Indian Institute of Technology Hyderabad (IITH) is a premier institute of science and technology established in 2008. IITH has been consistently ranked in the&nbsp;<a href="https://iith.ac.in/reports/" rel="noopener noreferrer">top 10 institutes</a>&nbsp;in India for Engineering&nbsp;<a href="https://www.nirfindia.org/2021/EngineeringRanking.html" rel="noopener noreferrer" target="_blank">according to NIRF</a>&nbsp;making it one of the most coveted schools for science and technology in the country.

IITH offers&nbsp;<a href="https://iith.ac.in/academics/under-graduate/">undergraduate programs</a>&nbsp;in all the classical engineering disciplines, applied sciences, design, as well as several modern interdisciplinary areas. Students are given a flexibility to explore a broad set of areas, and potentially pursue a minor or double major in a discipline that is not their own. Students who wish to seek a deeper understanding of their own discipline are strongly encouraged to get involved in cutting-edge research with the help of a faculty to mentor them, and earn an Honors in their own field.

The very foundation of IIT Hyderabad is based on&nbsp;<a href="https://iith.ac.in/research/">research and innovation</a>. The vibrant research culture is evident from the number of patents and publications that IITH produces consistently every year. IITH offers&nbsp;<a href="https://iith.ac.in/academics/programmes-offered/">graduate programs</a>&nbsp;at both a masters, and a doctoral level, in several diverse areas. There are separate programs for technology, design, science, and liberal arts. The&nbsp;<a href="https://iith.ac.in/academics/post-graduate/">MTech program</a>&nbsp;is offered in various modes and durations to cater to the ever-growing need of postgraduate level professionals in the country.

IITH encourages and supports&nbsp;<a href="https://iic-iith.netlify.app/index.html" rel="noopener noreferrer" target="_blank">innovation and entrepreneurship</a>&nbsp;at every stage. The minor program in entrepreneurship is open to all students of IITH, and many of the courses are offered by industrialists who are entrepreneurs themselves. There are various&nbsp;<a href="https://iith.ac.in/research/centres-incubators/">innovation centers and incubators</a>&nbsp;that promote entrepreneurship and help mentor young innovators. IITH has been very successful in building tie-ups with leading academic institutions around the globe.

IITH enjoys a very special relationship with Japanese universities and industries that goes beyond academic and research collaborations. In fact, some of the iconic buildings in IITH campus will carry the signature of Japanese architecture.

IITH creates a unique holistic ecosystem for education that offers interactive learning, a very flexible academic structure, cutting-edge research, strong industry collaboration, and entrepreneurship. This is an environment which enables students and faculty to translate their dreams into realities.

IIT Hyderabad

The bit error rate (BER) performance analysis of maximum-likelihood (ML) based decode and forward (DF) cooperative diversity systems has been a subject of considerable interest. Exact analysis of ML-DF transmission has been considered a challenging problem due to the nonlinear characteristic of the ML detector. In this paper, we provide exact expressions for the BER of ML-DF cooperative systems employing a single relay. We extend these results to the case of multiple relays for the piecewise linear (PL) combiner, that is known to be a close approximation of the ML detector. This is done by using a novel theory of conditionally Gaussian random variables. By expressing the ML decision variable in terms of functions of conditionally Gaussian variables, exact expressions for the BER of the ML-DF system are obtained. Through simulation results, we verify the validity of the derived analytical expressions. ©2009 IEEE.

Department of Electrical Engineering

World University root node

IEEE International Conference on Communications

Performance analysis of maximum likelihood decode and forward cooperative systems in Rayleigh fading

Tight closed form lower bounds for the average bit error rate (BER) are derived for a dual hop cooperative network employing nonregenerative relays for the multiple input multiple output (MIMO) relay channel experiencing Rayleigh fading. The bounds are obtained for three different nonregenerative relaying schemes. The lower bounds for the BER are obtained using the moment generating function (MGF) approach by evaluating the MGF of the end-to-end equivalent signal to noise ratio (SNR) of the system. From the BER expressions obtained, we also show that the diversity order for the MIMO Relay cooperative system with each relay having M antennas increases approximately by afactor M from that of a system with single-antenna relays. Simulation results confirm that the analytical expressions for the lower bounds are very tight and can thus be used to get approximate values of the BER.© 2009 IEEE.

IEEE Vehicular Technology Conference

Performance analysis of amplify and forward based cooperative diversity in MIMO relay channels

The network scenario is that of an infrastructure IEEE 802.11 WLAN with a single AP with which several stations (STAs) are associated. The AP has a finite size buffer for storing packets. In this scenario, we consider TCP-controlled upload and download file transfers between the STAs and a server on the wireline LAN (e.g., 100 Mbps Ethernet) to which the AP is connected. In such a situation, it is well known that because of packet losses due to finite buffers at the AP, upload file transfers obtain larger throughputs than download transfers. We provide an analytical model for estimating the upload and download throughputs as a function of the buffer size at the AP. We provide models for the undelayed and delayed ACK cases for a TCP that performs loss recovery only by timeout, and also for TCP Reno. The models are validated in comparison with NS2 simulations. © 2009 Elsevier B.V. All rights reserved.

Computer Networks

Modeling finite buffer effects on TCP traffic over an IEEE 802.11 infrastructure WLAN

Closed form expressions for the bit error rate (BER) for a multiple input multiple output (MIMO) relay system employing maximum likelihood (ML) based decode and forward (DF) cooperative diversity are obtained. The DF operation at the relay involves maximal ratio combining (MRC) on the source-relay link and space-time coding (STC) on the relaydestination link. Exact expressions of the BER are obtained for the case of a single relay supporting two antennas. For a system employing a large number of relays, each having two antennas, approximate expressions for the BER are obtained using the piecewise linear (PL) approximation for the ML detector. This is done by finding the statistics of conditionally Gaussian random variables, that appear in the decision variable. The validity of the analytical expressions is then verified through simulations. Through numerical results obtained from the BER expressions for large number of relays, it is then shown that the loss in diversity order due to DF can be compensated by using multiple antennas at the relay.

IEEE Wireless Communications and Networking Conference, WCNC

Performance analysis of maximum likelihood detection for decode and forward MIMO relay channels in rayleigh fading

In this work we show how existing network coding algorithms can be used to perform network tomography, i.e., estimate network topology. We first examine a simple variant of the popular distributed random network codes proposed by Ho et al. [14], and show how it can enable each network node to passively estimate the network topology upstream of it at no cost to throughput. The delays introduced by each upstream node and link can also be similarly estimated. We then consider the scenario wherein an adversary hidden in the network wishes to disrupt the estimation of network topology. We show how network error-correcting codes can be used to reliably perform network tomography if the network has sufficient connectivity, and demonstrate that network tomography is impossible otherwise.

2008 Information Theory and Applications Workshop - Conference Proceedings, ITA

<a href="https://www.scopus.com/record/display.uri?eid=2-s2.0-52949130644&amp;origin=resultslist&amp;sort=cp-f&amp;src=s&amp;st1=Sharma&amp;st2=G.+V.+V.&amp;nlo=1&amp;nlr=20&amp;nls=count-f&amp;sid=3dc2fb7a3bfec7f5d5dd7905b7aa9a86&amp;sot=anl&amp;sdt=aut&amp;sl=40&amp;s=AU-ID%28%22Sharma%2c+Girish+V.V.%22+57213751340%29&amp;relpos=1&amp;citeCnt=24&amp;searchTerm=">Network tomography via network coding</a>

Antenna sharing by multiple users using cooperative diversity has been shown to mimic the performance of traditional multiple input, multiple output (MIMO) systems. While this was originally done using a single antenna at each relay, the benefits of cooperative diversity based on multiantenna relays has been a subject of considerable interest. Maximum likelihood (ML) detectors for cooperative diversity through single antenna relays are well known. In this paper, we propose to combine the benefits of cooperative diversity, and transmit and receive diversity offered by MIMO systems. This is done within the ML based decode and forward (DF) cooperative diversity framework, by using multiple antennas at each relay, through ML based processing on the source-relay link and space-time coding on the relay-destination link. Through simulations, we then show that the performance of MIMO Relay based systems is superior to those having a single antenna at each relay. ©2008 IEEE.

Maximum likelihood detection for cooperative diversity in MIMO relay channels

In this correspondence, we average Q(∥X∥), where ∥X∥ is the Euclidean norm of an n × 1 complex circularly Gaussian vector X. This is done by finding the characteristic function of the decision variable and subsequently applying the Gil-Pelaez theorem to obtain a one-dimensional real integral. The integral is then converted to a contour integral which is evaluated using a variant of the Cauchy's integral formula to obtain an expression for E[Q(∥X∥)], where E[] is the expectation operator. © 2008 IEEE.

IEEE Transactions on Information Theory

Averaging Q(∥X∥) for a complex circularly Gaussian random vector X: A novel approach

In this paper, the performance of maximum-likelihood multiuser detection in space-time-coded code-division multiple-access (CDMA) systems with imperfect channel estimation is analyzed. A K-user synchronous CDMA system that employs orthogonal space-time block codes with M transmit antennas and N receive antennas is considered. A least-squares estimate of the channel matrix is obtained by sending a sequence of pilot bits from each user. The channel matrix is perturbed by an error matrix that depends on the thermal noise and the correlation between the signature waveforms of different users. Because of the linearity of the channel estimation technique, the characteristic function of the decision variable is used to obtain an exact expression for the pairwise error probability, and by using it, an upper bound on the bit error rate (BER) is obtained. The analytical BER bounds are compared with the BER obtained through simulations. The BER bounds are shown to be increasingly tight for large SNR values. It is shown that the degradation in BER performance due to imperfect channel estimation can be compensated by using a larger number of transmit/receive antennas. © 2006 IEEE.

IEEE Transactions on Vehicular Technology

Performance analysis of maximum-likelihood multiuser detection in space-time-coded CDMA with imperfect channel estimation

Orthogonal frequency division multiplexing (OFDM) based communication systems are very efficient in combating inter-symbol interference (ISI) in frequency-selective channels. However, carrier frequency offset (CFO) severely affects system performance by destroying the orthogonality between the OFDM subcarriers. In this paper, we estimate the CFO in a block OFDM system using maximum-likelihood estimation (MLE) and pilot subcarriers. Through simulations, we then show the deleterious effect of the CFO on the bit error rate (BER) and subsequently, the performance improvement after CFO compensation. © 2005 IEEE.

2005 13th IEEE International Conference on Networks jointly held with the 2005 7th IEEE Malaysia International Conference on Communications, Proceedings

Pilot based synchronization in OFDM systems using maximum likelihood estimation

Code division multiple access (CDMA) and Orthogonal frequency division multiplexing (OFDM) are two techniques that are being commonly used in most wireless communication systems. In this paper we examine the coexistence of the above schemes through a two user communication system, i.e., one user transmits using CDMA and the other transmits using OFDM. Using an OFDM based receiver, we derive the received symbols at the output of each branch of the OFDM demodulator. The symbols transmitted by the CDMA user are then detected using the minimum power distortionless response (MPDR) approach, an array processing technique commonly used in beamforming. Through simulations, we then show that the MPDR method is indeed very efficient in suppressing the OFDM interference. © 2005 IEEE.

IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC

Symbol detection in CDMA-OFDM coexistence

Space-time coding and multiuser detection are two widely used techniques that are known to substantially increase CDMA system capacity by using multiple transmit antennas and interference cancellation respectively. In this paper, we consider a space-time coded multiuser system based on real orthogonal designs. For this system, we study the performance of the minimum conditional probability of error (MCPOE) algorithm. The decision variable for MCPOE is the conditional probability of error, that is minimized to get the estimates of a set of filter coefficients. The filter coefficients are then used for symbol detection at the receiver. We find that the MCPOE algorithm scores over other adaptive multiuser detectors available in the literature, both in terms of convergence as well as bit error rate (BER) performance. © 2005 IEEE.

Minimum conditional probability of error based multiuser detection for space-time coded CDMA systems

In this paper we show that a one-hop repeater in an ultra-wideband (UWB) communication system for a wireless personal area network (WPAN) can be used to achieve diversity gain in a Rayleigh fading channel. We use maximal ratio combining (MRC) in the transmitter-repeater link and space-time coding (STC) in the repeater-receiver link, where the repeater has two antennas for transmission as well as reception. The repeater transmits at a higher rate than the transmitter so that the symbols are properly synchronized. We then derive the closed-form expression for the probability of bit error and show that there exists a trade-off between the bit error rate (BER) performance and the transmit powers of the transmitter and the repeater. Based on our BER curves, we then show that the performance of the proposed system is much better than a conventional repeater as well as the traditional communication system. © 2005 IEEE.

Diversity gain using a repeater in a wireless personal area network

In this paper, we analyze the performance of maximum-likelihood (ML) multiuser detection in space-time coded CDMA systems with imperfect channel estimation. A K-user synchronous CDMA system which employs orthogonal space-time block codes with M transmit antennas and N receive antennas is considered. A least-squares estimate of the channel matrix is obtained by sending a sequence of pilot bits from each user. The channel matrix is perturbed by an error matrix which depends on the thermal noise as well as the correlation between the signature waveforms of different users. Using the characteristic function of the decision variable, we derive an exact expression, in closed-form, for the pairwise error probability (PEP) of the joint data vector of bits from different users. Using this exact PEP expression, we obtain an upper bound on the average bit error rate (BER). The analytical BER bounds are compared with the BER obtained through simulations. The BER bounds are shown to be increasingly tight for large SNR values. It is shown that the degradation in BER performance due to imperfect channel estimation can be compensated by using more number of transmit/receive antennas. © 2004 IEEE.