Patent Description:
The 4th Generation mobile communication technology (<NUM>) Long-Term Evolution (LTE) or LTE-Advance (LTE-A) and the 5th Generation mobile communication technology (<NUM>) face more and more demands. As the number of applications and services for digital data continues to explode, the demands and challenges placed on network resources and operators will continue to increase. The utilization of the licensed radio spectrum, or spectrum for short, is already close to a saturation point. In addition, use of the licensed spectrum may come with a licensing cost for operators. For some regions with private network deployments, efficient use of the unlicensed spectrum with wider bandwidth (e.g., <NUM> or <NUM>), may reduce implementation complexity for both networks and terminals (e.g., user equipment or UE), compared to carriers of smaller bandwidth, when moving to address larger amounts of spectrum.

In an unlicensed spectrum, a listen-before-talk (LBT) applying a clear channel assessment (CCA) check is performed before transmitting. The CCA utilizes at least energy detection to determine the presence or absence of other signals on the channel in order to determine if the channel is occupied or clear, respectively. If the channel is occupied, the UE needs to wait for a while to proceed the next LBT. If the channel is clear, the UE can transmit. Due to the opportunity occupation characteristic, the UE may not transmit timely, or may not transmit for a while, or even have no chance to transmit. For unlicensed spectrum, if a transmission cannot be performed at the physical layer, it can impact the processing at the upper layer(s). For example, some procedures will not be terminated.

Thus, existing systems and methods for handling transmission failures in a wireless communication are not entirely satisfactory.

3GPP Draft R2-<NUM> is a related prior art document.

The exemplary embodiments disclosed herein are directed to solving the issues relating to one or more of the problems presented in the prior art, as well as providing additional features that will become readily apparent by reference to the following detailed description when taken in conjunction with the accompany drawings. In accordance with various embodiments, exemplary systems, methods, devices and computer program products are disclosed herein. It is understood, however, that these embodiments are presented by way of example and not limitation, and it will be apparent to those of ordinary skill in the art who read the present disclosure that various modifications to the disclosed embodiments can be made while remaining within the scope of the present disclosure.

<FIG> and their description are not in accordance with all aspects of the invention as defined in the independent claims. They are therefore present for illustration purposes or to highlight specific aspects or features of the claims.

Various exemplary embodiments of the present disclosure are described below with reference to the accompanying figures to enable a person of ordinary skill in the art to make and use the present disclosure. As would be apparent to those of ordinary skill in the art, after reading the present disclosure, various changes or modifications to the examples described herein can be made without departing from the scope of the present disclosure.

A typical wireless communication network includes one or more base stations (typically known as a "BS") that each provides geographical radio coverage, and one or more wireless user equipment devices (typically known as a "UE") that can transmit and receive data within the radio coverage. In the wireless communication network, a BS and a UE can communicate with each other via a communication link, e.g., via a downlink radio frame from the BS to the UE or via an uplink radio frame from the UE to the BS.

A transmission of a UE may be blocked due to some reasons, such as a listen-before-talk (LBT) failure in unlicensed spectrum, a power backoff, and a collision with ultra-reliable low-latency communication (URLLC) service. Once a transmission is blocked at the physical layer, it can affect the processing in the upper layer(s). In order to solve these problems, the present teaching discloses systems and methods for informing a unified indication to the upper layer.

In addition, when a transmission is blocked in the lower layer, the transmission failure indication is informed to the middle layer, that is lower than the upper layer and higher than the lower layer (e.g. physical layer). The failure numbers may be counted in the middle layer. In one embodiment, not being according to the invention as claimed, the transmission failure numbers are counted regardless whether the failures are continuous or discontinuous. In another embodiment, not being according to the invention as claimed, only continuous or consecutive transmission failure numbers are counted. In another embodiment, both a timer and counter are used. When a transmission failure indication is received, the counter is incremented by one, and the timer is started or restarted. When the timer expires, the counter is reset. In one embodiment, when the counter reaches a threshold, the transmission failure problem may be indicated to the upper layer. When the upper layer receives it, it may declare a radio link failure (RLF).

As used herein, the term "layer" refers to an abstraction layer of a layered model, e.g. the open systems interconnection (OSI) model, which partitions a communication system into abstraction layers. A layer serves the next higher layer above it, and is served by the next lower layer below it.

In various embodiments, a BS in the present disclosure can be referred to as a network side and can include, or be implemented as, a next Generation Node B (gNB), an E-UTRAN Node B (eNB), a Transmission/Reception Point (TRP), an Access Point (AP), etc.; while a UE in the present disclosure can be referred to as a terminal and can include, or be implemented as, a mobile station (MS), a station (STA), etc. A BS and a UE may be described herein as nonlimiting examples of "wireless communication nodes," and "wireless communication devices" respectively, which can practice the methods disclosed herein and may be capable of wireless and/or wired communications, in accordance with various embodiments of the present disclosure.

<FIG> illustrates an exemplary communication network <NUM> in which techniques disclosed herein may be implemented, in accordance with an embodiment of the present disclosure. As shown in <FIG>, the exemplary communication network <NUM> includes a base station (BS) <NUM> and a plurality of UEs, UE <NUM><NUM>, UE <NUM><NUM>. UE <NUM><NUM>, where the BS <NUM> can communicate with the UEs according to wireless protocols. The BS <NUM> and a UE, e.g. UE <NUM><NUM>, may communicate with each other either under a licensed spectrum or under an unlicensed spectrum.

In some countries and regions, there are corresponding regulatory policies for the use of unlicensed spectrum. For example, a UE must perform Listen Before Talk (LBT), also known as Clear Channel Assessment (CCA), before sending data using an unlicensed carrier. As such, only LBT-enabled devices or UEs can send data on the unlicensed carrier. Under NR licensed carriers, SS/PBCH blocks (synchronization signal/ physical broadcast channel blocks, abbreviated as SSB) have cell search, synchronization, and measurement functions. Due to the special nature of unlicensed carriers, such as the need to perform LBT before sending data, the transmission of SS/PBCH block and/or discovery signals faces uncertainty. In this case, when a UE encounters a transmission failure at the physical (PHY) layer, e.g. due to the LBT failure, the UE may indicate the transmission failure to its media access control (MAC) layer, that is higher than the PHY layer. Some statistics can be calculated at the MAC layer to determine whether to declare a radio link failure (RLF) at the radio resource control (RRC) layer or not.

<FIG> illustrates a block diagram of a user equipment (UE) <NUM>, in accordance with some embodiments of the present disclosure. The UE <NUM> is an example of a device that can be configured to implement the various methods described herein. As shown in <FIG>, the UE <NUM> includes a housing <NUM> containing a system clock <NUM>, a processor <NUM>, a memory <NUM>, a transceiver <NUM> comprising a transmitter <NUM> and receiver <NUM>, a power module <NUM>, a physical layer module <NUM>, a MAC layer module <NUM>, and a RRC layer module <NUM>.

In this embodiment, the system clock <NUM> provides the timing signals to the processor <NUM> for controlling the timing of all operations of the UE <NUM>. The processor <NUM> controls the general operation of the UE <NUM> and can include one or more processing circuits or modules such as a central processing unit (CPU) and/or any combination of general-purpose microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate array (FPGAs), programmable logic devices (PLDs), controllers, state machines, gated logic, discrete hardware components, dedicated hardware finite state machines, or any other suitable circuits, devices and/or structures that can perform calculations or other manipulations of data.

The transceiver <NUM>, which includes the transmitter <NUM> and receiver <NUM>, allows the UE <NUM> to transmit and receive data to and from a remote device (e.g., a BS or another UE). An antenna <NUM> is typically attached to the housing <NUM> and electrically coupled to the transceiver <NUM>. In various embodiments, the UE <NUM> includes (not shown) multiple transmitters, multiple receivers, and multiple transceivers. In one embodiment, the antenna <NUM> is replaced with a multi-antenna array <NUM> that can form a plurality of beams each of which points in a distinct direction. The transmitter <NUM> can be configured to wirelessly transmit packets having different packet types or functions, such packets being generated by the processor <NUM>. Similarly, the receiver <NUM> is configured to receive packets having different packet types or functions, and the processor <NUM> is configured to process packets of a plurality of different packet types. For example, the processor <NUM> can be configured to determine the type of packet and to process the packet and/or fields of the packet accordingly.

In a wireless communication, the UE <NUM> may perform a wireless transmission of a message at the physical layer, by the physical layer module <NUM> of the UE <NUM>. The physical layer module <NUM> may send an indication to the MAC layer module <NUM> to indicate whether there is a transmission failure of transmitting the message at the physical layer. The physical layer module <NUM> is configured for performing a process at the physical layer. The MAC layer module <NUM> is configured for performing a process at the MAC layer that is higher than the physical layer. According to various embodiments, the transmission failure is due to at least one of: a listen-before-talk (LBT) failure in unlicensed spectrum; a power backoff; and a collision with ultra-reliable low-latency communication (URLLC) service.

After the MAC layer module <NUM> obtains the indication from the physical layer module <NUM>, the MAC layer module <NUM> may analyze the indication to determine whether there is a transmission failure at the physical layer. The MAC layer module <NUM> may calculate statistics related to transmission failures at the physical layer, e.g. based on a counter and/or a timer, to determine whether to indicate the failure issue to the RRC layer module <NUM>.

The RRC layer module <NUM>, upon receiving an indication from the MAC layer module <NUM> about the transmission failure issue, may declare a radio link failure (RLF). The RRC layer module <NUM> is configured for performing a process at the RRC layer that is higher than the MAC layer. There may be additional modules working in the UE <NUM> on other layers, according to various embodiments. A detailed description about each of the physical layer module <NUM>, the MAC layer module <NUM> and the RRC layer module <NUM> will be provided with respect to <FIG>.

The power module <NUM> can include a power source such as one or more batteries, and a power regulator, to provide regulated power to each of the above-described modules in <FIG>. In some embodiments, if the UE <NUM> is coupled to a dedicated external power source (e.g., a wall electrical outlet), the power module <NUM> can include a transformer and a power regulator.

The various modules discussed above are coupled together by a bus system <NUM>. The bus system <NUM> can include a data bus and, for example, a power bus, a control signal bus, and/or a status signal bus in addition to the data bus. It is understood that the modules of the UE <NUM> can be operatively coupled to one another using any suitable techniques and mediums.

Although a number of separate modules or components are illustrated in <FIG>, persons of ordinary skill in the art will understand that one or more of the modules can be combined or commonly implemented. For example, the processor <NUM> can implement not only the functionality described above with respect to the processor <NUM>, but also implement the functionality described above with respect to the MAC layer module <NUM>. Conversely, each of the modules illustrated in <FIG> can be implemented using a plurality of separate components or elements.

<FIG> illustrates detailed block diagrams of several modules in a UE, in accordance with some embodiments of the present disclosure. <FIG> shows exemplary inner components of the physical layer module <NUM>, the MAC layer module <NUM> and the RRC layer module <NUM> of the UE <NUM> in <FIG>. As shown in <FIG>, the physical layer module <NUM> in this example includes an autonomous message generator <NUM>, a transmission failure generator <NUM>, and a message transmission controller <NUM>. The MAC layer module <NUM> in this example includes an indication analyzer <NUM>, a message transmission instructor <NUM>, a counter controller <NUM>, a timer controller <NUM>, and a failure issue indicator <NUM>. The RRC layer module <NUM> in this example includes a radio link failure declarer <NUM>. According to various embodiments, each of the physical layer module <NUM>, the MAC layer module <NUM> and the RRC layer module <NUM> may include additional component(s) and each component in the physical layer module <NUM>, the MAC layer module <NUM> and the RRC layer module <NUM> may optional. The various modules shown in <FIG> are coupled together and coupled to the components shown in <FIG> by the bus system <NUM>.

The message transmission controller <NUM> may perform, via the transmitter <NUM>, a wireless transmission of a message at the physical layer. In one embodiment, the message transmission controller <NUM> obtains, from the MAC layer module <NUM>, an instruction for transmitting the message at the physical layer. In another embodiment, the autonomous message generator <NUM> autonomously generates the message and sends the message to the message transmission controller <NUM> for transmission at the physical layer. The message may include information about at least one of: a preamble; a protocol data unit (PDU); and a scheduling request (SR).

The transmission failure generator <NUM> in this example may generate and send a transmission failure indication to the MAC layer module <NUM> to indicate whether there is a transmission failure of transmitting the message at the physical layer. In one embodiment, the indication is only generated and sent when there is a transmission failure, such that the MAC layer module <NUM> can be aware of a transmission failure when receiving the indication within a predetermined time, and be aware of a transmission success when not receiving the indication within the predetermined time.

The indication analyzer <NUM> in this example may obtain the indication from the physical layer module <NUM> and analyze the indication to determine whether there is a transmission failure of the UE <NUM> at the physical layer. The message transmission instructor <NUM> in this example may instruct the physical layer module <NUM> to transmit a message at the physical layer, wherein the transmission failure is a failure of transmitting the message at the physical layer. In one embodiment, the transmission failure is a failure of transmitting a message autonomously generated by the physical layer module <NUM> at the physical layer. The message may include information about at least one of: a preamble; a protocol data unit (PDU); and a scheduling request (SR).

In one embodiment, the indication analyzer <NUM> determines, based on the indication, there is a transmission failure of the UE at the physical layer, and informs the failure to the counter controller <NUM>. The counter controller <NUM> can then increase, in response to the determining of the indication analyzer <NUM>, a counter at the MAC layer by one.

In one embodiment, the indication analyzer <NUM> further informs the failure to the timer controller <NUM>. The timer controller <NUM> may then restart, in response to the determining of the indication analyzer <NUM>, a timer at the MAC layer. In response to an expiration of the timer, the timer controller <NUM> informs the counter controller <NUM> about the timer expiration, and the counter controller <NUM> may reset the counter at the MAC layer in response to the expiration of the timer.

In one embodiment, in response to the determining of the indication analyzer <NUM>, the timer controller <NUM> may start a timer that is not running at the MAC layer. In response to an expiration of the timer, the timer controller <NUM> informs the counter controller <NUM> about the timer expiration, and the counter controller <NUM> may reset the counter at the MAC layer in response to the expiration of the timer.

In one embodiment, the counter controller <NUM> determines and informs the failure issue indicator <NUM> that the counter reaches a predetermined threshold. The failure issue indicator <NUM> can then generate and send an indication to the RRC layer module <NUM> to indicate a transmission failure issue of the physical layer and/or the MAC layer.

In another embodiment, the indication analyzer <NUM> determines, based on the indication, there is no transmission failure at the physical layer by a predetermined time related to a message transmission, and informs the determination to the counter controller <NUM>. The counter controller <NUM> may then reset, in response to the determining of the indication analyzer <NUM>, a counter at the MAC layer. The counter is for counting transmission failure at the physical layer.

In another embodiment, the indication analyzer <NUM> determines, based on the indication, there is a failure of transmitting a message at the physical layer, and informs the failure to the counter controller <NUM>. The counter controller <NUM> can then increase, in response to the determining of the indication analyzer <NUM>, a counter associated with the message at the MAC layer by one. That is, there may be multiple counters each corresponding to a different type of message transmission. After the counter controller <NUM> determines and informs the failure issue indicator <NUM> that the counter reaches a predetermined threshold associated with the message, the failure issue indicator <NUM> can then generate and send an indication to the RRC layer module <NUM> to indicate a transmission failure issue associated with the message at the physical layer and/or the MAC layer.

In another embodiment, the indication analyzer <NUM> determines, based on the indication, there is a failure of transmitting a scheduling request (SR) at the physical layer, and informs the failure to the timer controller <NUM>. The timer controller <NUM> can then stop, in response to the determining of the indication analyzer <NUM>, a timer that is running and associated with SR transmission at the physical layer. Since the timer is stopped, the timer controller <NUM> can inform the physical layer module <NUM> to re-transmit the scheduling request (SR) at the physical layer in a next available SR transmission occasion that is pre-configured and independent of the timer.

In another embodiment, the indication analyzer <NUM> determines, based on the indication, there is a success of transmitting a scheduling request (SR) at the physical layer, and informs the failure to the counter controller <NUM> and the timer controller <NUM>. The counter controller <NUM> can then increase, in response to the determining of the indication analyzer <NUM>, a counter associated with the SR at the MAC layer by one. The timer controller <NUM> can restart, in response to the determining of the indication analyzer <NUM>, a timer that is associated with SR transmission at the MAC layer. In response to an expiration of the timer, the timer controller <NUM> can inform the physical layer module <NUM> to re-transmit the scheduling request (SR) at the physical layer.

The radio link failure declarer <NUM> in this example is configured for obtaining an indication from the MAC layer module <NUM> and analyzing the indication to determine a transmission failure issue at the physical layer and the MAC layer. Based on the indication of the transmission failure issue, the radio link failure declarer <NUM> can declare a radio link failure (RLF).

<FIG> illustrates a flow chart for a method <NUM> performed by a UE, e.g. the UE <NUM> in <FIG>, for indicating transmission failures, in accordance with some embodiments of the present disclosure. At operation <NUM>, the UE performs, by a first layer module (e.g. the physical layer module <NUM>) of the UE, a wireless transmission of a message at a first layer (e.g. the physical layer). At operation <NUM>, an indication is sent, from the first layer module to a second layer module (e.g. the MAC layer module <NUM>) of the UE to indicate whether there is a transmission failure of transmitting the message at the first layer. It is determined at the operation <NUM> whether a transmission failure is received by the second layer module within a predetermined time. If not, the process goes to operation <NUM> to reset a failure counter at the second layer. Otherwise, if a transmission failure is received by the second layer module within the predetermined time, the failure counter at the second layer is increased by one at operation <NUM>.

Then at operation <NUM>, it is determined whether the counter reaches a predetermined threshold. If so, the process goes to operation <NUM> to indicate a transmission failure issue to a third layer module (e.g. the RRC layer module <NUM>), which can declare radio link failure (RLF) at operation <NUM>. If not, the process goes to operation <NUM> to restart a timer at the second layer. When the time expires, the failure counter is reset at operation <NUM>.

<FIG> illustrates an exemplary control plane protocol stack in a UE and a network side (e.g., a <NUM> base station and a mobility management entity (MME)), in a <NUM> system, in accordance with some embodiments of the present disclosure. The UE <NUM> in this example includes a non-access stratum (NAS) layer, a radio resource control (RRC) layer, a data convergence protocol (PDCP) layer, a radio link control (RLC) layer, a medium access control (MAC) layer, and a physical (PHY) layer. The <NUM> BS <NUM> includes an RRC layer, a PDCP layer, an RLC layer, a MAC layer, and a PHY layer, and the MME includes an NAS layer.

The PDCP layer resides above the RLC layer, which resides above the MAC layer, which resides above the PHY layer. The RRC layer resides above the PDCP layer, which resides above the RLC layer, which resides above the MAC layer. There are many signaling procedures between the UE and the network side including layer <NUM> signaling procedures, (such as RRC signaling procedures and NAS signaling procedures), and layer <NUM> signaling procedures, (such as MAC control signaling or RLC related signaling procedure, such as RLC reset procedure). Timely execution of such control plane, (e.g., RRC), or user plane, (e.g., RLC or MAC), signaling procedures is a critical factor in achieving speedy and reliable communications.

In a first embodiment, not being according to the invention as claimed, a transmission may be blocked due to some reasons, e.g. LBT failures in unlicensed spectrum, power backoff, colliding with URLLC service and so on. In some cases, the transmission blocking may impact the processing of the other layers. Therefore, the other layers need to know the transmission outcome. According to this embodiment, an indication is informed to the other layers, such that the other layers may do something according to the indication.

According to a second embodiment, not being according to the invention as claimed, in unlicensed spectrum, a transmission may be blocked due to LBT failure, such as SR transmission, each message transmission in RACH procedure, and PUSCH transmission. When the transmission fails, it may impact the processing of the other layer, e.g. the MAC layer. For random access channel (RACH) procedure, when preamble transmission is blocked due to LBT failure, power ramping counter is not incremented. Therefore, the physical layer needs to inform transmission failure to the MAC layer, so that power ramping counter is not incremented in the next preamble transmission to avoid unnecessary power increase for re-transmission.

In addition, for SR procedure, when SR transmission is blocked due to LBT failure, the prohibit timer is not started in the MAC layer. Therefore, a transmission failure indication should be informed to the MAC layer, so that the prohibit timer is not started, or is stopped to avoid unnecessary waiting time for re-transmission.

For physical uplink shared channel (PUSCH) transmission, a transmission is blocked due to LBT failure, especially for configured grant transmission. If MAC protocol data unit (PDU) is indicated to the physical layer, a timer will be started in the MAC layer. If transmission is blocked due to LBT failure, UE will wait for the timer to expire to perform the next transmission, which increases the transmission delay. In this case, a transmission indication should be informed to the MAC layer, so that it may stop the timer and perform the next transmission as soon as possible.

Therefore, for SR procedure, RACH procedure, and PUSCH transmission, a transmission failure indication may be informed to the MAC layer, such that UE may perform the other operations according to the indication in order to increase the system performance.

According to a third embodiment, not being according to the invention as claimed, a transmission failure counter is introduced. When a transmission is blocked in the lower layer, a transmission failure indication is informed to the middle layer. Then the transmission failure counter is incremented by <NUM>. When the transmission failure counter reaches a threshold, the failure problem should be indicated to the upper layer.

For SR procedure, RACH procedure and PUSCH transmission procedure in the MAC layer, the transmission failure counter may be a uniform counter for these procedures. The transmission counter is not restricted to continuous transmission failure. For example, once a transmission failure is received, the counter is incremented. Taking RACH procedure as an example, when RACH procedure is triggered, the following steps may be performed.

Step <NUM>: the MAC layer selects preamble, and indicates it to the physical layer.

Step <NUM>: the physical layer performs LBT before transmission.

Step <NUM>: if LBT fails, the physical layer informs the transmission failure indication to the MAC layer.

Step <NUM>: when the MAC layer receives the transmission failure indication, the transmission failure counter is incremented by <NUM>, otherwise it is not incremented.

Step <NUM>: if the transmission failure counter reaches a threshold, it should indicate the transmission failure problem to the RRC layer.

Step <NUM>: when the RRC layer receives the transmission failure problem, it may declare radio link failure (RLF).

In addition to the transmission indicated by the MAC layer, there are some message transmissions which do not need to be indicated by the MAC layer and are directly transmitted in the physical layer, for example, transmitted HARQ feedback and channel state information (CSI) via physical uplink control channel (PUCCH), sounding reference signal (SRS). For these messages, when a transmission is blocked, if the transmission failure indication is not informed to the MAC layer, it means the transmission failure counter is only used for the statistics of transmission failure of indicated message in the MAC layer. If the transmission failure indication is informed to the MAC layer, the transmission failure counter will also be incremented once it is received. These detailed steps are described as follows.

Step <NUM>: HARQ feedback/CSI needs to be transmitted and only PUCCH resource may be used for transmission in the physical layer.

Step <NUM>: when the RRC layer receives the transmission failure problem, it may declare RLF.

According to a fourth embodiment, not being according to the invention as claimed, a transmission failure counter is introduced. When transmission is blocked in the lower layer, a transmission failure indication is informed to the middle layer. Then the transmission failure counter is incremented by <NUM>. When the transmission failure counter reaches a threshold, the failure problem should be indicated to the upper layer.

For each procedure, such as SR procedure, RACH procedure, and PUSCH transmission procedure, the transmission failure counter may be a uniform counter for these procedures. Herein the consecutive transmission failure numbers are counted. Once a transmission is indicated to the lower layer and the transmission failure indication is not received, the transmission failure counter is reset, otherwise it is incremented by <NUM>. When the transmission failure counter reaches a threshold, the middle layer should indicate the transmission failure problem to the upper layer. Taking RACH procedure as an example, when RACH procedure is triggered, the following steps may be performed.

Step <NUM>: when the MAC layer receives the transmission failure indication, the transmission failure counter is incremented by <NUM>, otherwise when the message transmission ends, if there is no indication to be received, the counter will be reset.

Step <NUM>: if the transmission failure counter reaches a threshold, the MAC layer should indicate the transmission failure problem to the RRC layer.

According to a fifth embodiment, not being according to the invention as claimed, when transmission is blocked in the lower layer, a transmission failure indication is informed to the middle layer. Then the transmission failure counter is incremented by <NUM>. When the transmission failure counter reaches a threshold, the failure problem should be indicated to the upper layer. For each procedure, such as SR procedure, RACH procedure, and PUSCH transmission procedure, the transmission failure counter may be a uniform counter for these procedures. Herein both a timer and a counter are used, when the transmission failure indication is received, the timer is started or restarted, and the transmission failure counter is incremented by <NUM>. When the transmission failure indication is not received within the timer, the transmission counter is reset. When the transmission failure counter reaches a threshold, the middle layer should indicate the transmission failure problem to the upper layer. Taking RACH procedure as an example, when RACH procedure is triggered, the following steps may be performed.

Step <NUM>: when the MAC layer receives the transmission failure indication, the transmission failure counter is incremented by <NUM> and the timer is started or restarted. When the timer expires, the transmission counter is reset.

In addition to the transmission indicated by the MAC layer, there are some message transmissions which do not need to be indicated by the MAC layer and are directly transmitted in the physical layer, for example, transmitted HARQ feedback and CSI via PUCCH, SRS. For these messages, when transmission is blocked, if the transmission failure indication is not informed to the MAC layer, it means the transmission failure counter is only used for the statistics of transmission failure of indicated message in the MAC layer. If the transmission failure indication is informed to the MAC layer, the transmission failure counter will also be incremented once it is received. These detailed steps are described as follows.

According to a sixth embodiment, not being according to the invention as claimed, for PUSCH, UE autonomously transmits PUSCH via configured grant resource. When the channel occupancy rate is very high, LBT failure always happens, such that transmission has been attempted. In order to terminate the transmission attempt procedure, a counter may be introduced. When the transmission fails due to LBT, a failure indication is informed to the MAC layer. When the MAC layer receives the indication, the counter is incremented by <NUM>. The failure indication may be continuous or discontinuous. A detailed procedure may be described as follows.

Step <NUM>: the MAC layer indicates the MAC PDU to the physical layer.

Step <NUM>: if LBT fails, a failure indication is informed to the MAC layer.

Step <NUM>: the MAC layer receives the indication, and the counter is incremented by <NUM>.

Step <NUM>: if the counter reaches a threshold, a transmission failure problem is indicated to the RRC layer.

Step <NUM>: when the RRC layer receives the transmission failure problem, it declares RLF.

According to a seventh embodiment, for PUSCH, UE autonomously transmits PUSCH via configured grant resource. When the channel occupancy rate is very high, LBT failure always happens, such that transmission has been attempted. In order to terminate the transmission attempt procedure, both a counter and a timer is introduced. When the transmission fails due to LBT, a failure indication is informed to the MAC layer. When the MAC layer receives the indication within the timer, the counter is incremented by <NUM>, and the timer is started or restarted. When the timer expires, the failure indication is not received, the counter will be reset. A detailed procedure may be described as follows.

Step <NUM>: the MAC layer receives the indication within the timer, the counter is incremented by <NUM>, and the timer is started or restarted. When the timer expires, the indication is not received, and the counter is reset.

According to an eighth embodiment, not being according to the invention as claimed, for unlicensed spectrum, SR is not transmitted due to LBT failure. In this case, the SR prohibit timer should not be started. It should perform SR transmission in the next available SR transmission occasion as soon as possible. Then an indication should be informed to the MAC layer. If a LBT failure indication is informed to the MAC layer, UE may stop the timer. In addition, SR counter should not be incremented in order to avoid unnecessary RLF. When LBT failure indication is informed to the MAC layer, the handling on SR procedure in the MAC layer may be modified as follows.

For the SR configuration corresponding to the pending SR: if the notification of transmission failure has been received from lower layer, and if sr-ProhibitTimer is running, stop sr-ProhibitTimer. Else if the notification of transmission failure has not been received from lower layer, increment SR_COUNTER by <NUM>.

When the MAC entity has an SR transmission occasion on the valid PUCCH resource for SR configured; and if sr-ProhibitTimer is not running at the time of the SR transmission occasion; and if the PUCCH resource for the SR transmission occasion does not overlap with a measurement gap; and if the PUCCH resource for the SR transmission occasion does not overlap with a UL-SCH resource, and if SR_COUNTER < sr-TransMax + <NUM>: instruct the physical layer to signal the SR on one valid PUCCH resource for SR; start the sr-ProhibitTimer.

If SR counter is not incremented, the SR procedure may not be terminated. In order to avoid the case, each of the third, fourth, fifth and tenth embodiments may serve as a solution to terminate the procedure.

According to a ninth embodiment, not being according to the invention as claimed, for unlicensed spectrum, SR is not transmitted due to LBT failure. In this case, SR prohibit timer should not be started. It should perform SR transmission in the next available SR transmission occasion as soon as possible. Then an indication should be informed to the MAC layer. In addition, SR counter should not be incremented in order to avoid unnecessary RLF. If a LBT success indication is informed to the MAC layer, the SR prohibit timer is started and SR counter is incremented by <NUM>. Otherwise the timer is not started, and the counter is not incremented. When LBT success indication is informed to the MAC layer, the handling on SR procedure in the MAC layer may be modified as follows.

For the SR configuration corresponding to the pending SR: if the notification of transmission success has been received from lower layer, increment SR_COUNTER by <NUM>; and start the sr-ProhibitTimer.

According to a tenth embodiment, not being according to the invention as claimed, if a transmission is blocked in the lower layer, a transmission failure indication is informed to the middle layer. Then the transmission failure counter is incremented. When the transmission failure counter reaches a threshold, the failure problem should be indicated to the upper layer.

For SR procedure, RACH procedure and PUSCH transmission procedure in the MAC layer, the transmission failure counter may be a uniform counter for these procedures. Besides the transmission failure counter, a timer is also used. When the transmission failure indication is received and the timer is not running, the timer is started and the transmission counter is incremented by <NUM>. If the transmission failure indication is received within the timer, the transmission failure counter is incremented by <NUM>. If the timer expires, the transmission counter is reset. When the transmission failure counter reaches a threshold, the middle layer will indicate the transmission failure problem to the upper layer. Taking RACH procedure as an example, when RACH procedure is triggered, the following steps may be performed.

Step <NUM>: when the transmission failure indicated is received and the timer is not running, the timer is started and the transmission failure counter is incremented by <NUM>. When the transmission failure indicated is received within the timer, the transmission failure counter is incremented by <NUM>. When the timer expires, the transmission failure counter is reset.

In addition to the transmission indicated by the MAC layer, there are some message transmissions which do not need to be indicated by the MAC layer and are directly transmitted in the physical layer, for example, transmitted HARQ feedback and CSI via PUCCH, SRS. For these messages, when a transmission is blocked, if the transmission failure indication is not informed to the MAC layer, it means the transmission failure counter is only used for the statistics of transmission failure of indicated message in the MAC layer. If the transmission failure indication is informed to the MAC layer, the transmission failure counter will also be incremented once it is received. These detailed steps may be described as follows.

According to an eleventh embodiment, not being according to the invention as claimed, when transmission is blocked in the lower layer, a transmission failure indication is informed to the middle layer. Then the transmission failure counter is incremented. When the transmission failure counter reaches a threshold, the failure problem should be indicated to the upper layer.

For SR procedure, RACH procedure and PUSCH transmission procedure in the MAC layer, the transmission failure counter may be a uniform counter for these procedures. Besides the transmission failure counter, a timer is also used. When the transmission failure indication is received and the timer is not running, the timer is started and the transmission counter is incremented by <NUM>. If the transmission failure indication is received within the timer, the transmission failure counter is incremented by <NUM>. If the timer expires, the transmission counter is reset. When the transmission failure counter reaches a threshold, the middle layer will indicate the transmission failure problem to the upper layer.

Taking RACH procedure as an example, when RACH procedure is triggered, the following steps may be performed. Multiple thresholds may be introduced, for example, a threshold for Message <NUM> (Msg3) transmission in the RACH procedure, a threshold for preamble transmission. When a transmission failure indication for Msg3 is received, the transmission failure counter is incremented. If the counter reaches the threshold for Msg3 transmission, the transmission failure problem is indicated to the RRC layer. When a transmission failure indication for preamble transmission is received, the transmission failure counter is incremented. If the counter reaches the threshold for preamble transmission, the transmission failure problem is indicated to the RRC layer.

According to a twelfth embodiment, not being according to the invention as claimed, when all UL transmissions are blocked in the lower layer, a transmission failure indication is informed to the upper layer. Then the transmission failure counter is incremented. When the transmission failure counter reaches a threshold, RLF will be triggered. For all uplink transmissions, a common counter and a timer are proposed. The statistics approaches of the failure indication in the third, fourth, fifth, and/or tenth embodiments may be used for this embodiment as well.

Claim 1:
A method performed by a wireless communication device, the method comprising:
obtaining, by a media access control, MAC, layer module of the wireless communication device, an indication from a physical layer module of the wireless communication device, wherein
the indication indicates a transmission failure of the wireless communication device at a physical layer, the transmission failure being due to a listen-before-talk, LBT, failure in unlicensed spectrum;
starting, in response to the indication, a timer at a MAC layer;
incrementing, in response to the indication, a counter at the MAC layer by one;
determining that the counter has reached a predetermined threshold; and
indicating a MAC layer transmission failure to a radio resource control, RRC, layer of the wireless communication device,
further comprising:
resetting the counter at the MAC layer in response to an expiration of the timer; and
restarting, in response to another indication indicating a transmission failure of the wireless communication device at the physical layer due to an LBT failure in unlicensed spectrum, the timer at the MAC layer.