Channel Estimation And Random Access Techiques In Enhancement Multicarrier Communication Systems

Orthogonal frequency division multiplexing with cyclic prefix(CP-OFDM) utilize cyclic prefix(CP) to fight against the inter symbol interference(ISI) in fading channels. However the insertion of CP is a wast of transmitted power as well as a loss of spectrum efficiency. As an alternative modulation scheme to CP-OFDM, filter bank-based multicarrier(FBMC) is a promising technique to achieve higher spectrum efficiency as well as strong robustness againse dispersive channels due to its time-frequency localization feature prototype filter. In contrast to the “complex-field orthogonality” in CP-OFDM systems, the pulse shaping filter in an FBMC system is relaxed to have the “real-field” orthogonality only, thus making channel estimation more challenging that that in CP-OFDM systems. In this dissertation, a number of existing channel estimation methods are studied and several novel algorithms are proposed for channel estimation of FBMC. In high-speed scenario of Long Term Envolution(3G LTE) systems, this dissertation provide a novel design of physical random access channel(PRACH) and corresponding multi-user random access detection technique.Firstly, the subcarrier waveforms in an FBMC system are only orthogonal in the real-field, giving rise to the intrinsic imaginary interference incurred from adjacent symbol. The dissertation has proposed an auxiliary preamble structure for channel estimation in FBMCsystem. Moreover, a dual dependent pilot scheme are presented for scattered pilot structure. In Multiple-Input Multiple-Output(MIMO) case, this paper proposed to reconstruct the complex-field orthogonality of MIMO-FBMC signals by complex training sequence decomposition.Secondly, for the uplink of LTE systems, the PRACH utilize Zadoff-Chu(ZC) seqeunces as preamble sequences. In the reciver side, reciving signals and local ZC sequences are adopted for correlation operation. If the correlation peak exceeds the decision threshold, access user located in the corresponding detection window is considered as an actived user. However, in high-speed scenario, multiple detection windows failed to find all the access users since the offset of correlation peak influenced by Doppler frequency shift. Through numerical analysis, we find the offsets of correlation peak can be controlled by the root number of ZC sequences. Therefore, we provide a strategy to generate the root number of ZC sequences. Consequently, a single detection window can be used to achieve multi-user detection.In the next generation wireless communication systems, novel air interface technology is important for data transmission. Meanwhile, communication connection needed to maintain in high-speed scenario. Thus, the research achievement in this paper provide several solutions for future wireless communication systems.