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In this paper, we consider interference cancellation (IC) schemes for uplink orthogonal frequency division multiple-access (OFDMA) systems with carrier frequency offsets (CFOs). To improve the detection performance without increasing the computational complexity of the detector, we propose a low-complexity multi-stage interference cancellation (MIC) scheme based on a grouped minimum mean squared error...
Spectrally Efficient Frequency Division Multiplexing (SEFDM) systems aim to reduce the utilized spectrum by multiplexing non-orthogonal overlapped carriers. Since the per carrier transmission rate is maintained, SEFDM yields higher spectral efficiency relative to an equivalent Orthogonal Frequency Division Multiplexing (OFDM) system. Yet, due to the loss of the orthogonality, detection of the SEFDM...
Orthogonal frequency division multiplexing (OFDM) is multi carrier modulation scheme. The channel estimation is a process of characterizing the effect of the transmission channel on the input signal. In this paper we compare the performance of Least Square (LS) and Linear Minimum Mean Square Error (LMMSE) channel estimation technique for Wavelet based OFDM system. The channel estimation based on block...
As an alternative to the OFDM transceiver, single carrier frequency domain equalization (SC FDE) based transceiver has received much attention because of its simple implementation and low peak to average power ratio (PAPR). In this paper, a minimum mean square error (MMSE) FDE for single carrier block transmission is presented to effectively equalize the channels with high frequency selectivity such...
Linear precoding plays an important role in the spatial multiplexing multiple-input multiple-output (MIMO)-orthogonal frequency-division multiplexing (OFDM) systems which are considered one of the primary candidates for the physical-layer techniques in the next-generation wireless communication systems. It requires the channel state information (CSI) at the transmitter to adapt the transmitted signal...
The channel estimation algorithms are employed in 3GPP Long Term Evolution (LTE) downlink system to assist the coherent demodulation of Orthogonal Frequency Division Multiplexing (OFDM) symbols. Based on the comparison of several exiting different channel estimation algorithms, we propose a joint time-frequency two-dimensional iterative Wiener filter (IWF) channel estimation algorithm for 3GPP LTE...
Linear constellation precoded orthogonal frequency division multiplexing (LCP-OFDM) requires a maximum likelihood (ML) decoder to fully collect multipath diversity gain. However, the complexity of ML increases exponentially with the channel memory, signal constellation size, and the number of transmit/ receive antennas. Therefore, linear equalizers are highly desirable. This paper mainly analyzes...
The performance reduction caused by inter-carrier interference (ICI) on orthogonal frequency division multiplexing (OFDM) systems over time-varying channels is relevant especially when large OFDM symbols are employed in order to achieve an higher throughput. In this paper we propose a design method of an equalization scheme using several full-length FFTs operating on non-overlapping windows of the...
Recently we presented a novel OFDM (orthogonal frequency division multiplexing) signaling concept, where the cyclic prefixes (CPs) are replaced by deterministic sequences which we call unique words (UWs). The UWs are generated by appropriately loading so-called redundant subcarriers. By that a complex number Reed Solomon (RS) code construction is introduced which can advantageously be exploited in...
In this paper we consider OFDM-based cognitive radios (CR) with linear precoders at the transmitter and minimum mean square error (MMSE) filters at the receiver, and formulate joint spectral allocation and power control subject to specified target signal-to-interference+noise ratio (SINR) as a constrained optimization problem. We discuss necessary and sufficient conditions for the optimal solution...
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...
This paper presents a novel adaptive multiuser detection scheme for MIMO OFDM, which we refer to as AMUD MIMO OFDM. It combines the adaptive minimum mean square error multiuser detection scheme with prior information of the channel and interference cancelation in the spatial domain. Simulation results show that joint channel parameters estimation has good performance compared to individual parameter...
Inter-symbol in0terference is a major limitation of wireless communications. It degrades the performance significantly if the delay spread is comparable or higher than the symbol duration. To mitigate ISI equalization need to be incorporated at the receiver end. Two of the most popular equalization algorithms are zero forcing (ZF) equalizer and minimum mean square (MMSE) equalizer. The paper shows...
Turbo equalization has been proved to effectively improve bit error rate (BER) over time varying channels. To improve the estimated accuracy of channel state information, we propose an iterative estimation by using pilots and soft decision signals; practically, the proposed algorithm is a minimum mean square error (MMSE) estimator. Furthermore, we propose a new turbo equalization schedule based on...
In pilot-aided OFDM systems, the minimum mean-square-error (MMSE) interpolator provides the optimum performance based on the channel statistics. And symbol timing offset (STO) introduces a linear phase rotation to data modulated on individual subcarriers. A MMSE channel estimator designed only using the wireless channel statistics performs only sub-optimally when subcarrier phase rotations due to...
MIMO-OFDM system has been currently recognized as one of the most competitive programs for 4G mobile wireless systems. MIMO-OFDM system can compensate for the lacks of MIMO systems and give play to the advantages of OFDM system. The signal detection technology of MIMO-OFDM system is mainly studied in the paper, including linear detection method of zero forcing (ZF) detection and the minimum mean square...
In recent year, to achieve a high data rate and high quality multimedia service in wireless communication systems, orthogonal frequency division multiplexing (OFDM) is attractive and widely studied. Moreover, orthogonal frequency division multiple access (OFDMA) which is combined OFDM and frequency division multiple access (FDMA) provides each user with a fraction of the available number of subcarriers...
Fractional sampling (FS) and Doppler diversity equalization in OFDM receivers can achieve two types of diversity (path diversity and Doppler diversity) simultaneously on time-varying multipath channels. However FS with a higher sampling rate requires the large amount of complexity in demodulation. In this paper, a novel sampling point selection (SPS) scheme with MMSE equalization in FS-OFDM receivers...
In orthogonal frequency division multiplexing (OFDM) based cellular systems, co-channel interference (CCI) from adjacent interfering base stations (BSs) would greatly degrade the bit error rate (BER) performance of cell-border users. In the previous work, a blind single antenna interference cancellation (SAIC) algorithm named least mean square-blind joint maximum likelihood sequence estimation (LMS-BJMLSE)...
In this work, we investigate Multi-User Multiple-Input Multiple-Output (MU-MIMO) systems within the frame of an Orthogonal Frequency Division Multiple Access (OFDMA) communication scheme. We look at the case where two User Terminals (UT) having two transmit antennas each, are simultaneously communicating in Up-Link (UL) with the Base Station (BS) equipped with two receive antennas. We propose the...
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