OFDM for Wireless Multimedia Communications
OFDM for Wireless Multimedia Communications
A Time-Frequency Well-localized Pulse for Multiple Carrier Transmission
Wireless Personal Communications: An International Journal
Communicating over nonstationary nonflat wireless channels
IEEE Transactions on Signal Processing
Time-Variant Channel Estimation Using Discrete Prolate Spheroidal Sequences
IEEE Transactions on Signal Processing
Nonorthogonal pulseshapes for multicarrier communications in doubly dispersive channels
IEEE Journal on Selected Areas in Communications
EURASIP Journal on Advances in Signal Processing - Special issue on applications of time-frequency signal processing in wireless communications and bioengineering
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In conventional Orthogonal Frequency Division Multiplexing (OFDM) systems, the Fast Fourier Transform processing corresponds to rectangular pulse shaping. Such a pulse has spectral leakage causing the modulated subcarriers to have considerable frequency dispersion during transmission and thus losing orthogonality at the receiver. In this paper, we exploit the frequency concentration of the Slepian or discrete prolate spheroidal sequences (dpss) to generate basis for OFDM with maximum energy concentration in each of the subcarrier bands. As such, minimum interference from other subcarriers occurs. Since the performance of the OFDM system depends on accurate estimation of the parameters of the transmission channel, we use a simple but effective estimation method based on chirps. This estimation method permits accurately estimation of the channel parameters: the number of paths, the time-shifts and the Doppler frequency-shifts associated with each path. The estimation problem becomes one of finding the frequency of complex exponentials embedded in noise, which can be done using a periodogram for which the accuracy of the parameters depends on the resolution of the Fast Fourier Transform used. In this paper we propose an improvement to the two-chirp channel estimation, previously proposed, by sending a frequency modulated cosine as pilot sequence instead of two chirps of different rates. In the simulations, the bit error rate (BER) results show that the proposed method is able to considerably increase the spectral efficiency of OFDM systems compared to bases using the conventional rectangular pulse, and that it performs as well as bases that use an optimized combination of Slepian pulses.