KR102042835B1 - Method and Apparatus for Small Cell Synchronization Based on the Precision Time Protocol and Network Listening - Google Patents

Abstract

A synchronization method in a small cell is provided. The method includes correcting a system clock time of the small cell by performing a Precision Time Protocol (PTP) Time of Day (TOD) procedure, and calculating a Network Listening (NL) start time based on the corrected system clock time. And re-calibrating the corrected system clock time by performing an NL at the NL start time.

Description

Method and Apparatus for Small Cell Synchronization Based on the Precision Time Protocol and Network Listening}

The present invention relates to a technique for synchronizing a small cell, and more particularly, to a technique for correcting a clock time of a small cell based on a Precision Time Protocol (PTP) and a Network Synchronization (NL).

Recently, a radio access network has a relatively small sized macro cell such as a micro cell, a pico cell, a femto cell, and the like. By interworking with the macro cell, it is evolving to improve service quality and expand coverage. A small cell, which is a small mobile communication base station, is a low-power wireless access node, which has a relatively narrower service area than a general cell, and is similar to a DSL modem to connect to a wired IP network in a home so that users can freely use wired and wireless communication with a terminal such as a mobile phone. Do it.

One of the basic requirements for a small cell, particularly a small cell based on a TDD system, to operate as a small mobile base station is frequency and time synchronization with the macro base station. As one of such synchronization methods, the IEEE 1588 Precision Time Protocol (PTP) is known. According to PTP, for example, a PTP slave, such as a small cell, receives periodic Sync messages sent from a PTP master (master server) and also sends and sends Delay Request messages as a response. Receive delay response messages from the PTP master. The PTP slave performs clock frequency and time synchronization by estimating clock frequency error and clock time error by applying an averaging method to delay times of sink messages and delay times of delay request messages. The estimation method using averaging has a problem in that it is difficult to provide accurate estimation results due to asymmetric delay, that is, packet delay variation (PDV) of the network. Using a boundary clock or transparent clock that supports PTP over Ethernet or optical networks can reduce synchronization estimation errors due to different delays in the uplink and downlink. However, it is difficult to meet the requirement of 1.5 microseconds in the LTE Long Term Evolution Time Division Duplex (TDD).

Another known synchronization method is a synchronization method by NL (Network Listening). According to this method, a small cell receives a synchronization signal from a base station (macro cell, etc.) that has already been synchronized to extract timing synchronization and frequency synchronization. Synchronization method using NL can estimate time error more accurately than PTP, but if macro base station and small cell serve in the same frequency band, it may be impossible to synchronize due to interference of macro base station signal. have.

An object of the present invention is to provide a small cell synchronization method and apparatus in which synchronization accuracy is improved by performing NL in an environment in which interference from neighboring cells is minimized.

The problem to be solved by the present invention is not limited to the above-mentioned problem, another task that is not mentioned will be clearly understood by those skilled in the art from the following description.

In one aspect, a synchronization method in a small cell is provided. The method includes correcting a system clock time of the small cell by performing a Precision Time Protocol (PTP) Time of Day (TOD) procedure, and calculating a Network Listening (NL) start time based on the corrected system clock time. And re-calibrating the corrected system clock time by performing an NL at the NL start time.

In one embodiment, correcting the system clock time of the small cell may be performed when the small cell is powered on.

에 따라 NL 시작 시간을 계산하는 단계 - 여기서 N은 NL 동기 수행 주기를 나타내는 1 이상의 정수이고,

는

보다 크지 않은 최대의 정수를 나타내고, T_{NL_start}는 NL 시작 시간을 나타내고, T_{NL_start_offset}은 사용자가 설정하는 시작 시간 옵셋으로서 0과 같거나 그 보다 크고 1보다 작은 임의의 수임 - 를 포함할 수 있다.In one embodiment, the step of calculating the NL start time is as follows:

Calculating an NL start time according to N, wherein N is an integer equal to or greater than 1 indicating an NL synchronization period, and

Is

T _{NL_start} represents an NL start time, and T _{NL_start_offset} is a start time offset set by the user, which may be any number greater than or equal to 0 and less than 1.

T_{sys_cur} < N * m + 1 (여기서 m은 0 이상의 정수임)]을 만족하는 시간(T_{sys_cur})에서 상기 NL 시작 시간을 계산하는 단계를 포함할 수 있다.In one embodiment, calculating the NL start time comprises the following conditions [N * m

Calculating the NL start time at a time T _{sys_cur} that satisfies T _{sys_cur} < N * m + 1, where m is an integer greater than or equal to 0.

In one embodiment, performing the NL at the NL start time to recalibrate the corrected system clock time may include receiving a macro base station signal for 20 msec from the NL start time.

In one embodiment, the macro base station signal received for 20msec from the NL start time may include at least one frame.

In one embodiment, performing the NL at the NL start time to recalibrate the corrected system clock time may include discontinuing service for at least 20 msec from the NL start time.

In one embodiment, performing the NL at the NL start time to re-calibrate the corrected system clock time may be performed using the following equation [(1) T _offset '= T _{Frame_start} -T _{NL_start} , (2) T _{sys_cur} ← T _{sys_cur} -T _offset ', if T _offset '<5msec; _Re -correcting the corrected system clock time according to T _{sys_cur} ← T _{sys_cur} -T _offset '+ 10 msec, else] _-where T _offset ' represents the system clock time offset of the small cell, and T _{Frame_start} is the small cell May be a start time of the at least one frame of the macro base station signal at a reference of T _{NL_start} is an NL start time and T _{sys_cur} indicates a current clock time of the small cell.

In one embodiment, the method may further comprise repeating calculating the NL start time and re-calibrating the corrected system clock time for every NL synchronization period.

In another aspect, an apparatus for performing synchronization in a small cell is provided. The apparatus includes a PTP time synchronizer configured to perform a PTP TOD procedure to correct a system clock time of the small cell, an NL start time calculator configured to calculate an NL start time based on the corrected system clock time, and the And an NL synchronizer configured to perform NL at an NL start time to re-calibrate the corrected system clock time.

In one embodiment, the PTP time synchronizer may be further configured to correct the system clock time of the small cell by performing the PTP TOD procedure when the small cell is powered on.

에 따라 NL 시작 시간을 계산하도록 더 구성될 수 있다. 여기서 N은 NL 동기 수행 주기를 나타내는 1 이상의 정수이고,

는

보다 크지 않은 최대의 정수를 나타내고, T_{NL_start}는 NL 시작 시간을 나타내고, T_{NL_start_offset}은 사용자가 설정하는 시작 시간 옵셋으로서 0과 같거나 그 보다 크고 1보다 작은 임의의 수이다.In one embodiment, the NL start time calculation unit is the following formula

And may be further configured to calculate the NL start time according to. Where N is an integer greater than or equal to 1 indicating an NL synchronization period,

Is

T _{NL_start} represents the NL start time, and T _{NL_start_offset} is a user-set start time offset that is any number greater than or equal to zero and less than one.

T_{sys_cur} < N * m + 1 (여기서 m은 0 이상의 정수임)]을 만족하는 시간(T_{sys_cur})에서 상기 NL 시작 시간을 계산하도록 더 구성될 수 있다.In one embodiment, the NL start time calculation unit is a condition [N * m

The NL start time may be further calculated at a time T _{sys_cur} that satisfies T _{sys_cur} <N * m + 1 where m is an integer greater than or equal to zero.

In one embodiment, the NL synchronizer may be further configured to receive a macro base station signal for 20 msec from the NL start time.

In one embodiment, the macro base station signal received for 20msec from the NL start time may include at least one frame.

In one embodiment, the NL synchronizer may be further configured to stop service for at least 20 msec from the NL start time.

In one embodiment, the NL synchronizer is represented by the following equation: (1) T _offset '= T _{Frame_start} -T _{NL_start} , (2) T _{sys_cur} ← T _{sys_cur} -T _offset ', if T _offset '<5 msec; T _{sys_cur} ← T _{sys_cur} − T _offset '+ 10 msec, else] may be further configured to correct the corrected system clock time again. T _offset 'represents a system clock time offset of the small cell, T _{Frame_start} is the start time of the at least one frame of the macro base station signal at the reference of the small cell, T _{NL_start} is NL start time, T _{sys_cur} represents the current clock time of the small cell.

In another aspect, a synchronization method in a small cell is provided. The method includes performing a PTP TOD procedure to correct a system clock time of the small cell, and performing an NL for a period from an NL start time to an NL end time to recalibrate the corrected system clock time. It may include. Recalibrating the corrected system clock time may include receiving a macro base station signal during the interval, not transmitting a small cell frame during the interval, and not receiving a signal from another small cell during at least a portion of the interval. May include steps that do not.

In one embodiment, the NL end time may be a time elapsed from 20msec from the NL start time.

In one embodiment, the method may further include calculating the NL start time based on the corrected system clock time after correcting the system clock time of the small cell.

In one embodiment, the method may further include repeating calculating the NL start time and recalibrating the corrected system clock time for every NL sync performance period.

According to embodiments of the present invention, there is a technical effect of improving the accuracy of the NL synchronization by performing the NL in an environment in which interference from neighboring cells is minimized.

1 is a diagram illustrating an embodiment of a network configuration in which small cells are wirelessly connected to a macro base station and a PTP master to obtain synchronization according to embodiments of the present invention.
FIG. 2 is a diagram illustrating an embodiment of a configuration block diagram of a small cell synchronization device mounted in the small cell of FIG. 1.
FIG. 3 is a flowchart illustrating an embodiment of a method of acquiring synchronization based on PTP and NL in a small cell.
4 is a diagram illustrating a PTP TOD procedure in which a small cell as a PTP slave performs clock synchronization with a PTP master by exchanging messages with the PTP master according to the PTP protocol.
FIG. 5 is a diagram illustrating performing NL synchronization and stopping service for 20 msec from NL start time in small cells when macro base station frames are transmitted from the macro base station.
6 and 7 are diagrams for describing a method of compensating for a time error in a small cell under the assumption that n in FIG. 5 is 1.

Advantages and features of the present invention and a method of accomplishing the same will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms, and the present embodiments merely make the disclosure of the present invention complete and have ordinary skill in the art to which the present invention pertains. It is provided to fully inform the scope of the invention, and the invention is defined only by the scope of the claims.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. For example, a component expressed in the singular should be understood as a concept including a plurality of components unless the context clearly indicates only the singular. In addition, in the specification of the present invention, terms such as 'comprise' or 'have' are merely intended to designate that the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification exist. The use of the term does not exclude the possibility of the presence or addition of one or more other features or numbers, steps, operations, components, parts or combinations thereof. In addition, in the embodiments described herein, 'module' or 'unit' may refer to a functional part performing at least one function or operation.

In addition, all terms used herein, including technical or scientific terms, unless otherwise defined, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be interpreted as having meanings consistent with the meanings in the context of the related art, and should be interpreted in ideal or excessively formal meanings unless expressly defined in the specification of the present invention. It doesn't work.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention in more detail. However, in the following description, when there is a risk of unnecessarily obscuring the gist of the present invention, a detailed description of well-known functions and configurations will be omitted.

1 is a diagram illustrating an embodiment of a network configuration in which small cells are wirelessly connected to a macro base station and a PTP master to obtain synchronization according to embodiments of the present invention.

As shown in FIG. 1, the small cells 111-113 are shaded of an indoor / outdoor, that is, a home, an enterprise, an urban area, an urban area, a rural area, and the like. 2G wireless communication networks such as a Global System for Mobile Communications (GSM) network, a Code Division Multiple Access (CDMA) network, and Wideband Code Division Multiple Access (WCDMA) for one or more terminals 170 distributed to and adjacent to the area. Wireless Internet networks such as LTE, Long Term Evolution (LTE) networks, Wireless Internet Platform for Interoperability (WiFi) networks, portable Internet networks such as Wireless Broadband Internet (WiBro) networks and Worldwide Interoperability for Microwave Access (WiMax) networks. Can provide access. The small cells 111-113 may transmit and receive signals with a macro base station (macro cell or macro eNB, 130) or a PTP master 140 such as an IEEE 1588 master server for synchronization acquisition. Although three small cells are shown in FIG. 1, it should be understood that more or fewer small cells may be disposed. The small cells 111-113 are low power radio access base stations and are small base stations having an operating range of at least 10 m to several hundred meters. The small cells 111-113 have overlapping coverages, indicated by reference numerals 121, 122, and 123, respectively, so that if one of these small cells transmits a signal, it will interfere with other small cells. Can work. The small cells 111-113 may be classified into femto cells, pico cells, metro cells, and micro cells according to the range and purpose of use. It should be understood as a concept. In addition, since a small cell is usually called a HeNB (Home eNB) in LTE, the small cells 111-113 should be understood as a concept including a HeNB. In the following description, each of the small cells 111-113 will be referred to collectively as the small cell 110.

FIG. 2 is a diagram illustrating an embodiment of a configuration block diagram of a small cell synchronization device mounted in the small cell of FIG. 1.

As illustrated in FIG. 2, the small cell synchronization device 200 may include a storage 210, a controller 220, and a communicator 230. The controller 220 may be configured to perform various operations for synchronizing the small cell 110 according to embodiments of the present invention in cooperation with the communication unit 230. The controller 220 may include a PTP time synchronizer 222, an NL start time calculator 224, and an NL synchronizer 226. The PTP time synchronizer 222 may be configured to perform a PTP TOD procedure to correct the system clock time of the small cell 110. In one embodiment, the PTP time synchronizer 222 may be further configured to correct the system clock time of the small cell 110 by performing a PTP TOD procedure when the small cell 110 is powered on. The NL start time calculator 224 may be configured to calculate the NL start time based on the corrected system clock time. The NL synchronizer 226 may be configured to recalibrate the corrected system clock time by performing NL at the NL start time. In one embodiment, the NL synchronizer 226 may be further configured to receive the macro base station signal for 20 msec from the NL start time. In one embodiment, the NL synchronizer 226 may be further configured to stop service for at least 20 msec from the NL start time.

The controller 220 described above is a hardware platform based on at least one of an application specific integrated circuit, a digital signal processor, a digital signal processing device, a programmable logic device, a field programmable gate array, a processor, a controller, a microcontroller, and a microprocessor. Can be implemented. The controller 220 may also be implemented as a firmware / software module executable on the aforementioned hardware platform. In this case, the software module may be implemented by a software application written in a suitable program language.

The storage unit 210 may be used to store one or more software / firmware modules that implement the functions of the control unit 220. The storage unit 210 may include a flash memory type, a hard disk type, a multimedia card, a card type memory (for example, an SD card or an XD card, etc.), RAM, SRAM, ROM, EEPROM, PROM, magnetic memory, magnetic disk, and the like. Although it may be implemented as one of the storage media of the optical disk, those skilled in the art will recognize that the implementation of the storage unit 1120 is not limited thereto.

The communication unit 230 may enable the small cell 110 to communicate wirelessly with the macro base station 130 or the PTP master 140 or with one or more terminals 170 within the coverage of the small cell 110. It can be implemented with hardware and / or firmware that implements various Radio Access Technologies (RATs), including GSM, CDMA, WCDMA, LTE / LTE-A, WiFi, WiBro, and WiMax. In one embodiment, the communication unit 230 may be implemented to comply with a wireless communication interface standard, such as LTE-Ue. In addition, the communication unit 230 may be configured to implement a communication protocol that enables the small cell 110 to transmit and receive packets to other small cells 110 through a wired network such as the Internet. In this case, the communication protocol may be implemented with appropriate hardware and / or firmware. In one embodiment, the communication protocol may include a TCP / IP protocol and / or a UDP protocol.

FIG. 3 is a flowchart illustrating an embodiment of a method of acquiring synchronization based on PTP and NL in a small cell.

As shown in FIG. 3, one embodiment of the method begins with step S310 of performing a PTP Time of Day (TOD). In one embodiment, step S310 may be performed every time the small cell 110 is powered on.

Referring to FIG. 4, which illustrates a PTP TOD procedure in which a small cell, which is a PTP slave, performs clock synchronization with the PTP master by exchanging messages with the PTP master according to the PTP protocol, the PTP master 140 is illustrated in FIG. 4. As described above, a sync message, which is a synchronization message, is periodically transmitted to the small cell 110, which is a PTP slave, every two seconds. In this case, the PTP master 140 measures the exact time of transmitting the sync message using hardware or software, and measures the measured transmission time once again using the follow-up message. To send). The small cell 110, which is a PTP slave, measures the reception time of the sync message by using hardware or software. Meanwhile, as shown in FIG. 4, the small cell 110, which is a PTP slave, periodically transmits a delay request message to the PTP master 140 and measures the exact time by using hardware or software. The PTP master 140 measures the reception time of the delay request message using hardware or software and informs the small cell 110 of the PTP slave through the delay response message.

Therefore, the procedure of performing the PTP TOD in the small cell 110 may include receiving a sink message from the PTP master 140 and a follow-up message including information on a transmission time at which the sink message is transmitted by the PTP master 140. Receiving the PTP master 140 from the PTP master 140, measuring the reception time of receiving the sync message in the small cell 110 using hardware or software, and periodically transmitting and transmitting a delay request message to the PTP master 140. An operation of measuring a time using hardware or software and receiving a delay response message from the PTP master 140 including information on a reception time of the delay request message measured by the PTP master 140. have.

Referring back to FIG. 3, in step S315, the clock time offset between the PTP master 140 and the small cell 110 is determined as shown in Equation 1 below, and the clock time of the small cell 110 is determined by the determined clock time offset. Can be corrected as in Equation 2 below. By the clock time correction as described below, it is possible to make the clock time of the small cell 110 different from the clock time of the PTP master 140 within ± 1 msec.

Here, T _offset represents a clock time offset, and T1, T2, T3, and T4 represent a time when the PTP master 140 transmits a sync message, a time when the small cell 110, which is a PTP slave, receives a sync message, and a PTP slave. The time at which the small cell 110 transmits the delay request message and the time at which the PTP master 140 receives the delay request message are shown.

Here T _{sys_cur} represents the current clock time of the small cell (110).

In operation S320, the NL start time may be calculated based on the corrected new clock time of the small cell 110. The NL start time may be calculated by the following Equation 3 in units of seconds.

는

보다 크지 않은 최대의 정수를 나타내고, T_{NL_start}는 NL 시작 시간을 나타내고, T_{NL_start_offset}은 사용자가 설정하는 시작 시간 옵셋으로서 0과 같거나 그 보다 크고 1보다 작은 임의의 수일 수 있다.Where N is an integer greater than or equal to 1 indicating an NL synchronization period,

Is

_Represents a maximum integer not greater than, T _{NL_start} represents an NL start time, and T _{NL_start_offset} is a start time offset set by the user and may be any number greater than or equal to 0 and less than 1.

T_{sys_cur} < 2m + 1 (여기서 m은 0 이상의 정수임)]의 조건을 만족하는 시간(T_{sys_cur})에서 수학식 3에 따라 NL 시작 시간을 계산할 필요가 있다. 일반화하면, NL 동기 수행 주기가 N일 경우 모든 소형 셀들(110)은 [N * m

T_{sys_cur} < N * m + 1 (여기서 m은 0 이상의 정수임)]의 조건을 만족하는 시간(T_{sys_cur})에서 수학식 3에 따라 NL 시작 시간을 계산할 필요가 있다. 이는 소형 셀들(110)에서 계산되는 시작 시간들이 모두 N의 배수가 되는 것을 보장해 주기 위함이다. 일 실시예에서, T_{NL_start_offset}은 0일 수 있는데, 이 경우 N이 1이라 가정하면 T_{NL_start}는 소형 셀(110)의 (보정된) 현재 클럭 시간 보다 큰 최소의 정수의 시간일 수 있다. 이 경우, 예컨대 소형 셀(110)의 현재 클럭 시간이 1.23초인 경우 T_{NL_start}는 2초가 될 수 있다. 다른 실시예에서, T_{NL_start_offset}은, 예컨대 0.5일 수 있는데, 이 경우 N이 1이라 가정하면 T_{NL_start}는 소형 셀(110)의 (보정된) 현재 클럭 시간 보다 큰 최소의 정수의 시간에 0.5를 더한 시간일 수 있다. 예컨대 N이 1이고 소형 셀(110)의 현재 클럭 시간이 1.23초라고 가정하면 T_{NL_start}는 2.5초가 될 수 있다. 요컨대 T_{NL_start_offset}을 적절히 조정함으로써 소형 셀(110)이 양의 정수의 초 단위의 주기적인 시간들(예컨대, N = 2인 경우, 2초, 4초, 6초, ....)에서 NL을 시작하거나 양의 정수의 초 단위의 주기적인 시간들에서 일정 시간(T_{NL_start_offset}) 만큼 옵셋된 시간들(예컨대, N = 5이고 T_{NL_start_offset}이 0.2인 경우, 5.2초, 10.2초, 15.2초 ....)에서 NL을 시작하도록 하는 것이 가능하다. 전술한 바와 같이 PTP TOD의 수행에 의해 소형 셀(110)이 1msec 이내의 정확도로 보정될 수 있으므로 T_{NL_start}는 PTP 매스터(140)의 클럭 시간과 ±1msec 이내로 차이 나는 값을 갖게 된다.In one embodiment, N may be 1, in which case the NL synchronization period is 1 sec. In another embodiment, N may be 2, in which case the NL synchronization performance period may be 2 sec. In this case, all the small cells 110 to perform NL synchronization are [2m].

It is necessary to calculate the NL start time according to Equation 3 at a time T _{sys_cur} satisfying the condition of T _{sys_cur} <2m + 1 (where m is an integer greater than or equal to 0). In general, when the NL synchronization period is N, all small cells 110 are [N * m

It is necessary to calculate the NL start time according to Equation 3 at a time T _{sys_cur} satisfying the condition of T _{sys_cur} <N * m + 1 (where m is an integer greater than or equal to 0). This is to ensure that the start times calculated in the small cells 110 are all multiples of N. In one embodiment, T _{NL_start_offset} may be 0, in which case assuming N is 1, T _{NL_start} may be a minimum integer time greater than the (corrected) current clock time of small cell 110. In this case, for example, when the current clock time of the small cell 110 is 1.23 seconds, T _{NL_start} may be 2 seconds. In another embodiment, T _{NL_start_offset} may be, for example, 0.5, where assuming N is 1, T _{NL_start} is the minimum integer time greater than (corrected) the current clock time of small cell 110 plus 0.5. It can be time. For example, assuming that N is 1 and the current clock time of the small cell 110 is 1.23 seconds, T _{NL_start} may be 2.5 seconds. In short, by appropriately adjusting T _{NL_start_offset} , the small cell 110 can determine _NL at periodic times in positive integer seconds (e.g., 2 seconds, 4 seconds, 6 seconds, ....) when N = 2). 5.2 seconds, 10.2 seconds, 15.2 seconds when starting or offset by a constant time (T _{NL_start_offset} ) from periodic times in positive integer seconds (eg, N = 5 and T _{NL_start_offset} is 0.2). It is possible to start NL at. As described above, since the small cell 110 can be corrected with an accuracy of 1 msec or less by performing the PTP TOD, T _{NL_start} has a value that is different from the clock time of the PTP master 140 within ± 1 msec.

In step S325, NL is performed at the NL start time T _{NL_start} calculated in step S320. By performing the NL, the LTE signal from the macro base station 130 may be received to estimate and compensate for a time error in the small cell 110. In one embodiment, the NL is performed for 20 msec corresponding to two frame times because the length of the LTE frame from the macro base station 130 is 10 msec, so that one or more LTE frames may be received for 20 msec. During this time, the small cell 110 stops transmitting the signal, thereby making it possible to perform the NL in an environment free of interference. That is, the small cells 110 to receive and synchronize signals from the macro base station 130 receive signals from the macro base station 130 while stopping transmission at the same time period, thereby achieving NL synchronization in an environment without interference. It can be done. In the environment as shown in FIG. 1, when the small cells 110 serve without stopping transmission, for example, the small cell 113 is interrupted by signals from the small cell 111 and the small cell 112. Receiving a signal from the macro base station 130 is difficult to synchronize. However, as in the embodiments of the present invention, when the small cell 111 and the small cell 112 interrupt the service to perform the NL in the same time period, the small cell 113 becomes an interference-free environment for this time. The signal from the macro base station 130 can be received and synchronized.

FIG. 5 is a diagram illustrating performing NL synchronization and stopping service for 20 msec from NL start time in small cells when macro base station frames are transmitted from the macro base station.

Referring to FIG. 5, the m-th macro base station frame is transmitted for 10 msec at n seconds, the (m + 1) -th macro base station frame is transmitted for 10 msec at n seconds + 10 msec, and (m + 2) at n seconds + 20 msec. The first macro base station frame is transmitted for 10 msec, and the (m + 3) th macro base station frame is transmitted for 10 msec at n seconds + 30 msec. Although the macro base station frame is actually continuously transmitted in a continuous manner, only four frames are shown in FIG. 5 for convenience of illustration. The small cell 111 stops service for 20 msec at the NL start time T _{NL_start} calculated as n seconds and performs NL. Although small cell 111 starts NL in n seconds, this time may be slightly slower than n seconds in reference to macro base station 130 as shown. As shown, the small cell 111 receives the m-th macro base station frame starting at T _{Frame_start} , which is the time at the reference of the small cell 111, and lasting for 10 msec during the _NL , which is included in the frame. T _{Frame_start} can be found by analyzing the primary synchronization signal (PSS) and the secondary synchronization signal (SSS). Meanwhile, the small cell 112 stops the service for 20 msec at the NL start time T _{NL_start} calculated as n seconds and performs the NL. Although small cell 112 starts NL in n seconds, as shown, this time may be slightly earlier than n seconds in reference to macro base station 130. As shown, the small cell 112 receives the (m + 1) th macro base station frame starting at T _{Frame_start} , which is the time at the reference of the small cell 112, and lasting 10 msec during the _NL . T _{Frame_start} can be found by analyzing the PSS and SSS included in the frame. In the case of the small cell 112, it should be noted that the performance of the NL lasts until n seconds + 20 msec.

When T _{Frame_start} is found, Equation 4 and Equation 5 below compensate for the time error of the small cell.

Here, T _offset 'represents a clock time offset, and T _{Frame_start} is an LTE frame start time of a macro base station signal at a reference of a small cell.

Here T _{sys_cur} represents the current clock time of the small cell (110).

T _offset 'it is because it is the time of a small cell 111 is faster than the time of the macro base station (130) T _offset, as in the case of small-cell 111 in Figure 5 is less than 5msec' small enough cell 111 Delay the time of correction. Anti-T _offset 'is because it is the time of the smaller cell 112 is slower than the time of the macro base station 130 as in the case of a small cell 112 in greater in Figure 5 than 5msec T _offset' mini cell 112 as To correct time quickly.

6 and 7 are diagrams for describing a method of compensating for a time error in a small cell under the assumption that n in FIG. 5 is 1.

First, referring to FIG. 6, which is a diagram of the case of the small cell 111 in which the time of the small cell is earlier than the time of the macro base station 130, the small cell 111 may be 1 second (T). _{NL_start} ) to start NL and receive a macro base station signal for 20 msec. The signal received for 20msec is analyzed to derive the LTE frame start time (T _{Frame_start} ) of the macro base station signal. If the derived T _{Frame_start} is 1.0003 seconds, the T _offset 'is 0.0003 seconds, that is, 0.3 msec, which is smaller than 5 msec, thereby correcting the time of the small cell 111 by subtracting the T _offset ' from the time of the small cell 111. Therefore, if the time (1.02 seconds) of the small cell 111 that has finished NL is called the current time (T _{sys_cur} ), then the new current time (T _{sys_cur} ) of the small cell 111 at this time is 1.0197 seconds (1.02-0.0003). do.

Next, referring to FIG. 7, which is a diagram of the case of the small cell 112, in which the time of the small cell is slower than that of the macro base station 130, the small cell 112 corresponds to 1 second (the small cell 112 time). T _{NL_start} ) to start NL and receive a macro base station signal for 20 msec. The signal received for 20msec is analyzed to derive the LTE frame start time (T _{Frame_start} ) of the macro base station signal. If the derived T _{Frame_start} is 1.0094 seconds, the T _offset 'is 0.0094 seconds, that is, 9.4 msec, which is larger than 5 msec, so that the time of the small cell 112 is corrected by subtracting the T _offset ' from the time of the small cell 112 and adding 10 msec. do. Therefore, if the time (1.02 seconds) of the small cell 112 that has finished NL is called the current time (T _{sys_cur} ), then the new current time (T _{sys_cur} ) of the small cell 112 at this time is 1.0206 seconds (1.02-0.0094 + 0.01). )

When time error compensation of the small cells 111 and 112 is completed, the small cells 111 and 112 start a service by transmitting frames. As shown in FIG. 5, in the small cell 111, the NL synchronization is completed before n seconds + 20 msec, and the service is started at n seconds + 20 msec. In the case of the small cell 112, the NL is performed as described above. This service lasts for more than n seconds + 20msec, so service starts at n seconds + 30msec.

3, when step S325 is completed, the process proceeds to step S320 to receive the LTE signal from the macro base station 130 by calculating the NL start time again and performing NL at the calculated NL start time. To estimate and compensate for the time error in the small cell. In this way, NL can be performed periodically. As described above, it is possible to perform NL synchronization every NL synchronization execution period (N).

In the above description, the description that a component is connected or coupled to another component means that the component is directly connected or coupled to the other component, as well as one or more other components interposed therebetween. It is to be understood to include the meaning that they may be connected or coupled through the element. In addition, terms for describing the relationship between the components (eg, 'between', 'between', etc.) should be interpreted in a similar sense.

In the embodiments disclosed herein, the arrangement of the components shown may vary depending on the environment or requirements on which the invention is implemented. For example, some components may be omitted or several components may be integrated and implemented as one. In addition, the arrangement order and connection of some components may be changed.

Although various embodiments of the present invention have been illustrated and described above, the present invention is not limited to the above-described specific embodiments, and the above-described embodiments deviate from the gist of the present invention as claimed in the appended claims. Without departing from the scope of the present invention pertains to those skilled in the art, various modifications may be made to those skilled in the art, and such modified embodiments should not be understood separately from the technical spirit or scope of the present invention. Accordingly, the technical scope of the present invention should be defined only by the appended claims.

100, 111-113: small cell
121, 122, 123: Coverage
130: macro base station
140: PTP Master
170: terminal
210: storage unit
220: control unit
230: communication unit

Claims (21)

As a synchronization method in a small cell,
Calibrating the system clock time of the small cell by performing a Precision Time Protocol (PTP) time of day (TOD) procedure;
Calculating a network listening (NL) start time based on the corrected system clock time, and
Performing an NL at the NL start time to recalibrate the corrected system clock time,
The step of calculating the NL start time is the following equation

Calculating an NL start time according to-where T _{sys_cur} represents the corrected system clock time, and N is an integer equal to or greater than 1 indicating an NL synchronization performance period,

Is

Small cell synchronization, including the largest integer not greater than, T _{NL_start} represents the NL start time, and T _{NL_start_offset} is a user-set start time offset that is any number greater than or equal to 0 and less than 1. Way.
The method of claim 1,
Correcting a system clock time of the small cell is performed when the small cell is powered on.
delete The method of claim 1,
The step of calculating the NL start time is the following condition
N * m

T _{sys_cur} <N * m + 1 (where m is an integer greater than or equal to 0)
And calculating the NL start time at a time T _{sys_cur} that satisfies.
The method of claim 1,
Performing the NL at the NL start time to recalibrate the corrected system clock time comprises receiving a macro base station signal for 20 msec from the NL start time.
The method of claim 5,
And the macro base station signal received for 20 msec from the NL start time includes at least one frame.
The method of claim 5,
Performing NL at the NL start time to recalibrate the corrected system clock time comprises discontinuing service for at least 20 msec from the NL start time. The method of claim 6,
Re-calibrating the corrected system clock time by performing NL at the NL start time may be as follows.
T _offset '= T _{Frame_start} -T _{NL_start}
T _{sys_cur} ← T _{sys_cur} -T _offset ', if T _offset '<5 msec
T _{sys_cur} ← T _{sys_cur} -T _offset '+ 10 msec, else
Correcting the corrected system clock time according to the step-where T _offset 'represents a system clock time offset of the small cell, and T _{Frame_start} represents the at least one frame of the macro base station signal at the reference of the small cell. T _{NL_start} is the NL start time, and T _{sys_cur} indicates the corrected system clock time. The method of claim 1,
Repeating calculating the NL start time for each NL synchronization period and recalibrating the corrected system clock time.
An apparatus for performing synchronization in a small cell,
A PTP time synchronizer configured to perform a PTP TOD procedure to correct a system clock time of the small cell;
An NL start time calculator configured to calculate an NL start time based on the corrected system clock time, and
An NL synchronizer configured to perform NL at the NL start time to recalibrate the corrected system clock time,
The NL start time calculation unit is the following equation

Is further configured to calculate an NL start time according to: where T _{sys_cur} represents the corrected system clock time, N is an integer of at least 1 representing an NL sync performance period,

Is

_{Represents the} largest integer not greater than, T _{NL_start} represents the NL start time, and T _{NL_start_offset} is a start time offset set by the user, which is any number greater than or equal to 0 and less than 1-small cell synchronizer.
The method of claim 10,
And the PTP time synchronizer is further configured to correct the system clock time of the small cell by performing the PTP TOD procedure when the small cell is powered on.
delete The method of claim 10,
The NL start time calculation unit under the following conditions
N * m

T _{sys_cur} <N * m + 1 (where m is an integer greater than or equal to 0)
And calculate the NL start time at a time T _{sys_cur} that satisfies.
The method of claim 10,
And the NL synchronizer is further configured to receive a macro base station signal for 20 msec from the NL start time.
The method of claim 14,
And the macro base station signal received for 20 msec from the NL start time includes at least one frame.
The method of claim 14,
And the NL synchronizer is further configured to stop service for at least 20 msec from the NL start time.
The method of claim 15,
The NL synchronizer is
T _offset '= T _{Frame_start} -T _{NL_start}
T _{sys_cur} ← T _{sys_cur} -T _offset ', if T _offset '<5 msec
T _{sys_cur} ← T _{sys_cur} -T _offset '+ 10 msec, else
Is further configured to recalibrate the corrected system clock time, wherein T _offset 'represents a system clock time offset of the small cell, and T _{Frame_start} is the at least one of the macro base station signal at the reference of the small cell. T _{NL_start} is the NL start time, and T _{sys_cur} is the corrected system clock time. Small cell synchronizer.
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