A Low Complexity Resource Allocation Method for OFDMA System Based on Channel Gain

In orthogonal frequency division with multiple access (OFDMA) systems dynamic radio resource allocation improves overall performance by exploiting the multiuser diversity gains. A key issue in OFDMA is the allocation of the OFDM subcarriers and power among users sharing the channel. This paper proposes a new rate adaptive resource allocation scheme in the OFDMA downlink transmission system. Our proposed algorithm is based on the users’ sensitivity to the subcarrier allocation which means how frequency selective is the channel from the user’s perspective. As a result of frequency selectivity of the channel, different subchannels of the same user experience different levels of fade. However, how different they undergo fading could be measured by difference between maximum and minimum channel gain of that user. Our proposed method is based on difference between maximum channel gain and minimum channel gain for each user and uniform distribution of power among subcarriers. Simulation results show that the proposed algorithm achieves higher capacity over fixed TDMA method, and reported suboptimal methods with acceptable rate proportionality.     

Rate, Sub-Carrier, and Power Allocations for Multi-Carrier CDMA with LMMSE Multiuser Detection

Multi-carrier code-division-multiple-access (MC-CDMA) is a promising transmission technique for high-speed wireless multimedia communication in frequency-selective fading channels. In this letter, allocations of physical transmission rate, sub-carrier, and power are proposed for a MC-CDMA system that applies multi-code (MC)/variable-spreading-length (VSL) multi-rate access to minimize total transmitted power, where we consider users have different data rate and BER.requirements and LMMSE multiuser detection is used in the receivers. We derive transmission rate capacity and propose a simple admission control criterion that linearly relates the code length, data rate and BER requests of all users. The proposed iterative allocation algorithm jointly allocates the sub-carrier power of each user and solves the sub-carrier allocation problem     

LTE下行信道估计算法研究

近年来,正交频分复用（OFDM）技术以其在高速数据传输中具有的良好的抗多径衰落的特性以及较高的频谱利用率等优点得到了广泛的应用。在OFDM通信系统中,信号在带宽小于信道相干带宽的多个正交子载波上发射和传输,以克服多径衰落信道所带来的信号频率选择性衰落。为了补偿各个子载波上的多径衰落,这就需要一个性能良好的信道估计方案。对LTE中基于导频的下行信道估计算法进行研究,首先在导频子载波处采用LS（最小二乘法）算法估计出信道参数,然后通过内插的方法在数据子载波处内插得到信道参数。频域内插主要采用拉格朗日内插或是LMMSE（线性最小均方误差）内插;时域内插采用拉格朗日内插。     

基于认知OFDM的子载波功率分配改进算法

在认知无线网络中,建立了基于认知OFDM多载波资源分配数学模型,在授权用户干扰受限条件下,以最大化传输速率为目标进行认知用户的子载波功率分配。传统注水法被证明是最优的单用户子载波功率分配算法,在传统注水法功率分配基础上,提出了两种可行的子载波功率分配改进算法,改进算法一是通过对水面值的粗略估计快速确定不分配功率子载波,改进算法二不需要通过迭代计算水面值,只通过线性计算就可以直接确定不分配功率的子载波,且对授权用户不产生干扰。仿真结果表明,在改进的两种子载波功率分配算法下,认知用户的数据传输速率优于传统注水法功率分配时认知用户的数据速率,所提改进算法具有自适应特性且计算复杂度大大降低。      

基于资源因子的电力线通信系统自适应资源分配

本文分析了电力线通信系统在每时隙内的最大总功率、各实时用户固定比特和非实时用户最小比特、各子载波允许最大功率和特定比特数的约束下,多用户多业务在多子载波上的自适应资源分配的多层多目标最优模型,并提出一种基于资源因子和用户优先级的功率和速率自适应相结合的资源分配算法。在典型电力线信道环境下其仿真结果表明,本文算法的性能忧于已有的多用户资源分配算法且能满足多用户多业务电力线通信资源分配的多目标要求。     

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。     

Novel Fairness Improved Radio Resource Management Schemes for Best-Effort Service in OFDMA Systems

In this paper, we propose a complete radio resource management procedure for best-effort service in OFDMA systems, which improves the system fairness with graceful throughput degradation compared to the upper bound of the system throughput. By the proposed bandwidth and power allocation algorithms, the user in the worst channel environment has almost the same probability of accessing the system as the user in the best channel environment. Furthermore, a novel sub-channel allocation algorithm is proposed to exploit frequency selectivity and multi-user diversity gains simultaneously in OFDMA systems, which is able to achieve the highest system throughput given each user’s channel environment.     

一种基于轮回的认知OFDM子载波分配方法

认知无线电技术是能够提高有限频谱利用率,进而缓解当前有限频谱资源短缺压力的有效手段。在多用户认知OFDM系统中,高效并合理地决定子载波分配对系统性能至关重要。本文提出了一种基于轮回思想的子载波分配算法。该算法首先通过基于轮回的初次分配达到兼顾公平性的目的,再通过二次分配对初次分配结果加以迭代优化。仿真结果表明,在不增加算法复杂度的前提下,该算法可以避免选择深度衰落的子信道,相比同类算法,该算法可以获得更优的误比特性能。     

OFDM固定中继系统中单中继多源用户资源分配方案

通过基站的反馈信息,一个固定中继节点可以用一个OFDM符号同时帮助多个源用户转发信息,这样可以有效地利用带宽。因此,为了进一步提高系统容量,降低中断概率,先在中继节点间进行子载波调整,然后以获取信道容量最大为原则,提出了源用户和中继节点间子载波配对和功率分配的联合优化算法。仿真结果表明,相对于随机中继子载波选择算法以及平均功率分配算法,所提算法的中继系统容量有较大提升,同时中断概率有较为明显的下降。     

基于公平度门限的多用户OFDM系统自适应资源分配算法

在传统的子载波分配过程中,具有优先权的用户将优先选择最好的载波,这将导致载波利用效率下降.许多改进算法通过牺牲一定的公平性来提升容量并降低复杂度,但是这可能会使用户间无法达到所要求的公平性.针对这些问题,提出了一种基于公平度门限的载波和功率自适应分配算法.在载波分配过程中,通过公平度门限来决定载波分配优先级,从而实现容量和公平度的粗略折中.载波分配后利用粒子群(PSO)算法进行功率分配来达到所要求的公平度门限.实验结果表明,该算法在满足所要求公平度门限的同时提升了系统容量.     

Optimum power control for CDMA with deterministic sequences in fading channels

We specify the capacity region for a power-controlled, fading code-division multiple-access (CDMA) channel. We investigate the properties of the optimum power allocation policy that maximizes the information-theoretic ergodic sum capacity of a CDMA system where the users are assigned arbitrary signature sequences in a frequency flat-fading environment. We provide an iterative waterfilling algorithm to obtain the powers of all users at all channel fade levels, and prove its convergence. Under certain mild conditions on the signature sequences, the optimum power allocation dictates that more than one user transmit simultaneously in some nonzero probability region of the space of all channel states. We identify these conditions, and provide an upper bound on the maximum number of users that can transmit simultaneously at any given time. Using these properties of the sum capacity maximizing power control policy, we also show that the capacity region of the fading CDMA channel is not in general strictly convex.     

一种基于用户需求的OFDM系统资源分配算法

提出了一种新的基于OFDM多用户通信系统的资源分配算法。该算法在总功率限制和用户数据率要求下,通过以下两步实现子载波、比特和功率的动态分配：第一步,基于用户的平均信道增益和数据率要求进行资源初分配（每个用户分配多少个子载波、功率）;第二步,对步骤1中的结果进行调整,最终决定每个用户分配到的子载波、功率以及比特载入方式。相比于Hujun Yjn等人提出的另一种基于用户需求的算法,新算法的基站发射功率略有增加,但复杂度大为降低,在实际运用中更有利用价值。     

Spectrum efficiency sub-carrier and energy efficiency power allocation for downlink multi-user CoMP in multi-cell system

Coordinated multi-point transmission/reception （CoMP） was proposed currently as an effective technology to improve cell-edge throughput in next-generation wireless systems. Most of the existing work discussed clustering methods mostly to maximize the edge user throughput while neglecting the problem of energy efficiency, such as those algorithm clustering base stations （BSs） of better channel condition and BSs of worse channel condition together. In addition, BSs usually increase the transmit power to achieve higher throughput without any considering of interference caused to other users, that may result in energy waste. The authors focus on the throughput maximizing problem while fully considering energy saving problem in CoMP systems. A coefficient is defined to describe the fitness of clusters. Then a sub-carrier allocation algorithm with clustering method is put forward for CoMP downlink, which can save the transmit power of BS and increase the throughput. Furthermore a power allocation scheme is proposed based on non-cooperation game; in which the transmit power is decreased by BSs generally to reach the Nash equation （NE）. Simulation shows that the proposed sub-carrier allocation scheme and power allocation algorithm are better than the existing ones on users＇ throughput while consumes much less energy.     

Pre-Coding for MIMO Systems in Frequency-Selective Fading Channels

Multiple input multiple output (MIMO) systems showed good utilization of channel characteristics. In MIMO systems multiple signals are transmitted using multiple antenna system. This provides each receiver the combined signals and hence, array processing techniques helps in reducing the effects of interference among them. In this paper we devise the use of pre-coded MIMO system to reduce the effects of frequency selectivity and hence, enhance the systems capacity and/or reduce the bit error rate. In this technique we introduce a temporal pre-coder on each antenna signal; this creates a deterministic multi-path signals similar to signals received when the channel is multi-path fading channel. The same antenna signal will arrive at each receiver forming orthogonal sub-space and the receiver will be simple add and delay of the received signals. Ant colony optimization is used in this paper to select the best pre-code. Results showed that we can diagonalize the channel matrix and practically eliminate the interference for frequency selective fading channel. Simulation of two transmitting two receiving antennas pre-coded MIMO system showed that the capacity can be doubled.     

一种MIMO-OFDM系统天线和子载波分配算法

在多输入多输出-正交频分复用(MIMO-OFDM)系统中,根据信道状况自适应地分配天线与子载波是使信道容量达到最大的关键技术。提出一种基于拥挤模型的差分进化算法,即拥挤差分进化算法(Crowding Differential Evolution Algorithm,CDE)用于解决MIMO-OFDM系统的自适应天线和子载波联合分配问题,利用该算法参数少、寻优能力强以及收敛速度快的特点,可快速确定最佳的天线和子载波联合分配方案,实现信道容量最大。     

基于非正交多址的室内可见光通信系统性能优化方法

室内可见光通信(Visible Light Communication, VLC)系统常用的非对称限幅光OFDM(Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing, ACO-OFDM)与直流偏置光OFDM(DC-biased Optical OFDM, DCO-OFDM)采用加循环前缀、信道均衡和载波复用等方法解决信道干扰及多用户复用问题,但均以牺牲有效性为代价。非正交多址(Non-orthogonal Multiple Access, NOMA)通过功率域复用提高频谱利用率,利用串行干扰消除(Successive Interference Cancelling, SIC)进行多用户信号处理,有效兼顾可靠性与有效性。将NOMA应用于室内可见光系统,建立基于NOMA-DCO-OFDM的可见光信号传输及信道增益模型。通过功率域多用户信道差异计算信道增益,进行功率分配实现功率域复用,提高系统容量和通信速率;利用SIC按功率分配算法对用户逐一解调,减弱信道干扰,提高可靠性。通过理论分析和仿真实验验证表明:该系统的通信速率达到6.8×107 bit·s?1,且合速率受用户数量的影响不显著。2用户下,误码率(Bit Error Rate, BER)为10?4时用户1有5.2 dB左右的性能提升,用户2有2.3 dB左右的性能提升,通信可靠性也明显提高。     

多天线系统中的二次注水功率分配

Aiming at the problem of resource allocation in multiuser multi-input multi-output （MIMO） systems, a new power allocation algorithm based on dual waterfilling is proposed. Block diagonalization is adopted to cancel the inter-user interference, and then the complete diagonalization method is employed to derive the spatial sub-channels for each user. The overall power of the system is divided among users based on each user＇s large scale fading; then the power of each user is further allocated to its spatial sub-channels based on the small scale fading. Simulation results show that compared with the existing resource allocation strategies, the proposed algorithm can provide more ergodic capacity for multi-user MIMO systems. When the total transmit power is 100w, it has 15% capacity advantage over the traditional waterfilling method.     

Maximized Channel Capacity Based Power Allocation Technique for Multi Relay Hybrid Decode-Amplify-Forward Cooperative Network

In this paper, a novel maximized channel capacity based power allocation using differential evolution (DE) algorithm for multi relay Hybrid Decode-Amplify-Forward cooperative network in a Rayleigh fading environment is proposed. The closed form expression for average channel capacity with the tight approximation is derived. The proposed parametric optimization problem is defined on basis of the decoding capability of the relay. Further, the relay powers are optimized using the optimized power allocation factor. The performance of the proposed technique is validated for different channel variances and for different relay locations. From the simulation analysis, it is observed that the proposed DE based power allocation scheme performs better than the existing equal power allocation scheme.     

多用户分布式MIMO-OFDM系统中天线与子载波分配算法研究

本文针对多用户分布式MIMO-OFDM系统中的资源联合分配问题,提出了一种基于端口选择的天线与子载波分配算法。该算法依据计算复杂度容限设定用户通信静态端口数,以此为每个用户选取信道状况最好的通信端口进行通信,进而通过天线端口与下属用户的相互配合,并行地完成天线与子载波的分配。仿真结果表明,该算法在系统天线数大于用户数的情况下容量性能优于MASA算法,且其端口并行处理机制可以有效提高资源分配效率。     

卫星通信系统中功率与时隙资源联合分配算法

提出联合优化卫星通信系统中的功率和时隙资源的方法,以提高星上有限资源的使用能效。挖掘了功率和时隙资源在容量提升上的相互补充相互依存关系,考虑了多个地球站的信道条件和容量需求的差异性,建立了资源联合分配的状态组合模型,以适应各地球站的多资源利用模式。并以最大化能效为目标,设计了联合分配的迭代对偶优化（IDO）算法,以较低复杂度获得了最优联合分配方案。仿真分析表明,资源联合优化比非联合优化提高了能量利用效率,尤其在频率资源（载波数目）较少时优势更加明显。