Cross Layer Issues in UMTS-LTE

8/12/2019 Cross Layer Issues in UMTS-LTE

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Cross Layer Issues in UMTS-LTE

Bujar [email protected]

2008-07-03

Mobile Communication Seminar
mailto:[email protected]:[email protected]


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Outline of Presentation

Date

1Bujar 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


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Introduction to layered system

Date


Why do we need Cross Layer Design (CLD) ?

Open System Interconnection (OSI)

Protocols

Quality of Service (QoS)

Types of Services


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Why do we need CLD ?

Date


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


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OSI model

Date


The International StandardizationOrganization (ISO) beganto 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


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Protocols

Date


In this model each layer communicates only with adjacent layerabove 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


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QoS and types of Services

Date 6Bujar 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 networkwhat type of netwok services the application requires [1]

Types of services are:

Minimum delayMaximum throughput

Maximum reliability

Minimum cost


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


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Cross

Layer

Design

Wireless

Networking

Signal Processing

Information Theory

Architecture:connection versusconnectionless

Energy efficient analysis

Scaling laws of large scalenetworks

Traffic theory

Protocols

Increasing spectral efficiency( bits / s / Hz )

Reducing Bit Error Rate (BER )

Reducing the transmission energyDetection and estimation algorithms

for multi-acces

Developing capacity limits

Designing efficient source codingand channel coding algorithms

CLD as an intersection of different disciplines


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Layer Interaction


Early work done in wireline networks shows that informationexchange 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


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Definition of CLD


The layered architecture like OSI defines a hierarchy of servicesto 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.


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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)

L3

L1

Super layer L2

L2


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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)

L3

L2

L1

Control

Transport channels

Logical channels

Applicat ion layer

Presentation layer

Session layer

Transport layer

Network layer

Data link layer

Physical layer

A shared database

A shared

database


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Future wireless communication like LTE requires optimization ofparameters 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 optimizationstrategy is defined as: [4]

there are possible joint strategies

AMP NNN APPAPPMACMACPHYPHYS ,...,,,...,,,..., 111

AMP NNNN *APP-application layer


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denote the number of adaptation and protectionstrategies 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

AMP NNN ,,

Pi NiPHY ,...,1,

Mi NiMAC ,...,1,

Ai NiAPP ,...,1, *ARQ-Automatic Repeat Request, FEC-Forward Error Coding


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Joint cross layer optimization


The joint CLO strategy is to find the best multimedia quality

where

))(()( xSQargmaxxSS

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 functionwhich is often

chosen to be concave and strictly increasing [5]

max

max

))((

))((

PxSPower

DxSDelay


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Joint cross layer optimization


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


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Utility function


The graph of choosen utility function is

We use this function to explain NUMby using mathematical

decomposition techniques for CLD [6]

)(xU

x

*NUM-Network Utility Maximization


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Network utility maximization


The simplest optimization problem is when the objective functioncontain 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 datarate and with higher reliability we have lower data rate

- source data rate

- reliability

S(l)s

ls

s

s

0xl,,Cxtosubject

)U(xmaximize

sx

R


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Network utility maximization


The graphical representation between data rate and reliabilityis:

Rate (log)

Reliability(lo

g)

Now the utility function U(.)will be defined as a function of rate

and reliability


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Differentiated dynamic reliability


The optimization problem that represents tradeoff between rateand reliability for differentiated dynamic reliabilitycase is: [6]

S(l)sl,,Cc0

S(l)sl,1,r0

s1,RR

s,xxx

l,Cc

S(l)sl,,cr

x

s),(rE1Rtosubject

)R,(xUmaximize

max

lsl,

sl,

smin

s

max

ss

min

s

S(l)s

max

lsl,

sl,

sl,

s

L(s)l

sl,ls

s

sss

- E error probability


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The network diagram for that optimization problem is:

Sources Linkl

Network

Network

sx

sR

)(

, )(1sLl

sll

s rER )(, )( lSsslr

)(, )( lSsslc

)()( lSssx

Network diagram contain just primal variables


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We use primal-dual mathematical decomposition techniques tosolve the optimization problem for rate-reliability tradeoff

The Lagrangian of the constrained optimization problem is

where

and

s

s

l lSs

sllsslslsl

ssss

s

sss

rErc

RxRxUcrRxL

)(

,,,,

'''

loglog

,),,,,,'(

)(

,

lSl

sl

s

ss xx log'


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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:

00tosubject

,Pminimize

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


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The diagram for distributed algorithm of the differentiateddynamic reliability is

Sources Linkl

Network

Network

sx

s

sR

)(

, )(1sLl

sll

srER

)(

,

sLl

sl

s

)(, )( lSssl

)(, )( lSsslr

)(, )( lSsslc

)()( lSssx

)(

)(lSss


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CLO based on layer description


Now we propose a concept of exchanging information betweenadjacent layers in terms of layer description [7]

The model is:

Layer (n+1)

Layer (n-1)

Layer (n)

1nD

Layer (1)

nD

1nD

1ny

ny

1D


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CLO based on layer description


The layer output set is defined as:

Layer function is

111 ,:),( ,0

nnnnN

nnnn DdxRdxfy n

noN

nnn RDf ,

1:

- set of feasible parameter values,- description of layer n-1

n

1nD


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Conclusions


OSI model can not be a dedicated model for next wirelesssystems

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


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References


[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 ahead2005

[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


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Thank you for your attention !

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Cross Layer Issues in UMTS-LTE