Modern CommunicationsChapter 1. Basic Concepts

Husheng Li

Min Kao Department of Electrical Engineering and Computer ScienceUniversity of Tennessee, Knoxville

Fall, 2016

1/35

Outline

1 Syllabus

2 Basic Concepts of Communications

3 History of Wireless Communications

4 Communication Channels

2/35

Syllabus

Course website: http://web.eecs.utk.edu/∼husheng/ECE653 2016.htm

Office hour: 3:30pm to 4:30pm, MWF

Final grade:

Homework: 20%Pop Quiz: 10%Labs: 10%Project: 20%Midterm: 20%Final: 20%

Homework: 4 problems assigned on each Friday; due date: the next Friday

Pop quiz: 5 times at random times; if you miss it, you can have a make-up one.

3/35

Labs

We only have one set ofequipments. So please formgroups of 2 or 3 students.

Lab 1. Use spectrum analyzerto capture and analyze FMsignals.

Lab 2. Use vector signalgenerator and spectrumanalyzer for modulation anddemodulation.

4/35

Projects

Project 1. dubbing for video: 3 to 4 silent video segments will beuploaded to the course website; you need to add voiceexplanation to them to explain the experiments in the video. Duedate: before midtermProject 2. Matlab simulations for error correcting coding anddecoding. Due date: Nov. 15thProject 3. An essay for surveying the technical and commercialaspects of 5G cellular systems.

5/35

Demonstration Classes

The demonstration classes will be held in MK226 (thecommunication labs).Class 1. An introduction to equipments and functionalities.Class 2. Characteristics of wireless channels.Class 3. Analog modulationClass 4. Digital modulation

6/35

Take Home Points (After The Semester)

Remember the basic concepts like modulations, coding, et al.When you turn on the radio in your car, ....When you cell phone loses signal, ...When you read 5G or millimeter wave WiFi, ...Have fun when operating the RF equipments.

7/35

Outline

1 Syllabus

2 Basic Concepts of Communications

3 History of Wireless Communications

4 Communication Channels

8/35

A Typical Communication System

The goal of communications is to convey information from thesource to the destination.Key points: randomness, noise and communication resources.

9/35

Analog and Digital Messages

Digital messages are orderedfinite symbols, while analogmessages have values rangingin a continuous range.

Digital messages are morerobust to noise.

10/35

Analog-to-Digital Conversion

We can use sampling andquantization to convert analogmessages to digital messages.

The sampling rate should be atleast 2B if the analog signalhas a bandwidth B.

11/35

Channel Effect

The characteristics of the communication channel are of key importancefor the analysis and design of communication systems.

Bandwidth B: the range of frequencies that the system can transmit withreasonability reliability.

Signal power P: it determines the signal-to-noise ratio (SNR).

Channel capacity: C = B log(1 + SNR) bits/second, when the noise isGaussian.

12/35

Modulation and Detection

Analog signals from the messagesource are often referred as thebaseband signal since they areusually lower pass.

We need to convert the lowfrequency signal to higherfrequencies, for a better radiationefficiency; this is called modulation.

The conversion from the highfrequency domain to the lower oneis called demodulation.

13/35

Source Coding and Channel Coding

In digital communications, we need to convert the random informationsource to a sequence of bits. Such a conversion is called the sourcecoding. A typical example is the Morse code.

When the communication channel is noisy, there could existtransmission errors. Channel coding helps to correct the mistakentransmissions. A typical example is the repetition code.

Source coding removes redundancies, while the channel coding addsredundancies.

14/35

Outline

1 Syllabus

2 Basic Concepts of Communications

3 History of Wireless Communications

4 Communication Channels

15/35

The Birth of Electromagnetic Wave

In 1887, Heinrich Hertz discovered electromagnetic wave.

Comments of Hertz on wireless: ”It’s of no use whatsoever[...] this is justan experiment that proves Maestro Maxwell was right - we just havethese mysterious electromagnetic waves that we cannot see with thenaked eye. But they are there.”

Asked about the ramifications of his discoveries, Hertz replied, ”Nothing,I guess.” — Definitely, he is WRONG!

16/35

The Birth of Wireless Communications

On 13 May 1897, Marconi sent the first wireless communicationover water. It crossed the Bristol Channel from Lavernock Pointto Flat Holm Island, 14 kilometers away.The message reads ”Are you ready?”

17/35

Development of Wireless CommunicationSystems

In 1934, AM mobile communication systems are set up for policein US.The technology of radio was greatly improved in World War II(e.g. matched filter based receiver)The first public mobile phone service was launched in 26 majorAmerican cities.In 1960s and 1970s, the concept of cellular radiotelephony wasproposed, mainly by Bell Lab guys.

18/35

The Development of Cellular Systems

19/35

Other Wireless Communication Systems

Satellite communications.Digital wireless TV broadcast.Blue tooth.Cordless phone.

20/35

Services of Wireless Communications

VoiceData (e.g. web browsing, checking email)Multimedia (watching movie on cell phone; video conferencing)Wireless gaming

21/35

Interference in Multiuser Systems

If two nodes transmit in the same time and the same frequencyband, their signal will collide. Signal becomes interference.Multiaccess: to separate multiple signals.

22/35

Different Multiple Access Schemes

TDMA: Separating in time domainFDMA: Separating in frequency domainCDMA: mixed in both time and frequency domains; separating bycodeCSMA: separated in time, but without scheduling

23/35

Mother of CDMA

Hedy Lamarr (1913-2000): a movie star in 1940s (six husbands).She has a star in the Hollywood Walk of Fame.On Aug. 11, 1942, US Patent 2,292,387 was issued to HedyLamarr and Antheil. This is the early version of frequencyhopping communications.

24/35

OFDM

OFDM: Orthogonal Frequency Division MultiplexingOFDM was born in 1960s in Bell Labs.Life begins at forty (John Lenon).Now OFDM is the fundamental signaling technique for 4Gcellular systems (UWB, LTE, WiMAX).

25/35

Big Picture of OFDM

The data is divided into many streams and transmitted on manysubcarriers (also called tones).

26/35

5G Cellular Systems

On July 14, 2016, FCC announced the allocation of 11GHzbandwidth for 5G cellular systems. On the next day, PresidentObama announced to allocate 400 million dollars for theresearch on 5G.Expectation of 5G systems:

Data rates of tens of megabits per second for tens of thousands ofusers1 gigabit per second simultaneously to many workers on the sameoffice floorSeveral hundreds of thousands of simultaneous connections formassive wireless sensor networket al.

27/35

Major Technologies of 5G Systems

Ultrahigh dense base stations: we will use much more base stationsthan before.

Millimeter waves provide much more bandwidth to us (why higherfrequency band can provide more bandwidth?).

Massive MIMO, consisting of hundreds of antennas.

28/35

Outline

1 Syllabus

2 Basic Concepts of Communications

3 History of Wireless Communications

4 Communication Channels

29/35

Two Features of Wireless Channels

1 Broadcast: The wireless signal can also be received byunintended receivers, thus being interference. This is differentfrom wired communications. Thus, in wireless communications,how to tackle interference is a key issue.

2 Fading: the wireless channel may experience deep fade in timeor frequency. Thus, in wireless communications, it is important tocombat fading for reliable data transmission. Fading can also beutilized for opportunistic communication.

30/35

Interference

When two RF signals aretransmitted at the same time andfrequency, they will interfere witheach other.WIFI signals may be interfered bymicro oven.Strong vs weak.Strong vs strong.

31/35

Jamming

You can send out jamming wave to destroy the victim signal bychoosing the correct time and correct frequency.

32/35

Two Types of Fading

Large scale fading: characterize the signal strength over longtransmitter-receiver distance (you may need to move 100 metersto see the change of signal strength).Small scale fading: characterize the rapid fluctuation over a smalldistance (you may need to move only half a meter to see thesignal strength changing rapidly).

33/35

Shadow Fading

Shadow fading means theblocking effect by largeobstacles.The attenuation of shadowfading (in dB scale) isusually Gaussiandistributed.

34/35

Wave Interference

Two waves interfere with each other, thus resulting cancellationsand enhancement.

35/35

Fast Fading

When there is a reflection, the original wave and the reflectedwave will interfere with each other. Hence, when the receivermoves in the order of wavelength, the signal strength maychange substantially.Tip: the wavelength of a 1GHz wave is 30cm.

36/35