认知OFDM系统中针对视频业务用户的资源分配

在多用户认知无线电OFDM系统中,针对实时视频业务用户,提出一种计算复杂度低的资源分配方案.该方案采用鱼群算法分配子载波,并提出简单功率干扰(Simple Power Interference,SPI)约束功率分配算法.目标是在满足总功率预算并且保证不干扰主用户的前提下,最大化系统的下行系统容量.仿真分析表明,在视频业务用户场景中,所提算法能有效提高下行系统速率,性能接近最优且复杂度低.     

基于正交空分复用的多用户调度策略

为了消除多用户MIMO下行系统的多用户间干扰以及改进系统的误码率性能,研究了块对角化预编码与几何均值分解的联合方案(BD-GMD).针对BD-GMD系统的资源分配和用户调度,对比了等功率分配和注水算法对系统的影响,并基于系统容量最大化,提出了一种根据用户信道的子空间特性的低复杂度的用户调度算法.此外,对比分析了穷举搜索算法和传统的贪婪算法.数值仿真结果表明,文中所提出的基于正交投影的多用户调度算法充在保证系统容量的同时降低了算法复杂度.     

多用户MIMO—OFDM系统低复杂度资源分配算法研究

在MIMO-OFDM系统下行链路下提出了一种低复杂度的子载波和功率分配算法,为了在满足用户QoS需求的情况下,最小化用户的发射功率,本文算法将子载波分配给在所有子信道上具有最大增益的用户。仿真结果显示所提算法在复杂度和性能都优于以前的算法。     

一种多用户MIMO/OFDM下行链路保障QoS的自适应传输机制

在用户QoS参数限制下,该文提出一种在多用户MIMO/OFDM下行链路使系统总速率最大的资源分配机制。基站应用空分多址接入,使得每个子载波可支持多个用户,应用线性预编码方法抵消用户间的干扰,提出保障QoS的自适应功率、比特分配方案。该文并提出两种可应用到实际系统的低复杂度的比特加载和比特去除算法,仿真结果表明,该两种方法性能可非常接近最优遍历算法。     

多用户MIMO-OFDM系统中的一种新的用户调度算法

本文针对多用户环境下的多天线正交频分复用下行系统,提出了一种新的基于迫零波束成型的用户调度算法。迫零波束成型是在发送端消除用户间的干扰生成多个独立的空间子信道,来实现空间复用。由于在多天线正交频分复用下行系统中最优的用户选择算法需要遍历所有可能的用户集合,算法复杂度非常大,本文提出了一种简化算法。所提算法在保证每个用户的速率要求的情况下,通过贪婪算法来选择每个子载波上的用户集合,以最小化系统的发送功率。仿真结果表明在满足用户的速率要求下能达到很好的系统性能。     

不完整CSI下OFDMA无线中继系统资源分配算法研究

针对实际OFDMA系统中下行无线链路信道状态信息(CSI)不完善的前提下,提出一种满足不同用户QoS需求的资源分配算法。在该方案中,首先确定用户与中继站之间的CSI,然后在总功率约束条件下,通过在等功率分配降低算法复杂度的基础上进行最佳中继选择和子载波的分配,最后再对子载波进行注水的功率分配来进一步提高系统容量。仿真结果表明,该方案在保证用户QoS的同时进一步提高系统容量。     

多用户MIMO-OFDM系统中的子信道与功率分配算法研究

针对多用户MIMO-OFDM系统下行链路,分析了通过遍历搜索来使容量最大化的最优子信道与功率分配算法,在此基础上提出了低复杂度的次优多用户子信道与功率分配算法,即MSPA算法。为了最大限度地保证用户之间的公平性,进一步提出了考虑每个用户速率要求的MSPA-RoU算法。仿真结果表明：本文提出的MSPA算法在复杂度可接受的情况下所获得的容量增益与最优算法十分接近,并且远远大于在MIMO环境下仅对子载波进行分配的算法;MSPA-RoU算法在考虑用户速率要求时仍能获得可观的容量增益。     

多载波超密集网络的抗干扰分布式节能功率分配

该文研究多载波超密集网络(UDN)上行链路能效最优功率分配方案,基于非合作博弈论提出一种抗干扰分布式功率分配方案,使每个小区独立优化能效的同时抑制邻小区干扰。由于最大传输功率和QoS约束下的能效函数具有不易解决的非凸特性,且小小区间存在严重干扰。针对以上挑战,该文在最佳响应过程中设计了一种高精度低复杂度的阶梯注水算法,基于该算法利用干扰信道增益提出了一种多用户抗干扰功率分配算法。仿真结果和数值分析表明该算法运算复杂度低,且能在保证系统频谱效率的同时大幅度提升系统能效。     

多载波超密集网络的抗干扰分布式节能功率分配

该文研究多载波超密集网络(UDN)上行链路能效最优功率分配方案,基于非合作博弈论提出一种抗干扰分布式功率分配方案,使每个小区独立优化能效的同时抑制邻小区干扰.由于最大传输功率和QoS约束下的能效函数具有不易解决的非凸特性,且小小区间存在严重干扰.针对以上挑战,该文在最佳响应过程中设计了一种高精度低复杂度的阶梯注水算法,基于该算法利用干扰信道增益提出了一种多用户抗干扰功率分配算法.仿真结果和数值分析表明该算法运算复杂度低,且能在保证系统频谱效率的同时大幅度提升系统能效.     

MIMO干扰信道下低复杂度的分布式干扰对齐算法

干扰对齐技术可以有效地提高干扰信道容量和抑制干扰,其问题归结为求得闭式解。传统的干扰对齐方案根据信道的互易性,采用迭代的方法（分布式）来逼近闭式解,但带来了较大的计算开销。本文在K用户MIMO干扰信道系统中提出一种低复杂度的分布式干扰对齐算法,通过对用户K的干扰协方差矩阵进行基于修正的Gram-Schmidt方法使用排序QR分解,选出酉矩阵Q最后的dk列作为用户近似的干扰抑制滤波矩阵,和传统分布式干扰对齐方案相比,在基本保持系统容量和迭代收敛速度的同时,系统的复杂度明显降低。仿真结果验证了算法的有效性。      

Variable Interleaver Allocation for Downlink OFDM-IDMA

In this letter, a variable interleaver allocation scheme is proposed to alleviate the high peak-to-average power ratio (PAPR) of downlink OFDM-IDMA (orthogonal frequency division multiplexing-interleave division multiple access). The basic idea is to allocate multiple interleaving patterns for each user, so as to decide the best pattern with the lowest peak value. Furthermore, a variable interleaver design scheme is combined to generate multiple patterns from an original one. It is shown that the proposed scheme can achieve the theoretical bound of PAPR reduction performance, while making a good tradeoff among PAPR reduction, system performance and computational complexity.     

改进的多用户OFDM系统子载波和比特分配算法

针对多用户正交频分复用（OFDM）系统资源分配问题,提出了一种改进的基于边缘自适应（MA）准则的子载波和比特分配算法。在采用比例公平准则为每个用户分配子载波集合基础上,以用户速率最大者-最小者（Max-Min）子载波交换为原则进行子载波调整,使用户功率递减同时兼顾用户的公平性;通过对信道状态信息进行判断,利用贪婪算法将用户子载波分配的比特取整,以实现系统功率最小化。实验结果表明,本文提出的改进次优算法的计算复杂度较传统分步算法稍高,但仍远低于最优算法,其系统性能得以提升,且接近最优算法。     

一种改进的大规模MIMO发射天线选择算法

为了降低天线选择算法在大规模多输入多输出（Multiple-Input Multiple-Output,MIMO）系统下的误码率和复杂度,以用户端接收的总功率为优化目标,提出一种最大化所有用户接收总功率的天线选择算法。该算法将优化目标函数转化为凸函数,并利用凸优化方法求得其有效解。仿真结果表明,所提天线选择算法与传统的最大和容量算法相比,具有较好的系统误码率性能,且运算复杂度低,但系统容量有所降低。     

OFDM系统中一种联合改进的低复杂度SLM峰均比抑制技术

高的峰值平均功率比(Peak-to-Average Power Ratio,PAPR)是光正交频分复用(Optical Orthogonal Frequency Division Multiplexing,O-OFDM)系统的一个主要缺点,选择性映射(Selective Mapping,SLM)法能有效降低高PAPR出现的概率,但它的计算复杂度较高.一些低复杂度的SLM方案能够有效地降低复杂度,但同时也降低了PAPR的抑制性能.为了平衡这两个因素,将低复杂度SLM方案与次优选择的思想相结合,文章提出了一种联合改进的PAPR抑制方案.在低复杂度方案中,通过将一个复频域信号分为两个实信号,再利用快速傅里叶变换(Fast Fourier Transform,FFT)的平移和反折性质将其重建成新的信号,以得到更多的备选信号,如此便能降低计算复杂度.然后,再结合次优选择的思想,选择PAPR最小的一路以得到最优的PAPR抑制性能.仿真结果验证了该方案的有效性.     

基于有限反馈的协作多播高效资源分配策略

提出了协作多播网络中基于有限反馈的联合子载波和功率分配策略,在满足QoS需求的条件下使功率消耗最小化。该策略首先利用有限的反馈信息在等速率分配下将子载波分给不同的多播组,并提出“公平子载波分配”策略,达到了功率消耗和公平性的折中。然后利用提出的“协作功率迭代”策略完成有效的功率分配,该策略利用注水定理确定每个子载波的目标速率后,又通过一个功率迭代过程实现功率最佳化。仿真结果显示,新的协作策略大大降低了上行反馈开销,且所需功率和多播业务中断概率远远小于直传策略。此外,协作功率迭代策略由于有较低的计算复杂度,因此更适合于实际系统。     

A Computationally Efficient Tree-PTS Technique for PAPR Reduction of OFDM Signals

The high peak-to-average power ratio (PAPR) of time domain signals has been a major problem in orthogonal frequency division multiplexing (OFDM) systems, and thus various PAPR reduction algorithms have been introduced. Partial transmit sequence (PTS) is one of the most attractive solutions because of its good performance without distortion. However, it is considered as an impractical solution for the realization of high-speed data transmission systems due to its high computational complexity. In this paper, a novel PAPR reduction algorithm based on a tree-structured searching technique is proposed to reduce the PAPR with low complexity. In the proposed scheme, the computational complexity of searching process is decreased by adjusting the size of tree with two parameters, width and depth, while preserving good performance. The simulation results show that proposed scheme provides similar performance with optimum case with remarkably reduced computational complexity.     

Bee colony optimization aided adaptive resource allocation in OFDMA systems with proportional rate constraints

Orthogonal frequency division multiple access (OFDMA) is a promising technique, which can provide high downlink capacity for the emerging wireless systems. The total capacity of OFDMA can be maximized by adaptively assigning subcarriers to the users with the best gains for those subcarriers, with power subsequently distributed by water-filling. In this paper, we propose the use of artificial bee colony (ABC) algorithm combined with Deb’s selection mechanism to handle the constraints. In this scheme, a probabilistic selection scheme assigns probability values to feasible solutions based on their fitness values and to infeasible individuals based on their violations, to allocate the resources to the users in downlink OFDMA system. Specifically we propose two approaches for resource allocation in downlink OFDMA systems using ABC algorithm. In the first approach, ABC algorithm is used for subcarrier allocation only, while in second approach the ABC algorithm is used for joint subcarrier and power allocation. It is shown that both these approaches obtain higher sum capacities as compared to that obtained by previous works, with comparable computational complexity. It is also shown that the joint subcarrier and power allocation approach provides near optimal results at the cost of slightly higher computational cost.     

QoS guarantee and power distribution for soft handoff connections in cellular CDMA downlinks

A two-phase power distribution scheme for supporting quality-of-service (QoS) and best effort traffic is proposed. We first formulate the power distribution for QoS traffic as an optimization problem so that the number of simultaneously transmitting connections is maximized. Optimum power distribution is difficult to implement in practice due to both the computational complexity and the requirement for global information about the mobile station (MS) locations, connection channel conditions, and traffic load in the system. We then propose a heuristic scheme of power distribution for soft handoff (SHO) connections. The full scheme includes an initial power distribution (IPD) and a power distribution adjustment (PDA). IPD allocates BS power resource based on the channel condition of each individual connection, while PDA further coordinates the power distribution between neighboring base stations (BSs) in order to accommodate more connections. The proposed power distribution scheme can achieve a capacity close to that of the optimum power distribution, while providing much higher transmission throughput for best effort data traffic. The proposed power distribution scheme can be applied to existing SHO schemes for efficient BS power resource usage. The scheme does not require global information, and its implementation can be further simplified by performing IPD only with slight performance degradation.     

A simplified adaptive modulation scheme for D-STTD systems with linear receivers

In this letter, we consider D-STTD (Double Space Time Transmit Diversity) with an adaptive modulation (AM) scheme. The simple criteria for AM are proposed according to linear receivers and the corresponding AM schemes are derived to minimize bit error rate under the constraint of the total data rate and total transmit power. The D-STTD system using the proposed AM scheme requires low computational complexity and small feedback information. The performance of D-STTD system using the proposed scheme is improved by 7 dB or more in signal to noise ratio corresponding to 10/sup -4/ bit error rate.     

光OFDM系统中一种联合改进的LC-SLM峰均比抑制技术

由于光正交频分复用(O-OFDM)系统中的峰值平均功率比(PAPR)较高,针对传统的选择性映射(C-SLM)方案计算复杂度较高,而一些低复杂度SLM(LC-SLM)方案的峰均比抑制性能不佳的问题,为了在降低计算复杂度的同时兼顾PAPR的抑制性能,提出一种基于LC-SLM方案和Clipping技术联合改进的PAPR抑制方案。在低复杂度方案中,O-OFDM信号的实部和虚部被分开处理以期获得更多的备选信号,再结合Clipping技术把信号限定在门限值范围内,最后再选择PAPR最小的一路信号从而得到最优的PAPR抑制性能。仿真结果表明该方案具有较好的优越性以及较高的利用价值。