KR101497895B1 - method for measuring link delay between nodes in cloud radio access network - Google Patents

Abstract

The present invention relates to a method for measuring a link delay between nodes in a CRAN, which is capable of measuring a link delay between a DU and a RU more efficiently and accurately. The method for measuring a link delay between nodes in a CRAN is performed in the CRAN where a DU is connected to one or more remote RUs. The method comprises the following steps: (a) generating, by the DU, a hyper frame for a DU-sided test including a test pattern and then transmitting the generated hyper frame to an RU upon counting; (b) generating, by the RU, a hyper frame for an RU-sided test and transmitting the generated hyper frame to the DU, in cases where the RU receives the hyper frame for a DU-sided test from the DU and a counting time between the reception time of the hyper frame for a DU-sided test and the reception time of the hyper frame for an RU-sided test to determine a frame offset (T_offset); (c) counting time between count starting time obtained in step (a) and the reception time of the hyper frame for an RU-sided test to determine T_14 that is a frame timing difference; and (d) calculating a link delay (T_12=T_34) by T_12=T_34=(T_14-T_offset)/2.

Description

Method for Measuring Link Delay between Nodes in a CRAN [

The present invention relates to a method for measuring inter-node link delays in a CRAN, and more particularly to a method for measuring inter-node link delay in a CRAN so as to more efficiently and accurately measure the link delay between DU and RU.

Recently, in the base station system, in order to reduce the facility investment cost (OPP) and operational expense (OPEX), the digital signal processing unit (DU) of the base station system and the wireless signal A centralized / cloud radio access network (CRAN) structure implemented by separating a radio unit (RU) is widely introduced.

In the CRAN, the DU is typically concentrated in a DU center, which is set up separately within the national territory, while the RU is installed in a service area away from it. DU and RU are physically connected to an optical link or UTP (Unshielded Twisted Pair) for high-speed transmission / reception of baseband I / Q signals.

Currently, the most widely used standard for transmitting and receiving I / Q data between DU and RU is CPRI (Common Public Radio Interface), and the specification of Ver 6.0 can support a line bit rate of up to 10,137.6 Mbps.

Standards similar or lower than CPRI include Open Baseband Remote Radiohead Interface (OBSAI) and Open Radio Interface (ORI) defined before CPRI. For the sake of simplicity, it is assumed that the CPRI standard is taken as an example, but OBSAI and ORI are not excluded.

FIGS. 1A to 1D show various connection forms of CRAN that can be supported by the CPRI standard. 1A shows a configuration in which a single REC (Radio Equipment Control) (corresponding to the DU) and one RE (Radio Equipment (corresponding to the RU described above) are connected by a single CPRI link. FIG. 1B shows a configuration in which one REC and one RE are connected by a plurality of CPRI links in order to improve performance.

FIG. 1C shows a configuration of a star topology in which a plurality of REs are connected to one REC. FIG. 1D shows a configuration of a chain topology in which one RE is connected to one REC and one RE is connected to the RE. Herein, 'node' may be used to refer to any one of subsystems implemented with REC and RE.

On the other hand, a link delay is inevitably generated in a CRAN located away from the DU and the RU, which may vary depending on the distance between the DU and the RU, the type and condition of the cable, and the like. In order to match the frame boundary of the radio signal transmitted from the RU, DU must transmit the data to the RU by the link delay in advance while grasping the link delay in advance.

2 is a diagram for explaining a reference point for link delay correction in a CRAN having a single hop configuration. As shown in Fig. 2, a reference point for cable (link) delay correction defined in the CPRI standard may be a connector of an input point and an output point of the equipment, for example, REC and RE.

In FIG. 2, the reference points R1 and R4 represent the output point and the input point of REC, respectively, and R2 and R3 respectively represent the input point and the output point of RE. Reference symbol Ra denotes an antenna. T ₁₂ denotes the delay of the downlink signal to the input point (R2) of the RE from an output point (R1) of the REC, T ₃₄ is uplink to the receiving point (R2) of the REC from the output point (R1) of the RE The delay of the signal.

T _offset is the frame offset between the input signal of reference point R2 and the output signal of reference point R3. Finally, T ₁₄ is the frame timing difference between the output signal of reference point R 1 and the input signal of reference point R 4. The REC can know in advance the frame offset (T _offset ) of each RE by reporting through the upper layer message from each RE.

However, according to the conventional CPRI standard, the CRAN only specifies that the input and output points of the equipment such as the connectors of REC and RE are used as reference points when measuring the inter-node link delay, It is not always easy to measure the link delay based on the position and it is difficult to obtain an accurate value.

- 10-2006-0097712 (Title of Invention: Interface, apparatus and method for communicating between a radio equipment control node and a remote radio equipment node in a radio base station) - 10-2007-0026341 Disclosure of the Invention Problem to be Solved by the Invention (Title of the Invention: Pre-startup Procedure for Internal Interface of Distributed Wireless Base Station)

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of measuring inter-node link delay in a CRAN that can more efficiently and accurately measure a link delay between a DU and an RU.

에 의해 링크 딜레이(T₁₂ = T₃₄)를 계산하는 (d) 단계를 포함하여 이루어진다.In order to accomplish the above object, a method for measuring inter-node link delay in a CRAN of the present invention is performed in a CRAN connected to one or more RUs at a remote location, wherein a DU stores a hyperframe for DU- (A) starting counting after generation and transmitting a DU-side test hyperframe to the RU; When the RU receives a DU-side test-use hyperframe from the DU, it generates an RU-side test-use hyperframe to be transmitted to the DU and then transmits the generated DUT-test-use hyperframe to the DU, (B) counting a time between transmission timings to determine a frame offset (T _offset ); When DU receives the RU side test hyperframe from the RU, it counts the time between the count start time of the RU side test use hyperframe reception time in the step (a) and determines as the frame timing difference T ₁₄ (c ) Step and

And (d) calculating a link delay (T ₁₂ = T ₃₄ ) by means of the link delay.

In the above-described configuration, the RU transmits the hyperframe for the RU side test in the hyperframe period arriving at the earliest in the step (b).

DU receives the frame offset (T _offset ) from the RU through an upper layer message.

The test pattern is recorded in a part or whole of an IQ data block of a specific basic frame belonging to a test hyperframe.

The test pattern of the DU side test hyperframe and the RU side test hyperframe are the same.

According to the inter-node link delay measurement method in the CRAN of the present invention, the link delay between DU and RU can be measured more efficiently and accurately.

Figures 1A-1D illustrate various connection forms of a CRAN that may be supported by the CPRI standard.
2 is a view for explaining a reference point for link delay correction in a CRAN having a single hop configuration;
3 is a structure diagram of a CPRI frame and a subchannel.
4 is a schematic diagram of a basic frame for a CPRI line bit rate of 614.4 Mbps;
5 is a sequence chart for explaining a method of measuring inter-node link delay in the CRAN of the present invention.

Hereinafter, a preferred embodiment of a method for measuring inter-node link delay in the CRAN of the present invention will be described in detail with reference to the accompanying drawings.

As described above, DU and RU are terms commonly used in CRAN, and REC and RE are terms used in correspondence with DU and RU in CPRI which is one of the interfaces used in CRAN. The present invention will be described.

As is well known, the CPRI standard is applicable to the UMTS (Universal Mobile Telecommunication System), the WiMAX Forum Mobile System Profile according to the IEEE standard 802.16-2009, Evolved UMTS Terrestrial Radio Access (E-UTRA) Hereinafter, description will be given taking E-UTRA, which is a wireless interface of 3GPP LTE (Long Term Evolution) as an example.

3 is a structure diagram of a CPRI frame and a subchannel. As shown in FIG. 3, the length of one CPRI radio frame (node B frame) is 10 ms. Since one CPRI radio frame is composed of 150 hyperframes, the length of each hyperframe is 66.7 Mu s. One hyperframe is again composed of a total of 256 basic frames, so that the length of each basic frame is 260.42 kHz (= 1 / 3.84 MHz).

4 is a schematic diagram of a basic frame for a CPRI line bit rate of 614.4 Mbps. As shown in FIG. 4, the user data is transmitted in an IQ data block in the CPRI basic frame in the form of a digital baseband IQ stream. The RE (RU) (Terminals). The CPRI Control and Management (C & M) data and the synchronization information are transmitted through the CPRI subchannel (specifically, the control word in the CPRI basic frame). DU (REC) and RU (RE) And is independent of the LTE layer.

Each basic frame is composed of one control word and fifteen payloads, and a total of 256 control words in one hyperframe are gathered to form 64 subchannels. The length of one word (T) of one basic frame depends on the line bit rate of the CPRI link. According to CPRI Ver.4.2 (2010.9.29 distribution), the minimum length of 8 bits (1 byte) (16 bytes).

5 is a sequence chart for explaining a method of measuring inter-node link delay in the CRAN of the present invention. As shown in FIG. 5, according to the inter-node link delay measurement method in the CRAN of the present invention, DU (REC) generates a hyper frame containing an arbitrary test pattern (step S10). Next, DU (REC) starts counting for link delay measurement (step S20) and transmits the test hyperframe generated in step S10 to RU (RE) (step S30).

Here, in the case of the test hyperframe, since there are 256 IQ data blocks of the basic frames belonging thereto, the area previously agreed between DU (REC) and RU (RE), that is, one or more of the test hyperframes A test pattern previously promised between DU (REC) and RU (RE) may be recorded in all or a part of a specific basic frame.

On the other hand, when an arbitrary hyperframe is received from DU (REC), the RU (RE) analyzes the data (step S40) and judges whether it is a test hyperframe (step S50). As a result of the determination in step S50, if the currently received hyperframe is not a test hyperframe, it is ignored (step S55). On the other hand, if the received hyperframe is a test hyperframe, the count is immediately started (step S60).

Next, in a state in which the test hyperframe to be sent to the DU (REC) is prepared, the RU (RE) waits until the hyperframe transmitting to the current DU (REC) ends (step S70). The test pattern recorded in the test hyperframe transmitted from the RU (REC) to the DU (RE) is preferably the same as the test pattern recorded in the test hyperframe transmitted from the DU (REC) to the RU (RE).

Next, the RU (RE) transmits the test hyperframe to the arriving DU (REC) of the next hyperframe period (step S90) and also checks the waiting time (T _offset ) (step S80) The waiting time T _offset is the frame offset between the input signal of the reference point R2 and the output signal of the reference point R3 in Fig. This frame offset (T _offset ) may then be reported to the DU (REC) for link delay computation at DU (REC) via higher layer messages.

Next, the DU (REC) analyzes the received hyperframe (step S100) and determines whether it is a test hyperframe (step S110). As a result of the determination in step S110, if it is not a test hyperframe, the test hyperframe is ignored (step S115). On the other hand, if the test hyperframe is a test hyperframe, And calculates a timing difference T ₁₄ .

Since DU (REC) by using a frame offset (T _offset) from a higher layer message forwarding (step S130) receiving, so transmission received frame offset (T _offset) from RU (RE) link delay (T ₁₂ = T ₃₄ ) the calculation (step S140), this link delay (T = ₁₂ to T ₃₄₎ can be obtained by equation 1 below.

While the preferred embodiments of the method of measuring inter-node link delay in the CRAN of the present invention have been described in detail above with reference to the accompanying drawings, it is to be understood that various changes and modifications may be made within the scope of the technical idea of the present invention . Accordingly, the scope of the present invention should be determined by the following claims.

Claims (5)

DU is performed on a CRAN connected to one or more RUs at remote locations,
(A) the DU starts counting after generating the DU-side test-use hyperframe containing the test pattern and transmits the DU-side test-use hyperframe to the RU;
When the RU receives a DU-side test-use hyperframe from the DU, it generates an RU-side test-use hyperframe to be transmitted to the DU and then transmits the generated DUT-test-use hyperframe to the DU, (B) counting a time between transmission timings to determine a frame offset (T _offset );
When DU receives the RU side test hyperframe from the RU, it counts the time between the count start time of the RU side test use hyperframe reception time in the step (a) and determines as the frame timing difference T ₁₄ (c ) Step and

(D) calculating a link delay (T ₁₂ = T ₃₄ ) by the link delay (T ₁₂ ). The method according to claim 1,
And the RU sends the RU-side test hyperframe in the hyperframe period that arrives at the earliest in the step (b). The method according to claim 1,
And the DU receives the frame offset (T _offset ) from the RU through an upper layer message. The method according to claim 1,
Wherein the test pattern is recorded in a part or whole of an IQ data block of a specific basic frame belonging to a test hyperframe. 5. The method according to any one of claims 1 to 4,
And the test pattern of the DU side test hyperframe and the RU side test hyperframe are the same.

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