Tag Archives: rate

Seg 3: wifi features and frequency band

  1. Features of Wifi
  • Constitution of network is flexible. It can be infrastructure mode, or a self-organizing mode;
  • Mature technology and rich application;
  • Low price devices;
  • Low power, small recover range;
  • Woring at the frequency 2.4GHz, which is the same as IMS (Industrial/Medical/Scientific). Thus, it may be relatively easy to be interfered. Moreover, Microwave ovens, and cordless phone are also working at IMS frequency.
  1. Wireless frequency band

ISM frequency band is reserved for the Industrial/ Scientific / Medical use, which is specialized by FCC. Nowadays, most countries all over the world open this frequency band by following this standard. But the ISM frequency is not unified in these countries. We cannot be allowed to use these frequency bands, i.e., 900MHz, 2.4GHz, 5.7GHz; but the transmitted power must be lower the specialized power (generally lower 1W) and the utilized frequency cannot interfere with other frequencies. At present, most of the wireless products are working at 2.4GHz. And the 802.11 protocol families are shown in Table 1-1.

Table 1-1 Wireless Frequency

802.11b

802.11a

802.11g

802.11n

Release time

Sept. 1999

Sept. 1999

June. 2003

Jan. 2004

frequency

2.4Ghz

5Ghz

2.4Ghz

2.4Ghz5Ghz(2.4Ghz or/and 5Ghz

modulation

CCK/DSSS

OFDM

CCK/OFDM

MIMO OFDM

range

About 100m

About 50m

<100m

Several Km

Max rate

11Mbps

54Mbps

54Mbps

600Mbps

compatible

11g

Not with 11b/g

11b

11b/a/g