Precise Analysis and Evaluation of OFDM Systems over a Mobile Frequency-Selective Nakagami-m Fading Channels

In this article, the symbol error probability (SEP) of OFDM systems using M-ary coherent demodulation communicating over time-varying sum of Nakagami-m fading channels is analyzed. The focus of this article is on the evaluation of OFDM signals in mobile radio applications, such as IEEE 802.11a, IEEE 802.16a, and digital video broadcasting (DVB) systems. The time variations of the channel during one OFDM symbol interval destroy the orthogonality of the adjacent subcarriers and generate power leakage among the subcarrier, known as inter-carrier interference (ICI). We first present an integral solution for the probability density function (PDF) of the sum of Nakagami-m random vectors (RVs). Second, we used this PDF expression to obtain an exact closed form for the error probability. The error rate analysis is then extended to systems using multichannel reception with maximal ratio combining (MRC). Based on Jakes’ model for Doppler effects, and an exponential multipath intensity profile, numerical results for the error probability are illustrated for several mobile speeds. An interesting observation was concluded that depending on the number of the channel taps, the error rate performance does not necessarily improve with increasing Nakagami-m fading parameter.