  Mechanisms for data recovery and packet reliability are essential components
of the upcoming 6th generation (6G) communication system. In this paper, we
evaluate the interaction between a fast hybrid automatic repeat request (HARQ)
scheme, present in the physical and medium access control layers, and a higher
layer automatic repeat request (ARQ) scheme which may be present in the radio
link control layer. Through extensive system-level simulations, we show that
despite its higher complexity, a fast HARQ scheme yields > 66 % downlink
average user throughput gains over simpler solutions without energy combining
gains and orders of magnitude larger gains for users in challenging radio
conditions. We present results for the design trade-off between HARQ and
higher-layer data recovery mechanisms in the presence of realistic control and
data channel errors, network delays, and transport protocols. We derive that,
with a suitable design of 6G control and data channels reaching residual errors
at the medium access control layer of 5 E-5 or better, a higher layer data
recovery mechanism can be disabled. We then derive design targets for 6G
control channel design, as well as promising enhancements to 6G higher layer
data recovery to extend support for latency-intolerant services.
