Faculty Publications
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Item Non-orthogonal space–frequency block codes from cyclic codes for wireless systems employing MIMO-OFDM with index modulation(Elsevier B.V., 2019) Raghavendra, R.; Shripathi Acharya, U.S.Space–frequency codes (SFC) having error correcting structure can be used to enhance the bit error rate (BER) performance of modern wireless systems (5G and beyond) employing multiple-input multiple-output (MIMO) and multi-carrier communication. In this work, the construction of non-orthogonal space–frequency block codes (NSFBC) from (n,k) cyclic codes has been proposed. In which, n represents the number of symbols in the codeword and k represents the number of symbols in the information sequence. The performance of proposed codes has been evaluated in MIMO systems employing orthogonal frequency division multiplexing and index modulation (MIMO-OFDM-IM). We initially obtained (n,k) full rank cyclic codes for any 1 q m . Further, NSFBCs are obtained from full rank codes using Rank preserving maps. In a 2 × 2 system and a 10-path MIMO channel, the proposed full rank NSFBC with rank-preserving IM mapping (FR-NSFBC-IM), over F 5 2 , provides he similar BER performance when compared to MIMO-OFDM-IM system with Rate-1 Alamouti code and QPSK. Moreover, it provides an improvement in spectral efficiency of about 0.9 b/s/Hz. When compared to the MIMO-OFDM-IM with BPSK, FR-NSFBC-IM codes over F 5 2 provide an asymptotic SNR gain of about 1 dB and also the spectral efficiency has been improved by about 0.6 b/s/Hz. In the 4 × 4 scenario, full rank NSFBCs over F 5 4 with rank deficient IM mapping (RD-NSFBC-IM) provide an improvement in spectral efficiency of about 1.3 b/s/Hz. However, BER performance is similar to that of MIMO-OFDM-IM with BPSK. © 2019Item Spatially Modulated Non Orthogonal Space Time Block Code: Construction and design from cyclic codes over Galois Field(Elsevier B.V., 2019) Godkhindi Shrutkirthi, G.S.; G.D., G.S.; Shripathi Acharya, U.S.A new class of non-binary Spatially Modulated Non-orthogonal Space Time Block Code designs (SM-NSTBC) has been proposed. These designs employ full rank, length n,(n|qm?1,m?n) cyclic codes defined over GF(qm). The underlying cyclic code constructions have the property that the codewords when viewed as m×n matrices over GF(q) have rank equal to m (Full rank). These codes are punctured to yield m×m full rank matrices over GF(q). Rank preserving transformations are used to map the codewords of full rank codes over a finite field to full rank Space Time Block Codes. The proposed scheme can be generalized to handle any number of transmit antenna greater than two. Due to the characteristics of Full rank cyclic codes employed, a coding gain of approximately 1.5 dB to 5 dB is obtained over conventional STBC-SM and SM-OSTBC schemes. This is demonstrated for spectral efficiencies of 4, 5, 7 and 8 bpcu. Analytical as well as Monte-Carlo simulations show that proposed SM-NSTBC outperforms STBC-SM and its variants. The upper bound on average bit error rate has been derived and the computation complexity for ML detection has been estimated. © 2019Item Generalized designs for precoded receive spatial modulation derived from non-orthogonal space time block codes(Springer, 2022) Shashikant, S.G.; G.D., G.D.G.; Shripathi Acharya, U.S.In this paper, a new MIMO scheme termed as precoded Spatially Modulated Non-orthogonal Space Time Block Code (precoded SM-NSTBC) is proposed. The primary concept of precoded SM-NSTBC is to activate a subset of receive antennas in a pre-defined manner and choose specific activated patterns to represent information symbols. We have synthesized schemes derived from full rank Cyclic codes defined over Galois field Rank preserving transformations are used to map the full rank codewords over a finite field to full rank Space Time Block Codes. Due to the characteristics of full rank Cyclic codes employed, a performance improvement of approximately 2 dB to 7 dB is observed. This advantage is realized when the performance of these schemes is compared with precoded SM-OSTBC and precoded STBC-SM. The improvement due to the coding gain is observed in both uncorrelated as well as correlated Rayleigh fading environments. An upper bound on the average bit error rate (ABER) is derived. Close correspondence between Monte-Carlo simulations and analytic values are observed. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Item Performance investigation of underwater wireless optical system for image transmission through the oceanic turbulent optical medium(Springer, 2022) Naik, R.P.; Shripathi Acharya, U.S.; Lal, S.; Krishnan, P.The importance of resources contained in the sea and on the sea floor is increasing with each passing day. Hence, exploration of the sea and sea floor has become a very important requirement. Underwater imaging is a science that has gained importance over the past two decades. Underwater images indicate the state of sea floor and transmitting such images through the harsh and turbulent oceanic medium can cause deterioration of the information contained in the image due to diminished color reproduction, low contrast and blur. In this paper, we have performed the simulation studies to understand perturbations induced during the transmission of sea floor images using high-speed optical signaling through the underwater channels. The transmitted irradiance often suffers from underwater turbulence and beam attenuation. The bit error rate (BER) of the system proposed to transmit information through channels has been determined through analytic means and validated through Monte-Carlo simulation. Comparison between the transmitted and received images in the presence of turbulence and attenuation have been presented. The BER performance of the proposed system is evaluated in the presence of beam attenuation and underwater turbulence. The turbulence induced errors are minimized using the transmit/receive diversity and multiple input multiple output (MIMO) techniques. In addition to the diversity techniques, median and adaptive median filters used to minimize the distortion in the received image. The BER results show that the 4 × 5 MIMO system gains 19.50 dB of transmit power at BER of 10 - 5, when compared with the single input single output system. Similarly, an improvement of at-least 18 dB peak signal to noise ratio obtain using the adaptive median filter based system over the un-filter based system. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Item Performance Analysis of MIMO-EGC System for the Underwater Vertical Wireless Optical Communication Link(Institute of Electrical and Electronics Engineers Inc., 2023) Savidhan Shetty, S.C.S.; Naik, R.P.; Shripathi Acharya, U.S.; Chung, W.-Y.In this paper, we have investigated the performance of an underwater vertical wireless optical communication (UVWOC) link employing multiple input-multiple output (MIMO) operating in conjunction with equal gain combing (EGC) techniques perturbed by weak and strong turbulence in the presence of pointing errors and attenuation losses. Vertical underwater turbulence, which varies from layer to layer due to temperature and salinity variation connected to depth, is modeled using hyperbolic tangent log-normal (HTLN) distribution in the case of weak underwater turbulence and gamma-gamma (GG) distribution in the case of strong underwater turbulence. Novel closed-form expressions quantifying the average bit error rate (BER) have been derived for the UVWOC MIMO EGC system for weak and strong turbulence regimes. The expression for the average BER associated with the UVWOC link for different values of pointing error, differing vertical layer depth, modulation types, and differing numbers of sources and detectors have been determined. In addition, closed-form expressions for the outage probability (OP) and ergodic channel capacity (ECC) have been derived for the UVWOC MIMO EGC system. The accuracy of all closed-form expressions derived in the paper has been verified using Monte Carlo simulations. © 2013 IEEE.