Methods, apparatus, and computer programs for automatically allocating physical layer cell identifiers A modulo 3 grouping and a modulo 30 grouping are provided for physical layer cell identifiers in a cellular communication system. The modulo 3 grouping is associated with first synchronization signal assignments and the modulo 30 grouping is associated with second synchronization signal assignments. A combination of first and second synchronization signals determines a physical layer cell identifier of a cell. A modulo 3 group is allocated to each of multiple cells of the system. After the allocation of the modulo 3 groups, a modulo 30 group is allocated to each of the multiple cells. The allocation of the modulo 30 groups incorporates the allocated modulo 3 group as a precondition for the modulo 30 grouping. To each cell, first and second synchronization signals are allocated on the basis of said allocation of the modulo 30 group.