OMNeT++ Framework for Efficient Simulation of Vertical...

TerminologyMotivation

The simulation frameworkResults

Conclusions and future work

OMNeT++ Framework for Efficient Simulation

of Vertical Handover Decision Algorithms

Doru Todinca Cosmin Cernazanu-Glavan

Department of Computers

Politehnica University of Timisoara

SACI 2013

D. Todinca, C. Cernazanu-Glavan OMNeT++ Framework for VHO Decision Algorithms




Outline

1 Terminology

2 Motivation

3 The simulation frameworkGeneral aspects regarding the simulation frameworkThe simulation model

4 Results

5 Conclusions and future work





Handover, Vertical handover

A handover (HO) takes place when a mobile user disconnectsfrom the base station that serves its current cell and connectsto the base station that serves another cell

When the two cells use different radio access technologies(RAT) or if they belong to different network operators, theprocess is called vertical handover (VHO)

otherwise the process is a horizontal handover (HHO)

VHO consists of 3 phases:

1 network discovery (handover information gathering)2 network selection decision3 handover execution

Only network selection decision is discussed in this work





The Importance of VHO

The wireless networks of the future (NGN - Next GenerationNetworks, or 4G) will consist of different radio accesstechnologies and a common, IP based, core network

It means that the importance of VHO will increase

While the HHO is a well established technical process, theVHO is much more complex, being a hot research topic





The Importance of VHO

The VHO decision can be based on different criteria:

technical factors, like bandwidth, throughput, received signalstrength, error rate, battery state, etccostsubjective factors, like user’s perceived quality of service (QoS)or even user’s preference for a certain radio access technologyor for a certain operator

VHO algorithms for network selection decision are based on

artificial intelligence (AI) methods (fuzzy logic, neuralnetworks)multicriteria decision making (MDM) methodsother methods (queueing, Markov decision processes, etc)combinations of these methods: neuro-fuzzy, fuzzy MDM, etc





The need of a simulation framework for VHO algorithms

There exist many VHO network selection algorithms

We need to compare their performance by simulation

For a fair comparison, the algorithms should be simulated inthe same conditions and in the same framework

Our goal is to develop a framework for efficient simulation ofVHO selection algorithms.

The chosen simulation tool is OMNeT++ (an open-sourcenetwork simulator)





General aspects regarding the simulation frameworkThe simulation model

Requirements for the simulation framework

1 To be flexible and modular

to include different radio access technologies (EGPRS, UMTS,LTE, WLAN, etc)to model different VHO selection algorithms

2 To be realized at a high level of abstraction

the detailed simulation models (close to emulators, thatimplement each protocol) need extremely long simulationsradio access technologies are too complex for a detailedimplementation, involving many network nodes (BTS, BSC,SGSN, etc) and many protocols

3 To be able to include the significant details of a radio accesstechnology and to increase the level of details, if necessary.






Simulation model: the time granularity

The events in a real VHO system have very different timegranularities:

scheduling of radio resources: intervals of milliseconds (from1ms in LTE to 20 ms in EGPRS)link adaptation to radio conditions: intervals hundreds ofmilliseconds to seconds (milliseconds in LTE)new data is generated at intervals of secondsusers move from or into a cell at tens of seconds or minutes

We model the data transfer at IP level, considering that,during the transfer of an IP packet, the radio conditions andthe cell load remain unchanged






Simulation model: the levels of the model

1 The system level

ensures a modular and flexible structure of the modelcontains the main modules (see next figure)

2 A technology independent high-level model of a radio accessnetwork (RAN)

can be used for any radio technologydata transfer is modeled at IP level:

the length of a data unit (a file) is decreased with the lengthof an IP packeta delay element models the time needed for the transfer of anIP packet

3 A technology related model of a RAN

models the changes of the radio conditions and of the network(cell) loadis specific to each radio technology






The model of a VHO system

Figure : The OMNeT++ model of a VHO systemD. Todinca, C. Cernazanu-Glavan OMNeT++ Framework for VHO Decision Algorithms





The model of a radio access network

Figure : The OMNeT++ model of a radio access network






The model of a cell

Figure : The OMNeT++ model of an UMTS cell






The model of a cell

the load condition generator module (loadCondGen)

models the increase or decrease of the cell loadthis corresponds to a user coming into the cell or leaving thecellthe cell capacity is decreased (or increased) by the resourcesconsumed (released) by that user

Radio condition generator module (radioCondGen)

models the changes of quality of the radio link for the modeleduser

external condition analyzer (extCondAnlyzr)

receives informations from the previous two modulescomputes the transfer rate of the modeled userthe transfer rate is sent to the delay element





The validation of our framework

We use the consumer surplus (CS) algorithm (Ormond et al[9]) in order to validate our framework

We compare our results with the results obtained in [9] with amore detailed simulation model

We use a similar simulation scenario:

FTP trafficfile lengths from 20 kB to 200 kB, like Ormond [9]the selection algorithm is invoked for each fileIP packets of 1000 bytes length

Unlike Ormond, we accept the files that exceed the tolerateddelay (the late files) and count them





Simulation setup and results

Three simulation configurations:1 two UMTS networks (cells), one ‘bad’ and one ‘good’ (with

better radio conditions)2 two UMTS cells, the ‘bad’ cell being congested (network load

close to its maximum)3 one UMTS and one EGPRS cell

All simulations performed for 100000 seconds, simulation time6 file lengths, 10 runs for each file lengthWe measured the mean file delay (next figure)Our results are quite similar with Olga Ormond’s results,The differences are around 20%, due to the differences in thesimulation modelsWe obtain very short simulation times: around 260 seconds ona laptop with Intel Core i7-2670QM CPU at 2.20 GHz,Windows 7 Enterprise 64bits





Results: mean file delay

Figure : Mean file delay for CS algorithm and two UMTS networks





Conclusions

We have implemented an OMNeT++ framework forsimulation of VHO selection algorithms

We implemented two radio access technologies: EGPRS andUMTS

We implemented the consumer surplus network selectionalgorithm in order to validate the framework

Our results with CS are quite close to the results obtained byOrmond et al

Our simulations are very short, which prove the efficiency ofour framework





Future work

To include other radio technologies in the framework: HSUPAand HSDPA, LTE, WLAN

To implement other network selection algorithms and tocompare their performance

To perform a sensitivity analysis in order to see how differentalgorithms behave for different parameter values

To obtain new VHO selection algorithms.


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