Periklis Chatzimisios

IEEE 802.11 packet delay-a finite retry limit analysis

The contribution of this paper is on the study of packet delays for the IEEE 802.11 wireless local area network DCF MAC protocol. A method is presented capable of taking into account retransmission delays with or without retry limits. We present an analytical model based on a Markov chain which allows us to derive closed form expressions for the packet delays, the probability of a packet being discarded when it reaches the maximum retransmission limit and the average time to drop such a packet for the basic and RTS/CTS access mechanisms. The results presented are for standard protocol parameters versus the number of contention stations. Finally, the accuracy of the analytical model is verified by simulations.

Performance analysis of IEEE 802.11 DCF in presence of transmission errors

IEEE 802.11 is worldwide established and the most used protocol for wireless local area networks (WLANs). In this paper, we propose an improved analytical model that calculates IEEE 802.11 DCF performance taking into account both the packet retry limits and transmission errors for the IEEE 802.11a protocol. Validation of our new analytical performance model results is carried out by comparison with the simulation results using the OPNET/sup TM/ simulation package. We explore the effect of transmission errors, packet retry limits, data rate and network size on the performance of the basic access scheme, in terms of throughput, packet delay, packet drop time and drop probability.

Throughput and delay analysis of IEEE 802.11 protocol

Wireless technologies in the LAN environment are becoming increasingly important. The IEEE 802.11 standard is the most mature technology for wireless local area networks (WLANs). The performance of the medium access control (MAC) layer, which consists of distributed coordination function (DCF) and point coordination function (PCF), has been examined over the past years. We present an analytical model to compute the saturated throughput of 802.11 protocol in the absence of hidden stations and transmission errors. A throughput analysis is carried out in order to study the performance of 802.11 DCF. Using the analytical model, we develop a frame delay analysis under traffic conditions that correspond to the maximum load that the network can support in stable conditions. The behaviour of the exponential backoff algorithm used in 802.11 is also examined.

Heterogeneous Vehicular Networking: A Survey on Architecture, Challenges, and Solutions

With the rapid development of the Intelligent Transportation System (ITS), vehicular communication networks have been widely studied in recent years. Dedicated Short Range Communication (DSRC) can provide efficient real-time information exchange among vehicles without the need of pervasive roadside communication infrastructure. Although mobile cellular networks are capable of providing wide coverage for vehicular users, the requirements of services that require stringent real-time safety cannot always be guaranteed by cellular networks. Therefore, the Heterogeneous Vehicular NETwork (HetVNET), which integrates cellular networks with DSRC, is a potential solution for meeting the communication requirements of the ITS. Although there are a plethora of reported studies on either DSRC or cellular networks, joint research of these two areas is still at its infancy. This paper provides a comprehensive survey on recent wireless networks techniques applied to HetVNETs. Firstly, the requirements and use cases of safety and non-safety services are summarized and compared. Consequently, a HetVNET framework that utilizes a variety of wireless networking techniques is presented, followed by the descriptions of various applications for some typical scenarios. Building such HetVNETs requires a deep understanding of heterogeneity and its associated challenges. Thus, major challenges and solutions that are related to both the Medium Access Control (MAC) and network layers in HetVNETs are studied and discussed in detail. Finally, we outline open issues that help to identify new research directions in HetVNETs.

Big data-driven optimization for mobile networks toward 5G

Big data offers a plethora of opportunities to mobile network operators for improving quality of service. This article explores various means of integrating big data analytics with network optimization toward the objective of improving the user quality of experience. We first propose a framework of Big Data-Driven (BDD) mobile network optimization. We then present the characteristics of big data that are collected not only from user equipment but also from mobile networks. Moreover, several techniques in data collection and analytics are discussed from the viewpoint of network optimization. Certain user cases on the application of the proposed framework for improving network performance are also given in order to demonstrate the feasibility of the framework. With the integration of the emerging fifth generation (5G) mobile networks with big data analytics, the quality of our daily mobile life is expected to be tremendously enhanced.

Low power wide area machine-to-machine networks: key techniques and prototype

As one of the fastest growing technologies, machine-to-machine (M2M) communications are expected to provide ubiquitous connectivity. M2M devices can be used for a wide range of emerging applications that have various communications requirements. While M2M communications have been developed for many years, major challenges still remain with their efficient implementation from the perspective of low energy consumption and wide coverage. To address these challenges, low power wide area (LPWA) technology is investigated as one of the potential candidate solutions. In this article, we first introduce some typical LPWA M2M application scenarios. Given their requirements, we highlight key techniques and standards that are explicitly designed for LPWA M2M communications. Finally, we present an LPWA prototype system to evaluate its performance and demonstrate its potential in bridging a technological gap for future Internet-of-Things (IoT) applications.

Performance analysis of the IEEE 802.11 MAC protocol for wireless LANs

SUMMARY Wireless local area networks (WLANs) are extremely popular being almost everywhere including business, office and home deployments. The IEEE 802.11 protocol is the dominating standard for WLANs. The essential medium access control (MAC) mechanism of 802.11 is called distributed co-ordination function (DCF). This paper provides a simple and accurate analysis using Markov chain modelling to compute IEEE 802.11 DCF performance, in the absence of hidden stations and transmission errors. This mathematical analysis calculates in addition to the throughput efficiency, the average packet delay, the packet drop probability and the average time to drop a packet for both basic access and RTS/CTS medium access schemes. The derived analysis, which takes into account packet retry limits, is validated by comparison with OPNET simulation results. We demonstrate that a Markov chain model presented in the literature, which also calculates throughput and packet delay by introducing an additional transition state to the Markov chain model, does not appear to model IEEE 802.11 correctly, leading to ambiguous conclusions for its performance. We also carry out an extensive and detailed study on the influence on performance of the initial contention window size (CW), maximum CW size and data rate. Performance results are presented to identify the dependence on the backoff procedure parameters and to give insights on the issues affecting IEEE 802.11 DCF performance. Copyright # 2005 John Wiley & Sons, Ltd.

Enhancing performance of the IEEE 802.11 distributed coordination function via packet bursting

During the past few years, wireless local area networks (WLANs) have become extremely popular. The IEEE 802.11 protocol is the dominating standard for WLANs employing the distributed coordination function (DCF) as its essential medium access control (MAC) mechanism. This paper presents a simple and accurate analysis using Markov chain modelling to compute IEEE 802.11 DCF performance, in the absence of hidden stations and transmission errors. This mathematical analysis calculates in addition to the throughput efficiency, the average packet delay and the packet drop probability for both the basic access and RTS/CTS medium access schemes. The derived analysis, which takes into account packet retry limits, is validated by comparison with OPNET simulation results. The mathematical model is used to study the effectiveness of the RTS/CTS scheme at high data rates and the performance improvements of transmitting a burst of packets after winning the contention for medium access. Packet bursting considerably increases both throughput and packet delay performance but lowers the short-term fairness on medium access.

An SMDP-Based Resource Allocation in Vehicular Cloud Computing Systems

Vehicular ad hoc networks are expected to significantly improve traffic safety and transportation efficiency while providing a comfortable driving experience. However, available communication, storage, and computation resources of the connected vehicles are not well utilized to meet the service requirements of intelligent transportation systems. Vehicular cloud computing (VCC) is a promising approach that makes use of the advantages of cloud computing and applies them to vehicular networks. In this paper, we propose an optimal computation resource allocation scheme to maximize the total long-term expected reward of the VCC system. The system reward is derived by taking into account both the income and cost of the VCC system as well as the variability feature of available resources. Then, the optimization problem is formulated as an infinite horizon semi-Markov decision process (SMDP) with the defined state space, action space, reward model, and transition probability distribution of the VCC system. We utilize the iteration algorithm to develop the optimal scheme that describes which action has to be taken under a certain state. Numerical results demonstrate that the significant performance gain can be obtained by the SMDP-based scheme within the acceptable complexity.

An access network selection algorithm for heterogeneous wireless environments

Ubiquitous service delivery requires the selection of the optimal access network in a heterogeneous wireless environment. However, since the selection of an access network in such an environment depends on several parameters with different relative importance (such as the network and the application characteristics, the user preferences, the service cost), it is a difficult task to be achieved. In this paper, an effective access network selection algorithm for heterogeneous wireless networks is proposed that combines two Multi Attribute Decision Making (MADM) methods, the Analytic Hierarchy Process (AHP) method and the Total Order Preference by Similarity to the Ideal Solution (TOPSIS) method. More specifically, the AHP method is used to determine weights of the criteria and the TOPSIS method is used to obtain the final access network ranking.