A comparison of wi-fi and wimax with case studies - Florida State ...
A comparison of wi-fi and wimax with case studies - Florida State ...
A comparison of wi-fi and wimax with case studies - Florida State ...
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codes ( (CTC) <strong>and</strong> low densityy<br />
parity cheeck<br />
(LDPC) ) codes aree<br />
optional mmodes.<br />
Sincce<br />
the IEEEE<br />
802.16 clause did nnot<br />
set up thhe<br />
b<strong>and</strong><strong>wi</strong>ddth<br />
<strong>and</strong> moddulation<br />
method,<br />
differrent<br />
con<strong>fi</strong>guurations<br />
<strong>wi</strong>lll<br />
end up <strong>wi</strong>th different<br />
speeds. Thus <strong>wi</strong>th AMC, the system cann<br />
have the mmaximum<br />
uusage<br />
<strong>of</strong> thee<br />
channell.<br />
Table 4-2[50]<br />
shows the modulaation<br />
<strong>and</strong> cooding<br />
suppoorted<br />
in WiMMax.<br />
[50]<br />
4.3.1.11.3.<br />
Chhannel-quality<br />
Meaasurement<br />
The e channel-qquality<br />
meassurement<br />
sccheme<br />
is thee<br />
fundamenntal<br />
<strong>of</strong> downnlink<br />
<strong>and</strong> upplink<br />
powerr<br />
control processes a<strong>and</strong><br />
modulattion<br />
<strong>and</strong> code<br />
rate adapptation.<br />
A MMS<br />
is requirred<br />
to send the channell<br />
quality feedback (CCQI)<br />
includding<br />
RSSI ( (Received SSignal<br />
Stren ngth Indicattor)<br />
<strong>and</strong> SIN NR (Signal-<br />
to-Interrference-pluus-Noise<br />
Raatio)<br />
to BS for f evaluatinng<br />
channel conditions. With this innformation,<br />
BS can: : [50]<br />
<br />
<br />
Change moodulation<br />
annd/or<br />
coding g rate for thee<br />
transmissiion<br />
Change thee<br />
power leveel<br />
<strong>of</strong> the asssociated<br />
DLL<br />
or UL trannsmissions.<br />
4.3.1.11.4.<br />
OFFDM<br />
in WWiMax<br />
Table 4-22<br />
Modulatioon<br />
<strong>and</strong> Codiing<br />
Supportted<br />
in WiMaax<br />
In <strong>fi</strong>xed-WiMa f ax, the FFTT<br />
size is onlly<br />
256. Therre<br />
are 192 ssubcarriers<br />
used for ca arrying data; ;<br />
8 for pilot p subcarrriers<br />
<strong>and</strong> thhe<br />
rest are guard subccarriers.<br />
Be ecause the FFFT<br />
size is s <strong>fi</strong>xed, thee<br />
subcarrier<br />
intervall<br />
is related to the channnel<br />
b<strong>and</strong>w<strong>wi</strong>dth.<br />
With larger bannd<strong>wi</strong>dth,<br />
thee<br />
subcarrierr<br />
intervall<br />
increases, but the symmbol<br />
time ddecreases.<br />
TThat<br />
means a larger pieece<br />
<strong>of</strong> fram mes needs too<br />
be alloccated<br />
properrly<br />
to overccome<br />
delay spread. The<br />
table 4-3[ [50] shows the OFDM parameterss<br />
used fo or WiMAX. The OFDMM-PHY<br />
<strong>of</strong> WiMax has<br />
a <strong>wi</strong>de raange<br />
<strong>of</strong> guaard<br />
times, th herefore thee<br />
networkk<br />
designerss<br />
can make e <strong>fi</strong>tting traade-<strong>of</strong>fs<br />
bettween<br />
specctral<br />
ef<strong>fi</strong>ciency<br />
<strong>and</strong> de elay spreadd<br />
robustnness.<br />
When using a 255<br />
percent guuard<br />
time, iit<br />
can deal <strong>wi</strong>th the mmaximum<br />
delay d spread d<br />
45
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