Narayan Prasad

122 papers A* 2A 1B 32C 1Misc 17Journal 49Unranked 20
YearRankTypeTitle / Venue / Authors
2024 — conf
Interference Randomization in Reconfigurable Intelligent Surface aided Communications.
ICC Workshops
Narayan Prasad, Yu-Chin Ou, Tao Luo, M. Ali Tassoudji, Junyi Li, Peter Gaal
2024 J jnl
Power-Constrained Pattern Design of Reconfigurable Intelligent Surfaces.
IEEE Wirel. Commun. Lett.
Narayan Prasad, Yavuz Yapici, Tao Luo, Junyi Li, Peter Gaal
2023 B conf
Optimal Pattern Determination in Reconfigurable Intelligent Surface aided Communications.
PIMRC
Narayan Prasad, Yavuz Yapici, Tao Luo, Junyi Li, Peter Gaal
2022 J jnl
Reconfigurable intelligent surface: design the channel - a new opportunity for future wireless networks.
Digit. Commun. Networks
Miguel Dajer, Zhengxiang Ma, Leonard Piazzi, Narayan Prasad, Xiao-Feng Qi, Baoling Sheen, Jin Yang, Guosen Yue
2021 Misc conf
Channel Reconstruction in Intelligent Surface aided Communications.
COMSNETS
Narayan Prasad, Md Moin Uddin Chowdhury, Xiao-Feng Qi
2021 — conf
Channel Reconstruction with Limited Feedback in Intelligent Surface Aided Communications.
VTC Fall
Narayan Prasad, Md Moin Uddin Chowdhury, Xiao-Feng Qi
2021 — conf
IRS Aided Communication Model for Compact MIMO Systems.
ICC
Divyakumar Badheka, Narayan Prasad, Zhengxiang Ma, Leonard Piazzi, Xiao-Feng Qi
2020 Misc conf
A Decoupling Property in Low-Resolution MIMO-OFDM Systems and its Applications.
COMSNETS
Narayan Prasad, Xiao-Feng Qi
2020 J jnl
Base Station Antenna Selection for Low-Resolution ADC Systems.
IEEE Trans. Commun.
Jinseok Choi, Junmo Sung, Narayan Prasad, Xiao-Feng Qi, Brian L. Evans, Alan Gatherer
2020 J jnl
New Equivalent Model of a Quantizer With Noisy Input and Its Applications for MIMO System Analysis and Design.
IEEE Access
Arkady Molev-Shteiman, Xiao-Feng Qi, Laurence Mailaender, Narayan Prasad, Bertrand M. Hochwald
2020 A* conf
Optimizing Resolution-Adaptive Massive MIMO Networks.
INFOCOM
Narayan Prasad, Xiao-Feng Qi, Arkady Molev-Shteiman
2020 J jnl
Reconfigurable Intelligent Surface: Design the Channel - a New Opportunity for Future Wireless Networks.
CoRR
Miguel Dajer, Zhengxiang Ma, Leonard Piazzi, Narayan Prasad, Xiao-Feng Qi, Baoling Sheen, Jin Yang, Guosen Yue
2019 J jnl
Base Station Antenna Selection for Low-Resolution ADC Systems.
CoRR
Jinseok Choi, Junmo Sung, Narayan Prasad, Xiao-Feng Qi, Brian L. Evans, Alan Gatherer
2019 B conf
Channel Reconstruction via Quadratic Programming in Massive MIMO Networks.
WiOpt
Narayan Prasad, Qian Zhang, Xiao-Feng Qi
2019 J jnl
New equivalent model of quantizer with noisy input and its application for ADC resolution determination in an uplink MIMO receiver.
CoRR
Arkady Molev-Shteiman, Xiao-Feng Qi, Laurence Mailaender, Narayan Prasad, Bertrand M. Hochwald
2019 Misc conf
Optimizing Beams and Bits: A Novel Approach for Massive MIMO Base-Station Design.
ICNC
Narayan Prasad, Xiao-Feng Qi, Alan Gatherer
2018 B conf
Downlink multi-user MIMO scheduling with performance guarantees.
WiOpt
Narayan Prasad, Xiao-Feng Qi
2018 J jnl
Optimizing Beams and Bits: A Novel Approach for Massive MIMO Base-Station Design.
CoRR
Narayan Prasad, Xiao-Feng Qi, Alan Gatherer
2017 J jnl
Exploiting Dual Connectivity in Heterogeneous Cellular Networks.
CoRR
Narayan Prasad, Sampath Rangarajan
2017 B conf
Exploiting dual connectivity in heterogeneous cellular networks.
WiOpt
Narayan Prasad, Sampath Rangarajan
2017 — conf
Link packing in mmWave networks.
ICC
Yasaman Ghasempour, Narayan Prasad, Mohammad Ali Amir Khojastepour, Sampath Rangarajan
2017 Misc conf
Managing analog beams in mmWave networks.
ACSSC
Yasaman Ghasempour, Narayan Prasad, Mohammad Ali Amir Khojastepour, Sampath Rangarajan
2017 — conf
Novel combinatorial results on downlink MU-MIMO scheduling with applications.
WONS
Yasaman Ghasempour, Narayan Prasad, Mohammad Ali Amir Khojastepour, Sampath Rangarajan
2017 J jnl
Optimizing Energy Efficiency Over Energy-Harvesting LTE Cellular Networks.
IEEE Trans. Green Commun. Netw.
Hajar Mahdavi-Doost, Narayan Prasad, Sampath Rangarajan
2016 Misc conf
Analysis and evaluation of a practical downlink multiuser MIMO scheduler over LTE advanced massive MIMO systems.
ACSSC
Rob Arnott, Kengo Oketani, Narayan Prasad, Sampath Rangarajan, Patricia Wells
2016 Misc conf
Energy efficient downlink scheduling in LTE-Advanced networks.
COMSNETS
Hajar Mahdavi-Doost, Narayan Prasad, Sampath Rangarajan
2016 B conf
Optimizing energy efficiency over energy-harvesting LTE cellular networks.
ISIT
Hajar Mahdavi-Doost, Narayan Prasad, Sampath Rangarajan
2015 Misc conf
On the delay optimal user association in heterogeneous wireless networks.
ACSSC
Narayan Prasad, Vaibhav Singh, Sampath Rangarajan
2015 J jnl
Optimizing User Association and Activation Fractions in Heterogeneous Wireless Networks.
CoRR
Vaibhav Singh, Narayan Prasad, Mustafa Y. Arslan, Sampath Rangarajan
2015 B conf
Optimizing user association and activation fractions in heterogeneous wireless networks.
WiOpt
Vaibhav Singh, Narayan Prasad, Mustafa Y. Arslan, Sampath Rangarajan
2015 B conf
Standards compliant CoMP scheduling over LTE heterogeneous wireless networks.
WiOpt
Rob Arnott, A. Gurung, C. Liang, Y. Maruta, D. Pham, Narayan Prasad, Sampath Rangarajan, Patricia Wells
2014 Misc conf
A two time scale approach for coordinated multi-point transmission and reception over practical backhaul.
COMSNETS
Narayan Prasad, Mustafa Y. Arslan, Sampath Rangarajan
2014 B conf
Enhanced interference management in heterogeneous cellular networks.
ISIT
Narayan Prasad, Mustafa Y. Arslan, Sampath Rangarajan
2014 — conf
Experimental time and frequency domain MIMO channel matrix characterization versus distance for 6×28Gbaud QPSK transmission over 40×25km few mode fiber.
OFC
Neda Cvijetic, Ezra Ip, Narayan Prasad, Ming-Jun Li, Ting Wang
2014 J jnl
Exploiting Cell Dormancy and Load Balancing in LTE HetNets: Optimizing the Proportional Fairness Utility.
IEEE Trans. Commun.
Narayan Prasad, Mustafa Y. Arslan, Sampath Rangarajan
2014 — conf
Exploiting cell dormancy and load balancing in LTE HetNets: Optimizing the proportional fairness utility.
ICC
Narayan Prasad, Mustafa Y. Arslan, Sampath Rangarajan
2014 J jnl
Multiuser Scheduling in the 3GPP LTE Cellular Uplink.
IEEE Trans. Mob. Comput.
Narayan Prasad, Honghai Zhang, Hao Zhu, Sampath Rangarajan
2014 — conf
User grouping and scheduling for large scale MIMO systems with two-stage precoding.
ICC
Yi Xu, Guosen Yue, Narayan Prasad, Sampath Rangarajan, Shiwen Mao
2013 B conf
Coordinated resource allocation over heterogeneous wireless networks.
GLOBECOM
Narayan Prasad, Guosen Yue, Sampath Rangarajan
2013 J jnl
Exploiting Hybrid Channel Information for Downlink Multi-User MIMO Scheduling
CoRR
Wenzhuo Ouyang, Narayan Prasad, Sampath Rangarajan
2013 B conf
Exploiting hybrid channel information for downlink multi-user MIMO scheduling.
WiOpt
Wenzhuo Ouyang, Narayan Prasad, Sampath Rangarajan
2013 Misc conf
Iterative MMSE-SIC receiver with low-complexity soft symbol and residual interference estimations.
ACSSC
Guosen Yue, Narayan Prasad, Sampath Rangarajan
2013 J jnl
Multi-User MIMO Scheduling in the Fourth Generation Cellular Uplink.
IEEE Trans. Wirel. Commun.
Narayan Prasad, Honghai Zhang, Hao Zhu, Sampath Rangarajan
2013 Misc conf
Multi-user MIMO scheduling in the fourth generation cellular uplink.
ACSSC
Narayan Prasad, Honghai Zhang, Hao Zhu, Sampath Rangarajan
2013 Misc conf
Residual error based CSI feedback enhancement for downlink multiuser MIMO.
CISS
Guosen Yue, Narayan Prasad, Meilong Jiang, Mohammad Ali Khojastepour, Sampath Rangarajan
2012 — conf
Design of coordinated multi-point (CoMP) transmission and reception schemes for the fourth generation cellular downlink.
ACSCC
Narayan Prasad, Ali Tajer, Xiaodong Wang
2012 — conf
Downlink multiuser MIMO scheduling in LTE Advanced systems.
ICC
Guosen Yue, Narayan Prasad, Sampath Rangarajan
2012 — conf
Enhanced DFT-Based Channel Estimation for LTE Uplink.
VTC Spring
Meilong Jiang, Guosen Yue, Narayan Prasad, Sampath Rangarajan
2012 A* conf
MIMO downlink scheduling in LTE systems.
INFOCOM
Honghai Zhang, Narayan Prasad, Sampath Rangarajan
2012 J jnl
Multi-User Scheduling in the 3GPP LTE Cellular Uplink
CoRR
Narayan Prasad, Honghai Zhang, Hao Zhu, Sampath Rangarajan
2012 B conf
Multi-user scheduling in the 3GPP LTE cellular uplink.
WiOpt
Narayan Prasad, Honghai Zhang, Hao Zhu, Sampath Rangarajan
2012 J jnl
Precoder Design for Physical Layer Multicasting.
IEEE Trans. Signal Process.
Hao Zhu, Narayan Prasad, Sampath Rangarajan
2012 — conf
Precoder design for physical layer multicasting.
ICC
Hao Zhu, Narayan Prasad, Sampath Rangarajan
2012 B conf
Precoder design for weighted sum delay minimization in MIMO physical layer multicasting.
GLOBECOM
Hao Zhu, Narayan Prasad, Sampath Rangarajan
2012 — conf
Standards-compliant LTE and LTE-A uplink power control.
ICC
Honghai Zhang, Narayan Prasad, Sampath Rangarajan, Sherif Mekhail, Said Said, Rob Arnott
2011 J jnl
A Message-Passing Approach to Distributed Resource Allocation in Uplink DFT-Spread-OFDMA Systems.
IEEE Trans. Commun.
Kai Yang, Narayan Prasad, Xiaodong Wang
2011 J jnl
Adaptive antenna selection and Tx/Rx beamforming for large-scale MIMO systems in 60 GHz channels.
EURASIP J. Wirel. Commun. Netw.
Ke Dong, Narayan Prasad, Xiaodong Wang, Shihua Zhu
2011 — conf
Efficient Link Adaptation for Precoded Multi-Rank Transmission and Turbo SIC Receivers.
ICC
Meilong Jiang, Narayan Prasad, Guosen Yue, Sampath Rangarajan
2011 J jnl
Efficient combining techniques for multi-input multi-output multi-user systems employing hybrid automatic repeat request.
IET Commun.
Narayan Prasad, Xiaodong Wang
2011 B conf
Enhancing Multiuser MIMO in Practical Cellular Systems.
GLOBECOM
Narayan Prasad, Guosen Yue, Meilong Jiang, Mohammad Ali Khojastepour, Sampath Rangarajan
2011 B conf
Improving downlink multiuser MIMO throughput in LTE-advanced cellular systems.
PIMRC
Guosen Yue, Narayan Prasad, Meilong Jiang, Mohammad Ali Khojastepour, Sampath Rangarajan
2011 Misc conf
Link adaptation in LTE-A uplink with Turbo SIC receivers and imperfect channel estimation.
CISS
Meilong Jiang, Guosen Yue, Narayan Prasad, Sampath Rangarajan
2011 J jnl
Multi-User MIMO Scheduling in the Fourth Generation Cellular Uplink
CoRR
Narayan Prasad, Honghai Zhang, Hao Zhu, Sampath Rangarajan
2011 — conf
On Robust Weighted-Sum Rate Maximization in MIMO Interference Networks.
ICC
Jubin Jose, Narayan Prasad, Mohammad Ali Khojastepour, Sampath Rangarajan
2011 J jnl
Optimally Efficient Max-Log APP Demodulation in MIMO Systems.
IEEE J. Sel. Top. Signal Process.
Narayan Prasad, Khalid Kalbat, Xiaodong Wang
2011 J jnl
Precoder Design for Physical Layer Multicasting
CoRR
Hao Zhu, Narayan Prasad, Sampath Rangarajan
2011 B conf
Resource Allocation in 4G MIMO Cellular Uplink.
GLOBECOM
Narayan Prasad, Honghai Zhang, Meilong Jiang, Guosen Yue, Sampath Rangarajan
2011 — conf
Resource allocation in MIMO multi-cellular networks via submodular optimization.
ACSCC
Narayan Prasad, Honghai Zhang, Luca Venturino, Jubin Jose, Mohammad Ali Khojastepour, Sampath Rangarajan
2011 J jnl
Robust Linear Precoder Design for Multi-Cell Downlink Transmission.
IEEE Trans. Signal Process.
Ali Tajer, Narayan Prasad, Xiaodong Wang
2011 J jnl
Weighted Sum-Rate Maximization in Multi-Cell Networks via Coordinated Scheduling and Discrete Power Control.
IEEE J. Sel. Areas Commun.
Honghai Zhang, Luca Venturino, Narayan Prasad, Peilong Li, Sampath Rangarajan, Xiaodong Wang
2010 J jnl
Beamforming and rate allocation in MISO cognitive radio networks.
IEEE Trans. Signal Process.
Ali Tajer, Narayan Prasad, Xiaodong Wang
2010 J jnl
Coordinated linear beamforming in downlink multi-cell wireless networks.
IEEE Trans. Wirel. Commun.
Luca Venturino, Narayan Prasad, Xiaodong Wang
2010 J jnl
Diversity-Multiplexing Tradeoff Analysis for OFDM Systems With Subcarrier Grouping, Linear Precoding, and Linear Detection.
IEEE Trans. Inf. Theory
Narayan Prasad, Luca Venturino, Xiaodong Wang
2010 B conf
Fair rate adaptation in multiuser interference channels.
ISIT
Ali Tajer, Narayan Prasad, Xiaodong Wang
2010 J jnl
High performance static and dynamic cooperative communication protocols for the half duplex fading relay channel.
IEEE Trans. Wirel. Commun.
Narayan Prasad, Mahesh K. Varanasi
2010 J jnl
Intercell Radio Resource Management through Network Coordination for IMT-Advanced Systems.
EURASIP J. Wirel. Commun. Netw.
Young-June Choi, Narayan Prasad, Sampath Rangarajan
2010 B conf
Optimally Efficient Max-Log APP Demodulation in MIMO Systems.
GLOBECOM
Narayan Prasad, Khalid Kalbat, Xiaodong Wang
2010 J jnl
Robust Linear Precoder Design for Multi-cell Downlink Transmission
CoRR
Ali Tajer, Narayan Prasad, Xiaodong Wang
2010 — conf
Robust Transceiver Design for the Multi-User Interference Channel.
ICC
Ali Tajer, Narayan Prasad, Xiaodong Wang
2010 B conf
Robust beamforming for multi-cell downlink transmission.
ISIT
Ali Tajer, Narayan Prasad, Xiaodong Wang
2009 J jnl
An auction approach to resource allocation in uplink OFDMA systems.
IEEE Trans. Signal Process.
Kai Yang, Narayan Prasad, Xiaodong Wang
2009 J jnl
Beamforming and Rate Allocation in MISO Cognitive Radio Networks
CoRR
Ali Tajer, Narayan Prasad, Xiaodong Wang
2009 J jnl
Coordinated Scheduling and Power Allocation in Downlink Multicell OFDMA Networks.
IEEE Trans. Veh. Technol.
Luca Venturino, Narayan Prasad, Xiaodong Wang
2009 Misc conf
Design of efficient receivers for DFT-S-OFDMA systems.
CISS
Meilong Jiang, Narayan Prasad, Xiaodong Wang
2009 — conf
Distributed Beamforming and Rate Allocation in Multi-Antenna Cognitive Radio Networks.
ICC
Ali Tajer, Narayan Prasad, Xiaodong Wang
2009 B conf
Efficient Soft-Output Demodulators for the Golden Code.
GLOBECOM
Narayan Prasad, Meilong Jiang, Xiaodong Wang
2009 J jnl
Efficient receiver algorithms for DFT-spread OFDM systems.
IEEE Trans. Wirel. Commun.
Narayan Prasad, Shuangquan Wang, Xiaodong Wang
2009 J jnl
Fair-rate allocation in multiuser OFDM-SDMA networks.
IEEE Trans. Signal Process.
Narayan Prasad, Kai Li, Xiaodong Wang
2009 J jnl
Key Enabling Physical Layer Technologies for LTE-Advanced.
IEICE Trans. Commun.
Meilong Jiang, Narayan Prasad, Yan Xin, Guosen Yue, Amir Khojastepour, Le Liu, Takamichi Inoue, Kenji Koyanagi, Yoshikazu Kakura
2009 C conf
Network-Assisted Radio Resource Management for Cell-Edge Performance Enhancement .
QSHINE
Young-June Choi, Narayan Prasad, Sampath Rangarajan
2009 J jnl
Outage minimization and rate allocation for the multiuser Gaussian interference channels with successive group decoding.
IEEE Trans. Inf. Theory
Narayan Prasad, Xiaodong Wang
2008 Misc conf
A successive convex approximation algorithm for weighted sum-rate maximization in downlink OFDMA networks.
CISS
Luca Venturino, Narayan Prasad, Xiaodong Wang
2008 J jnl
An Analysis of the MIMO-SDMA Channel With Space-Time Orthogonal and Quasi-Orthogonal User Transmissions and Efficient Successive Cancellation Decoders.
IEEE Trans. Inf. Theory
Narayan Prasad, Mahesh K. Varanasi, Luca Venturino, Xiaodong Wang
2008 B conf
An Auction Approach to Resource Allocation in Uplink Multi-Cell OFDMA Systems.
GLOBECOM
Kai Yang, Narayan Prasad, Xiaodong Wang
2008 J jnl
An optimization approach to decision feedback detection under modulation constraints for MIMO fading channels.
IEEE Trans. Wirel. Commun.
Narayan Prasad, Mahesh K. Varanasi
2008 J jnl
Analysis and Optimization of Diagonally Layered Lattice Schemes for MIMO Fading Channels.
IEEE Trans. Inf. Theory
Narayan Prasad, Mahesh K. Varanasi
2008 — conf
Coordinated linear beamforming in downlink multi-cell wireless networks.
ACSCC
Luca Venturino, Narayan Prasad, Xiaodong Wang
2008 J jnl
Design of Spherical Lattice Space-Time Codes.
IEEE Trans. Inf. Theory
Narayan Prasad, Inaki Berenguer, Xiaodong Wang
2008 J jnl
Interference Suppression Receivers for the Cellular Downlink Channel.
IEEE J. Sel. Areas Commun.
Narayan Prasad, Xiaodong Wang
2008 J jnl
Optimal Successive Group Decoders for MIMO Multiple-Access Channels.
IEEE Trans. Inf. Theory
Narayan Prasad, Guosen Yue, Xiaodong Wang, Mahesh K. Varanasi
2008 B conf
Outage Minimization and Fair Rate Allocation in Gaussian Interference Channels.
GLOBECOM
Narayan Prasad, Xiaodong Wang
2008 B conf
Outage minimization and fair rate allocation for the multiple access relay channel.
ISIT
Narayan Prasad, Xiaodong Wang
2008 J jnl
Quantized Multi-Rank Beamforming for MIMO-OFDM Systems.
IEEE J. Sel. Areas Commun.
Mohammad Ali Khojastepour, Narayan Prasad, Shuangquan Wang, Xiaodong Wang, Mohammad Madihian
2008 Misc conf
Quantized multi-rank beamforming for MIMO systems.
CISS
Mohammad Ali Khojastepour, Narayan Prasad, Shuangquan Wang, Xiaodong Wang, Mohammad Madihian
2007 J jnl
An Enhanced Deterministic Sequential Monte Carlo Method for Near-Optimal MIMO Demodulation With QAM Constellations.
IEEE Trans. Signal Process.
Pradeep Aggarwal, Narayan Prasad, Xiaodong Wang
2007 B conf
Analysis of Multiuser Stacked Space-time Orthogonal and Quasi-orthogonal Designs.
ISIT
Narayan Prasad, Luca Venturino, Xiaodong Wang, Mohammad Madihian
2007 J jnl
Design of Linear Dispersion Codes for Practical MIMO-OFDM Systems.
J. Sel. Topics Signal Processing
Luca Venturino, Narayan Prasad, Xiaodong Wang, Mohammad Madihian
2007 B conf
Diversity-Multiplexing Trade-Off Analysis of OFDM Systems with Linear Detectors.
GLOBECOM
Narayan Prasad, Luca Venturino, Xiaodong Wang, Mohammad Madihian
2007 — conf
Optimizing Linear Dispersion Codes for Wideband MIMO Systems.
ICC
Luca Venturino, Narayan Prasad, Xiaodong Wang, Mohammad Madihian
2006 Misc conf
An Enhanced Deterministic Sequential Monte Carlo Method for Near-Optimal MIMO Demodulation.
CISS
Pradeep Aggarwal, Narayan Prasad, Xiaodong Wang
2006 B conf
Design of optimal lattice space-time codes.
ISIT
Narayan Prasad, Inaki Berenguer, Xiaodong Wang, Mohammad Madihian
2006 B conf
High Performance Static and Dynamic Cooperative Communication Protocols for the Half Duplex Fading Relay Channel.
GLOBECOM
Narayan Prasad, Mahesh K. Varanasi
2006 Misc conf
Optimal successive group decoder for the slow-fading multiple access channel.
CISS
Narayan Prasad, Guosen Yue, Mohammad Amir Khojastepour, Xiaodong Wang, Mohammad Madihian
2006 J jnl
Outage Theorems for MIMO Block-Fading Channels.
IEEE Trans. Inf. Theory
Narayan Prasad, Mahesh K. Varanasi
2006 B conf
Throughput analysis for MIMO systems in the high SNR regime.
ISIT
Narayan Prasad, Mahesh K. Varanasi
2005 B conf
Design of minimium-error-rate lattice (space-time) codes via stochastic optimization and gradient estimation.
GLOBECOM
Inaki Berenguer, Xiaodong Wang, Narayan Prasad, Jibing Wang, Mohammad Madihian
2005 B conf
MIMO outage capacity in the high SNR regime.
ISIT
Narayan Prasad, Mahesh K. Varanasi
2004 J jnl
Analysis of Decision Feedback Detection for MIMO Rayleigh-Fading Channels and the Optimization of Power and Rate Allocations.
IEEE Trans. Inf. Theory
Narayan Prasad, Mahesh K. Varanasi
2004 B conf
Diversity and multiplexing tradeoff bounds for cooperative diversity protocols.
ISIT
Narayan Prasad, Mahesh K. Varanasi
2004 B conf
Outage capacities of space-time architectures.
ITW
Narayan Prasad, Mahesh K. Varanasi
2003 B conf
Outage analysis and optimization of a stacked orthogonal space-time architecture and near-outage codes.
GLOBECOM
Narayan Prasad, Mahesh K. Varanasi
2000 A conf
A framework to evaluate test tradeoffs in embedded core based systems-case study on TI's TMS320C27xx.
ITC
Jais Abraham, Narayan Prasad, Srinivasa Chakravarthy B. S., Ameet Bagwe, Rubin A. Parekhji