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Channel estimation for underwater acoustic (UWA) channels in orthogonal frequency division multiplexing (OFDM) systems is one of the most difficult problems in UWA communications. Because UWA channels are both frequency-selective and time-selective, the total number of channel coefficients to be estimated will significantly increase. Besides, the fast time-varying characteristics and strong Doppler...
Channel estimation for MIMO orthogonal frequency division multiplexing (MIMO-OFDM) systems has been improved observably based on compressive sensing (CS) techniques. Recently, some block-structured CS methods have been utilized in MIMO-OFDM systems. However, the block-coherence which characterizes the performance of a block-structured measurement matrix is still not optimized. In this paper, we proposed...
In this paper, a new equalization method without noise enhancement is proposed for dual PN padding TDS-OFDM systems. Using dual identical PN sequences as training sequences, payload and the subsequent PN sequence form a joint block. The preceding PN sequence is treated as cyclic prefix of the joint block, which leads to low-complexity equalization using single carrier frequency domain equalization...
In this paper, we propose a low-complexity single- carrier frequency-domain iterative receiver for triply-selective underwater acoustic (UWA) fading channels, which combines frequency domain decision feedback equalization (FD-DFE) with iterative channel estimation. Due to long multipath channels, frequency domain turbo equalization has to use large block size to achieve low computational complexity...
In this paper, a low complexity algorithm is proposed for dual pseudorandom noise (PN) time domain synchronous OFDM (TDS-OFDM) systems, to simultaneously estimate the carrier frequency offset (CFO) and the sampling frequency offset (SFO). The second PN of every OFDM frame is used in the estimation. Firstly, SFO is estimated under maximum likelihood (ML) criterion. After that, a closed-form solution...
Recently, a new orthogonal frequency division multiplexing (OFDM) scheme called time-frequency training OFDM (TFT-OFDM) has been proposed. Compared to the conventional cyclic prefix OFDM (CP-OFDM) or time-domain synchronous OFDM (TDS-OFDM) which only relies on either frequency-domain pilots or time-domain pseudo noise (PN) sequence for channel estimation, the proposed TFT-OFDM uses PN sequence to...
In this paper, we study the design of frequency domain turbo equalization (FDTE) in single carrier (SC) multiple-input multiple-output (MIMO) systems, and prove the equivalence of two typical FDTE schemes under constant-modulus modulation. In the design of FDTE schemes, received signals and soft decision symbols obtained at the previous iteration are utilized to recover the transmitted symbols under...
Time domain synchronous OFDM (TDS-OFDM) can achieve a higher spectrum efficiency than standard cyclic prefix OFDM (CP-OFDM). Currently, it can support constellations up to 64QAM, but cannot support higher-order constellations like 256QAM due to the residual mutual interferences between the pseudorandom noise (PN) guard interval and the OFDM data block. To solve this problem, we break the traditional...
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