Option 2 can be considered as a compromised solution between Option 1 and Option 3. That would cause an increase of the interference to the target beam. In Option 3, the power-ramping counter is increased after the transmit beam is switched. That would increase the latency of the random access procedure. But due to the reset of the power-ramping counter after switching to the target beam, the UE may need to try many times to achieve the transmission power level with which the PRACH transmission can be successfully received by the network. It can minimize the interference to the target beam. ![]() Option 1 is the most conservative power control scheme among those four options. Option 4: a separate power-ramping counter is used for each beam. Option 3: the power-ramping counter increase. ![]() Option 2: the power-ramping counter remains unchanged. Option 1: reset the power-ramping counter. Power control of PRACH during beam switching. The following four options were discussed, which are illustrated in Fig. Increasing transmit power along with switching the transmit beam on PRACH transmission may cause more change in interference level to the target beam and thus affect the signal transmission of other users. If the UE switches the transmit beam for a PRACH retransmission, whether the transmit power of the PRACH retransmission will be increased or not, is a problem and was extensively discussed during the standardization process. If the UE does not change the transmit beam on PRACH retransmission, the transmission power of the PRACH transmission climbs up on the basis of power of the last PRACH transmission until the random access process is successfully completed. If the UE supports multiple transmit beams, it can choose between switching the transmit beam on PRACH retransmission or keeping the transmit beam unchanged. During the random access procedure, if a UE transmits a PRACH preamble but does not receive the Random Access Response (RAR) or does not successfully receive the conflict resolution message, the UE can retransmit the PRACH preamble. The UE determines the uplink transmission power for the PRACH transmission based on the expected receiving power provided by the network and the path loss measured from the downlink reference signal. For a resource set to be used for downlink receiver-side beam adjustment, the repetition flag should thus be set.Īn open-loop power control mechanism is applied to PRACH transmission. In general, a configured resource set includes a “ repetition” flag that indicates whether or not a device can assume that all reference signals within the resource set are transmitted using the same spatial filter. ![]() At the same time, the device should be allowed to assume that the different reference signals in the resource set are transmitted using the same spatial filter, in practice the same transmit beam. To allow for analog beamforming at the receiver side, the different reference signals within the resource set should be transmitted in different symbols, allowing for the receiver-side beam to sweep over the set of reference signals. According to Section 8.2, the report quantity should thus be set to “None.” However, as the receiver-side beam adjustment is done internally within the device, there is no report quantity associated with receiver-side beam adjustment. ![]() Downlink receiver-side beam adjustment.ĭownlink receiver-side beam adjustment can be based on similar report configurations as for transmitter-side beam adjustment.
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