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Genetic Algorithm for Cdma-Based MUD Techniques Under Rayleigh Fading Environment
-- Kishor G Maradia, S M Joshi and Jayesh S Patel
Communication systems have the challenge of accommodating many users in a small area. With the advent of
spread spectrum, and hence, Code Division Multiple Access (CDMA), fixed bandwidth was used to accommodate many
users by making use of certain coding properties, modulation techniques and optimization algorithms. The aim of this
paper is to explore the concept of Genetic Algorithm (GA) for CDMA-based Multi-User Detection (MUD) system model
in multipath Rayleigh fading environment. MUD is the intelligent estimation/demodulation of transmitted bits in
the presence of Multiple Access Interference (MAI). MAI occurs in multi-access communication systems
(CDMA/TDMA/FDMA), where simultaneously occurring digital streams of information interfere with each other. Compared with
other algorithms, GA provides better performance, and therefore, can be believed to be the next generation algorithm for
the optimization problem. The proof of the statement is explored by analyzing and comparing simulated results
for different number of users, modulation techniques and spreading codes under the effect of Rayleigh fading channel.
Bit Error Rate (BER) and time profile are the measures of performance in this research document.
© 2009 IUP. All Rights Reserved.
Speech Enhancement in Non-Stationary Noise Environments: An Efficient Approach
-- Ch V Rama Rao, M B Rama Murthy and K Srinivasa Rao
In speech communication and particularly in mobile voice communication, noise reduction is a vital task
for improvement in the quality of communication. Several speech enhancement algorithms available in the literature
are mainly for the reduction of noise in stationary environments. In this paper, a two-stage noise reduction algorithm
is proposed, which suits both quasi-stationary and non-stationary noise environments. The algorithm is based on
two-stage noise filtering, using spectral gain and perceptually motivated weighting techniques. The proposed
speech enhancement algorithm and three other algorithms
are used to reduce noise in different noisy speech samples,
the results of which are compared and discussed.
© 2009 IUP. All Rights Reserved.
Performance Comparison of Adaptive
Cross-Layer Schemes in Wireless Ad Hoc Networks
-- T Aruna and M Suganthi
To enhance spectral efficiency and channel utilization in future high-speed wireless multimedia networks over
fading channels, Adaptive Modulation and Coding (AMC) and Automatic Repeat Request (ARQ) protocol are the key
techniques. In Truncated-ARQ (TARQ) protocols, retransmissions are activated only when necessary. This paper investigates
the additional gains achieved through the cross layer design between physical and data link layers under prescribed
delay and error performance constraints. The design is based on controlling the AMC transmission mode according
to instantaneous received Signal-to-Noise Ratio (SNR) and the length of the finite length buffer at the data link layer.
The paper compares the performance characteristics of the two cross layer schemes AMC-HARQ and AMC-TARQ.
The numerical results reveal that the AMC-TARQ system can provide better spectral efficiency than both the AMC
and AMC-HARQ systems, and the PER of the AMC-HARQ system can provide better spectral efficiency than both the
AMC and AMC-TARQ systems.
© 2009 IUP. All Rights Reserved.
Impact of SRS Nonlinear Effect of Optical Fiber in the Presence of Ultra Wide Band EDFAs in an OFDM Communication System
-- Neelam Srivastava
This paper considers the Optical Frequency Division Multiplexing (OFDM) system, where optical fiber link is
designed and ultra wide band Erbium Doped Fiber Amplifier (EDFA) is used as an in-line amplifier whose gain compensates
the loss of the optical fiber. The optical signal is degraded by the accumulated Amplified Stimulated Emission (ASE)
noise from the optical amplifier in the chain. At the photo detector, ASE noise is converted to electrical noise
primarily through signal—ASE beating, which leads to Bit Error Rate (BER) flooring. Other optical parameters in system
design consideration are channel power divergence and maximum channel power relative to the threshold levels of
optical nonlinearities—Stimulated Raman Scattering (SRS), Stimulated Brillouin Scattering (SBS), Four-Wave Mixing
(FWM), etc. The paper concludes that the product of the number of EDFAs and their gain decreases as the number of
channel multiplexed increases; this depends on the data rate. The paper compares the results for 1 GB, 10 GB and 40 GB
signal bit rates for the required bit error rate of
10_9 for Amplitude-Shift Keying (ASK) and Phase-Shift Keying (PSK)
modulation formats.
© 2009 IUP. All Rights Reserved.
An Application of PearsonICA
to DS-CDMA Detection
-- S D Parmar and Bhuvan Unhelkar
Commercial cellular networks, like the systems based on Direct Sequence-Code Division Multiple Access
(DS-CDMA), face many types of interferences such as multiuser interference inside each sector in a cell to
interoperate interference. While unintentional jamming can be present due to coexisting systems at the same band,
intentional jamming arises mainly in military applications. Independent Component Analysis (ICA) has been used as an
advanced preprocessing tool for blind suppression of interfering signals in DS-CDMA communication systems. The role of
ICA is to provide an interference-mitigated signal to the conventional detection. This paper evaluates the
performance of the PearsonICA algorithm to solve the symbol estimation problem of multiusers in a DS-CDMA
communication system. The main focus is on blind separation of convolved CDMA mixture and
on improvement of the downlink symbol estimation. The results of
the numerical experiments are compared with those obtained by the Single
User Detection (SUD) receiver, the ICA detector and
the combined SUD-ICA detector.
© 2009 IUP. All Rights Reserved.
A VHDL Implementation of Orthogonal Interleavers for the IDMA Scheme
-- M Shukla, V K Srivastava and S Tiwari
Interleavers are referred to as integral parts for many systems such as Code Division Multiple Access (CDMA),
Interleave Division Multiple Access (IDMA), and optical fiber communication. In case of CDMA, interleavers are used for
coding gain, while for IDMA, they are employed for user separation. In case of optical fiber communication, interleavers
are periodic optical filters that combine or separate a comb of dense wavelength division multiplexed signals. The
challenge is to implement these interleavers at affordable decoding complexity and speed with the current fabrication
technology. This paper first presents various orthogonal interleavers. It then performs the comparison on their performance
and computational complexity. Next, it implements various interleavers on Field Programmable Gate Array (FPGA)
using VHDL. After the comparison, it observes that the Tree-Based Interleaver (TBI) turns out to be the best compromise
in terms of performance and complexity.
© 2009 IUP. All Rights Reserved.
Tracking of Objects in the Images Received
from Imaging Sonar of Autonomous Underwater
Vehicles (AUVs)
-- S Swapna Rani, Rajkumar Goswami and G Sasi Bhushana Rao
Tracking of objects in the images received from sector scan sonar is a very important requirement for
Autonomous Underwater Vehicles (AUVs) in order to avoid the obstacles that may come in its path during its missions. This
involves proper segmentation where the image is segmented into objects, shadows and sea bottom reverberation
regions, followed by extraction of the edges of the objects. This then leads to identification of the objects of interest. The
objects detected in the images received from the sonar are then tracked and their trajectories are determined. These are
then correlated with the speed and direction of the AUV. Subsequently, by using the triangulation method, the
collision course on which the collision is expected to occur is calculated. Thereafter, by giving the suitable command to the
AUV, the collision is avoided. In this paper, segmentation, extraction of objects, tracking based on the centroids of
the objects, along with the calculation of collision course, have been presented. The calculation of the trajectory has
been done through the implementation of the Kalman filter, which has been undertaken in MATLAB.
© 2009 IUP. All Rights Reserved.
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