Ambient IoT PRACH RO Selection for Near-Far Power Control
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Solution Overview
Problem
In ambient IoT systems, multiple devices may select the same random access channel (RACH) occasion for PRACH transmissions, leading to significantly different received power levels, which can result in failed RACH procedures for devices at the cell edge, increasing delay and energy consumption.
Innovation Solution
Providing an RO pool with multiple RACH occasions corresponding to one SSB, allowing ambient IoT devices to select an RO based on signal strength measurements of downlink or sounding signals, to constrain the received power of signals to a limited range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple devices select the same RACH occasion for PRACH transmissions, then the RACH procedure can be initiated, but the received power levels become significantly different causing failed RACH procedures for cell edge devices
Solution Approach 1:
The patent divides the single RACH occasion into multiple RACH occasions within an RO pool, each associated with different SSBs. Devices are segmented into different groups based on their measured signal strength of downlink or sounding signals, and each group selects an appropriate RACH occasion from the pool. This segmentation ensures that devices at different locations (cell center vs. cell edge) select different RACH occasions, resulting in more uniform received power levels at the base station and improving RACH procedure success rate.
2Reliability
If devices at cell edge transmit with higher power to compensate for path loss, then received power can be improved, but energy consumption increases significantly
Solution Approach 1:
The patent implements preliminary action by having devices measure the signal strength of downlink or sounding signals before selecting a RACH occasion. Based on these pre-measured signal strength values, devices can proactively select an appropriate RACH occasion that will result in acceptable received power levels without requiring excessive transmit power. This preliminary measurement and selection process eliminates the need for cell edge devices to transmit at maximum power, thereby reducing energy consumption while ensuring reliable signal reception.
3Reliability
If devices perform repeated RACH transmissions to overcome failed procedures, then connection can be established, but transmission delays increase
Solution Approach 1:
The patent applies preliminary action by having devices measure signal strength and select appropriate RACH occasions from the RO pool before transmitting. This pre-selection based on measured signal strength ensures that devices, especially those at cell edge, choose RACH occasions that will result in successful reception on the first attempt. By performing this measurement and selection in advance, the patent eliminates the need for repeated RACH transmissions, thereby significantly reducing RACH procedure delay while ensuring reliable connection establishment.
Data Source
AI summary
Certain aspects of the present disclosure provide a method for wireless communications at an ambient internet of things (IoT) device. The ambient IoT device measures signal strength of a downlink signal transmitted from a gNodeB (gNB). The ambient IoT device estimates a pathloss between the gNB and itself based at least on the measured signal strength. Based on the pathloss between the ambient IoT device and the gNB, and together with measured received power from an assisting node, the ambient IoT device may select a random access channel (RACH) occasion (RO) so that a received power at the gNB from the ambient IoT device is constrained to a limited range.