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Lecture 12: Cross Layer Design (CLD) for Wireless Networks Future Wireless Systems Ubiquitous Communication Among People and Devices 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… Next Generation Network Architecture Internetworking Layer Mobility Services Layer Network Service Layer Local Service Layer Access Management Radio Layer Access Layer Access Interface Layer Mobile Terminal Layer Wireless Interface Layer Mobile Application Layer Internet Wireless PSTN Radio Access Network Mobile User Equipment (e.g. Win9X, Palm OS) Application Network Server (e.g. WinNT, Unix) Radio Access Network Radio Resource Mgmt Application IP Transport (TCP, UDP, RTP) Internet Protocol (IP) Ethernet Modem Radio Access IP Transport (TCP, UDP, RTP) Transport Agents Transport Agents Radio Access L2 L2 IP Internet Protocol (IP) Access Core L2 L2 Internet Radio Access L1 L1 Access Core L1 L1 Radio-Optimized IP Networking • Transparent to TCP/IP protocols • Enables deployment of IP-based consumer applications in next generation wireless systems Ethernet ATM Our simplified model for wireless systems OSI Model Application Presentation Session Simplified wireless network layered model App. Layer Transport Transport Layer Network Network Layer (MAC sublayer) MAC Layer Data Link Physical Physical Layer Separation principles Application, transport and physical layer can be separated if : Application Signal No errors at physical layer No losses and delays at transport layer Transport Packet No fluctuations in applications rate Physical Bits Each layer being perfect from the point of view of other layers 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 Wireline Backbone 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 • 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 Signal processing Architecture: Connection Vs Connectionless Energy efficient analysis of manets Traffic theory & protocols 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 MAC layer Access delay, throughput Network layer BER (Bit error rate) Delay, throughput, blocking probability, dropping probability Other important performance measures Energy (power consumption, network lifetime) User capacity Impact all layers QoS Requirements Voice Delay Packet Loss BER Data Video <100ms - <100ms <1% 0 <1% 10-3 10-6 10-6 Data Rate 8-32 Kbps Traffic Continuous 1-100 Mbps Bursty 1-20 Mbps Continuous 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 adhoc networks Physical layer + MAC Physical layer + network layer Adaptive beamforming and CSMA/CA Adaptive modulation and MAC Adaptive power control and MAC 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 – – • Link Design – • Resource allocation (power, rate, BW) Interference management Networking. – • Time-varying low capacity channel Multiple Access – – • Power or hard energy constraints Size constraints Routing, prioritization, and congestion control Application – – Real time media and QOS support Hard delay/quality constraints Multilayer Design Cross-layer Techniques Adaptive techniques Diversity techniques Link, MAC, network, and application adaptation Resource management and allocation (power control) Synergies with diversity and scheduling Link diversity (antennas, channels, etc.) Access diversity Route diversity Application diversity Content location/server diversity Scheduling Application scheduling/data prioritization Resource reservation Access scheduling