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OFDM can use frequency band efficiently and has strong characteristic for fading channel. But orthogonality collapse when carrier frequency offset and sample timing offset occur. Sample timing offset is represented as phase rotation and ISI. And Carrier frequency offset is represented as phase rotation and ICI. To compensate those effects, many studies were processed based on frequency domain. In...
Although time-domain oversampling of the received baseband signal is common for single-carrier transmissions, the counterpart of frequency-domain oversampling is rarely used for multicarrier transmissions. In this paper, we explore frequency-domain oversampling to improve the system performance of zero-padded OFDM transmissions over underwater acoustic channels with large Doppler spread. We use a...
An important research area in underwater acoustic (UWA) communication is the development of bandwidth efficient modulation and demodulation techniques with low complexity. Over the past two decades, single carrier with time domain equalization (SC-TDE) and orthogonal frequency division multiplexing (OFDM) were used for high data rate underwater information transmission. The performance of high data...
For single-carrier systems with frequency domain equalization, decision feedback equalization (DFE) performs better than linear equalization, and has a lower complexity and computational costs than optimum equalizers. The main challenge in DFE is the feedback symbol selection rule. In this paper, we give a theoretical framework for a simple, sparsity based thresholding algorithm. We feedback multiple...
In this paper, a blind method to detect and suppress narrow-band interference (NBI) for multi-band orthogonal frequency-division multiplexing (MB-OFDM) based ultrawideband (UWB) communications is proposed. The method utilizes mean-square-error (MSE) statistics in the frequency domain to detect subcarriers damaged by NBI. Approximating the MSE statistics by a decision-feedback (DF) scheme creates a...
In this paper, a new feedback equalization scheme to suppress inter-carrier interference (ICI) in an OFDM system using scattered pilot is investigated. On a fast fading channel severe ICI occurs due to a Doppler shift and it deteriorates a bit error rate (BER) seriously because of small subcarrier spacing. In an ISDB-T receiver the equalization is mainly processed in a frequency domain because the...
This paper proposes a differential codebook-based method to reduce the feedback overhead for closed-loop MIMO-OFDM systems. With the assumed multimode transmit precoding, both the number of data streams (rank) and the index of precoding matrix are fed back to the transmitter at each sub-band. By exploiting the channel correlation in frequency domain, an enhanced differential codebook (a subset of...
For orthogonal frequency division multiplexing (OFDM) communication systems, the orthogonality among subcarriers is lost in mobile radio channels due to the frequency offsets caused by mobility. As a direct result, intercarrier interference (ICI) is observed on each and every subcarrier, leading to significant performance degradation. Many ICI cancellation methods such as windowing and frequency domain...
Single-carrier frequency domain Equalization (SC-FDE) systems, which offer similar complexity and performance to Orthogonal Frequency Division Multiplexing (OFDM) systems but enjoy a lower peak-to-average power ratio (PAPR), are promising techniques in the future generation of wireless communications. In this paper, an improved SC-FDE system is proposed, in which the cyclic prefix (CP) is only inserted...
In conventional cyclic prefix (CP) based multicarrier code-division multiple-access (MC-DMA) systems, the major problem is the multiple-access interference (MAI) caused by frequency-selective fading, near-far effect and frequency offset. In order to eliminate MAI, we propose a linear minimum mean-square error (MMSE) detector for zero-padded (ZP) MC-CDMA systems based on frequency-domain oversampling...
In orthogonal frequency-division multiplexing (OFDM) systems operating over rapidly time-varying channels, the orthogonality between subcarriers is destroyed leading to inter-carrier interference (ICI) and resulting in an irreducible error floor. In this paper, a new and low-complexity maximum a posteriori probability (MAP) detection algorithm is proposed for OFDM systems operating over rapidly time-varying...
Subspace based blind channel estimation for OFDM systems has received considerable attention. Existing schemes mainly exploit inherent redundancy such as cyclic prefix and virtual subcarriers or artificial redundancy generated by pre-coding. In this paper, OFDM and multicarrier CDMA systems are considered. Frequency-domain oversampling is used at the receiver to perform detection and channel estimation...
In this paper we formulate OFDM signals based on explicit pulse shaping filtering. A rectangular pulse in time domain for shaping filtering is most often used, but it has SNR loss compared to a shaping filter with a brick-wall frequency domain filter since in practice both require guard time or guard band. Our formulation of OFDM signal based purely on shaping filter may provide a common platform,...
Orthogonal frequency-division multiplexing is sensitive to frequency offset between transmit and receive carriers. In this paper, frequency-domain oversampling is applied to tackle this problem. Our approach is motivated by the duality between time and frequency domains and the fact that time-domain oversampling has been successfully used to deal with timing errors. Theoretical minimum mean-square...
Direct conversion receivers in orthogonal frequency division multiplexing (OFDM) systems suffer from direct current (DC) offset, frequency offset, and IQ imbalance. We have proposed an IQ imbalance estimation scheme in the presence of DC offset and frequency offset, which uses preamble signals in the time domain. In this scheme, the DC offset is eliminated by a differential filter. However, the accuracy...
Orthogonal frequency division multiplexing (OFDM) signals are sensitive to the mismatching errors between the in-phase (I) and quadrature (Q) branches in the up and down-conversions. These mismatching errors including phase and amplitude mismatches make the signal constellation expand and rotate, which severely degrades the performance of OFDM systems. In this paper, a method of signal design for...
This paper proposes a semi-blind algorithm for frequency-domain (post-FFT) soft-decision concurrent equalization in OFDM systems. The objective is to improve system performance by increasing data throughput or decreasing power requirements, when compared with pilot based conventional channel estimation techniques. The constant modulus algorithm and the soft decision-directed technique were concurrently...
In this paper, we propose frequency-domain (FD) and time-domain (TD) beamforming (BF) schemes for cooperative orthogonal frequency division multiplexing (OFDM) networks with multiple amplify-and-forward relays. Whereas for FD-BF the BF weights are applied in the FD, for TD-BF cyclic BF filters (C-BFFs) are used on the TD signal avoiding discrete- time Fourier transform operations at the relays and...
In this paper, main single carrier (SC) and multicarrier (MC) systems with frequency domain equalization (FDE) are reviewed with the objective to identify key features of the evolution path of air interfaces towards 4G. In particular, this paper shows that the FFT/IFFT operation can be seen as the concatenation of two operations: S/P conversion and spreading. We show that the transmitter of an OFDMA...
A frequency-domain oversampling based scheme is proposed for OFDM systems. It is shown that a linear minimum mean-square error (MMSE) receiver with frequency oversampling can efficiently increase the capacity of OFDM. The improvement in capacity is determined by the number of multipath components of the channel. In contrast, the conventional MMSE receiver without frequency oversampling cannot exploit...
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