  The use of Space-Time Block Codes (STBCs) increases significantly the optimal
detection complexity at the receiver unless the low-complexity decodability
property is taken into consideration in the STBC design. In this paper we
propose a new low-complexity decodable rate-5/4 full-diversity 4 x 4 STBC. We
provide an analytical proof that the proposed code has the
Non-Vanishing-Determinant (NVD) property, a property that can be exploited
through the use of adaptive modulation which changes the transmission rate
according to the wireless channel quality. We compare the proposed code to the
best existing low-complexity decodable rate-5/4 full-diversity 4 x 4 STBC in
terms of performance over quasi-static Rayleigh fading channels, worst- case
complexity, average complexity, and Peak-to-Average Power Ratio (PAPR). Our
code is found to provide better performance, lower average decoding complexity,
and lower PAPR at the expense of a slight increase in worst-case decoding
complexity.
