# Integration of LTE 230 and LTE 1800 in Power Wireless Private Networks
## 4 Integration of the Access Network
### Downlink Synchronization and Cell Search  
In the LTE 1800 system, the traditional PSS detection method calculates the correlation between the received signal and the three local sequences separately [20]. The index of the local sequence which has the maximum correlation is \(N_{\mathrm{ID}}^{(2)}\). The corresponding time is the timing point. According to the mapping location relation between the PSS and SSS, the SSS can be found easily in the time domain. The most commonly used SSS detection method is working backwards according to the generation rule of the SSS sequence in the frequency domain. In this way, the intermediate parameters \(m_{0}\) and \(m_{1}\) can be acquired, which can decide \(N_{\mathrm{ID}}^{(1)}\).  
In the LTE 230 system, the proposed PSS detection method calculates the correlation between the received signal and the three local sequences separately. The index of the local sequence which has the maximum correlation is \(N_{\mathrm{ID}}^{(2)}\). The corresponding time is the timing point. According to the mapping location relation between the PSS and SSS, the SSS can be found easily in the time domain. Due to the special signal mapping form, the 448-point SSS in the time domain should be firstly transformed into a 62-point original sequence in the frequency domain. The most commonly used SSS detection method is working backwards according to the generation rule of the SSS sequence in the frequency domain. In this way, the intermediate parameters \(m_{0}\) and \(m_{1}\) can be acquired, which can decide \(N_{\mathrm{ID}}^{(1)}\).  
Figure 9 shows the simulation results of the timing performance of LTE 1800 and LTE 230. The simulation parameters for LTE 1800 were as follows: the subcarrier spacing was \(\Delta f_{\mathrm{s}}=15\) kHz, the length of the ZC sequence was 63, the root of the ZC sequence was 29, the synchronization signal period was 5 ms, and the Rayleigh channel was used. When the timing estimation error is larger than 1 us, we call it a timing detection error. The simulation parameters for LTE 230 were as follows: the subcarrier spacing was \(\Delta f_{\mathrm{s}}=2\) kHz, the length of the ZC sequence was 63, the root of the ZC sequence was 29, the synchronization signal period was 25 ms, and the Rayleigh channel was used. When the timing estimation error is larger than 7 us in the LTE 230 system, we call it a timing detection error.  
Figure 8: Illustration of the PSS and SSS in an LTE 230 subframe.  
Figure 9: Performance comparison of the timing performance between LTE 1800 and LTE 230.  
From Figure 9, we can see that when the received SNR is larger than 1 dB, the timing error of LTE 1800 is smaller than 1%. For LTE 230, about 7 dB is needed to guarantee that the timing error rate is less than 1%. Note that the pathloss values of LTE 230 and LTE 1800 are different with the same propagation distance. The pathloss of LTE 230 is smaller than that of LTE 1800 and the fading for these two systems is independent, so we can choose the better mode with higher detection performance as the transmission mode for a given time, such as the coherent time of the channel. For example, when the received SNR of LTE 230 is 6 dB larger than it is in LTE 1800, then the device will choose LTE 230 as its communication mode in the following transmission. The received SNR can be one of the criteria used to determine which mode will be active. The details of the mode selection will be discussed in the next section.