  In this paper, a link adaptation and untrusted relay assignment (LAURA)
framework for efficient and reliable wireless cooperative communications with
physical layer security is proposed. Using sharp channel codes in different
transmission modes, reliability for the destination and security in the
presence of untrusted relays (low probability of interception) are provided
through rate and power allocation. Within this framework, several schemes are
designed for highly spectrally efficient link adaptation and relay selection,
which involve different levels of complexity and channel state information
requirement. Analytical and simulation performance evaluation of the proposed
LAURA schemes are provided, which demonstrates the effectiveness of the
presented designs. The results indicate that power adaptation at the source
plays a critical role in spectral efficiency performance. Also, it is shown
that relay selection based on the signal to noise ratio of the source to relays
channels provides an interesting balance of performance and complexity within
the proposed LAURA framework.
