qos-aware resource allocation for slowly time-varying channels
DESCRIPTION
QoS-Aware Resource Allocation for Slowly Time-Varying Channels. InfoCom Department - University of Rome La Sapienza [email protected] [email protected] [email protected]. - PowerPoint PPT PresentationTRANSCRIPT
QoS-Aware Resource Allocation forQoS-Aware Resource Allocation forSlowly Time-Varying ChannelsSlowly Time-Varying Channels
InfoCom Department - University of Rome La [email protected]
[email protected]@acts.ing.uniroma1.it
Presented at the 58
Presented at the 58thth IEEE Vehicular IEEE Vehicular
Technology Conference, Orlando, U.S.A.,
Technology Conference, Orlando, U.S.A.,
October 2003October 2003
High level application
Physical
Channel
Data (packets)MACMACMedium Access Control
Two basic problems in the design of a MAC protocol are:
1) the efficient management of the resource
2) the need for fulfilling QoS requirements despite the unpredictable behaviour of the channel
We propose an analytical approach for resource allocation at the MAC level.
The resulting algorithm maximizes transmis-sion efficiency by adapting error protection to both channel status and required QoS.
Reference ScenarioReference Scenario
Traffic sources are characterized by two sets of parameters:
TspecsTspecs – collects parameters describing source traffic activityQspecsQspecs – defines QoS requirements
Tspecs
Tspecs
Qspecs
Qspecsp peak rater mean rateM max packet sizeb token buffer
Dmax maximum tolerable end-to-end delayF minimum tolerable percen-tage of packets delivered within Dmax
The MAC protocol works with fixed-size MAC Protocol Data Units (MACPDUMACPDUs)
headerpayload
HL EFFFECP LLL effective payload
FEC size
Model AssumptionsModel Assumptions
S
OU
RC
E
SO
UR
CE
B
UF
FE
RB
UF
FE
R
Resource Allocation (1/4)Resource Allocation (1/4)
Two functions are introduced in order to express in analytical terms the trade-off which exists between reserved capacity CC and the delay DD.
MbrpDD
MrbpDTspecs
sys
)()(
),(Capacity function
),( ,min, minRTspecsRTTNDTspecsC RMAX Required capacity in bps
sysDC
MMbrp
CpCTspecs
1
),(Delay function system
delay
Maximum number
Maximum number
of retra
nsmissions
of retra
nsmissions
Minimum
Minimum
capacity
capacityRound
Round
Trip Tim
e
Trip Tim
e
Resource Allocation (2/4)Resource Allocation (2/4)
)( RNCC
MACPDUsMACPDUs
FECFEC
Effective Effective
PayloadPayload
In order to evaluate the effect of segmentation on required capacity, the MAC must evaluate the size of required overhead on each MACPDU.
FECP
PDUeff LL
M
M
LCC Effective CapacityEffective Capacity
FEC size can be evaluated by taking into account the QoS parameter FF.
Resource Allocation (3/4)Resource Allocation (3/4)
1NL
REFF
M
L
FP
1
1001
Target packet loss Target packet loss probability on each probability on each MACPDUMACPDU
Given the required QoS, it depends on N NRR and on LLEFFEFF
)1(2)2(1
bp
bp
PL
LPerfc
bp
PLk
Corrective capability Corrective capability on each MACPDUon each MACPDU
It depends on channel status, i.e. on the BER value ppbb
The value of The value of kk detemines detemines the FEC sizethe FEC size
We obtain a new LLFECFEC which can affect the size of the effective payload LLEFFEFF
We propose an iterative algorithm based on successive approximations. This algorithm is computationally efficient and returns the FEC size which is necessary on each MACPDU.
Resource Allocation (4/4)Resource Allocation (4/4)
FECP
PDURbeff LL
M
M
LCNpQspecsTspecsC ),,,( Effective Effective
CapacityCapacity
ARQ
PDU
FeffRbPDU N
L
DCNpQspecsTspecsN 1),,,(
Required capacity in terms of Required capacity in terms of the number of MACPDUs per the number of MACPDUs per frame which are necessary for frame which are necessary for the application.the application.
DF is the frame durationNARQ is a corrective term due to the ARQ
Transmission efficiency is maximized by selecting the NNRR value leading to the minimum number of MACPDUs per frame.
Performance in static channelsPerformance in static channels
Number of MACPDU per frame vs. BER (solid line) and optimum number of retransmissions
(dotted line) for a typical real-time source.
Number of MACPDU per frame vs. BER (solid line) and optimum number of retransmissions
(dotted line) for a typical non-real-time source.
10 -3 10 -2 10 -1 0
10
20
Nu
mb
er
of
MA
CP
DU
s p
er
fra
me
10 -3 10 -2 10 -1
0
1
BER N
um
be
r of re
tran
sm
iss
ion
s
10 -4 10 -3 10 -2 10 -1 0
200
400
600
800
10 -4 10 -3 10 -2 10 -1
0
20
Nu
mb
er
of
MA
CP
DU
s p
er
fra
me
Nu
mb
er o
f retra
ns
mis
sio
ns
BER
Performance in slowly Performance in slowly time-varying channelstime-varying channels
Percentage of source packets delivered to destination as a function of the
receiver speed for a real-time source (circles) and a non-real-time source
(crosses).
0 0.1 0.2 0.3 0.4 0.5 0.6 0.790
100
speed of the receiver [m/s]
per
cen
tag
e o
f p
acke
ts d
eliv
ered
to
des
tin
atio
n
Performance of the proposed algorithm was verified in the case of a slowly time-varying channel.
The Jakes channel model was used for characterizing multipath propagation in a generic indoor environment.
Performance degradation is observed when the channel coherence time is comparablecomparable to the maximum end-to-end delay.
In a scenario with high mobility, QoS cannot be guaranteed for real-time applications only.
AcknowledgementsAcknowledgements
This work was supported by the European Union under This work was supported by the European Union under Project No. IST-2000-25197 "Whyless.com - The Open Project No. IST-2000-25197 "Whyless.com - The Open Mobile Access Networks" Mobile Access Networks"
……special thanks to special thanks to John SilverJohn Silver for providing the for providing the PDF conversion of the poster.PDF conversion of the poster.
Special thanks to all the people in the ACTS lab their Special thanks to all the people in the ACTS lab their contribution in both technical and contribution in both technical and not-technicalnot-technical issues. issues.
And finally…And finally…