Equalisation of CCSNo7 link availability

It is shown that the CCSNo7 link availability depends on both the signalling load and signalling unit length if the signal unit error rate monitor (SUERM) algorithm is built according to current ITU-T recommendations. A rearrangement of the SUERM algorithm is suggested so that the link availability has the largest and most constant possible value for the prescribed BER     

The Influence of Short Error Clusters on CCS No 7 Link Availability

We observe the Common Channel Signaling (CCS) No 7 link availability under short error bursts or clusters with high bit error rate (BER), and compare it to the availability of CCS No 7 link under equivalent random errors. It is shown that the mean time to changeover of the CCS No 7 link in the case of error clusters is greater than in the case of random errors of same intensity. The reason for this positive impact of short clusters with high BER is the concentration of more than one errored bits in one errored signal unit. In the same time the mean alignment time of CCS No 7 link (that is out of service) is shortest if errors are grouped in rare short error clusters. Hence, the availability of CCS No 7 link increases and frequency of CCS No 7 link oscillations decreases, if errors are grouped.     

Error monitoring issues for common channel signaling

Motivated by field data which showed a large number of link changeovers and incidences of link oscillations between in-service and out-of-service states in common channel signalling (CCS) networks, a number of analyses of the link error monitoring procedures in the SS7 protocol were performed by the authors. This paper summarizes the results obtained thus far and include the following: (a) results of an exact analysis of the performance of the error monitoring procedures under both random and bursty errors; (b) a demonstration that there exists a range of error rates within which the error monitoring procedures of SS7 may induce frequent changeovers and changebacks; (c) an analysis of the performance of the SS7 level-2 transmission protocol to determine the tolerable error rates within which the delay requirements can be met; (d) a demonstration that the tolerable error rate depends strongly on various link and traffic characteristics, thereby implying that a single set of error monitor parameters will not work well in all situations; and (e) some recommendations on a customizable/adaptable scheme of error monitoring with a discussion on their implementability. These issues may be particularly relevant in the presence of anticipated increases in SS7 traffic due to widespread deployment of advanced intelligent network (AIN) and personal communications service (PCS) as well as for developing procedures for high-speed SS7 links currently under consideration by standards bodies     

Analysis of the link error monitoring protocols in the commonchannel signaling network

Motivated by the excessive link status changes observed in some field operations of the common channel signaling (CCS) network, the authors provide a detailed analysis of the signaling link error monitoring algorithms in the Signaling System No. 7 (SS7) protocol. These algorithms determine when to fail a link due to excessive error rates and when to put a failed link back into service. The analysis shows that, under current SS7 specifications of the error monitoring algorithms, the probability of a signaling link oscillating in and out of service could be high, depending on the traffic load, signal unit size, and the statistical nature of errors (bursty or random). The link oscillation phenomenon could become worse as longer Transaction Capability Application Part (TCAP) messages for transaction-based services (e.g., 800 Service) are carried in the CCS networks. While the risk to the existing network may not be high due to the light loads carried at present, there is still a need to study the error monitoring issues thoroughly     

Antijam capability analysis of RS-coded slow frequency-hoppedsystems

The application of Reed-Solomon codes in slow frequency-hopped systems has been extensively studied. Earlier investigations assumed an infinite interleaving length and considered partial-band noise jammers only. This paper extends previous efforts by analyzing the effect of finite interleaving length and the impact of band multitone jammers. We also explain why two-threshold (2T) erasure-insertion methods (EIM) are needed and examine their performance. Numerical results are presented to compare the effectiveness of the EIM and jammer types and to study the relationships among the hop rate, the interleaver size, and the code rate. The use of 2T-EIM necessitates the estimation of several additional channel and signal parameters. Simple and effective estimation algorithms are provided as well     

Generalised model of SUERM algorithm in CCSNo7

A generalised model of the signal unit error rate monitor in CCSNo7 is described. It is shown that a desired link availability may be obtained by adjusting two parameters in the generalised model. The desired link availability may be, according to ITU-T recommendation Q.703, independent of load or equalised, and high and dependent on the signalling load and SU length     

Exact calculation of mean CCSNo7 link alignment time

Two methods of mean CCSNo7 link alignment time calculation are suggested. One of these methods is also applicable for mean CCSNo7 link changeover time calculation. The results obtained are compared to results of known methods and simulation results     

On the use of remotely sensed data to estimate spatially averaged geophysical variables

This paper examines certain errors that arise when estimating spatially averaged geophysical parameter fields from some satellite and other earth observation measurement systems. Of particular concern is the error that is caused by nonuniform sampling of radiance within the field of view. This effect causes a proportion of the amplitude of surface fluctuations in the parameter to be inherited as uncertainty by the estimated area average. This proportion is small if the correlation length for variations of the surface parameter is either much larger, or much smaller, than the size of the instrument's resolution element (suitably defined). It may be significant when the two length scales are similar. For Gaussian spatial sampling functions, it is shown that the error is minimized if the area over which the simple average is required is about one and a half to two times the square of the projected full width at half maximum of the Gaussian. The results are used to study the problem of estimating surface fractional cover from linear mixture models, where it is confirmed that significant errors can be encountered if the estimated fractions are carelessly assigned to areas defined by the sampling interval of an imaging system.     

Enhanced Low Complex Double Error Correction Coding with Crosstalk Avoidance for Reliable On-Chip Interconnection Link

As the technology scales down, shrinking geometry and layout dimension, on- chip interconnects are exposed to different noise sources such as crosstalk coupling, supply voltage fluctuation and temperature variation that cause random and burst errors. These errors affect the reliability of the on-chip interconnects. Hence, error correction codes integrated with noise reduction techniques are incorporated to make the on-chip interconnects robust against errors. The proposed error correction code uses triplication error correction scheme as crosstalk avoidance code (CAC) and a parity bit is added to it to enhance the error correction capability. The proposed error correction code corrects all the error patterns of one bit error, two bit errors. The proposed code also corrects 7 out of 10 possible three bit error patterns and detects burst errors of three. Hybrid Automatic Repeat Request (HARQ) system is employed when burst errors of three occurs. The performance of the proposed codec is evaluated for residual flit error rate, codec area, power, delay, average flit latency and link energy consumption. The proposed codec achieves four magnitude order of low residual flit error rate and link energy minimization of over 53 % compared to other existing error correction schemes. Besides the low residual flit error rate, and link energy minimization, the proposed codec also achieves up to 4.2 % less area and up to 6 % less codec power consumption compared to other error correction codes. The less codec area, codec power consumption, low link energy and low residual flit error rate make the proposed code appropriate for on chip interconnection link.     

有效折射率法的研究

分析了有效折射率法及其计算偏差的产生原因,提出了一种改进方法。这种方法克服了有效折射率法的由计算顺序不同导致的计算结果不一致的问题,并使计算精度有所提高。     

Relationship of the Signaling System No.7 protocol architecture tothe OSI reference model

The relationships that currently exist between the Signaling System No.7 (SS7) and Open Systems Interconnection (OSI) architectures are examined. The functions of each layer in the SS7 protocol stack, as well as the SS7 addressing mechanisms, are described to the extent necessary to show correspondences to those of OSI. Those areas where the two architectures do not align are highlighted. The criteria by which alignment of SS7 with OSI standards is judged are explained. Work in progress in CCITT in defining the evolution of various SS7 application layer standards, where a conscious effort is being made to attempt to align with OSI standards, is described     

天线时域平面近场测试的误差分析

天线时域近场测试技术对误差体系研究的缺失,导致测试结果的不确定度分析一直无法完成.为解决这一问题,以天线时域平面近场测试为例,对时域近场测试的误差进行研究,给出时域测试区别于频域测试技术的四个误差项:探头调制误差、信号源稳定度误差、时间采样间隔误差、时间采样长度误差.在给出误差项后,对误差的产生机理进行了讨论,通过仿真和实测给出了误差对测试结果的影响.     

Design of an ultra-compact 3 dB MMI coupler

The design of an ultra-compact SOI-based 1×2 3 dB multimode interference（MMI） coupler is proposed.The symmetric multimode interference structure and deeply-etched parabolically tapered multimode waveguide are used in the device.The length of the device is reduced by about 87% compared with general multimode interference straight couplers.Based on effective index method（EIM） and two dimensional beam propagation method（2D-BPM）,the structure parameters are optimized and the fabrication tolerances are analyzed.The results indicate that the performance of the coupler is deeply affected by the coupler＇s width,etching depth and photolithography alignment error in perpendicular direction.     

Performance of Hybrid Error Control Schemes of Satellite Channels

The effectiveness of hybrid error control schemes involving forward error correction (FEC) and automatic repeat request (ARQ) is examined for satellite channels. The principal features of the channel are: large round-trip transmission delay due to the satellite link, and burst errors introduced by the terrestrial links that connect the users to the satellite link. The performance is estimated for two channels described by Fritchman's simple partitioned finite-state Markov model, and is compared to that obtainable if the channel is considered as a binary symmetric channel of the same bit error probability. Results show that the hybrid schemes offer substantial improvement over ARQ and FEC, and that an optimum exists for the number of errors corrected to obtain maximum throughput efficiency.     

基于一种交织码的多位翻转容错技术研究

随着技术的发展和核心电压的降低,存储器更易受瞬时错误（软错误）影响,成为影响航天器件可靠性的主要原因。错误检测与纠正（EDAC）码（也称错误纠正码）常用来对SRAM型存储器中的瞬时错误进行纠正,由单个高能粒子引起的多位翻转错误（SEMU）是普通纠一检二（SEC-DED）编码所无法处理的。提出了一种交织度为2的(26,16)交织码,该码由两个能纠正一位随机错误、二位突发错误的(13,8)系统码组成,(26,16)交织码能够纠正单个码字中小于二位的随机错误和小于四位突发错误（DEC-QAEC）。通过理论分析和硬件平台实验表明,该交织码在存储资源占用率、实时性相当情况下可靠性优于同等长度的SEC DED码,能有效提高SRAM型存储器抗多位翻转错误的能力。      

Technical challenges to a decentralized phone system

Changes that followed in the wake of the divestiture of AT&T are examined. One of these is the growth of new services, particularly ISDN and Switching System No.7 (SS7) services. Another is that setting standards has become a public and global, rather than strictly AT&T-determined, process. Waiting for standards is slowing innovations in the networks, because major equipment vendors to not want to take risks in developing new features, functions, and capabilities before standards are decided on. Service gains and lags in the new environment are discussed     

Bounds on the probability of error for convolutional codes (Corresp.)

For the single error correcting convolutional codes introduced by Wyner and Ash, it is shown that if sufficiently few errors occur in an appropriate neighborhood of a block, the probability of correctly decoding that block is independent of errors outside that neighborhood. This fact is used to derive bounds on the bit error probability and the mean time to first error.     

视频流传输中的差错复原视频编码技术

视频压缩技术在采用预测技术、变换编码技术和可变长熵编码技术以减少冗余信息的同时,也降低了视频流的容错能力.传输信道中的差错,不仅严重损害了视频服务质量,甚至会使通信系统崩溃,因此,在有错信道上进行视频传输,差错复原视频编码技术就显得尤为重要.对差错复原视频编码技术进行了概括和总结,首先指出在视频传输过程中存在的由于传输错误而引发的比特流同步丢失及错误蔓延问题,然后研究了解决这些问题的差错复原视频编码方法,最后指出:可伸缩视频编码和多描述视频编码是差错复原视频编码的发展方向;多描述编码同多路径技术相结合,能显著提高压缩视频信号的错误恢复能力和传输信道的性能.     

七号信令紧耦合式多功能网桥设计

文中设计了一种紧耦合式信令网桥,通过转发信令链路信元,实现信元截取、话务阻断等功能,并实现了通话的实时监控,在公共安全等领域实用性强。紧耦合方式设计具有低延时、低负荷、隐蔽性好等优点,设计的重点是准确处理添加、截取信元后两个方向上信元的序号映射,以及网桥两侧链路故障的同步。该网桥经现场测试表明：能够灵活地实现各种业务,且实时性非常高。     

The predictability of continuous-time, bandlimited processes

In communications and signal processing, we can find examples of applications that could benefit from the prediction of a bandlimited random process. We consider a continuous-time linear predictor applied to a bandlimited process. We show that if the past values of the process are known over an interval of arbitrary positive length, the mean squared prediction error may be made arbitrarily small, regardless of how far in the future we wish to make the prediction. We also show that this is no longer true when a certain energy constraint is applied to the predictor. Furthermore, we discuss what this means for the case in which the prediction is based on past values that are corrupted by estimation errors