| Multi-carrier modulation technique has recently evoked considerable interests and widespread applications for its attractive qualities in resisting multi-path effects and mitigating ISI. Taken as an example, the OFDM technique has been adopted for some formed standards and even regarded as a candidate for the coming 4G-wideband mobile communication systems. However, OFDM has some intrinsic shortcomings: its orthogonality is susceptible to be destroyed in practical transmission, thus considerable overheads (CP and virtual carriers), strict synchronization and etc. are needed. In order to avoid these disadvantages of OFDM, a new multi-carrier modulation technique, named Filtered Multi-tone Modulation (FMT) is studied for its applications in wireless communication in this thesis, with some related aspects being investigated intensively.FMT is also a multi-carrier modulation technique based on filter banks technology. The main character of the technique is that its high-spectral constraint of each sub-carrier results in its non-sensitivity to frequency offset where OFDM enduring. However, FMT has inter-symbol interferences (ISI) which are caused by the non-ideal sub-channel filters. ISI has to be eliminated by per-sub-channel equalizers.We first introduced the basic concept of FMT system in this dissertation. FMT belongs to filter banks technology. Thus we give description of FMT system based on multi-rate signal processing and filter banks. Efficient realizations of both critically sampling system and non-critically sampling system are deduced. We also built up a FMT simulation system by Matlab. Through it, we studied how the relevant coefficients and algorithms influence the system's performance.For FMT system, one of the most key parameters is the prototype filter. Thus, we studied the design technology of the filter banks. Based on the characteristic of the FMT system, we first gave the design target of the prototype filter. Then, we gave some examples which could satisfy these requirements. Finally, we delivered a new scheme on optimizing the prototype filter. Simulation results showed that the optimum prototype filter could achieve better error probability performance and achievable bit rates simultaneously.Whether FMT system could be used in the wireless communication environment is depend on the complexity of its synchronization scheme. Therefore we studied this problem deeply. We analyzed how the timing offset, the carrier frequency offset and the carrier phase affect the system performance and compared them with the OFDM system. We simulated those algorithm efficiencies and studied the influence of the multi-path channel on the FMT system.We treated some familiar timing synchronization schemes of multi-carrier systems and schemes of FMT system. We gave a new timing synchronization scheme of FMT system in wireless communication and simulated the performance of some of the schemes. The simulation results showed that blind timing estimation algorithm could achieve better spectrum efficiency with the tradeoff of complexity. The improved H.Minn algorithm could achieve precision estimation with features of simple, little extra cost, one training symbol and strong anti-multi-path ability. We also investigated frequency synchronization schemes of multi-carrier systems. We modified SCA to accomplish frequency synchronization with only one training symbol, instead of two, without performance degradation. The redundancy of the training sequence was reduced to half. This reduction is critical especially in burst data transmission, for example, in WLAN.We also considered how to design the per-sub-carrier equalizers. FMT system should add per-sub-carrier equalizers at the output of the receiver to compensate ISI introduced by the non-ideal prototype filter. We gave some different equalization schemes, such as decision feedback equalizer and pre-equalizer, etc. We introduced data-aided equalizer to FMT system and presented a two-decision algorithm based on factor diagram. We also studied TCM scheme, which combined the trellis code with pre-equalizer, in FMT system and compared its performance with other equalization schemes under AWGN channel and multi-path fading channel. All the equalization scheme could achieve better performance and in the meantime guarantee without expanding band-width and data-rate varying.Channel estimation based on training sequence is considered as a performing scheme for burst data transmission on wireless communication system. Base on OFDM channel estimation algorithm, we proposed a set of channel estimation schemes based on pilot symbols. We gave the realization models of LS estimation algorithm in the time domain, the LS and LMMSE estimation algorithm in the frequency domain and two dimensions algorithm in time-frequency domain. The simulation results showed that these algorithms could achieve better performance in FMT system.The innovation research of this dissertation include in:1. We proposed the design targets of the prototype filter and gave an optimum design method of the prototype filter. Some papers present an optimizing scheme of the prototype filter which could only be used to design prototype filter for critically sampling FMT system. In this dissertation, we proposed a general optimizing scheme which could be adopt to design prototype filter for both critically sampling and non-critically sampling FMT system.2. We accomplished the relevant equalizer design of FMT system. We design different equalizers for different environments and introduced pre-equalizer and trellis coding technique in FMT system. We also introduced the DAE equalizer to FMT system and presented a two-decision algorithm based on factor diagram to overcome the non-causally of traditional DAE equalizer.3. We studied the FMT synchronization problem and compare its performance with OFDM. We also analyzed timing offset, frequency offset and phase offset on FMT system.4. Based on the channel estimation algorithm of OFDM, we presented channel estimation algorithms suitable for FMT system. These algorithms are based on training sequences and could achieve robust performance.However, there are still some problems should be solved when FMT is used in wireless environment, such as:1. How to solve high peak-average power ratio (PAR). It is well known that high PAR is one of the most difficult questions which should be overcomed first in OFDM system. Whether FMT has high PAR has no result at present. If FMT has PAR problem, what can we do?Intuitively, FMT has few sub-carriers (16,32,64 etc.). Thus PAR of FMT would be low than OFDM. If we could find a scheme which could guarantee lower PAR for FMT, the prospective of FMT will be bright.2. How to design the prototype filter self-adaptively? If we could adjust the coefficients of the prototype filter based on the different channel, we could get the optimal system. 3. As a non-overlapping multi-carrier modulation technique, FMT is suitable for wireless resource management. Therefore, it is valuable to research multi-access and asynchronous multi-user communication for FMT system.Moreover, it is deserved to further simplify synchronization algorithm.
|
PDF Full Text Request