where
38.6.2 LTE Receiver Architecture
A cellular LTE navigation receiver consists of four main stages: signal acquisition, system information extraction, tracking, and timing information extraction [64, 65]. This section discusses the various stages of the navigation LTE receiver depicted in Figure 38.30. Section 38.6.2.1 describes the acquisition of PSS and SSS. Section 38.6.2.2 discusses the extraction of relevant system information. Section 38.6.2.3 discusses the tracking stage. Section 38.6.2.4 describes the timing information extraction.
38.6.2.1 Acquisition
The first step in acquiring an LTE signal is to extract the transmitted frame timing and the eNodeB’s cell ID [66–68]. These two parameters are obtained by the PSS and SSS. To detect the PSS, the UE exploits the orthogonality of the Zadoff–Chu sequences and correlates the received signal with all the possible choices of the PSS according to
where
Figure 38.30 Block diagram of the LTE navigation receiver architecture (Shamaei et al. [65]).
Source: Reproduced with permission of IEEE.
where
After obtaining the frame timing, the UE estimates the frequency shift (Doppler frequency) using the CP in the received signal r(n). The apparent Doppler frequency, including the carrier frequency offset due to clock drift and the Doppler shift, can be estimated by the CP as
where NCP is the set of CP indices, and Ts is the sampling interval [69]. Upon estimating the Doppler frequency, the acquisition of the LTE signal is complete. Figure 38.31 summarizes the LTE signal acquisition process.
The normalized correlation of received LTE signals with locally generated PSS and SSS signals are presented in Figure 38.32. It can be seen that since the PSS is transmitted twice per frame, the correlation has two peaks in the duration of one frame, which is 10 ms. However, the SSS correlation has only one peak, since the SSS is transmitted only once per frame. The figure also shows that the highest PSS correlation peak was at
Figure 38.31 Signal acquisition block diagram (Shamaei et al. [64, 65]).
Source: Reproduced with permission of Institute of Navigation, IEEE.
Figure 38.32 PSS and SSS normalized correlation results with real LTE signals (Shamaei et al. [64, 65]).
Source: Reproduced with permission of Institute of Navigation, IEEE.
38.6.2.2 System Information Extraction
Parameters relevant for navigation purposes include the system bandwidth, number of transmitting antennas, and neighboring cell IDs. These parameters are provided to the UE in two blocks, namely, the master information block (MIB) and the system information block (SIB).
The UE starts acquiring with the lowest possible bandwidth of LTE, since it has no information about the actual transmission bandwidth. After acquisition, the signal is converted to the frame, and the bandwidth is obtained by decoding the MIB. Then, the UE can increase its sampling frequency to exploit the high bandwidth of the CRS. The UE can also utilize signals received from multiple eNodeB antennas to improve the TOA estimate.
Since the frequency reuse factor in LTE is 1, it may not be possible to acquire the received PSS and SSS signals from eNodeBs with low C/N0. This phenomenon is called the near‐far effect. In this case, one can use the neighboring cell IDs obtained by decoding the SIB to reconstruct the CRS sequence [65]. This section discusses the decoding of MIB and SIB.
MIB Decoding: In order to exploit the high‐bandwidth CRS signal, which improves the navigation performance in multipath environments and in the presence of interference, the UE must first reconstruct the LTE frame from the received signal. To do so, the actual transmission bandwidth and number of transmitting antennas, which are provided in the MIB, must be decoded. The MIB is transmitted on the