03-01-2013, 01:23 PM
Implementation of WiFi Mac Transmitter by VHDL Modelling
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Abstract:
For the wireless communication in radio frequency range, IEEE 802.11 is one of the many standard available. IEEE 802.11b defines the Medium Access Control Layer [MAC] for wireless local area networks. The wireless local area network, WLAN is dominated by IEEE 802.11 standard. It becomes one of the main focuses of the WLAN research. Now most of the ongoing research projects are simulation based as their actual hardware implementation is not cost effective.
The main core of the IEEE 802.11b standard are the CSMA\CA, Physical and MAC layers. But only MAC layer for transmitter is modeled in this paper using the VHDL. The VHDL (Very High Speed Hardware Description Language) is defined in IEEE as a tool of creation of electronics system because it supports the development verification synthesis and testing of hardware design, the communication of hardware design data and the maintenance, modification and procurement of hardware. It is a common language for electronics design and development prototyping.
INTRODUCTION
Due to technology advancement in the 21st Century, wireless Communication had been most popular choice of communication. More and more people are turning to wireless due to the convenience of mobility.
An 802.11 LAN is based on a cellular architecture where the system is subdivided in to cells, where each cell [called Basic Service Set or BSS] is controller by a Base Station [called Access point, or in short AP]. Even though that a wireless LAN may be formed by a single cell, with a Single Access Point [can also work without an Access Point], most installations will be formed by several cells, where the Access Points are connected through some kind of back bone [called Distribution System or DS], typically Ethernet, and in some cases wireless it self. The whole interconnected wireless LAN including the different cells, their respective Access Points and the Distribution System, is seen to the upper layers of the OSI model, as a single 802 network and is called in the standard as Extended Service Set [ESS]. The standard also defines the concept of a portal, a portal is a device that interconnects an 802.11 and another 802 LAN [3].
Overview of MAC layer:
The 802.11 protocol covers the MAC and physical layer, the standard currently defines a single MAC which interacts with three physical layers [all of them running at 1 and 2 Mbits\sec] i.e. Frequency Hopping Spread Spectrum in the 2.4GHz band, Direct Sequence Spread Spectrum in the 2.4GHz band and Infrared [3].
Wi-Fi features:
Wi-Fi Wireless Fidelity [802.11 family of standards] for LAN. WiFi is designed for local area networks, which are private, local (short range), but where competing cable systems run at very high speeds. WiFi achieves greater than 10MBit/Sec throughput for a user in many circumstances. Currently WiFi carries more user data than any other wireless technology. Evolution is to go further, faster and at lower power consumption [2].
Upstart wireless LAN [WLAN] technologies under the 802.11 (Wi-Fi) umbrella have leapfrogged towards cellular an other efforts edging towards broad band wireless [such as 802.16/WiMAX] and have led to the first wide spread, commercially successful broadband wireless access technology. Infact, Wi-Fi is a runaway success around the globe [5]
CONCLUSION
Various individual modules of Wi-Fi Transmitter have
been designed, verified functionally using VHDL -
simulator, synthesized by the synthesis tool .This design
of the WiFi transmitter is capable of transmitting the
frame formats. The formats include all 802.11 frames
i.e. MAC frame, RTS frame , CTS frame and ACK
frame. The transmitter is also capable of generating
errorchecking codes like HEC and CRC.