JPEXS
0
28. 11. 2007 v 1.1
Vypracovaná lekce 7
Tuto lekci pro vás vypracoval JPEXS. Lekce nemusí být vypracovaná správně, takže si
nestěžujte. Doporučuji, abyste si lekci udělali sami a případně až nakonec si to zkontrolovali se
mnou. Je dobrý si alespoň přečíst ten článek, abyste pak v závěrečném testu mohli napsat esej.
JPEXS
Verze 1.1 28.11.2007
- poznámky
http://technodrom.jpexs.com
JPEXS
1
28. 11. 2007 v 1.1
Adaptive Modulation
(QPSK, QAM)
Introduced below are the concepts of digital modulation used in many communication systems today.
Techniques described include quadrature phase shift keying (QPSK) and quadrature amplitude
modulation (QAM) and how these techniques can be used to increase the capacity and speed of a
wireless network. These modulation techniques are the basis of communications for systems like cable
modems, DSL modems, CDMA, 3G, Wi-Fi* (IEEE 802.11) and WiMAX* (IEEE 802.16).
Carrier Waves
Radio waves are electromagnetic waves that move at the speed of light in a sine wave formation and can
be used to carry a message over a distance. They can have different frequencies, which describes how
fast they are moving up and down, which is measured in cycles per second or hertz. Carrier waves with
different frequencies have different properties. For example, light waves are visible to the naked eye but
cannot travel through walls. Radio waves (especially those of lower frequency) can penetrate walls and
buildings as well as bend (diffract) around corners.
Modulation
Modulation is the process by which a carrier wave is able to carry the message or digital signal (series of
ones and zeroes). There are three basic methods to this: amplitude, frequency and phase shift keying.
Higher orders of modulation allow us to encode more bits per symbol or period (time). Amplitude shift
keying (ASK) involves increasing the amplitude (power) of the wave in step with the digital signal (in other
words, low = 0, high = 1) and is used in AM radio. Frequency shift keying (FSK) changes the frequency in
step with the digital signal. Systems that use this modulation (broadcast FM radio) tend to be more
resilient to noise since noise usually changes the amplitude of the signal. In Figure 1, different bits are
represented by different frequencies which can then be detected by a receiver.
Figure 1: Frequency Shift Keying
Phase shift keying (PSK) changes the phase of the carrier in step with the digital message. For binary
phase shift keying (BPSK), each symbol could indicate two different states or one bit per symbol (in other
words, 0 = 0, 180 = 1). In Figure 2, the second wave is shifted by half a period or 180 degrees. The
receiver can then recognize this shift indicating either a digital one or zero.
010
Adaptive Modulation (QPSK, QAM) Application Note
Figure 2: Phase Shift Keying
QPSK adds two more phases: 90 and 270 degrees. Now two symbols per bit can be transmitted. Each
symbol’s phase is compared, relative to the previous symbol; so, if there is no phase shift (0 degrees), the
bits “00” are represented. If there is a phase shift of 180 degrees, the bits “11” are represented.
Figure 3: Quadrature Phase Shift Keying
http://technodrom.jpexs.com
JPEXS
2
28. 11. 2007 v 1.1
ASK and PSK can be combined to create QAM where both the phase and amplitude are changed. The
receiver then receives this modulated signal, detects the shifts and demodulates the signal back into the
original data stream. In Figure 4 showing 16-QAM, each symbol can now represent four bits instead of just
the two bits per symbol with QPSK. Each point indicates a unique amplitude and phase of the wave (for
example, point (1,1) indicates 90 degrees and amplitude of 1).
Adaptive Modulation (QPSK, QAM) Application Note
Figure 5: Adaptive Modulation and Coding
Both QAM and QPSK are modulation techniques used in IEEE 802.11 (Wi-Fi*), IEEE 802.16 (WiMAX*)
and 3G (WCDMA/HSDPA) wireless technologies. The modulated signals are then demodulated at the
receiver where the original digital message can be recovered. The use of adaptive modulation allows
wireless technologies to optimize throughput, yielding higher throughputs while also covering long
distances.
Adapted
Author Biography
Sam W. Ho is a technical marketing engineer in the Wireless Networking Group, part of the Intel Communications Group. Since
joining Intel in 2000, he has worked on a variety of projects, including chipset design, chipset architecture, strategic marketing and
several wireless technologies including: BLUETOOTH*, Wi-Fi* (IEEE 802.11), ultra wideband, WiMAX* (802.16) and 3G. He is
currently researching future wireless technologies for mobility/portability including WiMAX*, 3G and beyond. He holds a B.S. in
computer engineering from the University of Kansas.
Intel Access
WiMAX* - Broadband Wireless Access Technology: www.intel.com/netcomms/technologies/wimax/index.htm
Other Intel Support: Intel Literature Center developer.intel.com/design/litcentr/
(800) 548-4725 7 a.m. to 7 p.m. CST (U.S. and Canada)
International locations please contact your local sales office.
General Information Hotline: (800) 628-8686 or (916) 356-3104 5 a.m. to 5 p.m. PST
http://technodrom.jpexs.com
JPEXS
3
28. 11. 2007 v 1.1
A. Vocabulary.
1. Find the words in the dictionary. Translate them into Czech. Be prepared to explain
their meaning in English.
to shift
posunout
to be resilient
odolný (v tomto kontextu)
instead of
místo
bending
ohýbající se
to tend to
být náchylný k
to recognize
rozeznat, rozlišit
2. What do the acronyms (a type of an abbreviation) stand for?
AM
Amplitude modulation
FM
Frequency modulation
PSK Phase shift modulation
BPSK Binary phase shift keying
FSK Frequency shifted keying
ASK Amplitude shifted keying
QPSK Quadrature phase shift keying
QAM Quadrature Amplitude Modulation
DSL Digital Subscriber Line
CDMA Common Data Multiple Access
Wi-Fi Wireless Fidelity
WMANs/ WiMAX
Wireless Metropolitan Area Networks,
Worldwide Interoperability for Microwave Access
WCDMA
Wireless CDMA
IEEE Institute of Electrical and Electronics
Engineers
Amplitudová modulace
Frekvenční modulace
Modulace fázového posunu
Binární fázově posouvané
klíčování
Frekvenčně posouvané klíčování
Amplitudově posouvané klíčování
Kvadraturní fázově posouvané
klíčování
Kvadraturní amplitudová modulace
Digitální účastnická linka
Společná data, vícenásobný
přístup
“bezdrátová přesnost”,
Bezdrátová síť
Bezdrátové metropolitní sítě
Celosvětově kompatibilní
mikrovlnný přístup
Bezdrátové CDMA (viz výše)
Institut elektrického a
elektronického inženýrství
3. Match the words with their meaning.
to travel through
diffraction
to penetrate
in step with
receiver
to yield
throughput
to gain, to (bring) profit
a device able to accept and process radio waves
pass through
in accordance with
an amount (of work etc.) done in a particular period of time
to move into or through st.
a change in the direction of e.g. light or sound wave
http://technodrom.jpexs.com
JPEXS
4
28. 11. 2007 v 1.1
4. Make a definition sentence.
Radio waves
Modulation
ASK
5.
high frequency magnetic waves
to add one signal to the another – to change form of the signal with proportion
Amplitude shift keying is modulating where amplitude is modified
Complete the text with the given words.
rate of transmission, bit/error rates, code rate, transmitter, receiver, power, channel,
fading channel, digital communications, wireless, time division duplex
Adaptive modulation is a transmission scheme in …… digital communications ………….. where the …………
receiver ……………………..adapts its transmission mode in accordance with the……… transmitter ……..
Depending on the condition of the channel, the transmitter could be adapting one or more of the following:
constellation size, ……… rate of transmission ……………….., and……… code rate …………………...
Adaptive modulation systems invariably require some channel information at the transmitter. This could be acquired in
……… wireless ……………………systems by assuming the channel from the transmitter to the ………… receiver
………………..is approximately the same as the channel from the receiver to the transmitter. Alternatively, the channel
knowledge can also be directly measured at the receiver, and fed back to the transmitter. Adaptive modulation
systems improve…………… time division duplex …………….., and/or……… bit/error rates …………………., by
exploiting the channel information that is present at the transmitter. Especially over …… fading channel
……………………..which model ………… power …………………propagation environments, adaptive modulation
systems exhibit great performance enhancements compared to systems that do not exploit channel knowledge at the
transmitter.
B. Text comprehension.
1. Decide whether the following statements are true or false; if false, explain why.
1. Different bits are represented by different frequencies which can then be detected by a
transmitter. FALSE Receiver!
2. If there is no phase shift (0 degrees), the bits “00” are represented. If there is a phase shift of 180
degrees, the bits “11” are represented. TRUE
3. Such modulated signal is received by the receiver, where the shifts are detected and then it is
demodulated back into the original data stream. TRUE
4. Adaptive modulation allows wireless technologies to optimize throughput, yielding higher
throughputs but it does not cover long distances. FALSE also covering long distances!
2. Answer the questions.
1. What can both adaptive modulation techniques be used for?
Transmitting audio, video signal or digital data
2. What type of communications systems are they used for?
Digital communication systems
3. How could you characterize radio waves?
Radio waves are some kind of sine electromagnetic waves with high frequency
3. Explain what electromagnetic waves are.
http://technodrom.jpexs.com
JPEXS
5
28. 11. 2007 v 1.1
C. Lexis.
1. Find the synonyms.
Speed
Increase
Different
Basic
For example
Visible
Rate, velocity
Boost, enlarge
dissimilar
essential
E.g.
evident
2. Find the antonyms (opposites).
Different
Previous
Visible
Receiver
Similar, same
next
invisible
transmitter
3. Classify the words according to the part of speech they represent.
Explain how you recognized it.
modulation recognize digital wireless
usual
include
higher optimize
encode
lower
Noun
modulation receiver
Verb
recognize increase include
Adjective
digital
Adverb
usually
wireless
different usually
increase
receiver demodulate
optimize
different usual
higher
demodulate encode
lower
D. Technical terms
What can …………?
travel through
penetrate
bend
diffract
carry the message or digital signal
reflect
waves, …
Make sentences.
http://technodrom.jpexs.com
JPEXS
6
28. 11. 2007 v 1.1
1. Notice the use of some technical terms. Fill in the proper wave type according to the
context.
WAVE
(1)
_____ Radio ________ waves are (2) _____ electromagnetic ________ waves that move at the
speed of light in a (3) ____ sin _________ wave formation and can be used to carry a message
over a distance. They can have different frequencies which describes how fast they are moving up
and down which is measured in cycles per second or hertz. (4) _____ Carrial ________ waves
with different frequencies have different properties. For example, (5) _____ light ________ waves
are visible to the naked eye but cannot travel through walls. (6) _____ Radio ________ waves
(especially those of lower frequency) can penetrate walls and buildings as well as bend (diffract)
around corners.
2. See the differences in the usage: COMMUNICATION x COMMUNICATIONS
Communication:
the way of sharing thoughts, feelings, ideas or information to others
through speech, writing, body movements or signals
Communications:
1. are the various methods of sending information
2. are the ways which people use to form the relationships with each other
Fill in the appropriate term into the context.
1. A breakdown in _____________ between staff and management led to the present situation.
2. With an hour’s walk to the nearest telephone, _____________ /to be/ not easy.
3. Less than 2% of all overseas aid is going to improve _____________ .
4. Television is an important means of _____________ .
5. _____________ between parents and children /to be/ often difficult.
6. It is clear from the report that we must invest in more and better _____________ systems.
7. There is very little _____________ between us, which must be improved.
E. Grammar.
Study the following compounds. Translate them into Czech.
Is there any difference in forming them if you compare the two languages?
communication systems
Komunikační systémy
quadrature phase shift keying (QPSK)
Kvadraturní klíčování fázového posuvu
quadrature amplitude modulation
Kvadraturní amplitudová modulace
modulation techniques
Modulační techniky
radio waves
Radiové vlny
a sine wave formation
Formování sinusové vlny
carrier waves
Nosné vlny
light waves
Světelné vlny
http://technodrom.jpexs.com
JPEXS
7
28. 11. 2007 v 1.1
Review the Passive voice. See http://jazyky.feld.cvut.cz/vyuka/A/Y04A2Z/
F. Now you … HW
1. Underline the passive voice structures used in the text.
2. Translate them into Czech. Notice how often the Czech language uses the first plural.
3. Translate into English:
Rádiové vlny jsou elektromagnetické vlny, které se pohybují rychlostí světla v sinusových vlnách a
mohou být použity k přenášení zpráv na dálku. Mohou mít různé frekvence, což popisuje, jak
rychle se pohybují nahoru a dolů, a to se měří v cyklech za sekundu nebo-li v hercích (Hz). Nosné
vlny o různých frekvencích mají různé vlastnosti. Na příklad, světelné vlny jsou viditelné pouhým
okem, ale nemohou procházet stěnami. Rádiové vlny (zvláště o nižších frekvencích) mohou
pronikat stěnami a budovami, stejně tak se mohou ohýbat za roh.
Radio waves are electromagnetic waves, which are moving at light speed in sine waves and can be used
for transmitting messages to long distances. They can have different frequencies which describes, how
fast are they moving up and down, which is measured in loops per second which means in Hertz (Hz).
Carrier waves with different frequencies have different properties. For example light waves are visible to
naked-eye but cannot travel through walls. Radio waves (especially with lower frequencies) can travel
through walls and buildings and also can bend over edges.
Presentation topic.
Some tips for you.




Electromagnetic radiation
Carrier wave
WiMAX
Wi-Fi
http://technodrom.jpexs.com
JPEXS
8
28. 11. 2007 v 1.1
Poznámky
Wave-form – průběh
Regular – pravidelný
Radius-radii [rejdyáj] – poloměr
Diameter – průměr
Propagation – šíření vlny
Pass through – vlna prochází
Penetrate – vlna proráží, proniká
Precede, succeed – předcházet, následovat
Channel – kanál v TV nebo La Manche
Canal – prokopaný kanál
Yield – výnos
Gain – přínos
U=R . I …R equals U times I
R=U/I …R equals U above I
The Ohms law: Resistance is directly proportional to Voltage and inversely proportional to current
Výkon P – power
Nature – také podstata (he reveals the nature of st…)
Varies with time – měnit se v čase
Infinite [infinit] – nekonečný
Finite [fajnajt] – konečný
Flow – tok
Flux – tok
Speed = rate
Rate také sazba
Commision – podíl v procentech
Admission – vstupný
Basic – fundamental – elementary – essential
Visible – transparent – evident –apparent x invisible - nonvisible
Different x identical – the same –similar - like
http://technodrom.jpexs.com