  As opposed to hybrid automatic repeat request with incremental redundancy
(HARQ-IR) that all the resources are occupied to resend the redundant
information, cross-packet HARQ (XP-HARQ) allows the introduction of new
information into retransmissions to substantially exploit the remaining
resources. This letter provides a profound investigation into the outage
performance of XP-HARQ. In particular, the exact outage expression of XP-HARQ
is derived if the maximum number of transmissions is two, and tight outage
bounds are obtained for more than two transmissions. Moreover, the asymptotic
outage analysis of XP-HARQ in the high signal-to-noise ratio (SNR) regime is
carried out not only to simplify the outage expression, but also to show that
full time diversity is achievable by XP-HARQ. The simulation results are
eventually presented for verifications.
