  Interleaved Frequency Division Multiple Access (IFDMA) and Orthogonal FDMA
(OFDMA) belong to a class of signal modulation and multiple-access techniques
in which information of multiple users are multiplexed and carried on
subcarriers within a shared spectrum. Compared with OFDMA, IFDMA has lower
Peak-to-Average Power Ratio (PAPR). However, IFDMA poses two rigid constraints
on subcarrier allocation: 1) the subcarriers occupied by a user must be
evenly-spaced among the available subcarriers. 2) the number of subcarriers
used by a user must be a divisor of the total number of subcarriers. This paper
investigates how to overcome these constraints to allow flexible and
fine-grained subcarrier allocation in IFDMA. Specifically, we put forth 1) a
bit-reversal subcarrier allocation scheme whereby the problem of allocating
evenly-spaced subcarriers is transformed to a more intuitive problem of filling
contiguous bins; 2) a multi-stream IFDMA scheme whereby a user can have an
arbitrary number of subcarriers. For the synchronous scenario in which user
requests arrive in a synchronous manner, we show that IFDMA can achieve the
same level of flexibility and granularity as OFDMA in subcarrier allocation.
For the asynchronous scenario in which user requests arrive and depart
asynchronously, we show that the blocking probability of IFDMA is only slightly
worse than that of OFDMA: specifically, the gap between the blocking
probabilities of IFDMA and OFDMA is only 2:56% at a moderate offered load.
