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IEEE 802.11 STANDARDS

Prajwal Sunil Birwadkar (1930331372032)

Ashwini Dinesh Shirke (1930331372033)

Shreeganesh Uday Phale (1930331372053)

Sushant Sunil Mhatre (1930331372054)

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IEEE 802.11 FHSS

IEEE 802.11 FHSS uses the frequency-hopping spread spectrum (FHSS) method. FHSS uses the 2.4-GHz ISM band. The band is divided into 79 sub-bands of 1 MHz . A pseudorandom number generator selects the hopping sequence. The modulation technique in this specification is either two-level FSK or four-level FSK with 1 or 2 bitslbaud, which results in a data rate of 1 or 2 Mbps.

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Fig. Physical layer of IEEE 802.11 FHSS

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IEEE 802.11 DSSS

IEEE 802.11 DSSS uses the direct sequence spread spectrum (DSSS) method . DSSS uses the 2.4-GHz ISM band. The modulation technique in this specification is PSK at 1Mbaud/s. The system allows 1 or 2 bitslbaud , which results in a data rate of 1 or 2 Mbps.

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Fig. Physical layer of IEEE 802.11 DSSS

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IEEE 802.11a OFDM

IEEE 802.11a OFDM IEEE 802.Ila OFDM describes the orthogonal frequency-division multiplexing (OFDM) method for signal generation in a 5-GHz ISM band. OFDM is similar to FDM, with one major difference: All the sub-bands are used by one source at a given time.

The band is divided into 52 sub-bands, with 48 sub-bands for sending 48 groups of bits at a time and 4 sub-bands for control information.

Dividing the band into sub-bands diminishes the effects of interference. If the sub-bands are used randomly, security can also be increased.

OFDM uses PSK and QAM for modulation. The common data rates are 18 Mbps (PSK) and 54 Mbps (QAM).

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IEEE 802.11b

IEEE 802.11b DSSS describes the high-rate direct sequence spread spectrum (HRDSSS) method for signal generation in the 2.4-GHz ISM band. HR-DSSS is similar to DSSS except for the encoding method, which is called complementary code keying (CCK). CCK encodes 4 or 8 bits to one CCK symbol. To be backward compatible with DSSS, HR-DSSS defines four data rates: 1,2, 5.5, and 11 Mbps. The first two use the same modulation techniques as DSSS. The 5.5-Mbps version uses BPSK and transmits at 1.375 Mbaudls with 4-bit CCK encoding. The II-Mbps version uses QPSK and transmits at 1.375 Mbps with 8-bit CCK encoding.

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Fig. Physical layer of IEEE 802.11b

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IEEE 802.11g

IEEE 802.11g was one of the main Wi-Fi standards to follow on from 802.11a and 802.11b. It built on the performance and played a pivotal role in further establishing Wi-Fi as a major wireless communications standard. In 2003, WLAN products supporting a newer standard called 802.11g emerged on the market. 802.11g attempts to combine the best of both 802.11a and 802.11b. 802.11g supports bandwidth up to 54 Mbps, and it uses the 2.4 GHz frequency for greater range. 802.11g is backward compatible with 802.11b, meaning that 802.11g access points will work with 802.11b wireless network adapters and vice versa.

The modulation scheme used in 802.11g is OFDM ( Orthogonal Frequency Division Multiplexing).