A Single-channel 40 Gbit/s Digital Coherent QAM Quantum Stream Cipher Transmission over 480 km
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We demonstrate a single-channel 40-Gbit/s QAM quantum stream cipher transmission over 480-km. By using a multi-bit encoded scheme and digital coherent transmission techniques, record data capacity and transmission distance of secure optical communication have been successfully realized.Keywords:
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By generalizing and modifying some existing cost-functions, we present two new, generic and efficient multimodulus families of blind equalization algorithms for use in higher-order quadrature amplitude modulation based digital communication systems. Proposed algorithms are shown to be capable of blindly equalizing and recovering carrier-phase at convergence speed much faster than existing counterparts on certain QAM sizes. We show that particular examples of the proposed cost-functions include a number of existing algorithms. We also provide detailed dynamic convergence analysis which is found in good conformation with those obtained from Monte-Carlo experiments.
QAM
Blind equalization
Modulation (music)
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In this paper we derive symbol error rate (SER) expression of stepped θ-quadrature amplitude modulation (QAM) and analyze SER performance in the presence of impulsive noise. We show that the SER performance of the stepped θ-QAM is superior to that of square QAM in an impulsive noise environment, and validate the theoretical results with simulation ones through computer simulations.
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Quadrature (astronomy)
Square (algebra)
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Blind modulation format identification (MFI) is essential in an elastic optical network (EON) due to unknown modulation format of the received signals. We propose an MFI method for square and non-square quadrature amplitude modulation (QAM) signals, quadrature phase-shift keying (QPSK), 8-QAM, 16-QAM, 32-QAM, 64-QAM, 128-QAM, 256-QAM, 512-QAM, 1024-QAM, and 2048-QAM. We identified these modulation formats by using two identification factors such as the amplitude variance and the optical signal-to-noise ratio (OSNR) of the received signal. The simulation results based on a look-up-table (LUT) and a neural network, respectively, show that the modulation format of the received signals can be identified correctly in the OSNR range of a bit error rate (BER) for communication, better than 10−2. We also investigate effects of both ONSR measurement errors and residual chromatic dispersion (CD) on the MFI performance.
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This paper studies non-integer power of two-ary quadrature amplitude modulation (QAM) for long-haul optical fiber transmission systems.Numerical simulations show that 12-QAM and 24-QAM provide intermediate solutions on reachable transmission distances among traditional M-QAM such as C8-QAM, 16-QAM, and 32-QAM.In addition, short block length probabilistic shaping of 24-QAM not only provides an intermediate solution with nonlinear tolerance, but also yields greater transmission distances than 16-QAM for the same information data rates.
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We introduce a fixed-point algorithm, the complex QAM (C-QAM) algorithm, for separation of quadrature amplitude modulated (QAM) sources through independent component analysis. The algorithm matches the input QAM distribution through a mixture of Gaussian kernels and uses fixed-point updates that fully take advantage of complex domain processing. We demonstrate the performance of the C-QAM algorithm through simulations and note that it provides improved performance over a wide range of operating conditions such as low signal-to-noise ratio, small sample sizes, and large number of sources.
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Quadrature amplitude modulation (QAM) is used for transmission at high data rate in band-limited channels. A great deal of attention has been devoted to derive expressions for bit error probability of QAM. In this paper, a generalized expression for bit error rate (BER) for odd bit QAM using symmetry properties of Gray code is derived and its performance is compared with existing closed form expression for arbitrary QAM constellation. New BER expression offers a convenient way to evaluate the performance of odd bit QAM for various cases of practical interest
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Gray code
Expression (computer science)
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In this paper, a phase-noise-tolerant two-stage carrier recovery concept for arbitrary quadrature amplitude modulation (QAM) constellations is presented. Possible implementations are evaluated in simulations of square 16-QAM, 64-QAM, and 256-QAM transmission systems, considering fourth-power and decision-directed carrier recovery for the first stage. The second stage uses QAM feedforward carrier recovery. It is shown that the two-stage concept achieves the same phase noise tolerance as the original QAM feedforward carrier recovery concept, but reduces the required hardware effort by factors of 1.5-3 depending on the order of the QAM constellation.
QAM
Carrier recovery
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Geometric constellation shaping is a promising technique to boost the transmission capacity of communication systems. Earlier, traditional optimization methods in constellation design lead to several advanced quadrature amplitude modulation (QAM) formats, such as star QAM, cross QAM, and hexagonal QAM. The difficulty in determining decision boundaries limited their use in real systems. To overcome this, machine learning based geometric constellation shaping has recently been proposed, where the detection is done via neural networks. Unfortunately, the resulting constellation shape is often unstable and highly dependent on initialization. In this paper, we use an autoencoder for constellation shaping and detection, with strategic initialization. We contrast initialization with hexagonal QAM and square QAM. We present numerical results showing the hexagonal QAM initialization achieves the best symbol error rate performance, while the square QAM initialization has better bit error rate performance.
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Initialization
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In this paper, we develop low-complexity methods to compute the soft estimation of quadrature amplitude modulation (QAM) symbols with applications to iterative receivers. To reduce the complexity of the soft QAM estimation, we first consider squared QAM constellations and present a bit flipping based soft estimation scheme. With the gray mapping we derive an efficient approach which has a very low complexity of O(log N) for an NQAM constellation. To further simplify the approach, we propose a method which completely removes the multiplication operations at a cost of a slight performance degradation. Finally, we extend the proposed method to the non-squared QAM.
QAM
Modulation (music)
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In this paper, a modified family of blind equalization algorithms is proposed for use in quadrature amplitude modulation (QAM) based digital communication systems. We have called this family: the generalized multimodulus algorithms: MMA(p, q). This family is derived by introducing two degrees of freedom in the conventional MM criterion. We have shown that one of the members of this family, MM(2, 1), (which, to the best of our knowledge, has never been discussed) exhibits the fastest convergence for 16-QAM signal. The dynamic convergence behavior of MM(2, 1) is analyzed and shown to be conforming with simulation results.
QAM
Blind equalization
Modulation (music)
SIGNAL (programming language)
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