27 research outputs found
Space time transceiver design over multipath fading channels
Imperial Users onl
Widely Linear vs. Conventional Subspace-Based Estimation of SIMO Flat-Fading Channels: Mean-Squared Error Analysis
We analyze the mean-squared error (MSE) performance of widely linear (WL) and
conventional subspace-based channel estimation for single-input multiple-output
(SIMO) flat-fading channels employing binary phase-shift-keying (BPSK)
modulation when the covariance matrix is estimated using a finite number of
samples. The conventional estimator suffers from a phase ambiguity that reduces
to a sign ambiguity for the WL estimator. We derive closed-form expressions for
the MSE of the two estimators under four different ambiguity resolution
scenarios. The first scenario is optimal resolution, which minimizes the
Euclidean distance between the channel estimate and the actual channel. The
second scenario assumes that a randomly chosen coefficient of the actual
channel is known and the third assumes that the one with the largest magnitude
is known. The fourth scenario is the more realistic case where pilot symbols
are used to resolve the ambiguities. Our work demonstrates that there is a
strong relationship between the accuracy of ambiguity resolution and the
relative performance of WL and conventional subspace-based estimators, and
shows that the less information available about the actual channel for
ambiguity resolution, or the lower the accuracy of this information, the higher
the performance gap in favor of the WL estimator.Comment: 20 pages, 7 figure
Adaptive DS-CDMA multiuser detection for time variant frequency selective Rayleigh fading channel
The current digital wireless mobile system such as IS-95, which is based on direct sequence Code Division Multiple Access (DS-CDMA) technology, will not be able to meet the growing demands for multimedia service due to low information exchanging rate. Its capacity is also limited by multiple accessed interference (MAI) signals.
This work focuses on the development of adaptive algorithms for multiuser detection (MUD) and interference suppression for wideband direct sequence code division multiple access (DS-CDMA) systems over time-variant frequency selective fading channels. In addition, channel acquisition and delay estimation techniques are developed to combat the uncertainty introduced by the wireless propagation channel. This work emphasizes fast and simple techniques that can meet practical needs for high data rate signal detection.
Most existing literature is not suitable for the large delay spread in wideband systems due to high computational/ hardware complexity. A de-biasing decorrelator is developed whose computational complexity is greatly reduced without sacrificing performance. An adaptive bootstrap symbolbased signal separator is also proposed for a time-variant channel. These detectors achieve MUD for asynchronous, large delay spread, fading channels without training sequences.
To achieve high data rate communication, a finite impulse response (FIR) filter based detector is presented for M-ary QAM modulated signals in a multipath Rayleigh fading channel. It is shown that the proposed detector provides a stable performance for QAM signal detection with unknown fading and phase shift. It is also shown that this detector can be easily extended to the reception of any M-ary quadrature modulated signal.
A minimum variance decorrelating (MVD) receiver with adaptive channel estimator is presented in this dissertation. It provides comparable performance to a linear MMSE receiver even in a deep fading environment and can be implemented blindly. Using the MVD receiver as a building-block, an adaptive multistage parallel interference cancellation (PIC) scheme and a successive interference cancellation (SIC) scheme were developed. The total number of stages is kept at a minimum as a result of the accurate estimating of the interfering users at the earliest stages, which reduces the implementation complexity, as well as the processing delay. Jointly with the MVD receiver, a new transmit diversity (TD) scheme, called TD-MVD, is proposed. This scheme improves the performance without increasing the bandwidth. Unlike other TD techniques, this TDMVD scheme has the inherent advantage to overcome asynchronous multipath transmission. It brings flexibility in the design of TD antenna systems without restrict signal coordination among those multiple transmissions, and applicable for both existing and next generation of CDMA systems.
A maximum likelihood based delay and channel estimation algorithm with reduced computational complexity is proposed. This algorithm uses a diagonal simplicity technique as well as the asymptotically uncorrelated property of the received signal in the frequency domain. In combination with oversampling, this scheme does not suffer from a singularity problem and the performance quickly approaches the Cramer-Rao lower bound (CRLB) while maintaining a computational complexity that is as low as the order of the signal dimension
Spatio-Temporal processing for Optimum Uplink-Downlink WCDMA Systems
The capacity of a cellular system is limited by two different phenomena, namely
multipath fading and multiple access interference (MAl). A Two Dimensional (2-D)
receiver combats both of these by processing the signal both in the spatial and temporal
domain. An ideal 2-D receiver would perform joint space-time processing, but at the
price of high computational complexity. In this research we investigate computationally
simpler technique termed as a Beamfom1er-Rake. In a Beamformer-Rake, the output of a
beamfom1er is fed into a succeeding temporal processor to take advantage of both the
beamformer and Rake receiver. Wireless service providers throughout the world are
working to introduce the third generation (3G) and beyond (3G) cellular service that will
provide higher data rates and better spectral efficiency. Wideband COMA (WCDMA)
has been widely accepted as one of the air interfaces for 3G. A Beamformer-Rake
receiver can be an effective solution to provide the receivers enhanced capabilities
needed to achieve the required performance of a WCDMA system.
We consider three different Pilot Symbol Assisted (PSA) beamforming techniques,
Direct Matrix Inversion (DMI), Least-Mean Square (LMS) and Recursive Least Square
(RLS) adaptive algorithms. Geometrically Based Single Bounce (GBSB) statistical
Circular channel model is considered, which is more suitable for array processing, and
conductive to RAKE combining. The performances of the Beam former-Rake receiver are
evaluated in this channel model as a function of the number of antenna elements and
RAKE fingers, in which are evaluated for the uplink WCDMA system. It is shown that,
the Beamformer-Rake receiver outperforms the conventional RAKE receiver and the
conventional beamformer by a significant margin. Also, we optimize and develop a
mathematical formulation for the output Signal to Interference plus Noise Ratio (SINR)
of a Beam former-Rake receiver.
In this research, also, we develop, simulate and evaluate the SINR and Signal to Noise
Ratio (Et!Nol performances of an adaptive beamforming technique in the WCDMA
system for downlink. The performance is then compared with an omnidirectional antenna
system. Simulation shows that the best perfom1ance can be achieved when all the mobiles
with same Angle-of-Arrival (AOA) and different distance from base station are formed in
one beam
Spatio-Temporal processing for Optimum Uplink-Downlink WCDMA Systems
The capacity of a cellular system is limited by two different phenomena, namely
multipath fading and multiple access interference (MAl). A Two Dimensional (2-D)
receiver combats both of these by processing the signal both in the spatial and temporal
domain. An ideal 2-D receiver would perform joint space-time processing, but at the
price of high computational complexity. In this research we investigate computationally
simpler technique termed as a Beamfom1er-Rake. In a Beamformer-Rake, the output of a
beamfom1er is fed into a succeeding temporal processor to take advantage of both the
beamformer and Rake receiver. Wireless service providers throughout the world are
working to introduce the third generation (3G) and beyond (3G) cellular service that will
provide higher data rates and better spectral efficiency. Wideband COMA (WCDMA)
has been widely accepted as one of the air interfaces for 3G. A Beamformer-Rake
receiver can be an effective solution to provide the receivers enhanced capabilities
needed to achieve the required performance of a WCDMA system.
We consider three different Pilot Symbol Assisted (PSA) beamforming techniques,
Direct Matrix Inversion (DMI), Least-Mean Square (LMS) and Recursive Least Square
(RLS) adaptive algorithms. Geometrically Based Single Bounce (GBSB) statistical
Circular channel model is considered, which is more suitable for array processing, and
conductive to RAKE combining. The performances of the Beam former-Rake receiver are
evaluated in this channel model as a function of the number of antenna elements and
RAKE fingers, in which are evaluated for the uplink WCDMA system. It is shown that,
the Beamformer-Rake receiver outperforms the conventional RAKE receiver and the
conventional beamformer by a significant margin. Also, we optimize and develop a
mathematical formulation for the output Signal to Interference plus Noise Ratio (SINR)
of a Beam former-Rake receiver.
In this research, also, we develop, simulate and evaluate the SINR and Signal to Noise
Ratio (Et!Nol performances of an adaptive beamforming technique in the WCDMA
system for downlink. The performance is then compared with an omnidirectional antenna
system. Simulation shows that the best perfom1ance can be achieved when all the mobiles
with same Angle-of-Arrival (AOA) and different distance from base station are formed in
one beam