University:
College
Course:
College Engineering
Academic year:

2023
Views:

387

Pages:

2
Author:

Dipin K.

Wireless LAN 802.11 Architecture The standard defines two kinds of services: the basic services set (BSS) and the extended service set (ESS). Basic service Set IEEE 802.11 defines the basic service set (BSS) at the building block of wireless LAN. A basic service set is made of stationary or mobile wireless stations and a possible control base station known as the Access Point (AP). The BSS without an AP is a stand-alone network and cannot find data to other BSSS. It is what is called an ad-hoc architecture. In this architecture, stations can form a network without the need of an AP ; they can locate each other and agree to be part of BSS. Station Types IEEE 802.11 defines three types of stations on their mobility in a wireless LAN: notransition, BSS-transition, and ESS-transition. No-Transition mobility: A station with no-transition mobility (riot moving) or moving only inside a BSS. BSS-Transition mobility: A station with BSS-transition mobility can move from one BSS to another, but the movement is confined inside one ESS. ESS- Transition mobility. A station with ESS-transition mobility can move from one BSS to another. However, IEEE802.11 does not guarantee that communication is continuous during the move. Physical layer. Defines specification for the conversion of bits to signal in the physical layer. Upper Layer 802.11 802.11 802.11 802.11a 802.11b 802.11g infrared FHSS DSSS OFDM HR-DSSS OFDM IEEE 802.11 FHSS FHSS describes the frequency-hopping spread spectrum (FHSS) method for signal generation in a 2.4 GHz ISM band. It uses PSK at 1 M baud is 15. The system allows 1 or 2 bits/s and two-level FSK or four-level FSK which results in a data rate of 1 or 2 Mbps. IEEE 802.11 DSSS describes the (direct sequence spread spectrum (DSSS)) Method for signal generation in a 2.4 GHz ISM band. Band DSSS uses a 2.4 GHZ ISM band. The bit sequence assuming entire band. Modulation and Data rate. The modulation techniques in this specification is PSK at Mbaud/s. The system allows 1 or 2 bits/baud (BPSK or QPSM), which results in a data rate of 1 or 2 Mbps. IEEE 802.1 1a OFDM IEEE 802.11 a OFDM describes the orthogonal frequency density multiplexing (OFDM) method for signal generation in a 5 GHz band. OFDM: OFDM is the same as FDM, with one major difference. All the subband are used by one source at a given time. Sources contend with one another at the data link layer for access. Modulation and data rate. OFDM uses PSK and QAM for modulation. The common data rates as 18 Mbps (PSK) and 54 Mbps (QAM) Quadrature amplitudes modulation (QAM). It is combination of ASK& QSK IEEE 802.11b HR DSSS High Rate direct sequence spread spectrum (DSSS). HR-DSS Complementary Code Keying (CCK) UR encodes 4 or 8 bits to the (CK symbol). Band the specification uses a 2.4 GHz ISM band. IEEE 802.11g OFDM This relatively new specification use OFDM with 2.4 GHz ISM band. The complex modulation techniques achieve a 54 Mbps data rate.