  This letter investigates an amplify-and-forward two-way relay network (TWRN)
for short-packet communications. We consider a classical three-node TWRN
consisting of two sources and one relay. Both two time slots (2TS) scheme and
three time slots (3TS) scheme are studied under the finite blocklength regime.
We derive approximate closed-form expressions of sum-block error rate (BLER)
for both schemes. Simple asymptotic expressions for sum-BLER at high
signal-to-noise ratio (SNR) are also derived. Based on the asymptotic
expressions, we analytically compare the sum-BLER performance of 2TS and 3TS
schemes, and attain an expression of critical blocklength, which can determine
the performance superiority of 2TS and 3TS in terms of sum-BLER. Extensive
simulations are provided to validate our theoretical analysis. Our results
discover that 3TS scheme is more suitable for a system with lower relay
transmission power, higher differences between the average SNR of both links
and relatively lower requirements on data rate and latency.
