Browsing by Author "Rashmi, H."

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Geometry-based stochastic channel modeling of a semi-urban environment using simultaneously transmitting and reflecting reconfigurable intelligentsurface
(Elsevier B.V., 2024) Rashmi, H.; Chaturvedi, A.; D'Souza, J.
Simultaneously Transmitting and Reflecting (STAR) Reconfigurable Intelligent Surface (RIS) demonstrates the ability to split incoming electromagnetic beams to transmit and reflect signals in a concurrent manner. Thus, compared to conventional RIS, service area coverage is extended on deploying STAR-RIS. This paper presents a geometry-based stochastic channel model (GBSM) of STAR-RIS-assisted outdoor wireless channel. For the considered semi-urban environment, STAR-RIS operates in energy-splitting mode. Channel between a base station (BS) and users (UR/UT) located on the reflect/transmit (R/T) side of STAR-RIS is characterised using a GBSM. An elliptical model incorporates the inevitable presence of scatterers in the considered semi-urban segment. Statistical properties of the wireless channel under test are analysed using space–time cross-correlation function (ST-CCF) and temporal auto-correlation function (ACF). Further, to gain holistic insight about the wireless channel behaviour, normalised Doppler power spectral density (ND-PSD) is estimated for semi-urban segment having three distinct underlying hypothesis as: (i) Wireless channel is governed by Rayleigh fading model, (ii) Wireless Channel is equipped with conventional RIS and (iii) STAR-RIS is an integral part of the considered wireless channel. Simulation results confirm that STAR-RIS performs at par with RIS, however, facilitating an additional degree of coverage. It is observed that temporal ACF and ST-CCF improves with an increase in the number of elements in STAR-RIS. © 2024 Elsevier B.V.
Performance Analysis of Eigendecomposition-based GFDM in Generalized Î±-Î¼ Fading Channels for 5G/6G Wireless Communication Applications
(Institute of Electrical and Electronics Engineers Inc., 2024) Bodempudi, N.S.; Rashmi, H.; Chaturvedi, A.
Generalized frequency division multiplexing (GFDM) offers more flexibility in choosing subsymbols, subcarriers, and pulse-shaping filters for efficient data transmission. Due to inherent non-orthogonality, GFDM produces intrinsic self-interference, namely inter-subsymbol interference (ISI) and inter-subcarrier interference (ICI). An Eigendecomposition-based GFDM (ED-GFDM) utilizes a matched filter (MF) receiver, this architecture can mitigate self-interference without any noise enhancement. Nevertheless, in wireless channels, the propagation of ED-GFDM is affected by channel characteristics like nonlinearity and non-homogeneity. Usually, a generalized Î±-Î¼ fading channel is modeled to capture the channel characteristics in terms of fading parameters Î± and Î¼. Specific combinations of Î± and Î¼ result in various fading environments like Rayleigh, Exponential, Nakagami-m, etc. This paper aims to derive accurate closed-form expressions for Symbol Error Rate (SER) and ergodic channel capacity for ED-GFDM using M-PSK modulation with a MF receiver. Obtained simulation results are analyzed and validated with the expected theoretical results. Â© 2024 IEEE.
Stochastic channel modelling of cooperative STAR-RIS-assisted wireless channels
(Taylor and Francis Ltd., 2025) Rashmi, H.; Chaturvedi, A.; Bodempudi, N.S.P.; D'Souza, J.
Insight into a wireless channel using a geometry-based three-dimensional (3D) channel model and its stochastic characterization is given in this paper. It is considered that the outdoor wireless channel is equipped with cooperative double (CODE), simultaneously transmitting and reflecting a reconfigurable intelligent surface (STAR-RIS). Other system elements include multiple-input multiple-output (MIMO) system realized using a transmitter (Tx), two distributed STAR-RISs and two users, (Formula presented.) and (Formula presented.). To use the advantage of (Formula presented.) coverage area of STAR-RIS, users are positioned on transmit-side ((Formula presented.)) and reflect-side ((Formula presented.)) of STAR-RIS. It is presumed that STAR-RIS operates with the energy splitting (ES) protocol as the underlying mechanism. Space-time cross-correlation function (ST-CCF) is an important time-domain performance measure to characterize a wireless channel. ST-CCF is estimated for parametric variations in the normalized antenna spacing of Tx, (Formula presented.) / (Formula presented.), position of STAR-RIS, array size of the STAR-RIS and its orientation with respect to the azimuth plane. Simulation results are analyzed in terms of leverage from cooperative STAR-RIS deployment and its practical inferences. © 2025 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.