3 research outputs found
Distortion-free Golden-Hadamard Codebook Design for MISO Systems
In this letter, a novel Golden-Hadamard codebook (GHC) scheme is proposed to
improve the performance of the traditional precoded Alamouti coding for
multiple-input and single-output systems. Although the traditional discrete
Fourier transform codebook (DFTC) performs satisfactorily with Alamouti coding
and offers numerous benefits for the Rayleigh fading channel, this scheme
inherently generates huge codeword distortion, which leads to a lower minimum
chordal distance (MCD). Furthermore, the uncertain format of all prior versions
of codebooks results in poorer minimum determinant (MD) values. Hence, the
proposed GHC scheme successfully deals with the issues of traditional DFTC to
achieve a better codebook format that completely overcome both MCD and MD
problems. The effectiveness of the proposed GHC scheme is confirmed, in terms
of bit-error-rate through Monte Carlo simulations.Comment: 4 pages,4 figures,2 table, Published (Early Access) in IEEE
Communications Letter
Combining Beamforming and Space-Time Coding Using Noisy Quantized Feedback
The goal of combining beamforming and space-time coding in this work is to
obtain full-diversity order and to provide additional received power (array
gain) compared to conventional space-time codes. In our system, we consider a
quasi-static fading environment and we incorporate both high-rate and low-rate
feedback channels with possible feedback errors. To utilize feedback
information, a class of code constellations is proposed, inspired from
orthogonal designs and precoded space-time block codes, which is called
generalized partly orthogonal designs or generalized PODs. Furthermore, to
model feedback errors, we assume that the feedback bits go through binary
symmetric channels (BSCs). Two cases are studied: first, when the BSC bit error
probability is known a priori to the transmission ends and second, when it is
not known exactly. In the first case, we derive a minimum pairwise error
probability (PEP) design criterion for generalized PODs. Then we design the
quantizer for the erroneous feedback channel and the precoder codebook of PODs
based on this criterion. The quantization scheme in our system is a channel
optimized vector quantizer (COVQ). In the second case, the design of the
quantizer and the precoder codebook is based on similar approaches, however
with a worst-case design strategy. The attractive property of our combining
scheme is that it converges to conventional space-time coding with low-rate and
erroneous feedback and to directional beamforming with high-rate and error-free
feedback. This scheme shows desirable robustness against feedback channel
modeling mismatch.Comment: In revision for IEEE Transactions on Communications, April 200
To Code or Not to Code Across Time: Space-Time Coding with Feedback
Space-time codes leverage the availability of multiple antennas to enhance
the reliability of communication over wireless channels. While space-time codes
have initially been designed with a focus on open-loop systems, recent
technological advances have enabled the possibility of low-rate feedback from
the receiver to the transmitter. The focus of this paper is on the implications
of this feedback in a single-user multi-antenna system with a general model for
spatial correlation. We assume a limited feedback model, that is, a coherent
receiver and statistics along with B bits of quantized channel information at
the transmitter. We study space-time coding with a family of linear dispersion
(LD) codes that meet an additional orthogonality constraint so as to ensure
low-complexity decoding. Our results show that, when the number of bits of
feedback (B) is small, a space-time coding scheme that is equivalent to
beamforming and does not code across time is optimal in a weak sense in that it
maximizes the average received SNR. As B increases, this weak optimality
transitions to optimality in a strong sense which is characterized by the
maximization of the average mutual information. Thus, from a system designer's
perspective, our work suggests that beamforming may not only be attractive from
a low-complexity viewpoint, but also from an information-theoretic viewpoint.Comment: 22 pages, 4 figures, Submitted to IEEE JSAC, Nov. 200