6 research outputs found
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
Iterative Joint Time-Variant Channel Estimation and Multi-User Detection for MC-CDMA
Joint time-variant channel estimation and multiuser detection are key building-blocks for wireless broadband communication for mobile users at vehicular speed. We propose an iterative receiver for a multi-carrier (MC) code division multiple access (CDMA) system in the uplink. Multi-user detection is implemented through iterative parallel interference cancelation and conditional linear minimum mean square error (MMSE) filtering. MC-CDMA is based on orthogonal frequency division multiplexing (OFDM), thus time-variant channel estimation can be performed for every subcarrier individually. The variation of a subcarrier over the duration of a data block is upper bounded by the maximum Doppler bandwidth which is determined by the maximum velocity of the users. We exploit results from the theory of time-concentrated and bandlimited sequences and apply a Slepian basis expansion for time-variant subcarrier estimation. This approach enables time-variant channel estimation without complete knowledge of the second-order statistics of the fading process. The square bias of the Slepian basis expansion is one order of magnitude smaller compared to the Fourier basis expansion. The square bias of the basis expansion is the determining factor for the performance of the iterative joint channel estimation and data detection. We present an iterative linear MMSE estimation algorithm for the basis expansion coefficients in a multi-user system. The consistent performance of the iterative receiver using the Slepian basis expansion is validated by simulations for a wide range of velocities