KR100591644B1 - Method and system for synchronizing time-division-duplexed transceivers - Google Patents

Abstract

An improved technique for synchronizing 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 frames in which the alignment error estimate is continuous. 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 discloses US application Ser. No. 08 / 707,322 entitled "Method and Apparatus for Crosstalk Erase" and US Application Ser. No. 08 / 501,250 entitled "Time Division Duplexed High Speed Data Transfer System and Method." And these two references are incorporated herein by reference.

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

Two-way digital data communication systems have recently been developed for high speed data communication. One standard for high speed data communication over developed twisted pairs is known as asymmetric digital subscriber line (VDSL). Another standard for high speed data communication over the currently proposed twisted pair is known as a high speed digital subscriber line (VDSL).

The Alliance For Telecommunications Information Solutions (ATIS), a group recognized by the American National Standard Institute (ANSI) Standards Group, finally decides on a discrete multi-tone based approach for the transmission of digital data over twisted pair lines. Built. This standard, known as ADSL, was originally designed for video data transmission and high-speed Internet access over conventional telephone lines, but it could also be used in many different applications. The North American standard was named the ANSI T1.413 ADSL standard (hereafter referred to as the ADSL standard), which is incorporated herein by reference. The transmission rate under the ADSL standard is designed to transmit information at 8 Mbit / s over twisted pair. This standardized system defines the use of a discrete multi-tone (DMT) system using 256 "tones" or "sub-channels" each having a width of 4.3125 kHz 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 location, which may be a terminal user (ie a resident or business user). The number of tones used in other systems can vary widely.

The ADSL standard also defines the use of reverse transmission at data rates in the range of 16 to 800 Kbit / s. Reverse transmission follows an upstream direction, for example, from a remote location to a central station. As such, the term ADSL stems from the fact that the data transfer 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 both the downstream and upstream signals are transmitted over the same twisted pair (ie, duplexed), they must be separated from each other in some way. The duplexing method used in the ADSL standard is frequency division duplexing (FDD) or echo cancellation method. In a frequency division duplexing 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 is establishing another standard for subscriber line-based transmission systems called the VDSL standard. This VDSL standard is intended to enable transmission rates of at least about 6 Mbit / s and up to about 52 Mbit / s in the downstream direction. At the same time, the Digital, Audio and Video Council (DAVIC) is working on a similar system called Fiber To The Curb (FTTC). The transmission medium from this "Curb" to the consumer is a standard unshielded twisted-pair (UTP).

A number of modulation methods have been proposed for use in the VDSL and FTTC standards (hereinafter referred to as VDSL / FTTC). For example, some possible VDSL / FTTC modulation methods include single carrier transmission methods such as quadrature amplitude modulation (QAM), carrierless amplitude and phase modulation (CAP), quadrature phase shift keying (QPSK), or residual sideband modulation. In addition, multi-carrier transmission methods such as discrete multi-tone modulation (DMT) or discrete wavelet multi-tone modulation (DWMT) are mentioned.

In addition, multicarrier modulated transmission methods require a great deal of attention due to the high data rates they provide. 1A is a schematic block diagram of a conventional transmitter 100 for a multicarrier modulation system. The conventional transmitter 100 is suitable for DMT modulation, for example in an ADSL or VDSL system. The transmitter 100 receives a data signal to be transmitted in the buffer 102. These data signals are then fed 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 fed to a data symbol encoder 106. Data symbol encoder 106 is operative to encode signals for a plurality of frequency tones associated with multicarrier modulation. When assigning data or bits of data to each of the frequency tones, the data symbol encoder 106 uses the data stored in the transmit bit allocation table 108 and the transmit energy allocation table 110. The transmit bit allocation table 108 includes an integer value for each of the carriers (frequency tones) of multicarrier modulation. This integer value indicates the number of bits to be assigned to a particular frequency tone. The value stored in the transmit energy allocation table 110 is used to effectively provide a fraction of bits of resolution through different allocations of energy levels to frequency tones of multicarrier modulation. In any case, after the data symbol encoder 106 encodes the data into respective frequency tones, the inverse fast Fourier transform (IFFT) unit 112 modulates the frequency domain data supplied by the data symbol encoder 106. And generate time domain signals to be transmitted. 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 multicarrier 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 these digital signals while converting them 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 the digital signals so that the attenuation and phase are equalized for the various frequency tones. The data symbol decoder 158 then receives the equalized digital signal. Data symbol decoder 158 operates to decode equalized digital signals to recover the data or data bits transmitted on each carrier (frequency tone). In decoding the equalized digital signals, the data symbol decoder 158 needs to access the bit allocation information and the energy allocation information that were used to transmit the data. Accordingly, the data symbol decoder 158 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 that were used to transmit the data. The data obtained from each of the frequency tones is then sent to a forward error correction (FEC) unit 164. FEC unit 164 performs error correction of the data to provide corrected data. The corrected data is then stored in buffer 166. The data may then be retrieved from buffer 166 and further processed by receiver 150. Alternatively, the received energy allocation table 160 may be supplied to the FEQ unit 166 and utilized.

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

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

Most of the proposed VDSL / FTTC transmission methods use a frequency division duplexing scheme (FDD) of upstream and downstream signals. On the other hand, one particular of the proposed VDSL / FTTC transmission methods uses a time division duplexing scheme (TDD) of upstream and downstream signals. More specifically, the time division duplexing scheme is synchronized in this case so that the periodically synchronized 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 synchronized. With this arrangement, all ultrafast transmissions in the same binder are synchronized and time division duplexed so that downstream communications are not transmitted at times overlapping with upstream communications transmissions. This is also referred to as (ie, "ping pong") based data transmission method. During the downtime, during which no data is being transmitted, upstream and downstream communication cycles are separated. When a synchronized time division duplexing method is used for the DMT, it is often referred to as a synchronized DMT (SDMT).

A common feature of the above mentioned transmission method is that twisted pairs are used as at least part of the transmission medium connecting the central station (e.g. telephone company) to the consumer (e.g. resident or business user). Although fiber optics can be used from the central station to the curve near the user's residence, twisted pairs are used to transmit signals from the curve to the user's home or office.

Stranded wire is grouped into binders. While the stranded wire is in the binder, the binder serves to provide considerable protection from external electromagnetic interference. However, in the binder, stranded wires 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 real. As a result, data signals transmitted over twisted pairs at high speed are significantly degraded by crosstalk interference caused by other twisted pairs in the binder. As the data transfer rate increases, this problem gets worse. The advantage of synchronized TDD (e.g., SDMT) based data transmission is that if all circuits are transmitting during the same period (i.e., in the same super frame format), crosstalk interference from other circuits in the binder is avoided. Is substantially eliminated.

Data transmission systems typically include a central station and a plurality of remote units. Each remote unit communicates with the central station via a data link (ie, a channel) installed between the central station and a particular remote unit. To establish such a data link, initial processing is done to initiate communication between the central station and each remote unit. For the following description, it is assumed that the central station 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 station and the remote unit. The central station 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.

US Patent No. 5,627,863, which is one of the prior art frame synchronization techniques that is required for the transmission of a predetermined sequence of data received by a receiver and is correlated with the selected and stored data sequence to determine the necessary adjustments for synchronization. Described below is a frame synchronization method suitable for systems using frequency division duplexing (FDD) or echo cancellation to provide duplexed operation (e.g., ADSL). This frame synchronization technique requires one special start-up training sequence to achieve frame synchronization. However, the above described frame synchronization method is a system that uses time division duplexing (e.g., synchronized TDD or not) because synchronization in time is not required for FDD or echo cancellation as in TDD to eliminate crosstalk. SDMT) is not suitable.

When the data transmission system operates in time division duplex (TDD), the transmitters and receivers of the central station and the remote unit 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 a central side transmitter to one or more remote side receivers, and upstream transmission is transmission from one or more remote side transmitters to a central side receiver. The center side transmitter and receiver can be combined as the center side transceiver and the remote side transmitter and receiver can be combined as the remote side transceiver.

Generally speaking, in a time division duplexing system, upstream signals alternate with downstream signals. Typically, upstream transmissions and downstream transmissions are separated into guard intervals or dormant periods. The guard interval is provided to enable the transmission system to redirect the data being transmitted so that the transmission can be received before the transmission in the opposite direction occurs. Certain transmission methods separate upstream and downstream transmissions into smaller units called frames. These frames can also be grouped into superframes that include a series of downstream frames and a series of upstream frames and a guard interval therebetween.

Time division duplexing is a simple way to share a channel (media) between two or more transceivers. Each transceiver is allocated one time slot during transmission, and there is an idle period (guard interval) while no unit needs to transmit. When time division duplexing is used on a channel that is susceptible to crosstalk (NEXT interference) between a plurality of contacts, synchronization must be made and maintained between all affected units. One example is a VDSL service that uses an existing twisted pair for transmission in the 13-52 Mb / s range on a loop within the 1.5 km range. Twisted pairs for 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 twisted pairs in the binder. To achieve the desired data rate on a 1.5 km long loop, DMT is a suitable multicarrier modulation method. This method makes it possible to use time division duplexing 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 unreliable in the presence of RF interference. Due to the potential for 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 a synchronized TDD system, it is important that synchronization is established and maintained so that crosstalk is reduced and adjusted and the received data is correctly restored.

Thus, there is a need for improved synchronization techniques in time division duplexing systems.

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 the 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 the multicarrier modulation unit (eg FFT unit). According to another feature of the invention, the improved synchronization technique uses crosstalk interference levels for synchronization. With this improved synchronization technique, the remote receivers in the data transmission system can be synchronized to the central transmitter, the central receivers can be synchronized to the remote transmitter, and the central transmitters 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.

The first transceiver receives a frame of data transmitted from a second transceiver via a transmission medium, wherein the first transceiver is associated with a data transmission system capable of bidirectional data transmission using time division duplexing. As a method of adjusting an alignment, 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, the receiving based on the measured amount of energy. Detection of the edges of multiple consecutive frames of data, and calculation of alignment error estimates using the edges detected in multiple 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 a first set of frames of the super frame transmission data is transmitted in a first direction and a second set of frames is in a second direction. send.

Receiving a data frame transmitted by a first transceiver from a second transceiver via a transmission medium, wherein the first transceiver is associated with a data transmission system capable of bidirectional data transmission using time division duplexing A readable computer medium comprising program instructions for alignment adjustment for a first computer readable code device for measuring the amount of energy of each of a plurality of consecutive frames of received data; 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 error estimation using the edges detected in the plurality of consecutive frames And a third computer readable code device for the calculation of.

A receiver of a data transmission system using time division duplexing for replacing transmission and reception of data, wherein an embodiment of the present invention receives an analog data transmitted to a receiver through a channel and converts it into a digital signal. 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 received frame boundary based on a time-varying property of energy of frequency domain data, a bit allocation table for storing bit allocation information used for transmission of data received at the receiver, receiving the frequency domain data, Bit allocation table Stored based on the bit allocation information to an output buffer for storing a data symbol decoder, and restoring the decoded data bits for decoding bits associated with the frequency domain data from the carrier frequency. 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 time division duplexing for replacing transmission and reception of data, another embodiment of the present invention provides an A / D converter for receiving and converting analog data transmitted to a receiver through a channel into a digital signal; 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 a frequency generated in the multicarrier demodulation unit Frame synchronization means for synchronizing a received frame boundary based on a time-varying property of energy of region data, a bit allocation table for storing bit allocation information used for transmission of data received at the receiver, and receiving the frequency domain data and receiving the bits. Me to the allocation table Based on the bit allocation information includes 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.

A central site for a plurality of transmitters transmitting data according to a super frame format including at least one quiet period, wherein the external site does not use an external clock signal to synchronize the plurality of transmitters In an equipped data transmission system, a method of synchronizing data transmission by a given one transmitter to another transmitter in accordance with an embodiment of the present invention is an operation of measuring energy due to data transmission of another transmitter in an idle period associated with the given transmitter. Comparing the measured energy with a threshold, and changing the synchronization of transmission by the given transmitter when the measured energy in the comparing operation exceeds a threshold.

A central site for a plurality of transmitters transmitting data according to a super frame format including at least one quiet period, wherein the external site does not use an external clock signal to synchronize the plurality of transmitters A computer readable medium comprising program instructions for synchronizing data transmissions in an equipped data transmission system, wherein an embodiment of the present invention provides for energy recovery due to data transmissions of other transmitters during idle periods associated with the given transmitter. A first computer readable code for measurement, a second computer readable code for comparison of the measured energy with a threshold, and a transmission by the given transmitter if the energy measured in the comparing operation exceeds a threshold. Third computer readable code for altering synchronization.

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 duplexing such as synchronized DMT or synchronized VDSL. Another advantage of the present invention is that it is relatively strong against noise in data transmission systems.

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.

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

The synchronization required in a time division duplexing system requires the transmission to be synchronized to the super frame structure. Conventional time domain methods, which tend to correlate samples, such as the first and last samples of a frame, for example to detect a cyclic prefix, indicate that RF interference of a received signal with the same power as the desired signal appears. Easy and not reliable However, the present invention provides an accurate technique for synchronizing transmissions in a time division duplexing system even if the time domain signal becomes unreliable by RF interference. The frequency domain scheme for synchronization provided by the present invention is quite robust against RF interference. In one embodiment, the improved synchronization technique utilizes the output signal of the multicarrier modulation unit (FFT unit), thereby avoiding frequency tones that are sensitive to RF interference.

Embodiments of the present invention are described with reference to FIGS. 1 to 12. 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 station 202. The central station 202 services 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 device 204. The processing and distribution device 204 is coupled to the central station 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 device 204 is typically called an optical network unit (ONU). Normally, central station 202 interacts with other processing and distribution devices (not shown) through high speed, multiplexed transmission lines 208 and 210, but only the operation of processing and distribution device 204 will be described below. This is explained. In one embodiment, the processing and dispensing device 204 includes one or more modems (central modems).

The processing and distribution device 204 services a plurality of individual subscriber lines 212-1 through 212-n. Each subscriber line 212 typically services 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 bound within the shielding binder 222 leaving the processing and dispensing apparatus 204. The 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. For most applications, the drop length does not exceed about 30 meters.

Crosstalk interference, including near-end crosstalk (NEXT) and far-end crosstalk (FEXT), occurs mainly in shielding binder 222 in which subscriber line 212 is densely packed and bound. 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 super frame structure in which data bits to be transmitted are allocated. For example, telecommunications 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, data transmission through all lines 212 in the shielding binder 222 associated with the processing and dispensing apparatus 204 need to be synchronized. As such, all active lines emerging from the processing and distribution device 204 can be transmitted in the same direction (ie, downstream or upstream) 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 data processing and distribution device 300 is a detailed implementation of the processing and distribution device 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, along with the processing device 302, sends output data from the processing device 302 to the appropriate analog card 310, and sends input from the analog card 310 to the processing device 302. The analog card 310 typically provides an analog circuit for use by the processing and distribution device 300 that performs effectively using analog components rather than using digital processing by the processing device 302. 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 into 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, these lines are stranded. 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 could instead be a single cart or circuit that supports 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. Then, processing for each line can be performed independently for each line. In this case, the modem can be placed on a single card along the analog circuit.

The NEXT interference problem occurs in lines adjacent to the output of the processing and distribution device 300. According to the block diagram shown in FIG. 3, NEXT interference is more prevalent near the output of the analog card 310, which is where the lines are adjacent to each other and the maximum power difference (between the transmitted and received signals). This is because it has a location. In other words, the lines are directed from the processing and distribution device 300 to the remote device. Typically, most of the distance is in a shielded binder that accommodates 50 twisted pairs, for example, and the remaining distance is beyond a single unshielded twisted pair. All these lines (e.g. stranded wire) are received close to the binder and crosstalk interference between the lines in the binder (i.e., NEXT) because it provides little individually shielding against electromagnetic coupling from other lines in the binder. Interference and FEXT interference).

Depending on the level of service provided, data transmissions implemented with SDMT may be symmetrical or asymmetrical for upstream and downstream transmissions. In the case of symmetric transmission, the DMT symbols are transmitted in alternately occurring directions during the same period. That is, the period during which the DMT symbol is transmitted downstream is the same as the period during which the DMT symbol is transmitted upstream. For asymmetric transmissions, DMT symbols tend to be sent downstream for longer periods than upstream.

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

4 illustrates an example super frame format 400 in which a level of service is provided. The super frame format 400 is an asymmetric frame that includes a downstream portion 402, a pause portion 404, an upstream portion 406, and a pause portion 408. The rest (pause) 404 and 408 are disposed between the downstream and upstream transmissions. In this asymmetric super frame format 400, the downstream portion 402 is substantially larger than the upstream portion 406. That is, longer bursts. This super frame format is useful in situations where the downstream traffic is considerably more than the upstream traffic. For example, referring to FIG. 2, super frame format 400 may include 16 symbols downstream; 1 resting period; Two symbols upstream; And one resting period.

By proper synchronization in the central unit (processing and distribution unit 204 or processing unit 302) and a uniform super frame, synchronized transmissions of the same duration are provided to all lines 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 synchronized 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. An 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. An edge is then detected 554 in the received data based on the measured energy values for n consecutive frames. 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 for transmission from the central device in accordance with 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 duplexing manner. The synchronization process 500 or 550 is also suitable for determining and adjusting the synchronization of the receiver of the central unit with the transmission from the remote unit.

6A and 6B are flowcharts of a synchronization process 600 according to a more detailed embodiment of the present invention. Once synchronization processing 600 is initiated, an FFT output is obtained for n consecutive contiguous frames of received data (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. Thus, the FFT output can be obtained from the output of the FFT device. The FFT output is a frequency domain signal.

Next, the FFT output susceptible to RF interference is removed (604). The remaining FFT output is then used for subsequent 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. For remote devices in a synchronized multicarrier VDSL system, where the frame has 256 frequency tones, the frequency tones 6 to 40 are generally free from RF interference by amateur radio users, and lower frequency tones are less attenuated. This results in less attenuation, which results in more reliable synchronization results. Thus, in one embodiment, frequency tones 6-40 from each of the n consecutive frames are used for subsequent processing.

Then, the energy value for the n consecutive frames of the remaining FET outputs is determined (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 and added together to produce a single energy value for the frame. Preferably, the energy value is a power value for a frame. By way of example, a single energy value for a frame can be obtained by summing the squared moduli of all outputs of the FET device in use. Alternatively, the energy value can be obtained by summing up the energy of the time domain samples after filtering out these time domain samples that are affected by a significant amount of RF interference.

Once the energy values for the n consecutive frames are determined (606), the synchronization process 600 detects (608) the burst edge in the received data based on the determined energy values. By detecting the burst edge, the receiver can be identified when the burst of data 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. It is also possible to detect the trailing edge of the received data and / or the characteristics (super frame information) of the super frame.

The alignment error estimate for frame boundary setting is then determined according to the detected burst edge (610). Here, using the detected burst edge (608), the alignment error estimate may be determined for frame boundary setting (610). In particular, from the determined energy value within the burst edge, the remote device synchronization process 600 can determine the alignment error (ie, frame synchronization error) for the frame. Normally, the alignment error is calculated as a fraction of the frame. Thereafter, the frame boundary may be adjusted 612 according to the alignment error estimate.

Once adjusted (612), frame synchronization must be set up. However, preferably, the synchronization process 600 continues to ensure that synchronization is achieved. Specifically, following block 612, it is determined at decision block 614 whether the absolute value of the alignment error estimate is lower than a predetermined threshold. If the alignment error estimate is not lower than the predetermined threshold, the synchronization process 600 returns to repeat with block 612 and subsequent blocks to iteratively reduce the size of the error. On the other hand, if it is determined in decision block 614 that the alignment error estimate is less than the predetermined threshold, information of the super frame is output (616). For example, the super frame information may indicate the start and end of the received transmission and / or the number of frames of the burst. 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 the predetermined threshold. Therefore, the synchronization process 600 must be repeated to generate a small amount of alignment error less than the 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 accurately generated with a high level of reliability.

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. Edge detection process 700 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 then 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 estimate processing 800 according to the present embodiment. Alignment error estimate processing 800 discloses additional details of block 610 of FIG. 6A in which alignment error estimates are determined. Alignment error estimate processing 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 estimate (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 may be turned off by this fraction of the frame. Following block 804, alignment error estimate processing 800 is completed and processing returns to block 612 of synchronization processing 600.

9A and 9B show diagrams of energy values e and energy difference Δe 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, diagram 902 shows the continuous energy difference value Δe for the determined energy values. The continuous energy difference Δe identifies the areas associated with the edge or transition point in the received data. The first edge represents an initial edge, or the beginning of a data burst, and is anywhere in area 904, and the second edge 906 represents the trailing edge, or the end of a data burst, and any area in area 906. In position. For example, the energy difference Δe is determined by block 702 of FIG. 7.

As can be seen from Figures 9A and 9B, the receiver is not properly synchronized with the transmission data coming from the remotely located transmitter. In particular, the start of the burst of data received from the transmitter starts at any position in frame 6. In order to be properly synchronized the data burst from the transmitter will in this embodiment start exactly at the beginning of frame 6. 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 anywhere within region 904, that is, within frame 6, and the trailing edge of the data burst is within region 906, that is, within frame 14. Show that you are in a position.

10a and 10b show the energy values 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 burst of data between frames 6, 14 having an initial edge 1002 at the beginning of frame 6 and a trailing edge 1004 at the end of frame 14. . In FIG. 10B, diagram 1006 shows the continuous energy difference value Δe for 20 frames including an initial maximum point 1008 and a 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. The length of the burst received from this information can be deduced (9 frames) and the super frame format can be identified (9-1-9-1).

Successive differences in the energy values observed in each frame of the super frame 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. In this continuous differential approach, it is only required that the energy of the "quiet" frame (not entirely idle 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.

When the data transmission system operates to delete the periodic prefix at the receiver, a dead zone, which is the width of the periodic prefix, is created in the frame / super frame alignment, because of the periodic prefix Elimination drops samples that are useful for frame synchronization, but are therefore not useful for FFT devices. One technique for solving this dead zone, where the frame has 512 samples and the periodic prefix has 40 samples, uses an energy estimate of 41 to 552 samples in addition to using 1 to 512 samples, which is then used in the burst detection process. The average of these energy estimates is used to find the combined energy estimates.

The above-described synchronization process is generally applied to remote side and center side synchronization. For synchronization processing at the remote device, the receiver at the remote device synchronizes and maintains data transmission (burst) with the transmitter of the central device. 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 adjusting the reception frame alignment for recovery of data transmission (burst) at the receiver.

Due to the round-trip delay of the line (or channel), the time the upstream transmission from the remote device reaches the central device is variable and would appear to be delayed by the length of the round-trip delay without correction. Thus, the central unit needs to adjust its receiver frame alignment so that the correct received sample is available to 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 determine the alignment correction to align the received frame boundary pointer with the frame of data received from the remote device after identifying the start of the upstream transmission burst.

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 duplexed transmission system. The structure of the receiver 1100 shown in FIG. 11 may be used in all or one of a central station transceiver and a remote device transceiver.

The receiver 1100 receives an analog signal 1102 transmitted through a channel from a transmitter (eg, a central station transmitter). The received analog signal is then fed to an analog-to-digital converter (DAC) that 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 retrieves a 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, the FFT device 1108 outputs frequency domain signals 1112 to the frame synchronization device 1114. The frame synchronization device 1114 operates to execute the synchronization process described above with respect to FIGS. 5 to 10B. The frame synchronization device 1114 outputs an alignment error estimate 1116 to the controller 1118. The controller 1118 then adjusts the receive frame boundary pointer 1110 to access data received from the input buffer 1106. Accordingly, the frame synchronization device 1114 provides frame synchronization to the time domain duplexing transmission system in a manner that is substantially immune to 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 divided between multiple transceivers or provided separately for each transmitter and receiver. Similarly, frame synchronization device 1114 may be implemented by a digital signal processor, microprocessor, or microcontroller or special circuitry.

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 is operative to decode the equalized signal and recover the transmitted data with respective frequency tones of the symbol being received. The decoding by the data symbol decoder 1122 is executed based on the bit allocation information stored in the received bit and the energy allocation table 1124. The decoded data is then provided to the FEC device 1126 and then stored in the output buffer 1128. The recovered data 1130 (stored decoded data) can then be retrieved from the output buffer 1128 as needed.

The receiver 1100 shown in FIG. 11 optionally 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 US Patent No. 5,285,474, entitled "POLY-PATH TIME DOMAIN EQUALIZATION," filed May 12, 1997, and US Application Serial No. 60 / 046,244 (Att. Dkt. No.: AMATP021 +). Included in

The present invention also provides a technique for synchronizing transmissions at the central side (i.e., central apparatus). By synchronized transmission at the central side, NEXT interference is substantially eliminated if all lines of the binder provide the same level of service (ie, super frame format). However, if the transmission from the center side through the line in the binder is not properly synchronized, 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 center side transmissions. If NEXT interference is not strong enough to be detected for synchronization purposes, it will be considered not strong during reception, so no synchronization is required.

Typically, the various transmitters at the center side can synchronize with each other by using all of the common master clocks supplied to the center side. However, sometimes this master clock is not available for one reason or another. Also, although available, the various transmitters may be placed slightly away from the master 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 flow diagram 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 (i.e. the transceiver). Transmissions from various transmitters all follow the same super frame format. Preferably, a second rest period (i.e. after upstream transmission) is used to measure energy since less echo tends to appear. Next, it is measured whether or not the energy measured at decision block 1204 is greater than or equal to the predetermined threshold. If the measured energy during the resting period is determined to be above a predetermined threshold, the presence of 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, the timing alignment can be modified by changing the oscillator frequency or by changing (increasing or decreasing) the length of the super frame. On the other hand, if the measured energy is determined to be below a predetermined threshold, the transmitter at the center side is considered sufficiently aligned and block 1206 is bypassed. If the predetermined threshold has not been exceeded, following block 1206 or next to block 1204, the synchronization process 1200 is complete 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 super frame 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 should transmit earlier. 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 should 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 an 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 the downstream transmission. 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 super frame structure. In VDSL, if the clocks of the center side transceivers are within 100 ppm of each other, the insertion of 1 sample per super frame (11,040 samples) will be sufficient to monitor the synchronization. If only the center side transceiver can insert, the center side transceiver will match at the lowest clock frequency of the group (with significant NET interference).

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, the sample (extra cycle) is inserted into the subsequent downstream transmission.

There are many advantages of the present invention. One advantage of the present invention is that synchronization can be obtained even in the presence of radio frequency (RF) interference due to amateur radio signals or the like. Another advantage of the present invention is that it is suitable for data transmission systems using time division duplexing such as synchronized DMT or synchronized VDSL. Another advantage of the present invention is that it is relatively less affected by background or receiver 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 super frame with a plurality of frames, a first set of frames in the super frame transmits 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 super frame 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 a 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 a method as described above, wherein the method further comprises (f) outputting super frame identification information.

Also included are alignment error calculations in which the calculation (b) detects an edge within a plurality of consecutive frames of received data based on the measured amount of energy and uses the edge detected in the plurality of consecutive frames. The method as described above including determining politics.

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 continuous 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 a step in which said calculating step (b) is one of said successive energy differences, said energy difference being one of said successive energy differences immediately preceding said maximum energy difference of said successive energy differences. And identifying the subsequent energy difference is one of the consecutive energy differences immediately following the maximum energy difference of the consecutive energy differences—aligned based on the previous energy difference and the subsequent energy difference. The method as described above comprising determining an error estimate.

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

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

Also included, the first transceiver identifies a frame start of a received super frame 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 a method as described above, wherein the alignment error estimate is an estimated alignment error as a piece of 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 super frame 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.

In addition, the above-mentioned method in which the amount of energy is an amount of power is also included.

In addition, the data transmission system transmits data using a super frame structure having a plurality of frames, some frames transmit data in a first direction, some frames transmit data in a second direction, and some frames super frame structure Include 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 super frame structure; Measuring an amount of energy of successive frames of a second set of received data for the super frame 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 super frame structure minus the length of the periodic prefix.

The combining step also includes the method described above, which determines average amounts of energy for each of the frames of the super frame structure including the periodic 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. The two transceivers are associated with a data transmission system that provides 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 alignment error estimate using an edge detected in a plurality of consecutive frames.

Also included is the computer readable medium 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; And 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 the computer readable medium described above, wherein the second computer readable medium comprises computer readable code devices for identifying a previous energy difference and a subsequent energy difference, wherein the previous energy difference is one of the consecutive energy differences. One of consecutive differences immediately before the largest difference, wherein the subsequent energy difference is one of consecutive differences immediately after the largest difference of the continuous 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 super frame 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 super frame 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 super frame structures; Computer readable code for measuring an energy amount of frames of received data for a second set of consecutive super frame 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 super frame that includes 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 super frame 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 demodulator for demodulating a digital signal into frequency domain data for a plurality of different carrier frequencies, and a multicarrier demodulator based on time-dependent variability of energy of frequency domain data generated by the multicarrier demodulator. A frame synchronization device for synchronizing a received frame boundary for the receiver; an allocation table for storing bit allocation information used for transmission data received at a receiver; and a carrier frequency based on bit allocation information for receiving frequency domain data and stored in the bit allocation table. Frequency And a data symbol decoder for decoding the bits associated with the area data, and an output buffer for storing the decoded bits as recovered 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 amount of alignment adjustment 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 to another transmitter in the center by a given transmitter is provided. More included. The method includes the steps of: (a) measuring energy associated with a given transmitter due to data transmission from another transmitter in the center in the idle period; (b) comparing the measured energy with a threshold; And (c) comparing (b) modifying the synchronization for the transmission with a given transmitter when the measured energy exceeds the threshold.

The method cited above further comprises the data transmission system transmitting data using time division duplexing, wherein 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 acts to distinguish between incoming data and incoming data reception from other transmitters, in which the operation (a) of measuring the energy associated with a given transmitter due to the transmission of data from another transmitter at the central part in idle period, The result measuring (a) further includes measuring energy at rest during the outgoing data transmission, not due to receiving data from the other transmitter.

And further comprising a computer readable medium including program instructions for synchronizing data transfer in a data transfer system having a plurality of transmitters in a central portion. The external clock signal is not useful here for synchronizing the transmitters, and the transmitters transmit data according to a super frame format including at least one idle period. The computer readable medium further comprises: a first computer readable code device for measuring energy in idle period associated with a given transmitter due to transmission of data from another transmitter in a central portion; 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, and 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.

1A is a simplified block diagram of a conventional transmitter in a multicarrier modulation system.

1B is a simplified block diagram of a conventional remote receiver in a conventional multicarrier 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 dispensing apparatus 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 a flow diagram of a synchronization process, in accordance with a more detailed embodiment of the present invention.

7 is a flow diagram of an edge detection process, in accordance with an embodiment of the present 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 flow diagram of a synchronization process for synchronization of adjacent transmitters to compensate for small synchronization differences.

<Description of symbols for main parts of the drawings>

300: processing and distribution unit

302: processing unit

304: data link

308: bus arrangement

Claims (14)

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, the method comprising: The first transceiver and the second transceiver are associated with a data transmission system that provides bidirectional data communication using time division duplexing, Measuring an amount of energy for each of the plurality of consecutive received data frames; Detecting edges in the plurality of consecutive received data frames based on the measured amount of energy, the detected edges being burst edges, wherein the detecting step comprises at least one of the plurality of measured amounts of energy Calculating a continuous energy difference and identifying the largest energy difference of the continuous energy differences, corresponding to the burst edge; And Determining an alignment error estimate using edges detected in the plurality of consecutive frames How to include. The data transmission system of claim 1, wherein the data transmission system transmits data using a super frame structure having a plurality of frames, wherein the first set of frames in the super frame transmits data in a first direction, and in the super frame. A second set of frames of data in a second direction. The apparatus of claim 2, wherein the first transceiver uses a frame boundary pointer to identify the beginning of a frame in a receiving super frame, Adjusting the frame boundary pointer according to the alignment error estimate. 4. The method of claim 3, wherein the alignment error estimate is an alignment error calculated as a fraction of a frame. The method of claim 3, Comparing the alignment error estimate with a threshold; And Repeating from the step measuring step to the determining step until the result of the comparing step is less than the threshold error of the alignment error; How to include more. A computer readable medium containing program instructions for adjusting an alignment of the first transceiver to receive a data frame transmitted from a second transceiver to a first transceiver via a transmission medium, The first transceiver and the second transceiver are associated with a data transmission system that provides bidirectional data communication using time division duplexing, First computer readable code devices for measuring an amount of energy for each of a plurality of consecutive received data frames; And Second computer readable code devices for calculating an alignment error estimate based on the measured amount of energy Including; The second computer readable code devices are at least Computer readable code devices for detecting edges in the plurality of consecutive received data frames based on the measured amount of energy—computer readable code devices for detecting the edges include at least the plurality of measured energy amounts Computer readable code devices for calculating a continuous energy difference of a computer and computer readable code devices for identifying a largest energy difference of the continuous energy differences, corresponding to a burst edge; And Computer readable code devices for determining an alignment error estimate using edges detected in the plurality of consecutive frames. A receiver for a data transmission system using time division duplexing that alternates between transmission and reception of data, the receiver comprising: An analog-to-digital converter for receiving analog data transmitted through 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 different carrier frequencies; Measuring an amount of energy for each of the plurality of consecutive received data frames; Detecting edges in the plurality of consecutive received data frames based on the measured amount of energy, wherein the detected edges are burst edges, wherein the detecting step comprises: determining a continuous energy difference of the plurality of measured amounts of energy; Calculating, identifying the largest energy difference among the consecutive energy differences corresponding to the burst edges, and determining alignment error estimates using edges detected in the plurality of consecutive frames. Includes-a frame synchronization device for synchronizing a received frame boundary for the multicarrier demodulation device; A bit allocation table for storing bit allocation information used for transmitting data being received at the receiver; A data symbol decoder that receives frequency domain data and decodes bits 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 recovered data Receiver for a data transmission system comprising a. In a data transmission system having a plurality of transmitters in a central site for transmitting data according to a super frame format including at least one quiet period, the data transmission by a predetermined transmitter is performed at the central site. As a method for synchronizing with other transmitters, (a) measuring energy in the idle period associated with the given transmitter at the central site by transmission of data from the other transmitters; (b) comparing the measured energy with a threshold; (c) changing the synchronization of transmissions by the given transmitter if the result of the comparing step (b) indicates that the measured energy exceeds the threshold; Synchronization method comprising a. In a data transmission system having the plurality of transmitters at a central site where an external clock signal for synchronizing a plurality of transmitters transmitting data according to a super frame format including at least one idle period is not available, synchronizing data transmissions A computer readable medium comprising program instructions for causing a computer program to be executed. The energy in the idle period associated with a given transmitter at the central site is measured by data transmission from other transmitters, Compare the measured energy with a threshold, And change the synchronization of transmissions by the predetermined transmitter if the result of the comparison indicates that the measured energy exceeds the threshold. 6. The method of claim 5, further comprising outputting super frame identification information. The method of claim 1, wherein the determining step, Identifying a previous energy difference and a subsequent energy difference, wherein the previous energy difference is one of the continuous differences immediately preceding the largest energy difference of the continuous energy differences, wherein the subsequent energy differences are the continuous One of the consecutive energy differences immediately after the largest energy difference of the ordinary energy differences; And Determining the alignment error estimate based on the previous energy difference and the subsequent energy difference. 12. The method of claim 11, wherein in the step of determining the alignment error estimate, calculating the amount of difference between the subsequent energy difference and the previous energy difference. 12. The method of claim 11, wherein in determining the alignment error estimate, generating the alignment error estimate by normalizing the difference amount after calculating the difference amount between the subsequent energy difference and the previous energy difference. The computer-readable medium of claim 6, wherein the second computer readable medium comprises: Computer readable code devices for identifying a previous energy difference and a subsequent energy difference, wherein the previous energy difference is one of the consecutive differences immediately preceding the largest energy difference of the continuous energy differences, The energy difference is one of the consecutive energy differences immediately after the largest energy difference of the consecutive energy differences; And Computer readable code devices for determining the alignment error estimate based on the previous energy difference and the subsequent energy difference.