7 research outputs found
Upper Bounds to the Performance of Cooperative Traffic Relaying in Wireless Linear Networks
No full textWireless networks with linear topology, where nodes generate their own traffic and relay other nodes' traffic, have attracted increasing attention. Indeed, they well represent sensor networks monitoring paths or streets, as well as multihop networks for videosurveillance of roads or vehicular traffic. We study the performance limits of such network systems when (i) the nodes' transmissions can reach receivers farther than one-hop distance from the sender, (ii) the transmitters cooperate in the data delivery, and (iii) interference due to concurrent transmissions is taken into account. By adopting an information-theoretic approach, we derive analytical bounds to the achievable data rate in both the cases where the nodes have full-duplex and half-duplex radios. The expressions we provide are mathematically tractable and allow the analysis of multihop networks with a large number of nodes. Our analysis highlights that increasing the number of coop- erating transmitters beyond two leads to a very limited gain in the achievable data rate. Also, for half-duplex radios, it indicates the existence of dominant network states, which have a major influence on the bound. It follows that efficient, yet simple, communication strategies can be designed by considering at most two cooperating transmitters and by letting half-duplex nodes operate according to the aforementioned dominant state
Study of Techniques For Reliable Data Transmission In Wireless Sensor Networks
No full textThis thesis addresses the problem of traffic transfer in wireless sensor networks (WSN). In such networks, the foremost challenge in the design of data communication techniques is that the sensor's transceiver circuitry consumes the major portion of the available power. Thus, due to stringent limitations on the nodes' hardware and power resources in WSN, data transmission must be power-efficient in order to reduce the nodes' power consumption, and hence to maximize the network lifetime while satisfying the required data rate. The transmit power is itself under the influence of data rate and source-destination distance. Thanks to the dense deployment of nodes in WSN, multi-hop communication can be applied to mitigate the transmit power for sending bits of information, i.e., gathered data by the sensor nodes to the destination node (gateway) compared to single-hop scenarios. In our approach, we achieve a reasonable trade-off between power-efficiency and transmission data rate by devising cooperative communication strategies through which the network traffic (i.e. nodes' gathered information) is relayed hop-by-hop to the gateway. In such strategies, the sensor nodes serve as data originator as well as data router, and assist the data transfer from the sensors to the gateway. We develop several data transmission schemes, and we prove their capability in transmitting the data from the sensor nodes at the highest possible rates allowed by the network limitations. In particular, we consider that (i) network has linear or quasi-linear topology, (ii) nodes are equipped with half-duplex radios, implying that they cannot transmit and receive simultaneously, (iii) nodes transmit their traffic at the same average rate. We compute the average data rate corresponding to each proposed strategy. Next, we take an information-theoretic approach and derive an upper bound to the achievable rate of traffic transfer in the networks under consideration, and analyze its tightness. We show that our proposed strategies outperform the conventional multi-hop scheme, and their average achievable rate approaches the upper bound at low levels of signal to noise ratio
The role of gastrostomy in the staged operation of esophageal atresia
No full textIntroduction: The aim of this study is to recommend criteria for
selection of patients who benefited from the use of gastrostomy rather
than emergency fistula closure during the staged operation of
esophageal atresia (EA). Materials and Methods: Between August 2004 and
July 2006, 75 cases of EA, were consecutively operated. Nineteen out of
75 (25%) underwent routine gastrostomy because they required a type of
staged operation: Group I: Five cases with pure atresia had gastrostomy
and esophagostomy; Group II: Six with severe pneumonia and congenital
heart disease (Waterson class C) had gastrostomy and conservative
management; Group III: Eight with long gap EA (2-4 vertebras); four out
of 8 cases underwent primary anastomosis with tension and the other
four had delayed primary anastomosis plus primary gastrostomy. Results:
GI: Only three cases survived after esophageal substitution; GII: Three
out of six cases with severe pneumonia (fistula size: f > 2.5 mm)
underwent emergency fistula closure with only one survival, but all (f
< 2.5 mm) recovered without complication, GIII: Four patients with
long gap and primary anastomosis with tension developed anastomotic
leakage; they required gastrostomy following the leakage, except for
those with delayed primary anastomosis, and all of them recovered
without early complications. Conclusion : All the cases with long gap,
although two esophageal ends can be reached with tension, should
undergo delayed primary closure with primary gastrostomy. Those were
brought with Waterson class C and the fistula size greater than 2.5 mm
should undergo emergency fistula closure; however, if fistula size was
less than 2.5 mm, it is better to be delayed by primary gastrostomy for
stabilization. In this study, we had a better outcome with gastric tube
for substitution than colon interposition in infants
The role of gastrostomy in the staged operation of esophageal atresia
No full textIntroduction: The aim of this study is to recommend criteria for
selection of patients who benefited from the use of gastrostomy rather
than emergency fistula closure during the staged operation of
esophageal atresia (EA). Materials and Methods: Between August 2004 and
July 2006, 75 cases of EA, were consecutively operated. Nineteen out of
75 (25%) underwent routine gastrostomy because they required a type of
staged operation: Group I: Five cases with pure atresia had gastrostomy
and esophagostomy; Group II: Six with severe pneumonia and congenital
heart disease (Waterson class C) had gastrostomy and conservative
management; Group III: Eight with long gap EA (2-4 vertebras); four out
of 8 cases underwent primary anastomosis with tension and the other
four had delayed primary anastomosis plus primary gastrostomy. Results:
GI: Only three cases survived after esophageal substitution; GII: Three
out of six cases with severe pneumonia (fistula size: f > 2.5 mm)
underwent emergency fistula closure with only one survival, but all (f
< 2.5 mm) recovered without complication, GIII: Four patients with
long gap and primary anastomosis with tension developed anastomotic
leakage; they required gastrostomy following the leakage, except for
those with delayed primary anastomosis, and all of them recovered
without early complications. Conclusion : All the cases with long gap,
although two esophageal ends can be reached with tension, should
undergo delayed primary closure with primary gastrostomy. Those were
brought with Waterson class C and the fistula size greater than 2.5 mm
should undergo emergency fistula closure; however, if fistula size was
less than 2.5 mm, it is better to be delayed by primary gastrostomy for
stabilization. In this study, we had a better outcome with gastric tube
for substitution than colon interposition in infants
