  To coexist with Wi-Fi friendly, a standalone long-term evolution network over
unlicensed spectrum (LTE-U) under listen-before-talk (LBT) mechanism can only
access channel in a random and intermittent way, which results in random and
time-variant delay in both data and signaling transmissions. In this work, we
explore the impact of randomly delayed channel state information (CSI) on the
performance of a standalone LTE-U network by analyzing its downlink throughput
and users' energy efficiency (EE) under different CSI feedback schemes and
frequency-domain schedulers. Further, aiming at maximizing users' EE of a
standalone LTE-U network while guaranteeing fair coexistence with Wi-Fi, joint
optimization on the medium access control (MAC) protocol and CSI feedback
scheme is studied. Due to the non-convex and non-concave characteristic of the
formulated optimization problems, decomposition-based low-complexity yet
efficient algorithms are proposed. Simulation results not only verify the
analysis and the effectiveness of the proposed algorithms but also show diverse
impacts of CSI feedback scheme, frequency-domain scheduler, and traffic load of
Wi-Fi on the standalone LTE-U network performance.
