OFDM Channel Estimation With Offset Filtering for Edge Subcarriers
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Solution Overview
Problem
Existing OFDM channel estimation methods suffer from reduced accuracy for subcarriers located towards the edges of narrow channels, particularly in LTE Category-M1, due to the higher probability of these subcarriers being allocated near the channel edge, leading to lower amplitude and worse signal-to-noise ratio (SNR) in channel estimates.
Innovation Solution
The method involves offsetting the channel filter from the center of the tuned channel to include out-of-channel reference signals when calculating channel estimates for subcarriers within the allocated frequency range, using both in-allocation and out-of-channel reference signals to improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the channel filter is centered on the tuned channel, then the channel filter passes the OFDM data signal and in-allocation reference signals, but out-of-channel reference signals are blocked, reducing channel estimation accuracy for edge subcarriers
Solution Approach 1:
The channel filter is made dynamically positionable in frequency by offsetting its center from the center of the tuned channel. The filter center can be adjusted to align with the center of the allocated frequency range rather than being fixed at the channel center, allowing the filter to adapt to different allocation scenarios and improve channel estimation accuracy for edge subcarriers.
Solution Approach 2:
The frequency position parameter of the channel filter is changed from a fixed center position to an offset position. By modifying the filter's center frequency parameter to align with the allocated subcarrier range rather than the channel center, the system enables inclusion of out-of-channel reference signals while maintaining data signal integrity.
2Measurement precision
If the channel filter is offset to include out-of-channel reference signals, then channel estimation accuracy improves, but the filter passband may include unwanted out-of-band signals
Solution Approach 1:
The filter offset is applied locally and selectively based on the allocation pattern. The channel filter is offset from the channel center by an amount that positions it to include out-of-channel reference signals while maintaining appropriate filtering characteristics. This localized adjustment allows the filter to adapt to the specific allocation scenario without compromising overall signal quality.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the accuracy and consistency of channel estimates for subcarriers near the channel edges by utilizing out-of-channel reference signals, resulting in improved signal-to-noise ratio and amplitude for channel estimates.
Implementation Method 1
receiving radio signals from the radio transmission system and mixing the radio signals with the periodic signal to generate a mixed signal
Implementation Method 2
passing the mixed signal through the channel filter, wherein the channel filter has a passband that corresponds to the bandwidth of the tuned channel
Data Source
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AI summary
A radio (15) receiver tunes a radio channel by generating a periodic signal, mixing the periodic signal with received radio signals and passing the mixed signal through a channel filter (15b) that has a passband that corresponds to the bandwidth of the tuned channel. The receiver receives allocation information identifying a set of subcarriers in the tuned channel on which to receive an OFDM data signal. It uses this information to receive the OFDM data, modulated on the allocated subcarriers. When the allocated subcarriers span an allocated frequency range that is less than the width of the tuned channel and that is offset from the centre of the tuned channel in an offset direction, the receiver offsets the channel filter from the centre of the tuned channel in the offset direction such that the channel filter passes i) said OFDM data signal, ii) an in-allocation reference signal, and ill) an out-of-channel reference signal. The receiver uses both reference signals to calculate a channel estimate for a subcarrier within the tuned channel.