Abstract

In this paper, we consider the problem of relay selection in a cognitive full-duplex two-way multiple-input multiple-output relaying network. The cognitive nodes operate on the same frequency as the licensed primary user (PU). The end-to-end communication between the secondary users (SU) via a secondary relay (SR) takes two time slots. The SR operates on amplify-and-forward (AF) protocol. In the first time slot, the SR relay with the highest receive signal-to-noise ratio is selected as the optimal relay. At the same time, the precoders at the SU are designed to limit the interference to the PU below a certain threshold. All the nodes in the network are assumed to have imperfect knowledge of channel state information of their loopback self-interference channels and hence experience residual self-interference (RSI). After selecting the optimal SR, in the next time slot, we design the SR precoder and SU receive filters, to mitigate the RSI. We do so by minimizing the sum of mean square error of the end-to-end communication with a transmit power constraint at SR. To curb the effect of cumulative RSI caused by the AF operation of the SR, we update the SR precoder and SU receive filters at each time slot. The efficacy of our proposed designs is illustrated in the simulation results.

Abstract

In this paper, we consider the design of optimal transceiver and relay processing algorithms for a full-duplex (FD) two-way amplify-and-forward (AF) multiple-input multiple-output (MIMO) relaying system. We assume the channel state information of loopback self-interference (SI) channels to be imperfect. The nodes employ pre-coders and receive filters for suppressing the residual SI. The optimal precoders at transceivers are designed by equalising the signal-to-interference-plus-noise ratio at the relay and transceiver. Using the transceiver precoders thus designed, we then design the optimal relay precoder and transceiver receive filters by minimizing the sum of mean square error at the transceivers. The optimal precoders and receive filters are continuously updated to account for the cumulative interference effect caused by AF operation of the FD relay. The secrecy performance of this system in the presence of a passive eavesdropper is analyzed by considering the relay signal to be artificial noise for the eavesdropper. The effectiveness of the proposed design is demonstrated in our simulation results.

Abstract

Millimeter wave (mmWave) communication is envisioned as a potential technology for next generation mobile communication as it can offer multi-gigabit-per-second data rate and a huge unlicensed spectrum. In this paper, we present a signal leakage-based low-complexity hybrid analog-digital transceiver design for a mmWave communication system operating in a K-user MIMO interference channel. Owing to higher cost and power consumption of components at mmWave frequencies, optimal system design with reduced hardware and computational complexity is critical to make the commercial use of mmWave communication viable. We achieve reduced hardware complexity of the proposed design by employing sparse approximation techniques for large antenna array. The proposed design is based on the maximization of signal- to-leakage-plus-noise ratio (SLNR) for all users. This leads to the reduced computational complexity of the overall system. Numerical results comparing the proposed design with existing iterative solution demonstrate that it can achieve comparable performance with reduced hardware and computational complexity. Performance of the proposed design with various dictionaries considered for beamforming has also been compared and illustrated in the simulation results.

Abstract

The existence of perceptually distinct numerosity ranges has been proposed for small (i.e., subitizing range) and larger numbers based on differences in precision, Weber fractions, and reaction times. This raises the question of whether such dissociations reflect distinct mechanisms operating across the two numerosity ranges. In the present work, we explore the predictions of a single-layer recurrent on-center, off-surround network model of attentional priority that has been applied to object individuation and enumeration. Activity from the network can be used to model various phenomena in the domain of visual number perception based on a single parameter: the strength of inhibition between nodes. Specifically, higher inhibition allows for precise representation of small numerosities, while low inhibition is preferred for high numerosities. The model makes novel predictions, including that enumeration of …

Abstract

Perception of time is an active process that takes place continually. However, we are yet to learn its exact mechanisms conclusively. The temporal bisection task is ideal to investigate the circuitry underlying time perception. Caffeine, a commonly used stimulant, has been known to play a role in modulation of time perception. The objective of this article is to explore the role of caffeine, a neuromodulator, in the perception of time in human beings by conducting suitable experiments. The experiment shows that an expansion of time is perceived by subjects after caffeine ingestion and that caffeine has an accelerating effect on our time perception system. Additionally, we present a preliminary 2-step decision model that fits the results of the experiment and potentially gives insights into the mechanisms of caffeine. We conclude by pointing out future directions towards a more biologically realistic computational model.

Abstract

An index coding (IC) problem consisting of a server and multiple receivers with different side-information and demand sets can be equivalently represented using a fitting matrix.A scalar linear index code to a given IC problem is a matrix representing the transmitted linear combinations of the message symbols. The length of an index code is then the number of transmissions (or equivalently, the number of rows in the index code). An IC problem I ext is called an extension of another IC problem I if the fitting matrix of Iis a sub matrix of the fitting matrix of I ext. We first present a straight forward mordern extension Iextof an IC problem I for which an index code is obtained by concatenating m copies of an index code of I. The length of the codes is the same for both I and Iext,and if the index code for I has optimal length then so does the extended code for I ext. More generally, an extended IC problem of I having the same optimal length as I is said to be a rank-invariant extension of I. We then focus on2-order rank-invariant extensions of I, and present constructions of such extensions based on in volutory permutation matrices.

Abstract

The index coding problem is a problem of efficient broadcasting with side-information. In uniprior index coding,the sets of side-information symbols possessed by different receivers are disjoint. For single uniprior index coding, in which each receiver has a single unique side-information symbol, a polynomial complexity construction of an optimal index code is known from prior work. In this work, we model the uniprior index coding problem as a super graph, and focus on a class of uniprior problems defined on special supergraphs known as generalized cycles in which the sizes of the demand set andthe side-information set are equal at each receiver. For such problems, we prove upper and lower bounds on the optimal broadcast rate. Using a connection with Eulerian directed graphs,we also show that the upper and lower bounds are equal fora subclass of uniprior problems. We show the NP-hardness offinding the lower bound for uniprior problems on generalized cycles, hence contrasting such uniprior problems with single uniprior problems. Finally, we look at a simple extension of the generalized cycle uniprior class for which we give bounds on the optimal rate and show an explicit scheme which achieves the upper bound

Abstract

Coded caching schemes on broadcast networks with user caches help to offload traffic from peak times to off-peak times by prefetching information from the server to the usersduring off-peak times and thus serving the users more efficiently during peak times using coded transmissions. We consider the problem of secretive coded caching which was proposed recently,in which a user should not be able to decode any information about any file that the user has not demanded. We propose a new secretive coded caching scheme which has a lower average rate compared to the existing state-of-the-art scheme, for the same memory available at the users. The proposed scheme is based one exploiting the presence of common demands between multiple users

Abstract

Linear index coding can be formulated as an inter-ference alignment problem, in which precoding vectors of theminimum possible length are to be assigned to the messagesin such a way that the precoding vector of a demand (at somereceiver) is independent of the space of the interference (non side-information) precoding vectors. An index code has rate1lif theassigned vectors are of lengthl. In this paper, we introduce thenotion of strictly rate1Lmessage subsets which must necessarilybe allocated precoding vectors from a strictlyL-dimensionalspace (L=1,2,3) in any rate13code. We develop a generalnecessary condition for rate13feasibility using intersections ofstrictly rate1Lmessage subsets. We apply the necessary conditionto show that the presence of certain interference configurationsmakes the index coding problem rate13infeasible. We alsoobtain a class of index coding problems, containing certaininterference configurations, which are rate13feasible based on theidea ofcontractionsof an index coding problem. Our necessaryconditions for rate13feasibility and the class of rate13feasibleproblems obtained subsume all such known results for rate13index coding

Abstract

MapReduce is a widely used framework for distributed computing. Data shuffling between the Map phase and Reduce phase of a job involves a large amount of data transfer across servers, which in turn accounts for increase in job completion time. Recently, Coded MapReduce has been proposed to offer savings with respect to the communication cost incurred in data shuffling. This is achieved by creating coded multicast opportunities for shuffling through repeating Map tasks at multiple servers. We consider a server-rack architecture for MapReduce and in this architecture, propose to divide the total communication cost into two: intrarack communication cost and cross-rack communication cost. Having noted that cross-rack data transfer operates at lower speed as compared to intrarack data transfer, we present a scheme termed as Hybrid Coded MapReduce which results in lower cross-rack communication than Coded MapReduce at the cost of increase in intra-rack communication. In addition, we pose the problem of assigning Map tasks to servers to maximize data locality in the framework of Hybrid Coded MapReduce as a constrained integer optimization problem. We show through simulations that data locality can be improved considerably by using the solution of optimization to assign Map tasks to servers.