WO2016048081A1

WO2016048081A1 - Wireless channel access method and device

Info

Publication number: WO2016048081A1
Application number: PCT/KR2015/010155
Authority: WO
Inventors: 차재선; 김은경; 박재준; 백승권; 송평중; 윤찬호; 장성철
Original assignee: 한국전자통신연구원
Priority date: 2014-09-26
Filing date: 2015-09-25
Publication date: 2016-03-31

Abstract

Provided are a base station and a channel access method for accessing a channel for an unlicensed band through the steps of: sensing a channel, at least once, relative to a channel of an unlicensed band in a channel sensing section of a frame; and broadcasting a reservation signal for a channel if the channel is empty.

Description

Wireless channel access method and device

The present invention relates to a method and apparatus for accessing a wireless channel in an unlicensed band.

Since the advent of 4G mobile communication, the wireless traffic serviced through the mobile communication system has been increasing every year, and mobile communication providers have been researching to increase the capacity of the mobile communication system. The easiest way to increase the capacity of a mobile communication system is to secure many frequencies necessary for data transmission and to transmit a lot of data at the same time. However, the frequency used in the mobile communication system is a licensed band frequency that can be used exclusively, and there is a problem in that the frequency can not be used as much as desired because the available frequency band is limited and the fee for use is also high. As a solution to this problem, the 3rd generation partnership project (3GPP) is studying how to provide mobile communication services through unlicensed band frequencies that are available at low or no cost.

Unlicensed band frequency is a frequency band that can be used by anyone who meets the regulatory requirements defined in a specific frequency band or region, and is currently used in systems such as wireless fidelity (WiFi) or Bluetooth (Bluetooth). Say frequency. Regulatory requirements are regulations that all devices in the unlicensed band must comply with in order to ensure that devices using the same unlicensed band frequencies can safely and fairly use each other. For example, a device that wants to use an unlicensed band frequency must check if another unlicensed band device is using that frequency before transmitting data over the unlicensed band frequency, and if that frequency is not used by another unlicensed band device. You can only transfer data.

However, since a mobile communication system such as LTE (long term evolution) is a system designed to provide a mobile communication service using a frequency of a licensed band, if the current system is installed in an unlicensed band as it is, The base station always occupies a portion of the unlicensed band frequency, and thus may cause a problem that other unlicensed band devices cannot use the frequency. Therefore, there is a need to improve the structure and function of current mobile communication systems in view of the regulatory requirements that must be observed to use unlicensed band frequencies. In this case, when a large part of the basic functions (for example, frame structure, resource allocation structure, etc.) of the mobile communication system is changed, the system development period and cost may increase, thereby minimizing the function change of the existing mobile communication system. At the same time, wireless communication systems need to be developed that comply with regulatory requirements and enable fair coexistence with other unlicensed band devices.

An object of the present invention is to take advantage of the structure of the existing mobile communication system, to comply with the regulatory requirements of the unlicensed band, channel occupancy method and apparatus that can coexist fairly with other existing unlicensed band devices existing To provide.

According to an embodiment of the present invention, there is provided a channel access method of a base station for an unlicensed band. The channel access method includes performing at least one channel sensing on a channel of an unlicensed band in a channel sensing period of a frame, and broadcasting a reservation signal for the channel when the channel is empty.

The broadcasting in the channel access method may include broadcasting a reservation signal until a start time of the next subframe if the next subframe does not start immediately after channel sensing.

In the channel access method, the channel sensing period may include at least one subframe, and the time length of the subframe may be an integer multiple of the channel sensing time of the channel sensing.

Performing channel sensing in the channel access method may include performing channel sensing based on an energy sensing scheme.

The channel access method may further include starting data transmission to a terminal in a transmission interval of a frame.

In the channel access method, the frame may further include a rest period not occupying a channel after the transmission period.

In the channel access method, the time length of the idle period may be 5% or more of the time length of the transmission interval.

The channel access method may include transmitting a request message requesting a radio channel access parameter to a server of a system including a base station or a first base station using a licensed band frequency before performing channel sensing, and a wireless channel. The method may further include receiving a response message from the server or the first base station, the response message including the access parameter.

In the channel access method, the wireless channel access parameter may include information about a channel sensing, a transmission interval, and a length of time of an idle period included in a frame.

The channel access method may include determining whether a change of a wireless channel access parameter is necessary while providing a data service to a terminal based on the wireless channel access parameter. The method may further include transmitting a change request message of the radio channel access parameter, and receiving a response message from the server or the first base station in response to the change request message including the new radio channel access parameter.

According to another embodiment of the present invention, a base station for performing channel access to an unlicensed band is provided. The base station includes at least one processor, a memory, and a wireless communication unit, and the at least one processor executes at least one program stored in the memory to perform at least one channel for the channel of the unlicensed band in the channel sensing period of the frame. Performing the sensing; and if the channel is empty, broadcasting the reservation signal for the channel.

At the base station, when at least one processor broadcasts, if a next subframe does not start immediately after channel sensing, the at least one processor may perform a step of broadcasting a reservation signal until a start time of the next subframe.

The channel sensing period in the base station may include at least one subframe, and the time length of the subframe may be an integer multiple of the channel sensing time of the channel sensing.

At least one processor in the base station may perform channel sensing based on an energy detect method when performing channel sensing.

At least one processor in the base station may further perform the step of starting at least one program to start data transmission to the terminal in the transmission interval of the frame.

The frame in the base station may further include an idle period that does not occupy a channel after the transmission interval.

The time length of the idle period in the base station may be 5% or more of the time length of the transmission interval.

At least one processor in the base station executes at least one program to request radio channel access parameters from a server of a system including the base station or a first base station using a licensed band frequency before performing channel sensing. Transmitting the request message and receiving a response message from the server or the first base station in response to the request message, the radio channel access parameter being included.

The radio channel access parameter in the base station may include information on the channel sensing, the transmission interval and the time length of the idle interval included in the frame.

At least one processor executing at least one program in the base station, and determining whether a change of a radio channel access parameter is required while providing a data service to a terminal based on a radio channel access parameter; If necessary, sending a change request message of the radio channel access parameter to the server or the first base station, and receiving a response message from the server or the first base station for the change request message, including the new radio channel access parameter. Can be further performed.

According to an embodiment of the present invention, when a base station provides a mobile communication service using a frequency of an unlicensed band, an unlicensed band can be used fairly with an existing unlicensed band device while complying with the regulatory requirements of the unlicensed band.

1 is a conceptual diagram illustrating an unlicensed band mobile communication system according to an embodiment of the present invention.

2 illustrates a LAA frame of a LAA system according to an embodiment of the present invention.

3A to 3C are diagrams illustrating a transmission section and a rest period of a LAA frame, set according to an embodiment of the present invention.

4 is a flowchart illustrating a method for setting a radio channel access parameter by a LAA base station according to an embodiment of the present invention.

5 is a diagram illustrating a radio frame of a frame-based system according to an embodiment of the present invention.

6 illustrates a LAA frame of a LAA system according to an embodiment of the present invention.

7 illustrates a LAA frame of a LAA system according to another embodiment of the present invention.

8 is a conceptual diagram illustrating a coexistence problem of a LAA system according to an embodiment of the present invention.

9 is a conceptual diagram illustrating a coexistence method of a LAA system according to an embodiment of the present invention.

10 is a flowchart illustrating a coexistence method of a LAA base station according to an embodiment of the present invention.

11 is a conceptual diagram illustrating a carrier aggregation method using an unlicensed frequency band according to an embodiment of the present invention.

12 is a conceptual diagram illustrating a carrier aggregation method using an unlicensed frequency band according to another embodiment of the present invention.

13 is a conceptual diagram illustrating a radio channel management method according to an embodiment of the present invention.

14 is a conceptual diagram illustrating a wireless channel estimation method according to an embodiment of the present invention.

15 is a conceptual diagram illustrating a channel access method according to an embodiment of the present invention.

16 is a flowchart illustrating a channel access method according to an embodiment of the present invention.

17 is a conceptual diagram illustrating a subframe channel access method according to an embodiment of the present invention.

18 is a conceptual diagram illustrating a channel occupation notification method according to an embodiment of the present invention.

19 is a conceptual diagram illustrating a dynamic carrier change method according to an embodiment of the present invention.

20 is a flowchart illustrating a dynamic carrier change method according to an embodiment of the present invention.

21 is a block diagram illustrating a wireless communication system according to an embodiment of the present invention.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, a terminal includes a mobile station (MS), a mobile terminal (MT), an advanced mobile station (AMS), a high reliability mobile station (HR-MS). ), Subscriber station (SS), portable subscriber station (PSS), access terminal (AT), user equipment (user equipment (UE)), machine type communication device ( MTC device) and the like, and may include all or some functions of MT, MS, AMS, HR-MS, SS, PSS, AT, UE, and the like.

In addition, a base station (BS) may be an advanced base station (ABS), a high reliability base station (HR-BS), a node B (node B), an advanced node B (evolved node B, eNodeB), access point (AP), radio access station (RAS), base transceiver station (BTS), mobile multihop relay (MMR) -BS, relay serving as a base station station (RS), relay node (RN) serving as base station, advanced relay station (ARS) serving as base station, high reliability relay station (HR) serving as base station -RS), small base station (femoto BS), home node B (HNB), home eNodeB (HeNB), pico base station (pico BS), macro base station (macro BS), micro base station (micro BS) ), Etc.), and all, such as ABS, Node B, eNodeB, AP, RAS, BTS, MMR-BS, RS, RN, ARS, HR-RS, small base station, or the like. It may include a negative feature.

1, a mobile communication system according to an embodiment of the present invention includes a mobile communication base station 110, a license assisted access (LAA) base station 120, an access point (AP) ( 130, the mobile terminal 140, and the unlicensed band user 150.

The mobile communication base station 110 performs control and data service provision of a terminal through a licensed band frequency.

The LAA base station 120 provides a data service to a terminal through an unlicensed band frequency, and typically manages a smaller coverage than the mobile communication base station 110. The mobile communication base station 110 and the LAA base station 120 may be connected to each other by a wired backhaul or disposed at the same physical location. In addition, depending on the network configuration, the mobile communication base station 110 and the LAA base station 120 may operate independently of each other, and the mobile communication base station 110 may control the LAA base station 120. In this case, since only the mobile communication base station 110 has control rights of the terminal, the mobile terminal 140 should always maintain the connection with the mobile communication base station 110 through the licensed band frequency, The data service may be provided through a carrier aggregation (CA) of the licensed band frequency and the unlicensed band frequency of the LAA base station 120. The LAA base station 120 may provide both uplink and downlink data services or only downlink data services depending on the network configuration.

The unlicensed band user 150 and the access point 130 perform data communication through a frequency of the same band as the unlicensed band frequency used by the LAA base station 120. Even in the same unlicensed frequency band, the frequency of the wireless channel used for the actual communication may be the same or different. When the same radio channel of the same unlicensed frequency band is used, coexistence and interference problems between the LAA base station 120 and the unlicensed band user 150 and the access point 130 may occur. One embodiment of the present invention described below describes a fair frequency sharing method between an unlicensed band mobile communication system (hereinafter referred to as a 'LAA system') and an existing unlicensed band system when the same wireless channel is used within the same frequency band. .

2, a LAA frame of a LAA system according to an embodiment of the present invention includes a channel sensing period 210, a transmission period 220, and an idle period 230. do. Each section may basically operate in a subframe unit defined in a mobile communication system using a licensed band.

The LAA frame according to the embodiment of the present invention according to FIG. 2 is applicable to both a case where both uplink and downlink data services are provided and only a case where only downlink data services are provided, and in one embodiment of the present invention, downlink An example of a LAA frame applied when only a data service is provided will be described.

The LAA base station according to an embodiment of the present invention determines whether an operating frequency is used by another unlicensed band device prior to data transmission. For example, the LAA base station may perform a channel sensing operation by using an energy detect method in the channel sensing section 210 before the transmission section 220. In this case, the channel sensing may be operated in a smaller unit than the subframe unit, which is a basic unit of the transmission period 220 and the idle period 230. In addition, the time (channel sensing time) that the LAA base station performs channel sensing is a value larger than the value defined in the regulatory requirement of the unlicensed frequency band, and may be determined as 1 / n of the time length of the subframe. For example, when the minimum channel sensing time defined in the regulatory requirements of the unlicensed frequency band is 20 ms and the time length of the LTE subframe is 1 ms, the channel sensing time is 20 ms (= 1 ms / 50), 25 ㎲ (= 1 ㎳ / 40), or 50 ㎲ (= 1 ㎳ / 20) or the like. In FIG. 2, the channel sensing time is illustrated as 25 ms (indicated by the dotted line in the subframe), and four channel sensing is possible in one subframe.

The LAA base station according to an embodiment of the present invention can determine whether the channel is occupied by measuring the energy of the radio channel during the channel sensing time. For example, if the measured energy is greater than the preset criterion, it may be determined that another device occupies the channel. If the measured energy is smaller than the preset criterion, the wireless channel may be determined to be empty. At this time, the LAA base station may repeat channel sensing (ie, measuring energy of the wireless channel) until it is determined that the wireless channel is empty. The LAA base station starts data transmission when it is determined that the radio channel is empty.

At this time, if the next subframe does not start immediately after channel sensing of the LAA base station (that is, immediately after the LAA base station senses that the channel is empty), the LAA base station broadcasts a reservation signal until the start time of the next subframe, whereby another device (E.g., another device in the unlicensed band) may not allow the LAA base station to occupy the radio channel to occupy. In this case, the reserved signal broadcasted by the LAA base station is a signal containing enough energy that other devices can recognize that the radio channel is occupied, and can be any type of signal such as a synchronization signal of a LTE system or a newly defined preamble signal. Do.

Referring to FIG. 2, the LAA base station determines that the channel is in use for five channel sensing (shaded parts of FIG. 2), and determines that the channel is empty in the sixth channel sensing. However, since the next subframe does not start immediately after the sixth channel sensing, the reserved signal may be transmitted for the remaining two channel sensing times in order to prevent another device from occupying the corresponding channel. Thereafter, at the start of the next subframe, the LAA base station starts downlink data transmission.

Meanwhile, the LAA base station according to an embodiment of the present invention may perform data transmission in a manner defined in a conventional mobile communication system during the preset transmission period 220. In addition, during the preset idle period 230, no signal is transmitted on the downlink (ie, does not occupy a channel) so that another device can use the corresponding radio channel. In addition, when the idle period 230 ends, the LAA base station may perform channel sensing operation again for data transmission and acquire the occupation of the wireless channel.

Regardless of the regulatory requirements of the area where the LAA base station is installed, the LAA base station must perform channel estimation operations to obtain channel occupancy, but the LAA base station is installed in the area where the LAA base station is installed, its operating frequency, and Therefore, the transmission section 220 and the idle section 230 may be set differently.

3 (A) shows a transmission section 220 and an idle section 230 when the LAA base station is installed in an area to which the regulatory requirements for the unlicensed band apply. When the LAA base station is installed in the region to which the regulatory requirements apply, the length of time of the transmission section 220 and the idle section 230 may be determined according to the length required in the regulatory requirement. For example, according to the regulatory requirements, the transmission section 220 may be determined to be at least 1 ms to a maximum of 10 ms, and the idle section 230 may be determined to have a time length of 5% or more of the transmission section 220. In this case, the channel sensing period 210 in which the channel access is performed is shortly determined.

3B illustrates a transmission interval 220 when a LAA base station is installed in an area where a regulatory requirement for an unlicensed band does not apply, and there are a plurality of other devices using the unlicensed band within coverage of the LAA base station. The idle section 230 is shown. Since the regulatory requirements do not apply, the length of the transmission section 220 and the idle section 230 may be longer, but the transmission section 220 and the idle section 230 may be used for fair channel sharing with other devices. It can be set at a similar ratio (eg 1: 1).

3C illustrates a transmission interval 220 when a LAA base station is installed in an area where a regulatory requirement for an unlicensed band does not apply, and there are a few other devices using the unlicensed band within coverage of the LAA base station. The idle section 230 is shown. In this case, since there are a few other devices using the unlicensed band in the coverage of the LAA base station, it may be assumed that there is little radio wave received from the other device. In this case, the length of the transmission section 220 can be set relatively longer than the rest section 230 to maintain the performance of the LAA base station to the maximum. However, the minimum rest period 230 may be maintained so that sudden operation of another device may be detected.

Referring to FIG. 4, when power is first applied to the LAA base station, the LAA base station completes self initialization and transmits a message (radio channel access parameter request message) for requesting a radio channel access parameter to a server (S401). Depending on the network configuration, the radio channel access parameter request message may be delivered to the server through the macro base station using the licensed band frequency, or the macro base station using the licensed band frequency may serve as a server.

After receiving the radio channel access parameter request message from the LAA base station, the server transmits a radio channel access parameter response message to the LAA base station in response (S402). In this case, the wireless channel access parameter response message may include information about the time length of the channel sensing, the transmission interval 220, and the idle interval 230 (that is, the wireless channel access parameter).

The LAA base station receiving the radio channel access parameter response message from the server performs a normal operation (for example, a channel access operation) by applying parameters included in the received response message (S403), thereby providing a data service to the terminal. Can be provided (S404).

While providing the data service to the terminal, the LAA base station and the terminal periodically measures whether there is another unlicensed band device adjacent to the surrounding, and the strength of the radio wave received from the adjacent unlicensed band device and the like periodically (S405). In case of the UE, the measurement result may be periodically reported to the LAA base station (S406). In addition, the measurement result report message for the adjacent unlicensed band device may be directly transmitted to the LAA base station through the unlicensed band frequency according to the network configuration, or after the macro base station is received after being transmitted from the terminal to the macro base station through the licensed band frequency The message may also be forwarded to the LAA base station.

Thereafter, the LAA base station analyzes its measurement result and the measurement result included in the report message of the terminal to determine whether the change of the radio channel access parameter is necessary (S407). If it is determined that the change of the radio channel access parameter is necessary, the LAA base station requests a new radio channel access parameter by transmitting a change request message of the radio channel access parameter to the server (S408). Upon receiving the change request message for the radio channel access parameter from the LAA base station, the server transmits a change response message (radio channel access parameter change response message) to the LAA base station in response thereto (S409). The LAA base station receiving the change response message may apply parameters related to the channel sensing time, the transmission period 220 and the length of the idle period 230 included in the radio channel access parameter change response message (S410).

Alternatively, the macro base station using the server or the licensed band frequency according to another embodiment of the present invention may determine whether the change of the radio channel access parameter is necessary according to the network configuration or the policy of the network operator. In this case, the result of the measurement for the adjacent unlicensed band device performed by the terminal and the LAA base station may be periodically transmitted to the server or the macro base station, and the server or the macro base station may determine the radio channel access parameter based on the periodically transmitted measurement result. The change can be determined. If it is determined that the change of the radio channel access parameter is necessary, the server or the macro base station transmits a radio channel access parameter change request message to the LAA base station. The LAA base station transmits the radio channel access parameter change response message to the server or the macro base station in response to the radio channel access parameter change request message. In this case, the radio channel access parameter change request message includes information about a channel sensing time, a transmission interval 220, and a length of the idle interval 230 for changing the radio channel access parameter.

On the other hand, when the LAA base station is installed in an area where it is not necessary to comply with the regulatory requirements of the unlicensed band, it may be valid only until the step of setting the radio channel access parameter in the method of setting the radio channel access parameter according to FIG. Changing the channel access parameter may not apply.

As described above, according to one embodiment of the present invention, when a base station provides a mobile communication service using a frequency of an unlicensed band, the unlicensed band device and the unlicensed band are fairly processed while complying with the regulatory requirements of the unlicensed band. Can be used.

In the European Telecommunication Standards Institute (ETSI), a radio frame used in frame based equipment (FBE) for a listen before talk (LBT) scheme for the use of unlicensed band frequencies in the 5 GHz band is illustrated in FIG. 5. It is defined as Referring to FIG. 5, a frame-based device may use a wireless channel of an unlicensed band in a fixed frame period. The fixed frame includes a channel occupancy time in which data can be transmitted and an idle period in which data is not transmitted. The frame-based device performs a channel estimation (clear channel assessment, CCA) immediately before the end of the idle interval to check whether the channel is empty. The channel estimation refers to an operation of measuring energy of a specific channel and determining that the channel is currently in use when the measured energy is higher than a preset reference, and determining that the channel is not currently in use if lower than the preset criterion. If it is determined through the channel estimation that the channel is not currently in use, the frame-based device transmits data during the channel occupancy time, and then enters the idle period. However, if the channel estimation determines that the channel is currently in use, the frame-based device does not perform data communication during the channel occupancy time and idle period.

Referring to FIG. 6, a radio frame of a mobile communication system synchronized with each subframe and a LAA frame of an LAA system are illustrated. In FIG. 6, the mobile communication system operates at the licensed band frequency, and the LAA system operates at the unlicensed band. The LAA frame (fixed) of the LAA system includes a downlink pilot time slot (DwPTS), a dormant period, and nine mobile communication subframes.

In an embodiment of the present invention, the time length of the DwPTS is one half of one mobile communication subframe, and includes seven orthogonal frequency division multiplex (OFDM) symbols.

The idle period corresponds to 7 OFDM symbol lengths including a channel estimation interval (CCA). In this case, the time length of one LAA frame is 10ms, and includes a channel occupancy period of about 9.5ms (9 mobile subframes + DwPTS) and a pause period of about 0.5ms (excluding a subframe of DwPTS in one subframe). do. Therefore, the following European LBT requirements can be complied with.

-Maximum channel occupancy time should be within 10ms.

-The minimum idle period should be at least 5% of the channel occupancy time.

Referring to FIG. 7, a radio frame of a mobile communication system synchronized with a subframe unit and a LAA frame of an LAA system are illustrated, and a time length of one LAA frame of the LAA system is 4 ms.

In FIG. 7, one LAA frame (fixed) of the LAA system includes three mobile communication subframes, a DwPTS and an idle period. In this case, the number of OFDM symbols included in the idle period may be changed according to the system configuration.

In an embodiment of the present invention, the ratio of the idle section to the channel occupation section (the idle section ratio) may be 5.7%. In this case, up to four OFDM symbols adjacent to the DwPTS among the seven OFDM symbols are used as channel occupancy intervals (three subframes including 14 OFDM symbols + 11 OFDM symbols), and only three OFDM symbols are used as idle intervals. Thus, the idle interval ratio may be about 5.7% (3 / (14 × 3 + 11) = 0.0566 ...).

Alternatively, in another embodiment of the present invention, the idle section ratio may be 14.3%. In this case, only up to DwPTS is used as the channel occupancy interval and all seven OFDM symbols are used as idle intervals. Thus, the idle interval ratio may be about 14.3% (7 / (14 × 3 + 7) = 0.1428 ...).

Therefore, the LAA frame of the LAA system shown in FIG. 7 can comply with the Japanese LBT requirement defined as the maximum time length of the channel occupancy interval is within 4 ms.

Since the LAA frame of the LAA system according to the embodiment of the present invention is designed based on a fixed frame, all channel estimation time points, data transmission points, or idle periods of the LAA system are fixed. In this case, since the channel estimation time is fixed, coexistence problems between the two systems may occur.

Referring to FIG. 8, the first LAA system may determine that the channel is empty after channel estimation and perform data transmission. However, since the channel estimation time of the second LAA system always matches the channel occupancy time of the first LAA system, it may be determined that the channel is always in use and the wireless channel may not be used.

Since the existing unlicensed band equipment performs LBT operation only when data transmission is required, the above problem can be automatically solved after a certain time. However, since the LAA system is designed based on a method of always occupying a radio channel using a licensed band, coexistence problems as described in FIG. 8 may be maintained for a considerable time.

9 is a conceptual diagram illustrating a coexistence method of a LAA system according to an embodiment of the present invention, and FIG. 10 is a flowchart illustrating a coexistence method of a LAA base station according to an embodiment of the present invention.

The coexistence problem occurs in a fixed frame-based radio frame structure because all systems using the same frequency band always perform channel estimation at a fixed time point. In the LAA system according to an embodiment of the present invention, one LAA base station occupying the channel intentionally stops using the channel for a second time after occupying the channel for the first time. In this case, the first time for channel occupancy or the second time for channel suspension (that is, channel access suspension) may be determined according to a random number (RN) selected by the LAA base station. For example, when the random number is applied to the first time, the second time may be fixed, or when the random number is applied to the second time, the first time may be fixed. Therefore, other devices in the same frequency band may use the same radio channel through channel estimation during the time when the LAA base station stops using the channel.

Referring to FIG. 10, a LAA base station of a LAA system first selects a random number before channel access (S701). If the channel occupies success, the LAA base station occupies a channel as many as the number of LAA frames corresponding to the random number (S702). Referring to FIG. 9, the LAA base station of the first LAA system selects 2, 3, and 1 as random numbers before channel access, and then occupies a channel for two LAA frames. The LAA base station of the second LAA system selects 4, 2, and 2 as random numbers, and fails to occupy the channel through channel estimation due to the LAA base station of the first LAA system and the LAA base station of the third LAA system. Occupies a channel in the frame and then occupies the channel for 4 LAA frames up to 7 LAA frames. The LAA base station of the third LAA system selects 1, 2, and 3 as random numbers, fails to occupy the channel through channel estimation due to the LAA base station of the first LAA system, and succeeds in occupying the channel in the LAA frame 3 Occupies a channel for one LAA frame. The LAA base station may transmit data on the occupied channel.

The LAA base station intentionally stops channel access in the next LAA frame (fixed second time) after the channel occupation (S703). Thus, during periods when the LAA base station has suspended channel access, devices in other systems are given the opportunity to occupy the same channel through channel estimation. At this time, one LAA frame may be a fixed frame having a length of 10 ms shown in FIG. 9 or a fixed frame having a length of 4 ms shown in FIG. 10. Referring to FIG. 9, the LAA base station of the first LAA system intentionally stops channel access in a LAA frame 3. The LAA base station of the second LAA system intentionally stops channel access in LAA frame eight. The LAA base station of the third LAA system intentionally stops channel access in LAA frame 4.

Alternatively, the LAA base station of the LAA system according to another embodiment of the present invention may occupy a channel by performing channel access for a fixed time, and then stop channel access during a LAA frame corresponding to a random number.

In general, a wireless communication system divides an entire frequency band into predetermined bandwidth units to provide a wireless communication service. For example, when a wireless communication service is provided in a 20 MHz bandwidth unit in a 5 GHz unlicensed frequency band, a plurality of available wireless channels in a 20 MHz bandwidth unit exist in the 5 GHz unlicensed frequency band.

When a plurality of carriers (ie, radio channels) are operated in one system, LAA frames having the same structure may be applied to each carrier. In this case, the LAA frame may be based on the LAA frame structure shown in FIG. 9 or 10, but the same frame structure may be applied to all carriers in the same system. That is, channel estimation may be performed at the same time point in all carriers, and a rest period may be started at the same time point.

Referring to FIG. 11, a LAA base station operating three carriers may perform channel estimation on all carriers at the same time and perform data transmission on all carriers that succeed in channel estimation according to the channel estimation result. In FIG. 11, the LAA base station succeeds in channel occupancy of the first carrier and the third carrier in the first LAA frame, performs data transmission, and uses a second carrier determined to be in use by another device according to channel estimation. Do not perform data transfer. Thereafter, the LAA base station may perform channel estimation again on all carriers immediately before the second LAA frame, and perform data transmission on the first carrier, the second carrier, and the third carrier in the second LAA frame. In the case of FIG. 11, the terminal includes a plurality of receiving apparatuses for receiving data, so that the terminal may simultaneously receive data from different wireless channels.

In the case of an unlicensed frequency band, since the same channel must be shared by a plurality of different devices, continuous data transmission cannot be guaranteed and a certain data rate cannot be guaranteed. However, if a wireless channel is dynamically switched to an available wireless channel among a plurality of available wireless channels, data is transmitted discontinuously in each wireless channel, but data transmission may be continuously performed from the viewpoint of the LAA base station and the terminal. Referring to FIG. 12, a terminal is connected to a mobile communication base station through a licensed band carrier and can receive data service through one carrier of one of a first carrier, a second carrier, and a third carrier corresponding to an unlicensed frequency band. have. That is, in the case of FIG. 12, the terminal includes one receiving apparatus for receiving data, and thus, the terminal may receive data from one radio channel at a time.

The LAA base station according to an embodiment of the present invention performs channel estimation on all carriers (first carrier, second carrier, and third carrier) in the unlicensed frequency band immediately before the first LAA frame, and according to the result Select the radio channel on which the transmission will be performed. The terminal transmits information about a carrier of the selected unlicensed frequency band to the terminal through a licensed band carrier. The terminal receives the data by switching to the corresponding carrier based on the information on the carrier on which the data transmission is performed, received through the licensed band carrier.

Referring to FIG. 12, the LAA base station according to an embodiment of the present invention determines that channel occupancy of the first carrier and the third carrier is possible through channel estimation in the first LAA frame, and is determined as a carrier to be used for data transmission. 1 Select the carrier. Thereafter, the LAA base station performs a physical downlink control channel including information on a carrier of an unlicensed frequency band, in which data transmission is to be performed, and radio resource allocation information about data to be transmitted in a first subframe of the carrier. , PDCCH) through a licensed band carrier.

In this case, since the LAA frame of the carrier of the unlicensed frequency band includes a plurality of subframes, the resource allocation information included in the PDCCH includes only the resource allocation information of the first subframe and includes the remaining subframes included in the first LAA frame. Resource allocation information may be transmitted on the first carrier.

Upon receiving the PDCCH from the licensed band carrier, the UE switches to the first carrier for one OFDM symbol time (1 symbol delay) and receives data on the first carrier. If the time length of the PDCCH is variable (for example, one OFDM symbol to three OFDM symbols), the time point at which the UE starts receiving data is also variable ('the length of the PDCCH + one OFDM symbol'). Can be.

If data is not transmitted through the first carrier until the terminal starts to receive data, another device in the unlicensed band may determine that the channel is empty and occupy the channel. To prevent this, the LAA base station according to an embodiment of the present invention may transmit dummy data through the first carrier until switching to the first carrier is completed. At this time, the content and format of the dummy data to be transmitted are not limited. However, the dummy data may be transmitted with energy such that the device of another unlicensed band can recognize the occupied state of the first carrier.

When data transmission in the first LAA frame is completed, the LAA base station according to an embodiment of the present invention performs channel estimation for all carriers immediately before the second LAA frame. Referring to FIG. 12, the LAA base station determines that channel occupancy is possible for the second carrier after the second channel estimation, and transmits a PDCCH including information about the second carrier and resource allocation information to the terminal through a licensed band carrier. do. The terminal receiving the PDCCH from the LAA base station switches to the second carrier to receive data. In the third LAA frame, the LAA base station performs a third channel estimation, transmits a PDCCH including information about the third carrier and resource allocation information to the terminal through the licensed band carrier, and the terminal switches to the third carrier to transmit data. Receive Subsequently, in the fourth LAA frame, the LAA base station transmits the PDCCH including the information about the third carrier and the resource allocation information to the terminal through the licensed band carrier, and the terminal transmits the PDCCH in the fourth LAA frame as in the third LAA frame. Switch to 3 carriers to receive data. In the fifth LAA frame, after performing channel estimation, the LAA base station determines that channel occupancy is possible for the first carrier, and transmits a PDCCH including information about the first carrier and resource allocation information to the terminal through a licensed band carrier. . Upon receiving the PDCCH including the information about the first carrier and the resource allocation information from the LAA base station, the terminal may switch to the first carrier to receive data. Accordingly, the LAA base station according to an embodiment of the present invention performs a CCA immediately before a specific LAA frame to select a carrier of an unlicensed frequency band to be used for data transmission, and selects a PDCCH including information about the selected carrier and resource allocation information. Transmit to the terminal through the licensed band carrier. Upon receiving the PDCCH, the UE may transmit dummy data to the carrier according to the information included in the PDCCH until the switching is completed, and may receive the data from the carrier when the switching is completed.

Referring to FIG. 13, when a plurality of radio channels exist in an unlicensed frequency band, the LAA base station may manage a radio channel for data transmission. First, in the first step, the LAA base station may manage a radio channel with possibility of data transmission. In this case, the first step may operate in a relatively long time unit. In the step, the LAA base station and the terminal may negotiate a list of candidate channels on which data communication will be performed in the future, and negotiate addition / deletion / change of a wireless channel. Alternatively, if a radar that is a primary service is detected in the wireless channel, the wireless channel may be changed according to dynamic frequency selection (DFS) regulation through a first step. In the first step, radio channel management may be performed through explicit exchange of control messages, such as radio resource control (RRC) connection reconfiguration messages.

In the next second step, switching or data transmission between the wireless channels defined in the first step may be performed. The second stage may operate in a relatively short time unit than the first stage. In the second step, explicit exchange of control messages is not required, and channel management may be performed through signaling of a physical layer unit such as a PDCCH.

Referring to FIG. 13, a LAA base station and a terminal may use a first channel, a third channel, a fifth channel, and a sixth channel as a wireless channel (available wireless channel) capable of data transmission through a channel management operation according to a first step. Choose. Thereafter, the LAA base station and the terminal perform data transmission and reception according to the carrier aggregation described above. In this case, when at least one of the following events occurs, the channel management operation according to the first step may be performed again.

-Detection of radar on a specific radio channel

-Increase or decrease the interference of a particular radio channel (change in interference)

When the quality of service (QoS) required by the terminal is changed (change in QoS requirements)

That is, referring to FIG. 13, at least one of the events described above occurs, and the LAA base station and the terminal select the second channel, the third channel, the fifth channel, and the sixth channel as available radio channels.

Meanwhile, in order to manage the radio channel of the first step, channel measurement may be performed not only for a currently serving radio channel but also for an adjacent radio channel that is not currently used. In this case, for channel measurement for a wireless channel that is not currently used, the LAA base station and the terminal may use a separate receiver for channel measurement. If the LAA base station and the terminal do not have a separate receiver for channel measurement, the overall performance may be degraded because the LAA base station and the terminal must terminate the data communication and perform channel measurement for a predetermined time through negotiation.

Referring to FIG. 14, the LAA base station may measure an adjacent radio channel without additional negotiation for the period indicated by the solid arrow. The LAA base station transmits data during the first frame and performs channel estimation immediately before the second frame. If the channel estimation determines that the radio channel is occupied by another device, the LAA base station may measure an adjacent radio channel during the channel occupation period of the second frame. Thereafter, the LAA base station may perform channel estimation immediately before the third frame and perform channel access according to the channel estimation result. At this point, the LAA base station may intentionally suspend channel access for coexistence with other devices (intentional idle frame), while the LAA base station performs channel measurement on the adjacent radio channel even during a frame where channel access is suspended. Can be done.

Referring to FIG. 14, the terminal may perform channel measurement for a period indicated by a dotted arrow. In this case, the terminal does not perform channel estimation, but the UE already knows when the LAA base station performs channel estimation and accordingly, when data transmission starts. That is, the terminal may perform channel measurement because no data is transmitted during the channel estimation by the LAA base station (section ①, section ③, section ④ and section ⑤). In addition, if no data is transmitted for a predetermined time after the channel estimation time of the LAA base station, the terminal assumes that the LAA base station has failed to occupy the channel, and performs channel measurement on the adjacent radio channel in the frame. (Section ②). In addition, when the LAA base station intentionally stops channel access (intentional idle frame), the terminal may determine that the LAA base station has failed to occupy a radio channel and perform measurement on an adjacent radio channel (section ⑥).

When a plurality of carriers are available in the same terminal or the same LAA base station, the channel measurement described above may be independently performed for each carrier. In this case, since the physical location of each carrier is the same, the measurement result measured for one carrier may be shared for all carriers, thereby reducing the number of measurements for the adjacent radio channel. In addition, the message exchange between the LAA base station and the terminal negotiates a list of radio channels requiring measurement, a measurement order, a number of measurements, a minimum measurement time for one radio channel, and so the efficiency of channel measurement can be increased.

As described above, the LAA base station according to an embodiment of the present invention coexists with a device of an existing unlicensed band through a LAA frame complying with regulatory requirements required by an unlicensed frequency band, and provides a wireless communication service to a terminal using an unlicensed frequency band. can do. In addition, the LAA base station according to an embodiment of the present invention may improve the quality of service through channel access and carrier aggregation based on the conventional mobile communication system.

15 is a conceptual diagram illustrating a channel access method according to an embodiment of the present invention, and FIG. 16 is a flowchart illustrating a channel access method according to an embodiment of the present invention.

Referring to FIG. 15, a time length of an LAA frame according to an embodiment of the present invention may be a maximum license time of an unlicensed band. Unlicensed band maximum occupancy time may be subject to local regulations, in which case the fixed length of the LAA frame may change. If the maximum occupancy time increases, the number of subframes used for data transmission in the LAA frame is increased. The channel access method according to an exemplary embodiment of the present invention may be applied to both uplink and downlink data services or only to downlink data services.

Referring to FIG. 15, a LAA frame according to an embodiment of the present invention may include a channel sensing (clear channel assessment, CCA) section, an extended channel sensing (eCCA) section, a channel reservation section, and It includes a transmission interval.

Referring to FIG. 16, the LAA base station according to an embodiment of the present invention performs CCA to determine whether a frequency channel is used by another unlicensed band device before data transmission (S301). In this case, the LAA base station may perform CCA through an energy detection method. For example, the LAA base station measures the energy of the radio channel during the channel sensing period and determines that the current radio channel is occupied by another device if the measured energy is higher than the preset reference, and if the measured energy is lower than the preset criterion It can be determined that the current wireless channel is empty.

As a result of the CCA, if it is determined that the channel is used by another unlicensed band device (S302), the LAA base station performs the eCCA (S303). The eCCA is the same as the CCA in that the purpose of the eCCA is to determine whether to use the channel. However, in the eCCA, unlike the CCA, the use of the channel is determined many times. For eCCA, the LAA base station may select an eCCA counter value within a predetermined range. Thereafter, the LAA base station performs channel sensing to decrease the eCCA counter value by 1 if the channel is empty. However, if the channel sensing result of the LAA base station channel is in use by another unlicensed band device, channel sensing is performed again without decreasing the eCCA counter value. The LAA base station executes the eCCA until the eCCA counter value becomes 0. After that, when the eCCA counter value becomes 0, the LAA base station starts transmitting the reserved signal according to the time point at which the eCCA ends (S304). Transmission can be started (S305).

Alternatively, if it is determined that the channel is empty as a result of the CCA, the LAA base station may start the transmission of the reservation signal according to the time point when the CCA is terminated without performing the eCCA (S304) and start the data transmission (S305).

In a mobile communication system which is a reference system of the LAA system, data transmission may be started and terminated based on a predetermined frame or subframe. Therefore, the LAA base station may not always start data transmission at the end of the CCA or eCCA. Referring to FIG. 15, when the eCCA is terminated in the first CCA, it is an intermediate point of the subframe, and therefore, the LAA base station cannot start data transmission through the corresponding channel even though the corresponding channel is empty. In this case, when the LAA base station stops channel access to the boundary point of the next subframe, the channel may be occupied by another unlicensed band device.

Accordingly, the LAA base station according to an embodiment of the present invention may broadcast a reservation signal immediately after the CCA or the eCCA until a point where data can be transmitted, so that the radio channel to be occupied by the LAA base station is not occupied by another unlicensed band device. have. In this case, the reserved signal is a signal that contains enough energy so that other unlicensed band devices can recognize that the wireless channel is occupied, and any type of signal may be used. For example, signals including energy only, signals of a conventional LTE system for downlink synchronization, signals such as a preamble for cell identification, and the like may be used as a reservation signal.

Referring to FIG. 15, a LAA base station according to an embodiment of the present invention recognizes that a channel is empty at a seventh OFDM symbol time point through CCA and eCCA in a first channel access. However, since the next subframe does not start immediately after the eCCA, the reservation signal is transmitted until the start time of the next subframe. Then, the LAA base station according to an embodiment of the present invention starts the downlink data transmission from the start time of the next subframe.

In a typical mobile communication system, start and end of data transmission may be performed in units of subframes. Therefore, in order to satisfy a limited channel occupancy time (eg, 4 ms), up to three subframes may be used for downlink data transmission after transmission of a reservation signal. However, at this time, since the actual channel occupancy time of the LAA base station is a time for transmitting the reservation signal (for example, 0.5 ms) and three subframe times (for example, 3 ms), the maximum channel occupancy time (4 ms in this case) Is less than Therefore, as the end time of the CCA or the eCCA according to an embodiment of the present invention approaches immediately after the start time of the subframe, the difference between the real channel occupation time and the maximum channel occupation time may increase.

Conventionally, in the mobile communication system such as LTE, since the start and end of data transmission should occur at the boundary of the subframe, the reserved signal according to an embodiment of the present invention is the next subframe from the time point of channel occupancy of the LAA base station. It can be transmitted until the start time. In this case, since the reserved signal is not a signal used for transmitting data of the user and affects the maximum channel occupancy time (shortening the effective channel occupancy time), it may cause a waste of radio resources. In addition, the maximum channel occupancy time may not be efficiently used at the boundary of the subframe and the efficiency of overall resource utilization may be reduced.

Referring to FIG. 17, for the first channel access of the LAA base station, the reservation signal was transmitted for 7 OFDM symbols because the CCA (or eCCA) was terminated at the midpoint of the subframe. Thus, in this case, the actual channel occupancy time at which data transmission is possible is 3 ms (ie, three subframes). In the case of the second channel access of the LAA base station, since the CCA (or eCCA) is terminated near the boundary of the subframe, there are not more reserved signals transmitted until the next subframe boundary time point than in the case of the first channel access. However, if the time from the channel occupancy point to the next subframe boundary is too short, the LAA base station lacks time to prepare downlink data transmission through scheduling, and in fact, the reservation signal until the boundary point of the next subframe of the next subframe. In some cases, it may be necessary to send more resources, and more resources may be wasted. Therefore, start and end of data transmission need to be performed based on a time unit shorter than a subframe in order to minimize resource waste. At this time, if the start and end of data transmission is performed in units of OFDM symbols, waste of resources can be minimized, but the structure of the current mobile communication system needs to be changed a lot, which may cause backward compatibility, product development and production costs. have.

The LAA base station according to an embodiment of the present invention may start and end data transmission in units of slots corresponding to half of the time length of the subframe. At this time, the start and end of data transmission may be performed in a special subframe of the LTE system. The LAA base station according to an embodiment of the present invention may use a downlink pilot time slot (DwPTS) included in a special subframe of the LTE system. The DwPTS is included in a special subframe of a time division duplex (TDD) frame of the LTE system and is located in front of the special subframe at the time of changing from the downlink to the uplink. LAA base station according to an embodiment of the present invention can maximize the real channel occupancy time by using the DwPTS at various positions of the subframe.

According to an embodiment of the present invention, the LAA base station may determine a start time of data transmission as a start point of a start time of a next subframe and a start time of a next slot. Referring to FIG. 15, in the first channel access, a reservation signal is transmitted until the start of the next subframe, and data transmission is also started in the next subframe. In a second channel access, however, data transmission can begin at the beginning of the next slot. In addition, the end point of the data transmission may be determined to be the point at which the real channel occupancy time is close to the maximum channel occupancy time among the end points of the next subframe and the end point of the next slot. Accordingly, the LAA base station and the LAA terminal according to an embodiment of the present invention can secure the real channel occupation time to be as close as possible to the maximum channel occupation time. In addition, when the reservation signal is additionally transmitted due to the constraint time according to the scheduling, the reservation signal may be transmitted in the slot unit instead of the subframe.

The LAA base station according to an embodiment of the present invention may perform CCA (or eCCA) at any time or occupy a channel at any time. Therefore, for smooth data communication between the LAA base station and the terminal, the terminal should be able to know when the LAA base station occupies the channel to transmit data. The terminal may detect whether the channel is occupied by the LAA base station by sensing whether the channel is occupied or whether the channel is occupied by the base station of the licensed band.

When the terminal detects whether the channel is occupied, the terminal may continuously try to receive data on the channel and determine whether the channel is occupied by the LAA base station according to whether the data reception is successful. When a specific channel is allocated to a secondary cell of the terminal by a channel or carrier management procedure, the terminal attempts to receive data every subframe and determines whether a reservation signal or a control channel (eg, PDCCH) is included in the subframe. When the reservation signal or the control channel is included in the subframe, the terminal may determine that the channel is occupied by the LAA base station.

However, when the terminal detects whether the channel occupies, power consumption may increase because the terminal must continuously try to receive data in the subframe. In particular, when the channel load is high, the probability that the LAA base station succeeds in occupying the channel is low, and as a result, the probability that the detection of whether the terminal occupies the channel becomes unnecessary becomes high. On the contrary, when the channel load is low, the channel occupancy success probability of the LAA base station is high, and thus the terminal can recognize whether the channel is occupied without wasting a lot of power. Therefore, depending on the channel load, the channel occupation detection method by the terminal and the channel occupation notification method by the base station may complement each other.

When the base station is notified of the channel occupancy of the LAA base station by the base station, the base station may inform the terminal whether the channel occupancy of the LAA base station and start receiving data when the LAA base station succeeds in occupying the channel. Since the terminal uses the carrier of the licensed band as the primary carrier and the carrier of the unlicensed band as the secondary carrier, the terminal always receives control information (for example, PDCCH) transmitted from the licensed band carrier. Therefore, when the LAA base station succeeds in occupying a channel after CCA (or eCCA), the LAA base station includes information on channel occupancy in the control channel and transmits the control channel to the licensed band carrier. The terminal receiving the control channel through the licensed band carrier may recognize the channel occupancy of the LAA base station and start receiving data.

Referring to FIG. 18, when the LAA base station succeeds in channel occupancy after CCA (or eCCA) in the unlicensed band, the LAA base station transmits a reservation signal and transmits a control channel including channel occupancy information to the terminal through a licensed band carrier in the next subframe. send. In this case, since the channel occupancy for the unlicensed band carrier must be maintained until the terminal decodes the control channel from the licensed band carrier and starts receiving data, the LAA base station reserves a reservation signal for a predetermined number of symbols even after the start of the next subframe. Send it.

The terminal receives the control channel through a licensed band carrier, and starts receiving data if the channel occupancy information is included in the received control channel. The channel occupancy notification method by the base station has an advantage of minimizing power consumption of the terminal compared to a case in which the terminal directly recognizes channel occupancy, and reserves more until the terminal decodes the control channel and starts receiving data. The disadvantage is that the signal needs to be transmitted.

Meanwhile, the LAA base station according to another embodiment of the present invention may deliver channel occupancy information to the terminal through other means than the control channel. For example, the LAA base station according to another embodiment of the present invention may include a new parameter for notifying whether the channel is occupied in the downlink control information (DCI) format. Alternatively, the LAA base station may use a dedicated DCI for delivering channel occupation information to the terminal. In this case, the LAA base station may use a dedicated DCI including only information about channel occupation without scheduling information. The dedicated DCI transmitted from the licensed band PCell may include a parameter that may indicate whether a channel is occupied for all unlicensed band SCells supported by the corresponding PCell, and may broadcast the dedicated DCI to all terminals included in the PCell. Therefore, the length of the dedicated DCI may be limited to the maximum number of unlicensed band SCells supported by the licensed band PCell. For example, when there are three maximum unlicensed band SCells supported by the licensed band PCell, the length of the dedicated DCI may be fixed to 3 bits, and each bit may indicate whether the SCell corresponding to each bit occupies the channel (eg, For example, 0: channel not occupied, 1: channel occupied).

Alternatively, the LAA base station according to another embodiment of the present invention may use a dedicated downlink control channel for transmitting channel occupation information. In this case, whether or not the channel is occupied can be notified through a dedicated control channel including a fixed size of information, and the overhead or transmission method is similar to the case of the dedicated DCI, but channel occupancy information through a dedicated control channel rather than a PDCCH. Can be delivered.

19 is a conceptual diagram illustrating a dynamic carrier change method according to an embodiment of the present invention, and FIG. 20 is a flowchart illustrating a dynamic carrier change method according to an embodiment of the present invention.

Since channels in the unlicensed frequency band cannot be used exclusively by a particular system and are shared by a plurality of unlicensed band devices, continuous data transmission may not be possible. In this case, if the available channels of the plurality of unlicensed bands are utilized to the maximum, continuity of data transmission may be ensured to the maximum.

When a plurality of available unlicensed band carriers are allocated to the LAA terminal as a SCell, the LAA base station selects a currently available carrier among candidate carriers through the CCA (or eCCA) and transmits data, and the terminal transmits data to the selected carrier. Can be changed and receive data. Carrier selection and change may be performed at every channel access, but carriers need to be selected and changed in the medium and long term in consideration of the channel load of each channel in order to minimize the overhead caused by carrier change.

Referring to FIG. 19, an LAA base station according to an embodiment of the present invention implements CCA (or eCCA) for not only an unlicensed band carrier currently used for data transmission but also other unlicensed band carriers, and two carriers of an unlicensed band. The carrier that can occupy the channel is determined. When a carrier capable of channel occupancy is selected, the LAA base station transmits a reservation signal to occupy the carrier, and instructs the UE to change the carrier through a PDCCH transmitted through a licensed band carrier in the next subframe. After receiving the carrier change indication through the PDCCH, the UE immediately changes the operation carrier to the indicated carrier and starts receiving data through the indicated carrier.

On the other hand, when the carrier does not change in the LAA base station and performs normal channel access, data transmission may start in the next subframe or the next slot after the channel occupancy of the LAA base station. However, in the case of dynamic carrier change, since it takes time for the terminal to receive the PDCCH and change the carrier, the LAA base station continues to transmit a reservation signal until the carrier is changed in the terminal. Referring to FIG. 19, both the time length of the PDCCH and the time length required for changing a carrier of the UE are shown as one OFDM symbol. In this case, even if the UE completes the carrier change, since the data can be transmitted at the start of the subframe or the special subframe, the reservation signal needs to be continuously transmitted until the start of the subframe or the special subframe.

The LAA base station according to an embodiment of the present invention transmits data through one unlicensed band carrier (first carrier) and continuously performs CCA (or eCCA) on another unlicensed band carrier (second carrier). Subsequently, if it is determined that channel occupancy for the second carrier is possible, the LAA base station determines whether to occupy or occupy the channel of the second carrier in consideration of the remaining channel occupation time of the first carrier.

Referring to FIG. 20, the LAA base station and the terminal perform data transmission and reception through the first unlicensed band SCell (S701). In addition, during data transmission and reception, the LAA base station may perform CCA (or eCCA) on the channel of the second unlicensed band SCell (S702). If channel occupancy is possible for the channel of the second unlicensed band SCell, the LAA base station determines whether to occupy the channel in consideration of the remaining channel occupancy time of the first unlicensed band SCell (S703). If the remaining channel occupancy time of the first unlicensed band SCell is significant, the LAA base station abandons channel occupancy (S704), and performs CCA (or eCCA) on the channel of the second unlicensed band SCell again after a preset time. can do.

However, when the LAA base station determines the channel occupancy, the LAA base station transmits a reservation signal, thereby occupying the unlicensed band channel of the second unlicensed band SCell (S705). The LAA base station transmits a control channel (for example, PDCCH) including a carrier change indication through a licensed band PCell (S706). Thereafter, when the terminal receiving the control channel through the licensed band PCell changes the operation carrier to the channel of the second unlicensed band SCell, the LAA base station and the terminal transmit and receive data through the channel of the second unlicensed band SCell (S707). In this case, the data transmission / reception operation in the second unlicensed band SCell is the same as that of the first unlicensed band SCell.

Meanwhile, the LAA base station continuously transmits the reservation signal to occupy the channel of the second unlicensed band SCell until the terminal receives the control channel and changes the operation channel to the channel of the second unlicensed band SCell. In addition, while performing data transmission and reception through the second unlicensed band SCell, the LAA base station performs CCA (or eCCA) for the first unlicensed band SCell and monitors whether channel occupancy is possible for the channel of the first unlicensed band SCell.

The LAA base station according to an embodiment of the present invention may attempt to change a channel in every channel access or, if the load of the operating channel is not large, try to change the channel in the medium / long term according to the load of the operating channel. In this case, the carrier change may be performed quickly and efficiently without exchanging messages between upper layers for carrier change.

As described above, the LAA base station according to an embodiment of the present invention can stably occupy a channel before data transmission is actually performed by transmitting a reservation signal when occupying a channel of an unlicensed band through the CCA. In addition, real channel occupancy time can be maximized through slot data transmission. In addition, when a plurality of unlicensed band carriers are operated, the LAA base station according to an embodiment of the present invention performs channel sensing on another unlicensed band channel simultaneously with data transmission through one unlicensed band channel. Depending on the carrier can be changed dynamically.

Referring to FIG. 21, a wireless communication system according to an embodiment of the present invention includes a base station 2110 and a terminal 2120.

The base station 2110 includes a processor 2111, a memory 2112, and a radio frequency unit (RF unit) 2113. The memory 2112 may be connected to the processor 2111 to store various information for driving the processor 2111 or at least one program executed by the processor 2111. The wireless communication unit 2113 may be connected to the processor 2111 to transmit and receive wireless signals. The processor 2111 may implement a function, process, or method proposed by an embodiment of the present invention. In this case, in the wireless communication system according to an embodiment of the present disclosure, the air interface protocol layer may be implemented by the processor 2111. The operation of the base station 2110 according to an embodiment of the present invention may be implemented by the processor 2111.

The terminal 2120 includes a processor 2121, a memory 2122, and a wireless communication unit 2123. The memory 2122 may be connected to the processor 2121 to store various information for driving the process 2121. The wireless communication unit 2123 may be connected to the processor 2121 to transmit and receive wireless signals. The processor 2121 may implement a function, step, or method proposed by an embodiment of the present invention. In this case, in the wireless communication system according to an embodiment of the present invention, the air interface protocol layer may be implemented by the processor 2121. Operation of the terminal 2120 according to an embodiment of the present invention may be implemented by the processor 2121.

In an embodiment of the present disclosure, the memory may be located inside or outside the processor, and the memory may be connected to the processor through various known means. The memory is various types of volatile or nonvolatile storage media, and for example, the memory may include read-only memory (ROM) or random access memory (RAM).

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

Claims

A channel access method of a base station for an unlicensed band,

Performing at least one channel sensing on the channel of the unlicensed band in a channel sensing period of a frame, and

If the channel is empty, broadcasting a reservation signal for the channel

Channel access method comprising a.
In claim 1,

The broadcasting step,

If a next subframe does not start immediately after the channel sensing, broadcasting a reservation signal until the start of the next subframe;

The channel access method comprising a.
In claim 1,

The broadcasting step,

If a next downlink pilot time slot (DwPTS) does not start immediately after the channel sensing, broadcasting a reservation signal until the start of the next DwPTS;

The channel access method comprising a.
In claim 1,

The channel sensing period includes at least one subframe, and the time length of the subframe is an integer multiple of the channel sensing time of the channel sensing.
In claim 1,

Performing the channel sensing,

Performing the channel sensing based on an energy detect method

The channel access method comprising a.
In claim 1,

In the transmission period of the frame, starting data transmission to the terminal

Channel access method further comprising.
In claim 1,

The frame further includes a dormant period that does not occupy the channel after the transmission period.
In claim 7,

The time length of the idle interval is 5% or more of the time length of the transmission interval.
In claim 1,

Prior to performing the channel sensing, transmitting a request message requesting a radio channel access parameter to a server of a system including the base station or a first base station using a licensed band frequency; and

Receiving a response message from the server or the first base station, the response message including the radio channel access parameter;

Channel access method further comprising.
In claim 9,

The radio channel access parameter includes information on the time sensing of the channel sensing, the transmission period and the idle period included in the frame.
In claim 9,

Determining whether a change of the radio channel access parameter is necessary while providing a data service to a terminal based on the radio channel access parameter;

Transmitting a change request message of the radio channel access parameter to the server or the first base station when the change of the radio channel access parameter is necessary; and

Receiving a response message from the server or the first base station in response to the change request message, the new radio channel access parameter being included;

Channel access method further comprising.
A base station performing channel access for an unlicensed band,

At least one processor,

Memory, and

Wireless communication unit

Including,

The at least one processor executes at least one program stored in the memory,

Performing at least one channel sensing on the channel of the unlicensed band in a channel sensing period of a frame, and

If the channel is empty, broadcasting a reservation signal for the channel

Base station to perform.
In claim 12,

When the at least one processor performs the broadcasting,

If a next subframe does not start immediately after the channel sensing, broadcasting a reservation signal until the start of the next subframe;

Base station to perform.
In claim 12,

When the at least one processor performs the broadcasting,

If a next downlink pilot time slot (DwPTS) does not start immediately after the channel sensing, broadcasting a reservation signal until the start of the next DwPTS;

Channel access method.
In claim 12,

The channel sensing period includes at least one subframe, the time length of the subframe is an integer multiple of the channel sensing time of the channel sensing.
In claim 12,

When the at least one processor performs the step of performing the channel sensing,

Performing the channel sensing based on an energy detect method

Base station to perform.
In claim 12,

The at least one processor executes the at least one program,

In the transmission period of the frame, starting data transmission to the terminal

The base station to perform more.
In claim 12,

The frame further includes a rest period not occupying the channel after the transmission period.
The method of claim 18,

The time length of the idle period is 5% or more of the time length of the transmission interval.
In claim 12,

The at least one processor executes the at least one program,

Prior to performing the channel sensing, transmitting a request message requesting a radio channel access parameter to a server of a system including the base station or a first base station using a licensed band frequency; and

Receiving a response message from the server or the first base station, the response message including the radio channel access parameter;

The base station to perform more.
The method of claim 20,

The radio channel access parameter, the base station, the base station includes information on the time length of the transmission period and the idle period included in the frame.
The method of claim 20,

The at least one processor executes the at least one program,

Determining whether a change of the radio channel access parameter is necessary while providing a data service to a terminal based on the radio channel access parameter;

Transmitting a change request message of the radio channel access parameter to the server or the first base station when the change of the radio channel access parameter is necessary; and

Receiving a response message from the server or the first base station in response to the change request message, the new radio channel access parameter being included;

The base station to perform more.
As a data transmission method of a base station,

Selecting a random number, transmitting data by occupying a wireless channel by the number of frames corresponding to the selected random number, and

Stopping channel access in the next frame after the occupancy

Data transmission method comprising a.
A method for a terminal to receive data through a channel of an unlicensed band,

Receiving a control channel on a carrier in a licensed band from a base station, and

Initiating data reception in a subframe or slot in which the control channel is received based on channel occupancy information for the channel in the unlicensed band of the base station included in the control channel;

Data receiving method comprising a.