OFDM Subcarrier Subset Selection for Information Capacity
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Solution Overview
Problem
Existing OFDM systems face limitations in increasing the quantity of information transmitted without increasing the number of subcarriers, and the additional information is often affected by transmission channel imperfections.
Innovation Solution
A method that selectively generates N-P subcarriers from a predetermined set of N mutually orthogonal frequencies, where P is chosen within a specific interval to maximize information transmission, allowing unused subcarriers to encode additional information and improve spectral efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If the number of subcarriers is increased to transport more information, then the quantity of information transmitted is improved, but the device complexity and channel limitations worsen
Solution Approach 1:
The patent introduces a new dimension for information encoding by using the selection of subcarrier subsets itself as an information-carrying mechanism. Instead of only modulating data on available subcarriers, the system encodes additional information in the choice of which subcarriers to activate (N-P subcarriers out of N total), effectively adding a combinatorial dimension to the information transmission capacity.
Solution Approach 2:
The patent changes the parameter P (number of deactivated subcarriers) within a specific interval [Pmax-N/5, Pmax+N/5] to optimize the balance between conventional information transmission on active subcarriers and additional information transmission through subset selection. This parameter optimization allows maximizing the total information capacity without increasing the total number of subcarriers N.
2Productivity
If additional information is encoded through subcarrier selection, then the spectral efficiency is improved, but the reliability under channel imperfections worsens
Solution Approach 1:
The patent performs preliminary optimization by determining the optimal number P of deactivated subcarriers before transmission, based on the digamma function relationship with the modulation scheme parameter B. This pre-calculated optimal point Pmax and its interval ensures that the system is pre-configured for maximum information capacity while maintaining robustness against channel variations.
Solution Approach 2:
The system uses feedback about the transmission channel conditions and performance to adjust the operating point within the optimal interval. The receiver can feed back information about channel quality, allowing the transmitter to adapt the subset selection strategy and maintain reliability while achieving high spectral efficiency.
Data Source
AI summary
The invention concerns a method for encoding data in an OFDM signal intended to be transmitted in a communication channel and formed from a predefined set of N mutually orthogonal frequencies, the OFDM signal comprising a plurality of subcarriers transporting data modulated according to a predefined modulation scheme, each subcarrier having a unique frequency chosen from the predefined set of frequencies, the method being characterised in that it comprises the steps of selecting a subset of N-P frequencies from the predefined set, from a symbol belonging to a set of transmittable symbols, each transmittable symbol being encoded by a unique subset of frequencies, and of selectively generating N-P subcarriers corresponding to the selected subset of N-P frequencies, in which the number P is chosen from the interval (Formula (I)), Pmax being the solution to the equation Ψ(Ν - P + 1) - Ψ(Ρ + 1) = B log2 2, in which Ψ is the digamma function, and B the number of bits per modulated symbol on each subcarrier, by means of the predefined modulation scheme.