KR19990045473A - Method and system for synchronizing time division duplexed transceivers - Google Patents

Abstract

An improved technique for synchronizing the transmission and reception of a data transmission system using time division multiplexing is disclosed. An improved synchronization technique takes advantage of the time varying energy of the received data to achieve synchronization. In one embodiment, the improved synchronization process 500 measures the energy in n consecutive frames of the received data (502), and then the measured energy value for the n consecutive frames in which the alignment error estimate is determined. Is calculated based on 504. In another embodiment, an improved synchronization technique provides the ability to avoid frequency tones susceptible to RF interference using output signals from a multi-carrier modulation device (FFT device). The improved synchronization technique also uses crosstalk interference levels to achieve synchronization. Remote receivers in a data transmission system may be synchronized to the central transmitters, and the central transmitters may be synchronized with each other.

Description

Method and system for synchronizing time division duplexed transceivers

The present invention relates to US application Ser. No. 08 / 707,322, entitled "Method and Apparatus for Crosstalk Cancellation," and US Application Ser. No. 08 / 501,250, entitled "Time Division Multiple High Speed Data Transmission System and Method." These two references are described here for reference.

The present invention relates to a data transmission system, and more particularly, to a data transmission system using a time division duplex method.

Two-way digital data communication systems have recently been developed for high speed data communication. One standard for high speed data communication over double helix telephone lines is known as asymmetric digital subscriber lines (VDSLs). Another standard for high-speed data communications over dual-helical telephone lines is known as high-speed digital subscriber lines (VDSLs).

The Committee for Communications Information Solutions (ATIS), recognized by the American Standards Institute (ANSI) Standards Group, has finally decided on discrete multi-tones based on methods for the transmission of digital data over double-helix telephone lines. This standard, known as ADSL, was originally designed for video data transmission and high-speed Internet access over telephone lines, but it could also be used in many different applications. The North American standard was named the ANSI T1.413 ADSL standard (hereinafter referred to as the ADSL standard), which is described in detail herein for reference. The baud rate under the ADSL standard is designed to transmit information at 8 Mbit / s over a double helix telephone line. The standardization system defines the use of discrete multi-tone (DMT) systems using 256 " tones " or " sub-channels " each 4.34.3 kHz wide in the forward (downstream). In the context of a telephone system, the downstream direction is defined as the transmission from a central office (usually owned by a telephone company) to a remote end user (ie, a resident or business user). In other systems the number of tones can vary widely.

The ADSL standard also defines the use of reverse transmission at data rates ranging from 16 to 800 Kbit / s. Reverse transmission follows the upstream direction, eg, from remote to central office. As such, the term ADSL comes from the fact that the data rate is significantly higher in the downstream direction than in the upstream direction. This is especially useful for systems used to transmit video programming or video conferencing information remotely over a telephone line.

Since the downstream and upstream signals are transmitted over the same twisted pair (ie they are duplex), they must be separated from each other in some way. The duplication method used in the ADSL standard is frequency division duplication (FDD) or echo cancellation. In a frequency division duplex system, upstream and downstream signals occupy different frequency bands, which are separated at the transmitter and receiver by a filter. In an echo cancellation system, upstream and downstream occupy the same frequency band and are separated by signal processing.

ANSI established another standard for subscriber line based transmission systems called the VDSL standard. This VDSL standard is intended to enable the use of higher data rates at least about 6 Mbit / s to about 52 Mbit / s or downstream. At the same time, digital, audio, and video committees are working on a similar system called fiber to the curb (FTTC). The transmission medium from this dense area to the consumer is a standard unshielded twisted pair.

A number of demodulation methods have been proposed for use with the VDSL and FTTC standards (hereinafter referred to as VDSL / FTTC). For example, some of the possible VDSL / FTTC demodulation methods are single carrier transmission methods such as quadrature amplitude modulation (QAM), carrierless amplitude and phase modulation (CAP), quadrature phase shift modulation (bena), or residual sideband modulation. In addition, it includes multi-carrier transmission methods such as Discrete Multi-tone Demodulation (DMT) or Discrete Wavelet Multi-Tone Demodulation (DWMT).

In addition, multiple demodulation transmission methods are receiving large amounts of notification due to the high data rates they provide. 1A is a schematic block diagram of a conventional transmitter 100 for a multicarrier demodulation system. The conventional transmitter 100 is suitable for DMT demodulation, for example in an ADSL or VDSL system. The transmitter 100 receives a data signal transmitted from the buffer 102. These data signals are then supplied from the buffer 102 to the forward error correction (FEC) unit 104. FEC unit 104 compensates for errors due to crosstalk noise, impulse noise, channel distortion, and the like. The signals output by the FEC unit 104 are supplied to a data sign encoder 106. Data sign encoder 106 operates to encode signals for a plurality of frequency tones associated with multi-carrier demodulation. When assigning data or bits of data to each frequency tone, the data sign encoder 106 uses the data stored in the transmit bit allocation table 108 and the transmit energy allocation tape 110. The transmit bit allocation table 108 includes an integer value for each of the carriers (frequency tones) of multicarrier demodulation. The values stored in the transmit energy allocation table 110 are used to effectively provide a fraction of bits of resolution through different assignments of energy levels to the frequency tones of multicarrier demodulation. In any case, after data sign encoder 106 encodes the encoder to each frequency tone, inverse fast Fourier transform (IFFT) unit 112 converts the frequency domain data supplied by data sign encoder 106. Demodulate and provide the transmitted time domain signals. The time domain signals are then fed to a digital-to-analog converter (DAC) 114 where the digital signal is converted into an analog signal. The analog signal is then transmitted over one channel to one or more remote receivers.

1B shows a schematic block diagram of a conventional remote receiver 150 for use in a multi-carrier modulation system. For example, the conventional remote receiver 150 is suitable for DMT demodulation in an ADSL or VDSL system. The remote receiver 150 receives analog signals transmitted over the channel by the transmitter. The received analog signals are fed to an analog-to-digital converter (ADC) 152. ADC 152 converts the received analog signals into digital signals. The digital signals are then fed to a fast Fourier transform (FFT) unit 154 which demodulates the digital signals while converting the digital signals from the time domain to the frequency domain. These demodulated digital signals are then fed to a frequency domain equalizer (FEQ) unit 156. The FEQ unit 156 performs equalization on digital signals to equalize attenuation and phase for various frequency tones. The data code decoder 158 then receives the equalized digital signal. Data code decoder 158 operates to decode equalized digital signals to recover data or data bits transmitted on each carrier (frequency tone). In decoding the equalized digital signals, the data code decoder 158 needs access to bit allocation information and energy allocation information used to transmit the data. As such, the data code decoder is coupled to the received bit allocation table 162 and the received energy allocation table 160, which respectively store the bit allocation information and the energy allocation information used to transmit the data. Data obtained from each of the frequency tones is sent to a forward error correction (FEC) unit 164. The FEC unit 164 performs error correction of the data to provide corrected data. The corrected data is then stored in buffer 166. Thereafter, data may be retrieved from the buffer 166 and further processed by the receiver 150. Optionally, the received energy allocation table 160 may be supplied to and used by the FEQ unit 166.

The bit allocation table and energy allocation tables used in the conventional transmitter 100 may be implemented as a single table or an individual table. As such, the bit allocation table and energy allocation table used in the remote receiver 150 may be implemented as a single table or as individual tables. Also, the transceiver 100 is usually controlled by a controller and the remote receiver 150 is typically controlled by a controller. Typically, the controllers are programmable controllers.

The transmitter 100 and remote receiver 150 shown in FIGS. 1A and 1B each optionally include other components. For example, the transmitter 100 may add a cyclic prefix to the sign after the IFFT unit 112, and the remote receiver 150 may remove the cyclic prefix before the FFT unit 112 thereafter. In addition, the remote receiver 150 may provide a time domain equalizer (TEQ) unit between the ADC 152 and the ALC FFT unit 154.

Most of the proposed VDSL / FTTC transmission methods use frequency division duplex (FDD) of upstream and downstream signals. On the other hand, one particular of the proposed VDSL / FTTC transmission methods uses time division duplex (TDD) of upstream and downstream signals. More specifically, the time division duplex method is tuned in this case so that the periodically tuned upstream and downstream communication periods do not overlap each other. That is, the upstream and downstream communication periods for all the lines sharing the binder are tuned. With this arrangement, all ultra-fast transmissions in the same binder are tuned and time-division duplexed so that downstream communications are not transmitted to new signals that overlap with upstream communications transmissions. This is also called a basic data transmission method (ie ping pong). A period in which no transmission takes place, while upstream and downstream communication periods are separated while no data is transmitted in either case. When the synchronization time division duplex method is used for DMT, it is often referred to as synchronized DMT (SDMT).

A typical feature of the above-mentioned transmission method is that twisted pairs are used as at least part of the transmission medium connecting the central office (eg telephone company) to the consumer (eg resident or business user). Although optical optics may be used from a central office to a dense area near the user's residence, twisted pairs may be used to transmit signals from the dense area to the user's home or office.

Stranded wire is grouped into a binder. While the stranded wire is in the binder, the binder provides a fairly good protection against external electromagnetic interference. However, stranded wires in the binder cause electromagnetic interference with each other. This type of electromagnetic interference is generally known as crosstalk interference, including near-end crosstalk (NEXT) interference and far-end crosstalk (FEXT) interference. As the transmission frequency increases, crosstalk interference (NEXT interference) becomes important. As a result, data signals transmitted over twisted pairs at high speed are significantly degraded by crosstalk interference caused by the different twisted pairs in the binder. As the data transfer rate increases, this problem gets worse. The advantage of data transmission based on synchronized TDD (such as SDMT) is that if there are transmissions on all circuits during the same period (i.e., in the same superframe format), crosstalk interference from other circuits in the binder is substantially practical. It will disappear.

The data transmission system typically includes a central office and a plurality of remote units. Each remote unit communicates with the central office through a data link established between the central office and a particular remote unit. To establish this data link, initial processing is done to initiate communication between the central office and each remote unit. For the following description, the central office includes a central modem (or central unit) and the remote unit includes a remote modem. These modems are transceivers that enable data transfer between the central office and remote units. The central office thus typically comprises a plurality of central side transceivers, each having a central side transmitter and a central side receiver, and typically the remote unit comprises a remote side transceiver having a remote side transmitter and a remote side receiver.

One conventional frame synchronization technique, US Pat. No. 5,627,863, which correlates with a selected and stored sequencer sequence to determine the necessary adjustments for synchronization and necessary for the transmission of the selected sequence of data received by the receiver. Illustrates a frame synchronization method suitable for a system (eg, ADSL) that uses frequency division duplication (FDD) or echo cancellation to provide redundant operation. This frame synchronization technique requires one special start-up training sequence to achieve frame synchronization. However, this described frame synchronization method is not suitable for a system using time division duplication because synchronization in time is not required for FDD or echo cancellation as in TDD to eliminate crosstalk.

When the data transmission system is operating in time division duplex (TDD), the transmitters and receivers of the central office and remote units must be synchronized in time so that transmission and reception are not duplicated in time. In a data transmission system, downstream transmission is transmission from the central side transmitter to one or more remote side receivers, and upstream transmission is transmission from one or more remote side transmitters to the central side receiver. The central side transmitter and receiver may be combined as a central side transceiver, and the remote side transmitter and receiver may be combined as a remote side transceiver.

Generally speaking, in a time division redundancy system, the upstream signals alternate with the down stream signals. Typically, upstream transmissions and downstream transmissions are separated into a ghat evening or no signal period. The guard interval is provided to make the transmission system available to redirect the data being transmitted so that one transmission can be received before there is a transmission in the opposite direction. Certain transmission methods separate upstream and downstream transmissions into smaller units called frames. These frames can also be grouped into superframes including a series of downstream frames and a series of upstream frames and guard intervals therebetween.

Time division duplication is a simple way to divide a channel (media) between two or more transceivers. Each transceiver is assigned one time slot during transmission and there is no signal period (guard interval) while no unit needs to transmit. When time division redundancy is used on a channel that is susceptible to crosstalk (NEXT interference) between a plurality of contacts, synchronization must be established and maintained between all affected units. One example is a VDSL service that uses existing twisted pairs for transmission in the 13-52 Mb / s range over a loop within the 1.5 km range. The twisted pairs towards the subscribers are tied together in a 25-100 twisted pair cable. The use of that range and high frequency (0.2-11 MHz signal width) causes severe crosstalk between adjacent strands in the binder. In order to achieve the desired data rate on a 1.5 km long loop, DMT is a suitable multi-carrier modulation method. This method allows time division redundancy to be used very well since a single FFT unit can be used during transmission and reception, eliminating the need for two such FFT units, and having other advantages in analog circuitry.

Conventional frame synchronization techniques are not only suitable for synchronized TDD, but also RF is unreliable in the presence of interference. Due to the energy of strong RF interference by the amateur radio frequency band, RF interference may in some cases have a signal power that is greater than or equal to the desired received signal power. However, in the synchronized TDD system, crosstalk is reduced and adjusted, and in order for the received data to be correctly restored, it is important to be synchronized and maintained.

Therefore, there is a need for an improved synchronization technique in a time division duplex system.

In general, the present invention relates to an improved technique for synchronizing the transmission and reception of a data transmission system using time division duplexing. An improved synchronization technique in accordance with one aspect of the present invention utilizes a time-varying nature of the energy of received data for synchronization. In one embodiment, the improved synchronization technique makes it possible to avoid frequency tones that are sensitive to RF interference by using the output signal of a multi-carrier modulation unit (eg FFT unit). With this improved synchronization technique, the remote receiver of the data transmission system can be synchronized with the central transmitter, the central receiver can be synchronized with the remote transmitter, and the central receivers can be synchronized with each other.

The invention can be implemented in a variety of ways, including as an apparatus, a system, a method or a computer readable media. Some embodiments of the invention are discussed below.

A first transceiver that transmits a frame of data transmitted from a second transceiver through a transmission medium to a first transceiver, wherein the first and second transceivers are associated with a data transmission system capable of bidirectional data transmission using a time division duplex communication scheme; As a method of adjusting an alignment for receiving, an embodiment of the present invention provides a method for measuring the amount of energy of each of a plurality of consecutive frames of received data, based on the measured amount of energy. Detection of edges of the plurality of consecutive frames of the received data, and calculation of alignment error estimates using the edges detected in the plurality of consecutive frames. In addition, the synchronization may later be adjusted according to the alignment error estimate. Optionally, the data transmission system utilizes a super frame structure having a plurality of frames, such that the first set of frames of the super frame transmission data is transmitted in a first direction and the second set of frames is in a second direction. send.

The first transceiver transmits a data frame transmitted from a second transceiver through a transmission medium to the first transceiver, wherein the first and second transceivers are associated with a data transmission system capable of bidirectional data transmission using a time division duplex communication scheme. A readable computer medium comprising program instructions for adjusting alignment for receiving, wherein an embodiment of the present invention provides a first computer readable code for measuring the amount of energy of each of a plurality of consecutive frames of received data. A device, a second computer readable code device for detecting the edges of the plurality of consecutive frames of the received data based on the measured amount of energy, and an alignment using the boundaries detected in the plurality of consecutive frames A third computer readable code device for calculating an error estimate.

A receiver of a data transmission system using a time division duplex communication method for replacing transmission and reception of data, wherein an embodiment of the present invention provides a method for receiving and converting analog data transmitted to a receiver through a channel into a digital signal. A D converter, an input buffer for temporarily storing the received digital signal, a multicarrier demodulation unit for demodulating the received digital signal stored in the input buffer into frequency domain data according to a plurality of different carrier frequencies, and the multicarrier demodulation unit A frame synchronization unit for synchronizing a reception frame boundary based on the time-varying property of energy of the frequency domain data generated in the second embodiment; a bit allocation table for storing bit allocation information used to transmit data received by the receiver; and receiving the frequency domain data. Bit allocation by Block based on the bit allocation information stored in the an output buffer that holds the data symbol decoder, and the decoded bits for decoding bits associated with the frequency domain data from the carrier frequency as the recovered data. The data transmission system is preferably a synchronized DMT system, and the multi-frequency demodulation unit preferably includes an FFT unit.

A receiver of a data transmission system using a time division duplex communication method for replacing transmission and reception of data, wherein another embodiment of the present invention provides an A / D for receiving and converting analog data transmitted to a receiver through a channel into a digital signal. A converter, an input buffer for temporarily storing the received digital signal, a multicarrier demodulation unit for demodulating the received digital signal stored in the input buffer into frequency domain data according to a plurality of different carrier frequencies, in the multicarrier demodulation unit Frame synchronization means for synchronizing a reception frame boundary based on the time-varying property of the energy of the generated frequency domain data, a bit allocation table for storing bit allocation information used for transmission of data received by the receiver, and receiving the frequency domain data The bit allocation table An output buffer for storing a cost to restore the data symbol decoder, and the decoded bits for decoding bits associated with the frequency domain data from the carrier frequencies based on the data stored in the bit allocation information.

A central site comprising a plurality of transmitters for transmitting data according to a super frame format including at least one quiet period, wherein an external clock signal for synchronizing the plurality of transmitters is not used at the central site. In a data transmission system provided in accordance with an embodiment of the present invention, a method for synchronizing data transmission by a given one transmitter to another transmitter is provided in which the energy due to the data transmission of another transmitter in the no signal period associated with the given transmitter is determined. Measuring operation, comparing the measured energy with a threshold, and changing the synchronization of transmissions by the given transmitter when the measured energy in the comparing operation exceeds a threshold.

A central site comprising a plurality of transmitters for transmitting data according to a super frame format including at least one quiet period, wherein an external clock signal for synchronizing the plurality of transmitters is not used at the central site. A computer readable medium comprising program instructions for synchronizing data transmissions in a data transmission system, wherein one embodiment of the invention is due to data transmissions of other transmitters in an unsigned period associated with a given transmitter. A first computer readable code for measurement of energy, a second computer readable code for comparison of the measured energy with a threshold, and by the given transmitter if the energy measured in the comparison operation exceeds a threshold. Including third computer readable code for changing the synchronization of the transmission .

The present invention has many advantages. One advantage of the present invention is that the synchronization can be achieved even in the presence of RF interference, such as by an amateur radio user. Another advantage of the present invention is that it is suitable for data transmission systems using time division duplex communication schemes such as synchronized DMT or synchronized VDSL. Another advantage is that it is relatively strong with respect to the sound collection of the data transmission system.

Other aspects and advantages of the invention will become apparent from the following detailed description, with reference to the accompanying drawings which illustrate the principles of the invention.

1A is a simplified block diagram of a conventional transmitter in a multi-carrier modulation system.

1B is a simplified block diagram of a conventional remote receiver in a conventional multi-carrier modulation system.

2 is a block diagram of an exemplary telecommunications network suitable for implementing the present invention.

3 is a block diagram of a processing and distribution unit 300, in accordance with an embodiment of the present invention.

4 illustrates an exemplary super frame format in which some level of service is provided.

5A is a flow diagram of a synchronization process, in accordance with the basic embodiment of the present invention.

5B is a flow diagram of a synchronization process, in accordance with an embodiment of the present invention.

6A and 6B are flow charts of a synchronization process, according to a more modest embodiment of the present invention.

7 is a flow diagram of a boundary detection process, in accordance with an embodiment of the invention.

8 is a flowchart of an alignment error estimation process according to an embodiment of the present invention.

9A and 9B show energy values and energy difference values of data received in a series of 20 frames.

10A and 10B show energy values and energy difference values of data received in a series of twenty frames illustrated in FIGS. 9A and 9B after implementation of the alignment adjustment according to the present invention.

11 is a block diagram of a receiver in accordance with an embodiment of the present invention.

12 is a flowchart of a synchronization process for synchronization of adjacent transmitters to compensate for small synchronization differences.

<Explanation of symbols for main parts of the drawings>

300: processing and distribution unit

302: processing unit

304: data link

308: bus arrangement

The present invention relates to an improved technique for synchronizing transmission and reception in a data transmission system using a time division duplex communication scheme. One aspect of the present invention is an improved synchronization technique that utilizes the time varying nature of received data for synchronization. Another aspect of the invention is an improved synchronization technique that utilizes a crosstalk interference level for synchronization. With this improved synchronization technique, the remote receiver of the data transmission system can be synchronized with the central transmitter, the central receiver can be synchronized with the remote transmitter, and the central receivers can be synchronized with each other.

The synchronization required in a time division duplex communication system requires the transmission to be synchronized to the super frame structure. Conventional time domain methods that tend to correlate the first and last samples of a frame to detect samples, e.g., circular prefixes, are less reliable because RF interference of a received signal with the same power as the desired signal is likely to appear. none. However, the present invention provides an accurate technique for synchronizing transmissions in a time division duplex system even if the time domain signal becomes unreliable due to RF interference. Synchronization by the frequency domain approach according to the present invention is quite robust against interference to RF. In one embodiment, the improved synchronization technique makes it possible to avoid frequency tones that are sensitive to RF interference by using the output signal of a multi-carrier modulation unit (eg FFT unit).

Embodiments of the present invention are described with reference to FIGS. However, it will be apparent to those skilled in the art that these drawings are for illustrative purposes and that the present invention may be extended without being limited to these embodiments.

2 is a block diagram of an exemplary telecommunications network 200 suitable for implementing the present invention. The telecommunications network 200 includes a central office 202. The central office 202 provides services to a plurality of distribution posts for data transmission and reception with various remote units. In this embodiment, each dispensing post is a processing and dispensing unit 204. The processing and distribution unit 204 is coupled to the central office 202 via a high speed, multiplexed transmission line 206 such as an optical fiber line. If the transmission line 206 is an optical fiber line, the processing and distribution unit 204 is typically called an optical network unit (ONU). Normally, the central office 202 interacts with other processing and distribution units (not shown) through the high speed, multiplexed transmission lines 208 and 210, but only the operation of the processing and distribution unit 204 is here. It is explained. The processing and distribution unit 204 can include one or more modems (central modems).

Processing and distribution apparatus 204 provides services to a plurality of individual subscriber lines 212-1 through 212-n. Each subscriber line 212 typically serves a single terminal user. The terminal user is equipped with a remote device suitable for communicating with the processing and distribution device 204 at a very high data rate. More specifically, the remote device 214 of the first terminal user 216 is coupled to the processing and distribution device 204 by the subscriber line 212-1, and the remote device of the second terminal user 220 ( 218 is coupled to the processing and distribution device 204 by subscriber line 212-n. Remote devices 214 and 218 include a data communication system capable of exchanging data with processing and distribution device 204. In one embodiment, the data communication system is a modem. Remote devices 214 and 218 may be embedded in a variety of devices including, for example, telephones, televisions, monitors, computers, video conferencing devices, and the like. 2 only shows a single remote device coupled to each subscriber line, it should be understood that multiple remote devices can be combined in a single subscriber line. Moreover, although FIG. 2 shows the processing and distribution device 204 as being centralized, it should be understood that the processing does not need to be centralized and that processing can be performed independently for each of the subscriber lines 212.

Subscriber lines 212 serviced by the processing and dispensing apparatus 204 may be aggregated into the shielding binder 222 leaving the processing and dispensing apparatus 204. Shielding provided by shielding binder 222 typically serves as an excellent insulator for the emission and reception of electromagnetic interference. However, the final segment of subscriber lines, commonly referred to as "drops," branches off the shielding binder 222 and couples directly or indirectly to the remote device of the terminal user. The “drop” portion of the subscriber line between each remote device and shielding binder 222 is typically an unshielded twisted pair wire. For most applications, the drop length does not exceed about 30m.

Crosstalk interference, including near terminal crosstalk (NEXT) and original terminal crosstalk (FEXT), occurs mainly in shielding binder 222 in which subscriber lines 212 are densely populated. Thus, as is generally seen when multiple levels of service are being provided, when data is transmitted on some subscriber lines 212 and other subscriber lines receive data, crosstalk interference that occurs is substantial to the receipt of appropriate data. It becomes an obstacle. Thus, to overcome this problem, data is transmitted using a superframe structure in which data bits to be transmitted are allocated. For example, the communication network 200 is particularly suitable for synchronized TDD transmission systems (eg, synchronized VDSL or SDMT) that provide different levels of service.

Thus, referring to the SDMT transmission system shown in FIG. 2, the data transmission on all lines 212 in the shielding binder 222 associated with the processing and distribution device 204 need to be synchronized. As such, all active lines from processing and distribution apparatus 204 can be transmitted in the same direction (ie, downward or upward) to substantially eliminate NEXT interference.

3 is a block diagram of a processing and dispensing apparatus 300 in accordance with an embodiment of the present invention. For example, the processing and dispensing apparatus 300 is a detailed implementation of the processing and dispensing apparatus 204 shown in FIG.

The data processing and distribution device 300 includes a processing device 302 for transmitting and receiving data over the data link 304. The data link 304 may be connected to an optical fiber cable of, for example, a telephone network or a cable network. The processing device 302 needs to operate to synchronize various processed transmissions and receptions. The data processing and distribution device 300 further includes a bus arrangement 308 and a plurality of analog cards 310. The output of the processing device 302 is connected to the bus array 308. The bus arrangement 308, in conjunction with the processing unit 302, directs output data from the processing unit 302 to the appropriate analog card 310 and directs input from the analog card 310 to the processing unit 302. . Analog card 310 typically provides an analog circuit for use by processing and distribution device 300 that performs more efficiently than using digital processing by processing device 302 using analog elements. For example, the analog circuit may include a filter, a transformer, an analog-digital converter or a digital-analog converter. Each analog card 310 is connected to a differential line. Typically, all lines for a given data transfer system 300 are bundled with a binder comprising about 50 lines (LINE-1 through LINE-50). Thus, in this embodiment, there are 50 analog cards 310 connected to 50 lines each. In one embodiment, the lines are twisted pair wires. The processing device 310 may be a general purpose computing device or a dedicated purpose device, such as a digital signal processor (DSP). The bus arrangement 308 can take a variety of arrangements and forms. The analog card 310 need not be designed for individual lines, but can instead be a single card or a circuit supporting multiple lines.

In the case where the processing is not centralized, the processing device 302 of FIG. 3 may be replaced with a modem for each line. The processing for each line can be performed independently for each line. In this case, the modem can be replaced with a single card with analog circuitry.

The NEXT interference problem occurs at the nodes adjacent to the output of the processing and distribution apparatus 300. With respect to the block diagram shown in FIG. 3, NEXT interference is more prevalent near the output of the analog card 310, where such positions are adjacent to each other and the maximum power differential (between the transmitted and received signals). This is because it has a location. In other words, the lines are connected to an apparatus remote from the processing and dispensing apparatus 300. Typically, most of the distance is in a shielded binder that accommodates 50 twisted pair wires, for example, and the remaining distance is beyond a single unshielded twisted pair wire. All these lines (e.g. twisted pair wiring) are received close to the binder and provide little individual shielding against electromagnetic coupling from other lines in the binder, so crosstalk interference between the lines in the binder (i.e., NEXT) Interference and FEXT interference).

Depending on the level of service provided, data transmission implemented in SDMT may be symmetrical or asymmetrical for uplink and downlink transmission. In the case of symmetric transmission, the DMT symbol is transmitted in both directions for the same period. That is, the period during which the DMT symbol is transmitted downward is the same as the period during which the DMT symbol is transmitted upward.

In VDSL, it has been proposed to have a superframe structure in which each frame is associated with a DMT symbol, including a fixed number of frames, for example about 20. In the frame format, the number of frames used for downlink transmission and the number of frames used for uplink transmission may vary. As a result, there are several different superframe formats that can occur. Typically, a superframe consists of a down burst of several frames and an up burst of several frames. A quiet frame is inserted between the up and down bursts to allow the channel to stabilize before the direction of transmission is reversed.

4 illustrates an example superframe format 400 in which level of service is provided. The superframe format 400 is an asymmetric format that includes a downward portion 402, a pause portion 404, an upward portion 406, and a pause portion 408. Pauses (pauses) 404 and 408 are disposed between downlink and uplink transmissions. In this asymmetric superframe format 400, the downward portion 402 is substantially larger than the upward portion 406. That is, longer bursts. This superframe format is useful in situations where downlink calls are considerably more than upcalls. For example, referring to FIG. 2, superframe format 400 may include 16 symbols down; 1 resting period; Two symbols up; And one resting period.

With proper synchronization in the central unit (processing and distribution unit 204 or processing unit 302) and a uniform superframe, synchronized transmissions of the same duration are provided to all circuits in the binder. Thus, the NEXT interference problem is effectively eliminated. Synchronization between the central unit and the remote unit is also important for accurate data recovery. This synchronization is required in synchronization VDSL and SDMT systems. An improved synchronization technique according to the present invention is described next with reference to FIGS. 5-12.

5A is a flow diagram of a synchronization process 500 in accordance with the basic embodiment of the present invention. Initially, synchronization process 500 measures 502 the energy within n consecutive frames of received data. The alignment error estimate is then calculated 504 based on the measured energy values for the n consecutive frames. After block 504, the synchronization process 500 is complete and ends.

5B is a flow diagram of synchronization processing 550 in accordance with an embodiment of the present invention. Initially, synchronization process 550 measures 552 the energy within n consecutive frames of received data. Next, an alignment error estimate is calculated from the position of the detected edge (556). Thereafter, the synchronization process 550 may adjust the synchronization criteria according to the alignment error estimate 558. After block 558, the synchronization process 550 is complete and ends.

By determining and adjusting the synchronization of the receiver of the remote device to the transmission from the central device according to the synchronization process 500 or 550, the remote device can establish synchronization with the central device. Once synchronized, the central unit and the remote unit can share a channel (transmission line) in a time division duplex manner. The synchronization process 500 or 550 is also suitable for determining and adjusting the synchronization of the receiver of the central device via transmission from the remote device.

6A and 6B are flowcharts of a synchronization process 600 according to a more detailed embodiment of the present invention. Once the synchronization process 600 is initialized, an FFT output is obtained for n consecutive contiguous frames of data received (602). Typically, the receiver side of the transceiver receives data from the transmission line as shown in FIG. 1B to transmit the received data to an analog-to-digital converter and then to the FFT apparatus. Therefore, the FFT output can be obtained from the output of the FFT device. The FFT output is a signal in the frequency domain.

Next, the FFT output, which is susceptible to RF interference, is removed. The remaining FFT output is then used for further processing. Typically, one frame includes a plurality of different frequency tones. Each of the frequency tones may have data encoded for transmission. However, certain frequency tones are more susceptible to RF interference than other frequency tones. If RF interference is generated by the amateur radio user, the frequency tone of the frame is likely to be subjected to RF interference by the amateur radio user.

In a remote device of a synchronized multicarrier VDSL system, where the frame has 256 frequency tones, the frequency tones 6-40 are generally unaffected by RF interference by amateur radio users, and lower frequency tones are lower. Since it has attenuation, it is less attenuated, and thus sufficient synchronization results can be obtained. Thus, in one embodiment, frequency tones 6-40 for each of n consecutive frames are used for the next processing.

The energy value for the n consecutive frames of the remaining FET outputs is then determined to be 606. By way of example, if the frequency tones 6-40 are used, the corresponding outputs from the FET device are obtained and then converted to the energy value, which together adds to produce a single energy value per frame. Preferably, said energy value is a power value for a frame. As an example, a single energy value per frame can be obtained by adding the squared moduli of all outputs of the FET device that can be used. Alternatively, the energy values can be obtained by adding the energy of the time domain samples after filtering out those time domain samples that are affected by a significant amount of RF interference.

Once the energy value for the n consecutive frames is determined to be 606, the synchronization process 600 detects 608 burst edges in the received data based on the predetermined energy value. By detecting the burst edge, the receiver can be identified when the data burst received from the transmitter begins. Thus, the burst edge identifies the start (or end) of the transmission received from the transmitter and further identifies the synchronization for the frame. Also, characteristics of the trailing edge and / or superframe (superframe information) of the received data can be obtained.

The alignment error estimate value for frame boundary setting is then determined to be 610 for the detected burst edge. Here, using the burst edge detected as 608, the alignment error estimate value may be determined as 610 for frame boundary setting. In particular, from a predetermined energy value within the burst edge, the remote device synchronization process 600 can determine per-frame alignment error (ie, frame synchronization error). Normally, alignment errors are detected as part of the frame. Thereafter, the frame boundary may be adjusted to 612 in accordance with the alignment error estimate.

Once adjusted to 612, frame synchronization can be set. However, preferably, the synchronization process 600 continues to ensure that synchronization is achieved. In particular, following block 612, decision block 614 determines whether the average value of the alignment error estimates is lower than a predetermined threshold. If the alignment error estimate is not lower than the predetermined threshold, the synchronization process 600 repeatedly returns to block 612 and the next blocks to iteratively reduce the magnitude of the error. On the other hand, if the decision block 614 determines that the alignment error estimate value is smaller than the predetermined threshold value, the information of the super frame is output to 616. For example, the superframe information may indicate the number of frames at the beginning and end and / or burst of the received transmission. Following block 616, the synchronization process 600 is completed and ends.

Typically, if the amount of frame synchronization is largely adjusted in block 612, the alignment error estimate is greater than a predetermined threshold. Therefore, the synchronization process 600 will repeat to generate a small amount of alignment error less than a predetermined threshold. Thereafter, the synchronization processing unit 600 may proceed to block 616. As another method, decision block 614 can be eliminated if the alignment error estimate is correctly generated with a high degree of confidentiality.

7 is a flowchart of edge detection processing 700 in accordance with an embodiment of the present invention. Edge detection processing 700 discloses additional details of block 608 of FIG. 6A in which a burst edge is detected. The edge detection process initially calculates a continuous energy difference for the n determined energy values (702). These consecutive energy differences can be indexed from 1 to i. Next, the maximum energy difference and its index j are determined (704). The energy difference at index j-1 and index j + 1 is stored for later retrieval (706). Following block 706, the edge detection process 700 is completed and the process returns to block 610 of the synchronization process 600.

8 is a flowchart of alignment error estimation processing 800 according to the present embodiment. Alignment error estimation process 800 discloses additional details of block 610 of FIG. 6A in which alignment error estimation is determined. The alignment error estimation process 800 initially determines the amount of difference from the energy values at index j + 1 and index j-1 (802). The energy values at the index j + 1 and the index j-1 are the energy values immediately before and immediately after the maximum energy difference amount at the index j. For example, the energy value may be a power value. Next, the difference amount is normalized to generate an alignment error calculation (804). In this embodiment, the alignment error estimate represents the fractional part of the frame. Thus, the synchronization of the receiver to the data transmitter can be turned off by this fractional part of the frame. Following block 804, the alignment error estimation process 800 is completed and the process returns to block 612 of the synchronization process 600.

9A and 9B show diagrams of energy values e and energy difference values DELTA e for received data on a sequence of 20 frames. In FIG. 9A, diagram 900 shows energy values e for 20 frames and shows a burst of data adjacent to frames 6-15. For example, the energy value e is generated by block 606 of FIG. 6A. In FIG. 9B, the diagram 902 shows the continuous energy difference value DELTA e for the determined energy values. The continuous energy difference value Δe identifies the areas associated with the edge or transition point in the received data. The first edge represents an initial edge, i.e., the beginning of a data burst, and anywhere in area 904, and the second edge 906 represents a trailing edge, or the end of a data burst, anywhere in area 906. have. For example, the energy difference value Δe is determined by block 702 of FIG. 7.

As shown in Figures 9A and 9B, the receiver is not properly synchronized with the transmission data coming from the remotely located transmitter. In particular, the starting point of the burst of data received from the transmitter starts at any location within the frame 6. In order to be properly synchronized, the data burst from the transmitter will start at exactly the beginning of frame 6 in this embodiment. By using the energy difference Δe, the technique significantly improves immunity to noise levels on the received data. Diagram 902 shows that the initial edge of the data burst is in region 904, ie anywhere in frame 6, and the trailing edge of the data burst is in region 906, ie, in frame 14. Show that you are in a position.

10a and 10b show the energy value e and energy of the received data for a series of 20 frames in the example shown in FIGS. 9a and 9b after alignment adjustment is made, ie after proper synchronization has been made. The difference value Δe is shown. In FIG. 10A, diagram 1000 shows a data burst between frames 6, 14 having an initial edge 1002 at the start of frame 6 and a trailing edge 1004 at the end of frame 14. . In FIG. 10B, the diagram 1006 shows the continuous energy difference value Δe for 20 frames including the initial maximum point 1008 and the terminal maximum point 1010. The initial edge of the data burst (frame 6) represents the start frame of the received data burst, and the negative edge (frame 15) represents the frame following the end of the data burst. From this information the length of the received burst can be deduced (9 frames) and the superframe format can be identified (9-1-9-1).

Successive differences in the energy values observed in each frame of the superframe during synchronization will show a positive or negative peak. Positive peaks indicate the leading edge of the burst and negative edges indicate the end of the burst. According to one embodiment of the present invention, the edge detection process adjusts the frame alignment so that the maximum difference increases, and the right adjacent energy difference is forced to zero. Once synchronization is obtained, the result is as shown in FIG. 10B. Note that the edge detection process is relatively unaffected by the absolute amplitude observed. This continuous differential approach requires only that the energy of the "quiet" frame (which is not actually inactive due to noise) should be less than the energy of the active frame and the energy should be approximately constant for each type of frame.

If the data transmission system operates to drop the cyclic prefix at the receiver, the dead-zone, which is the width of the cyclic prefix, is a frame / superframe because the cyclic prefix drops samples useful for frame synchronization. Generated in alignment, but not useful for FFT devices. One technique for solving this dead zone where the frame has 512 samples and the cyclic prefix has 40 samples uses an energy estimate of 41 to 552 samples in addition to using 1 to 512 samples, and is used in the burst detection process. The average of these energy estimates is used to calculate the estimated energy estimates.

The above-described synchronization process is generally applied to remote side and center side synchronization. For synchronization processing at the remote side, the receiver at the remote side synchronizes and maintains data transmission (burst) with the transmitter of the central unit. For synchronization processing in the central unit, the receiver at the central unit synchronizes with and maintains the data transmission (burst) with the transmitter of the remote unit. In one embodiment, synchronization is managed by setting or saving receiver frame alignment for recovery of data transmission (burst) at the receiver.

Due to the round-trip of the line (or channel), the time that upstream transmission from the remote device reaches the central device is variable and without constant correction it will appear to be as late as the length of the round-trip delay. Thus, the central unit needs to adjust its receiver frame alignment so that the correct received sample is used for the receiver at the central unit. The processing performed at the central unit to adjust its received frame alignment is similar to the synchronization process described above for the remote unit. In general, the energy in the received upstream frame is measured for the number of frames corresponding to the length of the upstream transmission burst from the remote device. This energy value is used to identify the start of an upstream transmission burst to determine the amount of alignment correction to align the frame of received data with the received frame boundary pointer.

11 is a block diagram of a receiver 1100 according to an embodiment of the present invention. Receiver 1100 is part of a time domain redundant transmission system. The structure of the receiver 1100 shown in FIG. 11 can be used in all or one of the central office receiver and the remote device transceiver.

Receiver 1100 receives an analog signal 1102 transmitted over a channel from a transmitter (ie, a central office transmitter). The received analog signal is fed to an analog-to-digital converter (DAC) which converts the received analog signal into a digital signal. The digital signal is then fed to an input buffer 1106 which temporarily stores the digital signal. The FFT apparatus 1108 reads the data frame from the input buffer 1106 according to the reception frame boundary pointer 1110 to generate a frequency domain signal.

In accordance with the present invention, FFT apparatus 1108 outputs frequency domain signals 1112 to frame synchronization apparatus 1114. The frame synchronization device 1114 operates to perform the synchronization process described above with respect to FIGS. 5-10B. The frame synchronizer 1114 outputs an alignment error estimate 1116 to the controller 1118. Controller 1118 then adjusts receive frame boundary pointer 1110 to access data received from input buffer 1106. On the other hand, the frame synchronization device 1114 provides frame synchronization to the time domain redundant transmission system in a manner that substantially guards against RF interference (eg, such as amateur wireless users). The controller 1118 also controls the overall operation of the receiver 1100. For example, controller 1118 controls receiver 1100 to execute initialization processing and monitor steady state data transmission. For example, the controller 1118 may be implemented by a digital signal processor, a microprocessor, or a microcontroller or special circuit. In the case where the receiver 1100 forms part of a transceiver, the controller 1118 may be used by the receiving side of both the transmission and the transceiver, split between multiple transceivers or provided separately for each transmitter and receiver. In addition, the frame synchronization device 1114 may be implemented by a digital signal processor, a microprocessor, or a microcontroller or special circuit.

The received data path frequency domain signals 1112 output by the FFT apparatus 1108 are then equalized by the FEQ apparatus 1120. The equalized signals are then provided to a data symbol decoder 1122. The data symbol decoder 1122 operates to decode the equalized signal into recover data sent on respective frequency tones of the received symbol. The data symbol decoder 1122 is executed based on the bit allocation information stored in the received bit and energy allocation table 1124. The decoded data is then provided to the FEC device 1126 and stored in the output buffer 1128. The recovered data 1130 (stored decrypted data) can then be retrieved from the output buffer 1128 as needed.

The receiver 1100 shown in FIG. 11 operatively includes other components. For example, when the corresponding transmitter adds a periodic prefix to the symbol following the IFET device, the receiver 1100 may remove the periodic prefix before the FFT device 1108. In addition, the receiver 1100 may provide a time domain equalizer (TEQ) between the ADC 1104 and the FFT device 1106. An additional listing on an airspace TEQ device is described in U.S. Patent No. 5,285,474, entitled "POLY-PATH TIME DOMAIN EQUALZATION," filed May 12, 1997, and U.S. Application Serial No. 60 / 046,244 (Att. Dkt. No.: AMATP021 +) Included in

Moreover, the present invention provides a technique for synchronizing transmissions at the central side (ie, central apparatus). With synchronized transmission at the central side, NEXT interference is substantially eliminated, and all the providing lines of the binder provide the same level of service (ie superframe format). However, if transmissions from the center side are not properly synchronized across the lines in the binder, NEXT interference is a substantial obstacle to the effective and correct operation of the data transmission system. Therefore, the present invention also relates to a technique for adjusting the transmission frame boundary at the central transmitter of the data transmission system. It is a general principle to use NEXT interference from other central transmitters. If NEXT interference is not strong enough to be detected for synchronization purposes, it will be assumed insufficient during the next reception, so synchronization is not necessary.

Conventionally, various transmitters at the center side can synchronize with each other by using all common main clocks supplied to the center side. However, sometimes this main clock is not useful for one reason or another. Also, although useful, the various transmitters can be placed slightly away from the main clock source to cause small synchronization differences between the various transmissions. Therefore, the synchronization technique according to the present invention can also be used to synchronize various transmissions at the central side.

12 is a flowchart of a synchronization process 1200 for synchronizing adjacent transmitters to compensate for small synchronization differences. If this small synchronization difference is incorrect, the degree of synchronization deterioration worsens over time. The synchronization process 1200 initially measures 1202 the energy received from the other transmitter at the center side. Here, during quiet periods (or guard periods), the energy received from the other transmitter at the center is measured by the receiver associated with the transmitter (ie the transceiver). Transmissions from various transmitters all follow the same superframe format. Preferably, a second rest period (i.e. after upstream transmission) is used to measure energy since less echo tends to appear. Next, decision block 1204 measures whether the measured energy is above a predetermined threshold. If the measured energy during the resting period is determined to be above a predetermined threshold, the presence of the next NEXT interference is detected. Since NEXT interference is detected, it is found that the transmitter at the center side is not synchronized. Therefore, the timing alignment at the transmitter is modified 1202 to synchronize the alignment with respect to the other transmitter at the center side. For example, timing alignment can be modified by changing the oscillator frequency or by changing (increasing or decreasing) the length of the superframe. On the other hand, when the measured energy is determined to be below a predetermined threshold, the transmitter at the next center side is considered to be sufficiently aligned and block 1206 is bypassed. Following block 1206 or after block 1204 when the predetermined threshold has not been exceeded, the synchronization process 1200 is completed and ends.

The synchronization process 1200 is performed by all transceivers at the center side. By repeating the synchronization process 1200, in particular, if the alignment is adjusted in only one direction, the alignment will gradually reach some steady state.

As shown in FIG. 4, it should be recalled that the superframe format has two pauses 404 and 408. The synchronization process 1200 uses one of two pauses 404 and 408. When the receiver at the center side hears NEXT interference during dormant 408, this means that the transceiver is delayed and must be transmitted in advance. Alternatively, if the receiver at the center side uses rest 404 and hears NEXT interference during rest 404, this means that the transceiver is early and must be transmitted later. However, before the transceiver adjusts the timing alignment at the center side, the transceiver can inform the corresponding remote device of the change to modify the timing alignment as well. For example, such notification to the remote device can be performed over the overhead channel.

The synchronization technique needs to distinguish between upstream and downstream NEXT interference. This can be accomplished in a number of different ways. For VDSL using DMT frames with 256 tones, one way to distinguish downstream and upstream transmissions is to use Nyquist / 2, tone 128 with only downstream transmissions. As mentioned above, the pause is used to measure interference from downstream transmissions that are adjacent to each other. If a downstream distinguishing feature is detected (by more than a threshold), this means that the clock in this device runs faster than the clock of the interfering transmitter.

The coordination of synchronization may be to modify the clock frequency of a particular transceiver clock, such as a voltage controlled oscillator. Alternatively, extra cycles can be inserted into the superframe structure. In VDSL, if the clocks of the center side transceivers are within 100 ppm of each other, insertion of 1 sample per superframe (11,040 samples) will be sufficient to monitor synchronization. If only the center side transceiver can insert, the center side transceiver will match at the lowest clock frequency of the group (which has a valid NEXT).

For example, the energy of tone 128 can be measured with a special single-tone DFT.

If the measured energy is greater than the predetermined threshold, a sample (extra cycle) is inserted into the next transmission.

There are many advantages of the present invention. One advantage of the present invention is that synchronization can be obtained even in radio frequency (RF) interference resulting from amateur radio signals. Another advantage of the present invention is that it is suitable for data transmission systems using time division duplex communication schemes such as synchronized DMT or synchronized VDSL. Another advantage of the present invention is that it is relatively less affected by background or received noise.

Therefore, the invention includes a method of adjusting the alignment of a first transceiver for receiving a frame of data transmitted from a second transceiver to a first transceiver via a transmission medium, wherein the first transceiver and the second transceiver are time-divisionally divided. A data transmission system providing bidirectional data communication using a dual communication scheme, the method comprising: (a) measuring an amount of energy for each of a plurality of consecutive frames of received data; Calculating an alignment error estimate based on the amount of energy.

Also included is a method as described above, wherein the alignment error estimate is an estimated alignment error such as a piece of frame.

Also included is that the data transmission system transmits data using a superframe with a plurality of frames, a first set of frames in the superframe transmit data in a first direction, and The second set is the method as described above for transmitting data in the second direction.

Also included is a frame boundary pointer for identifying the beginning of a frame within the superframe in which the first transceiver is to be received, the method comprising (c) adjusting the frame boundary pointer according to the alignment error estimate. The method as described above further comprising the step.

Also included is the method as described above, wherein the alignment error estimate is an estimated alignment error such as a piece of frame.

Also included are (d) comparing the alignment error estimate with a threshold, (e) until the comparison (d) indicates that the error estimate is less than the threshold; The method as described above including the step of repeating (d).

Also included is the method as described above, wherein the method further comprises (f) outputting superframe identification information.

Also included are calculations (b) for detecting an edge in a plurality of consecutive frames of received data based on the measured amount of energy and calculating alignment error using the detected edges in the plurality of consecutive frames. Method as described above, including determining the value.

Also included is the method as described above, wherein the detected edge is a burst edge.

Also included are the steps of: calculating a continuous energy difference in the plurality of measured energy amounts, and identifying a maximum energy difference among the consecutive energy differences, wherein the maximum of the continuous energy The energy difference is the method as described above corresponding to the burst edge.

Also included is that the calculating step (b) is one energy of the successive energy difference with the subsequent energy difference, wherein the previous energy difference is immediately preceding the maximum energy difference of the successive energy differences. Identifying a difference, wherein the subsequent energy difference is one of the consecutive energy differences immediately following a maximum energy difference of the consecutive energy differences, based on the previous energy difference and the subsequent energy difference. To determine the alignment error estimate.

Also included is a method as described above, wherein the determining of the alignment error estimate value calculates the difference between the subsequent energy difference and the previous energy difference.

Also included is the method as described above, wherein determining the alignment error estimate value calculates a difference between the subsequent energy difference and the previous energy difference, and then nominally equals the difference to produce an alignment error estimate. to be.

Also included, the first transceiver identifies a frame start of a received superframe using a frame boundary pointer, and the method includes (c) adjusting the frame boundary pointer according to the alignment error estimate. It further comprises a method as described above.

Also included is the method as described above, wherein the alignment error estimate is an estimated alignment error as a piece of the frame.

Also included are the steps of: (d) comparing the alignment error estimate with a threshold; (e) repeating steps (a) to (d) until the comparing step (d) indicates that the alignment error estimate is less than the threshold.

Also included is a method as described above, wherein the method further comprises (f) outputting superframe identification information.

Also included is a method as described above, wherein the first transceiver is a remote device and the second transceiver is a central device.

Also included is the method described above, wherein the second transceiver is a remote device and the second transceiver is a central device.

Also included is the method described above, wherein the amount of energy is the amount of power.

In addition, the data transmission system transmits data using a superframe structure having a plurality of frames, some frames transmit data in the first direction, some frames transmit data in the second direction, and some frames superframe structure Contains a cyclic prefix for

Measuring the amount of energy (a) comprises: measuring the amount of energy of successive frames of the first set of received data for the superframe structure; Measuring an amount of energy of successive frames of the second set of received data for the superframe structure, the second set of successive frames being offset from and overlapping from the first set of successive frames; And combining the amounts of energy from each successive frame from the first and second sets of successive frames to generate an amount of energy for calculation step (b).

Also included is the method described above, such that the number of frames of the first and second sets of consecutive frames is equal to the length of the length of the superframe structure minus the length of the cyclic prefix.

The combining step also includes the above-described method of determining average amounts of energy for each of the frames of the superframe structure including the cyclic prefix.

Also included is a computer readable medium comprising program instructions for adjusting an alignment for the first transceiver to receive frames of data transmitted from the second transceiver to the first transceiver via the transmission medium. A two transceiver is related to a data transmission system providing two-way data communication using time division duplexing, the computer readable medium comprising: a first for measuring an amount of energy for each of a plurality of consecutive frames of received data; Computer readable code devices; Second computer readable code devices for calculating an alignment error estimate based on the measured amounts of energy.

Also included is a computer readable medium as described above, wherein the second computer readable medium includes computer readable code devices for detecting edges of a plurality of consecutive received data frames based on the measured amount of energy; Computer readable code devices for determining an alignment error estimate using an edge detected in the plurality of consecutive frames.

Also included is a computer readable medium as described above, wherein the second computer readable medium includes computer readable code devices for computing a continuous energy difference of the plurality of measured amounts of energy; Computer readable code devices for identifying the largest difference of the consecutive energy differences, wherein the largest difference of the consecutive energy differences corresponds to a burst edge.

Also included is a computer readable medium as described above, wherein the second computer readable medium includes computer readable code devices for identifying a previous energy difference and a subsequent energy difference, wherein the previous energy difference is the consecutive energy differences. One of successive differences immediately before the largest difference, wherein the subsequent energy difference is one of successive differences immediately after the largest difference of the consecutive energy differences; Computer readable code devices for determining an alignment error estimate based on the previous energy difference and the subsequent energy difference.

Also included is a computer readable medium as described above, wherein the data transmission system transmits data using a superframe structure having a plurality of frames, some of the frames transmitting data in a first direction, and frames Some of which transmit data in a second direction, some of which comprise a cyclic prefix for the superframe structure, wherein the first computer readable code devices for measuring the energy amount Computer readable code for measuring an energy amount of frames of received data for a set of consecutive superframe structures; Computer readable code for measuring an energy amount of frames of received data for a second set of consecutive superframe structures, wherein the second set of consecutive frames is offset and overlapped from the first set of consecutive frames; And computer readable code for combining with the energy amount of each successive frame from the first and second sets of successive frames to produce an energy amount for the second computer readable code devices.

Also included is a computer readable medium as described above, wherein the combining determines an average amount of energy for each of the frames of the superframe including a periodic prefix.

Also included is a computer readable medium as described above, wherein the number of frames in the first and second sets of consecutive frames is equal to the length of the superframe structure less than the length of the periodic prefix.

Also included is a receiver for a data transmission system that uses time division duplexing to alternately transmit and receive data. The receiver includes an analog-to-digital converter that receives analog data that has been transmitted to the receiver over a channel and converts the received analog signal into a received digital signal, an input buffer that temporarily stores the received digital signal, and an input buffer received from the input buffer. A multicarrier demodulation device that demodulates a digital signal into frequency domain data for a plurality of different carrier frequencies, and a multicarrier demodulation device based on time-dependent variability of energy of frequency domain data generated by the multicarrier demodulation device. A frame synchronization device for synchronizing a received frame boundary, an allocation table for storing bit allocation information used for transmission data received at a receiver, and from the carrier frequencies based on the bit allocation information receiving frequency domain data and stored in the bit allocation table. cycle And a data symbol decoder for decoding bits associated with the domain data, an output buffer for storing the decoded bits as the restored data.

Also included is a receiver, where the frame synchronization device determines the amount of alignment adjustment, and the receiver further comprises a controller for controlling the overall operation of the receiver, the controller receiving the alignment adjustment amount from the frame synchronization device and accordingly Adjust the receive frame boundary pointer for the input buffer.

Also included is a receiver as described above, wherein at least one frame synchronizer and controller is implemented by a processor.

In addition, the above-described receiver, in which the frame synchronizing device is a processor, is included.

Also included is a receiver as described above, wherein the received data signal includes unexpected radio frequency interference and the frame synchronizer ignores the portion of frequency domain data that overlaps with the frequency ranges of radio frequency interference.

In addition, the above-described receiver, in which the data transmission system is a synchronized DMT system, and the multi-carrier demodulation device includes an FFT device, is included.

Also included is a receiver for a data transmission system using time division duplexing that alternates between transmission and reception of data, where the receiver: receives analog data transmitted to the receiver over a channel and receives the received analog signal. An A / D converter converting the digital signal into a digital signal; An input buffer for temporarily storing the received digital signal; A multicarrier demodulation device for demodulating received digital signals from an input buffer into frequency domain data for a plurality of different carrier frequencies; Frame synchronization means for synchronizing a frame boundary with respect to the multicarrier demodulation device based on a characteristic in which the energy of frequency domain data generated by the multicarrier demodulation device changes in time; A bit allocation table storing bit allocation information used to transmit data received at the receiver; A data symbol decoder that receives frequency domain data and decodes bits in association with frequency domain data from carrier frequencies based on bit allocation information stored in a bit allocation table; And output data for storing the decoded bits as recovered data.

In a data transmission system having a plurality of transmitters in the center, the transmitters transmit data according to a super frame format including at least one idle period, and a method for synchronizing data transmitted by a given transmitter to another transmitter in the center is provided. More included. The method comprises the steps of: (a) measuring energy associated with a given transmitter due to data transmission from another transmitter in the center during the idle period; (b) comparing the measured energy with a threshold; And (c) comparing (b) modifying the synchronization for the transmission by a given transmitter when the measured energy exceeds the threshold.

The method cited above further comprises that the data transmission system transmits data using time division duplexing, and the transmitter is part of a central transceiver.

The method cited above further comprises the data transmission system being a multi-carrier data transmission system.

The cited method further includes the step (c) of modifying includes adjusting timing alignment to reduce crosstalk interference.

The method cited above further includes the adjustment increasing or decreasing the length of the super frame format.

The method cited above further comprises that the adjustment changes the frequency of the local clock for a given transmitter.

The method cited above is that the data transmission system is a multi-carrier data transmission system, the external clock signal is not useful for synchronizing the transmitter, and the modifying (C) operation further includes adjusting timing alignment to reduce crosstalk interference. do.

The method cited above serves to distinguish between incoming and outgoing data transmissions from other transmitters, in which the operation (a) of measuring the energy associated with a given transmitter due to data transmissions from other transmitters in the center at rest periods (a). (A) The operation of measuring results further includes measuring the energy at rest during the outgoing data transmission and not due to incoming data reception from the transmitter.

And further comprising a computer readable medium containing program instructions for synchronizing data transmissions in a data transmission system having a plurality of transmitters in the center. The external clock signal is not useful here for synchronizing the transmitter, and the transmitter transmits data according to a super frame format including at least one idle period. The computer readable medium includes a first computer readable code device for measuring energy associated with a given transmitter due to transmission of data from another transmitter at a central portion in a rest period; A second computer readable code device for comparing the measured energy with a threshold; And when the comparison indicates that the measured energy exceeds the threshold amount, a third computer readable code device for modifying synchronization for transmission by a given transmitter.

The above-described computer readable medium is also included. Here, the data transmission system is a multi-carrier data transmission system for transmitting data using time division multiplexing, wherein the transmitters are part of transceivers. Here, the third computer readable code device operates to adjust the timing alignment to reduce crosstalk interference.

Many features and advantages of the invention are apparent from the detailed description. Accordingly, the appended claims are intended to cover all such features and advantages of the present invention. Furthermore, because various modifications and changes are possible to those skilled in the art, the present invention is not limited to the structures and operations shown and described. Accordingly, all suitable modifications and equivalents should be considered to be included within the scope of the present invention.

Claims (10)

12. A method of adjusting alignment of a first transceiver to receive a data frame transmitted from a second transceiver to a first transceiver via a transmission medium, wherein the first transceiver and the second transceiver are bidirectional using time division duplexing. Is associated with a data transmission system that provides data communication, (a) measuring an amount of energy for each of the plurality of consecutive received data frames; And (b) calculating an alignment error estimate based on the measured amount of energy How to adjust the alignment of the first transceiver comprising a. 2. The method of claim 1 wherein the alignment error estimate is an estimated alignment error as a frame fragment. The data transmission system of claim 1, wherein the data transmission system transmits data using a superframe structure having a plurality of frames, wherein the first set of frames in the superframe transmits data in a first direction, and the first in the superframe. And a set of two frames to adjust the alignment of the first transceiver to transmit data in the second direction. 4. The apparatus of claim 3, wherein the first transceiver uses a frame boundary pointer to identify the start of a frame in a receiving superframe, (c) adjusting the frame boundary pointer according to the alignment error estimate The method of adjusting the alignment of the first transceiver further comprising. 5. The method of claim 4, wherein the alignment error estimate is a calculated alignment error as a frame fragment. The method of claim 4, wherein (d) comparing the alignment error estimate with a threshold; And (e) repeating steps (a)-(d) until the comparison step (d) indicates that the alignment error estimate is less than the threshold The method of adjusting the alignment of the first transceiver further comprising. 16. A computer readable medium comprising program instructions for adjusting the alignment of the first transceiver to receive a data frame transmitted from a second transceiver to a first transceiver via a transmission medium, the computer comprising: the first transceiver and the second transceiver; The transceiver is associated with a data transmission system that provides bidirectional data communication using time division duplexing. A first computer readable code device for measuring an amount of energy for each of a plurality of consecutive received data frames; And A second computer readable code device for calculating an alignment error estimate based on the measured amount of energy Computer-readable medium comprising a. A receiver for a data transmission system using time division duplexing that alternates between sending and receiving data, An analog-to-digital converter transmitted over a channel to the receiver and converting the received analog signal into a received digital signal; An input buffer for temporarily storing the received digital signal; A multicarrier demodulation device for demodulating the received digital signal from the input buffer into frequency domain data for a plurality of carrier frequencies; A frame synchronization device for synchronizing a reception frame boundary of the multicarrier demodulation device based on a characteristic in which the energy of the frequency domain data generated by the multicarrier demodulation device changes in time; A bit allocation table for storing bit allocation information used for transmission of data being received at the receiver; A data symbol decoder that receives the frequency domain data and decodes a bit associated with the frequency domain data from the carrier frequency based on the bit allocation information stored in the bit allocation table; And An output buffer for storing the decoded bits as return data Receiver for a data transmission system comprising a. In a data transmission system having a plurality of transmitters in a central area for transmitting data according to a superframe format including at least one idle period, synchronizing data transmission by any transmitter in the central area to another of the transmitters. In the method, (a) measuring energy in said idle period associated with said any transmitter in said central region by transmission of data from another of said transmitters; (b) comparing the measured energy with a threshold; (c) modifying the synchronization of the transmission by the any transmitter if the comparison step (b) indicates that the measured energy exceeds the threshold Synchronization method comprising a. Synchronizing data transmissions when an external clock signal is not available for synchronizing the transmitters in a data transmission system having a plurality of transmitters in the central area transmitting data according to a superframe format including at least one idle period A computer readable medium comprising program instructions for A first computer readable code device for measuring energy in the dormant period associated with any transmitter in the central region by transfer of data from another transmitter in the transmitter; A second computer readable code device for comparing the measured energy with a threshold; And A third computer readable code device for modifying the synchronization of the transmission by the any transmitter if the comparison indicates that the measured energy exceeds the threshold Computer-readable medium comprising a.