KR20120072308A - Apparatus and method for controlling timing in relay system - Google Patents

Abstract

PURPOSE: A relay system timing control apparatus and method thereof are provided to accurately synchronize the signal timing between a base station and a terminal based on TA(Timing Advance) values. CONSTITUTION: A backhaul interface unit(21) acquires a downlink timing from a base station(10). The backhaul interface unit generates a reference signal from a downlink reception signal. An access interface unit(22) arranges a downlink transmission frame based on the reference signal generated from the backhaul interface unit. A relay downlink timing control apparatus periodically generates the reference signal based on the boundary of a downlink frame.

Description

Timing control device and method of relay system {APPARATUS AND METHOD FOR CONTROLLING TIMING IN RELAY SYSTEM}

The present invention relates to an orthogonal frequency division multiple access (OFDMA) relay system, and more particularly, to an apparatus and method for controlling (synchronizing) timing of uplink / downlink signals in a relay system.

The present invention is derived from a study performed as part of the next generation communication network industrial source technology development project of the Ministry of Knowledge Economy. [Task management number: 10035300, Assignment name: Multi-hop Relay technology development].

In 3GPP Long Term Evolution (LTE) -Advanced (4th generation mobile communication) system, a relay node (RN) system as well as a direct communication method between a base station and a terminal to support higher data rates and expand serviceable coverage. Signal transmission method using This technology enables high-speed data communication by reducing path loss by relaying signals in a path between an e-UTRAN NodeB (eNB) and a user equipment (UE) through a relay, and also enables a mobile terminal far from the base station. By passing signals, the service area can be extended.

The relay of the LTE-Advanced mobile communication system is used for the purpose of eliminating the shadow area in the cell, and is installed in the cell boundary area to improve the effective cell coverage and throughput. In addition, the relay can effectively transmit and receive signals in the wireless access section of the mobile communication network, thereby solving the problem of performance degradation and shadow area generation at the cell boundary. That is, the relay relays the signal of the base station to the terminal between the base station and the terminal, and relays the signal of the terminal to the base station. A backhaul link used for backhaul data transmission between a base station and a relay is called a "UN Link", and a link for data transmission between a relay and a terminal is called a "UU Link".

The relay receives backhaul data through the UN Link, demodulates and decodes it, and then encodes and modulates the backhaul data and transmits the same to the UE through the UU Link. At this time, the UN link and the UU link use the same frequency allocated to the downlink (DL).

In addition, the relay receives the demodulation and decoding of the terminal signal through the UU Link, and then encodes and modulates it again and transmits it to the base station again using the UN Link. At this time, the UN link and the UU link use the same frequency allocated to the uplink (UL).

In order to avoid self-interference (SI), the relay considers a time division method that separates a transmission / reception interval in time. SI occurs when the transmission / reception frequency of the relay uses the same band. In other words, SI means interference caused by the signal of the transmitting antenna when the signal is transmitted and received in the same band at the same time by the transmitting antenna and the receiving antenna of the relay. In detail, when the frequency band used between the relay and the terminal and the frequency band used between the base station and the relay are the same (inband method), the signal transmitted to the terminal through the transmission antenna of the relay is received by its reception antenna and is then signaled from the base station. Refers to a phenomenon that generates interference in receiving. This SI appears not only in the downlink period but also in the uplink period.

A method of using the same frequency band and separating the transmission / reception intervals in time is called an “inband half-duplex method”. In-band half-duplex relays receive signals from the base station (/ terminal) in the downlink (/ uplink) at predetermined times and frequencies. After performing the error correction process through the digital signal processing process, the received signal is modulated according to the transmission structure and retransmitted to the terminal (/ base station). At this time, the relay does not transmit data to the terminal (/ base station) at the time of receiving data from the base station (/ terminal). In this way, transmission / reception intervals are separated in time to avoid generation of SI.

Relay can't transmit / receive at the same time because it operates half-duplex method to solve SI phenomenon. That is, during the time period in which the relay receives a signal from the base station through a backhaul link, the relay may transmit any signal including a physical downlink control channel (PDCCH) to the terminal through an access link. none. The relay can receive data from the base station only for a time defined by a transmission gap (TG). 3GPP defines this TG as a Multimedia Broadcast Single Frequency Network (MBSFN) subframe.

The relay receives a signal from the base station only during the time (specified) specified by the MBSFN subframe defined by the TG, and during this time, no signal is transmitted to the terminal, including the PDCCH. However, the relay transmits the PDCCH to terminals belonging to the relay by using a predetermined OFDM symbol (for example, 0 and 1 symbols) of the subframe designated as the MBSFN subframe. The relay cannot receive the base station signal during the 0, 1st symbol period. Normal CP (cyclic prefix) or extended CP may be used for the 0 and 1st symbols. The relay receives the backhaul data received from the base station through the same frequency after transmitting the PDCCH through the 0 and 1st symbols, which requires a TT (Transition Time) to switch from the transmission mode to the reception mode. The data start point of the relay subframe and the start point of the backhaul data received from the base station are synchronized. In addition, when all the reception of the backhaul data is completed, a TT is required to switch from the reception mode to the transmission mode.

In order for the relay to work as above, it must process both DL Rx from UN Link and DL Tx from U Link with one RF (same frequency). In this case, RF requires mode change between Rx↔Tx, so minimum TT is required. Therefore, the timing between the DL Rx on the UN Link and the DL Tx on the UU Link must be exactly aligned as shown in FIG. 1. However, as shown in FIG. 2, if the timing is not aligned correctly, the signals of Tx / Rx are mixed, resulting in degradation of signal performance.

Figure 1 shows that the timing alignment (timing alignment) is made correctly, so that the margin A, B, C, D point required for the transition is maintained correctly, but as shown in Figure 2, the timing alignment is not correct, TT in the E, F part If is not secured, there is a problem that the Tx / Rx signals are mixed.

Therefore, if the DL DLx of the UN and the DL Tx of the UU can be correctly separated in time in the relay, the signal at the time of DL Tx / Rx is not mixed while securing the mode change time of the RF, and thus the signal between the base station and the terminal transmitting and receiving There is an urgent need for a method to accurately synchronize the timing of the signals.

Publication No. 10-2010-0102513 (published Sep. 24, 2010)

It is an object of the present invention to provide an apparatus and method for controlling (synchronizing) the timing of an uplink / downlink signal in a relay system.

According to one aspect of the present invention, an apparatus and method for controlling (synchronizing) timing of an uplink / downlink signal in a relay system is disclosed. According to this apparatus and method, in downlink, a downlink timing is obtained from a base station and a reference signal is generated from the downlink received signal, and the downlink transmission frame is aligned based on the reference signal. In the uplink, the uplink transmission frame is aligned based on a TA value measured and transmitted by the base station, and the uplink reception frame is aligned based on the change amount of the TA.

According to the present invention, there is an advantage that the timing of the signal can be accurately synchronized between the base station and the terminal to transmit and receive.

1 shows a result of precise timing alignment of a signal;
FIG. 2 is a diagram illustrating a result in which timing alignment of signals is not accurately performed and mixed transmission / reception signals. FIG.
3 illustrates a configuration of an exemplary relay system in which the present invention may be practiced.
4 is a diagram illustrating details of a relay in accordance with an embodiment of the present invention;
5 is a diagram illustrating a timing control process of a terminal.
6 is a diagram illustrating a timing control process of a relay according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, well-known functions or constructions will not be described in detail if they obscure the subject matter of the present invention.

3 is a diagram illustrating the configuration of an exemplary relay system in which the present invention may be implemented.

As shown in FIG. 3, the relay system includes a base station (eNB) 10, a relay (RN) 20, and a terminal (UE) 30, and a wireless backhaul between the base station 10 and the relay 20. A signal is transmitted and received through an interface (UN interface), and a signal is transmitted and received through an access interface (UU interface) between the relay 20 and the terminal 30 in the relay cell.

The base station 10 may provide a communication service through a radio link to a relay region and a terminal 30 in a coverage region or a cell in which the base station 10 provides a network access service.

The relay 20 may be configured to replace a repeater, and a frequency band A used for a backhaul link between the base station 10 and the relay 20 is a link between the relay 20 and the terminal 30. The same band as the frequency band B used for the (access link) can be used. That is, the relay 20 may be an inband half-duplex relay in which the frequency band A and the frequency band B are the same and apply separate transmission / reception intervals in time. In addition, the relay 20 may be an outband relay having different frequency bands A and B.

The relay 20 includes a donor antenna for communicating with the base station 10 and a service antenna for communicating with the terminal 30, thereby communicating between the base station 10 and the terminal 30. It acts as a communications mediator. Since the relay 20 uses a wireless backhaul rather than a wired backhaul link, there is no need to add a new base station or install a wired backhaul.

The relay 20 receives a signal at a predetermined time and frequency from the base station 10 (/ terminal 30) at the time of downlink (uplink) and DL / UL at the received signal. After removing the SI component, it modulates according to the transmission structure and performs retransmission to the terminal 30 (/ base station 10).

The relay 20 is located anywhere within the coverage of the base station 10 via a wireless backhaul and is recognized as a base station eNB for the UE, while one terminal for the base station 10. Recognized as (UE), it is possible to extend a communication coverage area by relaying a signal between the base station 10 and the terminals 30a to 30c.

In general, since the base station 10 has a fixed position, the flexibility of the mobile communication network configuration is low, and thus, it is difficult to provide an efficient communication service in a wireless environment in which traffic distribution or call demand is severely changed. In order to overcome this disadvantage, the relay system is a fixed relay (fixed RN) (20a, 20c) fixedly located at one point, or a mobile relay (mobile RN) (20b) mounted on a train or bus, etc. By configuring the mobile communication network in a multi-hop manner, the communication service area of the relay system can be expanded and the system capacity can be increased. In addition, the relay 20 may be a Nomadic RN mounted on a vehicle to support eventful subscriber congestion.

As shown, the base station 10 transmits data directly or via a relay 20a to the terminals 30a, 30b included in the communication coverage area of the base station 10, and the communication coverage area of the base station 10. The terminal 30c, which is located outside and cannot directly communicate, transmits data through the relay 20c. In addition, since the terminal 30c located outside the communication coverage area of the base station 10 cannot directly communicate with the base station 10 due to the limitation of the transmission power, the terminal 30c transmits data to the base station 10 through the relay 20c.

Terminals 30a-30c may include any type of portable wireless communication device or system, including, for example, a mobile phone, a portable computer having a mobile communication function, a PDA having a mobile communication function, or another device. Although FIG. 1 illustrates that one base station 10 supports only three relays 20a to 20c and three terminals 30a to 30c, the base station 10 includes more or fewer relays and Note that the terminal may be supported.

Although not specifically illustrated, the relays 20a to 20c or the terminals 30a to 30c transmit signals to the base station 10 through an uplink channel, and the base station 10 may be a relay 20a to 20c or the terminal ( 30a to 30c) transmit a signal through a downlink channel. In particular, the subframe of the downlink channel including information transmitted from the base station 10 through the relays 20a to 20c includes a control channel and data for transmitting control information for the relays 20a to 20c. It is configured to include a data channel for transmission, a control channel for transmission of control information for the terminals 30a to 30c, and a data channel for transmission of data. Each control channel for the relays 20a to 20c and the terminals 30a to 30c is positioned in advance of the remaining data channels on the time axis. This is to allow the relays 20a to 20c and the terminals 30a to 30c to determine whether to perform the data channel reception operation by first receiving the control channel and recognizing whether or not the data channel transmitted to the relay channel is transmitted. Therefore, when the relay 20a to 20c and the terminal 30a to 30c determine that there is no data channel transmitted from the control channel, the relays 20a to 20c do not need to receive subsequent data channels. You can save.

4 is a diagram showing in detail the configuration of a relay according to an embodiment of the present invention.

The apparatus for controlling downlink timing of the relay 20 according to the present invention includes a UN interface unit 21 and a UN interface unit 21 for acquiring downlink timing from the base station 10 and generating a reference signal from the downlink received signal. UU interface unit 22 for aligning the downlink transmission frame (UU DL Tx) on the basis of the reference signal generated in the).

Here, the UN interface unit 21 performs a function of generating a reference signal after obtaining the DL timing (reference signal generating function). In addition, the UU interface 22 has a function of receiving a reference signal generated by the UN interface unit 21 (reference signal reception function), a function of monitoring whether the reference signal changes (reference signal change measurement function), and a received reference signal. To perform DL function synchronization function (DL timing control function).

In addition, the uplink timing control apparatus of the relay 20 according to the present invention, UN for aligning the time point of the uplink transmission frame (UN UL Tx) based on the TA (Timing Advance) value measured and transmitted by the base station 10 The interface unit 21 and the UU interface unit 22 to align the uplink reception frame (UU UL Rx) based on the change amount of the TA transmitted from the UN interface unit 21.

Here, the UN interface unit 21 has a function of measuring the cumulative change amount of the UL TA value (TA value measuring function) and a function of transmitting the cumulative change amount of the UL TA value to the UU interface unit 22 (TA value transmission function). To perform. In addition, the UU interface 22 has a function of receiving a TA transmitted by the UN interface unit 21 (TA value receiving function) and a function of synchronizing UL timing by applying the received TA value (UL timing control function). To perform.

The method of obtaining timing in the UN interface unit 21 of the relay 20 is similar to the method of obtaining the timing by the terminal 30.

For reference, referring to the timing acquisition process of the terminal 30, as shown in FIG. 5, when a DL frame (UN DL Tx) is transmitted from the base station 10, a delay on air as much as Tp occurs. Is received by the terminal 30 (UN DL Rx). The terminal 30 obtains the DL timing by using a sync channel of the received DL frame. In addition, the terminal 30 receives a TA value measured and transmitted for each terminal 30 by the base station 10 so that the UL frame may be received by the base station 10 at the correct timing after the DL timing is acquired. Pull the transmission point of Tx) by TA to transmit.

However, in the process of obtaining timing in the UN interface unit 21 inside the relay 20, an additional operation for synchronizing timing with the UU interface unit 22 is added. Specifically, it is as follows.

Timing control can be divided into DL timing alignment and UL timing alignment. First, the DL timing alignment process will be described. .

The UN interface unit 21 acquires timing using the Sync channel of the DL and a reference signal received from the base station 10 (Step 1).

The UN interface unit 21 continuously monitors the timing variation and waits for operation in the "steady state" (Step 2). Here, the "steady state" means a case where the absolute value of the timing change amount is smaller than the reference value.

In addition, when entering the steady state, the UN interface unit 21 generates a reference signal (interrupt, etc.) in accordance with the boundary of the acquired DL frame (UN DL Rx) (see point A) (Step 3). Thereafter, the reference signal is periodically generated. In this case, the DL frame may be based on 0.5 ms, 1 ms, 10 ms, 1 sec, 2 sec, and the like.

Thereafter, the UU interface 22 operates various necessary time based interrupts and timers with reference to the reference signal generated in Step 3 (Step 4).

The UU interface unit 22 aligns the DL frame (UU DL Tx) with a reference signal generated by the UN interface unit 21 (see point C) (Step 5).

However, since the reference signal generated by the UN interface unit 21 is generated based on the DL received signal, and may change from time to time according to an air condition, the timing at which the reference signal is continuously received by the UU interface unit 22 is determined. Monitor the amount of change (Step 6). In this case, an input such as GPS can be used for monitoring. If the change in the timing of occurrence of the reference signal is measured above the reference value, the UU interface 22 applies reset or offset to the interrupt and timer used by the UU interface 22 if necessary. Reactivate (Step 7).

After that, the steps 6 and 7 are repeated.

Now let's look at the UL timing alignment process.

After the DL timing alignment process is completed, the UL timing alignment process at the UN interface unit 21 starts from the Tx timing setting of the general terminal 30. That is, the UN interface unit 21 receives the TA values measured and transmitted by the base station 10 and advances the transmission time by the received TA value (see point B) (Step 11). At this time, since the variation of TA may be somewhat large at the beginning, wait until it operates in the "steady state" (Step 12). Here, the "steady state" means a case where the absolute value of the accumulated amount of TA during the reference time does not exceed the reference value.

When the variation of the TA enters a steady state, the UN interface 21 transfers the total variation of the TA up to this time to the UU interface 22 (Step 13).

Thereafter, the UU interface 22 sets the UL Rx timing boundary of the UU link by using the same total change amount of the TA received from the UN interface 21 (see point D) (Step 14).

Here, the UN interface unit 21 periodically measures the change amount of TA and transmits the changed TA value to the UU interface unit 22 when the TA accumulation amount of the reference value or more occurs (Step 15). In addition, the UU interface 22 calculates and transmits a TA cumulative amount TAu for each terminal based on the point D so that UL channels of the terminals 30 connected to the UU link can be accurately received at the point D (Step). 16).

Thereafter, the steps 14 to 16 are repeated.

Through the above method, the timing of the UL link and the UU link can be effectively aligned as shown in FIG.

Although the method has been described through specific embodiments, the method may also be embodied as computer readable code on a computer readable recording medium. Computer-readable recording media include all kinds of recording devices that store data that can be read by a computer system. Examples of the computer-readable recording medium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, and the like, and may be implemented in the form of a carrier wave (for example, transmission over the Internet) . The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. In addition, functional programs, codes, and code segments for implementing the above embodiments can be easily deduced by programmers of the present invention.

Although the present invention has been described in connection with some embodiments thereof, it should be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention as understood by those skilled in the art. something to do. It is also contemplated that such variations and modifications are within the scope of the claims appended hereto.

10: base station (eNB) 20a to 20c: relay (RN)
30a ~ 30c: UE

Claims (8)

A downlink timing control device of a relay,
A backhaul interface unit for acquiring downlink timing from a base station and generating a reference signal from the downlink received signal; And
And an access interface unit for aligning downlink transmission frames based on a reference signal generated by the backhaul interface unit. The method of claim 1,
And the access interface unit monitors an amount of change in timing of the reference signal to reset or offset a time based interrupt and a timer. The method of claim 1,
The backhaul interface unit, the downlink timing control device of the relay periodically generated in accordance with the boundary (boundary) of the downlink frame. An uplink timing control device for a relay,
A backhaul interface unit for aligning time points of an uplink transmission frame based on a TA value measured and transmitted by a base station; And
And an access interface unit for aligning an uplink reception frame based on a change amount of the TA transmitted from the backhaul interface unit. The method of claim 4, wherein
The backhaul interface unit measures a change amount of the TA, and transmits the changed TA value to the access interface unit when a TA accumulation amount of a reference value or more occurs.
The access interface unit, uplink timing control apparatus for a relay for calculating the TA cumulative amount (TAu) for each terminal on the basis of the time point of the uplink reception frame, and transmits to the terminal. The method of claim 4, wherein
And the access interface unit sets the uplink reception timing boundary of the access link using the same total change amount of the TA received from the backhaul interface unit. As a timing control method of a relay,
In downlink, obtaining a downlink timing from a base station, generating a reference signal from the downlink received signal, and aligning a downlink transmission frame based on the reference signal; And
In uplink, timing control of a relay comprising aligning a start point of an uplink transmission frame based on a TA value measured and transmitted by a base station, and aligning an uplink reception frame based on a change amount of the TA. Way. The method of claim 7, wherein
And the relay is an inband half-duplex relay.

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