A random access scheme based on a special preamble for supporting emergency alarms

In emergency situations such as a disaster and a blackout, machine nodes should report emergency alarms, including the disaster type and disaster area to an M2M server. When many related machine nodes attempt a random access (RA) to report emergency alarms, and this may cause a physical random access channel (PRACH) overload. In this case, the machine nodes hardly access the network within a given delay requirement of emergency alarms. In this paper, we propose a novel random access scheme based on a special preamble for emergency indication in an emergency situation and adaptively reserve more PRACH resources in proportion to the number of machine nodes using the special preamble. The proposed RA scheme outperforms the conventional RA scheme in terms of access delay and can accommodate much more machine nodes in emergency situations, compared with the conventional RA scheme.