Interference cancellation for layered asymmetrically clipped optical OFDM with application to optical receiver design

© 1983-2012 IEEE. In this paper, we study a novel two-stage receiver to demodulate layered asymmetrically clipped optical orthogonal frequency division multiplexing for intensity modulation direct detection based visible light communications. Designed for avoiding the error propagation of the conventional receiver, the first stage of the receiver is a soft interference cancellation (SIC) module which evaluates the minimum mean square error (MMSE) estimates of the signals in different layers. For this stage, we derive the exact formula of the MMSE estimator, and compare the achieved mean square error and bit error rate (BER) with those of the existing simplified SIC receiver. We show that the estimation error in a layer has negligible impact on the design of estimators in the subsequent layers. Using the outputs of the SIC module, the second stage performs noise clipping to suppress the additive noise. For this stage, we present two schemes, the SIC-based iterative noise clipping (SIC-INC) and the SIC-based direct noise clipping (SIC-DNC). The simulation results show that SIC-INC can achieve BERs similar to those of the SIC-based diversity combining receiver with optimum combining coefficients. It is also shown that SIC-DNC outperforms the existing advanced receivers by up to 0.8 dB at the BER of 10{-4}

Matrix Normalization Based ZF Hybrid Precoded Multi-User MIMO mmWave Systems with Massive Array

© 2018 IEEE. The superiority of exploring millimeter wave (mmWave) frequencies for future wireless communication systems has pushed forward the development of large-scale antenna arrays for achieving sufficient array gain and high spectral efficiency. In this paper, we study the matrix normalization (MN) based zero-forcing (ZF) hybrid precoding in multi-user multi-input-multi-output (MU-MIMO) mmWave systems. We derive the upper bounds of the achievable rate for two representative hybrid array structures, i.e., fully-connected structure and partially-connected structure. Analytical and simulation results validate the tightness of the proposed performance upper bounds for both hybrid structures using massive array, and provide a comparison of the achievable rate using MN and vector normalization (VN)

Enhanced AoA estimation using localized hybrid dual-polarized arrays

© 2019 IEEE. With balanced system performance, implementation complexity and hardware cost, hybrid antenna array is regarded as an enabling technology for massive multiple-input and multiple-output communication systems in millimeter wave (mmWave) frequencies. Angle-of-arrival (AoA) estimation using a localized hybrid array faces the challenges of the phase ambiguity problem due to its localized nature of array structure and susceptibility to noises. This paper discusses AoA estimation in an mmWave system employing dual-polarized antennas. We propose an enhanced AoA estimation algorithm using a localized hybrid dual-polarized array for a polarized mmWave signal. First, the use of dual-polarized arrays effectively strengthens the calibration of differential signals and resulting signal-to-noise ratio with coherent polarization combining, leading to an enhanced estimate of the phase offset between adjacent subarrays. Second, given the phase offset, an initial AoA estimate can be obtained, which is used to update the phase offset. By employing the updated one, the AoA is re- estimated with improved accuracy. The closed-form mean square error (MSE) lower bounds of AoA estimation are derived and compared with simulated MSEs. The simulation results show that the proposed algorithm in combination with hybrid dual- polarized arrays significantly improves the estimation accuracy compared with the state of the art

Secure D2D Communication in Large-Scale Cognitive Cellular Networks with Wireless Power Transfer

In this paper, we investigate secure device-to-device (D2D) communication in energy harvesting large-scale cognitive cellular networks. The energy constrained D2D transmitter harvests energy from multi-antenna equipped power beacons (PBs), and communicates with the corresponding receiver using the spectrum of the cellular base stations (BSs). We introduce a power transfer model and an information signal model to enable wireless energy harvesting and secure information transmission. In the power transfer model, we propose a new power transfer policy, namely, best power beacon (BPB) power transfer. To characterize the power transfer reliability of the proposed policy, we derive new closed-form expressions for the exact power outage probability and the asymptotic power outage probability with large antenna arrays at PBs. In the information signal model, we present a new comparative framework with two receiver selection schemes: 1) best receiver selection (BRS), and 2) nearest receiver selection (NRS). To assess the secrecy performance, we derive new expressions for the secrecy throughput considering the two receiver selection schemes using the BPB power transfer policies. We show that secrecy performance improves with increasing densities of PBs and D2D receivers because of a larger multiuser diversity gain. A pivotal conclusion is reached that BRS achieves better secrecy performance than NRS but demands more instantaneous feedback and overhead

Secure D2D Communication in Large-Scale Cognitive Cellular Networks: A Wireless Power Transfer Model

In this paper, we investigate secure device-to-device (D2D) communication in energy harvesting large-scale cognitive cellular networks. The energy constrained D2D transmitter harvests energy from multi-antenna equipped power beacons (PBs), and communicates with the corresponding receiver using the spectrum of the primary base stations (BSs). We introduce a power transfer model and an information signal model to enable wireless energy harvesting and secure information transmission. In the power transfer model, three wireless power transfer (WPT) policies are proposed: 1) cooperative power beacons (CPB) power transfer, 2) best power beacon (BPB) power transfer, and 3) nearest power beacon (NPB) power transfer. To characterize the power transfer reliability of the proposed three policies, we derive new expressions for the exact power outage probability. Moreover, the analysis of the power outage probability is extended to the case when PBs are equipped with large antenna arrays. In the information signal model, we present a new comparative framework with two receiver selection schemes: 1) best receiver selection (BRS), where the receiver with the strongest channel is selected, and 2) nearest receiver selection (NRS), where the nearest receiver is selected. To assess the secrecy performance, we derive new analytical expressions for the secrecy outage probability and the secrecy throughput considering the two receiver selection schemes using the proposed WPT policies. We presented Monte-carlo simulation results to corroborate our analysis and show: 1) secrecy performance improves with increasing densities of PBs and D2D receivers due to larger multiuser diversity gain, 2) CPB achieves better secrecy performance than BPB and NPB but consumes more power, and 3) BRS achieves better secrecy performance than NRS but demands more instantaneous feedback and overhead. A pivotal conclusion is reached that with increasing number of antennas at PBs, NPB offers a comparable secrecy- performance to that of BPB but with a lower complexity

Low-complexity multiuser receiver for massive hybrid array mmwave communications

© 1972-2012 IEEE. In this paper, we study the low complexity reception of multiuser signals in uplink millimeter wave (mmWave) communications using a partially connected hybrid antenna array. Exploiting the mmWave channel property, we propose a low-complexity user-directed multiuser receiver with three novel schemes for allocating subarrays to users. This receiver only requires the knowledge of angles-of-Arrival (AoAs) for dominating paths and a small amount of equivalent channel information instead of perfect channel state information. For comparison, we also derive a successive interference cancellation-based solution as a performance benchmark. We design two types of reference signals with the channel estimation method to enable efficient and simple estimation for AoA and equivalent baseband channel. Also, we provide analytical results for the performance of the AoA estimation, using the lower bounds of mean square errors in line-of-sight dominated mmWave channels. The simulation results validate that the proposed channel estimation method is effective when employed in combination with a zero-forcing equalizer

The CTGF -945GC polymorphism is not associated with plasma CTGF and does not predict nephropathy or outcome in type 1 diabetes

The -945GC polymorphism (rs6918698) in the connective tissue growth factor gene promoter (CTGF/CCN-2) has been associated with end organ damage in systemic sclerosis. Because CTGF is important in progression of diabetic kidney disease, we investigated whether the -945GC polymorphism is associated with plasma CTGF level and outcome in type 1 diabetes

Noninvasive laser-induced photoacoustic tomography for structural and functional in vivo imaging of the brain

Imaging techniques based on optical contrast analysis can be used to visualize dynamic and functional properties of the nervous system via optical signals resulting from changes in blood volume, oxygen consumption and cellular swelling associated with brain physiology and pathology. Here we report in vivo noninvasive transdermal and transcranial imaging of the structure and function of rat brains by means of laser-induced photoacoustic tomography (PAT). The advantage of PAT over pure optical imaging is that it retains intrinsic optical contrast characteristics while taking advantage of the diffraction-limited high spatial resolution of ultrasound. We accurately mapped rat brain structures, with and without lesions, and functional cerebral hemodynamic changes in cortical blood vessels around the whisker-barrel cortex in response to whisker stimulation. We also imaged hyperoxia- and hypoxia-induced cerebral hemodynamic changes. This neuroimaging modality holds promise for applications in neurophysiology, neuropathology and neurotherapy