Dynamic Cyclic Prefix Configuration for 5G OFDM Delay Spread
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Solution Overview
Problem
In 5G cellular networks using Orthogonal Frequency Division Multiplexing (OFDM), the fixed cyclic prefix (CP) settings in LTE are inadequate for higher frequency bands, leading to inefficiencies in spectral usage and interference issues due to variable delay spreads, especially in environments with multiple base station signals.
Innovation Solution
A method where the User Equipment (UE) determines the delay spread from received transmission symbols and adjusts the cyclic prefix accordingly for both downlink and uplink transmissions, using techniques like channel estimation and SINR measurement to optimize CP length for improved link performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a fixed cyclic prefix length is used as in LTE, then implementation is simple, but spectral efficiency deteriorates at higher frequencies due to variable delay spreads
Solution Approach 1:
The patent implements dynamic cyclic prefix configuration where the base station determines delay spread for each user equipment and configures appropriate CP lengths (first CP length for delay spread ≤ threshold, second CP length for delay spread > threshold). This dynamic adaptation to channel conditions resolves the contradiction by making the system flexible enough to maintain high spectral efficiency at higher frequencies while keeping the implementation manageable through automated delay spread estimation and configuration.
2Reliability
If the cyclic prefix is extended to cover larger delay spreads, then interference is reduced, but overhead increases and spectral efficiency decreases
Solution Approach 1:
The patent applies local quality by configuring different cyclic prefix lengths for different user equipments based on their specific delay spread characteristics. Users with small delay spreads receive shorter CP configurations (first CP length) for high spectral efficiency, while users with large delay spreads receive longer CP configurations (second CP length) for reliable interference mitigation. This localized adaptation resolves the contradiction by optimizing CP length for each user's specific channel conditions rather than using a uniform configuration.
Solution Approach 2:
The patent changes the cyclic prefix length parameter dynamically based on measured delay spread values. The base station estimates delay spread for each UE and selects between at least two different CP length configurations, changing the CP parameter from a fixed value to a variable that adapts to channel conditions. This parameter change approach resolves the contradiction by allowing the system to use shorter CPs when possible (high spectral efficiency) and longer CPs only when necessary (interference mitigation).
3Productivity
If channel estimation is performed to determine delay spread for each user, then spectral efficiency is improved through adaptive CP configuration, but device complexity increases
Solution Approach 1:
The patent implements self-service by having the base station autonomously perform delay spread estimation using channel estimation techniques and automatically configure appropriate cyclic prefix lengths for each user equipment without requiring manual intervention or complex external processing. The base station uses existing channel estimation capabilities to determine delay spread and selects CP configurations based on predetermined thresholds. This self-service approach resolves the contradiction by making the adaptive CP configuration process automated and integrated into existing base station functions, improving spectral efficiency while managing complexity through automation rather than external complexity.
Data Source
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AI summary
A cyclic prefix is configured for transmissions on a cellular network using a Radio Access Technology based on Orthogonal Frequency Division Multiplexing (OFDM). At a User Equipment (UE) of the cellular network, information is determined for calculating a delay spread for transmission symbols from a base station of the cellular network to the UE. A cyclic prefix for the transmissions is identified based on the determined information. A delay spread can be established from received transmission symbols by: determining a coherence bandwidth based on whether a channel coefficient for each of the transmission symbols varies more than a predefined threshold, the delay spread being established using the determined coherence bandwidth; and/or determining a relationship between a cyclic prefix associated with the transmission symbols and a signal-to-interference-plus-noise ratio, SINR, for the received transmission symbols, the delay spread being established using the determined relationship.