Erasure Multiple Descriptions

We consider a binary erasure version of the n-channel multiple descriptions problem with symmetric descriptions, i.e., the rates of the n descriptions are the same and the distortion constraint depends only on the number of messages received. We consider the case where there is no excess rate for every k out of n descriptions. Our goal is to characterize the achievable distortions D_1, D_2,...,D_n. We measure the fidelity of reconstruction using two distortion criteria: an average-case distortion criterion, under which distortion is measured by taking the average of the per-letter distortion over all source sequences, and a worst-case distortion criterion, under which distortion is measured by taking the maximum of the per-letter distortion over all source sequences. We present achievability schemes, based on random binning for average-case distortion and systematic MDS (maximum distance separable) codes for worst-case distortion, and prove optimality results for the corresponding achievable distortion regions. We then use the binary erasure multiple descriptions setup to propose a layered coding framework for multiple descriptions, which we then apply to vector Gaussian multiple descriptions and prove its optimality for symmetric scalar Gaussian multiple descriptions with two levels of receivers and no excess rate for the central receiver. We also prove a new outer bound for the general multi-terminal source coding problem and use it to prove an optimality result for the robust binary erasure CEO problem. For the latter, we provide a tight lower bound on the distortion for \ell messages for any coding scheme that achieves the minimum achievable distortion for k messages where k is less than or equal to \ell.Comment: 48 pages, 2 figures, submitted to IEEE Trans. Inf. Theor

Presentation and Intraoperative Findings of Penetrating Abdominal Injuries in a Battle Field Hospital, Yemen 2018 – 2019

Background Abdominal war wounds have the strange history of all injuries suffered in times of armed conflict. Of all major life threatening injuries, wounds in the abdomen are ---      --the most amenable to surgical intervention likely to produce good results and the return of the patient to a productive life. Most patients with blunt and penetrating trauma were treated conservatively and surgically respectively. The cure rate is higher in surgical than in conservative management. Objective this study aimed to describe the presentation and intraoperative findings in penetrating abdominal injury in battle field hospital, Yemen War, 2018 – 2019 Methods An Observational, descriptive, hospital based cross sectional study was conducted in Field Hospital in Yemen within the period from September 2018 to March 2019. Data entered, cleaned and analyzed using SPSS version 25.0. Results This study covered 80 study participants. The majority of them were classified as military personnel (91.2%).. The majority of them were males with male: female ratio of 19: 1 with ages ranging from 10 to 53 years and a mean ± SD of 31.7 ± 9.9 . Our study found that two thirds of the patients had gun shots (66.3%), blast injury (16.3%), explosive injury (15%) and sharpness among only (8.8%). The average time from injury to laparotomy was less than one hour in more than three quarters of the study participants (80%). Concerning the presentation of the study participants, half of them (51.3%) were shocked, (21.3%) evisceration, and (61.4%) reported peritonism presentation. Nearly two thirds of the patients showed inlet only (65%), while (22.5%) presented with both inlet and outlet and only (12.5%) lost part of their abdominal wall. More than half of the study participants received Medical help outside the battle field hospital (53.8%), such as blood transfusion (53.5%) and intravenous fluids for the majority of them. Regarding the intraoperative findings, the majority of the patients (95%) had operated, on average, for five hours or less. Nearly half of them had been injured in 1 – 3 organs (45%) while (7.5%) of them was injured in more than six organs. The most affected organs were Jejunum (75.6%), Ileum (73.1%), and large colon (43.6%),while the liver and splenic injuries were(32.1%) and (17.9%) respectively . Furthermore, cardiac arrest occurred only among a small proportion (2.5%) of the study patients. Only (1.3%) mortality reported. Only (1.3%) had reactionary bleeding as an early post-operative complication among our study patients. Finally, our study realized that most of the patients (83.7) were evacuated within 6 to 12 hours. Conclusion and recommendation The majority of patients with abdominal gunshot wounds are best served by laparotomy; however, select patients may be managed expectantly. All cases of such injuries should have exploratory laparotomy as soon as possible with a short time interval between the injury and the operation to prevent morbidity and mortality

Minimum-cost multicast over coded packet networks

We consider the problem of establishing minimum-cost multicast connections over coded packet networks, i.e., packet networks where the contents of outgoing packets are arbitrary, causal functions of the contents of received packets. We consider both wireline and wireless packet networks as well as both static multicast (where membership of the multicast group remains constant for the duration of the connection) and dynamic multicast (where membership of the multicast group changes in time, with nodes joining and leaving the group). For static multicast, we reduce the problem to a polynomial-time solvable optimization problem, and we present decentralized algorithms for solving it. These algorithms, when coupled with existing decentralized schemes for constructing network codes, yield a fully decentralized approach for achieving minimum-cost multicast. By contrast, establishing minimum-cost static multicast connections over routed packet networks is a very difficult problem even using centralized computation, except in the special cases of unicast and broadcast connections. For dynamic multicast, we reduce the problem to a dynamic programming problem and apply the theory of dynamic programming to suggest how it may be solved

Fundamental Limits Of Delay And Security In Device-To-Device Communication

Distributed communication poses novel challenges for efficient operation of such networks and requires design considerations that are fundamentally different from those of classical point-to-point communication systems. This thesis studies two such design issues, (1) delay management and (2) security, and attempts to understand the information-theoretic limits of distributed communication with regard to these issues. First, the tradeoff between delay and partial reconstruction in peer-to-peer (P2P) networks is studied, i.e., the number of messages a peer must obtain to reconstruct a given fraction of the data. Using a binary erasure version of the multiple descriptions (MD) problem to model the P2P network, the thesis presents coding schemes based on systematic MDS (maximum distance separable) codes and random binning strategies that achieve a Pareto optimal delayreconstruction tradeoff. The erasure MD setup is then used to propose a layered coding framework for MD, which is then applied to vector Gaussian MD and shown to be optimal for symmetric scalar Gaussian MD with two levels of receivers and no excess rate at the central receiver. Second, delay-reconstruction tradeoffs are studied for a more decentralized network in which peers are allowed to encode and generate their own messages based on their current partial knowledge of the file, and a coding scheme based on erasure compression and Slepian-Wolf binning is presented. The cod- ing scheme is shown to provide a Pareto optimal delay-reconstruction tradeoff for the case of symmetric peers (i.e., each peer generates packets of the same rate). In the process of characterizing the aforementioned tradeoff, an improved outer bound on the rate region of the general multi-terminal source coding problem from information theory is also established. It is further shown that in the case of asymmetric peers, the aforementioned coding scheme is not optimal. Third, lossy compression is studied from the viewpoint of security. An adversarial lossy source coding problem is considered in which a source is encoded into n packets, any t of which may be altered in an arbitrary way by Byzantine adversaries. The decoder receives the n packets and, without knowing which packets were altered, seeks to reconstruct the original source to meet a distortion constraint. A layered architecture for this problem is examined, which separates lossy compression from coding for adversarial errors. This architecture is shown to be optimal for binary sources with Hamming distortion and Gaussian sources with quadratic distortion, yet suboptimal in general. Finally, an adversarial 3-encoder lossless source coding problem with multiple sources is considered in which the number of packets corrupted by adversaries is unknown to the honest entities in the network. It is shown that this problem is equivalent to an instance of the symmetric MLD (multi-level diversity) coding problem with three sources and three encoders, in which there are no adversaries but the decoder may receive only a subset of the three messages and then reconstructs a subset of the three sources

Economic aspects of network coding

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 73-77).We consider a single-hop cellular wireless system with a single source (base station) broadcasting a stream of incoming files to multiple receivers over stochastic time-varying channels with non-zero erasure probabilities. The base station charges a price per receiver per file with the aim of maximizing its profit. Customers who wish to transmit files to the receivers decide to enter the system based on the price, the queuing delay, and the utility derived from the transaction. We look at network coding and scheduling as possible strategies for file transmission, and obtain approximate characterizations of the optimal customer admission rate, optimal price and the optimal base-station profit as functions of the first and second moments of the service time processes under mild assumptions. We show that network coding leads to significant gains in the base station profits as compared to scheduling, and also demonstrate that the optimal network coding window size is highly insensitive to the number of receivers, which suggests that pricing and coding decisions can be decoupled. We also investigate the behavior of network coding in the case where the number of receivers is sufficiently large, and derive scaling laws for the asymptotic gains from network coding. We subsequently propose a way to extend our analysis of single-source, multiple-receiver systems to multiple-source, multiple-receiver systems in general network topologies and obtain explicit characterizations of the file download completion time under network coding and scheduling, also taking into account the effects of collisions and interference among concurrent packet transmissions by two or more sources.(cont.) Our formulation allows us to model multi-hop networks as a series of single-hop multiple-source, multiple-receiver systems, which provides a great deal of insight into the workings of larger and denser multi-hop networks such as overlay networks and peer-to-peer systems, and appears to be a promising application of network coding in such networks in the future.by Ebad Ahmed.M.Eng

On the scaling law of network coding gains in wireless networks

Abstract — We study the scaling law governing the delay gains of network coding as compared to traditional transmission strategies in unreliable wireless networks. We distinguish between two types of traffic, namely elastic and inelastic, where the elasticity of a flow is based on the delay constraints associated with it. This novel formulation is useful in that it allows for the modeling of real-time traffic more accurately. Considering the limited availability of feedback in such systems, we focus on strategies with minimal acknowledgement requirements. Under both traffic types, we provide an extensive analysis of the gains of network coding as compared to traditional transmission strategies in a single-hop setting, and show that the gains are significant in general and can be considerably large in some cases. We further provide a method for realizing these gains in multi-hop networks with general topologies using the analysis of the single hop scenario. I

Leptospirosis Presenting with Features of Thrombotic Microangiopathy

Leptospirosis is an exceptionally rare infectious disease in the Republic of Ireland. Leptospirosis can present with or mimic thrombotic microangiopathies (TTP/HUS). A 48-year-old male presented to a peripheral hospital with a short history of diarrhoea, anaemia, hyperbilirubinemia, raised lactate dehydrogenase, thrombocytopenia, and severe acute kidney injury and was transferred to our tertiary care kidney centre. A form of acute thrombotic microangiopathy (TMA) was suspected. However, no schistocytes were seen on the blood film, and the reticulocyte count was depressed. A kidney biopsy was performed before initiating any potential treatment which revealed acute interstitial nephritis (AIN). Leptospirosis was considered and subsequently serologically confirmed. The patient was managed with antimicrobials and supportive therapy. Acute kidney injury is common in leptospirosis and is often due to AIN. Initial presentation can mimic TMA; however, a differential diagnosis of leptospirosis should be considered even in nonendemic areas due to re-emergence of the disease