NR-U PRACH Interlaced Allocation for OCB-Compliant Multiplexing
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Solution Overview
Problem
NR-U PRACH waveforms face challenges in resource allocation that comply with unlicensed spectrum requirements while maintaining multiplexing capability and avoiding interference with neighboring channels having different subcarrier spacings.
Innovation Solution
Implementing tone-interlaced frequency-division multiplexing (T-IFDM) within block-interlaced frequency-division multiplexing (B-IFDM) to allocate PRACH preambles, ensuring compliance with OCB and PSD regulations and reducing interference through guard bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If interlaced waveform design is used to allocate PRACH frequency resources distributed within NCB, then compliance with OCB requirement is achieved, but resource allocation compatibility with interlaced-based NR PUSCH/PUCCH becomes complex when different SCS are used
Solution Approach 1:
The frequency resources for PRACH are segmented into multiple interlaces, where each interlace contains a subset of resource blocks distributed across the bandwidth. This segmentation allows the system to maintain OCB compliance while providing flexible allocation patterns that can accommodate different SCS values without requiring complex guard band calculations between neighboring channels.
Solution Approach 2:
The invention changes the allocation parameters by defining PRACH resources in terms of interlace indices and resource block offsets rather than contiguous blocks. This parameter transformation enables the same interlaced structure to support multiple SCS values (15kHz, 30kHz, 60kHz) by simply adjusting the resource block indexing, eliminating the need for complex guard band management between different SCS channels.
2Object-affected harmful factors
If guard bands are reserved between PUSCH/PUCCH and PRACH interlaces to avoid interference with different SCS, then interference is reduced, but overhead increases and multiplexing capability is reduced
Solution Approach 1:
The interlaced resource allocation structure serves multiple functions simultaneously: it provides frequency diversity for OCB compliance, enables support for multiple SCS values, and allows flexible multiplexing of different channel types (PUSCH, PUCCH, PRACH) without requiring dedicated guard bands. The same interlace framework that ensures spectral compliance also naturally prevents interference through its distributed structure.
Solution Approach 2:
The invention extracts the guard band requirement from the resource allocation design by using the inherent distributed nature of interlaced allocation. Instead of adding separate guard band resources, the system takes out the need for explicit protection by designing PRACH interlaces that are naturally separated from PUSCH/PUCCH interlaces through the interlacing pattern itself, thereby eliminating overhead while maintaining interference protection.
3Ease of manufacture
If contiguous frequency resources are allocated for PRACH, then resource allocation is simple, but transmit power is limited under PSD constraint which decreases cell coverage
Solution Approach 1:
The frequency resources are segmented into multiple distributed resource blocks across the bandwidth according to the interlaced structure. This segmentation allows the system to allocate PRACH power across multiple frequency points, thereby increasing total transmit power while maintaining PSD compliance at each individual resource block, ultimately extending cell coverage without complicating the allocation process.
Data Source
Figure 1A~1B
Figure 2A
Figure 2B
AI summary
Devices, methods and computer programs for saving frequency resources in wireless communications are disclosed. The invention allows using less frequency resources for a PRACH preamble transmission in a B-IFDM allocation of multiple user channels while still maintaining the same zero-autocorrelation zone for the PRACH preambles as that in prior art and thus similar timing estimation capability. Accordingly, transmission of PRACH preambles fulfilling regulatory requirements in unlicensed spectrum is enabled while multiplexing with other channels and preserving the ZAZ is possible.