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FAN Da CAO Zhigang 《电子学报:英文版》2008,(4):685-690
This paper investigates the frequency synchronization in the uplink of the Orthogonal frequency- division multiple access (OFDMA) system with interleaved subcarrier assignment. In such a system, one of the key problems is the multiuser frequency synchronization, which focuses on the multiple-parameter estimation of the Carrier frequency offsets (CFOs). In this paper, we propose a two-stage frequency offset estimation algorithm. The main advantage of the proposed method is that it can obtain the CFOs of all users simultaneously using only one OFDMA block. In addition, a novel CFO-compensation method is presented. Based on the inner signal structure of interleaved-OFDMA uplink, the new scheme uses adaptive beamformer to compensate the CFO of each user and isolate the signals of all users at the same time. Compared to the previously known methods, the proposed algorithm can provide accurate frequency synchronization and data detection without feeding CFO estimates back to active users for frequency adjustment. 相似文献
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现有正交频分多址接入(OFDMA)中继网络资源分配的研究均采用固定时域配置下的频域分配和功率分配,不能很好适应用户业务在时域上的变化。该文针对OFDMA中继网络提出一种可最优节能的资源分配策略和一种简化的节能资源分配策略,为资源分配问题建立一般化的模型,即动态分配时域资源、频域资源和功率资源,所建模型具有很强的灵活性和适应性,不仅适用于固定时域分配系统,也适用于非固定时域分配系统。此外针对非满负荷业务,在保证用户服务质量的情况下,以节能为目标对无线非协作中继网络的资源分配进行能效最大化建模,使用拉格朗日乘数法对模型求解。考虑到算法复杂度,应用指派问题中的匈牙利算法设计出一种简化的资源分配策略。理论和仿真结果表明,最优节能资源分配算法能够得到能效的最大化,而简化节能资源分配算法与最优节能资源分配算法在能效上的差距不足5%,但算法复杂度得到了显著降低。而且,动态分配时域资源比固定时域分配对用户分布不均或链路分布不均有更强的适应性。 相似文献
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本文对WiMAX的协议参考模型进行了描述,对WiMAX物理层的主要特点进行了分析,给出了WiMAX物理层的5种实现方式,最后简要介绍了正交频分复用(OFDM)、正交频分多址(OFDMA)、混合自动请求重传(HARQ)、自适应调制编码(AMC)的工作原理和优缺点。 相似文献
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为了减少LTE-A中继系统内的干扰,针对采用正交频分多址接入(OFDMA)技术的下行链路,提出了一种新的准动态频率资源划分方法。该方法适用于小区内所用频率资源不连续的场景。该方法通过将频率资源设定为已聚合的多个连续频率资源,避免了部分邻频干扰。依照基站及中继站的分布与数目,对频率资源进行均匀划分及合理调配,减少了同频干扰源的数目,提高了用户的平均频谱效率。通过准动态的空闲频率资源分配,提高了频率资源的利用率。大量的仿真结果表明,提出方法能够有效地提高用户的信号干扰噪声比(SINR)以及平均频谱效率。 相似文献
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MIMO-OFDMA技术是正交频分多址(OFDMA)技术与输入多输出(MIMO)系统结合形成的,该技术是在OFDMA传输系统中采用阵列无线实现空间、时间分集,提高系统容量和覆盖范围。基于OFDMA的MIMO系统具有逼近极限的系统容量和良好的抗衰落特性,人们普遍认为MIMO-OFDMA技术将是4G移动通信网络采用的核心技术。今年8月底,三星电子在韩国济州岛成功举办了“2006三星4G论坛”。在这次会议上,三星电子首次在全球公开演示了4G技术。这其中包括在以60公里时速行驶的汽车内进行100Mbps的数据传输;多个用户同时以1Gbps的速度下载32个频道的HD广播,并且同时使用超高速—巨联网上传下载、可视电话、论坛直播等服务;采用三星在小区边缘1bps/Hz干扰消除技术的4G通信系统无缝切换展示作为本次会议的主导者,三星电子延续了其Mobile WiMAX的神话,成功展示了在4G核心技术MIMO—OFDMAA的领先优势。下面,我来详细介绍一下三星4G核心技术。 相似文献
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Fractional frequency reuse (FFR) is an effective technique to mitigate co-channel interference in orthogonal frequency division multiple access (OFDMA)-based broadband cellular systems. In this paper, we present a generalized model for FFR under which all existing FFR schemes can be considered as its special cases. Additionally, quality factor has been proposed to indicate the quality of the subband. An interesting conclusion can be drawn that, as the power ratio in FFR is adjusted continuously, the corresponding quality factor varies smoothly. Subsequently, simulation is conducted based on worldwide interoperability for microwave access (WiMAX), and the result agrees well with our theoretical analysis. Finally, an effective range for power ratio is presented, which is very instructive to practical system design. 相似文献
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Bongkyoung Kwon Raheem A. Beyah Myunghwan Lee John A. Copeland 《Wireless Communications and Mobile Computing》2013,13(10):967-984
For wireless mobile multihop relay (MMR) networks, we have chosen orthogonal frequency division multiple access (OFDMA) and time division duplex as a multiple access scheme and a duplex communication technique, respectively. We have also selected nontransparent relay stations (nt‐RSs) as relay nodes to extend the MMR network coverage. Through the nt‐RSs, far‐off subscriber stations (SSs) or hidden SSs can communicate with a base station (BS) that is connected to backhaul networks. In these MMR networks, the way in which a BS and nt‐RSs use OFDMA resources (e.g., OFDMA symbols and subcarriers) and share them might reduce system capacity and network throughput. Therefore, we proposed a new adaptive OFDMA frame structure for both the BS and the nt‐RSs. The proposed scheme is the first approach that incorporates the adaptive technique for wireless MMR networks. Based on the proposed adaptive OFDMA frame structure, an adaptive OFDMA resource allocation for SSs within a BS as well as nt‐RSs was proposed. To derive the maximum OFDMA resource that nt‐RSs can be assigned and to synchronize access zones and relay zones between a superior station and its subordinate nt‐RSs, three properties are introduced: a data relay property, a maximum balance property, and a relay zone limitation property. In addition, we propose max‐min and proportional fairness schemes of the proposed adaptive frame structure. Our numerical analysis and simulations show that the proposed OFDMA allocation scheme performs better than the nonadaptive allocation scheme in terms of network throughput and fairness especially in the asymmetric distribution of subscriber stations between access zones and relay zones in the MMR networks. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Yanyan Shen Gang Feng Bo Yang Xinping Guan 《Wireless Communications and Mobile Computing》2014,14(2):269-283
We address the problem of subchannel and transmission power allocation in orthogonal frequency division multiple access relay networks with an aim to maximize the sum rate and maintain proportional rate fairness among users. Because the formulated problem is a mixed‐integer nonlinear optimization problem with an extremely high computational complexity, we propose a low‐complexity suboptimal algorithm, which is a two‐step separated subchannel and power allocation algorithm. In the first step, subchannels are allocated to each user, whereas in the second step, the optimal power allocation is carried out on the basis of the given subchannel allocation and the nonlinear interval Gauss–Seidel method. Simulation results have demonstrated that the proposed algorithm can achieve a good trade‐off between the efficiency and the fairness compared with two other existing relevant algorithms. In particular, the proposed algorithm can always achieve 100% fairness under various conditions. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Dionysis Xenakis Dimitris Tsolkas Nikos Passas Nancy Alonistioti Lazaros Merakos 《Wireless Communications and Mobile Computing》2012,12(11):985-998
Modern wireless orthogonal frequency division multiple access (OFDMA) systems incorporate dynamic resource allocation (DRA), adaptive modulation and coding (AMC), and power control (PC) to exploit multiuser diversity and achieve higher system throughput. In the literature, only a few proposed algorithms deal with the contiguous DRA problem according to which a contiguous collection of resources can be allocated to each user. This paper formulates this high complexity problem, provides a suitable decision metric and a simple yet efficient solution. The proposed algorithm allocates in each step a contiguous collection of resources to the pending user that leads to the highest estimated correctly received number of bits. Simulation results show that, in this way, considerably improved performance can be achieved in terms of overall system throughput, spectral efficiency, and served traffic. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Cellular relay networks adopting orthogonal frequency division multiple(OFDM)technology has been widely accepted for next generation wireless communication due to its advantage in enlarging coverage scale as well as improving data rate.In order to improve the performance of user equipments(UEs)near the cell edge,especially to avoid the interference from inter-cell and intra cell,an enhanced soft frequency reuse scheme is adopted in this paper to assure inter-cell interference coordination(ICIC).Compared with traditional frequency allocation work,the proposed scheme is interference-aware and load-adaptive,which dynamically assigns available frequency among UES under certain schedule method in variable traffic load condition and mitigates interference using information provided by interference indicator.It can improve signal-to-interference plus noise ratio(SINR)of the UE in each sub channel thus enable the system achieve better throughput and blocking probability performance.Simulation results prove that the proposed scheme may achieve desirable performance on throughput,blocking probability and spectral utilization in the sector under different traffic load compared with other schemes. 相似文献
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Lin Bai Chen Chen Bo Wu Jianhua He 《International Journal of Communication Systems》2013,26(7):912-926
In this paper, we propose a resource allocation scheme to minimize transmit power for multicast orthogonal frequency division multiple access systems. The proposed scheme allows users to have different symbol error rate (SER) across subcarriers and guarantees an average bit error rate and transmission rate for all users. We first provide an algorithm to determine the optimal bits and target SER on subcarriers. Because the worst‐case complexity of the optimal algorithm is exponential, we further propose a suboptimal algorithm that separately assigns bit and adjusts SER with a lower complexity. Numerical results show that the proposed algorithm can effectively improve the performance of multicast orthogonal frequency division multiple access systems and that the performance of the suboptimal algorithm is close to that of the optimal one. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Rate adaptive resource allocation in orthogonal frequency division multiple access system using multi‐objective immune algorithm 下载免费PDF全文
Chai Zheng‐Yi Zhu Si‐Feng Shen Lian‐Feng 《International Journal of Communication Systems》2014,27(11):3255-3265
Rate adaptive downlink resource allocation in orthogonal frequency division multiple access system is a constraint optimization problem, which is to maximize the minimum data rate of the user subject to constraint that total power cannot exceed a given value. How to handle the constraint is a key issue for constrained optimization problem. Different with the available schemes on constraint handling, the proposed algorithm converts the constraint into an objective. Then, the resource allocation is combined into a multi‐objective optimization problem. An improved multi‐objective optimization algorithm based on artificial immune system is proposed to solve it. The simulation results show that, compared with previous schemes, the proposed algorithm performs remarkable improvement in sum capacity. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Hiep H. Nguyen Suk‐Hwan Lee Won‐Joo Hwang 《International Journal of Communication Systems》2015,28(14):2020-2034
Because energy efficiency (EE) is inevitable in future wireless cellular networks, in this paper, we focus on improving the number of bits delivered to users for each unit energy consumption in the downlink of orthogonal frequency‐division multiple access cellular networks with base stations (BSs) coordination. Specifically, each BS shares the channel qualities of users with others and jointly choose the set of co‐channel users and the transmit power allocated to maximize the EE of the system subject to the transmit power ceiling of each BS and minimum required data rate. We formulate the problem as a nonlinear fractional optimization problem, using nonlinear fractional programming, the original hard‐to‐solve problem is transferred to a new one that has the same optimal solution and is easier to solve, this enables two iterative algorithms that achieve nearly the same maximum EE. Numerical results are provided to show the convergence and superiority of the two proposed. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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1 Introduction Next-generation wireless communication systems (systems beyond 3G) will be required to provide flexible and easy deployment solution to high-speed communications and to support a variety of services utilizing advanced multiple access techni… 相似文献
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ngela Hernndez Israel Guío Antonio Valdovinos 《Wireless Communications and Mobile Computing》2010,10(11):1409-1430
This paper focuses on the inter‐cell interference (ICI) management problem in the downlink channel for mobile broadband wireless OFDMA‐based systems. This subject is addressed from the standpoint of different interrelated resource allocation mechanisms operating in multi‐cell scenarios in order to exploit frequency and multi‐user diversity: ICI coordination/avoidance and adaptive subcarrier and power allocation. Even though these methods can be applied in a stand‐alone way, a significant performance improvement is achieved if they are jointly designed and operate in a combined basis. Several alternatives for mixed frequency and power ICI coordination schemes are proposed in this paper. Connected with a proper power mask‐based design, the potential gain of a flexible frequency sectorization solution, halfway between fractional/soft frequency reuse and pure frequency sectorization, is explored. The main objective is to outperform fractional/soft frequency reuse offering an attractive trade‐off between cell‐edge user data rates and average cell throughput. Proposals concerning ICI coordination/avoidance have been evaluated in combination with several heuristic adaptive subcarrier and power allocation algorithms. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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This article investigates two fairness criteria with regard to adaptive resource allocation for uplink orthogonal frequency division multiple access (OFDMA) systems. Nash bargaining solution (NBS) fairness and proportional fairness (PF) are two suitable candidates for fairness consideration, and both can provide attractive trade-offs between total throughput and each user's capacity. Utilizing Karush-Kuhn- Tucker (KKT) condition and iterative method, two effective algorithms are designed, to achieve NBS fairness and proportional fairness, respectively. Simulation results show that the proposed resource allocation algorithms achieve good tradeoff between the overall rate and fairness, with little performance loss from the total capacity. 相似文献