  In this paper the performance limits and design principles of rateless codes
over fading channels are studied. The diversity-multiplexing tradeoff (DMT) is
used to analyze the system performance for all possible transmission rates. It
is revealed from the analysis that the design of such rateless codes follows
the design principle of approximately universal codes for parallel
multiple-input multiple-output (MIMO) channels, in which each sub-channel is a
MIMO channel. More specifically, it is shown that for a single-input
single-output (SISO) channel, the previously developed permutation codes of
unit length for parallel channels having rate LR can be transformed directly
into rateless codes of length L having multiple rate levels (R, 2R, . . ., LR),
to achieve the DMT performance limit.
