  This article examines recent research in molecular communications from a
telecommunications system design perspective. In particular, it focuses on
channel models and state-of-the-art physical layer techniques. The goal is to
provide a foundation for higher layer research and motivation for research and
development of functional prototypes. In the first part of the article, we
focus on the channel and noise model, comparing molecular and radio-wave
pathloss formulae. In the second part, the article examines, equipped with the
appropriate channel knowledge, the design of appropriate modulation and error
correction coding schemes. The third reviews transmitter and receiver side
signal processing methods that suppress inter-symbol-interference. Taken
together, the three parts present a series of physical layer techniques that
are necessary to producing reliable and practical molecular communications.
