ASK-OFDM Subcarrier Modulation Bandwidth Efficiency
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Solution Overview
Problem
Existing OFDM systems face challenges in implementing M-ary amplitude-shift keying (ASK-OFDM) due to doubled subcarriers requiring twice the time period, and the use of inverse fast cosine transforms limits applications to real-valued systems, excluding complex-valued systems.
Innovation Solution
The proposed method organizes bits into blocks for 2N OFDM subcarriers, performs a 2N-point IFFT to generate time domain samples, and converts these samples into RF band signals, allowing for efficient transmission and reception of ASK-OFDM symbols with conjugate symmetry properties to maintain bandwidth efficiency and support complex systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If M-ASK-OFDM uses doubled subcarriers to achieve equivalent bandwidth efficiency, then bandwidth efficiency is improved, but the time period required doubles to 2T
Solution Approach 1:
The patent segments the time period by transmitting only the first N time domain samples corresponding to the first N frequency domain samples, effectively dividing the full 2N-point transform into two halves. This allows the system to achieve the bandwidth efficiency of doubled subcarriers while reducing the time period from 2T back to T, resolving the contradiction between productivity and duration.
2Ease of manufacture
If inverse fast cosine transform is used for implementation, then real-valued systems are simplified, but complex-valued systems are excluded
Solution Approach 1:
The patent changes the mathematical approach from using inverse fast cosine transform (which requires real-valued inputs) to using inverse fast Fourier transform (which handles complex-valued inputs). This parameter change in the transform type allows the system to maintain implementation efficiency while extending adaptability to support both real-valued and complex-valued OFDM systems.
3Measurement precision
If full 2N-point IFFT is performed to maintain orthogonality, then frequency resolution is improved, but computational complexity increases
Solution Approach 1:
The patent extracts and transmits only the first N time domain samples corresponding to the first N frequency domain samples, effectively taking out half of the full 2N-point transform. This extraction maintains sufficient frequency resolution for the application while reducing the computational complexity from a full 2N-point IFFT to only the first N points, achieving a balance between precision and complexity.
Data Source
AI summary
An OFDM system and method using amplitude shift keying (ASK) for subcarrier modulation is provided. Because ASK is used, the signal of each symbol in time domain is conjugate-symmetric. In addition, among the discrete numbers of each symbol, two of them are always real. These properties are utilized such that only half of the numbers of each symbol sequence are transmitted. The generated baseband signal can be a complex or a real signal. As a result, the bandwidth efficiency of the derived ASK-OFDM is the same as that of QAM-OFDM.