Networking

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


by BrainBellupdated
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