Cross Layer Issues in UMTS-LTE

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Cross Layer Issues in UMTS
-
LTE

Bujar Krasniqi

bujar.krasniqi@nt.tuwien.ac.at

2008
-
07
-
03

Mobile Communication Seminar

Outline of Presentation

Date

1

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


Introduction to layered system



Cross layer design approach



Layer interaction



Definition of Cross layer design



Cross layer proposals



Cross layer optimization



Conclusions


Introduction to layered system

Date

2

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


Why do we need Cross Layer Design (CLD) ?



Open System Interconnection (OSI)



Protocols



Quality of Service (QoS)



Types of Services



Why do we need CLD ?

Date

3

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


Wireless communication today is expected to be mixture of real


time traffic [1]



Different application requires differnet Quality of Service (QoS) [1]



By using Cross Layer Design (CLD) we try to offer dedicated


QoS for dedicated applications



We use CLD in order to have higher througphput, cheaper


networks, more bandwidth, which are some of the goals of LTE


OSI model

Date

4

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


The International Standardization

Organization (ISO) began


to work in 1980s [1]



This work led to design the Open System Interconnection(OSI)

Application layer
Presentation layer
Session layer
Transport layer
Network layer
Data link layer
Physical layer
OSI model
Protocols

Date

5

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


In this model each layer communicates only with adjacent layer


above and adjacent layer below [1]



Traditional approach has been to treat the layers as different


entities



TCP/IPv4 is the most succesful implementation in OSI model [1]

Physical and Datalink
IP
TCP
UDP
Application
TCP
/
IP and UDP in a network
QoS and types of Services

Date

6

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


In IPv4 QoS and routing tables were implemented differently [1]



Now QoS is a key design component of any communication


system



Types of services enable the application to tell the network


what type of netwok services the application requires [1]



Types of services are:


Minimum delay



Maximum throughput



Maximum reliability



Minimum cost


Cross layer design approach

Date

7

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


To design a wireless network, we need to identify each process


or module




Research community is split in different groups because each


process or module has been treated seperately



CLD approach to network architecture is located where the three


groups of research intersect [1]



There is a difference between CLD in wireless and CLD in


wireline



In wireless: fading, scattering and multipath can change channel


state

Cross layer design approach

Date

8

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE





Cross
Layer
Design
Wireless
Networking
Signal Processing
Information Theory
Architecture
:
connection versus
connectionless
Energy efficient analysis
Scaling laws of large scale
networks
Traffic theory
Protocols
Increasing spectral efficiency
(
bits
/
s
/
Hz
)
Reducing Bit Error Rate
(
BER
)
Reducing the transmission energy
Detection and estimation algorithms
for m
ulti
-
acces
Developing capacity limits
Designing efficient source coding
and
channel coding algorithms
CLD as an intersection of different disciplines
Layer Interaction

Date

9

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


Early work done in wireline networks shows that information


exchange between protocol layers is useful, i.e [2]



TCP packet loss information communicated to the application layer



Link
-
MAC layer tuning transmit power of the PHY based on BER


Layer interaction can be categorized as:



Upper to lower layers (Top
-
down approach)



Lower to upper layers (Bottom
-
up approach)


Also PHY layer transmit power and BER communicated to the


Link/MAC layer enables adaptation of error mechanisms

*PHY
-
Physical Layer, MAC
-
Medium Access Control, BER
-

Bit Error Rate

Definition of CLD

Date

10

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


The layered architecture like OSI defines a hierarchy of services


to be provided by individual layers



Services at layers are realized by designing protocols for


different layers



A higher layer protocol only makes use of services at lower layers


and is not concerned how the service is being implemented



Protocols can be designed by allowing direct communication


between protocols in nonadjacent layers



Such communication between layers is named CLD. However,


this is not the only definition for CLD.

Cross layer proposals

Date

11

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


Proposals can be divided by:



Bottom
-
up


Top
-
down


Creation of new interfaces


Merging adjacent layers (super layers)

Application layer
Presentation layer
Session layer
Transport layer
Network layer
Data link layer
Physical layer
Bottom
-
up
Application layer
Presentation layer
Session layer
Transport layer
Network layer
Data link layer
Physical layer
Top
-
down
Physical layer
Medium Access Control
(
MAC
)
Radio Resource Control
(
RRC
)
Radio Link Control
(
RLC
)
Packet Data Convergence Protocol
(
PDCP
)
L
3
L
1
Super layer L
2
L
2
Cross layer proposals

Date

12

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


The way of exchanging information between layers [3]



Direct communication between layers



A shared database across the layers

Physical layer
Direct communication
between different layers
Medium Access Control
(
MAC
)
Radio Resource Control
(
RRC
)
Radio Link Control
(
RLC
)
Packet Data Convergence Protocol
(
PDCP
)
L
3
L
2
L
1
Control
Transport channels
Logical channels
Application layer
Presentation layer
Session layer
Transport layer
Network layer
Data link layer
Physical layer
A shared database
A shared
database
Cross layer optimization

Date

13

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


Future wireless communication like LTE requires optimization of


parameters in all layers



For optimum performance, parameter setup should take into


account the properties of application



We formulate CLD problem as an optimization problem with


objective to select joint strategy across multiple OSI layers



Joint cross layer optimization

strategy is defined as: [4]





there are possible joint strategies



A
M
P
N
N
N
APP
APP
MAC
MAC
PHY
PHY
S
,...,
,
,...,
,
,...,
1
1
1

A
M
P
N
N
N
N



*APP
-
application layer

Cross layer optimization

Date

14

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


denote the number of adaptation and protection


strategies available in PHY, MAC and APP



Modulation, channel coding schemes existing for a UMTS or LTE


are contained on this set




Packetization, ARQ, scheduling, admission control and FEC are


contained on this set




Adaptation of video compression, traffic prioritization are


contained on this set

A
M
P
N
N
N
,
,


P
i
N
i
PHY
,...,
1
,



M
i
N
i
MAC
,...,
1
,



A
i
N
i
APP
,...,
1
,

*ARQ
-
Automatic Repeat Request, FEC
-
Forward Error Coding

Joint cross layer optimization

Date

15

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


The joint CLO strategy is to find the best multimedia quality





where

))
(
(
)
(
x
S
Q
argmax
x
S
S
opt



Finding the optimal solution is hard because the set
contains


a lot of parameters



Joint CLO means optimization utility for given constraints



The objective function can be a
utility function

which is often


chosen to be concave and strictly increasing [5]

max
max
))
(
(
))
(
(
P
x
S
Power
D
x
S
Delay


Joint cross layer optimization

Date

16

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


The conceptual scheme for joint CLO is: [4]


Optimize utility
given constraints
Different
layer
parameters
Output
(
Cross layer adaptation strategy
)
Constraints
(
delay
,
power
,
etc
.)
Input media
Utility function

Date

17

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


The graph of choosen utility function is













We use this function to explain
NUM

by using mathematical


decomposition techniques for CLD [6]


)
(
x
U
x
*NUM
-
Network Utility Maximization

Network utility maximization

Date

18

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


The simplest optimization problem is when the objective function


contain just a parameter







A higher throughput can be obtained on a link if tradeoff is made


between data rate and reliability



For example: with lower decoding reliability we have higher data


rate and with higher reliability we have lower data rate



-

source data rate



-

reliability








S(l)
s
l
s
s
s
0
x
l,
,
C
x
to
subject
)
U(x
maximize
s
x
R
Network utility maximization

Date

19

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


The graphical representation between data rate and reliability


is:

Rate
(
log
)
Reliability
(
log
)

Now the utility function
U(.)

will be defined as a function of rate


and reliability

Differentiated dynamic reliability

Date

20

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


The optimization problem that represents tradeoff between rate


and reliability for
differentiated dynamic reliability

case is: [6]

S(l)
s
l,
,
C
c
0
S(l)
s
l,
1,
r
0
s
1,
R
R
s
,
x
x
x
l
,
C
c
S(l)
s
l,
,
c
r
x
s
),
(r
E
1
R
to
subject
)
R
,
(x
U
maximize
max
l
s
l,
s
l,
s
min
s
max
s
s
min
s
S(l)
s
max
l
s
l,
s
l,
s
l,
s
L(s)
l
s
l,
l
s
s
s
s
s




























-

E
error probability

Differentiated dynamic reliability

Date

21

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


The network diagram for that optimization problem is:

Source
s
Link
l
Network
Network
s
x
s
R




)
(
,
)
(
1
s
L
l
s
l
l
s
r
E
R
)
(
,
)
(
l
S
s
s
l
r


)
(
,
)
(
l
S
s
s
l
c


)
(
)
(
l
S
s
s
x



Network diagram contain just primal variables

Differentiated dynamic reliability

Date

22

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


We use primal
-
dual mathematical decomposition techniques to


solve the optimization problem for rate
-
reliability tradeoff



The Lagrangian of the constrained optimization problem is


where




and


































s
s
l
l
S
s
s
l
l
s
s
l
s
l
s
l
s
s
s
s
s
s
s
s
r
E
r
c
R
x
R
x
U
c
r
R
x
L







)
(
,
,
,
,
'
'
'
log
log
,
)
,
,
,
,
,
'
(



)
(
,
l
S
l
s
l
s


s
s
x
x
log
'

Differentiated dynamic reliability

Date

23

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


Based on primal
-
dual mathematical decompositon

Source rates=Primal variables

Congestion prices=Dual variables


Lagrange multipliers and are dual variables



Dual problem is:





The Lagrange dual function is:





0
μ
0
λ
to
subject
μ
λ,
P
minimize


)
,
,
,
,
,
'
(
max
)
,
(




c
r
R
x
L
P
s
Constraint

Differentiated dynamic reliability

Date

24

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


The diagram for distributed algorithm of the differentiated


dynamic reliability is

Source

s
Link
l
Network
Network
s
x
s

s
R




)
(
,
)
(
1
s
L
l
s
l
l
s
r
E
R



)
(
,
s
L
l
s
l
s


)
(
,
)
(
l
S
s
s
l



)
(
,
)
(
l
S
s
s
l
r


)
(
,
)
(
l
S
s
s
l
c


)
(
)
(
l
S
s
s
x


)
(
)
(
l
S
s
s



CLO based on layer description

Date

25

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


Now we propose a concept of exchanging information between


adjacent layers in terms of layer description [7]



The model is:

Layer
(
n
+
1
)
Layer
(
n
-
1
)
Layer
(
n
)
1

n
D
Layer
(
1
)
n
D
1

n
D
1

n
y
n
y
1
D
CLO based on layer description

Date

26

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


The layer output set is defined as:





Layer function is





1
1
1
,
:
)
,
(
,
0







n
n
n
n
N
n
n
n
n
D
d
x
R
d
x
f
y
n

n
o
N
n
n
n
R
D
f
,
1
:





-

set of feasible parameter values,


-

description of layer n
-
1

n

1

n
D
Conclusions

Date

27

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE


OSI model can not be a dedicated model for next wireless


systems



By using CLD techniques we need to adapt OSI model for


dedicated wireless system



It is very important to have a communication between nonadjacent


layers



By using CLD we should try to be more energy efficient



References

Date

28

Bujar Krasniqi

2008
-
07
-
03

Cross Layes Issues in UMTS
-
LTE

[1] Frank Aune “
Cross
-
Layer Tutorial
” NTNU ,2004


[2] V.T. Raisinghani, S.Iyder “
Cross
-
Layer optimization in wireless protocols
” 2003


[3] V. Srivastava, M.Moutani “
Cross
-
Layer design: A survey and the road ahead”

2005


[4] M. Schaar, D.Shankar “
Cross
-
Layer wireless multimedia transmission: Challenges,


principles, and new paradigms”
, 2005


[5] S.Stanczak, M Wiczanowski and H.Boche “
Resource allocation in wireless networks



Springer 2006


[6] J. Lee, M.Chiang, R. Calderbank “
Network utility maximization and price
-
based distributed


algorithms for rate
-
reliability tradeoff
” 2006


[7] J.Brehmer and W.Utschick “
Modular cross
-
layer optimization based on layer descriptions



[8] S. Boyd and L. Vandenberghe “
Convex Optimization
” Cambridge , 2004

Thank you for your attention !