Uplink Random Access Channel Preamble Transmission Power Control
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Solution Overview
Problem
In SC-FDMA systems, the conventional power ramping up scheme for accessing the contention-based uplink RACH introduces an undesirable delay due to initial low transmit power and incremental power increments during retransmissions.
Innovation Solution
A WTRU randomly selects a RACH subchannel and signature, transmitting a preamble at a predetermined power level, and retransmits based on feedback, eliminating the need for incremental power ramping by ensuring a high enough initial power for successful detection, thereby reducing access delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transmit power ramping up scheme is used for accessing the RACH, then the initial transmit power is low and power is incremented during retransmissions, but this introduces an undesirable delay for uplink random access
Solution Approach 1:
The patent applies preliminary action by having the WTRU calculate and set the preamble transmit power to a predetermined level before transmission, rather than starting with minimum power and ramping up. This preliminary power calculation ensures the preamble is transmitted at sufficient power from the outset, eliminating the time-consuming incremental power ramping process while maintaining reliable detection.
2Loss of time
If a predetermined transmission power is used for preamble transmission, then the initial power is high enough for successful detection, but this requires accurate power calculation and control
Solution Approach 1:
The patent employs feedback mechanisms where the base station provides power control commands and timing advance information back to the WTRU. This feedback loop allows the system to maintain accurate power levels without requiring complex open-loop calculations, as the base station adjusts power requirements based on actual reception conditions and communicates these adjustments to the WTRU.
Data Source
AI summary
A method and apparatus for accessing a contention-based uplink random access channel (RACH) in a single carrier frequency division multiple access (SC-FDMA) system are disclosed. A wireless transmit/receive unit (WTRU) randomly selects a RACH subchannel and a signature among a plurality of available RACH subchannels and signatures. The WTRU transmits a preamble using the selected signature via the selected RACH subchannel at a predetermined or computed transmission power. A base station monitors the RACH to detect the preamble and sends an acquisition indicator (AI) to the WTRU when a signature is detected on the RACH. When receiving a positive acknowledgement, the WTRU sends a message part to the base station. If receiving a negative acknowledgement or no response, the WTRU retransmits the preamble.