Analysis of Alternative Metrics for the PAPR Problem in OFDM Transmission

The effective PAPR of the transmit signal is the standard metric to capture the effect of nonlinear distortion in OFDM transmission. A common rule of thumb is the log$(N)$ barrier where $N$ is the number of subcarriers which has been theoretically analyzed by many authors. Recently, new alternative metrics have been proposed in practice leading potentially to different system design rules which are theoretically analyzed in this paper. One of the main findings is that, most surprisingly, the log$(N)$ barrier turns out to be much too conservative: e.g. for the so-called amplifier-oriented metric the scaling is rather $\log[ \log(N)]$. To prove this result, new upper bounds on the PAPR distribution for coded systems are presented as well as a theorem relating PAPR results to these alternative metrics.Comment: 5 pages, IEEE International Symposium on Information Theory (ISIT), 2011, accepted for publicatio

On Interference Alignment and the Deterministic Capacity for Cellular Channels with Weak Symmetric Cross Links

In this paper, we study the uplink of a cellular system using the linear deterministic approximation model, where there are two users transmitting to a receiver, mutually interfering with a third transmitter communicating with a second receiver. We give an achievable coding scheme and prove its optimality, i.e. characterize the capacity region. This scheme is a form of interference alignment which exploits the channel gain difference of the two-user cell.Comment: Submitted to IEEE International Symposium on Information Theory (ISIT) 2011, 5 page

Performance Limits of Compressive Sensing Channel Estimation in Dense Cloud RAN

Towards reducing the training signaling overhead in large scale and dense cloud radio access networks (CRAN), various approaches have been proposed based on the channel sparsification assumption, namely, only a small subset of the deployed remote radio heads (RRHs) are of significance to any user in the system. Motivated by the potential of compressive sensing (CS) techniques in this setting, this paper provides a rigorous description of the performance limits of many practical CS algorithms by considering the performance of the, so called, oracle estimator, which knows a priori which RRHs are of significance but not their corresponding channel values. By using tools from stochastic geometry, a closed form analytical expression of the oracle estimator performance is obtained, averaged over distribution of RRH positions and channel statistics. Apart from a bound on practical CS algorithms, the analysis provides important design insights, e.g., on how the training sequence length affects performance, and identifies the operational conditions where the channel sparsification assumption is valid. It is shown that the latter is true only in operational conditions with sufficiently large path loss exponents.Comment: 6 pages, two-column format; ICC 201

Stable Wireless Network Control Under Service Constraints

We consider the design of wireless queueing network control policies with particular focus on combining stability with additional application-dependent requirements. Thereby, we consequently pursue a cost function based approach that provides the flexibility to incorporate constraints and requirements of particular services or applications. As typical examples of such requirements, we consider the reduction of buffer underflows in case of streaming traffic, and energy efficiency in networks of battery powered nodes. Compared to the classical throughput optimal control problem, such requirements significantly complicate the control problem. We provide easily verifyable theoretical conditions for stability, and, additionally, compare various candidate cost functions applied to wireless networks with streaming media traffic. Moreover, we demonstrate how the framework can be applied to the problem of energy efficient routing, and we demonstrate the aplication of our framework in cross-layer control problems for wireless multihop networks, using an advanced power control scheme for interference mitigation, based on successive convex approximation. In all scenarios, the performance of our control framework is evaluated using extensive numerical simulations.Comment: Accepted for publication in IEEE Transactions on Control of Network Systems. arXiv admin note: text overlap with arXiv:1208.297

Dressing Up: Exploring the Fictions and Frictions of Professional Identity in Art Educational Settings

What fictions do we tell ourselves in order to teach? How do our stories as educators impact how we see our learners? Building from auto-ethnography research I begin with the personal and then invite co-participants to further illuminate a shared experience (Chang, 2008). In this example, I highlight the self-reflective work toward revealing and concealing identities associated with “teacher.” Using collage pedagogy (Garoian & Gaudelius, 2008), students in a pre-service art education class, created paper doll narratives marking and unmarking themselves through collaged backdrops and clothing choices which performed identities that would impact their role of teacher. Future teachers also “undressed” themselves from fashions that impeded their abilities to see their students beyond stereotypes. Through the design of the dolls and reflexivity, we examined the frictions of identity and representation within the larger social, political, or institutional landscapes of what it means to be “teacher/student” in the 21st century school sphere

What (If Anything) Do Satisfaction Scores Tell Us about the Intertemporal Change in Living Conditions

This paper looks at the information content of satisfaction scores. It is argued that the information content depends on the extent to which people adapt to living conditions in general. Using data from the German Socio-Economic Panel Study (SOEP), the estimation of a dynamic panel data model provides evidence that adaptation takes place within a relatively short window of time: changes in living conditions are, for the most part, absorbed by an adjustment of the adaptation level within one year. This leads to the conclusion that the information content of satisfaction scores accentuates recent changes in living conditions. Remote changes are notcaptured by the according survey questions, even if these changes have long-term impact on living conditions. The usefulness of satisfaction scores as an indicator of people's living conditions is discussed.adaptation, dynamic panel data model, subjective well-being, satisfaction

Robust Iterative Interference Alignment for Cellular Networks with Limited Feedback

In theory coordinated multi-point transmission (CoMP) promises vast gains in spectral efficiency. But industrial field trials show rather disappointing throughput gains, whereby the major limiting factor is proper sharing of channel state information. Many recent papers consider this so-called limited feedback problem in the context of CoMP. Usually taking the assumptions: 1) infinite SNR regime, 2) no user selection and 3) ideal link adaptation; rendering the analysis too optimistic. In this paper we make a step forward towards a more realistic assessment of the limited feedback problem by introducing an improved metric for the performance evaluation which better captures the throughput degradation. We find the relevant scaling laws (lower and upper bounds) and how that they are different from existing ones. Moreover, we provide a robust iterative interference alignment algorithm and corresponding feedback strategies achieving the obtained scaling laws. The main idea is that instead of sending the complete channel matrix each user fixes a receive filter and feeds back a quantized version of the effective channel. Finally we underline our findings with simulations for the proposed system.Comment: 29 pages, 2 figures, submitted to IEEE Transaction on Wireless Communications, Presented in parts at Globecom Workshop on Emerging Technologies for LTE-Advanced and Beyond-4