Mobile Radio Environment Research Articles

Novel Electromagnetic-Interference-Free Indoor Environment Monitoring System by Mobile Camera-Image-Sensor-Based VLC

Long-term exposure to radio frequency waves can have adverse effects on human health. It may cause bad effects especially to elderly people, children, and patients with weak immune systems. On the other hand, visible light communication technologies that use a light-emitting diode (LED) light source and a photodetector to transmit and receive data through visible light have a severe demerit that the modulation and demodulation processes in the system can be complicated. This paper presents a low-cost wireless mobile indoor environment monitoring system with no additional complicated signal detecting device, except a mobile device and sensor modules. Temperature, humidity, and CO $_2$ concentration equivalent data are collected by sensor modules, and these data are modulated using frequency shift keying modulation. The modulated data are transmitted wirelessly by using a red–green–blue LED for transmitting multiple data concurrently. An Android application is developed to act as a light-signal receiver from multiple sensor modules. The image stream of the LED is captured and is processed locally in a mobile device. A single-receiver module with a camera image sensor can accept sensing data from six sensor modules simultaneously with a maximum transmission range up to 12 m and low error rate.

Host mobility key management in dynamic secure group communication

The key management has a fundamental role in securing group communications taking place over vast and unprotected networks. It is concerned with the distribution and update of the keying materials whenever any changes occur in the group membership. Wireless mobile environments enable members to move freely within the networks, which causes more difficulty to design efficient and scalable key management protocols. This is partly because both member location dynamic and group membership dynamic must be managed concurrently, which may lead to significant rekeying overhead. This paper presents a hierarchical group key management scheme taking the mobility of members into consideration intended for wireless mobile environments. The proposed scheme supports the mobility of members across wireless mobile environments while remaining in the group session with minimum rekeying transmission overhead. Furthermore, the proposed scheme alleviates 1-affect-n phenomenon, single point of failure, and signaling load caused by moving members at the core network. Simulation results shows that the scheme surpasses other existing efforts in terms of communication overhead and affected members. The security requirements studies also show the backward and forward secrecy is preserved in the proposed scheme even though the members move between areas.

Analysis of Geometric Multibounced Virtual Scattering Channel Model for Dense Urban Street Environments

This paper presents a generalized visual scattering channel model for car-to-car (C2C) mobile radio environments, in which an asymmetric directional antenna is deployed at the mobile transmitter (MT). The signals received at the mobile receiver (MR) from the MT are assumed to experience multibounced propagation paths. More importantly, the proposed model first separates the multibounced propagation paths into odd- and even-numbered-bounced propagation conditions. General formulations of the marginal probability density functions (pdfs) of the angle of departure (AoD) at the transmitter and the angle of arrival (AoA) at the receiver have been derived for the given two conditions, respectively. From the proposed model, we derive an expression for the Doppler frequency due to the relative motion between the MT and the MR, which broadens the research of the proposed visual street scattering channel model. The results show that the proposed model can fit those of the previous scattering channel models and the measurement results for dense urban street environments very well, which validate the generalization of the proposed virtual street channel model.

An Empirical Propagation Model for Path Loss Prediction at 2100MHz in a Dense Urban Environment

Objectives: Radio propagation models are used to predict signal strength in order to characterize the radio frequency channel. This will help in providing sufficient data required for the design of appropriate receivers that can recover the transmitted signal distorted due to fading and multipath effect. Methods/Statistical analysis: Data collection was carried out through drive test using TEst Mobile System, TEMS W995 phone interfaced with TEMS investigation tool version 13.1, Gstar GPS location finder and MapInfo professional and analyzed using Root Mean Squared Error (RMSE) statistical tool and tenth degree polynomial for fitting measured data with empirical models. Findings: Considering the contending empirical propagation models, the Ericsson model showed a better fit for the measured path loss data with root mean squared errors of 5.86dB, 5.86dB and 5.85dB at 1.0m, 1.5m and 2.0m mobile antenna heights respectively in comparison with Okumura model which is currently in use. It also outperformed other investigated models which are; Hata, COST 231, and SUI models at 2100MHz. These findings will help in revamping radio frequency planning and system design of the investigated and similar terrains thereby optimizing overall system performance while minimizing dropped calls, handover/quality issues and other network inherent failings. Application/Improvements: Results showed a minimum error estimate within the acceptable range of 6dB for signal prediction. This model can be used for signal prediction and channel characterization of any wireless mobile environment with similar channel characteristics. The other propagation models that over predicted the radio channel could be further investigated in future work and possibly tuned to accommodate dense urban areas.

Dealing Handover with Publish/Subscribe Middleware for Vehicular Networks: Modeling and Performance Analysis

Because of the high mobility of nodes and of the low node density, the vehicular networks is sparse, partitioned into several areas, and thus characterized by an intermittent connectivity. So, in such networks, the mobility management, providing an effective handover and the delivery of the messages with low loss, is a real challenge. The content based publish/subscribe middleware has proven its efficiency for messages delivery in networks with fixed clients. However, by its decoupling in space, time and flow content based, publish/subscribe becomes a good solution for mobile wireless environments which are characterized by frequent and unpredictable disconnections due to clients mobility or weak wireless channel. Yet, in such environments it is essential that, when clients disconnect from an attachment point and reconnect to another, they can receive the messages that were published after they disconnected. This paper propose a content-based publish/subscribe middleware as data dissemination and disconnections management solution, based on the OMG's Data Distribution Service (DDS), which performs effective handover and reroutes undelivered events with low loss rate. For performance evaluation, the paper proposal implements a content based publish/subscribe middleware prototype first to analyze the system and then to demonstrate, through these evaluations, that the publication/subscription system allows to adapt itself quickly to the frequent disconnections. Then it will be demonstrated that the handover management protocol can improve effectively the performances of the system.

Positioning sensor nodes and smart devices for multimedia data transmission in wireless sensor and mobile P2P networks

In recent, studies on multimedia data transmission have been progressing in a wireless sensor network that consist of a large number of sensor nodes and a mobile P2P network that consists of a large of number of smart devices such as smart phones and wearable devices. When multimedia data such as image, audio, and video are transmitted, it is important to figure out the positions of a sensor nodes and a smart device in the networks. However, existing positioning schemes do not consider network holes that can occur in real application areas, thereby causing many errors during positioning. In this paper, we propose a new positioning scheme considering holes in wireless sensor and mobile P2P network environments. In the proposed scheme, holes are detected based on neighboring node density when holes exist in a network, and the position of a sensor node or a smart device is estimated by conducting distance correction based on the cumulative number of hole-boundary nodes. Through the proposed scheme, highly accurate sensor positioning can be performed even in circumstances where holes are present over a network. To verify the good performance of the proposed scheme, a performance evaluation is conducted by comparing it with existing schemes. It is shown through experiments that the proposed positioning scheme transmits multimedia data to the destination node without data loss when the holes in the network exist.

Performance Analysis of TCP and its Enhancement for Quality of Service in Mobile Wireless Networks in Single Traffic Using Prioritised Hard Handoff (PH2)

The research activities in mobile computing and wireless networks strongly indicates that mobile computers and their wireless communication links will be an integral part of the current internet works. Communication over wireless links is characterised by limited bandwidth, high latency, high bit-error rates and temporary disconnections. Most often, networks with wireless links and mobile hosts incur significant losses due to handoff. It is also most important that in wireless environment TCP (transmission control protocol) causes degraded end-to-end performance. In this paper, we tried to give solutions to these problems. We adopt a new method to improve the end-to-end reliable transport performance in mobile wireless environment by incorporating changes to network-layer at the base station and mobile host and preserve end-to-end semantics of TCP. The methodology employs NDG (normalised delay gradient) loss-predictor function to determine congestion losses from that of transmission loss. The sender window can adjust its size depending on the loss information. If the loss is due to congestion, congestion control algorithm is invoked to decrease the flow rate. If the loss is due to handoff (transmission loss), immediate-recovery algorithm is invoked to recover the losses caused by the sender TCP. Stochastic equations are used to analyse, i) arrival rate handoff calls, ii) blocking probability of handoff request, iii) distinguish packet loss due to congestion or handoff, iv) dynamics of sender window, v) queue length at the ingress point of the BS router , vi) throughput, and vii) the losses due to congestion and handoff blocking. Our results provide better way understanding the problem of calls drop due to handoff, and providing most accurate solutions for mobile wireless system.

Push-pull cache consistency mechanism for cooperative caching in mobile ad hoc environments

Maintaining data consistency between data cached by a mobile client and data residing in the data server is a major issue in a wireless mobile environment. In this paper, we propose a push-pull cache consistency (2P2C) mechanism, with the intention of increasing the rate of serving requestors with recent up-to-date information or data from the cache of the intermediate nodes that are exact replicas of the data present in the origin server. This is a hybrid scheme that does not rely entirely either on the server or on the mobile client for maintaining consistency. Here we employ a registration process. Based on the registration process, the proposed 2P2C mechanism follows both a server- based consistency scheme and a client-based consistency scheme. Besides this, both the server and the cache nodes can legitimately accept client registrations. Hence, this 2P2C method highly decreases unnecessary communication overhead incurred in the network and thereby considerably reduces access latency.

The Real‐Time Simulation of Doppler Spread in Wireless Mobile Environment by RF Circuits

The time-varying characteristic of wireless channel under the high-speed mobile environments in tunnels causes the Doppler spread to the transmitted signals, which affects the performance of wireless communication systems. The real-time Doppler effect simulation methodology directly based on Radio frequency (RF) circuits is proposed to simulate different Doppler spread effects in real environments. Mixers and a Digital-to-analog (DA) converter circuit are utilized to spread the spectrum of RF signals. A PC platform with the interface written in C# is configured to control the spectrum spread parameters. This radio channel emulator with the proposed methodology can replace the expensive fading simulating instruments with only 25.1ns system delay. Such an emulator has been applied to test the Multi-carrier wireless information local loop (McWiLL) wireless vehicle communication system in the laboratory to meet the requirement of metro Communication based train control (CBTC) system.

An automaton-based index scheme supporting twig queries for on-demand XML data broadcast

XML data broadcast is an efficient way to deliver semi-structured information in a wireless mobile environment. In the literature, many approaches have been proposed to disseminate XML data via wireless broadcast. However, because of the existence of “*” and “//” in queries, their performance deteriorates. In this paper, we propose a novel indexing method called Deterministic Finite Automaton-based Index (abbreviated as DFAI) on the XPath queries. Different from existing approaches which build index based on XML documents, DFAI is built based on the submitted queries. The new index treats the XPath queries as a DFA and it improves the efficiency of broadcast systems significantly. We further propose a compression strategy to reduce the index size of DFAI as well. Besides, as an extension, we extend the DFAI to support twig queries. Experiment results show that our method achieves a much better performance in terms of both access time and tuning time when compared with existing approaches.

Key management paradigm for mobile secure group communications: Issues, solutions, and challenges

Group communication has been increasingly used as an efficient communication mechanism for facilitating emerging applications that require packet delivery from one or more sources to multiple recipients. Due to insecure communication channels, group key management which is a fundamental building block for securing group communication, has received increasing attention recently. Developing group key management in highly dynamic environments faces additional challenges particularly in wireless mobile networks due to their inherent complexities. On one hand, the constraints of wireless devices in terms of resources scarcity, and on the other hand the mobility of group members increase the complexity of designing a group key management scheme. This article illustrates a survey of existing group key management schemes that specifically consider the host mobility issue in secure group communications in wireless mobile environments. The primary constraints and challenges introduced by wireless mobile environments are identified in order to show their critical influence in designing a secure group communication. The explored schemes are scrutinized and then compared against some pertinent criteria. Finally, the remaining challenges that should be tackled are outlined, and future research directions are also discussed.

Authentication scheme for mobile OFDM based on security information technology of physical layer over time-variant and multipath fading channels

This work investigates security information technologies for wireless mobile environment. Traditionally, security is viewed as an independent feature addressed above the physical layer (PHY). All widely used cryptographic protocols are established assuming the PHY layer is merely used to provide an error-free link. However, with the emergence of ad hoc and decentralized networks, higher-layer security techniques are complex and hard to be implemented. To complement and enhance traditional security mechanism, we study a novel authentication scheme for mobile orthogonal frequency division multiplexing (OFDM) based on the channel power-delay profile (PDP),1The PDP is interchangeable with the channel-tap power in this study.1 considering channel time and frequency selectivities. More specifically, the PHY layer, employing the properties of OFDM signals over time-variant and multipath fading channels, is aimed to assist the overall authentication process. To identify different transmitters (TXs), we employ the hypothesis test based on their PDPs to distinguish different transmission terminals. It is advantageous to use the PDP as the wireless signature, because it depends on the surrounding environment and is therefore considered to be very hard to mimic. The proposed PDP estimation is obtained based on the redundancy of cyclic prefix (CP), which is a common feature for almost all OFDM systems. The performance is analyzed, and simulations confirm the advantages of the proposed method.

Effect of Variable Cyclic Prefix Length on OFDM System Performance over Different Wireless Channel Models

A Cyclic Prefix (CP) is a significant feature of an OFDM waveform. It is used to completely eliminate both Inter-Symbol Interference (ISI) and Inter-Carrier Interference (ICI) as long as the CP length is greater than the channel delay spread. By eliminating both ISI and ICI, the CP compensates for the effect of the multipath dispersion; but it consumes a considerable amount of the scarce spectrum and the power. Conventional OFDM uses a fixed and large CP length to overcome the ISI caused by channel delay spread under wireless mobile environment. This approach may degrade the overall spectral efficiency as well as consumes relatively more transmitter energy. Therefore, there is a need to adopt the CP length according to instantaneous channel parameters. In this paper, we presented a method for investigating the effect of varying the CP length on OFDM system performance over different multipath channel models. We estimated the variable CP length based on the RMS delay spread of the channels' power delay profile (PDP). According to this method, the estimated CP length optimizes the system capacity and improves the overall system performance. We showed that this approach could lead to a mathematical formula presenting the relationship between the CP length and the RMS delay spread of the channels.

A Survey of Green Information-Centric Networking: Research Issues and Challenges

Recently, a series of innovative information-centric networking (ICN) architectures have been designed to better address the shift from host-centric end-to-end communication to requester-driven content retrieval. With the explosive increase of mobile data traffic, the mobility issue in ICN is a growing concern and a number of approaches have been proposed to deal with the mobility problem in ICN. Despite the potential advantages of ICN in mobile wireless environments, several significant research challenges remain to be addressed before its widespread deployment, including consistent routing, local cached content discovery, energy efficiency, privacy, security and trust, and practical deployment. In this paper, we present a brief survey on some of the works that have already been done to achieve mobile ICN, and discuss some research issues and challenges. We identify several important aspects of mobile ICN: overview, mobility enabling technologies, information-centric wireless mobile networks, and research challenges.

Packet Scheduling and Access Priority Control for QoS and Fairness in Wireless LAN

Abstract In recent years, the increasing demand for multi-media communication, even in the wireless mobile environment overcrowding, QoS (Quality of Service) is important. In such environment, since many mobile stations (STAs) are using the same channel, it occurs the problem of unfair channel access time and downlink channel. In this paper, we propose a scheme to achieve a good balance of QoS, fairness and downlink/uplink traffic asymmetry by the combined operation of channel access priority control and packet scheduling with require modification only to AP and require no changes in STAs.

A Fuzzy Controller for TCP Improvement over Mobile Networks

The Transmission Control Protocol (TCP) is used for reliable delivery of data over unreliable networks. Practically, most TCP mechanisms have been carefully designed for wired networks. Neglecting the characteristics of wireless environments can lead to TCP implementations with poor performance. In order to use TCP in mobile networks, improvements have been proposed in this paper to enhance TCP algorithm to distinguish between the different types of loss events. In mobile or static wireless environments, losses are not always due to network congestion, as in the case of wired networks. In this paper, a modified algorithm is presented using fuzzy controller to differentiate the loss events (error loss from congestion loss) that intend at adapting TCP to mobile and static wireless environments with better performance. Simulation results were performed using OMNET simulator and have showed that the new proposal has better throughput than other TCP schemes.

Detection and Localization of Attackers in Wireless Networks

The adaptability and openness of remote networks empower an opponent to take on the appearance of different devices effortlessly. Spoofing attacks are the one that causes serious network threats as they can encourage an assortment of progressed attacks to challenge the typical operation of systems. On the other hand, the existing approach can just locate spoofing attacks when the exploited person node and the spoofing node are static and thus the correlation problem occurs in the same frequency region. In this research, a method has been proposed for detecting and locating spoofing attacks in the mobile wireless environment and also to develop a Distance based Attack Localization and Detection (DALD) system, which is based on the distance of each packet while travelling from source to destination and where every node alert its neighbors, source and destination node that costs to reach them. It utilizes the Distance Vector Routing Protocols (DVRP) for successfully discovering the attack, and the number of attacks that discover and strike the area with a moderate network overhead. Through this simulation, it shows that DALD achieves identifying accurate attack, localization and detection.

Regressive Prediction Approach to Vertical Handover in Fourth Generation Wireless Networks

The over increasing demand for deployment of wireless access networks has made wireless mobile devices to face so many challenges in choosing the best suitable network from a set of available access networks. Some of the weighty issues in 4G wireless networks are fastness and seamlessness in handover process. This paper therefore, proposes a handover technique based on movement prediction in wireless mobile (WiMAX and LTE-A) environment. The technique enables the system to predict signal quality between the UE and Radio Base Stations (RBS)/Access Points (APs) in two different networks. Prediction is achieved by employing the Markov Decision Process Model (MDPM) where the movement of the UE is dynamically estimated and averaged to keep track of the signal strength of mobile users. With the help of the prediction, layer-3 handover activities are able to occur prior to layer-2 handover, and therefore, total handover latency can be reduced. The performances of various handover approaches influenced by different metrics (mobility velocities) were evaluated. The results presented demonstrate good accuracy the proposed method was able to achieve in predicting the next signal level by reducing the total handover latency.

Channel Estimation and Combining Orthogonal Pilot Design in MIMO-OFDM System

The current technology of high speed wireless communication exist the following weaknesses, limited bandwidth, bad transmitted channel, complex mobile environment and the quality of service under limited service time. The dispersing pilot pattern and the method of channel estimation using in MIMO-OFDM system couldn’t eliminate the same frequency interference caused by the OFDM frequency among different transmit-receive antenna couples. Aiming at these problems, we proposed a method of MIMO-OFDM channel estimation combining orthogonal pilot design. The data format of pilot is designed. It can retain the orthogonality of different sub-carriers of OFDM which are produced by different transmit-receive antenna couples or transmit-receive antenna couple. In wireless mobile environment, it can better estimate the channel parameters without any prior channel information. This method proposed in the paper has finished the design of the completely orthogonal pilot data symbol among the different subcarriers position of different transmitting-receiving antenna pair. And the pilot data symbols are distributed in the entire time-frequency grid of the channel reasonably, therefore this paper uses a FFT unit whose points are equal to the number of the OFDM subcarriers to realize the least-square channel estimation algorithm. In the process of channel estimation, the channel parameters estimation precision has increased because of the noise getting better inhibition, which reduces the least squares estimate noise sensitivity to the requirements

Research on Query Mechanism of Moving Object Database

Since the mobile radio communication in a wireless mobile environment, which inevitably subject to fading and interference effects of the various signals, multipath and time-domain signal to bring the mobile domain and frequency dispersion problems, bandwidth resources restricted and transmission delay increases and so on. In this paper, the use of Class R-Tree data structure to store the data on the basis of historical trajectory, the update query results by the beach line iterative way to solve the problem of nearest neighbor queries efficiently update existing intermediate results.