A Random Access Scheme based on Device-to-Device Communications for Machine-Type Communications

Machine-type communication (MTC) that usually involves a huge number of devices performing small data transmissions introduces serious challenges for mobile communication networks. Through aggregating MTC devices with identical or similar traffic characteristics into a paging group and paging the devices in the group simultaneously by a single paging, group paging can largely reduce the paging traffic caused by the traditional one-by-one paging. Despite this advantage, group paging cannot tackle the problem of overload in the random access network (RAN), when during a short period a large number of devices in a paging group contend for the random access channel (RACH) to transmit their data after receiving a group paging. This paper proposes an improved random access scheme (I-RA scheme) exploring device-to-device (D2D) communications that may be supported in 4G networks, for MTC to address the above problem. Under the I-RA scheme, a MTC device in a paging group transmits its data either directly to a base station or through the relay of a cluster head, which serves as the communication gateway for the cluster that the device belongs to. The I-RA scheme partitions a paging interval into three periods. In the first period, devices that do not join any cluster contend for the RACH to transmit their data; and at the same time the cluster heads of different clusters poll their member devices to gather data. The second period is reserved solely for the cluster heads to transmit their gathered data. The third period is for the devices that failed in the first and the second period. The I-RA scheme can decrease the number of devices that perform direct random access (D-RA) and thus can deal with the RAN overload problem. A simulation shows that the I-RA scheme outshines the traditional D-RA scheme in successful access probability, access delay and RACH utilization.