A public warning system (PWS) is an emergency warning system that broadcasts early warning information via system information Blocks (SIBs) in 3^rd generation partnership project (3GPP) evolved-universal terrestrial radio access network (E-UTRAN) systems. In the current standards of 3GPP E-UTRANs, earthquake and tsunami warning systems (ETWSs) and commercial mobile alert service (CMAS) systems are used to support early warning services through their system information broadcast capability. The E-UTRAN system pages the user equipment (UE) to provide notification that the warning is being broadcast. The “warning message content” received by the E-UTRAN contains an instance of the warning notification. Depending on the size, the E-UTRAN may segment the secondary notification before sending it over to the radio interface [1].

The ETWS is a PWS developed to satisfy regulatory requirements for warning notifications related to earthquake and/or tsunami events. ETWS warning notifications can either be a primary or secondary notification providing detailed information [1]. Another PWS is a CMAS developed for the delivery of concurrent warning notifications. CMAS warning notifications are short text messages (CMAS alerts). The E-UTRAN manages the delivery of multiple CMAS warning notifications to the UE and manages any updates of CMAS warning notifications [1].

Because the connectivity of UE is crucial for disseminating the warning messages, their transceiving operation must be energy efficient to guarantee the successful notification of the emergency situation. However, current 3GPP E-UTRAN systems do not provide UE with any reduction method of energy consumption by PWS services [1]-[3]. Although Y. Musaka et al. [3] introduced a delivery sequence for early warning messages, where proximity service (ProSe) is integrated into the ETWS; however, it is not applicable to general 3GPP E-UTRANs without supporting the ProSe. Therefore, this paper proposes an energy-efficient scheme to transceive the warning information by avoiding unnecessary duplicate receptions in UE.

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

An evolved NodeB (eNB) sends a paging message to ETWS- and/ or CMAS-capable UE to inform the presence of ETWS and/or CMAS notifications. If the UE receives a paging message including the etws-Indication and/or cmas-Indication fields, it shall start 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 the UE shall continue acquiring ETWS and/or CMAS notifications based on the previously acquired schedulingInfoList until it re-acquires schedulingInfoList in SIB1 [2].

The ETWS notifications comprise primary and secondary notifications. The ETWS primary and secondary notifications are contained in SIB10 and SIB11, respectively. The CMAS notification is broadcast via SIB12. Segmentation can be applied for the delivery of the ETWS and/or CMAS notification (only for the secondary notification in the ETWS case). The segmentation size is fixed for the transmission of a specified segment with the same messageIdentifier, serialNumber, and warningMessageSegmentNumber within a cell [2].

To evaluate the energy efficiency of the proposed method, unit energy consumptions were measured for the ETWS or CMAS indication duration.

Figure 3 shows the accumulated unit energy consumption per unit time duration that was used to receive all the required warning messages. In this figure, the energy efficiencies of the legacy 3GPP E-UTRAN standard and the proposed scheme are compared from the time of “indication ON” to “indication OFF.” Cases I and II depend on the time at which all the transmissions of the warning message that should be received by the UE have been completed by a serving eNB without considering wireless channel conditions.

Figure 3: 
Performance evaluation of energy consumption

As shown in this figure, every UE in the legacy 3GPP E-UTRAN continues 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 proposed method provides information that enables a UE to determine the time to start and end the reception of the corresponding warning message, thereby preventing duplicate SIB reception. Hence, unnecessary reception power wastage can be minimized.

As the proposed scheme complies with the 3GPP E-UTRAN standard, it can be applied easily to commercial mobile communication services.