正交空時編碼之正交分頻多工系統中實虛部非協調與載波偏移之估測

Abstract

Nowadays, direct-conversion radio frequency (RF) receivers become more appealing due to its cost advantage. However, orthogonal frequency division multiplexing (OFDM) systems with direct-conversion RF receivers are very sensitive to non-idealities at the front-end of receiver, such as I/Q imbalance and carrier frequency offset (CFO). These non-idealities at the receiver result in inter-carrier interference (ICI). Accurate estimates of the non-idealities and channel response are required in OFDM systems. This thesis studies the CFO estimation for OFDM systems with multiple transmit antennas. The thesis consists mainly of two parts. In the first part, we consider OFDM systems with 2 transmit antennas. The Alamouti code is employed at the transmitter and both ST-OFDM and SF-OFDM systems are considered. For these systems with 2 transmit antennas, we extend two known blind CFO estimation algorithms (which were derived for OFDM systems with one transmit antenna) to solve the CFO estimation problem in ST and SF-OFDM systems. IN the second part, we consider OFDM systems with 3 transmit antennas. Orthogonal space time block codes (OSTBC) codes are used to encode the single at the transmitter. For this system, we derive a new blind CFO estimation algorithm. The idea is to exploit the fact that the rate of OSTBC is only 3/4. We show how to exploit the redundant information in OSTBC for blind CFO estimation. Moreover, the problem of I/Q imbalance is also consider in the second part. At the end, we also provide numerical simulation to verify the performance of the proposed methods.