  In this work, we investigate a coding strategy devised to increase the
throughput in hybrid ARQ (HARQ) transmission over block fading channel. In our
approach, the transmitter jointly encodes a variable number of bits for each
round of HARQ. The parameters (rates) of this joint coding can vary and may be
based on the negative acknowledgment (NACK) provided by the receiver or, on the
past (outdated) information about the channel states. These new degrees of
freedom allow us to improve the match between the codebook and the channel
states experienced by the receiver. The results indicate that significant gains
can be obtained using the proposed coding strategy, particularly notable when
the conventional HARQ fails to offer throughput improvement even if the number
of transmission rounds is increased. The new cross-packet HARQ is also
implemented using turbo codes where we show that the theoretically predicted
throughput gains materialize in practice, and we discuss the implementation
challenges.
