Randomized Isometric Linear-Dispersion Space-Time Block Coding for the DF Relay Channel
This paper presents a randomized linear-dispersion space-time block code for decode-and-forward synchronous relays. The coding matrices are obtained as a set of columns (or rows) of randomly-generated Haar-distributed unitary matrices. With respect to i.i.d.-generated codes, this particular isometric structure reduces the inter-symbol interference generated within each relay. The gain over i.i.d. codes in terms of spectral efficiency is analyzed for both the LMMSE and the ML receivers under the assumption of frequency-flat quasi-static fading. In this setting, the spectral efficiency is a random quantity, since it depends on the random coding matrices.