lec 10 - cellular wireless networks

7/24/2019 Lec 10 - Cellular Wireless Networks

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Background of Wireless

Communication

StudentPresentations andProjects

Wireless Communication

Technology

Wireless Networking and

Mobile IP

Wireless Local Area

Networks

Wireless Communication

Cellular Wireless NetworksCellular Wireless Networks


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Chapter 10


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Cellular Network Organization

Use multiple low-power transmitters (100 W or less)

Areas diided into cells

!ach sered "# its own antenna $ered "# "ase station consisting o% transmitter& receier&

and control unit

'and o% %reuencies allocated

Cells set up such that antennas o% all neigh"ors areeuidistant (heagonal pattern)


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*reuenc# +euse

Ad,acent cells assigned di%%erent %reuencies to aoid

inter%erence or crosstalk

O",ectie is to reuse %reuenc# in near"# cells

10 to 0 %reuencies assigned to each cell

.ransmission power controlled to limit power at that

%reuenc# escaping to ad,acent cells

.he issue is to determine how man# cells must interene"etween two cells using the same %reuenc#


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Approaches to Cope with /ncreasing

Capacit# Adding new channels

*reuenc# "orrowing %reuencies are taken %romad,acent cells "# congested cells

Cell splitting cells in areas o% high usage can "esplit into smaller cells

Cell sectoring cells are diided into a num"er o%

wedge-shaped sectors& each with their own set o%channels

icrocells antennas moe to "uildings& hills& andlamp posts


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Cellular $#stem Oeriew


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Cellular $#stems .erms

'ase $tation ('$) includes an antenna& a controller&and a num"er o% receiers

o"ile telecommunications switching o%%ice

(.$O) connects calls "etween mo"ile units .wo t#pes o% channels aaila"le "etween mo"ile unit

and '$ Control channels used to echange in%ormation haing to

do with setting up and maintaining calls

.ra%%ic channels carr# oice or data connection "etweenusers


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$teps in an .$O Controlled Call "etween

o"ile Users o"ile unit initialization

o"ile-originated call

2aging Call accepted

Ongoing call

3ando%%


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Additional *unctions in an .$O

Controlled Call Call "locking

Call termination

Call drop Calls to4%rom %ied and remote mo"ile su"scri"er


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o"ile +adio 2ropagation !%%ects

$ignal strength

ust "e strong enough "etween "ase station and mo"ile

unit to maintain signal ualit# at the receier

ust not "e so strong as to create too much cochannel

inter%erence with channels in another cell using the same

%reuenc# "and

*ading

$ignal propagation e%%ects ma# disrupt the signal and cause

errors


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3ando%% 2er%ormance etrics

Cell "locking pro"a"ilit# pro"a"ilit# o% a new call"eing "locked

Call dropping pro"a"ilit# pro"a"ilit# that a call is

terminated due to a hando%% Call completion pro"a"ilit# pro"a"ilit# that an

admitted call is not dropped "e%ore it terminates

2ro"a"ilit# o% unsuccess%ul hando%% pro"a"ilit# thata hando%% is eecuted while the reception conditionsare inadeuate


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3ando%% 2er%ormance etrics

3ando%% "locking pro"a"ilit# pro"a"ilit# that ahando%% cannot "e success%ull# completed

3ando%% pro"a"ilit# pro"a"ilit# that a hando%% occurs"e%ore call termination

+ate o% hando%% num"er o% hando%%s per unit time /nterruption duration duration o% time during a hando%%

in which a mo"ile is not connected to either "ase station

3ando%% dela# distance the mo"ile moes %rom the

point at which the hando%% should occur to the point atwhich it does occur


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3ando%% $trategies Used to 5etermine

/nstant o% 3ando%% +elatie signal strength

+elatie signal strength with threshold

+elatie signal strength with h#steresis +elatie signal strength with h#steresis and threshold

2rediction techniues


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2ower Control

5esign issues making it desira"le to include d#namic

power control in a cellular s#stem

+eceied power must "e su%%icientl# a"oe the "ackground

noise %or e%%ectie communication

5esira"le to minimize power in the transmitted signal %rom

the mo"ile

+educe cochannel inter%erence& alleiate health concerns& sae

"atter# power

/n $$ s#stems using C5A& it6s desira"le to eualize the

receied power leel %rom all mo"ile units at the '$


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.#pes o% 2ower Control

Open-loop power control 5epends solel# on mo"ile unit

No %eed"ack %rom '$

Not as accurate as closed-loop& "ut can react uicker to%luctuations in signal strength

Closed-loop power control Ad,usts signal strength in reerse channel "ased on metric

o% per%ormance '$ makes power ad,ustment decision and communicates to

mo"ile on control channel


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.ra%%ic !ngineering

/deall#& aaila"le channels would eual num"er o%su"scri"ers actie at one time

/n practice& not %easi"le to hae capacit# handle all

possi"le load *orNsimultaneous user capacit# andLsu"scri"ers

L 7N non"locking s#stem

L8N "locking s#stem


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'locking $#stem 2er%ormance 9uestions

2ro"a"ilit# that call reuest is "locked:

What capacit# is needed to achiee a certain upper

"ound on pro"a"ilit# o% "locking:

What is the aerage dela#:

What capacit# is needed to achiee a certain aerage

dela#:


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.ra%%ic /ntensit#

;oad presented to a s#stemrace%ul degradation s#stem onl# graduall#degrades as more users access the s#stem


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5raw"acks o% C5A Cellular

$el%-,amming arriing transmissions %rom multipleusers not aligned on chip "oundaries unless users are

per%ectl# s#nchronized

Near-%ar pro"lem signals closer to the receier arereceied with less attenuation than signals %artherawa#

$o%t hando%% reuires that the mo"ile acuires the

new cell "e%ore it relinuishes the old@ this is morecomple than hard hando%% used in *5A and.5A schemes


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o"ile Wireless C5A 5esign

Considerations

+AG! receier when multiple ersions o% a signalarrie more than one chip interal apart& +AG!receier attempts to recoer signals %rom multiple

paths and com"ine them .his method achiees "etter per%ormance than simpl#

recoering dominant signal and treating remaining signalsas noise

$o%t 3ando%% mo"ile station temporaril# connectedto more than one "ase station simultaneousl#


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2rinciple o% +AG! +eceier


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.#pes o% Channels $upported "# *orward

;ink

2ilot (channel 0) - allows the mo"ile unit to acuiretiming in%ormation& proides phase re%erence and

proides means %or signal strength comparison

$#nchronization (channel B?) - used "# mo"ilestation to o"tain identi%ication in%ormation a"outcellular s#stem

2aging (channels 1 to H) - contain messages %or one

or more mo"ile stations .ra%%ic (channels to B1 and BB to IB) the %orward

channel supports tra%%ic channels


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*orward .ra%%ic Channel 2rocessing $teps

$peech is encoded at a rate o% 0 "ps

Additional "its added %or error detection

5ata transmitted in ?-ms "locks with %orward errorcorrection proided "# a conolutional encoder

5ata interleaed in "locks to reduce e%%ects o% errors

5ata "its are scram"led& sering as a priac# mask


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*orward .ra%%ic Channel 2rocessing $teps

(contD)

2ower control in%ormation inserted into tra%%ic

channel

5$-$$ %unction spreads the 1D? k"ps to a rate o%

1D?? "ps using one row o% IJ IJ Walsh matri

5igital "it stream modulated onto the carrier using

92$G modulation scheme


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/.U6s Eiew o% .hird->eneration

Capa"ilities Eoice ualit# compara"le to the pu"lic switched

telephone network

1JJ k"ps data rate aaila"le to users in high-speedmotor ehicles oer large areas

BJ k"ps aaila"le to pedestrians standing or moingslowl# oer small areas

$upport %or ?D0J "ps %or o%%ice use

$#mmetrical 4 as#mmetrical data transmission rates

$upport %or "oth packet switched and circuit switcheddata serices


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/.U6s Eiew o% .hird->eneration

Capa"ilities

An adaptie inter%ace to the /nternet to re%lect

e%%icientl# the common as#mmetr# "etween in"ound

and out"ound tra%%ic

ore e%%icient use o% the aaila"le spectrum in

general

$upport %or a wide ariet# o% mo"ile euipment

*lei"ilit# to allow the introduction o% new sericesand technologies


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Alternatie /nter%aces


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C5A 5esign Considerations

'andwidth limit channel usage to 3z

Chip rate depends on desired data rate& need %or

error control& and "andwidth limitations@ B cps or

more is reasona"le

ultirate adantage is that the s#stem can %lei"l#

support multiple simultaneous applications %rom a

gien user and can e%%icientl# use aaila"le capacit#"# onl# proiding the capacit# reuired %or each

serice


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9KA

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lec 10 - cellular wireless networks

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