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EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same,...

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Digital Carrier Systems 1 EE442 Spring 2017 Lecture 12
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Page 1: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

Digital Carrier Systems

1

EE442 – Spring 2017 Lecture 12

Page 2: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

2

Digital Carrier Systems

So far we have studied baseband digital signals; that is, the modulating signal m(t) had not been frequency shifted.

However, for wireless and satellite communications we must use higher frequencies to transmit and receive communication signals.

Now we require a modulator and a demodulator – together they make a modem. There are two basic forms of carrier modulation – they are (1) amplitude modulation and (2) angle modulation (phase and frequency modulation). We have already studied both of these under the heading of analog modulation.

Lathi & Ding Section 7.8

pp. 423 - 427

Page 3: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

3

Example of Amplitude Shift Keying (ASK)

( )cosASK Cm t t

This is binary amplitude shift keying.

Page 4: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

4

Example of Multilevel ASK w/ Two Bit Coding

http://www.tmatlantic.com/encyclopedia/index.php?ELEMENT_ID=10420

This is multilevel amplitude shift keying.

Symbols 00, 01, 10 & 11 translate into four amplitude levels.

Page 5: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

5

Band Limiting Softens the Edges of ASK Waveforms

http://www.slideshare.net/Zeolite27/dc-ppt-final

You can see the correlation between ASK and analog AM because the amplitude of the modulated signal is proportional to m(t).

m(t)

This is more realistic case for actual ASK communication systems. In fact, all waveforms are softened by bandwidth limitations.

Page 7: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

7

Constellation Diagram For PSK

( )cos( )C CA m t t cos( ) for ( ) 1C C bA t m kT

cos( ) for ( ) 1C C bA t m kT

PSK

We can also express as I and Q components.

Q

I

Special case: on-off keying (OOK)

0

I

Q

Page 8: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

8

Expressing PSK as I and Q Components

cos forPSK C C k b b bA t kT t kT T

For PSK we can write,

cos( )cos sin( )sin

Therefore,

cos sin( ) for

PSK C k C C k C

PSK k C k C b b b

A t A t

a t b t kT t kT T

This is in polar form (I and Q)

For binary PSK we have k = 0 or This is 2-QAM but we don’t generally use this terminology for binary PSK. Note: Quadrature amplitude modulation (QAM) is a mixture of both amplitude modulation and phase modulation.

Page 9: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

9

Binary PSK (BPSK) Transmitter and Receiver

Carrier

cos(ct) Balanced

Modulator Amplifier BPF

LPF NRZ Data input

PSK

BPSK Modulator:

LPF S&H

+

cos(ct)

PSK d(t)

Comparator

Binary data output

( ) cos[2 ( )] cos[ ( )]Cr t B t t B t

BPSK Demodulator:

Sample at center of symbol

Page 10: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

10

Binary PSK (BPSK) Received Waveforms

Without noise With noise

After Lawrence Burns, “Digital Modulation and Demodulation,” Chapter 4 in RF and Microwave Circuit Design for Wireless Communications, edited by Lawrence E. Larson, Artech House Publishers, 1996. Pages 99 to 233. Lawrence Burns was an engineer at 3COM.

Page 11: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

11

Frequency Shift Keying (FSK)

In frequency shift keying each digital symbol has its own unique carrier signal frequency for encoding it. The signal amplitude and phase remain the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

Page 12: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

12

FSK Modulation and Demodulation

FSK Modulator:

Voltage Controlled oscillator

Amplifier BPF

NRZ Data input

FSK

RF Output

Vcontrol

t

Amplifier LPF BPF

Frequency Discriminator

FSK + m(t)

Comparator

Binary data output

FSK Demodulator:

Page 13: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

13

Multilevel Frequency Shift Keying (FSK)

This animation shows frequency shift keying of the sinusoidal carrier signal. A two-digit code modulates the carrier signal frequency into four frequencies

Symbol Binary code Frequency

“0” 00 4 kHz

“1” 01 3 kHz

“2” 10 2 kHz

“3” 11 1 kHz

Page 14: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

14

Comparing PSDs For Binary ASK, PSK and FSK

Lathi & Ding Section 7.8.2

pp. 427

FSK

PSK

ASK

Pow

er s

pec

tral

den

sity

[w

atts

/Hz)

Page 15: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

15

BPSK Waveforms and Noise

Page 16: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

16

Quadrature Phase Shift Keying (QPSK)

Sometimes this is known as quadri-phase PSK, 4-PSK, or 4-QAM. QPSK uses four points on the constellation diagram, equi-spaced around a circle. With four phases, QPSK can encode two bits per symbol,

Q

I

I = -1; Q = -1 I = +1; Q = -1

I = +1; Q = +1 I = -1; Q = +1

cos sinQPSK C CI t Q t

Page 18: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

18

Simple QPSK Modulator

Brute-force QPSK modulator using delay lines to set phase delay:

+45

+135

-135

-45

Delay lines (depend upon fC)

Switch Decoder and Driver

RF Input RF Output

Page 19: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

19

Widely-Used QPSK Modulator

QPSK Modulator

Amplifier BPF

LPF

NRZ Data input

PSK

LPF

Serial-to -Parallel Parser

cos( )Ct

sin( )Ct

I

Q t

Page 20: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

20

Basic Building Block: Quadrature Modulator

cos( )Ct

sin( )Ct

I

Q

I and Q can be either analog or

digital signals

2 2

1

( ) cos( ( ))

( )where ( ) tan

( )

Ct I Q t t

Q tt

I t

( )t

Page 21: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

21

QPSK Time Domain Waveforms

QPSK

Page 22: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

22

Data Demultiplexer (Serial to Parallel) For QPSK

Demodulator uses three D-type flip-flops and is driven by clock and clock/2.

Q

I

Page 23: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

23

QPSK Demodulator

C/R = clock/carrier recovery STR = symbol timing recovery

Page 24: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

24

M-ary Signaling With Quadrature Amplitude Modulation (QAM)

Quadrature Amplitude Modulation, QAM is a form of modulation that is a combination of phase modulation and amplitude modulation. The QAM scheme represents bits as points in a quadrant grid know as a constellation map.

16-ary QAM

APSK definition Definition: Amplitude and Phase-Shift Keying, APSK, is a digital modulation scheme that uses both the amplitude and the phase changes of on the carrier signal to provide the data transport mechanism for the information. Also called QAM.

Page 25: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

25

Number-Bases in M-ary Constellations

Variants of QAM are also used for many wireless and cellular technology applications. In addition, 64-QAM and 256-QAM are commonly used in digital cable television and cable modem applications. In the US, 64-QAM and 256-QAM are the mandated modulation schemes for digital cable as standardized by the SCTE in the standard ANSI/SCTE 07 2000.

Page 26: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

26

Bits/Symbol and Symbol Rates

Modulation Bits per Symbol

Symbol Rate

BPSK 1 1 bit rate

QPSK 2 1/2 bit rate

8-PSK 3 1/3 bit rate

16-QAM 4 1/4 bit rate

32-QAM 5 1/5 bit rate

64-QAM 6 1/6 bit rate

Page 27: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

27

WiFi systems use two primary radio transmission techniques.

802.11b (≤ 11 Mbps) − The 802.11b radio link uses a direct sequence spread spectrum technique (DSSS) called complementary coded keying (CCK). The bit stream is processed and then modulated using Quadrature Phase Shift Keying (QPSK).

802.11a and 802.11g (≤ 54 Mbps) − The 802.11a and g systems use 64-channel orthogonal frequency division multiplexing (OFDM). The transmitter encodes the bit streams onto 64 subcarriers using Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), or one of two levels of Quadrature Amplitude Modulation (16-QAM, or 64-QAM).

What Modulation Schemes Does Wi-Fi Use?

Page 28: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

28

Bandwidth Efficiency (aka Spectral Efficiency)

Given: Eb = energy per bit Rb = bit rate (bits/second) B = bandwidth of baseband signal N0 = noise spectral density (watts/Hz) N = noise power = N0B

Therefore, EbRb = total signal power We define the Bandwidth Use Efficiency as

In general,

bits/second

HzbR

B

2log 1b b bR E R

B NB

Example: GSM Digital Cellular Data rate = 270 kb/s B = 200 kHz, thus

Bandwidth efficiency = 1.35 bits/sec/Hz

Page 30: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

30

Circuit Switched Networks vs. Packet-Switched Network

Page 31: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

31

Circuit-Switched Network

Telephone Switch

Telephone Switch

Telephone Switch

Telephone Switch

Telephone Switch

Telephone Switch

Telephone Switch

Many paths are possible, but only one is selected per

call.

Once a connection is established, this

connection is maintained until call

is terminated.

Caller

= Dedicated connection (point-to-point)

Subscriber lines (or local loops)

Trunks (links between

Exchanges)

Central Office

Central Office

Central Office

PSTN = public switched telephone network

Full Duplex

Page 32: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

32

Packet Switched Network

Internet

Many paths possible for a single message as packets are routed to

the destination.

Packets are routed according to the best path available at the

time.

Receiver (destination)

Sender (source)

Message broken into packets and each addressed

Packets sequentially reassembled

to reveal message

= Packet

Router or Switch

(Data Packet or “Datagram”)

Large array of routers and data links.

Packet route

Page 33: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

33

Network Organization

Centralized Network Decentralized Network

(e.g., PSTN)

Distributed Network

(e.g., Internet)

In 1962, Paul Baran (RAND Corp.) envisioned a network of unmanned nodes using intelligent switches to route data node to node to their final destinations. Baran called this "hot-potato routing" or distributed communications. This was implemented in ARPANET which became the Internet.

Concept of hardened networks to deal with disasters.

This network

Is vulnerable.

Page 34: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

34

Packet-Switched Network Operation

• Adaptive routing – routers chose the best path by examining traffic loading along available paths. Routers create a “routing table” for the packet travel.

• All users share the same network resources.

• Packet-switching is more efficient than circuit-switching in networks when data is bursty (i.e., variable delays interspersed with periods of data transmission). More “efficient” means a better utilization of the network resources.

This is an example of

“bursty” data

Page 35: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

35

An Internet Packet and its Headers

• In IPv4, each packet is restricted to 1,500 bytes of data (i.e., payload)

• Each packet consists of the application data and headers

• The headers contain control and routing information such as:

– Source IP address and destination IP address

– Packet numbering for reconstruction at destination

• Every computer on the Internet has the TCP/IP program. The client/server model is used on the Internet.

• TCP (Transmission Control Protocol) puts the data or message into packets at the source and reassembles the data or message at the destination

• IP (Internet Protocol) does the packet addressing for the routing over the Internet

Application Data IP header TCP/UDP header

Internet Packet

The rules that govern communication – any form – are called “protocols.”

Page 36: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

36

TCP versus UDP Transmission

TCP is “reliable” because it has flow & congestion control, retransmission, & uses acknowledgements. UDP does not use these because it is focused only upon sending packets.

UDP

TCP and UDP Analogies:

Post Office Verifies delivery Registered

Letter

TCP

Page 37: EE442 Spring 2017 Lecture 12 - Sonoma State UniversityFrequency Shift Keying (FSK) ... the same, only the frequency is varied. In the figure binary frequency shift keying is illustrated.

37

Layer Pictorial View of Protocol Data Unit Entity

Application Data or

Message

Transport Segments

Internet or Network

Packets or Datagrams

Network Access

Frames

Data

Data Transport

Header

Data Transport

Header Network Header

Data Transport

Header Network Header

Frame Header

Frame Trailer

Protocol

SMTP HTTP, DNS

TCP UDP

IP

Ethernet Modem

FDDI

Number of segments 1

Bits transmitted over channel medium

TCP/IP Protocol Architecture Model


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