Anjana Ambika Mahesh

Scopus Publications

Cyclic Wrap-around Multi-Access Coded Caching with Private Caches
Dhruv Pratap Singh, Anjana A. Mahesh, B. Sundar Rajan
Proceedings IEEE Consumer Communications and Networking Conference Ccnc, 2026
We study a variant of the coded caching problem where a server, with a library of files, serves users through a broadcast link. Each user is equipped with a private cache and additionally connects to L neighboring access caches in a cyclic wrap-around manner. This setting generalizes the cyclic wraparound networks studied in coded caching by incorporating private caches. For this model, we propose a coded caching scheme under uncoded placement, characterize its achievable rate, and derive a cut-set-based lower bound on the optimal worst-case rate. The optimality of the scheme is proven in the large-memory regime and verified through numerical comparisons.
Combinatorial Multi-Access Coded Caching with Private Caches
Dhruv Pratap Singh, Anjana A. Mahesh, B. Sundar Rajan
IEEE Wireless Communications and Networking Conference Wcnc, 2025
We consider a variant of the coded caching problem where users connect to two types of caches, called private and access caches. The problem setting consists of a server with a library of files and a set of access caches. Each user, equipped with a private cache, connects to a distinct $r$-subset of the access caches. For this setting, we provide a coded caching scheme and derive a lower bound on the number of transmissions for this scheme. We also present lower and upper bounds for the optimal worst-case rate under uncoded placement for this setting using the rates of the Maddah-Ali-Niesen scheme for dedicated and combinatorial multi-access coded caching settings, respectively. Further, we derive a lower bound on the optimal worst-case rate for any general placement policy using cut-set arguments. Numerical plots comparing the rate of the proposed achievability scheme with the above bounds are also provided, from which it can be observed that the proposed scheme approaches the lower bound in the large-memory regime.
An Optimal Two-Step Decoding for PSK-Modulated Noisy Index Coding
Navya Saxena, Anjana A. Mahesh, B. Sundar Rajan
IEEE Transactions on Communications, 2024
Abstract-This paper studies noisy index coding problems over broadcast channels. The codewords from a chosen binary index code of length <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N are mapped to a 2 N -PSK constellation before being transmitted over an AWGN channel. The receivers follow the two-step decoding process of first estimating the PSK symbol using a maximum-likelihood decoder and then performing index code decoding. After estimating the PSK symbol, there is, in general, more than one decoding strategy at a receiver, i.e., more than one linear combination of index-coded bits along with a subset of side information bits, that can be used to estimate the requested message. Thomas et al. in [“Single Uniprior Index Coding With Min–Max Probability of Error Over Fading Channels,” IEEE Transactions on Vehicular Technology, pp. 6050-6059, July 2017] showed that for binary-modulated index code transmissions, minimizing the number of transmissions used to decode a requested message is equivalent to reducing the probability of error. This paper shows that this is no longer true while employing multi-level modulations. Further, we consider the side information available to each receiver also to be noisy and derive an expression for the probability that a requested message bit is estimated erroneously at a receiver. We also show that the criterion for choosing a decoding strategy that gives the best probability of error performance at a receiver changes with the signal-to-noise ratio at which the side information is broadcast. Hence, for a given index coding problem and a chosen index code, we give an algorithm to select the best decoding strategy for the receivers. The above results are shown to be valid over fading channels also.
Bandwidth-BER Trade-off with Multi-symbol M-PSK for Index Coding with Prioritized Receivers
Anjana A. Mahesh, B. Sundar Rajan
IEEE Wireless Communications and Networking Conference Wcnc, 2024
Consider single unicast index coding problems with prioritized receivers with transmissions over additive white Gaussian (AWGN) channels. In this setting, if a length-N index-coded vector is transmitted as a 2N-PSK symbol, there will exist some receivers, especially the lower priority ones, that would not see much improvement over the average bit error probability obtained for a 2N-PSK modulated transmission. On the other hand, if we use binary-modulated transmission, which gives the best probability of performance at the receivers, it will result in an N/2 -fold increase in the bandwidth consumed. Hence, in a setting where each receiver has to satisfy some quality of service requirements, we propose multi-symbol PSK-modulated transmission for a bandwidth-performance trade-off where the $N$ index-coded bits are mapped to complex symbols of multiple smaller-sized constellations. Depending on the available bandwidth, we can choose the number of symbols to which the N-bit index-coded vector should be mapped. In addition to proposing the multi-symbol modulated transmission, we present an algorithm that takes the $N$ bits of the index-coded vector and maps it to the multiple complex symbols in a way that guarantees that the highest priority receiver sees the best possible performance followed by the second-highest priority receiver and so on. For the special case of single unicast single uniprior index coding problems, we also describe optimal index code selection to ensure that the highest priority receiver sees the best performance.
Average Probability of Error for Single Uniprior Index Coding Over Binary-Input Continuous-Output Channels
Anjana A. Mahesh, Charul Rajput, Bobbadi Rupa, B. Sundar Rajan
IEEE Transactions on Information Theory, 2024
Ong and Ho developed optimal linear index codes for single uniprior index coding problems (ICPs) by finding a spanning tree for each strongly connected component of their information-flow graphs, following which Thomas et al. considered the same class of ICPs over Rayleigh fading channels. They developed the min-max probability of error criterion for choosing an index code from the set of bandwidth-optimal linear index codes. Motivated by the above works, this paper deals with single uniprior ICPs over binary-input continuous-output channels. Minimizing the average probability of error is introduced as a criterion for further selection of index codes which is shown to be equivalent to minimizing the total number of transmissions used for decoding the message requests at all the receivers. An algorithm that generates a spanning tree with a lower value of this metric than the optimal star graph is also presented. A couple of lower bounds for the total number of transmissions, used by any optimal index code, are derived, and two classes of ICPs for which these bounds are tight are identified. An improvement of the proposed algorithm for information-flow graphs with bridges and a generalization of the improved algorithm for information-flow graphs obtainable as the union of strongly connected sub-graphs are presented, and some optimality results are derived.
Role of Index Codes in Noisy Broadcasting With Side Information and Index Coded QAM For Prioritized Receivers
Anjana A. Mahesh, Anurag Chhetri, B. Sundar Rajan
IEEE Transactions on Communications, 2023
This paper considers the problem of broadcasting with side information (BWSI), where a central server broadcasts encoded transmissions using <inline-formula> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula>-ary modulation to a set of caching receivers over an additive white Gaussian noise channel. For this problem of noisy index coding with <inline-formula> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula>-ary modulated transmission, the ML decoder at any receiver does not involve demodulation to the complex signal point and then index code decoding to the requested message bit. Instead, it decodes directly to the requested message bit, raising the question of whether the central server’s encoding scheme is required to correspond to an index code or if any set of transmissions encoding across the entire library of messages is sufficient. This paper proves that index codes are necessary for solving noisy BWSI problems even with <inline-formula> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula>-ary modulated transmission. Further, we look at index-coded QAM for prioritized receivers. An algorithm for mapping index-coded vectors to signal points on a square QAM constellation is presented, which gives mappings that achieve the best ML decoding performance for the prioritized receivers. Expressions for the ML metric seen by the highest priority receiver while using <inline-formula> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula>-PSK and <inline-formula> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula>-QAM for transmission are derived. For the highest priority receiver, <inline-formula> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula>-PSK is shown to outperform <inline-formula> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula>-QAM.
Average Probability of Error for Single Uniprior Index Coding over Rayleigh Fading Channel
Anjana A. Mahesh, Charul Rajput, Bobbadi Rupa, B. Sundar Rajan
2023 IEEE Information Theory Workshop Itw 2023, 2023
Ong and Ho developed optimal linear index codes for single uniprior index coding problems (ICPs) by finding a spanning tree for each of the strongly connected components of the corresponding information-flow graphs, following which Thomas et al. considered the same class of ICPs over Rayleigh fading channel. They developed the min-max probability of error criterion for choosing an index code which minimized the probability of error at the receivers and showed that there always exist optimal linear index codes for which any receiver takes at most two transmissions to decode a requested message. Motivated by the above works, this paper considers single uniprior ICPs over Rayleigh fading channels for which minimizing average probability of error is shown to be a criterion for further selection of index codes. The optimal index code w.r.t this criterion is shown to be one that minimizes the total number of transmissions used for decoding the message requests at all the receivers. An algorithm that generates a spanning tree which has a lower value of this metric as compared to the optimal star graph is also presented. For a given set of parameters of single uniprior ICPs, a lower bound for the total number of transmissions used by any optimal index code is derived, and a class of ICPs for which this bound is tight is identified.
Performance of Maddah-Ali-Niesen Scheme for Multi-Access Coded Caching over Noisy Channels
Kakumani Sailahari, Anjana A. Mahesh, Charul Rajput, B. Sundar Rajan
IEEE International Symposium on Personal Indoor and Mobile Radio Communications PIMRC, 2023
Coded caching techniques help to reduce the traffic overload on the server during peak-traffic hours. Most of the existing schemes consider all transmissions to be over noiseless channels, whereas noise is inherent in wireless communication. In this paper, the multi-access coded caching scheme proposed in the paper [“Maddah-Ali-Niesen Scheme for Multi-access Coded Caching,” ITW 2021], is studied when the server-user shared link and all the cache-user links are noisy. This coded caching has been shown to be information-theoretically optimal in [“Fundamental Limits of Combinatorial Multi-Access Caching,” IEEE Transactions on Information Theory, Feb. 2023]. For binary modulated transmissions, the probability that a bit of a requested file is decoded in error at a user is derived when the transmissions are over binary-symmetric, AWGN, and Rayleigh fading channels. Further, the effect of varying the cache access degree (which is the number of caches accessed by each user), and the cache memory size on the probability of bit error performance at a user are also analyzed. Simulation results validating the findings in this paper are also presented.
Index Coded - NOMA in Vehicular Ad Hoc Networks
Sreelakshmi Pazhoor, Jesy Pachat, Anjana Ambika Mahesh, Deepthi P. P., B. Sundar Rajan
IEEE Transactions on Vehicular Technology, 2022
The demand for multimedia services is growing day by day in vehicular ad hoc networks (VANETs), resulting in high spectral usage and network congestion. Non-orthogonal multiple access (NOMA) is a promising wireless communication technique to solve the problems related to spectral efficiency effectively. The index coding (IC) is a powerful method to improve spectral utilization, where a sender aims to satisfy the needs of multiple receivers with a minimum number of transmissions. By combining these two approaches, in this work, we propose a novel technique called index coded NOMA (IC-NOMA), where we apply NOMA techniques on index coded data to reduce the number of transmissions further. This work shows that the IC-NOMA system demands a specific design for index codes to reap the advantages of NOMA. We have done the feasibility analysis of the proposed method in a general scenario and proposed an index code design to integrate IC over NOMA for the best efficiency. Through detailed analytical studies it is validated that the proposed transmission system provides improved spectral efficiency and power saving compared to conventional IC systems.
Embedded Index Coding With Consecutive Side Information in Vehicle to Vehicle Communication
Jesy Pachat, Anjana A. Mahesh, Deepthi P. P., B. Sundar Rajan
IEEE Transactions on Vehicular Technology, 2022
Embedded index coding problem is a variant of index coding problems, where each user functions as both broadcast sender and receiver. Consider a set of the messages, the indices of which form an ordered set. Each user owns a subset of these messages known as side information and tries to meet the demands of one another with a minimum number of transmissions. The side information is said to be consecutive if the elements of the index set of side information at a user are consecutive. We consider a practical vehicular ad-hoc network where the embedded index coding could be applied. In the scenario considered, the receiver demands all messages it does not possess, and the side-information is consecutive. Under this setup, a lower bound on the number of transmissions is determined. We present an optimal solution to achieve the bound. The constructed codes work over any field size, including binary.
Space Time Codes in Multi-Antenna Coded Caching Systems
Anjana A Mahesh, B. Sundar Rajan
IEEE International Symposium on Information Theory Proceedings, 2022
Minrank of Embedded Index Coding Problems and its Relation to Connectedness of a Bipartite Graph
Anjana Ambika Mahesh, B. Sundar Rajan
2022 IEEE Information Theory Workshop Itw 2022, 2022
Index Coded-NOMA in Vehicular Ad Hoc Networks
P Sreelakshmi, Jesy Pachat, Anjana A. Mahesh, P. P. Deepthi, B. Sundar Rajan
IEEE Vehicular Technology Conference, 2022
An Optimal Error Correction Scheme for the Shuffle Phase of a MapReduce Distributed Computing System
Anjana A. Mahesh, Nujoom Sageer Karat, B. Sundar Rajan
IEEE Communications Letters, 2021
Index Coded PSK Modulation in Vehicle to Vehicle Communication
Jesy Pachat, Nujoom Sageer Karat, Anjana A. Mahesh, Deepthi P. P., B. Sundar Rajan
IEEE Transactions on Vehicular Technology, 2021
A Coded Caching Scheme with Linear Sub-packetization and its Application to Multi-Access Coded Caching
Anjana Ambika Mahesh, B. Sundar Rajan
2020 IEEE Information Theory Workshop Itw 2020, 2021
Index Coded PSK Modulation in Vehicle to Vehicle Communication
Jesy Pachat, Nujoom Sageer Karat, Anjana A. Mahesh, Deepthi P. P, B. Sundar Rajan
IEEE Vehicular Technology Conference, 2021
Min-rank of Embedded Index Coding Problems
Anjana Ambika Mahesh, Nujoom Sageer Karat, B. Sundar Rajan
IEEE International Symposium on Information Theory Proceedings, 2020
Two Private Secure Distributed Coded Computation Schemes Using Extension Fields
Anjana A. Mahesh, Tushara Swapna Malladi, B. Sundar Rajan
IEEE International Conference on Communications, 2020
Index coded PSK modulation
Anjana A. Mahesh, B Sundar Rajan
IEEE Wireless Communications and Networking Conference Wcnc, 2016