Partial correction of transmission errors in d.p.c.m. without recourse to error correction coding

A method for partially correcting transmission errors in a 1st-order d.p.c.m. system, without recourse to channel coding, is described. A simple detection algorithm based on the statistical properties of a sequence of differences between adjacent samples of a modified decoded sequence is used to identify the erroneous samples. Three different correcting algorithms are described. Substantial improvements in the decoded waveform are achieved, and, for a Markov input process, an error rate of 0.04% in the first and second most significant digits, an improvement in s.n.r. of 7dB is achieved.     

Partial correction of transmission errors in Walsh transform image without recourse to error correction coding

A sequency difference detection and correction (s.d.d.c.) system is described which enables the partial correction of transmission errors in a Walsh-Hadamard transform image to be achieved without channel coding. Using a first-order two-dimensional random Gaussian Markov field as the image, the percentage mean-square error in the recovered signal is reduced with the aid of the s.d.d.c. system by two orders of magnitude for transmission error rates <3%.     

Error correction performance in digital subscriber looptransmission systems

The author describes an error correction system for digital subscriber loop transmission systems which use time compression multiplexing (TCM). An interleaved block code is used to correct the burst errors due to impulse noise from analog telephone circuits. This interleaving method requires no extra hardware and contributes no additional delay. To evaluate the transmission performance of this error correction system, the bit error rate after decoding is derived on the basis of a burst error model for 200 kb/s digital subscriber transmission using the alternate mark inversion (AMI) line code. The experimental results for a 200 kb/s TCM system show that burst errors are substantially reduced     

Detection and partial correction of isolated errors from the received data in a 1st-order d.p.c.m. codec

A detection and partial-correction (d.p.c.) system located at the receiver in a 1st-order d.p.c.m. system enables isolated transmission errors that would cause gross distortion in the recovered signal of a conventional d.p.c.m. decoder to be corrected from the received data, providing that the input signal does not exhibit a rapid change in its slope during a sampling period. The d.p.c. system is disabled when this occurs.     

Performance of an error correction scheme for PAL-TV teletext

The shortened (272, 190) difference set cyclic code has been adopted for the Japanese teletext system using NTSC vertical blanking periods. This system is known as BEST (burst and random error correction system for teletext) for NTSC-TV systems. A powerful error correction system adopting the (272, 190) code for PAL-TV teletext signals is described. To compare the error correction characteristics of this system to those of WST (World System Teletext), transmission experiments were carried out multiplexing both data packets with different lines during the vertical blanking period of the same TV signals. The validity of applying BEST to the PAL-TV signals was confirmed, particularly when there is ghost interference     

前向纠错技术在EPON中的应用研究

在EPON中引入前向纠错(FEC)技术,能有效地增加PON的光分路数和增大信号的传输距离。对于在EPON中加入FEC功能所涉及到的FEC线路综合编码、帧结构的设计以及兼容性等问题进行了分析,并进一步给出了相应的解决方案。     

ASMD with duty cycle correction scheme for high-speed DRAM

An analogue synchronous mirror delay with duty cycle-correction scheme (ASMDCC), to improve the data transmission performance between DRAM and system, is proposed. The ASMDCC achieves duty cycle correction and clock synchronisation at once within two clock cycles, by using a half value current source. The simulation results show the duty cycle of the internal clock is stabilised with less than ±100 ps deviation from 50% for the wide duty cycle range     

Unified deadtime correction model for PET

A model of deadtime for emission and transmission scans in positron emission tomography (PET) scanners with two-dimensional detectors has been developed. The model takes into account coincidence losses due to singles losses and multiple events, as well as mispositioning errors at higher count rates caused by pulse pile-up, within a detector block. The model is applicable to emission distributions and to spatially varying singles distributions seen with a rotating pin transmission source. An automatic procedure to determine the parameters of this model based on decaying emission studies has also been developed. Different singles dead time factors are required for emission and blank distributions due to differences in their energy spectra. The model was tested on emission and pin transmission data taken on the Scanditronix PC2048-15B scanner.     

Improved forward error correction technology of RS-LDPC cascade code in optical transport network

With the continuous development of optical communication and the increase in data transmission volume, optical transport network (OTN) has become the focus of research in next-generation transmission networks. In the process of data transmission, errors caused by noise often occur, resulting in an increase in the bit error rate (BER) and a decrease in the performance of the optical communication system. Therefore, we use forward error correction (FEC) technology in OTN for error control to improve the transmission efficiency of signals in OTN and reduce the BER. Standard FEC technology uses RS(255,239) code. On this basis, since the performance of low density parity check (LDPC) code is close to the Shannon limit, we propose a method of cascading RS code and LDPC code. Applying this improved FEC technology to OTN, the simulation results show that the improved FEC technology has a reduced BER compared with the standard FEC technology. When the BER is at the 10-3 level, the performance is improved by about 1.7 dB.     

基于OFDM的WLAN相位校正算法研究

相位校正对基于OFDM的高速数据传输系统至关重要.文章针对802.11a协议提出了一种使用导频进行相位校正的算法.该算法对接收导频样本进行最小二乘估计以获得相偏参数,算法综合考虑了抽样时钟偏移(SCO)和载波频偏(CFO)所引起的相位偏移.文章通过仿真比较了该算法与另一种相位校正算法在不同参数下的性能,结果证明在相偏主要由SCO和CFO引起的情况下该算法性能较好.     

数字组合式光电互感器的误差分析与校正

介绍了一种可以同时测量母线电压与电流的新型数字组合式光电互感器，详细分析了组合式光电互感器数据采样与传输系统的系统误差，提出了误差校正的数值计算方法。分析结果表明，采用误差校正算法可以使幅值与角差满足测量要求。此外，文中还给出了光电互感器内部基于光纤传输的数据帧格式及其数据恢复与同步方法。     

An algorithm for bit-skew correction in byte-wide WDM optical fibersystems

Some objectives for a bit-skew correction system are presented. The properties of optical fiber transmission which allow realization of these objectives are discussed. It is shown that the bit-skew limitation due to chromatic dispersion in byte-wide wavelength division multiplexing (WDM) optical fiber systems can be corrected automatically with no prior knowledge of the fiber parameters or link length and that the full potential of such systems can be attained with circuitry which is no faster than the bit subchannel data rate. In addition, the absolute wavelengths of the sources are not required as long as the channel spacing is constant     

Channel estimation and error correction for UWOC system with vertical non-line-of-sight channel

Recently, underwater wireless optical communication (UWOC) system has placed more attention towards increasing data rate, high accuracy, higher bandwidth and providing highly secured transmission. Generally, light propagation in underwater medium is disturbed due to some degrading effects such as turbulence, scattering and absorption which will degrade the performance. Therefore, channel estimation is essential and need to adapt suitable correction techniques that compensate the errors due to those effects. In this work, channel estimation and error correction technique are proposed for the UWOC system with vertical non-line-of-sight channel based on MIMO-OFDM approach. Initially, input sequence error is eliminated by HVD Turbo coding method and error rectified signal is modulated with M-ary OAM-PPM modulation technique. Modulated signal is transmitted through Vertical NLOS channel. During transmission, the signal undergoes scattering, absorption and channel fading. In receiver side, channel characteristics are estimated by invariant embedding method. Finally, estimated signal is demodulated and decoded by same techniques. MATLAB environment is used to implement the proposed work. Resultant performances like channel capacity, BER, SNR, data rate, receiving power and MSE for different water types like pure sea water, ocean water, costal water and turbid water are compared and results are examined.

     

A partial transmit sequence technique with error correction capability and low computation

Orthogonal frequency division multiplexing (OFDM) is a popular transmission technique in wireless communication. Although already widely addressed in many studies, OFDM still has flaws, one of which is the occurrence of high peak‐to‐average power ratio (PAPR) in the transmission signal. The partial transmit sequence (PTS) technique is one method adopted to reduce high PAPR in OFDM systems. However, as PTS utilizes phase factors to generate multiple candidate signals, large amounts of calculation and time are required to search the candidate signal with the minimal PAPR, which will then be adopted as the final transmission signal. This paper proposes a novel PAPR reduction method, which can be applied in OFDM systems with M‐ary phase‐shift keying modulation. It not only requires less computation but also possesses error correction capabilities. More precisely, the proposed method is to divide a block‐coded modulation code into the direct sum of a correcting subcode for encoding information bits and a scrambling subcode for generating phase factors. Our proposed method is a suboptimal technique with low computation, because it uses a genetic algorithm with a partheno‐crossover operator as the transmitted signal selection mechanism. Simulation results show our proposed method has better PAPR performance than the GA‐PTS scheme. Based on the simulation results in Figures 5 and 6, it is evident that our proposed method can be employed in any OFDM system by using M‐PSK modulation.Copyright © 2013 John Wiley & Sons, Ltd.     

Optimized interpolator filters for timing error correction in DMTsystems for xDSL applications

Discrete multitone (DMT) modulation is a multicarrier technique that allows the transmission of high speed data over band limited channels. This type of system is very sensitive to synchronization errors when used in digital subscriber loop applications (xDSL), due to the high number of carriers and high density constellations involved. This paper addresses the topic of all-digital timing error correction in a DMT system for xDSL applications, where the timing error correction procedure is based entirely on signal interpolation. An analytical study of the interpolator filter performance is carried out, arriving at an expression for the signal-to-distortion ratio (SDR) at the output of the receiver, as a merit figure. In this derivation, the fixed frequency domain equalizer (FEQ) plays an important role since it compensates for a great part of the distortion introduced by the interpolator. From this study, the design of the optimal interpolator filter in terms of SDR, based on a multirate approach with Kaiser window, is presented. Specific designs for ASIC and for DSP-based implementations are obtained. Performance results are excellent, yielding SDR values above 50 dB for all carriers while keeping the computational cost low     

基于DVI双链路的超大分辨率亮度校正系统设计

具备亮度校正功能的DVI-DVI处理器被应用到LED大屏幕显示,可以较好的解决工程上为了增加或升级亮度校正功能而更换显示控制系统的问题.但是DVI-DVI处理器的动态内存读取频率较低,不能发挥DVI双链路的数据传输性能.本文通过对动态内存中待读取的校正参量按照特定算法进行重组和压缩,将动态内存的等效读取频率从266MHz提高到330MHz,实现DVI双链路传输对超大分辨率的LED显示屏进行有效的亮度校正.     

Error correction and error detection techniques for wireless ATM systems

Error correction and error detection techniques are often used in wireless transmission systems. The Asynchronous Transfer Mode (ATM) employs Header Error Control (HEC). Since ATM specifications have been developed for high‐quality optical fiber transmission systems, HEC has single‐bit error correction and multiple‐bit error detection capabilities. When HEC detects multiple‐bit error, the cell is discarded. However, wireless ATM requires a more powerful Forward Error Correction (FEC) scheme to improve the Bit Error Rate (BER) performance resulting in a reduction in the transmission power and antenna size. This concatenation of wireless FEC and HEC of the ATM may effect cell loss performance. This paper proposes error correction and error detection techniques suitable for wireless ATM and analyzes the performance of the proposed schemes. This revised version was published online in June 2006 with corrections to the Cover Date.     

An analytical scatter correction for singles-mode transmission data in PET

We present an analytical scatter correction, based upon the Klein-Nishina formula, for singles-mode transmission data in positron emission tomography (PET) and its implementation as part of an iterative image reconstruction algorithm. We compared our analytically-calculated scatter sinogram data with previously validated simulation data for a small animal PET scanner with 68 Ge (a positron emitter) and 57 Co (approximately 122-keV photon emitter) transmission sources using four different phantom configurations (three uniform water cylinders with radii of 25, 30, and 45 mm and a nonuniform phantom consisting of water, Teflon, and air). Our scatter calculation correctly predicts the contribution from single-scattered (one incoherent scatter interaction) photons to the simulated sinogram data and provides good agreement for the percent scatter fraction (SF) per sinogram for all phantoms and both transmission sources. We then applied our scatter correction as part of an iterative reconstruction algorithm for PET transmission data for simulated and experimental data using uniform and nonuniform phantoms. For both simulated and experimental data, the reconstructed linear attenuation coefficients (mu-values-values) agreed with expected values to within 4% when scatter corrections were applied, for both the 68 Ge and 57 Co transmission sources. We also tested our reconstruction and scatter correction procedure for two experimental rodent studies (a mouse and rat). For the rodent studies, we found that the average mu-values for soft-tissue regions of interest agreed with expected values to within 4%. Using a 2.2-GHz processor, each scatter correction iteration required between 6-27 min of CPU time (without any code optimization) depending on the phantom size and source used. This extra calculation time does not seem unreasonable considering that, without scatter corrections, errors in the reconstructed mu-values were between 18%-45% depending on the phantom size and transmission source used.     

A built-in performance-monitoring/fault isolation and correction(PM/FIC) system for active phased-array antennas

A built-in performance-monitoring/fault isolation and correction (PM/FIC) system for an active phased-array antenna has been developed and tested. This PM/FIC system employs a transmission line signal injector embedded at the radiating aperture together with a phase-toggling technique for signal detection. Hardware components for a demonstration test-array have been developed, fabricated, and assembled. Eight active elements are fed by four dual-channel transmit/receive (T/R) modules in a column array. Far-field range tests and fault correction tests have also been performed to demonstrate the PM/FIC functions on this test array. Good results have been obtained from these tests. The measurement accuracy of the phase-toggling method is compared with an HP8510 measurement system