  By inserting interleavers between intermediate stages of the polar encoder, a
new class of polar codes, termed interleaved polar (i-polar) codes, is
proposed. By the uniform interleaver assumption, we derive the weight
enumerating function (WEF) and input-output weight enumerating function (IOWEF)
averaged over the ensemble of i-polar codes. The average WEF can be used to
calculate the upper bound on the average block error rate (BLER) of a code
selected at random from the ensemble of i-polar codes. Also, we propose a
concatenated coding scheme that employs P high rate codes as the outer code and
Q i-polar codes as the inner code with an interleaver in between. The average
WEF of the concatenated code is derived based on the uniform interleaver
assumption. Simulation results show that BLER upper bounds can well predict
BLER performance levels of the concatenated codes. The results show that the
performance of the proposed concatenated code with P=Q=2 is better than that of
the CRC-aided i-polar code with P=Q=1 of the same length and code rate at high
signal-to-noise ratios (SNRs). Moreover, the proposed concatenated code allows
multiple decoders to operate in parallel, which can reduce the decoding latency
and hence is suitable for ultra-reliable low-latency communications (URLLC).
