OTFS Tomlinson-Harashima Precoding for Low-Complexity MIMO Equalization
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Solution Overview
Problem
Existing communication systems face challenges in separating and equalizing parallel data streams in MIMO channels, particularly due to the computational cost of decision feedback equalizers and error propagation, as well as the inaccuracies in channel state information estimation in one-dimensional channel models.
Innovation Solution
The implementation of Orthogonal Time Frequency Space (OTFS) modulation, which transforms the time-varying multipath channel into a time-invariant delay-Doppler channel, enabling efficient channel state information estimation and linear scaling of throughput with the number of antennas, and allowing for accurate channel tracking and beamforming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a decision feedback equalizer (DFE) is used on the receiver side for equalization of parallel data streams in MIMO channels, then equalization performance is improved, but computational cost increases and error propagation occurs
Solution Approach 1:
The patent applies Tomlinson-Harashima precoding at the transmitter side instead of using a decision feedback equalizer at the receiver side. This inverts the traditional approach by performing equalization functions at the transmitter through precoding, thereby avoiding the computational complexity and error propagation issues associated with receiver-side DFE while achieving comparable or superior equalization performance
Solution Approach 2:
The precoding operation is performed in advance at the transmitter before signal transmission. By pre-compensating for channel effects and applying the precoding matrix to the data streams prior to transmission, the system eliminates the need for complex real-time equalization at the receiver, reducing computational cost and preventing error propagation
2Ease of manufacture
If traditional one-dimensional channel models are used for MIMO communication, then system implementation is simplified, but channel state information estimation accuracy deteriorates
Solution Approach 1:
The patent transitions from traditional one-dimensional channel models to two-dimensional channel models that incorporate both spatial and temporal dimensions. This dimensional expansion enables more accurate channel state information estimation by capturing channel variations in both space and time, while the structured approach to 2D modeling maintains reasonable system implementation complexity
3Productivity
If the number of antennas is increased to improve throughput in MIMO systems, then data transmission capacity increases, but computational complexity and channel estimation difficulty increase
Solution Approach 1:
The patent employs block-based processing where the 2D channel is segmented into manageable blocks, and precoding is applied in a structured manner. This segmentation approach allows the system to handle large numbers of antennas by breaking down the complex matrix operations into smaller, more manageable blocks, thereby maintaining computational tractability while supporting massive MIMO configurations
Solution Approach 2:
The patent utilizes 2D Fourier transforms and changes the domain of processing from time-space to frequency-delay domains. This parameter transformation simplifies the mathematical operations required for channel estimation and precoding in massive MIMO systems, reducing computational complexity while enabling support for a large number of antennas through efficient spectral domain processing
Data Source
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AI summary
A method for signal transmission using precoded symbol information involves estimating a two-dimensional model of a communication channel in a delay-Doppler domain. A perturbation vector is determined in a delay-time domain wherein the delay-time domain is related to the delay-Doppler domain by an FFT operation. User symbols are modified based upon the perturbation vector so as to produce perturbed user symbols. A set of Tomlinson-Harashima precoders corresponding to a set of fixed times in the delay-time domain may then be determined using a delay-time model of the communication channel. Precoded user symbols are generated by applying the Tomlinson-Harashima precoders to the perturbed user symbols. A modulated signal is then generated based upon the precoded user symbols and provided for transmission over the communication channel.