DFT-Spread OFDM Reference Symbol Structure for Channel Estimation
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Solution Overview
Problem
The existing reference symbol structure in LTE systems faces challenges in providing satisfactory performance in higher frequency spectra and mobile velocities, particularly due to increased Doppler spread, leading to difficulties in channel estimation and potential increases in overhead and interference.
Innovation Solution
A data transmission apparatus employing a discrete Fourier transform (DFT) precoder and a multiplexer to perform frequency division multiplexing (FDM) of data and reference symbols within the same OFDM symbol, allowing for frequent transmission of reference symbols without increasing overhead and minimizing Peak to Average Power Ratio (PAPR) increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of OFDM symbols transmitting reference symbols per slot is increased to improve channel estimation performance, then channel estimation accuracy is improved, but overhead increases and data transmission rate decreases
Solution Approach 1:
The patent merges reference symbols and data symbols into the same OFDM symbol through frequency division multiplexing. This allows reference symbols to be transmitted frequently for accurate channel estimation while sharing the same time resource with data symbols, thereby avoiding the overhead penalty of dedicating separate OFDM symbols for reference signals.
Solution Approach 2:
The patent transitions from time-domain multiplexing (TDM) where reference symbols occupy separate time slots, to frequency-domain multiplexing (FDM) where reference and data symbols coexist in the same time slot but different frequency subcarriers. This dimensional shift enables simultaneous transmission of both reference and data symbols without increasing time overhead.
2Loss of time
If data and reference symbol are multiplexed in a single OFDM symbol using TDM to decrease reference symbol proportion, then overhead remains constant and temporal frequency increases, but cyclic prefix overhead increases and interference between data and reference symbol increases
Solution Approach 1:
The patent segments the frequency spectrum into distinct subcarriers, assigning reference symbols to specific subcarriers and data symbols to other subcarriers within the same OFDM symbol. This frequency segmentation prevents time-domain interference that would occur with TDM, as reference and data symbols are separated in the frequency domain rather than competing for the same time resources.
3Measurement precision
If data and reference symbol are multiplexed in a single OFDM symbol using TDM before DFT, then reference symbol temporal frequency increases, but cyclic prefix overhead increases and channel estimation becomes complex
Solution Approach 1:
The patent performs frequency division multiplexing in the frequency domain after DFT processing, rather than time-domain multiplexing before DFT. This approach simplifies channel estimation because the DFT-spread OFDM structure maintains its inherent properties, and reference symbols can be extracted and used for channel estimation in a straightforward manner without complex time-domain interference cancellation.
Data Source
AI summary
Provided is a data transmission apparatus to transmit a reference orthogonal frequency division multiplexing (OFDM) symbol generated by frequency division multiplexing a reference symbol and a data symbol, and a data reception apparatus to estimate a channel using the reference OFDM symbol. Since the reference symbol and the data symbol are frequency division multiplexed, a Peak to Average Power Ratio (PAPR) may not increase greatly, and the transmission apparatus may transmit the reference OFDM symbol to the data reception apparatus more frequently. Accordingly, the data reception apparatus may estimate a channel accurately.