PRACH Preamble Segmentation for Link-Budget-Limited UE Access
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Solution Overview
Problem
Link-budget-limited user equipment (UE) devices face challenges in successfully initiating the random access procedure due to poor reception of the Physical Random Access Channel (PRACH) in wireless communication systems, particularly in areas with poor coverage or with poorly performing antennas.
Innovation Solution
The implementation of enhanced random access procedures for link-budget-limited UE devices, including the use of larger subcarrier spacing and temporal width for PRACH preambles, multiple instances of Zadoff-Chu sequences, and repeated transmissions with specific timing configurations, along with the base station's ability to combine received instances for improved decoding, and the use of special sets of Zadoff-Chu sequences based on measured Doppler shift for frequency diversity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PRACH formats are used by link-budget-limited UE devices, then the device complexity remains low, but the probability of successful decode at the base station deteriorates due to poor reception
Solution Approach 1:
The PRACH preamble is segmented into multiple instances of Zadoff-Chu sequences, where each instance can be independently received and combined at the base station. This segmentation allows the base station to improve decoding reliability by combining multiple received instances, even if individual instances are weak due to poor link budget
Solution Approach 2:
The patent introduces enhanced PRACH formats with larger subcarrier spacing and larger temporal width, adding dimensional enhancements to the traditional PRACH structure. These dimensional changes provide frequency and time diversity, improving the probability of successful decode without significantly increasing device complexity
2Reliability
If multiple instances of Zadoff-Chu sequences are used in PRACH preambles, then the probability of successful decode improves, but the PRACH preamble length increases
Solution Approach 1:
The patent defines multiple enhanced PRACH formats (Format A, B, C, D) with different configurations of subcarrier spacing, temporal width, and number of Zadoff-Chu sequence instances. The base station can dynamically select the appropriate format based on channel conditions and link budget requirements, optimizing the balance between preamble length and decoding reliability
3Reliability
If repeated transmissions of PRACH preamble are performed, then the probability of successful decode improves, but the access time increases
Solution Approach 1:
The base station is configured to expect and combine multiple instances of PRACH preambles within a defined time window. By preparing the combining operation in advance and knowing the expected time arrivals of repeated transmissions, the base station can efficiently process the combined signal without extending the overall random access procedure time
4Reliability
If larger subcarrier spacing and temporal width are used for PRACH preambles, then the probability of successful decode improves, but the frequency resources consumed increase
Solution Approach 1:
The patent modifies key parameters of the PRACH preamble including subcarrier spacing, temporal width, and the number of Zadoff-Chu sequence instances. These parameter changes allow the system to adapt to different link budget conditions, providing improved decoding reliability for link-budget-limited devices while managing frequency resource consumption through configurable format selection
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly increases the probability of successful decode of PRACH preambles and random access procedures for link-budget-limited UE devices, ensuring reliable communication even in challenging coverage areas.
Implementation Method 1
The base station may combine two or more received instances of the PRACH preamble, to increase probability of successful decode
Implementation Method 2
the use of special sets of Zadoff-Chu sequences based on measured Doppler shift for frequency diversity
Data Source
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AI summary
Enhanced random access procedures for link-budget-limited user equipment (UE) devices are disclosed. A user equipment device may transmit a first message containing a Physical Random Access Channel (PRACH). The PRACH contains instances of a Zadoff-Chu sequence, and may be transmitted repeatedly as part of a single random attempt, to facilitate correlation data combining at the base station. The available Zadoff-Chu sequences may be partitioned among a plurality of sets, each set being associated with a respective Doppler shift range (or frequency hop pattern or time repetition pattern). A UE device may signal Doppler shift (or other information) to the base station by selection of one of the sets. The first PRACH transmission and the following PRACH transmission may occur in consecutive subframes. A UE device may select from a special set of Zadoff-Chu sequences (different from a conventional set of sequences), to signal its status as a link-budget-limited device.