59 research outputs found
Beamforming and Multiuser Detection in CDMA Systems with External Interferences
Multiuser detection has been investigated to mitigate the near-far effect in CDMA systems. Antenna arrays have been shown to provide spatial diversity and cancel undesired signals. In this paper we consider the synergy of both multiuser detection and antenna arrays for the base station of a CDMA system. The receiver we proposed consists of the known multiuser decorrelator, which cancels multiple-access interferences followed by a beamformer for each user, which cancels the external interferences. This receiver adds an extra branch to the decorrelator. This additional branch, corresponding to a fictitious user with an unused code and zero power, allows to estimate the external interference signal subspace and compute a suitable beamforming weight-vector that cancels the external interferences. The receiver is also extended to the asynchronous case and all of this without any training signal or any a priori spatial information.Peer ReviewedPostprint (published version
Multiuser Detection and Channel Estimation for Multibeam Satellite Communications
In this paper, iterative multi-user detection techniques for multi-beam
communications are presented. The solutions are based on a successive
interference cancellation architecture and a channel decoding to treat the
co-channel interference. Beams forming and channels coefficients are estimated
and updated iteratively. A developed technique of signals combining allows
power improvement of the useful received signal; and then reduction of the bit
error rates with low signal to noise ratios. The approach is applied to a
synchronous multi-beam satellite link under an additive white Gaussian channel.
Evaluation of the techniques is done with computer simulations, where a noised
and multi-access environment is considered. The simulations results show the
good performance of the proposed solutions.Comment: 12 page
Channel Estimation And Multiuser Detection In Asynchronous Satellite Communications
In this paper, we propose a new method of channel estimation for asynchronous
additive white Gaussian noise channels in satellite communications. This method
is based on signals correlation and multiuser interference cancellation which
adopts a successive structure. Propagation delays and signals amplitudes are
jointly estimated in order to be used for data detection at the receiver. As, a
multiuser detector, a single stage successive interference cancellation (SIC)
architecture is analyzed and integrated to the channel estimation technique and
the whole system is evaluated. The satellite access method adopted is the
direct sequence code division multiple access (DS CDMA) one. To evaluate the
channel estimation and the detection technique, we have simulated a satellite
uplink with an asynchronous multiuser access.Comment: 14 pages, 9 figure
Interference cancellation detectors in a hardware implementation perspective
To combat interference between users in a DS/CDMA system, several multiuser detection schemes have been proposed. This paper presents a prestudy for a custom DSP implementation of a multi-user detector scheme based on non-decision directed interference cancellation. Two architectural implementation methods for asynchronous detection are suggested and mutually compared. Each of the architectures is shown to have its particular advantages and therefore, a design combining the methods described in this paper is worth future studies
Multiuser Detection in Asynchronous Multibeam Communications
This paper deals with multi-user detection techniques in asynchronous
multibeam satellite communications. The proposed solutions are based on
successive interference cancellation architecture (SIC) and channel decoding
algorithms. The aim of these detection methods is to reduce the effect of
cochannel interference due to co-frequency access, and consequently, improves
the capacity of the mulitbeam communications systems, by improving frequency
reuse. Channel estimation allows the determination of interference
coefficients, which helps their effects compensation. The developed multiuser
detections techniques are iterative. Therefore, detection quality is improved
from a stage to another. Moreover, a signals combining method, which is
integrated into these detection solutions, enhances their capability. The
proposed solutions are evaluated through computer simulations, where an
asynchronous multibeam satellite link is considered over an AWGN channel. The
obtained simulation results showed the robustness of these multi-user detection
techniques.Comment: 14 pages, 6 figure
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