PRACH Preamble Classification for Weak Uplink Signal Access
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Solution Overview
Problem
In cellular radio systems, user equipment (UE) with weak uplink signals often face difficulties in accessing the network due to RACH coverage problems, leading to failed random access preamble transmissions and subsequent RRC Connection Request messages, as the network cannot effectively combine or correlate these signals.
Innovation Solution
The method involves classifying user equipment based on received signals and providing a specific PRACH preamble scheme for connection setup requests, allowing the network to control the timing of these transmissions and combine subsequent receptions to improve signal strength and probability of successful decoding, including the use of PRACH preamble repetition and TTI bundling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the network uses standard RACH procedures for initial access, then the random access procedure follows the conventional four-step process, but user equipment with weak uplink signals cannot be successfully received due to insufficient signal strength
Solution Approach 1:
The network node performs preliminary classification of user equipment based on received signal strength before the random access procedure begins. UE are divided into different classes (e.g., coverage-limited and non-coverage-limited) based on downlink path loss or uplink signal quality measurements. This preliminary classification enables the network to apply different PRACH preamble schemes tailored to each UE class, ensuring that coverage-limited UE use schemes optimized for their signal conditions, thereby improving the reliability of random access procedures for weak signal devices.
Solution Approach 2:
The invention changes key parameters of the PRACH preamble transmission based on UE class. Coverage-limited UE are assigned different PRACH preamble formats, repetition factors, and timing advance values compared to non-coverage-limited UE. For example, coverage-limited UE may use longer preamble sequences, higher repetition factors, or extended time windows for preamble transmission. These parameter changes adapt the random access procedure to the signal conditions of weak UE, improving their chances of successful access while maintaining standard procedures for other devices.
2Reliability
If the network combines subsequent PRACH preamble receptions to improve signal strength, then the probability of successful decoding increases, but the processing complexity and time required at the network node increases
Solution Approach 1:
The network node prepares combining resources and algorithms in advance for each UE class. When PRACH preambles are received from coverage-limited UE, the network node already has pre-configured combining parameters, correlation templates, and resource allocations ready. This preliminary preparation allows the network to quickly perform signal combining and correlation operations without significant processing delays, thus improving decoding success rate while minimizing additional time loss.
Solution Approach 2:
The invention applies signal combining and correlation operations selectively only to PRACH preambles from coverage-limited UE, not to all UE. The network node identifies which UE are coverage-limited based on preliminary classification and applies enhanced processing only to their preambles. This localized application of complex processing reduces overall system overhead and time loss, as non-coverage-limited UE continue to use standard processing paths without additional delays.
3Adaptability or versatility
If the network provides class-specific PRACH preamble schemes to different user equipment, then the ability to handle coverage-limited UE improves, but the signaling overhead and system complexity increases
Solution Approach 1:
The invention segments the UE population into distinct classes (e.g., coverage-limited and non-coverage-limited) based on signal strength measurements. Each class is assigned a specific PRACH preamble scheme with tailored parameters. This segmentation allows the network to manage complexity by handling each class separately with dedicated processing paths, rather than attempting to optimize for all possible signal conditions simultaneously. The segmentation approach improves adaptability while controlling system complexity through modular, class-based management.
Solution Approach 2:
The network node implements a universal classification and routing mechanism that handles both coverage-limited and non-coverage-limited UE through a single integrated system. The same network node infrastructure processes all UE, automatically classifying them and routing to appropriate PRACH preamble schemes without requiring separate dedicated systems. This multi-functional approach provides adaptability for different coverage conditions while avoiding the complexity of multiple independent processing systems.
4Area of stationary object
If the network extends RACH coverage by combining signals and using TTI bundling, then coverage-limited UE can successfully access the network, but additional delay is introduced for these users
Solution Approach 1:
The invention implements periodic or repeated PRACH preamble transmissions for coverage-limited UE, where the UE transmits the same or different preambles in multiple time windows. The network node combines these periodic transmissions to improve signal strength. By spacing these transmissions appropriately and using efficient combining algorithms, the system extends coverage to areas where single transmissions would fail, while managing the additional delay through optimized repetition intervals and early termination when successful detection occurs.
Data Source
AI summary
Embodiments of the present disclosure generally relate to handling of connection setups. More particularly, they relate to a method performed in a UE (4) for requesting a connection set up with a network node (2). The UE (4) receives a signal comprising a set of classifying parameters and based on these parameters determines at least one class to which it belongs to. The UE (4) also receives a PRACH preamble scheme associated with said class to be used by the UE (4) during a connection setup request. The method further controls the timing of transmitting at least one request, signal for requesting a connection setup with the network node (2) according to the received PRACH preamble scheme. Embodiments herein also relate to a method performed in a network node (2), and to a network node (2) and to a UE (4).