Methods for allocating and choosing dedicated signatures for random access are provided. Options for allocating dedicated signatures include allocating the dedicated signatures from unused space of a random signature root index when there is unused space and allocating more dedicated signatures from the same root index using the same time/frequency resources if additional signatures are needed, and reserving some preambles from contention-based random access preambles from both sets of preambles. The dedicated signatures may be reserved in each of two sets of preambles.