Design And FPGA Realization Of The Base-band Modulator In WLAN System

WLAN(Wireless Local Area Network)technology is the product of the development of computer and communication technology, and it is also an important branch of wireless network technology. IEEE 802.11a protocol is one of the most influential WLAN standards. The WLAN system based on IEEE 802.11a employs OFDM (Orthogonal Frequency Division Multiplexing)i as its PHY(Physical)layer access technology and has been a great deal of concern as a typical burst packet transmission system.OFDM has been widely applied in BWA(Broadband Wireless Access)systems due to its high bandwidth efficiency and advantages in anti multi-path fading and anti narrow-band interference as well as other prominent advantages. Furthermore it has already become a research hotspot in radio communication field as the key technology for future mobile communication system.In this thesis, we look back the evolvement of mobile communications and broadband wireless access technology first, and have a introduction of the development of WLAN technology and the main IEEE 802.11 series standards. By the depth research of the radio channel propagation characteristics and the basic principles of OFDM technology, the thesis gives some detailed theoretical analysis and simulation for the key technologies of OFDM.Then the thesis reseaches IEEE802.11a standard and focuses on the analysis of physical layer frame structure and norms. On this basis, according to the basic knowledge of OFDM and the conditions which are provided by the self-designed hardware platform of broadband multi-carrier communication, a whole plan of base-band modulator in WLAN system is designed, which uses top-down design method. The key technology of the plan is simulated and analysed by Matlab.In the process of the plan realization on FPGA, the main chip is Altera CycloneII . Hardware description language Verilog HDL is used for the detailed design of various functional modules in the exploiting environment Altera's QuartusII. The corresponding structure and some simulation waveforms are given. The entire system is carried out in SignalTapII for timing simulation. Theoretical analysis and simulation results show that the system design is correct, and have a good system capability.Finally, the base-band modulator circuit is tested and analysed on multi-carrier broadband hardware platform through indoor wireless data transmission. The results validates the validity of the proposed base-band modulator system and its reliability in wireless transmission.