Multi Parameter Based Vertical Handoff Decision

in Next Generations Networks

Presentation by:

Anita, Lecturer, Computer Science & Engg. Deptt., DCR University of Science & Tech., Murthal, Sonipat, India.

Dr. Nupur Prakash, Professor and Dean, School of Information Tech., GGS Indraprastha University, New Delhi, India.

Vertical Handoff

Vertical Handoff means handoff is between two network access points or Base Stations that uses the different network access technologies.

Steps of Vertical Handoff

System Discovery: Mobile terminals equipped with multiple interfaces deploy a system discovery agent to determine which networks can be used and the services available in each network.

Handoff decision: Based on several parameters like RSS, availability of free channel and service charges, the mobile devices determine which network it should connect to.

Handoff execution: The connections are rerouted from the existing network to the new network in a seamless manner.

Overlay Structure

Cellular coverage

MT --

WLAN1

MT

WLAN2

Reasons for integration of the IEEE 802.11 WLAN and cellular 3G systems

WLAN and cellular networks coexist

Many cellular devices support dual RF interfaces for WLAN and cellular access

WLAN and cellular networks are complementary technologies.

Vertical Handoff Decision

The classes of metrics in the envisioned 4G system are:

Service type: if it is time bound (i.e. real time or non real time application) or reliable.

Monetary cost: Different networks employ different billing strategies and operational costs that may affect user’s choice of Handoff.

Network Conditions: network parameters like traffic, available bandwidth and number of users.

System Performance: has certain crucial parameters like battery power. If battery level is low the user may switch to a network with lower power requirements.

Mobile terminal condition: includes dynamic factors like moving speed, moving pattern of the terminal.

User preference: can be added to cater special requests.

Based on these above classes, seven input parameters are proposed for vertical Handoff decision.

Input Parameters for VHD

1. Available Bandwidth (BAV): It is the amount of unused bandwidth of the candidate Base Station (BS) or Access point (AP).WLAN have greater bandwidth than cellular Network (UMTS).

2. Speed of mobile terminal (VMT ): It is the velocity with which the mobile terminal (MT) is moving. For high speed MT, UMTS is preferred because of greater coverage area.

3. Number of Users (UN): The QoS of WLAN is UN sensitive. As the number of users increase, the collisions increase and results in poor QoS.

4. Received Signal Strength (RSS): It is the strength of the signal received, as the RSS of the neighboring network rises above the threshold the Vertical Handoff is feasible i.e. the handoff takes place if and only if RSS of the BS or AP is above the threshold.

Input Parameters for VHD

5. Battery Level (BL): The attachment to the closest AP or BS is known to consume the least power for individual mobile devices at a given instant. So if battery level is low the MT must handoff to the closest AP or BS provided RSS is above threshold. The number of users also increases the congestion and in turn even the nearest AP or BS consumes more power.

6. Cost of operation (C): It is the cost of the operation network. If the cost is above a certain threshold value, the user will consider that network to be too expensive to be viable.

7. Traffic Type ( TT ): It could be either real time or non-real time. For real time applications i.e. time bound services cellular networks are preferred and for non-real time applications WLAN is preferred.

Why Neuro-Fuzzy approach

• This blends elements of uncertainty of data by using Fuzzy and adaptive capabilities by using Neural network.

• It can tap the primary strength of fuzzy networks that in a system can be initialized by the existing semantic knowledge and have structured information extracted from it in an interpretable format.

• The reasons for using neural network are

parallel processing of information

Inherent learning capabilities

Proposed Neuro-Fuzzy Vertical Handoff Decision Steps

The various steps involved in the proposed system are :

Fuzzification : Converts real valued data into a fuzzified representation with the help of membership functions.

Training: The neural network is trained with the fuzzified information

Defuzzification: De-fuzzify the result to produce real values of the desired output. After the system is trained to satisfaction, fuzzy rules can be extracted from the trained neural network.

Membership Functions (mf)

The mf associated with a given fuzzy set maps a crisp input value to its appropriate membership value. Various mf are :

Piecewise linear functions: These are simple straight line mf namely trimf and trapmf.

Gaussian Distribution functions: These achieve smoothness but are unable to specify asymmetric mf. These are gaussmf, guass2mf and gbellmf.

Sigmoid Curve: Asymmetric and closed mf are sigmf, dsigmf and psigmf.

Quadratic and cubic polynomial curves: Three related mf are Z, S and Pi curves are named so because of their shape.

Since trimf is simple we use this mf for fuzzification as selective expansive mf function will further increase the complexity of system.

Membership Function for BAV

0

0.2

0.4

0.6

0.8

1

1.2

0 144 384 2000 54000 56000

Bandwidth (in Kbps)

Me

mb

ers

hip

Va

lue

Low Medium High Very_High

Membership Function for VMT

Very_Slow Slow Medium High

0

0.2

0.4

0.6

0.8

1

1.2

0.1 2 10 22 54 76

speed (in Meters/Sec)

Mem

ber

ship

Val

ue

Membership Values

Based on membership functions, the parameters are assigned the fuzzy membership values between [ 0 1]. BAV = {Low, Medium, High, Very High} = {LO, ME, HI, VH}

VMT = {Very slow, slow, Medium, High Speed} = { VS, SL,MS, HS }

UN = { Few, less, medium, more} = { FE, LE, ME, MO }

RSS = {Below-thresh, Above- thresh} = {BT, AT}

BL = {Very Low, Low, Medium, High} = { VL, LO, ME, HI }

C = {Low, Medium, High, Very High} = { LO, ME, HI, VH }

TT = { Non-real type, real type } = { NT, RT }

HandoffC = { Fit, Medium Fit, Low Fit, Not Fit } = { FI , MF , LF , NF }

The VMT and BL are the two input parameters related to mobile terminal and all other parameters are related to network.

Rules of Fuzzy Inference Engine

S No.

BAV

VMT UN BL C TT U to

WW to U

Remarks

1 LO/ME/HI VS/SL FE/LE ME/HI LC/MC NT FI MF This is ideal condition with BAV requirement not too high & only difference is TT=NT is supported by WLAN & TT = RT by UMTS.

2 LO/ME/HI VS/SL FE/LE ME/HI LC/MC RT MF FI

3 LO/ME/HI VS/SL FE/LE ME/HI HC NT NF LF High cost can only be supported by UMTS, because WLAN supports low cost. 4 LO/ME/HI VS/SL FE/LE ME/HI HC RT NF MF

5 LO/ME/HI VS/SL FE/LE ME/HI VH (VC) NT/RT NF NF Not viable because of very high cost

6 LO/ME/HI VS/SL FE/LE VL/LO LC/MC NT LF LF For BL=VL/LO wide coverage area is preferred, so that handoff is not required frequently.

7 LO/ME/HI VS/SL FE/LE VL/LO LC/MC RT NF MF

Vertical Handoff between WLAN and UMTS is not reversible i.e. the motive to handoff from WLAN to UMTS is quite different from UMTS to WLAN.

Rules of Fuzzy Inference Engine ( cont..2)

S No.

BAV

VMT UN BL C TT U to

WW to U

Remarks

8 LO/ME/HI VS/SL FE/LE VL/LO HC NT NF LFThough negative aspect, High cost is supported to some extend by UMTS & not by WLAN.

9 LO/ME/HI VS/SL FE/LE VL/LO HC RT NF MF

10 LO/ME/HI VS/SL FE/LE VL/LO VH NT/RT NF NF Not viable due to very high cost .

11 LO/ME/HI VS/SL ME ME/HI LC/MC NT LF MF As UN increases the QoS decreases as no. of users in WLAN share same channel ALOHA.

12 LO/ME/HI VS/SL ME ME/HI LC/MC RT NF F

13 LO/ME/HI VS/SL ME ME/HI HC NT NF MFHC is not supported by WLAN

14 LO/ME/HI VS/SL ME ME/HI HC RT NF F

Neural Network based VHD

A perceptron is created and it involves three main steps for calculation of weights by using supervised learning.

Initialization

Iterative Process

Termination

Flow chart for VHD

NN including connections (weights W & bias b) between neurons

Rule base Fuzzy Inference Engine

Target Vector TInput (P)

Trained weights W’

a= hardlim (W*P + b)

Calculate ΔW & ΔbIf e = 1, then ΔW = PTr

If e = -1, then ΔW= -PTr

Δb = (T-a) = e

Compare error e where e =T-a

Adjust weights

Wnew = Wold + ΔW bnew = bold + Δb

If e = 0,, ΔW = 0 , Δb= 0

ILLUSTRATION

Input (P) =

Neural networkInitial wts IW =[0 0 0 0 0 0 0]& Initial bias Ib=[0]; n = W*P + biasn= [0 0 0 0 ]hardlim(n) = {0 if n<0}{1 otherwise}

Rule base Fuzzy Inference Engine

(Rule No. 1)(Rule No. 1)

Trained weights W’=W & b’=b

a=hardlim(W*P+bias)a = [1 1 1 1 ]

e = 1, then ΔW =ePTr = PTr

e = -1,then ΔW = ePTr=-PTr

ΔW=[0 -1 -1 -1 -1 0 -1]Δb= (t-a) = [-3]

Compare error e

where e =T-ae=[ 0 -1 -1 -1]

Adjust weights Wnew = Wold + ΔWWnew=[ 0 -1 -1 -1 -1 0 -1]bnew = bold + Δb = [-3]

e = 0,e = 0, ΔW = 0, Δb = 0

Target Vector T= [1 0 0 0 ]

1 0 0 0

0 1 0 0

0 1 0 0

0 0 1 0

0 0 0 1

1 0 0 0

0 1 0 0

Epochs used in training

0 0.5 1 1.5 2 2.5 30

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

No. of Epochs

Tra

inin

g-B

lue

Goal-B

lack

Goal achieved in 3 Epochs

Defuzzification methods

The aggregate of a fuzzy set encompasses a range of output values so these values must be defuzzified in order to resolve a single output value from the set. Various defuzzification methods used by inference systems are:

• Centroid• Bisector• Middle of maximum/largest of

maximum/smallest of maximum

Conclusion 1. The multi parameter based vertical handoff decision helps determine

which network it should handoff to (as incorrect handoff decision will result in poor QoS and at times may even break off current communication).2. The multi parameter based Vertical Handoff decision would becomes efficient and has reduced complexity if NN is used. 3. The use of metrics increases the complexity of handoff process, making

the handoff decision more and more slow.4. The use of multi parameter based Vertical Handoff Decision implemented using NN, provides blue print for hardware implementation and is thus computationally efficient.

The future work involves the performance analysis of this multi parameter based Vertical Handoff decision with the conventional VHDA on parameters like :- Complexity Dropped Packets, Retransmitted packets comparison, WLAN delay comparison.

THANKS

Single perceptron

Back

Rules of Fuzzy Inference Engine (contd..3)

S No.

BAV

VMT UN BL C TT U-

>WW->U

Remarks

15 LO/ME/HI VS/SL ME ME/HI VH NT/RT NF NF Not viable due to high cost. Medium no. of users & VL/LO

BL results in disruption of connections. As UN = MO, more no. of users in N/W even if BL = MO/HI is not supported in (W+U), Because QoS falls below acceptable levels.

16 LO/ME/HI VS/SL ME VL/LO VH NT/RT NF NF

17 LO/ME/HI VS/SL MO VL/LO VH NT/RT NF NF

18 LO/ME/HI MS FE/LE(MS)

ME/HI LC/MC NT NF MF

If VMT = MS then U -› W is NF, because MT very frequently moves out of small coverage area of WLAN , therefore frequency Handoff.

19 LO/ME/HI MS FE/LE ME/HI LC/MC RT NF HF

20 LO/ME/HI MS FE/LE ME/HI HC NT NF MF

21 LO/ME/HI MS FE/LE ME/HI HC RT NF HF

Rules of Fuzzy Inference Engine (contd..4)

S No.

BAV

VMT

UN BL C TT U->W

W->U

Remarks

22 LO/ME/HI MS FE/LE ME/HI VC NT/RT NF NF Not viable due to very High cost.

23 LO/ME/HI MS FE/LE VL/LO LC/MC NT NF NF VL/LO =BL with MS is

still difficult then VMT VS/SL as thus would initiate more Handoff, with VL/LO battery life.

24 LO/ME/HI MS FE/LE VL/LO LC/MC RT NF LF

25 LO/ME/HI MS FE/LE VL/LO HC NT NF NFAs high cost of operation of N/W is hindrance for W ->U Handoff.26 LO/ME/HI MS FE/LE VL/LO HC RT NF LF

27 LO/ME/HI MS FE/LE VL/LO VC NT/RT NF NF Not feasible / viable.

28 LO/ME/HI MS ME ME/HI LC/MC NT NF MF If VMT= MS & UN is

high the QoS is reduced and high BLis required.

29 LO/ME/HI MS ME ME/HI LC/MC RT NF HF

Rules of Fuzzy Inference Engine (contd..5)

S No.

BAV

VMT

UN BL C TT U->W

W->U

Remarks

30 LO/ME/HI MS ME ME/HI HC NT NF LF

31 LO/ME/HI MS ME ME/HI HC RT NF MF

32 LO/ME/HI MS ME ME/HI VC NT/RT NF NF Not feasible.

33 LO/ME/HI MS ME VL/LO VC NT/RT NF NF Because high speed MT & more no. of users causes congestion which can’t

be controlled & if BL = VL/LO, Handoff is low.

34 LO/ME/HI MS MO VL/LO VC NT/RT NF NF Because high speed MT & too many users causes congestion and neither WLAN nor UMTS can handle these many users as QoS reduces sharply.

35 LO/ME/HI HS MO VL/LO VC NT/RT NF NF Not able to Handoff because of high speed.

36 VH Same as BAV ie LO/ME/HI NF Same as BAV LO/ME/HI & NF for

W -> U as high BW is not supported by UMTS.