KR101624643B1 - Apparatus and Method for Synchronizing Micro Base Station Using Wireless Link - Google Patents
Apparatus and Method for Synchronizing Micro Base Station Using Wireless Link Download PDFInfo
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- KR101624643B1 KR101624643B1 KR1020090126286A KR20090126286A KR101624643B1 KR 101624643 B1 KR101624643 B1 KR 101624643B1 KR 1020090126286 A KR1020090126286 A KR 1020090126286A KR 20090126286 A KR20090126286 A KR 20090126286A KR 101624643 B1 KR101624643 B1 KR 101624643B1
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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
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
However, IEEE 1588 is only used when the uplink transmission delay for transmitting data from the
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
The
When using a wireless LAN backhaul, the beacon of the
In such a configuration, the wireless LAN standard specifies a
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
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
At this time, the
The
More specifically, the supporting
The
The
The
The
The
Meanwhile, the
The
The
The
The
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
Here, the time
In addition, the backoff
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
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
At this time, the N_total wireless devices including the
For example, when two
In step S502, the
Let N_TS be the time slot number at the time of data packet transmission. At this time, the backoff value for the
(X% y) denotes a remainder obtained by dividing the integer x by an integer y, and SEED_AP denotes a seed allocated to the
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 .
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).
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
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
Here, when the beacon is received, the remote
The
When the beacon is received, the reception
The frequency and phase offset
The
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
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).
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
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
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).
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
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
The
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
Next, the
In addition, the
The
Thereafter, the
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
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
Accordingly, the
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
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,
315, 815:
330, 830:
333, 833:
340, 840: AT 343, 841: Time information restorer
347, 843:
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Cited By (2)
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WO2022131431A1 (en) * | 2020-12-17 | 2022-06-23 | 주식회사 지오플랜 | Method and device for hybrid synchronization |
WO2022131430A1 (en) * | 2020-12-17 | 2022-06-23 | 주식회사 지오플랜 | Wireless synchronization method and apparatus |
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JP7109214B2 (en) * | 2018-03-08 | 2022-07-29 | ソフトバンク株式会社 | Base station frame synchronization system |
JP7109213B2 (en) * | 2018-03-08 | 2022-07-29 | ソフトバンク株式会社 | Base station frame synchronization system |
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US20090097452A1 (en) | 2007-10-12 | 2009-04-16 | Qualcomm Incorporated | Femto cell synchronization and pilot search methodology |
US20090122773A1 (en) | 2007-11-09 | 2009-05-14 | Qualcomm Incorporated | Access point configuration based on received access point signals |
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US20090097452A1 (en) | 2007-10-12 | 2009-04-16 | Qualcomm Incorporated | Femto cell synchronization and pilot search methodology |
US20090122773A1 (en) | 2007-11-09 | 2009-05-14 | Qualcomm Incorporated | Access point configuration based on received access point signals |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
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WO2022131431A1 (en) * | 2020-12-17 | 2022-06-23 | 주식회사 지오플랜 | Method and device for hybrid synchronization |
WO2022131430A1 (en) * | 2020-12-17 | 2022-06-23 | 주식회사 지오플랜 | Wireless synchronization method and apparatus |
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