Inverse Filter Precoding for MIMO Channel Estimation
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Solution Overview
Problem
In wireless communication networks, non-orthogonal waveforms such as FBMC and GFDM pose challenges for accurate MIMO channel estimation due to intersymbol interference (ISI), limiting MIMO processing and making it difficult to reliably detect data elements at the receiver.
Innovation Solution
The approach involves preprocessing the signal pattern, such as a reference signal, using an inverse filter before pulse-shaping to ensure it remains non-pulse-shaped in the transmit signal, allowing for easy identification and use in channel estimation at the receiver, even under ISI conditions. This precoding technique combines with non-orthogonal waveforms to enable accurate MIMO channel parameter estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If non-orthogonal waveforms (FBMC, GFDM) are used for transmission, then spectral efficiency is improved and flexibility is enhanced, but MIMO channel estimation accuracy deteriorates due to intersymbol interference
Solution Approach 1:
The patent applies preliminary action by preprocessing the reference signal with an inverse filter before pulse-shaping in the transmitter. This inverse filtering compensates for the expected pulse-shaping effects in advance, ensuring that the reference signal maintains its original characteristics after transmission through the pulse-shaped waveform system, thereby enabling accurate MIMO channel estimation despite using non-orthogonal waveforms
Solution Approach 2:
The patent introduces an intermediary approach by using a specially preprocessed reference signal that acts as a mediator between the pulse-shaped data signal and the channel estimation process. This reference signal, after inverse filtering and pulse-shaping, maintains identifiable characteristics that allow the receiver to accurately estimate MIMO channel parameters without being corrupted by intersymbol interference from the non-orthogonal waveform
2Stability of the object's composition
If pulse-shaped filtering is applied to all signals including reference signals, then waveform consistency is maintained, but signal pattern identification becomes difficult due to intersymbol interference
Solution Approach 1:
The transmitter applies inverse filtering to the reference signal before pulse-shaping, preparing it in advance to counteract the pulse-shaping effects. This preliminary action ensures that after the reference signal passes through the pulse-shaped filtering in the transmitter and channel, its original pattern remains identifiable at the receiver, solving both waveform consistency and signal identification challenges
Solution Approach 2:
The patent changes the parameters of the reference signal by applying inverse filtering with specific filter coefficients that are the inverse of the pulse-shaping filter. This parameter transformation modifies the reference signal's frequency and time-domain characteristics in a controlled manner, allowing it to maintain consistency with the pulse-shaped waveform while preserving its identification features
3Measurement precision
If inverse filtering is applied to reference signals before pulse-shaping, then MIMO channel estimation accuracy is improved, but transmitter processing complexity increases
Solution Approach 1:
The patent manages transmitter complexity by changing the filter parameters to use the inverse of the pulse-shaping filter coefficients. This parameter transformation allows the inverse filtering to be implemented efficiently using the same filterbank structure as the pulse-shaping, merely by using inverted coefficient values, thereby minimizing additional hardware complexity while achieving improved channel estimation
Data Source
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AI summary
A receiver has an antenna to receive a pulse shaped transmit signal transmitted by a transmitter of a multi carrier (MC) pulse shaped transmission system. The pulse shaped transmit signal includes a predefined signal pattern. The predefined signal pattern not subjected to pulse shaping. The receiver includes a filter to pulse shape filter the pulse shaped transmit signal to obtain data for the receiver. The predefined signal pattern is retrieved from the pulse shaped transmit signal prior to filtering the pulse shaped transmit signal.