Initial access in high frequency wireless systems

A wireless transmit/receive unit (WTRU) comprising:

• a receiver configured to receive a plurality of random access (RA) resource sets, wherein each of the plurality of RA resource sets is associated with a node-B directional beam of a plurality of node-B directional beams, and each of the plurality of RA resource sets includes a plurality of resources;
• at least one processor configured to select an RA resource set from among the plurality of RA resource sets;
• the at least one processor configured to initiate an RA procedure based on the selected RA resource set, wherein the RA procedure includes determining the plurality of resources corresponding to the selected RA resource set, and selecting multiple preambles which include a preamble for each resource of the plurality of resources corresponding to the selected RA resource set;
• and
• a transmitter configured to sequentially transmit the selected multiple preambles to a node-B in sequential RA transmissions using the plurality of resources corresponding to the selected RA resource set,
• wherein the receiver and the processor are further configured to monitor for a plurality of random access responses (RARs) corresponding to the sequential RA transmissions such that monitoring for a first RAR at least partially overlaps with monitoring for a second RAR, and receive, from the node-B, in response to the sequential RA transmissions, at least one RAR, wherein each of the received at least one RAR corresponds to one of the transmitted multiple preambles.