Generalized Interference Alignment—Part II: Application to Wireless Secrecy

In contrast to its wired counterpart, wireless communication is highly susceptible to eavesdropping due to the broadcast nature of the wireless propagation medium. Recent works have proposed the use of interference to reduce eavesdropping capabilities in wireless wiretap networks. However, the concurrent effect of interference on both eavesdropping receivers (ERs) and legitimate receivers has not been thoroughly investigated, and careful engineering of the network interference is required to harness the full potential of interference for wireless secrecy. This two-part article addresses this issue by proposing a generalized interference alignment (GIA) technique, which jointly designs the transceivers at the legitimate partners to impede the ERs without interfering with LRs. In Part I, we have established a theoretical framework for the GIA technique. In Part II, we will first propose an efficient GIA algorithm that is applicable to large-scale networks and then evaluate the performance of this algorithm in stochastic wireless wiretap network via both analysis and simulation. These results reveal insights into when and how GIA contributes to wireless secrecy

Secure Degrees of Freedom Regions of Multiple Access and Interference Channels: The Polytope Structure

The sum secure degrees of freedom (s.d.o.f.) of two fundamental multi-user network structures, the K-user Gaussian multiple access (MAC) wiretap channel and the K-user interference channel (IC) with secrecy constraints, have been determined recently as K(K-1)/(K(K-1)+1) [1,2] and K(K-1)/(2K-1) [3,4], respectively. In this paper, we determine the entire s.d.o.f. regions of these two channel models. The converse for the MAC follows from a middle step in the converse of [1,2]. The converse for the IC includes constraints both due to secrecy as well as due to interference. Although the portion of the region close to the optimum sum s.d.o.f. point is governed by the upper bounds due to secrecy constraints, the other portions of the region are governed by the upper bounds due to interference constraints. Different from the existing literature, in order to fully understand the characterization of the s.d.o.f. region of the IC, one has to study the 4-user case, i.e., the 2 or 3-user cases do not illustrate the generality of the problem. In order to prove the achievability, we use the polytope structure of the converse region. In both MAC and IC cases, we develop explicit schemes that achieve the extreme points of the polytope region given by the converse. Specifically, the extreme points of the MAC region are achieved by an m-user MAC wiretap channel with (K-m) helpers, i.e., by setting (K-m) users' secure rates to zero and utilizing them as pure (structured) cooperative jammers. The extreme points of the IC region are achieved by a (K-m)-user IC with confidential messages, m helpers, and N external eavesdroppers, for m>=1 and a finite N. A byproduct of our results in this paper is that the sum s.d.o.f. is achieved only at one extreme point of the s.d.o.f. region, which is the symmetric-rate extreme point, for both MAC and IC channel models.Comment: Submitted to IEEE Transactions on Information Theory, April 201

Interference as an Issue and a Resource in Wireless Networks

This dissertation will be focused on the phenomenon of interference in wireless net- works. On one hand, interference will be viewed as a negative factor that one should mitigate in order to improve the performance of a wireless network in terms of achiev- able rate, and on the other hand as an asset to increase the performance of a network in terms of security. The problems that will be investigated are, first, the character- isation of the performance of a communication network modelled as an interference channel (IC) when interference alignment (IA) is used to mitigate the interference with imperfect knowledge of the channel state, second, the characterisation of the secrecy in the Internet-of-Things (IoT) framework where some devices may use artificial noise to generate interference to potential eavesdroppers. Different scenarios will be studied in the case where interference is unwanted; the first one is when the channel error is bounded. A lower bound on the capacity achievable in this case is provided and a new performance metric namely the saturating SNR is derived. The derived lower bound is studied with respect to some parameters of the estimation strategy when using Least-Square estimation to estimate the channel ma- trices. The second scenario deals with unbounded Gaussian estimation errors, here the statistical distribution of the achievable rate is given along with a new performance metric called outage probability that simplifies the study of the IC with IA under im- perfect CSI. The results are used to optimise the network parameters and extend the analysis further to the case of cellular networks. In the wanted interference situation, the secrecy of the worst-case communication is studied and the conditions for secrecy are provided. Furthermore the average number of secure links achievable in the network is studied according to a theoretical model that is developed for the IoT case