Time Domain Layer Separation in OFDM Receivers
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Solution Overview
Problem
Frequency-selective channels cause interference between layers multiplexed using frequency domain orthogonal cover codes (FD-OCC) across non-adjacent subcarriers in OFDM systems, making it difficult to recover data streams effectively, especially in wireless communication technologies like 5G NR.
Innovation Solution
A method and circuit for separating layers multiplexed using FD-OCC in the time domain by descrambling signals on non-adjacent subcarriers, applying inverse and fast Fourier transforms, and defining sampling windows to extract and de-noise layers, which improves orthogonality preservation and reduces inter-layer interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If frequency domain orthogonal cover codes (FD-OCC) are used to multiplex multiple layers on non-adjacent subcarriers, then spectral efficiency is improved, but frequency-selective channels cause interference between layers making it difficult to recover data streams
Solution Approach 1:
The received signal is segmented into multiple time-domain sampling windows after IFFT transformation. Each sampling window corresponds to a specific layer, allowing separate extraction and processing of each multiplexed layer. This segmentation enables effective separation of layers that were multiplexed in the frequency domain, resolving the interference problem caused by frequency-selective channels.
Solution Approach 2:
The inverse fast Fourier transform (IFFT) acts as an intermediary transformation that converts the frequency-domain multiplexed signal into the time domain, where layers become separable through sampling windows. This intermediary transformation enables the separation of layers that are interleaved in the frequency domain but separated in the time domain.
2Productivity
If layers are multiplexed using FD-OCC across non-adjacent subcarriers, then data transmission capacity is increased, but inter-layer interference increases in frequency-selective channels
Solution Approach 1:
The signal is divided into distinct time-domain sampling windows, each capturing energy from a specific layer. This segmentation prevents inter-layer interference by ensuring that each layer's energy is confined to its designated sampling window, allowing high-capacity multiplexing without interference.
Solution Approach 2:
The patent transitions from frequency-domain multiplexing to time-domain separation by applying IFFT. Layers that are multiplexed in the frequency dimension are separated in the time dimension through sampling windows, effectively using another dimension to resolve the interference problem while maintaining high transmission capacity.
3Device complexity
If conventional frequency domain demodulation is used, then implementation is simpler, but orthogonality between layers is not preserved in frequency-selective channels
Solution Approach 1:
The IFFT serves as an intermediary that transforms the signal to the time domain where orthogonality is naturally preserved through the sampling window separation. This transformation maintains orthogonality between layers even in frequency-selective channels, overcoming the limitations of direct frequency-domain demodulation.
Solution Approach 2:
The patent applies IFFT transformation and defines sampling windows before extracting layer signals. This preliminary action of transforming to time domain and establishing sampling boundaries ensures orthogonality is preserved from the outset, preventing interference before demodulation occurs.
Data Source
AI summary
A receiver circuit for separating a plurality of layers multiplexed in an orthogonal frequency domain multiplexed (OFDM) signal includes: a descrambling sub-circuit configured to descramble a plurality of signals received on non-adjacent subcarriers of the OFDM signal to generate a plurality of descrambled signals; an inverse fast Fourier transform sub-circuit configured to transform the descrambled signals from a frequency domain to a received signal including a plurality of samples in a time domain; and a layer separation sub-circuit configured to separate the layers multiplexed in the received signal by: defining a first time domain sampling window and a second time domain sampling window in accordance with a size of the inverse fast Fourier transform; extracting one or more first layers from the samples in the first time domain sampling window; and extracting one or more second layers from the samples in the second time domain sampling window.