Solving State Explosion Problem in Analytical Modeling of Next Generation Wireless Systems (NGWS): A Layered Approach

H. Birkan Yılmaz

yilmhuse@boun.edu.tr

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OUTLINE

• INTRODUCTION• NGWS DESIGN GOALS

• NGWS DEFINITIONS & NOTATIONS• AREA DEFINITION

• NEXT GENERATION CALL ADMISSION CONTROL (NGCAC)

• WHAT WE DID• WHAT WE ARE DOING• NUMERICAL RESULTS• FUTURE WORK

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INTRODUCTION

• NGWS incorporate multiple subsystems• PCS, WLAN, WiMAX, Satellite, ...• High bandwidth• Nomadic access

• Concept of integrating two or more communication systems is already in use

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LITERATURE SURVEY

• Akyildiz et. al.• AdapNet: An Adaptive Protocol Suite• Boundary Location Register

• Priscoli• Interworking of a Satellite System With the Terrestrial Networks

• Signaling Issues• Functional organization of the described interface

• Buddhikot et. al.• WLAN/CDMA2000 Interworking

• Ghaheri-Niri and Tafazolli• Cordless Cellular Network Integration for the 3rd Generation Personal

Communication Systems

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NGWS DESIGN GOALS

• Support for the “best” network selection

• Mechanism to ensure high-quality and security

• Seamless inter-system mobility

• Scalable architecture (any # of wireless systems)

• QoS provisioning

IP is recognized to become the core part of NGWS to support ubiquitous communication

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EXAMPLE INTERCONNECTION

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NGWS DEFINITIONS & NOTATIONS

• NGWS = (, HR) is the set of subsystems• HR is the global home register

• The ith access node of subsystems s is denoted by

• The set of all access nodes is denoted by

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SELECTION OF SUBSYSTEMS

• a

• a

• a

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AREA DEFINITION

• Classical wireless systems• Service area is split into cells

• NGWS• Multiple subsystems serving service area• Differentiate service area wrt accessible subsystems• Areas

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AREA EXAMPLE

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AREA PARAMETERS

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NEXT GENERATION CALL ADMISSION CONTROL (NGCAC)

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WHAT WE DID

• We derived transition probabilities in the first analytical model of NGWS

• State space explodes (Simple Topology)• 65 944 160 601 201 states• 8 962 362 486 784 effective states

• We assumed “The system operates in last three ‘layers’”

• Results can be found in• Tuna Tugcu, H. Birkan Yilmaz, and Feodor Vainstein, “Analytical

Modeling of CAC in Next Generation Wireless Systems”, Computer Networks, vol. 50, no. 17, pp. 3466 - 3484, December 2006.

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WHAT WE ARE DOING

• AVERAGE LAYER FLOW APPROXIMATION (ALFA)• Idea

• Introduce “layer” concept and represent states in a layer with one state

• Consider markov chain• Approximate “flow” between layers

• Not necessary to create all states (infeasible)• Randomly create states from a layer and approximate layer out flow

(feasible)• Solve by power method (Iteration)

• More complex scenarios are possible

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NUMERICAL RESULTS

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NUMERICAL RESULTS cont’d

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NUMERICAL RESULTS cont’d

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FUTURE WORK

• Confidence Intervals for ALFA Approximation

• Differentiating “homogeneous states” in layers (ALFA2) and adding new metric for quality of the network

• New NGCAC scheme (load balancing)

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QUESTIONS