Guard Interval Adaptation for Coordinated Beamforming Interference
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Solution Overview
Problem
In coordinated beamforming, synchronization errors among access points lead to interference due to imperfect nulling, which degrades performance, especially with high code rates and modulation orders, and existing methods lack effective interference mitigation.
Innovation Solution
Implementing a method where all access points agree to use larger guard intervals and signal two guard intervals to receiving stations, allowing for more relaxed synchronization requirements and the use of a cyclic postfix in addition to the cyclic prefix to mitigate interference from transients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If larger guard intervals are used to mitigate interference from transients in coordinated beamforming, then interference reduction is improved, but overhead increases
Solution Approach 1:
The guard interval is segmented into two distinct parts: a first guard interval (cyclic prefix) and a second guard interval (cyclic postfix). The first guard interval handles conventional intersymbol interference, while the second guard interval specifically addresses interference from transients caused by synchronization errors in coordinated beamforming. This segmentation allows targeted protection against different types of interference without unnecessarily extending the total guard interval duration.
Solution Approach 2:
The second guard interval (cyclic postfix) is appended in advance to the OFDM symbol before transmission. This preliminary action prepares the signal to tolerate synchronization errors and transient interference that occur during coordinated beamforming operations, ensuring that receiving stations can properly synchronize and decode signals even when access points are not perfectly synchronized.
2Productivity
If coordinated beamforming is implemented with high code rates and modulation orders, then spectral efficiency is improved, but susceptibility to synchronization errors increases
Solution Approach 1:
The patent applies beforehand cushioning by adding a second guard interval (cyclic postfix) to OFDM symbols transmitted in coordinated beamforming systems. This cushioning measure is implemented in advance to protect against synchronization errors that occur during transmission. The extended guard interval absorbs the impact of timing misalignment between access points, allowing high-order modulation and coding schemes to operate reliably without being overly sensitive to synchronization inaccuracies.
3Reliability
If guard intervals are extended to accommodate time dispersion, then channel robustness is improved, but transmission efficiency decreases
Solution Approach 1:
The patent applies local quality by making different parts of the guard interval structure serve different functions. The first guard interval (cyclic prefix) handles conventional time dispersion and intersymbol interference, while the second guard interval (cyclic postfix) specifically addresses transient interference from synchronization errors. This localized functional differentiation allows the system to achieve robustness against multiple types of channel impairments without uniformly extending the guard interval duration, thereby maintaining transmission efficiency.
Data Source
AI summary
A method of transmitting an Orthogonal Frequency Division Multiplexing, OFDM, symbol having a guard interval including a cyclically repeated part of an original symbol comprises applying a guard interval for the OFDM symbol, the guard interval including a first part, where the first part is a cyclic prefix, including an indication whether the applied guard interval has a second part, wherein the second part is a cyclic prefix and/or postfix, applying, when indicated to be present, the second part of the guard interval, and transmitting the OFDM symbol. A method of receiving the symbol, transmitter, receiver and computer programs for implementing the methods are also disclosed.