  In this paper, we investigate the performance of bidirectional relay
selection using amplify-and-forward protocol with imperfect channel state
information, i.e., delay effect and channel estimation error. The asymptotic
expression of end-to-end SER in high SNR regime is derived in a closed form,
which indicates that the delay effect causes the loss of both coding gain and
diversity order, while the channel estimation error merely affects the coding
gain. Finally, analytical results are verified by Monte-Carlo simulations.
