Beyond 3G Receivers Design
Date Issued
2004-07-31
Date
2004-07-31
Author(s)
DOI
922213E002038
Abstract
Beyond Third Generation (B3G)
wireless communications systems aim to
support high-rate multimedia services in
the mobile environment which makes a
highly distorted radio channel. In order
to combat multipath effects and make
better use of the system available
bandwidth（i.e. high spectral efficiency）,
orthogonal frequency division
multiplexing (OFDM) multicarrier
modulation technique which has been
widely used for many communication
systems such as digital audio
broadcasting (DAB), digital video
terrestrial broadcasting (DVB), IEEE
802.11a, IEEE 802.11g, etc. In addition,
we proposed multi-rate multi-carrier
CDMA receiver structure which shares
the similar concepts with OFDM
modulation to meet multi-user service
and variable data rate transmission.
Multi-Code (MC) and
Variable-Spreading-Length (VSL) are
two widely used schemes in CDMA
systems to support multiple rates
services. In the second year of the
project, we investigate the applications
of these two concepts to Multi-Tone
Code-Division-Multiple-Access
(MT-CDMA) for efficient multi-rate
transmission over
frequency-selective-fading channels.
The resulted signal properties and
transmission performance with the
receiver based on matched filters are
studied and compared for selecting the
appropriate multi-rate scheme in
MT-CDMA. Since the chip-level
orthogonality among sub-carriers is
inherently altered in MT-CDMA, we
analyze the involved interference effect
on MC and VSL schemes and identify
the key problems. Although VSL
concept is known advantageous in
DS-CDMA, MC scheme is shown
favorable in the concerns of BER and
spectrum utilization in MT-CDMA
systems.
Besides, we study the Weiner phase
noise effect in OFDM system and
propose a correction method.Performance degradation due to Wiener
phase noise which causes both common
phase error (CPE) and inter-carrier
interference (ICI) is a crucial challenge
to the implementation of OFDM systems,
especially in B3G systems. We propose
a common phase error estimator based
on maximum likelihood criterion.
Different from conventional maximum
likelihood approach which assumes the
inter-carrier interferences observed on
different subcarriers to be independent
identically distributed, we investigate
the covariance matrice among carriers
by autocorrelation function of the ICI
weighting and combine pilot-aided and
decision-directed approaches to yield a
generalized maximum likelihood
estimation scheme. The performance
degradation caused by ICI is accurately
analyzed and justified with simulation.
Subjects
Multi-Tone-CDMA
Multi-carrier
CDMA
OFDM
Variable-Spreading-Length
Phase
noise
noise
Maximum likelihood
estimation
estimation
Publisher
臺北市：國立臺灣大學電信工程學研究所
Type
report
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