3,699 research outputs found
Optimization of Fast-Decodable Full-Rate STBC with Non-Vanishing Determinants
Full-rate STBC (space-time block codes) with non-vanishing determinants
achieve the optimal diversity-multiplexing tradeoff but incur high decoding
complexity. To permit fast decoding, Sezginer, Sari and Biglieri proposed an
STBC structure with special QR decomposition characteristics. In this paper, we
adopt a simplified form of this fast-decodable code structure and present a new
way to optimize the code analytically. We show that the signal constellation
topology (such as QAM, APSK, or PSK) has a critical impact on the existence of
non-vanishing determinants of the full-rate STBC. In particular, we show for
the first time that, in order for APSK-STBC to achieve non-vanishing
determinant, an APSK constellation topology with constellation points lying on
square grid and ring radius \sqrt{m^2+n^2} (m,n\emph{\emph{integers}}) needs
to be used. For signal constellations with vanishing determinants, we present a
methodology to analytically optimize the full-rate STBC at specific
constellation dimension.Comment: Accepted by IEEE Transactions on Communication
L2 Orthogonal Space Time Code for Continuous Phase Modulation
To combine the high power efficiency of Continuous Phase Modulation (CPM)
with either high spectral efficiency or enhanced performance in low Signal to
Noise conditions, some authors have proposed to introduce CPM in a MIMO frame,
by using Space Time Codes (STC). In this paper, we address the code design
problem of Space Time Block Codes combined with CPM and introduce a new design
criterion based on L2 orthogonality. This L2 orthogonality condition, with the
help of simplifying assumption, leads, in the 2x2 case, to a new family of
codes. These codes generalize the Wang and Xia code, which was based on
pointwise orthogonality. Simulations indicate that the new codes achieve full
diversity and a slightly better coding gain. Moreover, one of the codes can be
interpreted as two antennas fed by two conventional CPMs using the same data
but with different alphabet sets. Inspection of these alphabet sets lead also
to a simple explanation of the (small) spectrum broadening of Space Time Coded
CPM
Algebraic Cayley Differential Space–Time Codes
Cayley space-time codes have been proposed as a solution for coding over noncoherent differential multiple-input multiple-output (MIMO) channels. Based on the Cayley transform that maps the space of Hermitian matrices to the manifold of unitary matrices, Cayley codes are particularly suitable for high data rate, since they have an easy encoding and can be decoded using a sphere-decoder algorithm. However, at high rate, the problem of evaluating if a Cayley code is fully diverse may become intractable, and previous work has focused instead on maximizing a mutual information criterion. The drawback of this approach is that it requires heavy optimization which depends on the number of antennas and rate. In this work, we study Cayley codes in the context of division algebras, an algebraic tool that allows to get fully diverse codes. We present an algebraic construction of fully diverse Cayley codes, and show that this approach naturally yields, without further optimization, codes that perform similarly or closely to previous unitary differential codes, including previous Cayley codes, and codes built from Lie groups
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