Modern Communications Chapter 1. Basic Concepts Husheng Li Min Kao Department of Electrical Engineering and Computer Science University of Tennessee, Knoxville

Fall, 2016

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Outline

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Syllabus

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Basic Concepts of Communications

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History of Wireless Communications

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Communication Channels

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.

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Labs

We only have one set of equipments. So please form groups of 2 or 3 students. Lab 1. Use spectrum analyzer to capture and analyze FM signals. Lab 2. Use vector signal generator and spectrum analyzer for modulation and demodulation.

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Projects

Project 1. dubbing for video: 3 to 4 silent video segments will be uploaded to the course website; you need to add voice explanation to them to explain the experiments in the video. Due date: before midterm Project 2. Matlab simulations for error correcting coding and decoding. Due date: Nov. 15th Project 3. An essay for surveying the technical and commercial aspects of 5G cellular systems.

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Demonstration Classes

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

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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.

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Outline

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1

Syllabus

2

Basic Concepts of Communications

3

History of Wireless Communications

4

Communication Channels

A Typical Communication System

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

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Analog and Digital Messages

Digital messages are ordered finite symbols, while analog messages have values ranging in a continuous range. Digital messages are more robust to noise.

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Analog-to-Digital Conversion

We can use sampling and quantization to convert analog messages to digital messages. The sampling rate should be at least 2B if the analog signal has a bandwidth B.

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Channel Effect

The characteristics of the communication channel are of key importance for the analysis and design of communication systems. Bandwidth B: the range of frequencies that the system can transmit with reasonability reliability. Signal power P: it determines the signal-to-noise ratio (SNR). Channel capacity: C = B log(1 + SNR) bits/second, when the noise is Gaussian.

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Modulation and Detection

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Analog signals from the message source are often referred as the baseband signal since they are usually lower pass. We need to convert the low frequency signal to higher frequencies, for a better radiation efficiency; this is called modulation. The conversion from the high frequency domain to the lower one is called demodulation.

Source Coding and Channel Coding

In digital communications, we need to convert the random information source to a sequence of bits. Such a conversion is called the source coding. A typical example is the Morse code. When the communication channel is noisy, there could exist transmission errors. Channel coding helps to correct the mistaken transmissions. A typical example is the repetition code. Source coding removes redundancies, while the channel coding adds redundancies.

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Outline

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1

Syllabus

2

Basic Concepts of Communications

3

History of Wireless Communications

4

Communication Channels

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 just an experiment that proves Maestro Maxwell was right - we just have these mysterious electromagnetic waves that we cannot see with the naked eye. But they are there.” Asked about the ramifications of his discoveries, Hertz replied, ”Nothing, I guess.” — Definitely, he is WRONG!

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The Birth of Wireless Communications

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

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Development of Wireless Communication Systems

In 1934, AM mobile communication systems are set up for police in 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 major American cities. In 1960s and 1970s, the concept of cellular radiotelephony was proposed, mainly by Bell Lab guys.

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The Development of Cellular Systems

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Other Wireless Communication Systems

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

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Services of Wireless Communications

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

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Interference in Multiuser Systems

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

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Different Multiple Access Schemes

TDMA: Separating in time domain FDMA: Separating in frequency domain CDMA: mixed in both time and frequency domains; separating by code CSMA: 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 Hedy Lamarr and Antheil. This is the early version of frequency hopping communications. 24/35

OFDM

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

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Big Picture of OFDM

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

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5G Cellular Systems

On July 14, 2016, FCC announced the allocation of 11GHz bandwidth for 5G cellular systems. On the next day, President Obama announced to allocate 400 million dollars for the research on 5G. Expectation of 5G systems: Data rates of tens of megabits per second for tens of thousands of users 1 gigabit per second simultaneously to many workers on the same office floor Several hundreds of thousands of simultaneous connections for massive wireless sensor network et al.

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Major Technologies of 5G Systems

Ultrahigh dense base stations: we will use much more base stations than before. Millimeter waves provide much more bandwidth to us (why higher frequency band can provide more bandwidth?). Massive MIMO, consisting of hundreds of antennas.

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Outline

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1

Syllabus

2

Basic Concepts of Communications

3

History of Wireless Communications

4

Communication Channels

Two Features of Wireless Channels

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Broadcast: The wireless signal can also be received by unintended receivers, thus being interference. This is different from wired communications. Thus, in wireless communications, how to tackle interference is a key issue.

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Fading: the wireless channel may experience deep fade in time or frequency. Thus, in wireless communications, it is important to combat fading for reliable data transmission. Fading can also be utilized for opportunistic communication.

Interference

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When two RF signals are transmitted at the same time and frequency, they will interfere with each other. WIFI signals may be interfered by micro oven. Strong vs weak. Strong vs strong.

Jamming

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

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Two Types of Fading

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

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Shadow Fading

Shadow fading means the blocking effect by large obstacles. The attenuation of shadow fading (in dB scale) is usually Gaussian distributed.

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Wave Interference

Two waves interfere with each other, thus resulting cancellations and enhancement.

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Fast Fading

When there is a reflection, the original wave and the reflected wave will interfere with each other. Hence, when the receiver moves in the order of wavelength, the signal strength may change substantially. Tip: the wavelength of a 1GHz wave is 30cm.

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