OFDM Bit and Power Loading for Throughput Precision
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Solution Overview
Problem
Orthogonal frequency division multiplexing (OFDM) systems typically use coarse throughput increments in response to signal-to-noise ratio changes, limiting the ability to achieve higher modulation rates without increasing redundancy, while maintaining a fixed bit error rate for multiple subcarriers.
Innovation Solution
Implementing a bit and power loading algorithm based on channel state information, combined with trellis coded modulation, to dynamically adjust subcarrier powers and rates, allowing for finer throughput adjustments without additional redundancy, and optimizing for a fixed bit error rate across varying signal-to-noise ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If coarse throughput increments (6 dB increments) are used in OFDM systems, then system complexity is reduced and ease of operation is improved, but throughput precision and adaptability to varying signal-to-noise ratios deteriorate
Solution Approach 1:
The patent divides the single OFDM stream into multiple parallel substreams, each processed independently with its own modulation and coding scheme. This segmentation allows each substream to be optimized for specific signal-to-noise ratio conditions, enabling finer throughput control without increasing overall system complexity
Solution Approach 2:
The system dynamically adjusts the number of active substreams and their respective modulation orders based on real-time signal-to-noise ratio measurements. This dynamic adaptation enables continuous throughput adjustment rather than coarse discrete steps, resolving the contradiction between operational simplicity and throughput precision
2Productivity
If higher modulation rates are used to increase throughput, then productivity is improved, but bit error rate increases unless additional redundancy is added
Solution Approach 1:
Different substreams are assigned different modulation orders and coding rates based on their individual channel conditions. Substreams experiencing better signal-to-noise ratio use higher modulation rates for maximum throughput, while substreams in poorer conditions use more robust modulation with higher redundancy, maintaining overall bit error rate performance
Solution Approach 2:
The system changes multiple parameters simultaneously - modulation order, coding rate, and number of active substreams - to optimize the throughput-reliability tradeoff. By adjusting these parameters based on signal-to-noise ratio, the system achieves higher productivity without sacrificing reliability
3Reliability
If additional redundancy is added to maintain fixed bit error rate at higher modulation rates, then reliability is improved, but device complexity and loss of information increase
Solution Approach 1:
Instead of adding redundancy to a single high-rate stream, the system segments the data into multiple substreams with different redundancy levels. This allows redundancy to be applied selectively only where needed, reducing overall system complexity compared to uniform redundancy across all data
4Reliability
If additional redundancy is added to maintain fixed bit error rate, then reliability is improved, but throughput decreases due to loss of information
Solution Approach 1:
Redundancy is applied locally to specific substreams based on their channel conditions rather than uniformly to all data. Substreams in good conditions use minimal redundancy for maximum throughput, while substreams in poor conditions use higher redundancy to maintain reliability, optimizing the overall throughput-reliability tradeoff
Data Source
AI summary
Briefly, in accordance with one embodiment of the invention, bit and power loading may be utilized to select a modulation rate and subcarrier power scaling based on channel state information. As a result, a higher data rate may be utilized for a given signal-to-noise ratio while maintaining a constant bit error rate.