Fundamentals of Communication...

“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)

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Chapter 9

Fundamentals of Communication Networks


Communication Network Architecture Communication devices Network nodes Communication links


Protocol Architecture Break communication task down into

subtasks Divide-and-conquer approach Hierarchical layers

Protocols Define subtask operation within a layer TCP/IP protocols


Switching Technologies Circuit switching Circuit establishment Data transfer Circuit termination


Switching Technologies Packet switching Store-and-forward Network resources allocated on-demand


Switching Technologies Virtual circuit switching Combining features of circuit switching

and packet switching Virtual circuit pre-established Link bandwidth shared efficiently


Encapsulation and Multiplexing


Naming and Addressing Domain name Domain Name System (DNS)

Port number Well-known port numbers Ephemeral port numbers


Naming and Addressing IP address Subnetting Socket: combination of an IP address

and a port number Medium Access Control (MAC)

address


Multiple Access Media shared in a broadcast network Rules for hosts to access the media Media Access Control (MAC)


Routing and Forwarding Network layer function Maintaining network topology

information Routing table

Forwarding packets Packets forwarded hop-by-hop


Congestion Control and Flow Control

Congestion control Router congestion

Flow control Fast transmitter and slow receiver


Error Control Checksum in TCP/IP Cyclic redundancy check (CRC) in

Ethernet Sequence numbers to detect lost

packets


New Challenges in Wireless Networks Wireless transmissions Different concept of communication link Coupled channels Capacity limited by SINR

Mobility Handoff in infrastructure-based wireless

networks Rerouting in infrastructureless wireless

networks Energy efficiency Significant impact in every layer


Mobility Modeling

The Random Waypoint Model


Mobility Modeling

Speed distribution

Average speed Location distribution


Perfect Simulation


Power Control and Multiuser Diversity

Uplink of a infrastructure-based wireless network

Received signal at the base station is

Frequency flat Reyleigh fading

Objective



No power control

Perfect power control

Optimal power control


Multiple Access Schemes

Classification of multi-access schemes


Polling

Queueing system with one server and m stations

Finite buffer and infinite buffer


Polling Service policies Limited service Exhaustive service Gated service


ALOHA and Slotted ALOHA ALOHA A station transmits a packet whenever it

wants to Maximum throughput 0.184

Slotted ALOHA Time is divided into slots Maximum throughput 0.368


CSMA User senses the medium before start

transmission Hold packets until the medium is free Strategies 1-persistent CSMA Non-persistent CSMA


CSMA

An example of collision in CSMA


CSMA

A typical cycle of CSMA operation


CSMA/CA


Hidden Terminal and Exposed Terminal Problems

Hidden terminal problem

Exposed terminal problem


Routing, Energy Efficiency and Network Lifetime


Maximizing Network Lifetime


Congestion Control in Wireless Networks

TCP is not suitable for wireless networks Basic assumption: all loss are due to buffer

overflow Suffers from frequent route failures and MAC

layer contention

TCP enhancements Link layer mechanisms Split TCP Explicit notification schemes


Cross-layer Design and Optimization


Cross-layer Principles

Interactions and the law of unintended consequences

Dependency graph Timescale separation and stability The chaos of unbridled cross-layer

design

Fundamentals of Communication...

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