1,780 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,
“VPITM TransmissionMaker 7.1” 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 10−9 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
Development And Implementation of a Novel Code Family for Optical Code Division Multiple Access Systems
Future telecommunication systems and networks are expected to provide a variety of
integrated broadband services to the customers. There has been a tremendous interest in
applying Code Division Multiple Access (CDMA) techniques to fiber optic
communication systems. This technique is one of the multiple access schemes that is
becoming popular because of the flexibility in the allocation of channels, ability to
operate asynchronously, enhanced privacy and increased capacity in bursty networks.
The performance of any Optical CDMA (OCDMA) system strongly depends on the
codes properties. In this study we introduce a new code for Optical CDMA namely
Double Weight Code family (DW). Double Weight Code (DW) has a basic fixed weight
of 2 and exists for every natural number. The DW codes possess ideal cross correlation
properties, which have important characteristics in OCDMA systems since these can
eliminate multiple access interference (MAI) and reduce noise. Also proposed in this study, a Modified Double-Weight (MDW) code, which is a variation of DW code family
that can have a variable weight greater than two. The MDW code possesses ideal crosscorrelation
properties and exists for every natural number too. It is shown through
simulations, theoretical analysis and partially by the experiments that the transmission
performance of DW code family is significantly better than that of existing codes such
as Modified Frequency Hopping code (MFH) and Hadarnard code.
The performance of DW code family, MFH and Hadamard codes were simulated using
commercial simulation software, OptiSystem Version 3.0. The performance of the
systems was characterized by referring to the bit error rate (BER) and the eye patterns.
DW code family has shown superior performance compared to other OCDMA codes.
The simulated eye pattern of one of the four MDW coded carriers running at lOGbps
over a cornrnunication-standard fiber shows a good quality transmission at the BER of
10 -12 as opposed to only 1o ' ~an d 1o 4 for Hadamard and MFH codes.
In optical CDMA systems, the detection process affects the design of transmitters and
receivers. Cross-correlation functions are generated which creates Multiple Access
Interference (MAI) and this will degrade the system performance. MA1 can be reduced
by using subtraction techniques. The most common subtraction technique is the
complementary subtraction technique and also known as balanced detection technique.
In this thesis, we also introduce a new approach called AND subtraction technique. This
method rejects unwanted signals that interfere with the original signals. Furthermore, the
purpose of this new subtraction technique is to reduce the receiver complexity and
increase system performance. It has been shown through theoretical analysis, simulation and experimental work, the performance of the system with AND subtraction technique
can be improved significantly. Based on the theoretical analysis, BER as good as 10-l2is
achieved at the bit rate of 622 Mbps over 70 km distance
Performance Evaluation Of Optical CDMA Ring Network Due To Self Interference Induced By Power Circulation
Presently, there is great interest in the telecommunication research community and industries on the optical code multiple access (OCDMA) techniques. This is due to the huge bandwidth offered by the optical link, highly efficient optical signal processing and decreasing cost of optical components. The performance of OCDMA systems depend on the code properties and detection scheme. In this thesis, an OCDMA system for a ring topology based on K-S code was proposed to be implemented in the metro environment. K-S code is a new code for Optical CDMA with variable weight greater than 2. In this thesis the weight of 4 is chosen. The code possesses ideal cross correlation properties which can reduce multiple access interference (MAI) and noise. However, there are two main types of interferences exist in the OCDMA ring topology. Besides MAI, there are another interference due to the circulation of power in the ring namely self–interference. It will deteriorate the next concurrent data stream for the same user to be transmitted into the ring and could make the system performance decreased.A direct detection scheme was used to eliminate MAI and hence only the effect of self-interference was investigated. Before performing the simulation, limited theoretical results on receive power were developed to show the trend of receive power at each receiver. The formula is depended on the transmitted power, fiber length, coupling ratio, number of nodes and the number of circulating power in the ring. The performance of the ring network was then simulated using commercial simulation software, OptiSystem Version 5.0. The network performance is evaluated against several design parameters by comparing the signal turns in the first and second transmission by referring to the bit error rate, BER, received power, Psr and the eye patterns. In this thesis, it was found that the effect of the self-interference is determined by the transmitted power, fiber length, coupling ratio and the bit rate. It proves that the self-interference is increased with the increment of transmitted power. It also experience losses with the increment of fiber span but the system will suffer the serious effect when the fiber length is shorter than 30 km at 1Gbps. Results also proves that the self-interference effect is worst at 30% coupling ratio although the system performance is better with the increment of coupling ratio until certain point. Finally, the best transmission rate for this system is 1Gbps while there were another optimum values for each parameter supported by the system in order to minimize the self-interference
Development of User-Interface Software Program for Double Weight Code Family for OCDMA
Optical Code Division Multiple Access (OCDMA) offers high statistical multiplexing gain in a busty traffic environment and is thought to be a more suitable solution in local-area network. There have been many codes proposed OCDMA systems, such as Hadamard code, Modified Frequency Hopping (MFH) code and Double Weight (DW) code family. The inspiration of this study is to improve the Modified Double Weight (MDW) code to give a better performance and to enhance the detection technique of DW code family. There are few aspects that have been identified in this study. First of all, the construction of MDW code is studied. Besides, the equation-based construction technique is examined and is then simulated using Virtual Basic software version 6.0. The findings of the project will lead to a new development of the MDW code by having new user-interface software program to generate the DW codeword with an ease
Wireless Communications Networking: and An Overview
This paper presents an overview of wireless local-area networks (LANs) and wireless personal area networks (PANs), with emphasis on the two most popular standards: IEEE 802.1 1, and Bluetooth. While there are many such surveys in the current literature and online, we attempt here to present wireless LANs and PANS in a unified fashion as a viable alternative to wired LANs, while stressing the remaining challenges and limitations
Enhanced 3-D OCDMA code family using asymmetric run length constraints
Abstract : This paper suggests an enhanced performance of the 3-D optical code division multiple access (OCDMA) codes, a space/wavelength/time spreading family of codes. The initial codes are in the format wavelength hopping/time sequence (WH/TS), selected according to their performance requirements and the TS sequence is constructed to achieve a linear space- time complexity. The asymmetric run length constraints are introduced in that regard, such that the positive bit positions align with the encoder/decoder frequency spacing pattern, yielding a 3-D WH/WS/TS. The selected 2-D OCDMA codes are one- coincidence frequency hopping codes (OCFHC) and optical orthogonal codes (OOC). As a time sequence code, the OOC code length is extended with a code rate of 0.04. The complexity and the bit error rate (BER) are herein given and compared with previous work. The results of the performance show not only an improvement in the number of simultaneous users due to the code length extension, but better correlation properties and hence a better signal-to-noise ratio
Complexity-Aware Scheduling for an LDPC Encoded C-RAN Uplink
Centralized Radio Access Network (C-RAN) is a new paradigm for wireless
networks that centralizes the signal processing in a computing cloud, allowing
commodity computational resources to be pooled. While C-RAN improves
utilization and efficiency, the computational load occasionally exceeds the
available resources, creating a computational outage. This paper provides a
mathematical characterization of the computational outage probability for
low-density parity check (LDPC) codes, a common class of error-correcting
codes. For tractability, a binary erasures channel is assumed. Using the
concept of density evolution, the computational demand is determined for a
given ensemble of codes as a function of the erasure probability. The analysis
reveals a trade-off: aggressively signaling at a high rate stresses the
computing pool, while conservatively backing-off the rate can avoid
computational outages. Motivated by this trade-off, an effective
computationally aware scheduling algorithm is developed that balances demands
for high throughput and low outage rates.Comment: Conference on Information Sciences and Systems (CISS) 2017, to appea
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