  As one of the Coordinated Multipoint (CoMP) techniques, Joint Transmission
(JT) can improve the overall system performance. In this paper, from the load
balancing perspective, we study how the maximum load can be reduced by
optimizing JT pattern that characterizes the association between cells and User
Equipments (UEs). To give a model of the interference caused by cells with
different time-frequency resource usage, we extend a load coupling model, by
taking into account JT. In this model, the mutual interference depends on the
load of cells coupled in a non-linear system with each other. Under this model,
we study a two-cell case and proved that the optimality is achieved in linear
time in the number of UEs. After showing the complexity of load balancing in
the general network scenario, an iterative algorithm for minimizing the maximum
load, named JT-MinMax, is proposed. We evaluate JT-MinMax in a Heterogeneous
Network (HetNet), though it is not limited to this type of scenarios. Numerical
results demonstrate the significant performance improvement of JT-MinMax on
min-max cell load, compared to the conventional non-JT solution where each UE
is served by the cell with best received transmit signal.
