Showing papers on "High-bit-rate digital subscriber line published in 2002"

Near-end crosstalk mitigation in ADSL systems

Abstract: Near-end crosstalk (NEXT) is one of the major impairments to the current asymmetric digital subscriber line (ADSL) downstream transmission. This paper presents two methods for an ADSL receiver to cancel one (dominant) NEXT signal from other types of services (such as HDSL (high-bit-rate DSL), SDSL (single-pair, symmetric DSL), T1, etc.). The methods exploit the fact that the crosstalk signal has a large excess bandwidth and its spectra in the main lobe and in the excess band are strongly correlated. The principal idea is then to estimate the crosstalk in some frequency bands (e.g., excess band) and cancel it in other frequency bands (e.g., main lobe). The frequency-domain analysis in this paper provides an intuitive explanation of the crosstalk estimation and cancellation, as well as a guidance to select the right frequency bands to observe the crosstalk signal. Moreover, a fast algorithm is proposed for practical implementation. This algorithm avoids matrix inversion and large matrix multiplication in every transmission block. Simulation results show that one of the proposed methods, minimum mean-squares error estimation and cancellation, is very effective to cancel one (dominant) NEXT and the improvement is significant in terms of the data rate and the line reach for the ADSL service. For example, using a real measured NEXT transfer function, the proposed method can increase the ADSL downstream data rate by 200% for some loops. The methods are extended to estimate and cancel two or more crosstalkers. The amount of improvement depends on the crosstalkers' characteristics and it is generally less than that of a single crosstalker case.

Power control of digital subscriber line

Abstract: This invention relates to power control arrangements of digital subscriber lines. The invention controls parallel subscriber lines simultaneously in an organized way, based on the measurements of crosstalk conditions of the sub-scriber lines. Different crosstalk conditions are measured. The organized way to control the transmission power levels ensures that the crosstalk does not increase to an unacceptable level in each of the subscriber lines.

Methods of summing crosstalk from mixed sources .II. Performance results

Abstract: For pt.I see ibid., vol.50, p.453-61, (Mar. 2002). In a companion paper, the problem of summing crosstalk from mixed sources has been deeply analyzed. The problem of determining a good model for the summation of mixed crosstalk is becoming more important now that many digital subscriber line (DSL) services are being deployed in the field. The straightforward application of the usual 1% worst-case model for only one kind of disturber to all the individual worst-case contributions is overly pessimistic. The most well-known methods of summing mixed crosstalk, the FSAN and the Mean PSD methods, are less pessimistic. Also, the two new summation methods presented previously, the Minkowski-bound and the Holder-bound methods, are less pessimistic and offer the appealing feature of choosing the level of pessimism or optimism through a parameter. However, the accuracy of these methods has never been quantified in the past. As more and more types of DSLs are deployed by multiple service providers, it is imperative to gain confidence in the methods of modeling worst-case mixed crosstalk and to understand their limitations. In this paper, the problem of defining an accurate statistical modeling of the pair-to-pair crosstalk power coupling losses is addressed first. This has been accomplished by exploiting a large measurement campaign performed on real cables. The results of a large simulation campaign that compares the accuracy of known and newly proposed methods of summing mixed crosstalk are then presented. In addition, it is proposed here to use the signal-to-noise ratio (SNR) as the metric for determining the actual system performance in the presence of mixed crosstalk. A Monte Carlo simulation is run that assigns randomly each disturber to a pair-to-pair NEXT coupling which matches the statistics of measured cables. The Monte Carlo method accurately determines the I % worst-case impact on the SNR of DSL systems affected by mixed crosstalk. ISDN, HDSL, HDSL2, T1 and ADSL are each simulated with many different numbers and types of mixed crosstalk.

Method for local exchange subscriber line conferencing

Abstract: A local conferencing exchange subscriber line conferencing system and method using a series of input signals from the phone of a subscriber, such as a dual-tone multifrequency (DTMF) sequence of key inputs starting with a star key input, to initiate the conference. The conference is set up in a bridge and the phone of the subscriber is connected to the bridge. All subsequent callers to the subscriber's phone number at the local exchange carrier are routed and connected to the conference at the bridge. When the conference call ends, the subscriber's phone is returned to normal service.

System and method for reducing noise induced by digital subscriber line (dsl) systems into services that are concurrently deployed on a communication line

Abstract: Systems and methods are presented for reducing noise induced by digital subscriber line (DSL) systems into services that are concurrently deployed on a communication line. In the disclosed technique, a power level of a discrete multi-tone (DMT) sub-carrier is adaptively calculated from a signal that is received from a communication line. The signal has information indicative of line conditions, which are further indicative of services deployed on the communication line.

Local exchange subscriber line conferencing

Abstract: A local conferencing exchange subscriber line conferencing system and method using a series of input signals from the phone of a subscriber, such as a dual-tone multifrequency (DTMF) sequence of key inputs starting with a star key input, to initiate the conference. The conference is set up in a bridge and the phone of the subscriber is connected to the bridge. All subsequent callers to the subscriber's phone number at the local exchange carrier are routed and connected to the conference at the bridge. When the conference call ends, the subscriber's phone is returned to normal service.

Cable Measurements Supporting xDSL Technologies

Abstract: The ongoing developments in the field of high-speed data transmission over twisted-pair cables (DSL-Digital Subscriber Line) leads to methods that can exploit the transmission media with increased efficiency. MIMO (Multiple-Input Multiple-Output) transmission, i.e., the coordinated use of many pairs within a bundle, is such an emering DSL technology. A further goal is to maintain a certain transmission quality in the presence of non-DSL noise. For example, cancellation techniques to combat narrowband radio interference, which is generated by radio amateur transmitters and may be picked up by the wire close to the subscriber or by the in-hourse wiring, become important.

Wide-band analog front-end for DSL applications

Abstract: An analog front-end circuit and method that supports multiple digital subscriber line (DSL) standards, including asymmetric digital subscriber line (ADSL) and very-high speed digital subscriber line (VDSL) is disclosed. The circuit incorporates multiple circuit blocks that can be selectively included into the transmit and receive paths of a DSL signal. It also permits selectable gain settings for signal amplifiers, and frequency bandwidth for signal filters that may be included in the transmit and receive paths. The receive path includes an analog-to-digital converter (ADC) that operates close to and exceeds the Nyquist sampling rate.

Channelized voice over digital subscriber line

Abstract: This article presents a promising voice over digital subscriber line (VoDSL) solution: an alternative method that uses physical layer transportation to provide channelized VoDSL (CVoDSL). This article also presents the advantages that the CVoDSL provides to the customers in terms of high-quality services and lower cost, and service providers in terms of market growth and success. It also offers a set of requirements, architectural design, and implementation scenarios that provide end-to-end solutions for CVoDSL.

Method for double-ended line qualification and monitoring of xDSL links

Abstract: A method for double-ended line qualification and monitoring of xDSL links employs a single test program which is sent by a first subscriber at one end of the xDSL link to a second subscriber at the other end of the xDSL link. Line qualification and/or monitoring is carried out by processing this test program and sending the test results obtained in this step back to the first subscriber. The line qualification and/or monitoring is triggered after the code of the test program has been transmitted by the first subscriber. In this method, the first subscriber represents a modem at the switching end and the second subscriber represents a modem at the subscriber end. The test program is a program module which is connected to other program modules via a message queue.

Efficient echo channel, estimation mechanism for an ADSL echo canceller

Abstract: An efficient dual time and frequency domain echo channel estimation scheme that does not need any multiplier in the implementation of its frequency domain component. The scheme applies to echo canceling in typical ADSL applications. It can be easily adapted and extended to other applications such as, but not limited to, HDSL and VDSL in which echo channel estimation and echo canceling are necessary.

Blind Crosstalk Cancellation for DMT Systems

Abstract: As the deployment of broadband communication systems such as DSL continues to grow, system performance in terms of capacity and error rates is severely limited by crosstalk interference. In order to continue deploying high speed DSL service, it becomes necessary to mitigate this crosstalk interference. All current crosstalk mitigation techniques require precise knowledge of the crosstalk coupling functions between the twisted pair wires carrying DSL service within a cable binder. In practice, this is near impossible to obtain, without coordination between the different DSL services. In this paper, we present a crosstalk cancellation technique that is blind to the coupling functions between the wire pairs. Our technique uses the statistical properties of the received crosstalk signal (that can be easily estimated), rather than the exact coupling functions themselves, making it very attractive for practical implementation. We show with the help of simulations for a realistic ADSL system with HDSL and T1 crosstalk interference using actual measured crosstalk coupling functions that the proposed blind crosstalk cancellation technique can achieve significant gains in terms of rate and reach improvement for the ADSL system. We also show that the performance of the proposed blind crosstalk cancellation technique is robust to a jitter in the crosstalk symbol timing estimate that is required to construct the cancellation signal. Keywords—crosstalk, NEXT, mitigation, blind, cancellation.

Combined equalization and alien crosstalk cancellation in ADSL receivers

Abstract: We address the problem of mitigating a dominant alien near-end crosstalker such as HDSL, SDSL or HPNA in DMT-based ADSL and VDSL receivers. Due to the different symbol rates of crosstalker and signal of interest, linear time-invariant filtering is not appropriate. Recently, Zeng et al. presented a method to tackle this problem [4]. In this paper, we present an alternative procedure, which, unlike the solution of [4], does not require any prior knowledge (such as transmission and crosstalk channel, noise characteristics, etc.) other than the crosstalker symbol rate. Moreover, it is fully adaptive, integrates equalization and crosstalk cancellation and optimizes the signal-to-noise ratio for each tone separately. Both algorithms exploit spectral correlation in the received crosstalking signal, thanks to oversampling and excess bandwidth. The method present here is based on the application of so called FREquency-SHift (FRESH) filtering.

High-speed digital subscriber line (HDSL) wander reduction

Abstract: An apparatus and method are described that allows for improved wander jitter reduction in communication devices and associated communication links, in particular on HDSL communication devices and links. The improved device apparatus and method detects the current data rate offset of the HDSL data rate being utilized and the data rate of the datastream being transmitted through the HDSL communication link and allows for the transmitting HDSL communication device to adjust the HDSL data rate to avoid high wander jitter “sweet spots”. The improved device apparatus and method also allows for the profiling of communication devices for their specific high wander jitter sweet spot maximum points by sweeping the input data rate being transmitted at differing HDSL data rates.

Performance of a 51.84-Mb/s VDSL transceiver over the loop with bridged taps

Abstract: This paper presents a study of the effects of bridged taps on very high-speed digital subscriber line (VDSL) transmission systems. It is shown that the short bridged taps, which affect VDSL signals, are much more damaging than the longer bridged taps, which affect other xDSL signals, such as high-rate digital subscriber line (HDSL) and asymmetric digital subscriber line (ADSL). Specifically, short bridged taps introduce a lot of linear distortion in the loop's transfer function. In addition, they also tend to introduce more overall propagation loss than longer bridged taps. The peak-power-to-average-power ratio (PAR) of the signal increases for the loop with short bridged taps, and thus more A/D bits are needed in the implementation of a digital VDSL transceiver as compared to the loop with long bridged taps. The performance of various equalizer structures is discussed in the presence of a severe channel distortion caused by the bridged tap.

High-speed digital subscriber line (HDSL) packet abort retry during channel blocking

Abstract: An apparatus and method is described that allows for improved transmission of EOC data over the EOC channels of communication devices and links, reducing the number of dropped EOC packets and increasing the bandwidth and robustness of the EOC channel. The improved device apparatus and method also allows for the reduction of the overhead of EOC channel error detection and correction on the limited resources of the communication device by aborting a corrupted or blocked EOC packet transmission and automatically resending. The improved device apparatus and method additionally allows the reduction of dropped EOC data packets due to corrupted transmission and the resultant miscommunication and corruption of high-level applications of the communication device, such as operation commands, remote configuration and management programs, and operation displays.

Universal network termination

Abstract: The invention concerns a method for supporting communication between a switching system and a PSTN terminal connected with a network termination unit through an analog subscriber line. Broadband traffic packets as well as a number of synchronous channels are transferred in both directions over a subscriber line between the network termination unit and the subscriber line board of the switching system. At least one ISDN-B channel and one ISDN-D channel is provided based on such synchronous channels. A protocol converter converts between an analog loop signaling applied on the analog subscriber line and digital signaling messages transported over the ISDN-D channel. An analog to digital conversion is performed between the analog subscriber line and the ISDN-B channel.

Resilient detection of repeaters

Abstract: An apparatus and method are detailed that allows for improved detection of communication devices and/or doublers in an associated physical communication links, in particular on HDSL communication links. The improved device apparatus and method additionally allows for the communication device to identify when all devices on a communication link have been detected and prevent premature termination of a discovery process. The improved device apparatus and method also allows the avoidance of improper detection of communication devices or doublers due to corrupted discovery response messages.

Power line communication front-ends based on ADSL technology

Abstract: The practical implementation of communication over power lines (PLC) using an Asymmetric Digital Subscriber Line (ADSL) front-end is discussed. Both PLC and ADSL modems are based on the same principle of using their respective transmission medium in a frequency range they were never originally designed for. One property both technologies share is the large power that is required when transmitting signals onto the communication medium. The frequency ranges are also comparable. Therefore, ADSL front-ends are evaluated as a power line interface. This paper presents the front-end topology and discusses the signal-to noise measurements that were performed to determine, using Shannon's theorem, the theoretical data throughput.

A polyphase IIR adaptive filter

Abstract: A polyphase structure for infinite-impulse response (IIR) adaptive filtering is proposed and compared to the direct structure in terms of their reduced error surface. It is shown that the general shape of its surface can make the polyphase structure have higher convergence speed, alleviating the problem of convergence speed in IIR adaptive filters and allowing their computational complexity gain over finite-impulse response (FIR) adaptive filters to be exploited. Benefits regarding filter stability are also achieved with the polyphase structure. An example of a high-speed digital subscriber line (HDSL) application is presented, for which the polyphase structure attains a gain of up to 70 times in convergence speed over an IIR direct structure, leading to roughly the same convergence speed of a FIR structure but with only 12% of its computational complexity. The question of uniqueness of the stationary points of the proposed structure is also discussed. It is pointed out that for white input and sufficient modeling, all stationary points are global minima, a result which does not follow directly from an equivalent property of the direct structure.

A novel tunable-complexity turbo-soft detector for high-throughput HDSL applications over ISI channels with crosstalk

Abstract: We present a novel iterative (turbo) receiver with tunable complexity for reliable detection of (uncoded) payload data transmitted over long intersymbol interference (ISI) channels affected by crosstalk, as those typically encountered in emerging HDSL2 services standardized by ANSI T1.418 recommendation. The proposed receiver combines in an original way "minimum mean square error (MMSE) estimation principle," "turbo-processing principle" and "crosstalk-prediction principle" for achieving both suboptimal maximum a posteriori probability channel equalization and reliable soft-mitigation of ISI tail plus crosstalk. More in detail, according to the turbo-processing principle, at each iteration suitable extrinsic information is extracted from the equalizing and interference-canceling modules and used as "a priori information" for the next iteration. Several simulation results on typical HDSL-like test-loops confirm the superiority of the proposed turbo-detector (TD) over current solutions based on conventional MMSE decision-feedback equalizers and precoders (such as the Tomlinson-Harashima precoder). The numerical tests also point out that performance of the presented TD on typical high bit-rate digital subscriber lines (HDSL) is not limited by error-floor phenomena, even at error-probabilities below 10/sup -7/.

Optimization of a DSL-compatible POTS line card

Abstract: A digital subscriber line (DSL) compatible plain old telephone service (POTS) line card that interface a telecommunications switching system to a subscriber over a two-wire subscriber line, wherein the subscriber line card detects whether a DSL line card is connected to the subscriber line. A digital signal processor on the POTS line card is configured to process voice-band signals with a first set of parameters if a DSL line card is connected to the subscriber line and to process voice-band signals with a second set of parameters if the DSL line card is not connected to the subscriber line. Detecting the presence of a DSL line card may be performed by sending a voice band tone on the subscriber line and the return loss measured. Additionally, a tone above voice band may be sent on the subscriber line and a return loss measured. The first set of parameters adjust frequency response of the subscriber line, return loss of the subscriber line and/or trans-hybrid loss of the POTS line card to compensate for the presence or absence of a DSL card connected to the subsource line.

Generalized DMT/OFDM with high performance

Abstract: A generalization of the well-known DMT/OFDM data transmission method is proposed which can utilize redundancy in the time domain as well as in the frequency domain to completely cancel intersymbol and interchannel interference caused by the channel impulse response. The new systems provide a considerable reduction in latency time and a high increase of bandwidth efficiency and thus open the way to a multiple carrier HDSL similar to the previously introduced ADSL.

Multi-split equalizers for HDSL channels

Abstract: The application of multi-split equalizers is proposed as a means of diminishing the training sequence length. Reductions in the order of four to six times are presented for practical HDSL channels. The new structure is suitable for numerous applications, for instance, as the front end of any joint equalization and decoding scheme that makes use of a DFE in an iterative way.

An Examination of High Bit Rate Data Transmission by Metallic Cables for Railways

Abstract: This report examines the elements needed for high bit rate data transmission such as used in Digital Subscriber Line (xDSL) transmissions along existing metallic cables. Old carrier systems used frequency division multiplex and time division multiplex are used in transmitting voice and data over these same cables for railway operations. As the need for higher rates of data transmission grows, it is hoped to be able to continue to use metallic cables. The report gives examples of the types of information transmitted through metallic cables on railways, with rate and frequency. The xDSL transceiver's relation to the existing system is important to knowing how it will perform. The researchers measured its basic performance under ideal conditions to less the maximum transmission distance and they concluded that transmissions could be completed without relays. They also tested how the xDSL and the existing system influenced each other and found acceptable performance if the cable arranged to reflect the needs when several xDSL transceivers are operating on the same local cable. They conclude that xDSL technology is likely to be useful and determined the basic data needed for introducing it into railway operations. More research should be able to produce enough information to create final guidelines.

Asymmetrical digital subscriber line (ADSL) an in-depth study

Abstract: Asymmetrical Digital Subscriber Line (ADSL) is one member of a group of broadband access technologies that uses the existing copper-based local loop of the analog PSTN for high-speed digital data transmission. One feature ofADSL is that it permits analog voice POTS transmissions to continue uninterrupted over the same wiring. Specifically, POTS continues to use the 0 to 4 KHz frequency range of the copper wiring, while ADSL uses bandwidth starting at 25 KHz and extending up to approximately 1.1 MHz for data transmission. The term "asymmetrical" refers to the fact that data rates downstream (to the user) and upstream (from the user) are not the same. Typical ADSL data rates range from 1.536 to 6.144 Mbps downstream and from 16 to 640 Kbps upstream. Local loop length, wire size, and the presence of devices to improve voice communication such as bridged taps and loading coils all affect ADSL data rates. Digital data is coded by one of two methods: Discrete Multitone Modulation (DMT) or Carrierless Amplitude and Phase Modulation (CAP). Echo control is also accomplished by one of two methods: Frequency DivisionMultiplexing (FDM) or echo cancellation. This paper consists of four sections: 1) A technical review and comparison of the CAP and DMT line encoding technologies. 2) A market review of the presence ofCAP and DMT technologies in customer premise equipment (CPE) such as modems and routers. 3) A review of the POTS physical layer that exists between the ADSL subscriber and the Telco CO, and its impact on ADSL availability and quality of service (QOS). 4) A technical review of the newer, splitterless, G.Lite technology

Inter networking apparatus and method using SDSL

Abstract: PURPOSE: An internetworking equipment using an SDSL(Symmetric Digital Subscriber Line) is provided to use an HDLC(High bit rate Digital Subscriber Line) controller, a high capacity packet processor, and a PCI(Peripheral Component Interconnect) bus, so as to construct a stable network communication environment. CONSTITUTION: The second SDSL modems(130) connected to subscribers are converted into data information having a bit serial type from SDSL modem signals transmitted from the subscribers. An HDLC controller(140) has many input ports connected to the second SDSL modems(130), and packetizes a digital bit serial transmitted from the second SDSL modems(130), then controls packets. A high capacity packet processor(160) controls data information transmitted from the HDLC controller(140) at a high speed. A PCI bus(150) processes the data information as bus types.

Subscribers-switching device and method of asymmetrical digital subscriber lines

Abstract: The present invention includes a subscriber-switching device and method in a system of asymmetrical digital subscriber lines ADSL. The subscriber-switching device includes multiple subscriber units including multiple subscriber ports, respectively; a redundancy subscriber unit including multiple subscriber ports, a network unit for transmitting data inputted from the multiple subscriber units to networks, a rear unit on a back plane of a shelf for transmitting data inputted from at least more than one of the subscriber lines to the subscriber unit, a common line board for connecting the subscriber lines of the rear unit to the redundancy subscriber unit through the common line, a switching means for switching among the subscriber port of the subscriber unit, the redundancy subscriber unit, and the common line board, and a controller for controlling mutual operation flows among the above units and means. Therefore, data inputted from the subscriber line is continuously serviced to the subscribers through the switched redundancy subscriber unit without data interruption. As a result, the reliability of the transmitting device and the quality of the services can be improved enormously.

In-building data-over-voice Internet access

Abstract: High speed Internet access is becoming an essential service in the workplace which often includes hotels. This paper investigates short-range Internet access methods suitable for hotels, hospitals, and historic office buildings where pervasive telephone service exists and there is a need for "always on" high speed Internet access. It is desirable to avoid the costly installation of new wires to provide this service. While digital subscriber line technologies have matured over the last decade, and these are more than capable of providing the required service, their cost is excessive, and when transmission distances are very short there is an opportunity to apply lower-cost data-over-voice solutions. This paper evaluates the suitability of various baseband line coding techniques for data transmission in a simultaneous voice and data environment. Through computer simulation, a number of potential line coding methods were characterized by their power spectral density and eye diagram. These characterizations were used to evaluate data transmission capacity, error performance and potential interference with voice communication. The paper shows that bipolar-return to zero (BPRZ) and bipolar-non return to zero (BPNRZ) ternary coding provide the greatest potential improvement in data transmission rate while sacrificing the least in transmission performance. Quaternary and pentary methods are shown to be poor, and 2B1Q coding (widely used in ISDN and HDSL) is not applicable for data-over-voice since low frequency data transmission is required.

Subscriber system data transmission system

Abstract: PROBLEM TO BE SOLVED: To provide XDSL service even for a remote subscriber at a long distance from an exchange at a sufficiently fast transmission rate nearly as high as that of a near subscriber at a short distance from the exchange. SOLUTION: A system which performs high-speed data transmission between a subscriber terminal 11 and the Internet connected to an XDSL center device 19 by connecting the subscriber terminal 11 to the XDSL center device 19 of the exchange 16 through an XDSL modem 12 and an analog telephone line 15 is characterized by that a repeating device 1 installed at a specified repeating point of the analog telephone line 15 between the subscriber terminal 11 and exchange 16 sends out a optical signal generated by photoelectrically converting a subscriber digital signal inputted from the subscriber terminal 11 to an optical fiber 3 and a distributing device 2 connected to the XDSL center device 19 of the exchange 16 sends out a subscriber digital signal generated by photoelectrically converting the optical signal inputted from the optical fiber 3, thereby shortening the length of the analog telephone line which transmits the subscriber digital signal. COPYRIGHT: (C)2003,JPO