Abstract
A beam alignment method for an antenna array is provided. In the method, a base station uses multi-modal beam patterns for transmitting several synchronization signals. User equipment scans the synchronization signals, determines a synchronization signal with the strongest received power and a receive beam direction corresponding thereto, and transmits an initial access message including index information indicating the strongest synchronization signal. The base station receives the initial access message on the random access channel by using the single-modal beam patterns, determines a single-modal beam pattern with the strongest access power for the initial access message, and compares the determined single-modal beam pattern with the strongest access power with a main lobe of the multi-modal beam pattern corresponding to the index information indicating the synchronization signal with the strongest received power in the initial access message, to determine an optimal beam direction for the transmission to the user equipment.