  In this paper, incremental decode-and-forward (IDF) and incremental selective
decode-and-forward (ISDF) relaying are proposed to improve the spectral
efficiency of power line communication. Contrary to the traditional
decode-and-forward (DF) relaying, IDF and ISDF strategies utilize the relay
only if the direct link ceases to attain a certain information rate, thereby
improving the spectral efficiency. The path gain through the power line is
assumed to be log-normally distributed with high distance-dependent attenuation
and the additive noise is from a Bernoulli-Gaussian process. Closed-form
expressions for the outage probability, and approximate closed-form expressions
for the end-to-end average channel capacity and the average bit error rate for
binary phase-shift keying are derived. Furthermore, a closed-form expression
for the fraction of times the relay is in use is derived as a measure of the
spectral efficiency. Comparative analysis of IDF and ISDF with traditional DF
relaying is presented. It is shown that IDF is a specific case of ISDF and can
obtain optimal spectral efficiency without compromising the outage performance.
By employing power allocation to minimize the outage probability, it is
realized that the power should be allocated in accordance with the inter-node
distances and channel parameters.
