Cross Layer Issues in UMTS-LTE Bujar Krasniqi Mobile Communication Seminar

Outline of Presentation Date 1 1 Bujar Krasniqi 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 2 Bujar Krasniqi 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 3 Bujar Krasniqi 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 4 Bujar Krasniqi 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)

Protocols Date 5 5 Bujar Krasniqi 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]

QoS and types of Services Date 6 6 Bujar Krasniqi 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 7 Bujar Krasniqi 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 8 Bujar Krasniqi Cross Layes Issues in UMTS-LTE

Layer Interaction Date 9 9 Bujar Krasniqi 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 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 Cross Layes Issues in UMTS-LTE Proposals can be divided by: Bottom-up Top-down Creation of new interfaces Merging adjacent layers (super layers)

Cross layer proposals Date 12 Bujar Krasniqi Cross Layes Issues in UMTS-LTE The way of exchanging information between layers [3] Direct communication between layers A shared database across the layers

Cross layer optimization Date 13 Bujar Krasniqi 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 *APP-application layer

Cross layer optimization Date 14 Bujar Krasniqi 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 *ARQ-Automatic Repeat Request, FEC-Forward Error Coding

Joint cross layer optimization Date 15 Bujar Krasniqi Cross Layes Issues in UMTS-LTE The joint CLO strategy is to find the best multimedia quality where 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]

Joint cross layer optimization Date 16 Bujar Krasniqi Cross Layes Issues in UMTS-LTE The conceptual scheme for joint CLO is: [4]

Utility function Date 17 Bujar Krasniqi 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] *NUM-Network Utility Maximization

Network utility maximization Date 18 Bujar Krasniqi 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

Network utility maximization Date 19 Bujar Krasniqi Cross Layes Issues in UMTS-LTE The graphical representation between data rate and reliability is: Now the utility function U(.) will be defined as a function of rate and reliability

Differentiated dynamic reliability Date 20 Bujar Krasniqi Cross Layes Issues in UMTS-LTE The optimization problem that represents tradeoff between rate and reliability for differentiated dynamic reliability case is: [6] - E error probability

Differentiated dynamic reliability Date 21 Bujar Krasniqi Cross Layes Issues in UMTS-LTE The network diagram for that optimization problem is: Network diagram contain just primal variables

Differentiated dynamic reliability Date 22 Bujar Krasniqi 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

Differentiated dynamic reliability Date 23 Bujar Krasniqi 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:

Differentiated dynamic reliability Date 24 Bujar Krasniqi Cross Layes Issues in UMTS-LTE The diagram for distributed algorithm of the differentiated dynamic reliability is

CLO based on layer description Date 25 Bujar Krasniqi 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:

CLO based on layer description Date 26 Bujar Krasniqi Cross Layes Issues in UMTS-LTE The layer output set is defined as: Layer function is - set of feasible parameter values, - description of layer n-1

Conclusions Date 27 Bujar Krasniqi 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 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

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