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In this paper we present the comparative abstract of the handover engineering. There are ever increasing demands of high-velocity informations applications in wireless systems with fast and seamless entree to voice and multimedia services and QoS guaranteed such as in Fourth Generation ( 4G ) Long Term Evolution ( LTE ) – Advanced system. We would discourse the public presentation, handover techniques, demands and characteristics, handover types ( soft and difficult ) , handover sweetening in LTE advanced relay webs, architecture and at the terminal the public presentation rating of transmittal control protocol ( transmission control protocol ) and user datagram protocol ( udp ) during lte handover.

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Keywords Lte handover, advanced handover techniques, 4G-relay web, combined handover, femtocell, macrocell, Qos.

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Introduction 1. Mobile high-bandwidth informations communicating is challenge for the telecommunication service suppliers in this epoch. User want to entree web services in anytime at any topographic point with high velocity from their nomadic devices. IEEE 802.11 radio engineering is developed to suit user ‘s mobility demands. With comparing to IEEE the newest engineering introduced by telecom sellers by name of LTE ( long term Evolution ) which is viing entree web engineerings in 4G radio web with WIMAX. It is backward compatible with GSM/UMTS cellular systems, this make LTE deployment much easier so WIMAX. [ 1 ] [ 6 ]

2. There are many challenges have to confront for heightening the mobility system in LTE advanced web. There would be two chief handover engineerings in wireless communicating systems difficult handover and soft handover. In LTE advanced system bearer collection technique is besides supported, that eNB could configure a set of cells for UE presently under its service extend. Therefore it ever consists of one primary cell and one or more secondary cells. [ 2 ] [ 7 ]

3. For the strong demand of multimedia services and broadband applications with higher information rate the IMT advanced system has been initiated for the following coevals nomadic communicating system 4G.LTE advanced system supports high mobility velocity upto 500km/h furthermore lte advanced expected to back up high informations rate upto 1gbps in downlink and 500mbps in uplink. The handover in lte-advanced system is strictly based on difficult handover. With the restriction of the bing handover technique in LTE system, it is necessary to find a new handover technique to accomplish these ends which include avoiding loss of informations, guarantee efficiency, reduced outage chance and to increased dependability of handover process for the hereafter following coevals LTE -Advanced system. [ 3 ] [ 8 ]

4. LTE is designed to supply higher throughput and lower latency than its predecessor, i.e. HSDPA ( high velocity downlink package entree ) which is besides known as 3GPP release 5 [ 3 ] . LTE besides introduces the all-IP web and all services are provided by IP. Therefore the throughput and hold public presentation must fulfill certain standards even in the mobility scenario.In add-on, there is a link break in the user plane during handover because LTE supports merely difficult handover, the break degrades the hold public presentation of UDP because no informations can be sent between eNB and UE during the break. It has besides been pointed out that longer break times may degrade the TCP throughput public presentation. If the break clip exceeds the retransmission timeout of a TCP session, the congestion turning away algorithm of TCP reduces the TCP throughput. This phenomenon is called specious timeout. This paper measure the TCP throughput and UDP hold by utilizing indoor and out-of-doorss testbeds. The indoor testbed consists of EPC ( evolved package nucleus ) , eNBs, and UEs ( user equipment ) in full conformity with 3GPP release 8. A fading simulator is used to emulate the extension environment between the eNBs and the UEs. The out-of-door testbed is located in Kumagaya metropolis in Japan. We evaluate the TCP public presentation in a existent extension environment. [ 4 ] [ 9 ]

5. The Long Term Evolution of UMTS is merely one of the latest stairss in an forward series of nomadic telecommunications systems. The 3GPP criterion for Home eNodeB, LTE femtocell, which is one of the best attacks to cut down the Operating Expenditures ( OPEX ) for operators. Femtocells are low- power entree points, supplying wireless voice and broadband services to clients chiefly in the place. With the deployment of the Home eNodeB, the handover between femtocell and 3GPP macrocell webs is become more and more of import in the LTE based webs. Thousand of femtocells within a macrocell country will make a big neighbour cell list and intervention job. So the alterations of handover processs for bing webs are needed. The optimisation of handover process and algorithm will better the public presentation of both the femtocell and LTE webs. [ 5 ] [ 10 ]

Handover Techniques

Handover techniques in radio communicating web can be classified into two chief handover techniques types. The first technique type is called Hard Handover ( HHO ) and the 2nd technique type is called Soft Handover ( SHO ) .

Hard handover The construct of HHO is to interrupt before brand. That means the old radio nexus connexion is broken from the beginning eNB before a new connexion is activated to the mark eNB. The UE can pass on with one eNB merely in each clip slot during HHO. That means, after let go of the connexion from beginning eNB, the new connexion is set up and activated to aim eNB. Whereas, after the signal strength from a mark eNB exceeds the signal strength from the beginning eNB the HO start the executing.

Soft handover The SHO handover technique is make-before-break method. That means a new radio nexus connexion to the mark eNB is established while the old connexion with beginning eNB is maintained. The UE at the same time receive all services informations from several active eNBs. Under this technique, there are two chief SHO techniques in radio nomadic communicating system. The first technique is called Macro diverseness Handover ( MDHO ) and the 2nd technique is called Fast Base Station Switching ( FBSS ) .

Macro Diversity handover ( MDHO ) In MDHO, a list of BSs is maintained by the MS and BS. This set of BSs is called an Active Set or Diversity Set. Under this technique, MS have the ability to pass on with all BSs in the Active Set as. For DL, MS received and performed informations from all the Diversity Set BSs. In the UL, all Diversity Set BSs are received and performed information from MS. Furthermore, the Neighbor BSs can have the signal from MS, but the signal strength is non sufficient to let Neighbor BS to be added to the Diversity Set. MDHO supports fast and seamless handover. In add-on, MDHO is more stable and gives better public presentation in term of fast and seamless handover. On the other side, MDHO is more complex for its architecture and during handover process than HHO. Therefore, using MDHO will increase system overhead and more web resources will be wasted. This technique is common in UMTS systems and besides applied in WiMAX household.

( II ) Fast base station exchanging ( FBSS ) In FBSS technique, MS and BS maintain a list of entree BS called a diverseness set and communicates with BS in each frame likewise as in MDHO. The MS continuously monitors the base Stationss in the Active Set and defines one BS as an “ Anchor BS ” based on the standard signal strength. The Anchor BS is the lone BS of the Diversity Set that MS can pass on with for all UL and DL messages including direction and traffic connexions. This type of handover supports smoother informations passage from beginning to aim eNBs and less system overhead than MDHO. In other side, FBSS has high informations lost latency and outage chance comparable to MDHO.

Fractional soft handover technique ( FSHT ) FSHO technique has been proposed in LTE-Advanced system based on Carrier Aggregation ( CA ) technique. The chief construct of FSHO technique is to partly execute soft handover for VoIP service. In this proposed technique, they classify the service to VoIP and non-VoIP services. During the handover process, VoIP services are transmitted from both beginning and mark eNBs, while non-VoIP service are transmitted by beginning or mark eNBs.

D. Combined partial resuse and soft handover This strategy proposed an inter-cell intervention extenuation strategy based on a combination of partial reuse and soft handover for an OFDMA DL system. The aim of this strategy is to better the norm cell throughput by sing the information rate equity among the users, compared to the conventional partial reuse strategy, particularly at the cell boundary and during handover happening from beginning to the mark eNBs in LTE- Advanced system. In add-on, using this strategy is ensuing in a low soft handover operating expense.

E. Semi soft handover technique ( SSHT ) SSHO technique has been proposed utilizing macro diverseness method, which permits both HHO and SHO advantages for services over multicarrier-based broadband webs to be retained. This intercrossed handover method is known as Site Selection Diversity Transmission ( SSDT ) . This technique represents a possible solution for multicarrier systems. The basic construct of SSDT is to selectively convey each downlink symbol harmonizing to channel quality from each BS.

F. Handover readying with handover dialogue In the readying phase beginning eNB prepares one or more mark cells so the beginning eNB selects the mark PCell and the beginning eNB alos provides the mark eNB with the list of cells. The mark eNB selects and identifies the SCells that are configured for usage after handover. The mark eNB usage RRC Connection Reconfiguration message, either including the mobility Control Info or non to configure SCells. Once mark eNB recives handover command message from the beginning eNB, the handover dialogue mechanism is executed between two eNBs. The mark eNB detects the current identifies SCells one time upon reciving the handover dialogue petition message. If there are duplicates between the identified SCells by mark eNB and the current configured SCell by beginning eNB, mark eNB will pre-assign CC for UE, besides the mark eNB should direct handover dialogue petition ask message back to beginning eNB.

G. Synchronous handover Execution When handover dialogue has been executed successfully a dedicated RACH preamble that is allocated for UE by mark PCell is send to beginning PCell with handover bid ACK message and transparently frontward to UE so handover executing is processed by agencies of RCC connexion reconfiguration including the mobility control info. UE reconfigures PCells and a set of SCells, so attempts to entree the mark PCell at the first available RACH juncture harmonizing to Random Access Resource Selection. Since there are duplicate between the reconfigured SCells by UE and original configured SCells by beginning PCell before handover i.e curren SCells maintain the user informations forwarded to UE by beginning eNB, so the duplicated SCell could provid UE with user informations during the RACH entree procedure i.e. the handover is synchronal.

LTE-Advanced System

1. Fast and seamless handover techniques

Fast and seamless handover are of import characteristics in wireless systems. Fast handover is a web re-entry process with minimal handover latency without any expressed involvement in package loss and break clip. While, seamless handover are a web re-entry process with the capableness for UE to reach with the mark eNB before originating a web re-entry control message dealing. Obviously fast and seamless handover depends on the type of user services. For illustration, the real-time applications such as picture conferencing and streaming media are required high informations rate and wider bandwidth. So that, there is diminishing for the connexion to these real-time applications ( i.e. picture conferencing and streaming media ) will be likely noted to the users during handover from the beginning to the mark eNBs. But in other side, shoping a web site or reassigning a file non required high informations rate comparison to the real-time applications, so the user does non hold noticed anything during handover procedure. As a consequence, the of import important factors for fast and seamless handover are the latency and package loss. These two factors have to be every bit little as possible to do the handover fast and seamless.

2. Supported for bequest handover

The bequest engineerings in LTE-Advanced system are refer to Global System for Mobile Communications ( GSM ) , Enhanced Data Ratess for GSM Evolution ( EDGE ) , radio entree web ( GERAN ) and Universal Mobile Telecommunications System ( UMTS ) households: Wideband Code-Division Multiple Access ( WCDMA ) , high-velocity information package entree ( HSDPA ) , and HSDPA+ [ 12 ] . LTE-Advanced system ( R10 ) specification is required to be rearward compatible with GSM household webs. The latest handover techniques in LTE-Advanced system have to back up for Legacy GSM web. Since deployment of LTE-Advanced system might be installed over the bing GSM, EDGE, GERAN, UMTS, WCDMA, HSDPA, HSDPA+ and LTE web, the LTE- Advanced UEs are designed to back up mobility capableness across the coexisting deployment of bequest and advanced webs without critical restraints on service continuance.

3. Lte-Advanced Relay Architecture

Each eNB has a limited helping country. But it is more hard to deploy a new eNB since occupants have much healthy concern about the electromagnetic moving ridge. Therefore, the thought of signal relaying by a smaller entity called relay node ( RN ) has been proposed and becomes an LTE-Advanced specification.There are two different RN types depending on its functionalities. Type 1 RN has the OSI bed 3 functionality that act as a regular eNB for UE and act like an UE for DeNB. Type 2 RN merely operates at OSI layer 2 functionality that provides messages decrypting and send oning mechanisms and is crystalline to both UE and DeNB. The system direction becomes more complicated if the operators deploy different types of RN. Although the architecture and signaling between DeNB and RN are still under treatment and design, RN relaying mechanism already becomes a cardinal engineering of LTE-Advanced. How to derive the benefit from RN, fit the QoS demands and cut downing entire cost of ownership are the important research subjects. An RN foremost connects to an eNB in order to enlarge eNB ‘s serving country. The eNB that connected with RN is called Donor eNB ( DeNB ) since it needs to supply more functionality for functioning both UE and RN. The interface used between RN and DeNB is called Un. The RN has S1 and X2 interfaces since it act as a regular eNB for UE. Furthermore, an RN is similar to a UE that is running with RRC ( Radio Resource Control ) and NAS ( Non Access Stratum ) functionalities.

TCP throughput Evaluation

We evaluate TCP throughput by utilizing two eNBs and three UEs. UE1 is traveling between eNB1 and eNB2. UE2 and UE3 are statically attached to eNB1 and eNB2, severally. Note here that the scheduler in each eNB assigns all available wireless resources to the UE ( s ) by utilizing a relative carnival algorithm. Therefore, the intervention from the neighbouring cell includes non merely mention and control signals, but besides the user plane signal if adequate user plane informations is supplied from the eNBs to the UEs. UE1 ( traveling UE ) is connected to both eNB1 and eNB2. At UE1, RSRP ( reference signal having power ) for eNB1 is controlled by the programmable attenuator and it is varied sporadically between -80 and -100dBm.The increase/decrease rate of RSRP is set at 1dBm/sec. On the other manus, RSRP for eNB2 is set to be a changeless at -90dBm. At first, UE1 is attached to eNB1 because RSRP for eNB1 is higher than eNB2. As the RSRP for eNB1 lessenings and if the RSRP for eNB2 is A dubnium higher than eNB1 for T msecs, where A is A3-offset and T is TTT, handover is triggered and eNB2 becomes the functioning eNB for UE1. In this manner, UE1 repeatedly hands over between eNB1 and eNB2. Note here that UE2 and UE3 remain affiliated to eNB1 and eNB2, severally. FSs ( Fading simulators ) are inserted between the eNBs and the traveling UE to emulate a wireless extension environment. The extension theoretical account used in the indoor experiment is ETU ( Extended Typical Urban ) and maximal Doppler frequence fD = 70Hz, which corresponds to speed of 35km/h. A server Personal computer is located at EPC side and client Personal computers are located at UEs. TCP watercourses are generated by Server and sent to Client 1, 2 and 3.The congestion turning away algorithm is BIC ( binary addition congestion control ) and FRTO ( send oning retransmission timeout ) is employed to avoid specious timeout. To more closely expression at the TCP throughput debasement merely earlier handover, we filtered the TCP throughput by mensurating RSRP for eNB1 and eNB2 at the same clip as the TCP throughput measuring. If the difference between the RSRP for the helping eNB ( RSRPserving ) and the RSRP for the mark eNB ( RSRPtarget ) is less than a predefined filtering threshold ( F ) , i.e.

RSRPserving – RSRPtarget & lt ; F, ( 1 )

The filtering threshold is set at F = 2dB. ( Handover was repeated for 60 times to garner many samples. ) , smaller A3-offset improves TCP throughput. Another interesting point here is that Ping-Pong handovers are observed when A = 0dB. Ping-Pong handovers generate more breaks and degrade the TCP throughput public presentation. However, we can obtain better TCP throughput public presentation with A = 0dB. Therefore we can reason that a Ping-Pong handover does non significantly affect TCP throughput public presentation.

UDP hold Evaluation

For UDP traffic transmittal rate is set at 1 Mbps. Since we set the UDP package size at 1250 bytes, a package is sent to Client 1 every 10ms. Probe1 and Probe2 in Fig. 3 measured one-way hold of UDP packages. When a package goes through both investigations, the transmit times are recorded. Since Probe1 and Probe2 are synchronized by GPS ( planetary placement system ) , it is possible to cipher the one manner downlink hold by taking the difference between the recorded times at Probe1 and Probe2 for each package. The one manner downlink transmittal delayaˆ?measured during LTE handover with A = 6dB and T = 320msaˆ?when the RSRP increase/decrease rhythm executed to trip four handover events. The spikes areaˆ?created by the breaks caused by the handovers. Theaˆ?observed break clip was about 80ms. Although theaˆ?results are non given here, we obtained similar interruptionaˆ?times for other A and T values in this peculiar radioaˆ?propagation environment and traffic form.

LTE Femtocell System Architecture

For the E-UTRAN HeNB architecture, the treatments for the LTE femtocell criterions are undergoing in the Femto Forum, in NGMN Alliance and in 3GPP. While the architecture has non been finalized, there is a strong consensus to maintain it every bit level as possible, following the rules of ‘all-IP ‘ webs adopted in the LTE criterions. The argument is still traveling on as to whether there is a demand for a signaling collection component or whether the evolved package nucleus ( EPC ) itself should be able to back up femtocells straight, which has a set of S1 interfaces to link the HeNB to the EPC. With the involved of Home eNB Gateway ( HeNB GW ) , it equivalent to spread outing the S1 interface between HeNB and nucleus web, and more HeNB can be deployed. We can presume that the HeNB GW worked at control plane, particularly the concentrator of the S1-MME. The HeNB side S1-U interface can be terminated at HeNB GW or the logical connexion between HeNB and S-GW by straight user-plane.

To incorporate with LTE macrocell webs better, the HeNB GW should appears to the MME as an eNB, the HeNB GW appears to the HeNB as an MME between the HeNB and the Core Network though there may be 10s of 1000s of femtocells in a traditional LTE macrocell, HeNB GW may besides hold interface to operator ‘s O & A ; M system for constellation and control.The S1 interface between the HeNB and the EPC is the same whether the HeNB is connected to the EPC via a HeNB GW or non. Here we choose the LTE femtocell system architecture based on concentrator.

The interfaces between the HeNB and the EPC are the standard S1-MME and S1-U, with the HeNB GW optionally supplying collection map for the S1- MME. The S1-U interface adopts a direct tunnel attack, but optionally besides this interface can be aggregated by the HeNB GW. In this instance, the HeNB GW may besides supply support for user plane multiplexing, for efficient transmittals over limited bandwidth links. The maps supported by the HeNB shall be the same as those supported by an eNB and the processs run between a HeNB and the EPC shall be the same as those between an eNB and the EPC.

Performance Analysis

Since UE supports merely difficult handover strategy in LTE- Advanced environment, UE has to unplug with beginning RN/eNB and so reconnect with RN/eNB among its handover process. By utilizing the forwarding mechanism can cut down the chance of package loss. In order to analyse send oning cost, we define the transmittal cost in each nexus listed as follows.

HPGW_SGW: the hop count between P-GW and S-GW HSGW_DeNB: the hop count between S-GW and DeNB HInter_DeNB: the hop count between Source DeNB and

Target DeNBaˆ? HRadio_RN: the hop count between DeNB and RN HRadio_UE: the hop count between RN and UE P_Timehandover: the per centum of handover period in

UEaˆ? Costdata_trans: the end-to-end transmittal cost in EPC and E-UTRAN

Regular transmittal cost

Costdata_trans = P_Timehandover ( HPGW_SGW + HSGW_DeNB + 3HRadio_RN + HInter_DeNB ) +

( 1 – P_Timehandover ) ( HPGW_SGW + ( HSGW_DeNB + HRadio_RN + HRadio_UE )

Smart send oning transmittal cost

Costdata_trans = P_Timehandover ( HPGW_SGW + HSGW_DeNB + HRadio_RN + HInter_DeNB ) +

( 1 – P_Timehandover ) ( HPGW_SGW + HSGW DeNB + HRadio RN + HRadio UE )

Parameter

Hop count value

HPGW SGW

2~5

HSGW_DeNB

5~10

HInter_DeNB

1~5

HRadio_RN

1

HRadio_UE

1

P_Timehandover

2 % ~10 %

Based on the transmittal cost listed supra, we can easy compare the difference between regular transmittal cost and the cost with proposed smart send oning strategy. The comparing of end-to-end transmittal cost between regular and proposed strategies shows the comparing of wireless entree part merely between regular and proposed strategies. The Physical frame construction that has been introduced in [ 17 ] is considered in our simulation. Based on that, the cell throughput can be calculated for every bomber bearers at the UE side. Where, it is measured in every loop clip during all the simulation clip and so taking the norm over all the users that are at the same time active in the cell. The rating public presentation in term of cell throughput is measuring is based on Shannon expression that has been defined in [ 18 ] . It can be formulated as

Data a = BW / a ten ( BWeff x log2 ( 1+SINRa / SINReff )

Where, BW is the entire system bandwidth in Hz, BWeff is the system bandwidth efficiency, SINR0 is the achieved SINR, 0 is frequency reuse factor, it is assumed to be one ( 0 =1 ) , which means merely 1/0th of the spectrum can be used by one cell and SINReff is SINR execution efficiency and formulated.

Decisions

1. Both LTE and LTE-Advanced are backward compatible with 3G/UMTS cellular systems and would see more hereafter chance and chance of going 4G criterion. The LTE-Advanced adds a new entity called relay node ( RN ) to enlarge service coverage.Performance analysis shows that the proposed strategy can expeditiously cut down send oning cost every bit good as wireless channel use during handover. [ 6 ]

2. CA technique is expected to play a polar function in future release of LTE Advance system by the assisting to heighten web coverage and better service quality the proposed strategy called combined handover strategy is a handover optimized scheme under CA manner. The proposed attack can cut down much of the break clip in handover part and it is flexible and easy to implement. [ 7 ]

3. The bing handover technique that is utilized in LTE- Advanced system is known as HHO. HHO offers cut down architecture and handover process complexnesss. But on the other manus, there are several restrictions when executing HHO, such as high latency, handover process undependability, high outage chance and information doomed. Those handover techniques support seamless handover, but suffer from some defects such as inter-cell intervention coordination ( ICIC ) , interference extenuation engineerings, latency, undependability and some informations lost during handover. Furthermore, implementing FSHO based on CA has been investigated, which result in improve system public presentation in term of cell throughput in everyplace in the cell and user ‘s handover Numberss much better than the system that has been implemented with one constituent bearer merely ( Non-CA ) . [ 8 ]

4. We evaluated TCP and UDP public presentation during LTE handover by utilizing both indoor and out-of-door experiments. A3-offset is a cardinal parametric quantity in LTE handover and several values were examined to find its impact on the public presentation of TCP and UDP during handover. TCP throughput is improved by utilizing a little A3-offset value because it efficaciously suppresses intervention from neighbouring cells. Decreasing the A3-offset value induces more Ping-Pong handovers, but this does non impact TCP throughput significantly. We besides confirmed that the break clip caused by a handover event was around 80ms. [ 9 ]

5. Modified signaling process of handover is presented in the Home eNodeB gateway based femtocell web architecture. A fresh handover mechanism based on the UE ‘s speed and QoS have been studied. The comparing with the traditional algorithm shows that the algorithms proposed in this paper have a better public presentation in the rate of unneeded handovers and the mean figure of handovers, particularly in Medium and High mobile velocity, for a little punishment of signaling overhead. In the hereafter, we plan to look into the quantitative consequence of different handover algorithms on the signaling operating expense. [ 10 ]

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