KR20110105200A - Apparatus and method for synchronizing micro base station in asymmetric communication links - Google Patents

Abstract

Embodiments of the present invention relate to a small base station synchronization apparatus and a synchronization method in an asymmetric communication link. According to an embodiment of the present invention, a small base station synchronization apparatus in an asymmetric communication link receives a first synchronization signal synchronized with a GPS signal from a core network, and generates a first packet including synchronization information of the core network. A master for transmitting and receiving a plurality of packets to provide delay time information according to a time delay of one packet; A wired network via the first packet and the plurality of packets; A first synchronization device configured to generate and initialize a second synchronization signal in synchronization with the first synchronization signal, and to first correct the second synchronization signal using the synchronization information and / or the delay time information; A slave for receiving the first packet to measure a reception time, a transmission time of a packet transmitted to the master among the plurality of packets, and extracting a time stamp value of a packet received from the master among the plurality of packets ; A second synchronization device for second-correcting the second synchronization signal using the reception time, the transmission time, and the timestamp value; And a small base station synchronized with the core network using the second corrected second synchronization signal.

Description

Apparatus and Method for Synchronizing Micro Base Station in Asymmetric Communication Links}

Embodiments of the present invention relate to a small base station synchronization apparatus and a synchronization method in an asymmetric communication link. More specifically, when the small base station uses the same communication standard as the macro base station, the FMS (Fixed Mobile Substitution) method for transmitting synchronization information to the small base station is applied.When the core network and the small base station are connected by wire or wirelessly, In contrast to the downlink transmission of data from the core network to the small base station, when the uplink transmission speed of the data transmission from the small base station to the network is different, the asymmetric communication link synchronizes the core network and the small base station. A small base station synchronization apparatus and a synchronization method.

In recent years, small base stations called femtocells or picocells have attracted much attention in terms of coverage of mobile communication networks, service quality improvement, and integration of wired and wireless communication services. A femtocell refers to a very small base station, which is very small compared to a macro base station in the size of a digital subscriber line router or a cable modem. Femtocells can operate in the official frequency bands or non-official frequency bands (ISM bands, etc.) assigned to mobile operators, with an output voltage of 10 to 200 mW and a communication distance of 50 to 100 m. Users can connect at the same time. It can be installed directly by the network operator or user, and is connected to the core network by using a separate communication network or by using a high speed internet network. The picocell is a medium concept between a femtocell and a macro base station, which is slightly larger than a femtocell and can be accessed by up to 30 users at the same time, and means a small base station that can be installed in a building office or a school.

In the case of the repeater, the signal received from the macro base station is transmitted as it is, so the coverage of the base station is expanded but the capacity is not increased. In proportion to the number, the capacity of the entire mobile communication network increases. Therefore, small base stations increase the capacity of the wireless network while expanding coverage. In particular, in the case of a mobile communication system that has been commercialized or standardized recently, the coverage of the macro base station is narrower than that of the existing mobile communication system because the carrier frequency used is high and the bandwidth is wide. In other words, when the network is built with only macro base stations, the number of required base stations increases and the network construction cost increases. In addition, as the mobile communication system evolves, the rate of data communication is increasing as compared to voice communication. Therefore, it is difficult to provide a high speed data communication service to a large number of users using only a macro base station. As an alternative, it is a viable alternative to provide a wireless communication service by installing a low-cost small base station in an office or home where people mainly use wireless communication.

These small base stations are largely classified into a fixed mobile convergence (FMC) using a dual mode terminal and a fixed mobile substitution (FMS) method using an existing mobile communication terminal. In particular, in the case of the FMS method, since the base station uses the same transmission method as the existing macro base station, the existing mobile phone supporting one mobile communication standard can be used to benefit from the increased coverage and capacity increase by the small base station. . On the other hand, in the case of the FMC method, since the mobile communication standards of the macro base station and the small base station are different, there is a disadvantage in that the user has to replace the existing terminal with a terminal supporting the dual mode.

Meanwhile, in order to simultaneously operate an existing macro base station and a small base station in a mobile communication network, the carrier frequency and signal transmission time of the small base station must be synchronized with the macro base station. Especially, when using time division duplex method such as mobile WiMAX (M-WiMax), if the signal transmission time of macro base station and small base station is out of order, the uplink / downlink signal of macro base station and small base station Since interference occurs between downlink and uplink signals, it is very important to synchronize the time between the macro base station and the small base station.

To this end, conventionally, in the case of the macro base station, since the transmitting and receiving antenna is installed outdoors, it receives global positioning system (GPS) information from the satellite to synchronize the macro base station with the macro network. However, the small base station is generally installed in a room that is difficult to receive GPS signals, such as an office, school, apartment, house, etc., and thus cannot be used to acquire GPS signals. In addition, even if the GPS signal can be received, the small base station has to be attached to a separate device for receiving the GPS signal has the disadvantage that the price of the small base station is expensive.

If a small base station cannot receive a GPS signal, a method of acquiring synchronization using a pilot signal transmitted from a macro base station has been proposed. However, this method has a disadvantage that it can be applied only when the downlink pilot signal of the macro base station can be received in the region where the small base station is installed. The small base station is mainly installed in an area where the macro base station signal is not transmitted, thereby expanding the wireless communication service area and expanding the capacity. However, if the small base station is to be installed in the coverage of the macro base station, the utility of the small base station is significantly reduced.

1 is a diagram illustrating a system for synchronization between a core network and a small base station using IEEE 1588 according to the prior art.

As shown in FIG. 1, when using IEEE 1588, the core network 100 and the small base station 140 are wired by an IP network 120. The core network 100 acquires synchronization using the GPS antenna 107 and the like, and transfers this information to the small base station 140 by wire. The IEEE 1588 master 110 is used for the core network 100 to transmit the synchronization information, and the IEEE 1588 slave 130 is used in the small base station 140. The IEEE 1588 master 110 periodically transmits a packet that records synchronization information of the core network 100 to the IEEE 1588 slave 130. The IEEE 1588 slave 130 estimates the time synchronization in consideration of the synchronization information and the transmission delay recorded in the received packet, and corrects the time synchronization of the small base station 140 using the value, thereby correcting the core network 100 and the small base station. The synchronization of 140 is made to match. Since the macro base station 105 is synchronized with the core network 100 using a GPS signal, the synchronization between the macro base station 105 and the small base station 140 is consistent.

However, IEEE 1588 is a downlink transmission of data from the core network 100 to the small base station 140, and conversely, if the uplink transmission delay of transmitting data from the small base station 140 to the core network 100 is the same. Applicable only to In other words, if the transmission rates of the uplink and the downlink are the same as those of the Ethernet, the accurate synchronization can be obtained using IEEE 1588. However, the digital subscriber line (DSL) such as the high-speed Internet is used. In this case, since there is a significant difference in the transmission rates of downlink and uplink, when the IEEE 1588 standard is applied as it is, serious synchronization estimation error occurs due to the transmission delay difference.

FIG. 2 is a diagram illustrating a process of synchronizing a clock between a master and a slave using IEEE 1588 in the system of FIG. 1.

2, the master first transmits a Sync () message to the slave, and immediately sends a Follow_up (t ₀ ) message including a transmission time t ₀ of the Sync () message to the slave.

The slave sends the Delay_Req () message to the master immediately after receiving the Follow_up (t ₀ ) message.

The master measures the time t ₃ at which the Delay_Req () message is received and sends the received time t ₃ to the slave by including it in the Delay_Res (t ₃ ) message.

T ₀ and t ₃ are measured by the master clock, and t ₁ and t ₂ are measured by the slave clock.

Suppose that the slave clock is t_offset faster than the master clock. Then, the relationship between t ₀ and t ₁ in the Sync () message transmission is expressed as Equation 1.

(Equation 1)

t ₁ = t ₀ + D_DL + t_offset

In this case, D_DL represents a time delay when transmitting a packet from a master to a slave. In the Delay_Req () message transmission, the relationship between t ₂ and t ₃ is given by Equation 2.

(Equation 2)

t ₃ = t ₂ + D_UL-t_offset

In this case, D_UL represents a time delay when transmitting a packet from a slave to a master.

For reference, the slave receives t ₀ and t ₃ using the Follow_up (t ₀ ) and Delay_Res (t ₃ ) messages, so we know all t ₀ , t ₁ , t ₂ , and t ₃ .

Suppose D_DL and D_UL are the same. Then, the slave may calculate t_offset using <Equation 1> and <Equation 2> as follows.

(Equation 3)

In a wired network, jitter occurs during packet transmission, so an error occurs when estimating t_offset using the equation (3).

When the core network and the small base station are connected by wire, when the down time delay D_DL and the uplink time delay D_UL are the same, the synchronization of the small base station can be obtained using IEEE 1588 by the method of Equation 3.

However, in a general network, when a routing path of uplink and downlink is different or a transmission rate of uplink and downlink is different, D_DL and D_UL may be different.

In this case, when estimating the clock difference between the master and the slave by the method of Equation 3, the estimated t_offset_est of t_offset is expressed as Equation 4.

(Equation 4)

That is, a bias by (D_DL-D_UL) / 2 occurs in the estimated value of t_offset.

The M-WiMax standard specifies that the clock time error should be less than ± 20 µs if the handover is not supported by the small base station.

However, when a small base station is connected to a commercial high-speed Internet network at home, the average value of D_DL and D_UL is several hundreds of milliseconds to several ms, and the difference between D_DL and D_UL is several tens of milliseconds to several ms.

For example, the result of measuring time delay in KT high-speed internet network shows that D_DL and D_UL differ by about 1 ms in the case of very high-data rate digital subscriber line (VDSL) network, and that of D_DL and D_UL is 70 There is a difference.

Therefore, in this case, the error calculated by (D_DL-D_UL) / 2 is larger than 20 ㎲, which does not satisfy the M-WiMax specification.

The embodiment of the present invention estimates and compensates a clock error in an IEEE 1588 slave when a downlink transmission delay and an uplink transmission delay occur asymmetrically due to asymmetric transmission rates of uplink and downlink. It is an object of the present invention to provide a small base station synchronization device and a synchronization method in an asymmetric communication link for synchronizing with a master clock.

An apparatus for synchronizing a small base station in an asymmetric communication link according to an embodiment of the present invention receives a first synchronization signal synchronized with a GPS signal from a core network, and generates a first packet including synchronization information of the core network. A master for transmitting and receiving a plurality of packets to provide delay time information according to a time delay of the first packet; A wired network via the first packet and the plurality of packets; A first synchronization device configured to generate and initialize a second synchronization signal in synchronization with the first synchronization signal, and to first correct the second synchronization signal using the synchronization information and / or the delay time information; A slave for receiving the first packet to measure a reception time, a transmission time of a packet transmitted to the master among the plurality of packets, and extracting a time stamp value of a packet received from the master among the plurality of packets ; A second synchronization device for second-correcting the second synchronization signal using the reception time, the transmission time, and the timestamp value; And a small base station synchronized with the core network using the second corrected second synchronization signal.

Further, the apparatus for synchronizing a small base station in an asymmetric communication link according to another embodiment of the present invention receives a first synchronization signal synchronized with a GPS signal from a core network and generates a first packet including synchronization information of the core network. A master for transmitting and receiving a plurality of packets to provide delay time information according to a time delay of the first packet; A wired network via the first packet and the plurality of packets; A first synchronization unit and a first packet configured to generate and initialize a second synchronization signal in synchronization with the first synchronization signal, and to first correct the second synchronization signal by using the synchronization information and / or the delay time information; Receiving the received time to measure the reception time, the transmission time of the packet transmitted to the master of the plurality of packets, extracting the time stamp value of the packet received from the master of the plurality of packets, the reception time, A slave having a second synchronization unit to second-correct the second synchronization signal using the transmission time and the timestamp value; And a small base station synchronized with the core network using the second corrected second synchronization signal.

In a synchronization method of an apparatus for synchronizing a small base station in an asymmetric communication link according to an embodiment of the present invention, receiving a first packet including synchronization information of a core network and a second packet including transmission time information of the first packet. ; Transmitting a third packet requesting delay time information according to a time delay of the first packet; Receiving a fourth packet including reception time information on the transmission of the third packet; Generating a synchronization signal and first correcting the synchronization signal using the synchronization information and / or the delay time information; Measuring a reception time of the first packet and a transmission time of the third packet; Extracting time stamp values of the second packet and the fourth packet; Secondly correcting the synchronization signal using the reception time, the transmission time, and the timestamp value; And synchronizing a small base station with the core network using the second corrected second synchronization signal.

According to an embodiment of the present invention, even when downlink transmission delay and uplink transmission delay occur asymmetrically due to asymmetric transmission rates of uplink and downlink, an IEEE 1588 slave estimates and compensates a clock error. It will be possible to synchronize the slave clock with the master clock.

1 is a diagram showing a system for synchronization between a core network and a small base station using IEEE 1588 according to the prior art;
2 is a diagram illustrating a process of synchronizing a clock between a master and a slave using IEEE 1588 in the system of FIG. 1;
3 shows a miniaturized base station synchronization apparatus in an asymmetric communication link according to an embodiment of the present invention;
4 is a diagram illustrating a first synchronization device of FIG. 3,
5 is a view showing a second synchronization device of FIG.
6 is a flowchart illustrating a process of transmitting time synchronization of a core network to a small base station using IEEE 1588;
FIG. 7 is a diagram illustrating a process of synchronizing an IEEE 1588 slave clock to a master clock when transmission delays of downlink and uplink are asymmetric in FIG. 6;
FIG. 8 is a diagram illustrating an operation procedure between a master and a slave according to the clock synchronization method of FIG. 7.

Hereinafter, exemplary embodiments of the present invention will be described in detail. In adding reference numerals to the elements of each drawing, it should be noted that the same elements may be denoted by the same reference numerals as much as possible because they may be displayed on different drawings. In addition, in describing the present invention, when it is determined that the detailed description of the related well-known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

In addition, in describing the component of this invention, terms, such as 1st, 2nd, A, B, (a), (b), can be used. These terms are only for distinguishing the components from other components, and the nature, order or order of the components are not limited by the terms. If a component is described as being "connected", "coupled" or "connected" to another component, that component may be directly connected to or connected to that other component, but there may be another configuration between each component. It is to be understood that the elements may be "connected", "coupled" or "connected".

3 is a diagram illustrating a small base station synchronization apparatus in an asymmetric communication link according to an embodiment of the present invention, FIG. 4 is a diagram illustrating a first synchronization apparatus of FIG. 3, and FIG. 5 is a diagram of a second synchronization apparatus of FIG. 3. It is a figure which shows.

3 to 5, the small base station synchronization apparatus in an asymmetric communication link according to an embodiment of the present invention is the IEEE 1588 master 310, the wired network 320, the first network synchronized to the core network 300 The synchronization device 330, the IEEE 1588 slave 340, the second synchronization device 350, and the small base station 360 are included. In this case, the small base station 350 is connected to the mobile communication terminal, and the mobile communication terminal may include a mobile phone, a notebook computer, and personal digital assistants (PDAs).

The core network 300 may be used to include all of the exchange, the macro base station 305, the base station controller and / or the GPS antenna 307, and support both synchronous and asynchronous. In the case of synchronous transmission and reception macro base station 305 will be a base-station transmission system (BTS), the transmission and reception base station controller will be a base station controller (BSC), and in case of asynchronous transmission and reception macro base station 305 RTS (Radio Transceiver Subsystem), the transmitting and receiving base station controller will be a Radio Network Controller (RNC). Therefore, in the exemplary embodiment of the present invention, the core network 300 may be referred to collectively as a signal repeater that may be used in an access network of a GSM network and a fourth generation mobile communication system to be implemented in the future.

The IEEE 1588 master 310 may be included in an exchange of the core network 300 and the like, and receives and synchronizes a synchronization signal (or first synchronization signal) synchronized with the GPS signal from the core network 300, and the core network 300. The packet in which the synchronization information is recorded (hereinafter, referred to as a first packet) is transmitted to the IEEE 1588 slave 340 via the wired network 320. In addition, the IEEE 1588 master 310 includes a packet including a transmission time to transfer the transmission time of the first packet to the IEEE 1588 slave 340 during transmission of the first packet in order to estimate time synchronization with respect to time delay. A second packet) is transmitted, and a response packet (hereinafter referred to as a third packet) corresponding to the second packet is received from the IEEE 1588 slave 340, and a response packet (hereinafter referred to as a fourth packet) for the third packet is transmitted. In this case, the first packet, the second packet, the third packet, and the fourth packet may correspond to a Sync message, a Follow_up message, a Delay_Req message, and a Delay_Res message according to the IEEE 1588 standard.

As such, when the process of the IEEE 1588 master 310 and the IEEE 1588 slave 340 transmitting and receiving from the first packet to the fourth packet is referred to as a synchronization protocol, the IEEE 1588 master 310 and the IEEE 1588 slave 340 may have several times. Dozens of periodic message exchanges using the synchronization protocol are performed. Here, the term "periodical" is defined by the IEEE 1588 master 310 to divide the size of the odd numbered first and the even numbered first packets, that is, the size of the sync message and the number of the first number of even numbered times, but repeating the same. Means that. For example, the first packet and the third packet every odd number of times have the same size as each other, and the first packet and the third packet every even number of times have the same size, but the first number of odd number of times is the first packet. The first packets with the even number of times have different sizes, and the third packets with the odd number of times and the third packets with the even number of times have different sizes.

The IEEE 1588 master 310 may include a physical layer, a 1588 detector, and an application layer to generate an IEEE 1588 message, i.e., a first, second and / or fourth packet. The application layer may include a 1588 that processes an IEEE 1588 packet. There may be code. If the 1588 code generates an IEEE 1588 message, the IEEE 1588 master 310 delivers the message to the physical layer through a media independent interface (MII), and the delivered message is sent back to the IEEE 1588 slave 340 through the wired network 320. Is sent.

Wired network 320 is an IP network, such as DSL, VDSL and optical LAN. Such an IP network is an asymmetric communication link for downlink transmission of data from the core network 300 to the small base station 360 and, conversely, uplink data transmission from the small base station 350 to the core network 300. This will cause a transmission rate bias. Of course, in the embodiment of the present invention, the wired network 320 is assumed to be an asymmetric communication link, but will not be limited thereto. In addition, the wired network 320 may include a device such as a router, a switch, a hub, and a modem that controls a packet transmission flow between a plurality of communication devices connected to the wired network 320 and is responsible for packet transmission and reception.

The first synchronization device 330 compensates for jitter generated during the transmission and reception of packet data between the IEEE 1588 master 310 and the IEEE 1588 slave 350, that is, a propagation delay and a scheduling delay. do. For example, the first synchronization device 300 may be individually included in devices such as a router, a switch, a hub, and a modem constituting the wired network 320, and in the process of transmitting a packet in the wired network 320. Compensates for propagation delays and scheduling delays that occur. In general, the time delay generated when exchanging packet data between the IEEE 1588 master 310 and the IEEE 1588 slave 340 is used to integrate propagation delay, scheduling delay, and transmission delay. Here, the propagation delay means the time taken for the radio wave to be physically transmitted between the network equipment, and is determined by the distance between the network equipment and the type of link connecting the network equipment. Scheduling delay is the time it takes for a network device to receive an IEEE 1588 packet and then resend it after scheduling with another packet. The transmission delay indicates the time until the reception is completed by starting the reception of the IEEE 1588 packet using the link between the network equipment.

Among them, in order to reduce propagation delay and scheduling jitter related jitter, the first synchronization device 330 may include, for example, a first physical layer 410, a queue 420, and a second physical layer, as illustrated in FIG. 4. 430, a first detector 415, a second detector 435, and a 1588 code 440. The first physical layer 420 is connected to the physical layer of the IEEE 1588 master 310 to receive the first, second and fourth packets and deliver them to the first detector 415 and the queue 420. The second physical layer 430 is connected to the physical layer of the IEEE 1588 slave 340 to receive and transmit a third packet to the second detector 435 and the queue 420. The queue 420 queues (or stores and sequentially) the first, second, and fourth packets provided through the first physical layer 410 to the physical layer 430 or the second physical layer 430. Wait for the third packet provided through) and provide it to the first physical layer 410. Also, the first detector 415 detects 1588 of the first, second, and fourth packets received by the first physical layer 410, and the second detector 435 receives the second physical layer 430. 1588 of the third packet is detected, and the 1588 code 440 processes the IEEE 1588 packets of the first to fourth packets provided by the first and second detectors 415 and 435, respectively.

In more detail, when the IEEE 1588 message is received by the first physical layer 410 of the first synchronization device 330, the first detector 415 detects the IEEE 1588 message and transmits the IEEE 1588 message to the 1588 code 440. In the 1588 code 440, the time difference between the reception time of the IEEE 1588 message and the time rescheduled after the scheduling is retransmitted to the IEEE 1588 slave 340, and the link delay between the first synchronization device 330 in the IEEE 1588 master 310 is corrected for the IEEE 1588 message. Record in the correction field. When the IEEE 1588 message is received through the wired link between the first synchronization device 330 and the IEEE 1588 slave 340, the second detector 435 connected to the IEEE 1588 slave 340 detects the IEEE 1588 message and then applies the 1588 of the application layer. Pass to code 440. Then, the clock of the slave 340 is mastered using the transmission / reception time of the IEEE 1588 message received in the 1588 code of the slave 340, a timestamp included in the IEEE 1588 message, a correction field of the IEEE 1588 message, and the like. 310). If the IEEE 1588 message is generated from the 1588 code of the slave 340, the IEEE 1588 message is transmitted from the first synchronization device 330 to the 1588 code of the IEEE 1588 master 310 in a process similar to the downlink described above. .

First, when the IEEE 1588 packet is received, the first synchronization device 330 measures an ingress timestamp. In addition, when the IEEE 1588 packet is retransmitted through a scheduling process in the first synchronization device 330, an egress timestamp is measured. If the propagation delay between the IEEE 1588 master 310 that transmitted the IEEE 1588 packet and the first synchronization device 330 is known, the propagation delay is recorded by the first synchronization device 330 as a link delay. . Immediately before retransmitting IEEE 1588, the correction field defined in IEEE 1588 is updated as shown in <Equation 5>.

(5)

 (correction field) = (correction field) + (egress timestamp)

-(ingress timestamp) + (link delay)

After transmitting the IEEE 588 packet from the IEEE 1588 master 310, the correction field is set in the first synchronization device 330 individually included in devices such as routers, switches, hubs, and modems through which IEEE 1588 passes. When sequentially accumulating as shown, when the IEEE 1588 slave 340 finally receives the IEEE 1588 packet, the sum of the propagation delay and the scheduling delay between the IEEE 1588 master 310 and the IEEE 1588 slave 340 can be known. Therefore, propagation delay and scheduling delay can be excluded from the total downlink time delay. Equation 1 is modified as in Equation 6.

(6)

t ₁ = t ₀ + D_DL-(correction field) + t_offset

In addition, after measuring propagation delay and scheduling delay in the uplink using the correction field of IEEE 1588 in the uplink, Equation 2 is modified as in Equation 7 except for this.

(7)

t ₃ = t ₂ + D_UL-(correction field)-t_offset

As such, when the propagation delay and the scheduling delay are corrected by using the correction field of the first synchronization device 330, the time delay difference between the downlink and the uplink is significantly reduced.

The IEEE 1588 slave 340 may be included in the small base station 360 together with the second synchronization device 330. The IEEE 1588 slave 340 generates a synchronization signal (or a second synchronization signal) that is initialized in synchronization with the first synchronization signal of the IEEE 1588 master 340, that is, a clock signal, and provides synchronization information provided through the wired network 320. And / or transmit the corrected synchronization information to the small base station 360 by using the time stamp as the delay time information, and respond to the synchronization information and / or the delay time information provided by the IEEE 1588 master 310, that is, the IEEE 1588. The third packet for the second packet transmitted from the master 310 is transmitted to the IEEE 1588 master 310 via the first synchronization device 330 and the wired network 320. When the third packet is transmitted, the IEEE 1588 slave 340 transmits the same size as the first packet of the IEEE 1588 master 310 corresponding to the odd-numbered and even-numbered numbers, respectively, as described above. Packets are changed in size and transmitted periodically.

The IEEE 1588 slave 340, like the IEEE 1588 master 310, includes a physical layer, a 1588 decoder, and an application layer. The application layer may have a 1588 code for processing an IEEE 1588 packet. When the IEEE 1588 message is generated from the 1588 code, the IEEE 1588 slave 340 transmits the message to the physical layer through the MII, and transmits the transmitted message to the IEEE 1588 master 310 via the wired network 320 again. In addition, as shown in FIG. 5, the IEEE 1588 slave 340 includes a packet reception time measuring unit 510, a packet decoding unit 520, a time stamp extractor 530, a message generator 540, and a packet encoding. The unit 550 includes a packet transmission time measuring unit 560.

Here, the packet reception time measuring unit 510 measures the reception time of the first packet among the first packet, the second packet, and / or the fourth packet provided through the wired link 500 with the first synchronization device 310. The measured time information is provided to the frequency error and phase error estimator 570. The packet decoding unit 520 decodes the first packet, the second packet and / or the fourth packet provided by the packet reception time measurer 510. The time stamp extractor 530 receives the decoded second packet and / or the fourth packet, extracts the time stamp, and provides the decoded time stamp to the frequency error and phase error estimator 570. The message generator 540 generates a message, that is, a third packet, and provides the message to the packet encoder 550. The packet encoder 550 encodes the third packet provided by the message generator 540. The packet transmission time measuring unit 560 measures the transmission time of the third packet provided by the packet encoding unit 550, and provides the measured transmission time information to the frequency error and phase error estimating unit 570. Is transmitted to the IEEE 1588 master 310 over the wired link 500.

The second synchronization device 350 compensates for time synchronization by using the frequency error and the phase error to compensate for the residual delay, ie, transmission delay, remaining after being compensated by the first synchronization device 330. To this end, the second synchronization device 350 may further include a frequency error and phase error estimator 570, a local clock generator 580, and a clock corrector 590. The frequency error and phase error estimator 570 may include a time stamp provided by the time stamp extractor 530, reception time information provided by the packet reception time measurement unit 510, and a packet transmission time measurement unit 560. Frequency and phase errors are estimated using the transmission time information.

According to this process, the second synchronization device 350 clocks when an asymmetric time delay occurs between the IEEE 1588 master 310 and the IEEE 1588 slave 340 due to asymmetric transmission rates of uplink and downlink. The corrector 590 adjusts the clock of the IEEE 1588 slave 340 using the frequency error and phase error provided by the frequency error and phase estimator 570 and the local clock provided by the local clock generator 580. Precisely synchronize to the clock of 310).

For example, when the timer of the master clock is called t_master and the timer of the slave clock is called t_slave, it can be expressed as in Equation 8 in consideration of the frequency error and the phase error between the master clock and the slave clock.

(Equation 8)

t_slave = at_master + b

Here, a denotes a ratio of the slave clock frequency to the master clock frequency, and b denotes a phase difference between the slave clock and the master clock.

The small base station 360 is a small base station in femtocell or picocell units. The small base station 360 is synchronized to the core network 300 according to the synchronization information corrected by the second synchronization device 350. As such, the small base station 360 receives the packet data in synchronization with the core network 300 and provides the packet data to the mobile communication terminal again. Here, the terminal is a mobile communication terminal such as a mobile phone, a PDA, a notebook used indoors.

In the embodiment of the present invention, for convenience of description, the first synchronization device 330, the IEEE 1588 slave 340, the second synchronization device 350, and the small base station 360 are described separately from each other. However, in some cases, the first synchronization device 330 and the IEEE 1588 slave 340 may be integrated and implemented, or the IEEE 1588 slave 340 and the second synchronization device 350 may be integrated and implemented. Furthermore, the first synchronization device 330, the IEEE 1588 slave 340, the second synchronization device 350, and the small base station 350 may be integrated and implemented. In this case, the first synchronization device 330 may be a first synchronization unit of the IEEE 1588 slave 340, and the second synchronization device 350 may be a second synchronization unit of the IEEE 1588 slave 340. Therefore, the present invention will not be particularly limited to how the first and second synchronization devices 330 and 350 are configured.

6 is a flowchart illustrating a process of transmitting time synchronization of a core network to a small base station using IEEE 1588.

Referring to FIG. 6, first, the macro base station 305 receives a GPS signal through the GPS antenna 307 and transmits the GPS signal to the core network 300 (S600). As a result, the clock of the core network 300 is synchronized with the macro base station 305 and the GPS signal.

Subsequently, the core network 300 transmits time synchronization information to the IEEE 1588 master 310 again (S601). In other words, the IEEE 1588 master 310 is synchronized to the core network 300 by driving the IEEE 1588 master 310 using the clock of the core network 300.

The IEEE master 310 exchanges an IEEE 1588 message with the IEEE 1588 slave 340 (S603). As such, during the message exchange, the propagation delay and the scheduling delay are substantially corrected between the IEEE 1588 master 310 and the IEEE 1588 slave 340 through the first synchronization device.

Subsequently, the IEEE 1588 slave 340 estimates the frequency error and the phase error of the received packet (S605a) and corrects the slave clock to be synchronized with the master clock by using this (S605b).

The small base station 360 receives the slave clock from the IEEE 1588 slave 340 (S607). The small base station 360 operates in synchronization with the core network 300 and the macro base station 305 by using the slave clock.

FIG. 7 is a diagram illustrating a process of synchronizing an IEEE 1588 slave clock to a master clock when transmission delays of downlink and uplink are asymmetric in FIG. 6.

As it viewed in Figure 7, first from the master at the time of t ₀ (n) and sends the Sync1 () message to the slave, the slave Sync1 () message and measures the reception time t ₁ (n). In this case, n represents the number of Sync () message transmissions. The master immediately transmits the transmission time t ₀ (n) of the Sync1 () message to the slave through the Follow_up () message.

The slave sends Delay_Req1 () message at the time t ₂ (n), and the master measures the reception time t ₃ (n) of the Delay_Req1 () message and delivers it to the slave through the Delay_Res () message.

Through this process, all information about t ₀ (n), t ₁ (n), t ₂ (n), and t ₃ (n) can be obtained from the slave.

In addition, the Sync1 () when sending the message to the time delay in the down-link D _DL1, Delay_Req1 () is defined as the time delay in the uplink when transmitting messages D _UL1 and, D _DL1 and D _UL1, based on the master clock In the case of measurement, Equations 9 and 10 are satisfied.

(Equation 9)

(Equation 10)

In this case, w _DL (n) and w _UL (n) represent downlink jitter and uplink jitter, respectively.

After a certain time, the master delivers the (n + 1) th Sync () message. At this time, the (n + 1) th transmits a Sync2 () message that is different in size from the nth Sync1 () message. The slave measures the Sync2 () message reception time t ₁ (n + 1), and the master sends the Sync2 () message transmission time t ₀ (n + 1) to the slave using the Follow_up () message.

The slave transmits the (n + 1) th Delay_Req2 () message having a different size from the nth Delay_Req1 () message, and measures the transmission time t ₂ (n + 1).

The master measures Delay_Req ₂ () message reception time t ₃ (n + 1) and sends it to the slave through Delay_Res () message.

At this time, the size of the Sync1 () message and the Delay_Req1 () message is the same, the size of the Sync2 () message and the Delay_Req2 () message is the same, and the size of the Sync1 () message and the Sync2 () message is set differently.

Sync2 () of the time delay in the uplink time when sending a message to send to the time delay in the down-link D _DL2, Delay_Req2 () message is defined as D _UL2 and is measured by the master clock the D _DL2 and D _UL2 In this case, Equations 11 and 12 may be satisfied.

(Equation 11)

(Equation 12)

In FIG. 7, a case in which two types of Sync () messages having different sizes are used for convenience of description is described. However, in an embodiment of the present invention, three or more Sync () messages having different sizes may be used when necessary for slave clock synchronization. have.

FIG. 8 is a diagram illustrating an operation procedure between a master and a slave according to the clock synchronization method of FIG. 7.

8, first, when the master and the slave are initialized, the number n of transmissions of the Sync () message is initialized to 1 (S801).

Subsequently, the master transmits a Sync1 () message, and the slave measures the reception time t ₁ (n) of the Sync1 () message (S803).

Then, the master transmits the transmission time t ₀ (n) of the Sync1 () message to the slave using the Follow_up () message (S805).

Next, the slave transmits a Delay_Req1 () message and stores the transmission time t ₂ (n) (S807).

The master measures the reception time t ₃ (n) of the Delay_Req1 () message and transfers it to the slave using the Delay_Res () message (S809).

In the next step, the master transmits a Sync2 () message, and the slave measures the reception time t ₁ (n + 1) of the Sync2 () message (S811).

The master transmits the transmission time t ₀ (n + 1) of the Sync2 () message to the slave using the Follow_up () message (S813).

Next, the slave transmits a Delay_Req2 () message and stores the transmission time t ₂ (n + 1) (S815).

The master measures the reception time t ₃ (n + 1) of the Delay_Req2 () message and transfers it to the slave using the Delay_Res () message (S817).

Since Sync () has been delivered twice through the above process, n is increased by 2 (S819) and the process of delivering Sync1 () message from the master is repeated.

If you repeat as above, the odd-numbered transmission uses the Sync1 () and Delay_Req1 () messages, and the even-numbered transmission uses the Sync2 () and Delay_Req2 () messages to exchange messages.

Now, referring back to FIG. 5, a method of estimating frequency error (a) and phase error (b) in the second synchronization device when exchanging IEEE 1588 messages between the master and the slave by the method described in FIGS. 7 and 8. Let's look at.

Referring to FIG. 5, when a slave receiver receives an IEEE 1588 message, the slave receiver measures a reception time and reports the reception time to the frequency error and phase error estimator 570. When the message received through packet decoding is Sync1 () or Sync2 (), the time at which the message is received is stored.

When the message received through packet decoding is a Follow_up () or Delay_Res () message, a timestamp value included in the message is extracted and transmitted to the frequency error and phase error estimator 570.

When transmitting a Delay_Req1 () or Delay_Req2 () message from the transmitter of the slave, the message transmission time is measured and transmitted to the frequency error and phase error estimator 570.

Since the propagation delay and the scheduling delay have been corrected with reference to FIGS. 7 and 8, the asymmetry of the uplink and the downlink caused by the propagation delay and the scheduling delay has been removed. Will be removed.

Therefore, if the propagation delay and the scheduling delay correction after the residual delay, that is, the transmission delay is D _P , D _P can be defined as the same value in the downlink and uplink.

Next, when transmitting the Sync1 () message, the transmission delay in the _downlink is called D _{T, DL} , and when the Delay_Req1 () message is transmitted, the transmission delay in the _uplink is defined as D _{T, UL} .

If you define the size of the Sync2 () message as the size of the Sync1 () message, the transmission delay when sending the Sync2 () message is 2D _{T, DL} , and the transmission delay is 2D _{T, UL} when the Delay_Req2 () message is sent. do.

Using Equation 9 defined above, the equations (9) to (12) are rearranged as shown in (13) to (16).

(Equation 13)

(Equation 14)

(Equation 15)

(Equation 16)

Where K is a constant greater than zero and not one.

A and b can be estimated by repeating a plurality of message exchange processes using the relations defined in Equations 13 to 16 above.

For example, when the Sync () message and the Delay_Req () message are exchanged four times, Equations 13 to 16 may be expressed in a vector-matrix form as shown in Equation 17.

(Equation 17)

In this case, c = aDp, d = aD _{T, DL} , e = aD _{T, UL} , and y, A, and w are defined as in Equation 18.

(Equation 18)

From Equation 18, a and b can be estimated using the least squares estimation technique as shown in Equation 19.

(Equation 19)

, 위상 오차

가 정해지면, 슬레이브 클럭을 <수학식 20>과 같이 보정하여 마스터 클럭에 동기화된 클럭을 생성할 수 있다.For reference, a and b can be estimated by various methods such as recursive least squares (RLS) estimation method, regression estimation method, and filtering estimation method, in addition to the least-squares estimation method shown above. Frequency error estimate

Phase error

Once determined, the slave clock can be corrected as shown in Equation 20 to generate a clock synchronized with the master clock.

(Equation 20)

In this case, t_sync represents a clock generated by the slave to be synchronized with the master clock.

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 not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

In addition, the terms "comprise", "comprise" or "having" described in the specification mean that a corresponding component may be included unless otherwise stated, and thus, other components are excluded. It should be construed that it may further include other components. All terms, including technical and scientific terms, have the same meanings as commonly understood by one of ordinary skill in the art unless otherwise defined. Terms used generally, such as terms defined in a dictionary, should be interpreted to coincide with the contextual meaning of the related art, and shall not be interpreted in an ideal or excessively formal sense unless explicitly defined in the present invention.

The embodiment of the present invention is applicable to a small base station synchronization apparatus and method in an asymmetric communication link, and the transmission delay of the downlink and the transmission delay of the uplink are asymmetrically generated by the asymmetric transmission rates of the uplink and the downlink. In this case, the clock error may be estimated and compensated by the IEEE 1588 slave and the slave clock may be synchronized with the master clock.

300: core network 310: IEEE 1588 master
320: wired network 330: first synchronization device
340: IEEE 1588 slave 350: second synchronization device
360: small base station 410: first physical layer
415: First detector 420: Cue
430: second physical layer 435: second detector
440: 1588 code 510: packet reception time measurement unit
520: packet decoding unit 530: time stamp extraction unit
540: message generating unit 550: packet encoding unit
560: packet transmission time measurement unit 570: frequency error and phase error estimation unit
580: local clock generator 590: clock correction unit

Claims (14)

Receiving a first synchronization signal synchronized with a GPS signal from a core network, generating a first packet including synchronization information of the core network, and providing a plurality of packets to provide delay time information according to a time delay of the first packet; Master for transmitting and receiving (master);
A wired network via the first packet and the plurality of packets;
A first synchronization device configured to generate and initialize a second synchronization signal in synchronization with the first synchronization signal, and to first correct the second synchronization signal using the synchronization information and / or the delay time information;
Receiving a first packet to measure a reception time, a transmission time of a packet transmitted to the master of the plurality of packets, and a timestamp value of a packet received from the master of the plurality of packets A slave to extract;
A second synchronization device for second-correcting the second synchronization signal using the reception time, the transmission time, and the timestamp value; And
A small base station synchronized with the core network using the second corrected second synchronization signal;
Small base station synchronization apparatus in an asymmetric communication link comprising a. The method according to claim 1,
The plurality of packets includes a second packet, a third packet, and a fourth packet, wherein the second packet and the fourth packet are packets transmitted by the master to the slave, and the third packet is determined by the master. Small base station synchronization apparatus in an asymmetric communication link, characterized in that the packet received from the slave. According to claim 2,
When the master and the slave exchange the first packet to the fourth packet two or more times, odd-numbered first packets and third packets have the same size, and even-numbered first packets and third packets Are the same as each other, wherein the odd-numbered first packets and the even-numbered first packets are different in size, and the odd-numbered third packets and the even-numbered third packets are different in size. Small base station synchronization apparatus in an asymmetric communication link, characterized in that different. The method of claim 2,
The first synchronization device includes a first physical layer, a second physical layer, queues, a first detector, a second detector, and a 1588 code.
The first physical layer is connected to the physical layer of the master to transfer the first, second and / or fourth packets provided to the first physical layer to the first detector and the queue,
The second physical layer is connected to the physical layer of the slave to transfer the third packet provided to the second physical layer to the second detector and the queue,
The queue stores the first, second and / or fourth packets provided to the first physical layer and sequentially provides them to the second physical layer or stores the third packets provided to the second physical layer. Are sequentially provided to the first physical layer,
The first detector detects 1588 of the first, second and / or fourth packets received by the first physical layer,
The second detector detects 1588 of the third packet received at the second physical layer,
And the 1588 code processes the IEEE 1588 packets of the first to fourth packets provided by the first and second detectors. The method of claim 2,
The slave includes a packet receiving time measuring unit, a packet decoding unit, a time stamp extracting unit, a message generating unit, a packet encoding unit and a packet transmission time measuring unit,
The packet reception time measuring unit measures reception time of the first packet to generate reception time information.
The packet decoding unit decodes the first to fourth packets,
The timestamp extractor extracts the timestamp values of the decoded second to fourth packets,
The message generator generates the third packet,
The packet encoding unit receives and encodes the third packet,
And the packet transmission time measuring unit measures transmission time of the third packet to generate transmission time information. The method according to claim 1,
The second synchronization device includes a frequency error and phase error estimator, a clock corrector, and a local clock generator,
The frequency error and phase error estimator estimates a frequency error and a phase error using the time stamp value, the reception time information, and the transmission time information, and outputs a result value.
And the clock correction unit performs secondary correction of the second synchronization signal using the resultant value and the local clock provided by the local clock generator. The method of claim 6,
In the asymmetric communication link, the frequency error and the phase error are estimated by any one of a least squares estimation method, a recursive least squares (RLS) estimation method, a regression estimation method, and a filtering estimation method. Small base station synchronization device. The method of claim 6,
The first and second corrected second synchronization signals are clock signals,
The clock signal t_slave of the first corrected second synchronization signal, the clock signal t_sync of the second corrected second synchronization signal, and the frequency error (

), Phase error (

)

Has a relation of,
And the frequency error is a ratio of the frequency of the slave to the clock frequency of the master, and the phase error is a phase difference between the clock of the slave and the master. Receiving a first synchronization signal synchronized with a GPS signal from a core network, generating a first packet including synchronization information of the core network, and providing a plurality of packets to provide delay time information according to a time delay of the first packet; Master for transmitting and receiving (master);
A wired network via the first packet and the plurality of packets;
A first synchronization unit and a first packet configured to generate and initialize a second synchronization signal in synchronization with the first synchronization signal, and to first correct the second synchronization signal by using the synchronization information and / or the delay time information; Receive a signal to measure the reception time, the transmission time of the packet transmitted to the master of the plurality of packets, and extracts a timestamp value of the packet received from the master of the plurality of packets, A slave having a second synchronization unit to second-correct the second synchronization signal by using a reception time, the transmission time and the timestamp value; And
A small base station synchronized with the core network using the second corrected second synchronization signal;
Small base station synchronization apparatus in an asymmetric communication link comprising a. Receiving a first packet including synchronization information of a core network and a second packet including transmission time information of the first packet;
Transmitting a third packet requesting delay time information according to a time delay of the first packet;
Receiving a fourth packet including reception time information on the transmission of the third packet;
Generating a synchronization signal and first correcting the synchronization signal using the synchronization information and / or the delay time information;
Measuring a reception time of the first packet and a transmission time of the third packet;
Extracting timestamp values of the second packet and the fourth packet;
Secondly correcting the synchronization signal using the reception time, the transmission time, and the timestamp value; And
Synchronizing a small base station with the core network using the second corrected second synchronization signal;
A synchronization method of a small base station synchronization device in an asymmetric communication link, characterized in that it comprises a. The method of claim 10,
The transmission and reception of the first and fourth packets are performed periodically several times. During periodic transmission and reception of the first and fourth packets, an odd number of first packets and an even number of first packets are different from each other. Asymmetric communication, characterized in that the size of the first packet and the third packet is received and transmitted in the same size, and the odd-numbered first and third packets are received and transmitted in the same size A method of synchronizing a small base station synchronization device on a link. The method of claim 10,
The second step of correcting the synchronization signal by using the reception time, the transmission time and the time stamp value
Calculating a result value by estimating a frequency error and a phase error by using the reception time, the transmission time, and the timestamp value; And
Receiving a local clock and performing secondary correction on the synchronization signal using the local clock and the resultant value;
A synchronization method of a small base station synchronization device in an asymmetric communication link, characterized in that it comprises a. The method of claim 10,
Receiving the second packet and the fourth packet and extracting a timestamp value comprises decoding the second packet and the fourth packet; How to sync. Measuring the transmission time of the third packet
Generating a third packet requesting the delay time information;
Encoding the third packet
A synchronization method of a small base station synchronization device in an asymmetric communication link, characterized in that it comprises a.

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