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Diversity-embedded codes for fading channels are high-rate codes that are designed so that they have a high-diversity code embedded within them \cite{DIMACS,Embed:Globecom}. This is equivalent to coding the data into two streams such that the high-priority stream has higher reliability (designed in terms of diversity order) than the low-priority stream. These codes also allow a form of opportunistic communication where the high-rate code opportunistically takes advantage of good channel realizations whereas the embedded high-diversity code ensures that at least part of the information is received reliably. In this paper we give the design for a class of such codes for a {\em fixed transmit alphabet} constraint. These constructions are a natural generalization of multilevel codes to diversity embedding. These codes give provable performance guarantees by using binary matrices with rank guarantees as the building blocks to generate the desired diversity embedding in the complex domain. We also investigate the systems implications of these codes by examining its applications to unequal error protection, rate opportunism and packet delay optimization. Preliminary results in these applications demonstrate that diversity-embedded codes can outperform traditional single-layer codes in moderate SNR regimes.