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Adaptive modulation schemes have been proposed to optimize Shannon's channel capacity in recent orthogonal frequency division multiplexing (OFDM) based broadband wireless standard proposals. By adapting the modulation type (effectively changing the number of bits per symbol) at the transmitter end one can improve the bit error rate (BER) during transmission at designated SNR. Blind detection of the...
Channel estimation and training sequence design for spatially correlated fading in multiple input multiple output with orthogonal frequency division multiplexing (MIMO-OFDM) systems are still open research topics of great interest. In this paper, we investigate the linear minimum mean square error (LMMSE) channel estimation for MIMO-OFDM systems in spatially correlated fading channels. We find the...
Orthogonal frequency division multiplexing based on offset quadrature amplitude modulation (OFDM-OQAM) signaling over frequency selective multipath channels shows inter-symbol interference (ISI) and Inter-Channel Interference (ICI) that degrade its performance. Channel equalization and channel estimation are needed to combat these intrinsic interferences. In this paper a novel modal channel estimator...
The wireless connection of fast moving platforms leads to high demands for the applied transmission scheme. Orthogonal frequency division multiplexing (OFDM), which is successfully used in several wireless standards, suffers from a performance degradation due to inter-carrier interference (ICI) in high mobility scenarios. To cope with these drawbacks we use a special windowing technique in the receiver...
One of the disadvantages that are associated with orthogonal frequency division multiplexing (OFDM) is high peak to average power ratio (PAPR). In most cases, this high peak signal often forces practical amplifiers to operate in the nonlinear region and causes additional degradation to the system's performance. Since the frequency bandwidth is a scarce resource, it is inevitable that a wireless communication...
The problem of cross-layer medium access control (MAC) in a SIMO-OFDM system is addressed and a space sensing based random access (SSRA) scheme is proposed. In SSRA scheme, the transmit slot is divided into three parts: space sensing period, channel estimation period and packets transmission period. Without orthogonal training sequences, users can sense the possible spatial collisions in the following...
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