Preamble Design Based On Comb-Type Pilots For Channel Estimation In OQAM/FBMC Systems

Filter Bank Multicarrier with Offset Quadrature Amplitude Modulation(OQAM/FBMC)is a popular non—orthogonal modulation technique with many advantages,such as high spectral efficiency and strong anti-interference capability.It is suitable for supporting the diverse transmission needs of future wireless communication and is one of the most potential research hotspot technologies in the future.However,the subcarriers are only orthogonal in real field of the OQAM/FBMC systems,which means that there exists the intrinsic imaginary interference among data symbols.Interference-free symbols are obtained only after channel equalization and taking the real parts.Under the circumstance of unknown channel,the interference is evidently a barrier for high-performance channel estimations.The channel estimation of the OQAM/FBMC system is generally based on a preamble sequence,that is,multiple columns of FBMC pilot symbols are transmitted at the front of the data packet.Data symbols and pilot symbols are separated by one or more columns of zero-value symbols to reduce the imaginary interference from data symbol,and the imaginary interference between the pilot symbols can be approximated or eliminated by reasonable design.Then,the channel information at each frequency point is calculated by the ratio of the demodulated symbols at the receiver to the pilot symbols at the transmitter.However,this channel estimation method clealy has a drawback: the length of the zero-value symbols should be long enough to completely eliminate the imaginary interference of the data symbols to the pilot symbols,which increases the length of the transmit sequence and reduces the spectral efficiency.In this thesis,we propose an efficient preamble design based on comp-type pilots(CTP)for channel estimation.The proposed preamble is similar to the CTP widely adopted in orthogonal frequency division multiplexing(OFDM)systems,within a specified window.Thus,it enables OFDM-like channel estimation with low complexity for OQAM/FBMC,and removes the ISI/ICI in OQAM/FBMC channel estimation,which results high-performance channel estimation.Moreover,we shorten the tail of transmitted sequence,so that the proposed preamble length could be very close to those of conventional preamble design such as ICM.The simulation shows that the proposed preamble design improves the accuracy of channel estimation.The proposed preamble design can be easily extended to support multiple input multiple output(MIMO).The channel estimation with the proposed preamble of MIMO-FBMC is no difference from that of single antenna FBMC when the pilot tones of one transmit antenna are not overlapped with those of other transmit antennas.Simulation results verify that the proposed preamble and channel estimation work effectively in MIMO systems as well as in SISO systems.