Systems and methods for multiplexing scheduling requests in unlicensed bands

According to certain embodiments, a method implemented in a wireless device is provided that includes determining that a scheduling request (SR) cannot be transmitted on an uplink during a scheduled SR opportunity. The SR is transmitted in a first transmission opportunity following a partial downlink (DL) subframe from a network node (115).

TECHNICAL FIELD

The present disclosure relates, in general, to wireless communications and, more particularly, to multiplexing scheduling requests in unlicensed bands.

BACKGROUND

The 3GPP Rel-13 feature “License-Assisted Access” (LAA) allows LTE equipment to also operate in the unlicensed 5 GHz radio spectrum. The unlicensed 5 GHz spectrum is used as a complement to the licensed spectrum. An ongoing 3GPP Rel-14 work item adds UL transmissions to LAA. Accordingly, devices such as LTE user equipment (UEs), for example, 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). Standalone operation of LTE in unlicensed spectrum is also possible and is under development by the MuLTEfire Alliance.

For the case of standalone LTE-U, the initial random access (RA) and subsequent uplink (UL) transmissions take place entirely on the unlicensed spectrum. Regulatory requirements may not permit transmissions in the unlicensed spectrum without prior channel sensing. Since the unlicensed spectrum must be shared with other radios of similar or dissimilar wireless technologies, a so-called listen-before-talk (LBT) procedure may be used. LBT involves sensing the medium for a pre-defined minimum amount of time and backing off if the channel is busy. Today, the unlicensed 5 GHz spectrum is mainly used by equipment implementing the IEEE 802.11 Wireless Local Area Network (WLAN) standard, also known under its marketing brand as “Wi-Fi.”

FIG. 1illustrates the basic LTE downlink physical resource. LTE uses Orthogonal Frequency Division Multiplexing (OFDM) in the downlink and Discrete Fourier Transform (DFT)-spread OFDM (also referred to as single-carrier FDMA (SC-FDMA)) in the uplink. The basic LTE downlink physical resource can thus be seen as a time-frequency grid, where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval. The 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.

FIG. 2illustrates the LTE time-domain structure. In the time domain, LTE downlink transmissions are organized into radio frames of 10 ms, each radio frame consisting of ten equally-sized subframes of length Tsubframe=1 ms as shown inFIG. 2. Each subframe comprises two slots of duration 0.5 ms each, and the slot numbering within a frame ranges from 0 to 19. For normal cyclic prefix, one subframe consists of 14 OFDM symbols. The duration of each symbol is approximately 71.4 μs.

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

Downlink transmissions are dynamically scheduled. Specifically, in each subframe the 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 the control information. A downlink subframe with CFI=3 OFDM symbols as control is illustrated inFIG. 3. The reference symbols shown there are the cell specific reference symbols (CRS) and are used to support multiple functions including fine time and frequency synchronization and channel estimation for certain transmission modes.

Uplink transmissions are dynamically scheduled, i.e., in each downlink subframe the base station transmits control information about which terminals should transmit data to the network node in subsequent subframes, and upon which resource blocks the data is transmitted. The uplink resource grid is comprised of data and uplink control information in the PUSCH, uplink control information in the PUCCH, and various reference signals such as demodulation reference signals (DMRS) and sounding reference signals (SRS). DMRS are used for coherent demodulation of PUSCH and PUCCH data, whereas SRS is not associated with any data or control information but is generally used to estimate the uplink channel quality for purposes of frequency-selective scheduling. An example uplink subframe is shown inFIG. 4. Note that UL DMRS and SRS are time-multiplexed into the UL subframe, and SRS are always transmitted in the last symbol of a normal UL subframe. The PUSCH DMRS is transmitted once every slot for subframes with normal cyclic prefix, and is located in the fourth and eleventh SC-FDMA symbols.

From LTE Rel-11 onwards, DL or UL resource assignments can also be scheduled on the enhanced Physical Downlink Control Channel (EPDCCH). For Rel-8 to Rel-10 only the Physical Downlink Control Channel (PDCCH) is available. Resource grants are UE specific and are indicated by scrambling the DCI Cyclic Redundancy Check (CRC) with the UE-specific C-RNTI identifier.

If a wireless device, which may include a UE, has uplink data waiting for transmission in its buffer but does not have any scheduled UL grants, it can send a 1-bit scheduling request (SR) to the serving or primary cell using available PUCCH resources. The SR can be sent using PUCCH Format 1, or be multiplexed with HARQ ACK/NACK feedback in PUCCH Formats 1a, 1b, or 3. The SR modulation is based on on-off keying where a ‘+1’ indicates the SR, and nothing is sent if SR is not transmitted. The UE-specific SR transmission periodicity and SR subframe offset are configured by higher-layer signaling, as shown in Table 1.

TABLE 1SR periodicity and offset configurations (TS 36.213 v. 12.3.0, Rel-12)SR configuration IndexSR periodicity (ms)SR subframe offsetISRSRPERIODICITYNOFFSET, SR0-45ISR5-1410ISR-515-3420ISR-1535-7440ISR-3575-15480ISR-75155-1562ISR-1551571ISR-157
Once an eNB receives a SR, it can send an UL grant to the UE and make additional scheduling decisions based on Buffer Status Reports sent by the UE on PUSCH.

The LTE Rel-10 standard supports bandwidths larger than 20 MHz. One important requirement on LTE Rel-10 is to assure backward compatibility with LTE Rel-8. This should also include spectrum compatibility. That would imply that an LTE Rel-10 carrier, wider than 20 MHz, should appear as a number of LTE carriers to an LTE Rel-8 terminal. Each such carrier can be referred to as a Component Carrier (CC). In particular for early LTE Rel-10 deployments it can be expected that there will be a smaller number of LTE Rel-10-capable terminals compared to many LTE legacy terminals. Therefore, it is necessary to assure an efficient use of a wide carrier also for legacy terminals, i.e. that it is possible to implement carriers where legacy terminals can be scheduled in all parts of the wideband LTE Rel-10 carrier. The straightforward way to obtain this would be by means of Carrier Aggregation (CA). CA implies that an LTE Rel-10 terminal can receive multiple CC, where the CC have, or at least the possibility to have, the same structure as a Rel-8 carrier. CA is illustrated inFIG. 5. A CA-capable UE is 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 CC as well as the bandwidth of the individual CC may be different for uplink and downlink. A symmetric configuration refers to the case where the number of CCs in downlink and uplink is the same whereas an asymmetric configuration refers to the case that the number of CCs is different. It is important to note that the number of CCs configured in a cell may be different from the number of CCs seen by a terminal: A terminal may for example support more downlink CCs than uplink CCs, even though the cell is configured with the same number of uplink and downlink CCs.

In typical deployments of WLAN, carrier sense multiple access with collision avoidance (CSMA/CA) is used 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 declared as Idle. In case the channel is declared as Busy, the transmission is essentially deferred until the channel is deemed to be Idle.

A general illustration of the listen before talk (LBT) mechanism of Wi-Fi is shown inFIG. 6. After a Wi-Fi station A transmits a data frame to a station B, station B shall transmit the ACK frame back to station A with a delay of 16 μs. Such an ACK frame is transmitted by station B without performing a LBT operation. To prevent another station interfering with such an ACK frame transmission, a station shall defer 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. Therefore, a station that wishes to transmit first performs a CCA 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 begin 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.

Using the LBT protocol, when the medium becomes available, multiple Wi-Fi stations may be ready to transmit, which can result in collision. To reduce collisions, stations intending to transmit select a random backoff counter and defer for that number of slot channel idle times. The random backoff counter is selected as a random integer drawn from a uniform distribution over the interval of [0, CW]. The default size of the random backoff contention window, CWmin, is set in the IEEE specs. Note that collisions can still happen even under this random backoff protocol when there are many stations contending for the channel access. Hence, to avoid recurring collisions, the backoff contention window size CW is doubled whenever the station detects a collision of its transmission up to a limit, CWmax, also set in the IEEE specs. When a station succeeds in a transmission without collision, it resets its random backoff contention window size back to the default value CWmin.

FIG. 7illustrates licensed-assisted access (LAA) to unlicensed spectrum using LTE carrier aggregation. Up to now, the spectrum used by LTE has been dedicated to LTE. This has the advantage that the LTE system does not need to care about the coexistence issue and the spectrum efficiency can be maximized. However, the spectrum allocated to LTE is limited, and the allocated spectrum cannot meet the ever increasing demand for larger throughput from applications and/or services. Therefore, a new study item has been initiated in 3GPP on extending LTE to exploit unlicensed spectrum in addition to licensed spectrum. Unlicensed spectrum can, by definition, be simultaneously used by multiple different technologies. Therefore, LTE needs to consider the coexistence issue with other systems such as IEEE 802.11 (Wi-Fi). Operating LTE in unlicensed spectrum in the same manner as in licensed spectrum can seriously degrade the performance of Wi-Fi, as Wi-Fi will not transmit once it detects the channel is occupied.

Furthermore, one way to utilize the unlicensed spectrum reliably is to transmit essential control signals and channels on a licensed carrier. That is, as shown inFIG. 7, a UE is connected to a PCell in the licensed band and one or more SCells in the unlicensed band. In this application, a secondary cell in unlicensed spectrum is referred to as a licensed-assisted access secondary cell (LAA SCell).

FIG. 8illustrates UL LAA listen before talk (LBT). In Rel-13 LAA, LBT for DL data transmissions follow a random backoff procedure similar to that of Wi-Fi, with CW adjustments based on HARQ NACK feedback. Several aspects of UL LBT were discussed during Release 13. With regard to the framework of UL LBT, the discussion focused on the self-scheduling and cross-carrier scheduling scenarios. UL LBT imposes an additional LBT step for UL transmissions with self-scheduling, since the UL grant itself requires a DL LBT by the eNB. The UL LBT maximum CW size should then be limited to a very low value to overcome this drawback, if random backoff is adopted. Therefore, Release 13 LAA recommended that the UL LBT for self-scheduling should use either a single CCA duration of at least 25 μs (similar to DL DRS), or a random backoff scheme with a defer period of 25 μs including a defer duration of 16 us followed by one CCA slot, and a maximum contention window size chosen from X={3, 4, 5, 6, 7}. These options are also applicable for cross-carrier scheduling of UL by another unlicensed SCell.FIG. 8illustrates an example UL LBT and UL transmission when the UL grant is sent on an unlicensed carrier.

SR transmission opportunities are not guaranteed for MuLTEfire due to LBT requirements and the possibility for any subframe to be used for either UL or DL transmissions. Therefore, a periodic SR opportunity may be blocked due to failed LBT or conflict with a DL transmission from the eNB. There is currently no solution for robust SR transmission and multiplexing in LBT systems with multiple users in general.

SUMMARY

To address the foregoing problems with existing solutions, disclosed is methods and systems for robust scheduling request (SR) transmission and multiplexing in LBT systems, such as MuLTEfire, Rel-14 LAA, and other versions of LTE in unlicensed bands.

According to certain embodiments, a method for multiplexing scheduling requests in unlicensed bands is implemented in a wireless device. The method includes determining that a scheduling request (SR) cannot be transmitted on an uplink during a scheduled SR opportunity. The SR is transmitted in a first transmission opportunity following a partial downlink (DL) subframe from a network node.

According to certain embodiments, a wireless device for multiplexing scheduling requests in unlicensed bands includes a memory storing instructions and a processor operable to execute the instructions to cause the processor to determine that a scheduling request (SR) cannot be transmitted on an uplink during a scheduled SR opportunity. The SR is transmitted in a first transmission opportunity following a partial DL subframe from a network node.

According to certain embodiments, a method for multiplexing scheduling requests in unlicensed bands is implemented in a network node. The method includes transmitting, by the network node, signaling that indicates a partial DL subframe to be subsequently transmitted to a wireless device. The partial DL subframe is transmitted to the wireless device. A scheduling request (SR) is received from the wireless device in a first transmission opportunity following the partial DL subframe.

According to certain embodiments, a network node for multiplexing scheduling requests in unlicensed bands is provided. The network node includes a memory storing instructions and a processor operable to execute the instructions to cause the processor to transmit signaling that indicates a partial DL subframe to be subsequently transmitted to a wireless device. The partial DL subframe is transmitted to the wireless device and a scheduling request (SR) is received from the wireless device in a first transmission opportunity following the partial DL subframe.

Certain embodiments of the present disclosure may provide one or more technical advantages. For example, in certain embodiments, deferred scheduling request transmissions may be multiplexed in an efficient and robust manner. This may advantageously improve overall system performance for such a system. Other advantages may be readily apparent to one having skill in the art. Certain embodiments may have none, some, or all of the recited advantages.

DETAILED DESCRIPTION

Scheduling request (SR) transmission opportunities are not guaranteed for MuLTEfire. For example, due to listen before talk (LBT) requirements, a periodic scheduling resource opportunity may be blocked. Additionally, because any subframe may be used for either uplink (UL) or downlink (DL) transmissions, there is the possibility that an UL SR may conflict with a DL transmission from a network node. Accordingly, there is a need for robust SR transmission and multiplexing in LBT systems that include multiple users.

Particular embodiments are described inFIGS. 1-27of the drawings, like numerals being used for like and corresponding parts of the various drawings.FIG. 9is a block diagram illustrating embodiments of a network100for multiplexing SRs in unlicensed bands, according to certain embodiments. Network100includes one or more wireless devices110A-C, which may be interchangeably referred to as wireless devices110or UEs110, and network nodes115A-C, which may be interchangeably referred to as network nodes115or eNodeBs115. A wireless device110may communicate with network nodes115over a wireless interface. For example, wireless device110A may transmit wireless signals to one or more of network nodes115, and/or receive wireless signals from one or more of network nodes115. The wireless signals may contain voice traffic, data traffic, control signals, and/or any other suitable information. In some embodiments, an area of wireless signal coverage associated with a network node115may be referred to as a cell. In some embodiments, wireless devices110may have D2D capability. Thus, wireless devices110may be able to receive signals from and/or transmit signals directly to another wireless device110. For example, wireless device110A may be able to receive signals from and/or transmit signals to wireless device110B.

In certain embodiments, network nodes115may interface with a radio network controller (not depicted inFIG. 9). The radio network controller may control network nodes115and may provide certain radio resource management functions, mobility management functions, and/or other suitable functions. In certain embodiments, the functions of the radio network controller may be included in network node115. The radio network controller may interface with a core network node. In certain embodiments, the radio network controller may interface with the core network node via an interconnecting network. The interconnecting network may refer to any interconnecting system capable of transmitting audio, video, signals, data, messages, or any combination of the preceding. The interconnecting network may include all or a portion of a public switched telephone network (PSTN), a public or private data network, a local area network (LAN), a metropolitan area network (MAN), a wide area network (WAN), a local, regional, or global communication or computer network such as the Internet, a wireline or wireless network, an enterprise intranet, or any other suitable communication link, including combinations thereof.

In some embodiments, a core network node (not depicted inFIG. 9) may manage the establishment of communication sessions and various other functionalities for wireless devices110. Wireless devices110may exchange certain signals with the core network node using the non-access stratum layer. In non-access stratum signaling, signals between wireless devices110and the core network node may be transparently passed through the radio access network. In certain embodiments, network nodes115may interface with one or more network nodes over an internode interface. For example, network nodes115A and115B may interface over an X2 interface.

As described above, example embodiments of network100may include one or more wireless devices110, and one or more different types of network nodes capable of communicating (directly or indirectly) with wireless devices110. Wireless device110may refer to any type of wireless device communicating with a node and/or with another wireless device in a cellular or mobile communication system. Examples of wireless device110include a mobile phone, a smart phone, a PDA (Personal Digital Assistant), a portable computer (e.g., laptop, tablet), a sensor, a modem, a machine-type-communication (MTC) device/machine-to-machine (M2M) device, laptop embedded equipment (LEE), laptop mounted equipment (LME), USB dongles, a D2D capable device, or another device that can provide wireless communication. A wireless device110may also be referred to as UE, a station (STA), a device, or a terminal in some embodiments. Also, in some embodiments, generic terminology, “radio network node” (or simply “network node”) is used. It can be any kind of network node, which may comprise a Node B, base station (BS), multi-standard radio (MSR) radio node such as MSR BS, eNode B, network controller, radio network controller (RNC), base station controller (BSC), relay donor node controlling relay, base transceiver station (BTS), access point (AP), transmission points, transmission nodes, RRU, RRH, nodes in distributed antenna system (DAS), core network node (e.g. MSC, MME etc.), O&M, OSS, SON, positioning node (e.g. E-SMLC), MDT, or any suitable network node. Example embodiments of network nodes115, wireless devices110, and other network nodes are described in more detail with respect toFIGS. 10 and 11, respectively.

AlthoughFIG. 9illustrates a particular arrangement of wireless network100, the present disclosure contemplates that the various embodiments described herein may be applied to a variety of networks having any suitable configuration. For example, wireless network100may include any suitable number of wireless devices110and network nodes115, as well as any additional elements suitable to support communication between wireless devices or between a wireless device and another communication device (such as a landline telephone). Furthermore, although certain embodiments may be described as implemented in a long term evolution (LTE) network, the embodiments may be implemented in any appropriate type of telecommunication system supporting any suitable communication standards and using any suitable components, and are applicable to any radio access technology (RAT) or multi-RAT systems in which the wireless device receives and/or transmits signals (e.g., data). For example, the various embodiments described herein may be applicable to LTE, LTE-Advanced, LTE-U UMTS, HSPA, GSM, cdma2000, WiMax, WiFi, another suitable radio access technology, or any suitable combination of one or more radio access technologies. Although certain embodiments may be described in the context of wireless transmissions in the downlink, the present disclosure contemplates that the various embodiments are equally applicable in the uplink and vice versa.

The SR multiplexing techniques described herein are applicable to both LAA LTE and standalone LTE operation in license-exempt channels. The described techniques are generally applicable for transmissions from both network nodes115and wireless devices110.

FIG. 10is a block diagram illustrating certain embodiments of a network node115for multiplexing SRs in unlicensed bands. Examples of network node115include an eNodeB, a node B, a base station, a wireless access point (e.g., a Wi-Fi access point), a low power node, a base transceiver station (BTS), transmission points, transmission nodes, remote RF unit (RRU), remote radio head (RRH), etc. Network nodes115may be deployed throughout wireless network100as a homogenous deployment, heterogeneous deployment, or mixed deployment. A homogeneous deployment may generally describe a deployment made up of the same (or similar) type of network nodes115and/or similar coverage and cell sizes and inter-site distances. A heterogeneous deployment may generally describe deployments using a variety of types of network nodes115having different cell sizes, transmit powers, capacities, and inter-site distances. For example, a heterogeneous deployment may include a plurality of low-power nodes placed throughout a macro-cell layout. Mixed deployments may include a mix of homogenous portions and heterogeneous portions.

Network node115may include one or more of transceiver210, processor220, memory230, and network interface240. In some embodiments, transceiver210facilitates transmitting wireless signals to and receiving wireless signals from wireless devices110(e.g., via an antenna), processor220executes instructions to provide some or all of the functionality described above as being provided by a network node115, memory230stores the instructions executed by processor220, and network interface240communicates signals to backend network components, such as a gateway, switch, router, Internet, Public Switched Telephone Network (PSTN), core network nodes130, radio network controllers120, etc.

In some embodiments, network interface240is communicatively coupled to processor220and may refer to any suitable device operable to receive input for network node115, send output from network node115, perform suitable processing of the input or output or both, communicate to other devices, or any combination of the preceding. Network interface240may include appropriate hardware (e.g., port, modem, network interface card, etc.) and software, including protocol conversion and data processing capabilities, to communicate through a network.

FIG. 11illustrates an example wireless device110for multiplexing SRs in unlicensed bands, in accordance with certain embodiments. As depicted, wireless device110includes transceiver310, processor320, and memory330. In some embodiments, transceiver310facilitates transmitting wireless signals to and receiving wireless signals from network node115(e.g., via an antenna), processor320executes instructions to provide some or all of the functionality described above as being provided by wireless device110, and memory330stores the instructions executed by processor320. Examples of a wireless device110are provided above.

Other embodiments of wireless device110may include additional components beyond those shown inFIG. 11that may be responsible for providing certain aspects of the wireless device's functionality, including any of the functionality described above and/or any additional functionality (including any functionality necessary to support the solution described above).

In 3GPP LTE, the uplink control information (UCI) including HARQ-ACK, SR and periodic Control System Information (CSI) can be transmitted on the Physical Uplink Control Channel (PUCCH). For standalone operation in unlicensed band, two PUCCH formats can be considered for UCI transmission depending on the network node timing configuration and HARQ protocol. Stated differently, the PUCCH format may be of two formats: Short PUCCH (sPUCCH) that is n symbols (between 1-4) and long PUCCH (ePUCCH) that is 13-14 symbols. It may be beneficial that each UL serving cell carries the HARQ feedback for the corresponding DL serving cell in standalone LTE-U. This avoids a scenario where one cell determining the HARQ-ACK feedbacks of all cells. This approach may be different from LTE where the PUCCH of the PCell typically carries the UCI for all SCells. However, in terms of channel utilization and PUCCH format design, it may be beneficial to have independent PUCCH for each standalone carrier.

In certain embodiments, a short PUCCH (sPUCCH) occupies 1-3 SC-FDMA/OFDM symbols in time domain and spans the whole bandwidth by interlacing. A sPUCCH can be transmitted in the end of a partial DL subframe or as a part of an UL subframe (if the PUSCH is scheduled to the same wireless device). In order to transmit sPUCCH, an aggressive LBT may be applied by the wireless device110. Alternatively, no LBT may be required if sPUCCH duration is below 5% of the duty cycle according to certain regulatory requirements.

FIG. 12illustrates an example of a short PUCCH400, in accordance with certain embodiments. As depicted, short PUCCH (or sPUCCH) occupies two SC-FDMA/OFDM symbols in time and one interlace in frequency domain. The DMRS and data symbol for PUCCH can be frequency multiplexed402or time multiplexed404. Multiple PUCCH wireless devices can be multiplexed in the frequency domain by assigning different interlacing patterns and/or in the code domain by applying, for example, different orthogonal cover codes (OCCs) within a single interlace. The number of symbols, interlacing patterns, and OCC configuration (if any) can be configured for a wireless device110by network node signaling.

The HARQ feedback and the corresponding process IDs could either be listed explicitly or e.g. be provided as a bitmap (one or two bits per process). To align the design with 3GPP Rel-13 CA, the UCI on sPUCCH is attached with an 8-bit CRC and encoded using Tail Biting Convolutional Code (TBCC). The encoded symbols are mapped to available REs in a frequency first time second manner.

FIG. 13illustrates an example of a long PUCCH (ePUCCH)500, in accordance with certain embodiments. A long PUCCH occupies a full subframe in time domain, and spans the whole bandwidth by interlacing. A long PUCCH can be explicitly scheduled by eNB where LBT is required at wireless device110to get access to the UL channel. The long PUCCH is compatible and can be multiplexed with PUSCH transmission from the same or different wireless devices110.

In the example embodiment depicted inFIG. 13, the ePUCCH500occupies one interlace in one subframe. There is one DMRS per slot occupying the whole bandwidth in frequency, which can be multiplexed with PUSCH DMRS by applying different cyclic shifts. Similarly to the sPUCCH depicted inFIG. 12, multiple PUCCH wireless devices110can be multiplexed in the frequency domain by assigning different interlacing patterns and/or in the code domain by applying, for example, different orthogonal cover codes (OCCs) within a single interlace. The remaining interlaces within the same subframe can be used for PUSCH transmission and PUCCH/PUSCH transmission from other wireless devices. The interlace pattern, CS and OCC configuration (if any) can be configured for a wireless device110by eNB signaling.

Similar to sPUCCH, the HARQ feedback and the corresponding process IDs could either be listed explicitly or e.g. be provided as a bitmap (one or two bits per process) on long PUCCH. The UCI on long PUCCH is attached with an 8-bit CRC and encoded using Tail Biting Convolutional Code (TBCC). The encoded symbols are mapped to available REs in a frequency first time second manner.

In 3GPP LTE, the UCI transmission on PUCCH includes HARQ-ACK, SR and periodic CSI. For standalone LTE-U, it would be difficult to support periodic CSI and hence aperiodic CSI feedback is more essential and should be supported on PUSCH scheduled by UL grant with or without UL-SCH data. If more than one UCI type is transmitted on PUCCH, e.g. HARQ and SR in the same subframe, they are concatenated, jointly encoded and sent on either sPUCCH or long PUCCH format according to the eNB configuration based on DL HARQ protocol.

Since Rel-8, the downlink HARQ protocol is asynchronous. Thus, the HARQ feedback (ACK/NACK) can be sent reliably on the PUCCH of a licensed PCell. However, for standalone operation (as well as for LAA with Dual Connectivity) also the UL Control Information (UCI) is transmitted on unlicensed spectrum. Currently, regulatory rules allow for the omission of LBT for control information (not for user plane data) if those transmissions do not occupy the medium for more than 5% in a 50 ms observation window. While it would be attractive from protocol point of view to design the PUCCH based on this rule, the resulting collisions could impact the system performance negatively. Furthermore, there may be attempts to modify or reject the 5% rule. Therefore, applying LBT to control signaling may be appropriate.

As of today, the LTE DL HARQ design relies solely on the fixed timing relation between the DL HARQ process and the corresponding HARQ feedback. Due to LBT, the time between DL transmission and HARQ feedback may vary. Accordingly, it may be appropriate to transmit the HARQ process ID in the HARQ feedback sent in the uplink.

Since any kind of bundling increases the RTT, immediate feedback (in subframe n+4) is generally preferable in terms of e2e latency. However, it may also require network node116and wireless device110to switch the transmission direction (i.e., from DL to UL or from UL to DL) more frequently which increases overhead. If the HARQ process ID needs to be included in the HARQ feedback anyway, the HARQ feedback for multiple downlink processes may be bundled into a single uplink message.

While immediate feedback per process reduces the latency observed on IP layer, the feedback bundling improves the spectral efficiency. Which of these “modes” is preferable depends e.g. on the system load and on the queue of the particular UE (e.g. TCP slow start vs. congestion avoidance phase). Therefore, network node115may have means to toggle dynamically between these modes, i.e., request wireless device110to send the HARQ feedback for each process individually or let wireless device110bundle feedback for multiple processes.

According to a first proposed embodiment, network node115controls whether wireless device110sends HARQ feedback immediately (n+4) or delays (and possibly bundles) it until a later point in time. This request could be either explicit as part of the DL assignment or wireless device110may determine it based on the availability of appropriate resources for sending UCI. The details may depend also on the PUCCH design(s) which are discussed below.

ACK/NACK feedback may be provisioned for downlink HARQ processes. In principle, it should be possible to transmit HARQ feedback (UCI) in:

1. the same subframe as PUSCH from the same wireless device110;

2. the same subframe as PUSCH from another wireless device110;

3. the same subframe as PDSCH for the same wireless device110;

4. the same subframe as PDSCH for another wireless device110; and

5. an empty subframe where wireless device110did neither receive an UL grant nor detect PDSCH.

FIG. 14depicts an example UCI600mapped to PUSCH of the same wireless device110. Specifically,FIG. 11depicts where wireless device110has received downlink data on PDSCH in four consecutive subframes as well as UL grants valid for the four subsequent subframes. Whenever wireless device has already been scheduled on PUSCH, it may be desirable to send the HARQ feedback (if any is available) and other UCI as early as possibly in order to minimize the protocol latency. The UCI600should be mapped onto those PUSCH resources to maintain preferable transmission characteristics. In certain embodiments, “PUCCH over PUSCH may be allowed.” As such, in response to a valid UL grant, pending HARQ feedback (and possibly other UCI) may be multiplexed onto PUSCH.

FIG. 15illustrates an example UCI700on ePUCCH together with PUSCH from another wireless device110. Specifically,FIG. 15depicts a case where the UCI700from wireless device110having received PDSCH in the first four subframes is mapped to the (long) ePUCCH that spans across all available symbols of the subsequent 4 subframes. The PUSCH resources are assumed to be allocated to another wireless device110. In certain embodiments, ePUCCH may be multiplexed with PUSCH in the same subframe on different interlaces. Multiple users can be multiplexed on the same ePUCCH interlace.

In the example ofFIG. 15, wireless device110provides HARQ feedback as early as possible (i.e., n+4) which is desirable in terms of latency. If the subframes are anyway used for PUSCH transmissions of other wireless devices, the additional overhead due to immediate HARQ feedback is negligible. If, however, network node115does not need the intermediate subframes, it may be desirable to leave those empty such that they are available for other systems and to let wireless device110bundle the HARQ feedback within a single PUCCH transmission. In order to follow the Rel-8 principle and to aim for low protocol latency, it is suggested that wireless device110sends by default the HARQ feedback at the earliest point in time where PUCCH resources are available. If the network intends to minimize wireless device power consumption or link occupancy, the network may indicate in the DL assignment that wireless device110shall postpone the HARQ feedback until having received another assignment without such indication.

FIG. 16illustrates a bundled ePUCCH transmission800, in accordance with certain embodiments. Specifically, network node115indicates in the first three downlink subframes that wireless device110shall defer HARQ feedback. Network node115omits this indication in the fourth downlink subframe. Consequently, wireless device110omits PUCCH in subframes5,6and7and then sends bundled feedback for all 4 HARQ processes in subframe8.

According to a second proposed embodiment, by default, wireless device110may send available HARQ feedback at the earliest point in time where PUCCH resources are available. Note that certain embodiments require wireless device110to have HARQ feedback for PDSCH available in n+4.

According to a third proposed embodiment, network node115may indicate in a DL assignment that wireless device110shall postpone the HARQ feedback corresponding to this HARQ process. Wireless device110shall send the HARQ process only upon reception of a subsequent DL assignment without this indication.

User traffic is often downlink-heavy. Hence, there will be occasions in which network node115intends to schedule more DL than UL subframes. Spending entire subframes for PUCCH would create an undesirable overhead. Therefore, a short PUCCH (sPUCCH) in addition to the ePUCCH may be supported. This sPUCCH may appear at the end of a shortened downlink (or special) subframe as described above and as shown inFIG. 17. The presence of a shortened downlink subframe may be announced on C-PDCCH and correspondingly the dynamic sPUCCH may be indicated by C-PDCCH.

FIG. 17illustrates a sPUCCH900with continuous PDSCH allocation, in accordance with certain embodiments. As depicted inFIG. 17, wireless device110is scheduled for PDSCH continuously. The HARQ feedback for the PDSCH received in subframe1could have been transmitted in subframe5in accordance with the legacy HARQ timeline. However, in this example, network node115used subframe5for another PDSCH transmission. As a result, wireless device110had to postpone the HARQ feedback in subframe1, depicted as902A. The same applies for the HARQ feedback corresponding to subframes2and3, depicted as902B-C. In subframe7, the C-PDCCH indicates that the subsequent subframe (subframe8) will be a shortened subframe904and that there will be an sPUCCH occasion. As such, wireless device110may send the HARQ feedback corresponding to subframe1, subframe2, subframe3, and subframe4at the end of subframe8. In this example, the indication in the DL assignment for postponing and bundling of the HARQ feedback would not have been necessary.

FIG. 18illustrates a sPUCCH1000where not all subframes are occupied by PDSCH continuously. As depicted, the sPUCCH has empty subframes. A similar scenario is also depicted inFIG. 16, discussed above. In the depicted example, wireless device110postpones the HARQ feedback, depicted as1002A-C. Wireless device110may, in certain embodiments, attempt to send its feedback using ePUCCH as soon as possible. To avoid that, network node115may instruct wireless device110in the DL assignment to postpone the HARQ feedback by indicating that a subsequent subframe will be a shortened subframe1004and that there will be an sPUCCH occasion.

According to another proposed embodiment, wireless device110sends pending HARQ feedback (and possibly other UCI) on sPUCCH if network node115indicates an sPUCCH opportunity using C-PDCCH.

The following discusses several issues related to LBT, including whether and when wireless device110should perform LBT prior to or in between UL transmissions.

Previous considerations included that wireless device110should perform only a short Clear Channel Assessment (25 μs) prior to a self-scheduled uplink transmission since network node115performed LBT with exponential back-off before sending the corresponding scheduling message. Accordingly, wireless device110may only verify that the channel is clear (which may in rare occasions not be the case due to “hidden node” effects) but not give others the opportunity to contend for the channel. In the same way as done for PUSCH, it may be possible to perform just a short LBT prior to the transmission of ePUCCH considering that the preceding PDSCH transmission was subject to a regular LBT. In other words, the ePUCCH uses the same LBT parameters as the scheduled PUSCH which allows multiplexing the transmissions in a single subframe.

According to certain other embodiments, wireless device110applies the same 25 μs defer-only CCA (“short LBT”) for scheduled PUSCH and ePUCCH which allows multiplexing such transmissions from different wireless devices110in a single subframe.

In the example inFIG. 15, the fourth PUCCH transmission by wireless device110needs to end early so that network node115may perform DL LBT prior to a subsequent DL subframe. This may be achieved by applying a sufficiently long timing advance to the wireless device's uplink transmission. As a consequence, the entire uplink burst may shift towards the left. The shortened DL subframe (SF4) may avoid overlap of the uplink burst with the preceding downlink burst. With this principle there is actually no need to shorten the uplink subframe itself at the end of the uplink burst (not depicted).

Besides the LBT upon transition from DL to UL and UL to DL, additional LBT phases are needed if different wireless devices110provide their PUCCH feedback or PUSCH transmissions in adjacent subframes. In certain embodiments, gaps may be allowed between subsequent UL subframes.FIG. 19illustrates a transmission scheme1100including UCI from two different wireless devices110in subsequent subframes, depicted as reference numerals1102and1104requiring additional LBT phase. Specifically, a first UE receives PDSCH in the first two subframes, depicted with reference numeral1102, and a second UE receives PDSCH in the third and fourth subframe, depicted with reference numeral1104. While network node115may perform the DL transmissions back-to-back, the second wireless device110needs to sense the channel to be empty before performing its PUCCH transmission.

When comparing the examples inFIG. 15andFIG. 19, it may be seen that a wireless device110cannot determine by itself whether to perform LBT prior to an uplink transmission. Even if it did transmit already in the preceding subframe, it may have to do another LBT prior to the subsequent subframe depending on whether or not other wireless devices110need to perform LBT in that subframe. Accordingly, in certain embodiments, network node115may indicate explicitly in UL grants (for PUSCH) and DL assignments (for PUCCH) whether wireless device110may skip LBT for the corresponding UL subframe. To avoid error cases, however, wireless device110may perform a short LBT in a scheduled uplink subframe if it had not performed a transmission in the preceding subframe. This mismatch could have occurred due to the wireless device's LBT in the preceding subframe or due to missing an UL grant or DL assignment.

According to still other embodiments, wireless device110may skip a short uplink LBT (prior to PUSCH and ePUCCH) if both of the following conditions are fulfilled:Wireless device110performed an UL transmission (PUCCH or PUSCH) in the preceding subframe; andNetwork node115explicitly permitted skipping LBT in the UL grant or DL assignment.

It may also be noted that in the examples ofFIG. 15andFIG. 19, wireless device110does not (need to) know whether its PUCCH transmission coincides with a PUSCH transmission of another wireless device110. In other words, the cases 2) and 5) in the list above are equivalent from the viewpoint of the wireless device110transmitting the PUCCH.

In certain embodiments, network node115may perform DL LBT prior to the start of a DL subframe. The network node115may shorten the last PDSCH subframe of a DL burst to make room for a subsequent LBT. Similarly, the last UL transmission (PUSCH or PUCCH) of a wireless device110may be shortened if another uplink transmission is supposed to follow.

In such scenarios, wireless device110may also perform UL LBT prior to the UL subframe. However, such an approach has drawbacks. For example, network node115may be required to decide whether the subsequent subframe will also be allocated to the same wireless device110. If so, the current subframe can span across all symbols; if not, the current subframe has to be shortened. Such “look-ahead” is processing heavy and increases the scheduling delay since it requires performing the uplink scheduling not only for subframe n+4 but also for n+5. Additionally, it is desirable that network node115have the ability to win LBT against one of the wireless devices110that intend to transmit PUCCH. As such, it may be desirable to perform UL LBT at the beginning of an UL subframe rather than at the end of the preceding subframe. As such, in certain embodiments, wireless device110may perform UL LBT at the beginning of the UL subframe rather than at the end of the preceding subframe. Following the principle of acknowledgements in Wi-Fi, wireless device110does not need to perform any LBT prior to the sPUCCH transmission because network node115performed LBT at the beginning of the preceding DL burst.

The “need for a gap between sPUCCH and PUSCH” is yet unresolved. According to certain embodiments, however, wireless device110perform a short LBT prior to its PUSCH subframe if it did not send sPUCCH in the preceding subframe. In a particular embodiment, for example, wireless device110may apply a 25 μs defer-only short LBT prior to transmission of sPUCCH. This scenario fits well with a situation where UL LBT is performed in the beginning of the UL subframe.

According to certain other embodiments, wireless device110may skip the short uplink LBT between sPUCCH and the subsequent PUSCH/ePUCCH if both of the following conditions are fulfilled:Wireless device110performed an UL transmission (sPUCCH) in the preceding subframe; andNetwork node115explicitly permitted skipping LBT in the UL grant or DL assignment.
If network node115intends to continue with a PDSCH transmission after the sPUCCH, network node115may do so after a short gap if that PDSCH belongs still to the same TxOP. Otherwise, network node115performs LBT including exponential back-off.

In LTE, network node115may configure a wireless device110that is RRC Connected with a Dedicated Scheduling Request (D-SR) resource on PUCCH. The periodicity (e.g. 2, 4, 10, 20 subframes) as well as the actual time/frequency resource may be configured semi-statically via RRC. Upon arrival of data (IP packets) from higher layer into the wireless devices110empty PDCP queue, a Buffer Status Report is triggered. If wireless device110does not have a valid uplink grant for sending the BSR, wireless device110sends a D-SR at its next D-SR occasion using the D-SR resource. The same principle could also be applied for standalone LTE in the unlicensed bands. However, it may be assumed that wireless device110performs LBT prior to the transmission of the D-SR on PUCCH.

FIG. 20illustrates a transmission scheme1200for transmitting a D-SR on sPUCCH. Specifically,FIG. 20depicts an example scenario where wireless device110receives UL data1202and is configured with a D-SR opportunity in every 4thsubframe. For example, the first subframe1203includes an unused D-SR opportunity for the wireless device110and possibly other wireless devices110too. At times when no wireless devices110connected with network node115is actively transmitting or receiving data, network node115minimizes downlink transmissions (DRS only) and most subframes will be empty. As depicted, network node115sends bundled uplink grants1206. Wireless device110attempts to send a D-SR1204in the third depicted D-SR occurrence and succeeds in transmitting a PUSCH after successful LBT1208in the beginning of the subframe.

Once the channel is occupied by UL or DL data transmissions (such as transmissions1210and1212, LBT prior to D-SR by wireless device110is likely to fail due to ongoing PDSCH/PUSCH data bursts. However, what might appear as a problem at a first glance may be considered a desirable property. For example, by using a more aggressive LBT configuration (still fair to Wi-Fi) than connected wireless devices110, network node115can grab the channel and schedule PDSCH/PUSCH efficiently as soon as data becomes available. To ensure that wireless devices110are able to inform network node115about available data, network node115may declare at least some of the wireless devices' D-SR occasions as shortened DL subframes1214or leave them empty. As shown in the latter part of the sequence inFIG. 20, wireless devices110will use those occasions for sending D-SR and HARQ feedback. Specifically, in the depicted example embodiment, network node115requests HARQ feedback to be sent in a corresponding subframe, shown at reference numeral1216. Wireless device110sends D-SR1218and HARQ Feedback1220on sPUCCH. Network node115sends UL grants1222. Wireless device110sends data and HARQ feedback1224on PUSCH.

According to certain particular embodiments, network node115may configure wireless device110with D-SR resources using RRC signaling. Wireless device110may send D-SR in the RRC-configured occasions on ePUCCH after successful short LBT. Alternatively, wireless device110may send D-SR in those occasions on sPUCCH if network node115announces the subframe to be a shortened DL subframe.

While there may be a need to multiplex HARQ feedback onto the wireless device's PUSCH resources, there is no need to do that with D-SR. The reason is that a wireless device110having a valid uplink grant will rather include a (more detailed) buffer status report inside the MAC PDU sent on PUSCH.

In addition to HARQ feedback and D-SR, PUCCH may also carry the channel state information (CSI). In LTE, CSI can be mapped to PUCCH as well as to PUSCH. In certain embodiments, aperiodic CSI reporting may be most essential. Like in LTE, the aperiodic CSI is mapped to PUSCH (possibly without UL user data). Such principles may also be followed for unlicensed standalone LTE.

In a particular embodiment, only aperiodic CSI feedback may be supported. The aperiodic CSI feedback may be mapped to PUSCH in accordance with the UL grant provided by network node115.

In certain embodiments, each UL serving cell may carry the HARQ feedback for the corresponding DL serving cell. This may be contrasted with LTE where typically the PUCCH of the PCell carries the UCI for all SCells but in terms of channel utilization and PUCCH format design we suggest to keep it separate in LTE unlicensed standalone. Accordingly, in a particular embodiment, each UL serving cell may carry the HARQ feedback for the corresponding DL serving cell.

In certain embodiments, there may not be a strong need to support a mode of operation with more downlink than uplink serving cells. In other words, wireless devices110may always support as many uplink as downlink carriers in Standalone LTE-U. This would follow the principles applied in Wi-Fi carrier bundling and may ease the definition of feedback formats. Accordingly, in a particular embodiment, multiplexing of feedback from multiple downlink serving cells onto a common uplink serving cell may not be supported. Specifically, wireless device110may always support as many uplink as downlink carriers in Standalone LTE-U.

In certain embodiments, wireless device110may determine the ePUCCH and sPUCCH resources to use. One possibility is that wireless device110derives them implicitly from the DL grants by similar mappings as defined in LTE. However, since network node115schedules the corresponding PDSCH transmission explicitly and the format of the ePUCCH is similar to that of the PUSCH, network node115may also grant the ePUCCH resources more explicitly. The transmission resources of ePUCCH may be selected according to L1 characteristics and the various UCI types.

FIG. 21illustrates a transmission scheme1300for deferring periodic SR transmissions by wireless devices110until an sPUCCH occurrence1302, according to certain embodiments. A dynamic sPUCCH may be signaled by CPDDCH. In certain embodiments, the dynamic sPUCCH1302may be the last n (to be chosen between 1 and 4) symbols of a subframe where the first 14-n symbols are not used for UL transmission.

In certain embodiments, wireless devices110associated with a cell may be configured with periodic SR transmissions using higher layer signaling. For example, as depicted wireless device110A may be configured with periodic SR transmissions in the first subframe1304and the third subframe1306of transmission opportunity1308. A second wireless device110B may be configured for periodic SR transmission in the fourth subframe1310. These SR opportunities associated with subframes1304,1306, and1310may be blocked if the network node115performs LBT procedure1311and allocates DL transmissions on the corresponding subframes. Accordingly, where wireless devices110A and110B are not scheduled for PUSCH, wireless devices110A and110B are unable to transmit SRs during the subframes1304,1306, and1310of transmission opportunity1308. Their SR transmissions are then deferred until the first UL transmission opportunity, which in this case is sPUCCH1302, which is depicted as the subframe following a partial DL subframe1314in fifth subframe1312. The occurrence of the sPUCCH1302is implicitly indicated by the eNB using common PDCCH signaling to indicate the presence of partial DL subframe1314. In certain embodiments, partial DL subframe1314may be equivalent to DwPTS. These SR transmissions can coincide with transmissions by other wireless devices110during the sPUCCH1302, such as HARQ ACK/NACK feedback associated with the first DL subframe1304. The sPUCCH1302duration may be between one to four symbols in the time domain, for example.

As used herein, a partial DL subframe refers to a DL subframe in which fewer than the full number of symbols are used for transmission. Thus, where a DL subframe is comprised of fourteen symbols, a partial DL subframe may be a subframe wherein less than all of the fourteen symbols is used. As such, the terms shortened subframe, partial subframe, partial DL subframe, shortened TTI, partial TTI, and partial DL TTI may be used interchangeably herein.

According to certain embodiments, the SR transmissions deferred to the sPUCCH1302need to be configured with appropriate transmission resources, including one or more of UL interlace, orthogonal cover code, and cyclic shift. An example of an UL interlace is a set of 10 resource blocks that are equally spaced in frequency and span the entire system bandwidth.

According to certain embodiments, wireless device110may be configured with two or more sets of PUCCH resources for SR transmission. One set is used when the periodic SR transmission opportunity is utilized. One of the additional sets is used when the SR transmission opportunity is deferred to the first available sPUCCH or ePUCCH. A cell-specific signal may be included in the common PDCCH or another control signal to dynamically indicate which of the additional sets should be utilized within a particular TXOP, when a DL-heavy TXOP allocation is signaled by the eNB. The eNB can utilize its knowledge of the expected ACK/NACK load in the sPUCCH to optimally select or configure the additional PUCCH resource set.

FIG. 22illustrates an example method1400by a wireless device110for multiplexing SRs in unlicensed bands, in accordance with certain embodiments. The method begins at step1402when wireless device110determines that an SR cannot be transmitted on an uplink during a scheduled SR opportunity. For example, returning toFIG. 21, wireless device110may determine that wireless device110cannot transmit SR during the first subframe1304when wireless device110detects a DL transmission from network node115in first subframe1304.

At step1404, wireless device110transmits the SR in a first transmission opportunity following a partial downlink (DL) subframe, which may also be referred to as a partial transmission time interval (TTI), from network node115. Returning toFIG. 21, for example, wireless device110may transmit the SR in the fifth subframe following partial DL subframe1314. In a particular embodiment, the first transmission opportunity following the partial DL subframe1314is a sPUCCH following the partial DL subframe1314. In a particular embodiment, the duration of the sPUCCH may be between one and four symbols in the time domain.

In certain embodiments, wireless device110may receive signaling from network node115that indicates the presence of the partial DL subframe. In a particular embodiment, for example, the signaling may include PDCCH signaling. Additionally or alternatively, wireless device110may receive configuration information identifying transmission resources to be used for transmitting the SR. For example, the configuration information may include an UL interlace, orthogonal cover code, and/or cyclic shift to be used for transmitting SR.

In certain embodiments, the SR may be transmitted at step1404concurrently (e.g., together with) with at least one additional transmission by another wireless device110. For example, the SR may be transmitted concurrently with ACK/NACK feedback associated with the partial DL subframe1314.

In certain embodiments, the methods for multiplexing SRs in unlicensed bands as described inFIG. 22may be performed by one or more virtual computing devices.FIG. 23illustrates an example virtual computing device1500for multiplexing SRs in unlicensed bands, according to certain embodiments. In certain embodiments, virtual computing device1500may include modules for performing steps similar to those described above with regard to the method illustrated and described inFIG. 22. For example, virtual computing device1500may include at least one determining module1502, at least one transmitting module1504, and any other suitable modules for multiplexing SRs in unlicensed bands. In some embodiments, one or more of the modules may be implemented using one or more processors320ofFIG. 11. In certain embodiments, the functions of two or more of the various modules may be combined into a single module.

The determining module1502may perform the determining functions of virtual computing device1500. For example, in a particular embodiment, determining module1502may determine that an SR cannot be transmitted on an uplink during a scheduled SR opportunity. For example, determining module1502may determine that the SR cannot be transmitted in response to detecting a DL transmission from a network node115.

The transmitting module1504may perform the transmitting functions of virtual computing device1500. For example, transmitting module1504may transmit the SR in a first transmission opportunity following a partial DL subframe from network node115. In a particular embodiment, transmitting module1504may transmit the SR on sPUCCH following the partial DL subframe.

Other embodiments of computer networking virtual apparatus1500may include additional components beyond those shown inFIG. 23that may be responsible for providing certain aspects of the wireless device's110functionality, including any of the functionality described above and/or any additional functionality (including any functionality necessary to support the solutions described above). The various different types of wireless devices110may include components having the same physical hardware but configured (e.g., via programming) to support different radio access technologies, or may represent partly or entirely different physical components.

FIG. 24illustrates an example method1600by a network node115for multiplexing SRs in unlicensed bands, in accordance with certain embodiments. The method begins at step1602when network node115transmits signaling that indicates a partial DL subframe, which may also be referred to as a partial DL TTI, is to be subsequently transmitted to a wireless device110. In a particular embodiment, for example, the signaling may include PDCCH signaling. Additionally or alternatively, network node115may transmit configuration information identifying transmission resources to be used for transmitting the SR. For example, the configuration information may include an UL interlace, an orthogonal cover code, and/or a cyclic shift to be used for transmitting SR.

At step1604, network node115transmits the partial downlink subframe to the wireless device110.

At step1606, network node115receives from the wireless device110a scheduling request (SR) in a first transmission opportunity following the partial DL subframe, which may also be referred to as a partial DL subframe. Returning toFIG. 21, for example, network node115may receive the SR in the fifth subframe following partial TTI1314. In a particular embodiment, the first transmission opportunity following the partial DL subframe1314is a sPUCCH following the partial DL subframe1314. In a particular embodiment, the duration of the sPUCCH may be between one and four symbols in the time domain.

In certain embodiments, the SR may be received concurrently with (e.g., together with) at least one additional transmission by another wireless device110. For example, the SR may be received concurrently with ACK/NACK feedback associated with the partial DL subframe1314.

In certain embodiments, the methods for multiplexing SRs in unlicensed bands as described inFIG. 24may be performed by one or more virtual computing devices.FIG. 25illustrates an example virtual computing device1700for multiplexing SRs in unlicensed bands, according to certain embodiments. In certain embodiments, virtual computing device1700may include modules for performing steps similar to those described above with regard to the method illustrated and described inFIG. 24. For example, virtual computing device1700may include at least one transmitting module1702, at least one receiving module1704, and any other suitable modules for multiplexing SRs in unlicensed bands. In some embodiments, one or more of the modules may be implemented using one or more processors220ofFIG. 10. In certain embodiments, the functions of two or more of the various modules may be combined into a single module.

The transmitting module1702may perform the transmitting functions of virtual computing device1700. For example, in a particular embodiment, transmitting module1702may transmit signaling that indicates a partial downlink Transmission Time Interval (DL TTI) to be subsequently transmitted to a wireless device110. In a particular embodiment, for example, the signaling may include PDCCH signaling. As another example, in a particular embodiment, transmitting module1704may transmit the partial DL subframe to the wireless device110.

The receiving module1704may perform the receiving functions of virtual computing device1700. For example, receiving module1704receives, from the wireless device110, a scheduling request (SR) in a first transmission opportunity following the partial DL subframe, which may also be referred to as a partial TTI.

According to certain other example embodiments, wireless device110may determine which set of PUCCH resources to use for SR transmission in the sPUCCH after the DL TTI. Specifically, wireless device110may take the number of subframes from the wireless device's most recent periodic SR opportunity to the sPUCCH/ePUCCH following the DL TTI into account. According to various embodiments, sPUCCH opportunities may or may not be periodic.

FIGS. 26A-26Dillustrate a method for determining, by a wireless device110, the set of PUCCH resources to use for deferred scheduling request transmissions. Specifically, four different cases exemplify how a wireless device110may determine the set of PUCCH resources for SR transmission.

FIG. 26Adepicts a scenario1800wherein a wireless device110may use a first set of PUCCH resources if a periodic SR occasion coincides with an UL subframe. Specifically,FIG. 26Adepicts that wireless device110is configured with periodic D-SR opportunities1802. In a particular embodiment, the configuration of the periodic D-SR opportunities1802may be received via RRC signaling. As depicted, at least the first of the D-SR opportunities1802is blocked by a burst of downlink transmissions1804. Wireless device110transmits the SR on PUCCH in the first configured periodic D-SR opportunity1802after a shortened DL subframe1806with UL sPUCCH in the last symbols.

FIG. 26Bdepicts a scenario1820wherein a wireless device110may use a second set of PUCCH resources if a periodic SR occasion coincides with a special subframe at the end of the DL TxOP. Specifically, wireless device110is configured with periodic D-SR opportunities1822. In a particular embodiment, the configuration of the periodic D-SR opportunities1822may be received via RRC signaling. As depicted, the second of the D-SR opportunities1822is blocked by a burst of downlink transmissions1824. Wireless device110transmits the SR on sPUCCH in the first configured periodic D-SR opportunity1802after a shortened DL subframe1826with UL sPUCCH in the last symbols.

FIG. 26Cdepicts a scenario1840wherein wireless device110may use a third set of PUCCH resources if a periodic SR occasion occurred in the subframe preceding the shortened subframe at the end of the DL TxOP. Specifically, wireless device110is configured with periodic D-SR opportunities1842. The second of the D-SR opportunities1842is blocked by a burst of downlink transmissions1844. The second of the D-SR opportunities corresponds with the subframe immediately preceding the shortened subframe1846, which may also be referred to as a partial DL subframe or partial DL TTI, at the end of the DL TxOP. According to certain embodiments, the second of the D-SR opportunities1842is postponed and transmitted on the sPUCCH in the next subframe following the partial DL subframe1846with UP sPUCCH in the last symbols.

FIG. 26Ddepicts a scenario wherein a wireless device110may use a fourth set of PUCCH resources if a periodic SR occasion occurred two subframes prior to the special subframe at the end of the DL TxOP. Specifically, wireless device110is configured with periodic D-SR opportunities1862. The second of the D-SR opportunities1862is blocked by a burst of downlink transmissions1864. The second of the D-SR opportunities1862corresponds to the subframe that is two subframes preceding the shortened subframe (i.e., partial DL subframe, which may also be referred to as a partial DL TTI)1866at the end of the DL TxOP. According to certain embodiments, the second of the D-SR opportunities1862is postponed and transmitted on the sPUCCH in the next subframe following the partial DL subframe1866with UP sPUCCH in the last symbols.

In certain embodiments, the special subframe may include the partial DL subframe, which may also be termed a partial DL subframe. Uplink control information can be carried in the UpPTS portion of the special subframe.

In a particular exemplary embodiment, wireless device110uses the PUCCH resource in an interlace of the sPUCCH region based on the number of subframes from the wireless device's110most recent periodic SR opportunity. In another embodiment, wireless device110may use a PUCCH resource given by x+SN mod M, where x is the PUCCH resource index number assigned to wireless device110for the wireless device's110most recent periodic SR opportunity subframe; S is the number of subframes from the wireless device's110most recent periodic SR opportunity; and N and M are positive integers with M>N, where M represent the available number of PUCCH resources in the sPUCCH region and N may represent the available number of PUCCH resources in a periodic SR opportunity subframe.

In certain embodiments, such as those described above, the two or more sets of PUCCH resources for SR transmission may be configured for the UE using RRC signaling. Wireless device110may then determine which one of the two or more sets of PUCCH resources to use.

In certain embodiments, any two of the two or more sets of PUCCH resources may differ from each other in at least one of the UL interlace, the orthogonal cover code or the cyclic shift. For example, the sets of resources determined by wireless device110in the cases ofFIGS. 26A and 26Bmay comprise a common interlace of UL PRBs but different orthogonal cover code. Furthermore, the sets of resources determined by wireless device110in the cases ofFIGS. 26C and 26Dmay include a common interlace of UL PRBs (different from the interlace used inFIGS. 26A and 26B) but different orthogonal cover code as shown in Table 2.

FIG. 27illustrates another example method1900by a wireless device for multiplexing SRs on unlicensed bands, according to certain embodiments. The method begins at step1902when the wireless device110obtains configuration information indicating at least two sets of PUCCH resources to be used for transmitting a scheduling request (SR) to a network node115. In certain embodiments, the at least two sets of PUCCH resources are located in one radio frame, such as one 3GPP LTE radio frame. In certain other embodiments, the at least two sets of PUCCH resources are located in different subframes of one radio frame.

In a particular embodiment, the at least two sets of PUCCH resources may include a main set of PUCCH resources that wireless device110and at least one additional set of PUCCH resources. Wireless device110may be configured to select the main set in response to non-fulfilment of a specific scheduling condition and the at least one additional set in response to fulfilment of the specific scheduling condition. In particular embodiments, the main set of resources may include a periodic SR transmission opportunity. In particular embodiments, the main set of PUCCH resources may be received separately from other configuration information, whereas the at least one additional set of PUCCH resources is indicated with the configuration information. In still other embodiments, the at least one additional set of PUCCH resources may be indicated implicitly by received PDCCH signaling. For example, a cell-specific signal may be received within a common PDCCH or within another control signal and may indicate one of the additional sets of PUCCH resources to be selected.

At step1904, wireless device110selects one of the indicated sets of PUCCH resources. In a particular embodiment, the selecting may be governed by a predefined selection rule dependent on a time duration separating a most recent periodic SR transmission opportunity of the wireless device and a subframe containing the additional sets of PUCCH resources.

In certain embodiments, at least two specific scheduling conditions are associated with respective additional sets of PUCCH resources. Selecting the PUCCH resources to use may include ascertaining whether one of the at least two specific scheduling conditions is fulfilled. In particular embodiments, the at least two specific scheduling conditions may be one of a coincidence of a periodic SR transmission opportunity and an uplink subframe, a coincidence of a periodic SR transmission opportunity and a special subframe at the end of a downlink transmission opportunity, a coincidence of a periodic SR transmission opportunity and subframe immediately preceding a special subframe at the end of a downlink transmission opportunity; and a coincidence of a periodic SR transmission opportunity and a subframe located two subframes prior to a special subframe at the end of a downlink transmission opportunity. In a particular embodiment, the special subframe may be composed of a partial subframe for downlink transmission and a remainder for uplink control data.

In certain embodiments, the configuration information may indicate at least two additional sets of PUCCH resources located in different subframes. Selecting the PUCCH resources to use may include ascertaining availability of an additional set of PUCCH resources located in an earliest subframe. If the additional set of PUCCH resources in the earliest subframe is available for transmission by the wireless devices, wireless device110may select this set of PUCCH resources. Conversely, if the additional set of PUCCH resources in the earliest subframe is not available, availability of an additional set of PUCCH resources located in the earliest subsequent subframe may be ascertained.

In certain embodiments, selecting the set of PUCCH resources may include ascertaining availability of one of the at least two sets of PUCCH resources by performing at least one of sensing an uplink grant to a different wireless device and performing channel sensing, such as by executing a listen-before-talk method.

In certain embodiments, selecting the PUCCH resources may be governed by a predefined selection rule having as input a time duration separating a most recent periodic SR transmission opportunity of the wireless device and a subframe containing the additional sets of PUCCH resources, and having as output an interlace index referring to an interlace within a predetermined resource region (sPUCCH). In other embodiments, selecting the set of PUCCH resources may be governed by a predefined selection rule having as input at least one of an index x of the PUCCH resource assigned to the wireless device at its most recent periodic SR transmission opportunity, a number S of subframes elapsed since a most recent periodic SR transmission opportunity of the wireless device, a number M of available PUCCH resources in a predetermined resource region (sPUCCH), and a number N<M of available PUCCH resources in a periodic SR transmission opportunity subframe. An index (x+SN mod M) of a PUCCH resource may be output for selection.

At step1906, wireless device110then transmits a SR using the selected set of PUCCH requests.

In certain embodiments, the methods for multiplexing SRs in unlicensed bands as described inFIG. 27may be performed by one or more virtual computing devices.FIG. 28illustrates another example virtual computing device2000for multiplexing SRs in unlicensed bands, according to certain embodiments. In certain embodiments, virtual computing device2000may include modules for performing steps similar to those described above with regard to the method illustrated and described inFIG. 27. For example, virtual computing device2000may include at least one obtaining module2002, at least one selecting module2004, at least one transmitting module2006, and any other suitable modules for multiplexing SRs in unlicensed bands. In some embodiments, one or more of the modules may be implemented using one or more processors320ofFIG. 11. In certain embodiments, the functions of two or more of the various modules may be combined into a single module.

The obtaining module2002may perform the obtaining functions of virtual computing device2000. For example, in a particular embodiment, obtaining module2002may obtain configuration information indicating at least two sets of PUCCH resources to be used for transmitting a scheduling request (SR) to a network node115.

The selecting module2004may perform the selecting functions of virtual computing device2000. For example, selecting module2004may select one of the indicated sets of PUCCH resources. In a particular embodiment, the selecting may be governed by a predefined selection rule dependent on a time duration separating a most recent periodic SR transmission opportunity of the wireless device and a subframe containing the additional sets of PUCCH resources.

The transmitting module2006may perform the selecting functions of virtual computing device2000. For example, transmitting module2006may transmit a SR using the selected set of PUCCH requests.

Other embodiments of computer networking virtual apparatus2000may include additional components beyond those shown inFIG. 28that may be responsible for providing certain aspects of the wireless device's110functionality, including any of the functionality described above and/or any additional functionality (including any functionality necessary to support the solutions described above). The various different types of wireless devices110may include components having the same physical hardware but configured (e.g., via programming) to support different radio access technologies, or may represent partly or entirely different physical components.

In certain other embodiments, if a periodic SR transmission is blocked on a particular unlicensed cell due to that subframe being used as a DL subframe, then the SR may be transmitted on another unlicensed cell if the other unlicensed cell has an UL subframe that is currently available. An example with two unlicensed SCells is shown inFIG. 29. As depicted, wireless devices110A-B are blocked from transmitting SRs on SCell2102. Specifically, network node115may perform a LBT procedure2104and then send a burst of downlink transmissions2106. As depicted, wireless device110A has periodic SR opportunities2108and wireless device110B has periodic SR opportunity2110. However, the uplink subframes on the sPUCCH corresponding to periodic SR opportunities2108and2110are blocked by downlink transmissions2106.

Where wireless devices110A-B are monitoring DL on SCell2112, however, wireless devices110-B may determine an earlier UL sPUCCH opportunity on SCell2112and transmit their SRs there. As depicted in the example embodiment, network node116may perform a LBT procedure2114before sending a burst of downlink transmissions2116. However, the last downlink TTI transmitted by network node115may include a partial DL subframe2118. In certain embodiments, wireless devices110A-B may transmit their SRs in the first transmission opportunity2120after the partial DL subframe2118. In certain embodiments, the SRs of one or more of wireless devices110A-B may contain additional information regarding the desired SCell on which the wireless devices110A-B would like to receive an UL grant.

According to certain embodiments, a method for multiplexing scheduling requests in unlicensed bands is implemented in a wireless device. The method includes determining that a scheduling request (SR) cannot be transmitted on an uplink during a scheduled SR opportunity. The SR is transmitted in a first transmission opportunity following a partial downlink (DL) subframe from a network node.

According to certain embodiments, a wireless device for multiplexing scheduling requests in unlicensed bands includes a memory storing instructions and a processor operable to execute the instructions to cause the processor to determine that a scheduling request (SR) cannot be transmitted on an uplink during a scheduled SR opportunity. The SR is transmitted in a first transmission opportunity following a partial DL subframe from a network node.

According to certain embodiments, a method for multiplexing scheduling requests in unlicensed bands is implemented in a network node. The method includes transmitting, by the network node, signaling that indicates a partial DL subframe to be subsequently transmitted to a wireless device. The partial DL subframe is transmitted to the wireless device. A scheduling request (SR) is received from the wireless device in a first transmission opportunity following the partial DL subframe.

According to certain embodiments, a network node for multiplexing scheduling requests in unlicensed bands is provided. The network node includes a memory storing instructions and a processor operable to execute the instructions to cause the processor to transmit signaling that indicates a partial DL subframe to be subsequently transmitted to a wireless device. The partial DL subframe is transmitted to the wireless device and a scheduling request (SR) is received from the wireless device in a first transmission opportunity following the partial DL subframe.

Certain embodiments of the present disclosure may provide one or more technical advantages. For example, in certain embodiments deferred SR transmissions may be multiplexed in an efficient and robust manner. This may advantageously improve overall system performance for such a system. Other advantages may be readily apparent to one having skill in the art. Certain embodiments may have none, some, or all of the recited advantages.