CSI Utilization In Time Varying Channels For SC-FDE System

SC-FDE (Single Carrier with Frequency Domain Equalization) is a broadband wireless communication scheme based on traditional single carrier and OFDM (orthogonal frequency division multiplexing). SC-FDE and OFDM are both block-wise transmission schemes based on CP (cyclic prefix). They both have immunity to multipath fading and almost the same complexity and spectrum efficiency.Compared with OFDM, a major problem in SC-FDE is that channel state information (CSI) isn't used at transmitter. When channel has spectrum nulls or deep fading points, it is difficult to eliminate the signal distortion only through a linear equalizer. Recently, the strategy of CSI utilization and various criterions based on OSS (Optimal Signal Subspace) have been proposed in SC-FDE. The method of CSI utilization is proposed for static channel and can improve the system performance in frequency selective channel remarkably. With the development of broadband wireless communication, communication system demands high performance in mobile environment. In outdoor vehicular environment, it is very likely that the time selectivity and frequency selectivity occur at the same time.First we introduce SC-FDE system regarding OFDM system as a reference and review the CSI utilization method which has been proposed in SC-FDE system. The main contents includes the concept of optimal signal subspace, the analysis of bit-error characteristic, the operation process of CSI utilization and two OSS dimension determination criteria.Furthermore we discuss the CSI utilization method in time varying channels. We introduce the character of time varying channels, and proposed a new OSS dimension determination criteria called equalized SNR criteria. The relevant method of adaptive feedback is discussed. The simulation results compare the adaptive OFDM and adaptive SC-FDE system and give the information rate and the feedback rate needed of the adaptive SC-FDE system. Our method can reduce the impairment of frequency selectivity and time selectivity and achieve good tradeoff between reliability and efficiency.Because channel estimation methods cannot provide the updated CSI in time varying channels, we choose channel prediction method to provide CSI needed by the CSI utilization method. We summarize several prediction methods and discuss adaptive MMSE prediction method. We proposed an improved adaptive RLS algorithm; give the improvement of convergence rate, prediction precision and the complexity. Finally we apply the prediction method to CSI utilization system and discuss the effect of forbidden subcarriers.