Measurement And Modeling Of Short Copper Cables For Ultra-wideband Communication

High-speed communication using the copper network, originally installed for telephony, is one of the dominant Internet access techniques. Several variants of a technology referred to as digital subscriber line (DSL) have been developed, standardized and installed during the last two decades. Essentially, DSL achieves high rates by exploiting wide bands of the copper cable channel. The shorter the cable, the wider the band that can be used efficiently for communication. Current DSL standards foresee the use of bands up to 30MHz. Cable properties have been studied by means of measurements, characterization and modeling up to frequencies of 30MHz. Recent investigations have shown that it is feasible both from technical and from economical point of view to exploit very short cables (up to 200m) even further and use bands above 30MHz. A prerequisite for further evaluation and the design of such ultra-wideband copper (UWBC) systems is the extension of existing cable models to higher frequencies. This paper presents wideband measurement results of insertion loss and crosstalk coupling in a 10-pair cable of various length values for frequencies up to 200MHz. 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Longitudinal Signals in DSL

The purpose of this contribution is twofold. First, we revisit the longitudinal component (also referred to as common-mode component, asymmetric component or antenna-mode component) occurring at the receive side of a twisted-pair loop. Second, we propose a simple setup for RFI tests that captures reality more accurately than performing differential-mode and common-mode tests separately. In essence, we agree with and support the test environments proposed in [1][2][3]. We stress the fact that differential-mode and common-mode signals should be generated jointly in order to account for their correlation

An approach to analog mitigation of RFI

Among all noise sources present in wireline transmission systems we focus on one special type: narrowband radio frequency interference generated by radio amateurs (HAM) and broadcast radio stations. This disturbance, characterized by high power and narrow bandwidth, has the potential of overloading the receiver's analog-to-digital converter (ADC). Once the ADC is in saturation, any countermeasure taken in digital domain will fail. A viable way to face this problem is cancellation using the common-mode signal as a reference. This paper describes in detail an adaptive, mixed-signal, narrowband interference canceller employing a modified recursive least-squares algorithm, which is split into an analog and a digital part. The mixed-signal approach enables the circuit to generate an interference-cancelling signal of several MHz while operating the adaptive algorithm at some kilohertz. Simulation as well as measurement results show a steady-state disturbance suppression of about 35 dB. The convergence speed is high enough to protect the ADC from overloading due to time-variant HAM interference

Splitting the Recursive Least-Squares Algorithm

Exponentially weighted recursive least-squares (RLS) algorithms are commonly used for fast adaptation. In many cases the input signals are continuous-time. Either a fully analog implementation of the RLS algorithm is applied or the input data are sampled by analog-to-digital (AD) converters to be processed digitally. Although a digital realization is usually the preferred choice, it becomes unfeasible for high-frequency input signals since fast AD converters are needed. This paper proposes a hybrid analog/digital approach essentially allowing the AD conversion rate to be as low as the update-rate of the RLS algorithm. This is basically accomplished by sampling exponentially weighted correlation products instead of the input signals. Furthermore, we propose a mixed-signal filter exactly realizing the exponential weighting according to the cost function. Applying this approach to an interference cancelling problem demonstrates its performance and attractiveness regarding implementation

An Adaptive Mixed-Signal Narrowband Interference Canceller For Wireline Transmission Systems

Narrowband radio transmitters like radio amateurs and broadcast radio stations are considered to be a serious problem for highbitrate data transmission over twisted pairs. Due to its high power level, radio frequency interference (RFI) has the potential of overloading the receiver's analog-to-digital converter (ADC). Once the ADC is in saturation, any countermeasure taken in digital domain will fail, so the problem has to be faced at least partly in the analog domain. This paper proposes an adaptive, mixed-signal, narrowband interference canceller employing a modified recursive leastsquares (RLS) algorithm which is split into an analog and a digital part. The mixed-signal approach enables the circuit to generate an interference-cancelling signal of several MHz while operating the adaptive algorithm at some kHz. The structure is fast enough to prevent the ADC from overloading due to radio amateur interference, thus protecting the data transmission from interruption. Simulation results as well as measurements indicate a practical disturbance rejection potential of about dB. 1

On the Capacity of the Copper Cable Channel Using the Common Mode

The common-mode (CM) signal in wireline transmission systems has proven to provide valuable information exploited for mitigating narrowband noise at the receive side. We focus on the case of broadband noise. Treating the CM signal as an additional receive signal, we investigate the capacity of the copper cable channel for different levels of coordination among the users. We introduce a channel model which includes the common-mode paths and derive a suitable form of the channel capacity formula. CM crosstalk measurement results, essential for evaluation of the channel capacity, are presented. Using the measurement data, exemplary results of capacity gain achievable by CM-aided data transmission over the copper cable are shown