Roadmap to Cross-Layer Optimization Roadmap to Cross Layer by bestt571


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                                                                                                • The future leads towards an ambient where wireless communications
                               Cross Layer
                    Roadmap to Cross-Layer Optimization                                           will exist in every scenario of life to provide the end user the
                                                                                                  “flexibility and choice”.
                                                                                                • The beyond 3G communication vision concerns scenarios where
                  Department of Information and Communication Systems Engineering                                                  service
                                                                                                  user will be able to attain any service, at any time on effectively any
                                       University of the Aegean                                   network that is optimised for the application at hand.
                                   Karlovassi, 83200, Samos, Greece                                   – Thus creating a future global infrastructure, where several systems can
                                                                                                        coexist to support transparent end-to-end communications, in an
                                                                                                        efficient, cost-effective manner; ABCS (Always Best Connected Systems)
                                                                                                • An important architectural issue is that of defining a next-generation
                                                                                                  wireless system, which acts as a “network-of-wireless-networks”
                                                                                                                g        y                     g
                                                                                                  accommodating a variety of radio technologies and mobile service
                                                                                                  requirements in a seamless manner.
                                                                                                      – Significant challenges in view of the devices heterogeneity, systems
                                                                                                        scale and network robustness requirements

George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”                    Page 1   George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”                  Page 2

                                                      Motivation                                                                                   Motivation

   • The next generation of mobile technology will probably incorporate                         • At an inter-system level the coexistence of communication entities
     innovations at many levels:                                                                  raises several issues:
         – At the device level new technologies such as UWB (Ultra Wideband) and                • First the quantification of interference levels, due to coexistence.
           MIMO (Multiple Input Multiple Output) have the potential to significantly                  – Many weak signals can accumulate and become strong enough to cause
           increase the physical data rates;                                                               bl           i ti     t   k
                                                                                                        problems on coexisting networks.
         – At the networking level multi-access technologies are proposed to
                                                                                                • Second of interoperability, given that currently Radio Access
           improve the reachability, availability and efficiency of wireless networks.
                                                                                                  Network (RAN) systems are designed and deployed to operate
   • At an intra-system level previous theoretical developments have                               ffi i tl in             t       i
                                                                                                  efficiently i a mono-system environment.  t
     indicated strong interactions between the PHY layer signalling
     schemes and channel conditions with the networking issues of                               • The ultimate vision of a network of wireless networks where the user
     resource allocation.                                                                         connects to the best available system, while conceptually simple,
                                                                                                  brings significant challenges:
                                                                                                  b i      i ifi   t h ll
   • Several problems traditionally considered as networking issues and                               – Detection: What accesses are currently available?
     are typically designed independently of the transmission techniques
                                                                                                      – Selection: What access to choose; which is “best”, one or multiple
                  re examined.
     need to be re-examined                                                                             accesses in parallel?
   • Cross-layer design and optimisation will be the key to adequately                                – Reselection: Under what conditions reselection is necessary; which
     exploit all the potential of next generation wireless communication                                network to choose? How reselection is accomplished?

George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”                    Page 3   George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”                  Page 4
                                    Cross-Layer Optimisation                                           Cross-Layer Optimisation

   • Layering is the dominating design methodology of                 • To cope with this variability of the wireless channel,
     communication protocol stacks. An essential feature                techniques have been developed either at the physical or at
                                                                        the MAC layer.
     of the layering principle is layer-independence
                                                                      • The main shortcoming of the strictly based PHY layer
     (modularity), which represents the classical
                                                                        approaches is that they do not take into account the impact on
     engineering approach to solve complex problems.                    the upper layers.
   • However, the strict layering approach presents                   • The main shortcoming of strict layering MAC layer based
     significant limitations when it comes to wireless                  schemes is that they are based on “hard” channels, i.e. they
               i ti                                                                                                      layer.
                                                                        use very limited information from the physical layer This
                                                                        implies that the throughput achievable at the upper layers is
   • The wireless networks are characterised by a                       only a small fraction of the capacity offered by the PHY layer.
     d       i topology (
     dynamic t      l                       d l       t
                         (users move around, also enter               • For example, consider IEEE 802.11a & g (fastest on the
     and leave); the link exhibits a time-varying quality               market): the highest PHY rate is 54 Mbps, but above the MAC
             fading, shadowing
     due to fading shadowing, in addition to multiuser                                                Mbps
                                                                        there is always less than 30 Mbps, and with RTS/CTS less than
     interference.                                                      24 Mbps is achieved, even under no contention.
                                                          Page 5
George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”   George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”   Page 6

                                    Cross-Layer Optimisation                      Cross-Layer Optimisation and Coexistence

   • The loss of efficiency is further aggravated if instead          • It is also easy to anticipate that if the optimum
     of considering only the two bottom layers, one                     performance is not achieved at the intra-system level
     considers E2E performance involving the whole                      because of cross-layer inefficiencies, performance is
     stack.                                                             further hampered when considering the coexistence
   • For example, certain routing protocols require that                of heterogeneous systems, which will be the
     nodes broadcast control messages to all neighbours                        di   f
                                                                        paradigm for B3G scenarios. i
     and wait for all of them to reply. This imposes a                • One of the key aspects to get the best from wireless
     t        d     t i      th
     tremendous strain on the medium access layer. Also,
                                    di            l     Al                   t      ill l
                                                                        systems will rely on:
     routing protocols tend to treat all neighbours equally                 – Cross-layer interactions;
     accessible.                                                              Definition f ffi i t           t        d
                                                                            – D fi iti of efficient cross-system procedures.
   • It is very important that the designers of the routing
     protocol of a system are aware of the limitations of
     the MAC protocol of that system, and vice versa. Page 7                                                                          Page 8
George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”   George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”
                                     Cross Layer Interactions                                                     Cross Layer Interactions

   • A cross-layer architecture encompasses an                                  • No universal answer to both questions.
     additional complexity relatively to a strictly-layered                     • The answer to the first question depends on the
     one, due to the fact that additional information                             specific algorithm at the given protocol layer.
                                                                                   p         g              g      p          y
     besides the one that defines the basic service                             • The answer to the second question also depend on
     provided by the layer has to be exchanged. The need                          several algorithm dependent aspects (centralised vs.
                                                                                             g         p            p    (
     t exchange additional cross-layer information (CLI)
     to    h        dditi   l       l      i f     ti                             distributed)    and    on    the    specific   systems
     leads to two fundamental questions:                                          architecture.
         – What information should be exchanged across protocol
           layers, and, how frequently should this exchange proceed?            Important Note
         – What are the adequate / efficient procedures to exchange             • Although, the use of cross-layering has the potential
                                                                                         g ,                     y    g         p
           this information?                                                      to significantly improve E2E throughput, its nature
                                                                                  obviously implies some loss of flexibility which is
                                                                                  inherent of the modular structure of a layered stack.
George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”   Page 9    George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”   Page 10

                                     Cross Layer Interactions                           Definition of efficient cross-system procedures

   • There are therefore significant challenges                                 • Beyond the problem of cross-layering optimisation
     associated with the development of a cross-layered                           that occurs at the intra-system level, the next
     protocol stack:                                                              problem that will be of paramount importance in the
   • Architectural challenges:                                                    “network of wireless networks” scenario envisioned
         – How to answer previous questions without excessive                     for B3G will be the definition of efficient, and secure
           overheads?                                                                       t          d       ll i th
                                                                                  cross-system procedures allowing the user to gett   t
         – How far to go in the cross-layering principle?                         always the best (quality, cheap, secure, etc.) system
         – Wh t are th t d
           What                  ff between improved th
                     the trade-offs b t      i               h t d
                                                     d throughput and             from the network
           loss of modularity?

George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”   Page 11   George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”   Page 12
           Definition of efficient cross-system procedures                                        Dynamic Resource Allocation (DRA) Issues

   • A cross-layer optimised radio access may lose its optimal                        • Research focuses on how to exploit additional cross-
     attributes in the presence of a heterogeneous network.                             system information (e.g. QoS metrics from IPv6
   • Thus there is a need for further L1-to-L3 algorithmic                              packets, accurate routing information, knowledge of
     optimisation in a bid to achieve virtual mono system
                                                                                        resource allocation strategies in neighbouring
     performance, and ensure transparent connectivity to multiple
     networks.                                                                          systems, current system interference statistics,
   • This raises new design challenges in algorithmic design:                              d l i
                                                                                        underlying PHY l         d h      l        t
                                                                                                        layer and channel parameters) to)t
         – Which set of additional cross-system information is required, and            allocate available radio resources to attain a trade-
           what signalling overhead is required to deliver this information                                                 throughput,
                                                                                        off among maximising cell service throughput
           and at which rate?                                                           minimising signalling overhead, reducing complexity,
      p          y,                q                   y
   • Specifically, solutions are required for current dynamic                                                                         users.
                                                                                        and achieving the intended priority between users
     resource allocation, and mobility protocols to ensure both
     efficient, and seamless connectivity and mobility between
     wireless systems can be achieved

George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”         Page 13   George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”     Page 14

                               Cross-system Mobility Issues                                          Cross-Layer Optimization Current Status

   • Although mobility protocols at L3 have extensively been                          • Physical layer engineers use specific tools where they
     investigated, there is a need:                                                     integrate very detailed models, and even at the PHY layer
         – To address a cohesive solution between L2, and L3, so that the               there are differences in terms of time-scale for
                    cross-system                   exchanged.
           relevant cross system parameters are exchanged                                                                base-band designs.
                                                                                        simulations between the RF and base band designs
         – To study the type of cross-system parameters, and signalling               • At the upper level, radio planning tools or network
           cost, which will have implications on service throughput.
                                                                                        simulators basically rely on simple abstract models
         – To analyse the detailed implications of the L3 mobility protocols
           on L2 handover.                                                              describing the behaviour of the lower layers.
         – To consider a joint design for the L2 L3 mobility protocol so
                                              L2-L3          protocol,                                                          p
                                                                                            – While for some scenarios simplified abstract models may be    y
           seamless mobility and connectivity between systems can be                          sufficient and do not significantly compromise accuracy of the
           achieved.                                                                          simulation results, they are often in place because detailed
                                                                                              models are too difficult to implement and to run efficiently.

George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”         Page 15   George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”     Page 16
                                                                                                                        “Cross-Layer Design: A Survey and the Road Ahead”
                                                                                                                                     V. Srivastava, M. Motani
            Review on Cross-Layer Algorithms and Design Issues                                                                             Magazine vol. 43, no.12, Dec.
                                                                                                                     IEEE Communications Magazine, vol 43 no 12 Dec 2005

                                                                                               • the upward information flow, where
                                                                                               specific information parameters from
                                                                                               lower layers are used from upper
                                                                                               • downward information flow,
                                                                                               parameters from upper layers are
                                                                                               used for optimizing behaviour of
                                                                                               lower layers,
                                                                                               • back-and-forth information flow, ,
                                                                                               which is the combination of the first
                                                                                               two cases,
                                                                                               • merging of adjacent layers, which
                                                                                               creates a ‘super’ layer from the                                                    cross layer
                                                                                                                                                                Different kinds of cross-layer design proposals
                                                                                               combination of two existing ones,
                                                                                               • the design coupling without new                        Implementation:
                                                                                                                                                        • Layer-to-Layer direct Communication via new interfaces
                                                                                               interfaces, ,                                            • Layers share a common database
                                                                                               • the vertical calibration, where the                    • Create new abstractions (no more typical layering approach)
                                                                                               performance seen at the level of the
                                                                                               application is a function of the
                                                                                                       t      t ll th l      b l    it
                                                                                               parameters at all the layers below it.

George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”                Page 17      George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”                                                           Page 18

                                                                                             “A Framework for Cross-layer Design of Energy-efficient Communication with QoS Provisioning
“Cross-Layer-Based Modeling for Quality of Service Guarantees in Mobile Wireless Networks”
                                                                                                                           in Multi-hop Wireless Networks”
                    X. Jhang, J. Tang, H. Chen, S. Chi, M. Guizani,
                                                                                                                        C. Kozat, I. Koutsopoulos, L. Tassiulas
                                        Magazine vol. 44, no.1, Jan.
                IEEE Communications Magazine, vol 44 no 1 Jan 2006
                                                                                                                      IEEE INFOCOM-2004 , Hong Kong, 2004

                                                                                                    In this work, cross – layer design is used between
       This cross-layer approach investigates the impact of the                                     physical and MAC layers. Power control and
       physical layer on the data-link layer in mobile wireless                                     Scheduling are jointly used in order to achieve
       networks.                                                                                    minimizing the total transmit power, and at the same
       At the physical layer MIMO diversity schemes as well as AMC                                  time maintain the proper QoS levels, in terms of
       (Advanced Modulation Coding) are taken into account                                                                    rate.
                                                                                                    bandwidth and bit error rate
       At the data-link layer, the influence of the physical                                        Input: Link gains, QoS parameters
       infrastructure on real time multimedia performance is
                                                                                                    O t t T          i i P          f     h d
                                                                                                    Output: Transmission Power for each node
       Input: Physical layer diversity schemes (number of transmit
       antennas) QoS reliability requirements (packet error rate -
       Output: Effective capacity

George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”                Page 19      George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”                                                           Page 20
“Topology-Aided Cross-Layer Fast Handoff Designs for IEEE 802.11/Mobile IP Environments”                                                           “Cross-Layer Feedback Architecture for Mobile Device Protocol Stacks”
                          C. Tseng, L. Yen, H. Chang, K. Hsu                                                                                                             V. Raisinghani, S. Lyer
                IEEE Communications Magazine, vol. 43, no.12, Dec. 2005                                                                                                                   vol. 44, no.1, Jan.
                                                                                                                                                          IEEE Communications Magazine vol 44 no 1 Jan 2006

          p gy                              q
       Topology-aided fast handoff technique for 802.11                                                                                          p p        g g                         y
                                                                                                                                           This paper highlights the need for cross-layer feedback
       networks.                                                                                                                           architecture and identifies key design goals for such
       Layer 3 handoff-related procedures (e.g., agent                                                                                     architectures.
       discovery address configuration and registration) can be
       discovery,                                                                                                                          Cross layer information exchange can be realised by:
       performed in parallel with or prior to those of layer 2                                                                             • additional blocks of code into layers,
       handoff (i.e. probe, authentication and reassociation).
                                                                                                                                           • the usage of ICMP messages,
                                                                                                                                                       g                g ,
              cross-layer           information
       Using cross layer topology information, such as
       association between APs and Mobile IP mobility agents,                                                                              • injection of cross-layer information into packet headers
       handoff related layer-2 triggers may reduce the delay                                                                               and
       between layer-2 handoff completion and the associated
       b t       l     2 h d ff        l ti     d th        i t d                                                                             i    lli        h i
                                                                                                                                           • signalling mechanisms.
       layer-3 handoff activation. This way, the handoff latency                                                                           In ECLAIR, a tuning layer (TL) for each layer, provides an
       time (e.g., AP probe delay, authentication delay, move                                                                              interface to read and update these protocol data-structures.
                                                                                                                                                                    p           p
       detection d l          t di        d l        i t ti d l
       d t ti delay, agent discovery delay, registration delay,                                                                            TLs are then used by protocol optimizers (POs), which
       etc.) can be reduced.
                                                                                                                                           contain cross-layer feedback algorithms, allowing even user
         p         p              p gy
       Input: Link performance, topology information
                                                                                                                                                         (e g
                                                                                                                                           feedback (e.g., application prioritization) for performance
       Output: Handoff triggers
George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”                                                   Page 21          George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”                           Page 22

              “Cross-layer Design of Ad Hoc Networks for Real-Time Video Streaming”                                                                             “Cross-Layering in Mobile Ad Hoc Network Design”
                          E. Setton, T. Yoo, X. Zhu, A. Goldsmith, B. Girod                                                                                   Marco Conti, Gaia Maselli, Giovanni Turi, Silvia Giordano
                      IEEE Wireless Communications Magazine, August 2005                                                                                                        Computer
                                                                                                                                                                          IEEE Computer, February 2004

  This paper explores a cross-layer design framework
       p p       p                y       g                                                                                                Advocates that the level of cross –
  for real-time video streaming, which maintains a                                                                                         layering that is necessary is not clear.
  general layered structure and identifies the key
  parameters to be exchanged between adjacent                                                                                              It proposes a new architecture for
  layers.                                                                                                                                  MANETs that introduces a new core
  • Link layer information adjusts packet size, symbol
  rate, and constellation size according to channel                                                                                        component, Network Status,
  conditions.                                                                                                                              responsible for the cross – layering
  •TTransport layer i f
              tl            ti
                     information enables smart
                                     bl       t                                                                                            d t sharing.
                                                                                                                                           data h i
  scheduling protecting video stream, and
  • MAC and Network layer information adjusts the                                                                                          Through this new architecture, the
  supported traffic rate.
     pp                                                                                                                                            y     g
                                                                                                                                           cross layering that is vital for functions
  Layers/systems referred to: Application, Transport,                                                                                      like energy management is present, all
  Network, MAC and Link Layer
                                                                                                                                           layers are capable of knowing
  Input: Symbol rate, constellations size, channel
  conditions capacity, video rate distortion and
  conditions, capacity                                                                                                                                                  layers,
                                                                                                                                           information from all other layers and
  latency requirements                                             Cross-layer design for real-video streaming in ad-hoc networks          at the same time, keep overhead to
  Output: Packet size, traffic rate, packet scheduling,                                                                                    acceptable levels.                                               MobileMan architecture.
  appropriate source rate

George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”                                                   Page 23          George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”                           Page 24
“Design and Implementation of a Simulator Based on a Cross-Layer Protocol between MAC and
             PHY Layers in a WiBro Compatible IEEE 802.16e OFDMA System”                         “Multivariate Analysis of the Cross-Layer Interaction in Wireless Networks Simulations”
          T. Kwon, H. Lee, S. Choi, J. Kim, D. Cho, S. Cho, S. Yun, W. Park, K. Kim                             Jean-Michel Dricot, Philippe De Doncker, Esteban Zimànyi
                     IEEE Communications Magazine, December 2005                                                                                     Ad-hoc
                                                                                                                International Workshop on Wireless Ad hoc Networks 2005

        In this paper cross-layer design frameworks for 802.16e
                      cross layer                                                                       p p                                        y
                                                                                                   This paper uses the mathematical tool of ANalysis Of VAriance
        OFDMA systems that are compatible with WiBro are                                           (ANOVA) in multivariate data, in order to study the interactions
                                                                                                   between the layers of a wireless system.
                                                                                                   The analysis p
                                                                                                            y                  y           g     y
                                                                                                                 proves not only that a single layer can affect the
        In the proposed model, the MAC layer contains a user                                       whole network operation, but also reveals the existence of
        grouper, scheduler, and resource controller. Each                                          interesting interactions between the layers of the system, as
        functional entity exploits PHY information to increase system                              shown between four variables:
        throughput.                                                                                • routing algorithm,
                                                                                                   • propagation conditions,
        In addition, a simulation framework for cross-layer analysis
                                                                                                   • nodes density and
        between the MAC and PHY layers in 802.16e systems is
                                                                                                   • mobility scheme.
        provided indicating improvement for the average cell
                                                                                                   The study also reveals a correlation of the routing protocol with
        throughput.                                                                                the type of environment (indoor / outdoor
        Output: User and packet scheduling

 George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”                Page 25    George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”                      Page 26

                             “A Cautionary Perspective on Cross-Layer Design”
                                        Vikas Kawadia, P. R. Kumar                                                Projects for Cross-layer Optimization
                          IEEE Wireless Communications Magazine, February 2005

        The trend to use cross – layer interaction in order to improve
                                     y                            p                            • The cross-layer optimisation projects are currently
        wireless networks’ performance is significant in our days.                               being targeted to attain an optimised solution, using
        This paper is on the opposite side, defending the traditional
                                                                                                 a cross profile support entity to gather and maintain
        In order to prove its point it conducts some simulation comparing                        user-specific and system information from all layers,
        some cross – layer algorithms with others not using this approach.                       e.g., MAGNET, 4MORE, WINNER.
        Agree that cross – layering is the only way to optimize certain
        parameters, and suggest points that protocol designers must
        • loss of modularity
        • the fact that every time a protocol is replaced, there will probably
        be a need for total redesign of the algorithm,
        • the dependencies between parameters shared between layers,
        • guarantee that the interactions between protocols are only those
        intended and the absence of unintended interactions.

 George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”                Page 27    George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”                      Page 28
                      Projects for Cross-layer Optimization                                 Project for Cross-layer/Cross-system Optimization

   • The WHYNET project (Scalable Testbed for Next Generation                   • UNITE builds through open APIs a VDT of
     Mobile Wireless Networking Technologies) [WHYNET]                            clusters/systems giving also the chance for cross-
     proposes to design and develop a Wireless HYbrid NETwork
     testbed to facilitate a detailed study of cross-layer
                                               cross layer
                                                                                  system and cross-layer operational scenarios
     interactions, that extend from the application layer down to the             running horizontally among a number of
     physical devices, and their impact on application level                      heterogeneous clusters.
         f          i h t                i l
     performance in heterogeneous wireless systems. t
   • The hybrid testbed is a networked federation of geographically
     distributed heterogeneous wireless physical testbeds with
     multiple protocol stacks.
   • The testbed itself will be accessible by the research
     community via a web-based mechanism that will allow remote
     uploading of models, implementations, and configurations.

George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”   Page 29   George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”   Page 30

                                             THANK YOU

George Kormentzas, “Roadmap to Cross-Layer Optimization for B3G”   Page 31

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