The physical layer of the network protocol stack refers to the signals transmitted, and received, over a physical medium, such as a wire (e.g. a twisted pair of wires or a coaxial cable), an electromagnetic wave (e.g. a satellite transponder, a cellular/PCS tower or a wireless local area network (WLAN) base station), or a recording medium (e.g. magnetic or optical disks). The research has a broad perspective, from the viewpoint of the physical medium, and a narrow focus in that the problems addressed all involve a form of forward error control (FEC). The research is directed in three areas: Mathematical methods and analysis algorithms for coding Problems in algebraic coding Turbo code error control In the first topic area, the following are considered: theory and practice of interleaving, a novel method for computing the weight distribution of a binary convolutional code, and problems concerning the capacity of wireless channels with and without side information on channel state. The second topic area concerns basic understanding and advances in the area of algebraic geometry (AG) coding. These AG codes show potential for application in transmission systems. Further understanding needs to be developed to enable the practical implementation of AG codes. In the final topic, new applications of "turbo coding" are identified, including systems with memory and turbo coded modulation.