Tone Pair Selection for OFDM IQ Imbalance Mitigation
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Solution Overview
Problem
In OFDMA systems, IQ imbalance causes interference due to image tones, leading to reduced signal reliability and quality, especially in ad hoc networks without centralized control, where interference from nearby devices can overwhelm intended signals.
Innovation Solution
Devices select tone pairs that include both the intended tone and its image tone for transmission, ensuring equal path loss and controlled transmission power, thereby mitigating interference and maintaining signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If devices transmit on arbitrary tones independently, then transmission flexibility is improved, but interference from image tones increases
Solution Approach 1:
The patent combines the selection of a tone and its image tone into a single tone pair unit. Devices must select both tones together as a pair, merging what were previously independent selection decisions. This ensures that when one tone is used for transmission, its image tone is also controlled by the same device, preventing uncontrolled interference to other devices.
Solution Approach 2:
The frequency spectrum is segmented into tone pairs, where each pair consists of a tone and its image tone. This segmentation creates discrete units of frequency resources that can be allocated and managed systematically. By dividing the spectrum into these paired units, the system can control interference at the pair level while maintaining flexibility in resource allocation.
2Object-affected harmful factors
If centralized control is implemented to manage tone assignments, then interference mitigation is improved, but system complexity increases
Solution Approach 1:
The patent enables devices to autonomously select and manage tone pairs for transmission without requiring centralized coordination. Each device independently determines which tone pairs to use based on its transmission needs, and the paired structure inherently prevents interference. This self-service approach eliminates the need for complex centralized control mechanisms while maintaining interference mitigation.
3Productivity
If image tone frequencies are assigned to different devices, then frequency resource utilization is improved, but signal reliability deteriorates
Solution Approach 1:
The patent merges the control of a tone and its image tone into a single tone pair unit that must be allocated together to the same device. This merging ensures that when one tone carries a signal, its image tone does not create interference for another device using the paired frequency. The combined allocation maintains both high resource utilization and signal reliability by preventing cross-device interference.
Data Source
AI summary
Methods and apparatus for determining, e.g., selecting, communications resources, e.g., tones, to use in a communications system are described. The methods are well suited for use in Orthogonal Frequency Division Multiplexing (OFDM) systems. Devices seeking to transmit information select tones in pairs for use in transmitting the information. Each tone pair includes a tone and the corresponding image tone. By restricting a communications device to select communications frequencies in pairs, the problem of interference and reduced dynamic range at a receiver due to IQ imbalance is reduced, as compared to the case where devices may use a tone independent of the corresponding image tone for transmission purposes, since the path loss from the transmitter to the receiver is likely to be the same for both tones and the transmission power level is controlled by an individual device using both of the tones.