11 research outputs found
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
xix
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
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 xix 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.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
A Novel Beam Forming Technique for CDMA 2000 Wireless Communication: Performance Analysis
A novel beamforming algorithm based on conjugate gradient methods is described and
its performance is computed in terms of bit error rate for practical CDMA 2000
communication systems. The proposed technique attempts to maximize signal-to-noise
plus interference of the received signal, and is based on solving the eigenvalue problem
where the optimization of the weight vector is done using the pilot channel. The
performance is simulated for practical CDMA 2000 1X communications systems in
wireless propagation environments with high angle spread. The performance of the
proposed beamforming algorithm is also compared with existing beamforming
algorithms. Simulation results show that the performance of the proposed algorithm
is more robust to higher angle spread
Unsupervised Texture Segmentation: Comparison of Texture Features
Texture is an important image-content that has been utilized for different machine intelligent tasks, like those in machine vision and remote sensing, which identify objects of interest by segmenting the image texture. This paper aims at comparing texture features based on Discrete Fourier Transform (DFT) with ones based on Gabor wavelets for unsupervised image segmentation. The comparison is realized theoretically, analytically, as well as empirically. Images of natural scenes from a standard image database have been taken as test images. Analytical comparison shows that the DFT-based features are computationally less expensive than those based on Gabor wavelets. Empirical results show that the performance of the texture features based on DFT is comparable to those based on Gabor wavelets
Monte-Carlo Simulation for PDC-Based Optical CDMA System
This paper presents the Monte-Carlo simulation of Optical CDMA (Code Division
Multiple Access) systems, and analyse its performance in terms of the BER (Bit Error
Rate). The spreading sequence chosen for CDMA is Perfect Difference Codes.
Furthermore, this paper derives the expressions of noise variances from first principles
to calibrate the noise for both bipolar (electrical domain) and unipolar (optical domain)
signalling required for Monte-Carlo simulation. The simulated results conform to the
theory and show that the receiver gain mismatch and splitter loss at the transceiver
degrades the system performance
Locating Center of Mass of Earth and Geostationary Satellites
CoM (Center of Mass) of earth is a very important factor which can play a major role in satellite communication and related earth sciences. The CoM of earth is assumed to be around equator due to geometrical shape of earth. However, no technical method is available in the literature which can justify the presence of CoM of earth around equator. Therefore, in this research work the CoM of earth has been located theoretically with the help of mathematical relations. It also presents the mathematical justification against the assumption that equator is the CoM of earth. The effect of calculated CoM of earth on geostationary satellites has also been discussed. The CoM of earth has been found mathematically by using land to ocean ratios and the data is collected from the Google earth software. The final results are accurate with an approximate error of 1%
Design, Development and Implementation of the IR Signalling Techniques for Monitoring Ambient and Body Temperature in WBANs
Healthcare systems such as hospitals, homecare, telemedicine, and physical rehabilitation are expected to be revolutionized by WBAN (Wireless Body Area Networks). This research work aims to investigate, design, optimize, and demonstrate the applications of IR (Infra-Red) communication systems in WBAN. It is aimed to establish a prototype WBAN system capable of measuring Ambient and Body Temperature using LM35 as temperature sensor and transmitting and receiving the data using optical signals. The corresponding technical challenges that have to be faced are also discussed in this paper. Investigations are carried out to efficiently design the hardware using low-cost and low power optical transceivers. The experimental results reveal the successful transmission and reception of Ambient and Body Temperatures over short ranges i.e. up to 3-4 meters. A simple IR transceiver with an LED (Light Emitting Diodes), TV remote control IC and Arduino microcontroller is designed to perform the transmission with sufficient accuracy and ease. Experiments are also performed to avoid interference from other sources like AC and TV remote control signals by implementing IR tag
LED Based Optical Wireless Communication System for WBAN
In this paper the O-WBANs (Optical Wireless Body Area Networks) is presented as an alternative to the
radio and microwave BANs which are plagued with issues like interference, power hungry, hazardous
and costly spectrum. Various experiments performed in this work demonstrate the feasibility of LED
(Light-Emitting Diode) based optical systems to be used for BANs. The system cost is kept as low as
possible. Mainly the effects on the optical link are observed under ambient light and with different
modulation schemes by varying link distance and line of sight in this paper. Experimental results reveal
the satisfactory link availability up to the distance of 7 feet (around 2m, the optimum range of WBAN) and
within the field of view of 30-60Âș. The low cost solution presented in this paper meets the WBANs data
rate requirement for physiological data (i.e. 10-100 kbps). As IR (Infra-Red) signals do not provide any
interference with the signals generated by the medical equipment of hospitals which is the problem in
case of RF or microwave signals, additionally the IR signals are confined within a room hence IR
signaling can prove to be potential candidate for WBAN fulfilling its security and limited access
requirement