OFDM Sub-carrier Allocation for Interference Avoidance
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Solution Overview
Problem
Wireless broadband communications systems operating in shared frequency bands face reliability issues due to noise and interference, as existing adaptive modulation techniques adjust based on average signal quality across the entire band, leading to reduced data rates or unusable frequency bands even when only portions are affected.
Innovation Solution
A wireless broadband communications system using orthogonal frequency division modulation (OFDM) identifies and allocates data to sub-carriers experiencing the lowest interference levels, reducing data rate and sub-carrier number only where necessary, and reallocating data to unused or less affected sub-carriers based on vector error measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adaptive modulation techniques adjust coding rate and modulation mode based on average signal quality over the entire operating frequency band, then system reliability is improved, but data transmission rate deteriorates when only portions of the band are affected by interference
Solution Approach 1:
The patent segments the operating frequency band into multiple sub-bands and evaluates signal quality independently for each sub-band rather than using a single average quality metric for the entire band. This allows the system to identify which specific portions are affected by interference and which remain clean, enabling selective adaptation of modulation and coding parameters per sub-band to maintain high data rates in unaffected regions while ensuring reliability in interfered regions.
Solution Approach 2:
The patent applies local quality assessment by measuring signal quality metrics (such as signal-to-interference-plus-noise ratio) separately for different frequency sub-bands or resource blocks. This local evaluation enables the system to assign different modulation and coding schemes to different portions of the spectrum based on their individual quality conditions, rather than applying a uniform scheme based on average quality, thereby preserving high data rates in clean sub-bands while maintaining reliability in interfered sub-bands.
2Adaptability or versatility
If wireless communications systems operate in shared frequency bands to avoid licensing fees, then cost and spectrum efficiency are improved, but reliability deteriorates due to increased noise and interference from multiple systems
Solution Approach 1:
The patent implements dynamic adaptation of transmission parameters based on real-time or near-real-time measurements of signal quality in each sub-band. The system continuously monitors interference conditions and adjusts modulation order, coding rate, and resource allocation dynamically to respond to changing interference patterns in shared bands, allowing reliable communication even when other systems are actively transmitting in the same frequency band.
Solution Approach 2:
The patent changes transmission parameters (modulation scheme, coding rate, sub-band allocation) based on measured signal quality conditions in different frequency portions. When interference is detected in certain sub-bands, the system changes parameters for those specific sub-bands (e.g., using more robust modulation and lower coding rates) while maintaining optimal parameters in clean sub-bands, thereby maintaining reliability across the entire shared band environment.
Data Source
AI summary
A wireless broadband communications system that provides increased reliability in environments in which portions of the available operating frequency band are subject to interference. The system determines whether the operating frequency band is being subjected to interference. If so, then the system determines whether such interference is affecting one or more portions of the band. If interference is affecting just portions of the band, then the system reduces the data rate and the number of sub-carriers used to transmit data. Next, the system allocates the data to be transmitted to the sub-carriers currently being subjected to the lowest levels of interference, while allocating no data to the sub-carriers currently being subjected to the highest levels of interference. In this way, the system allocates the data to be transmitted to the sub-carriers occupying optimal portions of the operating frequency band, in response to detected changes in the interference environment.