Research On Channel Estimation Of OWPM System

Orthogonal wavelet packet division multiplexing (OWPM) is one of multicarrier transmission systems. It realizes the modulation/demodulation of transmission signal using wavelet packet transform. OWPM system supports high bandwidth efficiency, little affect of interference and multirate wireless transmission. For the sake of high-speed transmission, channel estimation is one of the key technologies of OWPM system. So the researches of OWPM system and its channel estimation technical are very important and useful.On the basis of summarizing the theory of OWPM system, this thesis researches the channel estimation methods which fit for OWPM system under multi-path fading environment. Our contributions are concluded as follows:Because of the lack description of OWPM, a complete understanding of OWPM system is provided. First, the orthogonality of OWPM system is analyzed with the theory of wavelet transform and waveform orthogonality. Then, with the application of transmultiplexers in multicarrier communications, the realization of OWPM system which with arbitrary subchannel separation in terms of multirate filters is described. At last, the performance of OWPM under fading channel is presented.A method of inserting pilots with unequal interval is explored. Aim to the traditional pilot arrangement is not suitable for OWPM systems, two kinds of unequal pilot mode are emphasized. In the type of decomposition step by step, the pilot mode according to the different periods of symbols which belong to different decompose-level is proposed. Use geometric sequence to realize the unequal pilot arrangement. The deep decoposion-level is, the little pilots are inserted. In the type of full decomposition, the pilot mode according to the influence on the coherent time caused by frequency-domain characteristic is proposed. The method divides subcarrier into groups and use arithmetic theory to realize the unequal pilot arrangement. Simulation results indicate that the proposed methods realize the pilot arrangement optimally and perform excellent in multi-path fading channel.An optimal and compensated expectation-maximization algorithm based channel estimation method is proposed to minimize the effect of error propagation during estimation. Linear interpolation is introduced to do quadratic estimation between E-step and M-step, and the correlationship of subcarrier is used to reduce the complexity.With utilization of the coherence between the time and frequency domain of each subcarrier, the algorithm accuracy is improved and the convergence is accelerated.A robust channel estimation method using robust estimation theory is presented to mitigate inter-symbol interference (ISI) and inter-channel interference (ICI). Because OWPM system model with ISI and ICI is followed non-Gaussion distribution, a Huber interative estimation mehtod is introduced to the channel estimation. According to the different noise values, LS estimation and L1 estimation are used respectively. Simulation results show that ISI and ICI can be reduced effectively.