The bandwidth and latency demands driven by 5G wireless networks are putting a focus on analog radio-over-fiber techniques as a promising candidate for broadband optical fronthauling. In contrast to ...intensity modulation / direct detection systems, as they are commonly adopted for mobile fronthaul links due to their simplicity, we are exploring a migration option towards coherent radio-over-fiber transmission. A simplified coherent homodyne receiver based on an electro-absorption modulated laser is co-integrated at the die-level with a transimpedance amplifier and evaluated for analogue coherent radio-over-fiber transmission. This low-complexity homodyne receiver can unlock channel selectivity and high receiver sensitivity inherent to coherent detection, but without the need for digital signal processing. We will demonstrate a sensitivity that allows for an optical budget of 42 dB, and thus eases the fixed-mobile convergence in power-splitting fiber plants. We further show filterless radio signal reception in presence of modulated adjacent channels. Signal integrity is confirmed through transmission of orthogonally frequency multiplexed radio signals with 16-point quadrature amplitude modulated formats, with an error vector magnitude below the corresponding antenna limit.
Radio-over-fiber is a popular technique to establish communication links between a central location and many remote antenna units. Many different architectures are available for the downlink, i.e., ...for the communication link from the central unit to the remote antennas. On the contrary, the low-cost and low-complexity requirement of the remote units makes it difficult to devise architectures suitable for the uplink, i.e., for the communication link from the remote antennas to the central unit. In this article, we address this and propose a low-complexity, all-digital, time-division-duplex communication architecture. For the downlink, a band-pass sigma-delta-over-fiber is employed. In the receive mode, the uplink includes an all-digital pulse-width-modulation technique. The received radio frequency (RF) signal is quantized into a binary stream through comparison with a tailored reference signal provided by the central unit. The direct quantization of the RF signal eliminates any need for local-oscillator and mixer stages at the remote units. The performance of the proposed architecture is investigated through extensive simulations and measurements. For instance, the all-digital, time-division duplex communication link provides −30.0 dB and −25.5 dB normalized mean square error signal quality through downlink and uplink communication with 20-MHz, 64-quadrature amplitude modulation signals centered at 2.365-GHz, respectively.
Kernel Additive Models for Source Separation Liutkus, Antoine; Fitzgerald, Derry; Rafii, Zafar ...
IEEE transactions on signal processing,
08/2014, Letnik:
62, Številka:
16
Journal Article
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Source separation consists of separating a signal into additive components. It is a topic of considerable interest with many applications that has gathered much attention recently. Here, we introduce ...a new framework for source separation called Kernel Additive Modelling, which is based on local regression and permits efficient separation of multidimensional and/or nonnegative and/or non-regularly sampled signals. The main idea of the method is to assume that a source at some location can be estimated using its values at other locations nearby, where nearness is defined through a source-specific proximity kernel. Such a kernel provides an efficient way to account for features like periodicity, continuity, smoothness, stability over time or frequency, and self-similarity. In many cases, such local dynamics are indeed much more natural to assess than any global model such as a tensor factorization. This framework permits one to use different proximity kernels for different sources and to separate them using the iterative kernel backfitting algorithm we describe. As we show, kernel additive modelling generalizes many recent and efficient techniques for source separation and opens the path to creating and combining source models in a principled way. Experimental results on the separation of synthetic and audio signals demonstrate the effectiveness of the approach.
A spectral algorithm for processing staggered-pulse repetition time (SPRT) signals in weather radar is introduced. It includes new approaches for ground clutter filter and hydrometeor spectral ...moments estimation. The algorithm uses ideas similar to GMAP but applied to non-uniform sampled signals. This work is focused on staggered sequences 2/3, but can be extended to other staggered sequences. Monte Carlo experiments were used to evaluate the performance of the spectral moments estimators for simulated weather signal, in scenarios with and without the presence of ground clutter. When clutter is present, a study using different clutter-to-signal ratios was carried out, showing that the method can deal with a wide range of situations and is appropriate for implementation in real scenarios. A comparison against GMAP-TD was performed, showing similar estimation results for both algorithms and a fivefold processing speed improvement for the proposed method. The performance was also validated using real weather data RMA-12 from a radar located in San Carlos de Bariloche, Argentina. The proposed algorithm has an easy implementation and is a good candidate for real-time implementations.
Grounding on research about the role of signals in the attraction of equity finance, this paper studies the effects of diverse human capital signals on entrepreneurs' success in equity crowdfunding. ...We argue that the human capital of an entrepreneur, who launches (alone or with other teammates) an equity crowdfunding campaign to finance her start-up, constitutes a set of signals of the start-up quality. The impact of each human capital signal on entrepreneur's success in equity crowdfunding depends on both signal fit with start-up quality and signal ambiguity. Empirical estimates on 284 entrepreneurs who launched equity crowdfunding campaigns indicate that only entrepreneurs' business education and entrepreneurial experience, two human capital signals that have both a good fit with start-up quality and a low degree of ambiguity, significantly contribute to entrepreneurs' success in equity crowdfunding.
Recently, fingerprint-based localization has become a promising solution for indoor positioning because of its great performance in complex multipath environments. However, the extensive time and ...labor effort of constructing the radio map has become the bottleneck that hinders the adaptation of fingerprint-based localization in practice. In this article, we propose a novel cost-efficient radio map construction scheme, which relies on the fingerprint measurements from only a small number of reference points (RPs) via graph signal sampling and recovery techniques. First, using the topological characteristics of RPs, we model the radio map as a graph and design the angle fingerprint for the band-limited graph signal. Subsequently, the radio map is built based on graph clustering, sampling set selection and signal recovery. Extensive simulations are performed in a geometry-based ray tracing signal propagation model, which demonstrates that the proposed method can recover the radio map with low-collection cost and outperform existing solutions in terms of fingerprint accuracy and localization performance.
To better understand the response to mitochondrial dysfunction, we examined the mechanism by which ATFS-1 (activating transcription factor associated with stress—1) senses mitochondrial stress and ...communicates with the nucleus during the mitochondrial unfolded protein response (UPR mt ) in Caenorhabditis elegans. We found that the key point of regulation is the mitochondrial import efficiency of ATFS-1. In addition to a nuclear localization sequence, ATFS-1 has an N-terminal mitochondrial targeting sequence that is essential for UPR mt repression. Normally, ATFS-1 is imported into mitochondria and degraded. However, during mitochondrial stress, we found that import efficiency was reduced, allowing a percentage of ATFS-1 to accumulate in the cytosol and traffic to the nucleus. Our results show that cells monitor mitochondrial import efficiency via ATFS-1 to coordinate the level of mitochondrial dysfunction with the protective transcriptional response.
The polarization millimeter wave (mmWave) massive multiple-input multiple-output (MIMO) system has been deployed in next-generation wireless communication since it can provide a high-data stream and ...high space efficiency simultaneously. Polarization channel parameter estimation for polarized mmWave massive MIMO systems is extremely important for directional beamforming with data transmissions. In this paper, the base station (BS) equipped with a large polarization-sensitive array is considered in massive MIMO systems. The polarization channel consists of direction-of-arrival (DOA) and polarization parameters that are estimated from the coexistence of circular and non-circular signals. Based on the unconjugated covariance matrix, the initialized polarization channel estimation is achieved by multiple signal classification (MUSIC). Then, the high-accuracy polarization channel estimation for general non-circular rate signals is performed by reconstructing the corresponding noise matrix. The high-accuracy polarization channel estimation for circular signals is obtained based on covariance matrix differencing. Moreover, the dimension of parameter search is reduced based on the partial derivative of the spectrum function with respect to the non-circular phase. The high-accuracy polarization channel estimation for the maximum non-circular rate signal is finally achieved based on the initialized parameter estimation of the polarization channel. The proposed algorithm estimates different kinds of signals separately. The effect of different kinds of signals is reduced significantly, which means that the resolution probability of different kinds of signals can be dramatically improved. Numerical examples are provided to demonstrate the performance of the proposed algorithm, especially in small angular distances.
A low-power differential input to single-ended output digital-to-analog converter (DAC) is presented, which is capable of providing radio frequency (RF)-signals with a data rate of up to ...<inline-formula> <tex-math notation="LaTeX">\mathrm {8~G} </tex-math></inline-formula>bit/s. A constant direct current (dc) current source is realized as a self-bootstrapping device in the presented 0.25-<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> in-house gallium nitride (GaN) technology. First, measurements with a low-power 1-V peak-peak voltage (<inline-formula> <tex-math notation="LaTeX">V_{pp} </tex-math></inline-formula>) differential input signal show the feasibility of switching constant currents with a clock frequency of up to 2 GHz. Furthermore, a 2-b DAC that uses a differential sampling to generate RF-signals is introduced. Measurement results prove the feasibility of synthesizing custom-modulated voltage waveforms with data rates of up to 8 Gbit/s in the sub-6-GHz frequency range.
An extension of empirical mode decomposition (EMD) is proposed in order to make it suitable for operation on trivariate signals. Estimation of local mean envelope of the input signal, a critical step ...in EMD, is performed by taking projections along multiple directions in three-dimensional spaces using the rotation property of quaternions. The proposed algorithm thus extracts rotating components embedded within the signal and performs accurate time-frequency analysis, via the Hilbert-Huang transform. Simulations on synthetic trivariate point processes and real-world three-dimensional signals support the analysis.
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