Wireless mesh networks suffer of scalability problems when the number of nodes grows. To solve this issue, multi-interface wireless mesh networks were introduced. In such networks it is possible to use multiple channels to implement spatial reuse of frequencies. However, channel assignment schemes make this kind of networks complex to manage and limit their applicability in presence of mobile nodes. In this paper a novel technique is introduced for the optimization of resources allocation in a multi-interface wireless mesh network where channel assignment is fixed. With this technique the scalability of the network is improved and the support for mobility is easily granted.