| Orthogonal Frequency Division Multiplexing （OFDM） has been a popular technique of wireless communications in recent years. However, two drawbacks of OFDM limit its practical applications. Firstly, in order to resist the Inter-Symbol Interference （ISI） caused by the multipath fading channel, the adoption of Cyclic Prefix （CP） decline the systematic spectrum efficiency, meanwhile with a higher power consumption. Secondly, due to the use of the rectangular window as the pulse shaping filter, the high sidelobes of sine function result in OFDM system being sensitive to Inter-Carrier Interference （ICI）. To solve these problems, another kind of OFDM modulation system is considered in this paper, namely OFDM with Offset Quadrature Amplitude Modulation （OFDM/OQAM）. By selecting a pulse shaping filter with a good Time Frequency Localization （TFL）, ISI and ICI can be limited in a rational range without introducing any CP in OFDM/OQAM.However, there still are some open problems for OFDM/OQAM systems, such as the channel estimation, timing and carrier frequency offset synchronization and signal detection, the main work of this paper focus on these three aspects.In the aspect of channel estimation, this paper studies the principle and the implementation of OFDM/OQAM system. Moreover, the performance of existing typical channel estimation methods is verified by computer simulation, in order to get a initial understanding of the intrinsic interference of OFDM/OQAM systems.For techniques needed for synchronization, this paper has studied the existing synchronization algorithms of OFDM/OQAM system, especially the data-aided synchronization schemes. Several typical data-aided synchronization algorithms are selected, and an analysis of their data structure, argorithm and implemention is made. Motivated by these schemes, this paper proposes a data-aided synchronization algorithm named Window-based Synchronization algorithm （WBS）. By applying a window to the correlation sequence, the actual time of arrival can be found. In addition, a new Synchronization algorithm （MAP） is obtained by applying Maximum Posterior probability criterion to synchronization technology. By reconsidering the coarse timming estimated value and its adjacent values based on Maximum Posterior probability criterion, the final timing and carrier frequency offset （CFO） estimated value can be obtained. Finally, the computer simulation results show that in the typical channels of IEEE802.22standard, WBS and MAP are more accurate than the conventional shemes both in time and frequency synchronization.Furthermore, for techniques needed for signal detection, this paper studies the system model of OFDM/OQAM systems in doubly dispersive channels and analyses the intrinsic interference caused by the conventional signal detecting techniques, because of time delay spread and doppler spread, the operation of Zero-forcing （ZF） equalization will bring in some ISI and ICI. In order to solve this problem, a new signal detecting methods based on parallel interference cancellation （PIC） criterion are proposed in this paper, by reconstracting the intrinsic interference and removing it, the demodulation can be more accurate. In addition, this paper gives the theoretical derivation and the structure of the new methods at the recever side. Finally, the computer simulation results show that at the Bit Error Rate （BER） level of10-2, the new scheme outperform the conventional one for1.2dB. |
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