OFDM Transmitter Time-Multiplexing IFFT FFT Chip Area
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Solution Overview
Problem
OFDM signals for IM/DD optical transmission systems are complex and bipolar, requiring Hermitian symmetry to convert to real and positive signals, which doubles the size of IFFT and FFT components, increasing chip area and power consumption.
Innovation Solution
An OFDM transmission circuit that generates a complex time-varying digital signal with real and imaginary components, time-multiplexes these components, and uses a digital to analog converter to produce a positive OFDM signal for transmission, avoiding the need for Hermitian symmetry, thus reducing the size and power requirements of the IFFT and FFT modules.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Hermitian symmetry is applied to convert complex bipolar OFDM signals to real positive signals, then the signal becomes suitable for IM/DD optical transmission, but the size of IFFT and FFT components doubles, increasing chip area and power consumption
Solution Approach 1:
The patent segments the complex bipolar signal into separate real and imaginary components, processes them independently through parallel IFFT/FFT operations, and then recombines them. This allows using smaller N-point transforms instead of a single 2N-point transform, reducing the required chip area while maintaining signal integrity for IM/DD transmission
Solution Approach 2:
The patent merges the processing of real and imaginary components by combining parallel IFFT outputs and FFT inputs. By time-multiplexing and combining these components appropriately, the system achieves the equivalent of Hermitian symmetry processing but with smaller, more area-efficient transform blocks
2Reliability
If Hermitian symmetry is applied to convert complex bipolar OFDM signals to real positive signals, then the signal becomes suitable for IM/DD optical transmission, but power consumption increases due to larger transform components
Solution Approach 1:
By segmenting the signal processing into separate real and imaginary component paths with parallel N-point transforms, the patent reduces the computational complexity and power consumption compared to a single 2N-point transform, while still achieving the required signal conversion for IM/DD transmission
Solution Approach 2:
The patent employs time-multiplexed periodic switching to combine real and imaginary components at appropriate stages of the signal processing chain. This periodic action allows the use of smaller transform blocks that consume less power, while maintaining the functional equivalence of Hermitian symmetry processing
3Area of stationary object
If N-point IFFT and FFT transforms are used without Hermitian symmetry, then chip area and power consumption are reduced, but the output signals remain complex and bipolar rather than real and positive
Solution Approach 1:
The patent applies preliminary time-multiplexing and combining operations on the real and imaginary components before the final output stage. By preparing and combining these components in advance through controlled switching, the system ensures the final output is real and positive without requiring larger transform blocks
Solution Approach 2:
The patent introduces time-multiplexing switches and combining logic as intermediary elements between the N-point IFFT/FFT blocks and the final output. These intermediaries process the complex bipolar signals from the transforms and convert them into real positive signals suitable for IM/DD transmission, without requiring the transforms themselves to be larger
Data Source
AI summary
An OFDM (orthogonal frequency division multiplexing) transmitter includes an inverse fast Fourier transform circuit, which, in operation, generates, based on digital input data, a complex time-varying digital signal having real and imaginary components; and a multiplexer adapted to generate a time-multiplexed digital signal by time-multiplexing one or more of the real components with one or more of the imaginary components.