  For a low-mobile Poisson bipolar network and under
line-of-sight/non-line-of-sight (LOS/NLOS) path-loss model, we study repetitive
retransmissions (RR) and blocked incremental redundancy (B-IR). We consider
spatially-coded multiple-input multiple-output (MIMO) zero-forcing beamforming
(ZFBF) multiplexing system, whereby the packet success reception is determined
based on the aggregate data rate across spatial dimensions of the MIMO system.
Characterization of retransmission performance in this low-mobile configuration
is practically important, but inherently complex due to a substantial rate
correlation across retransmissions and intractability of evaluating the
probability density function (pdf) of aggregate data rate. Adopting tools of
stochastic geometry, we firstly characterize the rate correlation coefficient
(RCC) for both schemes. Our results show that, compared to RR scheme, B-IR
scheme has higher RCC while its coverage probability is substantially larger.
We demonstrate that the spotted contention between coverage probability and RCC
causes the mean transmission delay (MTD) of B-IR to become either smaller or
larger than the MTD of RR scheme. Finally, we develop a numerical approximation
of MTD, and evaluate the effective spatial throughput (EST), which is
reciprocal to MTD, of RR and B-IR schemes. Our numerical results highlight
fundamental tradeoffs between densification, multiplexing gain, block length,
and activity factor of nodes. We further observe that for dense networks 1) LOS
component is considerably instrumental to enhance EST; 2) EST of B-IR scheme
can be much higher than that of RR scheme; 3) When Doppler spread exists, it
can improve MTD of B-IR while it does not cast any meaningful effect on the MTD
of RR.
