非理想状态信息下SC-FDMA上行链路的信道调度

信道依赖调度(CDS)通过在信道里使用多用户分集和频率选择性来增加蜂窝系统的数据吞吐量,主要研究非理想信道状态信息(CSI)对CDS的影响。具体来说,当CSI有反馈延时,分析具有未编码自适应调制及CDS的上行链路单载波频分多址(SC-FDMA)系统的数据吞吐量。频域资源分配采用集中式和分布式的子载波映射方案。通过仿真可以看到在应用CDS时,集中式的子载波映射产生最高的总数据吞吐量,然而,当信道迅速变化时,集中式映射对CSI的质量以及信道容量增益的迅速减少非常灵敏。对于高机动性的用户来说,具有静态轮询调度方案的分布式映射更加合适。     

单频网多播系统中的开环半动态功率分配算法

在单频网多播传输中,传统的全反馈动态功率分配数算法需要根据每个时隙反馈的用户瞬时信道信息进行实时的调整,所以造成了资源分配频率快、上行反馈开销大的缺点。为了克服这个缺点,提出了一个低复杂度、没有用户反馈的单频网多播开环半动态功率分配算法。首先在各小区等功率分配的假设下,根据单频网的形状信息算出各小区等价信道增益,然后再根据这个增益值,实现满足速率需求情况下的各小区功率分配。仿真结果显示,与全反馈的动态功率分配算法相比,该算法以一小部分性能损失为代价,大大减少了单频网的上行反馈和资源分配的开销,因此更适用于实际的单频网多播系统。     

Optimal resource allocation in uplink SC-FDMA systems

We present algorithms for resource allocation in Single Carrier Frequency Division Multiple Access (SC-FDMA) systems, which is the uplink multiple access scheme considered in the Third Generation Partnership Project-Long Term Evolution (3GPP-LTE) standard. Unlike the well-studied problem of Orthogonal Frequency Division Multiple Access (OFDMA) resource allocation, the "subchannel adjacency" restriction, whereby users can only be assigned multiple subchannels that are adjacent to each other, makes the problem much harder to solve. We present a novel reformulation of this problem as a pure binary-integer program called the set partitioning problem, which is a well studied problem in operations research. We also present a greedy heuristic algorithm that approaches the optimal performance in cases of practical interest. We present simulation results for 3GPP-LTE uplink scenarios.     

蜂窝车联网中基于服务异构性的V2V通信资源分配算法研究

在支持车与车直接通信(V2V)的蜂窝网络场景下,针对密集环境下复用车与设备(V2I)上行链路的资源分配问题,在V2V的干扰下,利用移动链路的信道状态信息(CSI)的慢衰落统计,联合通信可靠性、功率控制,建立最大化V2I信道容量的优化模型以满足车辆网络服务的异构性的需求。基于此,该文提出一种基于超图理论和遗传算法的资源分配算法。仿真结果表明,该算法在保证V2V通信可靠性的前提下,提高了V2I的信道容量。     

中断概率在TD-LTE信道资源分配中的应用

TD-LTE(时分同步码分多址-长期演进)系统业务呈非对称状态,对下行数据率的要求要超过上行数据率,因而对系统信道上下行资源分配的要求更为严格。文章利用中断概率接纳控制算法对系统信道资源进行了智能动态分配,通过系统仿真证明了该策略能够灵活分配系统时隙资源。     

Resource Allocation and Adaptive Modulation in Uplink SC-FDMA Systems

In this paper, we study joint power and sub-channel allocation, and adaptive modulation in Single Carrier Frequency Division Multiple Access (SC-FDMA) which is adopted as the multiple access scheme for the uplink in the 3GPP-LTE standard. A sum-utility maximization problem is considered. Unlike OFDMA, in addition to the restriction of allocating a sub-channel to one user at most, the multiple sub-channels allocated to a user in SC-FDMA should be consecutive as well. This renders the resource allocation problem prohibitively difficult and the standard optimization tools (e.g., Lagrange dual approach widely used for OFDMA, etc.) can not help towards its optimal solution. We propose a novel optimization framework for the solution of this problem which is inspired from the recently developed canonical duality theory. We first formulate the optimization problem as binary-integer programming problem, and then transform this binary-integer programming problems into a continuous space canonical dual problem that is a concave maximization problem. Based on the solution of the continuous space dual problem, we derive joint power and sub-channel allocation algorithm whose computational complexity is polynomial. We provide conditions under which the proposed algorithms are optimal. We also propose an adaptive modulation scheme which selects an appropriate modulation strategy for each user. We compare the proposed algorithm with the existing algorithms in the literature to assess their performance. The results show a tremendous performance gain.     

基于LMS估计的卫星移动通信定时同步优化

针对采用长期演进(LTE)通信标准的地球静止轨道(GEO)卫星移动通信系统上行定时误差会影响单载波频分多址技术正交性的问题,在LMS线性估计算法的基础上提出了一种适用于大时延环境下单载波频分多址定时同步优化方法。该方法对用户与卫星之间传输时延的变化进行估计,通过闭环控制补偿减小上行定时误差。仿真表明:该方法在使用LTE标准帧结构时,能保护用户上行信号正交性,避免符号间干扰,且传输速率损失约为9%,远低于传统拓展帧结构方法带来的损失,验证了方法的优越性。     

非采样间隔信道的LTE上行信道估计新方法

为了解决非采样间隔信道的冲激响应能量泄漏和低信噪比下高斯白噪声的干扰问题,采用一种将小波去噪技术与改进的基于DFT的估计方法相结合的LTE上行系统信道估计的新方法。仿真结果表明,基于部分加权估计的时间窗函数的正确选择能有效地改善原有方法在高信噪比下的地板效应,与小波去噪结合能有效提高低信噪比下的信道估计性能。     

LTE上行多用户SC-FDMA系统中时变信道估计方法

针对高速移动时分双工长期演进(TDD-LTE,time division duplex-long term evolution)上行单载波频分多址(SC-FDMA,single carrier-frequency division multiple access)系统,提出了一种新型的变换域时变信道估计方法.在所定义的变换域中,基于两块导频符号的信道参数估计,提出利用基于判决导向的非线性内插方法来估计数据符号的信道参数.为了便于SC-FDMA系统均衡,推导给出了变换域信道与频域信道的转换表达式,利用该式可以直接将变换域信道参数估计转化为频域信道响应.计算机仿真结果表明,新方法的性能远远优于传统方法的估计性能,且具有低的计算复杂度.     

802.11ax系统中基于传输延迟的多用户调度与资源分配算法

IEEE 802.11ax系统中站点(Station,STA)数量众多和潜在的高数据包冲突率导致无线局域网通信效率显著降低,本文针对上行多用户传输中的无效帧填充问题,以每轮传输中用户组的传输延迟为优化目标,提出一种多用户调度和资源分配算法.基于OFDMA上行调度接入中动态传输时间的帧交互方案,接入点(Access Po...     

Opportunistic multichannel access with decentralized channel state information

This paper considers multiaccess control for the uplink in orthogonal frequency division multiple access wireless networks. To avoid the extensive information exchange associated with centralized approaches, we formulate the decentralized access control problem with the contention power constraint as a Bayesian game, mapping time‐varying channel state information into contention strategies. By exploiting the problem structure, a strategy where users access the channels with probability one if the observed channel gain is above a predetermined threshold is shown to be optimal. It is also shown that the energy consumption of the threshold strategy will not exceed that of randomized strategies. The game is then equivalently reformulated as one of finding the threshold value in a distributed manner, and the existence and uniqueness of Bayesian Nash equilibria is established. A distributed algorithm based on Lagrange duality is proposed to approach the unique equilibrium, and the algorithm is shown to be globally stable. In a homogeneous system, the performance loss of the proposed scheme is proved to be bounded compared with a centralized channel allocation scheme. Contrary to other proposals, our method allows for heterogeneous channel state information and achieves a comparable throughput with reduced power. Copyright © 2013 John Wiley & Sons, Ltd.     

Buffer-aware resource scheduling scheme for LTE-A uplink relay-assisted network

Due to the constraint of single carrier frequency division multiple access （SC-FDMA） adopted in long term evolution （LTE） uplink, subcarriers allocated to single user equipment （UE） must be contiguous. This contiguous allocation constraint limits resource allocation flexibility and makes the resource scheduling problem more complex. Most of the existing work cannot well meet UE＇s quality of service （QoS） requirement, because they just try to improve system performance mainly based on channel condition or buffer size. This paper proposes a novel resource scheduling scheme considering channel condition, buffer size and packet delay when allocating frequency resource. Firstly, optimization function is formulated, which aims to minimize sum of weight for bits still left in UE buffer after each scheduling slot. QoS is the main concern factor here. Then, to get packet delay information, this paper proposes a delay estimation algorithm. Relay node （RN） is introduced to improve overall channel condition. Specific RN selection strategy is also depicted in the scheme. Most important of all, a creative negotiation mechanism is included in the subcarrier allocation process. It can improve the overall system throughput performance in guarantee of user＇s QoS requirement. Simulation results demonstrate that the scheme can greatly enhance system performance like delay, throughput and jitter.     

Channel estimation and long-range prediction of fast fading channels for adaptive OFDM system

This correspondence presents the channel estimation and long-range prediction technique for adaptive-orthogonal-frequency-division-multiplexing (AOFDM) system. The efficient channel loading is accomplished by feeding the accurately predicted channel-state-information (CSI) back to transmitter. The frequency-selective wireless fading channel is modelled as a tapped-delay-line-filter governed by a first-order autoregressive (AR1) process; and an adaptive channel estimator based on the generalised-variable-step-size least-mean-square (GVSS-LMS) algorithm tracks AR1 correlation coefficient. To compensate for the signal fading due to channel state variations, a modified-Kalman-filter (MKF)-based channel estimator is utilised. In addition, channel tracking is also performed for predicting future CSI at receiver, based on the numeric-variable-forgetting-factor recursive-least-squares (NVFF-RLS) algorithm. Subsequently, adaptive bit allocation for AOFDM system is employed by using predicted CSI at transmitter. Here, the proposed combination of GVSS-LMS and MKF algorithms for robust channel estimation and the NVFF-RLS algorithm for efficient channel prediction is incorporated. The performance validation of presented method is carried out by using different channel realisations through simulation, and also by comparing it with fixed step-size LMS, MKF and fixed forgetting-factor RLS algorithm based conventional techniques. Eventually, the reliable performance of underlying AOFDM system can be achieved in terms of the lower mean squared estimation/prediction errors and alleviated symbol error rate.     

Novel Turbo Receiver for MU-MIMO SC-FDMA System

Single carrier-frequency-division multiple access (SC-FDMA) has been adopted as the uplink transmission standard in fourth-generation cellular networks to facilitate power efficiency transmission in mobile stations. Because multiuser multiple-input multiple-output (MU-MIMO) is a promising technology employed to fully exploit the channel capacity in mobile radio networks, this study investigates the uplink transmission of MU-MIMO SC-FDMA systems with orthogonal space-frequency block codes (SFBCs). It is preferable to minimize the length of the cyclic prefix (CP). In this study, the chained turbo equalization technique with chained turbo estimation is employed in the designed receiver. Chained turbo estimation employs a short training sequence to improve the spectrum efficiency without compromising the estimation accuracy. In this paper, we propose a novel and spectrally efficient iterative joint-channel estimation, multiuser detection, and turbo equalization for an MU-MIMO SC-FDMA system without CP-insertion and with short TR. Some simulation examples are presented for the uplink scenario to demonstrate the effectiveness of the proposed scheme.     

Joint user pairing and power allocation in uplink virtual MIMO with imperfect CSI

User pairing strategy for virtual multi-input multi-output （VMIMO） has been widely studied to improve system throughput, but most studies are based on perfect channel state information （CSI） and uniform power allocation. However, perfect CSI is very difficult or even impossible to obtain in practical system. Moreover power allocation has significant impact on algorithm performance. Therefore, in this paper, a low-complex joint user pairing and power allocation algorithm based on aggressive discrete stochastic optimization and Lagrangian dual solution is proposed for uplink VMIMO with imperfect CSI. Simulation results show that the proposed algorithm can achieve desirable throughput performance, and restrict inter-user interference （IUI） efficiently.     

LTE中的SC-FDMA技术研究

在上行链路方向,3GPPLTE采用SC-FDMA作为多址技术,该技术有助于实现较高的功率放大器效率,且对于FDD和TDD工作模式都是适用的。本文分析了SC-FDMA发射机和接收机结构与原理,描述了SC-FDMA系统的数据速率调整方法,讨论了SC-FDMA系统的资源分配过程,介绍了SC-FDMA的立方量度。     

基于补偿式CSI的分布式跨层联合资源分配算法

为消除过时信道状态信息(CSI)对分布式无线多跳网络环境下跨层资源分配效率的影响,提高跨层联合资源分配的准确性,基于信道相关性提出了一种补偿式跨层联合资源分配算法。利用瞬时和过时信道状态信息之间的条件概率密度函数,基于瑞利衰落信道模型求得信噪比(SINR) 模型下条件容量的闭式解。为补偿部分网络性能的损失,提出了一种考虑过时信道状态信息的联合拥塞控制、信道分配和功率控制的算法,在此过程中网络被建模成一个NUM 问题,可变的链路数据率和功率等资源限制作为约束条件。运用拉格朗日对偶分解技术,NUM问题被分布式求解。实验对比分析表明：在确保较低复杂度的前提下,该算法有效改善了分布式多跳网络资源分配的合理性,使其网络总体效用得到提升,降低了能耗。     

OFDMA vs. SC-FDMA: performance comparison in local area imt-a scenarios [recent advances and evolution of WLAN and WMAN standards]

The system requirements for IMT-A are currently being specified by the ITU. Target peak data rates of 1 Gb/s in local areas and 100 Mb/s in wide areas are expected to be provided by means of advanced MIMO antenna configurations and very high spectrum allocations (on the order of 100 MHz). For the downlink, OFDMA is unanimously considered the most appropriate technique for achieving high spectral efficiency. For the uplink, the LTE of the 3GPP, for example, employs SCFDMA due to its low PAPR properties compared to OFDMA. For future IMT-A systems, the decision on the most appropriate uplink access scheme is still an open issue, as many benefits can be obtained by exploiting the flexible frequency granularity of OFDMA. In this article we discuss the suitability of using OFDMA or SC-FDMA in the uplink for local area high-data-rate scenarios by considering as target performance metrics the PAPR and multi-user diversity gain. Also, new bandwidth configurations have been proposed to cope with the 100 MHz spectrum allocation. In particular, the PAPR analysis shows that a localized (not distributed) allocation of the resource blocks (RBs) in the frequency domain shall be employed for SC-FDMA in order to keep its advantages over OFDMA in terms of PAPR reduction. Furthermore, from the multiuser diversity gain evaluation emerges the fact that the impact of different RB sizes and bandwidth configurations is low, given the propagation characteristics of the assumed local area environment. For full bandwidth usage, OFDMA only outperforms SC-FDMA when the number of frequency multiplexed users is low. As the spectrum load decreases, instead, OFDMA outperforms SC-FDMA also for a high number of frequency multiplexed users, due to its more flexible resource allocation. In this contex different channel-aware scheduling algorithms have been proposed due to the resource allocation differences between the two schemes.     

TD-LTE-A上行信道估计中基于加权的插值算法

TD-LTE-A上行信道估计中的线性插值算法只利用数据两端的两个导频位置的信道响应进行插值,不能很好拟合信道响应。针对此问题,提出了基于加权平均的插值算法。该算法以线性插值算法为基础,首先利用连续3个导频位置的信道响应进行线性插值得到数据位置的两个初步插值结果,再在此基础上引入权值α,最后对初步插值结果进行加权得到数据位置的信道响应。在EPA环境下的MATLAB仿真结果表明,相对于线性插值算法,基于加权的插值算法在不过度增加计算复杂度的情况下能降低系统的误比特率。     

TDD-MIMO系统中由I/Q不平衡引起的信道非互易性补偿方法

分析了I/Q不平衡引起的信道互易性丧失对系统容量的影响,提出了一种基于信道状态测量的补偿算法。该算法中基站(BS)和移动台(MS)各自对接收信道进行测量而得到上下行链路的信道状态信息(CSI),然后将2条链路的CSI汇集到BS处,BS计算出分别用于BS和MS的校准矩阵。仿真结果表明所提算法能够有效地对I/Q不平衡进行校准,使信道互易性得到保持,从而使系统容量的损失得以弥补。