Terminal Random Access in Carrier Aggregation
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Solution Overview
Problem
Current LTE systems face inefficiencies in performing random access procedures, particularly in carrier aggregation and unlicensed band usage, which affect the reliability and efficiency of communication between terminal apparatuses and base stations.
Innovation Solution
The implementation of a terminal apparatus and base station communication method that utilizes carrier aggregation, Listen-Before-Talk (LBT) techniques, and adaptive transmit power control for the Physical Random Access Channel (PRACH), allowing for efficient random access procedures across multiple serving cells, including Licensed Assisted Access (LAA) cells, by managing transmission power and channel assessment to optimize access in both licensed and unlicensed bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If carrier aggregation is used to enable simultaneous transmission and reception in multiple serving cells, then communication capacity and efficiency are improved, but system complexity and interference management difficulty increase
Solution Approach 1:
The patent segments the carrier aggregation system into distinct functional components: separate random access procedure management for each serving cell, independent transmit power control for each cell, and differentiated LBT operation for licensed and unlicensed cells. This segmentation allows complex carrier aggregation to be managed through modular, cell-level operations rather than system-wide complexity.
Solution Approach 2:
The patent creates a universal random access procedure that works across both licensed and unlicensed cells within the carrier aggregation framework. The terminal apparatus applies the same fundamental random access mechanism (preamble transmission, response reception, contention resolution) uniformly across all serving cells, while the base station apparatus provides unified power control and LBT management. This multi-functionality approach allows the system to handle diverse cell types through a single standardized procedure.
2Reliability
If LBT techniques are implemented for unlicensed band usage, then interference reduction and fair spectrum access are improved, but access delay and procedure complexity increase
Solution Approach 1:
The patent implements preliminary LBT channel assessment actions before actual random access preamble transmission on unlicensed cells. The terminal apparatus performs clear channel assessment (CCA) and listens before talking (LBT) procedures in advance to determine channel availability. This preliminary action ensures that when the terminal gains channel access, interference is minimized and fair spectrum sharing is achieved, while the advance preparation reduces the likelihood of transmission failures that would cause retransmission delays.
Solution Approach 2:
The patent introduces dynamic adaptability in the random access procedure by allowing the terminal apparatus to adjust its behavior based on LBT outcomes and channel conditions. When LBT succeeds, the terminal proceeds with preamble transmission; when it fails, the terminal can retry after a backoff period or switch to alternative cells. This dynamic approach optimizes the balance between interference management (through LBT) and access delay (through adaptive retry strategies).
3Reliability
If adaptive transmit power control is applied for PRACH transmission, then access reliability and interference management are improved, but power control complexity and signaling overhead increase
Solution Approach 1:
The patent implements adaptive transmit power control by dynamically changing the PRACH transmit power parameter based on measured downlink path loss and base station feedback. The terminal apparatus calculates path loss from reference signals, applies power control adjustments, and transmits preambles at optimized power levels. This parameter adaptation ensures reliable access by compensating for channel variations while managing uplink interference, with the base station providing necessary power control parameters through standard signaling mechanisms.
Data Source
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AI summary
A terminal apparatus capable of efficiently performing a random access procedure is a terminal apparatus that communicates with a base station apparatus by using multiple serving cells including a primary cell and one or multiple secondary cells, and includes a medium access control layer processing unit (15) for starting a random access procedure in any one of the multiple serving cells based on a PDCCH order, a transmitter (10) for transmitting a random access preamble in any one of the multiple serving cells, and a receiver (10) for receiving a random access response, in which the medium access control layer processing unit (15), in a case that reception of the random access response is considered not successful, determines whether to automatically resume transmission of the random access preamble or not, at least based on which of the primary cell and the secondary cell is used to transmit the random access preamble.