Position, Navigation, and Timing Technologies in the 21st Century

UAV Results: Figure 38.20shows the BTS environment, the UAV trajectory, and the experimental hardware setup. Signals from two cellular BTSs corresponding to the US cellular provider Verizon Wireless were tracked. The BTSs transmitted at a carrier frequency of 883.98 MHz and their positions were mapped prior to the experiment [37, 39]. The ground‐truth reference for the UAV trajectory shown in Figure 38.20was taken from its onboard navigation system, which uses GPS, an INS, and other sensors. The distance D between the UAV and each BTS was calculated using the navigation solution produced by the UAV’s navigation system and the known BTS position. The pseudorange ρ was obtained from the cellular CDMA receiver that was mounted on the UAV. In order to validate the resulting pseudoranges, the variation of the pseudorange Δ ρ ≜ ρ − ρ (0) and the variation in distance Δ D ≜ D − D (0) are plotted in Figure 38.21for the two BTSs, where ρ (0) is the initial value of the pseudorange, and D (0) is the initial distance between the UAV and the BTS. It can be seen from Figure 38.21that the variations in the pseudoranges closely follow the variations in distances. The difference between Δ D and Δ ρ for a particular BTS is due to the variation in the clock bias difference and the noise v i.

Figure 38.20 BTS environment and experimental hardware setup for the UAV experiment. Map data: Google Earth (Khalife et al. [12]).

Source: Reproduced with permission of IEEE.

Figure 38.21 Variation in pseudoranges and the variation in distances between the receiver and two cellular CDMA BTSs for the UAV experiment (Khalife et al. [12]).

Source: Reproduced with permission of IEEE.

Ground Vehicle Results: Figure 38.22shows the BTS environment, ground vehicle trajectory, and the experimental hardware setup. Signals from two cellular BTSs corresponding to the US cellular provider Verizon Wireless were tracked. The BTSs transmitted at a carrier frequency of 882.75 MHz, and their positions were mapped prior to the experiment [37, 39]. The ground‐truth reference for the ground vehicle trajectory in Figure 38.22was obtained from the Generalized Radionavigation Interfusion Device (GRID) GPS SDR [58]. The change in the true range and the change in pseudorange are plotted in Figure 38.23, similarly to the UAV experiment. It can be seen from Figure 38.23that the variations in the pseudoranges closely follow the variations in distances. The difference between Δ D and Δ ρ for a particular BTS is due to the variation in the clock bias difference and the noise v i.

Two cars (mapper and navigator) were equipped with the cellular CDMA navigation receiver discussed in Section 38.5.2. The receivers were tuned to the cellular carrier frequency 882.75 MHz, which is a channel allocated to the US cellular provider Verizon Wireless. The mapper was stationary and was estimating the clock biases of the 3 BTSs via a WLS estimator as discussed in Section 38.4.1. The BTSs’ positions were known to the mapper, and the position states were expressed in a local 3D frame whose horizontal plane passes through the three BTSs and is centered at the mean of the BTSs’ positions. The height of the navigator was known and constant in the local 3D frame over the trajectory driven and was passed as a constant parameter to the estimator. Hence, only the navigator’s 2D position and its clock bias were estimated through the WNLS described in Section 38.4.1. The weights of the WNLS were calculated using Eq. (38.17)with s. For the first pseudorange measurement, the WNLS iterations were initialized by setting the navigator’s initial horizontal position states at the origin of the 3D local frame and the initial clock bias to zero. For each subsequent pseudorange measurement, the WNLS iterations were initialized at the solution from the previous WNLS. The experimental hardware setup, the environment layout, and the true and estimated navigator trajectories are shown in Figure 38.24. The ground‐truth trajectory was obtained from the GRID GPS SDR [58]. It can be seen from Figure 38.24that the navigation solution obtained from the cellular CDMA signals closely follows the navigation solution obtained using GPS signals.

Figure 38.22 BTS environment, true trajectory, and experimental hardware setup for the ground vehicle experiment. Map data: Google Earth (Khalife et al. [12]).

Source: Reproduced with permission of IEEE.

Figure 38.23 Variation in pseudoranges and the variation in distances between the receiver and two cellular CDMA BTSs for the ground vehicle experiment (Khalife et al. [12]).

Source: Reproduced with permission of IEEE.

Two identical UAVs (mapper and navigator) were equipped with the cellular CDMA navigation receiver discussed in Section 38.5.2. Here, both the mapper and navigator were mobile. The receivers were tuned to the cellular carrier frequency 882.75 MHz used by the US cellular provider Verizon Wireless. The mapper and navigator were listening to the same four BTSs with known positions. The mapper was estimating the BTSs’ clock biases via a WLS estimator as discussed in Section 38.4.1. Similar to the ground vehicle navigation setup, the height of the navigator was a known constant in the local 3D frame, and only the navigator’s 2D position and its clock bias were estimated through the WNLS, whose weights and initialization were calculated in a similar way as the ground vehicle navigation setup. The ground‐truth references for the mapper and navigator trajectories were taken from the UAVs’ onboard navigation systems, which use GPS, INS, and other sensors. Figure 38.25shows the BTS environment in which the mapper and navigator were present as well as the experimental hardware setup. The navigator’s true trajectory and estimated trajectory from cellular CDMA pseudoranges are shown in Figure 38.26.

Two different techniques can be employed to use LTE signals for PNT: network‐based and UE‐based. The network‐based technique was enabled in LTE Release 9 by introducing a broadcast positioning reference signal (PRS). The expected positioning accuracy with PRS is on the order of 50 m [59]. Network‐based positioning suffers from a number of drawbacks: