Random access method and device and communication system
A random access method and device and a communication system. The device includes: a first controller configured to control a terminal equipment to initiate a 2-step random access procedure; and a second controller configured to control the terminal equipment to initiate a non-contention random access procedure or a 4-step random access procedure when the 2-step random access procedure is not completed. The first and second controller may be provided by control circuitry.
1. A random access device, applicable to a terminal equipment, the device comprising:
first controlling circuitry configured to control the terminal equipment to initiate a two-step random access procedure; and
second controlling circuitry configured to control the terminal equipment to initiate a four-step random access procedure when a number of times of two-step random access preamble(s) transmission reaches a first maximum threshold and no random access response is received in a random access response reception window after a first message (MsgA) of the two-step random access procedure is transmitted,
wherein initiating the four-step random access procedure at least comprises initialization of:
a power ramping step factor of the four-step random access procedure; and
a maximum number of times of transmission of preambles of the four-step random access procedure,
wherein the initiating the four-step random access procedure comprises:
measuring synchronization reference signal (SS-RS) received power of synchronization signal/physical broadcast channel blocks (SS/PBCH Blocks, SSBs) transmitted by a network device, and selecting a synchronization signal/physical broadcast channel block (SS/PBCH block, SSB) used in the four-step random access procedure; and
determining a preamble of the four-step random access procedure to be transmitted according to the selected SSB.
2. The device according to claim 1 , wherein the determining the preamble of the four-step random access procedure to be transmitted according to the selected SSB comprises:
determining a preamble group used in the four-step random access procedure; and
randomly selecting a preamble from a preamble set of the determined preamble group to which the selected SSB corresponds as the preamble of the four-step random access procedure to be transmitted; wherein, probabilities of selecting each preamble in the preamble set of the preamble group are identical.
3. The device according to claim 2 , wherein the determining a preamble group used in the four-step random access procedure comprises:
determining the preamble group used in the four-step random access procedure as a preamble group selected in the two-step random access procedure that is not completed.
4. The device according to claim 1 , wherein,
the initiating the four-step random access procedure further comprises:
selecting uplink transmission resources for transmitting the preamble of the four-step random access procedure when the two-step random access procedure is not completed.
5. The device according to claim 4 , wherein the selecting uplink transmission resources for transmitting the preamble of the four-step random access procedure when the two-step random access procedure is not completed comprises:
selecting a next available physical random access channel (PRACH) transmission occasion from an allowed preamble transmission occasion set identified by a preamble transmission occasion configuration parameter in configuration information of the four-step random access procedure, and taking the selected next available physical random access channel (PRACH) transmission occasion as a physical random access channel (PRACH) transmission occasion of the preamble of the four-step random access procedure when the two-step random access procedure is not completed.
6. The device according to claim 4 , wherein the initiating four-step random access procedure further comprises:
calculating target received power of the preamble of the four-step random access procedure (four-step random access preamble);
calculating transmission power of the four-step random access preamble according to the target received power and the pathloss of the four-step random access preamble.
7. The device according to claim 6 , wherein the calculating the target received power of the four-step random access preamble comprises:
calculating the target received power of the four-step random access preamble according to an initial target received power parameter (preambleReceivedTargetPower) of the four-step random access preamble, a first target received power offset value (DELTA_PREAMBLE), a power ramping count value (PREAMBLE_POWER_RAMPING_COUNTER) of the four-step random access preamble, and the power ramping step factor (PREAMBLE_POWER_RAMPING_STEP) of the four-step random access preamble.
8. The device according to claim 7 , wherein,
the target received power of the four-step random access preamble is in addition calculated according to a second target received power offset value (delta_fallback_TargetPower); or,
the target received power of the four-step random access preamble is in addition calculated according to a target received power ramping step offset value (delta_fallback_step).
9. The device according to claim 8 , wherein, calculating the target received power of the four-step random access preamble comprises:
calculating the target received power of the four-step random access preamble as
PREAMBLE_RECEIVED_TARGET_POWER=preambleReceivedTargetPower+DELTA_PREAMBLE+(PREAMBLE_POWER_RAMPING_COUNTER−1)×PREAMBLE_POWER_RAMPING_STEP+delta_fallback_TargetPower.
10. The device according to claim 9 , wherein,
the second target received power offset value (delta_fallback_TargetPower) is a preset fixed value, or is linear correlated to a ramping amplitude of the target received power of the preamble of the two-step random access procedure that is not completed.
11. The device according to claim 10 , wherein, delta_fallback_TargetPower equals to β×(PREAMBLE_POWER_RAMPING_COUNTER′−1)×PREAMBLE_POWER_RAMPING_STEP′;
wherein, the β is a linear correlation factor, the PREAMBLE_POWER_RAMPING_COUNTER′ is a power ramping count value of the two-step random access procedure that is not completed, the PREAMBLE_POWER_RAMPING_STEP′ is a power ramping step factor of a preamble of the two-step random access procedure.
12. The device according to claim 7 , wherein,
an initial value of the power ramping count value (PREAMBLE_POWER_RAMPING_COUNTER) of the four-step random access preamble is:
a preset initial value; or
a preamble power ramping count value of the two-step random access procedure that is not completed.
13. The device according to claim 6 , wherein the initiating the four-step random access procedure further comprises:
according to the four-step random access preamble, the uplink transmission resources of the four-step random access preamble and the calculated transmission power of the four-step random access preamble, transmitting the four-step random access preamble when the two-step random access procedure is not completed.