If $\text{S}$ represents the carrier synchronization at the receiver and $\rho$ represents the bandwidth efficiency, then the correct statement for the coherent binary $\text{PSK}$ is
- $\rho=0.5, S$ is required
- $\rho=1.0, S$ is required
- $\rho=0.5, \mathrm{~S}$ is not required
- $\rho=1.0, S$ is not required