Fractional sampling (FS) and Doppler diversity equalization in OFDM receivers can achieve two types of diversity (path diversity and frequency diversity) simultaneously on time-varying multipath channels. However FS with a higher sampling rate requires the large amount of complexity in demodulation. In this paper, a novel sampling point selection (SPS) scheme with MMSE equalization in FS-OFDM receivers is proposed. On fast time-varying multipath channels, the proposed scheme selects the appropriate samples from the fractionally sampled signals. Through the computer simulation, it is demonstrated that with the proposed scheme, both path diversity gain and Doppler diversity gain can increase as compared to a conventional non-SPS scheme.

In this paper, the effect of the impulse response of pulse shaping filters on a fractional sampling orthogonal frequency division multiplexing (FS OFDM) system is investigated. FS achieves path diversity with a single antenna through oversampling and subcarrier-based maximal ratio combining (MRC). Though the oversampling increases diversity order, correlation among noise components may deteriorate bit error rate (BER) performance. To clarify the relationship between the impulse response of the pulse shaping filter and the BER performance, five different pulse shaping filters are evaluated in the FS OFDM system. Numerical results of computer simulations show that the Frobenius norm of a whitening matrix corresponding to the pulse shaping filter has significant effect on the BER performance especially with a small numbers of subcarriers. It is also shown that metric adjustment based on the Frobenius norm improves BER performance of the coded FS OFDM system.

Through fractional sampling, it is possible to separate multipath components and achieve diversity gain. However, power consumption grows as the sampling rate increases. This paper proposes a novel scheme for OFDM systems that selects the sampling rate according to the channel's frequency response. Numerical results through computer simulation show that the proposed sampling rate selection scheme reduces power consumption by reducing oversampling ratio when delay spread is small.

A diversity scheme with Fractional Sampling (FS) in an OFDM receiver has been investigated recently. Through FS, it is possible to separate multipath components and obtain diversity gain in OFDM systems. Enlargement of the bandwidth of the total frequency response between transmit and receive baseband filters allows the FS scheme to achieve path diversity. However, the transmit filter has to be designed according to the spectrum mask of the wireless standards such as IEEE802.11a/g to avoid interference to the other communication systems and the frequency response of the composite channel including the transmit and receive filters has often been set to minimal bandwidth to eliminate adjacent channel signals. In order to achieve the maximum signal-to-noise ratio (SNR), the same filter is commonly used in the transmitter and the receiver. In this paper, the trade-off among the SNR deterioration, adjacent channel interference, and the diversity gain due to the enlargement of the bandwidth of the receive filter is investigated. Numerical results from computer simulations indicate that the BER performance with wider bandwidth in the receiver shows better performance than that with the minimal bandwidth for maximizing the SNR in certain conditions.