Earlier it was proven by Vehkalahti and Lu how the unit group and diversity-multiplexing gain trade-off (DMT) of division algebra-based space-time codes are linked to each other through inverse determinant sums. This work explores this relation further, showing that indeed the density of unit group completely determines the growth of the inverse determinant sum. In particular, in the case of Q(i)-central division algebras, the lower bound obtained from the DMT and the upper bound derived from the growth rate of units coincide.
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