Joint Non-Orthogonal Multiple Access (NOMA) & Walsh-Hadamard Transform: Enhancing the Receiver Performance

Non-orthogonal multiple access(NOMA) is a new access method to achieve high performance gains in terms of capacity and throughput, so it is currently under consideration as one of the candidates for fifth generation(5 G) technologies. NOMA utilizes power domain in order to superimpose signals of multiple users in a single transmitted signal. This creates a lot of interference at the receive side. Although the use of successive interference cancellation(SIC) technique reduces the interference, but to further improve the receiver performance, in this paper, we have proposed a joint Walsh-Hadamard transform(WHT) and NOMA approach for achieving better performance gains than the conventional NOMA. WHT is a well-known code used in communication systems and is used as an orthogonal variable spreading factor(OVSF) in communication systems. Application of WHT to NOMA results in low bit error rate(BER) and high throughput performance for both low and high channel gain users. Further, it also reduces peak to average power ratio(PAPR) of the user signal. The results are discussed in terms of comparison between the conventionalNOMA and the proposed technique, which shows that it offers high performance gains in terms of low BER at different SNR levels, reduced PAPR, high user throughput performance and better spectral efficiency.

JOINT SPACE-FREQUENCY MULTIUSER SYMBOL DETECTOR FOR MC-CDMA SYSTEM WITH UNIFORM LINEAR ARRAY

The MultiCarrier Code Division Multiple Access (MC-CDMA) scheme is promising for relieving capacity limit problems of Direct Sequence (DS-) CDMA systems due to serious InterChip Interference (ICI) and MultiUser Interference (MUI) in high-data-rate wireless communication systems. In this paper, the Uniform Linear Array (ULA) is applied to the base station of macrocellular MC-CDMA systems in a frequency-selective fading channel environment. A joint space-frequency multiuser symbol sequence detector is developed for all active users within one macrocell without space-frequency channel estimation. Simultaneously, Directions-Of-Arrivals (DOAs) of all active users can also be estimated. By dividing the ULA into two identical overlapping subarrays, a specific auxiliary matrix is constructed, which includes both symbol sequence and DOA information of all active users. Then, based on the subspace method, performing the eigen decomposition on such auxiliary matrix, the closed-form solution of symbol sequences and DOAs for all active users can be obtained. In comparison with schemes based on channel estimation, our algorithm need not explicitly estimate the space-frequency channel for each active user,so it has lower computation complexity. Extensive computer simulations demonstrate the overall performance of this novel scheme.

Fair subcarrier-power allocation scheme for multiuser multicarrier systems

The main objective of multiuser orthogonal frequency division multiple access(MU-OFDM) is to maximize the total system capacity in wireless communication systems. Thus, the problem in MU-OFDM system is the adaptive allocation of the resources(subcarriers, bits and power) to different users subject to several restrictions to maximize the total system capacity. In this work, a proposed subcarrier allocation algorithm was presented to assign the subcarriers with highest channel gain to the users. After the subcarrier allocation, subcarrier gain-based power allocation(SGPA) was employed for power and bit loading. The simulation results show that the proposed subcarrier-power allocation scheme can achieve high total system capacity and good fairness in allocating the resources to the users with slightly high computational complexity compared to the existing subcarrier allocation algorithms.

CARRIER FREQUENCY OFFSET ESTIMATION FOR INTERLEAVED OFDMA UPLINK BASED ON SUBSPACE PROCESSING

This paper investigates Carrier Frequency Offset (CFO) estimation in the uplink of the Orthogonal Frequency-Division Multiple Access (OFDMA) systems with the interleaved subcarrier assignment. CFOs between the transmitters and the uplink receiver will destroy orthogonality among different subcarriers, hence resulting in inter-carrier interference and multiuser interference. A two-stage frequency offset estimation algorithm based on subspace processing is proposed. The main advantage of the proposed method is that it can obtain the CFOs of all users simultaneously using only one OFDMA block. Compared with the previously known methods, it not only has a relatively low implementation complexity but is also suitable for random subchannel assignment.

SINR-BASED ANTENNA COMBINING FOR MULTIUSER MIMO-OFDM WITH LIMITED FEEDBACK

A multiuser Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) broadcast channel is considered where both transmitter and receivers are equipped with multiple antennas. The Channel State Information (CSI) is quantized and provided through limited feedback links. In the first part of this work, the Maximum Expected SINR Combining (MESC) strategy for feedback decrease is investigated. Then a combination of MESC with subcarrier assigning is presented to further reduce the feedback load. The basic idea is the subcarriers are partitioned into resource blocks. For each block, only one quantized channel vector is feedback. The simulation results show MESC can obtain the performance gain over the relevant combiner strategies in MIMO-OFDM system. Moreover the effectiveness on the reduction of feedback overhead by the use of partitioning blocks in the studied system is evaluated.

A time domain multiple-CFOs and CIRs estimation algorithm over wireless multimedia sensor networks

Channel parameters estimation in an orthogonal frequency division multiple access(OFDMA)systemfor the receiver station is a multi-dimensional(MD)optimization problem,because every user node has aseparate local oscillator and every transmitter to receiver link has individual carrier frequency offset(CFO)and channel impulse response(CIR)parameters .In order to reduce the computational complexityfor MD optimization,a time domain CFOs and CIRs estimation algorithm over the OFDMA based wirelessmultimedia sensor networks(WMSN)is proposed in this paper.In this algorithm,the receiver stationcan decouple the signal from every node by correlation based on specially designed training sequences,sothat the MD optimization problem is simplified to an 1-D optimal problem.It is proved that the multipleCFOs can be identified from the correlation result using the phase shift of the consecutive training se-quences .Based on the CFOs estimation result,the CIRs can then be estimated according to the minimummean square error(MMSE)criterion.The theoretic analysis and simulation results show that the proposedalgorithm can effectively decouple the signal from different user nodes and the bit error rate(BER)per-formance curves are close to the ideal estimation when the user number is not large.

混合NOMA/OFDMA可见光通信系统资源分配算法

为了进一步降低混合非正交多址/正交频分复用多址(NOMA/OFDMA)技术的多用户多小区可见光通信系统的误码率,提出了一种功率和子载波的联合分配算法。该算法以最小化系统误符号率为优化目标,实现了子小区间载波和用户功率的联合最优分配。首先,理论推导出系统的误符号率表达式;然后,使用Matlab软件进行仿真,模拟可见光通信系统模型,并借助遗传算法得到最优的分配结果;最后,将该算法与现有的算法进行了对比。仿真结果表明,所提算法的误符号率性能更优。

智能反射面辅助OFDMA云接入网的资源分配方法

本文研究了智能反射面(IRS)辅助OFDMA(Orthogonal Frequency Division Multiple Access,正交频分多址接入)云无线接入网(C-RAN)的下行链路传输系统,其中基带处理单元(BBU)池通过多个远端射频头(RRH)与多个用户进行通信.RRH到用户的接入链路采用OFDMA接入技术.对于BBU池到RRH,采用无线前传链路,并且部署多个IRS以增强链路传输能力.在BBU池和每个RRH发射功率约束下,本文提出通过联合优化前传链路和接入链路资源配置使下行用户和速率最大化.由于该资源配置问题是非凸的,首先采用连续凸逼近(SCA)对目标以及约束条件进行转换.其次,将转换后的问题拆分成三个子问题来交替性求解.最后,计算机仿真结果显示了所提出的联合资源分配方法与其他基准方案相比具有显著的传输性能增益.

Resource Allocation based on Shared Criterion in OFDMA Distributed Radio Access Network

Distributed radio access network (DRAN) is a novel wireless access architecture and can solve the problem of the available spectrum scarcity in wireless communications. In this paper, we investigate resource allocation for the downlink of OFDMA DRAN. Unlike previous exclusive criterion based algorithms that allocate each subcarrier to only one user in the system, the proposed algorithms are based on shared criterion that allow each subcarrier to be allocated to multiple users through different antennas and to only one user through same antenna. First, an adaptive resource allocation algorithm based on shared criterion is proposed to maximize total system rate under each user's minimal rate and each antenna's maximal power constraints. Then we improve the above algorithm by considering the influence of the resource allocation scheme on single user. The simulation results show that the shared criterion based algorithm provide much higher total system rate than that of the exclusive criterion based algorithm at the expense of the outage performance and the fairness, while the improved algorithm based on shared criterion can achieve a good tradeoff performance.

基于多臂赌博机的卫星通信系统子载波分配算法

为了提升卫星通信系统的频谱效率,在卫星系统采用正交频分多址(Orthogonal Frequency Division Multiple Access,OFDMA)传输技术的情况下,提出了一种基于多臂赌博机(Multi⁃Armed Bandit,MAB)的子载波分配算法。首先,建立基于OFDMA的卫星系统上行链路多用户传输模型。然后建立以用户总速率最大化为目标,以用户最大发射功率和用户服务质量为约束条件的资源分配问题。接着,利用MAB能在环境信息部分未知时在线学习摇臂选择策略的特性来求解该优化问题,并获得子载波分配方案。仿真结果表明,所提算法能实现系统子载波的自适应分配,同时用户总速率与贪婪算法在已知信道状态信息下获得的用户总速率几乎相同。

IRS-OFDMA系统中基于用户QoS的下行资源分配方案

针对智能反射面(intelligent reflecting surface,IRS)辅助的正交频分多址(orthogonal frequency division multiple access,OFDMA)系统中最大化下行系统吞吐量问题,在保障用户服务质量(quality of service,QoS)的前提下,提出了一种有关子载波、功率和IRS反射相位的资源分配方案。在固定反射相位的情况下,基于用户优先级准则分配载波,载波分配后采用注水算法对用户载波间功率进行分配;在固定子载波和功率分配的情况下,通过连续凸逼近求出相位解;多次交替优化后在满足迭代次数及收敛精度要求时,得到子载波分配因子、功率分配系数和反射相位的近似解。仿真结果表明,方案相较于其他方案可以有效提高系统吞吐量且保障用户QoS速率。

基于OFDMA的多小区协作可见光通信系统二维功率分配算法

为了消除可见光通信系统中多小区和多用户信号干扰,提出一种基于正交频分多址(OFDMA)的多小区协作可见光通信系统二维功率分配算法。首先,根据信道情况,采用OFDMA多小区协作资源分配算法给信道情况差的用户分配更高的功率;然后,根据信道信息求解共照区域用户多个协作发光二极管(LED)的发送功率比,得到最优的目标叠加星座。仿真结果表明:与平均功率分配算法相比,一维功率分配算法误码率性能平均提升了16%;与一维功率分配算法相比,二维功率分配算法误码率性能平均提升了10%。

基于多波束GEO卫星的宽带移动通信系统

提出基于多波束天线静止地球轨道卫星的宽带移动通信系统方案,与常规结构同类系统用户相比,其容量更大、业务质量更好。采用时隙同步码分多址辅助的多频时分多址接入、程控交换与因特网协议交换结合的交换、时分复用和准正交时分复用下行链路传输体制,可显著增加用户量,简化星上设备,改善互联网应用业务质量。用户接入信道数为173 880,最高用户下载速率达155 Mbps。仿真结果表明,140个波束、每波束26个16幅度相移键控信号的用户下行链路传输比频分复用传输的链路性能改善11.65dB,使得宽带用户"动中通"天线等效口径缩小至原来的1/4,成本大幅降低。

OFDM调制技术在宽带高速电力线通信中的应用

介绍了电力线用做通信介质时高频部分的特性 ,以及应用于高速宽带电力线通信的 OFDM(正交频分复用 )调制的基本原理 ;分析了 OFDM应用于电力线通信的性能 ,并与其他调制技术进行了比较 ;结合一个典型应用的例子 ,介绍了国际上研究的最新进展。

认知无线电下行链路中的OFDMA资源分配算法

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.

保证混合业务质量的跨层OFDMA资源分配方法

提出了一种新的跨层正交频分多址(OFDMA)系统资源分配方法,其综合考虑了无线信道的时变特征和媒体接入子层(MAC)业务服务质量(QoS)要求,将MAC层分组调度和物理层的子信道分配及自适应调制编码进行联合设计,目的是在保证实时时延敏感业务和非实时业务的QoS基础上最大化系统吞吐量.在子载波分配过程中,分别采用了信道依赖的最早预期(CD-EDD)算法和最小速率需求(MRR)算法,对实时时延敏感业务和非实时业务进行调度.基于IEEE 802.16标准建立了动态仿真模型对算法性能进行评估,结果表明,本方法较传统的最大信噪比方法在系统吞吐量相近的情况下,在时延特性、用户公平性方面有较大性能提升.

LTE系统自适应软频率复用技术研究

提高小区边缘用户性能是蜂窝移动通信系统的经典难题.下一代蜂窝移动通信系统3GPP LTE通过有效的小区间干扰协调以及频率资源分配来改善小区边缘用户性能.提出一种自适应软频率复用算法,根据系统负载情况自适应地为各小区分配主、副载波及其发射功率,在实现系统吞吐量优化的同时保证小区中心和边缘区域速率需求.算法首先通过穷尽搜索和贪婪递减策略,获得单小区最优资源分配,然后在不同小区间迭代执行单小区算法直到系统吞吐量不变为止.仿真结果表明,算法通过多次迭代后,系统吞吐量保持不变并输出一种优化的资源分配方案.与同类频率分配算法相比,可以有效提升小区边缘用户的吞吐量,同时获得更高的系统容量,更适用于高速率的LTE系统.

基于时频联合扩频的OFDM-CDMA性能分析

提出了一种基于OFDM CDMA系统的新型时频2维联合扩频的方法,详细介绍了相应的系统结构以及接收机中不同的解扩合并方式.仿真结果表明,在时频选择性衰落信道中使用联合扩频方式的系统性能要优于MC CDMA系统.

基于博弈论的OFDMA系统多小区功率协调分配算法

提出了一种用于正交频分多址(OFDMA)通信系统下行链路的多小区功率协调分配算法,协调相邻小区在同频子信道上的发送功率,抑制小区间干扰,提高信道容量。将博弈论引入到多小区功率分配中,给出基于定价的多小区非合作功率分配博弈模型,并分析了该博弈的纳什均衡解的存在性和惟一性,给出了该模型的分布式求解算法。通过仿真分别给出了单小区场景与多小区场景下算法性能,讨论了定价因子对系统性能的影响。仿真结果表明,提出的多小区功率协调分配算法可以充分利用无线资源,提高系统吞吐量,降低平均发送功率。

用于OFDMA系统的多小区自适应资源分配算法

提出了一种用于正交频分多址通信系统下行链路的多小区自适应资源分配算法(MARA).为了降低系统复杂度,将子信道分配和功率分配分开实现,在小区内部进行动态子信道分配,并以单小区子信道分配结果为基础在相邻小区同频用户中进行功率分配.将非合作博弈论引入到多小区功率分配中,给出了基于代价函数的多小区分布式功率分配算法.通过协调相邻小区间同频子信道的发送功率,抑制小区间干扰,提高了无线资源利用率.仿真结果表明,与已有算法相比,本文提出的算法可以提高系统吞吐量.