Random Access Preamble Modulation via Interlaced Sequences
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Solution Overview
Problem
In cellular communication systems, random access preambles with large side-lobes in their auto-correlation function lead to increased mis-detection probability and time synchronization errors, while high cross-correlation among preambles results in false detection issues, particularly in unlicensed spectrum where power and bandwidth constraints are stringent.
Innovation Solution
A client device and network access node configuration that determines time-frequency resources for random access preambles using a modulation sequence based on near-orthogonal and constant envelope sequences, ensuring low Peak-to-Average-Power Ratio (PAPR) and suppressing side-lobes, thereby reducing mis-detection and false detection probabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Zadoff-Chu sequences are mapped onto contiguous subcarriers, then ideal auto-correlation properties with Zero-Auto-correlation-Zone are achieved, but the solution does not meet Power Spectral Density requirements in unlicensed spectrum
Solution Approach 1:
The patent segments the contiguous subcarrier mapping into non-contiguous interlaced resource blocks. Instead of mapping the Zadoff-Chu sequence onto a continuous frequency range, the sequence is distributed across multiple separated resource blocks that form an interlaced pattern, thereby reducing peak power spectral density while maintaining overall bandwidth occupation.
Solution Approach 2:
The patent changes the frequency domain parameters by introducing non-contiguous resource block allocation with specific interlacing patterns. The mapping parameters are adjusted to distribute the sequence energy across separated frequency resources, transforming the power spectral density profile to comply with regulatory requirements while preserving detection performance.
2Adaptability or versatility
If the detection window is larger than the Zero-Auto-correlation-Zone, then timing flexibility is improved, but large side-lobes cause increased mis-detection probability and time synchronization errors
Solution Approach 1:
The patent segments the frequency resources into interlaced non-contiguous blocks, which transforms the auto-correlation function to suppress side-lobes. This segmentation in the frequency domain corresponds to a more concentrated correlation peak in the time domain, enabling reliable detection even when the detection window exceeds the original ZAZ length.
Solution Approach 2:
The patent modifies the auto-correlation parameters by changing the frequency mapping structure. The interlaced resource block allocation alters the spectral distribution, which in turn changes the time-domain correlation properties to reduce side-lobe levels, enabling reliable detection with extended windows.
3Productivity
If multiple UEs transmit on the same time-frequency resource, then resource utilization is improved, but high cross-correlation among preambles results in false detection issues
Solution Approach 1:
The patent segments the frequency spectrum into multiple interlaced resource block sets that can be assigned to different UEs. By distributing preambles across these segmented frequency resources with specific interlacing patterns, the system enables multiple UEs to transmit simultaneously while maintaining low cross-correlation through the structured frequency separation.
4Reliability
If PRACH preambles use high transmit power to overcome interference, then detection reliability is improved, but Peak-to-Average-Power Ratio increases requiring larger power backoff
Solution Approach 1:
The patent changes the spectral distribution parameters by implementing interlaced non-contiguous resource block mapping. This parameter change in the frequency domain results in a more uniform power spectral density profile, which reduces the peak-to-average power ratio and allows the power amplifier to operate more efficiently with smaller backoff while maintaining detection reliability.
Data Source
AI summary
The invention relates to a client device (100) and a network access node (300) for transmitting and receiving a random access preamble. The modulation sequence for the random access preamble is based on a first sequence and a second sequence. The first sequence is a sequence from a set of near-orthogonal sequences and the second sequence is a sequence from a set of constant envelope sequences. Due to its construction, the random access preamble herein provides low PAPR and suppresses the side-lobes in its auto-correlation function while producing a set of preambles with low cross-correlation. Furthermore, the invention also relates to corresponding methods and a computer program.