Path Diversity Schemes in OFDM Transmitter and Receiver

Orthogonal frequency division multiplexing (OFDM) is a very attractive modulation technique for reliable broadband wireless communications such as wireless local area network (WLAN), worldwide interoperability for microwave access (WiMAX), etc. In wireless communications, multipath fading distorts a received signal and causes bit errors at a receiver side. To overcome the e ect of fading, diversity techniques have been proposed to improve the quality of the communication link. A fractional sampling (FS) scheme in OFDM has been proposed to achieve diversity with a single antenna. In the FS scheme, a received baseband signal is sampled with a rate higher than baud rate and combined to achieve path diversity on each subcarrier. Though the FS achieves diversity, it increases the power consumption of the receiver. In some channel conditions, the power of the received signal may be large enough to demodulate the information symbols with baud rate sampling. In this dissertation, the digital signal processing schemes for path diversity and the low power consumption of the receiver are proposed and investigated. Chapter 1 introduces the background of the OFDM receivers and the motivation of the research. In Chapter 2, path diversity schemes in receiver are investigated. In the rst subchapter, a sampling rate selection scheme is proposed. The sampling rate is selected according to channel conditions. The path diversity can be achieved while the power consumption is still saved with the proposed sampling rate selection scheme. In the second subchapter, sampling point selection scheme is investigated to achieve higher power e ciency. It is necessary to improve the quality of the communication link with the same sampling rate to save the power consumption. This scheme selects the sampling points according to the frequency response of a channel. It also eliminates the speci c sets of the sampling points and reduces the computational complexity for the sampling point selection. Chapter 3 proposes precoded transmit path diversity schemes. The FS scheme still necessitates high oversampling ratio at a receiver and it causes large power consumption in a small mobile terminal. The proposed schemes make use of the impulse response