Ratheesh Kumar Mungara

An Analytical Framework for Device-to-Device Communication in Cellular Networks

This paper presents a framework that enables characterizing analytically the spectral efficiency achievable by device-to-device (D2D) communication integrated with a cellular network. This framework is based on a stochastic geometry formulation with a novel approach to the modeling of interference and with the added possibility of incorporating exclusion regions to protect cellular receivers from excessive interference from active D2D transmitters. To illustrate the potential of the framework, a number of examples are provided. These examples confirm the potential of D2D communication in situations of strong traffic locality, as well as the effectiveness of properly sized exclusion regions.

System-Level Performance of Interference Alignment

Capitalizing on the analytical potency of stochastic geometry and on some new ideas to model intercell interference, this paper presents analytical expressions that enable quantifying the spectral efficiency of interference alignment (IA) in cellular networks without the need for simulation. From these expressions, the benefits of IA are characterized. Even under favorable assumptions, IA is found to be beneficial only in very specific and relatively infrequent network situations, and a blanket utilization of IA is found to be altogether detrimental. Applied only in the appropriate situations, IA does bring about benefits that are significant for the users involved but relatively small in terms of average spectral efficiency for the entire system.

Overhead and Spectral Efficiency of Pilot-Assisted Interference Alignment in Time-Selective Fading Channels

The spectral efficiency achievable by interference alignment (IA) in a K-user multiple-input-multiple-output interference channel is studied in the face of time-selective continuous fading explicitly estimated through pilot-symbol observations. The robustness of IA in such operationally relevant conditions is assessed through a joint optimization of the pilot overhead and the IA update interval, which are characterized - in high-power conditions - as solutions of a fixed-point equation. Variations of the formulation are given for both frequency-division duplexing (FDD) and time-division duplexing, the former requiring explicit feedback of the fading estimates and the latter relying on fading reciprocity. For the FDD variation, analog feedback is considered. In addition to arbitrary numbers of users and antennas and arbitrary temporal fading correlation functions, the derivations accommodate forward and reverse links with asymmetric power levels.

System-level performance of distributed cooperation

Distributed cooperation schemes such as Interference Alignment hold the promise of an increased number of spatial degrees of freedom and, with that, of substantially higher spectral efficiencies. Most results available to date, however, have been obtained in simplified settings featuring a small number of transmitters and receivers in isolation. While such controlled settings are excellent platforms to develop ideas and build intuition, they also conceal important aspects that are inherent to actual wireless systems. Chief among these is the fact that any small set of cooperating transmitters and receivers is bound to be embedded within a large system featuring many other transmitters and receivers. This paper studies the fundamental performance of IA, in the context of a large cellular network, and contrasts it with that of non-cooperative MIMO.

On the spatial spectral efficiency of ITLinQ

Device-to-device (D2D) communication allows serving local wireless traffic bypassing the systems infrastructure. The interference in D2D can be controlled by carefully allocating users to orthogonal channels. This paper analytically characterizes the spectral efficiency of the ITLinQ channelization technique. The analysis relies on a stochastic geometry formulation, which enables obtaining compact expressions while opening the door to an optimization of ITLinQs parameters.

Interference surge in full-duplex wireless systems

Historically unfeasible because of self-interference, full duplexing has now been experimentally demonstrated and is on the verge of commercial feasibility thanks to advances in self-interference cancellation. This will disrupt the interference landscape in wireless networks, bringing about an unprecedented richness whereby every transmitter interferes with every receiver. This paper characterizes the actual increase in system spectral efficiency given all this interference, and in the process it identifies new needs in interference management.

Performance evaluation of ITLinQ and FlashLinQ for overlaid device-to-device communication

We present a performance evaluation of ITLinQ and FlashLinQ, the two most popular schemes proposed to date to channelize D2D transmissions, i.e., to parse transmissions into noninterfering sets to be allocated to separate channels. Recognizing that it captures well the spatial characteristics of D2D networks, a stochastic geometry setting is utilized for this evaluation with the parameters of either scheme optimized in order to maximize the system spectral efficiency (bits/s/Hz per unit area). Although independently formulated and seemingly based on different principles, both schemes are found to exercise similar mechanisms to avoid situations of excessive interference, yielding substantial improvements with respect to unchannelized networks.

Overlaid device-to-device communication in cellular networks

We present an analytical characterization of the spectral efficiency achievable by D2D communication links overlaid on a cellular network. The analysis relies on a stochastic geometry formulation with a novel approach to the modeling and spatial averaging of interference, which facilitates obtaining compact expressions. These expressions are then applied to gauge the potential of D2D communication, which is found to be very sizeable in situations of strong traffic locality.

Pilot-assisted interference alignment in time-selective fading channels

The spectral efficiency achievable by IA (interference alignment) in a K-user interference channel is studied in the face of time-selective fading explicitly estimated through pilot-symbol observations. The robustness of IA is assessed through a joint optimization of the pilot overhead and the IA update interval, which are characterized-in the high-power conditions where IA is relevant-as solutions of a fixed-point equation.

Analytical Characterization of ITLinQ: Channel Allocation for Device-to-Device Communication Networks

Device-to-device (D2D) communication allows serving local wireless traffic bypassing the systems infrastructure. One way to control the interference in D2D networks is to carefully channelize transmissions. This paper presents an analytical characterization of ITLinQ, one of the principal D2D channelization schemes proposed to date. Recognizing that it captures well the spatial characteristics of D2D networks, a stochastic geometry setting is utilized for this analysis. The derived expressions enable gleaning insights on how ITLinQ avoids situations of excessive interference, and they facilitate optimizing the controllable parameters of ITLinQ so as to maximize the system spectral efficiency (bits/s/Hz per unit area). With the parameters thus optimized, the ultimate performance of ITLinQ can be evaluated with respect to other D2D channel allocation schemes. In particular, performance evaluation comparisons with the FlashLinQ scheme are provided, and the gains with respect to an unchannelized network are quantified.