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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IEEE 802.11n is the newest st<strong>and</strong>ard <strong>of</strong> WLAN (Wireless Local Area Network) next<br />
generation. In January 2006, Hawaii, IEEE passed a draft <strong>of</strong> the 802.11n st<strong>and</strong>ard. However the<br />
<strong>of</strong><strong>fi</strong>cial 802.11n universal st<strong>and</strong>ard is still in discussion. There are two main groups working on it,<br />
TGn Sync <strong>and</strong> WWiSE. In order to complete the st<strong>and</strong>ard earlier, these two groups composed a<br />
team called IPT (joint proposal team). [02]<br />
The follo<strong>wi</strong>ng section is going to introduce the capabilities <strong>of</strong> IEEE 802.11a/b/g theses three<br />
st<strong>and</strong>ards. Table 3-1 shows the IEEE 802.11 st<strong>and</strong>ard family members. [01][86]<br />
Table 3-1 Family <strong>of</strong> IEEE 802.11<br />
Protocol Release Date Op. Frequency<br />
11<br />
Throughput<br />
(Typ)<br />
Data Rate<br />
(Max)<br />
Legacy 1997 2.4 GHz 0.9 Mbps 2 Mbps<br />
802.11a 1999 5 GHz 23 Mbps 54 Mbps<br />
802.11b 1999 2.4 GHz 4.3 Mbps 11 Mbps<br />
802.11g 2003 2.4 GHz 19 Mbps 54 Mbps<br />
802.11j 2004 4.9 - 5 GHz 23 Mbps 54 Mbps<br />
802.11h 2004<br />
5,15 – 5,35 indoor<br />
5,47 – 5,725 indoor/outdoor<br />
23 Mbps 54 Mbps<br />
802.11n Sept, 2008 (est.) 2.4 GHz/5 GHz 74 Mbps 248 Mbps<br />
802.11y March, 2008 (est.) 3.7 GHz 23 Mbps 54 Mbps<br />
3.2. Capacity<br />
As shown in the Table 3-2 [16], although the operation b<strong>and</strong> <strong>of</strong> 802.11b is in 2.4 GHz, the<br />
FCC (Federal Communications Commission) is only allo<strong>wi</strong>ng it to carry a certain level <strong>of</strong><br />
frequency. Therefore for the U.S. the available WLAN channels are from 1 to11. This rule is also<br />
used on 802.11g. When building a WLAN, the interference is a very important factor. To avoid<br />
interference between channels in one area, the channels should not be overlapped <strong>and</strong> the<br />
interval <strong>of</strong> the frequency must be at least 25MHz. [04][05][16] That means, when selecting a<br />
channel, the number has to be <strong>fi</strong>ve numbers apart from each other, for example, 1, 6 <strong>and</strong> 11.<br />
Thus, for 802.11b, the maximum b<strong>and</strong><strong>wi</strong>dth capacity is 3*11 = 33Mbps <strong>and</strong> for 802.11g is 3*54<br />
= 162 Mbps. [11][14][17] - [20]<br />
The UNII is the initial for ‘Unlicensed National Information Infrastructure’. This b<strong>and</strong> is<br />
only free in certain countries, such as the U.S. <strong>and</strong> Taiwan. Table 3-3 [16] In the U.S., this b<strong>and</strong><br />
is divided into three sub-b<strong>and</strong>s <strong>and</strong> then each sub-b<strong>and</strong> is split up into four non-overlap channels.<br />
Therefore, the total available channels for 802.11a are twelve. Since the 5 GHz b<strong>and</strong> is not<br />
commonly used, it has a lower level <strong>of</strong> interference. When using 802.11a to build a WLAN, one