Apparatus and method for DRX mechanisms for single HARQ process operation in NB-IoT

One embodiment is directed to a method comprising determining if a HARQ RTT timer for a downlink HARQ process expires; if the HARQ RTT timer for the downlink HARQ process is determined expired, determining if the data of the corresponding downlink HARQ process was successfully decoded; starting a drx-retransmission timer for the corresponding downlink HARQ process if the data of the corresponding downlink HARQ process was not successfully decoded; and (re)starting a drx-inactivity timer if the data of the corresponding downlink HARQ process was successfully decoded; determining if a HARQ RTT timer for a uplink HARQ process expires; if the HARQ RTT timer for the uplink HARQ process is determined expired, starting a drx-retransmission timer for the corresponding uplink HARQ process.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to and claims the benefit and priority of U.S. Provisional Patent Application No. 62/294,620, filed Feb. 12, 2016, the entirety of which is hereby incorporated herein by reference.

BACKGROUND

This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application.

Third generation partnership project (3GPP) long term evolution (LTE) and its next generation LTE advanced (LTE-A) provide significantly enhanced services of existing mobile telecommunications system by means of higher data rates and lower latency with reduced cost. LTE-A will be a more optimized radio system fulfilling the international telecommunication union radio communication sector requirements for international mobile telecommunications—advanced, while maintaining backward compatibility with the current LTE release.

Machine to Machine (M2M) communication represents a significant growth opportunity for the 3GPP ecosystem. To support the so called internet of things (IoT), 3GPP operators have to address usage scenarios with devices that are power efficient (with battery life of several years), can be reached in challenging coverage conditions e.g. indoor and basements and, more importantly, are cheap enough so that they can be deployed on a mass scale and even be disposable. A study item in 3GPP was recently approved. The aim was to study both the possibility of evolving current system and the design of a new access system towards low complexity and low throughput radio access technology to address the requirements of cellular internet of things. The objectives of the study were: improved indoor coverage, support for massive number of low throughput devices, low delay sensitivity, ultra-low device cost, low device power consumption and (optimized) network architecture. The deployment of narrow band (NB) IoT may be inband LTE, a guard band to LTE, UMTS or other system as well as stand-alone on a specific carrier.

BACKGROUND

According to a first embodiment, a method may include determining whether a user equipment is a narrow band internet of things (NB-IoT) user equipment; determining whether a hybrid automatic repeat request round trip time (HARQ RTT) timer expires; and if the user equipment is a NB-IoT user equipment and the HARQ RTT timer expires, starting or restarting a discontinuous reception (DRX) inactivity timer.

According to a second embodiment, an apparatus can include at least one processor and at least one memory and computer program code. The at least one memory and the computer program code can be configured to, with the at least one processor, cause the apparatus at least to determine whether a user equipment is a narrow band internet of things (NB-IoT) user equipment; determine whether a hybrid automatic repeat request round trip time (HARQ RTT) timer expires; and if the user equipment is a NB-IoT user equipment and the HARQ RTT timer expires, start or restart a discontinuous reception (DRX) inactivity timer.

According to a third embodiment, an apparatus can include means for performing the method according to the first embodiment.

According to a fourth embodiment, a computer program product may comprise a computer readable medium bearing computer program code for performing a process including the method according to the first embodiment.

According to a fifth embodiment, a non-transitory computer readable medium may store instructions that, when executed in hardware, perform a process including the method according to the first embodiment.

DETAILED DESCRIPTION

Comparing with existing LTE mechanism, uplink (UL) hybrid automatic repeat request (HARQ) for NB-IoT will be asynchronous in the uplink instead of being synchronous as in existing LTE system and scheduled via physical downlink control channel (PDCCH) only without physical HARQ indicator channel (PHICH) for HARQ feedback (thereby excluding non-adaptive retransmissions). In addition, it is likely that only one HARQ process for UL and only one HARQ process for downlink (DL) will be used in order to achieve the cost saving at very low data rate.

In LTE, since release 8 (Rel-8), there are 8 HARQ processes in each direction (uplink and downlink). The benefit of having more than one HARQ process is that continuous transmissions is made possible despite HARQ round trip time (RTT) and the possible occurrence of retransmissions. The drawback is increased buffering requirements and costs. Current discontinuous reception (DRX) operation for LTE is specified in 3GPP TS 36.321 v13.0.0, which is incorporated herein by reference in its entirety, where the inactivity timer is restarted when a PDCCH for new transmission is received. For DL, drx-RetransmissionTimer is started upon HARQ RTT timer expiry and if the transport block (TB) was not successfully decoded. For UL, with synchronized HARQ and non-adaptive retransmission, the user equipment (UE) wakes up when it expects a grant for retransmission. While existing DRX mechanisms cope well with continuous transmissions and 8 HARQ processes, they do not allow power saving to be maximized when only one HARQ process is used.

In an example embodiment, in order to maximize DRX opportunities when only one HARQ process is used, for DL, as the UE has no other choice but to wait HARQ RTT for next transmission opportunity (new or retransmission):Inactivity timer should not be restarted upon reception of PDCCH for new transmission (HARQ RTT timer is started when a TB is received).Upon HARQ RTT expiry, retransmission timer is started for PDCCH monitoring for potential retransmissions if the TB is not decoded and inactivity timer is started if the TB is successfully decoded.Alternatively, if the same length can be used for the monitoring of new transmission and retransmission, the inactivity timer and retransmission timers can be combined into one timer.

In an example embodiment, in order to maximize DRX opportunities when only one HARQ process is used, for UL, HARQ RTT timer is started upon reception of the PDCCH grant:

The UE wakes up for a period of time upon HARQ RTTI timer expiry. Either inactivity timer or retransmission timer can be used but there is no need to have two different timers for UL since the UE would not be able to know which timer to start without PHICH for HARQ feedback. The UE only knows if the TB is successfully received by the evolved NodeB (eNB) until next PDCCH grant is received for new transmission or retransmission.

In an example embodiment, when a DRX cycle is configured and only one HARQ process is used, the Active Time includes the time while:onDurationTimer or drx-InactivityTimer or drx-RetransmissionTimer or mac-ContentionResolution Timer is running; ora Scheduling Request is sent on physical uplink control channel (PUCCH) and is pending; ora PDCCH indicating a new transmission addressed to the C-RNTI of the MAC entity has not been received after successful reception of a Random Access Response for the preamble not selected by the MAC entity.

But the Active Time does not include the time while an uplink grant for a pending HARQ retransmission can occur and there is data in the corresponding HARQ buffer.

In an example embodiment, when DRX is configured and only one HARQ process is used, the MAC entity shall for each subframe:if a HARQ RTT Timer for the DL HARQ process expires in this subframe:if the data of the corresponding HARQ process was not successfully decoded:start the drx-RetransmissionTimer for the corresponding HARQ process.else:(re)start the drx-InactivityTimer.if a HARQ RTT Timer for the UL HARQ process expires in this subframe:start the drx-RetransmissionTimer for the corresponding HARQ process.during the Active Time, for a subframe other than a PDCCH-subframe and for a UE not capable of simultaneous reception and transmission in the aggregated cells, if the subframe is a downlink subframe indicated by a valid eIMTA L1 signalling for the SpCell and if the subframe is not part of a configured measurement gap:monitor the PDCCH.if the PDCCH indicates a DL/UL transmission or if a DL assignment/UL grant has been configured for this subframe:start the HARQ RTT Timer for the corresponding HARQ process.stop the drx-RetransmissionTimer for the corresponding HARQ process.but not start or restart drx-InactivityTimer if the PDCCH indicates a new transmission (DL, UL or sidelink (SL)).

FIG. 1illustrates a flowchart in accordance with an example embodiment of the application. In the example ofFIG. 1, when DRX is configured and only one HARQ process is used, for each subframe, the MAC entity of a UE determines at step101whether a HARQ RTT timer for a DL HARQ process expires. If the HARQ RTT timer does not expire, the MAC entity will determine at step105whether a HARQ RTT timer for a UL HARQ process expires. If the HARQ RTT timer for the DL HARQ process expires at101, the MAC entity checks whether the data of the corresponding HARQ process was successfully decoded at step102. If the data was not successfully decoded, the MAC entity will start the drx-Retransmission Timer at103for the corresponding DL HARQ process; if the data was successfully decoded, the MAC entity will (re)start the drx-InactivityTimer at104. Either way, the MAC entity similarly determines at step105whether a HARQ RTT timer for a UL HARQ process expires. If the HARQ RTT timer for the UL HARQ process expires at step105, the MAC entity will start the drx-RetransmissionTimer at106for the corresponding UL HARQ process.

It is noted that as an example, the retransmission timer is used for UL after HARQ RTT timer expiry, it could be inactivity timer as well.

In an example embodiment, the above behavior may be configured by the eNB through broadcast signaling or dedicated signaling such as for example, the radio resource control (RRC) message. In another example embodiment, it may be implicitly activated for the UEs belonging to the NB-IoT category. An example embodiment is illustrated in the flowchart ofFIG. 2. InFIG. 2, a UE receives signaling message carrying the HARQ process and/or DRX configuration information at step201and at step202, the UE configures the HARQ process and/or DRX operation based on the received information.

Reference is made toFIG. 3for illustrating a simplified block diagram of an example apparatus that is suitable for use in practicing various example embodiments of this application. InFIG. 3, a user equipment, UE,301, is adapted for communication with other network entity, which is not shown for brevity. The UE301includes at least one processor305, at least one memory (MEM)304coupled to the at least one processor305, and a suitable transceiver (TRANS)303(having a transmitter (TX) and a receiver (RX)) coupled to the at least one processor305. The at least one MEM304stores a program (PROG)302. The TRANS303is for bidirectional wireless communications with other network entity.

As shown inFIG. 3, the UE301may further include a HARQ/DRX configuration unit306. The unit306, together with the at least one processor305and the PROG302, may be utilized by the UE301in conjunction with various example embodiments of the application, as described herein.

The PROG302is assumed to include program instructions that, when executed by the associated processor, enable the electronic apparatus to operate in accordance with the example embodiments of this disclosure, as discussed herein.

In general, the various example embodiments of the apparatus301can include, but are not limited to, cellular phones, personal digital assistants (PDAs) having wireless communication capabilities, portable computers having wireless communication capabilities, image capture devices such as digital cameras having wireless communication capabilities, gaming devices having wireless communication capabilities, music storage and playback appliances having wireless communication capabilities, Internet appliances permitting wireless Internet access and browsing, as well as portable units, machine type UE or other terminals that incorporate combinations of such functions.

The example embodiments of this disclosure may be implemented by computer software or computer program code executable by the processor305, or by hardware, or by a combination of software and hardware.

The MEM304may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. The processor305may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multi-core processor architecture, as non-limiting examples.

Without in any way limiting the scope, interpretation, or application of the claims appearing below, a technical effect of one or more of the example embodiments disclosed herein may be optimizing the power saving at low data rate. This is beneficial particularly in the case when just one HARQ process is used.

Further, the various names, such as for example, the names of timers used for the described parameters are not intended to be limiting in any respect, as these parameters may be identified by any suitable names.

If desired, the different functions discussed herein may be performed in a different order and/or concurrently with each other. Furthermore, if desired, one or more of the above-described functions may be optional or may be combined. As such, the foregoing description should be considered as merely illustrative of the principles, teachings and example embodiments of this invention, and not in limitation thereof.