1,562 research outputs found
Precoded FIR and Redundant V-BLAST Systems for Frequency-Selective MIMO Channels
The vertical Bell labs layered space-time (V-BLAST) system is a multi-input multioutput (MIMO) system designed to achieve good multiplexing gain. In recent literature, a precoder, which exploits channel information, has been added in the V-BLAST transmitter. This precoder forces each symbol stream to have an identical mean square error (MSE). It can be viewed as an alternative to the bit-loading method. In this paper, this precoded V-BLAST system is extended to the case of frequency-selective MIMO channels. Both the FIR and redundant types of transceivers, which use cyclic-prefixing and zero-padding, are considered. A fast algorithm for computing a cyclic-prefixing-based precoded V-BLAST transceiver is developed. Experiments show that the proposed methods with redundancy have better performance than the SVD-based system with optimal powerloading and bit loading for frequency-selective MIMO channels. The gain comes from the fact that the MSE-equalizing precoder has better bit-error rate performance than the optimal bitloading method
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Future transmitter/receiver diversity schemes in broadcast wireless networks
An open diversity architecture for a cooperating broadcast wireless network is presented that exploits the strengths of the existing digital broadcast standards. Different diversity techniques for broadcast networks that will minimize the complexity of broadcast systems and improve received SNR of broadcast signals are described. Resulting digital broadcast networks could require fewer transmitter sites and thus be more cost-effective with less environmental impact. Transmit diversity is particularly investigated since it obviates the major disadvantage of receive diversity being the difficulty of locating two receive antennas far enough apart in a small mobile device. The schemes examined here are compatible with existing broadcast and cellular telecom standards and can be incorporated into existing systems without change
Precoding by Pairing Subchannels to Increase MIMO Capacity with Discrete Input Alphabets
We consider Gaussian multiple-input multiple-output (MIMO) channels with
discrete input alphabets. We propose a non-diagonal precoder based on the
X-Codes in \cite{Xcodes_paper} to increase the mutual information. The MIMO
channel is transformed into a set of parallel subchannels using Singular Value
Decomposition (SVD) and X-Codes are then used to pair the subchannels. X-Codes
are fully characterized by the pairings and a real rotation matrix
for each pair (parameterized with a single angle). This precoding structure
enables us to express the total mutual information as a sum of the mutual
information of all the pairs. The problem of finding the optimal precoder with
the above structure, which maximizes the total mutual information, is solved by
{\em i}) optimizing the rotation angle and the power allocation within each
pair and {\em ii}) finding the optimal pairing and power allocation among the
pairs. It is shown that the mutual information achieved with the proposed
pairing scheme is very close to that achieved with the optimal precoder by Cruz
{\em et al.}, and is significantly better than Mercury/waterfilling strategy by
Lozano {\em et al.}. Our approach greatly simplifies both the precoder
optimization and the detection complexity, making it suitable for practical
applications.Comment: submitted to IEEE Transactions on Information Theor
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