Stefan Geirhofer

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In this paper we design a cognitive radio that can coexist with multiple parallel WLAN channels while abiding by an interference constraint. The interaction between both systems is characterized by measurement and coexistence is enhanced by predicting the WLAN’s behavior based on a continuous-time Markov chain model. Cognitive Medium Access (CMA) is derived(More)
In this paper we consider dynamically sharing the spectrum in the time-domain by exploiting whitespace between the bursty transmissions of a set of users, represented by an 802.11b based wireless LAN (WLAN). Realizing that exploiting the under-utilization of the channel requires a good model of the these users’ medium access, we propose a continuous-time(More)
In this work we are concerned with dynamically sharing the spectrum in the time-domain by exploiting whitespace between the bursty transmissions of a primary user, represented by an 802.11b-based wireless LAN (WLAN). For deriving such schemes we need to establish a model of the WLAN's medium access as to predict its behavior accurately. Moreover, a balance(More)
The problem of opportunistic access of parallel channels occupied by primary users is considered. Under a continuous-time Markov chain modeling of the channel occupancy by the primary users, a slotted transmission protocol for secondary users using a periodic sensing strategy with optimal dynamic access is proposed. To maximize channel utilization while(More)
Dynamic spectrum access is a promising approach to alleviate the spectrum scarcity wireless communications faces today. In short, it aims at reusing sparsely occupied frequency bands while causing no (or insignificant) interference to the actual licensees. This article focuses on applying this concept in the time domain by exploiting idle durations between(More)
In this paper we assess how coordination among base stations can be exploited to improve downlink capacity in fourth generation (4G) cellular networks. We focus on heterogeneous networks where low-power pico cells are deployed within the coverage area of an existing macro network with the aim of offloading traffic from the (potentially congested) macro(More)
As wireless systems continue to proliferate, interference management is becoming a concern in both military and commercial domains. This paper introduces a novel cognitive coexistence framework between infrastructure and adhoc networks. Based on sensing and predicting the ad-hoc network’s activity, the infrastructure system allocates power and transmission(More)