Presence Of Capture Research Articles

Impact of Segmentation and Capture on Slotted Aloha Systems Exploiting Interference Cancellation

The performance of the widely adopted slotted Aloha (SA) scheme has been recently improved thanks to the introduction of novel mechanisms, including interference cancellation (IC), packet segmentation, and slot slicing. The combined effect of these mechanisms in the presence of capture has however not yet deeply investigated, even if the resulting impact on the network behavior is determinant for properly quantifying the achievable throughput. To deal with this issue, this paper analyzes the influence of capture on a framed SA (FSA) system adopting IC, segmentation, and slicing, by considering a reliable decoding criterion that accounts for the actually experienced signal to interference-plus-noise ratio. A theoretical model is developed to evaluate the capture probability in fast and slow Rayleigh fading conditions, deriving closed-form expressions for the interference-limited case. The IC-based FSA throughput is then estimated adopting a Markov chain approach validated by Monte Carlo simulations. Finally, the performance of an actual system using a quadrature phase-shift keying modulation in conjunction with a turbo encoder is compared with that estimated by adopting the considered decoding criterion, in order to check its applicability to practical communication networks.

The n -ary stack algorithm for the wireless random access channel

The emergence of wireless and personal communication networks has brought random access protocols for packet radio networks back to the research forefronts. Most such protocols are based on the ever popular ALOHA protocol. Unfortunately, this protocol is inherently unstable and requires sophisticated schemes to stabilize it. Another class of random access schemes, called limited sensing or stack algorithms, has been proposed that is stable and allows for the dynamic incorporation of new stations into the network. In this paper, we will review the simple to implement n-ary stack algorithm, and we will study its performance under various system parameters in the presence of capture, and also in the presence of feedback errors. Finally, we will investigate its maximum system throughput under various traffic generation processes.

Asymptotic throughput bounds of ICMA with capture

Expressions are derived for the asymptotic throughput bounds for both slotted and nonslotted, nonpersistent ICMA assuming coherent addition of interfering signals in environments of pure Rayleigh fading, and Rayleigh fading combined with distance-dependent path loss. The asymptotic lower throughput bounds are shown to be nonzero in value in the presence of capture. Hence, the ICMA protocol under such conditions of fading and capture is stable.

Wide Complex Tachycardias: Differential Diagnosis and Management

The majority of wide complex tachycardias are secondary to VT. The differential diagnosis of wide complex tachycardia also includes SVT with aberrancy or underlying bundle branch block and antegrade SVT conduction over an accessory pathway (antidromic SVT). VT is usually the result of reentry and most commonly arises in an area of diseased myocardium in the setting of previous myocardial infarction or cardiomyopathy. VT, however, can also occur in patients with structurally normal hearts. Criteria useful in diagnosis of wide complex tachycardia include clinical criteria (presence of structural heart disease or a history of previous myocardial infarction) and electrocardiographic criteria (the presence of capture or fusion beats, relation of atrial or ventricular activity, QRS duration and axis, and morphology). The acute management of wide complex tachycardia includes cardioversion and intravenous pharmacologic therapy. Almost all patients with VT require chronic therapy, although in rare patients treatment of acute precipitating factors may be sufficient. While pharmacologic therapy has been the mainstay of treatment for these patients, there have been many exciting advances using surgical, device, and ablative therapies.

A window random access algorithm for environments with capture

The authors propose and analyze a stable random access algorithm which is a modification of the two-cell algorithm proposed by M. Paterakis (1984). The authors assume ternary feedback broadcast per slot, and in the presence of capture, identification of the captured packet by all the users in the system. It is also assumed that a successfully received signal transmission cannot be distinguished from a capture in the presence of multiple transmission. The performance of the algorithm is compared to an appropriate modification of J.I Capetanakis' (1979) dynamic algorithm. The proposed algorithm, and in contrast to the latter, it can be easily modified to operate in limited feedback sensing environments.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Splitting protocols in presence of capture

The effect of capture on splitting-type protocols in a slotted ALOHA broadcasting network is investigated. At first, it is assumed that the nodes of the network are divided into two groups, and only packets sent by nodes of one of the groups might be captured. The situation in which the receiver can distinguish between success slots and capture slots and that in which it cannot are both considered. For each of these situations, splitting-type multiple access protocols are described and their performance in terms of achievable throughputs is evaluated. Extensions of these protocols to a general capture model are also discussed.

The Effect of Capture on Collision-Resolution Algorithms

In many communication systems, the stronger of two or more overlapping packets might capture the receiver and thus be received without error. The effect of capture on collision-resolution algorithms in a slotted ALOHA type broadcasting network is investigated here. Extensions to the algorithms are suggested for both the situations in which the receiver can or cannot distinguish between success slots and capture slots. In particular, we present a class of retransmission schemes for packets that have been transmitted during capture slots but have not been received correctly. The performance analysis is confined to a simplified model in which the nodes of the network are divided into two groups and only packets sent by the nodes of one of them might be captured. For this simplified model and for each extended algorithm, explicit recursive equations are given, from which the average conditional collision-resolution interval length, as well as the maximal throughput, can be determined. As expected, we show that in the presence of capture, the performance of the network is improved and the maximal attainable throughput is increased. Extensions of the simplified model such as dividing the nodes into K groups instead of two, or considering the situation that capture depends on relative distances and transmission powers, are also discussed. For the latter situation we give simulation results.