# Vehicle Speed Estimation and Forecasting Methods Based on Cellular Floating Vehicle Data
## 2 Literature Review
### Traffic Information Estimation Methods
#### 2.2.1 Location Services  
Several location positioning methods, which were defined in the LCS specification of the 3 rd Generation Partnership Project (3 GPP), could be grouped into three classes, including: (1) assisted GPS (A-GPS) methods; (2) mobile scan report (MSR)-based location methods; and (3) database lookup methods [18; 19].  
For A-GPS methods, a GPS component should be equipped in each MS to determine the location of the MS. However, these methods cannot be performed for the MSs without GPS components. Therefore, A-GPS methods are not discussed and applied in this study.  
For MSR-based location methods, each MS can send periodically MSR messages (e.g., received signal strength indication (RSSI), round-trip delay and relative delay) to core networks in cellular networks (e.g., Global System Mobile Communications (GSM), Universal Mobile Telecommunications System (UMTS) and Long-Term Evolution (LTE)) [9]. Some studies analyzed the MSR messages to determine the locations of MSs, and these locations can be used to estimate traffic information. For instance, [PERSON] _et al._[9] proposed a fingerprint-positioning algorithm (FPA) based on the \(k\)-nearest neighbors (kNN) algorithm to analyze the RSSIs of MSR messages for generating the locations of MS in car, and the average vehicle speed and travel time between two locations of the same MS can be estimated by FPA. Because the interfaces of A-bis and Iub in radio networks should be monitored to retrieve RSSIs for FPA, it is required to have above 10,000 servers to deploy to proceed with recording and analysis by Taiwanese environment. However, core network signals (e.g., CA, HO, NLU and PLU) can be captured via the interfaces of A and IuCS, so only less than 100 servers are needed to be deployed by the Taiwanese environment. The experiment results of FPA showed a high accuracy of vehicle speed estimation, although this method may need higher signaling costs for sending MSR message between MSs and base stations.  
For database lookup methods, the information of cellular network signals, which include cell ID, CA, HO and NLU, are considered to generate the mapping table of cell ID, handoff-pair and geographic location. For instance, the cell ID can be retrieved to query the mapping table and to get the geographic location of the queried cell when the CA signal occurs, and the handoff-pair can be retrieved to query the mapping table and to get the geographic location of the queried handoff-pair when the HO signal occurs. When two or more locations of the same MS are determined by database lookup methods, the average vehicle speed and travel time between these locations can be estimated [20]. [PERSON] _et al._[21] recorded two handover signals to measure the retention period of each cell, and the time difference between handover signals and the length of the road segment covered by the cell could be analyzed for the estimation of vehicle speed.  
The locations of MSs can be precisely determined by using LCS methods, and traffic information can be obtained by the analyses of locations of MSs. However, the location of the MS should be traced, and the power consumption and time complexity of these methods are higher in runtime. Furthermore, the issue of the invasion of privacy should be considered and investigated.