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For CDMA-based WSNs, we quantitatively investigate and compare the optimal energy efficiencies and control complexities for three different power/time control (PTC) schemes: PTC with independent transmission power and time (PTC-IPT), PTC with unified transmission time (PTC-UT), and PTC with unified spreading gain (PTC-USG). These schemes provide different degrees of control and require different amounts of overhead. Under each scheme, the minimization of system's energy consumption is formulated as a non-convex optimization problem. The optimal transmission power and time are derived analytically through a variable-decoupling approach. The analytical nature of our results makes it feasible to compare the performance in closed form. Numerical examples and simulations are provided to validate our analysis.