  This paper studies the effect of bandwidth partitioning (BWP) on the
reliability and delay performance in infrastructureless wireless networks. The
reliability performance is characterized by the density of concurrent
transmissions that satisfy a certain reliability (outage) constraint and the
delay performance by so-called local delay, defined as the average number of
time slots required to successfully transmit a packet. We concentrate on the
ultrareliable regime where the target outage probability is close to 0. BWP has
two conflicting effects: while the interference is reduced as the concurrent
transmissions are divided over multiple frequency bands, the
signal-to-interference ratio (SIR) requirement is increased due to smaller
allocated bandwidth if the data rate is to be kept constant. Instead, if the
SIR requirement is to be kept the same, BWP reduces the data rate and in turn
increases the local delay. For these two approaches with adaptive and fixed SIR
requirements, we derive closed-form expressions of the local delay and the
maximum density of reliable transmissions in the ultrareliable regime. Our
analysis shows that, in the ultrareliable regime, BWP leads to the
reliability-delay tradeoff.
