KR20160116794A - Method for sharing frequency using time-division multiplexing in non-licensed band - Google Patents

Abstract

According to an embodiment of the present invention, a frequency sharing method through time-division multiplexing in an unlicensed band includes the steps of: determining a time-division multiplexing cycle according to an acceptable time delay; determining a length of an occupation section of a long term evolution in an unlicensed spectrum (LTE-U) system within the time-division multiplexing cycle according to a transmission request data amount of the system; and performing data transmission within the occupation section of the LTE-U system and terminating a motion within the corresponding time-division multiplexing cycle.

Description

[0001] The present invention relates to a frequency sharing method using time division multiplexing in a license-

The present invention relates to a frequency co-usage method using time division multiplexing in a license-exempted band, and more particularly, to an LTE system in which a license-exempt device such as WiFi, which uses an existing license- The present invention relates to a technique for jointly using frequencies through multiplexing.

Recently, LTE-unlicensed spectrum (LTE-U) technology is getting popular in 3GPP (3 ^rd Generation Partnership Project). The conventional LTE system operated only in the licensed band, but as the necessity of using the license-exempted band of the LTE system becomes higher due to the lack of the frequency, discussions about this have actively been conducted mainly by Qualcomm et al.

In order to utilize the license-exempted band, LTE system should solve the problem of coexistence with license-exempt devices operating in the conventional license-exempt band, and coexistence with the WiFi system, which is a typical license-exemption device, is becoming the biggest issue.

If the available channels in the license-exempted band are sufficient, the LTE system and the WiFi can solve the coexistence problem by using different channels. However, if there is a lack of available channels and LTE system and WiFi coexist in the same channel, Do.

As a solution to this problem, time division multiplexing is generally considered. This is a method in which a plurality of systems use frequencies in common by utilizing different time resources within the same frequency channel. Meanwhile, in this time division multiplexing scheme, there is a need for an additional method for ensuring smooth frequency sharing in the license-exempt band and guaranteeing the QoS of the LTE-U system.

In the embodiment of the present invention, considering the QoS of the LTE system when allocating time resources for LTE and WiFi systems, time-division multiplexing is performed in a license-exempt band where frequency can be efficiently used jointly while maximizing gain according to utilization of license- Frequency co-use method.

The technical problems of the present invention are not limited to the above-mentioned technical problems, and other technical problems which are not mentioned can be understood by those skilled in the art from the following description.

The method of frequency co-usage through time division multiplexing in a license-exempt band according to an embodiment of the present invention includes: determining a time division multiplexing period in accordance with an allowable time delay of the system; Determining a length of an occupancy period of the LTE-U system in the time division multiplexing period according to an amount of transmission request data of the system; And performing data transmission within the LTE-U system occupation interval and terminating the operation within the corresponding time division multiplexing period.

This technology satisfies QoS of LTE-U system by using time division multiplexing method according to requirements of LTE-U system when using frequency coexistence in license-exempt band between LTE-U system and WiFi, and coexistence in WiFi and license- Can be effectively performed.

1 is a diagram illustrating an example of frequency sharing using time division multiplexing of an LTE-U system and a WiFi system according to an embodiment of the present invention.
FIGS. 2A and 2B are diagrams for explaining variable allocation of a time division multiplexing period according to an allowable time delay of an LTE-U system according to an embodiment of the present invention.
3A and 3B are diagrams illustrating variable allocation of an LTE-U system occupation interval according to a data transmission request amount of the LTE-U system according to an embodiment of the present invention.
4A and 4B are views illustrating an example of resource usage of LTE-U when WiFi resources are not used in a time division multiplexing period according to an embodiment of the present invention.
5A and 5B are diagrams illustrating an LTE-U channel preemption interval for changing to an LTE-U system occupancy period in a WiFi system occupancy period according to an embodiment of the present invention.
6 is a flowchart illustrating a method of allocating a time division multiplexing period and an LTE-U occupied interval length according to system requirements according to an embodiment of the present invention.
7 is a flowchart illustrating a channel occupancy and utilization method of the LTE-U system according to WiFi channel occupancy characteristics according to an embodiment of the present invention.

Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference symbols as possible even if they are shown in different drawings. In the following description of the embodiments of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the difference that the embodiments of the present invention are not conclusive.

In describing the components of the embodiment of the present invention, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. Also, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the relevant art and are to be interpreted in an ideal or overly formal sense unless explicitly defined in the present application Do not.

The present invention proposes a frequency co-usage method using a time division multiplexing scheme between a license-exempt device such as an LTE-U system and a WiFi in a license-exempted band. When a conventional scheduling-based LTE-U system using licensed bands intends to utilize the license-exempted band, a time division multiplexing scheme is considered for common use with license-exempt band devices. This means that LTE occupancy period and WiFi The system occupies the time interval and uses it for each system. In the present invention, a method of determining the time division multiplexing period and the length of the LTE occupation interval in the time division multiplexing scheme according to the system requirements of the LTE is proposed.

Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 to 7. FIG.

1 is a diagram illustrating an example of frequency sharing using time division multiplexing of an LTE-U system and a WiFi system according to an embodiment of the present invention.

When LTE and WiFi use the same channel in the license-exempt band, scheduling-based LTE systems generally have priority over competing WiFi. In case of WiFi, CSMA / CA (Carrier Sensing Multiple Access with Collision Avoidance) includes functions for common use of license-exempted bands, such as when the current channel is occupied by another system. On the other hand, the scheduling-based LTE system transmits data during the operation of the WiFi because it carries out data transmission according to the scheduling of the system itself regardless of the operation of the other system. In this case, the performance of the WiFi deteriorates seriously.

In order to solve such a coexistence problem, a method for guaranteeing that the WiFi can use the corresponding time without using the corresponding channel for a specific time in the LTE-U system is shown in FIG.

Referring to FIG. 1, LTE-U system utilizes LTE-U time interval for communication of LTE-U system and WiFi is not used for WiFi. In this case, the time until LTE-U uses channel once, yields channel usage to WiFi, and LTE-U uses channel is called time division multiplexing period.

In one time division multiplexing period, the channel occupancy number 1 of the LTE-U system and the occupation number 1 of the WiFi system are basically considered, and a switching interval for channel occupancy conversion between the two systems is included. On the other hand, the length of the time occupied period of LTE-U and WiFi in one time division multiplexing period is variable.

The present invention relates to a method for determining a time division multiplexing period and an LTE-U system occupation interval in a frequency cooperative method using time division multiplexing as shown in FIG.

The most important factor in determining the time division multiplexing period is the allowable time delay of the LTE-U system. When the time division multiplexing period is large, the maximum length of the time interval that can be occupied by the LTE-U system at one time increases, but the length of the time interval for making concessions to other systems may also increase. Therefore, in determining the time division multiplexing period, Should be considered.

For example, according to the present invention, the LTE-U system can determine the time division multiplexing period according to the type of the service. For example, when providing a time delay sensitive service such as a video streaming service, the time division multiplexing period can be shortened to guarantee the QoS of the user. On the other hand, when real-time service provision is not required, such as simple data downloading, the time division multiplexing period is lengthened, and unnecessary channel occupancy fluctuation between LTE-U and WiFi is minimized so that the license-exempted bandwidth can be efficiently utilized.

FIGS. 2A and 2B are diagrams for explaining variable allocation of a time division multiplexing period according to an allowable time delay of an LTE-U system according to an embodiment of the present invention. That is, FIG. 2A shows an allocation example when the allowable time delay of the LTE-U system is short, and FIG. 2B shows an allocation example when the allowable time delay of the LTE-U system is long.

Referring to FIG. 2A, when the allowable time delay of the system is short, the time division multiplexing period is shortened to satisfy the service requirement of the LTE-U system. On the other hand, referring to FIG. 2B, when the allowable time delay of the system is long, the time division multiplexing period is set to be long to satisfy the service requirement of the LTE-U system while minimizing the frequency of channel occupancy switching between the LTE- Thereby increasing the channel use efficiency.

The time division multiplexing period T from the viewpoint of satisfying the service requirement of the LTE-U system can be defined as Equation 1 below.

Where dmin is the maximum allowable time delay of the system. In order to minimize the resource loss due to the channel occupancy switching between LTE-U and WiFi in addition to Equation (1) above, dmin = T. Therefore, the time division multiplexing period T can be set equal to dmin as an example of the present invention.

On the other hand, it is necessary to consider the length of the occupancy period of the LTE-U system in the time division multiplexing period. The parameter to be considered in determining the occupied interval length of the LTE-U system in the time division multiplexing period is the amount of data to be transmitted in the LTE-U system.

When the amount of data that the LTE-U system needs to transmit through the license-exempt band is determined, the amount of time resources required to transmit it can be calculated. For example, when transmitting data such as simple text, there is no problem in service provision even if the time occupied period of the LTE-U system is short, but when there is a large amount of data to be transmitted such as an image or a moving image, It needs to be long.

3A and 3B are diagrams illustrating variable allocation of an LTE-U system occupation interval according to a data transmission request amount of the LTE-U system according to an embodiment of the present invention. That is, FIG. 3A shows an allocation example in a case where LTE-U system transmission request data is large, and FIG. 3B shows an allocation example in a case where LTE-U system transmission request data is small.

Referring to FIG. 3A, when the amount of data to be transmitted in the LTE-U system is large, the LTE-U system occupancy period may be set to be long to satisfy the data transmission requirements. Referring to FIG. 3B, when the amount of data to be transmitted in the LTE-U system is small, the LTE-U system occupancy period is set to be short to satisfy the data transmission requirements, and at the same time, the WiFi system guarantees the maximum available resources.

The occupation interval K of the LTE-U in terms of data transmission requirements of the LTE-U system can be defined as Equation 2 below.

Where Rreq is the amount of data transmission that must be satisfied within the corresponding time division multiplexing period of the system and Runit is the amount of data that can be transmitted per unit of time. In addition to Equation (2) above, in order to maximize the channel occupancy time of the WiFi system from the viewpoint of frequency sharing with the WiFi system, K should be minimized, so Rreq / Runit = K. Therefore, the length of the LTE-U occupancy period in the time division multiplexing period can be set equal to Rreq / Runit.

On the other hand, we propose an efficient method in terms of channel occupancy change between LTE-U system and WiFi system. When the channel occupancy is changed from the LTE-U system to the WiFi system, when the LTE-U system performs data transmission and reception during the LTE-U system occupancy period within the corresponding time division multiplexing period and ends occupancy, the WiFi system transmits the CSMA / If you confirm that the channel is empty and use that channel, you can change the channel occupancy without any problems.

On the other hand, in the case of changing the occupancy of the channel from the WiFi system to the LTE-U system, it is difficult to know the end point of the data transmission of the WiFi system from the viewpoint of the LTE-U system and when the data transmission of the WiFi system is not finished, When the data transmission starts according to the schedule of the LTE-U system because the interval has arrived, there is an interference problem between the two systems. Therefore, it is necessary to consider additional methods.

Also, if data transmission of the WiFi system does not occur within the time division multiplexing period, a method for utilizing the resource by the LTE-U system may be considered.

First, when no data transmission occurs in the WiFi system within the time division multiplexing period, a method for utilizing the occupancy period of the WiFi system within the period will be described. Since the WiFi system uses a medium access control (MAC), it is difficult to know whether data is transmitted or not at the access point (AP) and each base station. Therefore, in case of LTE-U system, the WiFi system does not utilize the resource for the time resource allocated as the interval for the WiFi system. In this case, in order to increase the frequency resource utilization rate, the LTE-U system judges whether the WiFi system is utilized or not, so that the LTE-U system can further utilize the resource when it is not used.

4A and 4B are views illustrating an example of resource usage of LTE-U when WiFi resources are not used in a time division multiplexing period according to an embodiment of the present invention. FIG. 4A shows an example of common frequency division multiplexing based on frequency division multiplexing, and FIG. 4B shows an example of resource use of the LTE-U system when the WiFi system is not used.

Referring to FIG. 4B, the LTE-U system that has completed the data transmission using the occupancy period of the LTE-U system confirms whether the WiFi system occupation period of the WiFi system is used for a predetermined time. After determining whether the WiFi channel is used for a certain period of time, if the WiFi is not used after checking whether the WiFi channel is used, the LTE-U system can utilize the WiFi channel even if the WiFi channel is occupied.

In this case, the length of the interval for checking whether the WiFi system is used may be a maximum contention window length interval of the WiFi system. In case of WiFi system, transmission point is changed through random backoff during the competing window interval to prevent collision. If data transmission does not occur during the maximum competing window interval, it can be considered that there is no data to be transmitted from the WiFi system. The LTE-U system utilizes its resources. At this time, the LTE-U system can utilize the resources continuously with the LTE-U system occupancy period of the next time division multiplexing period.

Next, we propose an additional method for changing the occupancy of the WiFi channel to the occupancy of the LTE-U channel. In LTE-U system, it is possible to control the system to use only a given LTE-U system occupation period based on the scheduling, but it is possible to use a contention-based distributed MAC for time resource allocation between LTE-U system and WiFi system using time division multiplexing It is difficult to guarantee that only a specific time interval is actually used, and it is impossible to terminate the transmission at a predetermined time.

Therefore, in order for the LTE-U system to securely occupy the LTE-U system occupied period, the following additional method is required. 5A and 5B illustrate a method of setting an LTE-U system channel preemption interval for moving to an LTE-U system occupation interval in a WiFi system occupation interval. That is, FIG. 5A shows a case where the WiFi system data transmission ends before the LTE-U system channel preemption interval, and FIG. 5B shows a case where the WiFi system data transmission ends within the LTE-U system channel preemption interval.

The LTE-U system sets the LTE-U channel preemption interval before a certain time before the occupancy period of the LTE-U system starts. At this time, the length of the LTE-U channel preemble interval may be equal to the maximum length of the WiFi frame or one frame length in the LTE standard, and may be 10 ms.

Referring to FIG. 5A, when the actual WiFi data transmission ends before the occupancy period of the WiFi system, the LTE-U system starts occupying the channel from the LTE-U channel preemption period. In this case, the channel preemption of the LTE-U can be set after the DIFS (DCF InterFrame Space) time from the end of the actual WiFi data transmission. If the actual WiFi data transmission is terminated within the WiFi system occupancy period and the LTE-U channel occupancy period is set equal to one frame length in the LTE standard, the actual LTE-U system occupancy period is the conventional allocated LTE- And there is no problem in the operation of the system.

Referring to FIG. 5B, when the data transmission interval of the actual WiFi system exceeds the WiFi system occupation interval and reaches the LTE-U channel preemption interval, the LTE-U system continuously monitors whether WiFi channel occupation is within the corresponding interval When the channel occupancy of the WiFi is over, the channel occupancy of the LTE-U system is performed. At this time, the channel occupancy point of the LTE-U can be set after the DIFS (DCF InterFrame Space) time from the end point of the actual WiFi data transmission. This is to give the WiFi system priority to transmit Ack (Acknowledgment) message according to WiFi data transmission and to start occupying the channel of LTE-U after all data transmission / reception of WiFi system is normally completed.

In this way, when the data transmission of the WiFi system is terminated in an arbitrary section within the LTE-U channel preemble interval and the LTE-U system starts to occupy the channel, a problem of system time synchronization must be considered. As a result, , The LTE-U system can perform only a task for preempting a simple channel and perform data transmission like an LTE-U system occupied period. Whether preemption of a simple channel or data transmission is possible depends on whether the system can be time synchronized.

If the LTE-U system uses carrier aggregation technology that combines license and license-exempt bands at the same time, it can transfer the time-synchronization information of the license-exempted band through the license band, No problem occurs. Or if the LTE-U system itself can estimate the time synchronization in the license-exempted band, there is no problem in the operation of the system due to the time-synchronized reset according to the variation of the LTE-U system occupation interval. In this case, if the LTE-U occupancy period is set within the LTE-U preemption interval, the data transmission is performed and if the time synchronization can not be reconfigured, only the operation for channel preemption is performed within the LTE- Transmission is originally performed from the LTE-U system occupancy section.

Hereinafter, a method of allocating a time division multiplexing period according to LTE-U system requirements and a method of allocating an occupancy interval length of the LTE-U system according to an embodiment of the present invention will be described in detail with reference to FIG.

First, with respect to the time division multiplexing period, the LTE-U system determines a time division multiplexing period in accordance with the allowable time delay of the system (S101), and calculates the length of the occupancy period of the LTE- (S102).

Accordingly, the LTE-U system performs data transmission within a given LTE-U system occupation period and terminates the operation within the corresponding time division multiplexing period (S103).

Then, the LTE-U system determines whether the allowable time delay of the LTE-U system has changed with respect to the time division multiplexing interval (S104). If the allowable time delay has changed, the time division multiplexing period and the length of the LTE- The determination process is re-executed (S101, S102).

If the allowable time delay of the LTE-U system is the same, the LTE-U system determines whether the amount of the transmission request data of the system is changed (S105). If the allowable time delay is changed, The data transmission is performed using the same configuration as the previous time division multiplexing interval (S103).

Hereinafter, a channel occupancy and utilization method of the LTE-U system according to WiFi channel occupancy characteristics according to an embodiment of the present invention will be described in detail with reference to FIG.

The LTE-U system determines a time division multiplexing period according to the allowable time delay of the LTE-U system (S201) and determines the length of the LTE-U system occupation interval according to the amount of transmission request data of the LTE-U system (S202 ).

Within the determined time division multiplexing period, the LTE-U system determines whether the channel of the WiFi system is utilized in the WiFi system occupancy period (S203).

If it is determined in step S203 that the WiFi system does not use the corresponding channel in the WiFi system occupation period (S204), the corresponding WiFi system occupation period is used in the LTE-U system (S205).

On the other hand, if the WiFi system is using the occupation period, the channel occupancy ending point of the WiFi system is monitored (S206).

Then, the LTE-U system determines whether the data transmission of the WiFi system ends within the WiFi system occupation period (S207). If the data transmission of the WiFi system ends within the WiFi system occupation period, the LTE- The UE starts to occupy the channel using the LTE-U channel preemption interval immediately after the interval, and performs data transmission from the LTE-U channel occupation interval (S208).

On the other hand, if the data transmission of the WiFi system continues beyond the occupancy period of the WiFi system to the LTE-U preemption interval, the LTE-U system judges whether the time synchronization resetting is possible according to the time synchronization resetting or estimation of the LTE-U system (S209).

If the time synchronous resetting is possible, the data transmission of the LTE-U system is started immediately after the WiFi channel occupation termination (S210).

If the time synchronization resetting is impossible, only the channel occupation operation is performed in the LTE-U channel preemption interval and data transmission is started from the LTE-U system occupation interval (S211).

Thus, the present invention discloses a frequency co-usage method using a time division multiplexing scheme between a license-exempt device such as an LTE-U system and a WiFi in a license-exempt band. In particular, the present invention discloses a method of determining a time division multiplexing period and a length of an LTE occupation interval in accordance with a system requirement of an LTE system in the time division multiplexing system to guarantee QoS of an LTE-U system in a license- So that it can efficiently perform frequency joint use.

Although the LTE-U system and the WiFi system have been described in order to facilitate the description of the present invention, the present invention can be applied to all systems using a license-exempt band other than WiFi. It is possible to apply the present invention to a scheduling-based wireless communication system using a band. The terms and parameters used for the description of the present invention may be changed depending on the system to which the present invention is applied.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention.

Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

Claims (1)

Determining a time division multiplexing period in accordance with an allowable time delay of the system;
Determining a length of an occupancy period of the LTE-U system in the time division multiplexing period according to an amount of transmission request data of the system; And
Performing data transmission within the LTE-U system occupation interval and terminating the operation within the corresponding time division multiplexing period
A method for frequency co-use through time division multiplexing in a license-exempt band, including.

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