Interference (wave propagation)

About: Interference (wave propagation) is a research topic. Over the lifetime, 26086 publications have been published within this topic receiving 321110 citations.

Multi-User Two-Way Relay Networks with Distributed Beamforming

Abstract: We consider a two-way relay network consisting of multiple pairs of single-antenna users and multiple distributed single-antenna relays. The two communication peers in each pair of users transmit simultaneously to the relays in the first time slot, and the relays rebroadcast the received sum signal weighted by a complex gain, in the second time slot. For multi-user systems, the signal arriving at the users contains not only self interference from the back-propagation of user signals, but also inter-pair interferences from other pairs of users. In this paper, we use zero-forcing (ZF) to cancel the inter-user interference, assuming that channel-state information for all relay-peer connections are known at every relay, but no data exchange occurs between relays. We also derive two closed-form expressions for zero-forcing beamforming weights, corresponding to two different relay power constraints, which can be implemented in a distributed manner. The first approach uses standard ZF to null out every inter-pair interference and the second approach sets the total inter-pair interference to zero. We also derive a closed-form upper bound of the achievable sum-rate and show that both methods achieve the same multiplexing gain when the number of relays N is sufficient for perfect zero-forcing, namely 2K2 + K, where K is the number of user pairs. For the case of insufficient number of relays, we also propose two solutions for beamforming weights, i.e., based on diagonal loading and use of the pseudo-inverse, and compare their advantages and weaknesses.

Accelerating Optical Beams

Abstract: Thanks to their unique interference, accelerating beams appear to curve as they travel. They require no waveguiding structures or external potentials and appear even in free space. This beautiful phenomenon has led to many intriguing ideas and exciting new applications.

Secure Degrees of Freedom of $K$ -User Gaussian Interference Channels: A Unified View

Abstract: We determine the exact sum secure degrees of freedom (d.o.f.) of the $K$ -user Gaussian interference channel. We consider three different secrecy constraints: 1) $K$ -user interference channel with one external eavesdropper (IC-EE); 2) $K$ -user interference channel with confidential messages (IC-CM); and 3) $K$ -user interference channel with confidential messages and one external eavesdropper (IC-CM-EE). We show that for all of these three cases, the exact sum secure d.o.f. is ${K(K-1)}/{(2K-1)}$ . We show converses for IC-EE and IC-CM, which imply a converse for IC-CM-EE. We show achievability for IC-CM-EE, which implies achievability for IC-EE and IC-CM. Our converse is based on developing a direct relationship between the differential entropies of the channel inputs and the rates of the users, and quantifying the effect of eavesdropping on the rates in terms of the differential entropies of the eavesdroppers' observations. Our achievability is based on structured signaling, structured cooperative jamming, channel prefixing, and asymptotic real interference alignment. While the traditional interference alignment provides some amount of secrecy by mixing unintended signals in a smaller subspace at every receiver, in order to attain the optimum sum secure d.o.f., we incorporate structured cooperative jamming into the achievable scheme, and intricately design the structure of all of the transmitted signals jointly.

An analytic approximation of the uplink capacity in a UMTS network with heterogeneous traffic

Abstract: The fast computation of blocking probabilities and the resulting capacity is one of the crucial tasks in the planning process of UMTS networks. The admission control in WCDMA networks is based on the momentary interference which includes both own-cell and other-cell interference. Since both interference terms are stochastic values we speak of soft blocking. The number of users in the system is not sufficient for deciding whether to accept a new call or not. Instead, it is blocked with a certain probability depending on the number of users in the system, the activity of the users, and the other-cell interference. In this paper we present a time-efficient algorithm to compute blocking probabilities in a WCDMA network operating with several services. Assuming Bernoulli activity and modelling the other-cell interference as a lognormal random variable the blocking probabilities are computed using an approximation based on the Kaufman-Roberts recursion.

A Kind of Novel Method of Power Allocation With Limited Cross-Tier Interference for CRN

Abstract: A kind of novel method of power allocation with limited cross-tier interference for cognitive radio network (CRN) is proposed in this paper. In this method, an interference-limited power allocation algorithm based on filter bank multi-carrier-offset quadrature amplitude modulation (FBMC-OQAM) is put forward. In order to improve the energy efficiency of the entire network and protect secondary users (SUs) in the network from too much interference, cross-tier interference limit is adopted, at the same time, virtual queue is designed to transform the extra packet delay caused by the contention for the channel of multi-user into the queuing delay. Taking the energy efficiency as the objective function, a nonlinear programming approach with nonlinear constraints is innovatively proposed under the constraints of time delay and transmission power. An iterative algorithm in order to solve the problem is also put forward. In the new algorithm, the fractional objective function is transformed into polynomial form, and the global optimal solution is obtained by iteration after reducing the computational complexity. In addition, a sub-optimal algorithm is proposed to reduce computational complexity. The experimental results show that the optimal algorithm has higher performance while the sub-optimal algorithm has a lower computational complexity. The presented method has very good practical importance for the CRN.