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Cross Layer Issues in UMTS-LTE Bujar Krasniqi [email protected] 2008-07-03 Mobile Communication Seminar Outline of Presentation Introduction to layered system Cross layer design approach Layer interaction Definition of Cross layer design Cross layer proposals Cross layer optimization Conclusions Bujar Krasniqi 2008-07-03 Date 1 Cross Layes Issues in UMTS-LTE Introduction to layered system Why do we need Cross Layer Design (CLD) ? Open System Interconnection (OSI) Protocols Quality of Service (QoS) Types of Services Bujar Krasniqi 2008-07-03 Date 2 Cross Layes Issues in UMTS-LTE Why do we need CLD ? 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 Bujar Krasniqi 2008-07-03 Date 3 Cross Layes Issues in UMTS-LTE OSI model 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 Bujar Krasniqi 2008-07-03 Date 4 Cross Layes Issues in UMTS-LTE Protocols 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] Application TCP UDP IP Physical and Datalink TCP/IP and UDP in a network Bujar Krasniqi 2008-07-03 Date 5 Cross Layes Issues in UMTS-LTE QoS and types of Services 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 Bujar Krasniqi 2008-07-03 Date 6 Cross Layes Issues in UMTS-LTE Cross layer design approach 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 Bujar Krasniqi 2008-07-03 Date 7 Cross Layes Issues in UMTS-LTE Cross layer design approach Wireless Networking Architecture :connection versus connectionless Energy efficient analysis Scaling laws of large scale networks Traffic theory Protocols Signal Processing Cross Layer Design Increasing spectral efficiency ( bits / s / Hz ) Information Theory Developing capacity limits Reducing Bit Error Rate ( BER ) Reducing the transmission energy Detection and estimation algorithms for multi-acces Designing efficient source coding and channel coding algorithms CLD as an intersection of different disciplines Bujar Krasniqi 2008-07-03 Date 8 Cross Layes Issues in UMTS-LTE Layer Interaction 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 Bujar Krasniqi 2008-07-03 Date 9 Cross Layes Issues in UMTS-LTE Definition of CLD 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. Bujar Krasniqi 2008-07-03 Date 10 Cross Layes Issues in UMTS-LTE Cross layer proposals Proposals can be divided by: Creation of new interfaces Bottom-up Top-down Merging adjacent layers (super layers) Application layer Application layer Presentation layer Presentation layer Radio Resource Control (RRC) L3 Session layer Transport layer Top-down Bottom-up Packet Data Convergence Protocol (PDCP) Session layer Transport layer Network layer Network layer Data link layer Data link layer Physical layer Physical layer Radio Link Control (RLC) L2 Medium Access Control ( MAC) Physical layer Super layer L2 Bujar Krasniqi 2008-07-03 Date 11 Cross Layes Issues in UMTS-LTE L1 Cross layer proposals The way of exchanging information between layers [3] Direct communication between layers A shared database across the layers Application layer Radio Resource Control (RRC) Control L3 Presentation layer Packet Data Convergence Protocol (PDCP) Session layer Radio Link Control (RLC) Transport layer L2 Logical channels A shared database Network layer Medium Access Control ( MAC) Data link layer Transport channels L1 Physical layer Physical layer Direct communication between different layers Bujar Krasniqi 2008-07-03 Date A shared database 12 Cross Layes Issues in UMTS-LTE Cross layer optimization 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] S PHY1,...,PHYNP , MAC1,...,MACNM , APP1,..., APPN A there are N N P N M N A possible joint strategies *APP-application layer Bujar Krasniqi 2008-07-03 Date 13 Cross Layes Issues in UMTS-LTE Cross layer optimization denote the number of adaptation and protection strategies available in PHY, MAC and APP NP , NM , N A Modulation, channel coding schemes existing for a UMTS or LTE are contained on this set PHYi , i 1 ,..., N P Packetization, ARQ, scheduling, admission control and FEC are contained on this set MACi , i 1 ,..., NM Adaptation of video compression, traffic prioritization are contained on this set APPi , i 1 ,..., N A *ARQ-Automatic Repeat Request, FEC-Forward Error Coding Bujar Krasniqi 2008-07-03 Date 14 Cross Layes Issues in UMTS-LTE Joint cross layer optimization The joint CLO strategy is to find the best multimedia quality S opt ( x) argm axQ( S ( x)) S where Delay(S ( x)) Dmax Power(S ( x)) Pmax 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] Bujar Krasniqi 2008-07-03 Date 15 Cross Layes Issues in UMTS-LTE Joint cross layer optimization The conceptual scheme for joint CLO is: [4] Input media Different layer parameters Optimize utility given constraints Constraints (delay, power, etc.) Output ( Cross layer adaptation strategy ) Bujar Krasniqi 2008-07-03 Date 16 Cross Layes Issues in UMTS-LTE Utility function The graph of choosen utility function is U (x) x We use this function to explain NUM by using mathematical decomposition techniques for CLD [6] *NUM-Network Utility Maximization Bujar Krasniqi 2008-07-03 Date 17 Cross Layes Issues in UMTS-LTE Network utility maximization The simplest optimization problem is when the objective function contain just a parameter m axim ize U(x ) x C , l, x 0 s s subject to sS(l) s l 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 - xs source data rate - R reliability Bujar Krasniqi 2008-07-03 Date 18 Cross Layes Issues in UMTS-LTE Network utility maximization Reliability (log) The graphical representation between data rate and reliability is: Rate (log) Now the utility function U(.) will be defined as a function of rate and reliability Bujar Krasniqi 2008-07-03 Date 19 Cross Layes Issues in UMTS-LTE Differentiated dynamic reliability The optimization problem that represents tradeoff between rate and reliability for differentiated dynamic reliability case is: [6] m axim ize U (x , R ) R 1 E (r s s s s subject to s lL(s) l l,s ), s xs cl,s , l, s S(l) rl,s cl,s Clmax , l sS(l) min s min s x xs xsmax , s R Rs 1, s 0 rl,s 1, l, s S(l) 0 cl,s Clmax , l, s S(l) - E error probability Bujar Krasniqi 2008-07-03 Date 20 Cross Layes Issues in UMTS-LTE Differentiated dynamic reliability The network diagram for that optimization problem is: xs Rs Network ( xs )sS (l ) Sources Linkl R 1 s E (r l L ( s ) l l,s Network ) (cl , s )sS (l ) (rl , s )sS (l ) Network diagram contain just primal variables Bujar Krasniqi 2008-07-03 Date 21 Cross Layes Issues in UMTS-LTE Differentiated dynamic reliability We use primal-dual mathematical decomposition techniques to solve the optimization problem for rate-reliability tradeoff The Lagrangian of the constrained optimization problem is U x , R x L ( x ' , R , r , c, , ) ' s ' s s s ' s s Rs s l , s log cl , s log rl , s s El rl , s l sS ( l ) s s where s lS ( l ) and Bujar Krasniqi l ,s xs ' log xs 2008-07-03 Date 22 Cross Layes Issues in UMTS-LTE Differentiated dynamic reliability Based on primal-dual mathematical decompositon Source rates=Primal variables Congestion prices=Dual variables Lagrange multipliers and Dual problem is: are dual variables m inim ize Pλ ,μ subject to λ0 μ0 The Lagrange dual function is: P( , ) max L( x' , R, r , c, , ) Constraint s Bujar Krasniqi 2008-07-03 Date 23 Cross Layes Issues in UMTS-LTE Differentiated dynamic reliability The diagram for distributed algorithm of the differentiated dynamic reliability is xs Network s Rs ( xs )sS (l ) ( s )sS (l ) Source s Linkl s l L ( s ) R 1 s E (r l L ( s ) Bujar Krasniqi l,s l l,s Network ) 2008-07-03 Date 24 (cl , s )sS (l ) (l , s )sS (l ) (rl , s )sS (l ) Cross Layes Issues in UMTS-LTE CLO based on layer description Now we propose a concept of exchanging information between adjacent layers in terms of layer description [7] The model is: Dn 1 Layer (n+1) yn 1 Dn Layer (n) Layer (n-1) Layer (1) Bujar Krasniqi 2008-07-03 Date 25 yn Dn 1 D1 Cross Layes Issues in UMTS-LTE CLO based on layer description The layer output set is defined as: yn f n ( xn , dn1) R N0 ,n : xn n , dn1 Dn1 Layer function is f n : n Dn1 R N o ,n n - set of feasible parameter values, Dn1- description of layer n-1 Bujar Krasniqi 2008-07-03 Date 26 Cross Layes Issues in UMTS-LTE Conclusions 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 Bujar Krasniqi 2008-07-03 Date 27 Cross Layes Issues in UMTS-LTE 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 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 Bujar Krasniqi 2008-07-03 Date 28 Cross Layes Issues in UMTS-LTE Thank you for your attention !