12 research outputs found
Outage Analysis of Uplink Two-tier Networks
Employing multi-tier networks is among the most promising approaches to
address the rapid growth of the data demand in cellular networks. In this
paper, we study a two-tier uplink cellular network consisting of femtocells and
a macrocell. Femto base stations, and femto and macro users are assumed to be
spatially deployed based on independent Poisson point processes. We consider an
open access assignment policy, where each macro user based on the ratio between
its distances from its nearest femto access point (FAP) and from the macro base
station (MBS) is assigned to either of them. By tuning the threshold, this
policy allows controlling the coverage areas of FAPs. For a fixed threshold,
femtocells coverage areas depend on their distances from the MBS; Those closest
to the fringes will have the largest coverage areas. Under this open-access
policy, ignoring the additive noise, we derive analytical upper and lower
bounds on the outage probabilities of femto users and macro users that are
subject to fading and path loss. We also study the effect of the distance from
the MBS on the outage probability experienced by the users of a femtocell. In
all cases, our simulation results comply with our analytical bounds
MU-Massive MIMO with Multiple RISs: SINR Maximization and Asymptotic Analysis
In this letter, we investigate the signal-to-interference-plus-noise-ratio
(SINR) maximization problem in a multi-user massive
multiple-input-multiple-output (massive MIMO) system enabled with multiple
reconfigurable intelligent surfaces (RISs). We examine two zero-forcing (ZF)
beamforming approaches for interference management namely BS-UE-ZF and
BS-RIS-ZF that enforce the interference to zero at the users (UEs) and the
RISs, respectively.Then, for each case, we resolve the SINR maximization
problem to find the optimal phase shifts of the elements of the RISs. Also, we
evaluate the asymptotic expressions for the optimal phase shifts and the
maximum SINRs when the number of the base station (BS) antennas tends to
infinity. We show that if the channels of the RIS elements are independent and
the number of the BS antennas tends to infinity, random phase shifts achieve
the maximum SINR using the BS-UE-ZF beamforming approach. The simulation
results illustrate that by employing the BS-RIS-ZF beamforming approach, the
asymptotic expressions of the phase shifts and maximum SINRs achieve the rate
obtained by the optimal phase shifts even for a small number of the BS
antennas.Comment: Accepted for publication in IEEE Wireless Communications Letter
Energy-Efficient Mobility-Aware Caching Algorithms for Clustered Small Cells in Ultra-Dense Networks
Stochastic Modeling of Beam Management in mmWave Vehicular Networks
Mobility management is a major challenge for millimeter-wave (mmWave) cellular networks. In particular, directional beamforming in mmWave devices renders high-speed mobility support very complex. This complexity, however, is not limited to system design but also the performance estimation and evaluation. Hence, some have turned their attention to stochastic modeling of mmWave vehicular communication to derive closed-form expressions that can characterize the coverage and rate behavior of the network. In this article, we model and analyze the beam management for mmWave vehicular networks. To the best of our knowledge, this is the first work that goes beyond coverage and rate analysis. Specifically, we focus on a multi-lane divided highway scenario in which base stations and vehicles are present on both sides of the highway. In addition to providing analytical expressions for the average number of beam switching and handover events, we provide design insights for the operators to fine-tune their network through more informed choice of system parameters, including the number of resources dedicated to channel feedback and beam alignment operations