arXiv subjects

Rajan Shrestha

Publications and source records attributed to Rajan Shrestha.

2 recordsLinked to original sources

arXiv2026

Elevation-Aware Supplementary Uplink for Direct Satellite-to-Device Communications

Direct satellite-to-device (DS2D) communication enables standard mobile devices to connect directly to low Earth orbit (LEO) satellites, providing global coverage without reliance on terrestrial infrastructure. However, the DS2D uplink is fundamentally constrained by long propagation distances, severe path loss, and stringent user equipment (UE) power limits, making uplink reliability particularly challenging at low elevation angles and beam edges. This paper investigates the integration of supplementary uplink (SUL) technology into DS2D systems to enhance uplink robustness while preserving UE power efficiency. Leveraging the predictable geometry of LEO satellite orbits, we develop an elevation-aware SUL framework that adapts uplink operation across frequency bands based on elevation-dependent link margin estimates. The proposed approach schedules the UE to transmit on either a primary uplink carrier or a lower-frequency SUL carrier. An elevation-aware SUL activation algorithm with hysteresis is introduced to guide uplink carrier selection while preventing frequent switching. Simulation results demonstrate that the proposed SUL framework extends effective uplink coverage toward low-elevation and beam-edge regions, improves uplink availability over a satellite pass, and achieves stable operation with a minimal number of uplink transitions under realistic UE power constraints.

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arXiv2020

Exploiting Cell-Free Massive MIMO for Enabling Simultaneous Wireless Information and Power Transfer

The performance of simultaneous wireless information and power transfer (SWIPT) in downlink (DL) cell-free massive multiple-input multiple-output (MIMO) is investigated. Tight approximations to the DL harvested energy and the DL/uplink (UL) achievable rates are derived for two practical channel state information (CSI) cases by using a non-linear energy harvesting model for time-switching and power-splitting protocols. Max-min fairness-based transmit power control policies are employed to mitigate the deleterious near-far effects caused by distributed transmissions/receptions in cell-free massive MIMO. The achievable common DL energy-rate trade-off is derived, and thereby, it is shown that the proposed max-min power control guarantees user-fairness regardless of near-far effects in terms of both harvested energy and achievable rate. The benefits of user estimated DL CSI to boost the SWIPT performance are explored. These performance metrics are compared against those of the conventional co-located massive MIMO, and thereby, it is revealed that the reduction of path-losses and lower average transmit powers offered by cell-free massive MIMO can be exploited to boost the energy-rate trade-off of SWIPT at the expense of increased backhaul requirements.

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