System and method for beam-based physical random-access

A method in a network node for supporting random access from a wireless device, the method comprising:

• transmitting a set of downlink beam-specific reference signals (BRSs), each downlink BRS being unique per beam and known from standard specification;
• detecting a random-access preamble in a signal received from the wireless device on a Random Access Channel (RACH), said random-access preamble detection indicating a preferred downlink beam-specific reference signal (BRS) of said set of downlink BRSs, the preferred downlink BRS preferred by said wireless device according to one or more pre-defined association rules defining, for each downlink BRS in the set of downlink BRSs, an association between a random-access resource and the each downlink BRS;
• and
• transmitting a random-access response on RACH, wherein a beam, beam direction, and/or beamforming weight used for transmitting the random-access response is the same as a beam, beam direction, and/or beamforming weight of the preferred downlink BRS indicated by the random-access preamble detection.

A wireless device configured to perform random access to a network node, the wireless device comprising a processor and a memory, the memory containing instructions executable by the processor to:

• receive a set of downlink beam-specific reference signals (BRSs) from the network node, each downlink BRS being unique per beam and known from standard specification;
• determine a preferred downlink beam-specific reference signal (BRS) from the set of downlink BRSs based on a received signal power for each downlink BRS in the set of downlink BRSs;
• select, based on the preferred downlink BRS, a random-access resource to be used to transmit a random-access attempt to the network node, the random-access resource selected according to one or more pre-defined association rules defining, for each downlink BRS in the set of downlink BRSs, an association between a random-access resource and the each downlink BRS;
• and
• transmit a random-access attempt on a Random Access Channel (RACH) to the network node using the selected random-access resource;
• and
• receive a random-access response message on RACH in a downlink beam that is preferred by the wireless device and that is indicated by the selected random-access resource.

A network node configured to support random access from a wireless device, the network node comprising a processor and a memory, the memory containing instructions executable by the processor to:

• transmit a set of downlink beam-specific reference signals (BRSs), each downlink BRS being unique per beam and known from standard specification;
• detect a random-access preamble in a signal received from the wireless device on a Random Access Channel (RACH), said random-access preamble detection indicating a preferred downlink beam-specific reference signal (BRS) of said set of downlink BRSs, the preferred downlink BRS preferred by said wireless device according to one or more pre-defined association rules defining, for each downlink BRS in the set of downlink BRSs an association between a random-access resource and the each downlink BRS;
• and
• transmit a random-access response on RACH, wherein a beam, beam direction, and/or beamforming weight used for transmitting the random-access response is the same as a beam, beam direction, and/or beamforming weight of the preferred downlink BRS indicated by the random-access preamble detection.