Performance analysis of rate-adaptive modulation with imperfect estimation in OFDM systems

Based on the imperfect channel state information (CSI) from noisy channel estimation, the performance analysis of OFDM systems with continuous-rate adaptive modulation (AM) and imperfect estimation in Rayleigh fading channels is presented. Subject to a target bit error rate (BER) constraint, the average spectral efficiency (SE) of the system with imperfect CSI is analyzed and derived, and the conditional probability density function of fading gain is given. Based on these results and using the Taylor series expansion, tightly-approximate closed-form expressions of conditional SE and average SE are further derived, respectively. These expressions can provide the direct calculation of SE, and thus avoid the numerical search of SE in the existing reference. Moreover, they include those expressions under perfect CSI as special cases. Simulation results show that the derived theoretical SE is in good agreement with the corresponding simulation, and OFDM with AM can obtain higher SE than non-adaptive OFDM.