Per Åhag

Enhanced HARQ scheme based on rearrangement of signal constellations and frequency diversity for OFDM systems

In multi-carrier modulation systems such as OFDM, several subcarriers are used for transmission and their received signal quality is different from one subcarrier to another in frequency selective fading channels. In this paper, an enhanced hybrid ARQ scheme for OFDM systems is proposed. When data is requested for retransmission, we change the bit interleaving mode in such a manner that the data sequence is changed. Since the coded bit is assigned to different subcarriers and positions of modulation symbols in different retransmissions we can take advantage of this effect, and achieve both frequency- and modulation constellation diversity. Results from computer simulations confirm that the proposed scheme improves the throughput performance. After two transmissions, and with packet error rate (PER) of 10/sup -4/, the proposed scheme has a gain of approximately 3 dB compared to a scheme employing Chase combining. The performance gain is even more for three transmissions (2 retransmissions).

An Inequality for the Beta Function with Application to Pluripotential Theory

We prove in this paper an inequality for the beta function, and we give an application in pluripotential theory.

The Geometry of m-Hyperconvex Domains

We study the geometry of m-regular domains within the Caffarelli–Nirenberg–Spruck model in terms of barrier functions, envelopes, exhaustion functions, and Jensen measures. We prove among other things that every m-hyperconvex domain admits an exhaustion function that is negative, smooth, strictly m-subharmonic, and has bounded m-Hessian measure.

On the Błocki–Zwonek conjectures

Let be a bounded pseudoconvex domain in , and let be the pluricomplex Green function with pole at in . It was conjectured by Błocki and Zwonek that the function given by is convex. Here is the Lebesgue measure in . In this note we give an affirmative answer to this conjecture when is biholomorphic to the unit ball or to the polydisc in , .

A Counterexample to a Conjecture by Błocki–Zwonek

ABSTRACT For a bounded pseudoconvex domain and pluricomplex Green function gΩ(z, a) with pole at a ∈ Ω, it was conjectured by Błocki and Zwonek that β(t) = log λn({z ∈ Ω: gΩ(z, a) < t}) is a convex function on ( − ∞, 0). With Ω the annulus the Green function gΩ(z, a) with pole at a = 1 + 0i can be explicitly given in terms of Jacobi theta functions. We show numerically that in this case β is not convex.

Performance and capacity improvements of OFDM wireless LANs with multiple antennas and subchannel power control

Multiple transmit-and-receive antennas can be used in orthogonal frequency division multiplexing (OFDM) systems to improve communication quality and capacity. In this paper, we investigate the performance of a multiple antenna system with subchannel power control for OFDM Wireless LAN. Furthermore, we employed a turbo product code at the encoder to further enhance the quality of transmission for high data rate WLAN such as the ETSI BRAN HIPERLAN/2. Simulation results show that for a BER of 10/sup -4/, we gain 4.4 dB for the proposed scheme with turbo block codes and subchannel power control compared to the standardized 5 GHz OFDM wireless LANs.

Extension and approximation of m-subharmonic functions

Abstract Let be a bounded domain, and let f be a real-valued function defined on the whole topological boundary . The aim of this paper is to find a characterization of the functions f which can be extended to the inside to a m-subharmonic function under suitable assumptions on . We shall do so using a function algebraic approach with focus on m-subharmonic functions defined on compact sets. We end this note with some remarks on approximation of m-subharmonic functions.

Kolodziej's subsolution theorem for unbounded pseudoconvex domains

In this paper we generalize Kolodziejs subsolution theorem to bounded and unbounded pseudoconvex domains, and in that way we are able to solve complex Monge-Ampere equations on general pseudoconve ...

Performance of opportunistic scheduling schemes for MIMO-OFDM wireless LANs

In this paper, we propose and investigate scheduling algorithms for multiple-input multiple-output (MIMO) wireless local area networks (WLANs) based on <i>orthogonal</i> <i>frequency</i> <i>division</i> <i>multiplexing</i> (OFDM). We propose two new scheduling approaches which combines the channel states with queue states. The obtained results show that the proposed schemes outperform well known schemes such as <i>proportional</i> <i>fair</i> (PF) and <i>shortest</i> <i>remaining</i> <i>processing</i> <i>time</i> (SRPT) in terms of throughput and fairness.