Behavior of Crosstalk Loss for Adjacent Pairs at Low Frequencies

Measurements at the Northern Electric cable plant in Lachine [2] and elsewhere [3],[4] showed that at low frequencies near-end crosstalk loss (NEXT) and far-end crosstalk loss (FEXT) for adjacent pairs do not have slopes of 15 dB/decade and 20 dB/ decade, respectively. In this paper an approximation predicts a slope of 5 dB/decade for NEXT and long cable and 10 dB/decade for FEXT.     

Crosstalk Loss Requirements for PCM Transmission

We present in this paper a unified approach to the crosstalk interference problem arising in PCM transmission on paired cables. For bipolar signaling, and three types of commonly used channel shaping, viz., cosine, raised cosine, and Gaussian, we present the minimum average near-end crosstalk (NEXT) and far-end crosstalk (FEXT) loss requirements at any transmission rate as a function of repeater spacing and number of interfering pairs so as to meet a desired error rate objective. This will aid in indicating if new cables need to be developed for a proposed rate of transmission or, for a given cable, the error margin available for degradations other than crosstalk can be readily determined. Extension to other coding schemes is indicated, and crosstalk compatibility is examined for mixedTsystems, such asT1,T1C, andT2. Graphical results are presented to readily aid in system design of anyTcarrier with repeater spacings up to 70 dB.     

Loop survey in the Taiwan area and feasibility study for HDSL

About 2800 lines out of a total of 8,500,000 subscriber lines in Taiwan have been sampled and characterized. Various kinds of physical compositions and transmission characteristics were investigated and measured. It was found that the near-end crosstalk (NEXT) loss of Taiwan's subscriber loops is about 10 dB worse than that of US local loops. A corresponding new foam-skin PIC cable is proposed to reduce the NEXT loss. The new type of cable will be used to replace the paper cable and old foam-skin PIC cable step-by-step. Based on the measured data, the feasibility of HDSL (high bit rate digital subscriber line) service in Taiwan is studied. To improve the HDSL service distance via the existing subscriber lines, several cable models are discussed and suggested     

The Cyclostationary Nature of Crosstalk Interference from Digital Signals in Multipair Cable--Part I: Fundamentals

This paper considers the cyclostationary nature of digital signals when determining crosstalk interference between such signals in multipair cable. This approach is necessary as the interference is only relevant at the decision instants in the receivers of the disturbed systems and any time variation of this interference with respect to the sampling instants changes the effect of this interference; previous studies in the area have ignored the cyclostationary nature of the digital signal. Expressions for the time-varying mean and variance of far-end and near-end crosstalk (FEXT and NEXT) have been derived. These expressions demonstrate the inherently smaller time variation of the NEXT interference when compared to the FEXT interference. An interesting result is that the calculation of the time-averaged value of the variance of FEXT and NEXT interference still requires the use of the cyclostationary properties of the digital signal. The results of this paper are extended and applied to various examples of the engineering of digital line systems in multipair cable in Part II of this paper.     

The Cyclostationary Nature of Crosstalk Interference from Digital Signals in Multipair Cable--Part II: Applications and Further Results

In this paper, the results of Part I are applied to the engineering of primary-level digital line systems in multipair cable operating in either a nonsynchronous or a synchronous network. It is shown that the erstwhile incorrect assumption that crosstalk interference from digital line systems is wide sense stationary, and not cyclostationary, leads to an overestimation of system margin of less than 1 dB. It is also shown that the change from a nonsynchronous to a synchronous network leads to a reduction in system margin which is difficult to quantify exactly, but it is typically less than 2.5 dB for FEXT and 1.5 dB for NEXT. The paper concludes with a consideration of the cyclostationary nature of block,encoded digital signals such as 4B3T, MS43, etc., and extends some of the results of Part I.     

10 Gb/s adaptive receive-side merged near-end and far-end crosstalk cancellation circuitry in 65 nm CMOS

Crosstalk between neighboring channels can have significant impact on system bit-error rate (BER) as serial I/O data rates scale above 10 Gb/s. This paper presents receive-side circuitry which merges the cancellation of both near-end and far-end crosstalk (NEXT/FEXT) and can automatically adapt to different channel environments and variations in process, voltage, and temperature. NEXT cancellation is realized with a novel 3-tap FIR filter which combines two traditional FIR filter taps and a continuous-time band-pass filter IIR tap for efficient crosstalk cancellation, with all filter tap coefficients automatically determined via an on-die sign–sign least-mean-square (SS-LMS) adaptation engine. FEXT cancellation is realized by coupling the aggressor signal through a differentiator circuit whose gain is automatically adjusted with a power-detection-based adaptation loop. A prototype fabricated in a general purpose 65-nm CMOS process includes the adaptive NEXT and FEXT circuitry, along with a continuous-time linear equalizer (CTLE) to compensate for frequency-dependent channel loss. Enabling the crosstalk cancellation circuitry while operating at 10 Gb/s over coupled 4-in FR4 transmission line channels with NEXT and FEXT aggressors opens a previously closed eye and allows for a 0.2 UI timing margin at a BER = 10^?9. Total power including the NEXT/FEXT crosstalk cancellation circuitry, CTLE, and high-speed output buffer is 34.6 mW, and the core circuit area occupies 0.3 mm².     

Dynamic algorithm transforms for low-power reconfigurable adaptiveequalizers

In this paper, we present low-power reconfigurable adaptive equalizers derived via dynamic algorithm transforms (DATs). The principle behind DAT is that conventional signal processing systems are designed for the worst case and are not energy-optimum on average. Therefore, significant energy savings can be achieved by optimally reconfiguring the hardware in these situations. Practical reconfiguration strategies for adaptive filters are presented. These strategies are derived as a solution to an optimization problem. The optimization problem has energy as the objective function and a constraint on the algorithm performance (specifically the SNR). The DAT-based adaptive filter is employed as an equalizer for a 51.84 Mb/s very high speed digital subscriber loop (VDSL) over 24-pair BKMA cable. The channel nonstationarities are due to variations in cable length and number of far end crosstalk (FEXT) interferers. For this application, the traditional design is based on 1 kft cable length and 11 FEXT interferers. It was found that up to 81% energy savings can be achieved when cable length varies from 1-0.1 kft and the number of FEXT interferers varies from 11 to 4. On the average, 53% energy savings are achieved as compared with the conventional worst-case design     

Crosstalk Considerations for a 48 Channel PCM Repeatered Line

Extension of the 24 channelT1carrier concept to a 48 channel system requires a careful investigation of the limitations imposed by the increased crosstalk noise susceptibility of 48 channel regenerators. Results of this paper demonstrate the feasibility of dual cable and single-screened cable operation of 48 channel lines at repeater spacings comparable toT1spacing. Operation over singlecable facilities is limited by NEXT to cables with a large cross section and is further restricted to only selected conductors in such a cable. A final result establishes thatT1and 48 channel systems may operate simultaneously in facilities engineered according to 48 channel crosstalk requirements.     

Coordinated transmission for two-pair digital subscriber lines

The performance of two-pair dual-duplex systems is substantially improved if the transmission on one pair is coordinated with that on the other, so that the transmitted signals are two-dimensional vector pulses. The advantages of coordination of transmission in an optimal way are quantified. Signal processing gains of 1.8 dB can be achieved in this way by averaging the SNRs on the two pairs constituting the high rate digital subscriber line (HDSL) and by canceling the near-end crosstalk (NEXT) between them. Exploitation of pair-to-pair correlation of NEXT voltages on the constituent pairs provides an additional source of processing gain. Under reasonable assumptions concerning the distribution of NEXT coupling coefficients between cable pairs, there is a better than 50% chance that the signal processing gain achieved by exploiting pair-to-pair NEXT correlation will be greater than 1.5 dB. Coordinated transmission requires the adaptation of four flat gain amplifiers in transmitters to achieve its optimum system configuration     

Prediction of Crosstalk in Ribbon Cables: Comparison of Model Predictions and Experimental Results

The prediction of crosstalk in ribbon cables is investigated. Experimental results are obtained for a 20-wire ribbon cable and compared to the predictions of the multiconductor transmission line (MTL) model. Based on the experimental configuration tested, it would appear that accurate predictions of crosstalk can be achieved in these controlled-characteristic cables. The prediction accuracies are typically within ±1 dB for frequencies such that the line is electrically short and ±6 dB for frequencies such that the line is electrically long. It was found that the parasitic wires in the cable can have a significant effect (as much as 40 dB) on the coupling between a generator circuit and a receptor circuit in the cable. Therefore, to achieve accurate predictions in ribbon cables, one must consider the interactions between all wires in the cable. The wire insulation evidently cannot be ignored for frequencies such that the line is electrically long. The impedance of the reference wire cannot be ignored for low frequencies where the common-impedance coupling dominates the electromagnetic-field coupling.     

Novel FEXT Cancellation and Equalization for High Speed Ethernet Transmission

In high-speed multi-pair wireline communication systems, such as 10 Gigabit Ethernet over Copper (10GBASE-T), far-end crosstalk (FEXT) becomes a major impairment and needs to be suppressed to increase data rates. Conventional techniques based on crosstalk cancellation are not suitable for FEXT due to the fact that the disturbing source of FEXT is generally unknown to the victims. This paper presents two different approaches to efficiently deal with FEXT over unshielded twisted-pair (UTP) copper cables. To eliminate the error propagation problem in practice, both approaches use the Tomlinson–Harashima Precoding (THP) technique which however makes the transceiver design nontrivial. In the first approach, FEXT is treated as noise and a new feedforward FEXT canceller is proposed. Compared with conventional techniques, the proposed FEXT canceller can mitigate the non-causal part of FEXT, thus leading to better FEXT cancellation performance. In the second approach, FEXT is treated as signal, and the general multi-input multi-output (MIMO) equalization technique is combined with the TH precoding technique to deal with both intersymbol interference (ISI) and FEXT. Different from the existing works, the proposed designs comply with the 10GBASE-T standard and they are suitable in real applications. Simulation results verify that the proposed approaches can achieve much better performance in terms of decision-point signal-to-noise ratio (DP-SNR) than conventional techniques. It is also shown that the hardware complexity of the transceiver can be reduced by about 37.2% by utilizing the increased DP-SNR in the proposed designs.      

Reduction of crosstalk noise in modular jack for high-speeddifferential signal interconnection

Crosstalk noise has become a significant problem in the design of high-speed digital interconnections. In this paper, we demonstrate a crosstalk reduction method, which has been successfully applied to the design of a CAT-5E modular jack. The CAT-5E is a newly adopted cabling and connector standard for advanced cabling network systems to assure more robust, reliable and high-speed operation, which is based on differential mode signal transmission using unshielded twist pair (UTP) cable. The improved design of the modular jack shows minimal crosstalk noise and return loss over a wide range of manufacturing conditions. The improved crosstalk characteristics of the modular jack were accomplished by inserting embedded capacitors on the printed circuit board (PCB) of the modular jack. The embedded capacitors compensate for the unbalanced capacitive crosstalk that occurs in the plug and insert. In particular, the embedded balancing capacitor is designed to have maximum capacitance, with limited PCB area, by using a double-sided PCB design. Less than -45 dB near-end-crosstalk (NEXT) was achieved after the crosstalk noise compensation, satisfying the CAT-5E specification for frequencies up to 100 MHz     

VLSI systems design of 51.84 Mb/s transceivers for ATM-LAN andbroadband access

We present: (1) system design issues for the implementation of 51.84 Mb/s ATM-LAN and broadband access transceivers and (2) a pipelined fractionally spaced linear equalizer (FSLE) architecture. Signal-to-noise ratio (SNR) and bit-error rate (BER) along with VLSI constraints are addressed. For the LAN environment, major channel impairments include near-end crosstalk (NEXT), intersymbol interference (ISI), and impulse noise. The broadband access environment suffers from far end crosstalk (FEXT), ISI, radio-frequency interference (RFI), impulse noise, and splitter losses. Measured characteristics of the channel are compared with analytical models. These are employed in the design of the transmitter/receiver algorithms. The carrierless amplitude/phase (CAP) transmission scheme is presented as a practical bandwidth-efficient scheme for these applications. An adaptive FSLE employed in a CAP receiver eliminates ISI, suppresses NEXT (for ATM-LAN) and FEXT (for broadband access), and provides robustness to timing jitter. However, fractional tap spacing in combination with the high-data rates results in a high sample rate adaptive computation. Fortunately, throughput enhancing methods such as pipelining can be used for high-speed/low-power operation. A hardware-efficient pipelined architecture for the adaptive FSLE equalizer is presented. This has been developed using relaxed look-ahead, which maintains the algorithm functionality rather than the input-output mapping. Simulation and experimental results for high-speed digital CAP transceivers for LAN and broadband access are also presented     

Analysis of Crosstalk Data for Maximizing PCM System Application

This paper addresses the general problem of estimating the maximum number of PCM systems allowed on one cable repeater section given representative PCM repeater characteristics and cable data. NEXT is analyzed, and a regenerative repeater is characterized by a graph of acceptable NEXT attenuation versus repeater section loss. Crosstalk data are utilized by statistical summation (convolution) using a flexible method based on cumulants (semi-invariants) which can deal with multiple subpopulations. An example calculation is given to illustrate the procedure for a simplified case. The relationship between the standard deviations for single frequency measurements and widebank crosstalk is discussed.     

A pipelined adaptive NEXT canceller

A near-end crosstalk (NEXT) canceller using a fine-grain pipelined architecture is presented. The performance of the proposed pipelined NEXT canceller is demonstrated in the 125 Mb/s twisted-pair distributed data interface and 155.52 Mb/s asynchronous transfer mode local area network applications. In addition, we analyze the computational complexity of the proposed pipelined NEXT canceller. It is shown that this architecture can be clocked at a rate that is 107 times faster than the serial architecture with a maximum loss of 2.0 dB in signal-to-noise ratio (SNR)     

100BASE-T2: a new standard for 100 Mb/s Ethernet transmission overvoice-grade cables

100BASE-T2 is a new physical-layer specification for IEEE 802.3 LANs operating at 100 Mb/s (“Fast Ethernet”). It enables users of the prevailing 10BASE-T Ethernet LAN technology to upgrade their networks from 10 to 100 Mb/s performance while retaining an existing voice-grade cabling infrastructure. 100BASE-T2 transceivers will operate over two pairs in unshielded twisted-pair cables corresponding to EIA/TIA category 3 (UTP-3), as minimally required for 10BASE-T. In a four-pair UTP-3 cable, simultaneous operation of two 100BASE-T2 links, or one 100BASE-T2 and one 10BASE-T link, is permitted. Since voice-grade cables exhibit more signal attenuation and significantly higher crosstalk coupling between adjacent pairs than data-grade cables, sophisticated digital signal processing techniques are needed to achieve reliable duplex 100 Mb/s transmission over two pairs. The 100BASE-T2 standard defines dual-duplex baseband transmission at a modulation rate of 25 Mbaud. During each modulation interval, a four-bit data nibble or Ethernet-specific control information is encoded into a pair of quinary signals. These signals are transmitted simultaneously on the two wire pairs in both signaling directions. In the receivers, adaptive digital filters are required for echo and NEXT cancellation, equalization, and interference suppression     

Binder MIMO Channels

This paper introduces a multiple-input multiple-output channel model for the characterization of a binder of telephone lines. This model is based on multiconductor transmission line theory, and uses parameters that can be obtained from electromagnetic theory or measured data. The model generates frequency-dependent channel/binder transfer function matrices as a function of cable type, geometric line-spacing and twist-length parameters, and source--load configurations. The model allows the extraction of the magnitude and the phase of individual near end crosstalk, far end crosstalk, split-pair, and phantom transfer functions from the transfer function matrix of the binder. These individual crosstalk transfer functions are often found to be very sensitive to small imperfections in the binder. Examples of category 3 twisted pair American telephone lines and ldquoquadrdquo telephone cables are also presented.     

Statistics of Impulsive Noise Crosstalk in Digital Line Systems on Multipair Cable

Crosstalk theory is applied to the prediction of error rates in digital line systems due to analog telephony signaling events on adjacent pairs in the same cable. Measurements of the margin against impulsive noise at a given probability of error have been performed, and these show reasonable agreement with predictions based on crosstalk theory. For a simple switching event, the regenerator NEXT impulsive noise figure for the near-end crosstalk path is defined. Measurements of the mean and variance of near-end crosstalk attenuation are then used to calculate the maximum exchange section loss (from central office to first line regenerator) which satisfies a suggested error performance criterion.     

网络线缆分析仪近端串扰的校准研究

针对网络线缆分析仪近端串扰的校准,提出了一种利用阻抗转换器和步进衰减器来解决网络线缆分析仪和矢量网络分析仪量值传递中的阻抗不匹配、连接端口不同的难题的方法,并给出了详细的阻抗转换器的设计制作原理图.通过实验数据和不确定度评定分析,证明了阻抗转换器和步进衰减器校准近端串扰的有效性、可行性,为网络线缆分析仪校准规范的实施和...