A Fast Subcarrier, Bit, and Power Allocation Algorithm for Multiuser OFDM-Based Systems

In this paper, we propose a real-time subcarrier, bit, and power allocation algorithm for orthogonal frequency-division multiplexing-based multiuser communication systems in downlink transmission. Assuming that base stations know the channel gains of all subcarriers of all users, the proposed loading algorithm tries to minimize the required transmit power while satisfying the rate requirement and data error rate constraint of each user. The novel algorithm simultaneously determines subcarrier, bit, and power allocation by enhancing the suboptimal algorithm by Wong while having the same computational complexity. The proposed scheme offers better performance in terms of transmit power than that of Wong , as demonstrated in the simulation results, whereas the performance of the scheme in Wong was close to that of the optimal solution.     

A Low Complexity Algorithm for Subcarrier-and-Bit Allocation in OFDMA-Based LTE Systems

In this paper, we propose optimum and sub-optimum resource allocation and opportunistic scheduling solutions for orthogonal frequency division multiple access (OFDMA)-based multicellular systems. The applicability, complexity, and performance of the proposed algorithms are analyzed and numerically evaluated. In the initial setup, the fractional frequency reuse (FFR) technique for inter-cell interference cancellation is applied to classify the users into two groups, namely interior and exterior users. Adaptive modulation is then employed according to the channel state information (CSI) of each user to meet the symbol error rate (SER) requirement. There then, we develop subcarrier-and-bit allocation method, which maximizes the total system throughput subject to the constraints that each user has a minimum data rate requirement. The algorithm to achieve the optimum solution requires high computational complexity which hinders it from practicability. Toward this end, we propose a suboptimum method with the complexity extensively reduced to the order of O(NK), where N and K denote the total number of subcarriers and users, respectively. Numerical results show that the proposed algorithm approaches the optimum solution, yet it enjoys the features of simplicity, dynamic cell configuration, adaptive subcarrier-and-bit allocation, and spectral efficiency.     

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.     

A Radio Resource Management Framework for Multi-User Multi-Cell OFDMA Networks Based on Game Theory

This work proposes a radio resource management framework employing game theoretic concepts for orthogonal frequency division multiple access, the most prevalent multiple access technique for the next generation wireless networks. The subcarrier allocation problem is encountered as a combinatorial auction, where the base station auctions the subcarriers and the users bid for and buy bundles of subcarriers, aiming at minimising their required transmit power. Subsequently, each allocated subcarrier is loaded with a number of bits, decided by each user independently, and the power control process is set up as a non-cooperative game. Each user responds to the interference sensed in his environment and, through a best responses process, the game converges to the unique, Pareto optimal, Nash equilibrium. In order to guarantee convergence, a limit is imposed to the maximum modulation level for each subcarrier. Simulation results show that the auction algorithm follows closely the performance of the optimal algorithm, whereas it is of lower computational complexity and requires less feedback information. Similarly, the proposed distributed bit loading and power control scheme achieves lower transmit power per offered bit rate unit. However, the distributed nature of the algorithm results in lower total offered bit rate, because of the partial knowledge and exploitation of channel state information.     

MIMO Frequency Hopping Spread Spectrum Multi-Carrier Multiple Access: A Novel Uplink System for B3G Cellular Networks

In this paper, we propose and give the performance of a novel uplink system based on the combination of multi-carrier (MC), code division multiple access (CDMA) and multiple input multiple output (MIMO) techniques. First, we describe the interests of spread-spectrum multi-carrier multiple access (SS-MC-MA) scheme for uplink, especially compared to MC-CDMA. Classically, with SS-MC-MA, each user spreads its data symbols on a specific subset of adjacent or multiplexed subcarriers, to facilitate the channel estimation and reduce complexity at the reception. In order to compensate for the lack of frequency diversity of SS-MC-MA with adjacent subcarriers, we first combine it with an orthogonal space-time block code (STBC) and demonstrate the resulting spatial diversity gain. Then, we propose to allocate the subsets to the different users by applying a frequency hopping pattern (FH). In that case, each user benefits from the frequency diversity linked to the total bandwidth as with the multiplexed subcarriers solution, while keeping the advantages of the adjacent subcarriers solution. The gain provided by the use of the frequency hopping is stressed on. Finally, the performance of this scheme is evaluated over realistic MIMO channel with channel turbo coding for systems offering asymptotic spectrum efficiency of 1, 2, 3 and 4.5 bit/s/Hz. Thus, the efficiency of the novel proposed STBC FH SS-MC-MA system as a very promising multiple access and modulation scheme for the uplink of the future wideband wireless networks is successfully demonstrated.     

Minimum symbol error rate multiuser detection using an effective invasive weed optimization for MIMO/SDMA–OFDM system

Space division multiple access–orthogonal frequency division multiplexing system has become a potential wireless communication system by offering high spectral efficiency, performance and capacity. This article deals with minimum symbol error rate (MSER)‐based multiuser detection (MUD) technique for the space division multiple access–orthogonal frequency division multiplexing system using an efficient invasive weed optimization (IWO) algorithm. The IWO algorithm is used for finding optimal weights such that the probability of error is directly minimized rather than minimizing the mean square error. Because of this, the MSER MUD is able to detect users even in overload scenario, where the number of users is more than the number of receiving antennas, unlike several classical detection techniques. The IWO is inspired from the nature of invasive colonization of weeds and relatively simple compared with other optimization techniques. The bit error rate performance of the proposed IWO‐aided MSER MUD is found to be better than minimum means square error and differential evolution algorithm‐aided MSER MUDs. Simulation results show that the proposed IWO MSER achieves faster convergence and lower complexity compared with the differential evolution MSER MUD. Copyright © 2013 John Wiley & Sons, Ltd.     

一种群正交频码分多址系统

提出了一种群正交的频分与码分相结合的多址方案——群正交频码分多址，通过在发送端对用户进行分组，每组内采用码分多址，在接收端利用较低复杂度的分组最大似然检测，可以有效提高频谱利用率。从理论上分析了该系统所能达到的比特误码率性能，并进行了数值仿真，结果显示新系统在保持较低复杂度的同时，取得了更优异的比特误码率性能和更高的频谱利用率。     

认知无线电下行链路中的OFDMA资源分配算法

摘 要： 本文提出一种适用于下行认知无线电系统的正交频分多址接入资源分配算法,在总发射功率、误比特率和对授权用户的干扰受限的条件下最大化系统信息传输速率.本算法分两步实现：首先通过比较各认知用户在各子载波上单位信号发送条件下接收信号的信干噪比实现子载波分配;然后利用凸优化理论求解非负实数域内的比特数和功率值的最优解,并将其调整为符合实际系统需要的比特数和功率值,实现比特和功率分配.仿真结果表明,相比传统的基于频谱空洞的资源分配算法,本算法可以提供显著的系统信息传输速率增益.     

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     

Pre‐filtering technique for MAI cancellation in MC‐CDMA systems

Multicarrier code division multiple access (MC‐CDMA), is a promising multiplexing technique for future communication systems. In this study, we employ the well‐known Walsh‐Hadamard spreading codes for synchronous downlink transmission of MC‐CDMA systems. The spreading codes allow that the frequency diversity to be efficiently exploited. However, multipath propagation may cause orthogonality among users is distorted, and this distortion produces multiple access interference (MAI). To eliminate this effect, we propose a pre‐filtering‐based MC‐CDMA system which uses a pre‐filtering technique at the transmitter and an equal gain combining (EGC) scheme at the receivers, respectively. Our proposed pre‐filtering technique transforms the transmitted signals so that the MAI can be eliminated, and the EGC scheme weights the signals received from all subcarriers so that channel distortions can be compensated. Furthermore, the proposed technique can calculate the transmitted power over all subcarriers to satisfy the required quality of service of each user and archive MAI‐free. In this paper, performance in terms of bit error rate is analyzed; in comparison with the EGC, orthogonal restoring combining, and maximal ratio combining schemes at receiver, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Cross‐layer 1 and 5 user grouping/power allocation/subcarrier allocations for downlink OFDMA/NOMA video communications

Wang et al proposed cross‐layer resource allocation for orthogonal frequency division multiple access (OFDMA) video transmission systems. Unlike Wang et al, we add non‐orthogonal multiple access (NOMA) to the downlink OFDMA video transmission system and propose power allocation for users on each subcarrier (cluster) to minimize sum of video mean square error (MSE) to increase the peak signal‐to‐noise ratio (PSNR), the video quality. For OFDMA/NOMA video communication systems, we propose cross‐layer user clustering to reassign the subcarriers based on sum video distortion minimization and derive the optimal power allocation among NOMA users on the same subcarrier to minimize the sum video distortion. Numerical results show that the proposed scheme outperforms the previous OFDMA cross‐layer scheme by Wang et al by 2.2 to 4.5 dB in PSNR and previous OFDMA NOMA physical layer scheme by Ali et al by 2 to 4.4 dB in PSNR, when SNR = 15 dB, and the number of users is 6 to 12.     

Chunk‐based and fairness‐based resource allocation in multicast distributed MISO‐OFDMA systems

The resource allocation problem for the downlink of orthogonal frequency‐division multiple access (OFDMA) wireless multicast systems is investigated. It is assumed that the base station consists of multiple antennas in a distributed antenna system (DAS), whereas each user is equipped with a single antenna. The multicasting technology is able to support several groups of users with flexible quality of service (QoS) requirements. The general mathematical formulation is provided, but achieving the optimal solution has a high computational cost. In our approach, the allocation unit is not the subcarrier, as in conventional OFDMA systems, but a set of contiguous subcarriers, which is called ‘chunk’. For practical implementation, a suboptimal but efficient algorithm is proposed in order to maximize the sum of the maximum attainable data rates of multicast groups of users, subject to total available power and proportional maximum attainable data rate constraints among multicast groups of users. Simulation and complexity analyses are provided to support the benefits of chunk‐based resource allocation to multicast OFDMA DASs, supporting that the proposed algorithm can be applied to latest‐generation wireless systems that provide QoS guarantees. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

A Novel Multiuser Detection Algorithm for CDMA-Based MIMO-OFDM System

1Introduction Recently,MultipleInputMultipleOutput(MIMO)wirelesstechnologieshavecapturedalotofresearchin terest,giventhatthecapacityincreaseturnsouttobe achievable[1-2].OrthogonalFrequencyDivisionMulti plexing(OFDM)techniquehastheremarkablecharac teristic…     

基于天线波束成形的OFDMA系统的自适应资源分配

对正交频分复用接入系统在多用户多天线传输情况下的自适应资源分配策略进行了研究,提出了一种基于天线波束成形的,包括动态子载波分配、自适应调制、比特加载的无线资源分配方案.算法的优化设计目标是在满足总的恒定传输比特数和误比特率性能要求的情况下,使得系统总的发射功率最小.仿真结果表明,由于多天线阵列增益和多用户分集增益,系统整体性能得到了明显的优化.     

OFDM Link with a Better Performance Using Artificial Neural Network

In this paper, a scheme for reducing the peak-to-average power ratio (PAPR) primarily and bit error rate simultaneously in orthogonal frequency division multiplexing using feed forward artificial neural network is proposed and analyzed. The proposed scheme switches one or more null-carriers with data subcarriers to offer minimum PAPR and requires no channel side information during transmission. To reduce high computational complexity, a multilayer neural network with Levenberg–Marquardt training algorithm is used. The proposed scheme thus suits to supplement some of other PAPR-reduction methods with low rate hit and complexity.     

发送功率最小化自适应MIMO—OFDM系统研究

将自适应比特功率分配技术与空间分集技术结合起来,提出了一种与空时编码结合的固定速率自适应正交频分复用(OFDM)方案。该算法在保证给定的误比特率和信息速率的情况下,使总发送功率最小化。仿真结果表明,该算法在相同误比特率的情况下比不采用自适应技术的MIMO-OFDM系统节省了发送功率。     

An extension to the ordered subcarrier selection algorithm (OSSA)

In this letter, we propose an extension to the ordered subcarrier selection algorithm (OSSA) for orthogonal frequency division multiplexing (OFDM) systems. The result is a simple algorithm for minimizing the bit error rate of the OFDM system at a fixed throughput. The proposed algorithm employs multiple modulations (non-uniform bit loading) within an OFDM symbol. However, unlike existing bit loading algorithms that have a very high computational complexity, the proposed algorithm is based only on the ordered statistics of the subcarrier gains and is consequently very simple. After ordering the subcarriers based on their gains, progressively higher order modulations are used with increasing gains. The key aspect here that greatly simplifies the algorithm is that the modulation used on a subcarrier depends only on the position of its gain in the ordered set and not on the actual values of the gains. We show an analytical approach for determining the parameters of the algorithm.     

SLLR‐MDIC: Spatial log‐likelihood multiuser detection and interference cancelation scheme for OFDM‐IDMA

Wireless communication systems have gained huge attraction from research community, industrial, and academic field due to their significant impact on improving the communication efficiency, ease of deployment, and cost‐effective solution for real‐time communication. In this field of wireless communication, cellular communications have grown rapidly due to their daily usages and advantages. This increased demand of cellular communication systems has led to the evolution of 3G, 4G, and 5G communication systems, which in turn demands for higher efficiency and better bandwidth utilization. Due to heavy usage of network communication, multiple users may cause interference which subsequently may lead to the performance degradation which could be addressed using multiuser detection scheme. However, several schemes have been introduced for improving the system performance, but multiple access (MA) still remains a challenging task. Hence, in this work, we present a novel approach called Spatial Log‐Likelihood Multiuser Detection and Interference Cancelation (SLLR‐MDIC) that uses interleaving division multiple access (IDMA) to improve the communication and developed a multiuser detection approach using spatial log‐likelihood ratios. Further, we have developed orthogonal frequency‐division multiple access (OFDM)–IDMA‐based interference cancelation scheme in multiple access to improve the performance using rake receiver based approach. The performance of SLLR‐MDIC scheme is compared with existing techniques of multiuser detection in terms of bit‐error rate (BER) and symbol error rate (SER). The experimental analysis shows that proposed approach achieves improved performance when compared with existing techniques.