# A Novel Procedure of Enhancing the Throughput of a Mode-2 Sidelink Based on Partial Sensing
## 3 How to Combine All the Partial Sensing Results  
To describe the novel procedure of combining all the partial sensing results, we first introduce an additional UE, denoted RSU, in the region of mode-2 sidelink communications of interest. The RSU is a hardware entity that is generally defined as a terminal to assist vehicular communications in out-of-coverage areas [14]. Figure 3 illustrates a mode-2 sidelink signal environment, including several P-UEs within the coverage of an RSU. Each P-UE operates with partial sensing to perform mode-2 sidelink communication with minimal power consumption. We propose a novel procedure that combines all the partial sensing results under this signal environment, as shown in Figure 4.  
First, the RSU assigns a partial sensing window to each P-UE whenever a new P-UE (or new P-UEs) enters or exits its coverage area. When assigning the partial sensing window, it is important to ensure that each partial sensing window does not overlap among different P-UEs for efficient partial sensing. Second, the RSU collects all the partial sensing results from all P-UEs. As each P-UE decodes the sidelink control information from its PSCCH, the P-UE can determine how the resource block of its PSSCH is occupied. The resource block occupation is then transmitted from each P-UE to the RSU such that the state of the resource block occupation of all the P-UEs within the RSU coverage can be collected. Figure 3: A mode-2 sidelink signal environment consisting of an RSU and P-UEs. Figure 2: Partial sensing window and selection window. Third, the RSU transmits the collected information to all the P-UEs. Consequently, each P-UE becomes aware of all the sensing results for the other time slots, in addition to its own time slot. Finally, to check whether any P-UE enters or exits the RSU coverage, the RSU realigns all the partial sensing windows upon any changes within its coverage. Figure 5 illustrates how the partial sensing window is aligned for each P-UE within the entire period of reserving its resource, that is, 200 ms, with a window duration of 40 ms [15]. Note that each partial sensing window is assigned to a different P-UE, meaning that each window is assigned to a distinct P-UE. However, if the total number of P-UEs within the RSU coverage exceeds five, overlap is unavoidable. As shown in Figure 5, the first P-UE is assigned to the first window of 0-40 ms by the RSU. Similarly, the second and third P-UEs are assigned to the second and third windows, that is, for 40-80 ms and 80-120 ms, respectively. By aligning the partial sensing windows in this manner, the RSU can most efficiently acquire the state of resource occupation of all the P-UEs by summing the sensing results corresponding to all the different time slots. As the RSU transmits the combined sensing information to each P-UE, each P-UE becomes  
Figure 4: Proposed method of combining all the partial sensing results using the RSU. Figure 5: Aligning of partial sensing window for P-UEs. aware of the resource occupation state for the entire observation period of 200 ms, which is typically available only in the case of full sensing. Figure 6 illustrates a timing diagram for exchanging the sensing results between the RSU and each P-UE, which is briefly described in the second and third steps of Figure 4. Each P-UE sends its sensing result to the RSU during the current 200 ms period. As shown in Figure 6, the RSU collects all the sensing results from the corresponding five P-UEs before the end of the next observation period. When the combined sensing results are received from the RSU, each P-UE is ready to select an appropriate set of resources from the beginning of the second observation period, which is 400 ms away, because of the commencement of the partial sensing of the first P-UE (P-UE#1). Figure 7 illustrates how the partial sensing windows should be realigned as a P-UE (or P-UEs) exits the RSU coverage.