Together or separately? Evaluating the content free period in PRIME using SimPRIME

PoweRline Intelligent Metering Evolution (PRIME) is a Narrowband Powerline Communication (NB-PLC) technology widely deployed in the last mile of Advanced Metering Infrastructure (AMI) in Spain (Iberdrola, Union Fenosa), which is also quickly spreading globally. The present paper addresses the evaluation of the two medium access control mechanisms used in this technology: the Shared Contention Period (SCP), where all nodes content to access the channel; and the Contention Free Period (CFP), where time slots are reserved in order to guarantee some transmission opportunities. Whereas the SCP is the default behavior given its simplicity, the use of the CFP may be necessary when using applications that require a given level of Quality of Service (QoS). The paper first describes how the CFP has been implemented according to the standard in the PRIME network simulator SimPRIME. Moreover, the paper asseses how combining different number of nodes in the SCP and CFP affects the network performance in a series of illustrative scenarios. Results from simulations point out that, when all nodes transmit together in the SCP, it yields better network performance than using the CFP in general; and especially in highly populated networks. However, the paper also highlights trade-off solutions that allow guaranteeing QoS to certain nodes without compromising the performance of the rest of the network. Additionally, the paper proposes an amendment to the standard to increase the number of nodes that can use the CFP under the previous assumption.