Bho Matthiesen

Resource Allocation for Energy-Efficient 3-Way Relay Channels

Throughput and energy efficiency in 3-way relay channels are studied in this paper. Unlike previous contributions, we consider a circular message exchange. First, an outer bound and achievable sum rate expressions for different relaying protocols are derived for 3-way relay channels. The sum capacity is characterized for certain SNR regimes. Next, leveraging the derived achievable sum rate expressions, cooperative and competitive maximization of the energy efficiency are considered. For the cooperative case, both low-complexity and globally optimal algorithms for joint power allocation at the users and at the relay are designed so as to maximize the system global energy efficiency. For the competitive case, a game theoretic approach is taken, and it is shown that the best response dynamics is guaranteed to converge to a Nash equilibrium. A power consumption model for mmWave board-to-board communications is developed, and numerical results are provided to corroborate and provide insight on the theoretical findings.

Sampling Uniformly From the Set of Positive Definite Matrices With Trace Constraint

We derive a parameterization of positive definite matrices using the Cholesky decomposition in combination with hyperspherical coordinates. Based on the parameterization we develop a simple and efficient method to randomly generate positive definite matrices with constant or bounded trace according to a uniform distribution. Further, we present an efficient implementation using the inversion method and either rejection sampling or transforming a beta distribution. The matrix parameterization might be of independent interest, whereas the random sampling algorithm finds applications in Monte Carlo simulations, testing of algorithms, and performance studies. With the help of an abstract example we describe how the sampling method can be used to approximate the optimum in a difficult, e.g., nonconvex, optimization problem for which no solution or efficient global optimization algorithm is known. In this paper we consider real as well as complex matrices.

Energy Efficiency in MIMO Underlay and Overlay Device-to-Device Communications and Cognitive Radio Systems

This paper addresses the problem of resource allocation for systems in which a primary and a secondary link share the available spectrum by an underlay or overlay approach. After observing that such a scenario models both cognitive radio and D2D communications, we formulate the problem as the maximization of the secondary energy efficiency subject to a minimum rate requirement for the primary user. This leads to challenging nonconvex, fractional problems. In the underlay scenario, we obtain the global solution by means of a suitable reformulation. In the overlay scenario, two algorithms are proposed. The first one yields a resource allocation fulfilling the first-order optimality conditions of the resource allocation problem, by solving a sequence of easier fractional programs. The second one enjoys a weaker optimality claim, but an even lower computational complexity. Numerical results demonstrate the merits of the proposed algorithms both in terms of energy-efficient performance and complexity, also showing that the two proposed algorithms for the overlay scenario perform very similarly, despite the different complexity.

Spectral and energy efficiency in 3-way relay channels with circular message exchanges

Spectral and energy efficiency in 3-way relay channels are studied in this paper. First, achievable sum rate expressions for 3-way relay channels are derived for different relaying protocols. Moreover, an outer bound for the capacity of the 3-way relay channel is presented. Next, leveraging the derived achievable sum rate expressions, two algorithms for joint power allocation at the users and at the relay are designed so as to maximize the system energy efficiency. Numerical results are provided to corroborate and provide insight on the theoretical findings.

Energy Models for Communication of Future Computing Platforms

Energy efficiency is an essential requirement on future computer architectures. Thereby, the efficiency of the communication will play an important role. Within this paper, we present an energy model for a unicast multi-hop communication. The model allows to derive predictions about the energy of a future computing platform. Further, it can be used to identify which components of the system or tasks related to communication have a significant influence on the overall energy and, hence, require special attention in the design phase. We discuss how values for processing delays and power consumption can be determined for a future computing platform and present values for a target platform. The energy model is applied to derive energy predictions for this platform.

Instantaneous relaying for the 3-way relay channel with circular message exchanges

The 3-user discrete memoryless multi-way relay channel with circular message exchange and instantaneous relaying is investigated. We first show that this channel is effectively a 3-user interference channel with receiver message side information for every fixed (and instantaneous) relay mapping. Then, we extend the Han-Kobayashi coding scheme to this channel. Finally, we apply these results to Gaussian channels with amplify-and- forward relaying and present numerical results showing the gain of the proposed scheme compared to the state of the art.

Approaching the limits in routing in power line communication exploiting Network Coding

We address the single-source-destination routing problem in a mesh network with a broadcast channel, time-division multiplexing (TDM) and no spatial reuse, which is a special type of the PLC channel. First, the outer bound on the achievable data rate is evaluated. We show that the routing protocols (RPs) with static routing do not allow approaching this data rate limit. Then, we study RP with opportunistic routing (ORP). We show that its main disadvantage, extensive feedback, can be successively reduced when using Network Coding (NC). We propose the basic routing rules (BRR) based on ORP with NC. Then, we demonstrate that the data rate achievable with BRR approaches the outer bound when the coding window increases. Finally, we provide the simulation results, which prove the concept. In the considered scenarios, BRR allow the data rate up to 10% higher than RPs with static routing, which is just 5–10% away from the theoretical outer bound limit.

Energy-efficient MIMO overlay communications for device-to-device and cognitive radio systems

This paper studies the problem of resource allocation in overlay systems. A multiple-input single-output (MISO) primary link shares the spectrum with a multiple-input multiple-output (MIMO) secondary link, which in return acts as an amplify-and-forward (AF) relay, forwarding the primary message. The considered problem is the maximization of the secondary energy efficiency (EE) subject to a primary rate requirement. The resulting optimization problem is a fractional program which can not be tackled by traditional fractional optimization methods. Two algorithms are proposed, based on an interplay between fractional programming and sequential optimization theory, which trade-off performance and complexity. Numerical results demonstrate the merits of the proposed algorithms both in terms of energy-efficient performance and complexity.