WO2009140890A1

WO2009140890A1 - A method, a system, and an apparatus for realizing symbol synchronization

Info

Publication number: WO2009140890A1
Application number: PCT/CN2009/071662
Authority: WO
Inventors: 石操; 方李明
Original assignee: 华为技术有限公司
Priority date: 2008-05-19
Filing date: 2009-05-06
Publication date: 2009-11-26
Also published as: CN101588336B; CN101588336A

Abstract

A method, a system, and an apparatus for realizing symbol synchronization are provided. The method comprises: obtaining the starting position of the symbol period for the crosstalk signal (S301); synchronizing the starting position of the symbol period for the signal to be transmitted with the starting position of the symbol period for the crosstalk signal (S302); transmitting the signal according to the synchronized starting position of the symbol period. The invention achieves the symbol synchronization among the respective lines, and ensures the orthogonality for the symbols during signal transmission.

Description

Method, system and device for realizing symbol synchronization This application claims to be submitted to the Chinese Patent Office on May 19, 2008, the application number is 200810097933.1, and the invention name is "a method, system and device for realizing symbol synchronization". Priority of the application, the entire contents of which are incorporated herein by reference. Technical field

Embodiments of the present invention relate to the field of communications technologies, and in particular, to a method, system, and apparatus for implementing symbol synchronization. Background technique

Digital Subscriber Line (DSL) technology is a high-speed transmission technology for data transmission over a telephone twisted pair, Unshielded Twist Pair (UTP), including Asymmetric Digital Subscriber Line (Asymmetrical Digital). Subscriber Line, ADSL), Very-high-bit-rate Digital Subscriber Line (VDSL), ISDN Digital Subscriber Line (IDSL) based on Integrated Services Digital Network (ISDN) ) and Single-pair High-bit-rate Digital Subscriber Line (SHDSL).

In various digital subscriber line technologies (xDSL), in addition to DSL for baseband transmission such as IDSL and SHDSL, DSL using passband transmission utilizes frequency division multiplexing technology to enable DSL and Plain Old Telephone Service (POTS). Coexisting on the same pair of twisted pairs, where DSL occupies a high frequency band, POTS occupies a baseband portion below 4 kHz, and POTS signals and DSL signals are separated or combined by a splitter/integrator (Splitter). The passband transmission xDSL uses Discrete Multi-Tone Modulation (DMT) technology for modulation and demodulation.

The physical layer of the xDSL technology uses Orthogonal Frequency Divided Multiple (OFDM) technology, in one symbol (another Within the time range of the term "frame", a set of mutually orthogonal subcarriers are transmitted to carry bit information. The transceiver needs to use the symbol synchronization method to find the starting position of the symbol in the received signal and demodulate the received symbol.

As the frequency band used by xDSL technology increases, crosstalk, especially in high frequency bands, is becoming more and more prominent. Since the xDSL uplink and downlink channels adopt frequency division multiplexing, near-end crosstalk (NEXT) does not cause much harm to the performance of the system; however, far-end crosstalk (FEXT) will seriously affect the transmission performance of the line. When multiple users in a bundle of cables are required to open xDSL services, the far-end crosstalk (FEXT) will cause some line rates to be low, performance is unstable, or even impossible to open, which ultimately leads to a lower DSLAM outgoing rate.

Dynamic Spectral Management (DSM) technology has recently emerged to achieve an optimized result for each line from the power and signal levels. The signal level DSM mainly includes Multi-Input and Multi-Output (MIMO), Vectored DSL (Vector DSL) and so on. Vectored DSL technology has much in common with MIMO technology. The emergence of MIMO technology solves the problem that each line is affected by far-end crosstalk, and removes the influence of crosstalk in principle, and the performance is more optimized. From the perspective of current digital subscriber line technology, MIMO is the best performing digital subscriber line technology. From the modulation mode, MIMO technology still uses the currently popular OFDM, and the OFDM modulation technology is as follows:

The main idea of OFDM is to divide the entire transmission band into a number of sub-bands with relatively narrow frequencies. Each subband is used to carry a certain number of bits. As shown in Fig. 1, since the frequency width of each sub-band is relatively narrow, it can be approximated that the transfer function of the channel in this frequency band is a constant. Close to distortion-free transmission is convenient for receiver processing. On the other hand, since each subcarrier is completely orthogonal, there is no influence between the subcarriers.

The optimization of DSM technology and the crosstalk cancellation of MIMO technology are all based on the characteristics of orthogonality. Under normal circumstances, the receiving end of each xDSL modem treats the interference of other modems as noise, and the data rate ( ^b k" ) that can be reached on the kth tone of the nth user can be calculated by the Shannon channel capacity formula. :

Where ' represents the transfer function of the nth line on the kth subcarrier. The crosstalk function for the nth line on the kth subcarrier is indicated by the mth line. Indicates the noise power of the nth line on the kth subcarrier. Indicates the transmit power of the nth line on the kth subcarrier.

The inventors have found that the prior art has the following disadvantages:

It can be seen from the above calculation formula of the data rate that the rate calculation formula of the entire DSM is based on each subcarrier, which is mainly due to the orthogonality of the subcarriers. If the orthogonality of each subcarrier is destroyed. All DSM algorithms are subject to change. The algorithms listed above (including optimization of DSM technology and crosstalk cancellation by MIMO, Vectored DSL technology, etc.) cannot be used in this case.

This orthogonality is destroyed when the symbols of the lines are not synchronized. described as follows:

When the first line is interfered by the second line, as shown in Figure 2, the second line is not synchronized with the first line symbol. When the first line performs OFDM demodulation, part of the signals of frame 1 and frame 2 in the second line are processed. Equivalent to adding a window 2 and a window 3 respectively on the second line. Obviously, both window 2 and window 3 are shorter than the normal OFDM signal window (as shown in window 1), so that the window 1 and window 2 window 3 produce different spectral widths (see Figure 3), thus destroying the orthogonality of the frequency. Sex. That is to say, signals between different frequencies will also interfere with each other. Summary of the invention

Embodiments of the present invention propose a method for implementing symbol synchronization to ensure frame synchronization of each line, thereby avoiding the occurrence of disruption of orthogonality.

To achieve the above objective, an embodiment of the present invention provides a method for implementing symbol synchronization, including:

Obtaining a symbol period start position of the crosstalk signal; Synchronizing a symbol period start position of the pre-transmitted signal to a symbol period start position of the crosstalk signal;

The signal is sent at the start of the symbol period after synchronization.

An embodiment of the present invention further provides a communication device, including:

a first acquiring module, configured to acquire a symbol period start position of the crosstalk signal; a synchronization module, configured to synchronize a symbol period start position of the pre-transmitted signal to a symbol period start position of the crosstalk signal acquired by the first acquiring module ;

The sending module is configured to send a signal according to a symbol period start position of the signal synchronized by the synchronization module.

An embodiment of the present invention further provides a synchronization center manager, including: a selection module, configured to select a transceiver to issue a synchronization guiding signal, and send a synchronization guiding signal request to the selected transceiver;

Obtaining an information statistics module, configured to receive and collect the acquisition information reported by the transceiver; a timer, configured to: when the acquisition information statistics module does not receive the acquisition information reported by the transceiver within a predetermined time, prompting the selecting The module reselects the transceiver to transmit the synchronization pilot signal.

An embodiment of the present invention further provides a system for implementing symbol synchronization, including: a synchronization center manager, configured to select a transceiver to send a synchronization pilot signal, and after receiving the reported acquisition information, statistics and store the acquisition information, where When the acquisition information is not received within the predetermined time, the transceiver is selected to transmit the synchronization pilot signal in the transceiver that does not report the acquisition information or does not send the synchronization pilot signal.

a transceiver, configured to acquire a symbol period start position of the crosstalk signal, synchronize a symbol period start position of the pre-transmitted signal to a symbol period start position of the crosstalk signal, and send according to a symbol period start position of the synchronized signal signal.

The technical solution of the embodiment of the invention has the following advantages:

The symbol synchronization between the lines is realized; the problem of orthogonal frequency division multiplexing symbol synchronization is solved, and the orthogonality in the transmission process of the orthogonal frequency division multiplexing symbols is ensured. DRAWINGS 1 is a schematic diagram of an OFDM subcarrier in the prior art of the present invention;

2 is a schematic diagram of orthogonality destruction in the prior art of the present invention;

3 is a schematic flowchart of a method for implementing symbol synchronization in Embodiment 1 of the present invention; FIG. 4 is a schematic diagram of detecting a near-end crosstalk symbol in Embodiment 2 of the present invention; FIG. 5 is a schematic diagram of a synchronization center management system according to Embodiment 3 of the present invention; FIG. 6 is a schematic diagram of a synchronous pilot signal transmission and relay in the third embodiment of the present invention; FIG. 7 is a schematic diagram of a state of a synchronous center manager controlling a transceiver according to Embodiment 3 of the present invention;

8 is a schematic diagram of symbol synchronization of a pilot signal relay scheme according to Embodiment 3 of the present invention;

FIG. 9 is a schematic structural diagram of an apparatus for implementing symbol synchronization by a near-end crosstalk signal according to an embodiment of the present invention; FIG.

FIG. 10 is a schematic structural diagram of a system and apparatus for implementing symbol synchronization by using a synchronization pilot signal according to an embodiment of the present invention. detailed description

Embodiments of the present invention provide a method, system, and apparatus for implementing symbol synchronization, which effectively implement signal synchronization between lines; solve the problem of orthogonal frequency division multiplexing signal synchronization, and ensure orthogonal frequency division multiplexing Orthogonality in multiplexing signal transmission.

The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings and embodiments.

Crosstalk is an inevitable product of modern digital systems. It is the coupling between two signal lines. The mutual inductance and mutual capacitance between signal lines cause noise on the line. Capacitive coupling induces a coupled current, while inductive coupling induces a coupled voltage. PCB board layer parameters, signal line spacing, electrical characteristics of the driver and receiver, and line termination have a certain impact on crosstalk.

In the premise that all the lines use the same symbol length, the first embodiment of the present invention provides a method for implementing symbol synchronization. As shown in FIG. 3, the method includes the following steps: Step S301: Acquire a symbol period start position of the crosstalk signal.

Specifically, the symbol period start position of the near-end crosstalk signal may be obtained, or the symbol period start position of the crosstalk signal caused by the synchronization pilot signal sent by the transceiver may be acquired. After the synchronization pilot signal causes the crosstalk signal, the symbol period start position of the signal sent by the group transceiver may be the same as the symbol period start position of the crosstalk signal caused by the group, so that the symbol period of the signal sent by the group transceiver is The starting position is consistent, which avoids the crosstalk caused by each transceiver transmitting signals at the same time.

Step S302: Synchronize the symbol period start position of the pre-transmitted signal to the symbol period start position of the crosstalk signal.

Specifically, the pre-transmitted signal may be an orthogonal frequency division multiplexed signal, or may be a CDMA signal or a pulse signal or other custom signals.

Step S303: Send a signal according to the start position of the symbol period after synchronization.

The second embodiment of the present invention applies the first embodiment to a specific scenario, and uses the symbol period start position of the near-end crosstalk signal to transmit the orthogonal frequency division multiplexing signal. The specific process is as follows:

The transceiver VTU (the terminal transceiver is VTU-0, the client transceiver is VTU-R, the transceiver can be the digital subscriber line access multiplexer DSLAM) detects near-end crosstalk during the initialization phase, and transmits it through the transceiver. The symbol period start position of the orthogonal frequency division multiplexed signal is synchronized with the symbol period start position of the near-end crosstalk signal, and symbol synchronization between the lines is realized.

In the protocol of VDSL2 (G.993.2): During the activation of VDSL2, no signal is sent from both sides of the VTU at the beginning of the initialization phase. During this time, the central VDSL transceiver VTU-0 detects the near-end crosstalk signal, stores the symbol period start position of the near-end crosstalk signal, and causes the symbol period start position of the transmitted signal during the subsequent transmission of the signal. The symbol period start position of the near-end crosstalk signal coincides. FIG. 4 is a schematic diagram of detecting a near-end crosstalk signal in the second embodiment. As shown in the figure, the symbol period of the near-end crosstalk signal 1000 is the same as the symbol period of the OFDM. The implementation of this embodiment is as follows:

First, the transceiver acquires the symbol period start position 2000 of the near-end crosstalk signal. Second, the transceiver is based on a symbol period start position of the near-end crosstalk signal

2000, adjusting the start position of the symbol period of the transmit orthogonal frequency division multiplexed signal. The transceiver transmits the orthogonal frequency division multiplexed signal when a symbol period start position of the orthogonal frequency division multiplexed signal coincides with a symbol period start position of the near-end crosstalk signal. That is, the process indicated by 4000 in the figure is to synchronize the symbol period start position of the orthogonal frequency division multiplexed signal to the symbol period start position of the near-end crosstalk signal, due to the sign of the near-end crosstalk signal and the positive The symbol length and the symbol period of the cross-frequency division multiplexed signal are the same, which can effectively ensure the synchronization between signals. In the third embodiment of the present invention, a method for realizing symbol synchronization is provided under the premise that all lines use the same symbol length, and the synchronization center is selected by the synchronization center manager to transmit a synchronous pilot signal, so that multiple transceivers are synchronously transmitted. The frequency division multiplexed signal.

FIG. 5 is a schematic diagram of a synchronization center management system in the embodiment. The transceiver is described by taking a DSLAM as an example, including but not limited to a DSLAM.

FIG. 6 is a schematic diagram of the synchronization pilot signal transmission and relay in the synchronization center management system of the embodiment, as shown in the figure, including:

Step S1, when a DSLAM is started, the transceivers of all ports enter the state of detecting the NEXT signal. Any transceiver that selects the DSLAM by the synchronization center manager issues a first synchronization pilot signal 5000 that is passed through the crosstalk channel to other transceivers in the group of transceivers. The selection of the transceiver may be performed according to a preset rule, or may be randomly selected. Of course, the selected mode is not limited to the two modes described above. The symbol period of the crosstalk signal caused by the first synchronization pilot signal 5000 is the same as the period of the symbol of the orthogonal frequency division multiplexing signal at the Initialization/Showtime phase.

Step S2: After the transceiver detects the first synchronization guiding signal, acquire a symbol period start position of the first synchronization guiding signal 5000, and then report the obtaining information 6000 to the synchronization center manager. The acquisition information 6000 is used to indicate that the symbol period start position of the synchronization pilot signal has been acquired. Step S3: After receiving the acquisition information 6000, the synchronization center manager performs statistical storage on the information, and starts timing. Within a predetermined time period T, such as a fixed signal period, the synchronization center manager selects a transceiver in the transceiver that does not report the detection information in the group, and the transceiver issues a second synchronization pilot signal 5000 that is identical to the first synchronization pilot signal. By analogy, more transceivers of the group can receive the synchronization pilot signal, and the synchronization center manager is prevented from frequently selecting the transceiver to send the synchronization pilot signal. The fixed signal period is an integer multiple of one signal period, for example: M signal periods T (M*T).

FIG. 7 is a schematic diagram of a state in which a synchronization center manager controls a transceiver in a synchronization center management system according to the embodiment, in which a white circle indicates that the acquisition information is not reported and a synchronization guidance signal is not sent, and a black circle indicates that the acquisition information has been reported or the synchronization guidance has been sent. signal. As shown in Figure 7a, all transceivers do not report the acquisition information and do not send the synchronization pilot signal when the DLAM is started. As shown in Figure 7b, after the first synchronization transmission signal is sent, some transceivers have reported the acquisition information or sent. The synchronization guiding signal; as shown in FIG. 7c, when the reporting acquisition message of the transceiver is not received within a predetermined time, the new transceiver is reselected to send the synchronization guiding signal, and the above steps are repeated, after the Nth synchronization guiding signal is sent. Most transceivers have reported the acquisition information or sent the synchronization pilot signal. As shown in FIG. 7d, finally all the transceivers have reported the acquisition information or the synchronization guidance signal has been sent, that is, the symbol period of the synchronization pilot signal is not reported. The set of transceivers at the start position and transmitting the synchronization pilot signal is empty.

Step S4, FIG. 8 is a schematic diagram of symbol synchronization of the synchronous pilot signal relay scheme of any transceiver in the synchronization center management system according to the embodiment. As shown in the figure, when the transceiver first transmits a signal, the transceiver corresponds to The port records the symbol period start position 2000 of the transmission synchronization pilot signal, and in the active process, when the initialization phase is performed, the orthogonal frequency division is transmitted at the symbol period start position 2000 of the recorded synchronization pilot signal. Multiplexed signals. The step is implemented by the transceiver, comprising: acquiring a symbol period start position 2000 of the recorded synchronization pilot signal, and then at the symbol period start position of the orthogonal frequency division multiplexed signal and the synchronization pilot signal Transmitting the orthogonal frequency division when the symbol period start position 2000 coincides The multiplexed signal, the process represented by 4000.

In the second embodiment of the present invention, the periodic start position of the near-end crosstalk signal is detected by the transceiver in the initial stage of line activation, and symbol synchronization between the lines is realized. In the third embodiment of the present invention, the central manager directs and relays the synchronization pilot signal, and in the initialization phase of the line activation, the transceiver transmits the OFDM signal according to the symbol period start position of the synchronization pilot signal. The problem of OFDM symbol synchronization is solved. The performance of DSM is optimized to the best.

An embodiment of the present invention provides a system for implementing symbol synchronization, and the system can be used for a symbol synchronization system, which is used in a DSLAM, or a single DSLAM port. A communication device can be included.

The communication device can be applied not only to the DSLAM but also to the wireless field, for example: WiFi, Wimax, including:

The transceiver 1 is configured to acquire a symbol period start position of the crosstalk signal, synchronize a symbol period start position of the pre-transmitted signal to a symbol period start position of the crosstalk signal, and follow a symbol period start position of the synchronized signal Send a signal.

As shown in Figure 9, the transceiver 1 (which may also be other systems that implement symbol synchronization) includes:

The first obtaining module 11 is configured to acquire a symbol period start position of the crosstalk signal, and the synchronization module 12 is configured to synchronize a symbol period start position of the pre-transmitted signal to a symbol period of the crosstalk signal acquired by the first acquiring module 11 starting point;

The sending module 13 is configured to send a signal according to a symbol period start position of the signal synchronized by the synchronization module 12.

When the transceiver 1 transmits a signal based on the start position of the symbol period of the near-end crosstalk signal, the method further includes:

The second obtaining module 14 is configured to obtain a symbol period start position of the near-end crosstalk signal. After acquiring the symbol period start position of the near-end crosstalk signal, the second obtaining module 14 sends the symbol period start position of the near-end crosstalk signal to the synchronization module 12.

When the transceiver 1 is based on the start position of the symbol period of the synchronous pilot signal When sending a signal, as shown in Figure 9, it also includes:

The receiving module 15 is configured to receive a sending synchronization guiding signal request sent by the synchronization center manager;

The synchronization guiding signal sending module 16 is configured to send the synchronization guiding signal after receiving the request by the receiving module 15;

After the synchronization pilot signal sent by the synchronization pilot signal transmitting module 16 causes the crosstalk signal, the first acquisition module 11 acquires the symbol period start position of the crosstalk signal.

The reporting module 17 is configured to report the acquisition information when the first acquisition module 11 acquires the crosstalk caused by the synchronization guiding signal sent by the synchronization guiding signal sending module 16.

When the signal is transmitted according to the symbol period start position of the synchronization pilot signal, as in Fig. 10, the system may further include a synchronization center manager 2, the synchronization center manager 2 including:

The selecting module 21 is configured to select a transceiver to send a synchronization guiding signal, and send a synchronous guiding signal request to the selected transceiver.

Specifically, this request is received by the receiving module 15 in the transceiver.

The obtaining information statistics module 22 is configured to receive and collect the obtained information reported by the transceiver;

The timer 23 is configured to enable the selection module 21 to reselect the transceiver to send the synchronization guiding signal when the acquisition information statistics module 22 does not receive the acquisition information reported by the transceiver within a predetermined time.

Through the description of the foregoing embodiments, the embodiment of the present invention has the following advantages: *: detecting a near-end crosstalk signal or a synchronous pilot signal in an initial stage of line activation by a transceiver, starting from a symbol period of a near-end crosstalk signal or a synchronous pilot signal The position transmits signals to realize symbol synchronization between lines; solves the problem of symbol synchronization and ensures orthogonality during signal transmission.

A person skilled in the art can understand that the drawings are only schematic diagrams of a preferred embodiment, and the modules or processes in the drawings are not necessarily required to implement the invention.

Those skilled in the art can understand that the modules in the device in the embodiment can follow The description of the embodiments is distributed in the apparatus of the embodiment, and the corresponding changes may also be made in one or more apparatuses different from the embodiment. The modules of the above embodiments may be combined into one module, or may be further split into multiple sub-modules. Through the description of the above embodiments, those skilled in the art can clearly understand that the present invention can be implemented by hardware, or can be implemented by means of software plus necessary general hardware platform, and the technical solution of the present invention. It can be embodied in the form of a software product that can be stored in a non-volatile storage medium (which can be a CD-ROM, a USB flash drive, a mobile hard disk, etc.), including a number of instructions for making a computer device (may It is a personal computer, a server, or a network device, etc.) that performs the methods described in various embodiments of the present invention.

In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and scope of the present invention are intended to be included within the scope of the present invention.

Claims

Rights request

A method for implementing symbol synchronization, comprising:

Obtaining a symbol period start position of the crosstalk signal;

Synchronizing a symbol period start position of the pre-transmitted signal to a symbol period start position of the crosstalk signal;

The signal is sent at the start of the symbol period after synchronization.

2. A method of implementing symbol synchronization as claimed in claim 1, wherein said pre-transmitted signal is an orthogonal frequency division multiplexed signal.

The method for implementing symbol synchronization according to claim 1, wherein the acquiring a symbol period start position of the crosstalk signal specifically includes:

Get the start of the symbol period of the near-end crosstalk signal.

Obtain the symbol period start position of the crosstalk signal caused by the synchronous pilot signal.

The method for implementing symbol synchronization according to claim 4, wherein the acquiring the synchronization guiding signal specifically includes:

After any transceiver is selected by the synchronization center manager, a synchronous pilot signal is sent.

The method for implementing symbol synchronization according to claim 4 or 5, wherein after the obtaining the symbol period start position of the crosstalk signal caused by the synchronization pilot signal, the method further comprises:

Reporting the acquisition information to the synchronization center manager;

The acquisition information is used to indicate that a symbol period start position of the crosstalk signal caused by the synchronization pilot signal has been acquired;

The synchronization center manager collects and stores the reported acquisition information; the synchronization center manager starts timing, and when the acquisition information is not received within a predetermined time, the acquisition information is not reported or the synchronization guidance signal is not sent. The transceiver is selected from the transceiver to transmit the synchronization pilot signal.

7. The method for implementing symbol synchronization according to claim 5, wherein: After sending the synchronization boot signal, it also includes:

a port corresponding to the selected transceiver records a symbol period start position of the synchronization pilot signal;

When the selected transceiver transmits a signal again, the signal is transmitted in accordance with the symbol period start position of the recorded synchronous pilot signal.

8. A communication device, comprising:

a first acquiring module, configured to acquire a symbol period start position of the crosstalk signal; and a synchronization module, configured to synchronize a symbol period start position of the pre-transmitted signal to a symbol period start position of the crosstalk signal acquired by the first acquiring module ;

And a sending module, configured to send a signal according to a symbol period start position of the signal synchronized by the synchronization module.

The communication device of claim 8, further comprising: a second acquiring module, configured to acquire a symbol period start position of the near-end crosstalk signal.

The communication device of claim 8, further comprising: a receiving module, configured to receive a request for sending a synchronization pilot signal issued by the synchronization center manager;

a synchronization guiding signal sending module, configured to send a synchronization guiding signal after the receiving module receives the request;

The reporting module is configured to report the acquisition information when the first acquisition module acquires the crosstalk caused by the synchronization guiding signal sent by the synchronization guiding signal sending module.

11. A synchronization center manager, comprising:

a selecting module, configured to select a transceiver to send a synchronization guiding signal, and send a synchronous guiding signal request to the selected transceiver;

12. A system for implementing symbol synchronization, comprising:

a synchronization center manager, configured to select a transceiver to send a synchronous pilot signal, and receive the upper After obtaining the information, the acquisition information is counted and stored, and when the acquisition information is not received within a predetermined time, the transceiver is selected to send the synchronization in the transceiver that does not report the acquisition information or does not send the synchronization pilot signal. Guide signal