基于MIMO信道的DSL传输模式研究

DSL技术是当前主流的宽带接入技术,串音干扰是制约DSL系统传输性能的重要因素。提出一种利用MIMO技术降低DSL系统中串音干扰的方法。在分析串扰对线路影响的基础上,建立了基于离散多音调制下的MIMO信道模型,应用奇异值分解法消除串扰,采用注水算法解决了MIMO-DSL信道的功率分配问题。Matlab仿真结果表明,其速率可以达到non-MIMO信道的1.5倍,有效降低了DSL系统串音干扰的影响。     

过采样CPM信号的频域均衡

提出了一种直接对过采样的连续相位调制(CPM)信号进行单载波频域均衡的算法,同时提出了一种在插入循环前缀后发送CPM信号的相位仍然连续的方法。仿真结果表明,该单载波频域均衡算法能有效地消除大时延信道冲击响应下的CPM接收信号中的码间串扰。与现有的基于匹配滤波、符号抽样的CPM信号的单载波频域均衡算法相比,其性能和复杂度相当,但是CPM接收机的前端更为简单。     

一种应用于MRC pre/post-rake的抗抽头串扰算法

新兴的Pre／post-rake技术和传统rake接收机技术相比,在提高了输出信噪比的同时,也引入了更强的抽头串扰,并且该串扰在普遍的情况下将严重制约pre／post-rake的性能。为了有效地消除抽头串扰对接收性能的影响,文中提出了应用于pre／post-rake技术的抗抽头串扰算法,将该算法和MRC pre／post-rake技术相结合,通过理论计算和通过MATLAB仿真。在不影响其它性能的同时,使MRC pre／post-rake获得了更好的抗抽头串扰能力,从而提高了pre／post-rake的接收性能。     

片上网络中降低信号串扰的方法

NOC（片上网络）的体系结构解决了SOC（片上系统）在大规模集成IP核时面临的一些难题,但其串扰问题对电路性能的影响也越来越明显。基于DSM（深亚微米）下的总线模型,分析了信号串扰引起的总线延时问题,同时比较了3种减小总线串扰的编码方案。并采用0．13μmCMOS工艺对性能较优的DAP编码方案进行了电路仿真,得到了不同长度和宽度下的总线延时。结果表明,采用减少信号串扰的编码方法可以有效地降低总线的串扰,减少信号延时,这一效果当总线较宽或走线较长时尤其明显,同时也证明了0．13μmCMOS工艺下电路仿真结果与理论计算结果的一致性。     

扩展Benes光交换结构消除串扰路由算法

详细分析了扩展的Benes(DB)型光交换结构串扰特性,重点研究了一种改进扩展Benes结构(MDB)。从DB型光交换结构出发,提出了传输矩阵和结构矩阵的概念。通过本算法,选择合适光交换网络路由方式实现消除带内串扰。通过本算法可以完全消除MDB带内串扰,同时也可以大大降低一般DB光交换结构的带内串扰。     

一种基于CMA的变步长盲均衡算法研究

通信过程中因信道畸变而产生的码间干扰(ISI)严重影响通信质量,该问题常采用均衡技术来解决。介绍了传统定步长盲均衡CMA算法原理,仿真分析了其不能兼顾收敛速度快与稳态误差小的问题,为解决这一问题,提出一种基于Sigmoid函数的变步长盲均衡算法。为解决码间串扰问题,对CMA算法进行改进并对改进算法原理进行阐述,分析了参数对算法性能的影响。最后通过仿真实验证实了改进算法能够加快收敛速度,同时能保持较小的稳态误差。     

一种水下光通信中基于先验模型的预均衡方法

由于海水的散射特性,光在水下传输时会产生码间串扰(ISI)问题,传输环境较差时尤为严重.为解决该问题,文章将预均衡技术应用于基于直流偏置光正交频分复用(DCO-OFDM)调制的水下光通信系统中,并针对水下光的传输特性提出了一种基于先验信息的预均衡方法.在浑浊海港海水环境下与传统均衡算法进行了性能对比.仿真结果表明,在信...     

一种提高光网络攻击容忍性的RWA算法研究

通过研究光网络中带内串扰攻击及其传播原理,在基于串扰攻击有限传播的模型之上,提出了一种限制串扰攻击传播的波长路由分配(Routing and Wavelength Assignment,RWA)算法.该算法把分配后能产生最小串扰攻击传播最大值(Crosstalk Attack Propagation Maximum,CAPM)的波长路由分配给新的光路请求,从而减少全网的潜在的攻击传播范围.仿真结果显示,与常用的首次命中(Fist-fit)RWA算法相比,该算法能显著降低全网的串扰攻击传播最大值,从而提高光网络的攻击容忍性.     

宽谱光源对CMOS阵列电串扰的影响

CMOS阵列探测器中,像素单元间的串扰会影响其成像质量。为了解不同光源对CMOS电串扰的影响,针对CMOS图像传感器的电串扰特性建立了一个分析模型,结合CMOS图像传感器的工作原理定量计算了单色光、宽谱光源入射条件下的电串扰特性。分析结果表明CMOS图像传感器的电串扰随单色光波长、宽谱光源谱宽和中心波长的增大而增大,但中心波长与单色光波长相同的宽谱光源,其对电串扰的影响大于单色光。辐照功率为600 W,单色光波长为1 064 nm,电串扰大小约为50.611 mV;宽谱光源中心波长为1 064 nm,谱宽为400 nm时,电串扰的大小约为50.914 mV,相比于单色光电串扰增加了约0.303 mV。     

SC-FDE系统中信道估计和均衡算法的研究和实现

为了克服多径信道下码间串扰带来的影响,本文对SC-FDE系统中的信道估计和均衡算法进行研究。首先分析了DFT插值算法原理,提出采用格雷互补序列估计信道频率响应的方法,然后对MMSE均衡估计参数进行了详细推导,最后通过Matlab对均衡算法中时域滤波进行仿真验证,结果表明该方法能够有效滤除噪声,提升多径信道下系统接收性能,具有一定的应用价值。     

Dynamic spectrum management for next-generation DSL systems

The performance of DSL systems is severely constrained by crosstalk due to the electromagnetic coupling among the multiple twisted pairs making up a phone cable. In order to reduce performance loss arising from crosstalk, DSL systems are currently designed under the assumption of worst-case crosstalk scenarios leading to overly conservative DSL deployments. This article presents a new paradigm for DSL system design, which takes into account the multi-user aspects of the DSL transmission environment. Dynamic spectrum management (DSM) departs from the current design philosophy by enabling transceivers to autonomously and dynamically optimize their communication settings with respect to both the channel and the transmissions of neighboring systems. Along with this distributed optimization, when an additional degree of coordination becomes available for future DSL deployment, DSM will allow even greater improvement in DSL performance. Implementations are readily applicable without causing any performance degradation to the existing DSLs under static spectrum management. After providing an overview of the DSM concept, this article reviews two practical DSM methods: iterative water-filling, an autonomous distributed power control method enabling great improvement in performance, which can be implemented through software options in some existing ADSL and VDSL systems; and vectored-DMT, a coordinated transmission/reception technique achieving crosstalk-free communication for DSL systems, which brings within reach the dream of providing universal Internet access at speeds close to 100 Mb/s to 500 m on 1-2 lines and beyond 1 km on 2-4 lines. DSM-capable DSL thus enables the broadband age.     

Optimal multiuser spectrum balancing for digital subscriber lines

Crosstalk is a major issue in modern digital subscriber line (DSL) systems such as ADSL and VDSL. Static spectrum management, which is the traditional way of ensuring spectral compatibility, employs spectral masks that can be overly conservative and lead to poor performance. This paper presents a centralized algorithm for optimal spectrum balancing in DSL. The algorithm uses the dual decomposition method to optimize spectra in an efficient and computationally tractable way. The algorithm shows significant performance gains over existing dynamics spectrum management (DSM) techniques, e.g., in one of the cases studied, the proposed centralized algorithm leads to a factor-of-four increase in data rate over the distributed DSM algorithm iterative waterfilling.     

Advanced DSL management

Today's digital subscriber line deployments are often conservatively engineered to function in a statistically worst case environment. Crosstalk is treated as unknown and uncontrollable random noise, even though it is manmade. Other impairments are often treated by simply adding margin to crosstalk. While this simplistic practice currently suffices, it often provisions unnecessarily low bit rates. This article shows methods that can increase these bit rates and decrease DSL failure rates. Data can be collected about individual telephone lines and cables from loop databases, by automated test equipment, or from DSL modems. This data may then be fed into an advanced DSL management system with a database of DSL loop and noise characteristics, and an analysis engine that tailors DSL deployments to the actual individual line characteristics, to increase provisioned DSL bitrates while simultaneously increasing reliability and lowering maintenance costs. The maximum service can be provisioned with high accuracy, eliminating many service activation failures. Automated maintenance routines can even isolate faults before a customer experiences them. Dynamic spectrum management (DSM) treats crosstalk as the manmade noise it is, and jointly optimizes DSL transmit spectra and signals to minimize crosstalk and maximize received signals, allowing substantially higher DSL speeds than current practice. This opens the door for new services, including symmetric enterprise services and full video service, with minimal physical plant upgrade.     

Multiuser Margin Optimization in Digital Subscriber Line (DSL) Channels

This paper presents efficient multiuser margin optimization algorithms suitable for multicarrier digital subscriber line (DSL) systems using Dynamic Spectrum Management (DSM). The favorable monotonicity and fairness properties of multiuser margin are employed to formulate a box-constrained nonlinear least squares (NLSQ) problem for multiuser margin maximization, which is efficiently solved by using a scaled-gradient trust-region approach with Broyden Jacobian update. Based on this NLSQ formulation, a multiuser harmonized margin (MHM) optimization algorithm for resource allocation is developed. A Newton–Raphson method is also developed for fast margin estimation and used within the MHM. The MHM algorithm converges efficiently to a solution for the best common equal margin to all users, while explicitly guaranteeing their target rate requirements. (This is the reason for the term harmonized.) Furthermore, its predominantly distributed structure can be implemented in DSL/DSM scenarios with only Level 1 coordination. Simulation results of various cases verify the convergence to the unique optimal solution within 5–10 iterations.     

Crosstalk-aware dynamic spectrum management algorithm for green DSL systems

Dynamic spectrum management (DSM) techniques mitigate crosstalk in digital subscriber line (DSL) networks by adapting the transmit spectra to the actual noise and channel conditions. Conventional DSM schemes are designed based on single-objective optimization, either belonging to the rate-adaptive or margin-adaptive category. In this paper, an efficient crosstalk-aware DSM (CA-DSM) algorithm which jointly considers both the data rate and power is proposed to search for the best rate-power tradeoff solution based on the network conditions. The crosstalk-aware power strategy prevents transmitters which contribute excessive crosstalk from being allocated high power, thereby reducing the aggregate crosstalk noise in the system. A convex cost function is used to formulate the DSM optimization problem wherein two coefficients are introduced to make the CA-DSM algorithm adaptive to different network conditions. An iterative power update strategy is proposed for the CA-DSM algorithm to minimize the cost function. Convergence properties of the CA-DSM algorithm along with existence and uniqueness of optimal power solutions are examined analytically and illustrated graphically. Simulation results show that the proposed CA-DSM algorithm can provide a significantly better rate-power tradeoff performance compared to existing spectrum management schemes.     

System Prototype and Verification Using Metamodel-Based Transformations

Mapping domain-specific languages' core concepts into the concurrent object-oriented Petri nets formal specification language provides users with the semantics necessary for developing prototypes for these DSLs. Different knowledge domains demand different types of support from software languages. Domain engineers often use domain-specific languages to overcome this problem. DSLs are difficult to design, implement, and maintain and are often less efficient than hand-coded software. To address some of these problems, we propose transforming a DSL into the concurrent object-oriented Petri nets formalism. The DSL metamodel serves as the transformation's starting point. The transformation represents the semantic mapping between the DSL and CO-OPN. We aim both to provide a formally defined semantics for the DSL and, because we integrate CO-OPN in a framework, to provide the functionalities that allow model verification and fast prototype generation for the DSL     

Video on phone lines: technology and applications

This paper reviews the telephone loop plant characteristics, current DSL (digital subscriber line) technologies, recent efforts in video coding standards, and the interrelationship between DSL technologies and visual communications over subscriber lines. In overview of the loop plant characteristics we examine its physical makeup and transmission properties, where for the latter we discuss frequency and time responses of wire-pair lines and the impairments of echo, crosstalk, impulse noise, and radio frequency interference. We trace the historical development of various DSL technologies and comment on possible future evolution. Transmission technologies used in the ISDN basic-access DSL, the high bit-rate DSL, and the asymmetric DSL are portrayed. And the issue of spectrum compatibility among different transmission systems is explained. Several important video coding standards are briefly described, including ITU-T's H.261 and ISO's JPEG and MPEG series, which are either completed or emerging. The synergistic relationship between these standards and the DSL technologies is elucidated. As a result, DSL technologies provide the potential of delivering certain broadband services well in advance of direct fiber access for telephone subscribers     

Reduced-complexity simulation of the effect of non-stationary interference on DMT-based DSL systems

One of the factors affecting the performance of DSL systems is non-stationary interference, comprising of impulse noise and radio-frequency ingress (RFI). The evaluation of the impact of non-stationary interference becomes increasingly important as DSL systems operate at higher rates and the SNR margins are lowered. Because of the complexity of the models of non-stationary interference, simulations are often used for the accurate prediction of the performance of DSL systems. This study begins with a discussion on some issues that pertain to the simulation of the impact of non-stationary disturbances on DSL systems. Then, a reduced-complexity simulation method of the effect of non-stationary interference on DMT-based DSL systems is presented. It is argued that the method is a good candidate for the simulation of the impact of low-energy non-stationary disturbances. In addition to reducing the computations, it is shown that the method does not cause a significant loss of accuracy of the predicted error rate.     

DSL spectrum management standard

Different digital subscriber lines transmitting on loops in the same telephone cable generate crosstalk into each other. Two different DSLs are spectrally compatible if they can both use the same cable with low probability of significant degradation from crosstalk. Spectrum management is the process of ensuring spectral compatibility while optimizing the loop plant. Spectrum management requires knowledge of cable plant characteristics extending into higher frequency spectra (/spl sim/1 MHz), the different DSL types, and how to compute the impact of crosstalk. Also, definitions of the level of crosstalk from one DSL type that significantly degrades another DSL type is needed, which can only reach broad acceptance through industry-wide agreements. In the United States, DSL Access Standards Committee T1E1.4 has created a technical definition of spectral compatibility, the Spectrum Management Standard T1.417-2001. The details of DSL spectral compatibility and compliance with the standard are presented, as well as a history of the standard and some possibilities for the future.     

An overview of broad-band access technologies

The provision of broad-band services based on either the Internet or the asynchronous transfer mode (ATM) technique requires a new generation of access networks. In the short term, solutions such as x-digital subscriber line (DSL) and hybrid fiber coaxial (HFC), allowing the reuse of existing infrastructures look very promising. For the longer term, new infrastructures based either on radio or on optical access links seem preferable. Three x-DSL techniques aiming at high-bit-rate transmission over twisted pairs are presented: high-bit-rate DSL, asymmetrical DSL, and very-high-bit-rate DSL. An extension of existing cable television networks known as HFC is also described. Two other prospective approaches, wireless in the loop (WITL) and fiber in the loop (FITL), are then presented. Several techniques are considered for WITL: digital enhanced cordless telecommunication local multipoint distribution service, wireless ATM, and low Earth orbit satellite constellations. The various architectural alternatives for the FITL approach are discussed, a special interest being dedicated to the synchronous digital hierarchy self-healing loop and the ATM over a passive optical network. We mention the main experiments and the standardization activities inherent to the domain