Optimization of QoS in 4G Networks Using Handover Management

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1 Optimization of QoS in 4G Networks Using Handover Management NAMRATA KATTI, SEEMA SHIVAPUR, VIJAYALAKSHMI M. Department of Computer Science BVBCET, Hubli Abstract With the advent of new opportunities and user demands in the mobile technology, 4G is gaining popularity because of its faster service. The Long Term Evolution, LTE is a 4G wireless network developed by 3rd Generation Partnership Project (3GPP). The performance of LTE is highly influenced by QoS, in which Handover management is the major issue. Handover mechanism is the transfer of call from one network to another, where all networks are connected to the core network. The transfer of call occurs due to weakening of current signal or high availability of services to the user on another signal. Maintenance of call session during such transfers is crucial. There are three existing handover algorithms for LTE in 4G networks namely No-Op, A2-A4-Rsrq, and A3-Rsrp. The No-Op is the simplest algorithm where it does not include any interface methods for handover. The second one A2-A4-Rsrq utilizes the Reference Signal Received Quality (RSRQ) from Event A2 and A4. The third one A3-Rsrp aims to provide each user equipment (UE) with the best possible Reference Signal Received Power (RSRP). To improve QoS parameters; throughput, SINR, and number of handovers, authors propose a new Hybrid algorithm which utilizes the functionalities of both A2-A4-Rsrq and A3-Rsrp. The performance analysis of the proposed hybrid algorithm is conducted by comparing it with the existing algorithms using NS-3 network simulator. The first version of the algorithm has been implemented and the work is under progress to improve the results. Index Terms LTE, QoS, Rsrp, Rsrq, SINR I. INTRODUCTION 4G is the fourth generation of mobile communication standards. It provides mobile ultrabroadband internet access and it is a successor of the third generation (3G) standards, as it overcomes the disadvantages of 3G networks [1]. One important disadvantage is data rate of 4G goes up to 100 Mbps to 1 Gbps but of 3G is only up to 2 Mbps. So many of the researchers have explored on the recent technology i.e. 4G [2]. As 4G is the present working area of many researchers to increase the QoS parameters such as throughput, SINR, etc, there are many challenges such as delay, bit error rate, high packet-loss rate during handover, bandwidth limitation and fluctuations of the 398 available bandwidth, jitter, and power consumption in the 4G networks. To increase the QoS in 4G networks, the authors concentrated on one major issue i.e. handover management for LTE module. Handover mechanism is the transfer of call from one network to another, where all these networks are connected to the core network. The transfer of call occurs due to weakening of current signal or high availability of services to the user on another signal. Maintenance of call session during such transfers is crucial. There are three existing handover algorithms for LTE in 4G networks namely No- Op, A2-A4-Rsrq, and A3-Rsrp. The No-Op is the simplest algorithm where it does not include any interface methods for handover. The second one A2-A4-Rsrq utilizes the Reference Signal Received Quality (RSRQ) from Event A2 and A4. The third one A3-Rsrp aims to provide each user equipment (UE) with the best possible Reference Signal Received Power (RSRP). To improve QoS parameters; throughput, SINR, and number of handovers, authors propose a new Hybrid algorithm which utilizes the functionalities of both A2-A4-Rsrq and A3- Rsrp. The performance analysis of the proposed hybrid algorithm is conducted by comparing it with the existing algorithms using NS-3 network simulator. Here authors aim is to increase the efficiency of 4G networks by improving QoS parameters such as throughput, SINR, number of handover, packet loss, etc. In introduction author is giving brief explanation of the domain and discussing about purpose of the paper. Section II, deals with some papers which describe the journey towards the handover algorithms in 4G networks (LTE module). With the study of handover algorithms, author focuses on the proposed algorithm i.e. Hybrid algorithm with detailed explanation of handover process in section III. In Section IV explains about environment set up, parameters considered and comparative study with the existing handover algorithms. At last paper deals with conclusion and future work. II. LITERATURE SURVEY Handover management is the major issue in mobile communication, which degrade the performance of QoS parameters. The authors have performed number of studies to deal with handover management and different algorithms in LTE module for 4G networks. These algorithms use relative signal strength (RSS) parameter for measurement reports. The authors of the paper, dealt with vertical handoff management in heterogeneous network, means

2 switching from one network to another while maintaining the connection. The decision of handoff should be made at correct time for good resource allocation. In the vertical handoff decision phase, the mobile node determines whether the sessions should continue using the existing selected network or be switched to another network. The decision may depend on various parameters including the type of the application, minimum bandwidth, delay required by the application, access cost, and the user s preferences. The authors of another paper dealt with the handover process from one network to another which is shown through the implementation of video streaming application in ns3 platform [3]. The platform consists of 3 physical devices such as computers. One computer acts as a video streaming server. The second one contains LTE network for the simulation environment. The last device acts as the streaming client. The emulated LTE network is connected from one end to the server and other end to the client. The server sends video clips to client through the simulated environment using developed HIL (Hardware In the Loop) procedure. This procedure converts the real packets to the simulation-based format so that the packets can flow through the simulation environment on the second device and undergo the LTE network conditions. When the packets finish their journey in the simulated LTE environment, the HIL technique reconverts the packets back to the real data format so that they could be sent to the client. The platform supports multiple clients streaming [3]. The video streaming application may cause packets loss in the LTE environment during handover. This leads to start the real journey of LTE module in 4G networks. The authors explain different existing handover algorithms such as No-Op, A2-A4-Rsrq, and A3-Rsrp. These algorithms are derived on event-based trigger criterion. There are mainly 5 events; Event A1 (when serving cell becomes better than threshold), Event A2 (serving cell become worse than threshold), Event A3 (Neighbour becomes offset DB better than serving cell), Event A4 (Neighbour becomes better than threshold) and last Event A5 (serving becomes worst than threshold 1 and neighbour becomes better than threshold 2) [4]. No-Op is the first algorithm, which is simplest and it basically does not call any interface methods for handling handover [4]. The users may choose this algorithm if they are interested to disable automatic handover trigger in the simulation. Fig. 1. A2-A4-Rsrq Algorithm Flowchart Second is A2-A4-Rsrq handover algorithm which utilizes the Reference Signal Received Quality (RSRQ) measurements from Event A2 and A4 as shown in fig 1. Event A2 (serving cells RSRQ becomes worse than threshold) is to indicate that the user equipment (UE) is receiving very low signal quality and may benefit from a handover. Event A4 (neighbour cell RSRQ becomes better than threshold) is used to detect neighbouring cells and considering their RSRQ from every attached UE, which are stored internally by the algorithm. By default, the algorithm configures Event A4 with a very low threshold; so that the trigger criteria (handover) are always true [4]. The third existing one is A3-Rsrp which is also called as traditional power budget (PBGT) algorithm [4]. The goal is to provide each user equipment node with the best possible Reference Signal Received Power (RSRP) as shown in fig 2. This is achieved by performing a handover as soon as a better cell (i.e. with stronger RSRP) is detected and event A3 (neighbour cells RSRP become better than serving cells RSRP) is chosen. Handover is triggered for UE to the best cell in the measurement report. This handover algorithm is based on hysteresis and time-to-trigger parameters to the UE configuration. Hysteresis delays the handover in regard of RSRP. Time-to-trigger delays the handover in regard of time. 399

3 Input: Subscriber station sends a request for allocation of bandwidth Output: Bandwidth allocated or request rejected Purpose: Allocation of bandwidth based on subscriber station request The classifier work as follows Input: Packets are received from subscriber station Output: Packets are forwarded to scheduling module Purpose: Packets are classified based on priority given to users Scheduling work is as follows Input: Packets are received from classifier module Output: Packets are mapped to physical layer Purpose: Packets are scheduled based on priority given to traffic classes Fig. 2. A3-Rsrp Algorithm Flowchart The existing handover algorithms can be used for transforming data from one channel connected to another channel, while maintaining the session. In the next section, the author dealt with different modules to show how call get initiated and also deals with proposed handover algorithm to improve the efficiency of LTE module in 4G networks. III. PROPOSED WORK A. Overall Architecture There are different modules in 4G networks, for processing a call from one network to another. The different modules are CAC (Call Admission Control), Classifier, Scheduler, and Handover as shown in fig 3. When call gets initiated, allocation of available bandwidth based on subscriber station request takes place then classifier and scheduling based on priority given to user. At last, the handover takes place where selection of existing network or switching to other network is done based on the resources available. Fig. 3. Overall Architecture The fig 3 explains the input, output and purpose of different modules. In the next subsection author dealt with handover procedure, how handover is taking place between the nodes with the help of the interface. B. Handover Procedure The handover algorithm operates at the source enhanced node (enodeb) and is responsible for making handover decisions in an automatic manner. It interacts with an enodeb RRC instance via the Handover Management SAP interface [4]. The handover algorithm interface consists of the following methods [4]: AddUeMeasReportConfigForHandover (HandoverAlgorithm enodebrrc) This is used by the handover algorithm to request measurement reports from the enodeb RRC entity, by passing the desired reporting configuration. The configuration will be applied to all future attached user equipments(ues). ReportUeMeas (enodebrrc HandoverAlgorithm) Based on the UE measurements configured earlier in AddUeMeasReportConfigForHandover, UE may submit measurement reports to the enodeb. The enodeb RRC entity uses the ReportUeMeas interface to forward these measurement reports to the handover algorithm. TriggerHandover (HandoverAlgorithm enodebrrc) After examining the measurement reports (but not necessarily), the handover algorithm may declare a handover. This method is used to notify the enodeb RRC entity about decision, which will then proceed to start the handover procedure. The X2 interface interconnects two enhanced nodes enbs they are source enb node and target enb node as shown in fig 4 [4], [5].From a logical point of view, X2 interface is a point-to-point link between the two enbs and is implemented in the simulator. A pointto-point device is created in both enbs and the two point-to-point devices are attached to the point-to-point link. CAC is call admission control its duty is allocation of bandwidth 400

4 proposed new Hybrid handover algorithm to improve handover management in LTE module. IV. RESULT ANALYSIS A. Experiment Environment NS3 is an open, extensible network simulation platform, for networking and research. It focuses on different modules such as LTE, Wi-Fi, and many. Here, Simulation is done using NS3 for handover algorithms in LTE module [6]. Fig. 4. Handover Procedure C. Hybrid Algorithm The aim behind proposing new algorithm for handover is to improve QoS parameters such as throughput, SINR, and number of handover in the LTE module for 4G networks. Hybrid algorithm is the combination of two best algorithms; they are A2-A4- Rsrq and A3-Rsrp handover algorithms. The proposed algorithm concentrating on two important parameters; RSRQ and RSRP values. These values are taken from the nodes such as bestneighbourrsrq and bestneighbourrsrp as shown in the fig 5. Fig. 5. Hybrid Algorithm The Hybrid combined approach explains how two values are compared with the threshold. The two important values RSRQ and RSRP are taken from bestneighbourrsrq and bestneighbourrsrp nodes respectively. These values in turn taken from A2-A4- Rsrq and A3-Rsrp handover algorithms respectively. The procedure contains two conditions; bestneighbourrsrq is greater than threshold and bestneighbourrsrp is greater than threshold, if both conditions get satisfied, then trigger handover to new bestneighbourcellid. Otherwise trigger handover to bestneighbourrsrp. There are three algorithms in LTE module those are A2-A4-Rsrq, A3-Rsrp, and No-Op by their performance author conclude that A2-A4-Rsrq and A3- Rsrp algorithms are best as compared to No-Op algorithm so by combining these two algorithms author 401 B. Parameters Specification There are different parameters considered for the execution, which are used for handover campaign. These parameters are assigned the default values during execution. Table I explains lena-dual-stripe parameter configuration for handover campaign [7]. TABLE I LENA-DUAL-STRIPE PARAMETER CONFIGURATION FOR HANDOVER CAMPAIGN Parameter name value Description simtime 50 seconds simulation duration nblocks Disabling apartment buildings and femtocells nmacroenbsites 7=Number of macrocell sites (each site has 3 cells) nmacroenbsitesx 2 the macrocell sites will be positioned in a formation intersitedistance 500 m distance between adjacent macrocell sites macroenbtxpowerdbm 46 dbm Tx power for each macro cell epc Enable EPC mode epcdl Enable full-buffer DL traffic epcul Enable full-buffer UL traffic useudp Disable UDP traffic and enable TCP instead Determines number of UEs macrouedensity (translates to 48 UEs in our simulation) outdoorueminspeed Minimum UE movement speed in m/s (60 kmph) outdooruemaxspeed Maximum UE movement speed in m/s (60 kmph) macroenbbandwidth 5 MHz DL and UL bandwidth generaterem (Optional) For plotting the Radio Environment Map Some of the required assumptions are not available as parameters of lena-dual-stripe. In this case, author override the default attributes, as shown in Table II which explains overriding default attributes for handover campaign [7].The table contains the default parameter value name such as different handover algorithms, No-op, A2-A4-Rsrq, A3-Rsrp algorithm and hybrid algorithm can also add as default parameter. Table II also gives description about file names which are generated during execution. TABLE II OVERRIDING DEFAULT ATTRIBUTES FOR HANDOVER CAMPAIGN Parameter value name HandoverAlgorithm Description NoOpHandoverAlgorithm A3RsrpHandoverAlgorithm A2A4RsrqHandoverAlgorithm

5 Scheduler UseIdealRrc DlRlcOutputFilename UlRlcOutputFilename DlRsrpSinrFilename UlSinrFilename Proportional Fair scheduler Ideal RRC protocol=1 File name for DL RLC trace output File name for UL RLC trace output File name for DL PHY RSRP/SINR trace output File name for UL PHY SINR trace output C. Comparison Study NS3 provides different ways for passing configuration values into a simulation. For execution authors are using the command line arguments. It is basically done by appending the parameters and their values to the waf call during individual simulation [7]. So the waf call is same for all handover simulations. The -RngRun=1 argument is used for setting the run number by the random number generator in the simulation. -generaterem=1 argument is to generate the files necessary for generating the Radio Environment Map (REM) of the simulation. The fig 6 shows the position of enodebs and UEs at the beginning of a simulation using RngRun = 1 [7]. per execution The performance analysis of the proposed hybrid algorithm is conducted by comparing it with the existing algorithms using NS-3 network simulator. The first version of the algorithm has been implemented and the work is under progress to improve the results. V. CONCLUSION The authors dealt with 3 handover algorithms No-op, A2-A4-Rsrq, and A3-Rsrp(Strongest) algorithms, and proposed new Hybrid Algorithm. The paper explains the use hybrid algorithm in LTE module for handover management that helps in 4G networks which is the combination of A2-A4-Rsrq and A3-Rsrp algorithm. Here, the performance analysis of different parameters; throughput, SINR, and number of handover is conducted by comparing with existing algorithms using NS3. The first version of the algorithm has been implemented and the work is under progress to improve the results. A. Future Work In future, authors will improve the performance of proposed algorithm even better with respect to other algorithms. The proposed Hybrid algorithm is in development stage, which will be implemented further to increase throughput and SINR by comparing with existing handover algorithms. REFERENCES Fig. 6. REM obtained from a simulation in handover campaign After hours of running, the simulation campaign will eventually end. Post-processing is performed on the produced simulation output to obtain meaningful information out of it. GNU Octave is used for processing of throughput and SINR data and uses simple shell scripting to count the number of handover in the log file. The results show different handover algorithms in a mobility simulation which aims to improve both throughput and SINR significantly. The Table III shows the handover statistics of all the algorithms including our new hybrid algorithm when RngRun is set to unity. [1] S. Shukla, V. Khare, S. Garg, and P. Sharma, Comparative study of 1g, 2g, 3g and 4g. [2] A. Kumar and Suman, Comparision of 3g wireless networks and 4g wireless networks, International Journal of Electronics and Communication Engineering, vol. 6, no. 1, pp. 1 8, [3] A. Fouda, A. N. Ragab, A. Esswie, M. Marzban, A. Naser, M. Rehan, Ibrahim et al., Real-time video streaming over ns3-based emulated lte networks. [4] Design documentation, [5] Handover algorithm and procedure in lte, [6] Introduction, html. [7] User documentation, TABLE III RESULTS OF HANDOVER CAMPAIGN ANALYSIS Statistics No-op A2-A4- RSRQ A3-Rsrp Hybrid DL system throughput e e+ 04 UL system throughput DL SINR db db db db UL SINR db db db 0dB Number of handovers