Stochastic Analysis of Satellite Broadband by Mega-Constellations with Inclined LEOs

As emerging massive constellations are intended to provide seamless connectivity for remote areas using hundreds of small low Earth orbit (LEO) satellites, new methodologies have great importance to study the performance of these networks. In this paper, we derive both downlink and uplink analytical expressions for coverage probability and data rate of an inclined LEO constellation under general fading, regardless of exact satellites' positions. Our solution involves two phases as we, first, abstract the network into a uniformly distributed network. Secondly, we obtain a new parameter, effective number of satellites, for every user's latitude which compensates for the performance mismatch between the actual and uniform constellations. In addition to exact derivation of the network performance metrics, this study provides insight into selecting the constellation parameters, e.g., the total number of satellites, altitude, and inclination angle.Comment: Accepted in the 31st International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC) 202

Constrained Phase Noise Estimation in OFDM Using Scattered Pilots Without Decision Feedback

In this paper, we consider an OFDM radio link corrupted by oscillator phase noise in the receiver, namely the problem of estimating and compensating for the impairment. To lessen the computational burden and delay incurred onto the receiver, we estimate phase noise using only scattered pilot subcarriers, i.e., no tentative symbol decisions are used in obtaining and improving the phase noise estimate. In particular, the phase noise estimation problem is posed as an unconstrained optimization problem whose minimizer suffers from the so-called amplitude and phase estimation error. These errors arise due to receiver noise, estimation from limited scattered pilot subcarriers and estimation using a dimensionality reduction model. It is empirically shown that, at high signal-to-noise-ratios, the phase estimation error is small. To reduce the amplitude estimation error, we restrict the minimizer to be drawn from the so-called phase noise geometry set when minimizing the cost function. The resulting optimization problem is a non-convex program. However, using the S-procedure for quadratic equalities, we show that the optimal solution can be obtained by solving the convex dual problem. We also consider a less complex heuristic scheme that achieves the same objective of restricting the minimizer to the phase noise geometry set. Through simulations, we demonstrate improved coded bit-error-rate and phase noise estimation error performance when enforcing the phase noise geometry. For example, at high signal-to-noise-ratios, the probability density function of the phase noise estimation error exhibits thinner tails which results in lower bit-error-rate

Downlink Coverage and Rate Analysis of Low Earth Orbit Satellite Constellations Using Stochastic Geometry

As low Earth orbit (LEO) satellite communication systems are gaining increasing popularity, new theoretical methodologies are required to investigate such networks' performance at large. This is because deterministic and location-based models that have previously been applied to analyze satellite systems are typically restricted to support simulations only. In this paper, we derive analytical expressions for the downlink coverage probability and average data rate of generic LEO networks, regardless of the actual satellites' locality and their service area geometry. Our solution stems from stochastic geometry, which abstracts the generic networks into uniform binomial point processes. Applying the proposed model, we then study the performance of the networks as a function of key constellation design parameters. Finally, to fit the theoretical modeling more precisely to real deterministic constellations, we introduce the effective number of satellites as a parameter to compensate for the practical uneven distribution of satellites on different latitudes. In addition to deriving exact network performance metrics, the study reveals several guidelines for selecting the design parameters for future massive LEO constellations, e.g., the number of frequency channels and altitude.Comment: Accepted for publication in the IEEE Transactions on Communications in April 202

Frequency-Selective PAPR Reduction for OFDM

We study the peak-to-average power ratio (PAPR) problem in orthogonal frequency-division multiplexing (OFDM) systems. In conventional clipping and filtering based PAPR reduction techniques, clipping noise is allowed to spread over the whole active passband, thus degrading the transmit signal quality similarly at all active subcarriers. However, since modern radio networks support frequency-multiplexing of users and services with highly different quality-of-service expectations, clipping noise from PAPR reduction should be distributed unequally over the corresponding physical resource blocks (PRBs). To facilitate this, we present an efficient PAPR reduction technique, where clipping noise can be flexibly controlled and filtered inside the transmitter passband, allowing to control the transmitted signal quality per PRB. Numerical results are provided in 5G New Radio (NR) mobile network context, demonstrating the flexibility and efficiency of the proposed method.Comment: Accepted for publication as a Correspondence in the IEEE Transactions on Vehicular Technology in March 2019. This is the revised version of original manuscript, and it is in press at the momen

Downlink and Uplink Low Earth Orbit Satellite Backhaul for Airborne Networks

Providing backhaul access for airborne networks ensures their seamless connectivity to other aerial or terrestrial users with sufficient data rate. The backhaul for aerial platforms (APs) has been mostly provided through geostationary Earth orbit satellites and the terrestrial base stations (BSs). However, the former limits the achievable throughput due to significant path loss and latency, and the latter is unable to provide full sky coverage due to existence of wide under-served regions on Earth. Therefore, the emerging low Earth orbit (LEO) Internet constellations have the potential to address this problem by providing a thorough coverage for APs with higher data rate and lower latency. In this paper, we analyze the coverage probability and data rate of a LEO backhaul network for an AP located at an arbitrary altitude above the ground. The satellites' locality is modeled as a nonhomogeneous Poisson point process which not only enables tractable analysis by utilizing the tools from stochastic geometry, but also considers the latitude-dependent density of satellites. To demonstrate a compromise on the backhaul network's selection for the airborne network, we also compare the aforementioned setup with a reference terrestrial backhaul network, where AP directly connects to the ground BSs. Based on the numerical results, we can conclude that, for low BS densities, LEO satellites provide a better backhaul connection, which improves by increasing the AP's altitude.acceptedVersionPeer reviewe

Efficiency–Throughput Trade-off of Pulsed RF Waveforms in Simultaneous Wireless Information and Power Transfer

We study the receiver efficiency–throughput trade-off in a realistic radio frequency (RF) simultaneous wireless information and power transfer (SWIPT) system. Based on the energy harvesting receiver characteristics, we propose a continuously phase-modulated pulsed RF waveform to achieve maximum receiver efficiency at any input RF power level. We study the impact of varying the duty cycle of a pulsed RF waveform on the receiver efficiency of wireless power transfer along with the throughput of information transfer, and the trade-off thereof. The experiments confirm that a phase-shift keying (PSK) modulated pulsed RF waveform yields superior receiver efficiency than other digital baseband modulations as well as multisine signals despite they are designed particularly for power transfer. However, the optimal efficiency is attained at the expense of a significant loss in throughput due to pulsed transmission, depending on the average input RF power level.Peer reviewe

Reflecting Surface Assisted Energy Harvesting with Optimized NOMA Downlink Transmissions

This paper studies an intelligent reflecting surface (IRS) assisted wireless communication system with multiple downlink data and energy harvesting users. We assume that base station uses non-orthogonal multiple access (NOMA) for transmission and downlink users employ successive interference cancellation to decode their information from the received signal. With this setting, our goal is to maximize the harvested energy at the energy harvesting users while guaranteeing the minimum rate requirements of the individual data users. We propose an alternating optimization based algorithm, where semidefinite relaxation is used to obtain the optimal beamforming design at the base station and the IRS. Specifically, an iterative rank minimization approach is used to obtain the optimal reflection phase vector at the IRS. The convergence of the proposed algorithm is also proved. Finally, the efficacy of the proposed algorithm is demonstrated with the help of simulation results.acceptedVersionPeer reviewe