Cross Layer Design (CLD) for Wireless Networks

Future Wireless Systems Nth Generation Cellular Wireless Internet Access Wireless Video/Music Wireless Ad Hoc Networks Sensor Networks Smart Homes/Appliances Automated Vehicle Networks All this and more… Ubiquitous Communication Among People and Devices

Next Generation Network Architecture Mobility Services Layer Radio Access Layer Mobile Terminal Layer Internetworking Layer Local Service Layer Network Service Layer Access Management Layer Access Interface Layer Wireless Interface Layer Mobile Application Layer InternetWirelessPSTN

Radio Access Network Mobile User Equipment (e.g. Win9X, Palm OS) Application Network Server (e.g. WinNT, Unix) IP Transport (TCP, UDP, RTP) Internet Protocol (IP) Radio Access Modem Ethernet Application IP Transport (TCP, UDP, RTP) Internet Protocol (IP) Ethernet ATM Internet Transport Agents IP Radio Resource Mgmt Radio L1 Access L1 Radio L2 Access L2 Access L1 Core L1 Access L2 Core L2 Radio-Optimized IP Networking Transparent to TCP/IP protocols Enables deployment of IP-based consumer applications in next generation wireless systems

Our simplified model for wireless systems Application Presentation Session Transport Network Data Link Physical (MAC sublayer) OSI Model Physical Layer MAC Layer Network Layer Transport Layer App. Layer Simplified wireless network layered model

Separation principles  Application, transport and physical layer can be separated if :  No errors at physical layer  No losses and delays at transport layer  No fluctuations in applications rate  Each layer being perfect from the point of view of other layers Application Transport Physical Signal Packet Bits

Challenges  Wireless channels are a difficult and capacity-limited broadcast communications medium  Traffic patterns, user locations, and network conditions are constantly changing  Applications are heterogeneous with hard constraints that must be met by the network  Energy and delay constraints change design principles across all layers of the protocol stack These challenges apply to all wireless networks, but are amplified in ad hoc/sensor networks

Why is Wireless Hard? The Wireless Channel  Fundamentally Low Capacity: R< B log(1+SINR) bps  Spectrum scarce and expensive  Received power diminishes with distance  Self-interference due to multipath  Channel changes as users move around  Signal blocked by objects (cars, people, etc.)  Broadcast medium – everyone interferes d

…And The Wireless Network  Link characteristics are dynamic  Network access is unpredictable and hard to coordinate  Routing often multi-hop over multiple wireless/wired channels  Network topology is dynamic  Different applications have different requirements Wireline Backbone They are formed by nodes with radios – There is no a priori notion of “links” – Nodes simply radiate energy

What lead to CLD?  Advanced applications like VOIP, Web browsing, multimedia conferences & video streaming demanded  Widely varying and diverse QoS guarantees  Adaptability to dynamically varying networks & traffic  Modest Buffer requirements  High and effective Capacity utilization  Low processing overhead per packet  Video streaming high bandwidth requirements are coupled with tight delay constraints

Cross Layer Design  CLD is a way of achieving information sharing between all the layers in order to obtain highest possible adaptivity of any network.  This is required to meet the challenging Data rates, higher performance gains and Quality of Services requirements for various real time and non real time applications.  CLD is a co-operation between multiple layers to combine the resources and create a network that is highly adaptive

Cross Layer Design  This approach allows upper layers to better adapt their strategies to varying link and network conditions.  This helps to improve the end-to-end performance given networks resources.  Each layer is characterized by some key parameters, that are passed to the adjacent layers to help them determine the best operation modes that best suit the current channel, network and application conditions

Cross Layer Design  Wireless Networking  Architecture: Connection Vs Connectionless  Energy efficient analysis of manets  Traffic theory & protocols  Signal processing  Increasing the spectral efficiency  Reducing Bit Error Rate  Reducing transmission energy  Information Theory  Developing capacity limits  Designing efficient source coding and channel algorithms

Cross Layer Design  General framework for cross–layer design  Maintain the layered approach but exchange information between layers and jointly optimize the performance  Abstraction of layers  General models for different layers  capture important parameters which influence other layers  Identify the cross-layer information that has to be exchanged between layers  Implement adaptation protocols at each layer, using the information exchange between the layers  Several tools for analysis and optimization at different layers  Physical layer  determine SIR as a key performance measure for the physical layer  Optimize powers, receivers, antennas  MAC and Network layers  QoS measures: Delay and blocking performance  Optimize scheduling, routes, number of users allowed in the network

Cross Layer Signaling Methods  Method I – Packet headers  Method II – ICMP Messages  Method III – Local Profiles  Method IV – Networks Services

CLD Design goal ?  Deliver QoS  QoS measures  Physical layer  BER (Bit error rate)  MAC layer  Access delay, throughput  Network layer  Delay, throughput, blocking probability, dropping probability  Other important performance measures  Energy (power consumption, network lifetime)  User capacity Impact all layers

QoS Requirements VoiceVideoData Delay Packet Loss BER Data Rate Traffic <100ms- <1% Kbps1-100 Mbps1-20 Mbps ContinuousBurstyContinuous One-size-fits-all protocols and design do not work well Wired networks use this approach, with poor results

CLD  Hardware  Link  Access  Network  Application Delay Constraints Rate Constraints Energy Constraints Adapt across design layers Reduce uncertainty through scheduling Provide robustness via diversity

Examples of cross-layer integration for ad- hoc networks  Physical layer + MAC  Adaptive beamforming and CSMA/CA  Adaptive modulation and MAC  Adaptive power control and MAC  Physical layer + network layer  Adaptive power control + routing  Adaptive power control + receiver optimization + routing  Power control + routing + receiver optimization + admission control  Physical layer + MAC + routing  Adaptive modulation + MAC + routing  Adaptive beamforming + MAC + routing

Case 1: Adaptive beamforming + MAC + routing  In general, different MAC protocols differ based on  How RTS/CTS is transmitted (omni, directional)  Transmission range of directional antennas  Channel access schemes  Omni or directional NAVs  The antenna gains are different for omnidirectional (Go) and directional transmission(Gd): Gd > Go  An idle node listens omnidirectionally  Does not know who is going to transmit to it

Pros and Cons for directional antennas Advantages  Spatial reuse Multiple transmissions in the same neighborhood  Higher gains – better links  Two distant nodes may communicate with a single hop  Fewer hops in a route Disadvantages  Higher gains mean also high interference at distanced nodes There are three types of links  omnidirectional – omnidirectional : OO links – smallest range  directional – omnidirectional: DO links  directional –directional – largest range

Joint MAC and routing solution  Use the same MAC for directional antennas, but transmit RTS over multiple hops (MMAC protocol)  If source 1 wants to communicate with node 6  transmits a forwarding RTS with the profile of node 6, using DO links  when node 6 gets the RTS, it beamforms in the direction of 1, forming a DD link  Transmission from 1 to 9 on DD links requires only 2 hops

Performance Evaluation

Multilayer Design Hardware – Power or hard energy constraints – Size constraints Link Design – Time-varying low capacity channel Multiple Access – Resource allocation (power, rate, BW) – Interference management Networking. – Routing, prioritization, and congestion control Application – Real time media and QOS support – Hard delay/quality constraints Multilayer Design

Cross-layer Techniques  Adaptive techniques  Link, MAC, network, and application adaptation  Resource management and allocation (power control)  Synergies with diversity and scheduling  Diversity techniques  Link diversity (antennas, channels, etc.)  Access diversity  Route diversity  Application diversity  Content location/server diversity  Scheduling  Application scheduling/data prioritization  Resource reservation  Access scheduling