Uplink Scheduling Request Block Spreading for High Doppler
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current uplink scheduling request mechanisms in LTE networks face challenges in supporting high UE velocities, leading to performance degradation due to inter-code interference, especially at speeds above 360 km/h, where the existing on-off keying-based SR mechanism fails to maintain sufficient multiplexing capacity and orthogonality.
Innovation Solution
The solution involves modifying the scheduling request scheme by changing the spreading factor of block spreading to an even number, utilizing partial orthogonality properties of CAZAC sequences, and implementing sequence splitting to reduce inter-code interference, allowing for improved resistance against Doppler effects without additional signaling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the spreading factor of block spreading is maximized to maximize multiplexing capacity with CAZAC sequence modulation, then the number of simultaneous UEs is supported, but inter-code interference increases at high UE velocities causing performance degradation
Solution Approach 1:
The patent changes the spreading factor from an odd number (7) to an even number (6), which fundamentally alters the orthogonality properties of the spreading codes. This parameter change enables the system to maintain orthogonality at high Doppler frequencies while supporting high multiplexing capacity, resolving the contradiction between quantity of UEs and inter-code interference.
2Loss of energy
If the on-off keying-based SR mechanism is used for high speed UEs, then the system overhead is kept small, but the multiplexing capacity is insufficient at speeds above 360 km/h
Solution Approach 1:
The patent introduces dynamic adaptability by enabling the SR mechanism to automatically adjust to high Doppler conditions through the even spreading factor configuration. This allows the system to maintain both low overhead and high multiplexing capacity dynamically, rather than being fixed in performance at high speeds.
3Device complexity
If the existing SR mechanism is used without modification, then the implementation is simple, but performance degrades at high UE velocities due to loss of orthogonality
Solution Approach 1:
The patent applies a simple parameter change (spreading factor from 7 to 6) that maintains implementation simplicity while dramatically improving reliability at high velocities. This minimal modification preserves orthogonality properties without complicating the overall system architecture.
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
Block spreading generating partial orthogality is applied for the uplink control channel for E-UTRA. For instance, a problem of maximizing the multiplexing capacity leads to numerology causing odd-length sequences which do not have the favorable property of even-length sequences (partial orthogonality). The consequence of this is poor performance in cases of high Doppler effects. Maximal multiplexing capacity is taught without loss of performance at high Doppler by modifying an earlier scheduling request (SR) scheme. The earlier SR multiplexing scheme has a number of parallel SR resources per slot equal to 12*7=84. In one example, the spreading factor of block spreading is changed to an even number, e.g., from 7 to 6. This enables usage of the partial orthogonality properties of CAZAC sequences and as a result inter-code interference in the case of high Doppler is reduced. Other ways to generate partial orthogonality are shown with similar results.