Patent Description:
Mobile communication systems were developed to provide subscribers with voice communication services on the move. Recently, mobile communication systems have evolved to the level of supporting high speed data communication services beyond the early voice-oriented services. However, the resource shortage and user requirements for higher speed services are spurring evolution towards increasingly more advanced mobile communication systems.

Meanwhile, unlike voice services, data services are provided using the resources determined based on transmit data amount and channel condition. Accordingly, a wireless communication system, particularly a cellular communication system, is provided with a scheduler, which takes charge of resource allocation in consideration of the required resource amount, channel condition, data amount, etc. Typically, in most cellular communication systems, the scheduler is located in base stations for radio resource management, and this is the case even in the Long-Term Evolution (LTE) system as one of the next generation mobile communication systems.

In an LTE system operating on a licensed band frequency, the frequency owner may use the frequency resources exclusively in the way as intended. In the case of the communication devices operating in an unlicensed band, however, they have to operate on a frequency channel; thus, there is a need of a method for sharing the channel without collision. Listen Before Talk (LBT) is a technique for sensing a radio channel and, if the channel is not in use, starting transmission.

An LBT scheme may be performed in such a way of performing clear channel assessment (CCA) on a channel to determine whether the channel is occupied by another communication technology device and, if the channel is sensed idle, allowing transmission of signals. A CCA period may be set to <NUM> or more, <NUM>, or <NUM> depending on the type of LBT and radio communication technology and, in the case of using extended CCA (eCCA), the corresponding observation time is repeated N times (random factor). Typically, the channel occupancy is limited to a maximum channel occupancy time, even when the channel is sensed idle through CCA, because one device is not permitted to occupy the channel too much.

<CIT> discloses methods in which an unlicensed spectrum is used for LTE communications, wherein a first method includes comparing past transmission activity on an unlicensed spectrum to an activity threshold, transmitting a first subframe type in the unlicensed spectrum during a next active transmission when the past transmission activity is greater than the activity threshold, and transmitting a second subframe type in the unlicensed spectrum during a next active transmission when the past transmission activity is lesser than the activity threshold, the second subframe type comprising a more robust subframe type than the first subframe type.

The publication "<NPL> discusses different downlink/uplink solutions of Licensed Assisted Access with Listen-Before-Talk.

<FIG> is a diagram for explaining a problem that occurs when communicating data in an LTE communication system that uses an unlicensed band frequency channel.

In detail, <FIG> depicts an exemplary problem occurring at an evolved Node B (eNB) when the LTE communication system adopts the aforementioned LBT scheme for use of an unlicensed frequency.

In the case of using an LBT scheme in an LTE communication system, even when the channel is sensed as idle through CCA <NUM> of about <NUM>, the eNB has to wait until the next resource allocation period arrives because the resource allocation of the eNB is performed on a per subframe basis. In this case, while the eNB is waiting for the next subframe, another communication technology device, e.g., a wireless-fidelity (Wi-Fi) device <NUM>, may perform CCA <NUM> of about <NUM> and preoccupy the corresponding channel. That is, the LTE communication system with a resource allocation period longer than that of other communication systems has a relatively low channel occupancy rate on an unlicensed frequency, resulting in user service quality degradation.

The present invention has been conceived to solve the above problem and aims to provide a method for increasing channel occupancy rate of an eNB on an unlicensed frequency channel by transmitting a channel reservation signal at an interval shorter than the resource allocation period after sensing that the channel is idle through channel assessment for sharing the channel with other communication technology devices.

The data transmission method and apparatus of the present invention is advantageous in terms of improving system throughput on an unlicensed frequency while sharing the unlicensed frequency with different communication technology devices in such a way of transmitting, at an eNB, a channel reservation signal at an interval shorter than a predetermined resource allocation period upon sensing the idleness of the unlicensed frequency.

Exemplary embodiments of the present invention are described in detail with reference to the accompanying drawings.

Detailed descriptions of well-known functions and structures incorporated herein may be omitted to avoid obscuring the subject matter of the present invention. This aims to omit unnecessary description so as to make the subject matter of the present invention clear.

For the same reason, some elements are exaggerated, omitted, or simplified in the drawings and, in practice, the elements may have sizes and/or shapes different from those shown in the drawings. The same reference numbers are used throughout the drawings to refer to the same or like parts.

Advantages and features of the present invention and methods of accomplishing the same may be understood more readily by reference to the following detailed description of exemplary embodiments and the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this invention will be thorough and complete and will fully convey the concept of the invention to those skilled in the art, and the present invention will only be defined by the appended claims. Like reference numerals refer to like elements throughout the specification.

It will be understood that each block of the flowcharts and/or block diagrams, and combinations of blocks in the flowcharts and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general-purpose computer, special purpose computer, or other programmable data processing apparatus, such that the instructions which are executed via the processor of the computer or other programmable data processing apparatus create means for implementing the functions/acts specified in the flowcharts and/or block diagrams. These computer program instructions may also be stored in a non-transitory computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the non-transitory computer-readable memory produce articles of manufacture embedding instruction means that implement the function/act specified in the flowcharts and/or block diagrams. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions that are executed on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowcharts and/or block diagrams.

Furthermore, the respective block diagrams may illustrate parts of modules, segments, or codes including at least one or more executable instructions for performing specific logic function(s). Moreover, it should be noted that the functions of the blocks may be performed in a different order in several modifications. For example, two successive blocks may be performed substantially at the same time, or they may be performed in reverse order according to their functions.

According to various embodiments of the present disclosure, the term "module", means, but is not limited to, a software or hardware component, such as a Field Programmable Gate Array (FPGA) or Application Specific Integrated Circuit (ASIC), which performs certain tasks. A module may advantageously be configured to reside on the addressable storage medium and configured to be executed on one or more processors. Thus, a module may include, by way of example, components, such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. The functionality provided for in the components and modules may be combined into fewer components and modules or further separated into additional components and modules. In addition, the components and modules may be implemented such that they execute one or more CPUs in a device or a secure multimedia card.

<FIG> is a flowchart illustrating a channel reservation signal transmission operation of a base station for data transmission on an unlicensed frequency channel according to an embodiment of the present invention.

In detail, <FIG> is a diagram for explaining operations between a data unit (DU) <NUM> and a radio frequency (RF) module <NUM> in the base station. The base station may be equivalent to an eNB of an LTE system and a NodeB of a wideband code division multiple access (WCDMA) system. Although the description is made with particular reference to the LTE eNB for convenience of explanation, the terms "base station" and "eNB" may be used interchangeably hereinafter.

The DU <NUM> is a digital signal processing unit of the eNB that is responsible for encoding and decoding digital signals. The DU <NUM> may encode a signal to be transmitted to the UE and send the encoded signal to a radio unit (RU). The RU, as a radio signal processing unit of the eNB, includes a converter for converting the digital signal received from the DU <NUM> to an RF signal of a frequency band and sending the RF signal to an antenna and an RF amplifier for amplifying the RF signal.

In the case that the base station is an eNB of an LTE communication system, the RU of the eNB may transmit the RF signal to the UE based on a resource allocation period, i.e., scheduling period. The RU transmits the RF signal to the UE at an interval of <NUM> because the resource allocation unit of the LTE communication system is a subframe (<NUM>). Accordingly, in order to transmit a channel reservation signal at an interval shorter than one subframe, it is necessary for the eNB to have an RF module <NUM> for a different communication technology. The RF module <NUM> may transmit a signal at an interval shorter than the resource allocation period of the LTE communication system, e.g., Wi-Fi beacon frame.

The DU <NUM> may determine at step S220 whether a channel reservation is necessary. That is, the DU <NUM> may determine presence/absence of data to transmit to the corresponding terminal to determine whether the channel reservation is necessary. If there is no data to transmit and thus no channel reservation is necessary, the DU <NUM> may repeat the determination operation at a predetermined interval.

If the DU <NUM> detects the presence of data to transmit and the necessity of channel reservation, it may send a channel reservation request to the RF module <NUM> at step S230. The RF module <NUM> may perform channel sensing through CCA on the unlicensed frequency channel at step S240. Next, the RF module <NUM> may determine at step S245 whether the channel is idle. That is, the RF module <NUM> may determine whether the unlicensed frequency channel for use in transmitting the data is occupied by another communication technology device. If it is determined that the channel is idle, the RF module <NUM> may transmit a channel reservation signal at step S250. Examples of the channel reservation signal may be the aforementioned Wi-Fi beacon frame. The channel reservation signal may be transmitted periodically in order for other communication devices to sense that the channel is busy during their CCA and thus to not preoccupy the channel.

After transmitting the channel reservation signal, the RF module <NUM> may send a reservation success signal to the DU <NUM> at step S260. If the reservation success signal is received, the DU <NUM> may transmit downlink data to the terminal in the next resource allocation period at step S270. That is, the RU may transmit the downlink data to the terminal at the start time of the next subframe or symbol. Although not shown in the drawing, if the resource allocation is performed in unit of a symbol, the DU <NUM> may transmit the downlink data to the terminal at the next symbol. After transmitting the reservation success signal, the RF module <NUM> may stop transmitting the channel reservation signal in the next resource allocation period at step S280. That is, the DU <NUM> may stop transmitting the channel reservation signal at the start time of the next subframe as the next resource allocation period.

<FIG> is a diagram illustrating a channel reservation signal transmission method of an eNB for data transmission on an unlicensed frequency channel according to an embodiment of the present invention.

In detail, in the case where the eNB <NUM> shares the unlicensed frequency channel with a Wi-Fi access point (AP) <NUM> as another communication technology device, if the eNB <NUM> senses the idleness of the channel through CCA <NUM>, it transmits a channel reservation signal periodically as denoted by reference number <NUM> before arrival of the next subframe or symbol for data transmission as denoted by reference number <NUM>.

If the eNB <NUM> detects the necessity of data transmission on the unlicensed frequency channel, it performs channel sensing through CCA to determine whether a corresponding channel is idle. The CCA period <NUM> may be set to <NUM> or more, <NUM>, or <NUM> depending on the type of LBT and radio communication technology. If it is determined as the CCA result that the channel is idle, the eNB <NUM> may transmit the channel reservation signal periodically until the next subframe or symbol for transmitting data arrives as denoted by reference number <NUM>. If the channel reservation signal is a Wi-Fi signal, the eNB <NUM> may transmit the channel reservation signal on the unlicensed frequency channel at an interval of <NUM> by means of the RF module as denoted by reference number <NUM> because the Wi-Fi data symbol is <NUM>. Afterward, if the next subframe or symbol arrives, the eNB <NUM> may transmit data on the unlicensed frequency channel by means of the RU as denoted by reference number <NUM>.

If the Wi-Fi AP <NUM> performs CCA as denoted by reference number <NUM> while the eNB <NUM> is transmitting the channel reservation signal, the Wi-Fi AP <NUM> may detect the channel reservation signal and determine that the channel is preoccupied by another device. In this case, the Wi-Fi AP <NUM> transmits no data and waits as denoted by reference number <NUM>. That is, the eNB <NUM> may prevent the Wi-Fi AP <NUM> from occupying the unlicensed frequency channel before the time point when it can start data transmission by transmitting the channel reservation signal periodically before the arrival of the next subframe or symbol for transmitting data after CCA <NUM>.

<FIG> depict the methods for determining CCA, channel reservation signal transmission, and data transmission periods that are described with reference to <FIG> according to embodiments of the present invention. For convenience of explanation, CCA period is referred to as CCA check time, the sum of the channel reservation signal transmission time and data transmission time is referred to as channel occupancy time, and the period between the data transmission end time point and the signal transmission resuming time point is referred to as minimum idle time.

<FIG> is a diagram illustrating a channel reservation signal transmission method of an eNB for data transmission on an unlicensed frequency channel according to another embodiment of the present invention.

A description is made of the operation of an eNB with the CCA check time, channel occupancy time, and minimum idle time in compliance with the following conditions.

After the ending of the channel occupancy time <NUM> of a Wi-Fi AP <NUM> as another communication technology device sharing an unlicensed frequency channel, an RF module <NUM> of an eNB <NUM> may perform CCA for channel sensing as denoted by reference number <NUM>. In this case, the RF module <NUM> may perform CCA over <NUM> in compliance with the above condition. If the channel is assessed as idle (e.g., if the channel is not occupied by the Wi-Fi AP <NUM>), the RF module <NUM> may transmit a channel reservation signal during a predetermined period as denoted by reference number <NUM>, and then an RU <NUM> may transmit data to the terminal as denoted by reference number <NUM>.

The RF module <NUM> of the eNB <NUM> may transmit the channel reservation signal in a period as denoted by reference number <NUM> before arrival of the next resource allocation period (e.g., subframe) after the end of the CCA <NUM>. If it is assumed that the resource allocation period is a symbol, it may be possible to determine the data transmission time in consideration of the length of a symbol <NUM> and <NUM>. In order to fulfil the condition of the channel occupancy time, the eNB <NUM> may determine the data transmission time <NUM> based on the channel reservation signal transmission time <NUM>. That is, the eNB <NUM> may determine the data transmission time <NUM> by subtracting the channel reservation signal transmission time <NUM> from the channel occupancy time.

After transmitting data on the unlicensed frequency channel during the data transmission time <NUM>, the RU <NUM> of the eNB <NUM> may stay in the minimum idle time as long as <NUM>% of the channel occupancy time, and then the RF module <NUM> performs CCA as denoted by reference number <NUM> and transmits the channel reservation signal as denoted by reference number <NUM>.

Similar to the embodiment of <FIG>, a description is made of the operation of an eNB with the CCA (eCCA) check time and channel occupancy time in compliance with the following conditions.

In this embodiment, CCA is performed N timesusing extended CCA check. The number of CCA times N may be set to a value in the range between <NUM> and q, and q is determined, by an eNB manufacturer, in the range of <NUM> to <NUM>.

After the ending of the channel occupancy time <NUM> of an Wi-Fi AP <NUM> as another communication technology device sharing the unlicensed frequency channel, an RF module <NUM> of the eNB <NUM> may perform CCA <NUM> for channel sensing. In this case, the RF module <NUM> may perform CCA N times over <NUM> in compliance with the above condition. If the channel is assessed as idle (e.g., if the channel is not occupied by the Wi-Fi AP <NUM>), the RF module <NUM> may transmit a channel reservation signal <NUM> during a predetermined period.

The RF module <NUM> of the eNB <NUM> may transmit the channel reservation signal <NUM> before the arrival of the next resource allocation period (e.g., subframe) after the end of the CCA <NUM>. If it is assumed that the resource allocation period is a symbol, it may be possible to determine the data transmission time in consideration of the length of a symbol <NUM> and <NUM>. In order to fulfil the condition of the channel occupancy time, the eNB <NUM> may determine transmission time of the data <NUM> based on transmission time of the channel reservation signal <NUM>. That is, the eNB <NUM> may determine transmission time of the data <NUM> by subtracting transmission time of the channel reservation signal <NUM> from the determined channel occupancy time. Afterward, if the next subframe or symbol as the next resource allocation period arrives, an RU <NUM> may transmit data <NUM>.

Similar to the embodiment of <FIG>, a description is made of the operation of an eNB with the CCA (ECCA) check time, and channel occupancy time in compliance with the following conditions.

In this embodiment, ECCA is performed N times using extended CCA check. That is, an RF module <NUM> of the eNB <NUM> may observe to determine whether the unlicensed frequency channel is occupied by another communication technology device. Multiple ECCAs may have an observation period corresponding to multiple observation slots and may be referred to as ECCA(Exteneded CCA) check. Among the observation slots, a slot not in use by another communication technology device may be referred to as an unoccupied idle slot, and a slot in use by another communication technology device may be referred to as a busy slot. The number of ECCAs N may be set to a value in the range between <NUM> and q, and q is determined among <NUM> (initial value), <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> in an ascending order whenever the eNB performs ECCA.

After the ending of the channel occupancy time <NUM> of the Wi-Fi AP <NUM> as another communication technology device sharing the unlicensed frequency channel, an RF module <NUM> of the eNB <NUM> may perform CCA <NUM> for channel sensing. In this case, the RF module <NUM> may perform CCA <NUM> N times over <NUM> or ECCA <NUM> of <NUM> N times in compliance with the above condition. If the channel is assessed as idle (e.g., if the channel is not occupied by the Wi-Fi AP <NUM>), the RF module <NUM> may transmit a channel reservation signal <NUM> during a predetermined period. The RF module <NUM> of the eNB <NUM> may transmit the channel reservation signal <NUM> before the arrival of the next resource allocation period (e.g., subframe) after the end of the CCA <NUM>. If it is assumed that the resource allocation period is a symbol, it may be possible to determine the data transmission time in consideration of the length of a symbol <NUM> and <NUM>. In order to fulfil the condition of the channel occupancy time, the eNB <NUM> may determine transmission time of the data <NUM> based on transmission time of the channel reservation signal <NUM>. That is, the eNB <NUM> may determine transmission time of the data <NUM> by subtracting transmission time of the channel reservation signal <NUM> from the determined channel occupancy time. Afterward, if the next subframe or symbol as the next resource allocation period arrives, an RU <NUM> may transmit data <NUM> during the allocated transmission time.

<FIG> is a diagram illustrating a data transmission method of an eNB using a channel reservation signal of a neighboring eNB according to an embodiment of the present invention.

In detail, <FIG> depicts a data transmission method characterized in that, if an LTE eNB transmits a channel reservation signal and succeeds in channel reservation, a neighboring LTE eNB may perform data transmission simultaneously along with the LTE eNB during the data transmission time arriving after transmitting the channel reservation signal.

The description is made under the assumption of multiple eNBs <NUM> and <NUM> and other communication technology devices, e.g., Wi-Fi APs <NUM> and <NUM>. If the LTE eNB #<NUM><NUM> performs CCA <NUM> and senses idleness of an unlicensed frequency channel, it may transmit a channel reservation signal <NUM> before arrival of the next resource allocation period. In this situation, if the Wi-Fi AP <NUM> performs CCA <NUM> while the LTE eNB #<NUM><NUM> is transmitting the channel reservation signal <NUM> periodically, it may sense the busyness of the channel and transmit no data.

Afterward, the LTE eNB #<NUM> may determine, as denoted by reference number <NUM>, whether the channel is reserved by the LTE eNB #<NUM><NUM>. In this case, the LTE eNB #<NUM><NUM> may detect the channel reservation signal by means of its RF module and check the channel reservation signal for the identifier of the LTE eNB #<NUM><NUM> to identify the LTE eNB #<NUM><NUM> that transmits the channel reservation signal. The identifier of the LTE eNB #<NUM><NUM> may include a basic service set identifier (BSSID) or a service set identifier (SSID). If the LTE eNB #<NUM><NUM> identifies that the LTE eNB #<NUM><NUM> and the LTE eNB #<NUM> belong to the same operator based on the identifier of the LTE eNB #<NUM><NUM>, it may start transmitting data at the time point when the next resource allocation period of the LTE eNB #<NUM><NUM> arrives as denoted by reference number <NUM> without transmitting its own channel reservation signal.

It may also be possible for the two eNBs <NUM> and <NUM> to exchange messages to share the information on the channel reservation of the LTE eNB #<NUM><NUM> and, in this case, the two eNBs <NUM> and <NUM> may start transmitting data simultaneously at the time point of arrival of the next resource allocation period of the LTE eNB #<NUM> as denoted by reference number <NUM>. The message exchanged between two eNBs <NUM> and <NUM> may be an X2 interface message.

In this case, however, the LTE eNB #<NUM><NUM> may perform CCA <NUM> additionally before the arrival of the next resource period to sense neighboring other communication technology devices that are not sensed by the LTE eNB #<NUM>. In this case, the Wi-Fi AP #<NUM><NUM> may perform CCA <NUM> and sense the busyness of the channel during the data transmission of the LTE eNB #<NUM><NUM> as denoted by reference number <NUM> and thus it may not transmit data.

Since the LTE communication system adopts an inter-eNB interference cancellation technology that makes it possible for UEs to receive the data transmitted by the two eNBs simultaneously without interference, the data transmission method of the present invention is advantageous in terms of improving unlicensed frequency channel utilization efficiency even between LTE eNBs.

<FIG> is a diagram illustrating a channel reservation signal transmission method of an eNB for uplink signal transmission according to an embodiment of the present invention.

The above descriptions are directed to the channel reservation signal transmission methods for downlink data transmission from the eNB(s) to the UE(s). <FIG> depicts a channel reservation signal transmission method of the eNB for facilitating uplink transmission of a UE.

The eNB <NUM> may perform CCA <NUM> on an unlicensed frequency channel and, if the channel is sensed idle, transmit a channel reservation signal <NUM> periodically until the next resource allocation period arrives. Afterward, the eNB <NUM> transmits data <NUM> to the UE <NUM> and then the channel reservation signal <NUM> for occupying the unlicensed frequency channel for uplink transmission of the UE <NUM>. While the eNB <NUM> is transmitting the channel reservation signal <NUM> for uplink transmission periodically, a Wi-Fi AP <NUM> as another communication technology device may perform CCA <NUM> and sense the busyness of the channel and thus it may not transmit data.

The UE <NUM> may transmit data <NUM> to the eNB <NUM> at an uplink transmission timing as scheduled by the eNB <NUM>.

In this way, it may be possible to solve the problem caused by unlicensed frequency channel occupancy failure after the receipt of downlink data from the eNB, i.e., failure of transmission of a control signal such as acknowledgement (ACK) signal corresponding to the data received from the eNB.

<FIG> is a diagram illustrating a channel reservation signal transmission method of an eNB for facilitating uplink signal transmission according to another embodiment of the present invention.

This embodiment is identical with that of <FIG> in that the eNB transmits a channel reservation signal for uplink transmission of a UE as described with reference to <FIG> with the exception that the UE performs CCA before transmitting uplink signals at a timing as scheduled by the eNB to further sense whether another communication technology device has preoccupied the unlicensed frequency channel.

Afterward, the UE <NUM> may transmit data <NUM> to the eNB <NUM> at an uplink transmission timing as scheduled by the eNB <NUM>. However, the UE <NUM> may perform CCA <NUM> before the uplink transmission timing scheduled by the eNB <NUM> to determine whether the unlicensed frequency channel is occupied by another communication technology device. This is because the unlicensed frequency channel may be preoccupied by another communication technology device that is located around the UE <NUM> but is not detected by the eNB <NUM>.

In this way, it may be possible to for the UE solve the problem caused by unlicensed frequency channel occupancy failure after the receipt of downlink data from the eNB, i.e., failure of transmission of a control signal such as acknowledgement (ACK) signal corresponding to the data received from the eNB.

<FIG> is a block diagram illustrating a configuration of a base station according to an embodiment of the present invention.

In reference to <FIG>, the base station includes a first transceiver <NUM>, a second transceiver <NUM>, and a controller <NUM>.

The base station may transmit and receive signals by means of the first and second transceivers <NUM> and <NUM>. The first transceiver <NUM> may include a first Radio Unit(RU) for transmitting a signal in an LTE communication system, and the second transceiver <NUM> may include an RF module for transmitting a signal in a non-LTE communication system, e.g., radio communication system operating on an unlicensed frequency such as a Wi-Fi system. The base station is included in the LTE communication system, the first transceiver <NUM> may transmit a signal in unit of transmission time interval (TTI) as a scheduling (i.e., resource allocation period), i.e., subframe. The second transceiver <NUM> may transmit the signal at a transmission interval of the non-LTE communication system. If the second transceiver <NUM> includes an RF module for transmitting Wi-Fi signals, it may transmit the signal at the interval of <NUM>. Although the description is directed to the case where the first and second transceivers <NUM> and <NUM> transmit signals at respective intervals, it may also be possible to use a signal transceiver that is capable of transmitting signals at two different intervals.

Since the base station configured as above is capable of transmitting a signal on an unlicensed frequency channel at an interval different from the resource allocation period for data transmission on a licensed frequency channel, it may be possible for the base station to sense the idleness of the unlicensed frequency channel and transmit a signal on the unlicensed frequency channel before arrival of data transmission timing on the unlicensed frequency channel to prevent another communication technology device from preoccupying the unlicensed frequency channel.

The controller <NUM> may control the operations of the base station according to an embodiment of the present invention.

The controller <NUM> may determine whether a frequency channel is idle and, if so, transmit a first signal on the frequency channel before arrival of a data transmission timing and, upon arrival of the data transmission timing, transmit first data to the terminal. The first signal is transmitted periodically before the arrival of the data transmission timing. The arrival of the data transmission timing is a start of a resource allocation period arriving after sensing the idleness of the channel.

The first signal is transmitted before arrival of the data transmission timing at an interval shorter than the resource allocation period. The controller <NUM> may control to transmit a second signal before a data transmission timing of the terminal and to receive second data transmitted by the terminal at the data transmission timing of the terminal.

The controller <NUM> may detect a third signal transmitted by a neighboring base station on the frequency channel; check information of the neighboring base station; and transmit, when a data transmission timing arrives after detecting the third signal, third data to the terminal.

The controller <NUM> may control to determine whether the frequency channel is occupied by another device before arrival of the data transmission timing and, if the frequency channel is not occupied by another device, transmit the third data. The information of the neighboring base station may be of an identifier of the neighboring base station included in the first signal or information included in a message being exchanged between the base stations. The identifier of the neighboring base station may be a BSSID or SSID, and the message exchanged between the base stations may be an X2 interface message.

The controller <NUM> may control to sense the first signal transmitted by the neighboring base station on the frequency channel; check the information on the neighboring base station; and transmit, when the data transmission timing arrives after sensing the first signal, data to the terminal. The arrival of the data transmission timing is a start of a resource allocation period arriving after sensing the idleness of the channel. The first signal transmission interval may be shorter than the resource allocation period.

Claim 1:
A data transmission method in a wireless communication system, the method comprising:
performing (<NUM>), by a first base station (<NUM>), a channel sensing, to identify whether a channel in an unlicensed frequency band is idle;
transmitting (<NUM>), by the first base station (<NUM>), in a symbol where the channel sensing has completed, based on the channel being idle in the unlicensed frequency band, a first reservation signal for reserving the unlicensed frequency band for transmitting data before arrival of a next symbol for a first data transmission, the first reservation signal is transmitted via a first communication technology; and
transmitting (<NUM>), by the first base station (<NUM>), the first data to a terminal in the unlicensed frequency band during the next symbol and after transmitting the first reservation signal, the first data is transmitted via a second communication technology different from the first communication technology,
wherein, based on the transmission of the first reservation signal being identified by a second base station (<NUM>) using at least one of a basic service set identifier, BSSID, a service set identifier, SSID, or an X2 interface message, included in the first reservation signal, second data is transmitted to a second terminal, by the second base station (<NUM>), in the next symbol arriving after the symbol transmitting the first reservation signal without transmitting an own channel reservation signal for the second base station (<NUM>).