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Intelligent transportation vertical handoff using LTE-A networks.


Vehicular ad hoc networks (VANETs) have been envisioned to enhance the passenger safety and comfort in the near future. Vehicles will employ an onboard vehicle resources [1] which are underutilized by traditional vehicular applications offer an opportunity for improved computing and connectivity in Vehicular Ad hoc Networks (VANETs) [2]. Long Term Evolution- Advanced (LTE-A); LTE-A is the de facto fourth generation (4G) wireless system and is expected to dominate the next generation of wireless networks, and to support a wide variety of applications that require higher data rates with more reliable transmission. To meet such demands, wireless communication system designers need to optimize network performance in terms of better link reliability, fewer dropped connections and longer battery life [3]. LTE-A was ratified by the International Telecommunication Union (ITU) as an IMT-Advanced 4G technology in November 2010, and has adopted relaying for cost-effective throughput enhancement and coverage extension [4][5].

Vehicular ad hoc network(VANET)[6] becomes popular in many countries. It is imporatant element of the Intelligent Transporatation Systems(ITSs) [7].VANET is composed for a set of communicating vehicles equipped with wireless network devices that are able to interconnect each other without any pre-existing infrastructure (adhoc mode).

The exchange of information among the vehicles provides a great opportunity for the development of new driver assistance systems. These systems will be able to disseminate and to gather real time information about the other vehicles and the road traffic and environmental conditions. Such data will be processed and analyzed to facilitate the driving by providing the user with useful information. Network among the moving vehicle is known as VANET. VANET is to provide efficient vehicle-to-vehicle (V2V) and vehicle-to-RSU (V2R) communications [8][9]. Based on these two kinds of communications, VANETs can support many applications in safety, entertainment, and vehicle traffic optimization.

Vehicular networks are composed of mobile nodes, vehicles equipped with On Board Units (OBU) [10][11], and stationary nodes called Road Side Units (RSU) [10][11] attached to infrastructure that will be deployed along the roads. Both On Board Units (OBU) and Road Side Units (RSU) devices have wireless/wired communications capabilities. On Board Units (OBU) communicate with each other and with the RSUs in adhoc manner. The Road Side Units (RSU) can also communicate with each other and with other networks.

Vehicular Networks are expected to employ variety of advanced wireless technologies such as Dedicated Short Range Communications (DSRC) [12][13][24], which is an enhanced version of the Wi-Fi technology suitable for VANET environments. The Dedicated Short Range Communications (DSRC) [12][13] is developed to support the data transfer in rapidly changing communication environments, like VANET, where time-critical responses and high data rates are required [24]. The data dissemination techniques should be designed to efficiently deliver the safety data to the receivers on time. Safety messages are of a broadcast nature targeting vehicles in a certain geographic area. Therefore, safety message dissemination mechanisms should deal with different types of network densities to eliminate the redundant rebroadcasted data, especially in very high network density scenarios. The Special Characteristics are High Mobility, Rapid Topology Change, No Power Constraints, Localization, Abundant Network Nodes and Hard Delay Constraints

The frequent topology change characteristics pose another challenge for routing methods in VANET. In addition to the traditional routing challenges like broadcast problems, the VANET routing algorithms should be designed to ensure the quality and continuity of services for non-safety applications with high probability. Challenges of the vehicular networks are Frequent neighborhood change due to high mobility, Increasing channel load (high density environment) and Irregular connectivity due to the variation of the received signal power.

The rest of the paper is organized as follows: related work is reviewed in Section 2. Our Vertical Handoff methods are described in Section 3. The analysis and evaluation of our schemes are given in Section 4. Finally, Section 5 concludes the paper.

II. Related Work:

Vehicular Networks are a stylish, comfort and dynamic network of the Intelligent Transportation Systems (ITS) [14]. Vehicles reveal with each other via Inter-Vehicle Communication (IVC) as well as with roadside base stations. A VANET is a technology that uses moving cars as nodes in a network to create a mobile network, enables communication between moving vehicles and the road side units (RSU's) [15]. VANET is the special type of MANET, so the routing Protocols and IEEE standards used in MANET are also applied in VANET Environment [16]. Communications through Cellular Network connects vehicles to the Internet through cellular data networks using any of the following technologies: EV-DO, 3G, GPRS, etc. [17]. This service is already commercially available from car manufacturers [18] and from other thirdparties [16].

VANET is an advanced version of Mobile ad-hoc network (MANET). Most of the MANET features can be applied in the VANET environment also [19]. In VANET the vehicles move in an organized and predefined road. VANET is the special type of MANET, so the routing Protocols and IEEE standards used in MANET are also applied in VANET Environment [20][21]. In MANET, the nodes are moving at random and their speed is normal. Most of the existing research works have been done on MANET. However these works cannot be directly applied to VANET due to the fundamental difference between VANET and MANET. In vehicular network, the mobility nodes are vehicles which are moving in a high speed of nearly 200 km/hr on a predefined road. The movement of nodes is dependent on the road structure, traffic and traffic regulation.

Mobility is the most important feature of wireless networking system. Mobility can be attained by handoff mechanisms in wireless networks. Handoff is the process of changing the channel (frequency, time slot, spreading code, or combination of them) associated with the current connection while a call is in progress. Handoff is also an important issue in the drive-thru Internet. Current devices initiate a handoff only when disconnected, and connect to an AP with the strongest signal strength [23][25][28]. However, such a hard (maintain until broken) handoff mechanism does not fit the vehicular communication environments. This is because the quality of the drive-thru connectivity changes over time so that vehicles being connected may experience poor connectivity periods and miss the opportunity to handoff to an AP with stronger signal strength. The hard handoff also incurs large handoff delays Therefore, applicable handoff mechanisms should be specifically designed for the drive-thru Internet. In Long Term Evolution- Advanced (LTE-A) networks, the handoffs are classified into two main streams. Horizontal Handoff and Vertical Handoff [23][25].

Handoff between two base stations (BSs) of the same system is called Horizontal handoff. Horizontal handoff involves a terminal device to change cells within the same type of network (e.g., within a CDMA network) to maintain service continuity. The switching between points of attachment or base stations that belong to the different network technologies is called Vertical handoff and this is required in heterogeneous networks. The process of Vertical handoff can be divided into three steps, namely system discovery, handoff decision and handoff execution [23][25]. During the system discovery, mobile terminal equipped with multiple interfaces have to determine which networks can be used and what services are available in each network. During the handoff decision phase, the mobile device determines which network it should connect to. During the handoff execution phase, connections are needed to be re-routed from the existing network to the new network in a seamless manner [28].

Vehicular communication platforms that provide real-time access to wireless networks have drawn more and more attention in recent years. IEEE 802.11p is the main radio access technology that supports communication for high mobility terminals, however, due to its limited coverage, IEEE 802.11p is usually deployed by coupling with cellular networks to achieve seamless mobility [12]. In a heterogeneous cellular/802.11p network, vehicular communication is characterized by its short time span in association with a wireless local area network (WLAN) [12][26].

Vertical handoff refers to a network node changing the type of connectivity it uses to access a supporting infrastructure, usually to support node mobility. For example, a suitably equipped laptop might be able to use both a high speed wireless LAN and a cellular technology for Internet access. Wireless LAN connections generally provide higher speeds, while cellular technologies generally provide more ubiquitous coverage. Thus the laptop user might want to use a wireless LAN connection whenever one is available, and to 'fall over' to a cellular connection when the wireless LAN is unavailable. Vertical handovers refer to the automatic fall over from one technology to another in order to maintain communication .The vertical handoff mechanism allows a terminal device to change networks between different types of networks (e.g., between Long Term Evolution and Long Term Evolution- Advanced networks) in a way that is completely transparent to end user applications.

Everyone around the world would like to be connected seamlessly anytime anywhere through the best network. The Long Term Evolution- Advanced (LTE-A) wireless system must have the capability to provide high data transfer rates, quality of services and seamless mobility [4][5]. In Long Term Evolution- Advanced (LTE-A), there are a large variety of heterogeneous networks. The users for variety of applications would like to utilize heterogeneous networks on the basis of their preferences such as real time, high availability and high bandwidth [4][5]. When connections have to switch between heterogeneous networks for performance and high availability reasons, seamless vertical handoff is necessary.

A dynamic decision model is to make the right vertical handoff decisions by determining the "best "network at "best" time among available networks [23][25][28]. The decision to decide best network is based on static factors such as the bandwidth of each network (capacity), usage charges of each network, power consumption of each network interface and battery level of mobile device and dynamic factors are considered in handoff decisions for effective network usage [28].

III. Vertical Hanoff Methods:

In this paper proposed an efficient handoff mechanism for heterogeneous network selection of the best available wireless network during handoffs based on a set of predefined user preferences on a mobile device decision function in which the system considers all the available network and user parameters (e.g. host velocity, battery status, Wi-Fi AP's current load, and WiMAX BS's Quality of Service guaranties, and performs technology selection such that an overall system performance metric is optimized(i.e., throughput and capacity limitation) [27][28]. Defined a new system-wise entity that is activated when a user is in an area with overlapping access technologies and needs to decide the best technology to be used, where the entity performs technology selection in order to optimize the overall system performance metric in terms of throughput and capacity limitation [27][28]. The proposed method is capable of selecting the best available wireless network with a reasonable performance rate. The overall approach is based on artificial intelligence, combining some other metrics for decision model of Vertical Handoff, when ad hoc model is applied to Long Term Evolution-Advanced (LTE-A) wireless data networks [27][28].

A mobile agent is a program that can migrate during execution from machine to machine in a heterogeneous network. It can transport its state from one environment to another, with its data intact, and be capable of performing appropriately in the new environment. Mobile agents decide when and where to move. The appeal of mobile agents is quite alluring--mobile agents roaming the Internet could search for information, find us great deals on goods and services, and interact with other agents that also roam networks (and meet in a gathering place) or remain bound to a particular machine. In Long Term Evolution- Advanced (LTE-A) networks a mobile node in network could access services and bandwidth offered by other service providers without pre registration or pre-subscription [4][5]. To enable such diverse mobility options there is a need for an interface management technology.

Security becomes a major concern when multiple interfaces are involved in communication [11]. The interfaces have varied transmission rates, varied technologies, varied services and varied spectrum allocation. 802.16 supports Wireless MAN networks with transmission at data rates up to 120Mbps. At those frequencies, transmission requires line-of-site, and roofs of buildings provide the best mounting locations for base and mobile subscriber stations. The network reference model includes groups of base station units providing network service (not necessarily contiguous) to authorized mobile subscriber stations (MSS) in a geographic region. A group of BS units that share administrative affiliation, and are connected by a backbone (wired or unwired) are referred to as a provider network. Multiple provider networks of varying design, performance, and ownership/administration may coexist in the same region. Provider networks may employ specialized servers for AAA (Authorization, Authentication and Accounting), management, provisioning, and other functions [22]. Depending on a provider network's configuration and administrative policies, an MSS may perform a handover (HO) from one BS to another. A provider network's scheme for managing handovers might be localized in the relevant BSs [22].

IV Performance Analysis:

The performance analysis is respect to the communication and handoff on the channel.

A. Methodology:

VANET supports efficient one-hop and multi hop broadcast services on the control channel by using implicit acknowledgements for data transfer between vehicle to vehicle. Using Sniffer module will be placed at the entrance point of the client and the exit point of the server, it will collect data regarding transmission and receiving rate. This will able us to understand the traffic and analyze Handoff. The Handoff simulation monitors and decides which base station is the Serving base station and decides the different Handoff methods. Here the first method is responsible for traffic from the server to the client, and its main job is deciding on which base station the application data will be put on air towards the client. The second method is responsible for the broadcasting the client's data to the server using which base station. The third decides when a Handoff occurs and the type of handoff, the methods checks Handoff types every constant period of time for the purpose of comparison between the Handoff types. The sniffers and the part of Handoff simulation module which responsible for traffic from server to client will be based on sniffer. An open source library for packet captures and network analysis for low-level network.

B. Simulation Results:

Proposed system is providing better performance than earlier technique and methods. First packets arrive to the receiver and then handoff duration will increase. Little handoff duration we use horizontal handoff technique, because it takes less time. The probability is low if any failure occurs we can easily recover the packets. For bigger handoff duration almost and always packets enters into time out situation. When duration of handoff is less than the timeout. There are two main potential problems for this situation. First one is Packet loss in the starting time. The number of packet lost possible when the signal disconnected from the base station. We also face another problem i.e Out of order arrival of the packets can happen only if in the buffers of base stations. Here during handoff there is no communication between servers to client. To avoid packet drops during handoff, the time degradation doesn't depend on handoff duration. Here figure (a) shows the delay and timeout affect the handoff, figure(b) shows the percentage improvement when using the vertical handoff methods , figure (c) shows the output dependency based the handoff length i.e using horizontal and vertical handoff methods.





The vertical handoff will remain an essential component for Long Term Evolution- Advanced (LTE-A) wireless networks due to switching of mobile users amongst heterogeneous networks. The Long Term Evolution- Advanced (LTE-A) wireless networks create new handoff challenges due to multiple requirements for vertical handoff. The vertical handoff requirements are include high bandwidth, low handoff latency, lower power consumption, minimum network cost, balanced network load, network security, user preferences, and throughput of a switching network. Establishing the requirements of a vertical handoff mechanism for Long Term Evolution- Advanced (LTE-A) wireless networks is a critical milestone in the development of vertical handoff mechanism.

Future Enhancement:

The Handoff Manager provides a solution for determining the best network interfaces for the services. The decision is made by using the context information from the mobile phone, networks and the user as well as the RSS. It provides a good policy for the vertical handover using the context information with user's interventions. Handoff manager has four major functions such as monitoring, analyzing, planning and executing.


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(1) Gopi. R, (2) Dr.A. Rajesh, (3) Sumathi. A

(1) Research Scholar St. Peter's University, Chennai, India.

(2) HOD/CSE, C. Abdul Hakeem college of Engineering and Technology, Vellore, Tamilnadu, India.

(3) Dept of CSE, DhanalakshmiSrinivasan Engineering College, Perambalur, Tamilnadu, India.

Received 15 May 2016; Accepted 7 July 2016; Available 22 July 2016

Address For Correspondence:

Gopi. R, Research Scholar St.Peter's University, Chennai, India

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Author:Gopi, R.; Rajesh, A.; Sumathi, A.
Publication:Advances in Natural and Applied Sciences
Article Type:Technical report
Date:Jul 1, 2016
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