The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
Harald Haas - One of the best experts on this subject based on the ideXlab platform.
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augmenting the spectral efficiency of enhanced pam dmt based optical wireless communications
Optics Express, 2016Co-Authors: Mohamed Sufyan Islim, Harald HaasAbstract:The energy efficiency of pulse-amplitude-modulated discrete multitone Modulation (PAM-DMT) decreases as the Modulation Order of M-PAM Modulation increases. Enhanced PAM-DMT (ePAM-DMT) was proposed as a solution to the reduced energy efficiency of PAM-DMT. This was achieved by allowing multiple streams of PAM-DMT to be superimposed and successively demodulated at the receiver side. In Order to maintain a distortion-free unipolar ePAM-DMT system, the multiple time-domain PAM-DMT streams are required to be aligned. However, aligning the antisymmetry in ePAM-DMT is complex and results in efficiency losses. In this paper, a novel simplified method to apply the superposition Modulation on M-PAM modulated discrete multitone (DMT) is introduced. Contrary to ePAM-DMT, the signal generation of the proposed system, termed augmented spectral efficiency discrete multitone (ASE-DMT), occurs in the frequency domain. This results in an improved spectral and energy efficiency. The analytical bit error rate (BER) performance bound of the proposed system is derived and compared with Monte-Carlo simulations. The system performance is shown to offer significant electrical and optical energy savings compared with ePAM-DMT and DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM).
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Energy-efficient scheduling and bandwidth-energy efficiency trade-off with low load
IEEE International Conference on Communications, 2011Co-Authors: Stefan Videv, Harald HaasAbstract:This paper presents a novel adaptation of the score-based scheduling principle along with a method for trading-off bandwidth for energy efficiency for use in Long Term Evolution (LTE) systems. The score-based principle is adapted to make use of both a relative and absolute energy efficiency metric. This results in flexible energy efficient scheduling that preserves the quality of service (QoS), as well as reduces the interference in the system. The general principle behind bandwidth expansion is to extend a user's bandwidth by a factor of alpha. The currently achieved QoS is maintained by switching to a lower Order Modulation scheme and adjusting any other link parameters as necessary. Both, a purely theoretical and an empirical approach are used to evaluate the performance of the concept. Through a theoretical derivation, it is established that the higher the user's employed Modulation Order is, the greater the possible gains are from employing such a transmission mode. The calculated improvement ranges from approximately 43% to 98%, or approximately 2 to 50 times reduction in transmission energy. A realistic simulation tool is developed to empirically validate the theoretical results. When an expansion of bandwidth by a factor of 2 is simulated, the bandwidth expansion mode (BEM) is more efficient in 83% of the time, and energy is reduced 2.6 times on average, while retaining the established QoS.
Alan Pak Tao Lau - One of the best experts on this subject based on the ideXlab platform.
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low complexity carrier phase recovery based on principal component analysis for square qam Modulation formats
Optics Express, 2019Co-Authors: Julio Cesar Medeiros Diniz, Qirui Fan, Stenio M Ranzini, Faisal Nadeem Khan, Francesco Da Ros, Darko Zibar, Alan Pak Tao LauAbstract:We propose, numerically analyze and experimentally demonstrate a low-complexity, Modulation-Order independent, non-data-aided (NDA), feed-forward carrier phase recovery (CPR) algorithm. The proposed algorithm enables synchronous decoding of arbitrary square-quadrature amplitude Modulation (QAM) constellations and it is suitable for a realistic hardware implementation based on block-wise parallel processing. The proposed method is based on principal component analysis (PCA) and it outperforms the well-known and widely used blind phase search (BPS) algorithm at low signal-to-noise ratio (SNR) values, showing much lower cycle slip rate (CSR) both numerically and experimentally. For operation at higher SNR values, a hybrid two-stage implementation combining the proposed method and BPS is also proposed and their performance are investigated benchmarking them against the two-stage BPS (2S-BPS). The complexity of the proposed simple and hybrid methods are evaluated against 2S-BPS and computational complexity savings of 92% and 40% are expected for the simple and hybrid methods, respectively.
George K Karagiannidis - One of the best experts on this subject based on the ideXlab platform.
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adaptive subcarrier psk intensity Modulation in free space optical systems
IEEE Transactions on Communications, 2011Co-Authors: Nestor D Chatzidiamantis, Athanasios S Lioumpas, George K Karagiannidis, Shlomi ArnonAbstract:We propose an adaptive transmission technique for free space optical (FSO) systems, operating in atmospheric turbulence and employing subcarrier phase shift keying (S-PSK) intensity Modulation. Exploiting the constant envelope characteristics of S-PSK, the proposed technique offers efficient utilization of the FSO channel capacity by adapting the Modulation Order of S-PSK, according to the instantaneous state of turbulence induced fading and a pre-defined bit error rate (BER) requirement. Novel expressions for the spectral efficiency and average BER of the proposed adaptive FSO system are presented and performance investigations under various turbulence conditions, turbulence models, and target BER requirements are carried out. Numerical results indicate that significant spectral efficiency gains are offered without increasing the transmitted average optical power or sacrificing BER requirements, especially in moderate-to-strong turbulence conditions. Furthermore, the proposed variable rate transmission technique is applied to multiple input multiple output (MIMO) FSO systems, providing additional improvement in the achieved spectral efficiency as the number of the transmit and/or receive apertures increases.
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θ qam a parametric quadrature amplitude Modulation family and its performance in awgn and fading channels
IEEE Transactions on Communications, 2010Co-Authors: Koralia N Pappi, Athanasios S Lioumpas, George K KaragiannidisAbstract:We study a parametric quadrature amplitude Modulation (QAM) family, called θ-QAM, which includes other known constellations, such as square QAM (SQAM) and triangular QAM (TQAM), as special cases. The versatile structure of the θ-QAM signal constellation, which occurs from the varying angle between the signal points, results in achieving the minimum symbol error rate (SER) or bit error rate (BER), under an average power constraint. The theoretical study aims at providing insight into the trade-off between error performance and complexity of this parametric Modulation scheme. Exact analytical expressions are obtained for the SER in additive white Gaussian Noise (AWGN) and Nakagami-m fading channels, while highly accurate BER approximations are presented. Finally, we find the optimum angles, in a minimal SER or BER sense, for a specific signal-to-noise ratio (SNR) and Modulation Order, M. This serves as an indicator for the appropriate constellation with respect to channel conditions and SER or BER requirements. The presented theoretical analysis is validated via extensive computer simulations.
Volker Jungnickel - One of the best experts on this subject based on the ideXlab platform.
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Adaptive Modulation and Turbo Coding for 3GPP LTE Systems with Limited Feedback
2014 IEEE 79th Vehicular Technology Conference (VTC Spring), 2014Co-Authors: Konstantinos Manolakis, M. A. Gutierrez-estevez, Volker JungnickelAbstract:Link adaptation is recognized as a powerful tech- nique for enhancing spectral efficiency over wireless channels. While its theoretical aspects are well understood, it is not clear yet how to practically deal with limited feedback. In this paper, we study a frequency-selective link adaptation scheme for orthogonal frequency division multiplexing (OFDM). The Modulation Order is adjusted per resource block (smallest time-frequency unit assigned to a user), while a joint coding rate is used for all variable-length codewords, comprising resource blocks with different Modulations. In Order to meet the required coding rate, adaptive puncturing is applied after a fixed-rate Turbo encoder. Link adaptation is guided by an effective signal-to-noise ratio (SNR), which is calculated over several subcarriers by a mapping function. 3GPP LTE compliant link-layer simulations were performed for optimizing the SNR interface so that the spectral efficiency is maximized under a codeword error rate constraint and tradeoffs between feedback savings and spectral efficiency losses were elaborated. The result is a thoroughly tested link-layer abstraction for 3GPP LTE including adaptive Modulation and bit-interleaved coding that can be also used for system-level simulations towards future mobile radio systems.
Julio Cesar Medeiros Diniz - One of the best experts on this subject based on the ideXlab platform.
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low complexity carrier phase recovery based on principal component analysis for square qam Modulation formats
Optics Express, 2019Co-Authors: Julio Cesar Medeiros Diniz, Qirui Fan, Stenio M Ranzini, Faisal Nadeem Khan, Francesco Da Ros, Darko Zibar, Alan Pak Tao LauAbstract:We propose, numerically analyze and experimentally demonstrate a low-complexity, Modulation-Order independent, non-data-aided (NDA), feed-forward carrier phase recovery (CPR) algorithm. The proposed algorithm enables synchronous decoding of arbitrary square-quadrature amplitude Modulation (QAM) constellations and it is suitable for a realistic hardware implementation based on block-wise parallel processing. The proposed method is based on principal component analysis (PCA) and it outperforms the well-known and widely used blind phase search (BPS) algorithm at low signal-to-noise ratio (SNR) values, showing much lower cycle slip rate (CSR) both numerically and experimentally. For operation at higher SNR values, a hybrid two-stage implementation combining the proposed method and BPS is also proposed and their performance are investigated benchmarking them against the two-stage BPS (2S-BPS). The complexity of the proposed simple and hybrid methods are evaluated against 2S-BPS and computational complexity savings of 92% and 40% are expected for the simple and hybrid methods, respectively.