Developing Automated Test System for ADSL Equipment

In this paper the general ADSL (asymmetric digital subscriber line) noise environment is reviewed in the context of the telephone loop plant. Special attention is given to the unique unidirectional transmission nature of ADSL. A set of noise environments is presented for related computer simulation studies and hardware tests. A set of mid-CSA test loops is also proposed for performance evaluation under conditions of T1 NEXT interference. To simplify calibration procedures, noise and loop models are revealed in FIR (finite impulse response) filter form and can be measured in dB loss or dBm/Hz power density terms. A subchannel signal to noise ratio (SNR) based computer simulation method is then used to estimate potential ADSL performance under different noise environments for different serving areas. >

This paper presents the design and implementation of novel decimation filter structure for high speed asymmetric digital subscriber line (ADSL). Existing ADSL circuits use comb-FIR-FIR decimation filter structures, which have low throughput, more hardware and high power consumption. Unlike existing ADSL circuits, we design a novel high speed filter architecture and implement it using the minimal signed digit (MSD) representation. The MSD representation is suitable for common subexpression elimination, and it significantly reduces the number of adders required for the filter synthesis. Each digital-filter structure is simulated using Matlab, and its complete architecture is captured using DSP Blockset and Simulink. The resulting filter architecture has higher throughput, less hardware and consumes less power than the comb-FIR-FIR and comb-IIR-FIR architectures. The filter has been implemented on Xilinx FPGA using Virtex-2 technology. Compared to the comb-FIR-FIR and the comb-IIR-FIR architectures, the designed decimation filter architecture contributes to a hardware saving of 82% and 74%, respectively; in addition, it reduces the power dissipation by 91% and 79%, respectively.

Multidimensional TCM schemes can be used to improve the performance of the asymmetrical digital subscriber line (ADSL). The operating principle of how M-D (multidimensional) TCM works in an ADSL channel is analysed and criteria for evaluating and choosing effective multidimensional TCM schemes are described. The results of a simulation for evaluating the performance is presented.

ADSL (Asymmetric Digital Subscriber Line) adopts modulation scheme called DMT (Discrete multi tone), a multi carrier system. The process of allocating bits into various sub-channels is called bit-loading. In this paper, a new bit-loading algorithm that reduces the power required to transmit data is proposed. Comparison on power cut back with other algorithms is presented. Also the implementation of the algorithm in the transmitter is discussed. A Matlab simulation model has been developed to simulate ADSL transmitter (with bit-loading), channel and receiver. The ADSL system with bit-loading algorithm is also implemented in hardware using TT's DSK6713 kit and comparison of software and hardware results are tabulated.

The purpose of the paper is to describe a model that has been developed to predict the undesired coupled voltage at the network interface of the customer premises, caused by an ambient electric field incident on the drop wire. The model considered the effects of ground reflection, angle of incidence of the incoming wave on the plane of the drop wire, and the coupling caused by common-mode induced voltage due to network unbalance. The model has been simulated and verified in experiments at Bellcore's Chester facilities. The predicted results have also been compared with the measurements taken during surveys in different parts of the country that measured the coupled voltages at the network interface caused by high-power transmitters (that is, LORAN-C). The measured results show good agreement with those predicted by the model. The model is used to study electromagnetic interference at the asymmetric digital subscriber line (ADSL) transceiver caused by coupled voltage at the customer premises. >

Echo cancellation technique enables full duplex transmission using the same transmission band and thereby increases the aggregate data throughput of a channel. This tutorial paper introduces high speed echo cancellation for Full Rate (ITU-T Recommendation G.992.1) and Splitterless (ITU-T Recommendation G.992.2, aliased G.Lite) ADSL Transceivers. Symmetric and multirate Asymmetric echo cancellation Transceiver structures based completely on time domain or frequency domain as well as both time and frequency domain echo cancellation have been analyzed using different algorithms for performance and computational complexity. Combined Time and Frequency Domain Echo Cancellation (TAFDEC) structure with the so called DMT algorithm appears to be most suitable to achieve lower complexity with better performance as compared to echo cancellation in either time or frequency domain using LMS algorithm.

The discrete multitone (DMT) modulation/demodulation scheme is the standard transmission technique in the application of asymmetric digital subscriber lines (ADSL) and very-high-speed digital subsc...

The steadily growing deployment of resilience-critical Internet services is leading to an increasing number of Multi-Homed network sites. Asymmetric Digital Subscriber Lines (ADSL) are an inexpensive way to add a secondary Internet access connection. With the development of Multi-Path Transport Layer protocols - like Multipath TCP (MPTCP) and the Stream Control Transmission Protocol (SCTP) furnished by a Concurrent Multipath Transfer (CMT-SCTP) extension - there is also a strong interest in utilising all access connections simultaneously to improve the data throughput of the applications. However, combining network paths over ADSL with paths over other access technologies like fibre optic links implies highly dissimilar paths with significantly different bandwidths, delays and queuing behaviours. Efficient Multi-Path transport over such dissimilar paths is a challenging task for the new Transport Layer protocols under development. In this paper, we show the difficulties of Multi-Path transport in a real-world dissimilar path setup which consists of a high-speed fibre optic link and an ADSL connection. After that, we present an optimised buffer handling technique which solves the transport efficiency issues in this setup. Our optimisation is first analysed by simulations. Finally, we also show the usefulness of our approach by experimental evaluation in a real Multi-Homed Internet setup.

The design and optimization of the high-speed digital subscriber line (HDSL) need powerful computational strategies. Traditional techniques of distributing poles and zeros on Smith charts generally do not work. In the past, such approaches have lead to suboptimal designs for applications where the data capacity sought is considerably less than the Shannon capacity of the lines. Typical subscriber loops are less than perfect and for the current demands on the HDSL at T1/T2 and El rates every possible venue for the HDSL design needs to be investigated, if not exploited. In this Chapter, flexible computational techniques are presented that explore and optimize system components in view of the operating environment of the HDSL and/or the asymmetric digital subscriber line (ADSL) and inherent limitations of system components. The optimization occurs automatically by forcing the computer to track the effects of incremental changes of the subsystem performance (e.g., echo cancelers or equalizers), or the component values (Rs and Cs in the matching circuits) in context to the functional constraints of the (HDSL, ADSL, duplex, dual-duplex, triplex, etc.) line in conjunction with various subscriber loop environments (CSA loops, loops <18 kft., American, Australian, European, ANSI, ETSI, etc.)

Modern digital arrays radars (DAR) contain a large number of T/R modules. T/R module system is a critical part of digital array radar. It is necessary to test T/R module strictly before it is set up into the DAR. In practice, manual testing the T/R module with high performance is a complex and hard work, which for the difficulties of heavy test task and complex operations. In order to realize the automatic test of the active T/R modules, the advanced modern automatic test system (ATS) is built based on GPIB bus. The composition and the operation principle of the digital T/R module are introduced and the design of the hardware platform and software system is discussed. The high power measurement in transmitter and broadband data processing in receiver is researched. The timing control design is also introduced. Compared with manual test, the system is applied successfully shortens the test time to 1.5 hour from the manual 48 hours and the consistency of amplitude and phase between receiving channels is calculated automatically. The results showed the ATS can enhance the data processing speed and increase the testing efficiency of T/R module test.

The complexity of electronic-device testing varies widely, ranging from the simplest type manual testing to the most complex Automatic Test Equipment (ATE). Presently power controllers for electrostatic precipitator at industry are tested using simulators at the E-shop and controller development lab. The simulated inputs and outputs are generated manually through mechanical keys and push button switches. The verification process and documentation are also done manually and hence time consuming. To overcome these disadvantages, an intelligent, multipurpose simulator cum test equipment was proposed. ATE was developed using LPC2378 ARM processor with required input and output channels. The ATE has multiple communication interfaces like RS485, RS 232, CAN and Ethernet. It is also provided with Liquid Crystal Display (LCD), keypad and Local Area Network (LAN) communication. ATE completes the testing of controller without any manual intervention. Upon completion of testing, ATE sends out test reports to any computer connected to its LAN Port. The test report is generated in the form of Hyper Text Markup Language(HTML) pages with time stamping and controller particulars.

Telepathology began in Japan in the early 1990s in response to advances in computing and telecommunications equipment development and a dearth of pathologists. Telepathology in Japan is most often used for rapid intraoperative pathological diagnosis using frozen section, followed by second opinions and consultation. Intraoperatively, telepathology is used to determine malignancy, metastasis of malignant tumors, and the extent of excision. Infrastructure and equipment has evolved from analog lines to digital lines like integrated services digital network (ISDN) and asymmetric digital subscriber line (ADSL), and recently to fiber optics. The use of communications satellites is also being considered. Image quality is being improved to Hi-Vision (HDTV), and from still images to real-time video. Digital microscopy has been introduced, and is used in education and consultation.

This paper seeks to provide the concept of multimedia transmission across asymmetrical digital subscriber line (ADSL). After a brief overview of ADSL characteristics, we deal with multimedia service delivery including broadband Internet access. An example concerning Bosnia and Hercegovina is given, too.

Channel shortening filter, also known as time domain equalizer (TEQ), is generally used to reduce the effective length of a long multipath channel. This has the potential to reduce the cyclic prefix in a multitone based communication system such as asymmetric digital subscriber line (ADSL). The performance of a TEQ could however degrade considerably in the presence of channel estimation error, and we provide a robust channel shortening filter design incorporating worst case error scenario. We looked at channel estimation error in the presence of Gaussian and impulsive noise, and demonstrated superior performance of the proposed robust scheme.

In an asymmetrical speed channel environment like asymmetric digital subscriber line, the up-link bandwidth is normally smaller than the down-link bandwidth, which will lead to extremely low utilization of down-link bandwidth when current P2P video transmission is applied. To overcome this, a new fast P2P video transmission method applied in an asymmetrical speed channel environment is proposed in this paper. On the basis of the many-to-one concept, the proposed method uses a new multi-peer aggregation technique to enhance the utilization of down-link bandwidth. In addition, an adaptive peer assignment algorithm is also introduced in order to minimize the overall transmission time. Experimental results show that by using our proposed method, the utilization of down-link bandwidth is significantly improved, and the overall transmission time is greatly reduced.