Generalized carrier assisted differential detection with simplified receiver structure
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We propose the generalized carrier assisted differential detection schemes with reduced hardware complexity, which requires the same number of photodiodes and ADCs as the coherent homodyne counterpart but without the narrow-linewidth local oscillators. The performance of the simplified receiver is evaluated by 60-Gbaud 16-QAM OFDM signals.Keywords:
Direct-conversion receiver
Laser linewidth
Photodiode
QAM
We developed a control scheme of homodyne detection. To operate the homodyne detector as easy as possible, a simple Michelson interferometer is used. Here a motivation that the control scheme of the homodyne detection is developed is for our future experiment of extracting the ponderomotively squeezed vacuum fluctuations. To obtain the best signalto- noise ratio using the homodyne detection, the homodyne phase should be optimized. The optimization of the homodyne phase is performed by changing a phase of a local oscillator for the homodyne detection from a point at which a signal is maximized. In fact, in this experiment, using the developed control scheme, we locked the Michelson interferometer with the homodyne detector and changed the phase of the local oscillator for the homodyne detection. Then, we measured signals quantity changed by changing the phase of the local oscillator for the homodyne detection. Here we used the output from the homodyne detection as the signal.
Direct-conversion receiver
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Optical homodyne detection is examined in view of joint probability distribution. It is usually discussed that the relative phase between independent laser fields are localized by photon-number measurements in interference experiments such as homodyne detection. This provides reasoning to use operationally coherent states for laser fields in the description of homodyne detection and optical quantum-state tomography. Here, we elucidate these situations by considering the joint probability distribution and the invariance of homodyne detection under the phase transformation of optical fields.
Direct-conversion receiver
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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.
QAM
Quadrature (astronomy)
Square (algebra)
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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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Abstract A new optical receiver scheme which combines wavelength conversion and homodyne detection is proposed and its performance is analysed by means of simulation. The main advantage of the proposed structure stems from the use of the same laser source for both, the wavelength conversion and the homodyne detection blocks, avoiding the use of any optical phase‐locking loop. Results obtained show an improvement of the main performance parameters when compared with typical direct detection or homodyne receivers. Copyright © 2006 AEIT.
Direct-conversion receiver
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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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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.
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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, 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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