Effect of time diversity in hybrid ARQ considering space and path diversity for VSF-OFCDM downlink broadband wireless access

The paper investigates the effect of time diversity derived from hybrid automatic repeat request (ARQ) with packet combining considering space and path diversity schemes on variable spreading factor orthogonal frequency and code division multiplexing (VSF-OFCDM) packet wireless access in a downlink broadband multipath fading channel based on laboratory and field experiments. The results show that, for a fixed modulation and channel coding scheme (MCS), time diversity derived from hybrid ARQ is effective in reducing the required received signal-to-interference-plus-noise power ratio (SINR) according to an increase in the number of transmissions, M, up to 10, even when the diversity effects are obtained through two-branch antenna diversity reception and path diversity by a number of multipaths greater than 12 observed in a real fading channel. Meanwhile, in combined use with the adaptive modulation and channel coding (AMC) scheme associated with space and path diversity, we clarify that the gain derived through time diversity is almost saturated at M=4 in chase combining and M=2 in incremental redundancy, since the improvement in the residual packet error rate (PER) obtained through time diversity becomes small owing to the low PER in the initial packet transmission arising from appropriately selecting the optimum MCS in AMC.