WO2018205091A1

WO2018205091A1 - Discontinuous reception (drx) in wireless communication networks

Info

Publication number: WO2018205091A1
Application number: PCT/CN2017/083445
Authority: WO
Inventors: Zhan Zhang; Cecilia EKLOEF; Laetitia Falconetti
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2017-05-08
Filing date: 2017-05-08
Publication date: 2018-11-15
Also published as: WO2018207102A1

Abstract

Methods and related user equipment and radio network node are described in which Discontinuous Reception, DRX, is adapted to monitor transmissions of short Downlink Control Information, sDCI, during short Transmission Time Interval, sTTI.

Description

DISCONTINUOUS RECEPTION (DRX) IN WIRELESS COMMUNICATION NETWORKS

TECHNICAL FIELD

The present description generally relates to wireless communications and wireless communication networks， and more particularly relates to discontinuous reception (DRX) in wireless communication networks.

INTRODUCTION

LTE Frame Structure and Physical Channels for 1ms TTI

In 3GPP Long Term Evolution (LTE) systems， data transmissions in both downlink (i.e. from a radio network node or eNB to a user equipment or UE) and uplink (from a user equipment or UE to a radio network node or eNB) are organized into radio frames of 10 ms， each radio frame consisting of ten equally-sized subframes of length T_subframe ＝ 1 ms. An example of an LTE radio frame is shown in Figure 1.

LTE uses Orthogonal Frequency Division Multiple Access (OFDMA) in the downlink and Single Carrier FDMA (SC-FDMA) in the uplink. The basic LTE downlink physical resource can thus be seen as a time-frequency grid as illustrated in Figure 2， where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval.

Furthermore， the resource allocation in LTE is typically described in terms of resource blocks (RBs) ， where a resource block corresponds to one slot (0.5 ms) in the time domain and 12 contiguous subcarriers in the frequency domain. Resource blocks are numbered in the frequency domain， starting with 0 from one end of the system bandwidth.

Similarly， the LTE uplink resource grid is illustrated in Figure 3， where

is the number of resource blocks (RBs) contained in the uplink system bandwidth，

is the number subcarriers in each RB， typically

is the number of SC-FDMA symbols in each slot.

for normal cyclic prefix (CP) and

for extended CP. A subcarrier and a SC-FDMA symbol forms an uplink resource element (RE) .

Downlink data transmissions from a radio network node (generally referred to as an eNB in LTE) to a UE are dynamically scheduled， i.e.， in each subframe the eNB transmits control information about to which UEs data is transmitted and upon which resource blocks the data is transmitted in the current downlink subframe. This control signaling is typically transmitted in the first 1， 2， 3 or 4 OFDM symbols in each subframe. A downlink transmission with 3 OFDM symbols for control signaling is illustrated in Figure 4.

Transmissions in the uplink (from a UE to an eNB) are， as in the downlink， also dynamically scheduled through the downlink control channel. When a UE receives an uplink grant in subframe n， it transmits data in the uplink at subframe n +k， where k ＝ 4 for FDD system and where k varies for TDD systems.

In LTE， a number of physical channels are supported for data transmissions. A downlink or an uplink physical channel corresponds to a set of resource elements carrying information originating from higher layers (e.g.， MAC， RRC， etc. ) . while a downlink or an uplink physical signal is used by the physical layer but does not carry information originating from higher layers. Some of the downlink physical channels and signals supported in LTE are：

- Physical Downlink Shared Channel， PDSCH

- Physical Downlink Control Channel， PDCCH

- Enhanced Physical Downlink Control Channel， EPDCCH

- Cell Specific Reference Signals (CRS)

- DeModulation Reference Signal (DMRS) for PDSCH

- Channel State Information Reference Signals (CSI-RS)

PDSCH is used mainly for carrying user traffic data and higher layer messages in the downlink and is transmitted in a downlink subframe outside of the control region as shown in Figure 4. Both PDCCH and EPDCCH are used to carry Downlink Control Information (DCI) such as PRB allocation， modulation level and coding scheme (MCS) ， precoder used at the transmitter， etc. PDCCH is transmitted in the first one to four OFDM symbols in a downlink subframe， i.e.， in the control region， while EPDCCH is transmitted in the same region as PDSCH.

Some of the uplink physical channels and signals supported in LTE are：

- Physical Uplink Shared Channel， PUSCH

- Physical Uplink Control Channel， PUCCH

- DeModulation Reference Signal (DMRS) for PUSCH

- DeModulation Reference Signal (DMRS) for PUCCH

The PUSCH is used to carry uplink data and/or uplink control information from the UE to the eNB. The PUCCH is used to carry uplink control information from the UE to the eNB.

DCI Formats for 1ms TTI Scheduling

The current control channels carry control information， referred to as DCI. There are several DCI formats which have different options depending on e.g.， configured transmission mode. The DCI format has a CRC which is scrambled by a UE identifier， such as a C-RNTI， and when the CRC matches， after descrambling， a PDCCH with a certain DCI format has been detected. There are also identifiers that are shared by multiple UEs， such as the SI-RNTI which is used for transmission of system information.

DCI Formats for DL Scheduling Assignments

As described in 3GPP TS 36.212， there are currently a number of different DCI formats for downlink resource

assignments including format

1， 1A， 1B， 1C， 1D， 2， 2A， 2B， 2C and 2D. The downlink control information (DCI) for a downlink scheduling assignment contains information on downlink data resource allocation in the frequency domain (the resource allocation) ， modulation and coding scheme (MCS) and HARQ process information. In case of carrier aggregation， information related to which carrier the PDSCH is transmitted on may be included as well.

DCI Formats for UL Scheduling Grants

There are two main families of DCI formats for UL grants， DCI format 0 and DCI format 4. The latter was added in Release 10 for supporting uplink spatial multiplexing. Several DCI format variants exist for both DCI format 0 and format 4 for various purposes， e.g.， scheduling in unlicensed spectrum.

Latency Reduction with Short TTI

Packet data latency is one of the performance metrics that vendors， operators， and end-users (via speed test applications) regularly measure. Latency measurements are done in all phases of a radio access network system lifetime， when verifying a new software release or system component， when deploying a system and when the system is in commercial operation.

Shorter latency than previous generations of 3GPP RATs was one performance metric that guided the design of LTE. The end-users also now recognize LTE to be a system that provides faster access to Internet and lower data latencies than previous generations of mobile radio technologies.

Packet data latency is important not only for the perceived responsiveness of the system； it is also a parameter that indirectly influences the throughput of the system. HTTP/TCP is the dominating application and transport layer protocol suite used on the intemet today. According to HTTP Archive (http： //httparchive. org/trends. php) the typical size of HTTP based transactions over the internet are in the range of a few tens of Kbytes up to one Mbyte. In this size range， the TCP slow start period is a significant part of the total transport period of the packet stream. During TCP slow start， the performance is latency limited. Hence， improved latency can rather easily be showed to improve the average throughput， for this type of TCP based data transactions.

Latency reductions could positively impact radio resource efficiency. Lower packet data latency could increase the number of transmissions possible within a certain delay bound； hence higher Block Error Rate (BLER) targets could be used for the data transmissions freeing up radio resources potentially improving the capacity of the system.

One approach to latency reduction is the reduction of transport time of data and control signaling， by addressing the length of a transmission time interval (TTI) . By reducing the length of a TTI and maintaining the bandwidth， the processing time at the transmitter and the receiver nodes is also expected to be reduced， due to less data to process within the TTI. As described above， in LTE Release 8， a TTI corresponds to one subframe of length 1 millisecond. One such 1 ms TTI is constructed by using 14 OFDM or SC-FDMA symbols in the case of normal cyclic prefix and 12 OFDM or SC-FDMA symbols in the case of extended cyclic prefix. In LTE Release 14 in 3GPP， a study item on latency reduction has been conducted， with the goal of specifying transmissions with shorter TTIs， such as a slot or a few symbols. A work item with the goal of specifying short TTI (sTTI) has started in August 2016.

An sTTI can be decided to have any duration in time and comprises resources on any number of OFDM or SC-FDMA symbols， and starts at symbol position within the overall frame. For the work in LTE， the focus of the work is currently to only allow the sTTIs to start at fixed positions with durations of either 2， 3， 4 or 7 symbols. Furthermore， the sTTI is not allowed to cross neither slot nor subframe boundaries.

One example shown in Figure 5， where the duration of the uplink short TTI is 0.5 ms， i.e. seven SC-FDMA symbols for the case with normal cyclic prefix. Also a combined length of 2 or 3 symbols are shown for the sTTI. Here， the “R” in the figure indicates the DMRS symbols， and “D” indicates the data symbols. Other configurations are not excluded， and the figure is only an attempt to illustrate differences in sTTI lengths.

Although a shorter TTI has merits when it comes to latency， it can also have some negative impact to the uplink coverage since less energy is transmitted by the UE， specifically considering the UL control channel performance， which includes both HARQ bits， Channel Quality Information， CQI， and Scheduling Request.

Due to the limited UL coverage when transmitting a shortened TTI， it is possible to configure a longer TTI length on the UL than in the DL to combat these problems， with the standard supporting sTTI length combination in the {DL， UL} of {2， 7} . There is also the possibility of the network to schedule the UE with 1 ms TTI duration dynamically on a subframe-by-subframe basis.

DL and UL sTTI scheduling

To schedule an uplink or a downlink sTTI transmission， it is possible for the eNB to transmit the corresponding control information by using a new DCI format， referred to as short DCI (sDCI) ， in each DL sTTI. The control channel carrying this sDCI can be either PDCCH or short PDCCH (sPDCCH) . Since sPDCCH is included in each sTTI and there can be up to 6 sTTIs per LTE subframe， a UE would need to monitor sDCI in PDCCH and in up to 6 instances of sPDCCH per subframe.

Discontinuous Reception (DRX)

It is currently possible to configure the UE with Discontinuous Reception (DRX) . A DRX cycle is a periodic repetition of an on-duration period when the UE monitors PDCCH for data reception followed by an inactivity period when the UE can sleep in order to save UE battery. The UE is always configured with a long DRX cycle， but can also optionally be configured with a short DRX cycle. In case a short DRX cycle is configured， the UE will first enter short DRX for a period of time and then enter long DRX cycle.

The Active time is the time when the UE monitors PDCCH. It can be when any of the timers onDuration Timer， drx-InactivityTimer， drx-Retransmission Timer or drx-ULRetransmission Timer are running. During the Active time the UE monitors the PDCCH. If the UE finds a grant for it in PDCCH it stays active during the rest of the subframe. Otherwise， it skips monitoring the remaining subframe. When the onDurationTimer expires the UE can sleep based on short or long DRX cycle length， if any of the other timers above are not running.

The drx-InactivityTimer restarts every time data is scheduled in PDCCH (starts running in the next subframe) in order to keep the UE active for a longer time when data is transmitted. The drx-RetransmissionTimer and drx-ULRetransmissionTimer are for the UE to wake up again and monitor a possible retransmission in case the first transmission failed.

An example of a DRX configuration is shown in the Figure 6.

MA C Control Element (MA C CE)

In 3GPP TS 36.321， MAC Control Elements (MAC CE) are defined. The MAC CEs are a number of bits included in the MAC PDU for transferring of pre-defined information. There are e.g. MAC CEs defined for Buffer Status Reports， DRX Command for start or restart of DRX cycle and Power Headroom Reports. Figure 7 illustrates an example of a MAC packet data unit carrying different MAC CEs.

SUMMARY

The current DRX controls monitoring of PDCCH for a legacy DCI and but does not state any behavior for the monitoring of sDCI which can be transmitted on either sPDCCH or PDCCH. When configured with sTTI， the UE is required to monitor both PDCCH and sPDCCH the whole time which may consume a lot of UE battery. Even if the UE is only scheduled on PDCCH for a long period of time， it is still required to monitor sPDCCH. There is no RRC reconfiguration between scheduling on PDCCH and sPDCCH which means that the DRX cannot be reconfigured in-between.

In accordance with some embodiments， a DRX procedure adapted for sTTI， referred to as sDRX， is introduced. The sDRX controls the monitoring of sDCI on sPDCCH and PDCCH. The sDRX can be activated and deactivated with MAC Control Elements. The sDRX can be configured together with legacy DRX.

According to one aspect， some embodiments include a method in a User Equipment， UE. The method comprises monitoring at least one of a first downlink control channel and a second downlink control channel during an awake period of a sDRX cycle for at least one short downlink control information， sDCI.

In some embodiments， the method may comprise， or further comprises， receiving at least one sDCI on one of the first downlink control channel and the second control channel during the awake period of the sDRX cycle. In such embodiments， the method may further comprise decoding the received sDCI and then performing at least one operational task in accordance with the decoded sDCI.

In some embodiments， the method may comprise， or further comprises， receiving， from a radio network node， sDRX parameters， the sDRX parameters defining at least the sDRX cycle， the sDRX parameters being DRX parameters related to short Transmission Time Interval， sTTI. In such embodiments， the method may comprise receiving a Radio Resource Control， RRC， message from the radio network node comprising the sDRX parameters.

In some embodiments， the method may comprise， or further comprise， receiving， from the radio network node， a sDRX activation message to activate sDRX. In such embodiments， the sDRX activation message may be carried by a CE ora MAC message or may be a sDCI.

In some embodiments， the method may comprise， or further comprise， receiving， from the radio network node， a sDRX deactivation message to deactivate sDRX. In such embodiments， the sDRX deactivation message may be carried by a CE of a MAC message.

In some embodiments， the first downlink control channel may be a short Physical Downlink Control Channel， sPDCCH， and the second downlink control channel may be a Physical Downlink Control Channel， PDCCH.

According to another aspect， some embodiments include a UE configured， or operable， to perform one or more UE functionalities (e.g. steps， actions， etc. ) as described herein.

In some embodiments， the UE may comprise a communication interface configured to communicate with one or more radio network nodes and/or with one or more network nodes， and processing circuitry operatively connected to the communication interface， the processing circuitry being configured to perform one or more UE functionalities as described herein. In some embodiments， the processing circuitry may comprise at least one processor and at least one memory storing instructions which， upon being executed by the processor， configure the processor to perform one or more UE functionalities as described herein.

In some embodiments， the UE may comprise one or more functional modules configured to perform one or more UE functionalities as described herein.

According to another aspect， some embodiments include a non-transitory computer-readable medium storing a computer program product comprising instructions which， upon being executed by processing circuitry (e.g.， a processor) of the UE， configure the processing circuitry to perform one or more UE functionalities as described herein.

According to another aspect， some embodiments include a method in a radio network node. The method comprises， during an awake period of a sDRX cycle of a User Equipment， UE， transmitting a short DCI， sDCI， to the UE on one of a first downlink control channel and a second downlink control channel.

In some embodiments， the method may comprise， or further comprise， determining on which of the first downlink control channel and the second downlink control channel to transmit the sDCI to the UE.

In some embodiments， the method may comprise， or further comprise， transmitting， to the UE， sDRX parameters， the sDRX parameters defining at least the sDRX cycle， the sDRX parameters being DRX parameters related to short Transmission Time Interval， sTTI. In such embodiments， the method may comprise transmitting a Radio Resource Control， RRC， message to the UE comprising the sDRX parameters.

In some embodiments， the method may comprise， or further comprise， transmitting， to the UE， a sDRX activation message to activate sDRX. In such embodiments， the sDRX activation message may be carried by a CE of a MAC message or may be a sDCI.

In some embodiments， the method may comprise， or further comprise， transmitting， to the UE， a sDRX deactivation message to deactivate sDRX. In such embodiments， the sDRX deactivation message may be carried by a CE of a MAC message.

According to another aspect， some embodiments include a radio network node configured， or operable， to perform one or more radio network node functionalities (e.g. steps， actions， etc. ) as described herein.

In some embodiments， the radio network node may comprise a communication interface configured to communicate with one or more UEs， with one or more other radio network nodes and/or with one or more network nodes (e.g.， core network nodes) ， and processing circuitry operatively connected to the communication interface， the processing circuitry being configured to perform one or more radio network node functionalities as described herein. In some embodiments， the processing circuitry may comprise at least one processor and at least one memory storing instructions which， upon being executed by the processor， configure the processor to perform one or more radio network node functionalities as described herein.

In some embodiments， the radio network node may comprise one or more functional modules configured to perform one or more radio network node functionalities as described herein.

According to another aspect， some embodiments include a non-transitory computer-readable medium storing a computer program product comprising instructions which， upon being executed by processing circuitry (e.g.， a processor) of the radio network node， configure the processing circuitry to perform one or more radio network node functionalities as described herein.

Some embodiments may enable the UE to have awake or active time and sleep or inactive time related to sPDCCH in order to save UE battery. In some embodiments， the sDRX may be activated by a MAC CE with a subframe delay. The sDRX may also be deactivated by another MAC CE in order to save more battery ifthe UE is scheduled with legacy TTI for a period of time.

Other aspects and features will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will be described in more detail with reference to the following figures， in which：

Figure 1 illustrates a schematic diagram of an LTE time-domain structure.

Figure 2 illustrates a schematic diagram the LTE downlink resource grid.

Figure 3 illustrates a schematic diagram the LTE uplink resource grid.

Figure 4 illustrates a schematic diagram of an exemplary LTE downlink subframe.

Figure 5 illustrates schematic diagrams of exemplary 2/3-symbol sTTI configurations within an LTE uplink subframe.

Figure 6 illustrates a schematic diagram an exemplary Discontinuous Reception (DRX) .

Figure 7 illustrates a schematic diagram of an exemplary MAC PDU comprising a MAC header， MAC control elements， MAC SDUs and padding.

Figure 8 illustrates a schematic diagram of an example communication network in accordance with some embodiments.

Figure 9 illustrates timelines of exemplary DRX and sDRX according to some embodiments.

Figure 10 illustrates a signaling diagram in accordance with some embodiments.

Figure 11 illustrates a flow chart of operations of a UE in accordance with some embodiments.

Figures 12 illustrates a flow chart of operations of a radio network node in accordance with some embodiments.

Figure 13 illustrates a block diagram of a UE in accordance with some embodiments.

Figure 14 illustrates a block diagram of a radio network node in accordance with some embodiments.

Figure 15 illustrates another block diagram of a UE in accordance with some embodiments.

Figure 16 illustrates another block diagram of a radio network node in accordance with some embodiments.

DETAILED DESCRIPTION

The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments. Upon reading the following description in light of the accompanying drawing figures， those skilled in the art will understand the concepts of the description and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the description.

In the following description， numerous specific details are set forth. However， it is understood that embodiments may be practiced without these specific details. In other instances， well-known circuits， structures， and techniques have not been shown in detail in order not to obscure the understanding of the description. Those of ordinary skill in the art， with the included description， will be able to implement appropriate functionality without undue experimentation.

References in the specification to “one embodiment， ” “an embodiment， ” “an example embodiment， ” etc.， indicate that the embodiment described may include a particular feature， structure， or characteristic， but every embodiment may not necessarily include the particular feature， structure， or characteristic. Moreover， such phrases are not necessarily referring to the same embodiment. Further， when a particular feature， structure， or characteristic is described in connection with an embodiment， it is submitted that it is within the knowledge of one skilled in the art to implement such feature， structure， or characteristic in connection with other embodiments whether or not explicitly described.

As used herein， the singular forms ″a″ ， ″an″ and ″the″ are intended to include the plural forms as well， unless the context clearly indicates otherwise. It will be further understood that the terms “comprises， ” “comprising， ” “includes， ” and/or “including” when used herein， specify the presence of stated features， integers， steps， operations， elements， and/or components， but do not preclude the presence or addition of one or more other features， integers， steps， operations， elements， components， and/or groups thereof.

Several embodiments will be described in the context of 3GPP LTE standards. Still， references to 3GPP LTE standards and to their terminology should not be construed as limiting the scope of the present description to such standards. In that regard， various embodiments may also be applicable in the context of other standards， for instance， 3GPP UMTS and 3GPP NR (or 5G) .

Figure 8 illustrates an example of a wireless network 100 that may be used for wireless communications. Wireless network 100 includes UEs 110A-110B (collectively referred to as UE or UEs 110) and a plurality of radio network nodes 120A-120B (e.g.， NBs， RNCs， eNBs， gNBs， etc. ) (collectively referred to as radio network node or radio network nodes 120) directly or indirectly connected to a core network 130 which may comprise various core network nodes. The network 100 may use any suitable radio access network (RAN) deployment scenarios， including UMTS Terrestrial Radio Access Network， UTRAN， and Evolved UMTS Terrestrial Radio Access Network， EUTRAN. UEs 110 within coverage areas 115 may each be capable of communicating directly with radio network nodes 120 over a wireless interface. In certain embodiments， UEs may also be capable of communicating with each other via device-to-device (D2D) communication.

As an example， UE 110A may communicate with radio network node 120A over a wireless interface. That is， UE 110A may transmit wireless signals to and/or receive wireless signals from radio network node 120A. The wireless signals may contain voice traffic， data traffic， control signals， and/or any other suitable information. In some embodiments， an area of wireless signal coverage associated with a radio network node 120 may be referred to as a cell.

As indicated above， the existing DRX controls the PDCCH monitoring for possible DCI. The present description defines a new， separate sDRX in addition to the existing DRX. The sDRX controls the monitoring for possible sDCI， which may be sent on either sPDCCH or PDCCH. In some embodiments， the current timers for DRX are all duplicated for sDRX. The new timers can have different granularity than the current DRX timers as the cycle for sDRX may be shorter than for current DRX. If all the timers are duplicated， the same handling can be used for sDRX as for DRX but with the option of different values and granularity of the timers.

If the UE is configured with both DRX and sDRX， it will follow two DRX patterns and wake up according to the rules for each pattern. It is up to the radio network node to make a good configuration. The sDRX will most likely have a shorter cycle and the UE will wake up more often to check for sDCI on sPDCCH or PDCCH than it will to check for DCI on PDCCH for 1 ms TTI. An example of such a patterns is illustrated in Figure 9.

It is also possible to duplicate only a subset of the existing DRX timers for sDRX. In such embodiments， either only a short sDRX cycle could be created or only a long sDRX cycle. If only a short sDRX cycle is defined， the current behavior that the UE should not enter long DRX cycle after a number of short DRX cycles would probably not be reused. Instead it could be stated that the short sDRX is infinite.

With a very short DRX cycle for sDRX， there is very little opportunity for sleep. Ifthe UE is configured with sTTI， but is scheduled with 1ms TTI for a long period of time， it might be unnecessary to keep on monitoring sDCI on PDCCH and sPDCCH. A mechanism for deactivating sDRX may be required.

In some embodiments， a new MAC CE is defined for deactivation of sDRX. It can be used to deactivate sDRX when the UE is scheduled with 1ms TTI DCI on PDCCH for a long time. The UE then only needs to monitor PDCCH according to the legacy DRX pattern.

As the UE monitors PDCCH during legacy DRX， a fast way to activate sDRX again is to send an sDCI on PDCCH. The UE will know then that it is being scheduled with sTTI and can activate sDRX for monitoring of sPDCCH. Alternatively， another MAC CE could be defined to activate sDRX. That can be used when the network wants to schedule the UE with sTTI and if the sDRX is currently deactivated. The UE will then start monitoring sPDCCH/PDCCH for sDCI again. The MAC CEs are sent on PDSCH and the delay is one subframe， which is a reasonable delay for reaching the UE with an sTTI after having been scheduled on legacy TTI for a period of time.

In some embodiments， a dependency between DRX and sDRX may be defined. For instance， sDRX also has sleep periods when DRX has sleep periods. The sDRX cycle is then valid during the onDuration of DRX.

In some embodiments， as an enhancement to legacy DRX， a DCI sent during active time of sDRX (and inactive time of DRX) could be used to trigger active time of DRX. That would mean reduced latency also for 1ms TTI with DRX.

Referring now to Figure 10， as exemplary signaling diagram in accordance with some embodiments is illustrated. As shown， the radio network node 120 transmits sDRX parameters， that is DRX parameters related to short TTI transmission， sTTI， to the UE 110 (action S102) . The transmission of these sDRX parameters may be made via a RRC message (e.g. as part of the MAC-MainConfig information element of a RRC message) .

At some point in time， the radio network node 120 transmits an sDRX activation message to the UE 110 to instruct the UE 110 to start operating according to the sDRX parameters (action S104) . The sDRX activation message may be carried by a Control Element， CE， of a MAC message， or may be a sDCI transmitted on the PDCCH. As indicated above， when the UE 110 operates according to the sDRX parameters， the UE starts alternating between an awake or active period during which the UE monitors at least one of sPDCCH and the PDCCH for possible sDCI transmissions， and a sleep or inactive period during which the UE refrains from monitoring at least the sPDCCH for possible sDCI transmissions. Hence， upon receiving the sDRX activation message from the radio network node 120， the UE 110 starts monitoring at least one of the sPDCCH and the PDCCH for possible sDCI transmissions during the awake period of the sDRX cycle.

For its part， upon activation of sDRX at the UE 110， the radio network node 120 determines， when it needs to transmit a sDCI to the UE 110， on which of a first downlink control channel (e.g.， a sPDCCH) and a second downlink control channel (e.g.， a PDCCH) to transmit the sDCI to the UE 110 (action S106) . Then， during an awake period of the sDRX cycle (or of the DRX cycle) of the UE， the radio network node 120 transmits the sDCI on the determined one of the first downlink control channel and second downlink control channel (action S108) .

As indicated above， while in sDRX， the UE 110 monitors at least one of the first downlink control channel and the second downlink control channel during the awake period of the sDRX cycle (action S110) . If the UE so happen to receives a sDCI transmission while monitoring at least one of the first downlink control channel and the second downlink control channel， the UE 110 decodes the received sDCI transmission (action Sl12) and possibly performs at least one operational task (e.g.， retrieves the downlink data) in accordance with the decoded sDCI transmission (action S114) .

As some later time， the UE 110 may receive a sDRX deactivation message from the radio network node 120 to stop operating according to the sDRX parameters (action S116) . As for the sDRX activation message， the sDRX deactivation message may be carried by a Control Element， CE， of a MAC message.

Understandably， one or more of the above operations may be performed in a different order and/or may be optional.

Figure 11 is a flow chart that illustrates operations of the UE in accordance with some embodiments. As illustrated， the UE receives， from a radio network node， DRX parameters related to short Transmission Time Interval， sTTI， that is sDRX parameters， the sDRX parameters defining at least a sDRX cycle (action S202) . The sDRX parameters may be received as part of an information element of an RRC message. The UE subsequently monitors at least one of a first downlink control channel and a second downlink control channel during an awake period of the sDRX cycle for at least one sDCI transmission (action S204) . In some embodiments， the first downlink control channel may be a sPDCCH while the second downlink control channel may be a PDCCH. While monitoring at least one of the first downlink control channel and the second downlink control channel during the awake period of the sDRX cycle， the UE may receive a sDCI transmission. When the UE does receive a sDCI transmission during the awake period of the sDRX cycle， the UE decodes the sDCI transmission received either on the first downlink control channel or on the second downlink control channel (action S206) . After having decoded the received sDCI， the UE performs at least one operational task in accordance with the decoded sDCI transmission (action S208) .

Figure 12 is a flow chart that illustrates operations of the radio network node in accordance with some embodiments. As illustrated， the radio network node transmits， to a UE， DRX parameters related to short Transmission Time Interval， sTTI， that is sDRX parameters， the sDRX parameters defining at least a sDRX cycle (action S302) . The sDRX parameters may be transmitted as part of an information element of an RRC message. At a later time， upon determining the need to transmit a sDCI to the UE， the radio network node determines on which of a first downlink control channel and a second downlink control channel to transmit the sDCI to the UE (action S304) . In some embodiments， the first downlink control channel may be a sPDCCH while the second downlink control channel may be a PDCCH. Then， during an awake period of the sDRX cycle (or of the DRX cycle) of the UE， the radio network node transmits the sDCI on the determined first downlink control channel or second downlink control channel to the UE (action S306) .

Figure 13 is a block diagram of an exemplary UE 110， in accordance with certain embodiments. UE 110 includes one or more of a transceiver， processor， and memory. In some embodiments， the transceiver facilitates transmitting wireless signals to and receiving wireless signals from radio access node 120 (e.g.， via transmitter (s) (Tx) ， receiver (s) (Rx) and antenna (s)) . The processor executes instructions to provide some or all of the functionalities described above as being provided by UE 110， and the memory stores the instructions executed by the processor. In some embodiments， the processor and the memory form processing circuitry.

The processor may include any suitable combination of hardware to execute instructions and manipulate data to perform some or all of the described functions of UE 11 0， such as the functions of UE 1 10 described above. In some embodiments， the processor may include， for example， one or more computers， one or more central processing units (CPUs) ， one or more microprocessors， one or more application specific integrated circuits (ASlCs) ， one or more field programmable gate arrays (FPGAs) and/or other logic.

The memory is generally operable to store instructions， such as a computer program， software， an application including one or more of logic， rules， algorithms， code， tables， etc. and/or other instructions capable of being executed by a processor. Examples of memory include computer memory (for example， Random Access Memory (RAM) or Read Only Memory (ROM)) ， mass storage media (for example， a hard disk) ， removable storage media (for example， a Compact Disk (CD) or a Digital Video Disk (DVD) ) ， and/or or any other volatile or non-volatile， non-transitory computer-readable and/or computer-executable memory devices that store information， data， and/or instructions that may be used by the processor ofUE 110.

Other embodiments of UE 110 may include additional components beyond those shown in Figure 13 that may be responsible for providing certain aspects of the UE’s functionalities， including any of the functionalities described above and/or any additional functionalities (including any functionality necessary to support the solution described above) . As just one example， UE 110 may include input devices and circuits， output devices， and one or more synchronization units or circuits， which may be part of the processor. Input devices include mechanisms for entry of data into UE 110. For example， input devices may include input mechanisms， such as a microphone， input elements， a display， etc. Output devices may include mechanisms for outputting data in audio， video and/or hard copy format. For example， output devices may include a speaker， a display， etc.

Figure 14 is a block diagram of an exemplary radio network node 120， in accordance with certain embodiments. Radio access node 120 may include one or more of a transceiver， processor， memory， and network interface. In some embodiments， the transceiver facilitates transmitting wireless signals to and receiving wireless signals from UE 110 (e.g.， via transmitter (s) (Tx) ， receiver (s) (Rx) ， and antenna (s) ) . The processor executes instructions to provide some or all of the functionalities described above as being provided by a radio access node 120， the memory stores the instructions executed by the processor. In some embodiments， the processor and the memory form processing circuitry. The network interface communicates signals to backend network components， such as a gateway， switch， router， Internet， Public Switched Telephone Network (PSTN) ， core network nodes or radio network controllers， etc.

The processor may include any suitable combination of hardware to execute instructions and manipulate data to perform some or all of the described functions of radio access node 120， such as those described above. In some embodiments， the processor may include， for example， one or more computers， one or more central processing units (CPUs) ， one or more microprocessors， one or more application specific integrated circuits (ASICs) ， one or more field programmable gate arrays (FPGAs) and/or other logic.

The memory is generally operable to store instructions， such as a computer program， software， an application including one or more of logic， rules， algorithms， code， tables， etc. and/or other instructions capable of being executed by a processor. Examples of memory include computer memory (for example， Random Access Memory (RAM) or Read Only Memory (ROM)) ， mass storage media (for example， a hard disk) ， removable storage media (for example， a Compact Disk (CD) or a Digital Video Disk (DVD) ) ， and/or or any other volatile or non-volatile， non-transitory computer-readable and/or computer-executable memory devices that store information.

In some embodiments， the network interface is communicatively coupled to the processor and may refer to any suitable device operable to receive input for radio access node 120， send output from radio access node 120， perform suitable processing of the input or output or both， communicate to other devices， or any combination of the preceding. The network interface may include appropriate hardware (e.g.， port， modem， network interface card， etc. ) and software， including protocol conversion and data processing capabilities， to communicate through a network.

Other embodiments of radio access node 120 may include additional components beyond those shown in Figure 14 that may be responsible for providing certain aspects of the radio network node’s functionalities， including any of the functionalities described above and/or any additional functionalities (including any functionality necessary to support the solutions described above) . The various different types of network nodes may include components having the same physical hardware but configured (e.g.， via programming) to support different radio access technologies， or may represent partly or entirely different physical components.

Processors， interfaces， and memory similar to those described with respect to Figure 14 may be included in other network nodes (such as core network nodes) . Other network nodes may optionally include or not include a wireless interface (such as the transceiver described in Figure 14) .

In some embodiments， the UE 110 may comprise a series of modules configured to implement the functionalities of the UE described above. Referring to Figure 15， in some embodiments， the UE 110 may comprise at least a monitoring module configured to monitor at least one of a first downlink control channel and a second downlink control channel during an awake period of a sDRX cycle for at least one short downlink control information， sDCI.

It will be appreciated that the various modules may be implemented as combination of hardware and/or software， for instance， the processor， memory and transceiver (s) of UE 110 shown in Figure 13. Some embodiments may also include additional modules to support additional and/or optional functionalities.

In some embodiments， the radio network node 120 may comprise a series of modules configured to implement the functionalities of the radio network node described above. Referring to Figure 16， in some embodiments， the radio network node may comprise at least a transmitting module configured to， during an awake period of a sDRX cycle of a User Equipment， UE， transmit a short DCI， sDCI， to the UE on one of a first downlink control channel and a second downlink control channel.

It will be appreciated that the various modules may be implemented as combination of hardware and/or software， for instance， the processor， memory and transceiver (s) of radio network node 120 shown in Figure 14. Some embodiments may also include additional modules to support additional and/or optional functionalities.

Some embodiments may be represented as a non-transitory software product stored in a machine-readable medium (also referred to as a computer-readable medium， a processor-readable medium， or a computer usable medium having a computer readable program code embodied therein) . The machine-readable medium may be any suitable tangible medium including a magnetic， optical， or electrical storage medium including a diskette， compact disk read only memory (CD-ROM) ， digital versatile disc read only memory (DVD-ROM) memory device (volatile or non-volatile) ， or similar storage mechanism. The machine-readable medium may contain various sets of instructions， code sequences， configuration information， or other data， which， when executed， cause a processor to perform steps in a method according to one or more of the described embodiments. Those of ordinary skill in the art will appreciate that other instructions and operations necessary to implement the described embodiments may also be stored on the machine-readable medium. Software running from the machine-readable medium may interface with circuitry to perform the described tasks.

The above-described embodiments are intended to be examples only. Alterations， modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the description.

Claims

A method in a User Equipment， UE， the method comprising：

monitoring at least one of a first downlink control channel and a second downlink control channel during an awake period of a sDRX cycle for at least one short downlink control information， sDCI.
The method of claim 1， further comprising receiving at least one sDCI on one of the first downlink control channel and the second control channel during the awake period of the sDRX cycle.
The method of claim 2， further comprising：

decoding the received sDCI；

performing at least one operational task in accordance with the decoded sDCI.
The method of any of claims 1 to 3， further comprising receiving， from a radio network node， sDRX parameters， the sDRX parameters defining at least the sDRX cycle， the sDRX parameters being DRX parameters related to short Transmission Time Interval， sTTI.
The method of claim 4， wherein receiving the sDRX parameters from the radio network node comprises receiving a Radio Resource Control， RRC， message from the radio network node comprising the sDRX parameters.
The method of any of claims 1 to 5， further comprising receiving， from the radio network node， a sDRX activation message to activate sDRX.
The method of claim 6， wherein the sDRX activation message is carried by a CE of a MAC message.
The method of claim 6， wherein the sDRX activation message is a sDCI.
The method of any of claims 1 to 8， further comprising receiving， from the radio network node， a sDRX deactivation message to deactivate sDRX.
The method of claim 9， wherein the sDRX deactivation message is carried by a CE of a MAC message.
The method of any of claims 1 to 10， wherein the first downlink control channel is a short Physical Downlink Control Channel， sPDCCH， and wherein the second downlink control channel is a Physical Downlink Control Channel， PDCCH.
A User Equipment， UE， adapted to：

monitor at least one of a first downlink control channel and a second downlink control channel during an awake period of a sDRX cycle for at least one short downlink control information， sDCI.
The UE of claim 12， wherein the UE is further adapted to operate according to the method of any of claims 2 to 11.
A computer program product comprising a non-transitory computer readable storage medium having computer readable program code embodied in the medium， the computer readable program code comprising：

computer readable program code to monitor at least one of a first downlink control channel and a second downlink control channel during an awake period of a sDRX cycle for at least one short downlink control information， sDCI.
A computer program product as in claim 14， wherein the computer readable program code further comprises computer readable program code to operate according to the method of any of claims 2 to 11.
A method in a radio network node， the method comprising：

during an awake period of a sDRX cycle of a User Equipment， UE， transmitting a short DCI， sDCI， to the UE on one of a first downlink control channel and a second downlink control channel.
The method of claim 16， further comprising：

determining on which of the first downlink control channel and the second downlink control channel to transmit the sDCI to the UE.
The method claims 16 or 17， further comprising：

transmitting， to the UE， sDRX parameters， the sDRX parameters defining at least the sDRX cycle， the sDRX parameters being DRX parameters related to short Transmission Time Interval， sTTI.
The method of claim 18， wherein transmitting the sDRX parameters to the UE comprises transmitting a Radio Resource Control， RRC， message to the UE comprising the sDRX parameters.
The method of any of claims 16 to 19， further comprising transmitting， to the UE， a sDRX activation message to activate sDRX.
The method of claim 20， wherein the sDRX activation message is carried by a CE of a MAC message.
The method of claim 20， wherein the sDRX activation message is a sDCI.
The method of any of claims 16 to 22， further comprising transmitting， to the UE， a sDRX deactivation message to deactivate sDRX.
The method of claim 23， wherein the sDRX deactivation message is carried by a CE of a MAC message.
The method of any of claims 16 to 24， wherein the first downlink control channel is a short Physical Downlink Control Channel， sPDCCH， and wherein the second downlink control channel is a Physical Downlink Control Channel， PDCCH.
A radio network node adapted to：

during an awake period of a sDRX cycle of a User Equipment， UE， transmit a short DCI， sDCI， to the UE on one of a first downlink control channel and a second downlink control channel.
The radio network node of claim 26， wherein the radio network node is further adapted to operate according to the method of any of claims 17 to 25.
A computer program product comprising a non-transitory computer readable storage medium having computer readable program code embodied in the medium， the computer readable program code comprising：

computer readable program code to， during an awake period of a sDRX cycle of a User Equipment， UE， transmit a short DCI， sDCI， to the UE on one of a first downlink control channel and a second downlink control channel.
The computer program product of claim 28， wherein the computer readable program code further comprises computer readable program code to operate according to the method of any of claims 17 to 25.