  Cyclic Prefix Direct Sequence Spread Spectrum (CP-DSSS) is a novel waveform
that is proposed as a solution to massive machine type communications (mMTC)
for 5G and beyond. This paper analyzes the capacity of CP-DSSS in comparison
with Orthogonal Frequency-Division Multiplexing (OFDM). We show that CP-DSSS
achieves the same capacity as OFDM and can be optimized with similar precoding
methods (e.g., water-filling). Because of its spread spectrum nature, CP-DSSS
can operate as secondary network using the same spectrum as the primary 4G or
5G network, but transmitting at much lower power. Accordingly, the combination
of primary and secondary signals in the envisioned setup may be viewed as a
power NOMA (non-orthogonal multiple access) technique where primary signals are
detected and subtracted from the received signal first before detecting the
secondary signals. In order to operate at a sufficiently low interference level
to the primary network, details of CP-DSSS capacity for symbol rate reduction
and multi-antenna operation are developed. The capacity limits established in
this paper can be used as a baseline to evaluate the performance of future
CP-DSSS receiver architectures for single- and multi-user scenarios.
