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Wireless communication technology is finding increasing application in different aspects of human society. For example, smart phones with their myriad applications have significantly altered our daily lives, giving rise to an explosive demand for cellular services. To meet this ever increasing demand, the 4G standards are introducing a variety of spectrally efficient technologies such as the multipleantenna transmitters and receivers (MIMO), sophisticate interference management techniques, and relay stations to increase coverage and reliability. Besides the cellular network, these techniques will also improve the performance of other emerging wireless networks such as the sensor networks and the various cyber-physical systems. Such wide application of this technology and its influence on the society, makes our research in this area so exciting.

Research topics:

 

 


Secrecy in Wireless networks

[C] Mommad K. Hossan, Sanjay Karmakar and Anirban Ghosh, ``On the Secrecy Capacity of the Fading Gaussian Wiretap channel" , in proceedings of the 14th Canadian Workshop on Information Theory, St. John's, NL, Canada, July 6 to 9, 2015.

[C] Sanjay Karmakar and Anirban Ghosh,``Approximate Secrecy capacity region of an asymmetric MAC wiretap channel within 1/2 bits", in proceedings of the 14th Canadian Workshop on Information Theory, St. John's, NL, Canada, July 6 to 9, 2015.

[C] Mommad K. Hossan and Sanjay Karmakar, `` Secrecy Capacity of the Ergodic Layered Erasure Wiretap Channel" , in proceedings of the 49th Annual Conference on Information Systems and Sciences, Baltimore, Maryland, March 18 to 20, 2015.

[C] Sanjay Karmakar, `` On the sum-rate capacity of a 2-user Multiple Access Wiretap Channel with one secret user ", in Proceedings of  4th International Conference onWireless Communications, Vehicular Technology, Information Theory and Aerospace & Electronic Systems (VITAE), 2014, Aalborg, Denmark, May, 2014 . 

 

 

 


Interference network: Information theoretic performance analysis

All optimal wireless networks are interference-limited: if they are not so, it would be possible to increase the capacity of the network by merely accommodating more transmitters and receivers. Optimal interference management techniques are inevitable for the efficient deployment of such networks, which requires an information theoretic analysis. In addition, motivated by the importance of MIMO systems in futuristic wireless networks, we have characterized the capacity region of the two-user MIMO IC - which is the basic building block of any multiuser wireless network -approximately within a constant number of bits [J2, C4]. A high SNR analysis of this channel [J1, C5] revealed that, an information theoretic approach can yield an unbounded performance improvement over orthogonal interference management techniques, with increasing SNR. Starting from a more theoretical model of full channel state infromation at the transmitters (CSIT), we also analyze more realistic model of slow and fast fading channels with partial [J4, C6] and no-CSIT [C3].

[C8] Sanjay Karmakar and Noopur Modi, ``Capacity Region of Two Interfering MIMO Multiple Access Channels with Strong Interference" , in proceedings of the 49th Annual Conference on Information Systems and Sciences, Baltimore, Maryland, March 18 to 20, 2015.

[C7] Sanjay Karmakar and Mahesh K. Varanasi, ``Capacity region of a class of strong MIMO IC", in Proceedings of of 48th Annual Conference on Information Sciences and Systems (CISS), Princeton, NJ, USA, March, 2014. 

[J3]  Sanjay Karmakar and Mahesh K. Varanasi, ``The Generalize Diversity-Multiplexing Tradeoff of the MIMO Z Interference Channel”, IEEE Transactions on Information Theory, Vol 61, No. 06, June 2015, pp. 3427 - 3445. 

[J2]  Sanjay Karmakar and Mahesh K. Varanasi, ``The Capacity Region of the MIMO Interference Channel and its Reciprocity to Within a Constant Gap ", IEEE Transactions on Information Theory ,  Vol. 59, No. 08, Aug. 2013, pp. 4781 - 4797. Also available on Arxiv.

[J1] Sanjay Karmakar and Mahesh K. Varanasi, ``The Generalized Degrees of Freedom region of the MIMO Interference Channel and its achievability", IEEE Transactions on Information Theory, Vol. 58, N0. 12, Dec. 2012, pp. 7188-7203.

[C6] Sanjay Karmakar and Mahesh K. Varanasi, ``The Generalized Multiplexing gain region of the slow-fading MIMO Interference Channel and its achievability with limited feedback", Proceedings of International Symposium on Information Theory (ISIT), Cambridge, MA, July, 1 - July 6, 2012.

[C5] Sanjay Karmakar and Mahesh K. Varanasi, ``The Generalized Degrees of Freedom of the MIMO Interference Channel", Proceedings of IEEE International Symposium on Information Theory, (ISIT 2011), St. Petersburg, Russia, 30 July - 05 August, 2011.

[C4] Sanjay Karmakar and Mahesh K. Varanasi,``Capacity of the MIMO Interference Channel to Within a Constant Gap", Proceedings of IEEE International Symposium on Information Theory, (ISIT 2011), St. Petersburg, Russia, 30 July - 05 August, 2011.

[C3] Chinmay Vaze, Sanjay Karmakar and Mahesh K. Varanasi, ``On the Generalized Degrees of Freedom Region of the MIMO Interference Channel with No CSIT", Proceedings of IEEE International Symposium on Information Theory, (ISIT 2011), St. Petersburg, Russia, 30 July - 05 August, 2011.

[C2] Sanjay Karmakar and Mahesh K. Varanasi, ``The Diversity-Multiplexing Tradeoff of the symmetric MIMO 2-User Interference Channel", Proceedings of ISIT, Austin, Texas, June 13-18, 2010, available on Arxiv.

[C1] Sanjay Karmakar and Mahesh K. Varanasi, ``The Diversity-Multiplexing Tradeoff of the MIMO Z Interference Channel", Proceedings of ISIT, Austin, Texas, June 13-18, 2010, available on Arxiv.

 


Cooperative communication: Diversity-Multiplexing Trade-off (DMT)

A relay channel refers to a configuration, where the signal transmitted by the source node is forwarded by one or more helping nodes towards the destination node and thereby can achieve a better reliability and rate. In recently defined 4G standards provision for two types of relays are incorporated: 1) a relay station that will enhance the performance of a end user; and 2) a relay which will extend the coverage of the base station beyond its cell limit. We have characterized the fundamental information theoretic performance of such networks including the diversity-multiplexing tradeoff (DMT) of the 3-node MIMO relay channel [C4, J2], the dynamic decode and forward (DDF) protocol [J1] and the DMT of relay channel with ARQ [C1].

[C5] Sanjay Karmakar and Mahesh K. Varanasi, ``The diversity Multiplexing Tradeoff of the Half-Duplex Relay Network"  , in proceedings of the IEEE Information Theory Workshop, Hobart, Tasmania, Australia, 2-5 November 2014 .

[C4] Sanjay Karmakar and Mahesh K. Varanasi, ``Diversity-multiplexing tradeoff of the symmetric MIMO half-duplex relay channel", in Proceedings of ISIT, Austin, Texas, June 13-18, 2010.

[J2] Sanjay Karmakar and Mahesh K. Varanasi, ``The diversity-multiplexing tradeoff of the MIMO half-duplex relay channel", IEEE Transactions on Information Theory, Vol. 58, N0. 12, Dec. 2012, pp. 7168-7187.

[C3] Sanjay Karmakar and Mahesh K. Varanasi, `` Diversity Multiplexing Tradeoff of the Dynamic-Decode and Forward Protocol on a MIMO Half-Duplex Relay Channel ,'' Proceedings of ISIT 2009, Seoul, Korea, June 28 - July 3.

[C2] Sanjay Karmakar and Mahesh K. Varanasi, ``Optimal DMT of Dynamic Decode-and-Forward Protocol on a Half-Duplex Relay Channel With Arbitrary Number of Antennas at Each Node ", Proceedings of Asilomar Conf. on Signals, Systems and Computers, Pacific Grove, CA, Nov. 1 - Nov. 4, 2009.

[J1] Sanjay Karmakar and Mahesh K. Varanasi, ``Diversity-Multiplexing Tradeoff of Dynamic Decode-and-Forward protocol on a MIMO Half-Duplex Relay Channel", IEEE Transactions on Information Theory, Vol. 57, No. 10, Oct. 2011, pp. 6569-6590.

[C1] Sanjay Karmakar and Mahesh K. Varanasi, ``Diversity-Multiplexing-Delay Tradeoff of a DDF Protocol on a Half-Duplex ARQ Relay Channel ", Proceedings of Asilomar Conf. on Signals, Systems and Computers, Pacific Grove, CA, Nov. 1 - Nov. 4, 2009. The journal version of this paper is under preparation and to be submitted to the Transactions on wireless communications.

 

 

 

Space time Block Code design for MIMO communication systems

The discovery of enhanced capacity of a MIMO point-to-point channel, with respect to the capacity of a channel with single antennas at both the transmitter and receiver (SISO), led to the invention of a new class of codes, namely the space time block codes (STBC). In this class of codes, coding takes place across both the time and antenna dimensions as against to only the time dimension in classical single antenna communication links.

In this area of research, we have designed STBCs - for MIMO communication systems - which achieves a relatively better trade-off between decoding complexity and rate of transmission than the pre-existing STBCs. We have pioneered a novel mathematical framework involving the Clifford algebra enabling a systematic construction of these codes [J3]. Several classes of such codes with gradually larger rates and decoding complexities [J1],[J2] were constructed using this framework. 

[J1] Sanjay Karmakar, K. Pavan Srinath and B. Sundar Rajan, ``Maximum Rate of Unitary-Weight, Single-Symbol Decodable STBCs", IEEE Transactions on Information Theory, Vol. 57, No. 10, Dec. 2011, pp. 7972-7981.

[J2] Sanjay Karmakar and B. Sundar Rajan, ``High-rate, Multi-Symbol-Decodable STBCs from Clifford Algebras'', IEEE Transactions on Information Theory, Vol. 55, No. 06, Jun. 2009, pp. 2682-2695.

[J3] Sanjay Karmakar and B. Sundar Rajan, ``Multigroup-Decodable STBCs from Clifford Algebras'', IEEE Transactions on Information Theory, Vol. 55, No. 01, Jan. 2009, pp. 223-231.

[C1] Sanjay Karmakar and Mahesh K. Varanasi, `` On the rate versus ML-decoding complexity tradeoff of square LDSTBCs with unitary weight matrices,'' Proceedings  of IEEE GLOBECOM 2008, New Orleans, LA, USA, Nov.30-Dec.04, 2008. The journal version of this paper is under preparation and to be submitted to the Transactions on Information Theory.

[C2] Sanjay Karmakar and B. Sundar Rajan, `` High-rate Double-Symbol-Decodable STBCs from Clifford Algebras," Proceedings of IEEE GLOBECOM 2006, San Francisco, Nov.27-Dec.01, 2006.

[C3] Sanjay Karmakar and B. Sundar Rajan, `` Multi-group decodable STBCs from Clifford Algebras,'' Proceedings of IEEE Information Theory Workshop (ITW 2006), Chengdu, China, October 22-26, 2006, pp.448-452.

[C4] Sanjay Karmakar and B. Sundar Rajan, `` Minimum-decoding-complexity maximum-rate space-time block codes from Clifford algebras,'' Proceedings of IEEE International Symposium on Information Theory (ISIT 2006), Seattle, USA, July 09-14, 2006, pp.788-792.

[C5] Sanjay Karmakar and B. Sundar Rajan, `` Non-unitary weight space-time block codes with minimum decoding complexity,'' Proceedings of IEEE International Symposium on Information Theory (ISIT 2006), Seattle, USA, July 09-14, 2006, pp.793-797.

[C6] Sanjay Karmakar and B. Sundar Rajan, ``High-rate, Multi-Symbol-Decodable STBCs from Clifford Algebras,''Proceedings of Thirteenth National Conference on Communications (NCC 2007),, IIT Kanpur, January 27-29, 2007, pp.368-372.