An efficient handover optimization in wireless access networks using PCF based IEEE 802.21 Mill standards.
The evolution of many homogeneous networks makes mobile users to efficiently use banking, social networking, and web browsing and multimedia. Although many networks are available single network is not sufficient for to satisfy all the user needs. Many factors are needed to be considers in the case of broadband technologies like backward compatibility, cost factors and business competition. In order to satisfy all the user needs devices manufactures are manufacturing the devices with more compatible and interoperability with different networks. Many mobile phones nowadays support Wi-Fi and 3G networks. As a multimode device, operators with multiple networks should facilitate easy access among their heterogeneous technologies through a single device to support inter technology handover for seamless roaming. During handover, both service continuity and service quality should be promised to make seamlessly. The recent, systematic, and promising approach that deals with this problem is the initiative under the IEEE label of Media-Independent Handover (MIH) Services, which promises to enhance handover experience when users roam between any access technology, covering both IEEE 802 and non-IEEE 802 networks. Specifically, IEEE 802.21 MIH group (Ashutosh Dutta, 2008) introduced a new protocol above layer 2 which that combines different wireless access network technologies and provides intelligent handover when the mobile node changes its point of attachment.
The promising IEEE 802.21 MIH standard provides seamless vertical handover in heterogeneous environment without service disruption and maintains the quality of service to the users (Jose Jailton, 2013; Stenio Fernandes, 2012). Later (Daniel Corujo, 2011; Dong Ma, 2012; Kenichi Taniuchi, 2009; Enda fallon, 2009) performed a case study of vertical handoff delay analysis in WLAN-WiMAX internetwork using Point Coordination Function scheme as the efficient handover management technique to reduce the handover delay (Ian F. Akyildiz, 2004; Abraham George, 2008; Xiaohuan Yan, 2010). The remaining of the chapters is organized as follows. The following chapter describes an outline of the IEEE 802.21 MIH standard, and the section after that provides an overview of Point coordination function schemes. The Section IV defines the proposed integrated architecture. The simulation results and discussion are presented in section IV. Conclusion addresses the issues and challenges of vertical handover.
1. Overview of The IEEE 802.21 MIH Standard:
IEEE has developed a standard called as Media Independent Handovers (MIH) defined in IEEE 802.21. The IEEE 802.21 provides sufficient information to higher layers during handover operations across homogeneous and heterogeneous environments. So it is also called as Layer 2.5. The standard allows the mobile users to take the full advantage of the overlapping and overlaid heterogeneous network. It defines the architecture for discovering networks and executes the efficient handovers based on the received signal strength. The need for standards of vertical handover are: Extending the coverage area and preferred networks, improving the capacity and load balance, longer the battery life, no need to modify the existing radio access networks. The protocol stack of IEEE 802.21 architecture consist of a framework for transparent service continuity, set of handover functions and Service Access Point (SAP). The heart of MIH is the MIH Function (MIHF) placed between MIH User (MIHU) and the device interface as in Fig. 1. The MIH supports three important services as Media Independent Event Service (MIES), Command Service (MICS) and Information Service (MIIS). The MIHU is incorporated in network node and MIHF is incorporated in mobile node and reports its status to the higher layers.
Its important function is to report the lower layer information to higher layer through well-defined service access point (SAP). The MIH_LINK_SAP provides intelligent signaling information exchange between the MIHF and lower link layers device.
A. MIH Services -An Overview:
IEEE 802.21 MIH standard describes three efficient handover services which provide optimized vertical handovers across inter-domain environment (Ian F. Akyildiz, 2007): Event service, Command service and Information service. These three are primary services which are extremely well applicable for designing next generation networks. The management service consists of MIH capability, also the neighbor node exploration, processing and execution. Through the service management primitives, MIHF is capable of discovering other MIHF users. By providing a SAP, the MIHF can communicate with upper layers easily and effectively. Media specific SAPs (LINK_SAPs) enable the MIHF to get the media-specific information that can be propagated to the MIHU using a single media independent interface (MIH_SAP).
The MIES defines events that represent changes in dynamic link characteristics such as link status, link condition and link quality. The Event service indicates the status of the link characteristics at its current point of attachment and report to higher MIHU either by Link_Up, Link_Down or Link_Going_Down triggers. If a remote MIH user subscribed to this event, the local Link_Up event is delivered over the network to this remote MIH user.
The command service is used to cope and control the link state behavior. The commands are sent from the upper MIHU to lower link layer. MIHU use this command services to obtain the link status and condition and also to control the multi-mode device to use the heterogeneous networks efficiently.
The information service provides information about the candidate network in which MIHF can find and discover the other network for handover over the geographical area. The main objective of using MIIS service is to obtain the global information about neighbor network during initial network deployment phase. The MIIS also provides static and dynamic information of neighbor node by using request reply mechanism.
2. Proposed Architecture:
Point coordination function (PCF), a Media Access Control (MAC) technique which is used in IEEE 802.11 based WLANs. It lies in the access point which is also a point coordinator. It coordinates the function within the network. Since PIFS consumes less time than DIFS, the point coordinator can access the channel immediately. The MAC architecture contains two major functions: PCF and DCF. Polling function can be performed by PCF and DCF uses RTS/CTS. The protocol which used as first is like infrastructure model, while the proposed protocol is based on ad-hoc model. In PCF, time is divided into several super-frames where each superframe includes contention free period (CFP) and contention period (CP). Fig. 3 explains a super-frame where the AP arranging the mobile stations in the stack of CF. All stations and the AP search for the medium in CP. Before AP initiates CF, it should catch an idle medium in PIFS interval and send beacon frame.
There will be communication between AP and Mobile stations after a beacon frame. AP sends a CF- End frame and finally CP starts its communication. A device that is able to use point coordination function is one that is able to participate in a method to provide limited Quality of service (for time sensitive data) within the network. The architecture of WLAN/ WiMAX network with PCF is shown in fig. 3. It describes the integration of two networks WLAN / WiMAX. The architecture consists of multi interface mobile node (MN), correspondent node (CN), application server with backbone IP connectivity. The results are given below.
3. Simulation Results:
This section analyses the PCF in heterogeneous environments. The simulation done in OPNET modeler 14.5 software. The handover delay for the mobile node which moves from WLAN to WiMAX is around 0.027 sec for without PCF but while using PCF it reduced to 0.26 sec because the PCF will reduce the time required as in Fig. 4.
The connection information between WLAN/ WiMAX networks can passing the information for efficient handover with less time. It is more when using PCF as shown in Fig 5.
So the traffic is reduced when using PCF in networks as shown in Fig 6. The existence of neighbor WiMAX base station is measured and it is clearly shown in the Fig 7. From this graph it is clear that the existence of neighbor WiMAX base station which can provide mobile services to the user when the user moves away from present WLAN attached.The time required for mobile node to move from WLAN to WiMAX is called WiMAX Delay.
As shown in Fig 8, the delay is less when using PCF in network.Fig. 9 shows the sub channel transmission power and total transmission power for the packets transmission. It is shown that with PCF, the network remains in high power for better link quality.
From the Fig 10, it is clear that the uplink and downlink packet dropped is less while using PCF, so that the throughput is increased. Load balancing in networks is important by providing equal amount of services to all users. Here WLAN and WiMAX load is shown in Fig. 11. From this figure, it is clear that the amount of data provided by each network is high when using PCF.
The below table 1 shows the comparison between PCF and non-PCF functions.
The integrated WLAN / WiMAX architecture proves to provide an efficient handover by using IEEE 802.21 Media Independent Handover with PCF. This paper compares the performance of the two networks with PCF and without PCF. The results shows that the PCF performs better to yields the efficient handover in two wireless networks in terms of throughput, less handover latency and by efficient load balancing when compared without using PCF. Future work aims to provide the multi protocol layer solutions in heterogeneous environments.
Received 12 October 2014
Received in revised form 26 December 2014
Accepted 1 January 2015
Available online 25 February 2015
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(1) R.Tamilselvi, (2) C. Hepzibah, (3) Dr. G. Sivaradje
(1) Assistant Professor, PK1ET, Karaikal, Puducherry, India.
(2) Post Graduate Student, Pondicherry Engineering College, Puducherry, India.
(3) Professor, Pondicherry Engineering College, Puducherry, India.
Corresponding Author: R.Tamilselvi, Assistant Professor, PKIET, Karaikal, Puducherry, India.
Table 1: Comparison of with PCF and without PCF. Parameters Without PCF With PCF Handover Delay (sec) 0.027 0.025 Connection Information (bits) 0.1 0.85 Internet Traffic Dropped 0.11 0.08 (packets/sec) Total transmission power (dBm) 19 27 Neighbour advertisement 4500 10000 received (bits/sec) WiMAX delay (sec) 0.0044 0.0036 WiMAX load (bits/sec) 260 280 Packets Dropped (packets/sec) D/L, U/L: 7.5, 4 D/L, U/L:6.5,2.5
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|Title Annotation:||point coordination function|
|Author:||Tamilselvi, R.; Hepzibah, C.; Sivaradje, G.|
|Publication:||Advances in Natural and Applied Sciences|
|Date:||Jun 1, 2015|
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