Very High Bit Rate Digital Subscriber Line Research Articles

Wi-Fi for Affordable Broadband & 5G in Rural Areas

The importance of Internet in our lives today cannot be overemphasized. So much so that access to Internet has been declared a fundamental right of citizens in several countries such as Finland, Spain, and Greece [1]. In most of the developed countries, high-speed Internet connectivity is enabled through wired communication infrastructure such as Fiber-to-the-Home (FTTH) and Very high bit-rate Digital Subscriber Line (VDSL). Unfortunately, the situation is not particularly encouraging in developing countries due to non-availability of such a pervasive communication infrastructure. The difference in the fiber-deployed-to-population ratio across developed and developing countries further underscores this disparity; while this ratio is 1.2 in USA, it is barely 0.1 in India [2]. Owing to this inadequacy of fiber/DSL availability, cellular access technology has emerged as the primary broadband access mechanism in developing countries.
 However, the penetration of cellular network is limited in rural areas as its deployment becomes unviable due to challenges such as low average revenue per user, sparse population density, and intermittent availability of electricity. This situation leaves majority of the rural people unconnected thereby creating a massive rural urban digital divide. The next generation cellular system along with the use of unlicensed Wi-Fi Technology can bridge this divide if we overcome the above-mentioned challenges. However, since the Fifth Generation (5G) cellular technology has focus on requirements such as 10 Gbps data rate, 1 ms latency, and very high speed mobility, the problems of coverage and affordability are likely to persist, further widening the digital divide [3]. This article explains how Wi-Fi is being used for affordable high speed broadband in rural areas. A successfully implemented case study of Jharkhand state is also presented, and it can be adopted as reliable business model for 5G or 5G type services in rural areas [4].

Physical IC Design Layout of Memory-Based Real Fast Fourier Transform Architecture using 90nm Technology

In this paper we present a low complexity physical IC layout for memory based Real Fast Fourier Transform (RFFT) architecture using 90nm technology. FFT architectures are the most important algorithms in the modern communication systems like and very high bit rate digital subscriber line (VDSL) asymmetric digital subscriber line (ADSL). In this FFT algorithm is based on radix-2 decimation-in-frequency. In order to meet the real time requirements of very large scale integration (VLSI), we designed a low complexity and high speed FFT architecture. The RFFT architecture was realised using Verilog hardware description language (HDL). This architecture is simulated using Native code launch of cadence and synthesized using RTL code complier of cadence tool. Each step of application specific integrated circuit (ASIC) physical IC design flow was synthesized using cadence Innovus 90nm technology and we optimize the design to reduce the area, power and timing requirements.

A low complexity based spectrum management algorithm for ‘Near–Far’ problem in VDSL environment

In digital subscriber line (DSL) system, crosstalk created by electromagnetic interference among twisted pairs degrades the system performance. Very high bit rate DSL (VDSL), utilizes higher bandwidth of copper cable for data transmission. During upstream transmission, a ‘Near–Far’ problem occurs in VDSL system. In this problem the far end crosstalk (FEXT) is produced from near end user degrades the data rate achieved at the far end user. The effect of FEXT can be reduced by properly managing power spectral densities (PSD) of transmitters of near and far users. This kind of power allocation is called dynamic spectrum management (DSM). In this paper, a new distributed DSM algorithm is proposed in which power from only those sub channels of near end user are reduced which create interference to far end user. This power back off strategy takes place with the help of power spectral density (PSD) masks at interference creating sub channels of near end user. The simulation results of the proposed algorithm show an improvement in terms of data rate and approaches near to that of optimal spectrum balancing (OSB) algorithm.

A Modified Low Complexity Based Distributed Iterative Water-Filling (IWF) Spectrum Management Algorithm

In digital subscriber line (DSL) system, crosstalk created by electromagnetic interference among twisted pairs degrades the system performance. Very high bit rate DSL (VDSL), utilizes higher bandwidth of copper cable for data transmission. In upstream data transmission, a `Near---Far' problem occurs in VDSL system. In this problem the far end crosstalk is produced from near end user degrades the data rate achieved at the far end user. Several dynamic spectrum management (DSM) algorithms were proposed in literature to remove this problem. In this paper, a new distributed DSM algorithm is proposed in which power from only those subcarriers of near end user are reduced which create interference to far end user. This power back off strategy takes place with the help of power spectral density masks at those interference creating subcarriers of near end user. The results after simulating the low complex proposed algorithm show an improvement in terms of data rate and approaches near the rate of highly complex optimal spectrum balancing algorithm.

Bit Swap Established on EOC for VDSL

With the rapid development of VDSL (Very high-bit-rate Digital Subscriber Line) system, not all the tones have the same margin. In order to cope with the slowly-changing channel, Bit Swap is utilized to swap the tone pairs: the one has a high margin while the other one has a relatively low margin. Although the Bit Swap has been proposed before, there is no Bit Swap established on EOC and the proposed scheme also implements coarse and fine SNR margin tuning. The paper presents the architecture and process of Bit Swap based on EOC and also proposes the method to adjust the margin for tones calculated to be swapped. After thoroughly tested, the test results show that the proposed scheme functions well. Compared with the scheme without Bit Swap, it greatly improves the performance against crosstalk noise and can reduce the RS errors to zero.

Cross QAM의 선택적 성좌점을 사용하는 EVM 기반 SNR 추정 성능

본 논문에서는 ADSL, VDSL, DVB-C 등의 통신 시스템에 적용되고 있고, 적응변조나 blind equalization에서 유용하게 사용될 수 있는 Cross QAM의 SNR 추정 성능에 대해 분석하였다. 우선 레일리 페이딩 채널에서의 Cross QAM의 심볼에러율을 분석하였다. 그리고, Cross QAM의 성좌점에 대한 판정영역 특성에 착안하여, 성좌 점별로 EVM 기반의 SNR 추정기법을 사용하는 것을 제안하고, 성좌점별로 SNR 추정성능이 다르게 나타남을 시뮬레이션을 통해 확인하였다. 시뮬레이션 결과로부터 Cross QAM에서 SNR 추정에 사용하는 성좌점을 선택적으로 사용하면, AWGN 채널이나 라이시안 페이딩 채널에서 추정성능을 개선할 수 있음을 확인하였다. In this paper, we investigate the signal to noise ratio (SNR) estimation performance of Cross quadrature amplitude modulation (QAM), which is being used for asymmetric digital subscriber line (ADSL), very high bit rate digital subscriber line (VDSL), and digital video broadcasting - cable (DVB-C), and has been found to be useful in adaptive modulation and blind equalization. At first, the symbol error rate (SER) performance of Cross QAM is analyzed in Rayleigh fading channel. Then we suggest error vector magnitude (EVM) based SNR estimation utilizing the selected constellation points having different types of decision region from one another, and verify that SNR estimation performance of each points have different performance pattern through simulation. From the simulation results, it has been found that when suggested selected constellation points are used for SNR estimation in Cross QAM, estimation performance is enhanced in additive white Gaussian noise (AWGN) channel or Ricean fading channel.

Distributed Crosstalk Management for Upstream VDSL Using Dynamic Power Control

The severe interference from neighbor copper lines, commonly known as crosstalk, is a well-known limitation that can reduce the upstream rate of a victim user by 50% or more in dense VDSL (Very high bit-rate Digital Subscriber Lines) deployment. This problem has been partially addressed by the use of UPBO (Upstream Power BackOff). UPBO blindly controls transmit PSD (Power Spectral Densities) based on the pre-defined parameters and channel measurements without considering each user's target data rate. Although UPBO can provide fair protection against crosstalk, it still leaves room for practical improvement. This paper proposes a distributed algorithm that dynamically controls transmit power according to each line's need and capacity. The algorithm effectively improves data rates and line reaches in real VDSL deployment.

Quality-of-service-based interference cancellation in upstream very-high-bit-rate digital subscriber line systems

Crosstalk (XT) is the main performance limiter in digital subscriber line (DSL) systems such as very-high-bit-rate digital subscriber line (VDSL) systems. In order to overcome these limitations various XT cancellation techniques have been proposed to mitigate this effect. While leading to very high performance gains, the computational complexity grows quadratically with the number of lines in a binder. This motivates partial cancellation schemes, maximising the capacity based on a given computational complexity. However, the data rate increase could still be very high above the quality of service (QoS) requirements that must be enforced for each user, leading to a ‘waste’ of computational resources. Therefore a QoS-based partial cancellation algorithm is presented in this study which selects the lines to be cancelled based on the desired data rates of the users. It relies on partial zero-forcing XT cancellation but the used selection algorithm [QoS-based joint tone-line selection (QoS-JTLS)] aims at QoS fulfilment instead of data rate maximisation. Simulation results show that compared with other QoS-based algorithms and conventional selection algorithms, QoS-JTLS leads to better fulfilment of QoS demands for the same given computational complexity. In other words, the computational complexity needed to achieve the target data rates of the users is reduced when applying QoS-JTLS.

Investigation of Upstream Near-Far Problem in VDSL Systems via Complete Adaptive Iterative Water Filling Algorithm

Crosstalk is the main degrading factor in Digital Subscriber Line (DSL) systems which are the result of electromagnetic coupling between two adjacent twisted pairs in a cable. Very-high bit-rate Digital Subscriber Line (VDSL) systems which use higher frequencies for data transmission than the other DSL systems, this effect is more considerable in Bit Error Rate (BER) degradation. This paper considers a complete adaptive iterative water-filling (IWF) algorithm for Resolving Upstream Near-Far Problem in VDSL Systems. The new distributed dynamic spectrum management algorithm is proposed, which improve achievable bit rate of iterative water-filling algorithm. The paper proffers a new power back-off strategy of the spectral mask at the near-end users, in order to protect the far-end users. Simulation of the proposed algorithm indicates that the bit rate is increased considerably rather the IWF and adaptive water-filling (AIWF) algorithms by keeping their low complexity. Furthermore, by adding the number of users in network, the new algorithm achieves performance gains over the AIWF, completely adaptive.

A/D Conversion Using Asynchronous Delta-Sigma Modulation and Time-to-Digital Conversion

An analog-to-digital conversion (ADC) scheme based on asynchronous ΔΣ modulation and time-to-digital conversion is presented. An asynchronous ΔΣ modulator translates the analog input to an asynchronous duty-cycle modulated signal. Next, the edge locations are digitally measured using a time-to-digital converter (TDC). This information is then digitally processed into a conventional digital signal. The performance of this novel ADC scheme is theoretically analyzed and verified with simulations. With the proposed digital demodulation algorithm, 11-bit resolution can be obtained with an overcycling ratio (OCR) of only four, which is suitable for high bandwidth applications such as very high bit-rate digital subscriber line (VDSL). When a higher OCR can be tolerated, a gated ring-oscillator (GRO) TDC with an inherent first-order noise shaping property is suggested in combination with a digital continuous-time moving-average (CTMA) filter. This allows for resolutions in excess of 13 bits, which is suitable for ADSL2+. The proposed technique shifts the complexity toward the digital domain, leading to more compact ADC and reduced power consumption, and is, therefore, particularly suited for ADC in ultralow-voltage nanometer technologies that are used for high-speed data communication applications.

Adaptive Precoding for Downstream Crosstalk Precancelation in DSL Systems Using Sign-Error Feedback

The performance of many very high bit rate digital subscriber line (VDSL) systems is limited by the effects of crosstalk among the wires in a bundle. For the downstream, a precoder can compensate for this, provided that some crosstalk channel information is available at the transmitter. In this paper, we investigate the issue of precoder design based on a particular type of feedback: it is assumed that each receiver sends back the (complex) sign of the noise on the symbol detection as a way to provide the needed information on crosstalk channels. We derive an algorithm that makes use of this limited information in an adaptive way to iteratively compute the precoder. The performance of the proposed algorithm is extensively analyzed, both with theoretical evaluations and simulation results. The algorithm is also compared to other solutions, showing the efficient performance for the limited amount of overhead it requires.

Computationally efficient joint partial crosstalk cancellation and multi‐user power control algorithm in xDSL networks

AbstractFar‐end crosstalk (FEXT) is the major limitation to achieve high data rates in very high bit rate digital subscriber line (VDSL) systems. Full crosstalk cancellation (FCC) techniques have been proposed to mitigate the effect of crosstalk. However, these are too complex for application in typical VDSL binders. Considering the fact that there are only a few strongest cross‐talkers that contribute to main part of crosstalk, the crosstalk cancellation can be simplified to line selection (LS), tone selection (TS) and joint line‐tone selection (JLTS) partial crosstalk cancellation (PCC). These all result in much less online complexity. In this paper, first, we propose a new modified JLTS algorithm with significantly lower initialisation complexity than the optimal JLTS (OJLTS) algorithm and approximately with similar performance. Then a novel joint algorithm is presented that combines the multi‐user power control technique with the PCC scheme to achieve near the capacity rates. We also consider dynamic online complexity constraint for each user. This joint algorithm leads to a much larger online complexity reduction (around 60% for long lines) and higher data rates at the expense of slightly higher initialisation complexity. The performance of the proposed algorithm is verified by some simulation results and compared with current algorithms that use flat power spectral densities (PSDs) and other existing joint algorithms. Copyright © 2009 John Wiley & Sons, Ltd.

A Bandwidth Efficient Turbo Coding Scheme for VDSL Systems

The current forward error correction (FEC) scheme for very high bit-rate digital subscriber line (VDSL) systems in the ANSI standard employs a 16-state four-dimensional (4D) Wei code as the inner code and the Reed-Solomon (RS) code as the outer code. The major drawback of this scheme is that further improvement cannot be achieved without a substantial increase in the complexity and power penalty. Also, a VDSL system employing the 4D Wei-RS scheme operates far below the channel capacity. In 1993, powerful turbo codes were introduced whose performance closely approaches the Shannon limit. In this paper, we propose a bandwidth and power efficient turbo coding scheme for VDSL modems in order to obtain high data rates, extended loop reach and increased transmission robustness. We also propose a pipelined decoding scheme to reduce the latency at the receiver end. The objective of the proposed scheme is to provide a higher coding gain than that given by the 4D Wei-RS scheme, resulting in an improved performance of the VDSL modems in terms of bit rate, loop length and transmitting power. The scheme is investigated for various values of transmitting power, signaling frequencies and numbers of crosstalkers for a targeted bit error rate of 10−5 and is implemented in a system with a quadrature amplitude modulation in which a mixed set partitioning mapping is employed to reduce the decoding complexity. The effects of code complexity, interleaver length, the number of decoding iterations and the level of modulation on the performance of VDSL modems are explored. Simulation results are presented and compared to those of the 4D Wei-RS scheme. The results show that the choice of turbo codes not only provides a significant coding gain over the standard FEC scheme but also efficiently maximizes the loop length and bit rate at a very low transmitting power in the presence of dominant far-end crosstalk and intersymbol interference. In order to compare the hardware complexity, we synthesize the proposed and 4D Wei-RS schemes using SYNOPSYS with the target technology of Xilinx 4020e-3. The Xilinx field programmable gate array statistics of the proposed scheme is compared with that of the 4D Wei-RS scheme.

A Low Complexity Linear Precoding Technique for Next Generation VDSL Downstream Transmission Over Copper

In this paper, we study a simplified linear precoding scheme for far-end crosstalk (FEXT) cancellation in very high bit-rate digital subscriber line (VDSL) downstream transmission. We compare the proposed method to zero-forcing (ZF) FEXT cancellation and show that for multipair VDSL systems the method achieves rates that are close to the ZF precoding method. We also derive simple lower bounds on the performance that allows us to predict the performance of the proposed algorithm on each tone. We end up with testing the proposed method on theoretical and empirical channels. This is the first extensive study of VDSL precoding on measured channel data. The proposed method is less complex than ZF precoding and, therefore, alleviates the computational load at the initialization and tracking of precoded VDSL or VDSL2 systems. Finally, we discuss implementation complexity in terms of total Silicon area and show that the method has favorable implementation complexity, since only channel coefficients need to be stored during steady-state transmission.

Distributed Dynamic Spectrum Management for Digital Subscriber Lines

This paper investigates the dynamic spectrum management problem for digital subscriber lines. Two new distributed dynamic spectrum management algorithms, which improve upon the existing iterative water-filling algorithm, are proposed. Unlike the iterative water-filling algorithm, in which crosstalk interference is reduced by using adaptive power backoff, the new algorithms employ full power and mitigate crosstalk interference by shifting one user's spectrum away from the other's. Simulation results show that the new algorithms achieve significant performance gains over the iterative water-filling algorithm in mixed central office/remote terminal (CO/RT) deployment asymmetric digital subscriber line (ADSL) and upstream very-high bit-rate digital subscriber line (VDSL).

Transmit beamforming for physical-layer multicasting

This paper considers the problem of downlink transmit beamforming for wireless transmission and downstream precoding for digital subscriber wireline transmission, in the context of common information broadcasting or multicasting applications wherein channel state information (CSI) is available at the transmitter. Unlike the usual blind isotropic broadcasting scenario, the availability of CSI allows transmit optimization. A minimum transmission power criterion is adopted, subject to prescribed minimum received signal-to-noise ratios (SNRs) at each of the intended receivers. A related max-min SNR fair problem formulation is also considered subject to a transmitted power constraint. It is proven that both problems are NP-hard; however, suitable reformulation allows the successful application of semidefinite relaxation (SDR) techniques. SDR yields an approximate solution plus a bound on the optimum value of the associated cost/reward. SDR is motivated from a Lagrangian duality perspective, and its performance is assessed via pertinent simulations for the case of Rayleigh fading wireless channels. We find that SDR typically yields solutions that are within 3-4 dB of the optimum, which is often good enough in practice. In several scenarios, SDR generates exact solutions that meet the associated bound on the optimum value. This is illustrated using measured very-high-bit-rate Digital Subscriber line (VDSL) channel data, and far-field beamforming for a uniform linear transmit antenna array.

Combined per tone equalization and receiver windowing in DSL receivers: WiPTEQ

In this report, a novel technique is described for the combination of per-tone equalization (PTEQ) with receiver windowing. The PTEQ is an equalization technique for discrete multitone modulation (DMT) based modems, such as asymmetric digital subscriber line (ADSL) modems and very high bitrate digital subscriber line (VDSL) modems, optimizing the SNR (and thus capacity) of each carrier separately. Windowing functions are very useful in multitone communications systems, to prevent a narrow band noise source from causing wide band interference. Combining both techniques in a windowed PTEQ (referred to as WiPTEQ) leads to a robust communication system. The described technique is especially useful in case of a trapezoidal or raised cosine window, and when the window taper length is large compared to the number of equalizer filter taps.

Digital RFI Suppression in DMT-Based VDSL Systems

We propose a method for suppressing radio frequency interference (RFI) in discrete multitone (DMT) based very high bit rate digital subscriber line (VDSL) systems. The method operates in the frequency domain of a DMT system. First, we derive a model of how an unknown narrow-band RF signal is mapped onto the DMT carriers. Then, by measuring the RFI on a few unused DMT carriers we are able to subtract RFI estimates from every modulated subcarrier. Simulation results show that this method, applied to an RFI signal with the same average power as the VDSL signal, suppresses the RFI with 40-50 dB, which reduces the average SNR loss from about 20 to less than 0.3 dB.

Partial crosstalk precompensation in downstream VDSL

Very high bit-rate digital subscriber line (VDSL) is the latest generation in the ongoing evolution of DSL standards. VDSL aims at bringing truly broadband access, greater than 52 Mbps in the downstream, to the mass consumer market. This is achieved by transmitting in frequencies up to 12 MHz. Operating at such high frequencies gives rise to crosstalk between the DSL systems in a binder, limiting achievable data-rates. Crosstalk is typically 10–15 dB larger than other noise sources and is the primary limitation on performance in VDSL. In downstream transmission several crosstalk precompensation schemes have been proposed to address this issue. Whilst these schemes lead to large performance gains, they also have extremely high complexities, beyond the scope of current implementation. In this paper we develop the concept of partial crosstalk precompensation. The majority of the crosstalk experienced in a DSL system comes from only a few other lines within the binder. Furthermore its effects are limited to a small subset of tones. Partial precompensation exploits this by limiting precompensation to the tones and lines where it gives maximum benefit. As a result, these schemes achieve the majority of the gains of full crosstalk precompensation at a fraction of the run-time complexity. In this paper we develop several partial precompensation schemes. We show that with only 20% of the run-time complexity of full precompensation it is possible to achieve 80% of the performance gains.

객체지향 모델링을 이용한 케이블 데이터 가입자 망관리 시스템의 설계 및 구현

가입자 망에는 ADSL(Asymmetric Digital Subscriber Line), VDSL(Very high-bit rate Digital Subscriber Line), DOCSIS(Data Over Cable Service Interface Specifications) 등이 있으며, 다양한 형태가 있다. 다양한 종류의 접속방식과 이 기종의 장비를 이용하여 가입자에게 단일 형태의 초고속 인터넷 서비스를 제공하고 있다. 이러한 여러 가지 분산된 가입자 망을 효율적으로 관리하기 위해서는 다양한 형태의 접속방식을 지원하는 이 기종 장비 및 단말들의 상위 개념으로서 추상적이며 개념적인 객체 관리모델이 필요하다. 본 논문은 통합된 계층적 망 관리를 가능하게 하는 인터넷 가입자 망에 대한 모델링 구조를 RM-ODP를 이용하여 제시하였다. 그리고 가입자 망의 예로서 UML을 이용한 객체지향 방법론을 채택하여 DOCSIS의 HFC 가입자망에 대한 관리 시스템을 설계하고 구현하였다. There exist several types of distributed subscriber networks using Asymmetric Digital Subscriber Line(ADSL), Very high -bit rate Digital subscriber Line(VDSL), and Data Oner Cable Service Interface Specifications(DOCSIS). The efficient and concentrated network management of those several distributed subscribers networks and resources requires the general management information model of network, which has abstract and conceptual managed objects of the heterogeneous networks and its equipment to manage the integrated subscriber network. This paper presents the general Internet subscribers network modeling framework using RM-ODP to manage that network in the form of integrated hierarchy. This paper adopts the object-oriented development methodology with UML and designs and implements the HFC network of DOCSIS as an example of the subscriber network.