Читать книгу Position, Navigation, and Timing Technologies in the 21st Century - Группа авторов - Страница 102

In LTE systems, the PSS and SSS are transmitted with the lowest possible bandwidth. The ranging precision and accuracy of the SSS is analyzed in [73, 74], which shows that the SSS can provide very precise ranging resolution using conventional DLLs in an environment without multipath. However, because of its relatively low bandwidth, the SSS is extremely susceptible to multipath. To achieve more precise localization using LTE signals, the CRS can be exploited. The ranging precision of SSS and CRS in a semi‐urban environment with multipath was studied experimentally in [63], which showed that CRS is more robust to multipath.

In the timing information extraction stage of the receiver, the TOA can be estimated by detecting the first peak of the channel impulse response (CIR). The CIR can be computed from the received signal model in the i‐th symbol, given in Eq. (38.19). The subscript i will be dropped in the sequel for simplicity of notation. The estimated CFR of the u‐th eNodeB is given by

(38.24)

where . Equation 38.24 is obtained using the fact that . The CIR estimate is obtained by taking the IFFT of the estimated CFR, yielding

(38.25)

where .

The TOA estimate τ is then fed back to the tracking loops. A low pass filter (e.g. a moving average filter) can be used to remove outliers in the estimated τ. Figure 38.40 shows the block diagram of the timing information extraction stage.

The first peak detection approach was implemented in [17, 64]. While this method is computationally inexpensive, the first peak of the CIR cannot be detected when the multipath has a short range. An adaptive threshold approach was developed in [65] that yielded more robust performance in urban environments experiencing severe multipath. In contrast to peak detection algorithms, super resolution algorithms (SRAs) can be used [5, 11], which are computationally involved. A computationally efficient receiver that deals with the shortcomings of the SRA‐based and first peak detection‐based approaches was proposed in [15, 19].

Figure 38.40 Timing Information Extraction block diagram (Shamaei et al. [64, 65]).

Source: Reproduced with permission of Institute of Navigation, IEEE.