Types of handoff and their characteristics in mobile communication pdf
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- Handoff and Radio Resource Management in Cellular Systems
- Handoff in Mobile Connections
- Handoff in Mobile Connections
- Handoff in Mobile Connections
Metrics details. The proposed vertical handoff algorithm assumes a handoff decision process handoff triggering and network selection.
Handoff and Radio Resource Management in Cellular Systems
In this context, the paper proposes the definition of a Decision Maker DM , within the protocol stack of the MN, in charge of performing network selections and handover decisions. Among several MADM techniques considered, taken from the literature, the work is then focused on the TOPSIS approach, which allows introducing some improvements aimed at reducing the computational burden needed to select the RAT to be employed.
Finally, the numerical results, obtained through a large simulative campaign and aimed at comparing the performance and the running time of the D-TOPSIS, the TOPSIS, and the algorithms found in the literature, are reported and discussed. Natural disaster events such as earthquakes, hurricanes, and floods and man-made ones such as terrorist attacks and toxic waste spills are facts of these last few years.
Not only is the number of the disaster occurrences increasing very seriously, but also the number of killed and severely injured people is dramatically high. Environmental impacts on human health and quality of life are very high and there is an increase in disaster risk. Disaster management cycle is very complex and goes from prevention and mitigation to alert, response, and recovery. A quick deployment of a telecommunication infrastructure is essential in this case.
For this motivation the role of the Information and Communication Technology ICT is topical for the deployment of a telecommunication infrastructure for risk and emergency management, for the technology integration, and for the implementation of specific technological developments possibly offering quick reconfigurability, interoperability, and scalability.
Consequently, users can access a new set of services independently of their positions. It is worth noticing that different RATs have different characteristics and, of course, different strong points and weakness. These can also depend on the emergency conditions in which the MN is operating. Moreover, this paradigm enables the MNs to be aware of the heterogeneous and dynamic context where it is, represented by the available RANs status, and to adapt its behaviour consequently during the communication.
In this framework two processes cover a crucial role: i the handover that is the redirection of the active connections from a RAN to another one and ii the network selection that is a decisional process that selects the RAN that the MN has to use, among the available ones. According to the IEEE Both these functions are necessary to enable the MN to use the best RAN in terms of communications performance but they have stringent time requirements in their execution as stated in [ 3 ].
So an algorithm for the network selection must reduce the operations number necessary to perform the selection and, as a consequence, the needed time.
On the contrary, an increase in the employed algorithm computational complexity may have a negative effect on the considered handover process that must wait for the selection procedure. This waste of time can provoke a performance detriment of the QoS perceived by the user and, in the worst case, can determine a service interruption.
During the network selection process, each RAN can be evaluated considering several characteristics often called attributes. Considering the mobile scenario, it is possible to say that the values of some attributes change dynamically while other attributes keep their values constant independently of the MN position inside the considered coverage area. As a consequence, as presented in [ 4 ], the attributes may be divided into groups: static , dynamic , and semidynamic.
The main contributions of this paper are listed below: i A description of the mobile communications framework, regarding in particular handover process, network selection, and a possible applicative scenario, is included in Section 2. In this section the reference scenario used as a common test-bed to compare the considered algorithms is also described. The handover process can be divided into two categories: i horizontal handover and ii vertical handover.
While the former occurs when the user switches between the same technologies RAT for example, passing from a Wi-Fi network to another , the latter happens when the user moves from a technology to another. Three main contributions are included in this section: a possible applicative scenario, the description of the handover process, and finally the presentation of the network selection concept.
In Figure 1 a possible heterogeneous network composition is represented. Suppose that a member of a rescue team operating during an emergency event is connected to a remote host, for example, an Emergency Operation headquarter, through an MN equipped with several heterogeneous network interfaces. The MN is moving by following the trajectory represented by black, dotted line with the arrow.
Until he is in his house, the MN uses the domestic Wi-Fi connection. When he leaves the house, moving outside for the rescue operations, the Wi-Fi coverage area, the MN perceived that the quality of the Wi-Fi channel is degrading. Consequently, the MN decides to execute a handover and redirect the traffic to another RAN to prevent service interruption. Obviously, all these functions are executed automatically by the MN that maintains active the connection with the remote host, and the user is unaware of the handover execution.
While the user is walking along his path, the MN periodically controls the state of the system, represented by the value of the attributes used to evaluate each RAN, and executes the network selection algorithm. Until the selected network is in use represented by the black circles in Figure 1 , the MN does not perform any handover. Finally, when the user arrives at his office, the MN detects a Wi-Fi network that, according to the network selection algorithm, is better than the WiMAX in use, and it executes the handover.
Similar behaviour characterizes also different scenarios such as the Intelligent Transportation Systems applications, which constantly monitor a vehicle moving along its path or inside a port area or in a construction site. Obviously, each network selection algorithm can give different decisions and it is characterized by different performance depending on the speed of the MN, as reported in Section 6.
The term handover identifies the overall process that enables a Mobile Node MN to change the access network that it is using and to switch to another one among the available RANs. As report in [ 6 ] and briefly reprised at the beginning of this section, two different types of handover are defined according to the network technologies: i horizontal handover , when the RAT selected is the same one currently used by the MN, or ii vertical handover , when the target RAT is different from the one used by the MN.
To maintain the communication active, the MN changes the Point of Access PoA and connects itself to the radio base station of the cell in which it enters. On the other hand, a vertical handover occurs, for example, when an MN exits the coverage area of a Wi-Fi network and switches to the UMTS technology in order to maintain the connection active. Another classification of the handover process is proposed: i soft handover or make-before-break that represents the case in which an MN is connected to both PoAs during the switching phase and ii hard handover or break-before-make in which an MN can have contact with only one PoA at a time.
A further type of handover, called seamless , meets the following requirements: i it is a soft handover, which means that the communication is maintained active during the network switching; ii the whole handover process has a limited duration; iii the handover must not determine any Quality of Service QoS degradation.
Such a type of handover execution is also called transparent because the user is unaware of the RAN change performed by the mobile terminal. The network selection is a task that is in charge of selecting the most appropriate RAN that an MN must use among the available ones.
This procedure is tightly linked with the handover process. In fact, the decision taken by the network selection algorithm may trigger the handover execution when the selected network is not already used by the MN.
In other words, the network selection is in charge of determining when the MN has to switch from a RAN to another: an MN may execute a handover not only when it moves away from the cell in use but also when a different available RAN is better from the network selection algorithm view point.
In order to support the cooperation among different RATs the network is in charge of maintaining an efficient signalling architecture, efficiently managing the resource utilization, and assuring the security and the integration of the communications. On the other, hand the network selection decision can be taken by the core network i. In practice a Decision Maker DM entity evaluates only the quality of the channel and selects the PoA that assures the best channel conditions.
In fact, different users may have different preferences and requirements not only referring to the quality of the communication but also, for example, to the power consumption minimization or to the Monetary Cost reduction. Moreover the various RATs, which characterize a heterogeneous scenario, may differ from each other not only in the channel quality but also in the aforementioned metrics.
Consequently, another family of algorithms applied to solve the network selection problem is called multiattribute group; they are able to take advantages from the availability of different RATs and can select the best one evaluating more than one metric or attribute simultaneously [ 7 ].
More details about these groups of algorithms are reported in Section 4. The IEEE Its purpose is to assure to an MN the service continuity during the handover execution as well as after the handover. Moreover the standard is also aimed at assuring that the change of access network is not noticeable to the end user. As a logical consequence, it is mandatory not to decide the QoS degradation during the handover procedure limiting both packet losses and delay.
It is worth noticing that two different aspects of QoS are considered by the standard: i the QoS experienced by an application during a handover and ii the QoS considered as part of a handover decision. Therefore, it is clear that this standard supports the handover execution not only for assuring the service continuity but also for selecting the RAN that best fits the MN requirements, in terms of QoS.
In more detail, it represents a common interface between the upper layers and the lower layers inside the protocol stack: even if an MN can have multiple network interfaces inside the lower layers, the MIH Layer is unique for this reason, it is called technological dependent layer. A further logical element, defined by the standard, is a set of functions, called Media Independent Handover Function MIHF , whose aim is to support the handover process.
Indeed, this set of functions is in charge of activating the communication between the MIH Layer and the upper and the lower layers and providing the necessary information to support the handover procedures. More details about the aforementioned MIHF can be found in [ 2 , 8 ]. According to [ 2 ] the communication model proposed by the IEEE An important virtual entity is introduced: the Point of Service PoS. In other words, a PoS is a network element that is in charge of providing an MN with the necessary information to perform the handover.
In Figure 2 it is possible to see that there are two network portions, the client side where the MN is located and the network side that includes the PoS and the non-PoS elements, which are the network nodes that communicate with the MN indirectly.
It is possible to view that the PoSs are logically located inside the Points of Access PoAs currently in use, inside the target PoAs, and inside other network nodes that are not PoAs but can be, for example, a database that contains some information of the neighbour RANs. All these nodes communicate together directly or indirectly, inside a client-server communication model, where the MN is the client that requires some information to execute the handover, and the core network is the server that provides the necessary information.
As previously said, the IEEE IEEE The operations are divided into phases, as reported in Figure 4 : i Handover Initiation : This is phase one of the handover process. The initiation comprehends message exchange with the Point of Access along with some preliminary measurements on the available RANs.
Here the Mobile Node chooses the network that will be employed after the handover and the negotiation for resource reservation that aims to grant that QoS requirements begin. Some operations are included in the scope of the standard while others are only cited, but their implementation is not specified by the standard and, consequently, many different solutions can be applied.
These operations are identified by an asterisk in Figure 4. Among these, a very important function is the handover decision, which refers to decisional process in charge of determining when the MN has to perform the handover and which is the target network: in practice, it identifies the network selection engine. The decision of the appropriate algorithm is something that has not been determined yet. Indeed, the algorithm that can be applied in this context has to assure good performance but at the same time it is characterized by stringent time constraints.
It is worth noticing that a technique that selects the network may have a bad effect on the ongoing process, which remains in waiting status until the selection is performed. Each available network represents an alternative way that is validated trough one performance metric, named attribute.
The DM is used to choose the best possibility, among the available ones, in accord with the maximization or the minimization of the metric, used as a utility Cost function. Let be the possible RANs; we call the alternatives with an array. The - th alternative is defined as , where is the considered metric or attribute. The best option is denoted as and is achieved by using the following equation. Equation 1 is true if the employed metric needs to be maximized. If a metric needs to be minimized the operator is applied in 1.
Within the set of the possible metrics employed by the SPMO algorithms, a commonly taken decision is the RSSI, employed in [ 9 , 10 ], which represents the received power measured in [dB] and is the parameter taken as a reference during the horizontal handover.
Similarly, the same criterion could be employed for vertical handover. This represents a drawback that affects negatively the QoS of MNs. The SPMO family techniques require a low computational burden, a low running time, and a limited power consumption. Differently, they can yield scarce performance if the goal would be the optimization of multiple metrics. Target collision probability is another possible metric that has been used in network selection algorithms.
The authors evaluate their proposal by comparing it with other state-of-the-art strategies Random and Greedy algorithms showing its superior performance. More than one metric is considered at the same time [ 7 , 12 ].
Handoff in Mobile Connections
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Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. Gupta Published Technology is moving very fast with time. Mobile is very important part of our life. With increasing traffic and energy demand, it is necessary to achieve efficient network. We need to maintain high quality of service and optimize energy at high traffic and at low cost so that common people can use it.
However as the mobile moves out of one cell to another it must be possible to retain the connection. The process by which this occurs is known as handover or handoff. The term handover is more widely used within Europe, whereas handoff tends to be use more in North America. Either way, handover and handoff are the same process. The process of handover or handoff within any cellular system is of great importance.
handoff initiation and decision and discuss about different types of. handoff techniques The transfer of a current communication channel. could be in terms handoff time there are two possibilities: To drop the call or to. delay it for a to BS2 as a result of signal propagation characteristics. The. received.
Handoff in Mobile Connections
A cellular network or mobile network is a communication network where the last link is wireless. The network is distributed over land areas called " cells ", each served by at least one fixed-location transceiver , but more normally, three cell sites or base transceiver stations. These base stations provide the cell with the network coverage which can be used for transmission of voice, data, and other types of content. A cell typically uses a different set of frequencies from neighboring cells, to avoid interference and provide guaranteed service quality within each cell.
Handoff in Mobile Connections
To a wireless user, dropped calls, blocked calls, and calls riddled with static are unacceptable. Users expect to remain connected while traveling through cells of a service area. Users also expect to be able to make calls at any time and to have good, clear connections. These user demands are addressed through the management of radio resources.
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PDF | Handoff management is the essential issue that supports the phone network reuse frequency will be used,when (MS) divided into two different types—intra- and inter cell depends on its relative value as compared to the signal are developed and used to derive performance characteristics.
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