WO2009140890A1 - 一种实现符号同步的方法、***及装置 - Google Patents

一种实现符号同步的方法、***及装置 Download PDF

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Publication number
WO2009140890A1
WO2009140890A1 PCT/CN2009/071662 CN2009071662W WO2009140890A1 WO 2009140890 A1 WO2009140890 A1 WO 2009140890A1 CN 2009071662 W CN2009071662 W CN 2009071662W WO 2009140890 A1 WO2009140890 A1 WO 2009140890A1
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Prior art keywords
signal
synchronization
symbol period
start position
transceiver
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PCT/CN2009/071662
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English (en)
French (fr)
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石操
方李明
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华为技术有限公司
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2626—Arrangements specific to the transmitter only
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L25/03343—Arrangements at the transmitter end
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2662—Symbol synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/0001—Arrangements for dividing the transmission path
    • H04L5/0003—Two-dimensional division
    • H04L5/0005—Time-frequency
    • H04L5/0007—Time-frequency the frequencies being orthogonal, e.g. OFDM(A), DMT
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0037—Inter-user or inter-terminal allocation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0058—Allocation criteria
    • H04L5/0062—Avoidance of ingress interference, e.g. ham radio channels

Definitions

  • 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).
  • ADSL Asymmetric Digital Subscriber Line
  • VDSL Very-high-bit-rate Digital Subscriber Line
  • IDSL ISDN Digital Subscriber Line
  • ISDN Integrated Services Digital Network
  • SHDSL Single-pair High-bit-rate Digital Subscriber Line
  • 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.
  • DMT Discrete Multi-Tone Modulation
  • 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.
  • OFDM Orthogonal Frequency Divided Multiple
  • 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.
  • DSM Dynamic Spectral Management
  • the signal level DSM mainly includes Multi-Input and Multi-Output (MIMO), Vectored DSL (Vector DSL) and so on.
  • MIMO Multi-Input and Multi-Output
  • Vector DSL technology has much in common with MIMO technology.
  • MIMO Multi-Input and Multi-Output
  • MIMO Vectored DSL technology
  • MIMO is the best performing digital subscriber line technology.
  • MIMO technology still uses the currently popular OFDM, and the OFDM modulation technology is as follows:
  • OFDM orthogonal frequency division multiplexing
  • 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. :
  • ' 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.
  • 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.
  • the second line is not synchronized with the first line symbol.
  • the first line performs OFDM demodulation, part of the signals of frame 1 and frame 2 in the second line are processed.
  • 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.
  • an embodiment of the present invention provides a method for implementing symbol synchronization, including:
  • 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;
  • 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 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.
  • DRAWINGS 1 is a schematic diagram of an OFDM subcarrier in the prior art of the present invention
  • FIG. 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
  • FIG. 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. 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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:
  • the transceiver acquires the symbol period start position 2000 of the near-end crosstalk signal.
  • the transceiver is based on a symbol period start position of the near-end crosstalk 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.
  • 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 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.
  • 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.
  • 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.
  • a white circle indicates that the acquisition information is not reported and a synchronization guidance signal is not sent
  • a black circle indicates that the acquisition information has been reported or the synchronization guidance has been sent. signal.
  • FIG. 7a all transceivers do not report the acquisition information and do not send the synchronization pilot signal when the DLAM is started.
  • 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.
  • the new transceiver 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.
  • 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.
  • 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.
  • the transceiver 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.
  • 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.
  • 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.
  • 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
  • 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.
  • 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.
  • the transceiver 1 When the transceiver 1 is based on the start position of the symbol period of the synchronous pilot 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;
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • Non-volatile storage medium which can be a CD-ROM, a USB flash drive, a mobile hard disk, etc.
  • 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.

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Description

一种实现符号同步的方法、 ***及装置 本申请要求于 2008年 5月 19 日提交中国专利局， 申请号为 200810097933.1 , 发明名称为 "一种实现符号同步的方法、 ***及 装置" 的中国专利申请的优先权， 其全部内容通过引用结合在本 申请中。 技术领域
本发明实施例涉及通信技术领域，特别是涉及一种实现符号同 步的方法、 ***及装置。 背景技术
数字用户线 （ Digital Subscriber Line, DSL )技术是一种通过 电话双绞线， 即无屏蔽双绞线（ Unshielded Twist Pair, UTP )进行 数据传输的高速传输技术， 包括非对称数字用户线（Asymmetrical Digital Subscriber Line , ADSL ) , 甚 高 速数字 用 户 线 ( Very-high-bit-rate Digital Subscriber Line, VDSL ), 基于综合业 务数字网（ Integrated Services Digital Network, ISDN )的用户数字 线 （ ISDN Digital Subscriber Line, IDSL ) 和单线对高速数字用户 线 ( Single-pair High-bit-rate Digital Subscriber Line, SHDSL ) 等。
在各种数字用户线技术（ xDSL ) 中， 除了 IDSL和 SHDSL等 基带传输的 DSL夕卜，采用通带传输的 DSL利用频分复用技术使得 DSL与传统电话业务（ Plain Old Telephone Service, POTS )共存 于同一对双绞线上， 其中 DSL占据高频段， POTS占用 4KHz以下 基带部分， POTS信号与 DSL信号通过分离 /整合器 （Splitter ) 进 行分离或合并。 通带传输的 xDSL采用离散多音频调制 （Discrete Multi-Tone Modulation , DMT )技术进行调制和解调。
xDSL 技术物理层使用正交频分多路复用 （ Orthogonal Frequency Divided Multiple, OFDM )技术， 在一个符号 （另一种 说法叫做帧） 的时间范围内， 发送一组相互正交的子载波来承载 比特 （bit ) 信息。 收发器需要通过符号同步方法， 来寻找接收信 号中的符号起始位置， 并对接收符号进行解调。
随着 xDSL技术使用的频带的提高， 串扰（crosstalk ) 尤其是 高频段的串扰问题表现得日益突出。由于 xDSL上下行信道采用频 分复用， 近端串扰（NEXT )对***的性能不产生太大的危害； 但 远端串扰（FEXT )会严重影响线路的传输性能。 当一捆电缆内有 多路用户都要求开通 xDSL业务时， 会因为远端串扰（FEXT )使 一些线路速率低、性能不稳定、甚至不能开通等，最终导致 DSLAM 的出线率比较低。
近期出现了动态频谱管理 ( Dynamic Spectral Management, DSM ) 技术， 从功率层面和信号层面使各条线路达到一个优化的 结果。 信号层面的 DSM 主要包括多入多出 （Multi-Input and Multi-Output, MIMO ), Vectored DSL(矢量 DSL )等。 Vectored DSL 技术与 MIMO技术有许多的共同之处。 MIMO技术的出现解决了 各条线路受远端串扰影响的问题， 并从原理上去除了串扰所产生 的影响， 性能更加优化。 从目前数字用户线技术来看， MIMO 是 性能最优的数字用户线技术。 从调制方式上， MIMO 技术还是使 用目前比较流行的 OFDM, 有关于 OFDM调制技术如下所述：
OFDM 的主要思想是把整个传输频段分成许多频率比较窄的 子频带。 每个子频带用来承载一定的比特数。 如图 1 所示， 由于 每个子频带的频率宽度比较窄， 那么可以近似认为信道在这个频 带内的传输函数是一个常量。 接近于无失真传输便于接收端处理。 另一方面， 由于每个子载波完全正交， 各个子载波之间不会发生 影响。
DSM技术的优化和 MIMO技术的串扰抵消均是基于正交性这 个特点而提出来的。 在通常的情况下， 每个 xDSL modem的接收 端将其它 modem对它的干扰当作噪声， 则第 n个用户第 k个 tone 上可达到的数据速率 （ bk" ) 可用香农信道容量公式计算：
Figure imgf000005_0001
其中 '表示第 n条线路在第 k个子载波上的传输函数。 表 示第 m条线路在第 k个子载波上对第 n条线路的串扰函数。 表 示第 n条线路在第 k个子载波上的噪声功率。 表示第 n条线路在 第 k个子载波上的发送功率。
发明人发现现有技术存在以下缺点：
由上面的数据数率的计算公式可以看出整个 DSM的速率计算 公式都是基于各个子载波的， 这主要是由于子载波的正交性。 如 果各个子载波的正交性被破坏的话。 所有 DSM的算法均会发生改 变，上述所列举的算法（包括 DSM技术的优化和 MIMO、 Vectored DSL技术的串扰抵消等） 均不能用在这种情况下。
当各条线路的符号不同步的话， 就会破坏这种正交性。 说明 如下:
当第 1条线路受到第 2条线路的干扰， 如图 2所示， 第 2条 线路与第 1条线路符号不同步。 当第 1条线路进行 OFDM解调的 时候， 就会处理第 2条线路中帧 1和帧 2的部分信号。 相当于分 别在第 2条线路上分别加了一个窗 2和窗 3。 显然， 窗 2和窗 3都 比正常的 OFDM信号窗短 （如窗 1所示 ), 这样窗 1和窗 2窗 3 产生的频谱宽度不同 （如图 3 ), 这样就破坏了频率的正交性。 也 就是说不同频率间的信号也会互相干扰。 发明内容
本发明的实施例提出一种实现符号同步的方法， 以保证各条 线路的帧同步， 从而避免破坏正交性的情况发生。
为达到上述目的， 本发明实施例一方面提出一种实现符号同 步的方法， 包括：
获取串扰信号的符号周期起始位置； 将预发送信号的符号周期起始位置同步为所述串扰信号的符 号周期起始位置；
按照同步后的符号周期起始位置发送信号。
本发明实施例一方面还提出一种通信装置， 包括：
第一获取模块， 用于获取串扰信号的符号周期起始位置； 同步模块， 用于将预发送信号的符号周期起始位置同步为所 述第一获取模块获取的串扰信号的符号周期起始位置；
发送模块， 用于按照同步模块同步后的信号的符号周期起始 位置发送信号。
本发明实施例一方面还提出一种同步中心管理器， 包括： 选取模块， 用于选取收发器发出同步引导信号， 并向所述已 选取的收发器下发发送同步引导信号请求；
获取信息统计模块， 用于接收并统计收发器上报的获取信息； 定时器， 用于定时， 当所述获取信息统计模块在预定时间内 没有接收到收发器上报的获取信息时， 促使所述选取模块重新选 取收发器发送所述同步引导信号。
本发明实施例一方面还提出一种实现符号同步的***， 包括： 同步中心管理器， 用于选取收发器发送同步引导信号， 接收 到上报的获取信息后， 统计并存储所述获取信息， 在预定时间内 没有接收到所述获取信息时， 重新在未上报获取信息或未发送同 步引导信号的收发器中选取收发器发送所述同步引导信号。
收发器， 用于获取串扰信号的符号周期起始位置， 将预发送 信号的符号周期起始位置同步为所述串扰信号的符号周期起始位 置， 按照同步后的信号的符号周期起始位置发送信号。
本发明实施例的技术方案具有以下优点：
实现各线路间的符号同步； 解决了正交频分多路复用符号同 步的问题， 确保了正交频分多路复用符号发送过程中的正交性。 附图说明 图 1为本发明现有技术中的 OFDM子载波示意图；
图 2为本发明现有技术中的正交性破坏示意图；
图 3为本发明实施例一中的实现符号同步的方法流程示意图； 图 4为本发明实施例二中的检测近端串扰符号示意图； 图 5为本发明实施例三中的同步中心管理***示意图； 图 6为本发明实施例三中的同步引导信号发送和接力示意图； 图 7 为本发明实施例三中的同步中心管理器控制收发器的状 态示意图；
图 8 为本发明实施例三中的引导信号接力方案符号同步示意 图；
图 9 为本发明实施例中的通过近端串扰信号实现符号同步的 装置的结构示意图；
图 10为本发明实施例中的通过同步引导信号实现符号同步的 ***及装置的结构示意图。 具体实施方式
本发明实施例提供一种实现符号同步的方法、 ***及装置， 有效地实现各线路间的信号同步； 解决了正交频分多路复用信号 同步的问题， 确保了正交频分多路复用信号发送过程中的正交性。
下面结合附图和实施例， 对本发明的具体实施方式作进一步 详细描述：
串扰是现代数字***的必然产物， 是两条信号线之间的耦合， 信号线之间的互感和互容引起线上的噪声。 容性耦合引发耦合电 流， 而感性耦合引发耦合电压。 PCB 板层的参数、 信号线间距、 驱动端和接收端的电气特性及线端接方式对串扰都有一定的影 响。
在所有的线路使用相同的符号长度的前提条件下， 本发明实 施例一提供一种实现符号同步的方法， 如图 3 所示， 包括以下步 骤： 步骤 S301 , 获取串扰信号的符号周期起始位置。
具体的， 可以获取近端串扰信号的符号周期起始位置， 也可 以获取收发器发送的同步引导信号引起的串扰信号的符号周期起 始位置。 所述同步引导信号引起串扰信号后， 可以使本组收发器 发送的信号的符号周期起始位置与其引起的串扰信号的符号周期 起始位置相同， 这样本组收发器发送的信号的符号周期起始位置 一致， 可以避免各个收发器同时发送信号时产生的串扰现象。
步骤 S302, 将预发送信号的符号周期起始位置同步为所述串 扰信号的符号周期起始位置。
具体的， 预发送信号可以为正交频分多路复用信号， 也可以 为 CDMA信号或脉沖信号或者其他自定义信号。
步骤 S303 , 按照同步后的符号周期起始位置发送信号。
本发明实施例二将实施例一应用到具体的场景中， 利用近端 串扰信号的符号周期起始位置进行正交频分多路复用信号的发 送。 具体过程如下：
收发器 VTU (局端收发器为 VTU-0,用户端收发器为 VTU-R, 该收发器可以是数字用户线路接入复用器 DSLAM )在初始化阶段 检测近端串扰， 通过收发器发送的正交频分多路复用信号的符号 周期起始位置与近端串扰信号的符号周期起始位置同步的方式， 实现各线路间的符号同步。
在 VDSL2 ( G.993.2 )的协议中规定： VDSL2激活过程中， 初 始化阶段的起始部分， VTU 的双方都不发送任何信号。 在这个时 间里面， 局端 VDSL收发器 VTU-0检测近端串扰信号， 存储近端 串扰信号的符号周期起始位置， 并且在后续发送信号的过程中， 使发送信号的符号周期起始位置和近端串扰信号的符号周期起始 位置重合。 图 4 为本实施例二中检测近端串扰信号示意图， 如图 所示， 近端串扰信号 1000的符号周期与 OFDM的符号周期相同， 本实施例的实现如下所述：
首先， 收发器获取近端串扰信号的符号周期起始位置 2000。 其次， 该收发器根据所述近端串扰信号的符号周期起始位置
2000 , 调整发送正交频分多路复用信号的符号周期起始位置。 当 所述正交频分多路复用信号的符号周期起始位置与所述近端串扰 信号的符号周期起始位置重合时， 该收发器发送该正交频分多路 复用信号。 即图中 4000表示的过程为将正交频分多路复用信号的 符号周期起始位置同步为近端串扰信号的符号周期起始位置， 由 于所述近端串扰信号的符号与所述正交频分多路复用信号的符号 长度以及符号周期相同， 可以有效的保证信号之间的同步。 本发明实施例三在所有的线路使用相同的符号长度的前提条 件下， 提供一种实现符号同步的方法， 通过同步中心管理器选择 收发器接力发送同步引导信号， 实现多个收发器同步发送正交频 分多路复用信号。
图 5 为本实施例中的同步中心管理***示意图， 收发器以 DSLAM为例进行描述， 包括但不限于 DSLAM。
图 6 为本实施例同步中心管理***中的同步引导信号发送和 接力示意图， 如图所示， 包括：
步骤 S1 , 当一个 DSLAM启动之后， 所有端口的收发器进入 检测 NEXT信号状态。 由同步中心管理器选取 DSLAM的任一收 发器发出第一同步引导信号 5000,该第一同步引导信号 5000通过 串扰信道传递给本组收发器之中的其它收发器。 所述选取收发器 时可以根据预设的规则进行选取， 也可以随机选取， 当然选取的 方式并不限于以上所述的两种方式。 所述第一同步引导信号 5000 引起的串扰信号的符号周期与正交频分多路复用信号的符号在 Initialization/Showtime阶段的符号的周期相同。
步骤 S2, 当收发器检测到第一同步引导信号后， 获取该第一 同步引导信号 5000的符号周期起始位置， 然后向同步中心管理器 上报获取信息 6000。该获取信息 6000用于表示已获取到同步引导 信号的符号周期起始位置。 步骤 S3 , 同步中心管理器接收到获取信息 6000后对其进行统 计存储， 同时开始计时。 预定时间 T 内， 如一个固定信号周期， 同步中心管理器在本组未上报检测信息的收发器中选取一收发 器， 此收发器发出与第一同步引导信号相同的第二同步引导信号 5000。 以此类推， 可以使本组更多的收发器接收到该同步引导信 号， 避免同步中心管理器频繁地选择收发器发送同步引导信号。 所述固定信号周期为一个信号周期的整数倍， 例如： M 个信号周 期 T ( M*T )。
图 7 为本实施例同步中心管理***中的同步中心管理器控制 收发器的状态示意图， 以白色圓表示未上报获取信息且未发送同 步引导信号， 黑色圓表示已上报获取信息或已发送同步引导信号。 如图 7a所示， DLAM启动时所有收发器均未上报获取信息且未发 送同步引导信号； 如图 7b所示， 在第一次发送同步引导信号后， 部分收发器已上报获取信息或已发送同步引导信号；如图 7c所示， 在预定时间内没有收到收发器的上报获取消息时， 再重新选择新 的收发器发送同步引导信号， 重复上述步骤， 在第 N次发送同步 引导信号后， 绝大部分收发器已上报获取信息或已发送同步引导 信号； 如图 7d所示， 最终所有收发器已上报获取信息或已发送同 步引导信号， 即没有上报获取到同步引导信号的符号周期起始位 置且发送同步引导信号的收发器的集合为空。
步骤 S4, 图 8为本实施例同步中心管理***中任一收发器再 次发送信号的同步引导信号接力方案符号同步示意图， 如图所示， 当该收发器首次发送信号时， 该收发器对应的端口记录所述发送 同步引导信号的符号周期起始位置 2000, 在激活的进程中， 当进 行到初始化阶段的时候， 在所述记录的同步引导信号的符号周期 起始位置 2000发送正交频分多路复用信号。 该步骤由收发器来实 现， 包括： 获取记录的同步引导信号的符号周期起始位置 2000, 然后在所述正交频分多路复用信号的符号周期起始位置与所述同 步引导信号的符号周期起始位置 2000重合时， 发送所述正交频分 多路复用信号， 即 4000所表示的过程。
本发明实施例二通过收发器在线路激活的初始阶段检测近端 串扰信号的周期起始位置， 实现各线路间的符号同步。 本发明实 施例三通过中心管理器引导和接力同步引导信号， 在线路激活的 初始化阶段使收发器根据该同步引导信号的符号周期起始位置集 中发送 OFDM信号； 解决了 OFDM符号同步的问题， 使 DSM的 性能发挥到最佳的效果。
本发明实施例一方面提出一种实现符号同步的***， 该*** 可以用于多个 DSLAM之间，或者一个 DSLAM内部或者多个单板 端口同步等， 本发明实施例提供的实现符号同步的***可以包括 一种通信装置。
所述通信装置不仅是 DSLAM还可以应用于无线领域， 例如： WiFi、 Wimax, 包括：
收发器 1 , 用于获取串扰信号的符号周期起始位置， 将预发送 信号的符号周期起始位置同步为所述串扰信号的符号周期起始位 置， 按照同步后的信号的符号周期起始位置发送信号。
如图 9所示，该收发器 1(也可以是其它实现符号同步的***） 包括：
第一获取模块 11 , 用于获取串扰信号的符号周期起始位置； 同步模块 12, 用于将预发送信号的符号周期起始位置同步为 所述第一获取模块 11获取的串扰信号的符号周期起始位置；
发送模块 13 ,用于按照同步模块 12同步后的信号的符号周期 起始位置发送信号。
当该收发器 1 以近端串扰信号的符号周期起始位置为依据发 送信号时， 还包括：
第二获取模块 14, 用于获取近端串扰信号的符号周期起始位 置。该第二获取模块 14获取近端串扰信号的符号周期起始位置后， 将近端串扰信号的符号周期起始位置发送到同步模块 12。
当该收发器 1 以同步引导信号的符号周期起始位置为依据发 送信号时， 如图 9所示， 还包括：
接收模块 15 , 用于接收同步中心管理器下发的发送同步引导 信号请求；
同步引导信号发送模块 16,用于所述接收模块 15接收到请求 后， 发送同步引导信号；
该同步引导信号发送模块 16发送的同步引导信号引起串扰信 号后， 第一获取模块 11获取该串扰信号的符号周期起始位置。
上报模块 17 ,用于所述第一获取模块 11获取到所述同步引导 信号发送模块 16发送的同步引导信号引起的串扰时， 上报获取信 息。
当根据同步引导信号的符号周期起始位置发送信号时， 如图 10, 该***还可以进一步包括同步中心管理器 2, 该同步中心管理 器 2包括：
选取模块 21 , 用于选取收发器发出同步引导信号， 并向所述 已选取的收发器下发发送同步引导信号请求；
具体的， 此请求被收发器中的接收模块 15接收。
获取信息统计模块 22, 用于接收并统计收发器上报的获取信 息；
定时器 23 , 用于定时， 当所述获取信息统计模块 22在预定时 间内没有接收到收发器上报的获取信息时， 促使所述选取模块 21 重新选取收发器发送所述同步引导信号。
通过上述实施例的描述， 本发明实施例具有以下优 , *： 通过收发器在线路激活的初始阶段检测近端串扰信号或同步 引导信号， 根据近端串扰信号或同步引导信号的符号周期起始位 置发送信号， 实现各线路间的符号同步； 解决了符号同步的问题， 确保了信号发送过程中的正交性。
本领域技术人员可以理解附图只是一个优选实施例的示意 图， 附图中的模块或流程并不一定是实施本发明所必须的。
本领域技术人员可以理解实施例中的装置中的模块可以按照 实施例描述分布于实施例的装置中， 也可以进行相应变化位于不 同于本实施例的一个或多个装置中。 上述实施例的模块可以合并 为一个模块， 也可以进一步拆分成多个子模块。 通过以上的实施方式的描述，本领域的技术人员可以清楚地了解 到本发明可以通过硬件实现，也可以可借助软件加必要的通用硬件平 台的方式来实现基于这样的理解，本发明的技术方案可以以软件产品 的形式体现出来， 该软件产品可以存储在一个非易失性存储介质（可 以是 CD-ROM, U盘， 移动硬盘等） 中， 包括若干指令用以使得一 台计算机设备（可以是个人计算机， 服务器， 或者网络设备等）执行 本发明各个实施例所述的方法。
总之， 以上所述仅为本发明的较佳实施例而已， 并非用于限定本 发明的保护范围。 凡在本发明的精神和原则之内， 所作的任何修改、 等同替换、 改进等， 均应包含在本发明的保护范围之内。

Claims

权利要求
1、 一种实现符号同步的方法， 其特征在于， 包括：
获取串扰信号的符号周期起始位置；
将预发送信号的符号周期起始位置同步为所述串扰信号的符号 周期起始位置；
按照同步后的符号周期起始位置发送信号。
2、 如权利要求 1所述实现符号同步的方法， 其特征在于， 所述 预发送的信号为正交频分多路复用信号。
3、 如权利要求 1所述实现符号同步的方法， 其特征在于， 所述 获取串扰信号的符号周期起始位置具体包括：
获取近端串扰信号的符号周期起始位置。
4、 如权利要求 1所述实现符号同步的方法， 其特征在于， 所述 获取串扰信号的符号周期起始位置具体包括：
获取同步引导信号引起的串扰信号的符号周期起始位置。
5、 如权利要求 4所述实现符号同步的方法， 其特征在于， 所述 获取同步引导信号具体包括：
任一收发器被同步中心管理器选取后， 发送同步引导信号。
6、 如权利要求 4或 5所述实现符号同步的方法， 其特征在于， 所述获取同步引导信号引起的串扰信号的符号周期起始位置后还包 括：
向同步中心管理器上报获取信息；
所述获取信息用于表示已获取到同步引导信号引起的串扰信号 的符号周期起始位置；
所述同步中心管理器统计并存储所述上报的获取信息； 所述同步中心管理器开始计时，在预定时间内没有接收到所述获 取信息时，重新在未上报获取信息或未发送同步引导信号的收发器中 选取收发器发送所述同步引导信号。
7、 如权利要求 5所述实现符号同步的方法， 其特征在于， 所述 发送同步引导信号后， 还包括：
所述被选取的收发器对应的端口记录所述同步引导信号的符号 周期起始位置；
所述被选取的收发器再次发送信号时，按照所述记录的同步引导 信号的符号周期起始位置发送信号。
8、 一种通信装置， 其特征在于， 包括：
第一获取模块， 用于获取串扰信号的符号周期起始位置； 同步模块，用于将预发送信号的符号周期起始位置同步为所述第 一获取模块获取的串扰信号的符号周期起始位置；
发送模块，用于按照同步模块同步后的信号的符号周期起始位置 发送信号。
9、 如权利要求 8所述通信装置， 其特征在于， 还包括： 第二获取模块， 用于获取近端串扰信号的符号周期起始位置。
10、 如权利要求 8所述通信装置， 其特征在于， 还包括： 接收模块，用于接收同步中心管理器下发的发送同步引导信号请 求；
同步引导信号发送模块， 用于所述接收模块接收到请求后， 发送 同步引导信号；
上报模块，用于所述第一获取模块获取到所述同步引导信号发送 模块发送的同步引导信号引起的串扰时， 上报获取信息。
11、 一种同步中心管理器， 其特征在于， 包括：
选取模块， 用于选取收发器发出同步引导信号， 并向所述已选取 的收发器下发发送同步引导信号请求；
获取信息统计模块， 用于接收并统计收发器上报的获取信息； 定时器， 用于定时， 当所述获取信息统计模块在预定时间内没有 接收到收发器上报的获取信息时，促使所述选取模块重新选取收发器 发送所述同步引导信号。
12、 一种实现符号同步的***， 其特征在于， 包括：
同步中心管理器， 用于选取收发器发送同步引导信号，接收到上 报的获取信息后， 统计并存储所述获取信息， 在预定时间内没有接收 到所述获取信息时，重新在未上报获取信息或未发送同步引导信号的 收发器中选取收发器发送所述同步引导信号；
收发器， 用于获取串扰信号的符号周期起始位置， 将预发送信号 的符号周期起始位置同步为所述串扰信号的符号周期起始位置，按照 同步后的信号的符号周期起始位置发送信号。
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