  In this letter, we consider a typical scenario where the transmitter employs
different power adaption methods, including the optimal rate and power
algorithm, optimal rate adaption, channel inversion and truncated channel
inversion, to enhance the ergodic capacity (EC) with an average transmit power
constraint over fluctuating two-way fading channels. In particular, we derive
exact closed-form expressions for the EC under different power adaption
methods, as well as corresponding asymptotic formulas for the EC valid in the
high signal-to-noise ratio (SNR) region. Finally, we compare the performance of
the EC under different power adaption methods, and this also validates the
accuracy of our derived expressions for the exact and asymptotic EC.
