OFDM Transmitter Windowing for Adjacent Channel Interference Suppression
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Solution Overview
Problem
OFDM signals suffer from high spectral sidelobes leading to adjacent channel interference (ACI) due to rectangular transmit pulses, and conventional windowing techniques do not provide optimal time-frequency localization, resulting in suboptimal utilization of the available frequency band for ACI suppression and rejection.
Innovation Solution
Implementing per-subcarrier or common discrete prolate spheroidal windowing for both transmitter and receiver to shape each subcarrier, optimizing the confinement band based on the spectral location and guard band, which allows for maximum ACI suppression and rejection by utilizing the available guard band effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If rectangular transmit pulse is used in OFDM, then spectral confinement is achieved, but high spectral sidelobes are generated causing adjacent channel interference
Solution Approach 1:
The patent applies discrete prolate spheroidal windowing functions to transform the rectangular pulse shape into a optimized windowed pulse shape. This parameter change in the time-domain windowing function reduces the spectral sidelobes while maintaining the essential OFDM signal characteristics, thereby reducing adjacent channel interference without completely sacrificing spectral confinement.
Solution Approach 2:
The patent applies different windowing functions to different subcarriers (per-subcarrier windowing) or uses a common windowing function optimized for specific spectral locations. This local quality approach allows the system to optimize the time-frequency localization for each subcarrier or spectral region, achieving better ACI suppression in critical frequency bands while maintaining signal integrity.
2Reliability
If conventional windowing techniques are used, then time-frequency localization is improved, but optimal utilization of available frequency band for ACI suppression is not achieved
Solution Approach 1:
The patent optimizes the windowing function parameters (specifically the confinement band parameter) based on the spectral location and guard band requirements. This parameter optimization allows the system to achieve the best possible time-frequency localization while maximizing the utilization of the available frequency band for ACI suppression, outperforming conventional fixed windowing techniques.
Solution Approach 2:
The patent introduces dynamic adaptation by optimizing the windowing function for each subcarrier or spectral region based on local requirements. This dynamic approach allows the system to adaptively allocate the time-frequency resources, achieving optimal ACI suppression in each frequency band while maximizing overall frequency band utilization.
Data Source
AI summary
An optimum time domain windowing scheme for orthogonal frequency-division multiplexing (OFDM)-based waveforms in the sense of spectral concentration is proposed. Instead of evenly suppressing the sidelobes along the frequency, the sidelobe power is concentrated within a guard band while maximally suppressing the power for a desired frequency range. This is achieved by employing optimum finite duration pulses, prolate spheroidal wave functions (PSWF), to shape the OFDM transmit pulse. Also with per-subcarrier windowing scheme, the effect of inner subcarriers on sidelobes is diminished by utilizing the concentration bandwidth versus out-of-band power trade-off in PSWF and the multicarrier nature of the OFDM.