  To support Ultra-Reliable and Low Latency Communications (URLLC) is an
essential character of the 5th Generation (5G) communication system. Unlike the
other two use cases defined in 5G, e.g. enhanced Mobile Broadband (eMBB) and
massive Machine Type Communications (mMTC), URLLC traffic has strict delay and
reliability requirement. In this paper, an analysis model for URLLC traffic is
proposed from the generation of a URLLC traffic until its transmission over a
wireless channel, where channel quality, coding scheme with finite coding
length, modulation scheme and allocated spectrum resource are taken into
consideration. Then, network calculus analysis is applied to derive the delay
guarantee for periodical URLLC traffic. Based on the delay analysis, the
admission region is found under certain delay and reliability requirement,
which gives a lower bound on required spectrum resource. Theoretical results in
the scenario of a 5G New Radio system are presented, where the SNR thresholds
for adaptive modulation and coding scheme selection, transmission rate and
delay, as well as admission region under different configurations are
discussed. In addition, simulation results are obtained and compared with
theoretical results, which validates that the admission region derived in this
work provides a lower spectrum allocation bound.
