Fuzzy Handover in Heterogeneous Mobile Networks
TD-01-010-S
Presenter: Y.F. HuUniversity of Bradford, UK
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Contents
q Introductionq Handover Criteriaq Handover Algorithm
• Initiation• Decision
q Simulation Modelq Resultsq Conclusion and Further Work
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Introduction
q Integration of a satellite network into a set of terrestrial wireless networks consisting of different mobile networks:• Satellite• Universal Mobile Telecommunications System (UMTS)• General Packet Radio Service (GPRS)
q Objectives:• Propose a handover scheme which takes into account
different QoS parameters and user requirements• Separates the process of handover initiation and
handover decision.
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Network Architecture
MTSAT
MTUMTS
MTGPRS
T-IW
U
TE
NOC
FES
GaT
UTRAN
BSS
SGSN
HLR
GGSN
MSC
HLRSGSN
ER
ER
ER
HA
HA
IP based TE
IP based TE
3G3G
2G
FA
FA
FA
UMTS Core Network
GPRS Core Network
N-IWU
NIU
Logical connection between entities
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Handover Criteria
q Technology Based QoS Parameters:• Signal Strength• Network Latency• Available Bandwidth• Network Coverage and Reliability
q User Based QoS Parameters:• User’s Preferences/ Priority• Perceived QoS• Charging Models• Service Provision
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Why Fuzzy Logic?
q Can be used to solve highly complex problems where it is difficult to create a suitable mathematical model.
q Used to represent processes that are imprecise by nature.
q In fuzzy logic, an event or situation does not have to be either ‘true’ or ‘false’. Instead, these events can be classed as ‘quite true’, fairly true’, ‘very true’ or ‘not true’.
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Block Diagram for Handover
Network CoverageQoS Perceived
Bandwidth
LatencyReliability
Battery Status
Cost
Priority
SS’
QoS Application Used
Priority SegmentProhibited Segment
Terminal Type
Bit Error RateSystem Fuzzifier
Averaging SS SS’
FuzzyController
NewAVG INT
Inference
Fuzzy Rules
Defuzzifier Handover
Bandwidth
LatencyReliability
Battery Status
Cost
Priority
SS’
W_Bandwidth
W_LatencyW_Reliability
W_Battery Status
W_Cost
W_Priority
W_SS’
User
FuzzyOrdinalRanking
DetermineWeighting of Criteria M
ultip
le O
bjec
tive
Dec
isio
n M
akin
g
Chosen Segment
Handover Initiation
Handover Decision
Yes
No
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Handover Initiation
q Consists of 3 different stagesq 1st stage: Fuzzification
• Data collected from the system is fed into a fuzzifier, to be converted into fuzzy sets.
µ
SS1 SS2 SS3
1Medium StrongWeak
Signal Strength
µ
SS1 SS2 SS3
1Medium StrongWeak
Signal Strength
(a) Fuzzy Set (b) Crisp Set
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Handover Initiation
• Membership values are obtained by mapping the values of a particular parameter onto a membership function.
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Handover Initiation
q 2nd Stage: Inference Engine• A Set of IF-THEN rules is applied to the system• for eg:
• IF signal strength is strong AND QoS is good AND Bit Error Rate is Medium, AND Network Coverage is Medium, THEN handover =NO
SignalStrength
PerceivedQoS
BER Coverage Dec
Weak YMedium Medium Medium Bad PNMedium Medium Medium Medium PNStrong Good Medium Bad NStrong………
Good…….
Medium………..
Medium……….
IF-THENRuleà
N…
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Handover Initiationq 3rd Stage: Defuzzification
• combining the results of the first and second stage• Defuzzification performed using the centroid
calculation method, in which the center of gravity of the membership function is computed.
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Handover Decision
q Uses a Fuzzy Multiple Objectives Decision Making Algorithm.
q Objectives: Select a target segment that can fulfil the following objectives:• Low Cost• Good Signal Strength• Optimum Bandwidth• Low Network Latency• High Reliability• Long Battery Life
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Handover Decision
q Consists of 2 different stages.q Stage 1: Ordinal Ranking and Weighting of Criteria
• Ranking Procedure: Used to compare the performance of each segments for a particular handover decision criterion.
• for eg: if the following values are assigned to the three segments, GPRS performs best for that particular criteria followed by UMTS and SAT.
=SATUMTSGPRS
C 4925.0,6667.0,0000.11
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Handover Decision
• Weighting of Criteria: Developed by obtaining a ratio scale for the criteria based on a paired comparison of each criterion.
• Assume that C={C1,...CP } is a set of p handover criteria. A pairwise comparison of each criterion with respect to the other criteria is performed to obtain matrix, B:
• The final weighting is obtained by finding the unit eigenvector of the matrix, W, which corresponds to the maximum eigenvalue of B, and then multiplying the values with the number of criteria.
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Handover Decision
q 2nd Stage: Decision Making• The final decision is obtained by raising the fuzzy set
determined in stage 1 to α.• Therefore, the fuzzy subsets then becomes:
n
nCCCCCD ααααα ∩∩∩∩= ...4321
4321
⇒
=
131
311111
31313333
331333313
13
111331
131
311133
113
13
13
13
1131
131
313331
7
6
5
4
3
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1
7654321
CCCCCCC
CCCCCCC
B
=
1911.05108.07083.01959.01959.01276.03284.0
W ⇒α
==
1.33753.5756495821.37111.37110.89322.2988
Wn
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Simulation Model (Handover Initiation)
q Handover Initiation• Objectives: demonstrates how the value of the
handover factor changes when the inputs of the are varied using a normal distribution.
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Results and Analysis
q When values fed into the fuzzifier are weak, handover factor is high and vice versa.
q Results shows that the algorithm behaves correctly under different operating conditions.
00.10.20.30.4
0.50.60.70.80.9
1
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Handover Factor, h
P
Scenario 1 Scanario 2 Scenario 3
P(H
F≤h
)
Handover Initiation
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Simulation Model (Handover Decision)
q Handover Decision• Objectives: Demonstrates that by changing certain
inputs into the system, the choice of the selected segment will differ.
Criteria Attributes Applications Real-Time Delay Sensitive (A)
Real-Time, Delay Insensitive (B) Non Real-Time, Interactive (C)
Non Real-Time, Non Interactive (D) Net. Attr. GPRS UMTS SAT
Cost Charging 0.90 0.80 0.70 Bandwidth 0.80 0.90 0.70
Latency 0.60 0.80 0.50 Reliability 0.90 0.90 0.50
QoS
Sig. Str. 0.70 0.69 0.80 Battery 0.90 0.60 0.70 Others
Segment Priority 0.50 0.50 0.50
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Results and Analysis
012
3456
Charging Bandwidth Latency Reliability Sig.Strength
Battery Priority
A
B
C
D
0
1
2
3
4
5
6
Charging Bandwidth Latency Reliability Sig. Strength Battery Priority
A
B
C
D
Case (a)
Case (b)
Conditions Result
Real-Time Delay Sensitive UMTS, SAT
Real-Time, Delay Insensitive UMTS, SAT
Non Real-Time, Interactive GPRS, UMTS, SAT
Case (a)
Cost
Non Real-Time, Non Interactive GPRS, UMTS, SAT
Real-Time Delay Sensitive UMTS, SAT
Real-Time, Delay Insensitive SAT, UMTS
Non Real-Time, Interactive GPRS, UMTS, SAT
Case (b)
Quality
Non Real-Time, Non Interactive SAT, GPRS, UMTS
q Results show that a user’s requirements play an important role in determining the weighting of the criteria. The weightings arebased on user’s preferences and applications.
q In addition, it is also found that the chosen segment is not dependent only on one criterion but also takes into account other factors as well.
University of Bradford
COST272 1st MCM, Toulouse, 11-12 October 2001
Conclusion
q A handover algorithm based on the concept of fuzzy logic has been presented.
q The algorithm allows the system to decide not only on the time to initiate a handover but also on the best segment to transfer to.
q When tested under different environments, the algorithm produces correct handover responses.
q Thus, fuzzy logic offers a feasible solution in solving handover problems in a heterogeneous environment.