Cloud computing allows developers of mobile apps to overcome limited computing, storage, and power resources of modern smartphones. Besides these huge advantages, the hidden utilization of cloud services by mobile apps leads to severe privacy concerns. To overcome these concerns and allow users and companies to properly assess the risks of hidden cloud usage, it is necessary to provide transparency over the cloud services utilized by smartphone apps. In this paper, we present our ongoing work on TRINICS to provide transparent information on individual cloud service usage. To this end, we analyze network traffic of smartphone apps with the goal to detect and uncover cloud usage. We present the resulting statistics on cloud usage to the user and put these numbers into context through anonymous comparison with users' peer groups (i.e., users with similar sociodemographic background and interests). By doing so, we enable users to make an informed decision on suitable means for sufficient self data protection for their future use of apps and cloud services.

A network of three nodes mutually communicating with each other is studied. This multi-way network is a suitable model for three-user device-to-device communications. The main goal of this paper is to characterize the capacity region of the underlying Gaussian three-way channel (3WC) within a constant gap. To this end, a capacity outer bound is derived using cut-set bounds and genie-aided bounds. For achievability, the 3WC is first transformed into an equivalent star channel. This latter is then decomposed into a set of “successive” sub-channels, leading to a sub-channel allocation problem. Using backward decoding, interference neutralization, and known results on the capacity of the star-channel relying of physical-layer network coding, an achievable rate region for the 3WC is obtained. It is then shown that the achievable rate region is within a constant gap of the developed outer bound, leading to the desired capacity approximation. Interestingly, in contrast to the Gaussian two-way channel (TWC), adaptation is necessary in the 3WC. Furthermore, message splitting is another ingredient of the developed scheme for the 3WC, which is not required in the TWC. The two setups are, however, similar in terms of their sum-capacity pre-log, which is equal to 2. Finally, some interesting networks and their approximate capacities are recovered as special cases of the 3WC, such as the cooperative broadcast channel and multiple access channel.

A 3-user device-to-device (D2D) communications scenario is studied where each user wants to send and receive a message from each other user. This scenario resembles a 3-way communication channel. The capacity of this channel is unknown in general. In this paper, a sum-capacity upper bound that characterizes the degrees-of-freedom of the channel is derived by using genie-aided arguments. It is further shown that the derived upper bound is achievable within a gap of 2 bits, thus leading to an approximate sum-capacity characterization for the 3-way channel. As a by-product, interesting analogies between multi-way communications and multi-way relay communications are concluded.

We investigate the symmetric Degrees-of-Freedom (DoF) of a homogeneous multiple-input multiple-output (MIMO) 3-way channel with MTtransmit antennas and MRreceive antennas at each user. The 3-way channel extends the two-way channel to three users, who exchange six messages in total, i. e., there is one message from each user to each of the two other users. We assume that each user operates in a perfect full-duplex mode. Genie-aided upper bounds on the DoF of the channel are derived and it is shown that those are achievable by combining MIMO interference alignment, null-space beam-forming and zero-forcing. A particular gain from this homogeneous setup is that the symmetric DoF allocation providing complete fairness among all users is sum-DoF optimal.

We consider the problem of cyclic interference alignment (IA) on the 3 - user X- network and show that it is infeasible to exactly achieve the upper bound of equation degrees of freedom for the lower bound of n = 5 signalling dimensions and K = 3 user-pairs. We observe that this infeasibility goes beyond the problem of common eigenvectors in invariant subspaces within spatial IA. In order to gain non-asymptotic feasibility with minimal intervention, we first investigate a communication strategy that enables IA by feedforwarding a subset of messages with minimal rate. In a second step, we replace the proposed feedforward strategy by an analogous cyclic interference alignment and cancellation scheme with a backhaul network on the receiver side and also by its dual cyclic interference neutralization scheme with a backhaul network on the transmitter side.

In this work, we investigate the Interference Neutralization scheme on a 2×2×2 relay-interference channel w.r.t. the Cyclic Interference Alignment framework. We formulate sufficient and necessary conditions for this particular Interference Neutralization scheme to achieve the min-cut upper bound, i.e., two degrees of freedom, confirming the work on Aligned Interference Neutralization by Gou et al. Furthermore, we translate our proposed scheme to a generalized version of the asymptotic Aligned Interference Neutralization scheme based on spatial Interference Alignment.

A two-way relay-interference channel describes a system of four communicating transceivers with two interjacent parallel relays arranged in a bidirectional 2 × 2 × 2 relay-interference network. Two pairs of transceivers are each communicating bidirectionally with the aid of both relays. All transceivers and relays are assumed to operate in full-duplex mode. Since Interference Neutralization is known as a promising method to achieve the cut-set upper bounds on the data rates of the unidirectional relay-interference channel, we investigate a Cyclic Interference Neutralization scheme on the corresponding bidirectional relay-interference channel w.r.t. a conceptual channel model based on a polynomial ring. We show that, if the channel matrix satisfies a certain set of symmetry conditions, a total number of 4 degrees of freedom is asymptotically achievable.

The impact of significantly long delays is a central problem one has to face in the ergodic interference alignment scheme. In this work, we consider the delay-rate tradeoff in a fully connected K-user Gaussian interference channel through the lens of partial interference alignment. In the concept of partial interference alignment, only a subset of user-pairs with a favorable interference pattern is aligned. We explore two flexible communication schemes: At first, we propose a scheme with uniform delay-rate demands. Then we introduce the delay-rate tradeoff for a case of non-uniform demands such that also imbalanced delays and rates can be investigated.

We explore an algorithmic approximation of achievable lower bounds for the generalized degrees of freedom on finite-field linear deterministic K-user interference channels. With a heuristic greedy algorithm, derived from results on the maximum independent set problem in graph theory, the max-min generalized degrees of freedom for desired links are approached. The idea of interference alignment is implicitly contained in the algorithm. It is applied to deterministic interference channels with entirely symmetric cross-channel gains, and compared to the generalized degrees of freedom of a currently known coding scheme. The greedy heuristic also generalizes to deterministic interference channels with asymmetric channel gains.