In realistic deployments, several readers may be placed in the same area, forming a, so-called, dense reader environment. These scenarios are susceptible to suffer Reader Collision Problems, characterized by Reader-to-Tag and Reader-to-Reader interferences. Both affect network throughput, decreasing the overall number of tags identified per reader. This paper reviews the mechanisms proposed to mitigate the Reader Collision Problems. Besides, the constraints of these techniques are pointed out. The mechanisms have been evaluated to study the efficiency of the resources allocation.