OFDMA蜂窝通信系统子载波分配技术分析

介绍了正交频分复用多址接入方案(OFDMA),并分析、比较了瑞利衰落下系统采 用不同子载波分配方案的性能。结果表明:OFDMA系统中,若不使用自适应子载波分配时,采 取间隔扩展分配方式的系统性能要优于分组分配方式;若使用自适应分配时,系统性能可以得 到很大提高,但增加了实现复杂度。     

一种OFDMA实时子载波分配算法及仿真

正交频分多址(OFDMA)是以OFDM调制为基础的新一代无线接入技术,在这种方式中,多址是通过给每个用户分配可用子载波总数的一部分来实现的。介绍了一种OFDMA下行链路的实时动态子载波分配算法,算法根据各个子载波对各个用户的瞬时信道增益,在使系统总的发送功率最小的准则下,为各用户分配最优的子载波组。最后用MATLAB语言仿真实现了该算法.仿真结果表明该算法性能要优于传统的静态子信道方案。     

Interleaved-OFDMA中基于子空间的 上行链路载波频偏估计方法

在OFDMA系统中,通过为每个用户分配不同的子载波可以实现并行数据传输.采用Interleaved子载波分配方法可以提高频率分集和系统容量,但是发射机和接收机之间的载波频率偏移会破坏子载波间的正交性,从而导致本用户的载波间干扰(ICI)以及用户间干扰(MUI).本文提出了一种基于子空间的两阶段频偏搜索方法,该方法只采用一个OFDMA符号块就可以实现Interleaved-OFDMA上行链路多个用户频偏的联合估计,并且不需要知道接入的用户个数及用户所占用的子信道,因此适用于随机分配子信道的情况.仿真结果验证了算法的精确度和有效性.     

交织OFDMA上行系统CFO估计算法的研究

文中对OFDMA系统中的子载波分配方法进行了研究,介绍了两种子载波分配方法的原理,对两种子载波分配方法进行了仿真,结果显示在频率选择性衰落信道中交织分配的OFDMA系统要比块分配的OFDMA系统获得更多的频率分集.给出了交织OFDMA系统上行链路的信号结构,由于发射机和接收机之间存在的载波频率偏移(CFO)将会影响子载波间的正交性,对多用户的CFO估计提出了一种估计算法,仿真的结果显示所提出的算法具有较好的性能.     

基于ESPRIT算法的子载波交织型OFDMA上行链路频偏估计

频率同步问题对于OFDMA系统来说至关重要。本文针对子载波交织分配的OFDMA系统上行链路，利用其接收信号周期性的结构特征，提出一种基于ESPRIT算法的多用户频偏估计算法，通过子空间旋转不变的特点估计各用户的载波频偏。仿真表明，利用该算法进行频偏估计具有良好的准确性。     

OFDMA系统中子载波分配算法分析

分析和研究了OFDMA系统中总功率约束条件下的子载波分配算法,利用系统吞吐量增益和用户吞吐量公平比率两个评价参数,对几种典型的子载波分配算法进行了仿真和分析,并给出了分析结论,为实际系统中的资源调度算法设计提供了有益的参考。     

一种自适应的OFDMA系统下行分组调度算法

提出了一种适合于OFDMA（正交频分多址接入）系统的资源分配与调度算法,该算法利用物理层的信道信息和MAC层的队列状态信息,并综合考虑了数据分组传输的时延要求和业务的优先级,采取资源块与子载波分配相结合的资源分配方式。仿真结果表明,该算法在吞吐量和公平性方面都得到了较好的改善。     

OFDM系统中的子载波分配策略

正交频分复用(OFDM)技术是未来宽带无线通信中最流行的技术之一。研究了适用于多用户(OFDM)系统中的多业务间子载波自适应资源分配机制。考虑了每个用的不同业务需求,资源根据每个用户不同的服务质量要求来分配。提出了基于OFDM系统的自适应子载波重分配算法,该算法能够最大程度地灵活分配所有子载波。仿真表明,使用此算法能在很大程度上改善OFDM系统的性能。     

基于聚类-匈牙利方法的OFDMA子载波分配算法

针对在OFDMA无线通信系统中给用户分配子载波时频谱资源稀缺问题,提出了基于聚类的子载波分配方法,利用最大相关性准则对于某些具有一定相似度的资源进行聚类,分给相同的用户,使得子载波能够提供最大的链路速率。同时通过仿真结果可看出,该方法实现的用户速率最大,性能最优。     

应用于OFDMA中继网络的子载波分配方案

在OFDMA中继网络中,针对目前的子载波分配方案不能很好的解决速率和公平性有效结合的问题,提出了以传输速率、公平性为优化目标的子载波分配方案以及一种自适应的子载波分配方案,三种方案分别适用于用户数长时间较少、用户数长时间较多以及用户数目变化较频繁三种场景。通过仿真可以看出,所提方案可以有效地兼顾速率和公平性两方面因素,能够解决实际系统中存在的一些问题,有效提升用户的服务质量。     

Low-Complexity Orthogonal Spectral Signal Construction for Generalized OFDMA Uplink With Frequency Synchronization Errors

In orthogonal frequency-division multiplexing, the total spectral resource is partitioned into multiple orthogonal subcarriers. These subcarriers are assigned to different users for simultaneous transmission in orthogonal frequency-division multiple access (OFDMA). In an unsynchronized OFDMA uplink, each user has a different carrier frequency offset (CFO) relative to the common uplink receiver, which results in the loss of orthogonality among subcarriers and thereby multiple access interference. Hence, OFDMA is very sensitive to frequency synchronization errors. In this paper, we construct the received signals in frequency domain that would have been received if all users were frequency synchronized. A generalized OFDMA framework for arbitrary subcarrier assignments is proposed. The interference in the generalized OFDMA uplink due to frequency synchronization errors is characterized in a multiuser signal model. Least squares and minimum mean square error criteria are proposed to construct the orthogonal spectral signals from one OFDMA block contaminated with interference that was caused by the CFOs of multiple users. For OFDMA with a large number of subcarriers, a low-complexity implementation of the proposed algorithms is developed based on a banded matrix approximation. Numerical results illustrate that the proposed algorithms improve the system performance significantly and are computationally affordable using the banded system implementation     

Deterministic multiuser carrier-frequency offset estimation for interleaved OFDMA uplink

In orthogonal frequency-division multiple access (OFDMA), closely spaced multiple subcarriers are assigned to different users for parallel signal transmission. An interleaved subcarrier-assignment scheme is preferred because it provides maximum frequency diversity and increases the capacity in frequency-selective fading channels. The subcarriers are overlapping, but orthogonal to each other such that there is no intercarrier interference (ICI). Carrier-frequency offsets (CFOs) between the transmitter and the receiver destroy the orthogonality and introduces ICI, resulting in multiple-access interference. This paper exploits the inner structure of the signals for CFO estimation in the uplink of interleaved OFDMA systems. A new uplink signal model is presented, and an estimation algorithm based on the signal structure is proposed for estimating the CFOs of all users using only one OFDMA block. Diversity schemes are also presented to improve the estimation performance. Simulation results illustrate the high accuracy and efficiency of the proposed algorithm.     

Group-orthogonal multicarrier CDMA

In the presence of frequency-selective multipath fading channels, code-division multiple access (CDMA) suffers from multiuser interference (MUI) and intersymbol interference (ISI); but when properly designed, it enjoys multipath diversity. Orthogonal frequency-division multiple access (OFDMA) is MUI-free, but it does not enable the available channel diversity without employing error-control coding. On the other hand, coded OFDMA may achieve lower diversity than a CDMA system employing the same error-control codes. In this paper, we merge the advantages of OFDMA and CDMA to minimize MUI effects, and also enable the maximum available diversity for every user. In our group orthogonal multicarrier CDMA (GO-MC-CDMA) scheme, groups of users share a set of subcarriers. By judiciously choosing group subcarriers, we guarantee that every user transmits with maximum diversity. MUI is only present among users in the same group, and is suppressed via multiuser detection, which becomes practically feasible because we assign a small number of users per group. Performance is analyzed, and simulations are carried out to illustrate the merits of GO-MC-CDMA relative to existing alternatives.     

Bee colony optimization aided adaptive resource allocation in OFDMA systems with proportional rate constraints

Orthogonal frequency division multiple access (OFDMA) is a promising technique, which can provide high downlink capacity for the emerging wireless systems. The total capacity of OFDMA can be maximized by adaptively assigning subcarriers to the users with the best gains for those subcarriers, with power subsequently distributed by water-filling. In this paper, we propose the use of artificial bee colony (ABC) algorithm combined with Deb’s selection mechanism to handle the constraints. In this scheme, a probabilistic selection scheme assigns probability values to feasible solutions based on their fitness values and to infeasible individuals based on their violations, to allocate the resources to the users in downlink OFDMA system. Specifically we propose two approaches for resource allocation in downlink OFDMA systems using ABC algorithm. In the first approach, ABC algorithm is used for subcarrier allocation only, while in second approach the ABC algorithm is used for joint subcarrier and power allocation. It is shown that both these approaches obtain higher sum capacities as compared to that obtained by previous works, with comparable computational complexity. It is also shown that the joint subcarrier and power allocation approach provides near optimal results at the cost of slightly higher computational cost.     

Cooperation Strategies and Resource Allocations in Multiuser OFDMA Systems

Cooperative communication and orthogonal frequency-division multiplexing (OFDM) technology are both promising candidates for next-generation wireless communication systems. In this paper, we investigate cooperation strategies and resource-allocation algorithms for multiuser cooperative orthogonal frequency-division multiple-access (OFDMA) systems. There are two major contributions of this paper. First, we propose a novel cooperation strategy for the OFDMA system. When there are two users in the system, the strategy achieves the capacity region upper bound for decode-and-forward (DF) cooperation. When there are multiple users in the system, the strategy can achieve near upper-bound performance in certain network topologies. Moreover, the strategy always outperforms those that are previously proposed for cooperative OFDMA systems. The second contribution is that we develop novel centralized resource-allocation algorithms for cooperative OFDMA systems. The advantages of the algorithms are that they not only simultaneously solve relay, power, and subcarrier allocation but also have complexity that increases only linearly with the number of subcarriers in the systems.      

不同训练序列分配的OFDMA系统性能分析

正交频分多址接入系统作为一种新的多址接入技术受到了极大关注.在OFDMA中,由于子载波分配给不同的用户,用户信号在收端会叠加在一起,那么也给训练序列等信息序列的分配带来一定的困难.文中将分析连续和交织两种不同的训练序列的系统频偏估计性能.并通过仿真得出连续分配的训练序列性能更优.     

Subcarrier allocation and bit loading algorithms for OFDMA-based wireless networks

Orthogonal Frequency Division Multiple Access (OFDMA) is an emerging multiple access technology. In this paper, we consider OFDMA in the context of fixed wireless networks. This paper addresses the problem of assigning subcarriers and bits to point-to-point wireless links in the presence of cochannel interference and Rayleigh fading. The objective is to minimize the total transmitted power over the entire network while satisfying the data rate requirement of each link. We formulate this problem as a constrained optimization problem and present centralized algorithms. The simulation results show that our approach results in an efficient assignment of subcarriers and transmitter power levels in terms of the energy required for transmitting each bit of information. However, centralized algorithms require knowledge of the entire network topology and channel characteristics of every link. In a practical scenario, that would not be the situation and there is a need for distributed rate allocation algorithms. To address this need, we also present a distributed algorithm for allocating subcarriers and bits in order to satisfy the rate requirements of the links.