Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
In a mobile communication system, a base station may transmit a pilot signal such that mobile stations (such as a user's wireless communication device) may use the signal to perform cell selection and re-selection. In particular, mobile stations may measure power of a pilot signal to determine the level of coverage that the mobile stations may obtain from a particular base station. The pilot signal may typically be transmitted at a constant power level to provide a fixed reference for the mobile stations because pilot signals having a constant power level, in general, may clearly and simply define the coverage area of each individual cell.
However, generation and transmission of pilot signals with constant power levels may also cause a relatively high level of interference by base stations that may not be currently serving any mobile stations. Mass deployment of small-cell base stations in mobile communication systems may create further technical challenges, such as interference between neighboring small cells as well as between small cells and macro cells, because small cells may share the same licensed frequency spectrum with macro cells. For example, in a dense small cell environment such as crowded buildings or an apartment complex, a mobile station may fail to detect a pilot signal from a macro-cell base station, which is located at a relatively farther distance, due to a high level of interferences from neighbor small-cell stations.
In order to mitigate the above problem, orthogonal frequency reuse or correlation with orthogonal sequence techniques have been proposed. In a World Interoperability for Microwave Access (WiMax) system, a frequency reuse method may be used for cell search preamble transmission, where separate subcarrier sets may be allocated to different neighbor cells so that they do not collide at the same subcarrier position. Also, in a Long Term Evolution (LTE) system, a primary synchronization signal (PSS) with a Zadoff-Chu sequence may be used for obtaining good correlation properties of a cell search signal from neighbor cells. However, when a large number of small cells are densely installed in a limited area, hard partitioning of radio resources may degrade the resource utilization efficiency and cause shortage of sequences allocated for the cells.