Repeatable and Realistic Experimentation in Mobile Wireless Networks

Experimenting with mobile and wireless networks is challenging because testbeds lack repeatability and existing simulation models are unrealistic for real-world settings. We present practical models for the physical and MAC layer behavior in mobile wireless networks in order to address this challenge. Our models use measurements of a real network rather than abstract radio propagation and mobility models as the basis for accuracy in complex environments. We develop an adaptive measurement technique in order to maximize the accuracy of our models in dynamic environments. The models then predict the packet delivery, deferring, and collision probability in the same network for an arbitrary set of transmitters. This allows to explore the performance of different network and higher layer protocols in simulation or emulation under identical and realistic conditions. We evaluate the accuracy of our models empirically by comparing them to benchmark measurements. We find that our models are effective at reproducing mobile scenarios in various environments. Across many experiments in realistic environments, we are able to reproduce link delivery probabilities with RMS error below 12 percent, and the simulated throughput of data flows in the presence of interfering transmitters with an error that is below 10 percent.     

Ad hoc routing protocol's performance: a realistic simulation based study

Multiple wireless devices jointly create and maintain ad hoc networks; their employment is favored to happen in a variety of environments with distinct topological characteristics. Diversified environmental conditions are expected to vary network performance. In fact, obstacles, buildings and/or mountains may act as either barriers, or source of noise for the radio signals. Nevertheless, most of the previous performance evaluation studies based on simulation, neglected this consideration; they used simulation models that were too simplistic, and too narrow (i.e. idealistic) in their scopes. With this paper we propose a new, complete and realistic Urban Mobility Model (UMM). It models realistically users motion, and radio signals propagation in a city-like scenario. Our aim is to study the effects of realistic network simulation on routing performance. The results prove that a realistic scenario with roads and buildings has a significant impact on routing.     

Efficient Wireless Network Simulations with Detailed Propagation Models

Accurate simulation of wireless networks requires realistic models of the channel propagation medium. The widely used free space model is computationally efficient but ignores many attenuation components which affect wireless signal propagation. This paper describes the impact of the accuracy of the wireless channel model on the accuracy of the results and on the execution time of large-scale network models. It then introduces means to reduce the runtime execution when deploying such detailed propagation models.     

陆地高速移动环境下电波传播特性的建模与分析

采用有限状态的马尔克夫链得出陆地高速移动环境下电波传播路径的动态仿真模型。将模型与真实的陆地高速移动电波传播环境相结合,建立了更符合实际传播环境的电波传播仿真模型,通过该传播模型得出陆地高速移动环境下的电波传播特性。将得出的模型运用于较平坦地理环境,基站信号覆盖区域约为3km,存在视距(LOS)路径。通过仿真给出了高速列车在沿线不同位置和不同速度时的电波路径数目、各电波路径的衰减系数、延迟时间等,以及由此分析计算出的在该环境下的多普勒频谱、电平通过率等电波特性。最后,对这些仿真数据进行统计分析,证实了该传播模型的有效性。     

CogNS: A Simulation Framework for Cognitive Radio Networks

Cognitive radio technology has been used to efficiently utilize the spectrum in wireless networks. Although many research studies have been done recently in the area of cognitive radio networks (CRNs), little effort has been made to propose a simulation framework for CRNs. In this paper, a simulation framework based on NS2 (CogNS) for cognitive radio networks is proposed. This framework can be used to investigate and evaluate the impact of lower layers, i.e., MAC and physical layer, on the transport and network layers protocols. Due to the importance of packet drop probability, end-to-end delay and throughput as QoS requirements in real-time reliable applications, these metrics are evaluated over CRNs through CogNS framework. Our simulations demonstrate that the design of new network and transport layer protocols over CRNs should be considered based on CR-related parameters such as activity model of primary users, sensing time and frequency.     

Performance Evaluation of Bluetooth Systems With LDI, Modified LDI, and NSD Receivers

Bluetooth is a popular short-range low-power radio standard for wireless personal area networks. Bluetooth transmitters employ Gaussian frequency shift keying (GFSK) and simple block codes for error correction. Recently, two new receiver designs for Bluetooth devices, which are the so-called modified limiter-discriminator detector with integrate-and-dump filtering (LDI) and noncoherent sequence detection (NSD), have been proposed in the literature. While the modified LDI receiver is a concatenation of a conventional LDI detector with an improved error-correction decoder, the NSD receiver fully takes into account the memory introduced by the GFSK. Both receivers have been shown to improve the Bluetooth system performance in terms of physical-layer metrics such as bit-error rate and packet-error rate. In this paper, we present a comprehensive performance evaluation considering practically more relevant metrics such as throughput, delay, and delay jitter at the medium-access control layer. To this end, we develop an evaluation framework, which includes the spatial distribution of Bluetooth devices, path loss, fading, realistic data traffic models, scheduling, automatic repeat request, and baseband packet selection. Our numerical and simulation results verify that the newly introduced Bluetooth receivers, especially NSD, offer a significant performance enhancement for Bluetooth systems in terms of practically relevant measures.     

Numerical characterization and modeling of subject-specific ultrawideband body-centric radio channels and systems for healthcare applications

The paper presents a subject-specific radio propagation study and system modeling in wireless body area networks using a simulation tool based on the parallel finite-difference time-domain technique. This technique is well suited to model the radio propagation around complex, inhomogeneous objects such as the human body. The impact of different digital phantoms in on-body radio channel and system performance was studied. Simulations were performed at the frequency of 3-10 GHz considering a typical hospital environment, and were validated by on-site measurements with reasonably good agreement. The analysis demonstrated that the characteristics of the on-body radio channel and system performance are subject-specific and are associated with human genders, height, and body mass index. Maximum variations of almost 18.51% are observed in path loss exponent due to change of subject, which gives variations of above 50% in system bit error rate performance. Therefore, careful consideration of subject-specific parameters are necessary for achieving energy efficient and reliable radio links and system performance for body-centric wireless network.     

Cross-Layer Design of 2D Queuing Model for Multi-hop Wireless Networks

Based on cross-layer design, a modified 2-dimensional queuing model (2DQM) is proposed in this paper to tackle the problem of end-to-end quality of service (QoS) metric calculation. This model exploits the traffic arrival process, multi-rate transmission in the physical layer and error recovery technology with the protocol of truncated automatic repeat request in the data link layer. Based on this model, QoS metrics of wireless links can be evaluated hop by hop. The model can be used in more realistic scenarios of multi-hop wireless networks, although the computational complexity of 2DQM is slightly higher compared with existing 1-dimensional queuing model. Simulation results indicate that the proposed model can estimate the end-to-end packet loss-rate and average delay more accurately than existing models, and a model based QoS routing algorithm can find routes with better QoS performance (with lower end-to-end packet loss-rate and delay).     

Performance Modeling of MANET Interconnectivity

The proliferation of mobile wireless computing devices and the increasing usage of wireless networking have motivated substantial research in mobile ad hoc networks (MANETs). In addition, much has also been done to link autonomous MANETs to the Internet, and as MANETs become more prevalent, the need to interconnect multiple MANETs becomes increasingly important too. However, direct interconnection of MANETs has rarely been studied. In this paper, we first report an experimental study on the performance of interconnected MANETs running two different routing protocols, viz., the Ad hoc On-Demand Distance Vector (AODV) and Optimized Link State Routing (OLSR) protocols, which represent the two major categories, and show that with the use of multiple gateways, it is possible to viably interconnect multiple networks running different MANET routing protocols. We then follow with a simulation study to evaluate the performance in large networks, which not only validates the scalability of the proposed scheme, but also helps to identify various problems that were not apparent in small experimental networks.     

Partitioning WCN Models for Parallel Simulation of Radio Resource Management

Parallel Simulation techniques have been proposed as a possible solution to execution time and memory constraints often found in detailed simulations of Wireless Cellular Networks. However, partitioning represents a major challenge for models that encompass elements of radio propagation phenomena. This paper discusses the partitioning problem with respect to Parallel Discrete Event Simulation and we formulate an approach to study partitioning of a WCN model that includes radio propagation. Various options for a model of moderate size and where interference is calculated over the whole system are evaluated through experimentation and some limited mathematical analysis. Results indicate that radio spectrum based partitioning is preferable to geographically based partitionings for this model in many realistic scenarios. It is also noted that characteristics of the model differ sufficiently from other previously studied spatially explicit problems to reduce or even annihilate the effectiveness of some commonly used partitioning techniques.     

T-Ring 无线电综合测试场的构建

Outfield testing is an effective measure to check the performance of wireless networks and facilities. Current outfield testing environment has inherent fluctuation due to the wireless propagation condition and has other disadvantages such as nonsupport for multiple scenarios, and low level yet high cost auto control capability. In this paper, the conception of a radio testing environment, known as T Ring (Integrated Testing Ring), is proposed. It is based on a novel fitting degree evaluation frame. The testing ring can achieve high level of fitting degree to the real network so that the fluctuation of the wireless environment will be under control or even eliminated. This paper will choose some typical performance indicators and obtain corresponding statistical data in both the real network and system level simulation. A complete set of procedures is also given in this paper to evaluate the fitting degree of testing results and simulation results. It proves that the simulation highly fits to the real network and the simulation configuration can be used to construct the testing ring. At the same time, the advanced radio testing ring integrates multiple radio access technologies, scenarios and facilities from different manufacturers. It can improve the efficiency of wireless outfield testing and lower the cost of operators and manufacturers.     

Supporting QoS in Integrated Ad-Hoc Networks

Ad-hoc networking is becoming a promising solution to increase the radio coverage of wireless systems. Integrated mobile ad-hoc networks (MANETs), considered as multi-hop networks connected to fixed networks through one or more gateways, seem to be very profitable for both the provider and the user. This article describes an architecture for end-to-end QoS in such MANETs, developed within the IST project DAIDALOS II. In order to explain the framework’s functionality, the technology, service differentiation mechanisms, MAC layer measurements, and signalling protocols are discussed. The modules required by the network elements as well as their integration are also described. Additionally, the paper presents the results obtained during verification tests performed in exemplary testbed scenarios.     

On the Influence of the Propagation Channel in the Performance of Energy-Efficient Geographic Routing Algorithms for Wireless Sensor Networks (WSN)

In this paper, the influence of the features of the propagation channel in the performance of energy-efficient routing algorithms for wireless sensor networks is studied. Although there are a lot of works regarding energy-efficient routing protocols, almost no reference to realistic propagation channel models and influence is made in the literature. Considering that the propagation channel may affect the efficiency of the different energy-efficient routing algorithms, different propagation scenarios are proposed in this work, from the most simplistic free-space propagation model to more complex ones. The latter includes the effects of multipath propagation, shadowing, fading, etc. In addition, spatial diversity transmission/reception models are considered to mitigate the effects of hard propagation fading. Some results are provided comparing the performance of several energy-efficient routing algorithms in different scenarios.     

An Efficient and Scalable Routing for MANETs

Recently, Distributed-Hash-Table (DHT)-based routing protocols have been proposed for large scale mobile ad hoc networks (MANETs). The motive behind using DHT is to avoid/reduce network wide flooding in MANETs in route discovery phase leading to achieve more scalable network. The challenge of deploying DHT at network layer for routing purpose in MANETs is to achieve more matching between logical and physical networks. The paper describes that existing DHT-based routing protocols for MANETs lack this feature. The paper presents a new DHT based scheme [called an efficient and scalable routing for MANETs (ESR)] which reduces the ill-matching between logical and physical networks. This is achieved be distributing the logical identifier (LID) space of DHT structure among the nodes such that the physical neighbors have consecutive LID space portions, i.e. all physical neighbors of a node are also the logical neighbors of the node. Therefore the logical ID space portion of a node may be non-contiguous. Based on this logical structure, a node builds up binary-search-tree (BST) using both logical ID space portion of itself and its neighbors. This BST at the node is traversed to find the next hop for a query/message. Through simulation, the paper shows the proposed approach (ESR) performs better than the existing one in term of routing overhead, average end-to-end delay, path-stretch values and false-negative ratio.     

Bayesian inference approach for establishing efficient routes in wireless ad-hoc networks

Mobile ad hoc networks (MANETs) are dynamic wireless networks that have no fixed infrastructures and do not require predefined configurations. In this infrastructure-less paradigm, nodes in addition of being hosts, they also act as relays and forward data packets for other nodes in the network. Due to limited resources in MANETs such as bandwidth and power, the performance of the routing protocol plays a significant role. A routing protocol in MATET should not introduce excessive control messages to the network in order to save network bandwidth and nodes power. In this paper, we propose a probabilistic approach based on Bayesian inference to enable efficient routing in MANETs. Nodes in the proposed approach utilize the broadcast nature of the wireless channel to observe the network topology by overhearing wireless transmissions at neighboring nodes in a distributed manner, and learn from these observations when taking packet forwarding decision on the IP network layer. Our simulation results show that our routing approach reduces the number of control message (routing overhead) by a ratio up to 20 % when the network size is 60 nodes, while maintaining similar average route establishment delay as compared to the ad-hoc on demand routing protocol.     

基于多源异构数据融合与RT的高铁网络优化系统

在高速铁路建设中,采用的电力拖车、路堑、站台、桥梁、明洞等特殊、形状不规则的建筑物,会对电磁波传播机理和多通路产生一定的影响,使其呈现出明显的衰减特性。从空间上看,呈现出强烈的空间异同性和频度相关,从而导致经验模型无法准确表征铁路场景的电波传播特性,成为制约无线网络规划精确度与效率、限制铁路移动通信系统高质量发展的理论瓶颈之一。针对这一挑战性难题,本文开展了基于多源异构数据融合的铁路移动通信高精确度网络规划及优化系统研究。采用高性能射线跟踪(RT)技术针对铁路通信930 MHz频段下的高铁场景进行了网络优化仿真。仿真结果表明,90%的接收信号强度相较于优化前提高了13.9 dB,显著提升了铁路复杂场景中的无线网络质量。     

VANET网络中小尺度衰落信道仿真

车载网络（VANET）是智能交通系统的核心部分,能够提高道路交通的安全性与高效性。分析电波在VANET网络中的传播特点,着重分析该网络中双移动节点间的小尺度衰落信道,包括多普勒功率谱模型和用成型滤波器法仿真VANET网络中小尺度衰落信道特性,给出经历该信道后接收信号的包络。仿真结果表明,随着移动车辆速度比增大,接收信号衰落更深。该结果对于VANET网络下无线多媒体业务性能评估有着重要的作用。     

一种短波传输网络性能仿真方法

随着无线通信技术的应用越来越广泛,仿真技术已成为对无线通信网络进行研究和论证的有效手段。针对某基于短波传输的通信网络的性能研究,分析了短波信道和通信网络的仿真模型及其实现思路,提出了一种短波传输通信网络的信道级和网络级相结合的仿真实现方法。为短波传输的网络性能研究提供了一种符合无线传输特性的实现方式,可以推广作为进行无线通信的网络性能分析的研究方法。     

Performance analysis of multiple-antenna cooperative networks under Weibull fading

In wireless communications, cooperative relaying is well-known to enhance the overall system performance, but implementation and cost constraints stand against its wide deployment. This paper investigates the performance of cooperative relays with and without multiple antennas under independent and identically distributed (i.i.d.) Weibull faded channels in a two-hop wireless network. We consider the Weibull fading channel model due to its flexibility in describing the radio propagation environment more than the classical Rayleigh model. Our study relies on applying selection combining (SC) along with threshold decode and forward (TDF) protocol at the cooperative relays as a good compromise between cost and performance. In addition, maximal ratio combining (MRC) is used at the destination. We derive analytical expressions for the end-to-end (E2E) error performance of the network under such scenario and provide simulation results to confirm the validity of the obtained analytical expressions.     

Cross-Layer Radio Resource Allocation for Multicarrier Air Interfaces in Multicell Multiuser Environments

Packet scheduling over shared channels is one of the most attractive issues for researchers dealing with radio resource allocation in wireless networks as modern systems' different traffic types, with different application requirements, need to coexist over the air interface. Recently, attention has been attracted to multicarrier techniques and the application of cross-layer approaches to the design of wireless systems. In this paper, a radio access network using a multicarrier air interface is considered in a multicell multiuser context. We propose a new cross-layer scheduling algorithm that manages channel, physical layer, and application-related information; we compare its performance with a previously published cross-layer strategy and with simpler well-known channel-aware or channel-unaware techniques and then discuss its optimization. We investigate the performance in terms of perceived user quality and fairness in the presence of mixed realistic traffic composed of H.264 video streaming with tight bounds on the delay jitter and file transfer protocol (FTP) data. To support video traffic, application-suited buffer-management techniques are also considered in conjunction with scheduling, and link adaptation is implemented at the physical layer to better exploit channel fluctuations. The role of scheduling and resource-allocation functionalities are discussed. It is shown that the cross-layer strategy proposed guarantees the same performance obtained by the previously published algorithm while reducing complexity. Moreover, under heavily loaded conditions, the cross-layer scheduling strategy provides a significant gain with respect to simple channel-aware or channel-unaware techniques.