A.S. Madhukumar

Nanyang Technological University, Tumasik, Singapore

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Publications (191)105.99 Total impact

  • Rajendra Prasad Sirigina · A. S. Madhukumar
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    ABSTRACT: This work considers the interference management in Z-channel and full-duplex decode-and-forward (FD DF) relay-assisted Z-channel. In the case of Z-channel, closed-form expressions for the achievable diversity gain regions (DGRs) with both single-user (SU) codes and multi-user (MU) codes are presented. The closed-form expression for the achievable DGR of the clustered FD DF relay-assisted Z-channel with SU codes is also presented. In the Z-channel, if the interference-free receiver is constrained to operate at optimal diversity multiplexing tradeoff (DMT), the SU codes are shown to achieve better DGR than MU codes. Furthermore, in the Z-channel, the SU codes achieve DGR outer bound at low multiplexing gain region, and MU codes can never achieve DGR outer bound. Also, we have shown that Z-channel with two co-located antennas at the interfering transmitter achieves better DGR compared to that of the clustered FD DF relay-assisted Z-channel with single antenna at the interfering transmitter.
    No preview · Article · Nov 2015 · Wireless Networks
  • P. Jacob · A.S. Madhukumar · A.P. Vinod
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    ABSTRACT: The next-generation heterogeneous networks are expected to offer higher data-rate and better QoS to the customers by leveraging smaller cells like femtocells and making use of orthogonal frequency division multiple access (OFDMA). However, uncoordinated dense deployment of femtocells in a macrocell network pose unique challenges involving cross-tier interference and resource management which may lead to significant performance degradation in the system. As part of addressing these challenges, this paper proposes a Cross- Polarized Complementary Frequency Allocation (CPCFA) strategy which exploits frequency and polarization diversity to mitigate interference in two-tier femto-macro networks. This strategy combines the benefits of reverse frequency allocation (RFA) and orthogonal polarized transmission which is analyzed as a potential solution for maximizing spectral efficiency and minimizing interference in heterogeneous networks. The results of analytic and simulation studies prove that CPCFA increases the scope for an easily implementable, remarkable opportunity in the context of two-tier femto-macro network that can substantially increase the system capacity, area of interference-free femtocell exclusive region as well as the coverage probability without additional network complexities.
    No preview · Article · Jul 2015
  • R.P. Sirigina · A.S. Madhukumar
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    ABSTRACT: The present paper focuses on the interference management in a two-user Z-channel where one user is interference-limited while the other user is interference-free. The achievable diversity gain region (DGR) with interference forwarding by a full-duplex decode-and-forward (FD-DF) relay and successive interference cancellation (SIC) at the interference-limited destination is studied. The achievable DGR of the FD-DF relay is compared with that of the direct transmission scheme. The impact of the phase-noise in the self-interference cancellation circuit of the full-duplex relay and the impact of the number of blocks in the superposition block Markov (SPBM) encoding on the achievable DGR are studied. The direct transmission scheme with joint decoding at the interference-limited receiver is shown to perform well at the lower multiplexing gain region (MGR). If the multiplexing gain of the interference is high, then the interference forwarding by the DF relay does not help, and the direct transmission scheme with interference ignorant detection at the interference-limited receiver achieves better DGR. The FD-DF relay is shown to provide better DGR at only the moderate MGR.
    No preview · Article · Jul 2015
  • R.P. Sirigina · A.S. Madhukumar
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    ABSTRACT: In the present work, the diversity multiplexing tradeoff (DMT) for a decode-and-forward relay assisted two-user Z-channel with Nakagami-m fading is studied. In a two-user Z-channel, only one user is interference-limited while the other user is interference-free. Two transmission schemes, namely, common message only (CMO) and rate splitting (RS) schemes, are studied. In the CMO scheme, the interfering source uses single-user (SU) codes, and the interference-limited destination cancels the total interference. In the RS scheme, the interfering source uses multi-user (MU) codes, and the interference-limited user does partial interference cancellation. Closed-form expressions for the achievable DMTs with both the schemes are presented. The RS and the CMO schemes are shown to provide better DMT at the moderate and higher levels of interference, respectively.
    No preview · Article · Jul 2015
  • Ponnu Jacob · A.S. Madhukumar · A.P. Vinod
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    ABSTRACT: Dynamic frequency allocation enabled through cognitive spectrum sensing is being considered to replace the static spectrum allocation methodology in the aerospace domain as it promises a multitude of advantages in terms of spectral efficiency, seamless connectivity and enhanced capacity. This paper proposes an architecture for air-to-ground (A/G) communication system that enables dynamic frequency access for the aircrafts utilizing the spectrum sensing capabilities of the cognitive radio. Further it proposes an ingenious algorithm for efficient and interference-limited Time Frequency Unit (TFU) allocation to aircrafts within adjacent service volumes (SV). This is based on the interference volume penalty parameter that aims at curtailing the system wide interference score within acceptable ranges. Though the algorithm is developed with a focus for implementation in simulation environment, it could potentially be scaled to realtime aeronautical environment after extensive analysis and testing.
    No preview · Article · Jun 2015
  • Sumedh Dhabu · A. P. Vinod · A. S. Madhukumar

    No preview · Conference Paper · Jun 2015
  • Ponnu Jacob · A. S. Madhukumar
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    ABSTRACT: The next generation heterogeneous networks are expected to offer higher data-rate and better QoS to the customers by leveraging smaller cells like femtocells and making use of orthogonal frequency division multiple access. However, uncoordinated dense deployment of femtocells in macrocell network pose unique challenges involving cross-tier interference and resource management which results in significant degradation of the system performance. As part of addressing these challenges for the successful integration of both technologies, this paper proposes the deployment of a self-organizing femtocell network that employs an opportunistic smart frequency reuse technique -cross polarized complementary frequency allocation (CPCFA). It exploits the frequency and polarization diversity to mitigate interference in two-tier femto-macro networks. In this work, a strategy combining the adoption of reverse frequency allocation and orthogonal polarized transmission is analyzed as a potential solution for maximizing spectral efficiency and minimizing interference in the existing heterogeneous networks. Focus of the current work is on downlink transmission where the traffic is high and the deployment of femtocell is more beneficial. The results of analytic and simulation studies prove that CPCFA increases the scope for an easily implementable, remarkable opportunity in the context of two-tier femto-macro network that can substantially increase the system capacity as well as cell coverage without additional network complexities.
    No preview · Article · May 2015 · Wireless Networks
  • Ponnu Jacob · A.S. Madhukumar
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    ABSTRACT: The tremendous advancement in the field of information and communication technology has escalated energy consumption and environment concerns. At the same time, the backhaul constraints limit high data rate services considerably. These challenges motivated the deployment of low-power femto-cells which act as the most promising energy-efficiency enablers for future networks. However, the increasing number of underutilized femtocells result in unwanted energy consumption and spectrum occupancy. Hence, in the strive towards optimizing the energy consumption profiles, this paper proposes the concept of self-organizing femto-relay network capable of enhancing the system capacity with significant energy savings. It aims at routing the traffic of nearby macro-users through idle femto-users via multi-tier cooperation. Analysis and simulation results project a remarkable enhancement in system performance and at the same time improvement in energy efficiency of the network.
    No preview · Article · Jan 2015
  • Ashish James · A.S. Madhukumar
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    ABSTRACT: In rateless coded networks, packets get transmitted at rates dependent on the instantaneous channel states of the wireless links between nodes. The overall latency suffered by such networks forces to conserve the end-to-end delay, especially for real-time applications, by limiting the number of rateless coded transmissions. However in such delay constrained networks (DCNs), the performance of rateless codes deteriorates due to the lack of sufficient mutual information for successfully recovering the entire source packets. In this context, a novel spectrally efficient transmission scheme for reliable multihop data transfer is proposed in this paper. The proposed scheme ensures the reliable delivery of information packets to the nodes in the network by exploiting the broadcast nature of wireless transmission. This inherent implicit feedback channel is utilised to determine the packet loss across hops. This paper also analytically analyses the optimum number of packets retrievable within the specified delay constraint to minimize packet loss across hops.
    No preview · Article · Jan 2015
  • A. James · A.S. Madhukumar
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    ABSTRACT: Rateless code properties ideally suit multi-node transmissions and have been extensively employed in multihop delay tolerant networks (DTNs). However conventional multihop networks, where the transmission proceeds from one-hop to the next, may lead to starvation of some nodes with good channel conditions. In such instances, the overall latency can be alleviated by cooperation among the forwarding nodes. This paper analytically quantifies the latency of both conventional and cooperative rateless coded delay tolerant multihop networks by deriving the exact closed form equations for the channel usage. These are verified and supported with results from extensive simulation studies.
    No preview · Article · Jan 2015
  • Nguyen Duong · A.S. Madhukumar · Dusit Niyato

    No preview · Article · Jan 2015 · IEEE Transactions on Vehicular Technology
  • Rajendra Sirigina · A. S. Madhukumar

    No preview · Article · Jan 2015 · IEEE Transactions on Communications
  • Rajendra Sirigina · A.S. Madhukumar

    No preview · Article · Jan 2015 · IEEE Transactions on Wireless Communications
  • Ponnu Jacob · Ashish James · A. S. Madhukumar
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    ABSTRACT: With the introduction of third generation mobile services, femtocells are considered as an economically feasible solution for combining mobile and internet technologies, thereby giving fast and reliable access to data with a better coverage. However, it is well-known that the femtocells and macrocells sharing the same licensed frequency spectrum results in heavy cross-tier interference which degrades the downlink performance considerably. In this paper, we investigate a novel frequency–division duplex allocation strategy which eliminates the downlink cross-tier interference to the femtocell network from the macrocell base station throughout its coverage area. The proposed scheme seamlessly embed the femtocells within a macrocell resource network to create a heterogeneous two-tier system. It makes use of a cross-tier complementary spectrum sharing technique known as reverse frequency allocation (RFA) where the frequency carriers used in the macrocell transmission are reversed and allocated to femtocells. As a result, it better balances the requirement of greater inter-cell orthogonality and reduced inter-cell interference since macrocell and femtocell operates on different bands in uplink and downlink. It also assures enhanced spectral efficiency and the well-known benefit of reduced outage probability, especially for cell-edge users. This work further analytically quantifies and highlights through simulation results that RFA guarantees greater overall network throughput in the downlink and reduced cross-tier interference regardless of the positioning of the femtocell with respect to the macrocell base station. Also it is to be noted that, with recent academic surveys illuminating that the benefit of femtocells is reflected more in downlink, the focus of the current work is on downlink transmission where the traffic is high and the deployment is more beneficial.
    No preview · Article · Dec 2014 · Wireless Networks
  • S. Barman Roy · A. S. Madhukumar
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    ABSTRACT: For a multiple access channel, each user has its own power constraint. However, when a multiple access channel is being considered as the dual of a broadcast channel, it must exploit the additional freedom in power allocation and the constraint should be a sum power constraint. Duality helps us to transform the non-convex problems in a broadcast channel to convex problems in a multiple access channel. This helps to solve sum-rate optimisation problems with linear power constraints. However, maximising the sum-rate does not completely characterise the entire rate region boundary, formally called as the Pareto frontier. This work first reviews some of the existing results of polymatroid formulation from the Pareto optimality perspective and then proposes a complete characterisation of the Pareto frontier to show its relationship with the sum-rate optimisation problem. The significance of decoding order on the achievable rate region is considered. The work also shows some of the decoding orders to be suboptimal in Pareto sense and proposes an algorithm to find the correct decoding order based on power allocation. Simulation results are presented to support the theoretical arguments.
    No preview · Article · Dec 2014 · Wireless Networks
  • Ponnu Jacob · A. S. Madhukumar · A. Alphones
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    ABSTRACT: Multi-tier networks comprising of macro-cellular network overlaid with less power, short range, home-base station like femtocells provide an economically feasible solution for meeting the unrelenting traffic demands. However, femtocells that use co-channel allocation with macrocells result in cross-tier interference which eventually degrades the system performance. It is for this reason that, cross-polarized data transmission is proposed in this paper as a potential approach towards improving the spectral efficiency of cellular systems and at the same time permitting co-channel allocation. Here two independent information channels occupying the same frequency band can be transmitted over a single link. The paper evaluates a scenario where femtocell network makes use of right hand circular polarization (RHCP) and macrocell network makes use of left hand circular polarization (LHCP) for signal transmission. The polarizations being orthogonal to each other due to their sense of rotation ensure isolation between the networks and enable both of them to use the same spectral resources simultaneously. Analytical and simulation results prove that this opens the scope for an easily implementable, remarkable opportunity in the context of two-tier femto-macro network that can increase the system capacity. The paper closes by discussing the technical challenges involved in the implementation as well as the possible solutions to overcome the same.
    No preview · Article · Sep 2014 · Computer Communications
  • Ashish James · A. S. Madhukumar
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    ABSTRACT: Rateless code properties ideally suit multi-node transmissions with decode-and-forward based relaying strategy, and have been extensively employed in delay tolerant networks. The overall latency suffered by such networks forces to conserve the end-to-end delay, especially for real-time applications, by limiting the number of rateless coded transmissions. However, the performance of rateless codes deteriorates in such circumstances due to the lack of sufficient mutual information for successfully recovering the entire source packets. This performance degradation can be gauged by the average packet recovery and cooperation among nodes results in enhanced performance. The exact closed-form equations for the average packets retrieved based on the channel usage for such delay constrained networks (DCNs) is derived in this paper. These are verified and supported with results from extensive simulation studies.
    No preview · Conference Paper · Jun 2014
  • Nguyen Duy Duong · A. S. Madhukumar
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    ABSTRACT: This study addresses the problem of spectrum trading in a cognitive radio network with multiple primary users (PUs) competing to sell spectrum to a secondary user (SU). The spectrum trading process is modelled using a 'Cournot game model' of competition by which the PUs set the size of spectrum to sell. In this study, the spectrum requirements for the PUs?? services are not fixed but time varying, and the spectrum trading process is carried out before the realisation of these values. If the spectrum retained for a PU after selling is less than the spectrum requirement for the PU's service, a cost must be charged to the PU. The Nash equilibrium (NE) for a static game when the PUs have complete knowledge on the utility functions of other PUs is studied first. A dynamic game, in which the players adaptively change their strategies to reach the NE, is discussed subsequently. Finally, the trading problem is extended to a scenario which involves multiple SUs.
    No preview · Article · Jun 2014 · IET Signal Processing
  • Nguyen Duy Duong · A. S. Madhukumar
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    ABSTRACT: The invention of cognitive radio (CR) concept aims to overcome the spectral scarcity issues of emerging radio systems by exploiting under-utilization of licensed spectrum. Determining how to allocate unused frequency bands among CR is one of the most important problems in CR networks. Because different CRs may have different quality-of-service requirements, they may have different objectives. In voice communication, high-speed transmission is the most important factor; hence, voice radios always try to maximize their transmission rate. However, in data communication, the most important factor is the bit error rate. The data radios always try to maximize their signal-to-interference-plus-noise ratio (SINR). In this paper, two non-cooperative games named interference minimization game and capacity maximization game, which reflect the target of data radios and voice radios, respectively, are proposed. From the simulations, after these games are applied, the average SINRs of all players at each channel are improved. The average SINR of players in each channel after applying the capacity maximization game is smaller than that after applying the interference minimization game. However, in comparison with that after applying the interference minimization game, the average capacity of players after applying capacity maximization approach is larger. Copyright (c) 2012 John Wiley & Sons, Ltd.
    No preview · Article · Apr 2014 · Wireless Communications and Mobile Computing
  • Carlos G. Diaz · Walid Saad · Behrouz Maham · Dusit Niyato · A. S. Madhukumar
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    ABSTRACT: Wireless small cell networks and device-to-device (D2D) communications are seen as two major features of next-generation wireless networks. In this paper, a novel approach for enabling D2D communication underlaid on a wireless small cell network is proposed. Unlike existing works which focus on network performance analysis given a chosen communication mode, in this paper, the strategic selection of a desired wireless communication mode between pairs of users is studied. On the one hand, communication using the small cells can provide reliable transmission but is limited by interference and backhaul constraints. On the other hand, D2D communication can provide high capacity due to devices' proximity but is limited by increased interference. To capture these properties, the problem is modeled as a noncooperative game in which pairs of communicating users can strategically decide on whether to communicate with one another via the small cell infrastructure or via direct D2D communication. In this proposed game, each device selects its preferred communication mode while optimizing a utility function that captures the various involved tradeoffs between communication performance and associated costs. For solving this game, a distributed best response-based approach is proposed using which the users can reach a Nash equilibrium. Simulation results show that the resulting network at the equilibrium is composed of a mixture of D2D and small cell communication links. The results also show that the proposed approach yields a significant improvement in terms of the average utility per communicating pair when compared with the cases in which the users communicate via only the small cells or via only D2D.
    No preview · Conference Paper · Apr 2014

Publication Stats

716 Citations
105.99 Total Impact Points

Institutions

  • 1997-2015
    • Nanyang Technological University
      • • School of Computer Engineering
      • • Center for Multimedia and Network Technology
      Tumasik, Singapore
  • 2010
    • Tohoku University
      • Graduate School of Engineering
      Sendai-shi, Miyagi, Japan
  • 2003-2007
    • Institute for Infocomm Research
      Tumasik, Singapore
    • Singapore-MIT Alliance
      Cambridge, Massachusetts, United States
  • 2006
    • Nanyang Normal University
      Nan-yang-shih, Henan Sheng, China
  • 2004
    • National University of Singapore
      Tumasik, Singapore