Patent Description:
In a typical wireless communication network, a user equipment, UE, communicates with a base station serving the UE. Communication from the base station to the UE is referred to as downlink, DL communication, whereas communication from the UE to the base station is referred to as uplink, UL communication. Thus, the UE involves in bidirectional radio communication with the base station.

In some networks, communications between the base stations and the UE is subject to interference, resulting in loss of data during communication. A technique referred to as Hybrid Automatic Repeat Request, HARQ, is therefore sometimes employed. A HARQ protocol is used between the base station and UE as specified in the third-generation partnership project, 3GPP, technical specification, TS <NUM>. The purpose of the HARQ protocol is to recover from data decoding failures in both directions by sending feedback which includes either an acknowledgement, ACK, or negative acknowledgement, NACK, from a receiver, i.e., UE to a transmitting side, i.e., base station, allowing for retransmission.

There are several types of HARQ systems. In some HARQ systems, retransmission includes error correction and detection information, but no data retransmission. In other types of HARQ systems, a retransmission includes retransmission of data.

Further, a Radio Link Control, RLC, protocol is used for error correction of delivered data (i.e., PDU). In new radio, NR, systems, RLC is located on top of the Medium Access Control, MAC, layer, which the HARQ procedures are a part of. As such, an RLC retransmission is a tool used when the HARQ protocol fails to deliver the PDU. For each RLC PDU sent from base station to UE, an RLC ACK/NACK is expected to be returned. If such a PDU is lost, the UE can detect this using the sequence numbering, and send an RLC NACK after a certain amount of time.

<FIG> illustrates a schematic diagram of channels for a DL transmission when used with analogue beamforming, where slot n, slot n+<NUM> to slot n+<NUM> are shown. The slot n represents a DL slot where the UE when decoding the PDCCH <NUM> receives DL data in PDSCH <NUM> and the UE reports feedback of the decoded result (ACK or NACK) in PUCCH <NUM>. Reference numeral <NUM> indicates that the PDCCH contains a field representing where a PDSCH <NUM> data is received and in <NUM> the PDCCH contains a second field controlling when PUCCH <NUM> is transmitted to the base station.

The numerals <NUM>, <NUM>, <NUM> and <NUM> in the slots n through n+<NUM> represent DL slots and n+<NUM> represents UL slots. The configuration and positioning of DL and UL slots is decided by the base station and need not be determined in advance. However, the position of the possible PDCCH occasions (at the start of slots n through n+<NUM>) are configured by the base station in advance. The UE need to continuously attempt to decode every possible PDCCH.

For any transport block sent over PDSCH, there exists one bit representing the feedback-ACK or NACK which is included in the PUCCH (as indicated by the PDCCH). When the base station attempts to decode the PUCCH, there are three possibilities which can include the following options a) PUCCH is correctly decoded and the feedback bit indicates ACK b) PUCCH is correctly decoded and the feedback bit indicates NACK, or c) the base station fails to decode the PUCCH.

Option 'c' can occur due to interference or a weak UE signal at the time of the PUCCH, or alternatively because the UE did not send the PUCCH at all. Such a "missing PUCCH" may in turn occur because the UE failed to decode the original PDCCH, in which case the UE has not received the corresponding PDSCH.

As stated above, the purpose of the HARQ protocol is to recover from data decoding failures in both directions by sending feedback (ACK/NACK) from receiver to transmitting side allowing for retransmission. In the HARQ protocol, a new data indicator, NDI, is provided. The NDI is toggled, from a previous value when new data is handled by the HARQ process. The toggling of the NDI refers to a scenario when previous received NDI for single HARQ process is either '<NUM>' and new NDI is decoded as '<NUM>' or vice versa.

When there is a HARQ retransmission, NDI is retained to its previous value. The NDI indicates the UE that the UE is prepared to receive a PDSCH transmission with new data for the single HARQ process ID, when the NDI is toggled. If the NDI is not toggled, then the UE is prepared to receive a PDSCH retransmission for the single HARQ process ID, which means that the base station sends the same data as in the preceding transmission(s) belonging to the HARQ process, to help the UE decode the data even if the UE has not succeeded in decoding those previous transmissions.

During certain time periods, the UE operates in a Continuous Mode Discontinuous Reception, C-DRX, which is a mode of UE configuration where the UE refrains from decoding the PDCCH as described above in <FIG>. The purpose of the C-DRX mode is to allow the UE to reduce power consumption by creating a pattern of "sleep" periods when there is no application data to receive or transmit to and from the base station. The C-DRX configuration includes a C-DRX Inactivity timer, which is a timer running from <NUM> to a fixed time period. When the UE receives a PDCCH indicating a planned PDSCH or PUSCH containing new data, indicated by a toggled NDI, the C-DRX Inactivity timer is reset to <NUM>. If the C-DRX Inactivity timer ever runs out, i.e., if the maximum configured time interval is reached without the base station initiating any new data, then the UE enters an inactive state (i.e., the "sleep" period).

Further, in NR systems, each UE is connected to an evolved Node Base station, eNB, (in LTE) and a gNB simultaneously. Consequently, the UE can be configured to perform measurements necessary for the eNB connection in a regular pattern. Furthermore, during such a measurement occasion, the UE shall not be able to send or receive anything to/from the gNB. To the gNB, this appears as a measurement gap during which the UE is completely unreachable.

During the instances, where the UE is operating in C-DRX mode and the UE being configured with the measurement gap, the base station and the UE performs various steps for HARQ retransmission as described in <FIG>. The UE is configured with a C-DRX inactivity timer with a time interval set to <NUM> and the measurement gap for the UE is set to <NUM>.

Initially, at time t=<NUM> a new data transmission (indicated as #<NUM>) is initiated by the base station i.e., gNB, and PDCCH is signaled to the UE. This transmission consists of a MAC PDU which contains one or more RLC PDUs. The NDI for transmission #<NUM> was set to "<NUM>". When the UE receives the PDCCH, the C-DRX Inactivity timer is reset <NUM> and the C-DRX Inactivity timer runs out at t=<NUM>, unless reset <NUM> again. When the gNB decodes <NUM> the corresponding PUCCH, the feedback for transmission #<NUM> is NACK.

At time interval i.e., t=<NUM>, the measurement gap starts <NUM>. The gNB cannot send <NUM> anything to the UE until t=<NUM>. At t=<NUM>, the gNB has the option to send <NUM> a transmission #<NUM> to the UE. Since transmission #<NUM> was marked as NACK, the typical procedure is to perform a HARQ retransmission, which means sending the same data and using NDI=<NUM>, i.e., the NDI not toggled.

However, sending the same data by a HARQ retransmission without toggling the NDI shall not reset the C-DRX Inactivity timer. In the time between t=<NUM> and t=<NUM>, the gNB has a limited number of chances to transmit to the UE. If there are other connected UEs, and fairness between UEs is deemed desirable, it is likely that the UE only has one single attempt. To prevent the C-DRX Inactivity timer from elapsing, the gNB needs to send a transmission with a toggled NDI, indicating new data -which starts a second HARQ process in parallel to the first HARQ process, or causing the UE to discard the contents, losing transmission #<NUM>.

Thus, when the UE is operating in C-DRX mode with configured C-DRX inactivity timer and with configured measurement gap, the gNB has to decide for a trade-off i.e., to a) complete ongoing transmissions early and <NUM>) stop the UE from entering C-DRX inactive mode.

Consequently, there is a need of a new mechanism for handling downlink, DL and UL, HARQ retransmissions when the UE is operating in the C-DRX mode with a configured measurement gap.

Prior art document <CIT> discloses a method for handling interactions between measurement gap, automated repeat request, discontinuous reception and discontinuous transmission in wireless communications concerning real-time data and non-real time data in both an uplink and a downlink. Various alternatives for handling HARQ/Measurement gap interactions are provided.

Prior art document <CIT> shows a method that in the event that a user device is unable to make or receive a retransmission at a first predetermined opportunity because of a measurement period, ensure that the user device is out of an energy-saving mode in order to monitor a control channel for control information for the retransmission at a further predetermined opportunity after the end of the measurement period.

It is therefore an object of the present disclosure to provide a method, a base station, and a user equipment, UE, for handling HARQ transmissions that seek to mitigate, alleviate, or eliminate all or at least some of the above-discussed drawbacks of presently known solutions.

This and other objects are achieved by means of a method, a base station, and the UE as defined in the appended claims. The term exemplary is in the present context to be understood as serving as an instance, example or illustration.

According to a first aspect of the present disclosure, a method for handling downlink, DL, hybrid automatic repeat request, HARQ, transmissions for a user equipment, UE, operating in a connected discontinuous reception, C-DRX, mode is provided according to appended claim <NUM>.

According to a second aspect of the present disclosure, a method for handling uplink, UL, hybrid automatic repeat request, HARQ, transmissions from a user equipment, UE operating in a connected discontinuous reception, C-DRX, mode, is provided according to appended claim <NUM>.

According to a third aspect of the present disclosure, there is provided a method for handling uplink, UL HARQ transmissions to a base station, performed by a UE operating in a C-DRX mode, is provided according to appended claim <NUM>.

According to a fourth aspect of the present disclosure, there is provided a base station for handling downlink, DL hybrid automatic repeat request, HARQ, transmissions for a user equipment, UE, operating in a connected discontinuous reception, C-DRX, mode, according to appended claim <NUM>.

According to a fifth aspect of the present disclosure, there is provided a base station for handling uplink, UL hybrid automatic repeat request, HARQ, transmissions for a user equipment, UE, operating in a connected discontinuous reception, C-DRX, mode, according to appended claim <NUM>.

According to a sixth aspect of the present disclosure, there is provided a user equipment, UE, for handling uplink, UL, hybrid automatic repeat request, HARQ, transmissions, according to appended claim <NUM>.

An advantage of some embodiments is that alternative and/or improved approaches for handling downlink and uplink HARQ transmissions during C-DRX mode are provided.

An advantage of some embodiments is that the proposed method allows toggling the value of the NDI to restart the C-DRX inactivity timer, since the usage the same value of the NDI shall not restart the C-DRX-inactivity timer, and there may be a chance of the timer elapsing before any other UL transmission takes place.

In some embodiments, the proposed method allows toggling the value of the NDI on DL and UL HARQ retransmissions when a measurement gap has occurred between the previous transmission attempt and a new transmission attempt from the base station and the UE.

An advantage of some embodiments is that latency is reduced by toggling the value of the NDI to restart the C-DRX inactivity timer. It should be noted that, for real time critical applications, latency is vital. Thus, by toggling the value of NDI, the chances of entering the C-DRX inactive state, causing a long latency can be avoided. In some cases, retransmitting a MAC PDU which has already been received, costs far less in terms of latency for applications involving huge data traffic.

An advantage of some embodiments is that the proposed method allows for configuration of a C-DRX inactivity timer to a lower value, i.e., for example, the C-DRX inactivity timer may be configured with a time interval of <NUM> milli-seconds, ms, since the chance of the UE entering into the undesirable state is mitigated. A shorter C-DRX inactivity timer generally leads to reduced power consumption by the UE.

An advantage of some embodiments is that when the UE has an ongoing DL HARQ process but, due to a measurement gap, the C-DRX inactivity timer is about to expire. In such scenario, the base station i.e., gNB initiates a transmission on the same HARQ process ID, indicating to the UE that this transmission contains new data, while re-sending the same MAC PDU. This avoids losing the MAC PDU, while still preventing the UE from entering into the C-DRX inactive state.

An advantage of some embodiments is that when the UE has an ongoing UL HARQ process but, due to a measurement gap, the C-DRX inactivity timer is about to expire. In such scenario, the base station i.e., gNB initiates a transmission on the same HARQ process ID, indicating to the UE that this transmission contains new data, in order to prevent the UE from entering into the C-DRX inactive state.

An advantage of some embodiments is that when the UE is requested to start a new transmission on a previously used HARQ process ID shortly after a measurement gap as mentioned above, the UE shall re-send the same MAC PDU. This avoids losing the MAC PDU.

Aspects of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings. The apparatus and method disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein.

The terminology used herein is for the purpose of describing particular aspects of the disclosure only and is not intended to limit the invention. It should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps, or components, but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof.

It will be appreciated that when the present disclosure is described in terms of a method, it may also be embodied in one or more processors and one or more memories coupled to the one or more processors, wherein the one or more memories store one or more programs that perform the steps, services and functions disclosed herein when executed by the one or more processors.

In the following description of exemplary embodiments, the same reference numerals denote the same or similar components. Throughout the description, the terms base station and gNB are used interchangeably.

The following aspects have been presented herein for better understanding of various embodiments of the present disclosure.

The UE is connected to both eNB and gNB. The UE is configured with C-DRX on gNB. The UE is a New Radio, NR, capable UE, i.e., NR-UE. Further, the UE is configured to have LTE measurement gaps in its connection to gNB, and gNB is aware of the configured measurement gap such that gNB can take into account exactly when a measurement gap starts and ends.

The new data indicator, NDI flag according to 3GPP TS <NUM> is used by a base station i.e., either Node B or eNodeB as an indication for the UE. According to the existing 3GPP specification, the conditions for operating the NDI are specified herein:.

<FIG> is a flowchart illustrating example method steps for handling downlink, DL HARQ transmission according to some embodiments. A base station, i.e., a gNB implements various steps in method <NUM> for handling DL HARQ transmission as described herein. At step <NUM>, the method <NUM> comprises determining whether new information is available for DL transmission to a UE. If the base station determines that there is no new information available for DL transmission to the UE, then the base station continues to determine availability of new information for DL transmission to the UE.

If the base station determines that there exists new information for DL transmission to the UE <NUM>, then at step <NUM>, the method <NUM> comprises performing a first HARQ transmission related to a single HARQ process to the UE. For example, the first HARQ transmission comprises information related to the single HARQ process with an associated new data indicator, NDI. The NDI is a binary value which can be either "<NUM>" or "<NUM>". The NDI may be initialized to a value i.e., either "<NUM>" or "<NUM>" for performing the first HARQ transmission to the UE. The base station toggles the value of the NDI i.e., from either "<NUM>" to <NUM>" or from "<NUM>" to "<NUM>" to indicate a change of information of the single HARQ process over a previous HARQ transmission. In an example, if the base station initializes NDI to "<NUM>" for a first HARQ transmission, the base station toggles the NDI to "<NUM>" for a second HARQ transmission to indicate to the UE that the second HARQ transmission includes new information. Thus, the toggling of the NDI indicates a change of information of the single HARQ process over the previous HARQ transmission.

At step <NUM>, the method <NUM> comprises starting a C-DRX inactivity timer. In an example, the first HARQ transmission to the UE triggers an initiation or start of C-DRX inactivity timer at the UE and the base station. The C-DRX inactivity timer starts from a time interval "<NUM>" to a pre-configured timer interval i.e., <NUM> milli-seconds, ms. Thus, the time interval between the start and the expiry of the C-DRX inactivity timer is eight ms. In some examples, the time interval between start and the expiry of the C-DRX inactivity timer may be less than ten ms. In some examples, a difference between the time interval between the start and the expiry of the C-DRX inactivity timer and a time interval of the measurement gap is minimum.

When the C-DRX inactivity timer is running, at step <NUM>, the method <NUM> comprises determining whether a HARQ NACK is received in PUCCH. The base station <NUM> determines whether a HARQ NACK is received in PUCCH for the first HARQ transmission from the UE. If the base station determines that there is no HARQ NACK received in PUCCH for the first HARQ transmission, then the base station determines that the first HARQ transmission to the UE is successful and the method <NUM> loops back to the step <NUM> for determining if there is any new information for DL transmission to the UE.

At step <NUM>, if the base station determines that the HARQ NACK is received, then at step <NUM>, the method <NUM> comprises detecting whether the measurement gap has started. In an example, the measurement gap is pre-configured to the UE by the base station and the configured measurement gap may be <NUM>. During the measurement gap period i.e., <NUM>, the UE is not reachable for the base station to perform for any data transmission and the UE performs measurement of neighbouring cells during the measurement gap period.

When it is determined that the measurement gap has started, at step <NUM>, the method <NUM> comprises awaiting an end of the measurement gap. The measurement gap ends after the time interval of <NUM>. After the end of the measurement gap, at step <NUM>, the method <NUM> comprises determining whether the C-DRX inactivity timer has expired at a time where the measurement gap has ended. In an example, the C-DRX inactivity timer expires only after the end of the measurement gap, as the configured time interval i.e., <NUM>, of the C-DRX inactivity timer is greater than the configured measurement gap i.e., <NUM>. In some examples, the C-DRX inactivity timer is configured to expire in a pre-determined time interval after ending of the measurement gap. Thus, when the measurement gap is configured to be <NUM>, the C-DRX timer expires after the pre-determined time interval, which is <NUM>, in the above example. Therefore, it should be noted that the C-DRX inactivity timer is configured to expire in a shorter duration after ending of the measurement gap.

At step <NUM>, if it is determined that the C-DRX inactivity timer has not expired, then at step <NUM>, the method <NUM> comprises performing a second HARQ transmission which is a retransmission of the information, with associated NDI to the UE for the single HARQ process. The second HARQ transmission is a retransmission of the information transmitted in the first HARQtransmission. In the second HARQ transmission, value of the NDI is toggled in relation to a value of the NDI of the first HARQ transmission. Thus, the base station toggles the NDI for the second HARQ transmission though the second HARQ transmission is a retransmission of the information transmitted in the first HARQ transmission. The toggling of the NDI for the second HARQ transmission when the C-DRX inactivity timer has not expired, i.e., before the expiry of the C-DRX inactivity timer, resets or restarts the C-DRX inactivity timer, which may otherwise cause the C-DRX inactivity timer to expire, thereby allowing the UE to enter into sleep mode. Therefore, the base station performs second HARQ transmission by toggling the NDI to indicate the retransmission of the information as a new information to the UE, to reset or restart the C-DRX inactivity timer.

If at step <NUM>, it is determined that the C-DRX inactivity timer is expired after the ending of the measurement gap, then the method <NUM> loops back to the step <NUM> to determine the availability of new information for DL transmission to the UE.

Further, at step <NUM>, if it is detected that the measurement gap has not started, then at step <NUM>, the method <NUM> comprises determining whether the C-DRX inactivity timer has expired. If the C-DRX timer has not expired, then at step <NUM>, the method comprises performing a second HARQ transmission with same NDI. The second HARQ transmission is a retransmission of the information transmitted in the first HARQ transmission. The value of the NDI is not toggled for the second HARQ transmission. Thus, the base station <NUM> performs the second HARQ transmission with the same NDI for the second HARQ transmission. At step <NUM>, if it is determined that the C-DRX inactivity timer has expired then the method <NUM> loops back to the step <NUM> to determine the availability of new information for DL transmission to the UE.

It should be noted that a person skilled in the art may understand that the base station performs the second HARQ transmission, which is a retransmission of same information, thereby increasing the risk that the base station i.e., gNB transmits a MAC SDU which has already been successfully received by the UE and has been delivered to higher layers. Specifically, there is a possibility that transmission #<NUM> (<NUM>) was successful and decoded correctly by the UE, and that the PUCCH feedback (<NUM>) was corrupt due to interference or noise. In such a scenario, transmission #<NUM> (<NUM>) includes a second copy of the same MAC PDU. In such a case, for example, the RLC PDU contained inside the MAC PDU shall, according to the RLC protocol, be identified as duplicate and can be discarded.

It should be further noted that if incremental redundancy is being used, at step <NUM>, the incremental redundancy shall be reinitialized similar to that of new HARQ data transmissions.

<FIG> is an example schematic diagram showing various steps between a base station <NUM> and a UE for DL HARQ transmission according to the flow chart described in <FIG>. When the UE <NUM> is operating in C-DRX mode and is configured with a measurement gap which overlaps with the time interval of the C-DRX inactivity timer, the base station <NUM> and the UE <NUM> performs various steps for DL HARQ retransmission as described herein. The UE <NUM> is configured with a C-DRX inactivity timer with a time interval of <NUM> and the measurement gap for the UE is <NUM>.

Initially, at time t=<NUM>, a new data transmission (indicated as #<NUM>) is initiated by the base station i.e., gNB <NUM>, and the PDCCH is signalled <NUM> to the UE <NUM>. This transmission consists of a MAC PDU which contains one or more RLC PDUs. The NDI for transmission #<NUM> was set to "<NUM>". When the UE receives the PDCCH, the C-DRX Inactivity timer starts <NUM> and the C-DRX Inactivity timer runs out at t=<NUM> unless reset again. When the gNB <NUM> decodes the corresponding PUCCH <NUM>, the feedback for transmission #<NUM> is NACK <NUM>.

At time instance i.e., t=<NUM>, the measurement gap starts <NUM>. The gNB <NUM> cannot send <NUM> anything to the UE until t=<NUM>. At t=<NUM>, the gNB <NUM> performs data transmission indicated as transmission #<NUM> to the UE <NUM>. Since transmission #<NUM> was marked as NACK, the gNB <NUM> performs a HARQ transmission <NUM>, indicated as transmission #<NUM> to the UE <NUM>. Thus, the gNB <NUM> performs a HARQ transmission, which is a retransmission of the same information transmitted in the transmission #<NUM> with the toggled NDI, i.e., the value of the NDI is toggled to "<NUM>".

The gNB <NUM> transmits the same data by a HARQ retransmission with toggled NDI to indicate the UE that the HARQ retransmission is new information so as to restart the C-DRX inactivity timer. In response to reception of the HARQ retransmission from the gNB <NUM>, the C-DRX Inactivity timer is reset <NUM>.

<FIG> is a flowchart illustrating example method steps for handling uplink, UL, HARQ transmission according to some embodiments. A base station, i.e., gNB performs various steps in method <NUM> for handling UL HARQ transmission as described herein. At step <NUM>, the method comprises determining whether new information is available at the UE for UL transmission to the base station. If the base station determines that there is no new information available for UL transmission, then the base station continues to determining if there is any new information for UL transmission from the UE.

If the base station <NUM> determines that there exists new information for UL transmission from the UE, then at step <NUM>, the method comprises transmitting a request for a first HARQ transmission related to a single HARQ process with an associated NDI to the UE. The base station toggles the value of the NDI to indicate a change of information of the single HARQ process over a previous HARQ transmission.

At step <NUM>, the method <NUM> comprises receiving a first HARQ transmission from the UE.

Upon reception of the first HARQ transmission, at step <NUM>, the method <NUM> comprises starting a C-DRX inactivity timer. In an example, the first HARQ transmission to the UE triggers an initiation or start of C-DRX inactivity timer at the UE and the base station. The C-DRX inactivity timer starts from a time interval "<NUM>"ms to a pre-configured timer interval i.e., <NUM>.

At step <NUM>, the method <NUM> comprises determining whether a HARQ NACK is received in PUCCH. If the base station <NUM> determines that there is no HARQ NACK received in PUCCH for the first HARQ transmission, then the base station determines that the first HARQ transmission to the UE is successful and the method <NUM> loops back to the step <NUM> for determining if there is any new information for UL transmission from the UE.

If the base station determines that the HARQ NACK is received, then at step <NUM>, the method <NUM> comprises detecting whether the measurement gap has started. When it is detected that the measurement gap has started, then at step <NUM>, the method <NUM> comprises awaiting end of the measurement gap. The measurement gap ends after the time interval of <NUM>. After the end of the measurement gap, at step <NUM>, the method <NUM> comprises determining whether the C-DRX inactivity timer has expired at a time where the measurement gap has ended.

If at step <NUM>, it is determined that the C-DRX inactivity timer has not expired, then at step <NUM>, the method <NUM> comprises transmitting a request for second HARQ transmission with toggled NDI. The request for second HARQ transmission is a request for retransmission of the information transmitted in the first HARQ transmission.

When the UE receives the request for second HARQ transmission with toggled NDI, the UE transmits the second HARQ transmission which is a retransmission of information of the first HARQ transmission as in step <NUM>. At step <NUM>, the method <NUM> comprises receiving the second HARQ transmission. Thus, it should be noted that the base station receives a retransmission of the same information during the second HARQ transmission even though the NDI is toggled, to allow the UE to perform a new transmission.

If at step <NUM>, it is determined that the C-DRX inactivity timer is expired after the ending of the measurement gap, then the method <NUM> loops back to the step <NUM> to determine the availability of new information for UL transmission from the UE.

Further, at step <NUM>, if it is determined that the measurement gap has not started, then at step <NUM>, the method <NUM> comprises determining whether the C-DRX inactivity timer has expired. If the C-DRX timer has not expired, then at step <NUM>, the method comprises transmitting a request for a second HARQ transmission with same NDI. The request for the second HARQ transmission is for retransmission of the information transmitted in the first HARQ transmission.

At step <NUM>, the method <NUM> comprises receiving a second HARQ transmission. The second HARQ transmission is a retransmission of information of the first HARQ transmission.

At step <NUM>, if it is determined that the C-DRX inactivity timer has expired, then the method <NUM> loops back to the step <NUM> to determine the availability of new information for UL transmission from the UE.

It should be noted that a person skilled in the art may understand that the base station performs the second HARQ transmission, which is a retransmission of same information, thereby increasing the risk that the UE transmits a MAC SDU which has already been successfully received by the gNB and has been delivered to higher layers. Specifically, there is a possibility that transmission #<NUM> (<NUM>) was successful and decoded correctly by the gNB, so that the toggled NDI for transmission #<NUM> (<NUM>) actually indicates a request for new data. In such a scenario, transmission #<NUM> will include a second copy of the same MAC PDU. In such a case, for example the RLC PDU contained inside the MAC PDU shall, according to the RLC protocol, be identified as duplicate and discarded.

It should be further noted that if incremental redundancy is being used, at steps <NUM> and <NUM> (in <FIG>), the incremental redundancy shall be reinitialized similar to that of new HARQ data transmissions.

<FIG> is an example schematic diagram showing various steps between a base station <NUM> and a UE <NUM> for UL HARQ transmission according to the flow chart described in <FIG>. When the UE <NUM> is operating in C-DRX mode and is configured with a measurement gap which overlaps with the time interval of the C-DRX inactivity timer, the base station <NUM> and the UE <NUM> performs various steps for UL HARQ retransmission as described herein.

Initially, at time t=<NUM>, the base station i.e., gNB <NUM> initiates a transmission of a request (indicated as #<NUM>) for the first HARQ transmission and the PDCCH is signalled <NUM> to the UE <NUM>. The request for the first transmission is related to a single HARQ process and the request is transmitted along with an NDI. For example, the value of the NDI is set to "<NUM>". When the UE receives <NUM> the PDCCH, the C-DRX Inactivity timer starts <NUM> and the C-DRX Inactivity timer expires at t=<NUM> unless the C-DRX inactivity timer is reset. In response to the request from the base station <NUM>, the UE transmits the first UL HARQ transmission to the gNB <NUM>. The gNB <NUM> receives the first UL HARQ transmission from the UE <NUM>. When the gNB <NUM> decodes <NUM> the corresponding PUCCH <NUM>, the feedback for transmission #<NUM> is NACK.

At time interval i.e., t=<NUM>, the measurement gap has started <NUM>. The gNB <NUM> cannot send <NUM> any information to the UE <NUM> until t=<NUM>. After the end <NUM> of the measurement gap, i.e., at t=<NUM>, the gNB <NUM> transmits a request for a second HARQ transmission, indicated as transmission #<NUM> to the UE <NUM>. Since, the transmission #<NUM> was marked as NACK, the gNB <NUM> transmits <NUM> a request for second HARQ transmission, indicated as transmission #<NUM> to the UE <NUM>. Thus, the gNB <NUM> transmits the request for second HARQ transmission, which is a request for retransmission of the same information transmitted by the UE <NUM> in the transmission #<NUM>. The request for the second HARQ transmission is transmitted with the toggled NDI to indicate the UE <NUM> that the request for the second HARQ transmission is for new information, although the request for the second HARQ transmission is for retransmission of same information transmitted by the UE in the transmission #<NUM>. In response to second HARQ transmission from the UE <NUM>, the C-DRX Inactivity timer is reset <NUM>.

<FIG> is a flowchart illustrating example method steps for handling uplink, UL HARQ transmission according to some embodiments. The UE performs various steps in method <NUM> for handling UL HARQ retransmission as described herein. At step <NUM>, the UE receives a request for first HARQ transmission from a base station. In response to the request for first HARQ transmission from the base station, at step <NUM>, the method <NUM> comprises starting a C-DRX inactivity timer. When the C-DRX inactivity timer is running, at step <NUM>, the UE performs the first UL HARQ transmission to the base station. After the first UL HARQ transmission, at step <NUM>, the method <NUM> comprises detecting whether the measurement gap has started.

When it is determined that the measurement gap has started, then at step <NUM>, the method <NUM> comprises awaiting end of the measurement gap. After the end of the measurement gap, at step <NUM>, determining that the C-DRX inactivity timer has not expired at a time where the measurement gap has ended. When it is determined that the C-DRX inactivity timer has not expired, at step <NUM>, the method comprises receiving a request for second HARQ transmission from the base station. At step <NUM>, the method <NUM> comprises determining whether the NDI is toggled in the received request from the base station. If it is determined that the NDI is toggled, then at step <NUM>, the method comprises performing a second HARQ transmission to the base station <NUM>. The UE, during the second HARQ transmission, transmits the same information which it has transmitted to the base station in the first HARQ transmission at step <NUM>. Thus, the UE, at step <NUM>, performs the second HARQ transmission which is a retransmission of the same information that the UE has transmitted to the base station in step <NUM> even though the NDI is toggled, to allow the UE to perform a new transmission. Therefore, it should be noted that the UE performs retransmission of the same information during the second HARQ transmission to the base station, at step <NUM>. In response to the second HARQ transmission to the base station, the C-DRX inactivity timer is restarted.

If at step <NUM>, it is determined that the NDI is not toggled, then at step <NUM>, the method <NUM> comprises performing a retransmission of the same information during the second HARQ transmission. The UE transmits the same information which it has transmitted to the base station in the first HARQ transmission at step <NUM>. Therefore, it should be noted that the UE performs the retransmission of the same information when the NDI is not toggled (i.e., NDI is same in relation to the value of the NDI of the first HARQ transmission).

Further, at step <NUM>, if it is determined that the measurement gap has not started, then at step <NUM>, the method <NUM> comprises determining that the C-DRX inactivity timer has not expired. When it is determined that the C-DRX inactivity timer has not expired, at step <NUM>, the method <NUM> comprises receiving a request for second HARQ transmission. After receiving the request for second HARQ transmission, at step <NUM>, the method comprises determining whether the whether the NDI is toggled in the received request from the base station <NUM>. If it is determined that the NDI is toggled, then at step <NUM>, the method comprises performing a new HARQ transmission to the base station. The UE transmits new information to the base station during the new HARQ transmission at step <NUM>, when the NDI is toggled. Thus, when the NDI is toggled, the toggled NDI indicates the UE for a new information transmission and then the UE transmits new information to the base station. In response to the new HARQ transmission to the base station, the C-DRX inactivity timer is restarted.

In case, at step <NUM>, if it is determined that the NDI is not toggled, then at step <NUM>, the method <NUM> comprises performing a retransmission of the same information during the second HARQ transmission. As described above, the UE transmits the same information which it has transmitted to the base station in the first HARQ transmission at step <NUM>. Therefore, it should be noted that the UE performs the retransmission of the same information when the NDI is not toggled (i.e., NDI is same in relation to the value of the NDI of the first HARQ transmission) during the second HARQ transmission.

<FIG> is a block diagram of a base station showing functional modules for handling DL and UL HARQ transmissions according to the flow charts described in <FIG> and <FIG>. As depicted in <FIG>, the base station <NUM> comprises a scheduler, <NUM>, a plurality of input buffers, <NUM>, <NUM>, storing segments of data streams pertaining to individual UEs, i.e., for example, UEs 30a-30n. For each UE, a HARQ entity <NUM>, <NUM> each comprising a number of HARQ processes for handling simultaneous transmissions to several UEs, that is, for each UE. The base station <NUM> also comprises Layer <NUM> processing means <NUM> for transferring data from respective HARQ processes. The base station <NUM> moreover comprises a UE feedback decoder <NUM> and a Layer <NUM> receiver <NUM>.

Each HARQ process <NUM>, <NUM>, in a given UE is mirrored in the base station <NUM> and corresponds to a given data stream which is received by a particular UE. As explained above, more data streams may be used by the UE simultaneously corresponding to one application or more simultaneous applications running on the UE, possibly with different QoS requirements. Moreover, consecutive data may be transmitted for the same UE, the consecutive transmission belonging to different HARQ processes.

Furthermore, the base station <NUM> comprises one or more input buffer queues dedicated to a corresponding set of HARQ processes.

<FIG> is a block diagram of a UE <NUM> showing functional modules for handling UL HARQ transmissions according to the flow chart described in <FIG>. As depicted in <FIG>, the UE <NUM> includes a HS-SCCH decoding means, i.e., a channel decoder <NUM>, for decoding the downlink HD-PDSCH channel, arrangements comprising a number of HARQ processes <NUM> namely HARQ process <NUM> to HARQ process J, a reordering and queue <NUM>, and a Radio Link Control layer, RLC means, <NUM>. Further, the UE <NUM> is provided with a feedback processing means, <NUM>, and layer <NUM> processing, <NUM>, for providing feedback on the HS-DPCCH channel. Furthermore, buffer means <NUM> are provided for each HARQ process <NUM>. The buffer means <NUM> may be arranged as one resource or buffer means <NUM> may be a plurality of resources or buffers. The buffer means <NUM> may be arranged as a soft memory which is partitioned across the HARQ processes in a semi- static fashion through upper layer signalling.

The reordering and queue, <NUM>, routes the MAC-hs PDU's to the correct reordering buffer based on a Queue ID. The reordering and queue reorders received MAC-hs PDU's according to the received transmit sequence number, TSN. To recover from erroneous conditions when MAC-hs PDU are missing, the same avoidance handling as described in 3GPP TS <NUM> - <NUM>. <NUM>, re-ordering release timer and window-based stall avoidance, is used. There exists one reordering entity for each Queue ID configured at the UE <NUM>.

The RLC layer <NUM> in 3GPP can operate in three modes, transparent mode, unacknowledged mode and acknowledged mode, AM, which are described herein. In AM mode, incorrectly received Protocol Data Units, PDU's discovered by the receiving side are effected to be retransmitted by the transmitting side by means of an Automatic Repeat Request, ARQ, protocol. An AM RLC entity consists of a transmitting side, and a receiving side, where the transmitting side of the AM RLC entity transmits RLC PDU's and the receiving side of the AM RLC entity receives RLC PDU's. An AM RLC entity resides in the UE and in the radio network control, RNC respectively. The transmitting side segments and/or concatenates RLC service data units, SDU's into PDU's of a fixed length. The receiving side reassembles received PDU's into RLC SDU's and transmits these to higher data layers. Likewise, SDU's are received from the layer above the RLC layer. In AM mode, the RLC layer is responsible for the delivery of SDU's in consecutive order.

<FIG> illustrates an example computing environment <NUM> implementing a method, a base station and a user equipment for handling DL and UL HARQ transmissions as described in <FIG>, <FIG> and <FIG>. As depicted in <FIG>, the computing environment <NUM> comprises at least one data processing unit <NUM> that is equipped with a control unit <NUM> and an Arithmetic Logic Unit, ALU <NUM>, a memory <NUM>, a storage <NUM>, plurality of networking devices <NUM> and a plurality Input output, I/O devices <NUM>. The data processing unit <NUM> is responsible for processing the instructions of the algorithm. The data processing unit <NUM> is capable of executing software instructions stored in memory <NUM>. The data processing unit <NUM> receives commands from the control unit <NUM> in order to perform its processing. Further, any logical and arithmetic operations involved in the execution of the instructions are computed with the help of the ALU <NUM>.

The overall computing environment <NUM> can be composed of multiple homogeneous and/or heterogeneous cores, multiple CPUs of different kinds, special media and other accelerators. The data processing unit <NUM> is responsible for processing the instructions of the algorithm. Further, the plurality of data processing units <NUM> may be located on a single chip or over multiple chips.

The algorithm comprising of instructions and codes required for the implementation are stored in either the memory <NUM> or the storage <NUM> or both. At the time of execution, the instructions may be fetched from the corresponding memory <NUM> and/or storage <NUM> and executed by the data processing unit <NUM>.

In case of any hardware implementations various networking devices <NUM> or external I/O devices <NUM> may be connected to the computing environment to support the implementation through the networking devices <NUM> and the I/O devices <NUM>.

The embodiments disclosed herein can be implemented through at least one software program running on at least one hardware device and performing network management functions to control the elements. The elements shown in <FIG> include blocks which can be at least one of a hardware device, or a combination of hardware device and software module.

Access network <NUM> comprises a plurality of base stations 1112a, 1112b, 1112c, such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area 1113a, 1113b, 1113c. Each base station 1112a, 1112b, 112c is connectable to core network <NUM> over a wired or wireless connection <NUM>. A first UE <NUM> located in coverage area 1113c is configured to wirelessly connect to, or be paged by, the corresponding base station 1112c. A second UE <NUM> in coverage area 1113a is wirelessly connectable to the corresponding base station 1112a.

Host computer <NUM> may be under the ownership or control of a service provider or may be operated by the service provider or on behalf of the service provider.

Host computer <NUM> and the connected UEs <NUM>, <NUM> are configured to communicate data and/or signalling via OTT connection <NUM>, using access network <NUM>, core network <NUM>, any intermediate network <NUM> and possible further infrastructure (not shown) as intermediaries.

It's hardware <NUM> may include radio interface <NUM> configured to set up and maintain wireless connection <NUM> with a base station serving a coverage area in which UE <NUM> is currently located. The UE <NUM> further comprises software <NUM>, which is stored in or accessible by UE <NUM> and executable by processing circuitry <NUM>.

It is noted that host computer <NUM>, base station <NUM> and UE <NUM> illustrated in <FIG> may be similar or identical to host computer <NUM>, one of base stations 112a, 1112b, 1112c and one of UEs <NUM>, <NUM> of <FIG>, respectively.

Wireless connection <NUM> between UE <NUM> and base station <NUM> is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to UE <NUM> using OTT connection <NUM>.

Various embodiments described in the present disclosure can be used for reducing latency during delivery of Over-the-Top, OTT, services from the network to the UEs.

Thus, in the above implementation of delivering OTT services to the UEs, the OTT content can be delivered to the UEs by reducing the latency of the content being delivered from the base station to the UE.

It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the scope of the disclosure as defined by the appended claims.

Claim 1:
A method (<NUM>) performed by a base station (<NUM>) for handling downlink, DL, hybrid automatic repeat request, HARQ, transmissions for a user equipment, UE, (<NUM>) operating in a connected discontinuous reception, C-DRX, mode, wherein the method (<NUM>) comprises:
performing (<NUM>) a first HARQ transmission comprising information related to a single HARQ process to the UE (<NUM>) with an associated new data indicator, NDI, wherein a toggling of the NDI indicating at least a change of information of the single HARQ process over a previous HARQ transmission, said first HARQ transmission moreover starting (<NUM>) a C-DRX inactivity timer;
determining that a HARQ negative acknowledgment, NACK has been received (<NUM>), for the transmitted information from the UE (<NUM>);
detecting whether a measurement gap has started (<NUM>) and if the measurement gap has started, awaiting (<NUM>) an end of the measurement gap;
determining whether the C-DRX inactivity timer has expired (<NUM>) at a time where the measurement gap has ended; and
if the C-DRX inactivity timer has not expired, performing (<NUM>) a second HARQ transmission, which is a retransmission of said information, with associated NDI to the UE (<NUM>) for the single HARQ process, wherein a value of the NDI is toggled in relation to a value of the NDI of the first HARQ transmission.