Methods for allocating and choosing dedicated signatures for random access are provided. Options for allocating dedicated signatures include allocating the dedicated signature from the unused space of the 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 the contention-based random access preambles from both sets of preambles. The present invention also proposes that the dedicated signatures be reserved in each of two sets of preambles.