Bayesian techniques for equalization of rapidly fading frequency selective channels

This paper applies the Bayesian conditional decision feedback estimator (BCDFE) to rapidly fading frequency selective channels. The BCDFE is a model-based deconvolution algorithm which jointly estimates the transmitted data and channel parameters. The BCDFE smoothly transitions between trained and blind operation and consequently provides robust performance in rapidly fading channels. We provide a brief derivation of the BCDFE and characterize the performance on the land mobile radio channel. We assess the BCDFE's principle design characteristics and the resulting performance in both transient and steady-state operation. The effects of delay spread, Doppler spread, and cochannel interference on the bit error probability performance are also presented. The BCDFE demonstrates many of the desirable characteristics of an equalizer for mobile radio.     

Adaptive modulation and decision feedback equalization for frequency‐selective MIMO channels

In this paper, an adaptive modulation scheme for the multiple‐input multiple‐output (MIMO) frequency‐selective channels is investigated. We consider a scenario with precoded block‐based transceivers over spatially correlated Rayleigh multipath MIMO channels. To eliminate the inter‐block interference, the zero‐padding is used. The receiver is equipped with a MIMO minimum‐mean‐squared‐error decision feedback equalizer. The precoder aims to force each subchannel to have an identical signal‐to‐interference‐plus‐noise ratio (SINR). To adjust the constellation size, the unbiased mean square error at the equalizer output is sent back to the transmitter. To simplify our analysis, the feedback channel is considered as instantaneous and error free. We first derive the probability density function of the overall SINR for flat fading and frequency‐selective channels. On the basis of the probability density function of the upper bound of the SINR, we evaluate the system performance. We present accurate closed‐form expressions of the average spectral efficiency, the average bit error rate and the outage probability. The derived expressions are compared with Monte Carlo simulation results. Furthermore, we analyze the effect of the channel spatial correlation. Copyright © 2013 John Wiley & Sons, Ltd.     

端到端无线信道信号幅度和多普勒谱分布研究

利用理论和实验相结合的方法研究了室内宽带端到端(Device-to-Device,D2D)无线信道信号的幅度和多普勒频谱分布.结果表明:在不同的场景下,D2D信号幅度分布服从单瑞利、双瑞利和多瑞利的复合分布;在二维(Two-Dimension,2-D)和三维(Three-Dimension,3-D)散射环境下随电波到达角的分布不同,D2D信道多普勒频谱将遵循不同的分布规律.通过理论和实验结果的比较研究验证了本文结果的正确性.     

Comparative indoor RF channel soundings at 2, 5 & 17 GHz

There is a relatively large selection of results for indoor channel soundings at frequencies around 1 to 2 GHz but relatively few at the HIPERLAN frequencies of 5 and 17 GHz. This work provides some results taken at all three frequencies in order to redress this deficiency and also to compare results at these frequencies. A 20 GHz network analyser was used to perform the soundings. The analyser was capable of performing the Chirp Z transform to convert complex frequency response data to the time domain. Soundings were made in the Agency's office headquarters at Waterloo London and in their investigation facility at Whyteleafe. These two locations provided some diversity of sounding environments involving small offices, meeting rooms and large laboratories. Both buildings were of a 1930's style brick construction with some modern plaster board internal walls. Decay exponents and delay spreads are given for the test frequencies. Results show similar delay spreads at all frequencies.     

应用于10 Gbit/s光通信及背板传输的自适应均衡器设计

描述了一种既可用于背板传输也可用于光纤通信的高速串行收发器前端均衡器的设计。为适应光信号在传播中的色散效应,使用前馈均衡器(FFE)加判决反馈均衡器(DFE)的组合,取代了背板通信中常用的连续时间线性均衡器(CTLE)和DFE的组合。设计使用3 pre-tap、3 post-tap和1个main tap的抽头组合方式,兼顾pre-cursor和post-cursor的信号失真,有效补偿范围为15 dB。补偿系数采用完全自适应算法调整,对FFE采用模拟MSE算法调整,DFE引擎采用1/16速率数字sign-sign最小均方差(LMS)算法实现。芯片使用UMC 28 nm工艺流片,输入信号频率为10 Gbit/s。     

室内宽带多输入多输出抽头时延线新模型研究

根据室内无线电波传播规律和实测数据,研究建立了一个新的抽头时延线模型,该模型可以简单有效地估计视距和非视距路径下室内平均功率时延谱,并与实验结果一致.在广义平稳非相关散射信道前提下,通过分析抽头时延模型频率相关系数、抽头系数分布和相关性、抽头多普勒频谱等特性参数,给出了评估抽头时延线模型的新方法.文中建立的信道模型和参数,对于室内多输入多输出无线信道模拟仿真有较为重要的意义.     

一种面向112 Gb/s PAM4接收机的自适应均衡设计方案

提出了一种适用于超短距离（Very Short Reach,VSR）信道、面向112 Gb/s PAM4 (Pulse Amplitude Modulation 4)接收机的自适应均衡设计方案。在该方案中,接收机前端利用3个连续时间线性均衡器（Continuous Time Linear Equalizer,CTLE）对信号分别在高频、中频和低频进行补偿,可变增益放大器（Variable Gain Amplifier,VGA）和饱和放大器（Saturation Amplifier,SatAmp）则用于对信号幅值的缩放。除了3个数据采样器外,引入4个辅助采样器用于进一步改善阈值自适应算法性能。同时,采用符号最小均方算法,利用接收端数据采样器和辅助采样器之间的偏移推动辅助参考电压收敛到信号星座电平,从而确保PAM4接收信号的眼图在垂直方向上3个眼睛具有相等的间隔和恒定的信噪比（Signal瞭o睳oise Ratio,SNR）。仿真结果表明,所提出的112 Gb/s PAM4接收机能够在损耗为15 dB的信道上实现小于10-12的误码率,并且具有良好的眼图性能,其最差眼高为75 mV,眼宽为0.34 UI (Unit Interval),与传统方案相比具有显著的性能提升。     

一个用于背板通信的24Gb/s高速自适应组合均衡器

本文介绍了应用于背板通信系统中均衡器的设计与实现.该均衡器采用连续时间线性均衡器（Continuous Time Linear Equalizer,CTLE）和2抽头判决反馈均衡器（Decision Feedback Equalizer,DFE）的组合结构来消除信道码间干扰中的前标分量和后标分量.在设计中,CTLE采用双路均衡器结构补偿信道不同频率的损耗,减小了电路的面积和功耗;DFE采用半速率预处理结构来缓解传统DFE结构中关键反馈路径的时序限制,并采用模拟最小均方（Least Mean Square,LMS）算法电路控制DFE系数的自适应.电路采用IBM 0.13μm BiCMOS工艺设计并实现,测试结果表明对于经过18英寸背板后眼图完全闭合的24Gb/s的信号,均衡后的眼图水平张开度达到了0.81UI.整个均衡器芯片包括焊盘在内的芯片面积为0.78×0.8mm²,在3.3V的电源电压下,功耗为624mW.     

A co-designed coding,modulation and equalization scheme for the transmission of 155-52 Mbit/s data over a 72 MHz intelsat transponder. Part 2: Equalization

This paper reports on the application of co-designed coding, modulation and equalization techiques to an INTELSAT requirement for transmitting 155-52 Mbit/s data over a 72 MHz satellite channel. A specific solution as regards coding, modulation and equalization is proposed and analysed that differs from ‘standard’ concatenation in that the inner decoder integrates equalization, modulation and coding. In Part 2, a novel technique for integrating decision feedback equalization into the inner decoder is described. The gains in integrating the coding and equalization are shown to be significant for channels that need equalizing.     

Performance analysis of adaptive DFE using set-membership binormalized data-reusing LMS algorithm for frequency selective MIMO channels

This paper addresses the concern of complexity involved with adaptive equalization in wireless systems operating over time-varying and frequency selective multiple-input multiple-output (MIMO) channels. Here, we propose a decision feedback equalizer using binormalized data-reusing least mean square (BNLMS) algorithm with set-membership filtering for MIMO channels. The performance of the equalizer is investigated for a MIMO receiver in a multi-path fading environment as experienced in the indoor and pedestrian environment. The equalizer performance is also studied for channels having higher delay and Doppler spread. The convergence issues, BER performance and tracking capabilities are examined through computer simulations. Moreover, the computational complexity issue for this MIMO equalizer is compared with other existing data-selective algorithm based techniques.     

一种遥感卫星高码速VCM数传信道的均衡技术

在基于第二代数字卫星视频广播协议（DVB-S2）标准的遥感卫星可变编码调制（VCM）高码速数传信道中,宽带信号的大失真、大频偏和低信噪比会导致解调器载波环路不锁定。传统的DVB-S2解调器并不能解决这个问题。在载波环路前增加一个均衡器补偿失真,可以让载波环路稳定锁定。为了克服载波环路前信号的频偏和相偏对均衡器的影响,提出了一种均衡技术,利用起始序列（SOF）和导频的先验信息进行双重自相关变换,设计了一种新的误差函数和迭代过程。仿真结果表明,该均衡技术可在该应用条件下支持解调稳定工作。     

Discrete realization for receivers detecting signals over random dispersive channels. Part II: Doppler-spread channel

We propose a new suboptimal receiver for detecting signals transmitted over random doppler-spread channels. We discuss in particular the first order channel and a transmitted signal of a constant envelope. The proposed receiver is composed of an integrator, a sampler and a quadratic filter. We give numerical results concerning the performances of this receiver. In particular, we give the evolution of error probability versus the number of samples (or sampling rate). We show the important role of the ratio of signal duration to channel coherence time and we suggest how to choose the transmitted signal duration and the sampling rate for a given signal to noise ratio.     

40Gb/s光纤通信系统中自适应判决反馈均衡器的补偿性能

数值仿真了40Gbit/s 非归零码(NRZ)光纤通信系统中,基于最小均方差算法的非线性自适应判决反馈均衡器对系统传输损伤的补偿性能.仿真结果表明,对于单信道40 Gbit/s NRZ系统,在同时考虑色散和自相位调制情况下,自适应判决反馈均衡器的引入可以使系统色散容限(1 dB眼图张开度代价)得到明显改善.在信号丢失率为10-3条件下,PMD容限由补偿前的0.17/单位比特周期,可提高到补偿后的0.22/单位比特周期.     

Performance analysis of APSK modulation for DVB‐S2 transmission over nonlinear channels

For increased bandwidth efficiency and receiver performance, standards for satellite broadcasting systems are evolving by utilizing efficient transmission techniques. The second‐generation digital video broadcasting for satellites (DVB‐S2) adopts the amplitude phase shift keying (APSK) modulation for enhanced performance over nonlinear channels. In this paper, we derive error rate bounds for APSK modulated symbols and generalize the bounds to the case of distorted constellation, which occurs when the maximum transmission amplitude is saturated by the soft‐limiter type channel. The derived bound is shown to significantly improve the previously known result, to accurately predict both the symbol error rate and bit error rate in the entire signal‐to‐noise ratio (SNR) region of interest. Using the derived formula, the optimal input power level for the soft‐limiter channel is determined, and the corresponding minimal error rates for 16‐ and 32‐APSK are quantified. The result is also interpreted in terms of optimal input back‐off (IBO) for nonlinear power amplifiers by evaluating the performance degradation as a function of IBO. Copyright © 2009 John Wiley & Sons, Ltd.     

Cyclic prefix reduction for 20.48 Gb/s direct‐detection optical OFDM transmission over 2560 km of SSMF

Optical Orthogonal Frequency Division Multiplexing (O‐OFDM) provides major advantages in mitigating Group‐Velocity Dispersion (GVD) in Single Mode Fiber (SMF). Unfortunately, when the uncompensated long‐haul transmission ranges become very large, substantial dispersion is accumulated. Owing to the large accumulated dispersion, the Cyclic Prefix (CP) duration will occupy a substantial fraction of the OFDM frame. This effect sets some limitations on the overall throughput and the spectral efficiency. Moreover, the transmission is inefficient because of the energy wastage contained within the CP. In the case where the CP length is shorter than the Channel Impulse Response (CIR), energy wastage is reduced but the system performance is limited by the Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI). To overcome this problem, a Time Domain Equalizer (TEQ) immediately after the channel is proposed. It can cancel the residual ISI and ICI caused by both the GVD and the CP length being shorter than the CIR. The simulation results show that, using BER of 10^?3 as a reference, the system performance improves by 2.69thinspacedB while considering 6‐feedforward/5‐feedback‐weight Decision Feedback TEQ (DF‐TEQ) and 2.03 dB while considering 10‐tap Least Mean Square TEQ (LMS‐TEQ) even though the CP length is shorter than the CIR. This method reduces size of the CP, and consequently the performance of the system will be improved. Copyright © 2011 John Wiley & Sons, Ltd.     

A co-designed coding,modulation and equalization scheme for the transmission of 155-52 Mbit/s data over a 72 MHz intelsat transponder. Part 1: Coding and modulation performance

This paper reports on the application of co-designed coding, modulation and equalization techniques to an INTELSAT requirement for transmitting 155-52 Mbit/s data over a 72 MHz satellite channel. A specific solution as regards coding, modulation and equalization is proposed and analysed that differs from ‘standard’ concatenation in that the inner decoder integrates equalization, modulation and coding. In Part 1 results of extensive computer simulations are presented, examining the effect of adjacent channel interference, co-channel interference, non-linear distortion in representative ground and space TWTAs, multiplexers and filter distortion. In Part 2 a novel technique for integrating decision feedback equalization into the inner decoder is described. The gains in integrating the coding and equalization are shown to be significant for channels that need equalizing.