  In nonorthogonal multiple access (NOMA), the power difference of multiple
signals is exploited for multiple access and successive interference
cancellation (SIC) is employed at a receiver to mitigate co-channel
interference. Thus, NOMA is usually employed for coordinated transmissions and
mostly applied to downlink transmissions where a base station (BS) per- forms
coordination for downlink transmissions with full channel state information
(CSI). In this paper, however, we show that NOMA can also be employed for
non-coordinated transmissions such as random access for uplink transmissions.
We apply a NOMA scheme to multichannel ALOHA and show that the throughput can
be improved. In particular, the resulting scheme is suitable for random access
when the number of subchannels is limited since NOMA can effectively increase
the number of subchannels without any bandwidth expansion.
