wireless doc

7/26/2019 Wireless doc

1/20

There are two diferent kinds o mobility:

1. User mobility2. Device portability

User mobility reers to a user who has access to the same or similar

telecommunication services at diferent places, i.e., the user can be

mobile, and the services will ollow him or her. !amples or mechanisms

supportin" user mobility are simple call#orwardin" solutions

Device portability reers to the communication device moves $with or

without a user%. &any mechanisms in the network and inside the device

have to make sure that communication is still possible while the device is

movin". ' typical e!ample or systems supportin" device portability is the

mobile phone system, where the system itsel hands the device rom one

radio transmitter $also called a base station% to the ne!t i the si"nal

becomes too weak.

The term wireless is used with reerence to device which means way o

accessin" the network or other communication device without wire. The

wire is replaced by the transmission o electroma"netic wave throu"h the

air.

Thus communication device thus can be:#

1. Fixed and wired: e!ample o this con("uration is desktop device.

The power consumption and the wei"ht o devices do not allow or

mobile usa"es.

2. Mobile and wired:Device like laptops all in this cate"ory wherethe device is mobile and it can be connected to company)s network

or network via telephone network and a modem.*. Fixed and wireless:This con("uration is used or installin" the

networks. +or e!ample in historical buildin"s to avoid the dama"e

by installin" wires.. Mobile and wireless: -n this, a mobile device uses the wireless

network. !amples are mobiles, tablets etc.

Application of wireless networks:1. ehicles2. /usiness*. mer"encies. 0eplacement o wired network. -notainment1. Vehicle : or music, 34 etc.. !"siness: ' travellin" salesman today needs instant access to the

company)s database: to ensure that (les on his or her laptop re5ect thecurrent situation, to enable the company to keep track o all activities otheir travellin" employees, to keep databases consistent etc. with wireless

access, the laptop can be turned into a true mobile o6ce, but e6cient and

1


2/20

powerul synchroni7ation mechanisms are needed to ensure dataconsistency.

#. $mer%encies:8ireless networks are the only means o communication inthe case o natural disasters such as hurricanes or earth9uakes.

&. 'eplacement of wired network: historical buildin"s, remote sensin"etc.

(. )nfotainment :usin" internet everywhere by wireless networks.

*imple network reference model

1. This 3D' communicates with a base station in the middle o the

picture. The base station consists o a radio transceiver $sender andreceiver% and an interworkin" unit connectin" the wireless link with

the (!ed link.

2. Underneath each network element the protocol stack implementedin the system accordin" to the reerence model. nd#systems, suchas the 3D' and computer in the e!ample, need a ull protocol stack.

*. +unction o each layer:a. +hysical layer:

i. onversion o stream into si"nal and at receivin" end a"ainto bit rom si"nal

ii. +re9uency "enerationiii. 4i"nal detectioniv. eneration o carrier re9uenciesv. &odulation o data on to carrier re9uency

vi. ncryption;decryption

b. Data link layer:i. 'ccessin" the mediumii. &ultiple!in" o diferent data streamiii. orrection o transmission errorsiv. 4ynchroni7ation

c. ,etwork layer:

i. 0outin" o packetsii. 'ddressin" and device location

2


3/20

iii.


4/20


5/20


6/20

Antennas1. 'n antenna can be de(ned as an electrical conductor or system o

conductors used either or radiatin" electroma"netic ener"y or or

collectin" electroma"netic ener"y.2. +or transmission o a si"nal, radio4fre"ency electrical ener%y

rom the transmitter is converted into electroma%netic ener%yby

the antenna and radiated into the surroundin" environment

$atmosphere, space, water%.

*. +or reception o a si"nal, electroma%netic ener%ycontact on the

antenna is converted into radiofre"ency electrical ener%yand

ed into the receiver.

&. ' theoretical reerence antenna is theisotropic radiator, a point inspace radiatin" e9ual power in all directions, i.e., all points with

e9ual power are located on a sphere with the antenna as its center.The radiation patternis symmetric in all directions.

@


7/20

such type o antenna does not e!ist in real world.

. 0eal antennas all e!hibit directive e5ects, i.e., the intensity oradiation is not the same in all directions rom the antenna. Thesimplest real antenna is a thin, center#eddipole, also called 0ert6ian dipole. Thedipoleconsists o two collinear conductors

o e9ual len"th, separated by a small eedin""ap. The len"th o the dipole is not arbitrary,but, or e!ample, hal the wavelen"th G othe si"nal to transmit results in a verye6cient radiation o the ener"y. - mounted on the roo o a car, thelen"th o G; is eicient. This is also known as Marconi antenna.

@. G;2 dipole has a uniorm or 7mni4directional radiationpattern inone plane and a ("ure ei"ht pattern in the other two planes asshown in +i"ure. This type o antenna can only overcomeenvironmental challen"es by boostin" the power level o the si"nal.hallen"es could be mountains, valleys, buildin"s etc.

B. Directional antennas used certain (!ed preerential transmissionand reception direction. +i"ure below shows the radiation pattern odirectional antennas.

Directed antennas are typically applied in cellular systems. 4everaldirected antennas can be combined on a sin"le pole to construct asectori6ed antenna. ' cell can be sectori7ed into, or e!ample,three or si! sectors, thus enablin" re9uency reuse. The radiationpatterns o this sectori7ed antenna shown below:

B


8/20

>.*mart antennascombines multiple antenna elements $also calledantenna array% with si"nal processin" to optimi7e theradiation;reception pattern in response to the si"nal environment.These antennas can adapt to chan"es in reception power,transmission conditions and many si"nal propa"ation. 'ntennaarrays can also be used or beam ormin".

*i%nal +ropa%ation1. -n wireless networks, the si"nal has no wire to determine the

direction o propa"ation, whereas si"nals in wired networks only

travel alon" the wire.2. -n wired network si"nal e!hibits the same characteristics at each

point as lon" as the wire is not dama"ed.*. +or wireless transmission, this predictable behaviour is only valid in

a vacuum.. The situation would be as ollows:

H -ransmission ran%e: 8ithin a certain radius o the sender

transmission is possible, i.e., a receiver receives the si"nalswith low error rate to establish the communication betweensender and receiver.H Detection ran%e: 8ithin a secondradius, detection o the transmissionis possible, i.e., the transmitted poweris lar"e enou"h to difer romback"round noise.


9/20

+ath loss of radio si%nal1. -n ree space radio si"nals propa"ate as li"ht does i.e., they ollow a

strai"ht line $besides "ravitational efects%.

2. - such a strai"ht line e!ists between a sender and a receiver it iscalled line4of4si%ht8/7*9.

*. ven i no matter $thin"% e!ists between the sender and the receiver$i.e. i there is vacuum%, the si"nal still e!perience the free spaceloss.

. &ost radio transmission takes place throu"h the atmosphere Csi"nals travel throu"h air, rain, snow, o", dust particles, smo" etc.

. 8hile the path loss or atten"ation1does not cause too muchtrouble or short distances, e."., or E'Is.

@. The atmosphere heavily in5uences transmission over lon"distances, e."., satellite transmission. ven mobile phone systemsare in5uenced by weather conditions such as heavy rain.

B. 0adio waves can e!hibit three undamental propa"ation behavioursdependin" on their re9uency:

;ro"nd wave 8 M069:&obile phone systems, satellitesystems, cordless telephones etc. use even hi"herre9uencies. The emitted waves ollow a $moreor less% strai"htline o si"ht. This enables direct communication with satellites$no re5ection at the ionosphere% or microwave links on the"round.

1 Eoss o stren"th o si"nal in transmission.

A


10/20


11/20

b. Fre"ency hoppin% spread spectr"m.

Direct se"encin% spread spectr"m

1. +or direct se9uence spread spectrum $D444%, each bit in the ori"inalsi"nal is represented by multiple bits in the transmitted si"nal, usin"

a spreadin" code.2. Fne techni9ue or direct se9uence spread spectrum is to combine

the di"ital inormation stream with the spreadin% code bit streamusin" an e!clusive#F0 $KF0%.

*. KF0 obeys the ollowin" rules

. The spreadin% code bit stream sometimes may reer as chippedse"ence.

. The ollowin" ("ure shows e!ample o direct se9uencin" spread

spectrum.

@. ach user bit has a duration tb. The chippin" se9uence consists othe smaller pulse called chips, with a duration tc.

B. - the chippin" se9uence "enerated properly than it appears as arandom noise. This se9uence sometimes also code pse"do noise.

>. The spreadin% factor sLtb;tc determine the bandwidth o the

resultin" si"nal.A. - ori"inal si"nal need the bandwidth w, the resultin" si"nal will

need s.wbandwidth ater the spreadin".1?. ivil applications need the spreadin" actor between 1? to 1??

and military applications need up to 1?,???.11. D444 need additional components or transmittin" and

receivin".12. The D*** transmitter spread the user data with the

chippin" se9uence $di"ital modulation%. The spread si"nal thenmodulates with radio carrier.

11


12/20

1#. At the receiver end

a. 'dditional mechanism is carried out due to multipathpropa"ation or noise, to construct the ori"inal data.

b. -n the (rst step, the receiver demodulated the si"nal with thesame carrier re9uency used in transmittin".

c. -n the ne!t step, the receiver has to know the ori"inal chippin"se9uence

d. hippin" se9uences at the sender and receiver have to beprecisely synchroni7ed because the receiver calculates theproduct o a chip with the incomin" si"nal. This comprisesanother KF0 operation.

e. Durin" a bit period, which also has to be derived viasynchroni7ation, an inte%ratoradds all these products.

. alculatin" the products o chips and si"nal, and addin" theproducts in an inte"rator are also called correlation, thedevice a correlator.

". +inally, in each bit period a decision "nitsamples the sums"enerated by the inte"rator and decides i this sum representsa binary 1 or a ?.

Fre"ency hoppin% spread spectr"m

1. -n re9uency hoppin" spread spectrum $+


13/20

e. 4low hoppin" systems are typically cheaper and have rela!edtolerances, but they are not as immune to narrowbandintererence as ast hoppin" systems.

B. For fast hoppin% systemsa. The transmitter chan"es the re9uency several times durin"

the transmission o a sin"le bit.b. -n ollowin" ("ure, the transmitter hops three times durin" a

bit period.c. +ast hoppin" systems are more comple! to implement

because the transmitter and receiver have to staysynchroni7ed within smaller tolerances to perorm hoppin" atmore or less the same points in time.

d. . -he F** transmittera. The (rst step in an +


14/20

a. The receiver o an +.111. The - standard >?2.11 $-, 1AAA% speci(es the most amous

amily o 8E'Is in which many products are available.2. 's the standard)s number indicates, this standard belon"s to the

"roup o >?2.! E'I standards, e."., >?2.* thernet or >?2. Token

0in".*. This means that the standard speci(es the physical and medium

access layer adapted to the special re9uirements o wireless E'Is,

but ofers the same interace as the others to hi"her layers to

maintain interoperability.. The primary "oal o the standard was the speci(cation o a simple

and robust 8E'I which ofers time#bounded and asynchronousservices.

. 'dditional eatures o the 8E'I should include:a. The support o power mana"ement to save battery powerb. The handlin" o hidden nodes.c. The ability to operate worldwide.

1


15/20

*ystem architect"re

1. +i"ure illustrates the model developed by the >?2.11 workin" "roup.2. The smallest buildin" block o a wireless E'I is a basic service set

8!**93which consists o some number o stations $*-A9 e!ecutin"

the same &' protocol and competin" or access to the same

shared wireless medium.*. ' /44 may be isolated or it may connect to a backbone

distrib"tion system 8D*9throu"h an access point 8A+9.. The '3 unctions as a brid"e and a relay point.

. -n a /44, client stations do not communicate directly with oneanother. 0ather, i one station in the /44 wants to communicate

with another station in the same /44, the &' rame is (rst sent

rom the ori"inatin" station to the '3, and then rom the '3 to the

destination station.@. 4imilarly, a &' rame rom a station in the /44 to a remote station

is sent rom the local station to the '3 and then relayed by the '3

over the D4 on its way to the destination station.B. The D4 can be a switch, a wired network, or a wireless network.>. 8hen all the stations in the /44 are mobile stations, with no

connection to other /44s, the /44 is called an independent !**

8)!**9.A. 'n -/44 is typically an adhoc network. -n an -/44, the stations all

communicate directly, and no '3 is involved.1?. ' simple

con("uration is shown in +i"ure, in which each station belon"s to a

sin"le /44N that is, each station is within wireless ran"e only o other

stations within the same /44.11. -t is also

possible or two /44s to overlap "eo"raphically, so that a sin"lestation could participate in more than one /44.

1


16/20

12. The

association between a station and a /44 is dynamic. 4tations may

turn of, come within ran"e, and "o out o ran"e.1*. 'n

extended service set 8$**9consists o two or more basic service

sets interconnected by a distribution system.1. Typically,

the distribution system is a wired backbone E'I but can be any

communications network.1. The

e!tended service set appears as a sin"le lo"ical E'I to the lo"ical

link control $EE% level.1@. +i"ure

indicates that an access point $'3% is implemented as part o a

stationN the '3 is the lo"ic within a station that provides access tothe D4 by providin" D4 services in addition to actin" as a station.

1B. To

inte"rate the - >?2.11 architecture with a traditional wired E'I,

a portal is used. The portal lo"ic is implemented in a device, such

as a brid"e or router, that is part o the wired E'I and that is

attached to the D4.

+rotocol architect"re

+i"ure shows the most common scenario:

1@


17/20

1. 'n - >?2.11 wireless E'I connected to a switched - >?2.*

thernet via a brid"e.2. 'pplications should not notice any diference apart rom the lower

bandwidth and perhaps hi"her access time rom the wireless E'I.*. The 8E'I behaves like a slow wired E'I. onse9uently, the hi"her

layers $application, T3, -3% look the same or wireless nodes as or

wired nodes.. The upper part o the data link control layer, the lo"ical link control

$EE%, covers the diferences o the medium access control layersneeded or the diferent media.. The - >?2.11 standard only covers the physical layer +0Band

medi"m access layer MA@ like the

other >?2.! E'Is do.@. The physical layer is subdivided into

the physical layer conver%ence

protocol 8+/@+9 and the physical

medi"m dependent s"blayer

8+MD9.

B. The basic tasks o the MA@ layercomprisea. medium accessb. ra"mentation o user datac. and encryption.

>. +/@+ s"blayer provides a carrier sense si"nal, called clearchannel assessment$'%, and provides a common 3


18/20

c. ontrols authentication mechanisms, encryption,synchroni7ation o a station with re"ard to an access point,

d. 3ower mana"ement to save battery power.e. &' mana"ement also maintains the MA@ mana%ement

information base 8M)!9.

11. The main tasks o the +0B mana%ement include channeltunin" and 3


19/20

Ad hoc networkin%: ' device e9uipped with a /luetooth radio canestablish instant connection to another /luetooth radio as soon as itcomes into ran"e.

+rotocol architect"re1. /luetooth is de(ned as a layered protocol architecture consistin" o

core protocols, cable replacement and telephony control protocol, andadopted protocols. The core protocols orm a (ve#layer stack consistin"o the ollowin" elements:

a. 'adio:4peci(es details o the air interace, includin" re9uency,the use o re9uency hoppin", modulation scheme, and transmitpower.

b. !aseband:oncerned with connection establishment within apiconet $83'I%, addressin", packet ormat, timin", and powercontrol.

c. /ink mana%er protocol 8/M+9: 0esponsible or -ink setupbetween /luetooth devices and on"oin" link mana"ement. Thisincludes security aspects such as authentication and encryption,plus the control and ne"otiation o baseband packet si7es.

d. /o%ical link control and adaptation protocol $E2'3%:'dapts upper#layer protocols to the baseband layer. E2'3provides both connectionless and connection#oriented services.

e. *ervice discovery protocol 8*D+9: Device inormation,services, and the characteristics o the services can be 9ueriedto enable the establishment o a connection between two or

more /luetooth devices.

2. 0+F&& is the cable replacement protocol included in the/luetooth speci(cation. 0+F&& presents a virtual serial port that isdesi"ned to make replacement o cable technolo"ies as transparent aspossible.

1A


20/20

*. /luetooth speci(es a telephony control protocol. T4 /-I

$telephony control speci(cation#binary% is a bit#oriented protocol that

de(nes the call control si"nallin" or the establishment o speech and

data calls between /luetooth devices.

. The adopted protocolsare de(ned in speci(cations issued by otherstandards makin" or"ani7ations and incorporated into the overall/luetooth architecture. The /luetooth strate"y is to invent onlynecessary protocols and use e!istin" standards whenever possible.The adopted protocols include the ollowin":

a. +++: The point4to4point protocol is an -nternet standardprotocol or transportin" -3 data"rams over a point#to#point link.

b. -@+CUD+C)+:These are the oundation protocols o the T3;-3protocol suite.

c. 7!$: The obEect exchan%e protocol is a session#Eevelprotocol developed by the -nrared Data 'ssociation $-rD'% or

the e!chan"e o obJects. F/K provides unctionality similar tothat o

wireless doc

Documents