  In this paper, an incremental selective decode-and-forward (ISDF) relay
strategy is proposed for power line communication (PLC) systems to improve the
spectral efficiency. Traditional decode-and-forward (DF) relaying employs two
time slots by using half-duplex relays which significantly reduces the spectral
efficiency. The ISDF strategy utilizes the relay only if the direct link
quality fails to attain a certain information rate, thereby improving the
spectral efficiency. The path gain is assumed to be log-normally distributed
with very high distance dependent signal attenuation. Furthermore, the additive
noise is modeled as a Bernoulli-Gaussian process to incorporate the effects of
impulsive noise contents. Closed-form expressions for the outage probability
and the fraction of times the relay is in use, and an approximate closed-form
expression for the average bit error rate (BER) are derived for the binary
phase-shift keying signaling scheme. We observe that the fraction of times the
relay is in use can be significantly reduced compared to the traditional DF
strategy. It is also observed that at high transmit power, the spectral
efficiency increases while the average BER decreases with increase in the
required rate.
