On the Accuracy of Interference Models in Wireless Communications

We develop a new framework for measuring and comparing the accuracy of any wireless interference models used in the analysis and design of wireless networks. Our approach is based on a new index that assesses the ability of the interference model to correctly predict harmful interference events, i.e., link outages. We use this new index to quantify the accuracy of various interference models used in the literature, under various scenarios such as Rayleigh fading wireless channels, directional antennas, and blockage (impenetrable obstacles) in the network. Our analysis reveals that in highly directional antenna settings with obstructions, even simple interference models (e.g., the classical protocol model) are accurate, while with omnidirectional antennas, more sophisticated and complex interference models (e.g., the classical physical model) are necessary. Our new approach makes it possible to adopt the appropriate interference model of adequate accuracy and simplicity in different settings.Comment: 7 pages, 3 figures, accepted in IEEE ICC 201

Sublattice Interference in the Kagome Hubbard Model

We study the electronic phases of the kagome Hubbard model (KHM) in the weak coupling limit around van Hove filling. Through an analytic renormalization group analysis, we find that there exists a sublattice interference mechanism where the kagome sublattice structure affects the character of the Fermi surface instabilities. It leads to major suppression of Tc for d+id superconductivity in the KHM and causes an anomalous increase of Tc upon addition of longer-range Hubbard interactions. We conjecture that the suppression of conventional Fermi liquid instabilities makes the KHM a prototype candidate for hosting exotic electronic states of matter at intermediate coupling.Comment: 4+e pages, 3 figure

A novel interference rejection scheme for DS-CDMA using adaptive noise cancellation

This paper proposes a novel solution to the interference cancellation problem in mobile direct sequence code division multiple access (DS-CDMA) systems. Conventional adaptive interference cancellation techniques rely on a training sequence to update the taps of an adaptive filter or decision feedback equaliser (DFE). The strategy proposed in this paper replaces this conventional optimal filtering approach by one based on the principles of adaptive noise cancellation (ANC). As opposed to the conventional optimal filtering approach, the ANC approach exploits the cyclo-stationary properties of the multiple access interference, in order to model the interference generation process. Silent periods (c.f. voice activity factor) can be exploited to derive the interference model. This removes the need for a training sequence and associated system overheads. The scheme employs a conjugate matched filter (CMF) to generate an interference reference input to the adaptive noise canceller. A preliminary investigation of the performance of the proposed scheme is undertaken. The ANC scheme is shown to have a significantly better performance than the conventional receiver and the DFE in the multiple access interference limited environment. It is shown that the scheme can be extended to provide blind interference cancellation in the case of acute near-far conditions

Retrospective Interference Alignment

We explore similarities and differences in recent works on blind interference alignment under different models such as staggered block fading model and the delayed CSIT model. In particular we explore the possibility of achieving interference alignment with delayed CSIT when the transmitters are distributed. Our main contribution is an interference alignment scheme, called retrospective interference alignment in this work, that is specialized to settings with distributed transmitters. With this scheme we show that the 2 user X channel with only delayed channel state information at the transmitters can achieve 8/7 DoF, while the interference channel with 3 users is able to achieve 9/8 DoF. We also consider another setting where delayed channel output feedback is available to transmitters. In this setting the X channel and the 3 user interference channel are shown to achieve 4/3 and 6/5 DoF, respectively

A mixed-cell propagation model for interference prediction in a UMTS network

With the support of mixed cells and hierarchical cell structures in UMTS, propagation information (coverage and interference) between different cell types is required. A mixed-cell propagation model is presented which is suitable for predicting interference in mixed macrocellular and microcellular environments. The main features of the model are described together with examples of interference prediction including C/I and most-likely-server plots. Comparisons between model predictions and measurements for a mixed cell environment are also presented