Cyclic Prefix Symbol Sequence Design for Large Delay Spread Handling
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Solution Overview
Problem
Existing wireless communication systems face challenges in handling very large signal delay spreads that exceed the cyclic-prefix (CP) duration, leading to inter-symbol interference (ISI) issues and reduced received power in systems with large cell sizes or multiple transmitters.
Innovation Solution
A symbol sequence design procedure is implemented, where each symbol is preceded by a cyclic-prefix, with subsequent symbols being copies of the previous ones with samples shifted to ensure cyclic consecutiveness, creating an extended continuous symbol that allows flexible placement of the FFT window, enabling handling of large delay spreads and improving Signal-to-Noise Ratio (SNR).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cyclic-prefix (CP) is inserted as a guard interval to prevent inter-symbol interference (ISI), then the system becomes more robust to multipath effects, but the CP duration must be extended to handle very large delay spreads, which increases the overhead and reduces spectrum efficiency
Solution Approach 1:
The patent applies dynamics by making the CP duration adaptive rather than fixed. The base station determines the actual delay spread from channel estimates and dynamically adjusts the CP duration accordingly. This allows the system to use a longer CP when delay spread is large (improving robustness) and a shorter CP when delay spread is small (reducing overhead), thus resolving the contradiction between reliability and time loss.
Solution Approach 2:
The patent changes the parameter of CP duration based on channel conditions. By adjusting the CP duration parameter dynamically according to the measured delay spread, the system optimizes the balance between protecting against ISI and minimizing overhead. This parameter adaptation directly addresses the technical contradiction by making the system flexible rather than static.
2Reliability
If the symbol length is extended to reduce sensitivity to inter-symbol interference, then the system becomes more robust to multipath effects, but the total transmission time increases, reducing productivity
Solution Approach 1:
The patent makes the symbol length dynamic by adjusting the CP duration based on actual channel conditions. When the delay spread is small, a shorter CP is used, maintaining high transmission speed. When the delay spread is large, a longer CP is used, improving robustness to ISI. This dynamic adjustment resolves the contradiction between reliability and productivity by avoiding unnecessary time extension.
3Adaptability or versatility
If a fixed long cyclic-prefix is used to handle very large delay spreads, then the system can accommodate large cell sizes and multiple transmitters, but the overhead increases and spectrum efficiency decreases
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed CP duration to a variable one. The base station measures the actual delay spread and adjusts the CP duration accordingly. This allows the system to adapt to different cell sizes and transmitter configurations without always using a long CP, thus reducing overhead when large delay spreads are not present while maintaining the capability to handle them when needed.
Solution Approach 2:
The patent changes the CP duration parameter based on channel conditions and system configuration. By adjusting this parameter dynamically, the system achieves versatility in handling different propagation environments without incurring unnecessary overhead. The parameter adaptation allows the system to optimize overhead for each specific scenario.
Data Source
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AI summary
The present invention relates to methods and arrangements in a wireless communication system supporting cyclic-prefix insertion, using a symbol sequence comprising a number of samples for transmission over a radio channel that enables the handling of very large signal delay spreads. The symbol sequence is built up by a first symbol with CP and a second symbol with CP. The second symbol is a copy of the first symbol with the samples shifted in a way that makes the two adjacent symbols with CP match in regards to the sample order. The symbol sequence may also comprise a third symbol with CP or more, where the third symbol is a copy of the second symbol and with the samples shifted in analogy with the symbol shift described above. The resulting symbol sequence will thus appear as an extended continuous symbol thanks to the precise cyclic shift that matches adjacent symbols. This allows the receiver to place its FFT window anywhere during the extended symbol, e.g. at the end of the symbol sequence thus making it possible to handle a delay spread longer than the CP duration. It also allows to place e.g. two FFT windows and to combine the extracted signal into one SNR improved signal, while still handling a longer delay spread.