Public warning systems (PWSs) effectively transmit messages to warn people about serious emergencies in a timely manner. Commercial PWSs, the 3^rd generation partnership project (3GPP) evolved-universal terrestrial radio access network (E-UTRAN) systems, broadcast system information blocks (SIBs) that contain early warning information. According to the present standards of 3GPP E-UTRANs, the earthquake and tsunami warning system (ETWS) and commercial mobile alert service (CMAS) are designed for the transmission of warning information using the capability of system information broadcast [1]. The E-UTRAN system pages the user equipment (UE) to provide an indication that an early warning information is being broadcasted [2].

ETWS is a PWS developed to fulfill regulatory requirements for warning notifications related to natural disasters such as earthquake and/or tsunami events. An ETWS notification can be a primary or a secondary notification that provides detailed information [2]. Furthermore, CMAS is a type of PWS developed for the delivery of concurrent warning notifications. E-UTRAN manages the delivery of multiple CMAS warning notifications to the UE and the updates of CMAS warning notifications [2].

Since the connectivity of UE is crucial for the dissemination of warning messages, the energy-efficient transceiving of warning messages is required for the successful notification of an emergency situation for a sufficient time and to ensure safety. However, conventional 3GPP E-UTRAN systems do not consider the energy-efficient operation of UE during an emergency situation [2]-[4]. Y. Musaka et al. [4] introduced a delivery sequence for early warning messages, in which the proximity service (ProSe) was integrated into the ETWS. However, it was not applicable to conventional 3GPP E-UTRANs without supporting the ProSe. Y. –I. Joo [1] designed a transceiving scheme for warning messages. However, it consumed resources to indicate the serial number type and its related processing power. Therefore, this paper proposes an energy-efficient scheme to transceive warning information via paging messages.

This paper is organized as follows: Section 2 explains the message exchanging protocol for the PWS services defined in the 3GPP E-UTRAN standard. In Section 3, the proposed method for energy-efficient warning notifications is described. In Section 4, the performances of the proposed scheme are demonstrated by computer simulation. Finally, concluding remarks are presented in Section 5.

The paging message is sent by an evolved NodeB (eNB) to inform ETWS- and/or CMAS-capable UE about the presence of ETWS and/or CMAS notifications. When the ETWS- and/or CMAS-capable UE receives a paging message with the indication(s) (the etws-Indication and/or cmas-Indication fields) that are/is set to TRUE, the UE starts receiving the ETWS and/or CMAS notifications according to the schedulingInfoList contained in SIB1. If the UE receives a paging message including etws-Indication and/or cmas-Indication while it is acquiring ETWS and/or CMAS notification(s), then it shall continue acquiring ETWS and/or CMAS notifications based on the previously acquired schedulingInfoList until it re-acquires schedulingInfoList in SIB1 [3].

ETWS notifications include primary and secondary notifications. The SIB10 and SIB11 are broadcast containing primary and secondary ETWS notifications, respectively. SIB12 is used to broadcast CMAS notifications. Segmentation can be applied for the delivery of ETWS and/or CMAS notification (only for the secondary notification in the ETWS case) [3].

To evaluate the performance of the proposed method, the accumulated unit energy consumption per unit time duration was used to receive all the required warning messages.

Figure 3 shows the results. In this figure, the energy efficiencies of the legacy 3GPP E-UTRAN standard, the method proposed in [1], and the proposed scheme from the time of “indication ON” to “indication OFF” are compared. Cases I and II depend on the time at which the transmissions of the warning message that should be received by the UE were completed by a serving eNB without considering wireless channel conditions.

Figure 3: 
Performance evaluation of energy consumption

As shown in this figure, the UEs in the legacy system continue to receive the SIB(s) relevant to the PWS services until etws-Indication and/or cmas-Indication are reset, i.e., the fields do not appear in the paging message. The methods in [1] and this paper show a slightly greater energy consumption thana that of other methods till the completion time of warning messages since they have additional fields. However, these schemes demonstrate a better performance with respect to the overall energy efficiency. The proposed method is comparatively energy-efficient because it reduces the additional field in [1].

The proposed method reduces unnecessary reception power wastage with minimum additional field of message. As the proposed scheme complies with the commercial standard, it can be easily applied to legacy mobile communication services.