Comments on 'Precoding for secrecy rate maximisation in cognitive MIMO wiretap channels'.

Several gaps and errors in Fang et al. (2015) are identified. Their corrections as well as new results are reported. After these corrections, the successive convex approximation algorithm in Fang et al. (2015) is shown to generate an increasing, converging sequence of secrecy rates, which, for a degraded channel, converges to its secrecy capacity. The failure of the popular convex solver CVX to maximise secrecy rate is illustrated. Alternative algorithms are pointed out. [ABSTRACT FROM AUTHOR]