Degrees of Freedom of Interference Channels with CoMP Transmission and Reception

We study the Degrees of Freedom (DoF) of the K-user interference channel with coordinated multi-point (CoMP) transmission and reception. Each message is jointly transmitted by M_t successive transmitters, and is jointly received by M_r successive receivers. We refer to this channel as the CoMP channel with a transmit cooperation order of M_t and receive cooperation order of M_r. Since the channel has a total of K transmit antennas and K receive antennas, the maximum possible DoF is equal to K. We show that the CoMP channel has K DoF if and only if M_t + M_r is greater than or equal to K+1. For the general case, we derive an outer bound that states that the DoF is bounded above by the ceiling of (K+M_t+M_r-2)/2. For the special case with only CoMP transmission, i.e, M_r = 1, we propose a scheme that can achieve (K+M_t-1)/2 DoF for all K < 10, and conjecture that the result holds true for all K . The achievability proofs are based on the notion of algebraic independence from algebraic geometry.Comment: Submitted to IEEE Transactions on Information Theor

Are lead-free relaxor ferroelectric materials the most promising candidates for energy storage capacitors?

Dielectric capacitors offer high-power density and ultrafast discharging times as compared to electrochemical capacitors and batteries, making them potential candidates for pulsed power technologies (PPT). However, low energy density in different dielectric materials such as linear dielectrics (LDs), ferroelectrics (FEs), and anti-ferroelectric (AFEs) owing to their low polarization, large hysteresis loss and low breakdown strength, respectively, limits their real time applications. Thus, achieving a material with high dielectric constant, large dielectric breakdown strength and slim hysteresis is imperative to obtain superior energy performance. In this context, relaxor ferroelectrics (RFEs) emerged as the most promising solution for energy storage capacitors. This review starts with a brief introduction of different energy storage devices and current advances of dielectric capacitors in PPT. The latest developments on lead-free RFEs including bismuth alkali titanate based, barium titanate based, alkaline niobite based perovskites both in ceramics and thin films are comprehensively discussed. Further, we highlight the different strategies used to enhance their energy storage performance to meet the requirements of the energy storage world. We also provide future guidelines in this field and therefore, this article opens a window for the current advancement in the energy storage properties of RFEs in a systematic way.This study has been partially supported by (i) DST-SERB, Govt. of India through Grant ECR/2017/000068 (KCS), (ii) UGC through grant nos. F.4-5(59-FRP)/ 2014(BSR) and (iii) Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UIDB/FIS/04650/2020 (JPBS). The author A. R. Jayakrishnan acknowledges the Central University of Tamil Nadu, India for his Ph. D fellowship. The authors acknowledge the CERIC-ERIC Consortium for access to experimental facilities and financial support under proposal 20192055

Fixed Point Quantization of Deep Convolutional Networks

Abstract In recent years increasingly complex architectures for deep convolution networks (DCNs) have been proposed to boost the performance on image recognition tasks. However, the gains in performance have come at a cost of substantial increase in computation and model storage resources. Fixed point implementation of DCNs has the potential to alleviate some of these complexities and facilitate potential deployment on embedded hardware. In this paper, we propose a quantizer design for fixed point implementation of DCNs. We formulate and solve an optimization problem to identify optimal fixed point bit-width allocation across DCN layers. Our experiments show that in comparison to equal bitwidth settings, the fixed point DCNs with optimized bit width allocation offer &gt; 20% reduction in the model size without any loss in accuracy on CIFAR-10 benchmark. We also demonstrate that fine-tuning can further enhance the accuracy of fixed point DCNs beyond that of the original floating point model. In doing so, we report a new state-of-the-art fixed point performance of 6.78% error-rate on CIFAR-10 benchmark

Fluorocarbon adsorption in hierarchical porous frameworks

Metal-organic frameworks comprise an important class of solid-state materials and have potential for many emerging applications such as energy storage, separation, catalysis and bio-medical. Here we report the adsorption behaviour of a series of fluorocarbon derivatives on a set of microporous and hierarchical mesoporous frameworks. The microporous frameworks show a saturation uptake capacity for dichlorodifluoromethane of &#62;4 mmol g-1 at a very low relative saturation pressure (P/Po) of 0.02. In contrast, the mesoporous framework shows an exceptionally high uptake capacity reaching &#62;14 mmol g-1 at P/Poof 0.4. Adsorption affinity in terms of mass loading and isosteric heats of adsorption is found to generally correlate with the polarizability and boiling point of the refrigerant, with dichlorodifluoromethane &#62; chlorodifluoromethane &#62; chlorotrifluoromethane &#62; tetrafluoromethane &#62; methane. These results suggest the possibility of exploiting these sorbents for separation of azeotropic mixtures of fluorocarbons and use in eco-friendly fluorocarbon-based adsorption cooling

Multiuser Cognitive Radio Networks: An Information Theoretic Perspective

Achievable rate regions and outer bounds are derived for three-user interference channels where the transmitters cooperate in a unidirectional manner via a noncausal message-sharing mechanism. The three-user channel facilitates different ways of message-sharing between the primary and secondary (or cognitive) transmitters. Three natural extensions of unidirectional message-sharing from two users to three users are introduced: (i) Cumulative message sharing; (ii) primary-only message sharing; and (iii) cognitive-only message sharing. To emphasize the notion of interference management, channels are classified based on different rate-splitting strategies at the transmitters. Standard techniques, superposition coding and Gel'fand-Pinsker's binning principle, are employed to derive an achievable rate region for each of the cognitive interference channels. Simulation results for the Gaussian channel case are presented; they enable visual comparison of the achievable rate regions for different message-sharing schemes along with the outer bounds. These results also provide useful insights into the effect of rate-splitting at the transmitters, which aids in better interference management at the receivers.Comment: 50 pages, 15 figures, submitted to IEEE Transactions on Information Theor