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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, 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...
For digital terrestrial television broadcasting (DT-TB) systems, orthogonal frequency division multiplexing (OFDM) technique is considered to be an effective method to combat the frequency selective channel cause by multi-path effect. In the single frequency network (SFN) scenario, Alamouti space frequency block coding (SFBC) is introduced to provide spatial diversity gain and improve the link stability...
This paper presents a broadband multimedia transmission system for the ultra-high-speed mobile application. Based on the time-domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) system, training sequences in frame headers are regarded as samples of time-varying channel parameters under the fast-varying channel, instead of assuming that the channel impulse response remains constant...
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...
In this paper, we propose a time-domain oversampled receiver for orthogonal frequency division multiplexing (OFDM) in underwater acoustic communication. Without changing the structure of the transmitter, significant gains are acquired by time- domain oversampling at the receiver. Using time- domain oversampling, the energy of transmitted symbols is concentrated on the first N subcarriers, while additive...
Recently, compressive sensing (CS) is applied to time domain synchronous OFDM (TDS-OFDM), which has higher spectral efficiency and faster synchronization than standard cyclic prefix OFDM (CP-OFDM), to improve the performance over multi-path fading channels. The performance heavily relies on the sparsity level of the channel, which is unknown in practise. In this paper, a signal-to-noise ratio (SNR)...
Recently, compressive sensing (CS) algorithms have been adopted to improve the accuracy of channel estimation for wide-band wireless communication systems. Since the wireless channel is usually time and frequency doubly selective fading, the performance of CS based channel estimation is limited by the estimation accuracy of the channel's sparsity level. In this paper, an adaptive subspace pursuit...
In this paper, an iterative receiver with Turbo equalization and soft demapping is proposed for high data rate communication in multipath channels. Minimum mean square error (MMSE) equalization is adopted to avoid noise enhancement. With the assumption that the distribution of estimated symbols is Gaussian distribution, log likelihood ratios (LLR) of encoded bits are obtained with soft demapping....
Time-varying channel always plays great obstacle to OFDM (orthogonal frequency domain modulation) as it introduces intercarrier interference (ICI). In terrestrial digital television broadcasting systems, residual Doppler shift may exist and deteriorate the orthogonality of subcarrier signal, especially during high-speed transportation such as high-speed railways. This paper proposed a jointly Doppler...
Modern hospitals are beginning to adopt E-HEALTH as efficient complements to the traditional healthcare services. To support the E-HEALTH services, a locatable, radiation-free and high-capacity communication system is urgently needed in hospitals. Power line communication (PLC) system can use the ubiquitous power line network to power the light-emitting diode (LED) lights while serving as the backbone...
Recently, compressive sensing (CS) methods have been considered to improve the accuracy of channel estimation. Since the accurate estimation of the channel relies on the size of the observations, the fixed size of the observations is usually the trade-off between the channel estimation accuracy and the length of the channel delay to handle. In this paper, an adaptive compressive sensing (A-CS) algorithm...
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...
A time domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) scheme with dual Pseudonoise (PN) sequence is proposed for underwater acoustic (UWA) communication. Instead of using cyclic prefix (CP) or zero padding (ZP) as the guard interval, the proposed TDS-OFDM scheme uses two identical PN sequences as guard interval, and utilizes them for frame synchronization and channel estimation...
Time domain synchronous OFDM (TDS-OFDM) has higher spectral efficiency than cyclic prefix OFDM (CP-OFDM), but suffers from severe performance loss over fast fading channels. In this paper, a novel transmission scheme called time-frequency training OFDM (TFT-OFDM) is proposed. The time-frequency joint channel estimation for TFT-OFDM utilizes the time-domain training sequence without interference cancellation...
To reduce the complexity of existing transmit diversity solutions for time domain synchronous OFDM (TDS-OFDM), a simple transmit diversity scheme is proposed in this paper. The space shifted constant amplitude zero autocorrelation (CAZAC) sequence is used for time-domain channel estimation. Two types of flexible frame structures are investigated for cyclicity reconstruction of the received inverse...
The existing transmit diversity schemes for time domain synchronous OFDM (TDS-OFDM) is only suitable either for fast time-varying but weakly frequency-selective channels, or strongly frequency-selective but slow fading channels. In this paper, the space-time shifted constant amplitude zero autocorrelation (CAZAC) sequence based TDS-OFDM transmit diversity scheme is proposed for doubly selective channels...
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