Due to the strong ability in combating multipath fading, OFDM has been adopted in IEEE802.11a standard and has received considerable attention. The fundamental physical layer parts of OFDM-based IEEE802.11a are modeled and simulated in this paper. Second, we discussed the bit error rate performance of BCH, cyclic and convolutional coding in AWGN channel. Moreover, the system performance of four working modes defined in IEEE802.11a standard which are BPSK, QPSK, 16QAM and 64QAM are compared respectively. Especially, we analyze the system performance of PSK and QAM with or without Rayleigh fading. We conclude our work based on simulations and analysis.