This letter studies the performance of the line-ofsight underground mine channel in the millimeter wave band. Using a vector network analyzer (VNA) and three carefully chosen antennas, one omni and two horn antennas, we performed measurements at the 40 and 70 m levels in the CANMET mine located in Val-d'Or, Canada. The performance of the channel is studied in terms of its path loss exponent, shadowing and capacity. Results prove that the path loss exponent in an underground mine is smaller than the free space value. The shadow fading fits very well with the normal distribution. A model of the capacity as a function of the distance between transmitter and receiver is investigated. Channel capacity depends on the multipath characteristics; the capacity found in the narrow environment (70 m) is higher than in the wider environment (40 m). The results also show that it is better to use omnidirectional antennas for a wireless communication system in the millimeter wave band in an underground mine environment.
In this paper, we provide an analytical performance assessment of downlink non-orthogonal multiple access (NOMA) systems over Nakagami-m fading channels in the presence of nonlinear high-power amplifiers (HPAs). By modeling the distortion of the HPA by a nonlinear polynomial model, we evaluate the performance the NOMA scheme in terms of outage probability (OP) and ergodic sum rate. Hence, we derive a new closed-form expression for the exact OP, taking into account the undesirable effects of HPA. Furthermore, to characterize the diversity order of the considered system, the asymptotic OP in the high signal-to-noise (SNR) regime is derived. Moreover, the ergodic sum rate is investigated, resulting in new upper and lower bounds. Our numerical results demonstrate that the performance loss in presence of nonlinear distortions is very substantial at high data rates. In particular, it is proved that in presence of HPA distortion, the ergodic sum rate cannot exceed a determined threshold which limits its performance compared to the ideal hardware case. Monte-Carlo simulations are conducted and their results agree well with the analytical results. INDEX TERMS non-orthogonal multiple access (NOMA), high-power amplifiers (HPA), nonlinear polynomial model, outage probability (OP), ergodic sum rate.
This paper presents a new algebraic carrier frequency offset (CFO) estimation technique for multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) system, to overcome the sensitivity of algebraic space-time codes (ASTCs) to frequency synchronization in quasi-static correlated Rayleigh frequency-selective fading channels. The technique uses a preamble and is thus particularly suitable for burst-mode communications. The preamble consists of orthogonal training sequences that are simultaneously transmitted from the various transmit antennas. The proposed system exploits all subcarriers in the frequency domain, which provides a remarkable performance improvement, and reaches the Cramer-Rao lower bound (CRLB) at a high signal-to-noise ratio. The proposed method is compared with three known CFO estimators in the literature: Cyclic-Prefix-based (CP), Moose, and Classen techniques that show clear advantage
In this paper, a non‐orthogonal multiple access (NOMA) scheme is considered for downlink millimeter‐wave (mmWave) transmissions over beamspace massive multiple‐input multiple‐output (MIMO) channels. To improve the NOMA detection and reduce its complexity, it is assumed that users are grouped in clusters. The major benefit of the NOMA depends on the power allocation (PA) among users. In this context, to ensure the quality of service (QoS) of users, a threshold rate for each user is defined. The aim of this work is to propose a new PA strategy that takes into account the pre‐defined threshold rates and maximizes the achievable sum rate. Thereafter, considering the Karush‐Kuhn‐Tucker (KKT) conditions, a closed‐form solution for the PA issue under perfect and imperfect channel state information (CSI) assumptions is derived. Through simulation results, it is shown that the proposed scheme outperforms the conventional orthogonal multiple access techniques in terms of spectral efficiency (SE) and energy efficiency (EE). In addition, the proposed robust PA scheme for the imperfect CSI case reduces the performance loss due to the channel uncertainty.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.