無線分封數據服務網路之高使用率
資源分配策略與效能評估
High Utilization Resource Allocation and Performance
Evaluation for GPRS Networks
研 究 生：蔡鎮年
指導教授：柯開維 博士
Outline
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Introduction
Background
Resource Allocation Strategy for GPRS
Analytical Model
Numerical Result
Conclusion
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Introduction (1/2)
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Radio resource allocation for GPRS
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Single rate vs. multirate
Time slots vs. radio blocks
Different strategies to partition the
available cell capacity
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Complete Sharing (CS)
Complete Partitioning (CP)
Partial Sharing (PS)
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Introduction (2/2)
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This thesis
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Focuses on CP and PS strategy.
Allocates downlink radio resource by radio
blocks.
Two types (rates) of GPRS user.
Analyzes and evaluates performance for
different strategy.
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Background
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GPRS network architecture
GPRS air interface
TBF and TFI
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GPRS Network Architecture (1/2)
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It fits in with the existing GSM PLMN
Two new network elements
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Serving GPRS Support Node (SGSN)
Gateway GPRS Support Node (GGSN)
Many new interfaces
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Gb, Gi, Gn, etc.
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GPRS Network Architecture (2/2)
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GPRS Air Interface
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Frequency-Division Duplex, FDD
Combination of Frequency and Time
division multiple access, FDMA/TDMA
52-multiframe
Physical channels and logical channels
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GPRS Air Interface
52-multiframe
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GPRS Air Interface
Physical Channels
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Eight physical channels (TS0 to TS7) per
carrier.
The physical channel that is used for packet
logical channels is called a packet data
channel (PDCH).
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TBF and TFI (1/3)
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A temporary block flow (TBF) is a
physical connection between the MS
and the network side to support data
transfer.
Once the data transfer is finished, the
TBF is released.
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TBF and TFI (2/3)
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Each TBF is identified by a temporary
flow identity (TFI) assigned by the
network.
PDCH multiplexing

TBFs which belonging to different MS can
share the same PDCH.
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TBF and TFI (3/3)
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Resource Allocation Strategy
for GPRS
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Radio resource partition strategies
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Complete Partitioning (CP)
Partial Sharing (PS)
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Resource Allocation Strategy
Complete Partitioning
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TS0 to TS4 are GSM user only, and TS5
to TS7 are GPRS user only
This two partitions are independent
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Resource Allocation Strategy
Partial Sharing
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A shared time slot
This two partitions are dependent
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Analytical Model for CP
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In CP case, GSM and GPRS partitions
are independent, so we can analyze this
two partitions separately.
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System description
State definition
State transition diagrams
Balance equations
Performance metrics
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Analytical Model for CP
System Description
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Two types of user
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The request is Poisson.
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Class 1 (1+1) and class 2 (2+1)
Arrival rate are λ1 and λ2, respective.
The service time of each request is
exponential distribution
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Mean service time are 1/μ1 and 1/μ2,
respective.
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Analytical Model for CP
State Definition
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State x=(i, j, k)
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i = the number of PDCH is used
j = the number of class 1 user
k = the number of class 2 user
An example
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Analytical Model for CP
State Transition Diagrams
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Define R = j + 2k, and MAX_PDCH is
the maximum number of GPRS time slot
that can be used.
Four cases
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R  MAX _ PDCH  2
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0  R  MAX _ PDCH
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R  MAX _ PDCH
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R  MAX _ PDCH  1
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Analytical Model for CP
State Transition Diagrams
R  MAX _ PDCH  2
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The most straightforward
No need to consider i
An example
MAX_PDCH = 3
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Analytical Model for CP
State Transition Diagrams
Generalized state transition
diagram for case 1
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Analytical Model for CP
Balance Equations

   2 2  j 1  k 2   i , j ,k 

1 1
( j  1) 1 i , j 1,k  11 i , j 1,k  ( k  1) 2 i , j ,k 1   2 2 i , j ,k 1

   4 2   5 2  j 1  k 2   i , j ,k 

3 1
( j  1) 1 i 1, j 1,k   31 i 1, j 1,k  ( k  1)2 i  2, j ,k 1 
( k  1) 2 i 1, j ,k 1   42 i 2, j ,k 1

   2 2  j 1  k 2   i , j ,k 

1 1
( j  1) 1 i , j 1,k   31 i 1, j 1,k  (k  1) 2 i , j ,k 1   42 i 2, j ,k 1

   2 2  j 1  k 2   i , j ,k 

1 1
( j  1) 1 i , j 1,k  11 i , j 1,k  ( k  1) 2 i , j ,k 1   52 i 1, j ,k 1
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Analytical Model for CP
Performance Metrics

According steady-state probabilities, we
can fine the class 1 and class 2 blocking
probability (Pb1 and Pb2), and radio
resource utilization U.
Pb1 
Pb 2 
U
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
 i , j ,k

 i , j ,k 
i , j ,k E
 i , j , k E

 i , j , k F
 i , j ,k
1
i (i , j ,k )

MAX _ PDCH i , j ,k S
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Analytical Model for PS (1/2)
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PS case is more complex than CP case.
In addition to GPRS user, there is GSM
user in the system as well.
GSM user
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New call and handover call are Poisson
Arrival rate v  n  h
Service time is exponential distribution
Mean service time 1  v  1  s  d 
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Analytical Model for PS (2/2)
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State x=(i, j, k, l, m)
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i = the number of PDCH being used
j = the number of GPRS class 1 user
k = the number of GPRS class 2 user
l = the number of GSM user
m = indicate who is using shared TS
12 different cases, 12 different balance
equations.
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Analytical Model for PS
Performance Metrics (1/2)
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According to these balance equations,
we can calculate steady-state
probabilities, and compute performance
metrics as well.
GPRS class 1 blocking probability
P 
 

b1

( i , j , k ,l , m )H  I
( i , j , k ,l , m )
GPRS class 2 blocking probability
P 



b2
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( i , j , k ,l , m )I  H  J  K
( i , j , k ,l , m )
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Analytical Model for PS
Performance Metrics (2/2)
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GSM new call blocking probability
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n
n  h

( i , j , k ,l , m )L  M
 ( i , j , k ,l , m )
GSM handover call blocking probability
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
Pvn 
Pvh 
h
n  h

( i , j , k ,l , m )L  M
 ( i , j , k ,l , m )
Radio resource utilization

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U
1
 (i , j ,k ,l ,m ) (i  l )

GPRS _ TS  GSM _ TS  1 (i , j ,k ,l ,m )S
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Numerical Result
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Comparison between analytic and
simulated result.
Comparison between CP and PS for
GPRS traffic.
Utilization vs. load
Define
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GPRS load
GSM load
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1

 2 1 (erlang )
1
2

 v (erlang )
v
LGPRS 
LGSM
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Comparison between analytic
and simulated result (1/2)

CP case
1  2  0.1
0.6
class 1-理論值
0.5
class 1-模擬值
class 2-理論值
Blocking Probability
class 2-模擬值
0.4
0.3
0.2
0.1
0
3.6
7.2
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10.8 14.4
18
21.6 25.2 28.8 32.4
36
Offered Load
39.6 43.2 46.8 50.4
54
57.6
30
Comparison between analytic
and simulated result (2/2)

0.25
GPRS Load  3.2, 1  0.2, 2  0.4
class 1-理論值
class 1-模擬值
class 2-理論值
class 2-模擬值
GSM-理論值
GSM-模擬值
0.2
Blocking Probability
PS case
0.15
0.1
0.05
0
4
8
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16
20
24
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GPRS Load
32
36
40
44
48
31
Comparison between CP and
PS for GPRS request
GPRS Load  3.2, 1  0.2, 2  0.4, v  0.0083
0.5
0.45
class
class
class
class
Blocking Probability
0.4
0.35
0.3
1-CP
1-PS
2-CP
2-PS
0.25
0.2
0.15
0.1
0.05
0
4
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12
16
20
24
28
GPRS Load
32
36
40
44
48
32
Utilization vs. offered load
(1/2)
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CP case
1  0.2, 2  0.4, k  1 2
1.2
1
Utilization
0.8
0.6
0.4
k=1
k=5
0.2
0
1
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3
4
5
6
7
8
Offered Load (Erlangs)
9
10
11
12
33
Utilization vs. offered load
(2/2)

PS case
1  0.2, 2  0.4, v  0.0083
0.9
0.8
Utilization
0.7
0.6
4 erlangs
8 erlangs
18 erlangs
28.8 erlangs
0.5
0.4
0.3
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
GSM Load (Erlangs)
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Conclusion
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Radio block based CP and PS strategies
was proposed.
Built analytic model for both strategies.
Verified analytic model by simulation.
Showed that PS case scheme performed
better than CP one.
GPRS radio resource can be fully utilized
easily.
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Future work
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Impact of cell-reselection.
Priority for GSM handover call.
Preemptive mechanism.
Adaptive resource allocation.
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The End
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