TECHNICAL FIELD

Particular embodiments are directed to wireless communications and, more particularly, to methods and apparatus for scheduling multiple subframes in unlicensed spectrum.

INTRODUCTION

The Third Generation Partnership Project (3GPP) initiative referred to as License

Assisted Access (LAA) enables long term evolution (LTE) equipment to operate in the unlicensed 5 GHz radio spectrum. The unlicensed 5 GHz spectrum is used as a complement to the licensed spectrum. Accordingly, devices connect in the licensed spectrum (primary cell or PCell) and use carrier aggregation to benefit from additional transmission capacity in the unlicensed spectrum (secondary cell or SCell). To reduce the changes required for aggregating licensed and unlicensed spectrum, the LTE frame timing in the primary cell is simultaneously used in the secondary cell.

The standalone LTE-U forum and 3GPP Rel-14 work item on Uplink Licensed-Assisted Access (LAA) may specify that LTE user equipments (UEs) may transmit on the uplink in the unlicensed 5 GHz or license-shared 3.5 GHz radio spectrum. For the case of standalone LTE-U, all downlink and uplink transmissions take place entirely on the unlicensed spectrum.

Regulatory requirements may not permit transmissions in the unlicensed spectrum without prior channel sensing. This is because the unlicensed spectrum is shared with radios of similar or dissimilar wireless technologies. Wireless devices may perform channel sensing using a listen-before-talk (LBT) method. The LBT method includes sensing the transmission medium for a pre-defined minimum amount of time and backing off if the channel is busy.

Wi-Fi, LAA and Standalone LTE-U may operate in multi-carrier mode with simultaneous transmission across multiple unlicensed channels in the 5 GHz band. Wi-Fi follows a hierarchical multi-carrier LBT scheme across multiple carriers which are selected using specific channel bonding rules.

For LAA and Standalone LTE-U, uplink transmissions are explicitly scheduled by the eNB which has full control over when UEs are allowed to transmit. However, for carriers operating in unlicensed spectrum, UEs perform some form of LBT before transmitting on the carrier. The form of LBT may depend on the number of UEs that are scheduled, the number of subframes that are scheduled in succession, the length of the previous transmissions on the carrier and other such factors. It is known that some parameters related to LBT can be signaled by the eNB to UEs so that they may perform LBT before transmission. However, the known signaling parameters do not fully encompass all the use cases and problems that will be encountered for uplink transmissions in unlicensed spectrum. In the embodiments described herein, we disclose more signaling methods to solve these problems and address the new use cases. In addition, the embodiments described herein describe how some signaling parameters can be used to increase efficiency of LTE in unlicensed spectrum.

As background, LTE uses OFDM in the downlink and Discrete Fourier Transform (DFT)-spread OFDM (also referred to as single-carrier FDMA) in the uplink. The basic LTE downlink physical resource comprises a time-frequency grid as illustrated inFIG. 1.

FIG. 1illustrates an example OFDM symbol. The horizontal axis represents time and the other axis represents frequency. Each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval. An uplink subframe has the same subcarrier spacing as the downlink and the same number of SC-FDMA symbols in the time domain as OFDM symbols in the downlink. In the time domain, LTE downlink transmissions are organized into radio frames.

FIG. 2illustrates an example radio frame. Each radio frame is 10 ms and consists of ten equally-sized subframes of length Tsubframe=1 ms. For normal cyclic prefix, one subframe consists of 14 OFDM symbols. The duration of each symbol is approximately 71.4 μs.

Resource allocation in LTE is typically described in terms of resource blocks, where a resource block corresponds to one slot (0.5 ms) in the time domain and 12 contiguous subcarriers in the frequency domain. A pair of two adjacent resource blocks in time direction (1.0 ms) is known as a resource block pair. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the system bandwidth.

Downlink transmissions are dynamically scheduled. In each subframe a base station transmits control information about which terminals data is transmitted to and upon which resource blocks the data is transmitted in the current downlink subframe. This control signaling is typically transmitted in the first 1, 2, 3 or 4 OFDM symbols in each subframe and the number n=1, 2, 3 or 4 is known as the Control Format Indicator (CFI). The downlink subframe also contains common reference symbols, which are known to the receiver and used for coherent demodulation of e.g. the control information.

FIG. 3illustrates an example downlink subframe. The subframe includes reference symbols and control signaling. In the illustrated example, the control region includes 3 OFDM symbols (i.e., CFI=3). The reference symbols include cell specific reference symbols (CRS), which may support multiple functions including fine time and frequency synchronization and channel estimation for certain transmission modes.

For LTE Rel-8 to Rel-10, a base station schedules downlink transmissions using a Physical Downlink Control Channel (PDCCH). From LTE Rel-11 and onwards, downlink transmissions may also be scheduled on an Enhanced Physical Downlink Control Channel (EPDCCH).

The PDCCH/EPDCCH carries downlink control information (DCI) such as scheduling decisions and power-control commands. For example, the DCI includes downlink scheduling assignments such as Physical Downlink Shared Channel (PDSCH) resource indication, transport format, hybrid-ARQ information, and control information related to spatial multiplexing (if applicable). A downlink scheduling assignment also includes a command for power control of the Physical Uplink Control Channel (PUCCH) used for transmission of hybrid-ARQ (HARQ) acknowledgements in response to downlink scheduling assignments. The DCI may also include uplink scheduling grants such as Physical Uplink Shared Channel (PUSCH) resource indication, transport format, and hybrid-ARQ-related information. An uplink scheduling grant also includes a command for power control of the PUSCH. The DCI may also include power control commands for a set of terminals as a complement to the commands included in the scheduling assignments/grants.

One PDCCH/EPDCCH carries one DCI message containing one of the groups of information listed above. Because a base station may schedule multiple terminals simultaneously, and each terminal may be scheduled on both downlink and uplink simultaneously, multiple scheduling messages may be transmitted within each subframe. Each scheduling message is transmitted on separate PDCCH/EPDCCH resources. Consequently, multiple simultaneous PDCCH/EPDCCH transmissions are typically within each subframe in each cell. Furthermore, support for different radio-channel conditions may use link adaptation. In link adaptation the code rate of the PDCCH/EPDCCH is selected by adapting the resource usage for the PDCCH/EPDCCH to match the radio-channel conditions.

The LTE Rel-10 standard and above supports bandwidths larger than 20 MHz. One requirement of LTE Rel-10 is backward compatibility with LTE Rel-8. This includes spectrum compatibility. One way to provide compatibility is for an LTE Rel-10 carrier wider than 20 MHz to appear as a number of LTE carriers to an LTE Rel-8 terminal. Each such carrier may be referred to as a Component Carrier (CC).

For early LTE Rel-10 deployments, the number of LTE Rel-10-capable terminals will likely be smaller than the number of LTE legacy terminals already in existence. Thus, efficient use of a wide carrier is needed for legacy terminals, i.e. providing carriers where legacy terminals may be scheduled in all parts of the wideband LTE Rel-10 carrier. One solution uses carrier aggregation. Using carrier aggregation, an LTE Rel-10 terminal may receive multiple component carriers. The components carriers may have the same structure as a Rel-8 carrier.

FIG. 4illustrates an example of carrier aggregation. A system bandwidth of 100 MHz may be represented by 5 component carriers each with 20 MHz bandwidth. A UE capable of carrier aggregation may be assigned a primary cell (PCell), which is always activated, and one or more secondary cells (SCells) which may be activated or deactivated dynamically.

The number of aggregated component carriers as well as the bandwidth of the individual component carriers may be different for uplink and downlink. A symmetric configuration refers to a configuration where the number of component carriers in downlink is the same as in uplink. An asymmetric configuration refers to a configuration where the number of component carriers is different between downlink and uplink. The number of component carriers configured in a cell may be different from the number of component carriers seen by a terminal. For example, a terminal may support more downlink component carriers than uplink component carriers, even though the cell is configured with the same number of uplink and downlink component carriers.

Carrier aggregation may be used for LAA where the primary carrier (or PCell) operates in licensed spectrum, and one or more secondary carriers (or SCells) operate in unlicensed spectrum.

Another feature of carrier aggregation is the ability to perform cross-carrier scheduling. Cross-carrier scheduling enables a (E)PDCCH on one component carrier to schedule data transmissions on another component carrier using a 3-bit Carrier Indicator Field (CIF) inserted at the beginning of the (E)PDCCH messages. For data transmissions on a given component carrier, a UE expects to receive scheduling messages on the (E)PDCCH of just one component carrier (i.e., either the same component carrier, or a different component carrier via cross-carrier scheduling). The mapping from (E)PDCCH to PDSCH may be configured semi-statically.

In LTE, the scheduling information for uplink and downlink transmissions on the PCell is transmitted on the PCell using (E)PDCCH. LTE refers to this scheduling mechanism as a self-scheduling method. For a SCell, LTE supports two scheduling mechanisms—self-scheduling or cross-scheduling. Using SCell self-scheduling (similar to PCell self-scheduling), the uplink and downlink scheduling information for the SCell is transmitted on the same SCell using (E)PDCCH. In SCell cross-scheduling, the network configures a SCell via higher layer signaling to use a cross-scheduling mechanism. In this approach, the uplink and downlink scheduling information for a SCell is transmitted on a second cell using (E)PDCCH. The second cell may be the PCell or another SCell. In LTE, the downlink and uplink scheduling mechanisms are configured together (i.e., the downlink and uplink transmissions of a cell are either both self-scheduling or both cross-scheduling).

Another wireless network technology that may share unlicensed spectrum with LTE is a wireless local area network (WLAN). Typical WLAN deployments use carrier sense multiple access with collision avoidance (CSMA/CA) for medium access. This means that the channel is sensed to perform a clear channel assessment (CCA), and a transmission is initiated only if the channel is determined to be idle. If the channel is determined to be busy, then the transmission is deferred until the channel is idle. When the range of several access points using the same frequency overlap, all transmissions related to one access point might be deferred when a transmission on the same frequency to or from another access point which is within range is detected. Effectively, if several access points are within range of each other, they will need to share the channel in time, and the throughput for the individual access points may be severely degraded. A general illustration of the listen-before-talk (LBT) mechanism on a single unlicensed channel is shown inFIG. 5.

FIG. 5illustrates an example WLAN listen-before-talk mechanism. In the case of single-channel LBT, after a first Wi-Fi station transmits a data frame to a second Wi-Fi station, the second station transmits an ACK frame back to the first station with a delay of 16 μs. The ACK frame is transmitted by the second station without performing an LBT operation. To prevent another station interfering with the ACK frame transmission, a station defers for a duration of 34 μs (referred to as DIFS) after the channel is observed to be occupied before assessing again whether the channel is occupied.

Thus, a station that wishes to transmit first performs a clear channel assessment by sensing the medium for a fixed duration DIFS. If the medium is idle, then the station assumes that it may take ownership of the medium and begins a frame exchange sequence. If the medium is busy, the station waits for the medium to go idle, defers for DIFS, and waits for a further random backoff period. To further prevent a station from occupying the channel continuously and thereby preventing other stations from accessing the channel, after a successful transmission, a station performs a random backoff before transmitting again.

For multi-carrier operation, Wi-Fi uses a hierarchical channel bonding scheme to determine its transmission bandwidth for a frame, which could be 20 MHz, 40 MHz, 80 MHz, or 160 MHz, for example. In the 5 GHz band, wider Wi-Fi channel widths of 40 MHz, 80 MHz, 160 MHz or 80+80 MHz are formed by combining 20 MHz sub-channels in a non-overlapping manner. A pre-determined primary channel performs the contention window-based random access procedure after a defer period, if necessary, and then counts down the random number generated. The secondary channels perform a quick CCA check for a PIFS duration (generally 25 μs) before the potential start of transmission to determine if the additional secondary channels are available for transmission. Based on the results of the secondary CCA check, transmission is performed on the larger bandwidths; otherwise transmission falls back to smaller bandwidths. The Wi-Fi primary channel is always included in all transmissions (i.e., transmission on secondary channels alone is not allowed).

LTE has traditionally used dedicated frequency spectrum. An advantage of dedicated spectrum is that an LTE system does not need to coexist with other non-3GPP radio access technologies in the same spectrum, which can maximize spectrum efficiency. The spectrum allocated to LTE, however, is limited. It may not meet the ever increasing demand for larger throughput from applications/services. Therefore, 3GPP also specifies how LTE may use unlicensed spectrum in addition to licensed spectrum. In addition, Standalone LTE-U is under development by the MulteFire Alliance, in which LTE operates solely in unlicensed spectrum.

FIG. 6illustrates a user equipment with license assisted access to unlicensed spectrum. In license assisted access, a UE is connected to a PCell in the licensed band and one or more SCells in the unlicensed band. A secondary cell in unlicensed spectrum may be referred to as a LAA secondary cell (LAA SCell). The LAA SCell may operate in downlink-only mode or operate with both uplink and downlink traffic. In some scenarios, LTE nodes may operate in standalone mode in license-exempt channels without assistance from a licensed cell.

Unlicensed spectrum can, by definition, be used simultaneously by multiple different technologies. Therefore, LAA must coexist and cooperate with other systems, such as IEEE 802.11 (Wi-Fi). To coexist fairly with a Wi-Fi system, transmission on the SCell conforms to LBT protocols to avoid collisions which may cause severe interference to on-going transmissions. This includes both performing LBT before commencing transmissions, and limiting the maximum duration of a single transmission burst. The maximum transmission burst duration is specified by country and region-specific regulations (e.g., 4 ms in Japan and 13 ms according to EN 301.893). An example is illustrated inFIG. 7.

FIG. 7illustrates an example of license assisted access to unlicensed spectrum using LTE carrier aggregation and listen-before-talk.FIG. 7illustrates five example transmission bursts on an LAA SCell. Each transmission burst is constrained by a maximum allowed transmission duration of 4 ms. Before each LAA SCell transmission is a listening period. The example 8 ms burst is divided into two 4 ms bursts with a listening period before each.

Before the eNB transmit data in the downlink, it performs LBT to gain channel access. During the eNB's transmission duration, it also sends out control channels to schedule certain UEs to transmit in the uplink at specific time later. After the eNB releases the channel, the scheduled UEs perform LBT to determine whether they can transmit in the channel at said specific time.

FIG. 8illustrates an example of uplink license assisted access transmissions based on an uplink listen-before-talk protocol. The illustrated example divides an 8 ms occupancy time into 4 ms for downlink channel occupancy and 4 ms for uplink channel occupancy. After receiving a downlink transmission in subframes n−4 to n−1 (i.e., 4 ms), the UE performs a clear channel access for the uplink at subframe n. If the channel is clear, the UE transmits in uplink for subframes n to n+3 (i.e., 4 ms).

In another approach, the UE does not follow any LBT protocol to initiate channel access after receiving an uplink transmission scheduling command. LBT and CCA are performed by the eNB before the start of downlink transmissions. This may be referred to as a reverse direction grant protocol.

FIG. 9illustrates an example of uplink license-assisted access transmissions based on a reverse direction grant protocol. The illustrated example divides an 8 ms occupancy time into 4 ms for downlink channel occupancy and 4 ms for uplink channel occupancy. After receiving a downlink transmission in subframes n−4 to n−1 (i.e., 4 ms), the UE transmits in uplink for subframes n to n+3 (i.e., 4 ms) without performing a CCA.

When an eNB obtains an opportunity to transmit in unlicensed spectrum, the opportunity (also referred to as a transmit opportunity (TXOP)), may be shared with UEs that the eNB is serving. Transitions between transmissions from the eNB to transmissions from UEs may be handled in two ways, one where the UEs perform an LBT operation prior to transmission and one where the UEs do not perform an LBT operation.

The case where an LBT operation is not performed will most likely need the gap between downlink transmissions (from the eNB) and uplink transmissions (from the UE(s)) to be no more than 16 μs. When an LBT operation is to be performed for a particular subframe, gaps will need to be inserted in the uplink subframes to allow for the UE to perform a listen-before-talk operation without being interfered by transmissions from other UEs in the same serving cell. To avoid significantly degrading uplink throughput, the gaps should not be too large. Therefore, the gap in an uplink subframe of 14 DFT spread OFDM (DFTS-OFDM) symbols is likely to not be larger than one DFTS-OFDM symbol, which is approximately 71 microseconds in duration.

Performing LBT may generally include two broad categories of LBT operation. A first type uses an LBT procedure with full random backoff similar to what is used by IEEE 802.11 compliant nodes. These schemes are also referred to as Category 4 LBT schemes.

In these schemes a random backoff counter is drawn uniformly randomly in the interval {0, CW}, where CW is the contention window. The size of the contention window may be approximately doubled every time a collision on the channel is detected. Thus, this procedure may also be referred to as a binary exponential backoff.

The contention window size is limited by a minimum value, CWmin, and a maximum value, CWmax. The values of CWmin and CWmax may vary depending on the priority class of the traffic. For the highest priority class, the {CWmin, CWmax} values may be limited to { 3, 7} where these numbers are counted in increments of one slot which has a duration of9microseconds as shown inFIG. 5. There are four defined priority classes. The remaining three priority classes use contention window size pairs of {7, 15}, {15, 63} and {15, 1023}, respectively, for an access point (AP) or an eNB. For Wi-Fi STAs or UEs in LTE, the values of {15, 63} are not used.

In the second type of LBT procedure, a UE may perform an LBT operation for a fixed duration (e.g., 25 μs). Generally, the second type of LBT is preferable for transitions between downlink and uplink transmissions, because it minimizes the probability of another node completing its LBT operations and commencing transmissions on the channel. Many situations, however, may need to use a Category 4 LBT scheme.

One technique to minimize gaps between downlink and uplink transmissions is to use a timing advance command to advance the timing of the UEs transmissions on the uplink so that they occur earlier. This technique may be used where the eNB may employ transmissions only over a part of the subframe in the last downlink subframe of a transmission burst. In this case, there is a gap within the downlink subframe that can be occupied by uplink transmissions by UEs that have received timing advance (TA) commands.

The use of LTE carrier aggregation (CA), introduced in Rel-10, may increase the peak data rate, system capacity, and user experience by aggregating radio resources from multiple carriers that may reside in the same band or different bands. Rel-13 LAA and Standalone LTE-U offer an ability to operate on multiple carriers in unlicensed spectrum simultaneously. The extension of the CA framework beyond 5 carriers was completed in LTE Rel-13, which supports up to 32 carriers in both uplink and downlink.

3GPP specifications may include multi-subframe scheduling for Rel-14 LAA where one or more uplink grants transmitted in a single subframe can schedule uplink data in multiple subframes. The parameters that are signaled as part of the multi-subframe scheduling grant include hybrid ARQ acknowledgements (HARQ-ACKs) and related parameters. Specifically, the grants include legacy parameters (i.e., the new data indication (NDI), redundancy version (RV), and the HARQ-ACK bits themselves, which generally consist of one bit per transport block that is being acknowledged).

Signaling of LBT parameters for LAA may use both explicit and implicit methods. The solutions include signaling of random backoff parameters such as the random backoff counter, contention window sizes, and the LBT priority class to be used. The signaling of these parameters may vary depending on factors such as the load and the set of UEs being multiplexed in a single subframe. Implicit signaling of the LBT priority class to be used can be based on various factors including the number of contiguous subframes that have been scheduled to the UE. The contention window sizes to be used at the UE can also be implicitly signaled by indicating whether the transmission is a new transmission or a retransmission.

Existing signaling and contention window management methods, however, do not fully account for the problems that arise when using implicit signaling to indicate contention window size that the UE must use. When explicit signaling is used, it creates unnecessarily large signaling overhead.

SUMMARY

The embodiments described herein include efficiently signaling listen-before-talk (LBT) parameters for a Category 4 LBT scheme to a user equipment (UE), while ensuring that requirements on management of contention windows are met. Particular embodiments facilitate the management of uplink transmissions in unlicensed spectrum by varying the gaps between transmissions by different nodes. Signaling to enable the functionality is disclosed. The disclosure includes the following general solutions for signaling LBT parameters to a UE.

According to some embodiments, a method for use in a UE of transmitting uplink data in unlicensed spectrum comprises receiving, from a network node, an uplink grant comprising an indication of one or more subframes to use for transmitting uplink data. Each subframe comprises a plurality of symbols. The method further comprises obtaining an indication of a LBT type. The LBT type indicates a type of LBT procedure that the UE should perform before transmitting uplink data. The method further comprises determining, using the obtained LBT type, at least one of a starting symbol and a stopping symbol for transmitting uplink data, and transmitting uplink data according to at least one of the determined starting symbol and the determined stopping symbol.

In particular embodiments, the LBT type indicates a category 4 procedure, and the starting symbol comprises the second symbol of the plurality of symbols of the first subframe indicated by the uplink grant. The LBT type may indicate a short clear channel assessment (CCA) procedure, and the starting symbol may comprise the symbol 25 μs after the first symbol of the plurality of symbols of the first subframe indicated by the uplink grant.

In particular embodiments, the LBT type indicates a category 4 procedure or a short clear channel assessment (CCA) procedure, and the stopping symbol comprises the next to last symbol of the plurality of symbols of the last subframe indicated by the uplink grant. The method may further comprise determining that the UE is scheduled to transmit a sounding reference signal (SRS) in the last symbol of the plurality of symbols of the last subframe indicated by the uplink grant, and not transmitting the scheduled SRS.

In particular embodiments, the LBT type indicates no LBT procedure. When other radio technologies are present in the unlicensed spectrum, then the starting symbol comprises the symbol 16 μs after the first symbol of the plurality of symbols of the first subframe indicated by the uplink grant. When other radio technologies are not present in the unlicensed spectrum, then the starting symbol comprises the first symbol of the plurality of symbols of the first subframe indicated by the uplink grant.

In particular embodiments, obtaining the indication of the LBT type comprises receiving signaling from the network node. Obtaining the indication of the LBT type may comprise obtaining a predetermined LBT type unless an LBT type is signaled from the network node. Receiving signaling from the network node may comprise receiving common signaling over a broadcast channel or receiving direct signaling over a unicast channel.

According to some embodiments, a UE operable to transmit uplink data in unlicensed spectrum comprises a memory coupled to processing circuitry. The processing circuitry is operable to receive, from a network node, an uplink grant comprising an indication of one or more subframes to use for transmitting uplink data. Each subframe comprises a plurality of symbols. The processing circuitry is further operable to obtain an indication of a LBT type. The LBT type indicates a type of LBT procedure that the UE should perform before transmitting uplink data. The processing circuitry is further operable to determine, using the obtained LBT type, at least one of a starting symbol and a stopping symbol for transmitting uplink data, and transmit uplink data according to at least one of the determined starting symbol and the determined stopping symbol.

According to some embodiments, a method for use in a UE of transmitting uplink data in unlicensed spectrum comprises receiving, from a network node, an uplink grant comprising an indication of one or more subframes to use for transmitting uplink data; receiving, from the network node, an indication of a last subframe x that is within a maximum channel occupancy time (MCOT) limit based on a downlink burst after a successful category 4 LBT procedure performed by the network node; transmitting uplink data in the one or more subframes of the uplink grant prior to subframe x based on a short clear channel assessment (CCA) procedure; and transmitting uplink data in the one or more subframes of the uplink grant after subframe x based on a category 4 LBT procedure.

In particular embodiments, receiving the indication of the last subframe within the MCOT limit comprises receiving a number of subframes offset from the first subframe of the one or more subframes of the uplink grant. Receiving the indication of the last subframe within the MCOT limit may comprise receiving common signaling over a broadcast channel or receiving direct signaling over a unicast channel.

According to some embodiments, a UE operable to transmit uplink data in unlicensed spectrum comprises a memory coupled to processing circuitry. The processing circuitry is operable to: receive, from a network node, an uplink grant comprising an indication of one or more subframes to use for transmitting uplink data; receive, from the network node, an indication of a last subframe (x) that is within a MCOT limit based on a downlink burst after a successful category 4 LBT procedure performed by the network node; transmit uplink data in the one or more subframes of the uplink grant prior to subframe x based on a short CCA procedure; and transmit uplink data in the one or more subframes of the uplink grant after subframe x based on a category 4 LBT procedure.

Also disclosed is a computer program product. The computer program product comprises instructions stored on non-transient computer-readable media which, when executed by a processor, perform the act of receiving, from a network node, an uplink grant comprising an indication of one or more subframes to use for transmitting uplink data. Each subframe comprises a plurality of symbols. The instructions further perform the act of obtaining an indication of a LBT type. The LBT type indicates a type of LBT procedure that the UE should perform before transmitting uplink data. The instructions further perform the acts of determining, using the obtained LBT type, at least one of a starting symbol and a stopping symbol for transmitting uplink data, and transmitting uplink data according to at least one of the determined starting symbol and the determined stopping symbol.

Also disclosed is another computer program product. The computer program product comprises instructions stored on non-transient computer-readable media which, when executed by a processor, perform the acts of receiving, from a network node, an uplink grant comprising an indication of one or more subframes to use for transmitting uplink data; receiving, from the network node, an indication of a last subframe (x) that is within a MCOT limit based on a downlink burst after a successful category 4 LBT procedure performed by the network node; transmitting uplink data in the one or more subframes of the uplink grant prior to subframe x based on a short CCA procedure; and transmitting uplink data in the one or more subframes of the uplink grant after subframe x based on a category 4 LBT procedure.

Particular embodiments may exhibit some of the following technical advantages. For example, particular embodiments may improve uplink and/or system performance by reducing the amount of signaling, which may reduce network load and device complexity. Other technical advantages will be readily apparent to one skilled in the art from the following figures, description and claims.

