Patent Description:
Patent application <CIT> relates to techniques of providing burst frame structures, preamble designs, and channel reservation signal designs for Licensed Assisted Access (LAA) operation.

In wireless communications in a dedicated or licensed communication medium, devices may be scheduled with particular time slots and resources for transmission of data. In an unlicensed or shared communication medium, however, radio frequency spectrum may be available for use by different radio access technologies or multiple mobile network operators. Accordingly, devices may need to contend for medium access using various mechanisms. For example, before a device can begin transmission over an unlicensed communication medium, it may need to determine whether another device is already occupying the medium (i.e., whether signals from other devices are already being transmitted over the medium). In some cases, the device can perform energy detection by persistently listening to the medium for any active radio frequency (RF) energy. If the measured RF energy exceeds a particular threshold, the medium is considered busy, and the device will refrain from transmitting during periods when the medium is busy in order to avoid collisions. In some instances, a device may detect for specific signals in order to determine occupancy of the medium. For example, the device may detect for a preamble of a transmission from another device to determine whether other devices intend to occupy the medium for a certain amount of time.

Such mechanisms for avoiding collisions may be categorized as Listen Before Talk (LBT) procedures because a device listens to the medium to determine whether the medium is busy or not before the device transmits over the medium. LBT procedures may be performed by either a user equipment (UE) or base station for medium access. Among the various LBT procedures used, preamble detection may be more efficient than energy detection for indicating channel occupancy and avoiding collisions. In particular, the medium occupancy time may also be signaled with a preamble, which allows other devices to determine how long the medium will be occupied and avoids unnecessary random access by aggressor devices.

Combinations of energy detection and preamble detection may also be used. In some instances, a clear channel assessment (CCA) procedure is performed prior to transmission over a communication medium, where the CCA procedure may include aspects of both energy detection and preamble detection. Accordingly, once a transmitting device obtains channel access after a successful CCA procedure, it may transmit its own preamble to inform other devices that it intends to occupy the medium for a certain amount of time and allow the other devices to perform their own CCA procedures and detect for signals (i.e., preambles). In particular, the preamble transmitted by the transmitting device may be part of a channel reservation (CR) signal, which may include at least a CR preamble and a CR message. As used herein, a successful CCA procedure, or CCA clearance, may include the result of a procedure performed by a wireless device in which the wireless device determines that a communication medium is considered not occupied by communications from other devices (e.g., via energy detection and/or preamble detection) and is available for communication by the wireless device.

The CR preamble may indicate to other devices, such as potential aggressors, that a CR message is forthcoming. A transmitting device may send the CR preamble after a CCA procedure that indicates an available communication medium is completed, and then a CR message following the CR preamble, where the CR message may include a network allocation vector (NAV), a packet length, and/or beam training information. In some instances, the NAV indicates a duration of the channel occupancy time of the transmitting device and informs other devices the length of time for which they should defer from accessing the medium. In some implementations, the transmitting device may re-use a Physical Downlink Control Channel (PDCCH) and Demodulation Reference Signal (DMRS) format for the CR message to maximize inter-operability between licensed and unlicensed design.

In some instances, cellular communication systems may use a transmission timeline comprising Orthogonal Frequency Division Multiplexing (OFDM) symbols according to a fixed pattern. In particular, Long Term Evolution (LTE) and <NUM> New Radio (NR) systems may partition time resources into equally spaced symbols for scheduling of resources and synchronizing transmissions among devices within a network. In unlicensed spectrum, however, devices perform channel contention procedures before obtaining medium access, and medium access can be obtained at any time, including between symbol boundaries. In some instances, a LTE or NR device may compete with non-cellular devices, such as WLAN devices that do not operate under a similar time-partitioned symbol timeline, for medium access. Accordingly, a cellular device may obtain medium access (e.g., successful CCA procedure) at any time, but its transmissions, including CR message transmissions, may still need to follow a particular transmission timeline in accordance with system parameters.

To improve reliable and energy-efficient CR signal detection, a transmitting device may adapt its CR signal transmission to account for the gap between medium access timing (i.e., CCA clearance) and ODFM symbol boundaries in accordance with system timing, the difference between a system bandwidth of the transmitting device and a system bandwidth of potential aggressors, or differences of channel occupancy across different sub-bands and/or beam directions. In particular, techniques and apparatuses described herein provide for adaptive transmission of CR signals in unlicensed or shared spectrum. For example, a transmitting device may adapt a CR preamble based on an offset (i.e., gap) between a time at which channel access is obtained by the transmitting device and a following symbol boundary. The adaptive generation of the CR preamble may allow a following CR message to be transmitted in accordance with a predefined system timing and allow other devices to identify a particular symbol at which to expect the CR message. Further, in instances where bandwidth may be further divided into sub-bands and the occupancy duration by a device may differ across different sub-bands, the CR message may be adapted to indicate information regarding occupancy of multiple sub-bands. In other instances where a device may transmit beams in different directions, the CR message may be adapted to indicate information regarding occupancy of different beams.

The detailed description set forth below, in connection with the appended drawings and appendix, is intended as a description of various configurations and is not intended to limit the scope of the disclosure.

This disclosure relates generally to providing or participating in authorized shared access between two or more wireless communications systems, also referred to as wireless communications networks. In various embodiments, the techniques and apparatus may be used for wireless communication networks such as code division multiple access (CDMA) networks, time division multiple access (TDMA) networks, frequency division multiple access (FDMA) networks, orthogonal FDMA (OFDMA) networks, single-carrier FDMA (SC-FDMA) networks, LTE networks, GSM networks, as well as other communications networks. As described herein, the terms "networks" and "systems" may be used interchangeably.

3GPP Long Term Evolution (LTE) is a 3GPP project which was aimed at improving the universal mobile telecommunications system (UMTS) mobile phone standard. The present disclosure is concerned with the evolution of wireless technologies from LTE, <NUM>, <NUM>, and beyond with shared access to wireless spectrum between networks using a collection of new and different radio access technologies or radio air interfaces.

In particular, <NUM> networks contemplate diverse deployments, diverse spectrum, and diverse services and devices that may be implemented using an OFDM-based unified, air interface. In order to achieve these goals, further enhancements to LTE and LTE-A are considered in addition to development of a new radio (NR) technology. The <NUM> NR will be capable of scaling to provide coverage (<NUM>) to a massive Internet of things (IoTs) with an ultra-high density (e.g., ~<NUM> nodes/km2), ultra-low complexity (e.g., ~<NUM> of bits/sec), ultra-low energy (e.g., -<NUM>+ years of battery life), and deep coverage with the capability to reach challenging locations; (<NUM>) including mission-critical control with strong security to safeguard sensitive personal, financial, or classified information, ultra-high reliability (e.g., -<NUM>% reliability), ultra-low latency (e.g., ~ <NUM>), and users with wide ranges of mobility or lack thereof; and (<NUM>) with enhanced mobile broadband including extreme high capacity (e.g., ~ <NUM> Tbps/km2), extreme data rates (e.g., multi-Gbps rate, <NUM>+ Mbps user experienced rates), and deep awareness with advanced discovery and optimizations.

The <NUM> NR may be implemented to use optimized OFDM-based waveforms with scalable numerology and transmission time interval (TTI); having a common, flexible framework to efficiently multiplex services and features with a dynamic, low-latency time division duplex (TDD)/frequency division duplex (FDD) design; and with advanced wireless technologies, such as massive multiple input, multiple output (MIMO), robust millimeter wave (mmWave) transmissions, advanced channel coding, and device-centric mobility. Scalability of the numerology in <NUM> NR, with scaling of subcarrier spacing, may efficiently address operating diverse services across diverse spectrum and diverse deployments. For example, in various outdoor and macro coverage deployments of less than <NUM> FDD/TDD implementations, subcarrier spacing may occur with <NUM>, for example over <NUM>, <NUM>, <NUM>, <NUM>, and the like bandwidth. For other various outdoor and small cell coverage deployments of TDD greater than <NUM>, subcarrier spacing may occur with <NUM> over <NUM>/<NUM> bandwidth, for example. For other various indoor wideband implementations, using a TDD over the unlicensed portion of the <NUM> band, the subcarrier spacing may occur with <NUM> over a <NUM> bandwidth, for example. Finally, for various deployments transmitting with mmWave components at a TDD of <NUM>, subcarrier spacing may occur with <NUM> over a <NUM> bandwidth, for example. Other deployments of different subcarrier spacing over different bandwidths are also within the scope of the present disclosure.

The scalable numerology of <NUM> NR facilitates scalable TTI for diverse latency and quality of service (QoS) requirements. The efficient multiplexing of long and short TTIs may allow transmissions to start on symbol boundaries.

<FIG> is a block diagram illustrating a network <NUM> including various base stations and UEs configured according to aspects of the present disclosure. In some instances, the network <NUM> represents a <NUM> network, for example. The network <NUM> includes a number of evolved node Bs (eNBs) <NUM> and other network entities. An eNB may be a station that communicates with the UEs and may also be referred to as a base station, an access point, a gNB, and the like. Each eNB <NUM> may provide communication coverage for a particular geographic area. In 3GPP, the term "cell" can refer to this particular geographic coverage area of an eNB and/or an eNB subsystem serving the coverage area, depending on the context in which the term is used.

An eNB may provide communication coverage for a macro cell or a small cell, such as a pico cell or a femto cell, and/or other types of cell. An eNB for a small cell may be referred to as a small cell eNB, a pico eNB, a femto eNB or a home eNB. In the example shown in <FIG>, the eNBs 105d and 105e are regular macro eNBs, while eNBs 105a-105c are macro eNBs enabled with one of <NUM> dimension (3D), full dimension (FD), or massive MIMO. eNBs 105a-105c take advantage of their higher dimension MIMO capabilities to exploit 3D beamforming in both elevation and azimuth beamforming to increase coverage and capacity. eNB 105f is a small cell eNB which may be a home node or portable access point. An eNB may support one or multiple (e.g., two, three, four, and the like) cells.

For synchronous operation, the eNBs may have similar frame timing, and transmissions from different eNBs may be approximately aligned in time. For asynchronous operation, the eNBs may have different frame timing, and transmissions from different eNBs may not be aligned in time.

The UEs <NUM> are dispersed throughout the wireless network <NUM>, and each UE may be stationary or mobile. A UE may also be referred to as a terminal, a mobile station, a subscriber unit, a station, or the like. A UE may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, or the like. UEs 115a-115d are examples of mobile smart phone-type devices accessing network <NUM>. A UE may also be a machine specifically configured for connected communication, including machine type communication (MTC), enhanced MTC (eMTC), narrowband IoT (NB-IoT) and the like. UEs 115e-<NUM> are examples of various machines configured for communication that access network <NUM>. A UE may be able to communicate with any type of the eNBs, whether macro eNB, small cell, or the like. In <FIG>, a lightning bolt (e.g., communication links) indicates wireless transmissions between a UE and a serving eNB, which is an eNB designated to serve the UE on the downlink and/or uplink, or desired transmission between eNBs, and backhaul transmissions between eNBs.

The communication links depicted in <FIG> may include communication links in licensed, unlicensed, or shared radio frequency (RF) spectrum. In some instances, a shared spectrum band may refer to spectrum that is lightly licensed and/or in which there may be some level of coordination among communications of different radio access technologies (RATs) or some level of preference given to communications of a particular RAT, such as an incumbent RAT, for example. In other instances, a shared spectrum band may generally refer to spectrum in which different RATs coexist or operate within the same RF spectrum band, which may include lightly licensed/coordinated spectrum or, alternatively, purely unlicensed spectrum in which different RATs may freely contend for access to the channel medium using various channel contention techniques. The aspects described in the present disclosure may be applicable to various shared or unlicensed spectrum regimes. Accordingly, the terms shared spectrum and unlicensed spectrum are used interchangeably herein unless otherwise noted.

In operation at network <NUM>, eNBs 105a-105c serve UEs 115a and 115b using 3D beamforming and coordinated spatial techniques, such as coordinated multipoint (CoMP) or multi-connectivity. Macro eNB 105d performs backhaul communications with eNBs 105a-105c, as well as small cell, eNB 105f. Macro eNB 105d also transmits multicast services which are subscribed to and received by UEs 115c and 115d.

Network <NUM> also supports mission critical communications with ultra-reliable and redundant links for mission critical devices, such as UE 115e, which is a drone in the example depicted in <FIG>. Redundant communication links with UE 115e include from macro eNBs 105d and 105e, as well as small cell eNB 105f. Other machine type devices, such as UE 115f (thermometer), UE <NUM> (smart meter), and UE <NUM> (wearable device) may communicate through network <NUM> either directly with base stations, such as small cell eNB 105f, and macro eNB 105e, or in multi-hop configurations by communicating with another user device which relays its information to the network, such as UE 115f communicating temperature measurement information to the smart meter, UE <NUM>, which is then reported to the network through small cell eNB 105f. Network <NUM> may also provide additional network efficiency through dynamic, low-latency TDD/FDD communications, such as in a vehicle-to-vehicle (V2V) mesh network between UEs 115i-<NUM> communicating with macro eNB 105e.

In shared spectrum configurations, wireless devices such as base station <NUM> and UE <NUM> may need to determine that the shared medium is clear before transmitting over the medium. The wireless devices may also transmit channel reservation signals once channel access has been obtained to signal to other devices and potential aggressors that the channel has been reserved for a particular duration. Due to the contentious nature of shared spectrum and coexistence with various types of RATs, base station <NUM> or UE <NUM> may obtain channel access between OFDM symbol boundaries. Accordingly, base station <NUM> or UE <NUM> may use an adaptive channel reservation (CR) preamble based on the offset between a time at which channel access is obtained and the OFDM symbol boundary in accordance with system timing. The adaptive CR preamble may indicate to other devices (e.g., potential aggressors) that a CR message is forthcoming and allow for transmission of the CR message to align with an OFDM symbol boundary. The CR signal, which includes the CR preamble and CR message, may also be adapted based on the sub-bands or directional beams used by base station <NUM> or UE <NUM> for transmissions, as will be described in further detail herein.

The techniques described herein relate to transmission of CR signals by a wireless device before the wireless device intends to transmit further signals. Accordingly, the wireless device that transmits the CR signal may be referred to in the present disclosure as a "transmitting device," which may be any wireless device, including a base station <NUM> or a UE <NUM>.

<FIG> shows a block diagram of a design of a base station/eNB <NUM> and a UE <NUM>, which may be one of the base stations/eNBs and one of the UEs in <FIG>. At the eNB <NUM>, a transmit processor <NUM> may receive data from a data source <NUM> and control information from a controller/processor <NUM>. The control information may be for various control channels such as the PBCH, PCFICH, PHICH, PDCCH, EPDCCH, MPDCCH etc. The data may be for the PDSCH, etc. The transmit processor <NUM> may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The transmit processor <NUM> may also generate reference symbols, e.g., for the PSS, SSS, and cell-specific reference signal. A transmit (TX) multiple-input multiple-output (MIMO) processor <NUM> may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs) 232a through 232t. Downlink signals from modulators 232a through 232t may be transmitted via the antennas 234a through 234t, respectively.

At the UE <NUM>, the antennas 252a through 252r may receive the downlink signals from the eNB <NUM> and may provide received signals to the demodulators (DEMODs) 254a through 254r, respectively. A MIMO detector <NUM> may obtain received symbols from all the demodulators 254a through 254r, perform MIMO detection on the received symbols if applicable, and provide detected symbols.

On the uplink, at the UE <NUM>, a transmit processor <NUM> may receive and process data (e.g., for the PUSCH) from a data source <NUM> and control information (e.g., for the PUCCH) from the controller/processor <NUM>. The symbols from the transmit processor <NUM> may be precoded by a TX MIMO processor <NUM> if applicable, further processed by the modulators 254a through 254r (e.g., for SC-FDM, etc.), and transmitted to the eNB <NUM>. At the eNB <NUM>, the uplink signals from the UE <NUM> may be received by the antennas <NUM>, processed by the demodulators <NUM>, detected by a MIMO detector <NUM> if applicable, and further processed by a receive processor <NUM> to obtain decoded data and control information sent by the UE <NUM>. The processor <NUM> may provide the decoded data to a data sink <NUM> and the decoded control information to the controller/processor <NUM>.

The controllers/processors <NUM> and <NUM> may direct the operation at the eNB <NUM> and the UE <NUM>, respectively. The controller/processor <NUM> and/or other processors and modules at the eNB <NUM> may perform or direct the execution of the functional blocks illustrated in <FIG>, and/or other various processes for the techniques described herein. The controllers/processor <NUM> and/or other processors and modules at the UE <NUM> may also perform or direct the execution of the functional blocks illustrated in <FIG>, and/or other processes for the techniques described herein. The memories <NUM> and <NUM> may store data and program codes for the eNB <NUM> and the UE <NUM>, respectively. For example, memory <NUM> may store instructions that, when performed by the processor <NUM> or other processors depicted in <FIG>, cause the base station <NUM> to perform operations described with respect to <FIG>. Similarly, memory <NUM> may store instructions that, when performed by processor <NUM> or other processors depicted in <FIG>, cause the UE <NUM> to perform operations described with respect to <FIG>.

For example, the functions described with respect to the transmit processor <NUM>, the receive processor <NUM>, or the TX MIMO processor <NUM> may be performed by or under the control of processor <NUM>.

In some cases, UE <NUM> and base station <NUM> may operate in a shared radio frequency spectrum band, which may include licensed or unlicensed (e.g., contention-based) frequency spectrum. In an unlicensed frequency portion of the shared radio frequency spectrum band, UEs <NUM> or base stations <NUM> may traditionally perform a medium-sensing procedure to contend for access to the frequency spectrum. For example, UE <NUM> or base station <NUM> may perform a listen before talk (LBT) procedure such as a clear channel assessment (CCA) prior to communicating in order to determine whether the shared channel is available. A CCA may include an energy detection procedure to determine whether there are any other active transmissions. For example, a device may infer that a change in a received signal strength indicator (RSSI) of a power meter indicates that a channel is occupied. Specifically, signal power that is concentrated in a certain bandwidth and exceeds a predetermined noise floor may indicate another wireless transmitter. A CCA also may include detection of specific sequences that indicate use of the channel. For example, another device may transmit a specific preamble prior to transmitting a data sequence. In some cases, an LBT procedure may include a wireless node adjusting its own backoff window based on the amount of energy detected on a channel and/or the acknowledge/negative-acknowledge (ACK/NACK) feedback for its own transmitted packets as a proxy for collisions.

Use of a medium-sensing procedure to contend for access to an unlicensed shared spectrum may result in communication inefficiencies. This may be particularly evident when multiple network operating entities (e.g., network operators) are attempting to access a shared resource. In <NUM> network <NUM>, base stations <NUM> and UEs <NUM> may be operated by the same or different network operating entities. In some examples, an individual base station <NUM> or UE <NUM> may be operated by more than one network operating entity. In other examples, each base station <NUM> and UE <NUM> may be operated by a single network operating entity. Requiring each base station <NUM> and UE <NUM> of different network operating entities to contend for shared resources may result in inefficient communications, especially if channel contention procedures involve only energy detection, for example.

In some instances, wireless devices may send a channel reservation (CR) signal, comprising a CR preamble and a CR message, in order to indicate to potential aggressors that the transmitting device will occupy the shared spectrum for a particular amount of time. Before the transmitting device sends the CR signal, it may first need to clear a CCA procedure to obtain access to the shared spectrum. The time at which the transmitting device clears the CCA procedure, however, may not align with an OFDM symbol boundary of the system in which the transmitting device operates, while the transmitting device may still need to transmit the CR message in accordance with system timing. Accordingly, the transmitting device may use an adaptive CR signal that accounts for the potential offset between the time at which it obtains access to the shared spectrum and an OFDM symbol boundary.

<FIG> illustrates an example in which a transmitting device, such as base station <NUM> or UE <NUM>, may adapt a preamble length based on the offset between a time at which a CCA procedure determines the medium is clear (i.e., CCA clearance) and an OFDM symbol boundary. For example, as depicted in <FIG>, the transmitting device may obtain channel access at time <NUM>, which is not aligned with an OFDM symbol boundary. The next OFDM symbol boundary in the illustrated example occurs at time <NUM>. The transmitting device may accordingly generate CR preamble <NUM> such that the length of the CR preamble <NUM> spans an offset <NUM>, or the time gap, between time <NUM> and time <NUM>. In particular, the transmitting device may partition CR preamble <NUM> into three segments <NUM>, <NUM>, and <NUM>, where the CR preamble <NUM> comprises a different waveform in each segment.

The different waveforms in each segment may have different properties that allow for a receiver of the CR preamble <NUM> to efficiently identify the signal as a CR preamble and monitor for the following CR message at the appropriate time. In some instances, the transmitting device may apply different correlation types or filters such that the CR preamble <NUM> exhibits different properties in different segments. For example, an auto correlation type may be applied to a waveform of the first segment <NUM>. As a result, the properties of the CR preamble signal in segment <NUM> may include a gradual rising edge <NUM>, which may allow a receiver of the CR preamble <NUM> to detect the presence of the CR preamble <NUM> over the transmission medium and determine a general starting point of the CR preamble <NUM>.

The transmitting device may apply a different correlation type to the CR preamble <NUM> signal in segment <NUM>, however. In some instances, the transmitting device may apply a cross correlation type to a waveform of the third segment <NUM>. Based on the cross correlation type applied, the CR preamble <NUM> waveform in segment <NUM> may have a sharp peak <NUM>, which may indicate to a receiver of the CR preamble <NUM> a definite ending point of the CR preamble <NUM> and allow the receiver to identify a specific OFDM symbol boundary at which to begin monitoring for a following CR message at time <NUM>.

The transmitting device may further apply a different correlation type to the CR preamble <NUM> signal in segment <NUM>. The correlation type applied to segment <NUM> may be one of a plurality of correlation types, and selected such that at least a minimum signal is transmitted across the medium to indicate the presence of the CR preamble <NUM>. Further, the length of the CR preamble <NUM> waveform in segment <NUM> may be variable, with length adapted based on the offset <NUM>. Accordingly, while the length of segments <NUM> and <NUM> may be fixed or deterministic, the length of segment <NUM> may be vary depending on the offset <NUM> and may have longer or shorter duration in order to allow the entire CR preamble <NUM> signal to span the length of the offset <NUM>.

<FIG> illustrates example configurations <NUM> of adaptive CR preamble lengths based on the time at which a CCA clearance procedure is completed in relation to OFDM symbol timing. In some instances, the CR preamble lengths may be adapted using techniques described above with respect to <FIG>. In the illustrated example, a transmitting device may obtain channel access at time 410a during symbol k after a CCA clear procedure is complete. The offset 440a between the CCA clear 410a and the following available OFDM symbol boundary 420a may be greater than one symbol length 450a (i.e., the symbol boundary of symbol k may not be under consideration in this instance because the CR preamble 460a may need a minimum length of time for proper decoding at the receiver). Accordingly, the transmitting device may adapt a length of the CR preamble 460a so that it spans the length of time between time 410a and 420a. Once the CR preamble 460a is transmitted, the transmitting device transmits the CR message 470a in the following symbol at symbol k+<NUM>. In the present example, the CR message 470a may span one symbol length between symbol boundaries 420a and 430a.

In a second example illustrated in <FIG>, the transmitting device may obtain channel access at time 410b during symbol k+<NUM> after a CCA clearance procedure is complete. The offset 440b between the CCA clear 410b and the following available OFDM symbol boundary 420b may be less than one symbol length 450b. Accordingly, the transmitting device may adapt a length of the CR preamble 460b so that it spans the length of time between time 410b and 420b. Once the CR preamble 460b is transmitted, the transmitting device transmits the CR message 470b in the following symbol at symbol k+<NUM>. In the present example, the CR message 470b may span one symbol length between symbol boundaries 420b and 430b.

Other techniques for adaptive CR preamble generation are depicted in <FIG> and <FIG>. Instead of generating a CR preamble of multiple segments with different correlation properties, a transmitting device may generate a CR preamble of a particular length. In some implementations, the CR preamble may comprise a dual layer waveform construction, where a short spreading sequence is used for a first layer and a code cover sequence is used for a second layer. In the first layer, a short spreading sequence with time duration TO is used with a sampling rate of FS = K/T0, with the spreading sequence denoted by a length K vector <MAT>. Examples of the type of sequence that may be used may include CAZAC, Pseudo-Noise (PN), Walsh code, Golay code, etc. The second layer may include a length L code cover sequence, where LT0 spans an integer number of OFDM symbols. The code cover sequence may be denoted by a size L vector <MAT>. The preamble waveform samples (P) can be generated by cross product of spreading code cover B with sequence S, where P = B × S = [b<NUM>s<NUM>b<NUM>s<NUM>. b<NUM>sK b<NUM>s<NUM>b<NUM>s<NUM>. bLs<NUM>bLs<NUM>.

The dual layer waveform CR preamble may span a fixed length of LK. <FIG>, however, illustrates an example <NUM> in which an offset between a time at which channel access is obtained and a following OFDM symbol boundary is less than the CR preamble length. As depicted in <FIG>, in some instances a transmitting device may obtain channel access at a time <NUM> that does not align with an OFDM symbol boundary. If the gap or offset τ <NUM> between the CCA clear time <NUM> and a following OFDM symbol boundary <NUM> of symbol k is less than the CR preamble <NUM> length LK, the transmitting device may truncate the CR preamble <NUM> by a certain number of samples 540a, and transmit the truncated CR preamble <NUM> with the last sample of the CR preamble <NUM> aligned with the OFDM symbol boundary <NUM> of symbol k. In the illustrated example, the number of samples truncated is the first LK - τ samples. The CR message <NUM> is then transmitted in the following symbol k+<NUM>.

<FIG> illustrates an example <NUM> in which the offset τ between a time at which channel access is obtained and a following OFDM symbol boundary may be a longer duration than a preamble length. Here, a transmitting device determines at time <NUM> that the transmission medium is clear based on a CCA procedure. In the illustrated example, the offset τ <NUM> between time <NUM> and a following OFDM symbol boundary <NUM> of symbol k is greater than a CR preamble <NUM> length LK. In this instance, the transmitting device may align the CR preamble <NUM> to start at time <NUM>, and then add filler samples 640a after the end of the CR preamble <NUM> until the OFDM symbol boundary <NUM>. Various options may be used for the filler samples 640a. For example, the transmitting device may use a copy of the first τ - LK samples of the CR preamble <NUM> or a copy of the last τ - LK samples of the CR message <NUM>. Alternatively, the transmitting device may use a PN-like signal for the filler samples. Further, the CR preamble <NUM> may be adapted such that it has a minimum duration, notwithstanding OFDM symbol boundaries that may intersect the CR preamble <NUM>.

As described above, techniques for adaptive CR signal generation may include adapting a CR preamble to account for potential timing differences between when channel access is obtained and OFDM symbol boundaries of the system in which the transmitting device operates. A CR signal may also be adapted based on occupancy of different partitions of bandwidth used by a transmitting device. In particular, the bandwidth available to devices in a shared spectrum may be partitioned into equally spaced sub-bands to support channelization and make full use of shared resources. For example, in mmWave bands (e.g., <NUM>), a <NUM> system bandwidth may be partitioned into two sub-bands of <NUM> each. In another example, for the <NUM> band, an <NUM> system bandwidth may be partitioned into four sub-bands of <NUM> each. Each of the sub-bands may have different occupancy, including different occupancy associated with the same device. Accordingly, a device may reserve the channel for different sub-bands for different amounts of time, and CR signals may be sent for various combinations of sub-bands.

For example, <FIG> depicts example configurations <NUM> for adaptive CR signal generation based on occupancy of different sub-bands within an available bandwidth. In the illustrated example, a channel is partitioned into four sub-bands 701a, 701b, 701c, and 701d. A transmitting device may occupy each of the sub-bands at different times and for different durations. Accordingly, in some instances, the transmitting device may send a different and independent CR signal on each sub-band, where the CR signal indicates occupancy for the particular sub-band on which the CR signal is sent. In this configuration, a same CR preamble <NUM> is transmitted across each sub-band, and a payload of the CR message <NUM> includes information regarding occupancy for the sub-band on which the CR message <NUM> is sent. For example, a CR signal 702a transmitted on sub-band 701a would include a CR message payload <NUM> with a NAV value that indicates occupancy of sub-band 701a by the transmitting device. Similarly, a CR signal 702b transmitted on sub-band 701b would include a CR message payload <NUM> with a NAV value that indicates occupancy of sub-band 701b by the transmitting device, and so forth for sub-bands 701c and 701d.

In other instances, a CR signal may include correlated occupancy information for multiple or combinations of sub-bands. For example, a CR signal <NUM> transmitted on sub-band 701a may include a CR preamble <NUM> that is the same across each sub-band, while also including a payload CR message <NUM> that contains occupancy information regarding multiple sub-bands. In some instances, the CR message <NUM> may include a sub-band occupancy bitmap 725a that indicates the sub-bands for which the CR message <NUM> applies. In the illustrated example, CR signal <NUM> would include a sub-band occupancy bitmap 725a that indicates the occupancy information contained therein applies to both sub-band 701a and sub-band 701d, while CR signal <NUM> would include a sub-band occupancy bitmap 725a that indicates the occupancy information contained therein applies to both sub-band 701b and sub-band 701c. The CR message <NUM> may also include a NAV value 725b indicating occupancy of the sub-bands indicated by the sub-band occupancy bitmap 725a. As depicted in <FIG>, the occupancy of various sub-bands may change over time. Accordingly, the transmitting device may send CR signals for a different combination of sub-bands. For example, a transmitting device may later send a CR signal <NUM> indicating occupancy of sub-bands 701a and 701b and a CR signal <NUM> indicating occupancy of sub-bands 701c and 701d.

A CR signal may also be adapted based on occupancy of different directional beams. For example, a transmitting device may transmit a beam or signal in one particular direction among a plurality of possible directions. The CR signal sent by the transmitting device may include occupancy information for one or more of the possible directions in which the beam is sent. <FIG> illustrates an example configuration <NUM> for adaptive CR signals based on occupancy of different beams. In the illustrated example, the transmitting device is a base station <NUM> that may transmit a beam in one or more of three different directions 830a, 830b, and 830c. The channel over direction 830a may be available, while beam 830b is to be reserved for a period Tnav for a transmission to UE <NUM>. Beam 830c may be blocked due to interference or other factors. In this instance, transmitting device <NUM> may send a CR signal comprising a CR preamble <NUM> and CR message <NUM>. The payload of the CR message <NUM> may indicate a beam occupancy and NAV 820a for beam 830b, as well as availability 820b of other beams 830a and 830c. Accordingly, the transmitting device may adaptively generate CR signals to indicate reservation as well as availability of multiple beam directions.

<FIG> illustrates an example of a process flow <NUM> in a system that supports adaptive channel reservation signal techniques in accordance with aspects of the present disclosure. Process flow <NUM> may include base station <NUM> and UE <NUM>, which may be examples of the corresponding devices described with reference to <FIG>.

At <NUM>, a transmitting device such as base station <NUM> performs an LBT procedure to obtain channel access. In the present example, the transmitting device is base station <NUM>, but the transmitting device may also be UE <NUM>, and the operations described with respect to base station <NUM> herein may be performed by UE <NUM> as well. Similarly, the receiving device in the present example is UE <NUM>, but the receiving device may also be base station <NUM>.

At <NUM>, the base station <NUM> generates a channel reservation signal based on obtaining channel access. The channel reservation signal may be based on a timing at which channel access is obtained. For example, the waveforms used or number of samples included in a channel reservation preamble may be based on an offset between a time at which channel access is obtained and a symbol boundary of the system in which base station <NUM> and UE <NUM> operate. Additionally or alternatively, the channel reservation signal may be based on other factors, such as the occupancy of various sub-bands or beams available to the base station <NUM>.

At <NUM>, the base station <NUM> transmits the channel reservation preamble to the UE <NUM>. At <NUM>, the UE <NUM> determines that the signal received is a channel reservation preamble, and will then monitor a particular symbol for a following channel reservation message based on the received channel reservation preamble at <NUM>. The UE <NUM> may then receive the channel reservation message transmitted by base station <NUM> at <NUM>.

At <NUM>, the UE <NUM> determines channel occupancy based on the payload of the channel reservation message. In some instances, the UE <NUM> may determine occupancy of different sub-bands or beam directions based on the channel reservation message.

<FIG> shows a flowchart illustrating a process <NUM> for adaptive channel reservation signals in accordance with various aspects of the present disclosure. The operations of process <NUM> may be implemented by a device such as a base station or its components, or a UE or its components, as described with reference to <FIG> and <FIG>. For example, the operations of process <NUM> may be performed by the processor <NUM> or processor <NUM>, either alone or in combination with other components, as described herein. In some examples, the base station <NUM> or UE <NUM> may execute a set of codes to control the functional elements of the device to perform the functions described below. Additionally or alternatively, the base station <NUM> or UE <NUM> may perform aspects of the functions described below using special-purpose hardware.

At <NUM>, the base station <NUM> or UE <NUM> obtains channel access after a clear channel assessment operation. At <NUM>, the base station <NUM> or UE <NUM> determines an offset between a boundary of a symbol and a particular time at which the channel access is obtained. At <NUM>, the base station <NUM> or UE <NUM> generates a channel reservation preamble based on the offset, as described above with reference to <FIG>, <FIG>, <FIG>, or <FIG>. At <NUM>, the base station <NUM> or UE <NUM> transmits the channel reservation preamble.

At <NUM>, the base station <NUM> or UE <NUM> obtains channel access of a communication channel after a clear channel assessment operation, wherein the communication channel comprises a plurality of sub-bands. At <NUM>, the base station <NUM> or UE <NUM> generates at least one channel reservation signal based on the plurality of sub-bands, as described above with reference to <FIG>. At <NUM>, the base station <NUM> or UE <NUM> transmits the at least one channel reservation signal.

At <NUM>, the base station <NUM> or UE <NUM> obtains channel access after a clear channel assessment operation. At <NUM>, the base station <NUM> or UE <NUM> generate at least one channel reservation signal based on availability of beams in a plurality of possible directions, as described above with reference to <FIG>. At <NUM>, the base station <NUM> or UE <NUM> transmits the at least one channel reservation signal using one beam in a particular direction among the plurality of possible directions.

At <NUM>, the base station <NUM> or UE <NUM> receives a signal. At <NUM>, the base station <NUM> or UE <NUM> determines that the signal comprises a channel reservation preamble. At <NUM>, the base station <NUM> or UE <NUM> monitor a symbol for a channel reservation message, wherein the symbol follows an ending point of the channel reservation preamble. At <NUM>, the base station <NUM> or UE <NUM> identify channel occupancy information based on the channel reservation message.

The functional blocks and modules in <FIG> may comprise processors, electronics devices, hardware devices, electronics components, logical circuits, memories, software codes, firmware codes, etc., or any combination thereof.

Claim 1:
A method comprising:
obtaining channel access after a clear channel assessment, CCA, operation (<NUM>);
determining an offset between a boundary of a symbol and a particular time at which the channel access is obtained (<NUM>);
generating a channel reservation, CR, preamble based on the offset (<NUM>),
generating a CR message payload indicating reservations and/or availability of multiple beam directions;
wherein the generating the CR preamble includes partitioning the CR preamble into a plurality of segments, each segment comprising a different waveform for identification as a CR preamble and identification of a particular symbol at which to expect the CR message; and
wherein the plurality of segments comprises a first segment having a fixed duration, a second segment having a variable duration, and a third segment having a fixed duration; and
transmitting the CR preamble (<NUM>) and the CR message.