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.

Modeling and Analysis of OFDMA-NOMA-RA Protocol Considering Imperfect SIC in Multi-User Uplink WLANs

To address the problems of network congestion and spectrum resources shortage in multi-user large-scale scenarios,this paper proposes a twice random access OFDMA-NOMA-RA protocol combining the advantages of orthogonal frequency division multiple access(OFDMA)and non-orthogonal multiple access(NOMA).The idea of this protocol is that OFMDA is used to divide the entire frequency field into multiple orthogonal resource units(RUs),and NOMA is used on each RU to enable more users to access the channel and improve spectrum efficiency.Based on the protocol designed in this paper,in the case of imperfect successive interference cancellation(SIC),the probability of successful competition subchannels and the outage probability are derived for two scenarios:Users occupy the subchannel individually and users share the subchannel.Moreover,when two users share the channel,the decoding order of the users and the corresponding probabilities are considered.Then,the system throughput is obtained.To achieve better outage performance in the system,the optimal power allocation algorithm is proposed in this paper,which enables the optimal power allocation strategy to be obtained.Numerical results show that the larger the imperfect SIC coefficient,the worse the outage performance of weak users.Compared with pure OFDMA and NOMA,OFDMA-NOMA-RA always maintains an advantage when the imperfect SIC coefficient is less than a specific value.

Cooperative communications with hierarchical modulation in downlink OFDMA based cellular networks

Cooperative transmission is a promising way to improve system performance in orthogonal frequency division multiple access (OFDMA) based cellular networks.This paper proposes two heuristic cooperation schemes including relay selection and resource allocation using hierarchical modulation (HM) to fully exploit the radio resources in cellular networks where user equipments (UEs) relay for each other.The relay selection procedure considers both the channel conditions and the energies left in relays to make the cooperative communications behave better.To mitigate the spectrum efficiency loss due to the half-duplex mode,the bits of relayaided UE and its relay (which is also a UE) are transmitted simultaneously in one sub-channel using HM to improve the utilization efficiency of sub-channels.Besides,time resources are used effectively with the adaptively changed proportion of the two sub-frames divided for relay transmission.Simulation results show that the proposed schemes can improve the spectrum efficiency compared with the traditional schemes.

Hardware Implementation and Simulations of Joint Coding and Modulation Diversity MIMO-OFDM Scheme

This paper presents an efficient Joint Coding and Modulation Diversity ( JCMD ) scheme. The proposed scheme applied modulation diversity technique to MIMO-OFDM system which can effectively use time, frequency and space diversity combined with channel coding. In fading channel,the proposed scheme not only achieves high spectral efficiency,but also greatly enhances the reliability of wireless transmission. The self- developed hardware prototype system proves that the proposed scheme can be realized and has high reliability. Compared with traditional MIMO-OFDM scheme based on bit-interleaved coded modulation ( BICM) ,software and hardware simulation results show that the proposed scheme with the optimal rotational angle can obtain a significant performance advantage both for precoded and non-precoded system in the condition of non-perfect channel knowledge and non-ideal synchronization.

Modulation Techniques for Li-Fi

Modulation techniques for light fidelity （Li-Fi） are reviewed in this paper. Li-Fi is the fully networked solution for nmltiple users that combines communication and illumination simultaneously. Light emitting diodes （LEDs） are used in Li-Fi as visible light transmitters, therefore, only intensity modulated direct detected modulation techniques can be achieved. Single carrier modulation techniques are straightforward to be used in Li-Fi, however, computationally complex equalization processes are required in fre- quency selective Li-Fi channels. On the other hand, multiearrier modulation techniques offer a viable solution for Li-Fi in terms of power, spectral and computational efficiency. In particular, orthogonal frequency division multiplexing （OFDM） based modulation techniques offer a practical solution for Li-Fi, especially when direct current （DC） wander, and adaptive bit and power loading techniques are considered. Li-Fi modulation techniques need to also satisfy illumination requirements. Flickering avoidance and dimming control are considered in the variant modulation techniques presented. This paper surveys the suitable modulation techniques for Li-Fi including those which explore time, frequency and colour domains.

TIME-FREQUENCY 2-D LMS BASED LONG-RANGE CHANNEL PREDICTION FOR WIRELESS OFDM SYSTEMS

Adaptive modulation can optimize the spectrum efficiency and system performance with the channel state information achieved by the long-range channel prediction. To avoid re-estimating channel correlation function as the channel stationarity varies and to track the channel adaptively, LMS （Least-Mean-Square） based long-range channel prediction is discussed in the existing literature, but it needs long observation interval to reach the convergence. Given that all OFDM （Orthogonal Frequency Division Multiplexing） subcarriers have the identical time-domain correlation and stationarity during the same time interval, this paper proposed a 2-D LMS based predictor which updates the filter weights in both time and frequency domain. The proposed scheme can effectively decrease the observation intervals and significantly speed up the convergence than the conventional LMS and Parallel LMS （PLMS）. Complexity analysis and simulation results prove that the proposed scheme can improve the BER （Bit Error Rate） performance and spectrum efficiency with negligible complexity increase.

POWER ALLOCATION AND ADAPTIVE MODULATION STRATEGY FOR MIMO-OFDM SYSTEMS WITH IMPERFECT CSI

The presented scheme named M-CAP (Maximum CAPacity) uses the CSI (Channel State Information) and its statistics to deduce an equivalent channel according to which the transmit power is allocated to the subchannels. And then modulation scheme is determined adaptively according to the power allocated to each subchannel. The advantage of the M-CAP scheme is that it combines power allocation and adaptive modulation while maintaining a large capacity. We demonstrate by computer simulations that the proposed M-CAP scheme can significantly improve system performance compared with the traditional schemes.

SIGNAL CONSTELLATIONS DESIGN FOR DIFFERENTIAL UNITARY SPACE-TIME IN MIMO-OFDM SYSTEM OVER FREQUENCY-SELECTIVE FADING CHANNELS

In this paper, the design of signal constellations parameters is studied for Differential Unitary Space-Time Modulation (DUSTM) based on the design criterion of maximizing the diversity product. Further, noninteger searching method for the signal constellation parameters design is proposed in order to get better codes. Experimental results show that under the different Doppler spread and data transmission rate, the proposed design performs better than the previous design using integer parameters in Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system over frequency-selective fading channels.

Performance analysis of a rate adaptive multi-band ultra-wideband system based on quadrature fractal modulation scheme

A rate adaptive multi-band ultra-wideband (UWB) system based on the quadrature fractal modulation (QFM) scheme was proposed.Exploring the use of homogeneous signals as modulating waveforms in UWB system,the signal within each 528MHz sub-band was divided into 8 different frequency bandwidths using wavelets transform and these data sequences to be transmitted were embedded into homogeneous waveforms.It is found that the use of homogeneous signals in such UWB system is quite feasible,leadings to a novel multi-rate diversity strategy.Within each 528MHz sub-band,the UWB-QFM system can provide much higher data rates than that of the UWB orthogonal frequency division multiplexing (OFDM) system.Simulation results also show that the bit error rate (BER) performance of the UWB-QFM system achieves a greatly improvement over existing UWB-OFDM system.Due to the fractal properties of the homogeneous signals,these data sequences to be transmitted can be recovered using arbitrarily short receiver signal.

Spectrally Efficient Multi-Carrier Modulation Using Gabor Transform

Non Orthogonal Frequency Division Multiplexing (NOFDM) systems make use of a transmission signal set which is not restricted to orthonormal bases unlike previous OFDM systems. The usage of non-orthogonal bases generally results in a trade-off between Bit Error Rate (BER) and receiver complexity. This paper studies the use of Gabor based on designing a Spectrally Efficient Multi-Carrier Modulation Scheme. Using Gabor Transform with a specific Gaussian envelope;we derive the expected BER-SNR performance. The spectral usage of such a NOFDM system when affected by a channel that imparts Additive White Gaussian Noise (AWGN) is estimated. We compare the obtained results with an OFDM system and observe that with comparable BER performance, this system gives a better spectral usage. The effect of window length on spectral usage is also analyzed.

基于LWT的可见光OFDM-IM系统研究

针对索引调制正交频分复用(OFDM-IM)技术峰均比过高,对相位噪声和载波频偏敏感,系统复杂度高等问题,提出基于小波提升变换(LWT)的可见光OFDM-IM系统。首先选择正交小波基作为子载波,通过对信号的分裂、预测和更新,将信号分为高频信号和低频信号,再结合可见光信道构成LWT-OFDM-IM系统,最后通过理论分析和蒙特卡罗方法对系统的可靠性、峰均比特性和最佳小波分解层数进行了仿真验证,结果表明:当子载波N=256,子块中子载波数量L=4,激活子载波数量k=2,系统误码率为10~(-4)时,LWT-OFDM-IM比FFT-OFDM-IM改善约8 dB,相较于DWT-OFDM-IM提高约4 dB。当系统互补累计分布函数(CCDF)为10^(-1)数量级时,LWT-OFDM-IM的峰均比较FFT-OFDM-IM改善约2.3 dB。随着小波层数的递增,系统的误码性能越好,当小波层数为3层时,大约在10 dB附近,误码率可到10^(-5)量级。

基于多特征融合的MIMO-OFDM系统单-混信号调制识别算法

为解决非协作通信中多输入多输出正交频分复用(multiple-input multiple-output orthogonal frequency division multiplexing, MIMO-OFDM)系统的单-混信号调制识别问题,提出一种基于多特征融合和决策融合的调制识别方法。首先,利用特征矩阵的联合近似对角化(joint approximate diagonalization of eigenvalue matrix, JADE)算法从接收端恢复发送信号;然后,提取恢复后信号的四次方谱、循环谱和高阶累积量作为输入样本,利用多特征融合网络对输入样本进行训练;最后,使用决策融合策略根据每条支路输出得到最终判决结果。仿真实验结果表明,所提方法可以对MIMO-OFDM系统中的7种信号进行有效识别,在信噪比为10 dB时识别精度可达99.4%。

基于排序码本的水声自适应OFDM通信中信道状态信息反馈研究

水声(UWA)信道时延扩展大等特点导致信道频响(CFR)快衰落,水声通信(UWAC)技术发展受到挑战。发射端获取有效可靠的信道状态信息(CSI)是自适应通信的前提,针对水声自适应正交频分复用(OFDM)通信的需求,该文提出基于排序码本的信道状态信息分组排序拟合反馈算法(CSI-GSFF),包括分组、排序、数据拟合3个步骤。该算法首先将相邻导频子载波分组,以组为反馈单元;然后对各组内的导频子载波按照信道增益值进行排序,以减轻水声信道频响快衰落造成的反馈开销大等不利影响;最后进行多项式拟合,排序操作有效地降低了拟合阶数。通过实测海试时变信道数据仿真,结果表明,该文提出的信道状态信息反馈算法能够基本达到完美信道状态信息情形下的水声自适应OFDM通信系统误码率性能,同时可以有效地减少反馈开销。

下行SDM/OFDMA系统中基于效用函数的多用户调度算法

该文研究了空分复用/正交频分多址(SDM/OFDMA)无线通信系统中的多用户调度问题,针对该系统的空时频三维调度特点,提出一种基于效用函数的多用户调度算法。该算法利用空间多用户分集获得增益,同时兼顾系统的整体效率和用户的个体效用。通过计算机仿真验证了算法具有和穷举搜索算法相近的性能,但算法复杂度大大降低。

OFDMA中继系统下行链路资源分配算法研究

为了满足用户最小速率要求,提高OFDMA中继系统下行链路的和速率容量,在适用于TDMA和CDMA系统的M-LWDF资源分配算法基础上,提出了一种基于信道和缓冲队列状态信息的OFDMA中继系统资源分配算法。该算法同时考虑了各用户的信道状态和数据流的突发性,相对于现有算法,提出的新算法使OFDMA中继系统中断概率最小化的同时,可以获得更大的系统和速率容量。数值仿真结果也证明了上述结论。

一种用于OFDMA认知网络的低复杂度资源分配算法

针对功率受限的多用户正交频分多址接入(OFDMA)认知网络,提出了一种低复杂度的资源分配算法,包括子载波和功率分配.在子载波分配中,选取包含最差信道质量的子载波优先分配给用户,再将剩余的子载波信道质量值按方差的降序分配给用户,避免了最后未被分配的子载波恰好只能分配给对应信道质量最差用户的情况发生;在功率分配时,在传统线性注水算法的基础上增加了对主用户抗干扰阈值的判断,在最大化次用户吞吐量的同时,提高了主用户的抗干扰能力.仿真结果表明,与已有算法相比,该算法能够有效提升分配给用户的最差子载波信道质量,在用户吞吐量上接近于传统线性注水算法的性能上限,具有良好的主用户公平性,且计算复杂度低.

OFDMA系统中基于有限反馈的资源公平调度算法

OFDMA是下一代无线通信系统中在下行链路上实现大容量通信的一种有前途的技术,其中的关键技术之一是在共享信道的用户间公平合理地分配子载波和功率。分析了功率约束下系统最大吞吐量的实现方法,提出了一种基于有限反馈的资源公平调度算法,这种算法具有系统所需反馈信息量少、用户间公平性好等性能。

基于OFDMA的无线协作多播网络资源分配算法

在传统的无线多播传输中,多播组的系统性能受限于多播组内的最差用户的信道质量。为了克服多播组的系统性能受限的问题,将协作传输引入到基于正交频分多址(orthogonal frequency division multiple access,OFDMA)的无线多播网络中,并提出了在总传输速率受限的情况下,最小化总传输功率的动态资源分配算法。为了减少计算复杂度和保障公平性,提出了协作公平子载波分配算法(cooperative fair,CF)和迭代注水功率分配算法。仿真结果显示,在多播组的用户中进行协作传输的系统性能,要远高于采用传统多播直接传输的性能,并且所提算法也在保证系统性能的同时,实现了多播组间良好的公平性。

一种基于OFDMA系统的频率复用方法

频率复用作为提高小区边缘用户性能的有效方式已被广为研究。然而,如何在提高小区边缘用户性能的同时,使频谱利用率得到有效提高仍是一个有待解决的问题。在以正交频分多址(OFDMA)为基本多址方式的第4代(4G)系统中该问题尤为突出。为此,该文提出了一种OFDMA系统中的频率复用方法,通过抑制小区间干扰提高小区边缘用户性能;同时,根据小区中心与小区边缘通信环境的差异,分别对其实施不同的频率复用策略使频率复用系数接近于1以提高频谱利用率。仿真结果表明,与未经过频率规划的全频率复用相比,该文提出的频率复用方法提高了系统吞吐量并显著改善了小区边缘用户性能。

基于改进智能水滴算法的多用户OFDMA系统资源分配

在正交频分多址(OFDMA)系统中,合理的资源分配对于提升系统的性能具有重要的意义。针对多用户OFDMA系统,对最大化系统容量为目标的资源分配算法进行研究,提出了一种基于智能水滴算法的无向全连通图资源分配模型,以无向全连通图的顶点集和边集来描述用户与子载波之间的匹配关系。在此基础上,进一步对智能水滴算法进行改进。仿真结果表明,在满足用户比例公平性的条件下,与蚁群算法相比,基于改进智能水滴算法的全连通图分配方案能够提高2.17%~4.91%的系统速率,同时具有更快的收敛速度,提高了系统性能。