Cross-Layer design in HSDPA system to reduce the TCP effect

This paper focuses on the interaction between the transport control protocol (TCP) layer and the radio interface in the high-speed downlink packet access (HSDPA) wireless system. In the literature, studies of the interaction between TCP and wireless networks are focused on the evaluation of user bit rate in the case of dedicated channels. In this paper, the interaction between TCP, hybrid automatic repeat request (HARQ), and scheduling techniques (especially, proportional fair scheduling) is conducted. Analytical models to evaluate HSDPA cell capacity, user bit rate, and interaction with TCP layer are presented. Even if as expected the bit rate per flow decreases strongly with the congestion frequency in the wired network, it is shown that the overall capacity achieved by HSDPA is not as affected by the TCP layer. Using this result, a method to reduce the effect of TCP on wireless network without losing much cell capacity is proposed. This method has the advantage of modifying the scheduling algorithm only and of not requiring any change to the TCP protocol.     

Lock step: an algorithm to reduce wi-fi jitter

The exponential backoff algorithm used in IEEE 802.11 does not guarantee short term fairness between flows. We propose an algorithm based on IdleSense where each of N flows tries to transmit every W = 8N slots; i.e. 8 slots per flow with 7 idle. Each flow adaptively adjusts its contention window W based on the observed proportion of empty slots. One key aspect of Lock Step is setting a deterministic backoff after a successful transmission so that, for persistent flows, eventually all users are in lock step and transmit every 8N slots. Another key aspect is forcing a second collision between colliding users so all users can better estimate the proportion of idle slots per transmission thus allowing users to estimate N and hence the optimal backoff. This second collision can also be engineered to assist the ZigZag algorithm to decode the colliding packets. Even with transient flows Lock Step reduces jitter and can substantially increase the number of flows carrying Voice over IP traffic through a single access point.     

OMS: Opportunistic mules for short latency data collection in smart cities

In smart city scenarios, data collected by sensors are required to be conveyed to central controllers for processing. Thus, efficient data collection mechanisms considering the urban environment characteristics should take place. To that end, the data mules approach is proved to be efficient. However, being applied to urban environment leads to high data delivery latency due to the characteristics of this environment. Motivated by the need to reduce the collection latency of such an approach, we propose to provide each road segment with a data mule to create a process of distributed data collection. Our scheme leverages opportunistic inter‐vehicular communications for assigning the mule role to adequate vehicles. The simulation in realistic mobility settings reveals that our scheme can provide more than 80% of the area of interest with data mules in less than 1 minute. In addition, the data collection latency can be reduced from 24 hours to few minutes.     

Color image segmentation: a novel spatial fuzzy genetic algorithm

Image segmentation is a very important low-level vision task. It is the perceptual grouping of pixels based on some similarity criteria. In this article, we have applied spatial fuzzy genetic algorithm (SFGA) for the unsupervised segmentation of color images. The SFGA adds diversity to the search process to find the global optima. The performance of SFGA is influenced by two factors: first, K number of clusters—should be known in advance; second, the initialization of the cluster centers. To overcome these issues, a progressive technique based on self-organizing map is presented to find out the optimal K number of clusters automatically. To handle the initialization problem, peaks are identified using the image color histograms. The genetic algorithm with fuzzy behavior maximizes the fuzzy separation and minimizes the global compactness among the segments. The segmentation is performed on wavelet transform image which not only reduces the dimensionality and computational cost but also makes more compact segments. A novel pruning technique is proposed to handle the problem of over-segmentation. The results show that the proposed technique outperforms state-of-the-art methods.     

DRED: a random early detection algorithm for TCP/IP networks

It is now widely accepted that a RED [2] controlled queue certainly performs better than a drop‐tail queue. But an inherent weakness of RED is that its equilibrium queue length cannot be maintained at a preset value independent of the number of TCP active connections. In addition, RED's optimal parameter setting is largely correlated with the number of connections, the round‐trip time, the buffer space, etc. In light of these observations, we propose DRED, a novel algorithm which uses the basic ideas of feedback control to randomly discard packets with a load‐dependent probability when a buffer in a router gets congested. Over a wide range of load levels, DRED is able to stabilize a router queue occupancy at a level independent of the number of active TCP connections. The benefits of stabilized queues in a network are high resources utilization, predictable maximum delays, more certain buffer provisioning, and traffic‐load‐independent network performance in terms of traffic intensity and number of connections. Copyright © 2002 John Wiley & Sons, Ltd.     

Double-sided two-way ranging algorithm to reduce ranging time

In this Letter we propose a novel ranging algorithm for the asynchronous location positioning system. The main idea of the proposed algorithm is to reply with multiple acknowledgement packets to a single ranging request. The ranging algorithm reduces the number of packets used in ranging process and improves the ranging accuracy at the same time.     

K-means聚类算法在民航客户细分中的应用

针对客户关系管理中客户价值这一问题,通过对航空公司现有数据仓库中客户信息的分析,采用数据挖掘技术中的K-means聚类算法建立民航客户细分模型,并通过实验将民航客户细分为3类,提出了对这3类航空客户的相关营销策略。实验结果表明该方法能突出客户之间的行为特征差异,更加准确地划分客户类型,进而使得客户价值约提高30%。     

Unsupervised vector image segmentation by a tree structure-ICM algorithm

In recent years, many image segmentation approaches have been based on Markov random fields (MRFs). The main assumption of the MRF approaches is that the class parameters are known or can be obtained from training data. In this paper the authors propose a novel method that relaxes this assumption and allows for simultaneous parameter estimation and vector image segmentation. The method is based on a tree structure (TS) algorithm which is combined with Besag's iterated conditional modes (ICM) procedure. The TS algorithm provides a mechanism for choosing initial cluster centers needed for initialization of the ICM. The authors' method has been tested on various one-dimensional (1-D) and multidimensional medical images and shows excellent performance. In this paper the authors also address the problem of cluster validation. They propose a new maximum a posteriori (MAP) criterion for determination of the number of classes and compare its performance to other approaches by computer simulations.     

一种调节TCP非对称信道数据传输效率的算法

为了研究非对称信道对ＴＣＰ端到端性能的影响。本文以非对称信道数据传输效率为对象，分析了非对称环境下，上行、下行数据传输效率的关系。在此基础上找到一种调节ＴＣ 致锥道数据传输效率的可行算法，并以ＡＤＳＬ信道为模型，通过仿真对算法的性能进行验证和分析。     

Explicit window adaptation: a method to enhance TCP performance

We study the performance of TCP in an internetwork consisting of both rate-controlled and nonrate-controlled segments. A common example of such an environment occurs when the end systems are part of IP datagram networks interconnected by a rate-controlled segment, such as an ATM network using the available bit rate (ABR) service. In the absence of congestive losses in either segment, TCP keeps increasing its window to its maximum size. Mismatch between the TCP window and the bandwidth-delay product of the network results in accumulation of large queues and possibly buffer overflows in the devices at the edges of the rate-controlled segment, causing degraded throughput and unfairness. We develop an explicit feedback scheme, called explicit window adaptation, based on modifying the receiver's advertised window in TCP acknowledgments returning to the source. The window size indicated to TCP is a function of the free buffer in the edge device. Results from simulations with a wide range of traffic scenarios show that this explicit window adaptation scheme can control the buffer occupancy efficiently at the edge device, and results in significant improvements in packet loss rate, fairness, and throughput over a packet discard policy such as random early detection (RED)     

Evaluation based segmentation algorithm optimization: Idea and system

This paper conies up with a new idea that tries to optimize the performance of image segmentation algorithms based on their objective evaluation knowledge. A prototype expert system is designed and implemented according to this idea. Kxperimental results indicate that this system is feasible and practical. This idea also offers an efficient approach for algorithm optimization of image processing and analysis.     

细胞分割算法研究方法综述

随着现代科技的发展,用计算机处理细胞在医学诊断和医学图像处理领域有着重要的作用.细胞分割是细胞特征提取和细胞识别的基础,从医学图像中分割出精准的细胞图像是目前极具挑战性的课题.在细胞的自动识别的研究中产生了有效的分割算法的需求,人们提出了不同的分割算法根据图像的不同特征,如阈值法,分水岭算法等.本文对细胞分割的各种方法...     

Energy optimization in a smart community grid system using genetic algorithm

A smart community grid is an electrical network, which connects several producers, consumers, and prosumers to share energy in an intelligent and secure way. The main challenges of smart community grid are demand response, demand bidding, dynamic electricity tariffs, demand-side management, and prosumers handling. The current state-of-the-art smart grid decision making is focused on consumers and producers behavior while the aim of this research is to achieve prosumer's different goals in an optimized and intelligent way. A genetic algorithm (GA)-based solution is proposed to share energy in an optimized way without affecting the prosumers' preferences. Six prosumers smart community grids data sets are used to validate the performance of the proposed system. The results show that the proposed method significantly improves the loss of energy sharing without compromising the user's preferences.     

EM algorithm for image segmentation initialized by a tree structurescheme

In this correspondence, the objective is to segment vector images, which are modeled as multivariate finite mixtures. The underlying images are characterized by Markov random fields (MRFs), and the applied segmentation procedure is based on the expectation-maximization (EM) technique. We propose an initialization procedure that does not require any prior information and yet provides excellent initial estimates for the EM method. The performance of the overall segmentation is demonstrated by segmentation of simulated one-dimensional (1D) and multidimensional magnetic resonance (MR) brain images.     

模糊分段光滑图像分割模型及其快速算法

灰度分布不均图像是图像分割中一个难点,为此提出一种模糊分段光滑(FPS)图像分割模型.借鉴分段光滑Mumford-Shah(MS)模型与模糊聚类思想,新模型通过两个定义在图像域的光滑函数描述区域特征,并利用模糊隶属度函数代替MS模型中的特征函数.同时,边界检测算子的引入能够有效保护图像中的边界信息.数值求解采用分裂Br...     

次随机分块PTS-Clipping峰均比抑制算法

针对正交频分复用信号存在高峰均比问题,本文提出了一种基于次随机分块的部分传输序列(partial transmit se-quence,PTS)与传统限幅剪切联合处理的峰均比抑制算法.该算法在时域得到随机分块的子块序列,子块序列乘以相位旋转因子得到多个备选序列,从多个备选序列中寻找低峰值OFDM信号,最后利用频域滤波剪切算法限幅.仿真结果表明,所提算法在低复杂度下可以有效降低PAPR.     

Energy efficiency of TCP: An analytical model and its application to reduce energy consumption of the most diffused transport protocol

Energy efficient communications become a challenge for both industries and researchers. Incorporating energy efficiency into the design of network protocols and architectures represents a relevant issue in networking research. Currently, very few works address energy efficiency as a fundamental feature of network protocols. This paper benchmarks energy efficiency of TCP to understand the parameters and operational mechanics that determine and contribute to energy consumption. We propose an analytical model with energy consumption to protocol operation cycles and novel optimization techniques for reducing energy consumption of TCP. The evaluation results, obtained from NS2 simulations, demonstrate that even minor modifications of the protocol behavior can bring significant savings of energy. Copyright © 2015 John Wiley & Sons, Ltd.     

Hybrid MUSIC Dolph–Chebyshev algorithm for a smart antenna system

This paper presents practical design of a smart antenna system based on direction‐of‐arrival estimation and Dolph–Chebyshev beam forming. Direction‐of‐arrival estimation is based on the multiple signal classification algorithm for identifying the directions of the source signals incident on the sensor array comprising the smart antenna system. The smart antenna system design involves a hardware part, which provides real data measurements of the incident signals received by the sensor array. This paper presents the Dolph–Chebyshev method for the synthesis and design of antenna arrays with periodic element spacing. A Field‐Programmable Gate Array implementation is presented for an antenna array application employing digital beamforming. The array comprises 10 elements, equal in number receiving radio frequency and intermediate frequency components, as well as a Spartan‐3E Field‐Programmable Gate Array‐based unit, which is responsible for the control of the array. Low‐cost and switched‐beam, and fully adaptive antenna array suitable for 2‐GHz applications are proposed in this paper. Copyright © 2013 John Wiley & Sons, Ltd.     

FAST TCP: from theory to experiments

We describe a variant of TCP, called FAST, that can sustain high throughput and utilization at multigigabits per second over large distances. We present the motivation, review the background theory, summarize key features of FAST TCP, and report our first experimental results.     

一种减少频谱泄露的幅值和相位自校正算法

频谱泄露是影响谐波检测和频谱分析的重要原因,而采样频率与信号频率不同步是造成频谱泄露的根本原因。现提出一种幅值和相位自校正的算法,可通过自动校正减小异步采样时DFT产生的幅值和相位的误差,降低频谱泄露造成的影响,对同步采样条件下的DFT没有影响,并给出算法的实现步骤和仿真结果,证明了该算法能精确地得到信号的实际幅值和相位,对于采样点数较少的信号也能给出较高的测量精度,而且该算法具有迭代特性,原理简单,是频谱分析中的一种有效方法。