On error performance analysis of sub-channel modulation schemes of IEEE802.11a

Determining the effectiveness of any modulation scheme in mobile radio environment comprises reliability and error performance evaluation. The later involves determining the increase in E_b/N_o required to maintain a fixed BER. Thus, error performance plays a vital role in the selection of modulation scheme for specific applications. This paper begins with review of the conceptual difference between SNR and E_b/N_o performance metrics of communication system. The significance of BER for error performance analysis is verified by comparing the E_b/N_o characteristic plots for digital modulation schemes: M-PSK, M-QAM and M- FSK. The comparison parameters includes modulation order and simulation environment. The simulation environment considered are additive white Gaussian noise (AWGN) channel model and Rayleigh fading channel model. There are two important issues targeted in this paper. Firstly, the significance of the concept of multi-carrier modulation (MCM) used in wireless LAN standard IEEE802.11a is verified. The technology resolves the problem of multi-path in a piecewise manner, i.e. the linear relationship between error probability and E_b/N_o in case of wide-band Rayleigh fading channel is transformed into a number of narrow-band sub-channels with exponential relationship. Then, the sub-channel modulation schemes are compared by observing the effect of modulation order on BER, spectral usage, noise tolerance and trade-off issues. Finally, the inferences drawn out of the comparative analysis justifies the use of low-order PSK modulations for control and higher-order QAM for payload transmissions respectively, for OFDM implementation as in IEEE802.11a.