Non-orthogonal SSB Superposition for 5G NR Initial Acquisition
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Solution Overview
Problem
The extension of time for initial acquisition in 5G New Radio (NR) systems due to beamforming is problematic, as it slows down the process of connecting user equipment (UE) with the radio access network, especially with the introduction of additional search dimensions and increased complexity in detecting synchronization signal blocks (SSBs).
Innovation Solution
The use of time-and-frequency overlapped non-orthogonal SSBs, where multiple antenna panels of the gNB concurrently steer and superpose SSBs, allowing the UE to measure multiple TX beams simultaneously without central frequency re-tuning, and the introduction of a tertiary synchronization signal to facilitate beam index-dependent measurement, along with successive interference cancellation (SIC) algorithms to separate colliding PBCH signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If beamforming is used in 5G NR systems, then connectivity and data rate are improved, but initial acquisition time is extended
Solution Approach 1:
The patent merges multiple SSB transmissions by superposing them in the time-frequency domain. Multiple antenna panels transmit SSBs simultaneously, and the gNB combines these signals into a composite SSB that contains information from multiple beams, allowing the UE to receive multiple beam signals at once rather than sequentially.
Solution Approach 2:
The patent introduces a new dimension for beam differentiation by using beam index modulation in the PBCH signal. Instead of only using time-division multiplexing, the system adds beam index information as an additional dimension that can be detected by the UE to identify which beam transmitted the signal, enabling faster beam identification without sequential scanning.
2Adaptability or versatility
If multiple SSBs are transmitted sequentially for beam sweeping, then beam measurement coverage is improved, but acquisition time is extended
Solution Approach 1:
The patent combines multiple SSB signals from different antenna panels into a single composite SSB transmission. This merging allows the UE to receive and measure signals from multiple beams simultaneously through a single acquisition process, maintaining comprehensive beam coverage while dramatically reducing the time required compared to sequential transmission.
Solution Approach 2:
The patent enables continuous measurement of multiple beams by transmitting them simultaneously in the time-frequency domain. The UE can continuously process the composite signal to measure all beam directions at once, rather than having to pause between sequential beam transmissions, thus maintaining continuous useful action throughout the acquisition process.
3Difficulty of detecting and measuring
If orthogonal SSBs are used for beam sweeping, then signal detection is simplified, but time-and-frequency resources are consumed sequentially
Solution Approach 1:
Instead of using orthogonal signals that are mutually exclusive in time-frequency domain, the patent inverts the approach by using non-orthogonal signals that overlap in time and frequency. The SSBs from different beams are superposed rather than separated, allowing simultaneous transmission and measurement while using interference cancellation techniques to resolve the overlapping signals.
Solution Approach 2:
The patent introduces an intermediary processing step at the gNB side using successive interference cancellation (SIC). The gNB receives the composite SSB signal containing multiple overlapping beams, processes it through SIC algorithms to separate and identify individual beam contributions, and then transmits the processed information to the UE, facilitating detection of non-orthogonal signals.
4Productivity
If non-orthogonal SSBs are transmitted concurrently, then acquisition speed is improved, but signal separation complexity increases
Solution Approach 1:
The patent introduces an intermediary processing layer at the gNB using SIC algorithms. The gNB receives the composite non-orthogonal SSB signal, applies SIC processing to separate the overlapping beam signals, and then transmits the separated information to the UE. This intermediary processing reduces the complexity at the UE side, as the gNB handles the complex separation task centrally.
Solution Approach 2:
The patent changes the parameter of signal orthogonality from orthogonal to non-orthogonal, allowing time-frequency overlap. To manage the resulting complexity, the system uses beam index modulation in PBCH as an additional parameter that directly indicates which beam transmitted the signal, providing a simple decoding mechanism at the UE side that compensates for the non-orthogonal transmission.
Data Source
AI summary
Systems and methods of initial acquisition in a NR system are described. A UE receives time and frequency superposed SSBs from a gNB. If the PSS and SSS of each SSB is independent of a block index of the SSB, the UE receives an additional reference signal scrambled by a beam index of the SSB and uses the reference signal to discriminate between the SSBs. The reference signal is FDMed within a null-subcarrier region of the SSB or outside of the SSB. If the PSS and SSS of each SSB is scrambled using the block index, the UE separates the PBCH measurements, iteratively identifies a block index associated with a DMRS of the PBCH with the highest L1-RSRP level measurement, decodes and reconstructs the PBCH, and subtracts the reconstructed PBCH from the SSB before transmitting an indication of the PBCH with the highest L1-RSRP level measurement to the gNB.