Performance%20Analysis%20of%20a%20Preemptive%20and%20Priority%20Reservation%20Handoff%20Scheme%20for%20Integrated%20Service-Based%20Wireless%20Mobile%20Networks%20by%20Jingao%20Wang,%20Quing-An%20Zeng,%20and%20Dharma%20P.%20Agrawal

1
Performance Analysis of a Preemptive and Priority
Reservation Handoff Scheme for Integrated
Service-Based Wireless Mobile Networksby Jingao
Wang, Quing-An Zeng, and Dharma P. Agrawal

• Presented by Okan Yilmaz
• CS 6204 Mobile Computing
• Virginia Tech
• Fall 2005

2
Abstract

• Analytical Model Performance Analysis
• Call Types
• Originating calls
• Handoff requests
• Service Types
• Real-time
• Non-real-time
• Partitioning based system model
• Real-time service calls only
• Non-real-time service calls only
• Handoff requests only
• Preemptive priority handoff scheme

3
Abstract (cont)

• Multidimensional Markov Model to estimate
• Blocking probability of originating calls
• Forced termination probability of handoff calls
• Average transmission delays
• Simulation and Performance Analysis
• Different call holding times
• Several cell dwell time distributions
• Results
• Significantly reduces the forced termination
  probability of real-time calls
• Negligible packet loss of non-real-time calls

4
Introduction

• 2G Networks
• Limited and far from acceptable
• Voice
• Short message
• Low speed data
• 3G Networks
• Demand for Integrated services
• Business customers
• Any time, any place
• Employees, key customers
• e.g., brokerage, banking, emergency services,
  traffic reporting, navigation, gambling, etc.
• Wireless and VLSI Technology
• Multi-media-ready cell phones, pocket PCs, Palms

5
Challenges of Integrated Services

• True combination of real-time and non-real-time
  services
• Maximize the utilization of network
  infrastructure
• Quality of service (QoS)
• Handoff handling
• Forced termination of an outgoing call is more
  annoying than blocking of a new call

6
Handoffs

• Handoff changing parameters of a channel
• Frequency, time slot, spreading code, or
  combination of them
• When crossing cell boundary or deteriorating
  signal quality
• Cell structure
• Support a drastic increase of demand
• Microcell, picocell, hybrid cell
• Smaller cells ? More handoffs

7
Handoff Design Issues

• Forced termination versus new call blocking
• Increased channel utilization in a fair manner
• Goal
• Minimization of forced termination of real-time
  service
• Without drastically sacrificing the other QoS
  parameters
• Several studies based on voice based cellular
  networks
• Need for support of multiple service types
  simultaneously
• Keys for a good scheme
• Service dependent
• Delay sensitivity non-real-time versus real-time
• Preemptive model priority reservation handoff

8
SYSTEM MODEL

• Homogenous cell with fixed number of S channels
• Reference cell approach
• Call types
• Real-time originating call MU dials a number to
  place a real-time call
• Real-time handoff request MU holding a channel
  enters the handoff area
• Non-real-time originating call MU places a
  non-real-time call
• Non-real-time handoff request Non-real-time MU
  holding a channel approaches and crosses a cell
  boundary
• Cell boundary The points where the received
  signal strength between two adjacent cells is
  equal

9
Notation

• ?OR arrival rate of real-time originating calls
• ?HR arrival rate of real-time handoff requests
• ?ON arrival rate of non-real-time originating
  calls
• ?HN arrival rate of non-real-time handoff
  requests
• RC real-time service channels group with
  capacity SR
• CC common handoff channels group with capacity
  SC
• NC non-real-time service channels group with
  capacity SN
• RT only In CC, real-time service channels
  reserved exclusively for real-time handoff calls
  with capacity SE
• CH In CC, channels that can be used by both
  real-time and non-real-time handoff calls with
  capacity SC - SE
• RHRQ real-time service handoff request queue
  with capacity MR
• NHRQ non-real-time service handoff request queue
  with capacity MN

10
System model for a reference cell

• ?OR ?RC(SR)
• ?HR ?RC(SR) ? HC(Sc-Sc) ? RT(SE) ? RHRQ(MR)
• ?HN ?NC(SN) ? HC(Sc-Sc) ? NHRQ(MN)
• ?ON ?NC(SN)

11
Algorithm for Originating Calls
12
Algorithm for Handoff Requests
13
System Design (cont)

• Preemptive procedure real-time handoff request
  calls preempt non-real-time handoff request calls
  if a non-real-time in CC and NHRQ is not full
• Real-time handoff requests may preempt
  non-real-time handoff requests irrespective of
  NHRQ being full or not
• No need if very large NHRQ buffer
• Real-time handoff request are dropped
• If RHRQ is full (both RHRQ and NHRQ are full in
  preemptive scheme)
• If the handoff request in RHRQ cannot get
  service until it moves out of the handoff area

14
System Design (cont)

• Non-real-time handoff requests will never be
  dropped
• If NHRQ is large enough (not necessarily be
  infinite)
• Because the non-real-time handoff request is
  transferred from the reference cell to another
  cell
• Waiting time in NHRQ dwell time of
  non-real-time service subscribers
• Real-time handoff request calls can continue
  until signal strength becomes not enough to get
  service
• This is ignored in paper. It is assumed that the
  call is blocked.

15
Traffic Model

• Three characteristics
• Call arrival process
• Call holding time
• Cell dwell time
• Call arrival Poisson process
• Call holding time and cell dwell time
• Two approaches
• Traffic model general independent identically
  distributed (i.i.d.)
• Exponential, gamma, lognormal, hyper-exponential,
  hyper-Erlang
• Analytical model Users mobility, the shape and
  size of the cell, and exponential distribution
  are used to determine cell dwell and call holding
  time
• Paper uses the second for analytical modeling,
  both for numerical and simulation results

16
Dwell Time

• Two-dimensional fluid model
• fV(v) pdf of the speed V of MU
• EV mean of the speed of MU
• MU moves randomly any direction in 0,2?)
• Assumes uniform density of users

17
Cell Dwell Time

• Biased sampling theory in boundaries 1

• ? density of MUs in the cell
• NO number of cell outgoing MUs with moving speed
  v and v?v
• NT total number of cell outgoing MUs per unit
  time
• A area of the cell
• L length of the perimeter
• ?dwell average outgoing rate of an MU within a
  cell
• Tdwell cell dwell time with a random exponential
  distribution with mean 1/?dwell

18
Handoff Area Dwell Time

• fV(v) pdf of the speed of real-time service
  subscribers crossing cell boundary V
• D the length of moving path of mobile users in
  the handoff area
• Th dwell time of real-time service subscribers
  in the handoff area
• ETh Average handoff area dwell time
• Path length and velocity of MUs are independent

19
Channel Holding Time

• Exponential distribution
• TCR Call holding time of real-time calls
• TCN Call holding time of non-real-time calls
• ?CR Service rate of real-time calls
• ?CN Service rate of non-real-time calls
• TR Channel holding time of real-time service
  calls
• TN Channel holding time of non-real-time service
  calls

20
Arrival Process of Service Calls

• Poisson process
• ?OR arrival rate of real-time originating calls
• ?HR arrival rate of real-time handoff requests
• ?ON arrival rate of non-real-time originating
  calls
• ?HN arrival rate of non-real-time handoff
  requests
• Need to compute ?HR and ?HN from ?OR and ?ON,
  respectively
• Homogenous mobility pattern
• Mean number of incoming handoffs to reference
  cell mean number of outgoing calls from the
  reference cell

21
Arrival Process of Service Calls (cont)

• ECR average number of real-time calls holding
  channels in the reference cell
• ?OUTR departure rate of real-time handoff calls
  from the reference cell

22
Arrival Process of Service Calls (cont)

• ENN average number of both non-real-time
  service requests and calls in the reference cell
• ECN average number of non-real-time MUs
  holding channels in the reference cell
• ELN average length of NHRQ

• ? total arrival rate of calls

23
M/M/3/3

• M/M/3/3 2
• M Exponential or Poisson arrivals
• M Exponential or Poisson service
• 3 Number of servers
• 3 Maximum number of customers in the system
• P0 P1 P2 P31
• (??) P1 ? P0 2? P2
• Pblocking P3
• Throughput (1-P3) ?

24
PERFORMANCE ANALYSIS
i
j
k
m
l
25
Stable State diagram for (i1, j1, k1, l2, m0)
S SR SC SN 12 SR 6 SCSN3 SE1 MR5
MN50 NT3162
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Total number of states

• Four cases to consider
• Both RHRQ and NHRQ are empty
• 0 i SR0 j Sc - k 0 k Sc - SE 0 l
  SN m 0
• k0 ? j(0 .. Sc) Sc 1 possibilities
• k1 ? j(0 .. Sc -1) Sc possibilities
• k Sc-SE ? j(0 .. SE) SE 1 possibilities
• Total (Sc-SE 1) (Sc SE 2)/2 states
• N1(SR1)(Sc-SE 1)(Sc SE 2)(SN1)/2
  states
• RHRQ is not empty while NHRQ is empty
• i SR Sc lt j k
• i SR Sc-k1 j Sc MR k 0 k Sc-SE
  0l SN m0
• k0 ? j(Sc 1 .. Sc MR) MR possibilities
• k1 ? j(Sc .. Sc MR 1) MR possibilities
• k Sc-SE ? j(SE 1.. Sc MR) MR
  possibilities
• Total (Sc - SE 1) MR states
• N2(Sc - SE 1) MR (SN 1)/2 states

27
Total number of states (cont)

• RHRQ is empty NHRQ is not empty
• Sc-SE j k l SN
• 0i SR Sc-SE-k j Sc-k 0k Sc-SE lSN
  1m MN
• k 0 ? j(Sc - SE .. Sc) (SE 1) possibilities
• k 1 ? j(Sc SE - 1 .. Sc - 1) (SE 1)
  possibilities
• k Sc - SE ? j(0 .. SE) (SE 1) possibilities
• Total (Sc - SE 1) (SE 1) states
• N3 (SR 1) (Sc - SE 1) (SE 1) MN
• Both RHRQ and NHRQ are not empty
• i SR Sc lt j k l SN
• i SR Sc-k1 j Sc MR - k 0k Sc-SE
  lSN 1m MN
• k 0 ? j(Sc1 .. Sc MR) MR possibilities
• k 1 ? j(Sc .. Sc MR - 1) MR possibilities
• k Sc-SE ? j(SE 1.. SE MR) MR
  possibilities
• Total (Sc-SE 1) MR/2 states
• N4 (Sc-SE1) MR MN/2 states

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Normalizing Condition

• Both RHRQ and NHRQ are empty
• RHRQ is not empty while NHRQ is empty
• RHRQ is empty while NHRQ is not empty
• Both RHRQ and NHRQ are not empty

29
Average number of calls

• ECR average number of real-time calls holding
  channels in the reference cell
• 13 i j real-time calls
• 24 RC is full SC-k real-time calls

• ENN average number of both non-real-time
  service requests and calls in the reference cell
• 12 k l non-real-time calls
• 34 RN is full SNk real-time calls m calls in
  NHRQ

30
Pseudo-code to solve (NT2) independent nonlinear
equations
31
Blocking Probabilities

• Originating real-time calls are blocked when i
  SR
• Forced termination of real-time service handoff
  requests
• BHR Blocking probability
• MR is full
• DR dropping probability
• MR is not empty

32
Channel and RHRQ buffer utilizations

• Utilizationmean channel used/ S
• ECN average number of calls holding channels
• 12 kl non-real-time calls
• 34 NC is full SNk real-time calls m calls in
  NHRQ
• RHRQ utilization mean number of channels in
  RHRQ/MR
• ELR average length of RHRQ
• 12 jk-SC real-time handoff requests waiting in
  RHRQ

33
NHRQ Buffer Utilization and Forced Termination
probability

• NHRQ utilization mean number of channels in
  LHRQ/MN
• ELN average length of NHRQ
• 12 m non-real-time handoff requests waiting in
  NHRQ
• Ph Probability that a real-time service call
  triggers a handoff request in the reference cell
• Real-time service call holding time gt the cell
  dwell time
• Phf Forced termination probability of real-time
  handoff calls
• (l-1) successful handoff followed by a forced
  termination

34
Transmission Delay of non-real-time service

• Td The lifetime transmission delay of
  non-real-time service
• Sum of Tws
• Tw transmission delay on non-real-time service
  in each cell
• Littles Law
• Mean waiting time mean number of customers in
  queue / throughput
• BON blocking probability of originating
  non-real-time calls
• 1 - PNC?SN
• ETS Average serving time of non-real-time
  calls
• (mean number of calls getting service in queue)
  / (total throughput)
• BHN blocking probability of non-real-time
  service handoff requests
• NHRQ is full m MN

35
Average transmission delay of non-real-time
service (cont)

• Nh average number of handoff per a non-real-time
  handoff request
• (delay due to Nh handoffs call holding time) by
  average serving time
• ETN average transmission delay of
  non-real-time service
• Handoff arrival probability times average delay
  each handoff request ecounters

36
Numerical and Simulation Results

• Integrated service homogenous cellular system
• Call arrivals
• Poisson
• Call holding and cell dwell times
• Scenario 1 exponentially distributed as in
  performance analysis
• Scenario 2 iid with Gamma distribution
• Cell and handoff area dwell times with ?? 1.5
• Call holding time with ?? 2
• Same mean value
• Cell shape hexagonal
• Each neighbor has equal probability to receive
  handoff

37
Simulation Results Comparison of QoS Parameters

• Scen1 and analytical analysis results are
  consistent
• lt 4 difference in BOR, BON, and Phf
• Accuracy of analysis is substantiated
• Scen1 and Scen2 results are comparable
• Phf Scen2 is 20 less
• BOR, BON Scen2 is 6 and 2 larger,
  respectively
• TN Scen2 is 28 less
• Reasonable Gamma has smaller standard deviation
• Parallel trend
• Analytical formula with tolerable error margins

• BOR, BON blocking probability of real-time
  non-real-time service
• Phf Forced termination probability of real-time
  service calls
• TN Transmission delay of non-real-time service
  calls

38
Simulation Results Performance Comparison of
real-time calls

• Schemes
• Standard guard channel (base)
• Priority reservation
• Preemptive priority handoff
• Higher QoS parameters when higher arrival rates
  (lower service quality)

• Fhr Phr
• Priority and preemptive have 14.7 and 30.9
  improvements over guard channel, respectively
• BOR almost the same
• Priority especially with preemptive procedure is
  effective in decreasing forced terminations

39
Simulation Results Performance comparison of
non-real-time calls

• TN increases with higher traffic
• Guard channel performs better
• Channels available for non-real-time decreases
  due to lower priority
• Largest TN is 3.91sec. 6.5 of whole service
  time
• 31 decrease in forced termination probability is
  more important
• 7 increase in blocking probability of
  originating non-real-time calls
• Forced termination probability of non-real-time
  is negligibly small
• Proposed scheme is better in terms of the
  performance

40
Conclusions

• A handoff scheme is proposed
• Priority reservation
• Preemptive priority policy
• Analytical model for performance analysis has
  been proposed
• Simulation results match the analytical model
• Several QoS parameters have been evaluated
• Forced termination probability of handoff
  requests of real-time calls can be decreased
• Non-real-time service handoff requests do not
  fail
• A reasonable 6.5 transmission delay increase

41
References

• 1 Priority handoff analysis, Vehicular
  Technology Conference, 1993 IEEE 43rd, Xie, H.
  Kuek, S., Page(s) 855-858, Digital Object
  Identifier 10.1109/VETEC.1993.510945
• 2 CS5214 Course notes, Ing-Ray Chen, 2004.