Minimizing Access Delay for M2M Traffic in Multi-RAT HetNets

We study the cell selection techniques for M2M traffic between an LTE macrocell and WLAN femtocells in a heterogeneous network deployment scenario. With the dense deployment of femtocells (operating in WLAN), M2M traffic can primarily be served by them while the macrocell (operating in LTE) can be used by the machines in case of congestion in their own femtocell. We study various load balancing strategies that aid the machines to select a proper cell in such a multi-RAT heterogeneous network deployment scenario so that the access delay for the M2M traffic is minimized. In particular, we derive the optimal static policy of choosing between the WLAN femtocell and the LTE macrocell. In addition, we develop dynamic policies based on the information about the arrivals and the number of backlogged users, and compare their performance against each other and with the optimal static policy. Our results indicate that the potential gains from the dynamic policies can be significant. Moreover, simple backlog-based heuristics perform close to or better than the optimal static policy.