ItemNetwork Dimensioning, QoE Maximization, and Power Control for Multi-Tier Machine-Type Communications(IEEE-Institute of Electrical Electronics Engineers Inc, 2018-10-12) Han, Dong; Minn, Hlaing; Tefek, Utku; Lim, Teng Joon; 0000-0003-0774-569X (Minn, H); Han, Dong; Minn, HlaingFor a radio resource-limited multi-tier machine-type communication (MTC) network, controlling random access congestion while satisfying the unique requirements of each tier (type) and guaranteeing fairness among nodes is always a challenge. In this paper, we study the network dimensioning and radio resource partitioning for the uplink of an MTC network with the signal-to-interference ratio-based clustering and relaying, where the MTC gateways (MTCGs) capture and forward the packets sent from MTC devices (MTCDs) to the base station (BS). Specifically, under transmission outage probability constraints, we investigate the trade-off between network utility (in terms of transmission capacity and revenue) and resource allocation fairness. With both outage probability constraints and minimum MTCD density constraints, we propose approaches to maximize the weighted sum of quality of experience of different tiers of MTCDs. Furthermore, a transmit power control strategy for MTCG-to-BS link is proposed to achieve a constant data rate. ItemAngle-Domain Approach for Parameter Estimation in High-Mobility OFDM with Fully/Partly Calibrated Massive ULA(IEEE-Institute of Electrical Electronics Engineers Inc, 2018-12-04) Ge, Yinghao; Zhang, Weile; Gao, Feifei; Minn, Hlaing; 0000-0003-0774-569X (Minn, H); Minn, HlaingIn this paper, we consider a downlink orthogonal frequency division multiplexing system from a base station to a high-speed train equipped with fully/partly calibrated massive uniform linear antenna-array (ULA) in wireless environments with abundant scatterers. Multiple Doppler frequency offsets (DFOs) stemming from intensive propagation paths together with transceiver oscillator frequency offset (OFO) result in a fast time-varying frequency-selective channel. We develop an angle domain carrier frequency offset (CFO, a general designation for DFO and OFO) estimation approach. A high-resolution beamforming network is designed to separate different DFOs into a set of parallel branches in angle domain such that each branch is mainly affected by a single dominant DFO. Then, a joint estimation algorithm for both maximum DFO and OFO is developed for fully calibrated ULA. Next, its estimation mean square error performance is analyzed under inter-subarray mismatches. To mitigate the detrimental effects of inter-subarray mismatches, we introduce a calibration-oriented beamforming parameter and develop the corresponding modified joint estimation algorithm for partly calibrated ULA. Moreover, the Cramer-Rao lower bound of CFO estimation is derived. Both theoretical and numerical results are provided to corroborate the proposed method. ItemRFI Cancellation for an Array Radio Astronomy System with Receiver Nonlinearity(Institute of Electrical Electronics Engineers Inc., 2019-01-07) Abdelgelil, Mahmoud E.; Minn, Hlaing; 0000-0001-6741-9146 (Abdelgelil, M); 0000-0003-0774-569X (Minn, H); Abdelgelil, Mahmoud E.; Minn, HlaingRadio frequency interference (RFI) is an important problem for a radio astronomy system (RAS) due to the very weak radio astronomical signals. Rapid expansions of active wireless systems (AWSs), as well as more demands for spectrum access by both AWS and RAS will result in scenarios with strong RFI. This will cause RAS's low-noise amplifier (LNA) to operate in a nonlinear region and impose a more challenging nonlinear RFI issue. We address this issue for RAS with the antenna array. We develop a new signal model at the output of RAS array processing when the LNA at each RAS receiver behaves nonlinearly. We show that the two existing methods to address RFI in RAS array systems fail to deal with the nonlinear RFI. Next, we propose two modified methods to address the nonlinear RFI. Analysis of the squared error of the RAS signal correlation estimate is also presented. The numerical results show the severe effects of nonlinear RFI and the capability of the proposed methods to keep the squared error almost as low as that of a linear system. ItemPrecompensation and System Parameters Estimation for Low-Cost Nonlinear Tera-Hertz Transmitters in the Presence of I/Q Imbalance(Institute of Electrical and Electronics Engineers Inc.) Ramadan, Yahia R.; Minn, Hlaing; Abdelgelil, Mahmoud E.; 0000-0002-9907-0943 (Ramadan, YRAM); 0000-0003-0774-569X (Minn, H); Ramadan, Yahia R.; Minn, Hlaing; Abdelgelil, Mahmoud E.Tera-Hertz (THz) transmission can offer several attractive applications, yet developing low-cost energy-efficient THz devices is at an early stage. The most promising low-cost THz transmitter architecture in the literature is the so-called frequency-multiplier-last architecture. However, it is incapable of transmitting quadrature amplitude modulation (QAM) due to the architecture’s inherent nonlinear distortions. We study such nonlinear THz communication systems by incorporating the nonlinearity aspects of the low-cost THz devices and the inphase and quadrature (I/Q) imbalance effect into the signal model. Then, we propose a precompensation scheme to compensate the nonlinearity and I/Q imbalance effects, thus enabling QAMcapable frequency-multiplier-last architecture for THz systems. The proposed precompensation scheme requires the knowledge of the system parameters. To estimate the system parameters, we propose a maximum-likelihood (ML) estimator and its practical implementation via an alternating estimation algorithm. We also derive closed-form expressions for the Cramér–Rao lower bounds (CRLBs) of the system parameters estimation, and design the pilot sequence used in estimating the system parameters. Numerical results show that the proposed precompensation schemes overcome the prominent problems experienced in the existing THz systems, namely severe nonlinear distortions of the modulation symbols as well as spectral spreading and/or large spectrum sidelobes, and mitigate the I/Q imbalance effect.