Optimal time-division for bidirectional relaying using superposition encoding

Bidirectional wireless communication between two nodes is enabled by a half-duplex relay node using a two-phase decode-and-forward protocol. In the first phase, the messages of two nodes are transmitted to the relay node, which broadcasts a superposition of the re-encoded messages in the succeeding phase. Individual mean transmit power constraints averaged over both phases are considered so that they are inversely proportional to the time division between the phase. An equivalent characterization of the achievable rate region with optimal time division is presented. Moreover, it is proved that the rate region is convex, which makes efficient algorithmic optimization solutions feasible.     

Piggyback a Common Message on Half-Duplex Bidirectional Relaying

In this work we consider the achievable rates of a joint resource allocation for a three-node network where a halfduplex relay node enables bidirectional communication between nodes 1 and 2 and thereby adds an own multicast message to the communication. In the multiple access phase nodes 1 and 2 transmit their message to the relay node, which decodes the messages and forwards them in the succeeding broadcast phase. Therefore, the relay node encodes the multicast and bidirectional messages using the superposition encoding strategy. We do not allow cooperation between the encoders of nodes 1 and 2, but since both nodes know a priori its own bidirectional message, both nodes can cancel the interference caused by their own message before decoding the unknown messages. It shows that for both nodes it is always optimal to decode the relay message first. Furthermore, the total sum-rate maximum is determined by the sum-rate optimum of the bidirectional broadcast phase. From the closed form solutions of the combinatorial problems we can characterize the bidirectional rate pairs where the total sum-rate remains constant. In the end the obtained results are discussed and illustrated by means of some working examples. The joint resource allocation improves the overall spectral efficiency and enables new trade-offs between the routing tasks.     

Invertierung von Multion-Funktionen in fast linearen Systemen

Übersicht Die Identifikation von linearen Systemen hat in der jüngsten Zeit ein grosses Interesse erzielt. Reale Systeme besitzen stets nichtlineare Teilsysteme. Diese nichtlinearen Teilsysteme erzeugen stets Fehler bei der Systemidentifikation. Wenn die zu analysierenden Systeme nur für die Verarbeitung von Signalen mit relativ kleinen Amplituden vorgesehen sind, so können diese Systeme für den interessierenden Bereich als lineare Systeme modelliert werden. Für die Systemidentifikation ist es somit wichtig, Multiton-Funktioner mit relativ kleinen Spitzenwerten zu finden. In der Arbeit wird das Verhalten von Multiton-Funktionen untersucht. Es wird die Frage nach der Invertierbarkeit von Multiton-Funktionen analysiert. Die Resultate der Arbeit lösen eine von Professor J. Massey vorgeschlagene Problemstellung.

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Inversion of multione-functions in almost linear systems

Identification of linear systems with multitone functions has received a great deal of attention in recent years. Identification errors will be caused by nonlinear distortions. If the object is simply to model the system for only small signal deviations from an operating point, then the nonlinear effects may be minimized and the system regarded as linear. So it is important for practical applications to find multitone functions with small peak values. The behavior of a certain class of multitone functions is investigated in this paper. The question of the inversion of multitone functions is analyzed. The results solve a problem proposed by Professor J. Massey.

     

A Superlinearly and Globally Convergent Algorithm for Power Control and Resource Allocation With General Interference Functions

In wireless networks, users are typically coupled by interference. Hence, resource allocation can strongly depend on receive strategies, such as beamforming, CDMA receivers, etc. We study the problem of minimizing the total transmission power while maintaining individual quality-of-service (QoS) values for all users. This problem can be solved by the fixed-point iteration proposed by Yates (1995) as well as by a recently proposed matrix-based iteration (Schubert and Boche, 2007). It was observed by numerical simulations that the matrix-based iteration has interesting numerical properties, and achieves the global optimum in only a few steps. However, an analytical investigation of the convergence behavior has been an open problem so far. In this paper, we show that the matrix-based iteration can be reformulated as a Newton-type iteration of a convex function, which is not guaranteed to be continuously differentiable. Such a behavior can be caused by ambiguous representations of the interference functions, depending on the choice of the receive strategy. Nevertheless, superlinear convergence can be shown by exploiting the special structure of the problem. Namely, the function is convex, locally Lipschitz continuous, and an invertible directional derivative exists for all points of interest.     

Nullstellenverteilung bandbegrenzter Signale

Übersicht In der Arbeit wird das Zero-Crossing von bandbegrenzten Signalen untersucht. Es werden reellwertige bandbegrenzte Signale mit endlicher Energie angegeben, welche keine reellen Nullstellen besitzen. Diese Signale können nicht mit Hilfe von Zero-Crossing-Algorithmen rekonstruiert werden.

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Zero value distribution of band limited signals

Contents In this paper is analysed the zero-crossing behaviour of bandlimited signals. There are constructed real valued bandlimited signals with finite energy, which don't have a real zero. It is impossible to reconstruct these signals with the help of zero-crossing algorithm.

     

The interplay of link layer and physical layer under MIMO enhancement: benefits and challenges

This article provides an analysis of the impact of the multi-antenna enhancement of the physical layer on the link layer performance of a wireless network. We first remain within the network-centric design philosophy and characterize the influence of MIMO enhancement on the stability-oriented scheduler design. We quantify the benefits in terms of average delay and work in the system under stability-optimal operation. Finally, the use of MIMO is discussed in the approach of minimum service provision, pertaining to the opposite user-centric design philosophy.     

Secrecy results for compound wiretap channels

We derive a lower bound on the secrecy capacity of a compound wiretap channel with channel state information at the transmitter which matches the general upper bound on the secrecy capacity of general compound wiretap channels given by Liang et al. [1], thus establishing a full coding theorem in this case. We achieve this with a stronger secrecy criterion and the maximum error probability criterion, and with a decoder that is robust against the effect of randomization in the encoding. This relieves us from the need of decoding the randomization parameter, which is in general impossible within this model. Moreover, we prove a lower bound on the secrecy capacity of a compound wiretap channel without channel state information and derive a multiletter expression for the capacity in this communication scenario.     

Grenzen der Anwendbarkeit der Theorie der analytischen Signale

Zusammenfassung Bei der praktischen Anwendung der analytischen Signale ist es erforderlich, die Ermittlung der Hilbert-Transformation numerisch durchzuführen. Dazu wurden u.a. Verfahren von H.W. Schü?ler, R. Unbehauen und G. Wunsch vorgeschlagen. In der Arbeit werden allgemeine Ergebnisse zur numerischen Umsetzung der Hilbert-Transformation dargestellt. Es wird gezeigt, da? alle praktisch realisierbaren Verfahren für bestimmte Signale divergieren. Damit ist es m?glich, die in der Experimentalphysik schon l?nger bekannten Schwierigkeiten bei der Umsetzung der Hilbert-Transformation zu erkl?ren.