Method and apparatus of random channel access over zero energy air-interface
Methods, apparatuses, systems, etc., directed to random channel access over zero energy (ZE) air-interface(s) are disclosed herein. In an embodiment, a wireless transmit/receive unit (WTRU) may receive a first reference signal. For example, the WTRU may determine that a first signal strength of the received first reference signal may fail to satisfy a strength condition, and responsively the WTRU may: (i) receive a transmission, (ii) determine a sequence and an occasion based on the received transmission, (iii) transmit using the determined sequence on the determined occasion, and (iv) receive a second reference signal from an interrogating WTRU.
1 . A method implemented in a first wireless transmit/receive unit (WTRU), the method comprising:
receiving a first reference signal from a base station;
determining that a first signal strength of the first reference signal fails to satisfy a signal strength condition;
monitoring for a second reference signal from a second WTRU based on the determination that the first signal strength of the first reference signal fails to satisfy the signal strength condition;
receiving the second reference signal from the second WTRU;
determining, based on the received second reference signal, a physical random-access channel (PRACH) preamble and a random-access channel (RACH) occasion; and
transmitting the determined PRACH preamble on the determined RACH occasion.
2 . The method of claim 1 , wherein transmitting the determined PRACH preamble on the determined RACH occasion is any of a backscattered transmission and a non-backscattered transmission.
3 . The method claim 1 , wherein the first signal strength of the first reference signal fails to satisfy the signal strength condition on a condition that the first signal strength is below a threshold.
4 . The method of claim 1 , comprising performing synchronization with the second WTRU based on the received second reference signal.
5 . The method of claim 1 , wherein the determined PRACH preamble and the determined RACH occasion belong to respectively a set of PRACH preambles and a set of RACH occasions associated with a backscattering operation that comprises backscattering a signal to the base station based on a reference signal received from a network element different from the base station.
6 . The method of claim 1 , wherein the PRACH preamble and the RACH occasion are further determined according to any of a WTRU class, a WTRU backscattering capability, and a WTRU battery level.
7 . The method of claim 6 , wherein the WTRU class indicates any of a passive WTRU and a semi-passive WTRU.
8 . A first wireless transmit/receive unit (WTRU) comprising circuitry, including any of a transmitter, a receiver, a processor, and a memory, the WTRU being configured to:
receive a first reference signal from a base station;
determine that a first signal strength of the first reference signal fails to satisfy a signal strength condition;
monitor for a second reference signal from a second WTRU based on the determination that the first signal strength of the first reference signal fails to satisfy the signal strength condition;
receive the second reference signal from the second WTRU;
determine, based on the received second reference signal, a physical random-access channel (PRACH) preamble and a random-access channel (RACH) occasion; and
transmit the determined PRACH preamble on the determined RACH occasion.
9 . The method of claim 1 , comprising receiving configuration information indicating a plurality of RACH occasions and a plurality of reference signal preambles, wherein each reference signal preamble of the plurality of reference signal preambles is associated with one or more RACH occasions of the plurality of RACH occasions.
10 . The method of claim 9 , wherein the second reference signal comprises a second reference signal preamble of the plurality of reference signal preambles, and wherein the PRACH preamble is determined based on one or more RACH occasions associated with the second reference signal preamble.
11 . The method of claim 9 , wherein the configuration information indicates any of: (1) a support of backscattering RACH transmission and (2) a monitoring configuration for monitoring the second reference signal.
12 . The method of claim 9 , wherein the configuration information is received through system information.
13 . The method of claim 2 , wherein it is determined whether to transmit the backscattered transmission or the non-backscattered transmission based on any of the first signal strength and a second signal strength of the second reference signal.
14 . The method of claim 4 , comprising receiving a random-access response (RAR) including timing advance information indicating a differential timing advance to be used for timing adjustment with respect to the synchronization with the second WTRU for subsequent uplink transmissions.
15 . The first WTRU of claim 8 , wherein the first signal strength of the first reference signal fails to satisfy the signal strength condition on a condition that the first signal strength is below a threshold.
16 . The first WTRU of claim 8 , configured to receive configuration information indicating a plurality of RACH occasions and a plurality of reference signal preambles, wherein each reference signal preamble of the plurality of reference signal preambles is associated with one or more RACH occasions of the plurality of RACH occasions.
17 . The first WTRU of claim 16 , wherein the second reference signal comprises a second reference signal preamble of the plurality of reference signal preambles, and wherein the PRACH preamble is determined based on one or more RACH occasions associated with the second reference signal preamble.
18 . The first WTRU of claim 8 , configured to determine whether to transmit a backscattered transmission or a non-backscattered transmission on the determined RACH occasion based on any of the first signal strength and a second signal strength of the second reference signal.
19 . The first WTRU of claim 8 , configured to perform synchronization with the second WTRU based on the second reference signal.
20 . The first WTRU of claim 19 , configured to receive a random-access response (RAR) including timing advance information indicating a differential timing advance to be used for timing adjustment with respect to the synchronization with the second WTRU for subsequent uplink transmissions.