Zipper: a duplex method for VDSL based on DMT

We present a new duplex scheme, called Zipper, for discrete multitone (DMT)-based very high bit-rate digital subscriber line (VDSL) systems on copper wires. This scheme divides the available bandwidth by assigning different subcarriers for the upstream and downstream directions. It has high flexibility to divide the capacity between the up and downstream, as well as good coexistence possibilities with other systems such as ADSL. Simulation results show the high bit-rate performance in different environments such as mixed ADSL and VDSL traffic under radio frequency interference and with different background noise sources     

VDSL技术及发展

首先介绍了VDSL系统的主要技术要求、噪声环境及频谱兼容性，然后分析和比较了几种线路编码技术和双工方式，着重讨论了Zipper双工技术，最后介绍了VDSL的应用及发展现状。     

TDD-VDSL兼容ADSL频谱的子频带抑制方法

VDSL是数字用户线技术中的最新技术,宽带接入的最佳方案之一。为了提高VDSL系统的传输速率,它有必要兼容现行ADSL系统的频谱。本文通过对VDSL系统的双工方式及兼容ADSL系统的可行性分析,提出了VDSL系统的可用功率谱密度及TDD-VDSL系统兼容ADSL频带的子频带抑制方法,并进行了仿真分析。结果表明在不同的运行环境下,都有很好的性能,是一种有效的实用方案。1     

适用于VDSL系统的Zipper双工方式

文章在概述VDSL系统技术特点的基础上,针对该系统的应用局限性,介绍了一种应用于基于DMT的VDSL系统中的Zipper双工方式。该方式利用循环后缀和符号定时解决了回波问题,采用脉冲成形和加窗技术解决了异步工作的问题。     

利用二维光谱色散和透镜列阵改善靶面辐照均匀性

利用二维光谱色散平滑技术和透镜列阵(LA)来改善激光驱动器中靶面的辐照均匀性.通过消衍射透镜列阵可得到包络陡峭且中小空间尺度均匀性较好的焦斑.当在光路中加入二维光谱色散平滑单元后,光束在两个互相垂直的方向发生光谱色散,多光束干涉所引起的细密条纹也将在很大程度上被抹平,如果把横向热传导平滑效应也考虑在内,高空间频率的强度波动可进一步被消除.二维理论模拟结果表明采用该方案可获得顶部平坦边缘陡峭的焦斑,而且该方案无需仔细调整靶面的位置,实际应用较方便.     

基于PSP-LMS的MIMO全双工数字干扰对消

提出了一种MIMO同时同频全双工系统下的数字干扰对消算法,综合考虑了系统非线性对干扰对消的影响.该算法通过基于逐幸存路径处理的方法,对自干扰信号与待接收信号进行联合信道估计,采用维特比算法实现自干扰信号数字对消和待接收信号最大似然接收.通过对MIMO全双工系统仿真实验表明,该算法能够有效抑制系统非线性失真且有着良好的自干扰对消性能.     

The Hybrid Transmission Scheme of a 900 MHz Digital Land Mobile Radio System

The hybrid transmission scheme of MATS-D uses different transmission principles on both directions of a duplex radio link. Based on the analysis of the radio transmission characteristics and of multiple-access methods, the two directions are designed independently from each other. In the downlink (from base station to mobile station) a combination of TDM and CDM is applied. In the uplink (from mobile station to base station) single channel per carrier FDMA with generalized tamed frequency modulation (GTFM) is employed. Both transmission schemes have been implemented. Measurements with fading generators as well as field tests were carried out. Experimental results are presented for the performance of both transmission schemes, expressed in terms of the bit error rate versus the signal-to-noise ratio and the signal-to-interference ratio.     

Bit- and power-allocation algorithm for symmetric operation ofDMT-based DSL modems

Discrete multi-tone (DMT) based digital subscriber loop (DSL) modems must allocate power and information bits to the discrete tones for quadrature amplitude modulation. The bit allocation (also referred to as bit-loading) algorithms in the literature are designed for modems that operate in the simplex mode in which the upstream and downstream signals use nonoverlapping frequency bands. However, greater data transmission capacity can be achieved by using overlapping frequency bands and echo cancelled duplex operation. The conventional bit-loading algorithms are not well suited for the allocation of data bits for transmission in the duplex mode, and the problem of bit loading for duplex operation has not yet been considered in the literature. This article introduces an algorithm suitable for echo-canceled duplex DMT modems that use overlapping frequency bands for upstream and downstream transmissions for the purpose of transmitting equal data rates in both directions. Moreover, the algorithm performs the bit loading while jointly minimizing a weighted sum of the power used by the central office and the customer premise transmitters. Simulation results are included to show the higher data rates that are possible with the duplex operation as a function of varying levels of echo return loss enhancement     

宽带系统中有记忆大功率功放的数字预失真器研究

针对高峰均比的宽带输入信号,提出了一套联合峰均比抑制技术和基带自适应预失真技术的数字预失真器设计方案,并仿真了峰值抵消算法和自适应预失真算法.结果表明对于峰均比为8.4 dB的输入信号,经过1.5 dB的削峰处理后,预失真器改善带外频谱抑制27 dB,非常有效地补偿了功放的非线性失真,提高了功放效率,对发射机功放线性化技术有一定的实用价值.     

一种通用的OFDM发射机设计

正交频分复用（OFDM）系统参数众多,设计灵活,可以根据不同用途、信道环境以及接收机的性能等,设计出很多不同的OFDM系统。针对此问题,提出了一种通用的基于训练序列的OFDM发射机设计方案。从性能的角度出发,设计了OFDM符号结构和传输帧结构,并重点分析了OFDM数字基带调制模块的组成,最终在Xilinx开发板上实现了该方案,并获得了OFDM各模块的仿真时序图、OFDM射频信号频谱和误比特率图。研究结果表明,该方案频谱利用率高,复杂度低,通用性好。     

Improving the frequency resolution of digitally synthesized periodic signals by a sequential addressing scheme

In the digital synthesis of wideband periodic signals using an Arbitrary Waveform Generator （AWG）, the frequency resolution and spectral complexity of the synthesized signals are commonly limited by the memory capacity and clock frequency of the AWG. This paper proposes a novel sequential addressing scheme and then presents several sequences to improve the frequency resolution of the synthesized periodic signals without changing their spectral envelopes and basic time-domain characteristics under the condition of a fixed memory capacity and a fixed clock frequency. The main idea of the scheme is using the address generator in an AWG to program and produce addresses to read fixed waveform data in variable order, and thus to generate waveforms of various periods and profiles. The scheme is applied in simulating signal scenarios for military communication countermeasure experiments, and achieves high performance.     

An adaptive digital filter for improving the signal-to-noise ratio of a signal with additive noise (Corresp.)

An adaptive digital filtering scheme is developed to deal with the problem of improving the signal-to-noise ratio of a signal corrupted by noise when only general {em a priori} assumptions regarding the signal and the noise are possible. Specifically, the noise is assumed to be white zero-mean and uncorrelated; while the signal is considered to be band-limited, possibly with slowly varying spectrum. The proposed adaptive digital filtering scheme is based upon a class of variable wave digital filters. Adaptation of the digital filter multipliers is accomplished through the use of an identification procedure based on an adaptive spectral estimation method.     

Spectral efficiency evaluation of full‐duplex mode of communications based on SLNR approach

Full‐duplex (FD) mode of communication with efficient transmission scheme is a promising approach for 5G wireless systems by improving the spectral efficiency. This can be attained by making use of various precoding approaches. We propose a new co‐channel interference (CCI)‐aware improvement to signal‐to‐leakage‐and‐noise ratio (SLNR) technique and a suppression filter at the receiver to whiten the interference for the downlink channel. As well, for the uplink (UL) communication, we propose a self‐interference (SI)‐aware enhancement to SLNR scheme and designing a precoder using self‐interference plus noise covariance matrix. The total spectral efficiency is obtained from the sum‐rates of both downlink and uplink communication systems. Simulation results verify that the spectral efficiency (SE) of FD using the proposed scheme performs well relative to the half‐duplex system for all Rician factor and for small powers at the base station (BS) and UL communication channel users. Moreover, as the number of users grows, which entails that as the number of receiving antennas greater than the number of antennas at the BS the SLNR scheme still works, nonetheless, zero‐forcing (ZF) and block‐diagonalization (BD) precoding schemes failed. This is due to the fact that designing a precoder based on SLNR scheme supports multiple numbers of antennas at the base station and users compared with ZF and BD by compromising the interference and noise. However, for the cases of ZF and BD approaches failed due to both schemes require the number of transmit antennas at the BS to be larger than the sum of the receiving antennas at all users.     

Pseudo-analog speech transmission in mobile radio communicationsystems

A low-complexity pseudo-analog speech transmission scheme is proposed for portable communications. It uses a speech coder based on adaptive differential pulse code modulation (ADPCM) in combination with a multilevel digital modulation technique such as M-ary DPSK or M-ary FSK and features low quantization noise, bandwidth efficiency, and robustness to transmission errors. A nonsymmetric M -ary DPSK scheme called skewed M-ary DPSK is proposed to enhance the noisy channel performance. Comparison to conventional analog FM and a digital speech transmission scheme using adaptive predictive coding and forward error correction (FEC) based on convolutional coding shows that the pseudo-analog system has the best objective signal-to-noise ratio performance under most channel conditions. Informal subjective evaluations rate the digital system superior to the pseudo-analog scheme for bad channels and conversely for good channels. It is concluded that the pseudo-analog system can be designed with low delay and high speech quality for good channels with high spectral efficiency     

A concept of digital terrestrial television broadcasting

The future terrestrial television broadcasting system should support the transmission of a digital HDTV signal with a high spectral efficiency. In addition, this system should maintain graceful degradation as the actual analog systems, and should be compatible with the SDTV. The system compatibility can be achieved by using a hierarchical HDTV source-coding scheme that can provide at least two (HDTV, SDTV) or three (HDTV, EDTV, SDTV) hierarchy levels: SDTV image quality will be expected for portable receivers, and HDTV/EDTV image quality will destinate to stationary receivers with roof-top antennas. Taking into account the receivers' antenna gains and the different channel conditions, there will be a difference of 25–30 dB between the received powers of the stationary and the portable receivers. Therefore, the design of a powerful and a suitable transmission scheme for the future broadcasting of the digital HDTV signal will be a technological challenge. In this article we describe a concept of a flexible reconfigurable hierarchical digital terrestrial TV broadcasting system for clear and taboo channels. The flexibility of the proposed scheme easily permits the receivers to support different reconfigurable modes: One HDTV program or multi-programming EDTV or SDTV (for fixed receivers up to 5 × SDTV in clear and up to 2 × SDTV in taboo channels; for portable receivers up to 2 × SDTV.) The system achieves a high interoperability with the Satellite Baseline system. It maintains a graceful degradation and provides a hierarchical complexity. It is based on a concatenated coding scheme. The inner code of the concatenated coding scheme is combined with multi-resolution modulation. The basic constellation is a 64-QAM, which will be operated in clear channels. It can be reconfigured to a 16-QAM in the case of taboo channels. The principle of OFDM with very rugged frequency/time synchronization mechanisms is used to combat the frequency selectivity and the co-channel interference (CCI) in the channel. Known pilot symbols are sent regularly in order to perform coherent detection.The authors are within the RACE-dTTb and the German HDTV-T project.     

基于体光栅的多阵元光纤激光组束

针对外腔谱组束和主振荡功率放大(MOPA)组束方案中存在的问题,基于体光栅极窄的波长选择性和角度选择性,提出了两种多阵元光纤激光组束方案.为克服外腔谱组束中阵元数目受衍射元件有限频谱范围的限制,提出了一种基于级联体光栅的谱组束方案,该方案可使组束阵元数目随光栅数目倍增;提出了一种基于重叠体光栅的MOPA组束方案,该方案通过重叠体光栅的双向复用提供光学反馈,使系统无需复杂的相位检测与控制就可实现各阵元光束的相位锁定.     

Multiuser carrier frequency offsets estimation for OFDMA uplink with generalized carrier assignment scheme

The frequency synchronization issue of multiuser in the uplink of an orthogonal frequency-division multiple-access (OFDMA) system is investigated in this letter. We develop a subspace based blind carrier frequency offsets (CFOs) estimation algorithm for the base station (BS) equipped with uniform linear array (ULA). Due to the adoption of ULA at the BS and the narrowband signal assumption, CFOs of different users can be separated by their spatial information. Thus, unlike existing blind alternatives, which are subject to some specific carrier assignment schemes (CAS) or rely on null subcarriers, our proposed method can support generalized carrier assignment scheme (GCAS) and fully loaded systems, i.e., all subcarriers are available to users. Consequently, the dynamic channel assignment is available and the bandwidth efficiency is higher. Moreover, the closed-form directions of arrival (DOAs) of all active users are also obtained, which can be used in downlink beamforming in frequency division duplex (FDD) systems. Performance of the proposed scheme is evaluated by computer Monte Carlo simulations.     

一种改进的混沌扩频序列研究

通过对混沌映射的研究,针对单一映射产生的扩频序列其系统复杂度低,容易通过反向逆推估计出系统初值的缺点,以Logistic映射为基础,构造出一种新的映射。该映射容易被数字电路实现,且具有较高的系统复杂度。该序列由两个不同初始值的两个Logistic映射复合而成,具有较高的安全性。在此,对复合混沌序列初值敏感性、平衡性、自相关性、功率谱密度进行了分析。研究结果表明,这种新型的序列具有较高的初值敏感性、优良的平衡性、自相关性和伪随机性,是一种有效和可靠的扩频序列。     

基于V-BLAST的数字—模拟域混合预编码技术在多用户大规模MIMO中的应用

在大规模MIMO 系统中,全复杂度单一基带预编码（如全复杂度破零预编码FC-ZF）需要与天线阵元数目相同的射频链路,进而以高复杂度的硬件实施为代价,混合预编码（HP）技术可以大大降低射频链路数,且性能上接近全复杂度单一基带预编码技术,因此HP技术具有较高的研究价值。提出的自适应数字—模拟域混合预编码（自适应混合预编码/AHP）技术较传统数字—模拟域混合预编码（传统混合预编码）技术可以进一步有效地降低硬件的复杂度,并将其与V-BLAST技术相结合,可以同时获得阵列增益和复用增益。仿真结果表明,提出的方案具有较高的频谱效率、较低的硬件复杂度及比较理想的误码率性能。     

协作干扰下的非可信中继与全双工目的节点系统的遍历安全容量分析

研究了一种非可信放大转发中继与全双工目的节点相结合的传输模型。为提升系统安全性能,提出了全双工目的节点干扰(full duplex-destination based jamming,FD-DBJ)策略。同时结合半双工目的节点干扰策略以及放大转发中继策略对比分析系统安全性能。在瑞利衰落信道下,通过合理的近似分析推导出三种策略遍历安全容量的近似闭合表达式。分析与仿真结果显示,在高信噪比下,理论分析曲线与蒙特卡洛仿真结果基本吻合,并对三种策略的性能进行对比,凸显出FD-DBJ策略的性能优越性。并分析了FD-DBJ传输策略的最优功率分配因子。