频率选择性衰落信道中多用户OFDM系统的自适应分配算法

本文提出一种适用于多径频率选择性衰落信道中多用户OFDM系统的自适应分配算法.算法根据信道瞬时估计值,自适应地为多用户分配子信道和传输比特数,在给定误比特率的条件下,使系统总的发送功率达到最小.作者根据时分复用的基本思想,提出多用户最佳子信道和比特分配算法,导出系统最小发送功率的下限,并在此基础上,进一步提出次佳自适应分配算法.数值模拟表明:次佳算法所需的发送功率比下限值高约1dB;与等比特分配方案相比自适应分配算法可节省功率约3-4dB;与静态信道分配方案相比,自适应分配算法可节省功率6-8dB.     

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。     

Joint subchannel and power allocation in multiuser OFDM systems with minimal rate constraints

In this paper, we study the adaptive resource allocation in multiuser orthogonal frequency division multiplexing (OFDM) systems. We try to maximize the sum capacity of an OFDM system with given transmission power budget, while meeting users' minimal rate requirements. Unlike other resource allocation schemes, which generally separate subchannel allocation and power distribution into independent procedures, our proposed algorithm implements joint subchannel and power allocation. Given a set of subchannels, the required power to satisfy a user's minimal rate constraint is calculated by water‐filling policy. Then, the user who requires the maximum power to meet the rate requirement has a priority to obtain an additional subchannel. The procedure continues until all subchannels are consumed, by which time the consumed power to meet all users' rate requirements is also worked out. Finally, the margin power is allocated among all subchannels in an optimal manner to maximize the sum capacity of the OFDM system. Simulation results show that our proposed algorithm performs better than other existing ones. The solution produced by our proposed algorithm is close to the upper bound, while its complexity is relatively lower compared with other methods, which makes it attractive for applications. Copyright © 2012 John Wiley & Sons, Ltd.     

基于多用户MIMO/OFDM系统的空间子信道分配算法

对多用户MIMO/OFDM系统空间子信道进行了研究,以获取最大的系统吞吐量为目标,推导了子载波分配准则,提出了一种自适应空间子信道分配算法,并给出了相应的算法流程。仿真结果表明,该算法具有良好的性能,有效地提高了系统的传输速率。     

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     

基于多用户MIMO-OFDM系统的子信道和功率分配算法

在多用户MIMO-OFDM系统中，当总功率受限时，为了使整个系统的数据传输速率最大．已有的最优算法的计算十分复杂，这里采用了一种次最优算法。在发射端，基于已知信道状态信息。应用奇异值分解将MIMO信道转化为并行的子信道，并将表征信道增益的信道特征值用于子信道自适应调制优化设计中。在自适应过程中．用到了子信道和功率联合分配算法。仿真结果表明，这种算法能使系统的性能明显提高。     

基于用户公平性的MIMO-OFDM空间子信道分配算法

对多用户"多入多出-正交频分复用"(MIMO-OFDM)系统的空间子信道分配算法进行了研究,提出了使系统吞吐量最大化并且满足用户速率最小要求的多用户无线资源调度算法.仿真结果表明,与波束形成相比.所提算法具有更好的性能,既充分利用空间子信道,提高了系统容量,又采取有效措施保障了用户的公平性.     

Resource allocation with proportional rate fairness in orthogonal frequency division multiple access relay networks

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.     

一种基于均值反馈模型的自适应空间子信道分配算法

MIMO/OFDM是未来宽带无线通信接口的有效架构。该文针对多用户MIMO/OFDM系统,提出了一种基于均值反馈模型的自适应空间子信道分配算法,以获取最大的系统吞吐量为目标,推导了子载波分配准则,并给出了相应的算法流程。仿真结果表明,该算法具有良好的性能,有效地提高了系统的传输速率。     

Resource allocation for multiuser cognitive OFDM networks with proportional rate constraints

In this paper we study the resource allocation problem for the multiuser orthogonal frequency division multiplexing (OFDM)‐based cognitive radio (CR) systems with proportional rate constraints. The mutual interference introduced by primary user (PU) and cognitive radio user (also referred to secondary user, SU) makes the optimization problem of CR systems more complex. Moreover, the interference introduced to PUs must be kept under a given threshold. In this paper, the highest achievable rate of each OFDM subchannel is calculated by jointly considering the channel gain and interference level. First, a subchannel is assigned to the SU with the highest achievable rate. The remaining subchannels are always allocated to the SU that suffers the severest unjustness. Second, an efficient bit allocation algorithm is developed to maximize the sum capacity, which is again based on the highest achievable rate of each subchannel. Finally, an adjustment procedure is designed to maintain proportional fairness. Simulation results show that the proposed algorithm maximizes the sum capacity while keeping the proportional rate constraints satisfied. The algorithm exhibits a good tradeoff between sum capacity maximization and proportional fairness. Furthermore, the proposed algorithm has lower complexity compared with other algorithms, rendering it promising for practical applications. Copyright © 2011 John Wiley & Sons, Ltd.     

速率比例公平下多用户OFDM系统的自适应资源分配

在多用户正交频分复用(MU-OFDM)系统中,考虑各个用户之间具有比例数据传输速率限制条件下的一种公平的自适应资源分配方案的最优算法计算量巨大,为此,提出了一种将子信道分配和功率分配相分离的次优算法.首先,在假设相同功率分配的情况下进行子信道的分配,然后在保持一定比例公平条件下使总容量最大时进行最优功率分配.对该算法的仿真表明,在用户数为2、子信道数为10的系统中,所提算法的容量性能接近最优算法,而计算量由指数增长变为线性增长.所提资源分配算法的总容量比以前的算法在用户间的分配更公平也更灵活.     

Adaptive Power and Subchannel Allocation for Dual-Class OFDMA Packet Data Networks

Adaptive Radio Resource Allocation exploiting the inherent frequency selectivity of the wireless medium as well as the multi-user diversity effect is expected to play a crucial role in providing high QoS on emerging OFDMA-based wireless networks. Although a plethora of studies concerning exclusively constant bit rate (CBR) or variable bit rate/best effort (BE) traffic has been published to date, limited amount of work has been devoted to the more practical mixed CBR-BE data traffic scenario over OFDM radio access networks. In this paper we attempt to deal with the specific heterogeneous allocation problem, namely the maximization of elastic users’ sum-throughput while providing minimum data rate service to a subset of non-elastic users. The contribution of this work is twofold. First, due to the high complexity of the resource allocation problem, we propose a relaxation method based on the prioritization of CBR- over BE-class users during the subchannel allocation procedure. We devise a method for obtaining the exact performance penalty induced by the specific hypothesis when compared to the optimal (unprioritized) decision. Secondly, we develop a polynomial complexity approximation algorithm for allocating power and bandwidth, that employs the CBR-prioritization idea. The scheme is shown to experience a relatively low performance penalty compared to its upper bound and to outperform two representative algorithms from the literature.     

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.     

Distributed subchannel and rate assignment for multi-carrier multi-cell networks

A distributed subchannel and rate assignment (DSRA) algorithm, which integrates the subchannel allocation and the rate assignment to minimize the number of subchannels needed for meeting the rate requirements, is proposed for the multi-carrier multi-cell networks. The DSRA algorithm need not measure the channel gains and executes the distributed power control to allocate the subchannel and transmission rate. One can decrease the number of subchannels used in the DSRA algorithm by increasing the number of iterations.     

Multiuser MIMO OFDM Based TDD/TDMA for Next Generation Wireless Communication Systems

Multiple-input multiple-output (MIMO) wireless technology in combination with orthogonal frequency division multiplexing (MIMO OFDM) is an attractive air-interface solution for next-generation wireless local area networks (WLANs), wireless metropolitan area networks (WMANs), and fourth-generation mobile cellular wireless systems. In this paper, one multiuser MIMO OFDM systems with TDD/TDMA was proposed for next-generation wireless mobile communications, i.e., TDD/TDMA 4G, which can avoid or alleviate the specific limitations of existing techniques designed for multiuser MIMO OFDM systems in broadband wireless mobile channel scenarios, i.e., bad performance and extreme complexity of multiuser detectors for rank-deficient multiuser MIMO OFDM systems with CDMA as access modes, extreme challenges of spatial MIMO channel estimators in rank-deficient MIMO OFDM systems, and exponential growth complexity of optimal sub-carrier allocations for OFDMA-based MIMO OFDM systems. Furthermore, inspired from the Steiner channel estimation method in multi-user CDMA uplink wireless channels, we proposed a new design scheme of training sequence in time domain to conduct channel estimation. Training sequences of different transmit antennas can be simply obtained by truncating the circular extension of one basic training sequence, and the pilot matrix assembled by these training sequences is one circular matrix with good reversibility. A novel eigenmode transmission was also given in this paper, and data symbols encoded by space–time codes can be steered to these eigenmodes similar to MIMO wireless communication systems with single-carrier transmission. At the same time,, an improved water-filling scheme was also described for determining the optimal transmit powers for orthogonal eigenmodes. The classical water-filling strategy is firstly adopted to determine the optimal power allocation and correspondent bit numbers for every eigenmode, followed by a residual power reallocation to further determine the additional bit numbers carried by every eigenmode. Compared with classical water-filling schemes, it can also obtain larger throughputs via residual power allocation. At last, three typical implementation schemes of multiuser MIMO OFDM with TDMA, CDMA and OFDMA, i.e., TDD/TDMA 4G, VSF-OFCDM and FuTURE B3G TDD, were tested by numerical simulations. Results indicated that the proposed multiuser MIMO OFDM system schemes with TDD/TDMA, i.e., TDD/TDMA 4G, can achieve comparable system performance and throughputs with low complexity and radio resource overhead to that of DoCoMo MIMO VSF-OFCDM and FuTURE B3G TDD.     

Rate adaptive resource allocation for OFDM downlink transmission

In this paper, we present a multiuser rate adaptive resource allocation for OFDM downlink transmission. This new algorithm assign one bit at a time to user that has the minimum total power in the subcarrier that requires the least additional power. Simulation results show that the proposed algorithm achieves a higher capacity than previous existing algorithms and distributed the overall capacity more fairly among users.     

基于应用时间窗多用户MIMO-OFDM系统中的比例公平算法

该文针对基于延时信道状态信息的多用户MIMO-OFDM系统,在用户比例速率要求和功率限制的情况下,以最大化时间窗内系统吞吐量为目标,提出了一种基于应用时间窗比例公平算法。该算法首先设计各子载波上满足用户误比特率要求的星座距离,然后把系统中每个用户按照其比例映射为相应数目的虚拟用户,最后根据影子价格把子载波最优地分配给虚拟用户。仿真结果表明,该算法在保证用户公平性的基础上,有效地提高了系统吞吐量。     

Block adaptive subcarrier allocation for wireless multiuser OFDM system

In this paper, a blockwise adaptive subcarrier allocation algorithm for multiuser Orthogonal Frequency Division Multiplexing (OFDM) system is introduced. Assuming the knowledge of channel information for all users, the algorithm minimizes the total transmit power while satisfying the total power and users‘ rate constraints. The result of simulation shows that the proposed algorithm reduces the average bit Signal-to-Noise Ratio (SNR) by approximately 4 dB compared with OFDM-Frequency Division Multiple Access (OFDM-FDMA), and supports more users in a multiuser Rayleigh fading channel. As assigning subcarriers in block, the computational complexity of the algorithm is much lower than that of the derivation of “water-filling” algorithm.     

Optimum DMT-based transceivers for multiuser communications

The paper considers discrete multitone (DMT) modulation for multiuser communications when multiple users are supported by the same system, a zero-padding redundancy is employed at the transmitter output, and linear redundancy removal is used at the channel output. These users may have differing quality of service (QoS) requirements, as quantified by bit rate and symbol-error rate specifications, and are each assigned an equal number of subchannels. Our goal is to minimize the transmitted power, given the QoS specifications and subject to the knowledge of the channel and the second-order statistics of the colored interference at the receiver input. In particular, we find an optimum bit-loading scheme that distributes the bit rate transmitted across the various subchannels belonging to each user, and, subject to this bit allocation, we determine the precise subchannels assigned to each user, the optimum transceiver characterized by the input/output block transforms, and the redundancy removal operation. A major conclusion is that even though the optimum bit-rate allocation differs from the single-user case, the optimum transceiver does not. Further, it is determined entirely by the channel and interference conditions, and is unaffected by the QoS requirements.     

Precoded OFDM with adaptive vector channel allocation for scalable video transmission over frequency-selective fading channels

Orthogonal frequency division multiplexing (OFDM) has been applied in broadband wireline and wireless systems for high data rate transmission where severe intersymbol interference (ISI) always occurs. The conventional OFDM system provides advantages through conversion of an ISI channel into ISI-free subchannels at multiple frequency bands. However, it may suffer from channel spectral s and heavy data rate overhead due to cyclic prefix insertion. Previously, a new OFDM framework, the precoded OFDM, has been proposed to mitigate the above two problems through precoding and conversion of an ISI channel into ISI-free vector channels. In this paper, we consider the application of the precoded OFDM system to efficient scalable video transmission. We propose to enhance the precoded OFDM system with adaptive vector channel allocation to provide stronger protection against errors to more important layers in the layered bit stream structure of scalable video. The more critical layers, or equivalently, the lower layers, are allocated vector channels of higher transmission quality. The channel quality is characterized by Frobenius norm metrics; based on channel estimation at the receiver. The channel allocation information is fed back periodically to the transmitter through a control channel. Simulation results have demonstrated the robustness of the proposed scheme to noise and fading inherent in wireless channels.