Reduced ML-Decoding Complexity, Full-Rate STBCs for 2a Transmit Antenna Systems

For an n
_t
transmit, n
_r
receive antenna system (n
_t
× n
_r
system), a fall-rate space time block code (STBC) transmits n
_min
= min(n
_t
, n
_r
) complex symbols per channel use and in general, has an ML-decoding complexity of the order of M
^n
t
n
min
(considering square designs), where M is the constellation size. In this paper, a scheme to obtain a fullrate STBC for 2
^a
transmit antennas and any nτ, with reduced ML-decoding complexity of the order of M
ⁿ
_t
(n
_min
-
³
/
₄
)
^-0.5
, is presented. The well known Silver code for 2 transmit antennas is a special case of the proposed scheme. Further, it is shown that the codes constructed using the scheme have higher ergodic capacity than the well known punctured Perfect codes for n
_r
<; n
_t
. Simulation results of the symbol error rates are shown for 8 × 2 systems, where the comparison of the proposed code is with the punctured Perfect code for 8 transmit antennas. The proposed code matches the punctured Perfect code in error performance, while having reduced ML-decoding complexity and higher ergodic capacity.