EVOLUTION OF VERTICAL HANDOFF TO VOICE OVER LTE VIA GENERIC ACCESS (VOLGA)

International Journal of Electronics and Communication Engineering and Technology (IJECET) Volume 7, Issue 4, July-August 2016, pp. 40 47, Article ID: IJECET_07_04_005 Available online at http://www.iaeme.com/ijecet/issues.asp?jtype=ijecet&vtype=7&itype=4 Journal Impact Factor (2016): 8.2691 (Calculated by GISI) www.jifactor.com ISSN Print: 0976-6464 and ISSN Online: 0976-6472 IAEME Publication EVOLUTION OF VERTICAL HANDOFF TO VOICE OVER LTE VIA GENERIC ACCESS (VOLGA) Prashant N. Swam M. Tech. (Comm.) Vidarbha Institute of Technology, RTM Nagpur University, Nagpur, Maharashtra, India Prof. Nilesh Bodne Assistant Professor (M. Tech. ECE) Vidarbha Institute of Technology, RTM Nagpur University, Nagpur, Maharashtra, India ABSTRACT In Wireless Mobile Cellular Networks, users usually move between heterogeneous networks. In this type of environment, handoff procedure algorithm, handoff decision and its management is very important issue. Wireless Mobile Cellular Network supports the handoff process for users between various wireless technologies such as WLAN, CDMA and modern 3G networks. Heterogeneous networks are integrated in 4G wireless. To have seamless communication and mobility between these heterogeneous wireless access networks, support of vertical handoff (EVH) is required. Vertical handover is the convergence of heterogeneous networks for e.g.:- handover process between wireless cellular networks and WLAN. In this paper one of the handoff algorithms is discussed for different path loss models. Actually, the requirement to initiate handoff arises when the Received Signal Strength of the current base station falls below the threshold value. It adaptively controls the handoff according to the requirements of cells. The paper gives a theoretical overview and comparison of 3rd Generation Generic Access Networks with LTE s VoLGA. Migration towards Packet Switched Technology brought significant changes on Voice and Text services because of their circuit switched nature. Keywords: Cellular Network, Heterogeneous Network, Handoff, BS (Base Station), Received Signal Strength, Network Capacity, CDMA Networks and Call Blocking Probability, Generic Access Network (GAN), 3GPP, Mobility, LTE, VoLGA, Adaptive Keep-alive Interval (AKI) and resources Unlicensed Mobile Access (UMA). http://www.iaeme.com/ijecet/index.asp 40 editor@iaeme.com

Evolution of Vertical Handoff To Voice Over LTE Via Generic Access (Volga) Cite this Article: Prashant N. Swam and Prof. Nilesh Bodne, Evolution of Vertical Handoff To Voice Over LTE Via Generic Access (Volga), International Journal of Electronics and Communication Engineering and Technology, 7(4), 2016, pp. 40 47. http://www.iaeme.com/ijecet/issues.asp?jtype=ijecet&vtype=7&itype=4 1. INTRODUCTION In a cellular communication system, mobiles move in the service area and require communication services in the form of a wireless connection. In this system, total area is divided into smaller parts called cells to allow frequency reuse concept to increase the number of users in the network (Network Capacity). Large capacity with good service quality and minimum noise is always advantageous and also desirable. Frequencies used in one wireless service cell of the cluster can be reused in other distant cells. Every cell is controlled by its own transmitter and receiver to serve the mobile customers within its range. Calls can be handed off from one cell to another cell to maintain good quality phone service as the mobile moves between cells. A group of mobile customers having mobiles with a large range of mobility can access around in the overall network generating heavy flow of mobile traffic [11] and [12]. When the traffic load is concentrated in a cell, this cell becomes the hotspot cell. Therefore, the need arises for a proper traffic driven handoff management scheme [2]- [4]; so that mobile users will automatically move from congested cell to allow the network to balance itself dynamically in this situation. In the past decade, the telecommunications industry has witnessed an ever accelerated growth of the usage of the mobile communications. As a result, the mobile communications technology has evolved from the so-called second-generation (2G) technologies, GSM in Europe, IS-95(CDMA) and IS-136 (TDMA) in USA, to the third generation (3G) technologies. Along with the standards development for providing voice service to mobile users, a group of standards to deliver data to the mobile users have evolved from both SDOs (Standards development organisations) and industry. Systems and applications, such as Short Message Service (SMS) for sending and receiving short text messages for mobile phone users, have been built and continue to be developed. The genius of the cellular system is the division of a city into small cells. This allows extensive frequency reuse across a city, so that millions of people can use cell phones simultaneously. In a typical analog cell-phone system in the United States, the cell-phone carrier receives about 800 frequencies to use across the city. The carrier divides the entire city into cells. Each cell is typically sized at about 10 square miles (26 square kilometers). Cells are normally thought of as hexagons on a larger hexagonal grid. http://www.iaeme.com/ijecet/index.asp 41 editor@iaeme.com

Prashant N. Swam and Prof. Nilesh Bodne Figure 1 VoLGA Architecture 2. VOLGA ARCHITECTURE In VoLGA architecture, the basic element is VAN-C which links different standards in order to facilitate voice and text services to the LTE user transparently. From LTE side, VAN-C is connected to the S-GW/P-GW through SGi interface. Taking into account, that both signaling and packets are transferred on the same link (Figure1). For EPC (Evolved Packet Core) of LTE, VAN-C acts as a simple IP based external node on which packets will be send and received. The HLR/HSS is connected to the VAN-C directly so that fall back technologies can access the databases of the 4th Generation users when the reverse flow of voice and text from GSM/UMTS is active. The Architectural behavior can be understood easily by taking a practical example. When a handset is turned on and detects an LTE network, MME registers it to the HLR/HSS (Home Location Register/Home Subscriber Server) over S6a interface. Then a secured IP Connection is provided by the VAN-C to the LTE handset (for IP assignment DHCP can be used). Once connection is established the transfer of voice and text on the fall back technologies can be done easily over SGi interface as discussed before. Circuit Switched end of VoLGA In Figure, the VAN-C is connected with the MSC of a GSM Network and also with the MSC of UMTS Network. It gives two important understandings of the VoLGA Architecture: 3. HANDOFF In a wireless mobile cellular network handoff is the transition for any given user of signal transmission from one BS to an adjacent BS as the mobile user moves around [1]. In ideal cellular telephone network, each end user s mobile or modem (hardware of the subscriber) is always within the range of a BS. The area covered by each BS is called Cell [1]. The size and shape of cell depends upon the nature of the terrain. The cells in the network can overlap. For some time the hardware of subscriber may be in the range of two cells. The network decides which BS to handle the signal from the subscriber. Each time a mobile passes from one cell to another, the network automatically switches the responsibility of coverage from one BS to other. It is called, Hand OFF [8]. http://www.iaeme.com/ijecet/index.asp 42 editor@iaeme.com

Evolution of Vertical Handoff To Voice Over LTE Via Generic Access (Volga) 4. PURPOSE To provide reliable wireless connectivity during the movement of mobiles between two cells. In non CDMA communication networks when the channel used by the mobile customer becomes interfered by other mobile user using the same channel in some other cell, the call is transferred to a different channel in the same cell or to a different channel in another cell in order to avoid the interference [1] [16]. Again in non CDMA networks, when the behavior of user changes. Example: Traffic based, when a fast traveling user connected to a large umbrella cell stops, Then the call may be transferred to a smaller macro cell or even to a microcell in order to free capacity on the umbrella cell for other fast travelling users. Additional purpose of handoff is also to decrease the possible interference with other cells or users. This works in reverse also [1][15] and [16]. When the capacity of connecting new calls for the given cell is used up. An ongoing call located in an area overlapped by some other cell is transferred to that cell to free some capacities [4]. In CDMA networks a soft handoff may be induced in order to reduce the interference to a smaller neighboring cell due to the Near Far Effect, even when the mobile customer still has an excellent connection in its current cell [1]. When a user is detected moving faster than a particular threshold, the cellular call can be transferred to a larger umbrella cell in order to reduce the frequency of the handovers due to the movement [1]. 5. HARD HANDOFF Hard Handoff [6], [9] and [10] is the process in which the channel in the current cell is released and only then the channel in the new cell is engaged. Thus the connection to the current cell is broken before the connection to the new cell is made. That s why these handovers are called as, Break before Make. Hard handovers are intended to be instantaneous in order to minimize the disruption to the call / to reduce the possibility of ending of call / Call Blocking Probability. A hard handover is perceived by communication network engineers as an event during the call. 6. SOFT HANDOFF Soft Handoff [6], [9] and [10] is the process in which the channel of current cell is retained. It is used for some time in parallel with the channel in the new target cell. In this case the connection to the new target cell is established before the connection to the source cell (previous) is broken. So, this type of handoff is also called, Make before Break. This time duration, during which both two channels are used in parallel, will be very brief. Due to this reason the soft handover is perceived by the communication network engineers as a state of call, rather than a brief event. Soft handover involves use of channels / connections of more than two cells. Example: Three, four or more cells can be maintained by one phone at the same time. When the call is in the state of soft handoffs, the signal of the best of all used channels can be used for the call at a given instant of time or all the signals can be combined to generate a clear copy of the signal. The later is better choice. When such combinations are used, both in the down link and up link, the handover process is known as Softer. Softer calls can be possible only when the cells involved in the handovers have a single cell site [15] and [16]. http://www.iaeme.com/ijecet/index.asp 43 editor@iaeme.com

Prashant N. Swam and Prof. Nilesh Bodne 7. HANDOFF IMPLEMENTATION For realization of handoffs in a wireless cellular network practically, each cell is assigned with a list of potential new target cells. These cells can be used to hand over calls from the original source cells to them. These assigned target potential cells are called as Neighbors and the list is called Neighbor List. Creation of these lists requires special computer tools. They are used to implement different algorithms. They may use input data obtained from field measurements or computer predictions of radio wave propagation in the regions covered by the cells [1], [8]. During a mobile call one or more parameters of the signal in the channel in the original source cell are monitored and assessed in order to decide when a handover is required. The handover may be requested by the user mobile or BTS of the current source cell. In some systems handover may be requested by the BTS of the neighbouring cell. The mobile user and the BTSs of the neighbouring cells monitor signals of each other. The best candidates are selected among the neighbouring cells. In CDMA, a target candidate may be selected among the cells which are not in the list of neighbour. This is done to reduce the probability of interference due to near far effect [15] [17] and [18]. 8. HANDOFF IN NETWORKS The services provided by the public switched telephone networks (PSTN) [23] are leveraged by wireless mobile telephone network of public land mobile networks (PLMN). PSTNs ate backbones to PLMNs. Infrastructure for wireless access, mobility management and external network gateways are provided by the network elements of PLMNs. A simple PLMN [23] consists of the following components: Base stations Mobile switching service centres (MSC) Home Location Register (HLR) Visitor Location Registers (VLR) Authentication Centre (AUC) Equipment Identification Register (EIR). Figure 2 Simple PLMN Radio interface for mobile subscribers are used to provide network access by the base stations. Managing base stations, consulting PLMN database to establish subscriber access rights, routing mobile traffic is managed by MSC. MSC also serves http://www.iaeme.com/ijecet/index.asp 44 editor@iaeme.com

Evolution of Vertical Handoff To Voice Over LTE Via Generic Access (Volga) as a gateway to external networks. Subscriber profiles, location encryption codes and equipment data are stored in PLMN databases. HLR, VLR, AVC and EIR are PLMN databases. All telephone networks require fundamental services like Call establishment and connection maintenance. Call initiation signalling, connection path establishment, alerting called party, call acceptance and preservation of connection until end of session signalling is detected consists of the PSTN call process for two authorized fixed location subscribers. The PSTN uses the fixed location of the subscriber to simplify network functions. Authentication, call establishment and call preservation are simplified by fixed subscriber location. Subscriber mobility significantly complicates network operations, although a PLMN call process performs the same functions of a PSTN. PLMNs must implement mobility management technologies to provide PSTN services. These technologies enable PLMNs to establish and maintain calls to authorized mobile subscriber. Mobility Management uses the HLR, VLRs, MSCs and Base Stations. Call quality, reliability and availability are strongly influenced by Mobility Management technologies. Mobility Management is the ability of a PLMN to orchestrate calls for its subscribers and radio management maintains the call regardless of the mobility of the subscribers. PLMNs must track and dynamically route calls to its subscribers in a transparent fashion. The main functions of mobility management are locating, authenticating and tracking mobile subscribers. PLMNs use a registration process to report a mobile station s right to access network services. Roaming allows authorized mobile subscribers to use networks other than their home PLMN. Signal quality assessments, base station selection and switching constitute Radio Resource Management (RRM). 9. PERFORMANCE, FUNCTIONALITY AND ENERGY EFFICIENCY The network change times between a public cellular network and an infrastructure WLAN are presented in Fig. 3. The results show that the handover times are around 204 ms. During the measurements, the WLAN network was not used by other users. This is significantly better than the around one second without any modifications [12]. The handover measurements started from the DISCONNECT event the handover time itself was unaffected by the previous network. The handover time is within limits of suitability to real-time communication. The times around 200 ms are generally regarded as a limit for the real-time communication. On the other hand, as the handover concept did not offer any solution for mobility management, its up to the service to deal with the connection change. As a result of simultaneous connections the tradeoff is energy efficiency. The idle state, without any communication, the difference in energy consumption is presented in Fig. 4. It shows that although the base consumption can be near the same level as with a single connection, the mandatory keepalive signalling will resulting higher energy consumption. http://www.iaeme.com/ijecet/index.asp 45 editor@iaeme.com

Prashant N. Swam and Prof. Nilesh Bodne Figure 3 Energy Efficiency Tradeoff in Idle Figure 4 Handover Power Consumption REFERENCES [1] M. Sauter, VoLGA A Whitepaper 2009. [2] Wireless Moves -- http://www.wirelessmoves.com [3] The VoLGA Forum http://www.volga-forum.com [4] Wikipedia http://www.wikipedia.com [5] Oleg Stepaniuk, Voice over LTE via Generic Access (VoLGA) as a possible solution of mobile network transformation IEEE. [6] 3GPP Generic Access Network: 3GPP TS43.318, Mobile Broadcasting with Wimax ; Amitabh Kumar, 2009. [7] VoLGA: Voice Over LTE via Generic Access, Kineto Wireless A Whitepaper ; March 2009. [8] 3GPP. Generic Access Network (GAN); Stage 2. TS 23.206, 3 rd Generation Partnership Project (3GPP), December 2007. [9] 3GPP. IP Multimedia Subsystem (IMS); Stage 2. TS 23.228, 3 rd Generation Partnership Project (3GPP), September 2008. [10] 3GPP. E-UTRAN Improved network controlled mobility between EUTRAN and 3GPP2/mobile WiMAX radio technologies. TS 36.938, 3rd Generation Partnership Project (3GPP), January 2010. http://www.iaeme.com/ijecet/index.asp 46 editor@iaeme.com

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