KR20190055541A - Method for Controlling LBT on LTE-LAA and Nobe-B thereof - Google Patents

Abstract

Disclosed is a listen before talk (LBT) control method based on a long term evolution-license assisted access (LTE-LAA). According to the present invention, an LBT control method allows a Wi-Fi channel and the LTE-LAA to share unlicensed band in a way that maximizes a bandwidth while minimizing mutual interference by adjusting a threshold value adaptively according to an LTE data occupancy rate without fixing the threshold value of a reception signal used for carrier sensing.

Description

[0001] The present invention relates to an LTE-LAA based LBT control method,

The present invention relates to a carrier sensing method for an LBT between an LTE-LAA and a WiFi, and more particularly, to an LBT control method for adjusting a threshold value of a received signal strength, which is a reference for carrier sensing adaptively according to a license-exempt band occupancy rate between LAA and WiFi .

Since the frequency resources are limited, the lack of frequency resources is already a normal situation. Currently, LTE (Long Term Evolution) mobile communication service uses so-called "license band" which is authorized as exclusive channel for LTE. However, since the traffic of mobile communication network continues to increase, Traffic becomes increasingly difficult to afford.

However, since it is necessary to pay a considerable fee to obtain a new frequency band as an additional license, efforts have been made to make use of the license-free band that can be used free of charge with mobile network equipment manufacturers of multinational companies. As a result, LTE-U (LTE-Unicensed Spectrum) and LTE-LAA (LTE-UA) that aggregate frequencies of license-denied and licensed bands under the name of Licensed-assisted Access (LAA) in 3rd Generation Partnership Project (3GPP) -Assisted Access) technology has been proposed. The problem is that the license-exempt band used by the LTE camp is 5 ㎓, which is already used by wi-fi.

The difference between LLTE-U and LTE-LAA is to perform a Listen Before Talk (LBT) process for carrier sensing. The LTE-LAA performs LBT. The LAA uses the LTE license band as an anchor and bundles the licensed and license-exempted bands together using Carrier Aggregation (CA) technology. In the LTE-LAA, the terminal always uses the service by accessing the network with the license band. Instead, the base station offloads the traffic of the license band to the license-exempt band by combining the licensed band and the license- do. At this time, the license band is referred to as a primary cell (PCell), and the license-exempted band is referred to as a secondary cell (SCell). Even if the traffic is divided by offloading, the system control information is provided to the primary channel, and only the user data is provided to the secondary channel which is the license-exempt band. The secondary cell is a license-exempt band that also uses other wireless devices such as wi-fi, and thus has a disadvantage that the channel state is not relatively excellent.

On the other hand, for the Listen Before Talk (LBT) protocol, the LAA performs sensing for the same frequency channel. When the wireless signal of the license-exempted band is detected through the frequency sensing, it is determined that the license-exempted band is occupied by another wireless signal, and the LTE data is not transmitted. Since frequency sensing measures the strength (RSSI) of the radio signal received in the corresponding license-exempted band and actually measures the strength of the output signal of the WiFi AP (Access Point) with the RSSI of the received signal, There is a problem that it is difficult to judge how much the WiFi service terminal is interfered with without considering the location or channel state of the WiFi service terminal in the LBT.

In a situation where interference occurs, it is difficult to set the threshold value of the strength of the received signal as a reference for sensing a wireless signal (WiFi signal) to be one in various environmental conditions. Interference between signals is greatly affected by the channel status of the UE. When the threshold value of the received signal strength (reception sensitivity) for LTE-OFF (termination of transmission of LTE data) is increased, the LAA transmission cycle is increased, Lt; / RTI > increases. If the channel state of the terminal is not good, the transmission period of the WiFi is also short and the probability of interference increases, which adversely affects the existing WiFi service and causes the advantage of the LBT to deteriorate. Conversely, lowering the threshold for received signal strength for LTE-OFF will reduce the probability of interfering with the WiFi channel, but it will reduce the opportunity for LAA transmission, which may reduce the use of license-exempt bandwidth through the LAA compared to WiFi.

Since the LBT detects the output signal of the WiFi AP instead of the channel status of the actual WiFi terminal and measures the strength of the received signal, the received signal strength is determined by the mutual position of the LAA small cell and the WiFi AP, The position or distance between the WiFi service terminal where the actual interference occurs and the WiFi AP is not considered. If the WiFi service terminal has a weak electric field, the amount of data transmitted by the WiFi AP is small. Therefore, there is an opportunity to transmit more data through the license-exempted band of the LAA, . That is, the WiFi terminal of weak electric field has a possibility of further performance deterioration due to the LBT operation. Conversely, if the receiver sensitivity is set low to compensate for performance degradation in the weak electric field, the possibility of detecting the WiFi signal is increased, so the utilization of the license-exempted band is inevitable even though the channel state is good.

[Related Prior Art]

Korean Patent Publication No. 10-2016-0138556 (devices and methods for searching and using neighbor WLAN information for LTE LAA operation)

The present invention relates to a method for requesting information on a license-exempt band from a terminal for LAA operation.

An object of the present invention is to provide a carrier sensing method for LBT between LTE-LAA and WiFi, which is an LBT control method for adjusting a threshold value of received signal strength that is a reference of carrier sensing adaptively according to the license- .

In order to solve the above problem, the present invention is based on the fact that the utilization frequency of the same frequency band is equalized regardless of the channel state of the WiFi service terminal, so that the LAA can exhibit efficient performance in a state coexisting with WiFi, We propose a method to adjust the threshold of received signal strength by comparing the LAA occupancy and the WiFi occupancy for the license - exempted band.

The present invention relates to a method of controlling a Listen Before Talk (LBT) based on an LTE-LAA, and more particularly, to a method of controlling an LBT (Listen Before Talk) Determining that the secondary channel is usable as a secondary channel; The base station apparatus calculating an LTE occupancy rate of the license-exempt zone; The base station apparatus compares the LTE occupancy with the occupancy rate of the other wireless services to control the LTE occupancy ratio to be higher by raising the threshold when the occupancy rate of the LTE occupancy is low and lower the threshold value when the occupancy rate of the LTE is high, And controlling the occupancy rate to be low.

The step of calculating the LTE occupancy rate may further include comparing the time when the base station device transmits the LTE data with the license-exempted bandwidth to the secondary channel and the time when the wireless signal using the license-exempted bandwidth is sensed, Can be calculated.

Further, in the step of calculating the LTE occupancy rate, the time required for carrier sensing for the LBT operation may be determined as the time when another radio signal using the license-exempted band is sensed.

According to another embodiment, the step of calculating the LTE occupancy rate may be performed at a predetermined time period, and the occupancy rate of the ELT may be calculated as the time occupied by the LAA at the predetermined time.

The present invention is also applicable to a base station apparatus that performs an LBT (Listen Before Talk) control method based on the LTE-LAA to adaptively control the LTE occupancy in the license-exempt band.

According to the present invention, when the occupancy rate of the LAA for the license-exempted band is low, the occupancy rate of the LAA is increased by raising the threshold of the received signal strength, and when the occupancy rate of the LAA for the license- To reduce the LAA's share of the WiFi channel.

Therefore, LTE-LAA license-exempt band and WiFi channel band are most efficient regardless of the channel state of the WiFi service terminal, as compared with a conventional WiFi AP signal measurement method, in which the band is minimized while minimizing interference. You can coexist.

FIG. 1 is a block diagram of a channel between a mobile communication base station and a mobile communication terminal according to the present invention.
2 is a flow chart provided in the description of the adaptive reception sensitivity control method for the LBT of the present invention, and
3 is an exemplary diagram illustrating an LTI based on an LBT in a license-exempt band and a WiFi occupation state.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to the drawings.

Referring to FIG. 1, the mobile communication base station apparatus 110 according to the present invention includes a primary cell 110a and a secondary cell 110b. The primary cell 110a is a license band and the secondary cell 110b is a license- And is connected to the communication terminal 130.

Here, the primary cell 110a and the secondary cell 110b are classified from the viewpoint of the mobile communication base station apparatus 110, and the primary cell 110a is dedicated to a radio channel conforming to the LTE protocol Means a cell or its radio channel that uses a licensed frequency band for use.

The secondary cell 110b is a cell or its radio channel using a license-exempt frequency band that has never been permitted to be dedicated to a specific radio channel. Since the license-exempt band is not licensed to be used exclusively on a specific radio channel, other radio channels as well as mobile communications may be used. For example, the 5 ㎓ band is a license-exempt band and is the band that WiFi uses first. The following description will be made by taking the 5 GHz band as an example. It is assumed that the secondary cell 110b is activated together with the primary cell 110a by carrier aggregation performed by the base station apparatus 110 and does not process the LT traffic by itself.

1, the LBT senses an output signal of a WiFi AP (Access Point) 10, not a channel state of a real WiFi terminal, and measures a strength of a received signal, And the position or distance between the WiFi service terminal 150 and the WiFi AP 10 where actual interference occurs are not considered. Therefore, there is a problem that the share of WiFi between Elite and WiFi in the license-exempted band is not distributed equally. However, as described below, the base station apparatus 110 of the present invention adjusts the LBT reception sensitivity (the threshold value of the received signal strength) adaptively according to the rate of occupation of the data, thereby minimizing mutual interference, Wifi channels and LTE-LAAs can share a license-exempt spectrum.

Hereinafter, a method of adjusting the threshold value of the adaptive received signal strength of the present invention will be described with reference to FIGS. 2 and 3, focusing on the operation of the base station apparatus 110. FIG.

<Periodically calculating the eleti share per unit time of the license-exempt zone: S201>

The base station apparatus 110 calculates 'terminal occupancy per unit time' in the license-exempt band in a predetermined unit time period in order to adaptively adjust the threshold of the received signal strength as a reference for carrier sensing in the license-exempt band.

Eltie's share is the time that Eltie occupied the license-exempt zone for a unit of time. Here, the unit time can be set arbitrarily, and can be set to, for example, 1 second (sec) or 2 seconds. As described below with reference to FIG. 3, the secondary cell 110b, which is the license-exempt band, is filled with the time occupied by the LTE, the idle time, and the time occupied by the other wireless channel. Other wireless channels include all wireless signals except LTE using the license-exempt band including WiFi. Hereinafter, WiFi will be described as an example.

Here, since the time occupied by the LTE exists only in the downlink data physical channel (PDSCH) in the secondary cell in the LAA protocol, the physical layer (PHY) of the base station device 110 determines the scheduled time of the PDSCH physical channel , Which is the time occupied by transmitting and receiving the Ethernet data packet through the OO license exemption zone.

On the other hand, the WiFi share corresponding to the ELT occupancy is the time when another wireless signal (e.g., WiFi) occupies the license-exempted band for a unit time. The time when the WiFi occupies the license-exempted band is a time when the WiFi transmits data, and it is difficult for the base station device 110 to directly obtain the time. However, because WiFi performs frequency sensing before data transmission, WiFi does not transmit data during ELT data transmission. Therefore, it is possible to regard as a WiFi occupation time a time period during which the LBT does not transmit the eld data during a back-off period. Therefore, the base station apparatus 110 can check the time occupied by the WiFi by querying the physical layer (PHY) and inquiring the time that it has not been able to transmit the latency data and is waiting (Back-Off).

FIG. 3 schematically shows the occupancy of the secondary cell 110b. The transmission period t1 in which the LT data is transmitted is displayed as a blank space, and the frequency sensing period t2 in which frequency sensing occurs is indicated by a hatched And an idle section where there is no LT data transmission is marked by a dot. One cell can be regarded as an LTE scheduling period of 1 ms (0.001 second).

The transmission of the LT data through the secondary cell 110b does not always occur but occurs when a certain condition (for example, when the throughput of the terminal is equal to or larger than a predetermined size) is satisfied. At this time, if the strength of the WiFi signal received through the carrier sensing is less than the adaptively adjusted threshold, the base station apparatus 110 activates the secondary cell 110b and transmits the LT data. If the LAA does not need to occupy the secondary cell 110b, it enters the idle period.

When there is EL data to be transmitted through the secondary cell 110b, the LAA physical layer PHY of the base station device 110 first senses the secondary cell 110b through the LBT operation, and the WiFi signal is transmitted to the secondary cell 110b. If it does not occupy the data, it immediately transmits the data. However, if the WiFi signal occupies the secondary cell 110b, the base station device 110 waits (back-off) and tries again to sense the carrier. As a result of repeated frequency sensing, when the WiF signal is not detected in the secondary cell 110b beyond the threshold value, the base station apparatus 110 transmits the LT data again.

Here, since the transmission period t1 is the time occupied by the LTE and the sensing period t2 is the time occupied by the WiFi, the base station apparatus 110 transmits the terminal occupancy time for a predetermined period (for example, one second) Can be cumulatively calculated.

&Lt; Threshold adjustment according to the occupancy rate of the license-exempt zone: S203 to S207 >

The base station apparatus 110 compares the ELAME occupancy rate and the WiFi occupancy rate calculated in step S201. In other words, the elite occupancy time is compared with the WiFi occupation time for a unit time (S203). If the LTI occupancy rate is smaller than the WiFi occupancy rate, the LTI occupancy rate is increased (S205). If the LTI occupancy rate is larger than the WiFi occupancy rate, the threshold value is lowered to lower the LTI occupancy rate (S207) Adjust the threshold adaptively.

The following Table 1 shows the occupancy rate in the conventional coexistence state of LTE and WiFi, and Table 2 shows the occupancy rate when the threshold value is adjusted by the present invention. Here, the LTE occupancy rate is calculated by taking the sum of LTE occupation time and WiFi occupation time as 100%, and idle time is not considered.

WiFi AP
Received signal strength
Threshold RSSI of WiFi terminal LTE Share (%) WiFi Share (%) - 50dBm
Powerful system (-55dBm) 50 50 Weak electric field (-75 dBm) 80 20 - 90dBm
Powerful system (-55dBm) 20 80 Weak electric field (-75 dBm) 50 50

WiFi AP
Received signal strength
Threshold RSSI of WiFi terminal LTE Share (%) WiFi Share (%) According to market share
Threshold adjustment

- 50dBm to -90dBm Powerful system (-55dBm)
50
50 Weak electric field (-75 dBm)

Referring to Table 1, it can be seen that the occupancy rate is biased toward one side according to the reception sensitivity (threshold value). However, if the threshold is adjusted adaptively according to the present invention, it can be seen that the ELTI occupancy rate and the WiFi occupancy rate are equally distributed.

The method of the present invention is carried out in the above manner. According to the present invention, LTE and WiFi can ideally coexist by dividing the license-exempted bandwidth fairly in terms of time sharing.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be construed as limiting the scope of the invention as defined by the appended claims. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention.

Claims (5)

A method of controlling a Listen Before Talk (LBT) based on an LTE-LAA,
Detecting a received signal strength of a license-exempted band and determining that the license-exempted band is usable as a secondary channel if the received signal strength is below a preset threshold;
The base station apparatus calculating an LTE occupancy rate of the license-exempt zone; And
The base station apparatus compares the LTE occupancy with the occupancy rate of the other wireless services to control the LTE occupancy ratio to be higher by raising the threshold when the occupancy rate of the LTE occupancy is low and lower the threshold value when the occupancy rate of the LTE is high, And controlling the occupancy rate of the LBT to be lowered.
The method according to claim 1,
Wherein calculating the LTE occupancy comprises:
And the LTE occupancy rate is calculated by comparing the time when the base station device transmits the LTE data with the license-exempted band to the secondary channel and the time when the other wireless signal using the license-exempted band is sensed. Control method.
3. The method of claim 2,
Wherein the time required for carrier sensing for the LBT operation is determined as a time when another radio signal using the license-exempted band is sensed in the step of calculating the LTE occupancy rate.
The method according to claim 1,
Wherein the step of calculating the LTE occupancy rate is performed at a predetermined time period, and the occupancy rate of the LTI is calculated as the time occupied by the LAA at the predetermined time, .
The base station apparatus according to claim 1, wherein the base station apparatus performs an LBT (Listen Before Talk) control method based on the LTE-LAA to adaptively control the terminal occupancy in the license-exempt band.

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