Abstract-In this paper we consider an adaptive modulation system with multiple-input multiple-output (MIMO) antennas in conjunction with orthogonal frequency division multiplexing (OFDM) operating over frequency selective Rayleigh fading environments. In particular, we consider a type of beamforming with a maximum ratio transmission, maximum ratio combining (MRT-MRC) transceiver structure. For this system we derive a central limit theorem for various block-based performance metrics. This motivates an accurate Gaussian approximation to the system data rate and the number of outages per OFDM block. In addition to data rate and outage distributions, we also consider the subcarrier SNR as a random process in the frequency domain and compute level crossing rates (LCRs) and average fade bandwidths (AFBs). Hence, we provide fundamental but novel results for the MIMO OFDM channel. The accuracy of these results is verified by Monte Carlo simulations, and applications to both performance analysis and system design are discussed.
Abstract-In this paper we compare the performance of OFDM with a cyclic prefix (CP) and isotropic orthogonal transform algorithm (IOTA) OFDM without cyclic prefix under typical system imperfections such as channel estimation errors and frequency offset. The IOTA-OFDM system is based on offset quadrature amplitude modulation (OQAM) and promises an increased immunity to both inter-carrier interference (ICI) and inter-symbol interference (lSI). Moreover, IOTA-OFDM does not require a CP which makes it spectrally more efficient. Our simulation results show that compared to CP-OFDM, IOTA-OFDM is spectrally efficient and more tolerant to interference and frequency offset. Imperfect channel estimation may reduce the gains of IOTA-OFDM but considerable throughput advantages are still obtained for a fixed HER.
Abstract-In this paper, we consider an adaptive modulation system with multiple-input-multiple-output (MIMO) antennas in conjunction with orthogonal frequency-division multiplexing (OFDM) operating over frequency-selective Rayleigh fading environments. In particular, we consider a type of beamforming with a maximum ratio transmission/maximum ratio combining (MRT-MRC) transceiver structure. For this system, we derive a central limit theorem for various block-based performance metrics. This motivates an accurate Gaussian approximation to the system data rate and the number of outages per OFDM block. In addition to the data rate and outage distributions, we also consider the subcarrier signal-to-noise ratio (SNR) as a process in the frequency domain and compute level crossing rates (LCRs) and average fade bandwidths (AFBs). Hence, we provide fundamental but novel results for the MIMO OFDM channel. The accuracy of these results is verified by Monte Carlo simulations, and applications to performance analysis and system design are discussed.Index Terms-Adaptive modulation, average fade bandwidth (AFB), beamforming, eigenvalues, level crossing rate (LCR), multiple-input-multiple-output orthogonal frequencydivision multiplexing (MIMO OFDM), Rayleigh fading channels.
Abstract-In this paper we consider the variation of eigenvalues and eigenvalue sums across the frequency bins of a MIMO OFDM system. In particular, we consider the changes in the ordered eigenvalues and the eigenvalue sum or link gain between two distinct frequency bins. The size of such changes has an important effect both on system performance and design. In addition these results have applications in other areas, including temporal variation, feedback delay and channel estimation. Novel results presented include distributions and moments for changes in link gain and the maximum eigenvalue and autocorrelation functions for the link gain and maximum eigenvalue. Furthermore, some very simple approximate results for the ordered eigenvalue differences are presented and the accuracy of the analysis is verified by Monte Carlo simulations.
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