Faculty Publications
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Item Non-orthogonal full rank space-time block codes over Eisenstein-Jacobi integers for MIMO systems(Institute of Electrical and Electronics Engineers Inc., 2017) Raghavendra, R.; G.D., G.S.; Shripathi Acharya, U.In this work we present a full rank Space Time Block Codes with Non-orthogonal designs designated as NSTBCs constructed from cyclic codes over GF(qm). Rank-Preserving Eisenstein-Jacobi map is employed to map the codewords over finite field to codewords over complex field. A generalized procedure for designing NSTBCs for MIMO system containing Nt Transmit antennas and Nr receive antennas is obtained. The computational complexity of the MIMO system employing the presented NSTBC with ML detection has been derived and an upper bound on the average probability of error is presented. It is shown that under quasi-static Rayleigh flat fading channel conditions at an ABER of 10-4 the proposed NSTBC MIMO system provides a gain of approximately 3 dB in compared with C (4,2,4) code. © 2017 IEEE.Item Modified signal design for multistream spatial modulation over spatially correlated channels(Institute of Electrical and Electronics Engineers Inc., 2017) G.D., G.S.; Koila, K.; Raghavendra, R.; Sripati, U.In this paper, we describe a modified signal design for Multistream Spatial Modulation (MSM). The fundamental idea behind MSM is to activate multiple antennas and transmit complex symbols along with active antenna indices. Here, a modified MSM technique explicitly designed to combat the effect of spatial correlation in realistic channel scenarios is proposed. In this MSM scheme, two antennas are made active all the time, mapping for antenna selection is judiciously adopted from primary and secondary constellation points. Secondary constellations are obtained through single geometric interpolation of the primary constellation points. Simulation studies show that for a fixed number of antenna combinations and spectral efficiency, the proposed scheme produces a performance improvement of at least 4 dB at a ABER of 10-5 over all traditional Spatial Modulation (SM) systems, more specifically Enhanced Spatial Modulation (ESM), Quadrature Spatial Modulation (QSM) and Double Spatial Modulation (DSM) systems when employed over dense spatially correlated channels. Furthermore, an upper bound on the average bit error probability (ABEP) for the modified MSM scheme has been derived and quantified. Monte Carlo simulation results corroborate the close correspondence between analytical and the obtained simulation results. © 2017 IEEE.Item Abelian codes over Eisenstein-Jacobi integers for MIMO systems(Institute of Electrical and Electronics Engineers Inc., 2017) Raghavendra, R.; G.D., G.S.; Udupi, S.In this work we present construction of Space Time Block Codes (STBC) from Abelian codes. A well known Eisenstein-Jacobi rank preserving map is applied to map the codeword matrix symbols to symbols in the complex plane. We then propose an NT X NR MIMO (multiple input, multiple output) communication system employing the constructed STBC. An analysis on the receiver (decoder) computational complexity and an upper bound on the average probability of error is presented. Performance of the proposed system is evaluated for a 4 X 2 MIMO system. Simulation results show that at an average bit error rate (ABER) of 10-4 the STBC over F7 result in a coding gain of approximately 4 dB as compared to C(4; 2; 4) code. © 2017 IEEE.Item Redesigned Spatial Modulation for Spatially Correlated Fading Channels(Springer New York LLC barbara.b.bertram@gsk.com, 2017) G.D., G.S.; Koila, K.; Neha, N.; Raghavendra, R.; Sripati, U.In this paper, a new variant of Spatial Modulation (SM) Multiple-Input Multiple-Output (MIMO) transmission technique, designated as Redesigned Spatial Modulation (ReSM) has been proposed. In ReSM scheme, a dynamic mapping for antenna selection is adopted. This scheme employs both single antenna as well as double antenna combinations depending upon channel conditions to combat the effect of spatial correlation. When evaluated over spatially correlated channel conditions, for a fixed spectral efficiency and number of transmit antennas, ReSM exhibits performance improvement of at least 3 dB over all the conventional SM schemes including Trellis Coded Spatial Modulation (TCSM) scheme. Furthermore, a closed form expression for the upper bound on Pairwise Error Probability (PEP) for ReSM has been derived. This has been used to calculate the upper bound for the Average Bit Error Probability (ABEP) for spatially correlated channels. The results of Monte Carlo simulations are in good agreement with the predictions made by analytical results. The relative gains of all the comparison plots in the paper are specified at an ABER of 10?4. © 2017, Springer Science+Business Media, LLC.Item A comprehensive framework for Double Spatial Modulation under imperfect channel state information(Elsevier B.V., 2017) G.D., G.S.; Koila, K.; Raghavendra, R.; Shripathi Acharya, U.The essential requirement for a 5G wireless communication system is the realization of energy efficient as well as spectrally efficient modulation schemes. Double Spatial Modulation (DSM) is a recently proposed high rate Index Modulation (IM) scheme, designed for use in Multiple Input Multiple Output (MIMO) wireless systems. The aim of this scheme is to increase the spectral efficiency of conventional Spatial Modulation (SM) systems while keeping the energy efficiency intact. In this paper, the impact of imperfect channel knowledge on the performance of DSM system under Rayleigh, Rician and Nakagami-m fading channels has been quantified. Later, a modified low complexity decoder for the DSM scheme has been designed using ordered block minimum mean square error (OB-MMSE) criterion. Its performance under varied fading environments have been quantified via Monte Carlo simulations. Finally, a closed form expression for the pairwise error probability (PEP) for a DSM scheme under conditions of perfect and imperfect channel state information has been derived. This is employed to calculate the upper bound on the average bit error probability (ABEP) over aforementioned fading channels. It is observed that, under perfect and imperfect channel conditions DSM outperforms all the other variants of SM by at least 2dB at an average bit error ratio (ABER) of 10?5. Tightness of the derived upper bound is illustrated by Monte Carlo simulation results. © 2017 Elsevier B.V.Item Signal constellations employing multiplicative groups of Gaussian and Eisenstein integers for Enhanced Spatial Modulation(Elsevier B.V., 2017) G.D., G.S.; Raghavendra, R.; Koila, K.; Shripathi Acharya, U.In this paper, we propose two new signal constellation designs employing Gaussian and Eisenstein Integers for Enhanced Spatial Modulation (ESM). ESM is a novel technique which was propounded by Cheng et al. The advantage of ESM over other Spatial Modulation (SM) schemes lies in its ability to enhance spectral efficiency while keeping the energy efficiency intact. This is done by activating either one or two antennas judiciously depending upon the required trade-off. In ESM, information radiated from the antennas depends upon index of the active transmit antenna combination(s) and also on the set of constellation points chosen, which may include points from multiple constellations. In this paper, we propose signal constellations based on multiplicative groups of Gaussian and Eisenstein integers. The set comprising of Gaussian and Eisenstein integers serves as primary and secondary constellation points for Gaussian Enhanced Spatial Modulation (GESM) scheme. The secondary constellation points are deduced from a single geometric interpolation from the primary constellation points. The Monte Carlo simulation results indicate that the proposed nonuniform constellations achieve impressive SNR gains compared to conventional constellation points used in the design of ESM. This new design has been described for MIMO employing 4 × 4 and 8 × 8 antenna configurations with only two active antennas. Furthermore, a closed form expression for the pairwise error probability (PEP) for the GESM scheme has been deduced. The PEP is utilized to determine the upper bound on the average bit error probability (ABEP). Our simulations indicate that the proposed GESM from Gaussian and Eisenstein integers scheme outperforms all the other variants of SM including conventional ESM by at least 2.5 dB at an average bit error ratio (ABER) of 10?5. Close correspondence between the theoretical analysis and the Monte Carlo simulation results are observed. © 2017 Elsevier B.V.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 A new deep learning architecture for dehazing of aerial remote sensing images(Springer, 2022) Kalra, A.; Sequeira, A.; Manjunath, A.; Lal, S.; Raghavendra, R.A major problem in most aerial remote image processing applications is the presence of haze in images. It is a phenomenon by which particles in the atmosphere disperse light, thus altering the quality of the overall image. This can be detrimental to the performance of vision-based algorithms such as those concerned with object detection. There have been numerous attempts using traditional image processing techniques as well as using deep learning approaches to eliminate this haze. In most cases, models tend to make assumptions on the nature of haze that are rarely true in reality. In this paper, we propose an end-to-end deep learning architecture that can dehaze aerial remote sensing images efficiently with minimal deviation from the ground truth. Many of the assumptions made in other models are eliminated and the relationship between hazed and dehazed images is directly computed. The proposed model is based on the observation that identifying structural and statistical portions separately from an image and using those features to reconstruct the image can give a realistic dehazed image. It also makes use of information exposed by different color spaces to achieve this using lesser computation. The experimental quantitative and qualitative results of the proposed architecture are compared with recent benchmark dehaze models on NYU hazy dataset and real-world hazy images. Experimental results yield that the proposed architecture outperforms benchmark models on test aerial remote sensing images. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.