KR101624643B1 - Apparatus and Method for Synchronizing Micro Base Station Using Wireless Link - Google Patents

Abstract

In order to simultaneously operate the macro base station and the small base station in the mobile communication network, the carrier frequency and the signal transmission time of the small base station must be synchronized with the macro base station. To this end, the time synchronization information of the macro base station is transmitted to the small base station And a small base station synchronization apparatus and method using a wireless link for detecting time synchronization information of a small base station and matching time synchronization between a small base station and a macro base station. The small base station synchronization apparatus according to the first embodiment of the present invention includes a receiver A beacon signal synchronized to the GPS signal and / or a data packet of the data, and to transmit the beacon signal and / or the data packet backoff time An access point having a back-off controller for transmitting An access terminal having a jitter reduction unit for receiving a transmitted beacon signal and / or the data packet and outputting a synchronization signal in which jitter is reduced using synchronization time information of the transmitted beacon signal and time information of the received beacon signal, And a small base station connected to the access terminal to receive the synchronization information of the synchronization signal whose jitter is reduced and to perform synchronization with the base station according to the synchronization information.

 Macro base station, small base station, femto, pico, backoff controller, time jitter

Description

Technical Field [0001] The present invention relates to a small base station synchronization apparatus and method using a wireless link,

In order to simultaneously operate a macro base station and a small base station in a mobile communication network, a carrier frequency and a signal transmission time of a small base station are transmitted to a macro base station In order to accomplish this, a small base station synchronization apparatus and method using a wireless link that transmits time synchronization information of a macro base station to a small base station and detects time synchronization information in a small base station and synchronizes time synchronization between the small base station and the macro base station .

In recent years, a compact base station called femtocell or picocell has attracted much attention in terms of expansion of coverage of mobile communication network, improvement of service quality, and integration of wired / wireless communication services. A femtocell refers to a very small base station, such as a digital subscriber line router or a cable modem, which is much smaller than a macro base station. The femtocell can operate in the authorized frequency band or the unofficial frequency band (ISM band) allocated to the mobile communication service provider. The output voltage is 10 ~ 200 mW, the communication distance covers 50 ~ 100 m, Users can access simultaneously. It can be installed directly by a network operator or a user, connected to a core network using a separate communication network or using a high-speed Internet network. And picocell is a medium concept between femtocell and macro base station. It refers to a small base station that can be accessed by up to 30 users at the same time, which can be installed in a building office or a school, and is somewhat larger than a femtocell.

In the case of a repeater, since the signal received from the macro base station is transmitted as it is, the coverage of the base station is enlarged but the capacity is not increased. On the other hand, in the case of the small base station, The capacity of the entire mobile communication network increases in proportion to the number. Therefore, in the case of small base stations, the coverage increases and the capacity of the wireless network increases. Especially, in a mobile communication system which is being commercialized or standardized recently, the coverage of a macro base station is narrower than that of a conventional mobile communication system because a carrier frequency used is high and a bandwidth is wide. That is, when the network is constructed only by the macro base station, the number of required base stations increases and the network construction cost increases. In addition, since the rate of data communication is increased as compared with the voice communication in accordance with the evolution of the mobile communication system, it is difficult to provide a high-speed data communication service to a large number of users using only the existing 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 a home where people mainly use wireless communication.

Such a small base station is classified into fixed mobile convergence (FMC) using a dual mode terminal and fixed mobile substitution (FMS) using an existing mobile communication terminal intact. In particular, the FMS scheme uses the same transmission scheme as that of the existing macro base station using a small base station, so that it can benefit from the coverage increase and the capacity increase by the small base station using the existing mobile phone supporting one mobile communication standard . On the other hand, in the case of the FMC method, since the mobile communication standard between the macro base station and the small base station is different, the user must replace the existing terminal with a terminal supporting the dual mode.

Meanwhile, in order to simultaneously operate the macro base station and the small base station in the mobile communication network, the carrier frequency and the signal transmission time of the small base station must be synchronized with the macro base station. In particular, when a time division duplex scheme such as Mobile WiMAX (Mobile WiMAX, domestic name WiBro) is used, if the signal transmission time of the macro base station and the small base station is shifted, the uplink / downlink signal of the macro base station and the downlink / Uplink signals, interference between the macro base station and the small base station is very important.

To this end, conventionally, in the case of a macro base station, a transmitting / receiving antenna is installed outdoors, so that global positioning system (GPS) information is received from a satellite to synchronize the core network and the macro base station. However, since a small base station is installed in a room such as an office, a school, an apartment, or a home, which is generally difficult to receive GPS signals, a GPS signal can not be used for acquiring the synchronization. In addition, even if a GPS signal can be received, a separate device for receiving GPS signals must be attached to a small base station, so that the price of a small base station is high.

In the case where the GPS signal can not be received from the small base station, a method of acquiring the synchronization using the pilot signal transmitted from the macro base station has been proposed. However, this method is disadvantageous in that it can be applied only when the downlink pilot signal of the macro base station can be received in the area where the small base station is installed. A small base station is installed in an area where a macro base station signal is not transmitted, thereby widening a wireless communication service area and enlarging the capacity. However, if a small base station is installed within the coverage of a 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.

1, when the IEEE 1588 is used, the core network 100 and the small base station 140 are connected by an IP network 120 in a wired manner. In the core network 100, synchronization is acquired using a GPS or the like, and the information is transmitted to the small base station 140 through a wire. An IEEE 1588 master 110 is used for the core network 100 and an IEEE 1588 slave 130 is used for the small base station 140 for synchronous information delivery. IEEE 1588 periodically transmits a data packet in which synchronization information of the core network 100 is recorded to the IEEE 1588 slave 130. The IEEE 1588 slave 130 estimates 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, So that the synchronization of the base station 140 coincides. In the case of the macro base station, synchronization is established between the macro base station and the small base station 140 because the synchronization is synchronized with the core network 100 using the GPS signal.

However, IEEE 1588 is only used when the uplink transmission delay for transmitting data from the small base station 140 to the core network 100 is the same as the downlink for transmitting data from the core network 100 to the small base station 140 Applicable. That is, when the transmission speeds of the uplink and the downlink are the same as those of the Ethernet, accurate synchronization can be obtained using IEEE 1588. However, when a digital subscriber line (DSL) is used as in the case of a high-speed Internet, a considerable difference occurs in the transmission speeds of the downlink and the uplink. Therefore, when applying the IEEE 1588 standard, An error will occur.

For example, the data measured by SK Broadband network in our company showed that the synchronization estimation error due to the asymmetry of the uplink and downlink was measured to be several hundred ms to several ms. Therefore, there is a problem that the synchronous transmission method using IEEE 1588 does not satisfy the synchronization error standard within ± 20 μs required by the mobile WiMAX standard.

2 is a diagram showing a synchronization acquisition system of a small base station using a wireless LAN as a backhaul.

2, the macro base station 210 receives a GPS signal using a GPS antenna 215 installed outdoors and transmits the GPS signal to a base station controller 220 and a core network 200 So that the macro base station 210 and the core network 200 are synchronized with each other. In addition, the timer 231 in the access point (AP) 230 is driven in synchronization with the GPS signal.

The timer 231 informs the wireless LAN AP 230 of the transmission time of the beacon. For example, the timer 231 is initialized to 1023, and the value of the timer 231 is decremented by 1 for every clock synchronized with the GPS, and when the timer 231 becomes 0, the beacon is set to be transmitted. At this time, the timer 231 becomes 0 and then initialized to 1023 again on the next clock. In this manner, a beacon is transmitted every time the timer 231 becomes 0 with a period of 1024 clocks.

When using a wireless LAN backhaul, the beacon of the beacon generator 233 and the data packet of the data packet generator 235 are temporally mixed and transmitted to the small base station 250, and the wireless LAN access terminal (AT) 240 acquires time synchronization information by separating a beacon from the packets received through the demultiplexer 241. Through this process, time synchronization information of the macro base station 210 can be transmitted to the small base station 250.

In such a configuration, the wireless LAN standard specifies a random backoff 239 in order to minimize packet collision during multiple access between a plurality of terminals, and uses a random backoff scheme through the random backoff 239. That is, if there is no UE transmitting data in a specific time slot, the mobile station transmits the packet after a random number of time elapses. This is designed to lower the collision probability by making the packet transmission time different because the probability of packet collision is very high if two or more UEs check the data transmission in the same slot slot and then transmit the packet at the same time. That is, the WLAN AP 230 generates a beacon containing a time stamp of the WLAN AP 230 every time the timer 231 informing the beacon transmission time becomes '0'.

However, the generated beacon is not transmitted immediately but is transmitted after being delayed for a predetermined time due to the random backoff operation of the wireless LAN described above. However, since the wireless LAN AT 240 receiving the beacon can not know the delayed time due to the random backoff, a time error as much as a time delay due to the random backoff occurs in the synchronization information transmitted to the small base station 250 .

For example, in the case of using the orthogonal frequency division multiplexing (OFDM) scheme defined in the IEEE 802.11 standard and using a bandwidth of 20 MHz, the delay due to the random backoff is arbitrarily set between 9 ms and 135 ms. In case of mobile WiMAX standard, the time synchronization error should be within ± 20 ㎲ in case of not considering handover, so it is very difficult to satisfy the time synchronization error specified by the standard considering the delay due to the random backoff operation .

The embodiment of the present invention changes the beacon transmission method of the wireless LAN AP to reduce the time error as much as the time delay due to the random backoff and applies a new time synchronization estimation technique to the wireless LAN AT, And to provide a small base station synchronization apparatus and method using a link.

A small base station synchronization apparatus using a wireless link according to a first embodiment of the present invention includes a base station for providing received GPS signals and / or data; An access point having a backoff controller for generating a beacon signal synchronized with the GPS signal and / or a data packet of the data, and transmitting the beacon signal and / or the data packet by varying the backoff time upon backoff transmission; An access having a jitter reduction unit for receiving the transmitted beacon signal and / or the data packet and outputting a synchronization signal in which jitter is reduced using synchronization time information of the transmitted beacon signal and time information of the received beacon signal; terminal; And a small base station connected to the access terminal to receive synchronization information of the synchronization signal whose jitter is reduced and to perform synchronization with the base station according to the synchronization information.

Also, a synchronization method of a small base station synchronization apparatus using a wireless link according to a first embodiment of the present invention includes: receiving a GPS signal and / or data synchronized with a base station; Generating a beacon signal synchronized with the GPS signal and / or a data packet of the data, and transmitting the beacon signal and / or the data packet with a backoff time during backoff transmission; Receiving the transmitted beacon signal and / or the data packet, and outputting a synchronization signal in which jitter is reduced using the synchronization time information of the transmitted beacon signal and the received time information of the beacon signal; And synchronizing the synchronization signal with the base station according to the synchronization information, the synchronization signal being provided with the jitter-reduced synchronization signal.

Meanwhile, a small base station synchronization apparatus using a wireless link according to a second embodiment of the present invention includes a base station for providing received GPS signals and data; An access point having a backoff controller for generating a beacon signal synchronized with the GPS signal and transmitting the beacon signal by varying a backoff time during backoff transmission; An access terminal for receiving the transmitted beacon signal and for outputting a synchronization signal with reduced jitter using the synchronization time information of the transmitted beacon signal and the received time information of the beacon signal; A small base station which is connected to a communication network connected to the base station and receives the data and is connected to the access terminal to receive synchronization information of the synchronization signal with reduced jitter and performs synchronization with the base station according to the synchronization information, .

In addition, a method of synchronizing a small base station synchronizing apparatus using a wireless link according to a second exemplary embodiment of the present invention includes: receiving a GPS signal synchronized with a base station and / or a core network; Generating a beacon signal synchronized with the GPS signal, transmitting the beacon signal while varying the backoff time during the backoff transmission; Receiving the transmitted beacon signal, outputting a synchronization signal in which jitter is reduced using synchronization time information of the transmitted beacon signal and time information of the received beacon signal; Receiving data provided via the core network and synchronization information of the synchronization signal in which the jitter is reduced, and performing synchronization with the base station according to the synchronization information.

According to the embodiment of the present invention as described above, even when the uplink and downlink of the backhaul are asymmetric, accurate link synchronization can be achieved by establishing a radio link for synchronous transmission. In particular, when using a wireless LAN based wireless backhaul for the convenience of installation of a small base station, time synchronization of a small base station can be obtained by using a beacon of a wireless LAN without using a separate packet for synchronous information transmission . As a result, it is possible to significantly reduce the installation position restriction of the small base station.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference numerals as possible, as they can be displayed on different drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

In describing the components of the present invention, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. When a component is described as being "connected", "coupled", or "connected" to another component, the component may be directly connected to or connected to the other component, It should be understood that an element may be "connected," "coupled," or "connected."

3 is a block diagram of a small base station synchronization apparatus according to a first embodiment of the present invention.

3, the handheld base station synchronization apparatus according to the first embodiment of the present invention includes a base station 310, 320 providing a received GPS signal and / or data, a beacon signal synchronized to a GPS signal, and / An Access Point (AP) 330 having a backoff controller 339 for generating data packets for data and transmitting back beacon signals and / or data packets with backoff time upon backoff transmission, A jitter reducer 347 for receiving a transmitted beacon signal and / or a data packet and outputting a synchronization signal in which jitter is reduced using synchronization time information of the transmitted beacon signal and time information of the received beacon signal, (AT) 340 having an access terminal (AT) 340, a small base station 350 connected to the AP 330 to receive synchronization information of a synchronization signal with reduced jitter, and performing synchronization with a base station according to synchronization information And there.

At this time, the AP 330 includes a timer 331 for connecting to the macro base station 330, a beacon generator 333 for connecting to the timer 331, a data packet generator 335 for connecting to the base station controller 320, A multiplexer 335 connected to the generator 333 and the data packet generator 335 and a backoff controller 339 connected to the multiplexer 335.

The AT 340 also includes a demultiplexer 341 for separating the received beacon and data packets from each other, a time information reconstructor 343 connected to the demultiplexer 341, a data decoder 345 connected to the demultiplexer 341, And a time jitter reducer 347 connected to the time information reconstructor 343. [

More specifically, the supporting stations 310 and 320 may be divided into a macro base station 310 and a base station controller 320. The macro base station 310 may include a GPS module such as an outdoor antenna or a GPS antenna 315 for receiving a GPS signal from GPS. The macro base station 310 may receive a GPS signal and transmit the GPS signal to the base station controller 320, And is configured to be synchronized with the network 300.

The timer 331 is synchronized with the GPS signal provided by the macro base station 310 and informs the transmission time of the beacon signal generated in the beacon generator 330 when the beacon signal is initialized on the basis of a predetermined period. For example, when one clock period of the timer 331 is 1 ms and a transmission period of the beacon signal is 1 ms, the timer 331 is initialized to 999, and the value of the timer 331 The timer 331 is decremented by one and the beacon signal is transmitted when the timer 331 becomes zero. At this time, the timer 331 becomes 0 and then initialized to 999 again on the next clock. Accordingly, since the beacon signal is transmitted every time the timer 310 becomes 0 with a cycle of 1000 clocks, the transmission period of the beacon signal becomes 1 ms, and the transmission time of the beacon signal can be synchronized with the GPS clock do.

The beacon generator 330 is a generator related to generation or generation of a beacon, and provides the generated beacon to the multiplexer 337. Here, the beacon is transmitted periodically to notify the AT 340 of the operation area of the AP 330, the transmission standard, the frequency band, the beacon transmission period, the ID information of the AP 330, Signal. Even if there is no data to be transmitted by the AP 340, the beacon is always transmitted periodically.

The data packet generator 335 packetizes the data provided by the base station controller 320.

The multiplexer 337 mixes the data packet provided by the data packet generator 335 with the beacon provided by the beacon generator 333 and provides it to the backoff controller 339. In general, when using a wireless LAN backhaul, both the beacon and the data packet are transmitted to the small base station 350 through the wireless backhaul, and the AP 330 can transmit one packet at a time, so that the multiplexer 337 transmits the beacon and the data packet Are mixed and output in a temporal manner.

The backoff controller 339 receives the beacon and the data packet output from the multiplexer 337, and adjusts the backoff value when transmitting in the backoff method. For example, it is possible to transmit data packets in a manner that reduces the transmission time change of the beacon, that is, the backoff time. In the case of a wireless LAN, in the case of a wireless LAN, the AP 330 and the plurality of ATs 340 use the same frequency resource, Is a method used to lower the collision probability.

Meanwhile, the demultiplexer 341 of the AT 340 can be connected to, for example, a receiving antenna or a receiving antenna module of the AT 340. The demultiplexer 341 separates beacons and data packets provided via the antenna module, Are output on different paths.

The time information reconstructor 343 receives the beacon output from the demultiplexer 341 and uses the beacon to restore synchronization information on the synchronization time of the macro base station 310 or the core network 300. [

 The time jitter reducer 347 reduces the synchronization time error or jitter of the recovered synchronization information when the synchronization information is restored in the time information reconstructor 343.

The data decoder 345 receives the data packet from the demultiplexer 341 and decodes the provided data packet.

The small base station 350 may be a femto base station, for example, receiving jitter-reduced synchronizing signals through the time jitter reducing unit 347 and data from the data decoder 345, And so on.

FIG. 4 is a diagram illustrating a detailed structure of the backoff controller of FIG. 3, and FIG. 5 is a flowchart illustrating an operation process of FIG.

4, the backoff controller according to the embodiment of the present invention includes an AP and a backoff seed allocator 410 for allocating a backoff seed for an AT capable of simultaneously connecting to the AP at the initial operation of the AP, A backoff time calculation unit 413, a packet detection unit 415, a backoff time reduction unit 417, a backoff time detection unit 419, a packet transmission unit 421, And a base 423.

Here, the time slot designation unit 411 assigns the time slot number of the data packet by dividing the transmission time at regular intervals using the clock linked to the GPS signal. The backoff time calculator 413 calculates a backoff time of a data packet. The packet detector 415 detects whether a data packet is transmitted by another AT other than its own AT in the current time slot to be transmitted do.

In addition, the backoff time reduction unit 417 reduces the backoff time when no data packet is detected in another AT, and the backoff time detection unit 419 checks whether the backoff time becomes "0" If the decremented backoff time is "0 ", the packet transmission unit 421 transmits a data packet of its AT and returns to the time slot designation unit 411. [ If a data packet is detected in another AT, the time slot waiting unit 423 maintains the backoff time in the AT's current time slot, waits for one time slot, and returns to the packet detecting unit 415. [

Referring to FIG. 5 together with FIG. 3, when the operation of the backoff controller is further examined, if the number of portable personal terminals (or terminal stations) which can be simultaneously accessed when the AP 330 starts operating is N_total, Can be defined as Equation (1).

N_total = N_AT + 1

Here, N_AT is the number of personal portable terminals that can be connected at the same time.

For example, N_AT = 1 and N_total = 2 when a backhaul is formed by connecting AP 330 and AT 340 one to one, and two AT 340s are connected to one AP 330 , N_AT = 2 and N_total = 3.

At this time, the N_total wireless devices including the AP 330, i.e., the personal portable terminal, are allocated different backoff seeds from 0 to (N_total-1) (S501).

For example, when two APs 340 are connected to one AP 330, the backoff seed can be expressed as Equation (2), Equation (3) and Equation (4).

(backoff seed for AP) = 0

(backoff seed for AT1) = 1

(backoff seed for AT2) = 2

In step S502, the AP 330 allocates a time slot number by dividing the transmission time by a predetermined interval using a clock linked to the GPS.

Let N_TS be the time slot number at the time of data packet transmission. At this time, the backoff value for the AP 330 is calculated as shown in Equation (5).

(X% y) denotes a remainder obtained by dividing the integer x by an integer y, and SEED_AP denotes a seed allocated to the AP 330. Here, [x] denotes a maximum integer equal to or smaller than x.

For example, a seed is allocated as shown in Equation (5). If N_total = 3 and P = 8, a T_backoff value according to N_TS is calculated as Equation (6), Equation (7), and Equation .

T_backoff = 0 if 0? N_TS? 7, 24? N_TS? 31, 48? N_TS?

T_backoff = 1 if 8? N_TS? 15, 32? N_TS? 39, 56? N_TS?

T_backoff = 2 if 16 N_TS 23, 40 N_TS 47, 64 N_TS 71,

After the T_backoff value is calculated in the same manner as in Equation (5) (S503), if no packet transmission is detected by another wireless device in the current time slot (S504), the T_backoff value is calculated by Equation ≫ (S505).

T_backoff = T_backoff - 1

When the T_backoff value becomes 0 through the calculation as in Equation (5) (S506), the packet is transmitted (S507) and is calculated again from N_TS.

If another wireless device is transmitting a packet in the current time slot, the T_backoff value is maintained as it is, and the packet is waited for one time slot (S508).

As a whole, the T_backoff value allocated to the AP 330 changes every time the P time slot elapses according to Equation (5), and the packet is transmitted only when the T_backoff value becomes '0'.

Through such a backoff procedure, it is possible to prevent collision between packets transmitted by wireless devices, and each wireless device can be equally allocated a packet transmission priority.

FIG. 6 is a block diagram of the time information reconstructor and the jitter reduction of FIG. 3;

6, the time information restorer 343 and the time jitter reducer 347 of FIG. 3 include a remote timer information extracting unit 610, a remote timer information extracting unit 610 A time error adjusting unit 620 for receiving the beacon signal and the local time clock, a time error adjusting unit 620 for receiving the beacon signal and the local time clock, a time error adjusting unit 620 and a receiving time measuring unit 630, An offset estimator 640, and a local timer 650 for connecting to the frequency and phase offset estimator 640. [ In this case, the local timer 650 may include a local time clock generator and a time jitter calculator.

Here, when the beacon is received, the remote timer information extractor 610 extracts the remote time clock information of the timer of the AP using the time stamp information of the received beacon.

The time error adjuster 620 outputs the value of the distance-time clock information provided by the remote timer information extractor 610 together with the media_delay value. In this case, media_delay represents the sum of the signal transmission delay at the transmitting end, the transmission time from the transmitting end antenna to the receiving end antenna, and the signal transmission delay at the receiving end.

When the beacon is received, the reception time measuring unit 630 measures the time when the beacon is received using the local time clock provided by the local time clock generator of the wireless LAN AT, for example.

The frequency and phase offset estimator 640 estimates the frequency ratio and the phase difference of the local time clock with respect to the far time clock. For this, it can be estimated by various methods such as LS (Least Squares) estimation method, RLS (Recursive Least Squares) estimation method, regression estimation method, and filtering estimation method.

The local timer 650 updates the local time clock using the frequency and phase offset information provided by the frequency and phase offset estimator 640 so that the local time clock is synchronized with the far time clock. Accordingly, the local timer 650 may be more specifically a local time clock generator for providing a local time clock to the reception time measurer 630, and a time jitter calculator for synchronizing the local time clock with the remote clock have.

Next, the operation of the time information restoring unit and the jitter reducing operation of FIG. 6 will be described.

First, when a beacon is received, the remote timer information extracting unit 610 extracts the remote time clock using the beacon time stamp information.

If the time stamp value of the n-th beacon is t (n), the time at which the n-th beacon is actually transmitted is expressed by Equation (10).

s (n) = t (n) + w (n)

Here, w (n) represents time synchronization jitter due to backoff delay at the transmitting end.

However, since the time actually received by the AT includes a signal transmission delay at the transmitting end, a transmission time from the transmitting end antenna to the receiving end antenna, and a signal transmission delay at the receiving end, when all these are added to express "media_delay" The time when the second beacon is received by the AT, or more precisely, the time error adjustment unit 620 of the AT, is expressed by Equation (11).

(n) = s (n) + media_delay = x (n) + w (n)

Here, x (n) = t (n) + media_delay.

Accordingly, when the n-th beacon is received at the time u (n) based on the remote clock, that is, the time clock of the AP, the reception time measurer 630 outputs the local time clock, , Which is expressed as Equation (12).

y (n) = a 占 (n) + b

Here, the constant a represents the frequency ratio of the local time clock to the far time clock, and the constant b represents the phase difference of the local time clock relative to the far time clock.

Substituting u (n) in Equation (11) into Equation (12), Equation (13) can be expressed as Equation (13).

       y (n) = a x (n) + b + aw (n)

In Equation (13), x (n) can be calculated using the time stamp t (n) recorded in the beacon and the constant value media_delay, y (n) can be measured using the local time clock, and w n) is modeled as noise with an average of zero.

Therefore, if a plurality of beacons are transmitted, the frequency and phase offset estimator 640 can estimate constants a and b using the relationship between x (n) and y (n).

For example, when x (n) and y (n) values are measured for N beacons, the constants a and b are estimated through LS (Least Squares) estimation as shown in Equation (14) can do.

For reference, the constants a and b can be estimated by various methods such as RLS (Recursive Least Squares) estimation method, regression estimation method, and filtering estimation method in addition to the LS estimation method shown in Equations (14) and .

When the constants a and b are determined, the time synchronization error e (n) in the local timer 650 is calculated as shown in Equation (16).

The local timer 650 can update the local time clock as Equation (17) to synchronize the local time clock and the remote time clock.

local_time = local_time - e (n)

Each time a beacon is received, the above procedure is repeated to maintain the synchronization of the local time clock and the remote time clock.

As a result, the small base station synchronizes with the macro base station or the core network according to the synchronization information provided by the AT.

FIG. 7 is a signal flow diagram illustrating a process of transmitting time synchronization of a macro base station to a small base station in the small base station synchronization apparatus of FIG. 3;

First, the macro base station 310 receives the GPS signal through the GPS module including the GPS antenna 315, more precisely the GPS antenna 315 (S700).

Next, the macro base station 310 causes the core network 300 to be synchronized using the GPS signal (S701).

In addition, the macro base station 310 transmits the synchronization information to the AP 330 (S703). At this time, the AP 330 uses the synchronization information to drive the timer and interwork with the timer to periodically generate a cone.

The backoff controller 339 adjusts the backoff value when the AP 330 transmits the beacon to the AT 340 in a backoff manner, and transmits the adjusted backoff value (S705).

Thereafter, the AT 340 receives the beacon provided by the AP 330, or more precisely the backoff controller 339, and provides a jitter-reduced synchronization via the time information reconstructor 343 and the time jitter reducer 347 Information to the small base station 350 (S707).

8 is a diagram illustrating a structure of a small base station synchronization apparatus according to a second embodiment of the present invention.

8, a small base station synchronization apparatus according to a second embodiment of the present invention includes base stations 810 and 820 for providing received GPS signals and data, a beacon signal synchronized to a GPS signal, An AP 830 having a back-off controller 835 for transmitting a back-off time when back-off transmission is performed, an AP 830 for receiving a transmitted beacon signal, synchronization time information of the transmitted beacon signal, The AT 840 having a time jitter buffer 843 for outputting a jitter reduced synchronous signal and the communication network 800 and 805 connected to the base stations 810 and 820 to receive data and transmit data to the AT 840 And a small base station 850 that receives synchronization information of the synchronization signal with reduced jitter and performs synchronization with the base stations 810 and 820 according to the synchronization information.

8, a beacon signal with a time-synchronized jitter is compared with a small-sized base station synchronizer according to the first embodiment of FIG. 3, for example, The data is provided to the AT 840 at the base station 830 but the data is provided to the small base station 850 through the core network 800 and the IP network 805. [

Accordingly, the AP 830 includes a timer 831 that connects to the macro base station 810, a beacon generator 833 that connects to the timer 831, and a backoff controller 839 that connects to the beacon generator 833 The AT 840 includes a time information reconstructor 841 for reconstructing the time information of the received beacon signal and a time jitter reducer 847 connected to the time information reconstructor 841.

Other details, other than these parts, are similar to those of the small base station synchronizing apparatus of FIG. 3, so that further description will be omitted.

Also, in the synchronization method of the small base station synchronization apparatus according to the second embodiment of the present invention, similar to the contents of the invention in the synchronization method of the small base station synchronization apparatus of FIG. 7, further description will be omitted.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

The terms "include", "comprise", or "have" in the specification do not exclude other components, unless the context clearly indicates otherwise. But should be construed to include other elements. All terms, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, unless otherwise defined. Commonly used terms, such as predefined terms, should be interpreted to be consistent with the contextual meanings of the related art, and are not to be construed as ideal or overly formal, unless expressly defined to the contrary.

The embodiment of the present invention is applicable to a small base station synchronization apparatus using a wireless link, and even when the uplink and downlink of the backhaul are asymmetric, a radio link for synchronous transmission can be established to obtain accurate time synchronization. In particular, when using a wireless LAN based wireless backhaul for the convenience of installation of a small base station, time synchronization of a small base station can be obtained by using a beacon of a wireless LAN without using a separate packet for synchronous information transmission . As a result, it is possible to significantly reduce the installation position restriction of the small base station.

1 illustrates 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 showing a synchronization acquisition system of a small base station using a wireless LAN as a backhaul;

3 is a diagram illustrating a structure of a small base station synchronization apparatus according to a first embodiment of the present invention,

4 is a diagram showing the detailed structure of the back-off controller of Fig. 3,

FIG. 5 is a flowchart showing the operation process of FIG. 4,

FIG. 6 is a block diagram showing the detailed structure of the time information decompressor and the time jitter buffer of FIG. 3;

FIG. 7 is a signal flow diagram illustrating a process of transmitting time synchronization of a macro base station to a small base station in the small base station synchronization apparatus of FIG. 3;

8 is a diagram illustrating a structure of a small base station synchronization apparatus according to a second embodiment of the present invention.

DESCRIPTION OF REFERENCE NUMERALS

300, 800, core network 310, 810: macro base station

315, 815: GPS antenna 320, 820: base station controller

330, 830: AP 331, 831: timer

333, 833: Beacon generator 339, 835: Backoff controller

340, 840: AT 343, 841: Time information restorer

347, 843: Time jitter reduction 350, 850: Small base station

Claims (9)

A base station for providing received GPS signals and / or data; A backoff controller for generating a beacon signal synchronized with the GPS signal and / or a data packet of the data, and transmitting the beacon signal and / or the data packet by varying the backoff time upon backoff transmission An access point (AP); A time jitter for receiving the transmitted beacon signal and / or the data packet and for outputting a synchronization signal in which jitter is reduced using synchronization time information of the transmitted beacon signal and time information of the received beacon signal; An access terminal (AT) having a weakener; A small base station connected to the access terminal and being provided with synchronization information of the synchronization signal in which the jitter is reduced and performing synchronization with the base station in accordance with the synchronization information; The base station synchronizing apparatus using the wireless link. The method according to claim 1, The backoff controller A time slot designation unit for assigning a time slot number of the data packet by dividing a transmission time by a constant interval using a clock linked to the GPS signal; A backoff time calculator for calculating a backoff time of the data packet; A packet detector for detecting transmission of a data packet by another AT other than its own AT in a current time slot to be transmitted; A backoff time reduction unit for decreasing the backoff time when a data packet by the another AT is not detected; A backoff time detector for checking whether the decremented backoff time is "0 "; A packet transmission unit transmitting the data packet of the AT itself and returning to the time slot designation unit if the decremented backoff time is "0 "; And When a data packet is detected by the another AT, the backoff time is maintained and waits for one time slot, The base station synchronizing apparatus using the wireless link. 3. The method of claim 2, Wherein the backoff controller further comprises a backoff seed allocator for allocating backoff seeds to the ATs connected to the AP and the APs at the initial operation of the AP, . delete The method according to claim 1, The time jitter reducer A remote timer information extracting unit for extracting remote time clock information using time stamp information of the transmitted beacon signal; And outputting a time delay error of adding a media delay value obtained by adding a value of the extracted far-time clock information, a signal transmission delay at the AP, a transmission time from the AP to the AT, and a signal transmission delay at the AT, An adjusting unit; A reception time measuring unit for measuring a reception time of the received beacon signal using a local time clock of the AT; A frequency and phase offset estimator for estimating a frequency ratio of the long time clock and the local time clock and a phase difference of the local time clock relative to the long time clock; Updating the local time clock using information of the frequency and phase offset, and setting a local timer to synchronize the updated local time clock with the far time clock The base station synchronizing apparatus using the wireless link. delete A base station for providing received GPS signals and data; An access point (AP) having a backoff controller for generating a beacon signal synchronized with the GPS signal and transmitting the beacon signal with a backoff time when the backoff signal is transmitted; An access terminal having a time jitter reduction unit for receiving the transmitted beacon signal and outputting a synchronization signal in which jitter is reduced using synchronization time information of the transmitted beacon signal and time information of the received beacon signal Access Terminal: AT); A small base station which is connected to a communication network connected to the base station and receives the data and is connected to the access terminal to receive synchronization information of the synchronization signal with reduced jitter and performs synchronization with the base station according to the synchronization information, The base station synchronizing apparatus using the wireless link. Receiving GPS signals and / or data synchronized to the base station; Generating a beacon signal and / or a data packet of the data synchronized with the GPS signal, transmitting the beacon signal and / or the data packet with a backoff time varying during a backoff transmission; Receiving the transmitted beacon signal and / or the data packet, and outputting a synchronization signal in which jitter is reduced using synchronization time information of the transmitted beacon signal and time information of the received beacon signal; Receiving the synchronization information of the synchronization signal with reduced jitter and performing synchronization with the base station according to the synchronization information, And synchronizing the base station synchronizing apparatus with the wireless link. Receiving a GPS signal synchronized to a base station and / or a core network; Generating a beacon signal synchronized with the GPS signal, transmitting the beacon signal while varying a backoff time during a backoff transmission; Receiving the transmitted beacon signal, outputting a synchronization signal in which jitter is reduced using synchronization time information of the transmitted beacon signal and time information of the received beacon signal; Receiving synchronization information of data provided via the core network and a synchronization signal whose jitter is reduced, and performing synchronization with the base station according to the synchronization information; And synchronizing the base station synchronizing apparatus with the wireless link.

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