First-Passage Time and Large-Deviation Analysis for Erasure Channels with Memory

This article considers the performance of digital communication systems transmitting messages over finite-state erasure channels with memory. Information bits are protected from channel erasures using error-correcting codes; successful receptions of codewords are acknowledged at the source through instantaneous feedback. The primary focus of this research is on delay-sensitive applications, codes with finite block lengths and, necessarily, non-vanishing probabilities of decoding failure. The contribution of this article is twofold. A methodology to compute the distribution of the time required to empty a buffer is introduced. Based on this distribution, the mean hitting time to an empty queue and delay-violation probabilities for specific thresholds can be computed explicitly. The proposed techniques apply to situations where the transmit buffer contains a predetermined number of information bits at the onset of the data transfer. Furthermore, as additional performance criteria, large deviation principles are obtained for the empirical mean service time and the average packet-transmission time associated with the communication process. This rigorous framework yields a pragmatic methodology to select code rate and block length for the communication unit as functions of the service requirements. Examples motivated by practical systems are provided to further illustrate the applicability of these techniques.Comment: To appear in IEEE Transactions on Information Theor

On the Performance of Short Block Codes over Finite-State Channels in the Rare-Transition Regime

As the mobile application landscape expands, wireless networks are tasked with supporting different connection profiles, including real-time traffic and delay-sensitive communications. Among many ensuing engineering challenges is the need to better understand the fundamental limits of forward error correction in non-asymptotic regimes. This article characterizes the performance of random block codes over finite-state channels and evaluates their queueing performance under maximum-likelihood decoding. In particular, classical results from information theory are revisited in the context of channels with rare transitions, and bounds on the probabilities of decoding failure are derived for random codes. This creates an analysis framework where channel dependencies within and across codewords are preserved. Such results are subsequently integrated into a queueing problem formulation. For instance, it is shown that, for random coding on the Gilbert-Elliott channel, the performance analysis based on upper bounds on error probability provides very good estimates of system performance and optimum code parameters. Overall, this study offers new insights about the impact of channel correlation on the performance of delay-aware, point-to-point communication links. It also provides novel guidelines on how to select code rates and block lengths for real-time traffic over wireless communication infrastructures

Role of serosal cavity resident leukocytes in the orchestration of leukocyte recruitment following the induction of experimental inflammation

This study evaluated the role of resident peritoneal and pleural macrophages (Mφ) in neutrophil (PMN) recruitment in acute peritoneal and pleural inflammation. I also investigated the role of lymphocytes (Lρ) in peritoneal inflammation by studying experimental peritonitis in mice deficient in various Lρ populations.The conditional M(t> ablation mice used in these studies are transgenic for the human diphtheria toxin receptor (DTR) under the CDllb promoter (CDllb-DTR mice) and exhibit >97% depletion of resident serosal Mφ following intraperitoneal (IP) administration of diphtheria toxin (DT). I determined leukocyte numbers by flow cytometry in peritoneal or pleural lavage exudates at various time points after the initiation of inflammation with various agents following Mφ depletion (peritoneum: Brewer's thioglycollate [BTG], zymosan; pleural cavity: carrageenan and fixed staphylococci). I also induced BTG peritonitis in RAG-1 knockout (KO) mice (mature B and T Lρ deficient), NUDE mice (T Lρ deficient), μMT mice (B Lρ deficient) and their respective controls.Mφ ablation markedly inhibited peritoneal and pleural PMN recruitment at early time points compared to wild type (WT) controls. Administration of Mφ-rich resident cells, unlike Mφ-depleted resident cells, significantly restored PMN infiltration. Analysis of PMN C-X-C chemokines in lavage exudate showed that Mφ-depleted mice had significantly reduced levels of peritoneal and pleural MIP-2 and KC at the lhr time point compared to control mice with more marked MIP-2 reduction compared to KC (>90% reduction vs 25-40%). Reduced levels of monocyte C-C chemokine and various cytokines were evident in the Mφ-depleted ii mice at early time points. In vitro studies demonstrated that the production of these chemokines and cytokines from peritoneal and pleural cells was Mφ-dependent. RAG-1 KO mice exhibited increased early PMN infiltration and blunted Mφ infiltration. NUDE exhibited increased early PMN infiltration and increased Mφ infiltration whilst pMT KO mice exhibited decreased PMN influx and a reduced Mφ influx. Although chemokine analysis of peritoneal exudates in RAG-1 KO mice and NUDE mice demonstrated some differences in MCP-1 levels, there were no clear differences evident in μMT KO mice.These data suggest that resident Mφ play a pivotal role in the orchestration of PMN infiltration with Mφ-dependent production of MIP-2 being important. The data suggests that Lρ can modulate leukocyte recruitment in experimental peritonitis with T cells possibly acting as suppressor cells and B cells facilitating Mφ recruitment. However, the exact mechanisms of Lρ action remain elusive

On the Queueing Behavior of Random Codes over a Gilbert-Elliot Erasure Channel

This paper considers the queueing performance of a system that transmits coded data over a time-varying erasure channel. In our model, the queue length and channel state together form a Markov chain that depends on the system parameters. This gives a framework that allows a rigorous analysis of the queue as a function of the code rate. Most prior work in this area either ignores block-length (e.g., fluid models) or assumes error-free communication using finite codes. This work enables one to determine when such assumptions provide good, or bad, approximations of true behavior. Moreover, it offers a new approach to optimize parameters and evaluate performance. This can be valuable for delay-sensitive systems that employ short block lengths.Comment: 5 pages, 4 figures, conferenc

The impact of the unilateral EU commitment on the stability of international climate agreements

In this paper we analyze the negotiation strategy of the European Union regarding the formation of an international climate agreement for the post-2012 era. We use game theoretical stability concepts to explore incentives for key players in the climate policy game to join future climate agreements. We compare a minus 20 percent unilateral commitment strategy by the EU with a unilateral minus 30 percent emission reduction strategy for all Annex-B countries. Using a numerical integrated assessment climate-economy simulation model, we find that carbon leakage effects are negligible. Ther EU strategy to reduce emissions by 30% (compared to 1990 levels) by 2020 if other Annex-B countries follow does not induce participation of the USA with a similar 30% reduction commitement. However, the model shows that an appropriate initial allocation of emission allowances may stabilize a larger and more ambitious climate coalition than the Kyoto Protocol in its first commitment period.Climate change, Coalition theory, Integrated assessment model, Kyoto protocol

Thermoelectrical Field Effects in Low Dimensional Structure Solar Cells

Taking into account the temperature gradients in solar cells, it is shown that their efficiency can be increased beyond the Shockley-Queisser limit (J. Appl. Phys. 32 (1961) 510). The driving force for this gain is the temperature gradient between this region and its surroundings. A quantitative theory is given. Though the effect is found to be weak in conventional solar cells, it is argued that it can be substantially increased by proper choice of materials and design of the device. In particular, it is shown that the insertion of a quantum well can enhance the efficiency beyond one of the single gap cell, due to the presence of temperature jumps at the heterojunctions.Comment: Published in Special issue Physica E 14 (1-2) on Nanostructures in Photovoltaic