Over the past two decades, advances in wireless technologies have enabled mobile services to provide both voice service and high data transfer services. The modern techniques used to achieve high data transfer speeds over the wireless medium include orthogonal frequency division multiplexing (OFDM), advanced forward error correction (FEC), and multiple-input multiple-output (MIMO) physical layer techniques. Standard communication systems operate by isolating these physical layer processes from the rest of the system, that is, the physical layer is responsible only for providing the transfer of bits from the source to the destination, without any regard to the type of information being transmitted. This thesis examines the change to this legacy communications paradigm, by modelling the physical layer to be capable to simultaneously support various levels of reliability depending on the type of information. We achieve this through super-position of data, in the form of diversity-embedded space-time codes. This change enables more efficient use of resources. In this thesis, we develop a new method to analyze the performance of space-time codes, including diversity-embedded space-time codes, through the notion of effective coding gain. Unlike the standard notion of coding gain, this method explicitly incorporates the notion of nearest neighbours to predict the space-time code performance for any SNR. We also use this technique to compare the performance of space-time codes, and demonstrate that codes with low diversity order may out-perform comparable fully-diverse codes in the practical low-to-moderate SNR regime. We also introduce new constructions for diversity embedding by using multilevel coding for the parallel MIMO channel. We implement these codes for video applications, and demonstrate that the new diversity embedded schemes produces a much better video quality than codes without diversity embedding. In the provided examples, we show a gain in observable quality of over 4 dB. In the non-MIMO realm, we develop a coding scheme based on Low-Density Parity-Check Codes. This coding strategy achieves diversity embedding through superposition of a different type: concatenation of information bits. Finally, we discuss the process of standardization, through the example of cooperative relaying in the IEEE 802.16j standard. We also discuss how diversity embedding can be implemented in OFDM-based systems.