基于认知OFDM的子载波功率分配改进算法

在认知无线网络中,建立了基于认知OFDM多载波资源分配数学模型,在授权用户干扰受限条件下,以最大化传输速率为目标进行认知用户的子载波功率分配。传统注水法被证明是最优的单用户子载波功率分配算法,在传统注水法功率分配基础上,提出了两种可行的子载波功率分配改进算法,改进算法一是通过对水面值的粗略估计快速确定不分配功率子载波,改进算法二不需要通过迭代计算水面值,只通过线性计算就可以直接确定不分配功率的子载波,且对授权用户不产生干扰。仿真结果表明,在改进的两种子载波功率分配算法下,认知用户的数据传输速率优于传统注水法功率分配时认知用户的数据速率,所提改进算法具有自适应特性且计算复杂度大大降低。      

电力线通信系统的功率注水分配

针对电力线信道在总功率、功率谱密度和各子载波比特数的约束,文中探讨了单用户在电力线信道自适应OFDM系统的功率分配模型,提出了两种新的基于开关和地窖的混合迭代注水功率分配算法。在典型电力线通信环境下的仿真结果表明,穷举搜索算法和功率比较算法的性能一样,但穷举搜索算法的仿真时间长且变化大。     

基于跨层优化的HE-PDS最优传输算法设计

针对信道状态时变性以及无线设备电量有限性的影响,从跨层设计的角度出发,联合物理层发送功率和信道状态条件以及链路层的缓冲队列拥塞控制来寻找最优传输策略,并提出一种启发式评估后决策算法(HE-PDS)进行求解。仿真分析表明该算法在动态无线环境下能以较快的速度收敛于最优传输策略,对于不同的延时和吞吐量限制,该算法的性能要明显优于传统的Q学习算法和后决策状态学习算法。     

OFDMA系统中最优能效功率分配

该文研究了OFDMA系统中基于能效的功率分配问题。区别于已有研究,该文利用了能效函数关于功率矢量的严格伪凹特性,证明了最优能效功率分配一定具有一种特殊的注水功率结构能效注水结构。通过该结构,功率分配问题被简化为关于水位线的一元优化问题,进而求得最优能效功率的闭合解。在此基础上,该文进一步提出了一种最优能效功率分配算法,该算法通过顺序搜索有限个水位线区间的方式求得最优解。仿真表明该算法能够快速得到最优能效功率,其计算复杂度远小于已有的能效功率分配算法。     

多跳CC-HARQ中继网络的频谱有效性跨层设计

在瑞利衰落信道中,为改善采用Chase合并混合自动重传请求( CC-HARQ)协议的多跳中继网络的频谱效率性能,考虑发送帧长和发送功率的跨层优化,研究了提升其频谱效率的跨层优化策略。不同于传统的中断概率分析,通过利用对数域线性阈值的平均误帧率估计方法,给出了多跳CC-HARQ协议频谱效率的精确表达式,在发送功率固定时设计了最优发送帧长策略,在发送帧长固定时设计了最优发送功率分配方案,进一步提出了跨层的联合优化方案。仿真结果验证了所设计优化方案在理论上的正确性和有效性,同时在仿真中可以观察到采用跨层的优化策略后,多跳 CC-HARQ中继网络的频谱效率获得了显著的提升,其中跨层的联合优化方案比传统的固定帧长等功率策略在频谱效率上提升了0.014 b/s·Hz-1。     

基于线性规划的超宽带WSN功率控制策略

能耗开销是无线传感器网络(WSN)性能的瓶颈问题之一,而功率控制是解决这一问题的最有效方法。针对超宽带(UWB)WSN,该文以实现网络功耗最小化为目标,从跨层优化的角度提出了基于UWB最优功率分配策略模型;然后,给出了在lexicographic max-min(LMM)策略下的线性规划求解方法。仿真结果表明,LMM策略可较大改善节点平均功耗和链路成功接通率。     

最佳中继协作通信系统的功率分配算法

 为提高基于最佳中继选择的协作通信系统的性能,提出了以最小化系统中断概率为目标的功率分配算法.首先建立了系统的优化模型并证明了待解的优化问题实质是凸优化问题,由此提出了最优功率分配算法并给出了算法步骤.其次,在此基础上提出了一种有效的次最优功率分配算法,该算法计算简单且仅需已知各个中继节点的平均信道状态信息,无需在传输中实时更新,因而不增加系统的额外开销.仿真结果表明,本文提出的最优算法和次最优算法所得到的功率分配方案与穷举搜索方法的结果非常接近;与等功率分配方案相比,这两种算法均能显著提高系统的中断概率性能.     

红外无线系统的变步长自适应功率分配算法

红外无线通信系统中,为了在功率和误码率一定的限制下进一步提高系统容量,提出了一种新的变步长自适应功率分配算法,该算法以每比特分配功率的代价最小为原则(一次可分配多个比特)来选择最佳的调制技术.分析了其速度原理,并在建立模型的基础上,通过仿真研究了新算法的系统性能,并与理想注水算法以及传统的简单速率量化算法进行比较.仿真...     

OFDM和MIMO系统中的快速注水功率分配算法

针对传统注水算法需要进行复杂的搜索注水线计算的特点,提出了一种新的低计算复杂度的快速注水算法。在多信道无线通信系统中,注水算法是在给定功率下最大化系统容量的基本功率分配算法。通过对注水问题的分析,利用注水性质快速调整注水线从而移除了复杂的搜索注水线计算。仿真结果表明,与已有的算法相比,提出的算法节省了大量的计算时间。     

一种改进的MIMO-OFDM系统注水功率分配算法

鉴于目前MIMO—OFDM系统中大多数比特功率分配算法需要多次迭代,复杂度较高,及系统比特分配离散性的特点,本文结合贪婪功率分配算法逐步优化的思想,提出了修正的二次注水功率比特分配算法。该算法首先利用注水功率分配方案得到连续速率最优的功率分配,接着针对实际数据速率量化的误差对不同特征模式下的功率进行微调,实验证明改进后的算法有效提高了系统的总体传输速率。     

Delay-bounded packet scheduling of bursty traffic over wireless channels

In this paper, we study minimal power transmission of bursty sources over wireless channels with constraints on mean queuing delay. The power minimizing schedulers adapt power and rate of transmission based on the queue and channel state. We show that packet scheduling based on queue state can be used to trade queuing delay with transmission power, even on additive white Gaussian noise (AWGN) channels. Our extensive simulations show that small increases in average delay can lead to substantial savings in transmission power, thereby providing another avenue for mobile devices to save on battery power. We propose a low-complexity scheduler that has near-optimal performance. We also construct a variable-rate quadrature amplitude modulation (QAM)-based transmission scheme to show the benefits of the proposed formulation in a practical communication system. Power optimal schedulers with absolute packet delay constraints are also studied and their performance is evaluated via simulations.     

基于上下文学习的电力物联网接入控制方法

针对6G时代电力物联网海量终端接入冲突严重、队列积压大、能量效率低等问题,提出了一种基于上下文学习的接入控制算法。所提算法基于强化学习和快速上行链路授权技术,考虑终端活跃与休眠2种状态,优化目标为在终端接入服务质量需求的长期约束下最大化网络总能量效率。利用李雅普诺夫优化对长期优化目标与约束进行解耦,将长期优化问题转化为单时隙独立的确定性子问题,并利用基于终端状态感知的上置信界算法进行求解。仿真结果表明,所提算法能够在满足终端接入服务质量需求的同时,有效提高网络总能量效率。相较于传统快速上行链路授权算法,所提算法可提高平均能量效率48.11%,提高满足接入服务质量需求的终端比例54.95%,降低平均队列积压83.83%。     

RED gateway congestion control using median queue size estimates

This paper focuses on the queue size estimation problem in random early detection (RED) gateways. Queue size estimation plays a fundamental role in the congestion control dynamics of RED, as it determines gateways' awareness of network congestion, which in turn determines the packet dropping/marking decision. Conventional RED gateways use exponentially weighted moving averages (EWMA) to estimate the queue size. These infinite impulse response (IIR) filters require very small EWMA weights in order to effectively avoid nonlinear instabilities in RED and to filter out bursty increases in the queue size. While small EWMA weights enable gateways to accommodate transient congestion, they also lead to gateways' failure to closely track rapid queue size depletion and thus causes link under utilization. We investigate the use of simple nonlinear queue size estimators. In particular, we study the congestion control dynamics of a network where adaptive weighted median filters are used for queue size estimation by the gateways. Analytical results for the expected queue size in the steady state are derived. Under this new queue size estimation framework, design guidelines for the remaining RED parameters are provided. Simulation results show that the proposed algorithm provides greater network power, better prevention of global synchronization, and a fairer treatment to bursty traffic than the RED algorithm does.     

Server allocation with delayed state observation: Sufficient conditions for the optimality of an index policy

In this paper we study an optimal server allocation problem, where a single server is shared among multiple queues based on the queue backlog information. Due to the physical nature of the system this information is delayed, in that when the allocation decision is made, the server only has the backlog information from an earlier time. Queues have different arrival processes as well as different buffering/holding costs. The objective is to minimize the expected total discounted holding cost over a finite or infinite horizon. We introduce an index policy where the index of a queue is a function of the state of the queue. Our primary interest is to characterize conditions under which this index policy is optimal. We present a fairly general method bounding the reward of serving one queue instead of another. Using this result, sufficient conditions on the optimality of the index policy can be derived for a variety of arrival processes and packet holding costs. These conditions are in general in the form of sufficient separation among indices, and they characterize the part of the state space where the index policy is optimal. We provide examples and derive the indices and illustrate the region where the index policy is optimal.     

无线信道中基于时延约束下的一种调度策略

该文研究无线信道中基于时延约束下功率最小化的调度策略。文章首先将该优化问题转化为非约束Markov动态决策过程,随后用动态规划的方法获得了最优解。由于动态规划是基于整个决策阶段而不是在单个阶段做出最后决策,因而复杂度较高,实时性较差。有鉴于此,该文提出了一种简便策略,该策略只根据当前信道状态和队列长度做出决策,实时性好,算法简单,而且能使队列具有平稳分布的特征,保证了系统的稳定性。仿真结果显示该策略的性能接近最优策略。     

A Novel Method of Feedback Reducing and Cross-layer Scheduling Based on Traffic Rates for Relay System

This paper studies the scheduling schemes in multiuser downlink relay systems with orthogonal frequency division multiple access (OFDMA) where base station (BS) supports different traffic rates for different users. We formulate the problem as a cross-layer design of joint feedback reducing and OFDMA scheduling to support traffic rates and minimize packet loss rate. In most previous scheduling mechanisms with feedback, the parameters of traffic arrival process were not taken into account, consequently, the requirement of user traffic can not be guaranteed. In this paper, a dynamic threshold feedback mechanism (DTFM) based on traffic rates is proposed, of which the user with channel gain being larger than the dynamic threshold is only allowed to send its channel state information, thereby reducing the number of required feedback users and the computational burden of exhaustive search for best users at the BS. A cross-layer scheduling algorithm of traffic and queue proportional fairness (TQPF) taking into consideration the traffic fairness, the user queue length and the user transmission rate (related to its channel quality) is then proposed. Finally, a method of feedback reducing and cross-layer scheduling, i.e., TQPF based on DTFM (TQPF-DTFM), is proposed. Theoretical and simulation results show that DTFM reduces feedback by more than 90%, and TQPF-DTFM successfully meets user traffic rates that is, the user with high traffic rate can obtain more transmission rate than the user with low traffic rate and deceases packet loss rate of the system by almost 50% than the conventional methods.     

无线多跳网络快速跨层资源优化分配算法

针对背压路由算法容易造成大量队列积压和收敛速度慢的缺陷,该文研究了无线多跳网络中节点功率受限情况下的联合拥塞控制、路由和功率分配的跨层优化问题。以最大化网络效用为目标,以流平衡条件、功率等为约束条件建模,基于牛顿法提出了一种具有超线性收敛性能的算法,并运用矩阵分裂技术使该算法能够分布式实施。仿真结果表明,该算法在实现网络效用最大化的同时,能够有效提高网络中的能量效用,且能将网络中的队列长度稳定在一个较低水平,降低包传输延时。     

Hierarchical queue‐length‐aware power control for real‐time applications over wireless networks

We consider the problem of optimal power control for quality‐of‐service‐assured wireless communication. The quality of service (QoS) measures of our consideration are a triplet of data rate, delay, and delay bound violation probability (DBVP). Our target is to develop power control laws that can provide delay guarantees for real‐time applications over wireless networks. The power control laws that aim at optimizing certain physical‐layer performance measures, usually adapt the transmission power based on the channel gain; we call these “channel‐gain‐based” (CGB) power control (PC). In this paper, we show that CGB‐PC laws achieve poor link‐layer delay performance. To improve the performance, we propose a novel scheme called hierarchical queue‐length‐aware (HQLA) power control. The key idea is to combine the best features of the two PC laws, i.e., a given CGB‐PC law and the clear‐queue (CQ) PC law; here, the CQ‐PC is defined as a PC law that uses a transmission power just enough to empty the queue at the link layer. We analyze our proposed HQLA‐PC scheme by the matrix‐geometric method. The analysis agrees well with the simulation results. More importantly, our results show that the proposed HQLA power control scheme is superior to the corresponding CGB‐PC in both average power consumption and effective capacity. Copyright © 2010 John Wiley & Sons, Ltd.     

Queue length aware power control for delay‐ constrained communication over fading channels

In this paper, we study efficient power control schemes for delay sensitive communication over fading channels. Our objective is to find a power control law that optimizes the link layer performance, specifically, minimizes the packet drop probability, subject to a long‐term average power constraint. We assume the buffer at the transmitter is finite; hence packet drop happens when the buffer is full. The fading channel under our study has a continuous state, e.g., Rayleigh fading. Since the channel state space is continuous, dynamic programming is not applicable for power control. In this paper, we propose a sub‐optimal power control law based on a parametric approach. The proposed power control scheme tries to minimize the packet drop probability by considering the queue length, i.e., reducing the probability of those queue‐length states that will cause full buffer. Simulation results show that our proposed power control scheme reduces the packet drop probability by one or two orders of magnitude, compared to the time domain water filling (TDWF) and the truncated channel inversion (TCI) power control. Copyright © 2010 John Wiley & Sons, Ltd.     

Queue management based duty cycle control for end-to-end delay guarantees in wireless sensor networks

In this paper, we propose an analytical method for duty cycle adaptation in wireless sensor networks so that delay requirement is guaranteed while power consumption is minimized. The proposed method, named Dual-QCon, provides a formal method for stabilizing controller design based on queue management in order to control both duty cycle and queue threshold according to changing network conditions. Dual-QCon also provides a delay notification mechanism in order to determine an appropriate queue threshold of each node according to the application-dependent and time-varying delay requirements. Based on control theory, we analyze the adaptive behavior of the proposed method and derive conditions for system stability. Asymptotic analysis shows that Dual-QCon guarantees end-to-end delay requirement by controlling parameters of local nodes. Simulation results indicate that Dual-QCon outperforms existing scheduling protocols in terms of delay and power consumption.