A novel adaptive OFDM algorithm based on sub-band division

Some classical adaptive OFDM algorithms, such as P.S. Chow algorithm , Greedy algorithm and Fischer algorithm can provide higher performance, but these algorithms require a large number of operations to achieve the cycle, affecting communication rate. The idea of sub-band division algorithm is to sub-carrier group of the bundle, the same set of subcarriers use the same modulation to further reduce signaling overhead, computation is also reduced accordingly. In this paper, based on the sub-band division algorithm, an adaptive algorithm with low complexity OFDM is proposed. This algorithm is based on gain sorting. In the premise of communication quality required for bit error rate (BER), according to the level of each sub-channel fading dynamic distribution of bits and power so that the required minimum total power emission. Simulation results show that the adaptive OFDM algorithm can better improve the performance of OFDM systems.     

Adaptive power loading based on unequal-ber strategy for OFDM systems

An adaptive power loading algorithm with uniform (nonadaptive) bit allocation is proposed for constant data rate OFDM systems in this letter. This algorithm aims to minimize the transmit power while guaranteeing the target mean bit error rate (BER). The power loading is based on the Unequal-BER (UBER) strategy which permits unequal mean BERs on different subcarriers. The closed-form expressions for optimal BER and power distributions are derived. Simulation results indicate the superiority of the proposed algorithm.     

Adaptive subcarrier allocation and bit loading for voice/data transmission in multiuser OFDM systems

A new algorithm of adaptive subcarrier allocation and bit loading (A‐SABL) is proposed for simultaneous voice and data transmission in multiuser OFDM systems. The algorithm takes advantage of the frequency diversity and the voice/data transmission requirements to dynamically assign the number of subcarriers and bits/per symbol on each subcarrier for each user in a single cell. Due to the strict delay requirement of voice service, the subcarriers with low channel gains are assigned for voice transmission with a small number of bits per symbol to guarantee its required bit‐error‐rate (BER) and transmission rate. Based on the remaining subcarriers with high channel gains and the transmission power, the throughput of data transmission is then maximized by loading as many bits as possible on each subcarrier to achieve the required transmission bit rate and BER. Theoretical analysis and simulation on the proposed algorithm show that a better performance is obtained than previously reported schemes. Copyright © 2008 John Wiley & Sons, Ltd.     

基于梳状导频的OFDM分组自适应比特装载与功率控制

无线通信环境中信道信息(ChannelStateInformation,CSI)随时间变化明显,需要不断地更新自适应比特装载和功率控制的策略。现有的OFDM自适应比特装载方法需要大量的信令来传递当前比特装载的策略,不适用于无线通信的应用环境。为此,本文针对OFDM系统的特征提出了一种利用插入梳状导频的信道估计得到的带有误差的信道信息,来完成自适应比特装载的算法。首先把OFDM子载波进行分组,然后利用基于梳状导频的信道估计对信道时变进行跟踪,使用即时获得的CS完成自适应比特装载算法。仿真实验证明,在保证算法简单、实用及保证要求的误码率(BER)性能的情况下,信道信令的开销低于传统算法的10%。     

Deepen spectrum notch and reduce PAPR in OFDM systems via combining subcarriers precoding with tone reservation

In orthogonal frequency division multiplexing (OFDM) systems,spectrum notch can be generated to mitigate interference to other narrow-band services by turning off corresponding subcarriers.However,the inter-carrier interference may limit considerably the produced notch depth.Another problem in OFDM is the high peak-to-average power ratio (PAPR).In this paper,a technique combining subcarriers precoding with tone reservation is proposed to deepen spectrum notch and simultaneously reduce peak-to-average power ratio.Simulation results show that this presented joint algorithm can produce satisfied results to solve these problems at the expense of a moderate loss in bit error rate (BER) performance.     

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。     

New adaptive bit allocation algorithms for multiuser OFDM/CDMA systems

An adaptive bit allocation algorithm is proposed for multiuser transmission in OFDM/CDMA systems. The proposed scheme takes advantage of frequency diversity to dynamically allocate a suitable number of bits/per symbol on subcarriers of each user based on the transmitting objectives such as the required transmission rate and BER. A suboptimal solution to the problem of the bit allocation on subcarriers for each user is derived by minimizing the interference power from each user. Then an algorithm for adjusting the number of allocated bits is used to further reduce the interference without changing the total transmitted data rate. The performance obtained by minimizing the interference resulting from each user is studied in terms of BER, transmission data rate and the system capacity supporting multiple users. The theoretical analysis and simulation results show that the proposed algorithm substantially outperforms those reported previously.     

多用户OFDM系统中子载波比特分配算法

针对多用户OFDM系统中的功率优化问题,提出了一种新的子载波、比特分配算法。利用匈牙利算法对子载波进行初始分配,然后根据信道的状态信息为每个子载波动态地分配比特,最后对分配的结果作进一步调整,直到发射总功率不再减小为止。仿真结果表明,调整后的结果比原有方法有所改善,在满足传输速率和误码率要求的条件下,有效地降低了系统发射总功率。     

Multiuser OFDM with adaptive subcarrier, bit, and power allocation

Multiuser orthogonal frequency division multiplexing (OFDM) with adaptive multiuser subcarrier allocation and adaptive modulation is considered. Assuming knowledge of the instantaneous channel gains for all users, we propose a multiuser OFDM subcarrier, bit, and power allocation algorithm to minimize the total transmit power. This is done by assigning each user a set of subcarriers and by determining the number of bits and the transmit power level for each subcarrier. We obtain the performance of our proposed algorithm in a multiuser frequency selective fading environment for various time delay spread values and various numbers of users. The results show that our proposed algorithm outperforms multiuser OFDM systems with static time-division multiple access (TDMA) or frequency-division multiple access (FDMA) techniques which employ fixed and predetermined time-slot or subcarrier allocation schemes. We have also quantified the improvement in terms of the overall required transmit power, the bit-error rate (BER), or the area of coverage for a given outage probability     

一种无线OFDM系统中的高效功率和比特分配算法

在限定无线OFDM通信系统的传输速率和最大误码率的情况下,该文提出了一种最小化发射功率的高效功率和比特分配算法。该算法首先利用注水水平和系统传输速率之间的关系求出无需预设步长和初始值的注水水平迭代公式,然后在部分子载波上使用简化的Greedy算法进行强制收敛。由于充分地利用了注水算法和Greedy算法的优点,该文算法不仅有效地避免了传统自适应算法的收敛性、初始值和步长选择等问题,而且计算效率更高。仿真结果验证了该算法的有效性。     

基于贪婪算法自适应比特功率分配的MIMO-OFDM系统性能

OFDM技术、MIMO技术和自适应调制技术的结合可以有效的抗无线信道的各种衰落,最大限度提高系统的容量和传输质量。借助于贪婪算法的最佳比特功率分配,本文深人研究了基于贪婪(greedy)算法自适应比特功率分配的MIMO- OFDM系统性能,对贪婪算法、等比特功率分配算法及CHOW算法下的系统误比特率(BER)进行比较,并对不同天线配置下的MIMO-OFDM系统的误比特率(BER)进行比较,推导及仿真结果表明：基于贪婪算法自适应比特功率分配的MIMO-OFDM系统BER要好于采用传统比特功率分配算法的系统BER,其频谱效率也要优于另外两种算法；同时,在采用相同的贪婪算法自适应动态比特分配策略下,MIMO-OFDM系统的BER要好于SISO-OFDM系统的BER。     

一种基于错误传播补偿的V—BLAST自适应比特和功率分配算法

本文探讨了V-BLAST系统在总发射功率受限和一定目标误码率要求的前提下,基于自适应调制时间块的比特、功率分配问题,分析和比较了系统在采用不同串行干扰抵消顺序时的抗信道时变性能和抗错误传播性能,找出了在BER和速率两方面性能最优的串行干扰抵消顺序。针对错误传播对系统BER性能的冲击,提出了一种新的基于错误传播补偿的V-BLAST自适应比特、功率分配方案。仿真结果表明,该方案能显著提高系统在时变信道下的BER性能,有效增大自适应调制块长度,减小反馈开销。     

Adaptive Power and Bit Allocation in Multicarrier Systems

We present two adaptive power and bit allocation algorithms for multicarrier systems in a frequency selective fading environment. One algorithm allocstes bit based on maximizing the channel capacity, another allocates bit based on minimizing the bit-error-rate （BER）. Two algorithms allocate power based on minimizing the BER. Results show that the proposed algorithms are more effective than Fischer＇s algorithm at low average signal-to-noise ration （SNR）. This indicates that our algorithms can achieve high spectral efficiency and high communication reliability during bad channel state. Results also denote the bit and power allocation of each algorithm and effects of the number of subcarriers on the BER performance.     

一种新的自适应OFDM算法的探讨

在具有多径干扰的无线信道中仅应用传统OFDM既影响通信速率,也浪费资源.由于信道的频率选择性衰落,OFDM系统的每个子信道具有不同的传输能力.文中提出一种计算量较小、简单实用的自适应OFDM算法,在保证通信质量所需BER的前提下,按照各个子信道衰落程度动态的分配比特和功率,使所需要的发射总功率最小.仿真结果表明,采用该自适应OFDM算法可以提高OFDM系统的性能.     

OFDM闭环发射分集结合自适应功率分配

将自适应功率分配技术应用于多发送多接收天线正交频分复用(MIMO-OFDM)系统,如何在载波和天线间分配能量是个关键问题。该文提出:对不同发射天线的各个子载波采用闭环发射分集方案;接着再进行载波间的功率分配,该算法的目标是使误码率最小。文中用数学方法证明了此方案是使总误码率最小的最佳方案。仿真结果显示:在误码率取0.1%时,对于两根发射天线一根接收天线4个子载波的OFDM系统,与传统的将开环发射分集与OFDM相结合的算法相比,此算法能带来6.5dB的增益。     

An Efficient Adaptive Modulation Scheme for Wireless OFDM Systems

An adaptive modulation scheme is presented for multiuser orthogonal frequency‐division multiplexing systems. The aim of the scheme is to minimize the total transmit power with a constraint on the transmission rate for users, assuming knowledge of the instantaneous channel gains for all users using a combined bit‐loading and subcarrier allocation algorithm. The subcarrier allocation algorithm identifies the appropriate assignment of subcarriers to the users, while the bit‐loading algorithm determines the number of bits given to each subcarrier. The proposed bit‐loading algorithm is derived from the geometric progression of the additional transmission power required by the subcarriers and the arithmetic‐geometric means inequality. This algorithm has a simple procedure and low computational complexity. A heuristic approach is also used for the subcarrier allocation algorithm, providing a trade‐off between complexity and performance. Numerical results demonstrate that the proposed algorithms provide comparable performance with existing algorithms with low computational cost.     

Extended Subcarrier Weighting for Sidelobe Suppression in OFDM Based Cognitive Radio

Subcarrier weighting (SW) is a recognized technique for sidelobe suppression in OFDM systems. In this paper SW is discussed in the context of cognitive radios where some portion of the spectrum is shared with primary users so it is required to notch that portion. A major disadvantage with SW scheme is bit error rate (BER) degradation due to unequal power distribution among different subcarriers therefore the primary objective of the paper is to enhance the performance of SW without additional degradation in BER performance. To this extent we propose an Elliptical-SW scheme by expanding the locus of weights to elliptical region. Simulation results show that the proposed scheme can produce deeper notch as compared to Conventional-SW for same BER performance. In second part we present a Partial-SW scheme by applying SW to lesser number of subcarriers. It can enhance BER performance significantly with negligible loss in sidelobe suppression capacity. Another scheme namely Guarded-SW is also proposed in this paper to provide further means to obtain very deep notches without any additional degradation in BER however it has to scarify some throughput. Finally an effective way of implementing SW in MIMO systems is presented by jointly optimizing weights over selected number of antennas.     

OFDM系统中动态子信道和功率的分配

在分析一种多用户OFDM系统中自适应子信道和比特功率分配算法的基础上,根据多径频率选择性衰落信道的瞬时特性,动态地为多用户分配子信道和传输比特数,并服从MA优化准则.并且进一步考虑了系统中有固定速率用户和可变速率用户同时存在的情况:在子信道分配时,先给固定速率的用户分配子信道,再给可变速率用户按照子信道链路增益最大化分配剩余的子信道;在信号发射功率分配上,按照"注水"法则分配,链路增益大的子信道分配的功率大,链路增益小的子信道分配的功率小,则系统的目标函数,总传输速率可以达到最大.仿真证明了此方案优于一般的方案.     

OFDM中自适应比特及功率分配的分析

在宽带移动OFDM(正交频分复用)系统中,不同的子信道经受不同的信道衰落,因此具有不同的传输能力。根据子信道的增益对子信道上加载的比特数进行自适应分配,可在满足一定误码率(BER)性能要求下使系统的总传输功率达到最小。本文研究了一种在一定传输速率下的自适应比特及功率分配算法。该算法可适用于多径频率选择性衰落信道。仿真结果表明,采用自适应技术可大大提高OFDM系统的性能。     

自适应比特分配算法在高速遥测系统中的应用

提出了一种简单、快速的正交频分复用(OFDM)系统的自适应调制算法。该算法在子信道分配已经完成的前提下,通过信道参数的估计,动态地分配子信道上的比特和功率,使得发送的每个符号的总比特数最大,从而提高信道的利用率及数据传输速率,满足了高速遥测系统所要求的传输速率及误码率。仿真结果表明,与等比特分配算法相比,本自适应比特分配算法相对简单,降低了系统的传输功率,其误码率性能明显好于等比特分配算法。