  Joint transmission is a kind of cooperative transmission technology, which
converts other cell interference into signal. In this letter, for single-user
joint transmission, we propose that a power pool can be created in order to
increase the system sum-rate or lower the power consumption. Then, we
investigate the sum-rate maximization problem under this framework. Since it is
impossible that subchannel gains for the two base stations are identical, we
can obtain a much more concise structure and reduce variables to the half of
original problem. And that the closed-form water-filling solution is unique and
global optimum, because it is a convex optimization problem. Compared to the
power allocation without pooling, the performance gain is verified by
simulation.
