/12

• 1 Introduction

• 2 Architecture and Building Blocks

• 3 New Challenges in Wireless Networks

• 4 Mobility Modeling

• 5 Power Control and Multiuser Diversity

• 6 Multiple Access Schemes

• 7 Routing, Energy Efficiency, and Network Lifetime

• 8 Congestion Control in Wireless Networks

• 9 Cross-Layer Design and Optimization

Main Topics:

/12

In this chapter, the fundamentals of wireless networks(WN) are discussed. The chapter starts with a review of the protocol architecture and building blocks. It follows with new challenges brought about by wireless communications. The design of different layers are then examined and discussed. The remaining parts of chapter are allocated for description and consideration of special characteristics of WN such as mobility modeling, congestion control etc.

The chapter ends with a conclusion about the above mentioned subjects in the cross-layer design and optimization in the context of WNs.

Introduction

/12

• A communication network (CN) consists of hosts and network nodes, interconnected with links.

• Metcalfe’s law :• The value of a telecommunication network is proportional to the square of the number of

Connected users of the system.

• Divide-and-Conquer approach:• Each task is broken down into subtasks which are organized in a “hierarchical way”.

• Classifications of CN, (based on the switching tech. employed) :• Circuit switching net. (e.g. PSTN)

• Packet switching net. (e.g. LAN)

• Virtual circuit switching net. (e.g. ATM)

• Combining features of both circuit switching and packet switching.

2 Architecture and Building Blocks

/12

• Naming and Addressing: Used to uniquely identify different computers.• IP address, Application layer.

• Medium Access Control (MAC), Link layer.

• Routing and Forwarding: Main functions of the network layer.• 1.Maintaining network topology information

• 2.Forwarding packets.

• Congestion Control and Flow Control: • Store-and-Forward technique

• Error Control:• Checksum algorithm : to detect bit errors in the header of a received packet.

• One’s complement sum

• Cyclic redundancy check : to detect errors in the entire frame

• Sequence numbers : to detect lost packets.

2 Architecture and Building Blocks

/12

• Wireless Transmissions :• Path attenuation• Doppler effect• Multipath fading• Shadowing

• Mobility :• Mobility management is needed due to:

• Doppler shift• Varying obstacles• Reflecting and diffracting environment• Varying distance

• Energy Efficiency:• Power control: not only conserves energy but also reduces interference.• IEEE 802.11: the power-saving mode. Asleep nodes

3 CHALLENGES IN WIRELESS NETWORKS

/12

• Mobility Models:• Single-node mobility models:

• where the movement of a single node is specified,

• Group mobility models:

• which prescribe how users move in loosely defined groups.

• The Random Waypoint (RWP) Model:• Simplicity

• Flexibility

• Decreasing simulation time

• Most common random traffic model

• Perfect Simulation for better RWP Model• Guarantee the existence of stationary distributions

• Remove the transient phase and ensure convergence to the stationary distributions

4 MOBILITY MODELING

/12

• Diversity: (Time, Frequency, Space)• Using multiple independent paths between the transmitter and receiver (e.g. MIMO)

• Resulted in combating fading.

• Diversity Achievement:• Over time by interleaving coded bits

• Over frequency by combining multiple paths in spread-spectrum systems

• Over space by adopting multiple antennas

• Multiuser Diversity:• Main idea: Power control

More (less) power allocated to a user with stronger (weaker) channel.

5 POWER CONTROL AND MULTIUSER DIVERSITY

/12

How to fairly allocate power not to kill weaker channels!?

• Medium Access Control: • Sharing the channel among the users efficiently and fairly.

• Resulted in high spectrum efficiency & overall throughput.

6 MULTIPLE ACCESS SCHEMES

Developedfor packet

radio networks.

Simple but effective enhancement of

ALOHA, for solving the low throughput

problem.

/12

ALOHA doesn’t try to avoid collision!!

• Energy efficiency: most important issue in WNs.

• Sensor nodes may not be able to recharge their batteries which may put them out of contention! Nodes are facing lots of “lifetime” problems.

Energy-Efficient Routing Protocols:

• Using optimization to optimally direct the flow of data within the network, to achieve balanced reduction of energy consumption at each node.

7 ROUTING, ENERGY EFFICIENCY, AND NETWORK LIFETIME

/12

• The key function of the transport layer

• TCP infers network congestions by timeout or duplicate Acks, • By following “end-to-end principle”.

• Multihop wireless networks:• As the hop count , the end-to-end TCP throughput .

• Enhancements to improve the TCP performance:• Class of link layer mechanisms

• Class of split TCP solutions

• Class of explicit notification schemes

8 CONGESTION CONTROL IN WNs

/12

• Cross-layer design :

• sharing information among layers.• Efficient use of network resources

• Achieving high adaptivity

• Cross-layer principles:• Interactions and the Law of Unintended Consequences

• Dependency Graph

• Timescale Separation and Stability

• The Chaos of Unbridled Cross-Layer Design

9 CROSS-LAYER DESIGN AND OPTIMIZATION

/12