resource allocation. The DL persistent resource is then released and an indication that the DL persistent resource has been released is transmitted.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

The basis for uplink (UL) and downlink (DL) scheduling is dynamic scheduling. In a long term evolution (LTE) wireless communication system, scheduling information is transmitted during transmission timing intervals (TTIs) to a wireless transmit/receive unit (WTRU) via a physical downlink control channel (PDCCH). It has been agreed by radio access network (RAN) working groups (i.e., RAN2) to support semi-persistent scheduling for the DL and the UL in LTE. For semi-persistently scheduled WTRUs in a TTI, a DL/UL grant does not need to be sent for initial data transmission. The only exception is when an evolved Node-B (eNB) wants to override the persistent resource assignment, which by definition should be infrequent. Otherwise, the sole purpose of a DL/UL persistent resource assignment is lost. As an optimization for voice over Internet protocol (VoIP), persistent scheduling is used for both DL and UL, where the resource for the initial transmissions is persistently allocated and the resources for the hybrid automatic repeat request (HARQ) retransmissions is dynamically allocated.

Persistent resource scheduling is configured and controlled, (e.g., turned on and off), by radio resource control (RRC) signaling. For instance, persistent resource scheduling may be controlled based on the periodicity of a resource allocation. HARQ processes that are used for persistent scheduling are provided using RRC signaling.

The exact timing, resources, and transport format parameters used for a persistent DL assignment are sent on a layer 1 (L1)/layer 2 (L2) control channel as a normal DL assignment. For example, an HARQ process identification (ID) may be used to indicate that the assignment should be stored. If the persistent DL assignment is missed, which occurs when there is no acknowledgment or non-acknowledgment (NACK), then an evolved Node-B (eNB) resends the assignment.

For VoIP service, the release of semi-persistent resources in both the DL and UL is important. Both explicit resource release and implicit resource release have been previously discussed, but there has yet to be a decision made as to the implementation of these features.

Furthermore, there is a need to clarify potential new signalings to support the release of a persistent resource using both explicit and implicit methods, procedures for either explicit or implicit persistent resource release, a failure case handling when persistent resource release signaling is lost or corrupted, new signaling for the activation of the persistent resource, and new signalings for the reconfiguration of the persistent resource allocation.

There exists the need for new signalings and rules for the activation, deactivation, reconfiguration, and release of UL and DL persistent resources in LTE systems.

SUMMARY

A method and apparatus for signaling the release of a persistent resource in LTE are disclosed. An indication of the release of a DL persistent resource is received by a WTRU from an eNB via a PDCCH. A positive acknowledgement (ACK) is transmitted by the WTRU which denotes that the indication has been received. A PDCCH signaling or a medium access control (MAC) control element (CE) may be used by the eNB to signal the indication. At least one bit may be added to contents of the PDCCH to signal whether the PDCCH is for DL or UL persistent or dynamic resource allocation. The DL or UL persistent resource is then released and an indication that the DL or UL persistent resource has been released is transmitted.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receive unit (WTRU)” includes but is not limited to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a computer, or any other type of user device capable of operating in a wireless environment.

When referred to hereafter, the terminology “evolved Node-B (eNB)” includes but is not limited to a base station, a site controller, an access point (AP), or any other type of interfacing device capable of operating in a wireless environment.

FIG. 1shows a wireless communication system100including a WTRU105and an eNB110, which communicate over a physical downlink control channel (PDCCH)115and a physical uplink control channel (PUCCH)120. The WTRU105includes a transmitter125, a receiver130, a processor135and a buffer140. The eNB110includes a transmitter145, a receiver150and a processor155.

An indication of the release of a DL persistent resource is transmitted by the transmitter145in the eNB110, and is received by the receiver130of the WTRU105via the PDCCH115. The transmitter125in the WTRU105transmits an ACK to the ENB110which denotes that the indication has been received. The buffer140is used to store a DL assignment and DL transmitted data. A PDCCH or a MAC CE may be used by the eNB110to signal the indication. At least one bit may be added to contents of the PDCCH to signal whether the PDCCH is for DL persistent or dynamic resource allocation. The DL persistent resource is then released and an indication that the DL persistent resource has been released is transmitted by the transmitter125in the WTRU105.

Explicit DL Persistent Resource Release

A method for signaling the release of a DL persistent resource using explicit signaling is disclosed. When explicit signaling is used to signal the release of a DL persistent resource from the eNB110to the WTRU105, as shown inFIG. 1, either a PDCCH or a MAC CE may be used to signal the release of the DL persistent resource.

If a PDCCH115is used for explicit signaling, then one bit is added in the PDCCH115to signal whether the PDCCH115is for DL persistent or dynamic resource allocation. The one bit added to the PDCCH115may also signal the WTRU105to use separate cell radio network temporary identifiers (C-RNTIs), or to use a reserved value of some other field, such as a transmit power control (TPC) field.

Then, the WTRU105transmits an ACK/NACK to the eNB110to confirm the receipt of the PDCCH release signaling. Alternatively, after the WTRU105releases the DL persistent resource, the WTRU105transmits an indication to the eNB110to confirm the successful release of the DL persistent resource. With respect to the release of an UL persistent resource, the eNB110implicitly confirms the resource release by a loss of detection of the previously allocated resource.

A field on a PDCCH not used for persistent allocation may be used to indicate the release of DL or UL persistent resource. For example, two bits in a TPC field may be used, in which “00” indicates the release of a DL persistent resource, and two bits “01” in the TPC field may be used to indicate the release of a UL persistent resource.

A special MAC CE may be used to signal the release of a DL and UL persistent resource. For example, the two bits “00” in a MAC CE may indicate the explicit release of the DL persistent resource, and the two bits “01” may indicate the explicit release of the UL persistent resource. The number of bits in the MAC CE may vary, and a different digit permutation may be predefined for DL and UL persistent resource release.

If the WTRU105does not successfully receive the PDCCH or blind detection does not indicate any new DL voice packets in preconfigured TTIs for M times, then the WTRU105may release the DL persistent resource. The TTIs are used for persistent reception. This method may be characterized as a WTRU implicit resource release. Depending on whether the WTRU105can still receive DL dynamic traffic, the WTRU105should follow the rules to enter either a long or short discontinuous reception (DRX) cycle. After release of the DL persistent resource, it is optional whether the WTRU105transmits an indication to eNB110, informing the eNB110of the autonomous release of the DL persistent resource. The indication may be transmitted using the next available periodic PUCCH, or through a new UL MAC CE.

Alternatively, when the WTRU105receives a first DL system identification number (SID) from the eNB110after the WTRU105entered a talk-spurt duration state, the WTRU105releases the DL persistent resource because the WTRU105determines that a talk-spurt duration state is finished. The WTRU105may then optionally transmit an indication to the eNB110, indicating the release of the DL persistent resource.

Implicit DL Persistent Resource Release

A method for signaling the release of a DL persistent resource using implicit signaling is disclosed. The rules for the WTRU's implicit release of the DL persistent resource is similar to the failure handling when an explicit DL persistent resource signal is not received. However, there are differences in the WTRU rules for handling an implicit DL persistent resource release.

If the WTRU105does not successfully receive the PDCCH115, and/or blind detection does not indicate any new DL voice packets in the preconfigured TTIs for M times, then the WTRU105may release the DL persistent resource. Depending on whether the WTRU105can still receive DL/UL dynamic traffic, the WTRU105should follow the rules to enter either long or short DRX cycle. When the WTRU105changes from a long DRX cycle to a short DRX cycle, or changes from a short DRX cycle to a long DRX cycle, then the WTRU105should report the change to the eNB110within the on-duration (or active time) of a new DRX cycle so that the eNB110knows the change of WTRU DRX cycle and avoids transmitting DL signaling in a wrong cycle's on-duration.

After the implicit release of the DL persistent resource, the WTRU105may then optionally transmit an indication to eNB110indicating the autonomous release of the DL persistent resource. This indication confirms the release of the DL persistent resource. The indication may be transmitted using the next available periodic PUCCH or through a new UL MAC CE.

Alternatively, when the WTRU105receives a first DL SID from the eNB110after the WTRU's talk-spurt duration, the WTRU105releases the DL persistent resource and enters a silent period because the WTRU105determines that a talk-spurt duration state is finished. The WTRU105may then optionally transmit an indication to the eNB110indicating the release of the DL persistent resource. The indication may be transmitted using the next available periodic PUCCH, or through a new UL MAC CE.

Explicit UL Persistent Resource Release

A method for signaling the release of an UL persistent resource using explicit signaling is disclosed.

After the WTRU105transmits an empty buffer (or padding) buffer status report (BSR) to the eNB110which indicates that there is no UL data for the WTRU105to transmit to the eNB110, an indication of the explicit release of an UL persistent resource is transmitted from the eNB110using the PDCCH. The transmission of the indication of the explicit UL persistent resource release may be generated multiple times to decrease the probability of unsuccessful reception at the WTRU105. The WTRU105may optionally provide feedback with an ACK/NACK. The transmission of the indication of the explicit UL persistent resource release may be piggybacked or multiplexed with other MAC PDUs. The indication of the explicit UL persistent resource release may be transmitted using the next available PDCCH or through a new DL MAC CE.

After the UL persistent resource is successfully received by the WTRU105, the WTRU105may then transmit an indication to eNB110to acknowledge the release of the UL persistent resource.

Alternatively, confirmation of the release of the UL persistent resource is accomplished implicitly when the eNB110fails to detect subsequent UL transmissions on the UL persistent resource.

When the explicit UL persistent resource release signal is transmitted from the eNB110to the WTRU105, there may be failure cases in which the indication is lost or in error. To handle the failure cases, the following methods are disclosed.

If the eNB110does not receive a NACK from the WTRU105after transmitting the explicit release of the UL persistent resource signal, then the eNB10transmits the explicit release of the UL persistent resource signal again until a maximum number of retransmissions is reached. At the expected subframe when the WTRU105should receive the explicit release of the UL persistent resource signal from the eNB110, after the WTRU105transmits the empty BSR, if the WTRU105does not receive any feedback from the eNB110, then the WTRU105releases the UL persistent resource autonomously if the WTRU105does not have any new UL VoIP packets in the buffer after N TTIs.

Alternatively, the WTRU105immediately releases the UL persistent resource when the WTRU105does not receive any feedback from the eNB110after transmitting the empty BSR.

Alternatively, if the WTRU105transmits the empty BSR and does not receive an explicit release of the UL persistent resource signal from the eNB110, then the WTRU105does not release the UL persistent resource until there is an UL SID available. Then, the WTRU105sends a scheduling request (SR) for SID transmission to the eNB110, enabling the eNB110to determine that the WTRU105transitioned from a talk-spurt duration state to a silent period. As a result, the UL persistent resource is already autonomously release by the WTRU105.

Alternatively, after the WTRU105releases the UL persistent resource and enters a new DRX cycle, (depending on the DL/UL dynamic traffic), the WTRU105transmits an UL indication to the eNB110, wherein the indication denotes the release of UL persistent resource and the start of the new DRX cycle to synchronize the WTRU105with the eNB110. The UL indication may be transmitted in the next PUCCH using physical (PHY) signaling. Alternatively, the UL indication may be in the physical uplink shared channel (PUSCH) as a new MAC CE or radio resource control (RRC) signaling. The new MAC CE indicates the implicit release of UL persistent resource by the WTRU105.

Implicit UL Persistent Resource Release

A method for signaling the release of an UL persistent resource using implicit signaling is disclosed.

After the WTRU105detects that there is no more UL voice data packet, the WTRU105transmits an empty buffer (or padding) BSR, a PHY indication in PUCCH, or a MAC CE to the eNB110indicating the status change and immediately releases the UL persistent resource implicitly. The WTRU105transmits the empty buffer (or padding) BSR on N consecutive semi-persistent subframes.

In an alternative embodiment, the WTRU105transmits the empty (or padding) BSR only once and waits for N−1 consecutive semi-persistent subframes to determine whether there is new voice data available in a buffer. If there is no new voice data in the buffer during this period, then the WTRU105releases the UL persistent resource.

Alternatively, the WTRU105releases the UL persistent resource when the WTRU105has a first UL SID packet to transmit since entering the talk-spurt state. The WTRU105may release the UL persistent resource when the WTRU105has the SID packet in the buffer, after the WTRU105sends the SR, or after the WTRU105transmits the first UL SID packet.

Alternatively, after the WTRU105releases the UL persistent resource and enters a new DRX cycle, (depending on the DL/UL dynamic traffic), the WTRU105transmits an UL indication to the eNB110, wherein the indication denotes the release of UL persistent resource and the start of the new DRX cycle to synchronize the WTRU105with the eNB110. The UL indication may be transmitted in the next PUCCH using PHY signaling. Alternatively, the UL indication may be in the PUCCH as a new MAC CE or radio resource control (RRC) signaling. The new MAC CE indicates the implicit release of UL persistent resource by the WTRU105.

Activation and Reconfiguration Signaling for Persistent Resource

A method for signaling the activation and reconfiguration of a persistent resource using implicit signaling is disclosed. A new field is added to the PDCCH115to indicate the start time for either DL or UL persistent resource allocation. The new field may be in the form of a starting system frame number (SFN). Alternatively, either a DL or UL persistent resource allocation may be triggered, without using the start time, when a WTRU105successfully decodes the PDCCH115for persistent allocation. The DL or UL persistent resource allocation is triggered immediately at a next subframe or N subframes, after successfully decoding the PDCCH115for persistent allocation.

For reconfiguration of both the UL and DL persistent resource, either the PDCCH115or the MAC CE may be used, in addition to using RRC signaling. When using the PDCCH115and/or MAC CE to reconfigure a persistence resource, the following may be used to reconfigure an UL or DL persistent resource.1) If only the radio resource and transport format need to be reconfigured, then the PDCCH115may be used to include the new resource and transport format (TF) information without significantly changing the PDCCH115content.2) If information such as periodicity and/or at least one new HARQ process needs to be configured with the resource and transport format, then both the PDCCH115and MAC CE may be used to reconfigure the new resource and TF.3) If only periodicity and/or at least one new HARQ process needs to be reconfigured, then only the MAC CE may be used for the reconfiguration of the persistent resource.4) A new field is added to the PDCCH115for the configuration or reconfiguration of the persistent resource, wherein the new field includes parameters for periodicity and at least one HARQ process. The new field permits the PDCCH115to be used for the reconfiguration of all necessary parameters including periodicity, at least one HARQ process, exact start timing, resources, and transport format.5) A MAC CE is used for the reconfiguration of all necessary parameters including periodicity, at least one HARQ process, exact start timing, resources, and transport format.