一种基于最小误码率的OFDM自适应比特及功率分配算法

OFDM自适应调制技术根据各子载波在频率选择性衰落信道中不同的瞬时增益,动态地分配数据比特和发射功率,可以优化系统性能,提高频谱效率。该文主要研究OFDM系统发射功率和传输比特数不变时误码率最小化的自适应(MA)算法。提出一种以注水门限为迭代参数的MA算法,并引入有记忆步长迭代法,提高算法的稳定性。仿真结果表明,与过去的算法相比,该算法能以较低的复杂度获得更好的性能。     

一种基于自适应天线的OFDM自适应比特分配算法

本文提出了一种利用自适应天线阵列实现自适应OFDM系统的方案。该方案利用抽样矩阵求逆(SMI)算法对天线阵列进行最优权值的估计,并根据天线权值计算出的信噪比(SNR)。在各个子载波上进行自适应的比特分配。仿真结果表明。与传统的OFDM系统相比,利用此方案实现的自适应OFDM系统,误码率性能可以得到有效的改善。     

基于MMSE准则自适应预处理算法研究

自适应OFDM(Orthogonal Frequency Division Multiplexing)系统根据信道情况自适应地分配各个子载波发送的比特和功率,在频率选择性衰落信道条件下,它比传统的OFDM系统有更好的误比特性能。提出了一种基于MMSE准则的自适应预处理算法,并将该算法应用于自适应OFDM系统,与基于最大信息速率设计的自适应OFDM系统相比,误比特性能有了显著提高。     

光OFDM系统设计

随着网络技术发展,光OFDM混合接入技术具有光通信高速宽带和无线接入灵活、无所不在的优点,成为当今的研究热点.搭建光OFDM通信系统,在光接入网中使用OFDM调制方式,利用OFDM系统极佳的频带利用率特性,提高了光接入系统的带宽利用率,并降低了系统的误码率.在搭建的实验系统中,成功地在不足2.5GHz带宽的光信道中完成...     

自适应比特功率分配的MIMO OFDM系统性能

该文首先分析了多天线发射和接收(MIMO)的OFDM系统模型。然后针对在多径衰落信道下,OFDM中一些深度衰落的子载波降低了系统性能。该文把一般多载波系统中的自适应比特功率分配算法推广应用到多天线OFDM系统中。同时研究了自适应MIMO OFDM系统的频谱效率。仿真结果表明,自适应比特功率分配提高了MIMO OFDM的误比特率性能和频谱效率。     

OFDM系统中的一种新的比特功率分配算法

针对自适应OFDM系统中满足用户QoS(这里主要指用户带宽及误码率这两个指标)要求的比特功率分配这一问题,提出了一种新的算法,该算法以每次比特分配时,使得每比特(一次可分配多比特信息)的功率代价最小为原则,获得了良好的性能,仿真结果表明,该算法在满足用户QoS要求的情况下,其发射总功率比现有的同类算法小,性能更佳。摘要     

一种基子自适应天线的OFDM自适应比特分配算法

本文提出了一种利用自适应天线阵列实现自适应OFDM系统的方案.该方案利用抽样矩阵求逆(SMI)算法对天线阵列进行最优权值的估计,并根据天线权值计算出的信噪比(SNR),在各个子载波上进行目适应的比特分配.仿真结果表明,与传统的OFDM系统相比,利用此方案实现的自适应OFDM系统,误码率性能可以得到有效的改善.     

OFDM系统信道估计和自适应分配算法的研究

在多径衰落的信道中,用固定调制方式的分配技术可能会造成OFDM系统资源浪费,考虑如何将自适应分配技术与OFDM相结合成为提高移动通信性能的关键技术。本文中提出一种基于动态信噪比SNR切换门限的自适应算法,该算法在保证通信质量所需BER的前提下,结合OFDM和PSK/QAM调制方式的优势,按照各个子信道的状态分配比特信息量和功率大小,使所需要的发射功率达到最优化。本算法能提高OFDM的频谱利用率,也能使系统获得更优的性能。     

自适应调制技术在OFDM系统中的应用

基于OFDM系统的自适应调制与解调根据信道估计的结果进行比特和功率的分配,进而自适应的选择相应的调制方式,能够最大限度的提高频谱利用率和系统的整体性能。介绍一种主流的自适应调制算法,并进行了系统仿真,得到误码率曲线图,比较直观的对比出采用自适应调制和固定调制方法的优劣。     

MIMO-OFDM自适应比特分配算法研究

针对当前OFDM系统中的比特分配算法复杂度比较高,不适合运用于自适应调制系统中,提出改进的自适应比特分配调整算法,采用变步长调整的思想,进一步简化比特分配的复杂度。在此基础上,将OFDM和MIMO技术结合,进行MIMO-OFDM系统的相关参数仿真并进行分析。通过仿真说明本文介绍的算法计算复杂度小,成本较低,适用多用户,能够很好的应用到实际中。     

Analysis and Simulation of a Plastic Optical Fiber Access Network Based on OCDMA Technology

In this paper a plastic optical fiber (POF) access network based on optical code-division multiple access (OCDMA) technology is proposed. Recently, optical transmission using POF has received much attention due to its low weight, large core diameter, flexibility, and easy installation. Specially, its high bandwidth makes POF a very attractive candidate for a transmission media in an access network based on OCDMA technology. A conventional OCDMA system only allows a finite number of units to transmit and access simultaneously according to the number of channels which is restricted by BER. To resolve this problem a novel protocol is also proposed in this paper. The protocol can efficiently support variable-sized messages, and any new unit can join the network at any time without requiring network initialization. To implement the demonstration, each optical network unit is equipped with a fixed and a tunable optical encoder/decoder. The optical encoder/decoder employing planar holographic optical processors (HOPs) in this system may be of low fabrication cost. The network throughput and average delay using various system parameters has been investigated by numerical analysis and simulation experiments. It is shown that the dynamic control protocol in this POF access network based on OCDMA technology is valid and efficient.     

一种采用光学相位分集接收技术的相干光正交频分复用远端接入系统

提出了一种采用基于光学相位分集接收技术实现远程相干光正交频分复用(CO-OFDM)信号的远程光接入方案,并进行了理论研究和仿真验证。在本方案中,没有使用色散补偿光纤(DCF)或者色散补偿模块(DCM)补偿光纤信道色散导致的负面效应,原因是CO-OFDM信号能有效抵抗传输过程中色度色散(CD)和偏振模色散(PMD)引起的负面效应。仿真结果表明,10Gbit/s CO-OOFDM信号在标准单模光纤(SMF-28)传输320km后,采用相位估计技术得到的OFDM电信号,其时域波形的相位抖动幅度更小;与采用光载波自提取技术接收相位调制COOFDM的方案进行比较,测试误差向量幅度(EVM)的结果表明,本文方案可以获得更好的COOFDM信号接收性能,星座图中星座点收敛更加紧凑,接收的CO-OFDM信号质量更高。     

Power-efficient schemes using directly modulated lasers for intensity modulation and direct detection OFDM-PONs

The intensity modulation and direct detection (IM/DD) passive optical network (PON) has been demonstrated as a cost-effective solution for a long-reach (\(>\!80\,\hbox {km}\)) access system because it can be easily installed and maintained with low cost and complexity. Meanwhile, orthogonal frequency division multiplexing (OFDM) has been widely used in PONs due to its high spectral efficiency and strong resistance to dispersion impairments. So, the IM/DD OFDM-PON emerged. The power efficiency has attracted great research interests in IM/DD OFDM-PONs. The previous works achieved power savings from the perspective of MAC-layer or hardware-level optimization, but they neglected designing appropriative algorithms, and the long-reach transmission performance cannot be guaranteed. In this paper, we propose an improved Hughes-Hartogs algorithm (IHHA) to adjust the number of bits and power level allocated for each subcarrier, with the objective to minimize the electrical transmitting power of all subcarriers. The OFDM signal is generated according to the bit/power allocation result of IHHA, and we conduct extensive simulations to verify the long-reach transmission performance of our system. Simulation results show that our system has high power efficiency by using IHHA, and bit error rate satisfies the forward error correction limitation after 100 km single-mode fiber transmission.     

Modal bandwidth enhancement in a plastic optical fiber by W-refractive index profile

A plastic optical fiber (POF) having a W-shaped refractive index profile (W-shaped POF) was prepared for the first time that had a possibility to realize a higher bit rate transmission than those of the conventional silica-based multimode fiber and graded index (GI) POF links. Since the W-shaped POF has a valley of the refractive index at the boundary of the core and cladding of the conventional graded-index (GI) POF, the group delay of higher order modes is strongly influenced, and the modal dispersion in the GI POF is compensated. By comparing the propagating mode properties of the W-shaped POF with those of the GI POF, we clarified theoretically and experimentally that the index valley has a remarkable modal dispersion compensation effect.     

塑料光纤在高速局域网中的应用

文章主要叙述了塑料光纤(POF)的性能及其应用.随着网络技术及其各种服务的发展,短距离高速通信网络将是人们的一个追求目标,而POF因其具有性能好、传输速率高、价格低廉、连接方便等一系列优点将会成为高速局域网的首选传输介质.     

光纤OFDM系统中的色散补偿技术研究

为了减小光纤的色度色散对光纤正交频分复用（OFDM）系统性能的影响,提出了将无线通信中的信道估计器引入光纤OFDM系统进行信道估计的色散补偿方法。在理论上分析了光纤的色度色散对于传输OFDM信号的影响,并在实验中采用梳状导频的形式,在每个OFDM码元的特定的子载波上插入导频,在接收端通过基于最小平方（LS）原则的LS估计器进行信道估计,得到了OFDM光纤传输的信道幅度响应和相位响应,通过使用LS估计器,直接调制的光OFDM信号在单模光纤中传输200km,误比特率低于10-6 ,功率代价小于2dB。结果表明,高频子载波较低频子载波更容易受到色散的影响,在光纤OFDM系统中引入信道估计器进行信道估计能够有效补偿由色度色散带来的相位偏移和幅度衰减。     

Low-cost adaptive directly modulated optical OFDM based on semiconductor optical amplifier

Low cost optical OFDM has great potential for next generation optical access networks and PONs, due to its high flexibility in bandwidth manipulation, and high spectral efficiency. Here, a low cost optical OFDM is proposed, based on adaptive direct modulation semiconductor optical amplifier. Adaptive current loading techniques for PAPR (peak to average power ratio) reduction are proposed and analyzed. Simulations show that the proposed adaptive techniques enable significant BER improvement.     

Design of Low-Loss Graded-Index Plastic Optical Fiber Based on Partially Fluorinated Methacrylate Polymer

As a promising candidate of optical home network, a novel Gigabit Ethernet prepared by inexpensive partially fluorinated polymer-based graded-index plastic optical fiber (GI POF) was proposed. Poly (2,2,2-trifluoroethyl methacrylate) (P3FMA) was selected as a base material for the GI POF because of its high transparency, low material dispersion, and low cost. The transmission characteristics were investigated, and it was clarified that the newly developed GI POF has low-loss (71 dB/km at 650 nm), high humidity stability, and high-bandwidth (4.86 GHz for 50-m transmission) property. Moreover, 1.25-Gbps data transmission over 50 m was demonstrated by P3FMA-based GI POF.      

A novel design of orthogonal frequency division multiplexing-based passive optical networks

Orthogonal frequency division multiplex (OFDM) has been successfully used in wireless communications, and now people begin to see it as an excellent candidate technique in optical access networks. In this article, we first make comparison between OFDM-based passive optical network (PON) and traditional PONs, and then review some previous work of OFDM PON. After that we introduce our physical layer scheme. In addition, network architecture, medium access control (MAC) protocol, and three dynamic bandwidth allocation schedules that optimized for OFDM communication are recommended. At last, computer simulation results are given to demonstrate the performance of the three schedules.     

一种基于塑料光纤的计算机网络的研制与开发

提出一种基于塑料光纤(POF)传输媒质的计算机网络.该网络由个人计算机、光发射/接收单元和650nm的POF组成,光发射/接收模块用Agilent公司生产的HFBR-1505/2505A.为满足数字光纤通信系统对线路编码的要求,采用传号反转码并由光收发单元实现码型变换.研究结果表明,该网络具有高带宽、高可靠性的特点.通过编写的Visual C 网络语音电话程序,验证了该方案的有效性和可行性.