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Performance of Blind Successive Interference Canceller for Multi-Carrier CDMA Systems
-- P A Haris, E Gopinathan and C K Ali
An efficient multiple user access over the wireless channel necessitates a communication system design that
can overcome the adverse impact of multipath propagation such as Inter Symbol Interference (ISI) and Multiple
Access Interference (MAI). This being the objective, a Multi-Carrier Code Division Multiple Access (MC-CDMA)
communication system is discussed in this paper. MC-CDMA, being a combination of Direct Sequence Code Division Multiple
Access (DS-CDMA) and Orthogonal Frequency Division Multiplexing (OFDM), converts a frequency selective fading
channel into multiple flat fading channels, thereby mitigating Inter Symbol Interference (ISI). To overcome the effect of
Multiple Access Interference (MAI), Multi-User Detection (MUD) receiver has been suggested. The performances of Blind
Successive Interference Cancellation (BIC) technique is compared with Matched Filter (MF) receiver and Block-based
Minimum Mean Square Error (BMMSE) receiver by simulating the entire system. The BIC is a MUD technique that uses
knowledge of the desired user's signature sequence and his timing to estimate his information. This is done by executing
interference cancellation in a successive manner, starting from the most dominant component and
successively canceling the weaker ones. The simulation results show that the BIC scheme outperforms conventional
MF receiver and BMMSE receiver.
© 2009 IUP. All Rights Reserved.
A Novel Link Adaptation Schemefor Wideband CDMA
-- K Jayanthi and P Dananjayan
The goal for the next generation cellular systems is to seamlessly integrate a wide variety
of communication services in addition to voice. Wideband Code Division Multiple Access (WCDMA), a radio
access technology, has been recommended by European Telecommunications Standards Institute (ETSI) as a strong
candidate for 3G systems. Multiple Access Interference (MAI) is one of the important performance-limiting factors in a
WCDMA system. In addition to this, the unreliable radio links further complicate this issue. Consequently, it is highly
challenging to ensure guaranteed Quality of Service (QoS) requirements for the multi-service users. The unreliability of
transmission medium is mainly due to time varying long-term and short-term fading. Evidently, in order to combat
adverse propagation conditions and interference, mobile radios can adapt various transmission controls like
transmission power, source/channel codes, etc., to meet the desired performance requirements. This paper suggests and analyzes
a novel link adaptive mechanism for WCDMA systems. The proposed algorithm provides relatively a better
system performance in terms of outage probability, convergence time and power consumption.
© 2009 IUP. All Rights Reserved.
Diverse QoS Support of Multiclass Data
Services Using Cross-Layer Scheduling
-- G Indumathi and K Murugesan
As the cellular and PC worlds collide with Wireless LANs and Internet-based packet data, new networking approaches
will support the integration of voice and data on the composite infrastructure of cellular base stations and
Ethernet-based wireless access points. A
cross-layer networking is where the physical and Medium Access Control (MAC) layer knowledge
of the wireless medium is shared with higher layers in order to provide efficient methods
of allocating network resources and applications over the Internet. With the rapid growth
of the Internet and other Internet-protocol related applications, many improvements have been made in the data
link layer in wireless systems to support a wider variety of data services. However, further improvements in packet
data admission, scheduling and policing between nodes in the network are necessary to maximize throughput and
user satisfaction. In the above three, to facilitate diverse QoS support and to provide user satisfaction, scheduling has
the greatest impact on system throughput. In the two broad categories of scheduling algorithms like priority and
fair scheduling, a majority of them focus on either minimizing packet delay or maximizing user throughput. In this
paper, an adaptive cross-layer priority and fair scheduling algorithms have been proposed for multiclass data services that
can outperform with respect to user throughput and packet delay. It is also shown that a better performance measure
is achieved when validated with NS2 simulations.
© 2009 IUP. All Rights Reserved.
DSP Implementation of QPSK
and 8-QAM Transmitter
for Software Defined Radio
-- V Mathuranathan, M N Satyanarayan and Shikha Tripathi
Future wireless communication services will require a reconfigurable transmitter capable of switching between
several modulation techniques. Reconfigurability could be achieved by defining the transmitter in software. To adapt
to different wireless standard, future radios have to be implemented in software. Software modem radios for 2 and
2.5 Generations have already been implemented (Jeffrey, 2002). In this paper, software defined transmitter capable
of switching between Quadrature Phase Shift Keying (QPSK) and 8-Quadrature Amplitude Modulation (QAM)
techniques has been implemented on a Digital Signal Processor (DSP) TMS320VC5416 platform. A single coupled
standard quadrature recursive oscillator has been used in the design instead of two oscillators required for the two
modulation schemes. This saves program memory. The results obtained are in accordance with the simulation and
theoretical analysis.
© 2009 IUP. All Rights Reserved.
Global GNSS Multi-Constellation Scenario: Present and Future
-- S Mariappan, Swarna Ravindra Babu and G Sasi Bhusana Rao
The future Global Navigation Satellite System (GNSS) is proposed to be multi-constellation with multiple civil
frequency transmissions. The multi-constellation GNSS is very important as this can provide improved accuracy, reliability,
integrity and continuity of service to the users with more visible satellites than any standalone GNSS system. Moreover, by
using common RF frequencies, the complexity of the receiver's RF-front end can be considerably reduced. This
paper presents the existing constellations, upcoming ones and signal structures of some of the civil navigation signals. It
also discusses various accuracy optimization techniques. Some important issues in a multi-constellation scenario, such
as compatibility and interoperability, are also discussed.
© 2009 IUP. All Rights Reserved.
A Survey of VLSI Architectures for FFT Computation in Signal and Image
Processing Applications
-- Chandan Kumar Jha, M Suresh and A K Panda
The increasing demands of speed and performance in modern signal and image processing applications
necessitate design and applications of massive parallel processors technology. Due to the availability of low-cost, high
density, high speed Very Large Scale Integration (VLSI) devices and emerging computer aided design, there has been a
dramatic worldwide growth in research and development efforts on mapping various signal and image processing
applications onto such VLSI architectures. Modern image processing technology depends critically on the device and
architectural innovations of the computing hardware. This paper attempts to survey some of the VLSI architectures that
have already been reported for computation of Fast Fourier Transform (FFT) in signal and image processing
applications. Primarily, pipeline-based, parallel architecture is discussed and parallel-pipeline FFT processor architectures are
also touched upon. In the end, the paper also discusses the importance of using CORDIC algorithms for design
and implementation of efficient VLSI architectures for the said computing method.
© 2009 IUP. All Rights Reserved.
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