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Cross Layer Issues in UMTS-LTE

Cross Layer Issues in UMTS-LTE. Bujar Krasniqi bujar.krasniqi@nt.tuwien.ac.at 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

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Cross Layer Issues in UMTS-LTE

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  1. Cross Layer Issues in UMTS-LTE Bujar Krasniqi bujar.krasniqi@nt.tuwien.ac.at 2008-07-03 Mobile Communication Seminar

  2. 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 Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 1 2008-07-03

  3. Introduction to layered system • Why do we need Cross Layer Design (CLD) ? • Open System Interconnection (OSI) • Protocols • Quality of Service (QoS) • Types of Services Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 2 2008-07-03

  4. 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 Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 3 2008-07-03

  5. OSI model • The International StandardizationOrganization (ISO) began • to work in 1980s [1] • This work led to design the Open System Interconnection(OSI) Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 4 2008-07-03

  6. 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] Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 5 2008-07-03

  7. 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 Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 6 2008-07-03

  8. 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 Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 7 2008-07-03

  9. Cross layer design approach Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 8 2008-07-03

  10. 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 Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 9 2008-07-03

  11. 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. Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 10 2008-07-03

  12. Cross layer proposals • Proposals can be divided by: • Creation of new interfaces • Bottom-up • Top-down • Merging adjacent layers (super layers) Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 11 2008-07-03

  13. Cross layer proposals • The way of exchanging information between layers [3] • Direct communication between layers • A shared database across the layers Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 12 2008-07-03

  14. 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] • there are possible joint strategies *APP-application layer Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 13 2008-07-03

  15. Cross layer optimization • 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 Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 14 2008-07-03

  16. Joint cross layer optimization • 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] Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 15 2008-07-03

  17. Joint cross layer optimization • The conceptual scheme for joint CLO is: [4] Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 16 2008-07-03

  18. Utility function • 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 Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 17 2008-07-03

  19. Network utility maximization • 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 Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 18 2008-07-03

  20. Network utility maximization • The graphical representation between data rate and reliability • is: • Now the utility function U(.) will be defined as a function of rate • and reliability Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 19 2008-07-03

  21. Differentiated dynamic reliability • The optimization problem that represents tradeoff between rate • and reliability for differentiated dynamic reliability case is: [6] - E error probability Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 20 2008-07-03

  22. Differentiated dynamic reliability • The network diagram for that optimization problem is: • Network diagram contain just primal variables Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 21 2008-07-03

  23. 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 where and Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 22 2008-07-03

  24. Differentiated dynamic reliability Source rates=Primal variables Congestion prices=Dual variables • Based on primal-dual mathematical decompositon • Lagrange multipliers and are dual variables • Dual problem is: • The Lagrange dual function is: Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 23 2008-07-03

  25. Differentiated dynamic reliability • The diagram for distributed algorithm of the differentiated • dynamic reliability is Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 24 2008-07-03

  26. 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: Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 25 2008-07-03

  27. CLO based on layer description • The layer output set is defined as: • Layer function is - set of feasible parameter values, - description of layer n-1 Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 26 2008-07-03

  28. 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 Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 27 2008-07-03

  29. 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 Date Cross Layes Issues in UMTS-LTE Bujar Krasniqi 28 2008-07-03

  30. Thank you for your attention !

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