| Iterative Equalization based on Energy Spreading Transform can spreads symbol energy to different frequencies and times. While frequency-domain spreading gains frequency diversity, time-domain spreading significantly increases the reliability of the feedback signal. Moreover, EST technology receives widespread concern because system performance can make the approximation of matched filtering performance through iterative detection technology without channel coding. Single Carrier Frequency Domain Equalization and Orthogonal Frequency Division Multiple are special cases of EST. In future wireless communication systems, due to high Spectrum utilization and anti-frequency selective fading, SC FDE and OFDM are becoming the prime candidate. Compared with the SC system and the OFDM systems, in some channel conditions, EST system can get good performance by iteration. This paper studies on detection technologies in OFDM system, SC system and the EST system signal on doubly-selective channels.The second chapter first studies on PAPR characteristics in OFDM system, and then studies on Signal Detection technology of OFDM System in doubly-selective channels. The equalization technology is studied in both SISO and MIMO, including the zero-forced equalization and minimum mean square error equalizer. Comparing ZF equalizer with MMSE equalizer, ZF equalizer does not consider noise while signals are detected, while MMSE takes the effect of noise into account, but there will be ISI in detection, the performance will also be affected. Simulation result shows that ZF equalizer and MMSE equalizer can achieve similar properties, as amended MMSE equalizer can achieve better performance than ZF and MMSE equalizer in SISO system. In MIMO systems, we mainly discuss linear equalizer and layered equalizer. In layered equalization, the first detected signal can be served as feedback to the next level of signal received, the simulation shows that layered equalization can chieve better performance than non-layered.In the third Chapter,we study on signal detection in on doubly-selective channels in SC system. With the commercial use of LTE, SC systems has attracted widespread attention because of the low PAPR characteristics of transmission signals. In this chapter, firstly, the PAPR of SC system is studied, and is compared with that of OFDM systems. Then we study on signal detection techniques both in SISO and MIMO systems. We can see that MMSE equalization can get better performance than the ZF equalization in low SNR in the SISO system though simulation. With frequency domain and time domain feedback equalization combined together, SC system can get better performance than the linear equalizer with a higher complexity. In MIMO systems, we mainly discussed linear equalizer and layered equalizer. In layered equalization, the first detected signal can be served as feedback to the next level of signal received, the simulation shows that layered equalization can chieve better performance than non-layered, layered MMSE equlazation has better performance than ZF equlazation.Then we study on the EST system in Chapter IV. Firstly, energy spreading transform matrix extension principle and performance of multi-symbol energy spreading transform are studied, and then we analyse PAPR characteristics in EST system. We mainly study on signal detection technologies in EST both in the SISO and MIMO system, with the complexity analyzed. Because energy spreading of Single symbol can get good performance, we study on energy spreading of multi-symbol performance by simulation analysis. Iterative EST system needs to know channel information very well, and then we study on channel estimation error on system performance in EST system. Finally, EST iterative detection technique is analyzed and compared by simulation in quasi-static channel, doubly-selective channels,we can see that in the channels that we selected EST system can gain better Performance than SC and OFDM systems. |
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