Random Access Power Ramping for Low-Latency L1/L2 Mobility
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Solution Overview
Problem
Existing wireless communication systems face challenges in efficiently managing layer 1 and 2 triggered mobility (LTM) procedures, particularly in 4G/5G networks, due to inefficiencies in random access procedures and timing advance acquisition during cell handovers.
Innovation Solution
A method involving a wireless device that receives a first PDCCH order initiating a random access procedure with a preamble power ramping counter (PPRC) setup, followed by transmitting preambles with adjusted powers based on PPRC increments, and subsequent PDCCH orders for retransmissions, to facilitate early timing advance acquisition during LTM.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a wireless device transmits preambles with increased power using power ramping during random access procedure, then the reliability of timing advance acquisition is improved, but the energy consumption increases
Solution Approach 1:
The network configures the wireless device with a predetermined power ramping counter (PPRC) value before the random access procedure begins. This preliminary configuration allows the device to quickly determine the number of power ramping iterations needed, reducing unnecessary energy consumption while ensuring reliable timing advance acquisition through pre-planned power adjustment steps.
2Reliability
If the network sends multiple PDCCH orders for random access retransmissions, then the reliability of mobility procedure is improved, but the latency increases
Solution Approach 1:
The network utilizes feedback from the wireless device regarding the outcome of random access attempts to dynamically control subsequent PDCCH order transmissions. When the device successfully acquires timing advance or detects failure, it signals this back to the network, which then adjusts whether to send additional retransmission orders, optimizing both reliability and latency by avoiding unnecessary retransmissions.
Solution Approach 2:
The network pre-configures the PPRC value indicating the maximum number of power ramping iterations allowed. This preliminary setup enables the device to autonomously manage the random access procedure within defined boundaries, reducing the need for multiple interactive PDCCH orders and thereby minimizing latency while maintaining reliability through controlled retransmission attempts.
3Reliability
If the wireless device implements power ramping with counter increments, then the probability of successful random access is improved, but the device complexity increases
Solution Approach 1:
The wireless device autonomously manages the power ramping process by independently incrementing the PPRC counter and adjusting transmission power based on pre-configured parameters received from the network. This self-service approach eliminates the need for complex network-controlled power adjustment mechanisms, reducing overall system complexity while maintaining high random access success probability through device-side adaptive power control.
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3
AI summary
A method may include receiving, by a wireless device, a first physical downlink control channel (PDCCH) order initiating a random access procedure. The first PDDCH order may include a first field indicating a first candidate cell as well as a second field indicating an initial transmission. Based on the first field and the second field of the first PDCCH order, the wireless device may set a preamble power ramping counter (PPRC) to an initial value and may transmit a first preamble via the first candidate cell with a first power. The method may further include receiving a second PDCCH order transmitting, a second preamble via the first candidate cell with a second power determined based on increasing the PPRC by one, in response to a first field of the second PDCCH order indicating the first candidate cell and a second field of the second PDCCH order indicating a retransmission.