3,433 research outputs found
A NOVEL CONSTRUCTION OF VECTOR COMBINATORIAL (VC) CODE FAMILIES AND DETECTION SCHEME FOR SAC OCDMA SYSTEMS
There has been growing interests in using optical code division multiple access
(OCDMA) systems for the next generation high-speed optical fiber networks. The
advantage of spectral amplitude coding (SAC-OCDMA) over conventional OCDMA
systems is that, when using appropriate detection technique, the multiple access
interference (MAI) can totally be canceled. The motivation of this research is to
develop new code families to enhance the overall performance of optical OCDMA
systems. Four aspects are tackled in this research. Firstly, a comprehensive discussion
takes place on all important aspects of existing codes from advantages and
disadvantages point of view. Two algorithms are proposed to construct several code
families namely Vector Combinatorial (VC). Secondly, a new detection technique
based on exclusive-OR (XOR) logic is developed and compared to the reported
detection techniques. Thirdly, a software simulation for SAC OCDMA system with
the VC families using a commercial optical system, Virtual Photonic Instrument,
âVPITM TransmissionMaker 7.1â is conducted. Finally, an extensive investigation to
study and characterize the VC-OCDMA in local area network (LAN) is conducted.
For the performance analysis, the effects of phase-induced intensity noise (PIIN), shot
noise, and thermal noise are considered simultaneously. The performances of the
system compared to reported systems were characterized by referring to the signal to
noise ratio (SNR), the bit error rate (BER) and the effective power (Psr). Numerical
results show that, an acceptable BER of 10â9 was achieved by the VC codes with 120
active users while a much better performance can be achieved when the effective
received power Psr > -26 dBm. In particular, the BER can be significantly improved
when the VC optimal channel spacing width is carefully selected; best performance
occurs at a spacing bandwidth between 0.8 and 1 nm. The simulation results indicate
that VC code has a superior performance compared to other reported codes for the
same transmission quality. It is also found that for a transmitted power at 0 dBm, the
BER specified by eye diagrams patterns are 10-14 and 10-5 for VC and Modified
Quadratic Congruence (MQC) codes respectively
DWDM/OOC and large spectrum sources performance in broadband access network
This work presents a performance evaluation based on elaborated analytical
expressions of error probability for broadband access network in the case of a
combined technique of dense wavelength division multiplexing (DWDM) and one
dimensional optical orthogonal codes (1D-OOC). Optical sources with relatively
large spectrum has been considered and simulated. Besides the Multiple Access
Interference (MAI) at the receiver due to the access method which is optical
code division multiple access (OCDMA), the emitted radiation of these sources
in a dense WDM communication link introduces additional interference.
Conventional correlation receiver (CCR) and parallel interference cancellation
(PIC) receiver limitations are discussed. This paper has investigated the kind
of optical sources with large spectrum bandwidth which could be accepted for a
targeted bit error rate (BER) and given number of users in broadband access
network supporting DWDM with optical orthogonal codes.Comment: (IJDPS) Vol.3, No.3, May 2012, International Journal of Distributed
and Parallel Systems (IJDPS) Vol.3, No.3, May 201
Applications of perfect difference codes in fiber-optics and wireless optical code-division multiplexing/multiple-access systems
After establishing itself in the radio domain, Spread spectrum code-division
multiplexing/multiple-access (CDMA) has seen a recent upsurge in optical
domain as well. Due to its fairness, flexibility, service differentiation and
increased inherent security, CDMA is proved to be more suitable for the bursty
nature of local area networks than synchronous multiplexing techniques like
Frequency/Wavelength Division Multiplexing (F/WDM) and Time Division
Multiplexing (TDM). In optical domain, CDMA techniques are commonly known
as Optical-CDMA (O-CDMA). All optical CDMA systems are plagued with the
problem of multiple-access interference (MAI). Spectral amplitude coding (SAC)
is one of the techniques used in the literature to deal with the problem of MAI.
The choice of spreading code in any CDMA system is another way to ensure the
successful recovery of data at the receiving end by minimizing the effect of MAI
and it also dictates the hardware design of the encoder and decoder.
This thesis focuses on the efficient design of encoding and decoding hardware.
Perfect difference codes (PDC) are chosen as spreading sequences due to their
good correlation properties. In most of the literature, evaluation of error
probability is based on the assumptions of ideal conditions. Such assumptions
ignore major physical impairments such as power splitting losses at the
multiplexers of transmitters and receivers, and gain losses at the receivers, which
may in practice be an overestimate or underestimate of the actual probability of
error.
This thesis aims to investigate thoroughly with the consideration of practical
impairments the applications of PDCs and other spreading sequences in optical
communications systems based on spectral-amplitude coding and utilizing codedivision
as multiplexing/multiple-access technique. This work begins with a
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general review of optical CDMA systems. An open-ended practical approach has
been used to evaluate the actual error probabilities of OCDM/A systems under
study. It has been concluded from results that mismatches in the gains of
photodetectors, namely avalanche photodiode (APDs), used at the receiver side
and uniformity loss in the optical splitters results in the inaccurate calculation of
threshold level used to detect the data and can seriously degrade the system bit
error rate (BER) performance. This variation in the threshold level can be
compensated by employing techniques which maintain a constant interference
level so that the decoding architecture does not have to estimate MAI every time
to make a data bit decision or by the use of balanced sequences.
In this thesis, as a solution to the above problem, a novel encoding and decoding
architecture is presented for perfect difference codes based on common zero code
technique which maintains a constant interference level at all instants in CDM
system and thus relieves the need of estimating interference. The proposed
architecture only uses single multiplexer at the transmitters for all users in the
system and a simple correlation based receiver for each user. The proposed
configuration not only preserves the ability of MAI in Spectral-Amplitude Coding
SAC-OCDM system, but also results in a low cost system with reduced
complexity. The results show that by using PDCs in such system, the influence of
MAI caused by other users can be reduced, and the number of active users can be
increased significantly.
Also a family of novel spreading sequences are constructed called Manchestercoded
Modified Legendre codes (MCMLCs) suitable for SAC based OCDM
systems. MCMLCs are designed to be used for both single-rate and Multirate
systems. First the construction of MCMLCs is presented and then the bit error rate
performance is analyzed.
Finally the proposed encoding/decoding architecture utilizing perfect difference
codes is applied in wireless infrared environment and the performance is found to
be superior to other codes
Performance analysis of 2D-OCDMA system in long-reach passive optical network
International audienceIn this paper, a performance analysis is reported for optical code division multiplexing (OCDM) system for long-reach passive optical network (LR-PON) systems by taking into account multiple access interference (MAI), single-mode fiber (SMF) channel effects and receiver noise. The mathematical model representing the 2-D optical code parameters for different receiver structures used in optical code division multiplexing access (OCDMA) are developed, optimized and implemented using Matlab simulations, where channel imperfections, such as attenuation losses and chromatic dispersion have been considered. In the proposed system configuration, we have investigated the probability of error for Back-to-Back (B2B) with conventional correlation receiver (CCR), SMF with CCR receiver and SMF channel with successive interference cancelation (SIC) receiver. Additionally, SMF channel with SIC receiver system performance has been addressed by taking into account two key metrics, such as BER and Q-factor as function of simultaneous users, and fiber length, respectively. We have managed to substantially improve simultaneous multiuser data transmission over significant fiber lengths without use of amplification, where Q-factor of 6 at fiber length of 190 and 120 km, while a SIC receiver using 5 stages cancelation is employed for 2D prime hop system (2D-PHS) and for 2D hybrid codes (2D-HC), respectively
Indoor Radio Measurement and Planning for UMTS/HSPDA with Antennas
Over the last decade, mobile communication networks have evolved tremendously with a key focus on providing high speed data services in addition to voice. The third generation of mobile networks in the form of Universal Mobile Telecommunications System (UMTS) is already offering revolutionary mobile broadband experience to its users by deploying High Speed Downlink Packet Access (HSDPA) as its packet-data technology. With data speeds up to 14.4 Mbps and ubiquitous mobility, HSDPA is anticipated to become a preferred broadband access medium for end-users via mobile phones, laptops etc. While majority of these end-users are located indoors most of the time, approximately 70-80% of the HSDPA traffic is estimated to originate from inside buildings. Thus for network operators, indoor coverage has become a necessity for technical and business reasons.
Macro-cellular (outdoor) to indoor coverage is a natural inexpensive way of providing network coverage inside the buildings. However, it does not guarantee sufficient link quality required for optimal HSDPA operation. On the contrary, deploying a dedicated indoor system may be far too expensive from an operator\u27s point of view. In this thesis, the concept is laid for the understanding of indoor radio wave propagation in a campus building environment which could be used to plan and improve outdoor-to-indoor UMTS/HSDPA radio propagation performance. It will be shown that indoor range performance depends not only on the transmit power of an indoor antenna, but also on the product\u27s response to multipath and obstructions in the environment along the radio propagation path.
An extensive measurement campaign will be executed in different indoor environments analogous to easy, medium and hard radio conditions. The effects of walls, ceilings, doors and other obstacles on measurement results would be observed.
Chapter one gives a brief introduction to the evolution of UMTS and HSDPA. It goes on to talk about radio wave propagation and some important properties of antennas which must be considered when choosing an antenna for indoor radio propagation. The challenges of in-building network coverage and also the objectives of this thesis are also mentioned in this chapter.
The evolution and standardization, network architecture, radio features and most importantly, the radio resource management features of UMTS/HSDPA are given in chapter two. In this chapter, the reason why Wideband Code Division Multiple Access (WCDMA) was specified and selected for 3G (UMTS) systems would be seen. The architecture of the radio access network, interfaces with the radio access network between base stations and radio network controllers (RNC), and the interface between the radio access network and the core network are also described in this chapter. The main features of HSDPA are mentioned at the end of the chapter.
In chapter three the principles of the WCDMA air interface, including spreading, Rake reception, signal fading, power control and handovers are introduced. The different types and characteristics of the propagation environments and how they influence radio wave propagation are mentioned. UMTS transport, logical and physical channels are also mentioned, highlighting their significance and relationship in and with the network.
Radio network planning for UMTS is discussed in chapter four. The outdoor planning process which includes dimensioning, detailed planning, optimization and monitoring is outlined. Indoor radio planning with distributed antenna systems (DAS), which is the idea and motivation behind this thesis work, is also discussed.
The various antennas considered and the antenna that was selected for this thesis experiment was discussed in chapter five. The antenna radiation pattern, directivity, gain and input impedance were the properties of the antenna that were taken into consideration. The importance of the choice of the antenna for any particular type of indoor environment is also mentioned.
In chapter six, the design and fabrication of the monopole antennas used for the experimental measurement is mentioned. The procedure for measurement and the equipment used are also discussed. The results gotten from the experiment are finally analyzed and discussed. In this chapter the effect of walls, floors, doors, ceilings and other obstacles on radio wave propagation will be seen.
Finally, chapter seven concludes this thesis work and gives some directions for future work
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
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