WO2017111857A1

WO2017111857A1 - Laa burst frame structure/preamble design and crs design

Info

Publication number: WO2017111857A1
Application number: PCT/US2015/000436
Authority: WO
Inventors: Gang Xiong; Hwan-Joon Kwon; Hong He; Jong-Kae Fwu; Jeong Julie LEE; Seunghee Han
Original assignee: Intel IP Corporation
Priority date: 2015-12-24
Filing date: 2015-12-24
Publication date: 2017-06-29

Abstract

Technology described herein relates to systems, methods, and computer readable media to provide novel burst frame structures, preamble designs, and channel reservation signal designs for Licensed Assisted Access (LAA) operation. An evolved Node B (eNB) can perform a clear channel assessment (CCA) or an extended CCA to determine that an unlicensed carrier is available. The eNB can then send an LAA burst on the unlicensed carrier. The LAA burst's frame structure can include a channel reservation signal, an LAA preamble, and a Physical Downlink Control Channel (PDCCH). Matter described herein also provides technology for generating various types of LAA preambles and channel reservation signals.

Description

LAA BURST FRAME STRUCTURE/PREAMBLE DESIGN AND CRS DESIGN

BACKGROUND

[0001] Wireless mobile communication technology uses various standards and protocols to transmit data between a node (e.g., a transmission station) and a wireless device (e.g., a mobile device). Some wireless devices communicate using orthogonal frequency-division multiple access (OFDMA) in a downlink (DL) transmission and single carrier frequency division multiple access (SC-FDMA) in an uplink (UL) transmission. Standards and protocols that use orthogonal frequency-division multiplexing (OFDM) for signal transmission include the third generation partnership project (3GPP) long term evolution (LTE), the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard (e.g., 802.16e, 802.16m), which is commonly known to industry groups as WiMAX (Worldwide interoperability for Microwave Access), and the IEEE 802.1 1 standard, which is commonly known to industry groups as WiFi.

[0002] In 3GPP radio access network (RAN) LTE systems, the node in an

Evolved Universal Terrestrial Radio Access Network (E-UTRAN) system is referred to as an eNode B (also commonly denoted as evolved Node Bs, enhanced Node Bs, eNodeBs, or eNBs), which communicates with the wireless device, known as a user equipment (UE). The downlink (DL) transmission can be a communication from the node (e.g., eNodeB) to the wireless device (e.g., UE), and the uplink (UL) transmission can be a communication from the wireless device to the node.

[0003] In LTE, data can be transmitted from the eNodeB to the UE via a physical downlink shared channel (PDSCH). A physical uplink control channel (PUCCH) can be used to acknowledge that data was received. Downlink and uplink channels or transmissions can use time-division duplexing (TDD) or frequency-division duplexing (FDD).

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Features and advantages of the disclosure will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the disclosure; and, wherein: [0005] FIG. 1 illustrates an LAA burst frame structure in accordance with example;

[0006] FIG. 2a illustrates an LAA preamble structure in accordance with an example;

[0007] FIG. 2b illustrates an LAA preamble structure in accordance with another example;

[0008] FIG. 2c illustrates an LAA preamble structure in accordance with another example;

[0009] FIG. 3a illustrates an LAA preamble structure in accordance with another example;

[0010] FIG. 3b illustrates an LAA preamble structure in accordance with another example;

[0011] FIG. 3c illustrates an LAA preamble structure in accordance with another example;

[0012] FIGs. 4a-b illustrate reference signal structures for an LAA preamble in accordance with an example;

[0013] FIGs. 5a-e illustrate additional examples of reference signal structures for an LAA preamble;

[0014] FIGs. 6a-b illustrate additional examples of reference signal structures for an LAA preamble;

[0015] FIG. 7 is a table illustrating OCCs that can be applied to pairs of consecutive reference symbols in the same PRB in accordance with an example;

[0016] FIG. 8 illustrates the timing relationship between a CCA or extended CCA and a channel reservation signal in accordance with an example;

[0017] FIG. 9 illustrates an example of channel reservation signal generation based on a long CP in accordance with an example;

[0018] FIG. 10 is a table illustrating shortened OFDM symbol durations for different subcarrier separations in accordance with an example;

[0019] FIG. 1 1 illustrates the generation of a channel reservation signal using aggregated subcarners to produce one or more shortened OFDM symbols in accordance with an example; [0020] FIG. 12 is a table showing the number of possible subcarriers N_$c for reference symbol transmission for various LAA system bandwidths in accordance with an example;

[0021] FIG. 13 is a table showing the number of aggregated subcarriers N_$c for reference symbol transmission for various LAA system bandwidths in accordance with an example;

[0022] FIG. 14 illustrates a scheme for reference symbol generation in accordance with an example;

[0023] FIG. 15 illustrates a scheme for reference symbol generation in accordance with an example;

[0024] FIG. 16 illustrates a scheme for reference symbol generation in accordance with an example;

[0025] FIG. 17 illustrates a scheme for reference symbol generation in accordance with an example;

[0026] FIG. 18 illustrates functionality of an eNB in accordance with an example;

[0027] FIG. 19 illustrates functionality of an eNB in accordance with an example;

[0028] FIG. 20 illustrates a diagram of radio frame resources (e.g., a resource grid) for a downlink (DL) transmission including a legacy physical downlink control channel (PDCCH) in accordance with an example;

[0029] FIG. 21 provides an example illustration of a wireless device in accordance with an example;

[0030] FIG. 22 provides an example illustration of a user equipment (UE) device, such as a wireless device, a mobile station (MS), a mobile wireless device, a mobile communication device, a tablet, a handset, or other type of wireless device; and

[0031] FIG. 23 provides an example illustration of an eNB device in

communication with a mobile wireless device such as a UE or MS.

[0032] Reference will now be made to the exemplary embodiments illustrated and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of is thereby intended.

DETAILED DESCRIPTION

[0033] Before some embodiments are disclosed and described, it is to be understood that the claimed subject matter is not limited to the particular structures, process operations, or materials disclosed herein, but is extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular examples only and is not intended to be limiting. The same reference numerals in different drawings represent the same element. Numbers provided in flow charts and processes are provided for clarity in illustrating operations and do not necessarily indicate a particular order or sequence.

[0034] An initial overview of technology embodiments is provided below and then specific technology embodiments are described in further detail later. This initial summary is intended to aid readers in understanding the technology more quickly, but is not intended to identify key features or essential features of the technology nor is it intended to limit the scope of the claimed subject matter.

[0035] A conventional Third Generation Partnership Project (3GPP) Long-Term

Evolution (LTE) system utilizes the spectrum that is exclusively assigned to the corresponding LTE service provider (or operator). However, due to an upsurge in demand for wireless broadband data, it is critical to increase data throughput of an LTE systems by transmitting data through unlicensed spectrum as well as licensed spectrum. Towards this end, a new study item, "Study on Licensed Assisted Access using LTE," has been approved by the 3GPP in the Radio Access Network (RAN) #65 meeting. One basic concept of Licensed Assist Access (LAA) is to extend LTE technology into unlicensed deployments to enable operators and vendors to leverage existing or planned investments in LTE and Evolved Packet Core (EPC) hardware in the radio and core network. In such a network, LAA is a technology that can coexist with other technologies and allow the network to continue fulfilling applicable regulations.

[0036] In LAA, Carrier Aggregation (CA) mechanisms defined in LTE-Advanced are employed to leverage unlicensed spectrum to complement the licensed spectrum for offloading best-effort traffic. Under this scenario, an existing licensed-LTE primary cell (Pcell) can carry critical control signaling, mobility, and user data that should receive high quality of service (QoS). Less-demanding, best-effort traffic can be carried on a secondary cell (Scell) on unlicensed spectrum. In this regard, the joint operation and flexible offload between licensed and unlicensed carriers can be easily achieved.

[0037] At the Radio Access Network 1 (RAN 1 ) meeting #79, the following agreements were made regarding the transmission of the channel reservation signal. First, a downlink (DL) LAA design should assume subframe boundary alignment according to the 3GPP Release 12 CA timing relationships across serving cells aggregated by CA. For Load-Based Equipment (LBE), some signal(s) can be transmitted (e.g., to reserve a channel) by an eNB between the time eNB is permitted to transmit and the start of the actual data transmission. This does not imply that the data transmission can start only at the subframe boundary, though a possible restriction on starting position of data transmission may be considered. The duration of this signals(s) is part of the maximum transmission duration. The content, additional function, and duration of this signal(s) is for future study (FFS). This does not imply network synchronization

[0038] According to the agreements made in RAN 1 meeting #79, the existing frame structure in the LTE specification may not be reused due to the fact that an LAA burst is transmitted in an opportunistic manner and a channel reservation signal is used to reserve the channel prior to the transmission of data or a control channel in the LAA Burst. To address this issue, a new LAA burst frame structure can be defined to allow efficient LAA operations.

[00391 Systems and technologies of the present disclosure provide a novel burst frame structure and preamble design for LAA operation. One example includes an LAA burst frame structure that includes a channel reservation signal, an LAA preamble, an optional Clear to Send (CTS) communication, an enhanced Physical Downlink Control Channel (ePDCCH), and a data transmission. Another example includes an LAA preamble structure to multiplex an LAA burst control channel, a Primary Synchronization Signal (PSS), and/or a Secondary Synchronization Signal (SSS) in one or more fractional or full Orthogonal Frequency Division Multiplexing (OFDM) symbols. Another example includes a mechanism to generate a fractional OFDM symbol for the transmission of an LAA preamble. Another example includes a Reference symbol (RS) structure and a scheme for RS sequence generation for an LAA preamble.

[0040] Additional systems and technologies of the present disclosure provide channel reservation signal designs for LAA operation. Some examples provide mechanisms to generate channel reservation signals. Additional examples provide reference symbol designs for cases in which a channel reservation signal is generated based on a subcarrier spacing larger than the subcarrier spacing of 3GPP LTE release 8. LAA burst frame structure [0041] Since an LAA burst can be transmitted in an opportunistic manner and a channel reservation signal can be used to reserve a channel for the LAA burst prior to the transmission of data or a control channel, the existing frame structure in 3GPP LTE release 8.0 may not be reused.

[0042] FIG. 1 illustrates an LAA burst frame structure in accordance with example. A channel reservation signal of variable length can be transmitted at the beginning of the LAA burst after an eNB performs a Clear Channel Assessment (CCA) or an extended CCA and detects that an unlicensed carrier to be used for an LAA burst is idle. An LAA preamble can be transmitted after the channel reservation signal in order to, for example, facilitate Automatic Gain Control (AGC), facilitate coarse and/or fine synchronization for UEs, provide an optional Request to Send (RTS), and/or provide certain information regarding the transmission of the LAA burst. In general, the LAA preamble can be aligned with an OFDM symbol boundary and a gap between the starting position of the LAA burst and the OFDM symbol boundary can be used to transmit the channel reservation signal.

[0043] In examples where the LAA preamble provides the functionality for a

RTS, a Clear-to-Send (CTS) signal may be transmitted by one or more UEs to feedback whether the channel is idle. The PDCCH or ePDCCH may be transmitted either after the LAA preamble or CTS signal (as shown in FIG. 1 ) or in a first full subframe of the LAA burst. The position where the ePDCCH is transmitted may also depend on the number of available OFDM symbols in the first subframe of the LAA burst.

LAA preamble structure

[0044] Depending on the duration of time allotted for LAA preamble

transmission, various options can be considered for the design of an LAA preamble. In some examples, an LAA preamble can be transmitted a fractional (e.g., less than 1 )

OFDM symbol, in one full OFDM symbol, or in multiple OFDM symbols (e.g., two full OFDM symbols or one full OFDM symbol plus a fractional OFDM symbol). In addition, a PSS and/or an SSS can be multiplexed together with an LAA burst control channel within the LAA preamble to facilitate coarse or fine synchronization for UEs on unlicensed carriers.

[0045] In one example, if a PSS and/or an SSS is supported in the LAA preamble, the existing 3GPP-LTE-Release-8 PSS signal or SSS signal may be reused. In particular, the PSS can carry 3 cell identities and the SSS can carry 168 cell-identity groups according to a physical-layer cell identity of a cell. Root indices for these three PSS sequences can be defined as M = 25, 29, 34 (as in 3GPP LTE Release 8).

[0046] In another example, a root index that is different from the root indices of

3GPP LTE Release 8 can be defined for the transmission of PSS signal in the LAA preamble. In particular, a root index that can achieve low cross-correlation with the existing PSS sequences can be selected.

[0047] Depending on the LAA preamble structure that is used, the resource mapping of the PSS and/or the SSS may be different from the resource mapping specified in 3GPP LTE Release 8.

[0048] FIG. 2a illustrates an LAA preamble structure in accordance with an example (option 1 for LAA preamble structures occupying a number of OFDM symbols less than or equal to one). As shown in FIG. 1, neither a PSS nor an SSS is transmitted in the LAA preamble. An LAA burst control channel occupies the entire LAA preamble and spans the entire system bandwidth. Note that this option may be desirable when LAA- capable UEs already achieve synchronization with a secondary cell by some other means (e.g., through a primary cell) such that transmission of a PSS in the LAA preamble for secondary cell is unnecessary.

[0049] FIG. 2b illustrates an LAA preamble structure in accordance with another example (option 2 for LAA preamble structures occupying a number of OFDM symbols less than or equal to one). In this option, a PSS and an LAA burst control channel are transmitted within the LAA preamble. When the LAA preamble spans one full OFDM symbol, the PSS can occupy the central 6 Physical Resource Blocks (PRBs). When LAA preamble spans less than one OFDM symbol (e.g., a fractional OFDM Symbol), the PSS can occupy the central X PRBs, where X is a predefined value and X > 6. The value of X can depend on the number of aggregated subcarriers used for transmission of the LAA preamble. For example, when 2 subcarriers are grouped together to form 30 Hz subcarrier spacing, the PSS may occupy the central 12 PRBs (i.e., X = 12). The LAA burst control channel can be rate-matched on some or all available Resource Elements (REs) around the PSS.

[0050] FIG. 2c illustrates an LAA preamble structure in accordance with another example (option 3 for LAA preamble structures occupying a number of OFDM symbols less than or equal to one). In this option, a PSS, an SSS, and an LAA burst control channel can be multiplexed within the LAA preamble. In particular, the PSS can occupy the central X PRBs (e.g., where X is a predefined value and/or is greater than 6) and the SSS can occupy X/2 PRBs on both sides of the PSS. In addition, the LAA burst control channel can be rate-matched on some or all available REs around the PSS and SSS.

[0051] FIG. 2d illustrates an LAA preamble structure in accordance with another example (option 4 for LAA preamble structures occupying a number of OFDM symbols less than or equal to one). In this option, a PSS, an SSS, and LAA burst control channel are multiplexed within the LAA preamble. In particular, the PSS can occupy the central X PRBs (e.g., where X is a predefined value and/or is greater than 6) and the SSS can occupy X PRBs on one side of PSS. As shown in FIG. 2d, the SSS can occupy the right side of the PSS signal. However, the SSS can also be transmitted on the left side of the PSS signal. In addition, the LAA burst control channel can be rate-matched on some or all available REs around the PSS and SSS.

[0052] FIG. 3a illustrates an LAA preamble structure in accordance with another example (option 1 for LAA preamble structures occupying a number of OFDM symbols greater than one and less than or equal to two). In this option, Neither a PSS nor an SSS is transmitted within the LAA preamble. The LAA burst control channel occupies the whole LAA preamble and spans the system bandwidth.

[0053] FIG. 3b illustrates an LAA preamble structure in accordance with another example (option 2 for LAA preamble structures occupying a number of OFDM symbols greater than one and less than or equal to two). In this option, a PSS and an SSS are transmitted in the first and second OFDM symbol, respectively. The LAA burst control channel can be rate-matched around the PSS and the SSS and can span the system bandwidth. The positions of the PSS and the SSS, as shown in FIG. 3b, can be swapped (i.e., the SSS can be transmitted in first OFDM symbol and the PSS can be transmitted in the second OFDM symbol).

[0054] FIG. 3c illustrates an LAA preamble structure in accordance with another example (option 3 for LAA preamble structures occupying a number of OFDM symbols greater than one and less than or equal to two). In this option, a PSS or an SSS can transmitted in the first OFDM symbol, but not both (i.e., the PSS xor the SSS is transmitted). Although FIG. 3c shows a PSS, an SSS signal can also be transmitted in the first OFDM symbol. The remaining REs can be occupied by dummy symbols or reference symbols as transmitted in the second OFDM symbol. In another example, an eNB implementation can determine what signals are transmitted on the remaining REs of the first OFDM symbol. The LAA burst control channel can be transmitted in the second OFDM symbol and can span the system bandwidth.

[0055] In the options 1-3 for LAA preamble structures occupying a number of

OFDM symbols greater than one and less than or equal to two, the LAA preamble can be transmitted in the first full OFDM symbol and a fractional second OFDM symbol. In addition, different numbers of OFDM symbols can be used to transmit the LAA preamble; various combinations of full and/or fractional OFDM symbols can be used. LAA preamble: fractional OFDM symbol generation

[0056] As described above, an LAA preamble may span a fractional OFDM symbol to minimize the overhead within an LAA burst. To generate a fractional OFDM symbol, several options can be considered as follows.

[0057] In one example, a larger subcarrier spacing can be employed to create a fractional OFDM symbol. For instance, a 30 kilohertz (KHz) subcarrier spacing can be used to generate an OFDM symbol with a duration of 33.3μ$. The larger subcarrier spacing can be defined, for example, as Af = K^■ Af, where Af = 15KHz refers to the subcarrier spacing as defined in 3GPP LET Release 8. In order to keep the same sampling rate as 3GPP LTE release 8 (or an integer multiple thereof), K = 2^N subcarriers can be specified (where N > 1 is an integer).

[0058] In another example, an Interleaved Frequency Division Multiple Access (IFDMA) signal structure can be adopted. With IFDMA, a fractional OFDM symbol can be generated by puncturing one or more repetition blocks in the time domain. In particular, data or reference symbols can be mapped in every K subcarriers in the frequency domain and remaining subcarriers can be set to zero. This IFDMA structure with a RePetition Factor (RPF) of K can create K repeated blocks in the time domain. A fractional OFDM symbol can be generated by By puncturing one or more repetition blocks. For example, when K = 2, data or reference symbols can be mapped to every even subcarrier such that two repeated blocks in the time domain are created. A 33.3 $ OFDM symbol duration can be generated if one of the two repeated blocks is punctured. Again, in order to keep the same sampling rate as 3GPP LTE release 8 (or an integer multiple thereof), K = 2^N subcarriers can be specified (where N > 1 is an integer). LAA preamble: reference symbol (RS) generation [0059] When an LAA burst control channel is transmitted within an LAA preamble, reference signals (RSs) should be inserted in resources other than the resource allocated for the transmission of a PSS or SSS to ensure proper channel estimation. As described below, several options can be considered for the design of RSs when the LAA preamble spans one OFDM symbol. The design principles of the options below can be straightforwardly extended to cases where the LAA preamble spans fractional or multiple OFDM symbols. In one example, the same RS structure used in a first OFDM symbol can apply for any remaining OFDM symbols. In another example, when fractional OFDM symbol is adopted, an aggregated subcarrier (e.g., two subcarriers with 30 Hz spacing) can be used to replace the subcarrier in the following options. In addition, while antenna ports (APs) 0, 1 , 2, and 3 are used as examples for RS transmission for an LAA preamble, different APs can also be used.

[0060] FIGs. 4a-b illustrate examples of reference signal structures for an LAA preamble (i.e., reference signal structure option 1 ). In this option, an existing cell-specific RS (CRS) structure on the first OFDM symbol can be reused. FIG. 4a illustrates an example in which an evolved Node B (eNB) employs one AP. FIG. 4b illustrates an example in which an eNB employs two APs. For this option, 2 is the maximum AP number that can be specified.

[0061] In one example, cell-specific frequency shift is not applied for the RS transmission in the LAA preamble. Since the eNB transmits the preamble and data on unlicensed carriers in an opportunistic manner, the benefits of applying cell-specific frequency shift can be limited. In another example, a cell-specific frequency shift (e.g., ( ,"¹¹ mod 6)) can be applied to avoid time-frequency collisions between common RSs from up to six adjacent cells.

[0062] FIGs. 5a-e illustrate additional examples of reference signal structures for an LAA preamble (i.e., reference signal structure option 2). In this option, one, two, and four APs can all be supported by an eNB. More specifically, four reference-signal (RS) positions can be evenly distributed for each AP, while a single RS location can be actually allocated for RS transmission for each AP. RS locations that are not allocated for RS transmission can be set to zero.

[0063] In one example, a cell-specific frequency shift is not applied. In another example, to avoid time-frequency collisions between common RSs from adjacent cells, a cell-specific frequency shift can be applied. However, due to the specific structure of the RS in the option illustrated in the examples of FIGs. 5a-e, the frequency shift can be defined as (/V,^c _D ^e" mod 3).

[0064] FIGs. 6a-b illustrate additional examples of reference signal structures for an LAA preamble (i.e., reference signal structure option 3). In this option, one, two, and four APs can all be supported at an eNB. More specifically, four RS positions can be evenly distributed for each AP (as shown in FIG. 6a) or located in the middle of one PRB (as FIG. 6b). Further, two RS locations can be used for RS transmissions. RS locations that are not used for RS transmissions can be set to zero for each AP. For this option, an orthogonal cover code (OCC) can be applied to pairs of consecutive reference symbols in the same PRB to cancel interference for channel estimation between different APs.

[0065] FIG. 7 is a table illustrating OCCs that can be applied to pairs of consecutive reference symbols in the same PRB.

[0066] For the examples of FIGs. 6a-b, A reference signal sequence can be generated in the same way as defined in section 6.10.1.1 of 3GPP Technical Specification (TS) 36.21 1 for a CRS or in section 6.10.3.1 of 3GPP TS 36.21 1 for a UE-specific RS for an AP p G {7,8, ··· , v + 6}. In one example, to simplify the design and reduce the implementation cost, the slot number and the OFDM symbol number n_s = I = 0 can be used for the generation of the RS sequence. In another example, the slot number and the OFDM symbol number for the transmission of the LAA preamble can used for the RS sequence generation.

[0067] If the CRS is reused to generate an RS sequence for the LAA preamble,

N_CP = 1 can be specified in an equation for the initialization of a pseudo-random sequence generator. If a UE-specific RS is reused, n_saD = 0 can be specified in an equation for the initialization of the pseudo-random sequence generator.

Channel reservation signal design

[0068] One purpose of a channel reservation signal is to fill out and potentially utilize the gap between the end position of a CCA or extended CCA and the starting OFDM symbol boundary in a secondary cell. As a result, depending on the end position of the CCA or extended CCA, the length of a channel reservation signal can vary.

[0069] FIG. 8 illustrates the timing relationship between a CCA or extended CCA and a channel reservation signal. In FIG. 8, the length of the cyclic prefix (CP) can be 4.7 microseconds (με) and 5.2^s for a normal CP case and 16.7μ5 for an extended CP. [0070] The channel reservation signal may also be used to facilitate automatic gain control (AGC), facilitate coarse or fine timing and frequency synchronization for UEs, and allow UEs to determine the starting position of the LAA burst. Hence, a predefined structure for the design of the channel reservation signal would be helpful. Furthermore, as shown in FIG. 2, the length of the channel reservation signal can be longer than one OFDM symbol. This length can help improve detection performance of the channel reservation signal, especially when the end position of the CCA or extended CA is very close to the OFDM symbol boundary.

[0071] To generate the channel reservation signal with variable length, several options can be considered. In one example, the channel reservation signal can be generated based on an eNB's implementation. The timing for power ramp-up and ramp- down can follow the timing relationship as shown in FIG. 2. Further, in a simple example, the eNB can transmit a dummy signal solely for the purpose of reserving the channel. In addition, the transmission of the dummy signal can fulfill a minimum bandwidth occupancy regulation defined in a standard such as an Institute of Electrical and

Electronics Engineers (IEEE) 802.1 1 standard (e.g., the nominal channel bandwidth can be at least 5 megahertz (MHz) and the occupied channel bandwidth can be between 80% and 100% of the nominal channel bandwidth).

[0072] In another example, the channel reservation signal can comprise a cyclic prefix (CP) with a variable length and an OFDM symbol that contains a cell-specific reference symbol (CRS), a channel state information RS (CSI-RS), and/or a positioning RS (PRS). The OFDM symbol may or may not contain a data symbol. In addition, the CP can be generated by duplicating the last part of the OFDM symbol, whereby the length is determined by the gap between the end point of the CCA or extended CCA and OFDM symbol boundary.

[0073] FIG. 9 illustrates an example of channel reservation signal generation based on a long CP in accordance with an example. As shown in FIG. 9, the long CP can be generated by duplicating the last part of the first OFDM symbol. Although the duration of the channel reservation signal is less than one OFDM symbol in FIG. 9, the duration of the CRS can also be longer than one OFDM symbol. When a channel reservation signal spans multiple OFDM symbols, the channel reservation signal can appear to be a repetition. [0074] In one example, the channel reservation signal can be the CP of the first

OFDM symbol that is transmitted in the LAA burst or the first OFDM symbol within the first full subframe of the LAA burst. If the channel reservation signal spans multiple OFDM symbols, the first OFDM symbol to be transmitted within LAA burst can appear to be a repetition. Similarly, the length of the CP can be determined by the gap between the end point of the CCA or extended CCA and the OFDM symbol boundary.

[0075] In another example, the channel reservation signal can comprise of a copy of the NOFDM symbols within the first full subframe of the LAA burst and a long CP. One option is to copy the first NOFDM symbols as the channel reservation signals. In this case, the PDCCH or Physical Downlink Shared Channel (PDSCH) decoding performance can be improved when UEs buffer the channel reservation signal and combine the transmission within the first subframe of the LAA burst. Another option is to copy the last N OFDM symbols within the first full subframe of the LAA burst as the channel reservation signals. In this case, channel estimation performance can be improved when a DeModulation Reference Symbol (DM-RS)-based transmission mode is used to transmit the PDSCH.

[0076] The remaining fractional portion of the channel reservation signal can generated by the long CP. In addition, the value Ncan be predefined in a specification, configured by higher layers, or simply defined as the available OFDM symbols in the first fractional subframe within the LAA burst.

[0077] In another example, the channel reservation signal can be generated based on a subcarrier spacing that is larger than the subcarrier spacing of 3GPP LTE release 8. In addition, one or more shortened OFDM symbols can be grouped together to create the channel reservation signal.

[0078] Although the channel reservation signal is generated for a downlink (DL) transmission in some examples, the same principles applied to CRS generation for DL transmission can be straightforwardly extended to CRS generation for UL transmission. In one option, an uplink DM-RS and a sounding RS (SRS) can be considered to be part of the channel reservation signal. The remaining fractional part of the channel reservation signal can be generated by the long CP.

[0079] In addition, although some CRS designs target the existing LTE LAA system (e.g., where the maximum system bandwidth is 20MHz), these CRS designs can be straightforwardly extended to future LTE LAA systems that have a system bandwidth larger than 20MHz.

Channel reservation signal design based on a larger subcarrier spacing

[0080] A larger subcarrier spacing can be introduced to create a shortened OFDM symbol relative to the typical LTE subcarrier spacing of Af = 15 KHz. Furthermore, one or more shortened OFDM symbols can be grouped together to generate the channel reservation signal. The larger subcarrier spacing can be defined as Af = K^■ Af, where Af = lSKHz is the subcarrier spacing as defined in the existing LTE specification. In order to keep the same sampling rate of 3GPP LTE release 8 or an integer multiple thereof, it may be desirable to specify K = 2^N subcarriers, where N > 1 is an integer.

[0081] FIG. 10 is a table illustrating shortened OFDM symbol durations for different subcarrier separations. In FIG. 10, T_s = 1/(15000 x 2048) second is defined as the minimum sampling interval in the 3GPP LTE release 8.

[0082] If the gap between the end point of the CCA or extended CCA and the OFDM symbol boundary or the next OFDM symbol boundary is referred to as T_avaU, then the number of shortened OFDM symbols (L) for the channel reservation signal can be calculated as

L = [T_avail Af'\ = [T_avail K - 15 X 10M

Accordingly, the channel reservation signal duration can be calculated as

L

^Γ- ⁼ * · 15 Χ 10^{3 (seCOnd)}

[0083] After L shortened OFDM symbols have been filled, a certain gap with of a duration (J avail ~ Tres) ^may exist. To ensure that WiFi will not transmit the data during this interval, the gap duration can be constrained to be no longer than a Short Interframe Space (SIFS) or a Distributed Coordination Function (DCF) Interframe Space (DIFS). For example, if the SIFS duration of 16μς for the IEEE 802.1 1 ac standard is used, then a subcarrier spacing of Af ≥ 120KHz can ensure that the gap duration is less than an SIFS. In general, an OFDM symbol duration is inversely proportional to an applicable subcarrier spacing.

[0084] FIG. 1 1 illustrates the generation of a channel reservation signal using aggregated subcarriers to produce one or more shortened OFDM symbols. A shortened OFDM symbol with a duration of (66.7 /Κ)με can be generated by aggregating K subcarriers. L shortened OFDM symbols can transmitted after an eNB performs a CCA or an extended CCA and determines the channel is idle. As shown in FIG. 1 1 , a potential gap may exist between the channel reservation signal and the OFDM symbol boundary.

[0085] In some examples, different shortened OFDM symbols can use the same CRS structure. In such examples, UEs may be able to achieve fast frequency

synchronization with an eNB due to the repeated structure of the channel reservation signal. Alternatively, different shortened OFDM symbols can use different CRS structures.

[0086] In order to allow a UE to detect a channel reservation signal quickly with a low-complexity signal detector, a subcarrier separation that results in a shorter symbol duration and a smaller number of samples in the time domain can be selected. However, a relatively large number of samples can ensure detection robustness for the channel reservation signal. Hence, when selecting a subcarrier spacing, it may be helpful to strike a balance between detection complexity and detection performance.

[0087] In one example, the subcarrier spacing can be specified as Δ/' = 240KHz

(i.e., K = 16) to aggregate 16 of the existing 3GPP LTE Release 12 subcarriers. This creates a shortened OFDM symbol duration of 4.17^s, or 128 samples with respect to T_s in the time domain. An eNB can transmit L shortened OFDM symbols depending on the interval between the end position of the CCA or extended CCA and the OFDM symbol boundary or next OFDM symbol boundary.

[0088] In another example, the subcarrier spacing can be specified as Δ/' =

480K z, (i.e., K = 32). This creates a shortened OFDM symbol duration of 2.08μχ, or 64 samples with respect to T_s in the time domain.

[0089] In some examples, the central subcarrier within the DL system bandwidth can be reserved as the Direct Current (DC) subcarrier on which no signal is transmitted by the eNB.

[0090] The subcarrier spacing does not have to be limited to the above examples.

In addition, K can also be defined as any integer value rather than 2^N.

Channel reservation signal design: reference symbol generation

[0091] For different subcarrier separations, the number of subcarriers N_$c for reference symbol transmission

[0092] Where N_sc is the number of subcarriers in 3GPP LTE release 8. For instance, for a system bandwidth of 20MHz, N_sc = 1200. N_sc' can also be defined as the largest even number such that N_$c≤ -^] or Ns_C < or the smallest even number such that N^≥ ^f\ or Λ& > [¾£].

[0093] At the RANI #79 meeting, the following agreements were made regarding the system bandwidth for LAA operations. An LAA design option should support a sstem bandwidth option of at least 20MHz in the 5GHz band. System bandwidths less than 5 MHz are not considered for physical layer options in LAA.

[0094] FIG. 12 is a table showing the number of possible subcarriers N^ for reference symbol transmission for various LAA system bandwidths when N_$c— 1° one example, for an LAA system bandwidth of 20MHz when Δ/' = 240KHz (i.e., K = 16), the total number of aggregated subcarriers (240KHz) that can be allocated within the system bandwidth for the reference symbol transmission is 75.

[0095] FIG. 13 is a table showing the number of aggregated subcarriers N _c for reference symbol transmission for various LAA system bandwidths when N_sc' is defined as the smallest even number such that N^_c≥ \~^\ - 1° ^one example, for an LAA system bandwidth of 20MHz when Δ/' = 2AQKHz (i.e., K = 16), N_$c = 76.

[0096] In general, UEs should be apprised of a channel reservation signal's design in order to allow the UEs to achieve synchronization with an eNB and determine the starting position of the LAA burst. In one example, the channel reservation signal design can be predefined or fixed in a specification. In another example, the channel reservation signal can be generated in accordance with a physical cell identity or a virtual identity configured by higher layers.

[0097] In a fashion similar to that of existing PSS designs, a Zadoff-Chu (ZC) sequence can be adopted for reference symbol generation for the transmission of a channel reservation signal. One element of the ZC sequence can be punctured to avoid transmission on the DC subcarner. In addition, for different LAA system bandwidths with different numbers of subcarriers, the length of the ZC sequence can be different. N_zc can be defined as the length of the ZC sequence. N_zc can be an odd value or a prime number. [0098] With respect to reference symbol generation, several options can be considered depending on whether the length of ZC sequence (N_zc) is less than the number of subcarriers (Λ^) within the LAA system bandwidth or not.

[0099] In one example, when the length of a ZC sequence is less than the number of subcarriers within an LAA system bandwidth, certain subcarriers in the edge of the system bandwidth can be left unused to allow efficient operation. In addition, the middle element of the ZC sequence can be punctured for the DC subcarrier.

[00100] FIG. 14 illustrates a scheme for reference symbol generation (i.e., option 1 for reference symbol generation) in accordance with an example. A reference symbol sequence can be generated as follows:

where u is the root index that can be fixed or defined as a function of a physical cell identity or a virtual identity configured by higher layers by a primary cell or a secondary cell.

[00101] Further, the mapping of the sequence to the resource elements for the reference symbol can be defined as follows:

[00102] where a_k is the transmitted reference symbol on the kth subcarrier and k = 0,1, ·• , — 1. In addition, the resource elements where

can be reserved and not used for the transmission of the channel reservation signal.

[00103] For the option illustrated by FIG. 14 (i.e., option 1 for reference symbol generation), the length of the ZC sequence should be selected to fulfill a regulation that the occupied channel bandwidth be between 80% and 100% of the nominal channel bandwidth. [00104] In one example, for LAA system bandwidth of 20MHz, when Δ/' = 240KHz (i.e., K = 16 and Ν_$ = 76), the ZC sequence length can be defined as N_zc = 73 and the reference symbol can be generated as follows:

*u 0 =

[00105] Then, the mapping of the sequence to the resource elements for reference symbol can be defined as

«fe = ^u("). n = 0,1,— ,71

k = n + 2

[00106] In addition, the following subcarriers are reserved and are not used for the transmission of the channel reservation signal:

k = 0,1,74,75.

[00107] In another example, when the length of the ZC sequence is less than the number of subcarriers within the LAA system bandwidth, cyclic extension of the ZC sequence can be employed for reference symbol generation. Similarly, one element of the ZC sequence can be punctured for the DC subcarrier.

[00108] FIG. 15 illustrates a scheme for reference symbol generation (i.e., option 2 for reference symbol generation) in accordance with an example. In this option, the reference symbol sequence can be generated as follows:

Ofe = x_u{k mod (N_zc - 1))

where a_k is the transmitted reference symbol on the fcth subcarrier and k = 0,1, ··· , N_$c— 1. In addition, x_u n) =

[00109] Similarly, the root index u can be fixed or defined as a function of a physical cell identity or a virtual identity configured by higher layers of a primary cell or a secondary cell. [00110] In one example, for an LAA system bandwidth of 20MHz, when Δ/' = 240KHz (i.e., K = 16 and N_$c = 76), the ZC sequence length can be defined as N_zc = 73 and the reference symbol can be generated as follows:

a_k = x_u(k mod 72)

Where

7^'7run(n+l) } η = 0,1, ··· ,37

[00111] 73

*u0 = { ;^'7ru(n+l)(n+2)

exp ] η = 38, · · , 71

73

[00112] In another example, when the length of the ZC sequence is greater than or equal to the number of subcarriers within the LAA system bandwidth, certain elements in the ZC sequence can be punctured for the reference symbol generation. Similarly, one element of the ZC sequence can be punctured for the DC subcarrier.

[00113] FIG. 16 illustrates a scheme for reference symbol generation (i.e., option 3 for reference symbol generation) in accordance with an example. In this option, the reference symbol sequence can be generated as follows:

a_k = x_u(k)

where a_k is the transmitted reference symbol on the fcth subcarrier and k = 0,1, ··· , N^c ~ 1. In additio

[00114] Similarly, the root index u can be fixed or defined as a function of a physical cell identity or a virtual identity configured by higher layers of a primary cell or a secondary cell.

[00115] In one example, for an LAA system bandwidth of 20MHz, when Δ/' = 240 fWz (i.e., K— 16 and N_$c = 76), the ZC sequence length can be defined as N_zc = 79 and the reference symbol can be generated as follows:

ak = *u(k)

where

⁷⁵ [00116] In the aforementioned options for reference symbol generation, different reference symbols— and thus different channel reservation signals— are generated for LAA systems with different system bandwidths. To simplify the design of the channel reservation signal and minimize the implementation cost, a unified design for a channel reservation signal for LAA systems with different system bandwidths can be defined. Such a unified design can enable a UE to search the channel reservation signal within the minimum system bandwidth supported for an LAA system only, thereby reducing UE power consumption for channel reservation signal detection.

[00117] In another example, the reference symbols based on the ZC sequence can be generated for the minimum system bandwidth supported for an LAA system. In particular, options 1-3 for reference symbol generation can be adopted for the channel reservation signal. Furthermore, for a system bandwidth greater than the minimum system bandwidth, remaining subcarriers can be reserved for the transmission of certain signals in order to fulfill at regulation that the occupied channel bandwidth shall be between 80% and 100% of the nominal channel bandwidth.

[00118] In one example, an eNB implementation can determine which signals are transmitted on the remaining subcarriers outside the minimum system bandwidth. The signals can be, for example, dummy signals or other types of symbols. In another example, the reference symbols can be transmitted in the remaining subcarriers.

[00119] FIG. 17 illustrates a scheme for reference symbol generation (i.e., option 4 for reference symbol generation) when the LAA system bandwidth is greater than the minimum system bandwidth in accordance with an example. More specifically, within the minimum system bandwidth supported for LAA operation, the 3 options as proposed above based on a ZC sequence can be used for reference symbol generation. Outside the minimum system bandwidth, a dummy signal or other reference symbols can be transmitted.

[00120] In one example, the minimum system bandwidth for LAA operation can be defined as 5MHz. For this minimum system bandwidth for LAA operation, Δ/' = 120KHz can be used (i.e., K = 8 and N_$c = 38). According to option 1 as shown in FIG. 14, the ZC sequence length can be defined as N_zc = 37 and the reference symbol generation can follow the design principle in option 1. Note that options 2 and 3 for reference symbol generation can also be adopted. When the LAA system bandwidth is greater than 5MHz, the remaining subcarriers outside the 5MHz can be used to transmit a dummy signal.

[00121] Reference symbol generation does not have to be limited to a ZC sequence. An M-sequence, a Hadamard sequence, or another sequences which can satisfy the Constant Amplitude Zero Autocorrelation (CAZAC) property can be used for the reference symbol generation for the transmission of the channel reservation signal.

[00122] FIG. 18 illustrates functionality 1800 of an eNB in accordance with an example. The functionality 1800 can be implemented as a method or the functionality can be executed as instructions on a machine (e.g., by one or more processors), where the instructions are included on at least one non-transitory computer-readable storage medium.

[00123] As in block 1810, the one or more processors and memory at the eNB can be configured to perform a Clear Channel Assessment (CCA) (which may be an extended CCA in some examples).

[00124] As in block 1820, the one or more processors and memory at the eNB can be further configured to determine that an unlicensed carrier is available based on the CCA.

[00125] As in block 1830, the one or more processors and memory at the eNB can be configured to send, on the unlicensed carrier, a Licensed Assisted Access (LAA) burst having an LAA-burst frame structure, the LAA-burst frame structure comprising: a channel reservation signal to reserve the unlicensed carrier, a Licensed Assisted Access (LAA) preamble that includes a Licensed Assisted Access (LAA) burst control channel, and a Physical Downlink Control Channel (PDCCH) or an enhanced Physical Downlink Control Channel (ePDCCH).

[00126] In some examples, the LAA preamble can serve as a Request To Send (RTS) signal and the one or more processors and memory are further configured to receive a Clear To Send (CTS) signal from a user equipment (UE).

[00127] In some examples, the LAA preamble can also span a number of

Orthogonal-Frequency-Division-Multiplexing (OFDM) symbols less than or equal to one and the LAA burst control channel can fully occupy the LAA preamble and span an entire bandwidth of the unlicensed carrier.

[00128] The LAA preamble can further comprise a Primary Synchronization Signal (PSS). [00129] In some examples, the LAA preamble spans one OFDM symbol and the one or more processors and memory are further configured to: send the PSS using six central Physical Resource Blocks (PRBs); and rate match resource elements (REs) of the LAA burst control channel that are not used to send the PSS.

[00130] In some examples, the one or more processors and memory are further configured to: use 30kilohertz (kHz) subcarrier spacing in the bandwidth of the unlicensed carrier; send the PSS using twelve central Physical Resource Blocks (PRBs); and rate match resource elements (REs) of the LAA burst control channel that are not used to send the PSS.

[00131] In some examples, the LAA preamble further comprises a Secondary Synchronization Signal (SSS), the LAA preamble spans a number of Orthogonal- Frequency-Division-Multiplexing (OFDM) symbols less than or equal to one, and the one or more processors and memory are further configured to: send the PSS using X central Physical Resource Blocks (PRBs) , wherein X is a predefined value; send the SSS using X/2 PRBs that are adjacent to a higher-frequency edge of the X PRBs used for the PSS and using X/2 PRBs that are adjacent to a lower-frequency edge of the X PRBs used for the PSS; and rate match resource elements (REs) of the LAA burst control channel that are not used to send the PSS or the SSS.

[00132] In some examples, the LAA preamble further comprises a Secondary Synchronization Signal (SSS), the LAA preamble spans a number of Orthogonal- Frequency-Division-Multiplexing (OFDM) symbols less than or equal to one, and the one or more processors and memory are further configured to: send the PSS using X central Physical Resource Blocks (PRBs), wherein X is a predefined value; send the SSS using X PRBs that are adjacent to either a higher-frequency edge of the X PRBs used for the PSS or a lower-frequency edge of the X PRBs used for the PSS; and rate match resource elements (REs) of the LAA burst control channel that are not used to send the PSS or the SSS.

[00133] In some examples, the LAA preamble spans a number of Orthogonal- Frequency-Division-Multiplexing (OFDM) symbols greater than one and less than or equal to two, and the LAA burst control channel fully occupies the LAA preamble and spans an entire bandwidth of the unlicensed carrier.

[00134] In some examples, the LAA preamble spans a number of Orthogonal- Frequency-Division-Multiplexing (OFDM) symbols greater than one and less than or equal to two, and the LAA preamble further comprises a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS), and the one or more processors and memory are further configured to: send, in a first OFDM symbol of the number of OFDM symbols, the PSS using X central Physical Resource Blocks (PRBs), wherein X is a predefined value; send, in a second OFDM symbol of the number of OFDM symbols, the SSS using the X central PRBs; and rate match resource elements (REs) of the LAA burst control channel that are not used to send the PSS or the SSS.

[00135] In some examples, the LAA preamble spans a number of Orthogonal- Frequency-Division-Multiplexing (OFDM) symbols greater than one and less than or equal to two; the LAA preamble further comprises a synchronization signal that is a

Primary Synchronization Signal (PSS) or a Secondary Synchronization Signal (SSS); the one or more processors and memory are further configured to send, in a first OFDM symbol of the number of OFDM symbols, the synchronization signal using X central Physical Resource Blocks (PRBs), wherein X is a predefined value; the LAA burst control channel is located in a second OFDM symbol of the number of OFDM symbols and fully spans the bandwidth of the unlicensed carrier; and the one or more processors are further configured to send, in the second OFDM symbol of the number of OFDM symbols and in the X PRBs, dummy symbols or reference symbols.

[00136] In some examples, the one or more processors and memory are further configured to: generate a fractional OFDM symbol to be used for transmission of the LAA preamble using a subcarrier spacing greater than 15 kiloHertz (kHz) wherein the subcarrier spacing is defined by the equation Af= K · Af, wherein Af = 15kHz, Af= the subcarrier spacing, and K = 2^N, and N is an integer greater than one; and send the LAA preamble of the LAA burst in the fractional OFDM symbol.

[00137] In some examples, the one or more processors and memory are further configured to: generate a fractional OFDM symbol to be used for transmission of the LAA preamble using an interleaved Frequency Division Multiple Access (FDMA) signal structure by puncturing one or more time-domain repetition blocks; and send the LAA preamble of the LAA burst in the fractional OFDM symbol.

[00138] In some examples, the one or more processors and memory are further configured to: generate a Reference Symbol (RS) for the LAA preamble; and send the RS using resources for the LAA burst control channel that are not used to send a primary synchronization signal (PSS) or a secondary synchronization signal (SSS). [00139] In some examples, the one or more processors and memory are further configured to: generate the RS using a cell-specific reference signal structure defined in Third Generation Partnership Project (3GPP) Long-Term Evolution (LTE) Release 8.0; and send the RS using one or two antenna ports (APs) of the eNB either without applying a cell-specific frequency shift or applying a cell-specific frequency shift defined as (Ν_/β" mod 6), where Nfg¹¹ is a physical cell identifier (PCI) of the eNB and mod is a modulus operator.

[00140] In some examples, the one or more processors and memory are further configured to: send the RS using one, two, or four antenna ports (APs) of the eNB and either without applying a cell-specific frequency shift or applying a cell-specific frequency shift defined as (Nfg¹¹ mod 3), where N/p" is a physical cell identifier (PCI) of the eNB and mod is a modulus operator, wherein four RS positions corresponding to Resource Elements (REs) in a Physical Resource Block (PRB) and in an OFDM symbol are evenly spaced, wherein each antenna port sends the RS signal in exactly one of the four RS positions.

[00141] In some examples, the one or more processors and memory are further configured to: send the RS using one, two, or four antenna ports (APs) of the eNB, wherein four RS positions corresponding to Resource Elements (REs) in a Physical Resource Block (PRB) and in an OFDM symbol are either evenly spaced or are central relative to the PRB, wherein each antenna port sends the RS signal in exactly two of the four RS positions; and apply an orthogonal cover code (OCC) to pairs of consecutively sent reference signals in the PRB.

[00142] FIG. 19 illustrates functionality 1900 of an eNB in accordance with an example. The functionality 1900 can be implemented as a method or the functionality can be executed as instructions on a machine (e.g., by one or more processors), where the instructions are included on at least one non-transitory computer-readable storage medium.

[00143] As in block 1910, the one or more processors and memory at the eNB can be configured to perform a Clear Channel Assessment (CCA).

[00144] As in block 1920, the one or more processors and memory at the eNB can be further configured to determine, based on the CCA, that an unlicensed carrier is available for Licensed Assisted Access (LAA). [00145] As in block 1930, the one or more processors and memory at the eNB can be further configured to generate a channel reservation signal.

[00146] The channel reservation signal can comprise a long Cyclic Prefix (CP) and an Orthogonal Frequency Division Multiplexing (OFDM) symbol that includes one or more of: a cell-specific reference symbol; a channel-state information reference symbol (CSI-RS); a positioning reference symbol (PRS); a demodulation reference signal (DM- RS); a sounding reference signal (SRS); or a data transmission, wherein a length of the long CP is bounded by a gap between an ending time of the CCA and an OFDM symbol boundary.

[00147] As in block 1940, the one or more processors and memory at the eNB can be further configured to send, in a first fractional sub-frame of a Licensed Assisted Access (LAA) burst, the channel reservation signal to reserve the unlicensed carrier.

[00148] In some examples, the one or more processors are further configured to: send the channel reservation signal using a long cyclic prefix (CP) of a first Orthogonal Frequency Division Multiplexing (OFDM) symbol of the first fractional sub-frame of the LAA burst or a first full sub-frame of the LAA burst, wherein a length of the long CP is bounded by a gap between an ending time of the CCA and an OFDM symbol boundary.

[00149] In some examples, the one or more processors are further configured to send data in N Orthogonal Frequency Division Multiplexing (OFDM) symbols of a first full sub-frame of the LAA burst; N is an integer that is predefined in a specification, configured by higher layers at the eNB, or defined as a number of available OFDM symbols in the first fractional sub-frame of the LAA burst; the channel reservation signal comprises a long Cyclic Prefix (CP) and a copy of the data sent in the N OFDM symbols of the first full sub-frame of the LAA burst; and a length of the long CP is bounded by a gap between an ending time of the CCA and an OFDM symbol boundary. The N OFDM symbols can be in N first symbol OFDM positions of the first full sub-frame of the LAA burst or in N last OFDM symbol positions of the first full sub- frame of the LAA burst.

[00150] In some examples, the one or more processors and memory are further configured to generate the channel reservation signal using one or more shortened OFDM symbols, wherein the one or more shortened OFDM symbols are based on a subcarrier spacing greater than 15 kilohertz (kHz). [00151] In some examples, the one or more processors and memory are further configured to generate the channel reservation signal in accordance with a physical cell identity or a virtual identity of the eNB.

[00152] In some examples, the one or more processors and memory are further configured to generate a reference symbol for the channel reservation signal based on a Zadoff-Chu (ZC) sequence. A length of the ZC sequence can be less than a number of subcarriers within a bandwidth of the unlicensed carrier and the one or more processors and memory can be further configured to: leave unused one or more subcarriers on one or more edges of the bandwidth; and puncture a middle element of the ZC sequence for a Direct Current (DC) subcarrier. Alternatively, a length of the ZC sequence can be less than a number of subcarriers within a bandwidth of the unlicensed carrier and the one or more processors and memory can be further configured to perform cyclic extension of the ZC sequence to fill in the number of subcarriers and puncture one element of the ZC sequence for a Direct Current (DC) subcarrier. In another alternative, a length of the ZC sequence can be greater than or equal to a number of subcarriers within a bandwidth of the unlicensed carrier and the one or more processors and memory can be further configured to puncture certain elements of ZC sequences to match with the number of subcarriers and one element of the ZC sequence for a Direct Current (DC) subcarrier.

[00153] In some examples, the one or more processors and memory are further configured to: generate reference symbols for the channel reservation signal for a minimum supported LAA bandwidth based on a ZC sequence; send, using one or more remaining subcarriers, one or more of: a dummy signal, a cell-specific reference symbol (CRS), a channel-state information reference symbol (CSI-RS), or a positioning reference symbol (PRS).

[00154] FIG. 20 depicts constitutive elements, with respect to time and frequency, of the Orthogonal Frequency Division Multiplexing (OFDM) transmission scheme employed by the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) standards. However, other OFDM and non-OFDM modulation schemes are possible. With respect to time in the example, a single radio frame 2002, with a duration of 10 milliseconds (ms), is depicted from a stream of frames. The single radio frame comprises a set of 10 sub-frames 2004, numbered from #1 to #10 in the expanded cutout of the radio frame. Each sub- frame has a duration of 1 ms. A sub-frame can be further subdivided into two slots (#0 2006a, #1 2006b), a slot having a duration of 0.5 ms. [00155] The 0.5 ms duration of a slot can coincide with the temporal duration of a physical resource block (PRB) 2008a-x. A PRB, as further defined in 3 GPP TS 36.21 1, Sections 5.2.3 and 6.2.3 for 3GPP LTE release 12 (or an earlier release), can be the smallest unit of resource allocation assigned by a transmission point scheduler unit within 3GPP LTE standards. Other standards can define analogous units, for purposes of resource assignment, with respect to time and frequency. For example, a 5G radio frame may include frames and sub-frames with significantly shorter time durations. For instance, each frame in a 5G system may have a duration of 0.5 ms, 1.0 ms, 2 ms, 5 ms, or another desired time duration.

[00156] In addition to its 0.5 ms temporal span in this example, a PRB also spans a range of frequencies. Individual PRBs have distinct frequency spans, as depicted by the ascending series of PRBs with respect to frequency in FIG. 20. More specifically, an individual PRB 2008a-x can include 12 different 15 kHz subcarriers 2010 (on the frequency axis) and 6 or 7 time symbols 2020 (on the time axis) per slot 2006, per subcarrier, depending on whether a normal Cyclic Prefix (CP), 7 time symbols, or an extended CP, 6 time symbols, is used. The various subcarriers and time symbols with respect to frequency and time dimensions can create a grid of 84 Resource Elements (REs) 2014, where a PRB 2008k comprises 7 time symbols. In a 5G system, the PRBs may include more subcarriers, fewer subcarriers, a greater bandwidth per subcarrier, a lesser bandwidth per subcarrier, and a different CP length.

[00157] FIG. 21 provides an example illustration of a mobile device, such as a user equipment (UE), a mobile station (MS), a mobile wireless device, a mobile

communication device, a tablet, a handset, or other type of wireless device. The mobile device can include one or more antennas configured to communicate with a node, macro node, low power node (LPN), or, transmission station, such as a base station (BS), an evolved Node B (eNB), a baseband processing unit (BBU), a remote radio head (RRH), a remote radio equipment (RRE), a relay station (RS), a radio equipment (RE), or other type of wireless wide area network (WWAN) access point. The mobile device can be configured to communicate using at least one wireless communication standard such as, but not limited to, 3GPP LTE, WiMAX, High Speed Packet Access (HSPA), Bluetooth, and WiFi. The mobile device can communicate using separate antennas for each wireless communication standard or shared antennas for multiple wireless communication standards. The mobile device can communicate in a wireless local area network (WLAN), a wireless personal area network (WPAN), and/or a WWAN.

[00158] The mobile device can also comprise a wireless modem. The wireless modem can comprise, for example, a wireless radio transceiver and baseband circuitry (e.g., a baseband processor). The wireless modem can, in one example, modulate signals that the mobile device transmits via the one or more antennas and demodulate signals that the mobile device receives via the one or more antennas.

[00159] The mobile device can include a storage medium. In one aspect, the storage medium can be associated with and/or communication with the application processor, the graphics processor, the display, the non-volatile memory port, and/or internal memory. In one aspect, the application processor and graphics processor are storage mediums.

[00160] FIG. 21 also provides an illustration of a microphone and one or more speakers that can be used for audio input and output from the mobile device. The display screen can be a liquid crystal display (LCD) screen, or other type of display screen such as an organic light emitting diode (OLED) display. The display screen can be configured as a touch screen. The touch screen can use capacitive, resistive, or another type of touch screen technology. An application processor and a graphics processor can be coupled to internal memory to provide processing and display capabilities. A non-volatile memory port can also be used to provide data input/output options to a user. The non-volatile memory port can also be used to expand the memory capabilities of the mobile device. A keyboard can be integrated with the mobile device or wirelessly connected to the wireless device to provide additional user input. A virtual keyboard can also be provided using the touch screen.

[00161] FIG. 22 provides an example illustration of a user equipment (UE) device 2200, such as a wireless device, a mobile station (MS), a mobile wireless device, a mobile communication device, a tablet, a handset, or other type of wireless device. The UE device 2200 can include one or more antennas configured to communicate with a node or transmission station, such as a base station (BS), an evolved Node B (eNB), a baseband unit (BBU), a remote radio head (RRH), a remote radio equipment (RRE), a relay station (RS), a radio equipment (RE), a remote radio unit (RRU), a central processing module (CPM), or other type of wireless wide area network (WWAN) access point. The UE device 2200 can be configured to communicate using at least one wireless communication standard such as, but not limited to, 3 GPP LTE, WiMAX, High Speed Packet Access (HSPA), Bluetooth, and WiFi. The UE device 2200 can communicate using separate antennas for each wireless communication standard or shared antennas for multiple wireless communication standards. The UE device 2200 can communicate in a wireless local area network (WLAN), a wireless personal area network (WPAN), and/or a WWAN.

[00162] In some embodiments, the UE device 2200 may include application circuitry 2202, baseband circuitry 2204, Radio Frequency (RF) circuitry 2206, front-end module (FEM) circuitry 2208 and one or more antennas 2210, coupled together at least as shown.

[00163] The application circuitry 2202 may include one or more application processors. For example, the application circuitry 2202 may include circuitry such as, but not limited to, one or more single-core or multi-core processors. The processor(s) may include any combination of general-purpose processors and dedicated processors (e.g., graphics processors, application processors, etc.). The processors may be coupled with and/or may include memory/storage (e.g., storage medium 2212) and may be configured to execute instructions stored in the memory /storage (e.g., storage medium 2212) to enable various applications and/or operating systems to run on the system.

[00164] The baseband circuitry 2204 may include circuitry such as, but not limited to, one or more single-core or multi-core processors. The baseband circuitry 2204 may include one or more baseband processors and/or control logic to process baseband signals received from a receive signal path of the RF circuitry 2206 and to generate baseband signals for a transmit signal path of the RF circuitry 2206. Baseband processing circuity 2204 may interface with the application circuitry 2202 for generation and processing of the baseband signals and for controlling operations of the RF circuitry 2206. For example, in some embodiments, the baseband circuitry 2204 may include a second generation (2G) baseband processor 2204a, third generation (3G) baseband processor 2204b, fourth generation (4G) baseband processor 2204c, and/or other baseband processors) 2204d for other existing generations, generations in development or to be developed in the future (e.g., fifth generation (5G), 6G, etc.). The baseband circuitry 2204 (e.g., one or more of baseband processors 2204a-d) may handle various radio control functions that enable communication with one or more radio networks via the RF circuitry 2206. The radio control functions may include, but are not limited to, signal modulation/demodulation, encoding/decoding, radio frequency shifting, etc. In some embodiments, modulation/demodulation circuitry of the baseband circuitry 2204 may include Fast-Fourier Transform (FFT), precoding, and/or constellation

mapping/demapping functionality. In some embodiments, encoding/decoding circuitry of the baseband circuitry 2204 may include convolution, tail-biting convolution, turbo, Viterbi, and/or Low Density Parity Check (LDPC) encoder/decoder functionality.

Embodiments of modulation/demodulation and encoder/decoder functionality are not limited to these examples and may include other suitable functionality in other embodiments.

[00165] In some embodiments, the baseband circuitry 2204 may include elements of a protocol stack such as, for example, elements of an evolved universal terrestrial radio access network (EUTRAN) protocol including, for example, physical (PHY), media access control (MAC), radio link control (RLC), packet data convergence protocol (PDCP), and/or radio resource control (RRC) elements. A central processing unit (CPU) 2204e of the baseband circuitry 2204 may be configured to run elements of the protocol stack for signaling of the PHY, MAC, RLC, PDCP and/or RRC layers. In some embodiments, the baseband circuitry may include one or more audio digital signal processor(s) (DSP) 2204f. The audio DSP(s) 2204f may include elements for compression/decompression and echo cancellation and may include other suitable processing elements in other embodiments. Components of the baseband circuitry may be suitably combined in a single chip, a single chipset, or disposed on a same circuit board in some embodiments. In some embodiments, some or all of the constituent components of the baseband circuitry 2204 and the application circuitry 2202 may be

implemented together such as, for example, on a system on a chip (SOC).

[00166] In some embodiments, the baseband circuitry 2204 may provide for communication compatible with one or more radio technologies. For example, in some embodiments, the baseband circuitry 2204 may support communication with an evolved universal terrestrial radio access network (EUTRAN) and/or other wireless metropolitan area networks (WMAN), a wireless local area network (WLAN), a wireless personal area network (WPAN). Embodiments in which the baseband circuitry 2204 is configured to support radio communications of more than one wireless protocol may be referred to as multi-mode baseband circuitry. [00167] The RF circuitry 2206 may enable communication with wireless networks using modulated electromagnetic radiation through a non-solid medium. In various embodiments, the RF circuitry 2206 may include switches, filters, amplifiers, etc. to facilitate the communication with the wireless network. RF circuitry 2206 may include a receive signal path which may include circuitry to down-convert RF signals received from the FEM circuitry 2208 and provide baseband signals to the baseband circuitry 2204. RF circuitry 2206 may also include a transmit signal path which may include circuitry to up-convert baseband signals provided by the baseband circuitry 2204 and provide RF output signals to the FEM circuitry 2208 for transmission.

[00168] In some embodiments, the RF circuitry 2206 may include a receive signal path and a transmit signal path. The receive signal path of the RF circuitry 2206 may include mixer circuitry 2206a, amplifier circuitry 2206b and filter circuitry 2206c. The transmit signal path of the RF circuitry 2206 may include filter circuitry 2206c and mixer circuitry 2206a. RF circuitry 2206 may also include synthesizer circuitry 2206d for synthesizing a frequency for use by the mixer circuitry 2206a of the receive signal path and the transmit signal path. In some embodiments, the mixer circuitry 2206a of the receive signal path may be configured to down-convert RF signals received from the FEM circuitry 2208 based on the synthesized frequency provided by synthesizer circuitry 2206d. The amplifier circuitry 2206b may be configured to amplify the down-converted signals and the filter circuitry 2206c may be a low-pass filter (LPF) or band-pass filter (BPF) configured to remove unwanted signals from the down-converted signals to generate output baseband signals. Output baseband signals may be provided to the baseband circuitry 2204 for further processing. In some embodiments, the output baseband signals may be zero-frequency baseband signals, although other types of baseband signals may be used. In some embodiments, mixer circuitry 2206a of the receive signal path may comprise passive mixers, although the scope of the embodiments is not limited in this respect.

[00169] In some embodiments, the mixer circuitry 2206a of the transmit signal path may be configured to up-convert input baseband signals based on the synthesized frequency provided by the synthesizer circuitry 2206d to generate RF output signals for the FEM circuitry 2208. The baseband signals may be provided by the baseband circuitry 2204 and may be filtered by filter circuitry 2206c. The filter circuitry 2206c may include a low-pass filter (LPF), although the scope of the embodiments is not limited in this respect.

[00170] In some embodiments, the mixer circuitry 2206a of the receive signal path and the mixer circuitry 2206a of the transmit signal path may include two or more mixers and may be arranged for quadrature down-conversion and/or up-conversion respectively. In some embodiments, the mixer circuitry 2206a of the receive signal path and the mixer circuitry 2206a of the transmit signal path may include two or more mixers and may be arranged for image rejection (e.g., Hartley image rejection). In some embodiments, the mixer circuitry 2206a of the receive signal path and the mixer circuitry 2206a may be arranged for direct down-conversion and/or direct up-conversion, respectively. In some embodiments, the mixer circuitry 2206a of the receive signal path and the mixer circuitry 2206a of the transmit signal path may be configured for super-heterodyne operation.

[00171] In some embodiments, the output baseband signals and the input baseband signals may be analog baseband signals, although the scope of the embodiments is not limited in this respect. In some alternate embodiments, the output baseband signals and the input baseband signals may be digital baseband signals. In these alternate

embodiments, the RF circuitry 2206 may include analog-to-digital converter (ADC) and digital-to-analog converter (DAC) circuitry and the baseband circuitry 2204 may include a digital baseband interface to communicate with the RF circuitry 2206.

[00172] In some dual-mode embodiments, a separate radio IC circuitry may be provided for processing signals for each spectrum, although the scope of the

embodiments is not limited in this respect.

[00173] In some embodiments, the synthesizer circuitry 2206d may be a fractional- N synthesizer or a fractional N/N+l synthesizer, although the scope of the embodiments is not limited in this respect as other types of frequency synthesizers may be suitable. For example, synthesizer circuitry 2206d may be a delta-sigma synthesizer, a frequency multiplier, or a synthesizer comprising a phase-locked loop with a frequency divider.

[00174] The synthesizer circuitry 2206d may be configured to synthesize an output frequency for use by the mixer circuitry 2206a of the RF circuitry 2206 based on a frequency input and a divider control input. In some embodiments, the synthesizer circuitry 2206d may be a fractional N N+l synthesizer.

[00175] In some embodiments, frequency input may be provided by a voltage controlled oscillator (VCO), although other types of devices may also provide the frequency input. Divider control input may be provided by either the baseband circuitry 2204 or the applications processor 2202 depending on the desired output frequency. In some embodiments, a divider control input (e.g., N) may be determined from a look-up table based on a channel indicated by the applications processor 2202.

[00176] Synthesizer circuitry 2206d of the RF circuitry 2206 may include a divider, a delay-locked loop (DLL), a multiplexer and a phase accumulator. In some embodiments, the divider may be a dual modulus divider (DMD) and the phase accumulator may be a digital phase accumulator (DPA). In some embodiments, the DMD may be configured to divide the input signal by either N or N+l (e.g., based on a carry out) to provide a fractional division ratio. In some example embodiments, the DLL may include a set of cascaded, tunable, delay elements, a phase detector, a charge pump and a D-type flip-flop. In these embodiments, the delay elements may be configured to break a VCO period up into Nd equal packets of phase, where Nd is the number of delay elements in the delay line. In this way, the DLL provides negative feedback to help ensure that the total delay through the delay line is one VCO cycle.

[00177] In some embodiments, synthesizer circuitry 2206d may be configured to generate a carrier frequency as the output frequency, while in other embodiments, the output frequency may be a multiple of the carrier frequency (e.g., twice the carrier frequency, four times the carrier frequency) and used in conjunction with quadrature generator and divider circuitry to generate multiple signals at the carrier frequency with multiple different phases with respect to each other. In some embodiments, the output frequency may be a LO frequency (fLO). In some embodiments, the RF circuitry 2206 may include an IQ/polar converter.

[00178] FEM circuitry 2208 may include a receive signal path which may include circuitry configured to operate on RF signals received from one or more antennas 2210, amplify the received signals and provide the amplified versions of the received signals to the RF circuitry 2206 for further processing. FEM circuitry 2208 may also include a transmit signal path which may include circuitry configured to amplify signals for transmission provided by the RF circuitry 2206 for transmission by one or more of the one or more antennas 2210.

[00179] In some embodiments, the FEM circuitry 2208 may include a TX/RX switch to switch between transmit mode and receive mode operation. The FEM circuitry may include a receive signal path and a transmit signal path. The receive signal path of the FEM circuitry may include a low-noise amplifier (LNA) to amplify received RF signals and provide the amplified received RF signals as an output (e.g., to the RF circuitry 2206). The transmit signal path of the FEM circuitry 2208 may include a power amplifier (PA) to amplify input RF signals (e.g., provided by RF circuitry 2206), and one or more filters to generate RF signals for subsequent transmission (e.g., by one or more of the one or more antennas 2210.

[00180] In some embodiments, the UE device 2200 may include additional elements such as, for example, memory/storage, display (e.g., touch screen), camera, antennas, keyboard, microphone, speakers, sensor, and/or input/output (I/O) interface.

[00181] FIG. 23 illustrates a diagram 2300 of a node 2310 (e.g., eNB and/or a Serving GPRS Support Node) and a wireless device 2320 (e.g., UE) in accordance with an example. The node can include a base station (BS), a Node B (NB), an evolved Node B (eNB), a baseband unit (BBU), a remote radio head (RRH), a remote radio equipment (RRE), a remote radio unit (RRU), or a central processing module (CPM). In one aspect, the node can be a Serving GPRS Support Node. The node 2310 can include a node device 2312. The node device 2312 or the node 2310 can be configured to communicate with the wireless device 2320. The node device 2312 can be configured to implement technologies described herein. The node device 2312 can include a processing module 2314 and a transceiver module 2316. In one aspect, the node device 2312 can include the transceiver module 2316 and the processing module 2314 forming a circuitry for the node 2310. In one aspect, the transceiver module 2316 and the processing module 2314 can form a circuitry of the node device 2312. The processing module 2314 can include one or more processors and memory. In one embodiment, the processing module 2322 can include one or more application processors. The transceiver module 2316 can include a transceiver and one or more processors and memory. In one embodiment, the transceiver module 2316 can include a baseband processor.

[00182] The wireless device 2320 can include a transceiver module 2324 and a processing module 2322. The processing module 2322 can include one or more processors and memory. In one embodiment, the processing module 2322 can include one or more application processors. The transceiver module 2324 can include a transceiver and one or more processors and memory. In one embodiment, the transceiver module 2324 can include a baseband processor. The wireless device 2320 can be configured to implement technologies described herein. The node 2310 and the wireless devices 2320 can also include one or more storage mediums, such as the transceiver module 2316, 2324 and/or the processing module 2314, 2322.

Examples

[00183] The following examples pertain to specific embodiments and point out specific features, elements, or steps that can be used or otherwise combined in achieving such embodiments.

[00184] Example 1 includes an evolved node B (eNB) comprising one or more processors and memory configured to: perform a Clear Channel Assessment (CCA); determine that an unlicensed carrier is available based on the CCA; and signal transceiver circuitry at the eNB to send, on the unlicensed carrier, a Licensed Assisted Access (LAA) burst having an LAA-burst frame structure, the LAA-burst frame structure comprising: a channel reservation signal to reserve the unlicensed carrier, a Licensed Assisted Access (LAA) preamble, and a Physical Downlink Control Channel (PDCCH) or an enhanced Physical Downlink Control Channel (ePDCCH).

[00185] Example 2 includes the eNB of example 1 , wherein the LAA preamble serves as a Request To Send (RTS) signal and the one or more processors and memory are further configured to identify a Clear To Send (CTS) signal received from a user equipment (UE).

[00186] Example 3 includes the eNB of example 1 , wherein the LAA preamble comprises a Licensed Assisted Access (LAA) burst control channel.

[00187] Example 4 includes the eNB of example 3, wherein: the LAA preamble spans a number of Orthogonal-Frequency-Division-Multiplexing (OFDM) symbols less than or equal to one; and the LAA burst control channel fully occupies the LAA preamble and spans an entire bandwidth of the unlicensed carrier.

[00188] Example 5 includes the eNB of example 3, wherein the LAA preamble further comprises a Primary Synchronization Signal (PSS).

[00189] Example 6 includes the eNB of example 5, wherein the LAA preamble further comprises a Secondary Synchronization Signal (SSS), and wherein: the PSS carries three cell identities; the SSS carries 168 cell-identity groups according to a physical-layer cell identity of a cell associated with the eNB; and root indices for three PSS sequences associated with the three cell identities are defined as M = 25, 29, and 34 as in Third Generation Partnership Project (3GPP) Long-Term Evolution (LTE) release 8.0. [00190] Example 7 includes the eNB of example 5, wherein a root index that is different from the existing PSS sequences described in 3GPP LTE Release 8.0 is used for the PSS.

[00191] Example 8 includes the eNB of example 5, wherein the LAA preamble spans a number of Orthogonal-Frequency-Division-Multiplexing (OFDM) symbols less than or equal to one.

[00192] Example 9 includes the eNB of example 8, wherein the LAA preamble spans one OFDM symbol and the one or more processors and memory are further configured to: signal the transceiver circuitry at the eNB to send the PSS using six central Physical Resource Blocks (PRBs); and rate match resource elements (REs) of the LAA preamble that are not used to send the PSS.

[00193] Example 10 includes the eNB of example 8, wherein the LAA preamble spans a fraction, less than one, of an OFDM symbol and the one or more processors and memory are further configured to: signal the transceiver circuitry at the eNB to send the PSS using more than six central Physical Resource Blocks (PRBs); and rate match resource elements (REs) of the LAA burst control channel that are not used to send the PSS.

[00194] Example 1 1 includes the eNB of example 10, wherein the one or more processors and memory are further configured to: use 30 kilohertz (kHz) subcarrier spacing in the bandwidth of the unlicensed carrier; signal the transceiver circuitry at the eNB to send the PSS using twelve central Physical Resource Blocks (PRBs); and rate match resource elements (REs) of the LAA burst control channel that are not used to send the PSS.

[00195] Example 12 includes the eNB of example 8, wherein the LAA preamble further comprises a Secondary Synchronization Signal (SSS), and wherein the one or more processors and memory are further configured to: signal the transceiver circuitry at the eNB to send the PSS using X central Physical Resource Blocks (PRBs), wherein X is a predefined value; signal the transceiver circuitry at the eNB to send the SSS using X/2 PRBs that are adjacent to a higher- frequency edge of the X PRBs used for the PSS and using X/2 PRBs that are adjacent to a lower-frequency edge of the X PRBs used for the PSS; and rate match resource elements (REs) of the LAA burst control channel that are not used to send the PSS or the SSS. [00196] Example 13 includes the eNB of example 8, wherein the LA A preamble further comprises a Secondary Synchronization Signal (SSS), and wherein the one or more processors and memory are further configured to: signal the transceiver circuitry at the eNB to send the PSS using X central Physical Resource Blocks (PRBs), wherein X is a predefined value; send the SSS using X PRBs that are adjacent to either a higher- frequency edge of the X PRBs used for the PSS or a lower-frequency edge of the X PRBs used for the PSS; and rate match resource elements (REs) of the LAA burst control channel that are not used to send the PSS or the SSS.

[00197] Example 14 includes the eNB of example 3, wherein the LAA preamble spans a number of Orthogonal-Frequency-Division-Multiplexing (OFDM) symbols greater than one and less than or equal to two.

[00198] Example 15 includes the eNB of example 14, wherein the LAA burst control channel fully occupies the LAA preamble and spans an entire bandwidth of the unlicensed carrier.

[00199] Example 16 includes the eNB of example 14, wherein the LAA preamble further comprises a Primary Synchronization Signal (PSS) and a Secondary

Synchronization Signal (SSS), and wherein the one or more processors and memory are further configured to: signal the transceiver circuitry at the eNB to send, in a first OFDM symbol of the number of OFDM symbols, the PSS using X central Physical Resource Blocks (PRBs), wherein X is a predefined value; signal the transceiver circuitry at the eNB to send, in a second OFDM symbol of the number of OFDM symbols, the SSS using the X PRBs that are used to send the PSS; and rate match resource elements (REs) of the LAA burst control channel that are not used to send the PSS or the SSS.

[00200] Example 17 includes the eNB of example 14, wherein: the LAA preamble further comprises a synchronization signal that is a Primary Synchronization Signal (PSS) or a Secondary Synchronization Signal (SSS); the one or more processors and memory are further configured to signal the transceiver circuitry at the eNB to send, in a first OFDM symbol of the number of OFDM symbols, the synchronization signal using X central Physical Resource Blocks (PRBs), wherein X is a predefined value; and the LAA burst control channel is located in a second OFDM symbol of the number of OFDM symbols and fully spans the bandwidth of the unlicensed carrier.

[00201] Example 18 includes the eNB of example 17, wherein the one or more processors are further configured to signal the transceiver circuitry at the eNB to send, in the second OFDM symbol of the number of OFDM symbols and in the X PRBs, dummy symbols or reference symbols.

[00202] Example 19 includes the eNB of example 3, wherein the one or more processors and memory are further configured to: generate a fractional OFDM symbol to be used for transmission of the LAA preamble using a subcarrier spacing greater than 15 kiloHertz (kHz); and signal the transceiver circuitry at the eNB to send the LAA preamble of the LAA burst in the fractional OFDM symbol.

[00203] Example 20 includes the eNB of example 19, wherein the subcarrier spacing is defined by the equation Af= K^■ Af, wherein Af = 15kHz, Af= the subcarrier spacing, and = 2^N, and N is an integer greater than one.

[00204] Example 21 includes the eNB of example 19, wherein the subcarrier spacing is 30kHz and the fractional OFDM symbol has a duration of approximately 33.3 microseconds (us).

[00205] Example 22 includes the eNB of example 3, wherein the one or more processors and memory are further configured to: generate a fractional OFDM symbol to be used for transmission of the LAA preamble using an interleaved Frequency Division Multiple Access (FDMA) signal structure by puncturing one or more time-domain repetition blocks; and signal the transceiver circuitry at the eNB to send the LAA preamble of the LAA burst in the fractional OFDM symbol.

[00206] Example 23 includes the eNB of example 3, wherein the one or more processors and memory are further configured to: generate a Reference Symbol (RS) for the LAA preamble; and send the RS using resources for the LAA burst control channel that are not used to send a primary synchronization signal (PSS) or a secondary synchronization signal (SSS).

[00207] Example 24 includes the eNB of example 23, wherein the one or more processors and memory are further configured to: generate the RS using a cell-specific reference signal structure defined in Third Generation Partnership Project (3GPP) Long- Term Evolution (LTE) Release 8.0; and signal the transceiver circuitry at the eNB to send the RS using one or two antenna ports (APs) of the eNB.

[00208] Example 25 includes the eNB of example 24, wherein the one or more processors and memory are further configured to: apply a cell-specific frequency shift to send the RS, wherein the cell-specific frequency shift is defined as (Nfp ¹¹ mod 6), where Nfp ^U is a physical cell identifier (PCI) of the eNB and mod is a modulus operator. [00209] Example 26 includes the eNB of example 24, wherein the one or more processors and memory are further configured to: signal the transceiver circuitry at the eNB to send the RS without applying a cell-specific frequency shift.

[00210] Example 27 includes the eNB of example 23, wherein the one or more processors and memory are further configured to: signal the transceiver circuitry at the eNB to send the RS using one, two, or four antenna ports (APs) of the eNB, wherein four RS positions corresponding to Resource Elements (REs) in a Physical Resource Block (PRB) and in an OFDM symbol are evenly spaced, wherein each antenna port sends the RS signal in exactly one of the four RS positions.

[00211] Example 28 includes the eNB of example 27, wherein the one or more processors and memory are further configured to: apply a cell-specific frequency shift to send the RS, wherein the cell-specific frequency shift is defined as (N,"¹¹ mod 3), where N,"^u is a physical cell identifier (PCI) of the eNB and mod is a modulus operator.

[00212] Example 29 includes the eNB of example 27, wherein the one or more processors and memory are further configured to: signal the transceiver circuitry at the eNB to send the RS without applying a cell-specific frequency shift.

[00213] Example 30 includes the eNB of example 27, wherein the one or more processors and memory are further configured to: generate the RS using a cell-specific reference signal sequence as defined in Third Generation Partnership Project (3GPP) Technical Specification (TS) 36.21 1 , section 6.10.1.1.

[00214] Example 31 includes the eNB of example 23, wherein the one or more processors and memory are further configured to: signal the transceiver circuitry at the eNB to send the RS using one, two, or four antenna ports (APs) of the eNB, wherein four RS positions corresponding to Resource Elements (REs) in a Physical Resource Block (PRB) and in an OFDM symbol are either evenly spaced or are central relative to the PRB, wherein each antenna port sends the RS signal in exactly two of the four RS positions; and apply an orthogonal cover code (OCC) to pairs of consecutively sent reference signals in the PRB.

[00215] Example 32 includes the eNB of example 31 , wherein the one or more processors and memory are further configured to: generate the RS using a user-equipment (UE) specific RS sequence as defined in Third Generation Partnership Project (3GPP) Technical Specification (TS) 36.21 1 , section 6.10.3.1. [00216] Example 33 includes the eNB of example 32 (or 29 or 24), wherein the one or more processors and memory are further configured to: initialize a pseudo-random sequence generator using a slot number n_s equal to zero and an OFDM symbol number 1 equal to zero; and generate the RS using the pseudo-random sequence generator.

[00217] Example 34 includes the eNB of example 32 (or 29 or 24), wherein the one or more processors and memory are further configured to: initialize a pseudo-random sequence generator using a slot number and an OFDM symbol number for transmission of the LAA preamble; and generate the RS using the pseudo-random sequence generator.

[00218] Example 35 includes the eNB of example 30, wherein the one or more processors and memory are further configured to: initialize a pseudo-random sequence generator using a value Ncp = 1 to denote a normal cyclic prefix (CP) length; and generate the RS using the pseudo-random sequence generator.

[00219] Example 36 includes the eNB of example 32, wherein the one or more processors and memory are further configured to: initialize a pseudo-random sequence generator using a value HSCID ⁼ 1 ; and generate the RS using the pseudo-random sequence generator.

[00220] Example 37 includes an evolved node B (eNB) comprising one or more processors and memory configured to: perform a Clear Channel Assessment (CCA); determine, based on the CCA, that an unlicensed carrier is available for Licensed Assisted Access (LAA); generate a channel reservation signal; and signal the transceiver circuitry at the eNB to send, in a first fractional sub-frame of a Licensed Assisted Access (LAA) burst, the channel reservation signal to reserve the unlicensed carrier.

[00221] Example 38 includes the eNB of example 37, wherein a bandwidth of the unlicensed carrier is less than or equal to 20 megahertz (MHz).

[00222] Example 39 includes the eNB of example 37, wherein a bandwidth of the unlicensed carrier is greater than 20 megahertz (MHz).

[00223] Example 40 includes the eNB of example 37, wherein the channel reservation signal comprises: a long Cyclic Prefix (CP); and an Orthogonal Frequency Division Multiplexing (OFDM) symbol that includes one or more of: a cell-specific reference symbol, a channel-state information reference symbol (CSI-RS), or a positioning reference symbol (PRS); wherein a length of the long CP is bounded by a gap between an ending time of the CCA and an OFDM symbol boundary. [00224] Example 41 includes the eNB of example 37, wherein the one or more processors are further configured to: signal the transceiver circuitry at the eNB to send the channel reservation signal using a long cyclic prefix (CP) of a first Orthogonal Frequency Division Multiplexing (OFDM) symbol of the first fractional sub-frame of the LAA burst or a first full sub-frame of the LAA burst, wherein a length of the long CP is bounded by a gap between an ending time of the CCA and an OFDM symbol boundary.

[00225] Example 42 includes the eNB of example 37, wherein: the one or more processors are further configured to signal the transceiver circuitry at the eNB to send data in N Orthogonal Frequency Division Multiplexing (OFDM) symbols of a first full sub-frame of the LAA burst; N is an integer that is predefined in a specification, configured by higher layers at the eNB, or defined as a number of available OFDM symbols in the first fractional sub-frame of the LAA burst; the channel reservation signal comprises a long Cyclic Prefix (CP) and a copy of the data sent in the N OFDM symbols of the first full sub-frame of the LAA burst; and a length of the long CP is bounded by a gap between an ending time of the CCA and an OFDM symbol boundary.

[00226] Example 43 includes the eNB of example 42, wherein the N OFDM symbols are in N first symbol OFDM positions of the first full sub-frame of the LAA burst.

[00227] Example 44 includes the eNB of example 42, wherein the N OFDM symbols are in N last OFDM symbol positions of the first full sub-frame of the LAA burst.

[00228] Example 45 includes the eNB of example 37, wherein the channel reservation signal comprises: a long Cyclic Prefix (CP); and an Orthogonal Frequency Division Multiplexing (OFDM) symbol that includes one or more of: a demodulation reference signal (DM-RS), a sounding reference signal (SRS), or a data transmission, wherein a length of the long CP is bounded by a gap between an ending time of the CCA and an OFDM symbol boundary.

[00229] Example 46 includes the eNB of example 37, wherein the one or more processors and memory are further configured to generate the channel reservation signal using one or more shortened OFDM symbols, wherein the one or more shortened OFDM symbols are based on a subcarrier spacing greater than 15 kilohertz (kHz).

[00230] Example 47 includes the eNB of example 46, wherein a format for the channel reservation signal is predefined. [00231] Example 48 includes the eNB of example 46, wherein the one or more processors and memory are further configured to generate the channel reservation signal in accordance with a physical cell identity or a virtual identity of the eNB.

[00232] Example 49 includes the eNB of example 46, wherein the one or more processors and memory are further configured to generate a reference symbol for the channel reservation signal based on an M-sequence, a Hadamard sequence, or another Constant Amplitude Zero Autocorrelation (CAZAC) sequence.

[00233] Example 50 includes the eNB of example 46, wherein the one or more processors and memory are further configured to generate a reference symbol for the channel reservation signal based on a Zadoff-Chu (ZC) sequence.

[00234] Example 51 includes the eNB of example 46, wherein a length of the ZC sequence is less than a number of subcarriers within a bandwidth of the unlicensed carrier and the one or more processors and memory are further configured to: leave unused one or more subcarriers on one or more edges of the bandwidth; and puncture a middle element of the ZC sequence for a Direct Current (DC) subcarrier.

[00235] Example 52 includes the eNB of example 46, wherein a length of the ZC sequence is less than a number of subcarriers within a bandwidth of the unlicensed carrier and the one or more processors and memory are further configured to puncture one element of the ZC sequence for a Direct Current (DC) subcarrier.

[00236] Example 53 includes the eNB of example 46, wherein a length of the ZC sequence is greater than or equal to a number of subcarriers within a bandwidth of the unlicensed carrier and the one or more processors and memory are further configured to puncture one element of the ZC sequence for a Direct Current (DC) subcarrier.

[00237] Example 54 includes the eNB of example 46, wherein the one or more processors and memory are further configured to: generate reference symbols for the channel reservation signal for a minimum supported LAA bandwidth based on the ZC sequence; signal the transceiver circuitry at the eNB to send, using one or more remaining subcarriers, one or more of: a dummy signal, a cell-specific reference symbol (CRS), a channel-state information reference symbol (CSI-RS), or a positioning reference symbol (PRS).

[00238] Example 55 includes the eNB of example 37, wherein the CCA is an extended CCA. [00239] Various techniques, or certain aspects or portions thereof, may take the form of program code (i.e., instructions) embodied in tangible media, such as floppy diskettes, compact disc-read-only memory (CD-ROMs), hard drives, non-transitory computer readable storage medium, or any other machine-readable storage medium wherein, when the program code is loaded into and executed by a machine, such as a computer, the machine becomes an apparatus for practicing the various techniques. A non-transitory computer readable storage medium can be a computer readable storage medium that does not include signal. In the case of program code execution on programmable computers, the computing device may include a processor, a storage medium readable by the processor (including volatile and non- volatile memory and/or storage elements), at least one input device, and at least one output device. The volatile and non-volatile memory and/or storage elements may be a random-access memory (RAM), erasable programmable read only memory (EPROM), flash drive, optical drive, magnetic hard drive, solid state drive, or other medium for storing electronic data. The node and wireless device may also include a transceiver module (i.e., transceiver), a counter module (i.e., counter), a processing module (i.e., processor), and/or a clock module (i.e., clock) or timer module (i.e., timer). One or more programs that may implement or utilize the various techniques described herein may use an application programming interface (API), reusable controls, and the like. Such programs may be implemented in a high level procedural or object oriented programming language to communicate with a computer system. However, the program(s) may be implemented in assembly or machine language, if desired. In any case, the language may be a compiled or interpreted language, and combined with hardware implementations.

[00240] As used herein, the term "circuitry" may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor

(shared, dedicated, or group), and/or memory (shared, dedicated, or group) that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable hardware components that provide the described functionality. In some embodiments, the circuitry may be implemented in, or functions associated with the circuitry may be implemented by, one or more software or firmware modules. In some embodiments, circuitry may include logic, at least partially operable in hardware.

[00241] While the flowcharts presented for this technology may imply a specific order of execution, the order of execution may differ from what is illustrated. For example, the order of two more blocks may be rearranged relative to the order shown. Further, two or more blocks shown in succession may be executed in parallel or with partial parallelization. In some configurations, one or more blocks shown in the flow chart may be omitted or skipped. Any number of counters, state variables, warning semaphores, or messages may be added to the logical flow for enhanced utility, accounting, performance, measurement, troubleshooting, or other purposes.

[00242] As used herein, the word "or" indicates an inclusive disjunction. For example, as used herein, the phrase "A or B" represents an inclusive disjunction of exemplary conditions A and B. Hence, "A or B" is false only if both condition A is false and condition B is false. When condition A is true and condition B is also true, "A or B" is also true. When condition A is true and condition B is false, "A or B" is true. When condition B is true and condition A is false, "A or B" is true. In other words, the term "or," as used herein, should not be construed as an exclusive disjunction. The term "xor" is used where an exclusive disjunction is intended.

[00243] As used herein, the term processor can include general-purpose processors, specialized processors such as VLSI, FPGAs, and other types of specialized processors, as well as base-band processors used in transceivers to send, receive, and process wireless communications.

[00244] It should be understood that many of the functional units described in this specification have been labeled as modules, in order to more particularly emphasize their implementation independence. For example, a module can be implemented as a hardware circuit (e.g., an application-specific integrated circuit (ASIC)) comprising custom VLSI circuits or gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components. A module can also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like.

[00245] Modules can also be implemented in software for execution by various types of processors. An identified module of executable code can, for instance, comprise one or more physical or logical blocks of computer instructions, which can, for instance, be organized as an object, procedure, or function. Nevertheless, the executables of an identified module do not have to be physically located together, but can comprise disparate instructions stored in different locations which, when joined logically together, comprise the module and achieve the stated purpose for the module. [00246] Indeed, a module of executable code can be a single instruction, or many instructions, and can even be distributed over several different code segments, among different programs, and across several memory devices. Similarly, operational data can be identified and illustrated herein within modules, and can be embodied in any suitable form and organized within any suitable type of data structure. The operational data can be collected as a single data set, or can be distributed over different locations including over different storage devices, and can exist, at least partially, merely as electronic signals on a system or network. The modules can be passive or active, including agents operable to perform desired functions.

[00247] As used herein, the term "processor" can include general purpose processors, specialized processors such as VLSI, FPGAs, and other types of specialized processors, as well as base band processors used in transceivers to send, receive, and process wireless communications.

[00248] Reference throughout this specification to "an example" means that a particular feature, structure, or characteristic described in connection with the example is included in at least one embodiment. Thus, appearances of the phrases "in an example" in various places throughout this specification are not necessarily all referring to the same embodiment.

[00249] As used herein, a plurality of items, structural elements, compositional elements, and/or materials can be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and examples can be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous.

[00250] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the foregoing description, numerous specific details are provided, such as examples of layouts, distances, network examples, etc., to provide a thorough understanding of some embodiments. One skilled in the relevant art will recognize, however, that the some embodiments can be practiced without one or more of the specific details, or with other methods, components, layouts, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of different embodiments.

[002511 While the forgoing examples are illustrative of the principles used in various embodiments in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the embodiments. Accordingly, it is not intended that the claimed matter be limited, except as by the claims set forth below.

Claims

CLAIMS What is claimed is:

1. An evolved node B (eNB) comprising one or more processors and memory configured to:

perform a Clear Channel Assessment (CCA);

determine that an unlicensed carrier is available based on the CCA; and signal transceiver circuitry at the eNB to send, on the unlicensed carrier, a Licensed Assisted Access (LAA) burst having an LAA-burst frame structure, the LAA-burst frame structure comprising:

a channel reservation signal to reserve the unlicensed carrier, a Licensed Assisted Access (LAA) preamble that includes a Licensed Assisted Access (LAA) burst control channel, and

a Physical Downlink Control Channel (PDCCH) or an enhanced Physical Downlink Control Channel (ePDCCH).

2. The eNB of claim 1 , wherein the LAA preamble serves as a Request To Send (RTS) signal and the one or more processors and memory are further configured to identify a Clear To Send (CTS) signal received from a user equipment (UE).

3. The eNB of claim 1 or 2, wherein:

the LAA preamble spans a number of Orthogonal-Frequency-Division- Multiplexing (OFDM) symbols less than or equal to one; and

the LAA burst control channel fully occupies the LAA preamble and spans an entire bandwidth of the unlicensed carrier.

4. The eNB of claim 1 or 2, wherein the LAA preamble further comprises a Primary Synchronization Signal (PSS).

5. The eNB of claim 4, wherein the LAA preamble spans one OFDM symbol and the one or more processors and memory are further configured to:

signal the transceiver circuitry at the eNB to send the PSS using six central Physical Resource Blocks (PRBs); and rate match resource elements (REs) of the LAA burst control channel that are not used to send the PSS.

6. The eNB of claim 4, wherein the one or more processors and memory are further configured to:

use 30 kilohertz (kHz) subcarrier spacing in the bandwidth of the unlicensed carrier;

signal the transceiver circuitry at the eNB to send the PSS using twelve central Physical Resource Blocks (PRBs); and

rate match resource elements (REs) of the LAA burst control channel that are not used to send the PSS.

7. The eNB of claim 4, wherein the LAA preamble further comprises a Secondary Synchronization Signal (SSS), wherein the LAA preamble spans a number of Orthogonal- Frequency-Division-Multiplexing (OFDM) symbols less than or equal to one, and wherein the one or more processors and memory are further configured to:

signal the transceiver circuitry at the eNB to send the PSS using X central Physical Resource Blocks (PRBs), wherein X is a predefined value;

signal the transceiver circuitry at the eNB to send the SSS using X/2 PRBs that are adjacent to a higher-frequency edge of the X PRBs used for the PSS and using X/2 PRBs that are adjacent to a lower-frequency edge of the X PRBs used for the PSS; and

rate match resource elements (REs) of the LAA burst control channel that are not used to send the PSS or the SSS.

8. The eNB of claim 4, wherein the LAA preamble further comprises a Secondary Synchronization Signal (SSS), wherein the LAA preamble spans a number of Orthogonal- Frequency-Division-Multiplexing (OFDM) symbols less than or equal to one, and wherein the one or more processors and memory are further configured to:

signal the transceiver circuitry at the eNB to send the PSS using X central

Physical Resource Blocks (PRBs), wherein X is a predefined value; signal the transceiver circuitry at the eNB to send the SSS using X PRBs that are adjacent to either a higher-frequency edge of the X PRBs used for the PSS or a lower-frequency edge of the X PRBs used for the PSS; and

9. The eNB of claim 1 or 2, wherein the LAA preamble spans a number of Orthogonal- Frequency-Division-Multiplexing (OFDM) symbols greater than one and less than or equal to two, and wherein the LAA burst control channel fully occupies the LAA preamble and spans an entire bandwidth of the unlicensed carrier.

10. The eNB of claim 1 or 2, wherein the LAA preamble spans a number of Orthogonal- Frequency-Division-Multiplexing (OFDM) symbols greater than one and less than or equal to two, and wherein the LAA preamble further comprises a Primary

Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS), and wherein the one or more processors and memory are further configured to:

signal the transceiver circuitry at the eNB to send, in a first OFDM symbol of the number of OFDM symbols, the PSS using X central Physical Resource Blocks (PRBs), wherein X is a predefined value;

signal the transceiver circuitry at the eNB to send, in a second OFDM symbol of the number of OFDM symbols, the SSS using the X central PRBs; and rate match resource elements (REs) of the LAA burst control channel that are not used to send the PSS or the SSS.

1 1. The eNB of claim 1 or 2, wherein:

the LAA preamble spans a number of Orthogonal-Frequency- Division-Multiplexing (OFDM) symbols greater than one and less than or equal to two;

the LAA preamble further comprises a synchronization signal that is a Primary Synchronization Signal (PSS) or a Secondary Synchronization

Signal (SSS);

the one or more processors and memory are further configured to signal the transceiver circuitry at the eNB to send, in a first OFDM symbol of the number of OFDM symbols, the synchronization signal using X central Physical Resource Blocks (PRBs), wherein X is a predefined value; the LAA burst control channel is located in a second OFDM symbol of the number of OFDM symbols and fully spans the bandwidth of the unlicensed carrier; and

the one or more processors are further configured to signal the transceiver circuitry at the eNB to send, in the second OFDM symbol of the number of OFDM symbols and in the X PRBs, dummy symbols or reference symbols.

12. The eNB of claim 1 or 2, wherein the one or more processors and memory are further configured to:

generate a fractional OFDM symbol to be used for transmission of the LAA preamble using a subcarrier spacing greater than 15 kiloHertz (kHz) wherein the subcarrier spacing is defined by the equation Af= · Af, wherein Af = 15kHz, Af = the subcarrier spacing, and K = 2^N, and N is an integer greater than one; and signal the transceiver circuitry at the eNB to send the LAA preamble of the LAA burst in the fractional OFDM symbol.

13. The eNB of claim 1 or 2, wherein the one or more processors and memory are further configured to:

generate a fractional OFDM symbol to be used for transmission of the LAA preamble using an interleaved Frequency Division Multiple Access (FDMA) signal structure by puncturing one or more time-domain repetition blocks; and signal the transceiver circuitry at the eNB to send the LAA preamble of the LAA burst in the fractional OFDM symbol.

14. The eNB of claim 1 or 2, wherein the one or more processors and memory are further configured to:

generate a Reference Symbol (RS) for the LAA preamble; and signal the transceiver circuitry at the eNB to send the RS using resources for the LAA burst control channel that are not used to send a primary synchronization signal (PSS) or a secondary synchronization signal (SSS).

15. The eNB of claim 14, wherein the one or more processors and memory are further configured to:

generate the RS using a cell-specific reference signal structure defined in Third Generation Partnership Project (3GPP) Long-Term Evolution (LTE)

Release 8.0; and

signal the transceiver circuitry at the eNB to send the RS using one or two antenna ports (APs) of the eNB either without applying a cell-specific frequency shift or applying a cell-specific frequency shift defined as (Nf ^u mod 6), where Nfg¹¹ is a physical cell identifier (PCI) of the eNB and mod is a modulus operator.

16. The eNB of claim 14, wherein the one or more processors and memory are further configured to:

signal the transceiver circuitry at the eNB to send the RS using one, two, or four antenna ports (APs) of the eNB and either without applying a cell-specific frequency shift or applying a cell-specific frequency shift defined as

/o" mod 3), where Ν?β¹¹ is a physical cell identifier (PCI) of the eNB and mod is a modulus operator, wherein four RS positions corresponding to Resource Elements (REs) in a Physical Resource Block (PRB) and in an OFDM symbol are evenly spaced, wherein each antenna port sends the RS signal in exactly one of the four RS positions.

17. The eNB of claim 14, wherein the one or more processors and memory are further configured to:

signal the transceiver circuitry at the eNB to send the RS using one, two, or four antenna ports (APs) of the eNB, wherein four RS positions corresponding to Resource Elements (REs) in a Physical Resource Block (PRB) and in an OFDM symbol are either evenly spaced or are central relative to the PRB, wherein each antenna port sends the RS signal in exactly two of the four RS positions; and apply an orthogonal cover code (OCC) to pairs of consecutively sent reference signals in the PRB.

18. An evolved node B (eNB) comprising one or more processors and memory configured to:

perform a Clear Channel Assessment (CCA);

determine, based on the CCA, that an unlicensed carrier is available for Licensed Assisted Access (LAA);

generate a channel reservation signal; and

signal the transceiver circuitry at the eNB to send, in a first fractional sub- frame of a Licensed Assisted Access (LAA) burst, the channel reservation signal to reserve the unlicensed carrier.

19. The eNB of claim 18, wherein the channel reservation signal comprises:

a long Cyclic Prefix (CP); and

an Orthogonal Frequency Division Multiplexing (OFDM) symbol that includes one or more of:

a cell-specific reference symbol;

a channel-state information reference symbol (CSI-RS);

a positioning reference symbol (PRS);

a demodulation reference signal (DM-RS);

a sounding reference signal (SRS); or

a data transmission,

wherein a length of the long CP is bounded by a gap between an ending time of the CCA and an OFDM symbol boundary.

20. The eNB of claim 18 or 19, wherein the one or more processors are further configured to:

signal the transceiver circuitry at the eNB to send the channel reservation signal using a long cyclic prefix (CP) of a first Orthogonal Frequency Division

Multiplexing (OFDM) symbol of the first fractional sub-frame of the LAA burst or a first full sub-frame of the LAA burst, wherein a length of the long CP is bounded by a gap between an ending time of the CCA and an OFDM symbol boundary.

21. The eNB of claim 18 or 19, wherein: the one or more processors are further configured to signal the transceiver circuitry at the eNB to send data in N Orthogonal Frequency Division

Multiplexing (OFDM) symbols of a first full sub-frame of the LAA burst;

N is an integer that is predefined in a specification, configured by higher layers at the eNB, or defined as a number of available OFDM symbols in the first fractional sub-frame of the LAA burst;

the channel reservation signal comprises a long Cyclic Prefix (CP) and a copy of the data sent in the N OFDM symbols of the first full sub-frame of the LAA burst; and

a length of the long CP is bounded by a gap between an ending time of the

CCA and an OFDM symbol boundary.

22. The eNB of claim 21, wherein the N OFDM symbols are in N first symbol OFDM positions of the first full sub-frame of the LAA burst or the N OFDM symbols are in N last OFDM symbol positions of the first full sub-frame of the LAA burst.

23. The eNB of claim 18 or 19, wherein the one or more processors and memory are further configured to generate the channel reservation signal using one or more shortened OFDM symbols, wherein the one or more shortened OFDM symbols are based on a subcarrier spacing greater than 15 kilohertz (kHz).

24. The eNB of claim 23, wherein the one or more processors and memory are further configured to generate the channel reservation signal in accordance with a physical cell identity or a virtual identity of the eNB.

25. A cellular base station comprising one or more processors and memory configured to:

perform a Clear Channel Assessment (CCA);

generate a channel reservation signal using one or more shortened OFDM symbols, wherein the one or more shortened OFDM symbols are based on a subcarrier spacing greater than 15 kilohertz (kHz); generate a reference symbol for the channel reservation signal based on a Zadoff-Chu (ZC) sequence; and

signal transceiver circuitry at the cellular base station to send, in a first fractional sub-frame of a Licensed Assisted Access (LAA) burst, the channel reservation signal to reserve the unlicensed carrier.

26. The cellular base station of claim 25, wherein a length of the ZC sequence is less than a number of subcarriers within a bandwidth of the unlicensed carrier and the one or more processors and memory are further configured to:

leave unused one or more subcarriers on one or more edges of the bandwidth; and

puncture a middle element of the ZC sequence for a Direct Current (DC) subcarrier.

27. The cellular base station of claim 25, wherein a length of the ZC sequence is less than a number of subcarriers within a bandwidth of the unlicensed carrier and the one or more processors and memory are further configured to perform cyclic extension of the ZC sequence to fill in the number of subcarriers and puncture one element of the ZC sequence for a Direct Current (DC) subcarrier.

28. The cellular base station of claim 25, wherein a length of the ZC sequence is greater than or equal to a number of subcarriers within a bandwidth of the unlicensed carrier and the one or more processors and memory are further configured to puncture certain elements of ZC sequences to match with the number of subcarriers and one element of the ZC sequence for a Direct Current (DC) subcarrier.

29. The cellular base station of claim 25, wherein the one or more processors and memory are further configured to:

generate reference symbols for the channel reservation signal for a minimum supported LAA bandwidth based on a ZC sequence;

signal the transceiver circuitry at the cellular base station to send, using one or more remaining subcarriers, one or more of: a dummy signal, a cell- specific reference symbol (CRS), a channel-state information reference symbol (CSI-RS), or a positioning reference symbol (PRS).