  There is a growing interest in the transition from 4-step random access to
2-step random access in machine-type communication (MTC), since 2-step random
access is well-suited to short message delivery in various Internet of Things
(IoT) applications. In this paper, we study a 2-step random access approach
that uses code division multiple access (CDMA) to form multiple channels for
data packet transmissions with a spreading factor less than the number of
channels. As a result, the length of data transmission phase in 2-step random
access can be shorter at the cost of multiuser interference. To see how the
decrease of the length of data transmission phase can improve the spectral
efficiency, we derive the throughput as well as the spectral efficiency. From
the results of analysis, we can show that the 2-step CDMA-based random access
approach can have a higher spectral efficiency than conventional 2-step
approach with orthogonal channel allocations, which means that the performance
of MTC can be improved by successfully transmitting more data packets per unit
time using CDMA. This is also confirmed by simulation results.
