In a cellular communications network, such as one employing orthogonal frequency division multiple access (OFDMA), each cell employs a base station that communicates with user equipment, such as a cell phone or a laptop that is actively located within its cell. When the user equipment is first turned on, it has to do an initial cell search in order to be connected to the cellular network. This involves a downlink synchronization process between the base station and the user equipment wherein the base station sends a synchronization signal to the user equipment.
As part of the synchronization process, a front-end filter may be used to filter the received signal so that only the synchronization sequence is processed. In this case, if data carrying subcarriers are chosen next to those occupied by the synchronization sequence, a low pass filter with a very short transition band is needed. This condition also has a direct implication on the front-end sampling frequencies. If the adjacent data subcarriers cannot be adequately filtered out by the low pass filter, then a greater-than-Nyquist sampling frequency (with respect to the bandwidth occupied by the synchronization sequence) may be needed. Since cellular communications systems offer increasingly greater flexibility for use, improvements would prove beneficial in the art.
USPTO Backgrounds
USPTO Backgrounds