  Secure transmission in large-scale MISO systems employing artificial noise
(AN) is studied under the per-antenna constant envelope (CE) constraint.
Achievable secrecy rate of the per-antenna CE precoding scheme for large-scale
MISO is analyzed and compared with that of the matched filter linear precoding.
A two-stage per-antenna CE precoding scheme for joint signal-plus-AN
transmission is proposed. The first stage determines the per-antenna CE
precoding for the information-bearing signal. A properly generated AN using an
iteration algorithm is incorporated into the transmit signal in the second
stage such that the combined signal-plus-AN satisfies the per-antenna CE
constraint and the AN is orthogonal to the user channel. It is shown that
compared to conventional per-antenna CE transmission, this joint signal-plus-AN
secure transmission scheme does not require additional transmit power. An
alternative low-complexity AN generation scheme which uses a separate antenna
to cancel the AN leakage to the intended user introduced by randomly generated
AN is also proposed.
