| Troposcatter communication is a communication method that can realize over-the-horizon(OTH)transmission.Due to its high data transmission rate and strong anti-interference ability,troposcatter communication has been widely used in military and emergency communication fields of various countries.With the in-depth study of troposcatter communication systems,more and more attention has been paid to how to break through high-order modulation and realize anti-multipath transmission to improve transmission capacity.Aiming at the troposcatter communication system,this paper combines time-reversal spacetime block coding(TR-STBC)and orthogonal frequency division multiplexing(OFDM)technology to give a broadband transmission scheme.This scheme not only has lower transmit power consumption,potential multipath diversity,but also can effectively effectively combat channel zeros.The traditional TR-STBC based MIMO-OFDM system is demodulated in the time domain,so the decoding complexity of the receiver is relatively high.To solve this problem,this paper deals with demodulator complexity in frequency domain.First,time reversal,conjugation and cyclic shift are performed on the received signal at the receiving end,so that the time domain convolution of the signal and the channel is converted into matrix multiplication in the frequency domain,and then demodulated in the frequency domain.Compared with the traditional time-domain based demodulation algorithm,the improved frequency-domain based TR-STBC-OFDM system has lower complexity and better performance.Channel estimation and equalization techniques are studied for TR-STBC-OFDM system.First,this paper introduces the selection and insertion of pilot sequence,studies and optimizes the least square estimation method based on pilot,and gives a set of channel estimation scheme of scattering communication system.Then two methods of zero forcing(ZF)equalization and minimum mean square error(MMSE)equalization are studied and analyzed,and a set of frequency domain equalization scheme based on minimum mean square error is presented.The simulation results show that compared with the channel estimation and equalization scheme in time domain,the channel estimation and equalization scheme based on TR-STBC-OFDM system presented in this paper can not only reduce the influence of noise,estimate the channel accurately,but also effectively reduce the complexity. |
