OFDM系统中的迭代并行子载波间干扰消除技术

由于实际信道的时变性，OFDM系统中每一子载波上的接收信号受到其它子载波上所传输信号的影响，形成载波间干扰(ICI)并造成误码性能降低。本文提出了适用于OFDM系统的迭代并行子载波间干扰消除接收技术，分析和仿真结果表明此方法可以有效地消除载波间干扰，在归一化多普勒频移为0．1和0．001时，分别提高接收机的性能0.8dB和0．5dB。     

Parallel Channel Estimator and Equalizer for Mobile OFDM Systems

Mobile OFDM refers to OFDM systems with fast moving transceivers, in contrast to traditional OFDM systems whose transceivers are stationary or have a low velocity. In this paper, we use the basis expansion model (BEM) to model time-varying OFDM channels. Using different BEM’s, we investigate various architectures to implement the least-squares (LS) channel estimation and its corresponding zero-forcing (ZF) channel equalization. The experimental results show that our implementation for mobile OFDM systems is capable of combatting the time variation of mobile OFDM channels, and more hardware resource utilization is necessary compared with a traditional OFDM design which fails in a time-varying scenario. For mobile OFDM systems, different BEM’s are available for the channel modeling. We observe that the so-called Critically sampled Complex-Exponential BEM (CCE-BEM) leads to the most efficient hardware architecture while still maintaining high modeling accuracy.     

Joint synchronization and parameter estimation in OFDM signaling

Challenges in cognitive radio and tactical communications include recognizing anonymously received signals and estimating parameters in a blind or semiblind manner. In this paper, we examine this issue for orthogonal frequency division multiplexing (OFDM) signaling. There are several parameters in OFDM signaling, and the blind receiver must extract and consider the synchronization issue. We assume that the blind receiver is aware of modulation type, OFDM, and not aware of chip duration and the length of cyclic prefix. First, we present new criteria based on kurtosis to estimate these parameters and compare their performance at different levels of additive white Gaussian noise with methods based on correlation, kurtosis, maximum likelihood, and matched filter. Then, we perform synchronization and estimate the start time based on these criteria and several new criteria in two steps: fine and coarse synchronization. Finally, in a more practical setup, we present the idea of jointly estimating the mentioned parameters and the signal start time as coarse synchronization. We compare different criteria and show that one of the proposed criteria has the highest efficiency.     

Error performance of OFDM signaling over doubly-selective Rayleighfading channels

A simple method for the evaluation of the error rate performance of OFDM signals transmitted over doubly-selective fading channels is described. The accuracy of the proposed technique is exemplified by simulation results     

基于并行干扰抵消的OFDM/OQAM系统中的信号检测方法

在多径衰落信道中,基于交错正交幅度调制的正交频分复用(OFDM with Offset QAM, OFDM/OQAM)系统使用迫零均衡器进行信号检测时,不能完全消除信道复数特性和滤波器实数正交特性引入的时域符号间干扰和频域子载波间干扰,及信道估计误差导致的误码率性能损失。该文利用对数据初始判决并重构相邻载波及符号间干扰的思想,通过分析采用迫零均衡信号检测时的残余干扰与信道估计误差干扰,提出了一种基于并行干扰抵消和迫零均衡器结合的OFDM/OQAM信号检测方法,并在IEEE 802.22 技术标准的两种典型多径衰落信道中进行了计算机仿真与比较研究。仿真结果表明,与基于迫零均衡的检测方法相比,基于并行干扰抵消的迭代信号检测方法在误码率为1%时,可获得1 dB至2 dB的性能提升。     

Adaptive Modulation and Coding with Selective Retransmission under OFDM signaling

In this paper, we present bandwidth efficient selective retransmission method in conjunction with adaptive modulation and coding (AMC) scheme for OFDM waveform. In the proposed method, when a packet failure occurs, receiver requests retransmission of information symbols prone to error corresponding to the low signal-to-noise ratio (SNR) sub-carriers of OFDM modulation. The selective retransmission avoids unnecessary retransmission and AMC chooses a proper modulation and coding scheme with an objective to maximize the throughput. Our method achieves higher throughput as compared to conventional retransmission methods such as Chase combining hybrid automatic repeat reQuest (CC-HARQ) and incremental redundancy hybrid automatic repeat reQuest (IR-HARQ). We also provide the throughput and delay analysis of the proposed method for non-truncated ARQ. The simulation results demonstrate throughput gain without significant impact on delay as compared to the conventional retransmission approaches.     

Multidimensional parallel combinatory transform domain communication system

Transform domain communication system is an adaptive anti‐interference system that can dynamically generate interference‐orthogonal waveforms. As a spread spectrum system, its low spectrum efficiency limits potential practical applications. In TDCS, cyclic code shift keying is an orthogonal modulation, whose symbols can be regarded as scalars in different dimensions. However, the constellation is restricted by signal time‐bandwidth product. In this study, extending constellation is proven to be a valid approach to improve spectrum efficiency. The combinatory of multidimensional vectors is designed mathematically to increase the variety of the scalars with the minimum orthogonality damage. On the basis of the design, an efficient modulation scheme, namely, multidimensional parallel combinatory transform domain communication system, is proposed, whose fundamental modulation symbols can be represented by the combinatory of a series of cyclic code shift keying symbols with phase shift keying modulation. Compared with the existing methods, multidimensional parallel combinatory transform domain communication system can achieve a considerably higher spectrum efficiency. The bit error rate performance is also improved to various extents. Theoretical spectrum efficiency and bit error rate of the proposed method are derived for additive white Gaussian noise and typical multipath fading channels. System with different spectral conditions and channel estimation methods is also simulated and analyzed to confirm the practical usability.     

Optimized Pipelined Fast Fourier Transform Using Split and Merge Parallel Processing Units for OFDM

Wireless Personal Communications - This paper presents a new optimized design to implement Fast Fourier Transform in orthogonal frequency division multiplexing for real valued signals. The proposed...     

Parallel links with current-mode incremental signaling and per-pin skew compensation

This paper proposes a new inter-signal timing skew compensation technique for parallel links with current-mode incremental signaling. Both the transmitter and receiver of the links are current-mode configured to utilize the intrinsic advantages of current-mode signaling. The receiver maps the direction of its channel currents representing the logic state of the incoming data to two voltages whose values are largely different, enabling a convenient recovery of both the logic state and timing information of the received current-mode data in the voltage-mode domain, and suppression of the common-mode disturbances coupled to the channels. Inter-signal timing skews are compensated by inserting a delay line in each channel whose time delay is determined by the phase difference between the transmitted master clock and the output of the recovering comparator. To assess the effectiveness of the proposed inter-signal timing skew compensation technique, a 2-bit 1 Gbytes/s parallel link has been designed in IBM- CMOS technology and analyzed using SpectreRF with BSIM3V3 device models. Simulation results of the parallel link with the proposed deskewing scheme demonstrate that inter-signal timing skews can be effectively compensated using the proposed deskewing scheme.     

Parallel interference cancellation for carrier frequency offset in OFDM assisted with recursive least squares algorithm

Parallel interference cancellation (PIC) assisted with recursive least squares (RLS) algorithm is proposed to cancel the interference due to the carrier frequency offset (CFO) in orthogonal frequency division multiplexing (OFDM) system. The proposed algorithm is composed of two stages, which are RLS scheme and PIC scheme. RLS scheme is selected to compensate the frequency offset in the time domain in the first stage, and the interference induced by residual frequency offset is canceled by the PIC scheme in the frequency domain in the second stage. The result of bit error rate (BER) shows that its performance is robust for cancellation as comparison criteria, even though the frequency offset is 0.45. The 16QAM constellation is also simulated to observe the improvements from the proposed suppression schemes.     

新型排列组合高压缩多载波调制系统

提出一种基于高压缩多载波调制(HC-MCM,high compaction multi-carrier modulation)技术和排列组合正交频分复用(PC-OFDM,parallel combinatory OFDM)技术的新型调制系统,即排列组合高压缩多载波调制(PC/HC-MCM)系统。同PC-OFDM系统相比,PC/HC-MCM能够大幅度提高系统的带宽效率。同时给出了2种PC/HC-MCM系统的仿真性能。PC/HC-MCM系统稍加改造可以应用于不同的多载波系统。     

基于组合逻辑电路实现方法的探究

为缩短理论与实践的距离,提高灵活应用数字元器件的能力,提出了组合逻辑电路设计的第五步.组合逻辑电路设计通常有四步,设计完成画出符合功能要求的逻辑图,一般是把其转换成TrL与非门形式的逻辑图.第五步研究用多少个、何种逻辑门、译码器、数据选择器,怎样实现组合逻辑电路.实践证明,只要把逻辑电路与选择实现功能器件相互对应输入输...     

组合逆变充电在高性能发射机上的应用

介绍了一种供线型调制器用的大功率组合逆变充电电源。阐述了它的工作原理,分析了充电电流的参数,讨论了组合应用时的注意事项。说明了此种调制器的优点,给出了实际应用的测试波形。     

A novel algorithm for solution of a combinatory set partitioning problem

A novel efficient algorithm for solution of the problem of equal partitioning of a set with predefined weights of elements is proposed. The algorithm is based on calculation of a linear group preserving an invariant: the set of zeros of a cubic form. Algorithms for solution of related problems, including the problem of the search for the second solution if the first solution is known, are discussed.     

OFDM报告

正交频分复用技术(OFDM)利用相互正交的多个子载波束传送信息。具有高的频谱利用率和良好的抗多径干扰能力，已被应用于数字音频广播、高清晰度电视和无线局城网等方面，并且被看作是第四代移动通信的核心技术之一。介绍了OFDM的基本原理、信号收发器和加载算法，并在分析了这一技术的优缺点后，展望了它的发展前景。     

N-continuous OFDM

In this letter we report a new OFDM signalling format characterized by a precoder that renders the emitted signal's phase and amplitude continuous. It achieves superior out-of- band power characteristics at the price of a slightly reduced receiver sensitivity.     

基于OFDM的无线接入技术

本文首先介绍了正交频分复用技术(OFDM)的原理、技术优点,它在无线局域网中的应用特点.然后分析了在宽带无线接入技术中,三种基于OFDM而发展起来的技术,VOFDM、WOFDM和flash-OFDM的性能特点,最后展望了OFDM在未来移动通信系统中的应用.     

VLSI for OFDM

This article discusses the VLSI implications of high-speed coded orthogonal frequency-division multiplexing modulation. This is achieved by looking at practical examples of the computational blocks that constitute a COFDM modem and then examining examples of COFDM chips     

Correlatively coded OFDM

A class of correlative codes is proposed to significantly improve the spectral performance of the rectangularly pulsed orthogonal frequency-division multiplexing (OFDM) signal with or without cyclic prefix or zero padding. It is analytically shown that the correlatively coded OFDM signal can achieve very high spectral efficiency while yielding an extremely small fractional out-of-band power.