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FHSS, DSSS, and 802.11 Standards

The original 802.11 standard had two variationsboth offering the same speeds but differing in the RF spread spectrum used. One of the 802.11 used FHSS. This 802.11 variant used the 2.4GHz radio frequency band and operated with a 1 or 2Mbps data rate. Since this original standard, wireless implementations have favored DSSS. The second 802.11 variation used DSSS and specified a 2Mbps-peak data rate with optional fallback to 1Mbps in very noisy environments. 802.11, 802.11b, and 802.11g use the DSSS spread spectrum. This means that the underlying modulation scheme is very similar between each standard, enabling all DSSS systems to coexist with 2, 11, and 54Mbps 802.11 standards. Because of the underlying differences between 802.11a and the 802.11b/g, they are not compatible. Table 8 summarizes each of the wired standards discussed in the previous sections.

Table 8 IEEE 802 Wireless Network Standards

IEEE Standard Frequency/Media Speed Topology Transmission Range Access Method Spread Spectrum
802.11 2.4GHz RF 1 to 2Mbps Ad-hoc/infra-structure CSMA/CA DSSS
802.11 2.4GHz RF 1 to 2Mbps Ad-hoc/infra-structure CSMA/CA FHSS
802.11a 5GHz Up to 54Mbps Ad-hoc/infra-structure 25 to 75 feet indoors range can be affected by building materials CSMA/CA OFDM
802.11b 2.4GHz Up to 11Mbps Ad-hoc/infra-structure Up to 150 feet indoors; range can be affected by building materials CSMA/CA DSSS
802.11g 2.4GHz Up to 54Mbps Ad-hoc/infra-structure Up to 150 feet indoors; range can be affected by building materials CSMA/CA DSSS
IrDA Infrared light beam Up to 16Mbps Ad-hoc 1 meter N/A N/A
Bluetooth 2.4GHz RF 720Kbps Ad-hoc 10 meters N/A FHSS

轉載于:https://blog.51cto.com/aajs800/137692