# Time and Energy Efficient Relay Transmission for Multi-Hop Wireless Sensor Networks
## 3 Proposed Scheme
### New Superframe Structure for the Proposed Relay Scheme  
Figure 10 shows novel superframe structure for the proposed relay transmission scheme. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Name** & **Type** & **Valid Range** & **Description** \\ \hline PIBAttribute & Octet string & Attribute specific & The name of the PIB attribute to write \\ PIBAttributeValue & Various & Attribute specific & The value to write to the indicated PIB attribute. \\ RelayFunction & Boolean & TRUE, FALSE & If TRUE, the MAC sublayer supports the relay function for data frame transmission. If FALSE, the MAC sublayer doesn’t support the relay function. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The proposed MLME-SET.request parameter. Figure 9: The relay function activation process of the coordinator. In Figure 10, the PAN coordinator periodically broadcasts the beacon frame in the beacon period. The superframe is composed of numerous time slots with the fixed length, and the time slot is the basic unit of a CAP offset and a CFP offset. In the proposed scheme, because the beacon frame includes the information of the CAP offset and the CFP offset, devices which receive the beacon frame can recognize the length of the CAP and the CFP. Figure 11 shows the format of the proposed beacon frame. In Figure 11, the CAP offset is composed of a CAP starting slot field and a CAP length field. The CAP starting slot field indicates the time slot number at the beginning of the CAP, and the CAP length field indicates the number of time slots belonging to the CAP. In the same way, the CFP offset is composed of a CFP starting slot field and a CFP length field. The CFP starting slot field indicates the time slot number at the beginning of the CFP, and the CFP length field indicates the number of time slots belonging to the CFP. The sum of the CAP offset and the CFP offset cannot exceed the value of BI. In the proposed scheme, the PAN coordinator and coordinators can adjust the length of the CAP and the CFP. The RP field contains the information of the RP. Figure 12 illustrates the format of the RP fields. In Figure 12, the RP descriptor count field specifies the number of RP descriptors contained in the RP List field of the beacon frame. If the value of this field is equal to zero, the RP List field of the beacon frame is not present. The RP Permit field is set to one if the coordinator is accepting RP request. Otherwise, the RP permit field shall be set to zero. The size of the RP List field is defined by the values specified in the RP specification field of the beacon frame and contains the list of RP descriptors that represents the RP that is being maintained. Figure 11: The format of the proposed beacon frame. Figure 10: New superframe structure for the proposed relay scheme. Figure 13 shows the format of each RP descriptor. In Figure 13, the DevAddr field contains the short address of the device which is allocated the RP from the PAN coordinator or high-level coordinator (parent coordinator). The direction field indicates the direction of the data transmission. If the value of this field is zero, the parent coordinator or the PAN coordinator transmits a data frame to the low-level coordinator (child coordinator) after transmitting the beacon frame. Then, the low-level coordinator transmits the data frame. If the value of this field is one, the low-level coordinator transmits data frame after transmitting the beacon frame. The RP starting slot field indicates the time slot number in which the CFP allocated for the relay communication is begun, and the RP length field indicates the number of time slots belonging to the RP. Figure 14 shows the superframe structure constructed by the coordinator with the relay function. In the proposed scheme, the coordinator can connect to the high-level coordinator or the PAN coordinator. Also, it can connect to the low-level coordinator. In Figure 14, the superframe managed by the coordinator consists of the beacon period, the CAP, the CFP, the inactive period, and the RP.