| Summary: | 碩士 === 國立成功大學 === 電腦與通信工程研究所 === 104 === In recent years, cooperative communications have received much attention. The concept of cooperative communications is to let un-used mobile units help the transmission of other users. Through the neighbor nodes, the transmitted signal can be relayed to the destination. Cooperative communications can reinforce the point-to-point transmission channel. Based on the cooperative communications, we attain a scenario that is like there are several transmit antennas at the transmitter, and this achieves the effect of multiple-input multiple-output (MIMO) system. In fact, the transmitter needs the forward channel state information (CSI) to improve the performance of system. Sometimes, the transmitter needs to estimate the channel responses (CRs) and/or channel amplitude, and forward these CRs to the receiver, and this increases the forward load.
In order to efficiently forward the CSI, we propose an efficient method that forward the estimated channel responses (CRs) to the receiver based on the Karhunen-Loève Expansion (KLE). The coefficients of the KLE are used as the parameters for rebuilding the CRs. The number of coefficients of the KLE is much fewer than the size of the original block of CRs, and the KLE leads to efficient compression. These coefficients are Gaussian distribution and nearly uncorrelated. To efficiently forward the coefficients for the cooperative OFDM system, we use the Gaussian quantization (GQ) to reduce the quantization error. The simulation results show that the proposed algorithms can attain good error performance for the cooperative OFDM systems with low forward load in time-varying and frequency-selective channels.
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