  This paper investigates the outage performance of overhearing
amplify-and-forward (AF) cooperative relaying, where a source transmits
information to its destination through multiple helping overhearing AF relays
with space-time network coding (STNC) employed. Firstly, the transmission
protocol of such a relaying system, i.e., cooperative relaying with overhearing
AF relays based on STNC (STNC-OHAF) is presented. Then, the instantaneous
end-to-end SNR expression of STNC-OHAF is analysed. Based on this, an explicit
expression of the outage probability for STNC-OHAF over independent but not
necessarily identically distributed (i.n.i.d) Rayleigh fading channels is
theoretically derived. Numerical results validate our theoretical analysis and
show that by introducing overhearing among relays, the outage performance of
the system can be greatly improved. It also shows that there is a trade-off
between system sum outage capacity and the transmitted number of symbols.
