Initial Cell Search Method Based on Two-Step Frequency Offset Estimation for Small Cells in Heterogeneous Networks

This paper proposes a fast initial cell search method based on two-step frequency offset estimation for a small cell in Long Term Evolution (LTE) heterogeneous networks using different frequency spectra. In the proposed cell search method, a set of user equipment (UE) first estimates the frequency offset of a received primary synchronization signal (PSS) from a macrocell and computes the frequency offset of a received PSS for a small cell in Step 1 assuming the same frequency error of a temperature compensated crystal oscillator (TCXO) of a UE. The UE detects the PSS received timing from the maximum PSS correlation after compensating for the frequency offset by using the estimated value in Step 1 for the small cell. In Step 2, the UE estimates the residual frequency offset by taking a partial correlation of the PSS from the small cell. The UE detects the best secondary synchronization signal (SSS) sequence by taking the SSS sequence correlation for the received signal after compensating for the frequency offset using the estimated value in Step 2. System-level simulation results show that the proposed cell search method achieves a fast initial cell search time within approximately 150 ms to satisfy the cell ID detection probability of 95% even for the carrier frequency of a small cell up to 6 and 11 GHz, assuming the free-running frequency error of the UE TCXO of 3 and 1 ppm, respectively.