CS 5813: Principles of Wireless Networks

Tingting Chen Department of Computer Science Fall 2013

Schedule for Today

Syllabus of this course Introduction of wireless networks Physical Layer (if time allows)

Goals of this Course

Understand fundamental principles and mechanisms in wireless networks at different layers
E.g., radio propagation and wireless medium access

Learn how different types of wireless networks work

E.g., cellular networks, wireless local area networks

Get experience in working with wireless networks

Implement and measure wireless protocols

Get some view of the ongoing research in the area of the wireless networks

Course Content
Introduction Radio propagation Physical layer Wireless medium access MAC Layer Cellular networks WLAN -- 802.11 Series WPANs Routing in MANET, Wireless Mesh Networks, and Sensor Networks Wireless Network Security

Administrative stuff
Prerequisites: CS 4283 or ECEN 4283
Basic networking and programming knowledge

Recommended Textbook: William Stallings, Wireless Communications & Networks, 2nd edition, Prentice Hall, 2005.
Will not cover all the material in the book Not all material is in the book Lecture slides may be from various sources

Course materials will be posted in D2L system. Office hours

Thursday 9:30 am 11:30 am 212 MSCS tingting@cs.okstate.edu

Grading
Grade distribution
Paper Presentation : 30% Exams (midterm and final): 30% Project: 30%
Based on simulators or testbed At most 3 people in a team

Class participation: 10%

TAs for this course

Shiyu Ji, shiyu@cs.okstate.edu Jiyoung Shin, jiyouns@cs.okstate.edu

Course timeline

Wireless Devices
Wireless sensors Limited proc. power Small battery

RFID tag A few thousands of logical gates Responds only to the RFID reader requests (no battery)

Mobile phones voice, data web access location based services

Laptop functionally eq. to desktop standard applications

Satellites
Launched in 1960s Iridium satellites
66 active satellites Supports 1100 concurrent phone calls Orbit altitude: approx. 780 km Frequency band: 1616-1626.5 MHz 30 satellites currently Orbit altitude: approx. 20,200 km Frequency: 1575.42 MHz Bit-rate: 50 bps
Iridium 9505A Satellite Phone Iridium Satellite

Global Positioning System (GPS)

BTCC-45 Bluetooth GPS receiver

Mobile phones
2-way 2-party communication using digital transmission technology In 2002 the number of mobile phones exceeded that of land lines Currently, more than 1 billion mobile phones! Applications
SMS text messaging Voice Web access Location based services

Global System for Mobile Communications (GSM)

GSM was developed in Europe in 1980s and became an international standard 13 years later Mobile phones connect to it by searching for cells in the immediate neighborhood. Uses TDMA framework Over 250 GSM Networks are presently operating in 110 countries Most 3G networks in Europe operate in the 2100 MHz frequency band. Data rates: 9.6Kbps to 14.4Kbps

Wi-Fi
Connect end devices to internet through access points/hotspots. Wi-Fi devices:
Smartphone, personal computer, video game console, etc.

An access point has a range of about 20 meters indoors. City-wide wifi Campus-wide wifi IEEE 802.11 standards
802.11 b: limited to 11 mbps

WiMax
Wireless Last-mile Enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL Maximum range of 50 km, with higher bitrates when reducing the range A city-wide deployment of WiMAX in Perth, Australia
Cell edge typically 1-4 Mbps

IEEE 802.16 wireless-networks standard WiMAX PA3500 directional antenna

Frequency band: 3200-3800 MHz

Ad Hoc Networks
No backbone infrastructure. Peer-to-peer communications. Routing can be multihop. Topology is dynamic. Applications
Military networks Appliances and entertainment units at home

Vehicle to Vehicle Communications

The vehicles form an ad hoc WLAN The system continuously monitors the position, speed, distance and direction of surrounding road users. Data is centralized and sent to the drivers to warn them of traffic conditions ahead. Drivers can view information on a display, and receive safety warnings through advanced interfaces.

Bluetooth
Cable replacement RF technology (low cost) Short range (10m, extendable to 100m) 2.4 GHz band (crowded)

1 Data (700 Kbps) and 3 voice channels

Widely supported by telecommunications, PC, and consumer electronics companies Few applications beyond cable replacement

Radio-frequency identification
Data transfer from an electronic tag (RFID tag) to a reader, using radio waves, to identify or track the object. Applications
Attached to cars, computer equipment, books, mobile phones E.g., financial institutions use RFID to track key assets
ISO14443-A and B (13.56 MHz) Operating distance: 1cm Communication speed: up to 848 Kbit/s
SDI 010 RFID Reader RFID tag

Wireless Technologies

Difference between wireless networks and fixed networks

Higher data loss-rates due notably to interferences
Emissions of e.g., engines, lightning, other wireless networks, micro-wave ovens

Lower transmission rates

From a few kbit/s (e.g., GSM) to a few 100s of Mbit/s (e.g. WLAN)

Restrictive regulations of frequencies

Usage of frequencies has to be coordinated, useful frequencies are almost all occupied (or at least reserved)

Lower security (higher vulnerability)

Shared radio links Unknown variable points

Recommended books
In addition to the textbook
L. Buttyan and JP Hubaux: Security and Cooperation in Wireless Networks Cambridge University Press, 2008 A. Goldsmith: Wireless Communications, Cambridge University Press, 2005 D. Tse and P. Viswanath: Fundamentals of Wireless Communication, Cambridge University Press, 2005

Physical Layer
Radio frequency introduction Channel capacity Modulation and multiplexing

Electromagnetic Signal
Electromagnetic waves travel at the speed of light. Radio frequency ranges 3KHz to 300 GHz. Wavelength ranges 100 km to 0.1cm. Electromagnetic Signal is essentially a function of time. Can also be expressed as a function of frequency

Time-Domain View
Analog signal - signal intensity varies in a smooth fashion over time Digital signal - signal intensity maintains a constant level for some period of time and then changes to another constant level
No breaks or discontinuities in the signal

Periodic signal - analog or digital signal pattern that repeats over time

Aperiodic signal - analog or digital signal pattern that doesn't repeat over time

where T is the period of the signal

s(t +T ) = s(t )

Simple example: Sine Wave

RF signal travels at the speed of light Can look at a point in space: signal amplitude will change in time according to a sine function Can take a snapshot in time: signal will look like a sine function in space
At a particular instant of time, the intensity of the signal varies as a function of distance from the source

Parameters of Periodic Signal

Peak amplitude (A) - maximum value or strength of the signal over time; typically measured in volts Frequency (f )

Rate at which the signal repeats, in cycles per second, or Hertz (Hz) Period (T ) - amount of time it takes for one repetition of the signal

Phase () - measure of the relative position in time within a single period of a signal Wavelength () - distance occupied by a single cycle of the signal
Or, the distance between two points of corresponding phase of two consecutive cycles

T = 1/f

Sine Wave Parameters

General sine wave
s(t ) = A sin(2ft + )

The following figure shows the effect of varying each of the three parameters: A, f,
(a) A = 1, f = 1 Hz, = 0; thus T = 1s (b) Reduced peak amplitude; A=0.5 (c) Increased frequency; f = 2, thus T = (d) Phase shift; = /4 radians (45 degrees)

note: 2 radians = 360 = 1 period

Sine Wave Parameters

Frequency-Domain Concepts
Any electromagnetic signal can be shown to consist of a collection of sine waves at different frequencies , with different amplitudes and phases The period of the total signal is equal to the period of the fundamental frequency
All other frequencies are integer multiples of the fundamental frequency.

The Frequency Domain

A signal can be viewed as a sum of sine waves of different strengths.
Corresponds to energy at a certain frequency

The Frequency Domain

Signal = sum of sine waves

Frequency-Domain Concepts
Fundamental frequency - when all frequency components of a signal are integer multiples of one frequency, its referred to as the fundamental frequency Spectrum - range of frequencies that a signal contains Absolute bandwidth - width of the spectrum of a signal Effective bandwidth (or just bandwidth) - narrow band of frequencies that most of the signals energy is contained in

Modulation and Multiplexing

Analog Signals
Analog Signals: continuously varying; may be propagated over a variety of media, depending on frequency Examples of media:
Copper wire media Fiber optical cable Wireless: Atmosphere or space propagation

Cannot recover from distortion or noise

Digital Signals
Digital Signals: A sequence of voltage pulses that may be transmitted over a copper wire medium
Generally cheaper than analog signaling Less susceptible to noise interference Can regenerate digital signal along the path (repeater vs amplifier)

Modulation
Modulation: Sender changes the nature of the signal in a way that the receiver can recognize. Amplitude modulation (AM): change the strength of the carrier based on the information to be sent, typically between on and off.

Frequency (FM) and phase modulation (PM): change the frequency or phase of the signal Can also combine modulation types.

Amplitude and Frequency Modulation

Baseband vs Carrier Modulation

Baseband modulation: send the bare signal. Baseband modulation has limited use
E.g., some media only transmit higher frequencies, e.g. optical

Carrier modulation: use the signal (information to be sent) to modulate a higher frequency signal (carrier).
Can be viewed as the product of the two signals Corresponds to a shift in the frequency domain

Same idea applies to frequency and phase modulation.

E.g. change frequency of the carrier instead of its amplitude

Amplitude Carrier Modulation

Amplitude

Signal

Carrier Frequency

Amplitude

Modulated Carrier

Multiple Channels
Determines Bandwidth of Link

Amplitude

Frequency

Determines Bandwidth of Channel

Different Carrier Frequencies

Multiplexing
Capacity of transmission medium usually exceeds capacity required for transmission of a single signal Multiplexing - carrying multiple signals on a single medium
More efficient use of transmission medium

Multiplexing Techniques
Frequency-division multiplexing (FDM)
Useful when bandwidth exceeds the required bandwidth of a given signal Divide the capacity in the frequency domain

Time-division multiplexing (TDM)

Divide the capacity in the time domain Fixed or variable length time slices

Frequency-division Multiplexing

Time-division Multiplexing

Frequency-division vs Time-division
Frequency-division multiplexing:
Different users use different parts of the frequency spectrum Each user can send all the time at reduced rate. Hardware is slightly more expensive

Time-division multiplexing:
Different users send at different times Each user can send at full speed at some of the time There is some transition time between time slots.

The two solutions can be combined