144 research outputs found
Performance analysis of slotted fiber-optic code-division multiple-access (CDMA) packet networks
This paper examines code-division multiple-access (CDMA) techniques used in slotted fiber-optic packet networks. Since the inherent properties and signal processing of the conventional communication channels are different from those of the fiber-optic channels, new code sequences must be constructed for fiber-optic applications. The goal of our research is to analyze the performance of fiber-optic CDMA packet networks using code sequences with given orthogonality properties. © 1997 IEEE.published_or_final_versio
Performance analysis of unslotted fiber-optic code-division multiple-access (CDMA) packet networks
This paper examines code-division multiple-access (CDMA) techniques used in unslotted fiber-optic packet networks. Since the inherent properties and signal processing of the conventional communication channels are different from those of the fiber-optic channels, new code sequences must be constructed for fiber-optic applications. In unslotted systems, the exact solution is very difficult to obtain. Therefore, two approximation methods are presented to analyze the performance of such systems. Simulation is performed to verify the accuracy of the results.published_or_final_versio
Overlapped CDMA system in optical packet networks : resource allocation and performance evalutation
Dans cette thĂšse, la performance du systĂšme CDMA Ă chevauchement optique (OVCDMA) au niveau de la couche de contrĂŽle d'accĂšs au support (MAC) et l'allocation des ressources au niveau de la couche physique (PRY) sont Ă©tudiĂ©es. Notre but est d'apporter des amĂ©liorations pour des applications Ă dĂ©bits multiples en rĂ©pondant aux exigences de dĂ©lai minimum tout en garantissant la qualitĂ© de service (QoS). Nous proposons de combiner les couches PRY et MAC par une nouvelle approche d'optimisation de performance qui consolide l'efficacitĂ© potentielle des rĂ©seaux optiques. Pour atteindre notre objectif, nous rĂ©alisons plusieurs Ă©tapes d'analyse. Tout d 'abord, nous suggĂ©rons le protocole S-ALOHA/OV-CDMA optique pour sa simplicitĂ© de contrĂŽler les transmissions optiques au niveau de la couche liaison. Le dĂ©bit du rĂ©seau, la latence de transmission et la stabilitĂ© du protocole sont ensuite Ă©valuĂ©s. L'Ă©valuation prend en considĂ©ration les caractĂ©ristiques physiques du systĂšme OY-CDMA, reprĂ©sentĂ©es par la probabilitĂ© de paquets bien reçus. Le systĂšme classique Ă traitement variable du gain (YPG) du CDMA, ciblĂ© pour les applications Ă dĂ©bits multiples, et le protocole MAC ±round-robinÂż rĂ©cepteur/Ă©metteur (R31), initialement proposĂ© pour les rĂ©seaux par paquets en CDMA optique sont Ă©galement pris en compte. L'objectif est d ' Ă©valuer comparativement la performance du S-ALOHA/OY-CDMA en termes de l'immunitĂ© contre l'interfĂ©rence d'accĂšs lTIultiple (MAI) et les variations des charges du trafic. Les rĂ©sultats montrent que les performances peuvent varier en ce qui concerne le choix du taux de transmission et la puissance de transmission optique au niveau de la couche PRY. Ainsi, nous proposons un schĂ©ma de rĂ©partition optimale des ressources pour allouer des taux de transmission Ă chevauchement optique et de puissance optique de transmission dans le systĂšme OY-CDMA comme des ressources devant ĂȘtre optimalement et Ă©quitablement rĂ©parties entre les utilisateurs qui sont regroupĂ©s dans des classes de diffĂ©rentes qualitĂ©s de service. La condition d'optimalitĂ© est basĂ©e sur la maximisation de la capacitĂ© par utilisateur de la couche PHY. De ce fait, un choix optimal des ressources physiques est maintenant possible, mais il n'est pas Ă©quitable entre les classes. Par consĂ©quent, pour amĂ©liorer la performance de la couche liaison tout en Ă©liminant le problĂšme d'absence d'Ă©quitĂ©, nous proposons comme une approche unifiĂ©e un schĂ©ma Ă©quitable et optimal pour l'allocation des ressources fondĂ© sur la qualitĂ© de service pour des multiplexages temporels des rĂ©seaux par paquets en CDMA Ă chevauchement optique. Enfin, nous combinons cette derniĂšre approche avec le protocole MAC dans un problĂšme d'optimisation d'allocation Ă©quitable des ressources Ă contrainte de dĂ©lai afin de mieux amĂ©liorer le dĂ©bit du rĂ©seau et le dĂ©lai au niveau de la couche liaison avec allocation Ă©quitable et optimale des ressources au niveau de la couche PHY
Throughput Performance Evaluation of Multiservice Multirate OCDMA in Flexible Networks
\u3cp\u3eIn this paper, new analytical formalisms to evaluate the packet throughput of multiservice multirate slotted ALOHA optical code-division multiple-access (OCDMA) networks are proposed. The proposed formalisms can be successfully applied to 1-D and 2-D OCDMA networks with any number of user classes in the system. The bit error rate (BER) and packet correct probability expressions are derived, considering the multiple-access interference as binomially distributed. Packet throughput expressions, on the other hand, are derived considering Poisson, binomial, and Markov chain approaches for the composite packet arrivals distributions, with the latter defined as benchmark. A throughput performance evaluation is carried out for two distinct user code sequences separately, namely, 1-D and 2-D multiweight multilength optical orthogonal code (MWML-OOC). Numerical results show that the Poisson approach underestimates the throughput performance in unacceptable levels and incorrectly predicts the number of successfully received packets for most offered load values even in favorable conditions, such as for the 2-D MWML-OOC OCDMA network with a considerably large number of simultaneous users. On the other hand, the binomial approach proved to be more straightforward, computationally more efficient, and just as accurate as the Markov chain approach.\u3c/p\u3
Future benefits and applications of intelligent on-board processing to VSAT services
The trends and roles of VSAT services in the year 2010 time frame are examined based on an overall network and service model for that period. An estimate of the VSAT traffic is then made and the service and general network requirements are identified. In order to accommodate these traffic needs, four satellite VSAT architectures based on the use of fixed or scanning multibeam antennas in conjunction with IF switching or onboard regeneration and baseband processing are suggested. The performance of each of these architectures is assessed and the key enabling technologies are identified
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Application priority framework for fixed mobile converged communication networks
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The current prospects in wired and wireless access networks, it is becoming increasingly important to address potential convergence in order to offer integrated broadband services. These systems will need to offer higher data transmission capacities and long battery life, which is the catalyst for an everincreasing variety of air interface technologies targeting local area to wide area connectivity. Current integrated industrial networks do not offer application aware context delivery and enhanced services for optimised networks. Application aware services provide value-added functionality to business applications by capturing, integrating, and consolidating intelligence about users and their endpoint devices from various points in the network. This thesis mainly intends to resolve the issues related to ubiquitous application aware service, fair allocation of radio access, reduced energy consumption and improved capacity. A technique that measures and evaluates the data rate demand to reduce application response time and queuing delay for multi radio interfaces is proposed. The technique overcomes the challenges of network integration, requiring no user intervention, saving battery life and selecting the radio access connection for the application requested by the end user. This study is split in two parts. The first contribution identifies some constraints of the services towards the application layer in terms of e.g. data rate and signal strength. The objectives are achieved by application controlled handover (ACH) mechanism in order to maintain acceptable data rate for real-time application services. It also looks into the impact of the radio link on the application and identifies elements and parameters like wireless link quality and handover that will influence the application type. It also identifies some enhanced traditional mechanisms such as distance controlled multihop and mesh topology required in order to support energy efficient multimedia applications. The second contribution unfolds an intelligent application priority assignment mechanism (IAPAM) for medical applications using wireless sensor networks. IAPAM proposes and evaluates a technique based on prioritising multiple virtual queues for the critical nature of medical data to improve instant transmission. Various mobility patterns (directed, controlled and random waypoint) has been investigated and compared by simulating IAPAM enabled mobile BWSN. The following topics have been studied, modelled, simulated and discussed in this thesis: 1. Application Controlled Handover (ACH) for multi radios over fibre 2. Power Controlled Scheme for mesh multi radios over fibre using ACH 3. IAPAM for Biomedical Wireless Sensor Networks (BWSN) and impact of mobility over IAPAM enabled BWSN. Extensive simulation studies are performed to analyze and to evaluate the proposed techniques. Simulation results demonstrate significant improvements in multi radios over fibre performance in terms of application response delay and power consumption by upto 75% and 15 % respectively, reduction in traffic loss by upto 53% and reduction in delay for real time application by more than 25% in some cases
Using Direct-Sequenced Spread Spectrum in a Wired Local Area Network
Code division multiple access provides an ability to share channel bandwidth amongst users at the same time. Individual user performance is not degraded with the addition of more users, unlike traditional Ethernet. Using direct sequenced spread spectrum in a wired local area network, network performance is improved. For a network in overload conditions, individual station throughput is increased by nearly 212% while mean end-to-end delay was reduced by 800%. The vast improvement demonstrated by this research has the capability to extend legacy-cabling infrastructures for many years to come while easily accommodating new bandwidth intensive multimedia applications
Performance Studies of a Double-Layered All-Optical Network Architecture
Transmission in complete lightform is now realised with advancements in technology. These include new developments in fabricating the fiber carrier
medium, low loss fiber coupling devices, optical switching components for routing
lightwave trans mission; laser light sources and sensitive photonic detectors. The
in creasing speeds of new generation electronic microprocessors, is capable of
resolving the differences in processing and transmission speeds. Access to the
medium is regulate d by the medium access control protocol, that permits multiple
users to share limited transmission resources of the network. The double-layere dhierarchical all-optical network architecture is proposed, that consists of an upper
layer to inter connect sub-networks of the lower layer. The data packets are
differentiate d for the two layers . The architecture implements wavelength -space
trans mission of wavelength division multiplexed channels. The architecture affords spatial reuse of channels in the lower layer. A non-contentious token-passing
medium access protocol is utilised. The token-passing variant that uses one token to
provide access to multiple channels is introduced.
The performance of the arrayed transmitter of the access node is gauged to
determine the suitability of the architecture with the access protocol in supporting
multiple accesses. The transmitter can queue a number of data packets awaiting
transmission depending on the size of the buffer. Performance indication can be
obtained from probabilistic modelling of the changing event states of the
transmitter. Performance causal parameters which include the number of nodes,
channel allocation and buffer size are defined. The results from the probabilistic
models are then analysed and verified with simulation. The architecture provides an
inherent feature termed as the bypass that is capitalised to improve performance of
the lower layer. Performance indication shows that the architecture is capable of
supporting the two types of data packets effectively, and the access protocol is
suitable for its purpose. Performance indication of average packet delay improves
when the when the bypass feature is implemented. The probabilistic models are
found to provide a logical and systematic approach to study and gauge performance
of the token-passing access protocol. In conclusion, the double-layered hierarchical
AON architecture and the medium access protocol, together serve as a reference for
the study of similar scaleable network architectures and their performance
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