channel allocation for gprs
DESCRIPTION
Channel Allocation for GPRS. From: IEEE Tran. Veh. Technol., Vol. 50, no. 2, 2001. Author: P. Lin and Y.-B. Lin CSIE, NTU & CSIE, NCTU. Outline. Introduction GPRS architecture Packet data logical channel Channel allocation schemes System model Analysis results - PowerPoint PPT PresentationTRANSCRIPT
Channel Allocation for GPRS
From: IEEE Tran. Veh. Technol., Vol. 50, no. 2, 2001.
Author: P. Lin and Y.-B. Lin
CSIE, NTU & CSIE, NCTU
Outline Introduction GPRS architecture Packet data logical channel Channel allocation schemes System model Analysis results Simulation method Performance Conclusion
Introduction
GPRS shares GSM frequency bands with telephone and circuit-switched data traffic
GPRS uses the same TDMA/ FDMA structure as that of GSM to form physical channels
Allocation of channel for GPRS is flexible where one to eight channels can be allocated to a user or one channel can be shared by several users
GPRS architecture
Packet data logical channel Packet data traffic channel (PDTCH)
Employed for transferring of user data Packet broadcast control channel (PBCCH)
Broadcast control Packet common control channel (PCCCH)
The packet random access channel (PRACH) The packet paging channel (PPCH) The packet access grant channel (PAGCH) The packet notification channel (PNCH)
Packet dedicated control channels The packet associated control channel (PACCH) The packet timing advance control channel (PTCCH)
Packet data logical channel (cont’d) Group Name Direction Function
PTC PDTCH Downlink and uplink Data
PBCCH PBCCH Downlink Broadcast
PCCCH PRACH Uplink Random access
PPCH Downlink Paging
PAGCH Downlink Access grant
PNCH Downlink Multicast
PDCH PTCCH Downlink and uplink Timing advance
PACCH Downlink and uplink Associated control
Dynamic allocation: uplink data transfer
Dynamic allocation: downlink data transfer
Channel allocation schemes:•Fixed Resource Allocation (FRA): For a data request of K channels, the BS assigns exact K channels to GPRS packet request •Dynamic Resource Allocation (DRA): For a data request of K channels, DRA allocates at most K channels to the request •Fixed Resource Allocation with Queue Capability (FRAQ) FRAQ_N: a queue for the new calls only FRAQ_H: a queue for the handoff calls only FRAQ_NH: a queue for both new and handoff calls•Dynamic Resource Allocation with Queue Capability (DRAQ) DRAQ_N: similar to FRAQ_N
DRAQ_H: similar to FRAQ_H
DRAQ_NH: similar to FRAQ_NH
A GPRS data request specifies K channels for transmission
The GSM voice call arrival and GPRS packet requests to a cell form Poisson streams with rates and , respectively
The voice call holding time and packet transmission time are exponentially distributed with mean times and , respectively
System model
v p
p/1v/1
: the residence time of voice user at a cell j, which are independent and identically distributed random variables with a general function with mean
jmt ,
vct ,
vcvtuvvcvc eutf ,)( ,,
: the voice call holding time, which is assumed to be exponentially distributed with the density function
jmt ,
η1)( , jmm tf
The timimg diagram
vhλ
bvP
bpP
: the new call blocking probability for the GSM
: dropping/ blocking probability for the GPRS
: voice handoff call arrival rate to a cell
vη : GSM voice user mobility rate
: probability that a GSM voice call is not completed (either blocked or forced to terminate)
ncvP
: the GSM voice call traffic load v
p : the GPRS packet call traffic load
Analytic model for FRA
)]()1(1[
)](1)[1(*
vmfvv
vv*mbvv
vh ufPu
ufP
)]()1(1[
)](1)[()([1)(
*vmfvv
v*mv
*mbvfvbvv
v
vv ufPu
ufufPP+Pη
u
λ=ρ
jmst
t jmmm dtetfsf jm
jm,,
* ,
0,
)()(
where
(1)
(2)
Analytic model for FRA (cont’d)
)!
)(!
()( 1
p
np
v
nv
nnGnp
pv
(3)
(4)
K
CnandCnCKnnnnS pvpvpvFRA 0 ,0,),(
fvvmfvv
vv*mbvv
bv
fvv
hvbvnc
PufPu
ufPP
PPPv
)]()1(1[
)](1)[1(
*
,
state space : FRAS
stationary probability:
Analytic model for FRA (cont’d)
}0,0,)|,{(
)(
K
CnCnCKnnnnn
bv
pvpvpv
npP
}0 0 {(
)(
K
CnC,nC,KnnK)|C,nnn
bp
pvpvpv
npP
])!
)(!
[(
FRA
pv
Sn p
np
v
nv
nnG
ppp where
(5)
(7)
(6)
The iterative algorithm for FRA Step 1: Select an initial value for Step 2: Step 3: Compute and using (2) and (4)-(7) Step 4: Compute using (1) Step 5: If then go to step 2. Otherwise
,go to step 6. Note that is a predefined threshold
say Step 6: The values for , and converge. Compute
from (3)
vhλ
vholdvh λλ ←,
bpPbvP
ncvP
vhλ
vholdvhvh δλλλ ≥- ,
710
vhλ bvPbpP
Analytic model for DRA
}0 ,2
0
,3
≤≤0,≤≤0
,≤23≤0|),,,{(
ClandC
k
CjCi
ClkjilkjiSDRA
vvv ηuM +=
vhvv λλ +=Λ
vvv ηuM +=where
The state transition for DRA
Let’s consider the case when K=3
Analytic model for DRA (cont’d) The balance equations for the Markov process are expressed:
1,,,
,1,,,,1,,,,1
1,,,1,1,,2,,1,3,,,1
,,,321
)1(
)1(2)1(3)1(
)23
lkjip
lkjiplkjiplkjiv
lkjiplkjiplkjiplkjiv
lkjippppppvv
l
kjMi
lkjiM
Analytic model for DRA (cont’d)
Cl
andC
kC
jCi
ClkjilkjiE
0
,2
0,3
≤≤0,≤≤0
,23≤0|),,,(1
1),,,(
,,,Elkji
lkjifvbvbp PPP
: the set of the states where no free channel is available1E
Analytic model for FRAQ
K
CyQCx
QCKyyxS NFRAQ
0 ,0
,x0|),{(_
CKy x0:I Case
Analytic model for FRAQ (cont’d)
CKy x:II Case
QCKy x0:III Case
Analytic model for FRAQ (cont’d)
KC
y
KyQC
KyCxyxfvP
0,
K
CyQCxQCKyxKCyxE 0 ,0 ,|),(2
2),(
,Eyx
yxbpP
KC
y
KyQC
KyCx vv
yxvbv KyCxMKyC
KyCxP
0
,
)1()(
)1(
: a packet request is dropped if the number of free channels is smaller than K
2E
Simulation method We consider a 6x6 wrapped mesh cell
structure The model follows the discrete event
simulation approach
6X6 wrapped mesh cell structure
Performance of FRA ( )
Performance of GPRS data rate: increase as K increase
Effects of packet size :in Fig. 6(b) Effect of voice call arrival: in Fig. 6(c) Effect of voice user mobility: in Fig. 6(d)
voice user mobility has no apparent effect on
bpP
bpP
bpP
Performance of FRA ( )
Effect of packet size: in Fig. 7(b) Effect of voice call arrival: in Fig. 7(c)
packet request have less chance to served as K
increases, and decreases as K increases Effect of voice user mobility: in Fig. 7(d)
high mobility, handoffs are more likely to occur in a voice call,thus for high mobility is larger
ncvP
ncvP
ncvP
Comparison for the FRA and DRA algorithms Performance of
DRA algorithms (with or without queueing) always outperform FRA (with or without queueing)
Performance of
the DRAQ_NH outperforms other algorithms ncvP
bpP
Effect of the variations of the distribution for input parameters
The average number of channels assigned to packet transmission
The average waiting time for the accepted voice call request
Conclusion
The dynamic allocation effectively increases the GPRS packet acceptance rate and queueing mechanisms significantly reduce the voice call incompletion probability