WO2018143876A1

WO2018143876A1 - Monitoring of short tti spdcch control channels

Info

Publication number: WO2018143876A1
Application number: PCT/SE2018/050074
Authority: WO
Inventors: Malik Wahaj ARSHAD; Laetitia Falconetti; Henrik Enbuske
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2017-02-03
Filing date: 2018-02-01
Publication date: 2018-08-09

Abstract

According to some embodiments, a method in a network node comprises: determining a short transmission time interval (sTTI) monitoring cycle for a short physical downlink control channel (sPDCCH); and communicating the sPDCCH sTTI monitoring cycle to a wireless device. The sPDCCH sTTI monitoring cycle may comprise an on-off monitoring pattern at a modulation symbol granularity, or a number of sPDCCH to monitor per cycle. The sPDCCH sTTI monitoring cycle may apply during an ON duration of a one millisecond transmission time interval (TTI) discontinuous reception (DRX) cycle, and not apply during the OFF duration. The sPDCCH sTTI monitoring cycle may be activated/deactivated automatically upon switching from/to using sTTI grants to using one millisecond TTI grants. A method in a wireless device may comprise: receiving a configuration for a sTTI monitoring cycle for a sPDCCH; and monitoring a received wireless signal for sPDCCH according to the received sPDCCH sTTI monitoring cycle.

Description

MONITORING OF SHORT TTI SPDCCH CONTROL CHANNELS

TECHNICAL FIELD

Particular embodiments are directed to wireless communications and, more particularly, to a monitoring cycle for a short physical downlink control channel (sPDCCH) in a short transmission time interval (sTTI).

BACKGROUND

In Third Generation Partnership Project (3GPP) long term evolution (LTE) systems, data transmissions in both downlink (i.e. from a network node or eNB to a wireless device or user equipment (UE)) and uplink (i.e., from a wireless device or UE to a network node or eNB) are organized into radio frames of 10 ms. Each radio frame consists of ten equally- sized subframes of length Tsubframe = 1 ms, as shown in Figure 1.

FIGURE 1 is a block diagram illustrating an example LTE time-domain structure. The horizontal axis represents time. The 1 ms subframe is divided into 10 subframes (#0-#9).

LTE uses orthogonal frequency division multiplexing (OFDM) in the downlink and DFT-spread OFDM (also referred to as SC-FDMA) in the uplink (see 3 GPP TS 36.211). The basic LTE downlink physical resource can be represented as a time-frequency grid as illustrated in FIGURE 2.

FIGURE 2 illustrates an example LTE downlink physical resource. Each square of the grid represents one resource element. Each column represents one OFDM symbol including cyclic prefix. Each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval.

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.

FIGURE 3 is a block diagram illustrating an example LTE uplink resource grid. In the illustrated example, is the number of resource blocks (RBs) contained in the uplink system bandwidth and N^_C ^B is the number of subcarriers in each RB. Typically N^_C ^B = 12. Nsymb ^{1S me} number of SC-OFDM symbols in each slot. N^_y ^L _mb = 7 for normal cyclic prefix (CP) and N^y_mb = 6 for extended CP. A subcarrier and a SC-OFDM symbol form an uplink resource element (RE). FIGURE 4 illustrates an example downlink subframe. Downlink data transmissions from an eNB to a UE are dynamically scheduled (i.e., in each subframe the base station transmits control information about to which terminals data is transmitted and upon which resource blocks the data is transmitted in the current downlink subframe). The control signaling is typically transmitted in the first 1, 2, 3 or 4 OFDM symbols in each subframe. The illustrated example includes a downlink system with 3 OFDM symbols as control.

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

LTE supports a number of physical channels for data transmissions. A downlink or an uplink physical channel corresponds to a set of resource elements carrying information originating from higher layers. 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: (a) Physical Downlink Shared Channel (PDSCH); (b) Physical Downlink Control Channel (PDCCH); (c) Enhanced Physical Downlink Control Channel (EPDCCH); and reference signals such as (d) Cell Specific Reference Signals (CRS); (e) DeModulation Reference Signal (DMRS) for PDSCH; and (f) Channel State Information Reference Signals (CSI-RS).

PDSCH is used mainly for carrying user traffic data and higher layer messages in the downlink. PDSCH is transmitted in a downlink subframe outside of the control region as shown in FIGURE 4. Both PDCCH and EPDCCH are used to cany downlink control information (DCI) such as physical resource block (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., 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: (a) Physical Uplink Shared Channel (PUSCH); (b) Physical Uplink Control Channel (PUCCH); (c) DeModulation Reference Signal (DMRS) for PUSCH; and (d) DeModulation Reference Signal (DMRS) for PUCCH. The PUSCH is used to carry uplink data or/and uplink control information from the UE to the eNodeB. The PUCCH is used to carry uplink control information from the UE to the eNodeB. One goal of LTE is latency reduction. Packet data latency is one of the performance metrics that vendors, operators and end-users (via speed test applications) regularly measure. Latency measurements are performed in all phases of a radio access network system lifetime, such as when verifying a new software release or system component, when deploying a system, and when the system is in commercial operation.

One performance metric that guided the design of LTE is to achieve shorter latency than previous generations of 3GPP RATs. LTE is recognized by end-users as 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; but it also indirectly influences the throughput of the system. HTTP/TCP is the dominating application and transport layer protocol suite used on the internet today.

According to HTTP Archive (available at httparchive.org/trends.php) the typical size of HTTP based transactions over the internet are in the range of a few lO's of Kbyte up to 1 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. Thus, improved latency can improve the average throughput for this type of TCP based data transaction.

Radio resource efficiency may also be positively impacted by latency reductions. Lower packet data latency can increase the number of transmissions possible within a certain delay bound. Thus, higher Block Error Rate (BLER) targets may be used for the data transmissions, freeing up radio resources and potentially improving the capacity of the system.

One approach to latency reduction is a reduction of transport time of data and control signaling by adjusting the length of a transmission time interval (TTI). Reducing the length of a TTI and maintaining the bandwidth may reduce processing time at the transmitter and the receiver nodes because of less data to process within the TTI.

In LTE release 8, a TTI corresponds to one subframe (SF) 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. Other LTE releases, such as LTE release 13 may specify transmissions with shorter TTIs, such as a slot or a few symbols. A short TTI (sTTI) may have any duration in time and comprise resources on a number of OFDM or SC-FDMA symbols within a 1 ms subframe. As one example, the duration of the uplink short TTI may be 0.5 ms (i.e., seven

OFDM or SC-FDMA symbols for the case with normal cyclic prefix). As another example, the duration of the short TTI may be 2 symbols.

Scheduling may be modified to accommodate sTTI. Some options for a short TTI scheduling scheme include single level DCI and two level DCI. If a UE gets an indication of

UE specific short TTI information in the PDCCH, the UE may possibly skip monitoring sPDCCH and potentially save energy.

For single level DCI, RRC indicates the sPDCCH frequency region and the UE specific information is located in sDCI. Thus, the UE has to read sPDCCH to get an indication if a sTTI allocation is available for it.

Two level DCI has three variants. In a first variant, UE specific information is included in sDCI, which is similar to single level DCI in terms of short TTI allocation search time for the UE. A second variant of two level DCI has the ability to include UE specific information in the PDCCH as well. Thus, the UE gets an indication if there is a sTTI allocation in sDCI just by reading the PDCCH. In the second variant of two level DCI, it is compulsory information whereas in a third variant of two level DCI, it is optional to include

UE specific information in PDCCH. Only in the second variant of the two level DCI is the

UE partially informed about its short TTI allocations in PDCCH. In all other proposals, the

UE has to read the sPDCCH to receive sTTI grants.

Even in the second variant of two level DCI, however, the UE still needs to read both

PDCCH and sPDCCH. This means that the second variant of two level DCI has room for improvement in terms of DRX efficiency.

As a means of reducing power consumption, a UE in Connected mode may be moved to Connected mode DRX. This can be done automatically when a dedicated DRX timer expires, defined by the eNB over RRC. When a UE is in connected mode DRX, the UE sleeps (in sleep mode) but wakes up to read PDCCH in certain subframes according to a predefined pattern. If the UE does not find a grant in the PDCCH, then it goes back to sleep.

The eNB can also directly move the UE to Connected DRX by transmitting a DRX

Command as a MAC Control Element (CE).

The DRX cycle determines the specific subframes during which the UE is supposed to monitor the PDCCH. In LTE the drx-Inactivity -Timer specifies the number of consecutive subframes the UE is active after receiving a PDCCH indicating an allocation for UL or DL.

The timer is (re-)started for every instance a PDCCH for the UE is detected, and at expiry the UE moves to the configured DRX mode. If the UE finds a grant for it in PDCCH, it stays active during the rest of the subframe; otherwise, it just skips monitoring the remaining frame till the next PDCCH arrives.

This continues until the onDurationTimer (specified in DRX configuration) expires. After the on duration expires, the UE can sleep based on the short or long DRX cycle length. When DRX is not configured, the UE continuously monitors the PDCCH on all the subframes. Thus, the DRX cycle defines a pattern in which a UE is supposed to monitor PDCCH in specific subframes and skip the PDCCH monitoring in the remaining subframes of the DRX cycle.

A goal of DRX is to provide battery saving opportunities to the terminal by controlling the time instances when the network can access the UE. The introduction of short TTI may affect DRX timers. For example, the DRX functionality includes several timers that are all based on subframe level granularity (i.e., subframes in which the UE should monitor the PDCCH).

Inefficiencies arise when the eNB does not schedule a sTTI for a long duration while the UE is still required to monitor for both PDCCH and sPDCCH. This may happen if the eNB switches from short TTI to 1 ms TTI during TCP ramp up procedure, for example. After the switch to 1 ms TTI, the UE continues to monitor the sPDCCH along with receiving PDSCH. This creates an unnecessary burden for the UE to read PDCCH, PDSCH, and sPDCCH even though the scheduler would not move to short TTI until the current transfer is completed or another parallel session starts.

Depending on the sTTI partem, the number of sPDCCH per 1 ms subframe can vary. For example, 2 symbol sTTI includes a maximum of six sTTIs per 1 ms subframe. This means that the UE has to monitor a total of six sPDCCH symbols along with at least one PDCCH symbol (i.e., a six fold increase in UE monitoring occasions). As a result, the UE stays active during the entire 1 ms subframe period compared to legacy 1 ms TTI where the UE only needs to search for the PDCCH at the beginning of the subframe, more precisely in the first 3 OFDM symbols. Thus, DRX power saving opportunities decrease with the number of short TTI symbols per 1 ms time frame because of increased sPDCCH monitoring requirements.

The alternatives described in the Background section are not necessarily alternatives that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the alternatives described in the Background section are not prior art and are not admitted to be prior art by inclusion in the Background section.

SUMMARY

The embodiments described herein include a short TTI monitoring cycle for a short physical downlink control channel (sPDCCH) that may be activated or deactivated by a MAC control element. The short TTI sPDCCH monitoring cycle includes an on-off partem like normal DRX, but with a granularity at symbol level TTI. A short TTI sPDCCH monitoring cycle configuration enables the UE to skip reading sPDCCH occasions when scheduled with 1 ms TTI.

According to some embodiments, a method in a network node comprises: determining a short transmission time interval (sTTI) monitoring cycle for a short physical downlink control channel (sPDCCH); and communicating the sPDCCH sTTI monitoring cycle to a wireless device.

According to some embodiments, a network node comprises processing circuitry. The processing circuitry is operable to: determine a sTTI monitoring cycle for a sPDCCH; and communicate the sPDCCH sTTI monitoring cycle to a wireless device.

In particular embodiments, the sPDCCH sTTI monitoring cycle comprises an on-off monitoring pattern at a modulation symbol granularity, or the monitoring cycle comprises a number of sPDCCH to monitor per cycle. The sPDCCH sTTI monitoring cycle may comprise a sTTI discontinuous reception (DRX) cycle. The sPDCCH sTTI monitoring cycle applies during an ON duration of a one millisecond transmission time interval (TTI) discontinuous reception (DRX) cycle, and does not apply during an OFF duration of a one millisecond TTI DRX cycle.

In particular embodiments, the sPDCCH sTTI monitoring cycle is activated via a media access control (MAC) control element (CE), activated automatically to coincide with an ON duration of a one millisecond TTI DRX cycle, or activated automatically upon switching from using sTTI grants to using one millisecond TTI grants.

In particular embodiments, wherein the sPDCCH sTTI monitoring cycle is deactivated via a MAC CE, deactivated automatically to coincide with an OFF duration of a one millisecond TTI DRX cycle, or deactivated automatically when switching from using one millisecond TTI grants to using sTTI grants.

According to some embodiments, a method in a wireless device comprises: receiving a configuration for a sTTI monitoring cycle for a sPDCCH; and monitoring a received wireless signal for sPDCCH according to the received sPDCCH sTTI monitoring cycle.

According to some embodiments, a wireless device comprises processing circuitry. The processing circuitry is operable to: receive a configuration for a sTTI monitoring cycle for a sPDCCH; and monitor a received wireless signal for sPDCCH according to the received sPDCCH sTTI monitoring cycle.

According to some embodiments, a network node comprises a determining module and a communicating module. The determining module is operable to determine a sTTI monitoring cycle for a sPDCCH. The communicating module is operable to communicate the sPDCCH sTTI monitoring cycle to a wireless device.

According to some embodiments, a wireless device comprises a receiving module and a monitoring module. The receiving module is operable to receive a configuration for a sTTI monitoring cycle for a short physical downlink control channel sPDCCH. The monitoring module is operable to monitor a received wireless signal for sPDCCH according to the received sPDCCH sTTI monitoring cycle.

Also disclosed is a computer program product. The computer program product comprises instructions stored on non-transient computer-readable media which, when executed by a processor, perform the steps of: determining a sTTI monitoring cycle for a sPDCCH; and communicating the sPDCCH sTTI monitoring cycle to a wireless device.

Another computer program product comprises instructions stored on non-transient computer-readable media which, when executed by a processor, perform the steps of: receiving a configuration for a sTTI monitoring cycle for a sPDCCH; and monitoring a received wireless signal for sPDCCH according to the received sPDCCH sTTI monitoring cycle.

Particular embodiments may exhibit some of the following technical advantages. For example, particular embodiments facilitate enhanced battery saving for a UE by skipping monitoring of sPDCCH occasions based on short TTI sPDCCH monitoring cycle configuration. Other technical advantages will be readily apparent to one skilled in the art from the following figures, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments and their features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a block diagram illustrating an example LTE time-domain structure; FIGURE 2 illustrates an example LTE downlink physical resource;

FIGURE 3 is a block diagram illustrating an example LTE uplink resource grid;

FIGURE 4 illustrates an example downlink subframe;

FIGURE 5 is a block diagram illustrating an example wireless network, according to some embodiments;

FIGURE 6 is a timing diagram illustrating a sPDCCH sTTI monitoring cycle configuration to skip sPDCCH monitoring, according to some embodiments;

FIGURE 7 is a timing diagram illustrating the relationship between a 1 ms TTI DRX cycle and a short TTI sPDCCH monitoring cycle, according to some embodiments;

FIGURE 8 is a flow diagram illustrating an example method in a network node, according to some embodiments;

FIGURE 9 is a flow diagram illustrating an example method in a wireless device, according to some embodiments;

FIGURE 1 OA is a block diagram illustrating an example embodiment of a wireless device; FIGURE 10B is a block diagram illustrating example components of a wireless device;

FIGURE 11A is a block diagram illustrating an example embodiment of a network node; and

FIGURE 1 IB is a block diagram illustrating example components of a network node.

DETAILED DESCRIPTION

A Third Generation Partnership Project (3 GPP) long term evolution (LTE) wireless network may use a reduced or shortened transmission time interval (sTTI) to reduce latency. A sTTI includes fewer symbols than a traditional TTI.

A goal of discontinuous reception (DRX) is to provide battery saving opportunities to the terminal by controlling the time instances when the network can access the user equipment (UE). Short TTI may affect DRX timers because the DRX functionality includes several timers that are all based on subframe level granularity.

Inefficiencies arise when the eNB does not schedule a sTTI for a long duration while the UE is still required to monitor for both PDCCH and sPDCCH. For example, 2 symbol sTTI includes a maximum of six sTTIs per 1 ms subframe, which means that the UE has to monitor a total of six sPDCCH symbols along with at least one PDCCH symbol (i.e., a six fold increase in UE monitoring occasions). As a result, the UE stays active during the entire 1 ms subframe period compared to legacy 1 ms TTI where the UE only needs to search for the PDCCH at the first three OFDM symbols. Thus, power saving opportunities decrease with the number of short TTI symbols per 1 ms time frame because of increased sPDCCH monitoring requirements.

Particular embodiments obviate the problems described above and include a short TTI sPDCCH monitoring configuration that may be activated or deactivated by a MAC control element. The short TTI sPDCCH monitoring includes an on-off partem like normal DRX, but with a granularity at symbol level TTI. The short TTI sPDCCH monitoring configuration enables the UE to skip reading sPDCCH occasions when scheduled with 1 ms TTI. Particular embodiments facilitate enhanced battery saving for a UE by skipping monitoring of sPDCCH occasions based on short TTI sPDCCH monitoring cycle configuration.

The following description sets forth numerous specific details. It is understood, however, 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 this description. Those of ordinary skill in the art, with the included descriptions, 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.

Particular embodiments are described with reference to FIGURES 5-1 IB of the drawings, like numerals being used for like and corresponding parts of the various drawings. LTE and NR are used throughout this disclosure as an example cellular system, but the ideas presented herein may apply to other wireless communication systems as well.

FIGURE 5 is a block diagram illustrating an example wireless network, according to a particular embodiment. Wireless network 100 includes one or more wireless devices 110 (such as mobile phones, smart phones, laptop computers, tablet computers, MTC devices, or any other devices that can provide wireless communication) and a plurality of network nodes 120 (such as base stations or eNodeBs). Wireless device 110 may also be referred to as a UE. Network node 120 serves coverage area 115 (also referred to as cell 115).

In general, wireless devices 110 that are within coverage of network node 120 (e.g., within cell 115 served by network node 120) communicate with network node 120 by transmitting and receiving wireless signals 130. For example, wireless devices 110 and network node 120 may communicate wireless signals 130 containing voice traffic, data traffic, and/or control signals. A network node 120 communicating voice traffic, data traffic, and/or control signals to wireless device 110 may be referred to as a serving network node 120 for the wireless device 110. Communication between wireless device 110 and network node 120 may be referred to as cellular communication. Wireless signals 130 may include both downlink transmissions (from network node 120 to wireless devices 110) and uplink transmissions (from wireless devices 110 to network node 120).

Each network node 120 may have a single transmitter 140 or multiple transmitters 140 for transmitting signals 130 to wireless devices 110. In some embodiments, network node 120 may comprise a multi -input multi-output (MIMO) system. Similarly, each wireless device 110 may have a single receiver or multiple receivers for receiving signals 130 from network nodes 120 or other wireless devices 110.

Wireless signals 130 may include transmission units or transmission time intervals (TTI) (e.g., subframes) such as those described with respect to FIGURES 1-4. The TTI may include shortened TTI (e.g., TTI comprising two, three, seven, etc. symbols). Wireless device 110 may monitor for wireless signals 130 according to a DRX cycle. In particular embodiments network node 120 may configure wireless device 110 to monitor wireless signals 130 according to a 1 ms DRX cycle and/or a sTTI sPDCCH monitoring cycle. Wireless device 110 may monitor wireless signal 130 according to the configured DRX cycle or cycles. Particular algorithms for configuring and monitoring according to a sTTI sPDCCH monitoring cycle are described in more detail with respect to FIGURES 6-9.

In wireless network 100, each network node 120 may use any suitable radio access technology, such as long term evolution (LTE), LTE-Advanced, UMTS, HSPA, GSM, cdma2000, NR, WiMax, WiFi, and/or other suitable radio access technology. Wireless network 100 may include any suitable combination of one or more radio access technologies. For purposes of example, various embodiments may be described within the context of certain radio access technologies. However, the scope of the disclosure is not limited to the examples and other embodiments could use different radio access technologies.

As described above, embodiments of a wireless network may include one or more wireless devices and one or more different types of radio network nodes capable of communicating with the wireless devices. The network may also include any additional elements suitable to support communication between wireless devices or between a wireless device and another communication device (such as a landline telephone). A wireless device may include any suitable combination of hardware and/or software. For example, in particular embodiments, a wireless device, such as wireless device 110, may include the components described with respect to FIGURE 10A below. Similarly, a network node may include any suitable combination of hardware and/or software. For example, in particular embodiments, a network node, such as network node 120, may include the components described with respect to FIGURE 11 A below.

A potential problem associated with DRX efficiency is during a switch from short TTI to 1 ms TTI. The main use case for short TTI grants is during the TCP ramp up procedure. Short TTI grants are allocated during the TCP ramp up and then the grants are switched to 1 ms TTI (legacy) to reduce control overhead gains. After the switch to 1 ms grants, the UE continues to monitor the sPDCCH along with receiving PDSCH grants for the remaining parts of TCP connection. This creates an unnecessary burden for UE to read PDCCH, PDSCH and sPDCCH even though the scheduler would not move to short TTI until the transfer is completed or a parallel TCP session starts. Thus, there is a need to improve the power saving opportunities for the UE in this situation.

Particular embodiments include a short TTI sPDCCH monitoring configuration that is activated immediately or soon after the switch from short TTI to 1 ms TTI. The short TTI sPDCCH monitoring includes an on-off pattern like normal DRX, but with a granularity at symbol level TTI as illustrated in FIGURE 6.

FIGURE 6 is a timing diagram illustrating a sPDCCH sTTI monitoring cycle configuration to skip sPDCCH monitoring, according to some embodiments. The horizontal axis represents time. In general, a wireless device, such as wireless device 110, monitors sPDCCH in the on duration and does not monitor sPDCCH in the off duration. When the Inactivity timer of the 1 ms TTI DRX cycle expires, the 1 ms TTI OFF duration starts and prevails over the short TTI sPDCCH monitoring cycle which is implicitly deactivated or deconfigured.

In some embodiments, the short TTI sPDCCH monitoring on-off partem may be configured by RRC like conventional DRX. Some embodiments may include activation via a MAC-CE. The MAC-CE may be sent at the switch point from short TTI to normal 1 ms TTI as illustrated in FIGURE 6, or in scenarios with very long onDurationTimer values. Once the MAC CE for short TTI sPDCCH monitoring configuration is sent, the wireless device activates the short TTI sPDCCH monitoring.

In some embodiments, the MAC-CE may activate a stored RRC configured sPDCCH monitoring configuration or a specific set of parameters associated with a sTTI switch whereas the detection of an uplink or downlink allocation in a PDCCH subframe (PDCCH and/or sPDCCH) starts an inactivity timer. The wireless device may continue to receive the 1 ms grants on PDSCH for the remaining parts of the TCP connection and follow short TTI sPDCCH monitoring configuration for sPDCCH monitoring. This avoids the situation when the wireless device has to monitor all sPDCCH instances together with receiving downlink data on PDSCH.

In some embodiments, the short TTI sPDCCH monitoring is configured via RRC in a similar manner as the conventional 1 ms TTI DRX is configured. This simplifies the configuration process by configuring the wireless device with a sPDCCH monitoring configuration for 1 ms TTI as well as a DRX configuration for short TTI.

Particular embodiments may configure a wireless device with two separate DRX cycles. Some embodiments may configure separate parameters or parameter sets conditioned to and/or activated independently by an active sTTI allocation or a switch from sTTI to 1 ms TTI or other.

One DRX cycle may correspond to the 1 ms TTI DRX and the second DRX cycle corresponds to the short TTI sPDCCH monitoring. Alternatively, in using a single configuration the active/activated parameter sub-set may define the DRX mode and the DRX cycle with associated parameters, constant and values. The corresponding parameters of the DRX cycles may be independent from each other. The parameters for the short TTI sPDCCH monitoring cycle can include an on duration timer for short TTI, a total short TTI sPDCCH monitoring cycle duration, and an inactivity timer.

In some embodiments, the short TTI sPDCCH monitoring configuration consisting of short DRX-cycle and onDurationTimer can be defined in terms of 1 ms subframe. In some embodiments, the short TTI sPDCCH monitoring configuration consisting of short DRX- cycle and onDurationTimer can be defined in terms of number of OFDM symbols or in terms of number of sPDCCH monitored.

Alternatively, the timer referenced time in PDCCH subframes may include or alternatively define the presence of PDCCH occasions such that a timer may instead count the number of possible occasions for which an allocation in PDCCH and/or PDCCH may be detected. This facilitates a smaller granularity of sPDCCH monitoring and enables the eNB to schedule a sPDCCH monitoring pattern in which the UE monitors specific time instances where sPDCCH occurs and skip the remaining sPDCCH time instances within a short sPDCCH monitoring cycle.

In another embodiment, the length of the short TTI onDurationTimer does not exceed the length of onDurationTimer for 1 ms TTI. This is because it would not provide a benefit and may create ambiguity in terms of monitoring of sPDCCH when the PDCCH subframe monitoring is skipped by 1 ms TTI DRX configuration.

In some embodiments, when the short TTI DRX cycle is following short TTI onDurationTimer, the wireless device monitors the sPDCCH. When the onDurationTimer expires, the wireless device stops monitoring sPDCCH. In some embodiments, the short TTI sPDCCH monitoring is activated by a network node via a MAC control element. This enables fast activation of the short TTI sPDCCH monitoring whenever the network node deems necessary.

In some embodiments, a wireless device enters the onDuration phase of the short TTI sPDCCH monitoring when it has been activated when the inactivity timer of the short TTI sPDCCH monitoring cycle expires.

In some embodiments, the short TTI DRX is implicitly deconfigured under the following conditions: (a) legacy 1 ms TTI DRX inactivity timer expires and the wireless device enters OnDurationTimer for 1 ms TTI DRX; (b) wireless device receives a sTTI grant on sPDCCH; and (c) a number of n PDCCH "monitoring occasions" for after n>x which no wireless device specific uplink or downlink grant is detected; where x may be hard-coded in standard, configured by RRC or set in MAC-CE.

In some embodiments, the network node may reactivate the short TTI sPDCCH monitoring configuration via a MAC activation even when it is implicitly released due to any of the above conditions. This is because there could be 1 ms TTI DRX configuration with quite long onDurationTimers configured specially for scenarios when latency critical services are not served in the cell. In such situations, it is beneficial to trigger short TTI sPDCCH monitoring and skip sPDCCH monitoring (i.e., DRX configuration with 200 ms subframes).

FIGURE 7 is a timing diagram illustrating the relationship between a 1 ms TTI DRX cycle and a short TTI sPDCCH monitoring cycle, according to some embodiments. The horizontal axis represents time. The example illustrates that the short TTI sPDCCH monitoring cycle can only be applied in the ON duration of the 1 ms TTI DRX cycle.

Particular embodiments may include methods in a network node and a wireless device. The examples and embodiments described above may be generally represented by the flowcharts in FIGURES 8 and 9.

FIGURE 8 is a flow diagram illustrating an example method in a network node, according to some embodiments. In particular embodiments, one or more steps of FIGURE 8 may be performed by components of wireless network 100 described with respect to FIGURE 5.

The method begins at step 812, where the network node determines a sTTI sPDCCH monitoring cycle. For example, network node 120 may determine a sTTI sPDCCH monitoring cycle for a sTTI comprising two OFDM symbols. In particular embodiments, the sTTI sPDCCH monitoring cycle comprises an on-off pattern at a modulation symbol granularity, or based on a number of monitored sPDCCH.

The sTTI sPDCCH monitoring cycle may apply to an ON duration of a 1 ms TTI DRX cycle. The sTTI sPDCCH monitoring cycle may be activated via a media access control (MAC) control element (CE), or automatically to coincide with an ON duration of a 1 ms TTI DRX cycle. The sTTI sPDCCH monitoring cycle may be deactivated via a MAC CE, or automatically to coincide with an OFF duration of a 1 ms TTI DRX cycle. In particular embodiments, the sTTI sPDCCH monitoring cycle may be determined according to any of the embodiments described with respect to FIGURES 6 and 7.

At step 814, the network node communicates the sTTI sPDCCH monitoring cycle to a wireless device. For example, network node 120 may communicate the sTTI sPDCCH monitoring cycle to wireless device 110 based on any of the embodiments described above (e.g., MAC CE, RRC, etc.).

Modifications, additions, or omissions may be made to method 800. Additionally, one or more steps in method 800 of FIGURE 8 may be performed in parallel or in any suitable order. The steps of method 800 may be repeated over time as necessary.

A wireless device, such as wireless device 110, may receive the sTTI sPDCCH monitoring configuration and use it to monitor a wireless signal. An example is illustrated in FIGURE 9.

FIGURE 9 is a flow diagram illustrating an example method in a wireless device, according to some embodiments. In particular embodiments, one or more steps of FIGURE 9 may be performed by components of wireless network 100 described with respect to FIGURE 5.

The method begins at step 912, where the wireless device receives a configuration for a sTTI sPDCCH monitoring cycle. For example, wireless device 110 may receive a configuration for a sTTI sPDCCH monitoring cycle from network node 120.

In particular embodiments, the sTTI sPDCCH monitoring cycle comprises an on-off pattern at a modulation symbol granularity, or based on a number of monitored sPDCCH.

The sTTI sPDCCH monitoring cycle may apply to an ON duration of a 1 ms TTI DRX cycle. The sTTI sPDCCH monitoring cycle may be activated via a MAC CE, or automatically to coincide with an ON duration of a 1 ms TTI DRX cycle. The sTTI sPDCCH monitoring cycle may be deactivated via a MAC CE, or automatically to coincide with an OFF duration of a 1 ms TTI DRX cycle. In particular embodiments, the sTTI sPDCCH monitoring cycle may be determined according to any of the embodiments described with respect to FIGURES 6 and 7.

At step 914, the wireless device monitors a received wireless signal according to the received sTTI sPDCCH monitoring cycle. For example, wireless device 110 may monitor received wireless signal 130 based on any of the embodiments described above.

Modifications, additions, or omissions may be made to method 900. Additionally, one or more steps in method 900 of FIGURE 9 may be performed in parallel or in any suitable order. The steps of method 900 may be repeated over time as necessary.

FIGURE 1 OA is a block diagram illustrating an example embodiment of a wireless device. The wireless device is an example of the wireless devices 110 illustrated in FIGURE 5. In particular embodiments, the wireless device is capable of receiving a sTTI sPDCCH monitoring cycle configuration and monitoring a received wireless signal according to the received sTTI sPDCCH monitoring cycle.

Particular examples of a wireless device include a mobile phone, a smart phone, a PDA (Personal Digital Assistant), a portable computer (e.g., laptop, tablet), a sensor, a modem, a machine type (MTC) device / machine to machine (M2M) device, laptop embedded equipment (LEE), laptop mounted equipment (LME), USB dongles, a device-to- device capable device, a vehicle-to-vehicle device, or any other device that can provide wireless communication. The wireless device includes transceiver 1010, processing circuitry 1020, memory 1030, and power source 1040. In some embodiments, transceiver 1010 facilitates transmitting wireless signals to and receiving wireless signals from wireless network node 120 (e.g., via an antenna), processing circuitry 1020 executes instructions to provide some or all of the functionality described herein as provided by the wireless device, and memory 1030 stores the instructions executed by processing circuitry 1020. Power source 1040 supplies electrical power to one or more of the components of wireless device 110, such as transceiver 1010, processing circuitry 1020, and/or memory 1030.

Processing circuitry 1020 includes any suitable combination of hardware and software implemented in one or more integrated circuits or modules to execute instructions and manipulate data to perform some or all of the described functions of the wireless device. In some embodiments, processing circuitry 1020 may include, for example, one or more computers, one more programmable logic devices, one or more central processing units (CPUs), one or more microprocessors, one or more applications, and/or other logic, and/or any suitable combination of the preceding. Processing circuitry 1020 may include analog and/or digital circuitry configured to perform some or all of the described functions of wireless device 110. For example, processing circuitry 1020 may include resistors, capacitors, inductors, transistors, diodes, and/or any other suitable circuit components.

Memory 1030 is generally operable to store computer executable code and data. Examples of memory 1030 include computer memory (e.g., Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (e.g., a hard disk), removable storage media (e.g., 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.

Power source 1040 is generally operable to supply electrical power to the components of wireless device 110. Power source 1040 may include any suitable type of battery, such as lithium-ion, lithium-air, lithium polymer, nickel cadmium, nickel metal hydride, or any other suitable type of battery for supplying power to a wireless device. In particular embodiments, processing circuitry 1020 in communication with transceiver 1010 receives a sTTI sPDCCH monitoring cycle configuration and monitors a received wireless signal according to the received sTTI sPDCCH monitoring cycle.

Other embodiments of the wireless device may include additional components (beyond those shown in FIGURE 10A) responsible for providing certain aspects of the wireless device's functionality, including any of the functionality described above and/or any additional functionality (including any functionality necessary to support the solution described above).

FIGURE 10B is a block diagram illustrating example components of a wireless device 110. The components may include receiving module 1050 and monitoring module 1052.

Receiving module 1050 may perform the receiving functions of wireless device 110. For example, receiving module 1050 may receive a configuration for a sTTI sPDCCH monitoring cycle. Receiving module 1050 may receive the sTTI sPDCCH monitoring cycle configuration according to any of the embodiments described with respect to FIGURES 6-9. In certain embodiments, receiving module 1050 may include or be included in processing circuitry 1020. In particular embodiments, receiving module 1050 may communicate with monitoring module 1052.

Monitoring module 1052 may perform the monitoring functions of wireless device 110. For example, monitoring module 1052 may monitor a wireless signal 130 according to the received sTTI sPDCCH monitoring cycle, according to any of the embodiments and examples described above (e.g., step 914 of FIGURE 9). In certain embodiments, monitoring module 1052 may include or be included in processing circuitry 1020. In particular embodiments, monitoring module 1052 may communicate with receiving module 1050.

FIGURE 11A is a block diagram illustrating an example embodiment of a network node. The network node is an example of the network node 120 illustrated in FIGURE 5. In particular embodiments, the network node is capable of determining a sTTI sPDCCH monitoring cycle configuration and communicating the sTTI sPDCCH monitoring cycle configuration to a wireless device.

Network node 120 can be an eNodeB, a nodeB, gNB, a base station, a wireless access point (e.g., a Wi-Fi access point), a low power node, a base transceiver station (BTS), a transmission point or node, a remote RF unit (RRU), a remote radio head (RRH), or other radio access node. The network node includes at least one transceiver 1110, processing circuitry 1120, at least one memory 1130, and at least one network interface 1140. Transceiver 1110 facilitates transmitting wireless signals to and receiving wireless signals from a wireless device, such as wireless devices 110 (e.g., via an antenna); processing circuitry 1120 executes instructions to provide some or all of the functionality described above as being provided by a network node 120; memory 1130 stores the instructions executed by processing circuitry 1120; and network interface 1140 communicates signals to backend network components, such as a gateway, switch, router, Internet, Public Switched Telephone Network (PSTN), controller, and/or other network nodes 120. Processing circuitry 1120 and memory 1130 can be of the same types as described with respect to processing circuitry 1020 and memory 1030 of FIGURE 10A above.

In some embodiments, network interface 1140 is communicatively coupled to processing circuitry 1120 and refers to any suitable device operable to receive input for network node 120, send output from network node 120, perform suitable processing of the input or output or both, communicate to other devices, or any combination of the preceding. Network interface 1140 includes appropriate hardware (e.g., port, modem, network interface card, etc.) and software, including protocol conversion and data processing capabilities, to communicate through a network. In particular embodiments, processing circuitry 1120 in communication with transceiver 1110 determines a sTTI sPDCCH monitoring cycle configuration and communicates the sTTI sPDCCH monitoring cycle configuration to a wireless device. Other embodiments of network node 120 include additional components (beyond those shown in FIGURE 11 A) responsible for providing certain aspects of the network node's functionality, including any of the functionality described above and/or any additional functionality (including any functionality necessary to support the solution 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.

FIGURE 1 IB is a block diagram illustrating example components of a network node 120. The components may include determining module 1150 and communicating module 1152.

Determining module 1150 may perform the determining functions of network node 120. For example, determining module 1150 may determine a sTTI sPDCCH monitoring cycle configuration. Determining module 1150 may determine the sTTI sPDCCH monitoring cycle configuration according to any of the embodiments described with respect to FIGURES 6-9. In certain embodiments, determining module 1150 may include or be included in processing circuitry 1120. In particular embodiments, determining module 1150 may communicate with communicating module 1152.

Communicating module 1152 may perform the communicating functions of network node 120. For example, communicating module 1152 may communicate a sTTI sPDCCH monitoring cycle configuration to wireless device 110 according to any of the embodiments described with respect to FIGURES 6-9. In certain embodiments, communicating module 1152 may include or be included in processing circuitry 1120. In particular embodiments, communicating module 1152 may communicate with determining module 1150.

Modifications, additions, or omissions may be made to the systems and apparatuses disclosed herein without departing from the scope of the invention. The components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses may be performed by more, fewer, or other components. Additionally, operations of the systems and apparatuses may be performed using any suitable logic comprising software, hardware, and/or other logic. As used in this document, "each" refers to each member of a set or each member of a subset of a set.

Modifications, additions, or omissions may be made to the methods disclosed herein without departing from the scope of the invention. The methods may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. Although this disclosure has been described in terms of certain embodiments, alterations and permutations of the embodiments will be apparent to those skilled in the art. Accordingly, the above description of the embodiments does not constrain this disclosure. Other changes, substitutions, and alterations are possible without departing from the spirit and scope of this disclosure, as defined by the claims below.

The attached following examples provide a non-limiting example of how certain aspects of the proposed solutions could be implemented within the framework of a specific communication standard. In particular, the following examples provide a non-limiting example of how the proposed solutions could be implemented within the framework of a 3GPP TSG RAN standard. The changes described by the examples are merely intended to illustrate how certain aspects of the proposed solutions could be implemented in a particular standard. However, the proposed solutions could also be implemented in other suitable manners, both in the 3GPP specification and in other specifications or standards.

With sTTI as currently defined in LTE, latency in downlink and uplink is reduced by allowing transmissions on a shorter timescale. All current MAC timers are defined in terms of 1 ms subframe. The following examples analyze the potential changes for the current MAC timers and DRX in sTTI operation.

Particular examples use the following assumptions. The minimum timing for uplink grant to uplink data and for downlink data to downlink HARQ is n + k sTTI for short TTI operation. The processing time is greater than or equal to the legacy processing time linearly downscaled with TTI length 4 <= k <= 8. Note that sTTI refers to sPUSCH sTTI for the uplink grant to uplink data timing, and sPDSCH sTTI for the downlink data to downlink HARQ feedback timing. The unit for HARQ RTT timer counting is the TTI length of the TB that starts the timer. Mac-ContentionResolutionTimer is in number of subframes regardless of which TTI length is used.

Particular examples may select a sTTI scheduling scheme among the following candidates for each sTTI length. For single level DCI the scheduling scheme may include:

(a) RRC configuration of sPDCCH search space and/or sPDCCH frequency region; or (b) UE-specific information in sDCI related to sPDSCH/sPUSCH. For two level DCI, RRC configuration may or may not at least partially indicate sPDCCH frequency region/search space for the following variants: (l)(a) slow DCI: non UE-specific information in PDCCH;

(b) fast DCI: UE-specific information in sDCI; (2)(a) slow DCI: UE-specific information in PDCCH; (b) fast DCI: UE-specific information in sDCI; and (3)(a) slow DCI: UE-specific information in PDCCH and/or sPDCCH; and (b) fast DCI: UE-specific information in sDCI.

The sTTI scheduling scheme may be the same or different for different sTTI length. A UE can be dynamically (with a subframe to subframe granularity) scheduled with legacy TTI unicast PDSCH and/or short TTI unicast PDSCH. If the UE is indicating the capability of decoding PDSCH and sPDSCH assigned with C-RNTI/SPS C-RNTI in the same subframe for a given carrier, then if valid downlink assignments are detected based on C-RNTI/SPS C- RNTI in PDCCH/EPDCCH for PDSCH and PDCCH/sPDCCH for sPDSCH in the same subframe for a given carrier, the UE should decode the PDSCH in addition to sPDSCH. The UE shall provide HARQ-ACK feedback for both PDSCH and sPDSCH. No special consideration is specified for overlapping of sPDSCH and PDSCH.

Otherwise, if valid downlink assignments are detected based on C-RNTI/SPS C-RNTI in PDCCH/EPDCCH for PDSCH and PDCCH/sPDCCH for sPDSCH in the same subframe for a given carrier, the UE should decode the sPDSCH and is not required to decode PDSCH. The UE shall provide HARQ-ACK feedback for both PDSCH and sPDSCH

In current LTE, absolute timing of scheduling and transmission (i.e., the physical layer frame-structure) is kept mostly transparent to LTE MAC. Therefore, the term "TTI" is employed in the MAC specification, not referring to an absolute time length. In the current LTE operation, the TTI length for (most of downlink/uplink transmission cases) is one subframe (i.e., 1 ms). It can be assumed that the scheduling and transmission operation on MAC scales for short TTI, which relate to a shorter subframe length, of e.g. 2 OFDM symbols or 7 OFDM symbols. The behavior of the timers and DRX, which are closely related to scheduling/transmission, i.e. TTI, is however defined on the absolute subframe length and therefore needs to be reviewed.

With respect to MAC timers, LTE MAC employs a number of subframe-based timers.

The following analyzes whether the timers should be kept on 1 ms-subframe operation, or should employ shorter minimum values, given the shorter sub-subframe lengths in sTTI operation. The analysis includes review of the operation of further MAC timers, which are configured with subframe-based expiry times.

One timer, the sr-ProhibitTimer, refers to SR-periods as its basis, i.e. it can be considered a counter. Therefore, it scales automatically when shorter SR-periods are employed due to usage of sPUCCH. No change of this timer's behavior is needed. timeAlignmentTimer: at expiry the UE time alignment is considered lost, so that UE needs to re-synchronize to the network. Because the drifting of the UE clock is not expected to be different for sTTI, this timer does not need changes in sTTI operation.

periodicBSR-Timer, retxBSR-Timer, logicalChannelSR-ProhibitTimer: Faster BSR reporting is not foreseen for sTTI operation. While sTTI allows transmission with lower latency, in case of large buffers, the buffers are not emptied faster with sTTI, therefore faster BSR reporting is not needed. Nevertheless, in case faster BSR changes below the current minimum period of 5 ms are considered worthwhile for reporting, a new minimum value of 1 ms could be introduced (the value of 1 ms would reflect the scaling of 14 os TTI to 2 os TTI well enough).

periodicPHR-Timer, prohibitPHR-Timer: The power headroom might change with changes in pathloss, but because dynamic path loss changes to be reported do not occur faster with sTTI, also this timer does not require changes.

mac-ContentionResolutionTimer: does not require changes, because it is RACH related and therefore independent (operates before the start) of sTTI.

sCellDeactivationTimer: does not need changes, because SCell handling in CA is also independent of sTTI usage.

With respect to PDCCH and sPDCCH monitoring, the DRX cycle determines the specific subframes during which the UE is supposed to monitor 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 frame until the next PDCCH arrives. This continues until the onDurationTimer (specified in DRX configuration) expires.

After the on duration expires, the UE can sleep based on short or long DRX cycle length. If DRX is not configured, the UE continuously monitors the PDCCH on all the subframes. Thus, the DRX cycle defines a partem in which a UE is supposed to monitor PDCCH in specific subframes and skip the PDCCH monitoring in the remaining subframes of the DRX cycle.

A goal of DRX is to provide battery saving opportunities to the terminal by controlling the time instances when network can access the UE. With the introduction of short TTI, it is important to assess its effect on DRX timers. The DRX functionality has quite a few associated timers which are all based on subframe level granularity,i.e subframes in which UE needs to monitor the PDCCH. Because the current definition of DRX is associated with PDCCH monitoring only, it needs to be enhanced to include monitoring of sPDCCH when configured with short TTI.

If the UE is configured with short TTI, it should monitor both PDCCH and sPDCCH. This means that if DRX onDurationTimer is running, the UE needs to monitor both PDCCH as well as sPDCCH. This result in increased UE battery consumption because the UE had less time to sleep.

Depending on the sTTI partem, the number of sPDCCH per 1 ms subframe can vary. In case of 2 symbol TTI, there is a maximum of six symbols per 1 ms subframe. This means that the UE has to monitor a total of six sPDCCH symbols along with at least one PDCCH symbol, i.e. six fold increase in UE monitoring occasions. As a result, the UE stays active during the entire 1 ms subframe period compared to legacy 1 ms TTI where the UE only needs to read the first, second or third symbol allocated for the PDCCH.

3GPP is considering multiple options for a scheduling scheme which includes single level DCI and two level DCI as described above. If the UE gets an indication of UE specific short TTI information in the PDCCH, there is a possibility to skip monitoring sPDCCH and potentially save energy. In case of single level DCI, RRC indicates the sPDCCH frequency region and then the UE specific information is located in sDCI. Thus, UE has to read sPDCCH to get an indication if a sTTI allocation is available for it.

Two level DCI has three variants. In first variant, UE specific information is included in sDCI, which is almost similar to single level DCI in terms of short TTI allocation search time for UE. The variant 2 of two level DCI have the possibility to include UE specific information in the PDCCH as well. Thus, the UE gets an indication if there is a sTTI allocation in sDCI, just by reading the PDCCH. In variant 2 of two level DCI, it is compulsory information whereas in variant 3 of two level DCI, it is optional to include UE specific information in PDCCH.

Only variant 2 of the two level DCI is the UE partially informed about its short TTI allocations in PDCCH. In all other proposals, the UE has to read the sPDCCH to receive sTTI grants.

Even in case of variant 2 of two level DCI, however, the UE still needs to read both PDCCH and sPDCCH. This means that in case of variant 2 of two level DCI there could be potential improvement in terms of DRX efficiency, if LTE includes a possibility for UE to skip reading sPDCCH when there is no UE specific information in PDCCH. A potential problem associated with DRX efficiency is during a switch from short TTI to 1 ms TTI. The main use case for short TTI grants is during the TCP ramp up procedure. Short TTI grants are allocated during the TCP ramp up and then the grants are switched to 1 ms TTI (legacy) to reduce control overhead gains. After the switch to 1 ms grants, the UE continues to monitor the sPDCCH along with receiving PDSCH. This creates an unnecessary burden for UE to read PDCCH, PDSCH and also sPDCCH even though the scheduler would not move to short TTI until the transfer is completed. Thus, there is a need to improve the power saving opportunities for the UE in this situation.

One solution is to use a short TTI DRX configuration which is active immediately after the switch from short TTI to 1 ms TTI. The short TTI DRX introduces an on off partem like normal DRX but with a granularity at symbol level TTI as shown in FIGURE 6. This may be configured by RRC like current DRX and may also include activation via a MAC- CE. The short TTI DRX supports the UE to skip reading some sPDCCH based on this sTTI DRX configuration.

The following analyses the DRX-related MAC timers.

drx-Inactivity Timer: does not need scaling because it already provides a granularity of down to one subframe.

shortDRX-cycle and longDRX-cycle: the current starting range of shortDRX-cycle include 2,5,8, 10 ms and for longDRX-cycle it is 10,20,32 and 40 ms, respectively. Long DRX-cycle does not affect sTTI grants because in case of latency critical services and other sTTI use cases, LongDRX-cycle would not be configured to avoid long latency. Thus, no changes are required in longDRX-cycle.

The minimum value of 2 ms for shortDRX-cycle timer is significant for 1 ms TTI operation. For short TTI, shortDRX-cycle timer value of 2 ms is long because it is equivalent to 12 symbols for 2 symbol TTI so it should be possible for UE to sleep earlier in terms of short TTI. Also, the requirement for the UE to monitor both PDCCH and sPDCCH leads to DRX inefficiency when the UE is operating on 1 ms TTI. Because the shortDRX-cycle granularity is optimum to support 1 ms TTI operation, it should not be changed otherwise a significant switching is required to adapt the shortDRX-cycle to short TTI and legacy 1 ms TTI all the time. The solution proposed above to handle the switch scenario from short TTI to lms TTI would require a sTTI shortDRX-cycle which would support granularity up to symbol level. This shortDRX-cycle should be activated immediately after the switch from short TTI to 1 ms TTI and it would potentially increase DRX efficiency by reducing sPDCCH monitoring when the UE is scheduled with PDSCH resources.

drx-RetransmissionTimer: defines an additional On' period when a downlink retransmission is expected. This would prevent the UE from missing a retransmission after entering the DRX mode. It is triggered if the HARQ round trip time (RTT) expires due to problems with decoding the downlink transmission. The HARQ RTT is fixed at 8 subframes for FDD. Because the HARQ RTT is based on symbol level for short TTI, the requirement for minimum value of drx-Retransmission timer is also reduced. Abbreviations used in the preceding description include:

3 GPP Third Generation Partnership Project

BCH Broadcast Channel

BLER Block Error Rate

BTS Base Transceiver Station

CSI Channel State Information

D2D Device to Device

DCI Downlink Control Information

DL Downlink

DMRS Demodulation Reference Signal

DRX Discontinuous Reception

ePDCCH enhanced Physical Downlink Control Channel

eNB eNodeB

FDD Frequency Division Duplex

FS Frame Structure

GP Guard Period

HARQ Hybrid Automatic Repeat Request

LTE Long Term Evolution

M2M Machine to Machine

MAC Medium Access Control

MCS Modulation and Coding Scheme

MIMO Multi-Input Multi-Output

MTC Machine Type Communication

NAK Negative Acknowledgement NR New Radio

OFDM Orthogonal Frequency Division Multiplex

PDCCH Physical Downlink Control Channel

PDSCH Physical Downlink Shared Channel

PMI Precoding Matrix Indicator

PRB Physical Resource Block

PUCCH Physical Uplink Control Channel

PUSCH Physical Uplink Shared Channel

RAN Radio Access Network

RAT Radio Access Technology

RB Resource Block

RBS Radio Base Station

RE Resource Element

RI Rank Index

RNC Radio Network Controller

RRC Radio Resource Control

RRH Remote Radio Head

RRU Remote Radio Unit

RS Reference Signal

SC-FDMA Single Carrier- Frequency Division Multiple Access sPDCCH short Physical Downlink Control Channel sPDSCH short Physical Downlink Shared Channel sPUSCH short Physical Uplink Shared Channel

SF SubFrame

sTTI Shortened TTI

TDD Time Division Duplex

TTI Transmission Time Interval

UCI Uplink Control Information

UE User Equipment

UL Uplink

UL-SCH Uplink Shared Channel

UTRAN Universal Terrestrial Radio Access Network

WAN Wireless Access Network

Claims

CLAIMS:

1. A method in a network node, the method comprising:

determining (812) a short transmission time interval (sTTI) monitoring cycle for a short physical downlink control channel (sPDCCH); and

communicating (814) the sPDCCH sTTI monitoring cycle to a wireless device.

2. The method of Claim 1, wherein the sPDCCH sTTI monitoring cycle comprises an on-off monitoring pattern at a modulation symbol granularity.

3. The method of Claim 1, wherein the sPDCCH sTTI monitoring cycle comprises a number of sPDCCH to monitor per cycle.

4. The method of any of Claims 1-3, wherein the sPDCCH sTTI monitoring cycle applies during an ON duration of a one millisecond transmission time interval (TTI) discontinuous reception (DRX) cycle.

5. The method of any of Claims 1-4, wherein the sPDCCH sTTI monitoring cycle does not apply during an OFF duration of a one millisecond TTI DRX cycle.

6. The method of any of Claims 1-5, wherein the sPDCCH sTTI monitoring cycle is activated via a media access control (MAC) control element (CE).

7. The method of any of Claims 1-5, wherein the sPDCCH sTTI monitoring cycle is activated automatically to coincide with an ON duration of a one millisecond TTI DRX cycle.

8. The method of any of Claims 1-5, wherein the sPDCCH sTTI monitoring cycle is activated automatically upon switching from using sTTI grants to using one millisecond TTI grants.

9. The method of any of Claims 1-5, wherein the sPDCCH sTTI monitoring cycle is deactivated via a MAC CE.

10. The method of any of Claims 1-5, wherein the sPDCCH sTTI monitoring cycle is deactivated automatically to coincide with an OFF duration of a one millisecond TTI DRX cycle.

11. The method of any of Claims 1-5, wherein the sPDCCH sTTI monitoring cycle is deactivated automatically when switching from using one millisecond TTI grants to using sTTI grants.

12. The method of any of Claims 1-11, wherein the sPDCCH sTTI monitoring cycle comprises a sTTI discontinuous reception (DRX) cycle.

13. A network node (120) comprising processing circuitry (1120), the processing circuitry operable to:

determine a short transmission time interval (sTTI) monitoring cycle for a short physical downlink control channel (sPDCCH); and

communicate the sPDCCH sTTI monitoring cycle to a wireless device (110).

14. The network node of Claim 13, wherein the sPDCCH sTTI monitoring cycle comprises an on-off monitoring pattern at a modulation symbol granularity.

15. The network node of Claim 13, wherein the sPDCCH sTTI monitoring cycle comprises a number of sPDCCH to monitor per cycle.

16. The network node of any of Claims 13-15, wherein the sPDCCH sTTI monitoring cycle applies during an ON duration of a one millisecond transmission time interval (TTI) discontinuous reception (DRX) cycle.

17. The network node of any of Claims 13-16, wherein the sPDCCH sTTI monitoring cycle does not apply during an OFF duration of a one millisecond TTI DRX cycle.

18. The network node of any of Claims 13-17, wherein the sPDCCH sTTI monitoring cycle is activated via a media access control (MAC) control element (CE).

19. The network node of any of Claims 13-17, wherein the sPDCCH sTTI monitoring cycle is activated automatically to coincide with an ON duration of a one millisecond TTI DRX cycle.

20. The network node of any of Claims 13-17, wherein the sPDCCH sTTI monitoring cycle is activated automatically upon switching from using sTTI grants to using one millisecond TTI grants.

21. The network node of any of Claims 13-17, wherein the sPDCCH sTTI monitoring cycle is deactivated via a MAC CE.

22. The network node of any of Claims 13-17, wherein the sPDCCH sTTI monitoring cycle is deactivated automatically to coincide with an OFF duration of a one millisecond TTI DRX cycle.

23. The network node of any of Claims 13-17, wherein the sPDCCH sTTI monitoring cycle is deactivated automatically when switching from using one millisecond TTI grants to using sTTI grants.

24. The network node of any of Claims 13-23, wherein the sPDCCH sTTI monitoring cycle comprises a sTTI discontinuous reception (DRX) cycle.

25. A method in a wireless device, the method comprising:

receiving (912) a configuration for a short transmission time interval (sTTI) monitoring cycle for a short physical downlink control channel (sPDCCH); and

monitoring (914) a received wireless signal for sPDCCH according to the received sPDCCH sTTI monitoring cycle.

26. The method of Claim 25, wherein the sPDCCH sTTI monitoring cycle comprises an on-off monitoring pattern at a modulation symbol granularity.

27. The method of Claim 25, wherein the sPDCCH sTTI monitoring cycle comprises a number of sPDCCH to monitor per cycle.

28. The method of any of Claims 25-27, wherein the sPDCCH sTTI monitoring cycle applies during an ON duration of a one millisecond transmission time interval (TTI) discontinuous reception (DRX) cycle.

29. The method of any of Claims 25-28, wherein the sPDCCH sTTI monitoring cycle does not apply during an OFF duration of a one millisecond TTI DRX cycle.

30. The method of any of Claims 25-29, wherein the sPDCCH sTTI monitoring cycle is activated via a media access control (MAC) control element (CE).

31. The method of any of Claims 25-29, wherein the sPDCCH sTTI monitoring cycle is activated automatically to coincide with an ON duration of a one millisecond TTI DRX cycle.

32. The method of any of Claims 25-29, wherein the sPDCCH sTTI monitoring cycle is activated automatically upon switching from using sTTI grants to using one millisecond TTI grants.

33. The method of any of Claims 25-29, wherein the sPDCCH sTTI monitoring cycle is deactivated via a MAC CE.

34. The method of any of Claims 25-29, wherein the sPDCCH sTTI monitoring cycle is deactivated automatically to coincide with an OFF duration of a one millisecond TTI DRX cycle.

35. The method of any of Claims 25-29, wherein the sPDCCH sTTI monitoring cycle is deactivated automatically when switching from using one millisecond TTI grants to using sTTI grants.

36. The method of any of Claims 25-35, wherein the sPDCCH sTTI monitoring cycle comprises a sTTI discontinuous reception (DRX) cycle.

37. A wireless device (110) comprising processing circuitry (1020), the processing circuitry operable to:

receive a configuration for a short transmission time interval (sTTI) monitoring cycle for a short physical downlink control channel (sPDCCH); and

monitor a received wireless signal for sPDCCH according to the received sPDCCH sTTI monitoring cycle.

38. The wireless device of Claim 37, wherein the sPDCCH sTTI monitoring cycle comprises an on-off monitoring pattern at a modulation symbol granularity.

39. The wireless device of Claim 37, wherein the sPDCCH sTTI monitoring cycle comprises a number of sPDCCH to monitor per cycle.

40. The wireless device of any of Claims 37-39, wherein the sPDCCH sTTI monitoring cycle applies during an ON duration of a one millisecond transmission time interval (TTI) discontinuous reception (DRX) cycle.

41. The wireless device of any of Claims 37-40, wherein the sPDCCH sTTI monitoring cycle does not apply during an OFF duration of a one millisecond TTI DRX cycle.

42. The wireless device of any of Claims 37-41, wherein the sPDCCH sTTI monitoring cycle is activated via a media access control (MAC) control element (CE).

43. The wireless device of any of Claims 37-41, wherein the sPDCCH sTTI monitoring cycle is activated automatically to coincide with an ON duration of a one millisecond TTI DRX cycle.

44. The wireless device of any of Claims 37-41, wherein the sPDCCH sTTI monitoring cycle is activated automatically upon switching from using sTTI grants to using one millisecond TTI grants.

45. The wireless device of any of Claims 37-41, wherein the sPDCCH sTTI monitoring cycle is deactivated via a MAC CE.

46. The wireless device of any of Claims 37-41, wherein the sPDCCH sTTI monitoring cycle is deactivated automatically to coincide with an OFF duration of a one millisecond TTI DRX cycle.

47. The wireless device of any of Claims 37-41, wherein the sPDCCH sTTI monitoring cycle is deactivated automatically when switching from using one millisecond TTI grants to using sTTI grants.

48. The wireless device of any of Claims 37-47, wherein the sPDCCH sTTI monitoring cycle comprises a sTTI discontinuous reception (DRX) cycle.

49. A network node (120) comprising a determining module (1150) and a communicating module (1152);

the determining module operable to determine a short transmission time interval (sTTI) monitoring cycle for a short physical downlink control channel (sPDCCH); and

the communicating module operable to communicate the sPDCCH sTTI monitoring cycle to a wireless device (110).

50. A wireless device (110) comprising a receiving module (1050) and a monitoring module (1052);

the receiving module operable to receive a configuration for a short transmission time interval (sTTI) monitoring cycle for a short physical downlink control channel (sPDCCH); and

the monitoring module operable to monitor a received wireless signal for sPDCCH according to the received sPDCCH sTTI monitoring cycle.