Virtual Trajectories Receiver for Doubly Selective Channels
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Solution Overview
Problem
Existing multicarrier wireless communication systems face challenges in transmitting data at high speeds over doubly selective channels while maintaining spectral efficiency, particularly due to inter-symbol interference (ISI) in single carrier systems and intercarrier interference (ICI) in orthogonal frequency division multiplexing (OFDM) systems, which require complex channel estimation and equalization processes.
Innovation Solution
A novel multicarrier communication system with low complexity that operates on doubly selective channels using virtual trajectories, allowing for coherent and incoherent reception, and exploits channel diversity without direct estimation of time-varying channel impulse response matrices or matrix inversions, using linear precoders and DFT spreading to achieve high performance and spectral efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional OFDM systems are used to transmit data at high speeds over doubly selective channels, then data transmission rate is improved, but intercarrier interference (ICI) increases and spectral efficiency deteriorates
Solution Approach 1:
The patent segments the doubly selective channel into multiple virtual trajectories, each representing a distinct propagation path with unique time-delay and Doppler-shift characteristics. By separating the channel into these virtual trajectories, the system can process each trajectory independently, reducing intercarrier interference while maintaining high data transmission rates.
Solution Approach 2:
The patent introduces virtual trajectories as an intermediary representation between the physical channel and the OFDM signal processing. These virtual trajectories serve as a mathematical model that captures the essential characteristics of the doubly selective channel, enabling efficient equalization and interference mitigation without direct matrix inversions.
2Reliability
If complex channel estimation and equalization processes are applied to combat interference in high-speed transmission, then data transmission reliability is improved, but computational complexity increases
Solution Approach 1:
The patent changes the parameter representation of the channel from time-domain impulse response to frequency-domain virtual trajectories characterized by time-delay and Doppler-shift parameters. This parameter transformation enables simpler estimation and equalization operations, reducing computational complexity while maintaining reliable data transmission.
Solution Approach 2:
The patent employs lightweight pilot symbols as disposable reference signals for channel estimation. These short-duration pilot sequences are transmitted periodically to estimate virtual trajectory parameters, providing sufficient reliability without requiring complex continuous estimation processes.
3Measurement precision
If direct estimation of time-varying channel impulse response matrices is performed, then channel characterization accuracy is improved, but computational complexity and processing time increase
Solution Approach 1:
The patent extracts the essential characteristics of the time-varying channel by identifying and separating distinct virtual trajectories with unique time-delay and Doppler-shift pairs. Instead of estimating the complete time-varying impulse response matrix, the system extracts only the dominant virtual trajectory parameters, achieving accurate channel characterization with reduced processing time.
Solution Approach 2:
The patent applies partial estimation by focusing only on the most significant virtual trajectories that contribute most to the received signal. By estimating parameters for only the dominant trajectories rather than all possible paths, the system achieves sufficient channel characterization accuracy with minimal processing time.
Data Source
AI summary
A modified orthogonal frequency-division multiplexing (OFDM) communication system based on virtual decomposition of the channel is proposed. The system is fully compatible with standard OFDM transmitters and maintains several blocks of standard OFDM receivers. The proposed approach achieves also incoherent reception of multicarrier signals even with a simple autocovariance DPSK detector. This novel system substantially surpasses the performance of current approaches while requiring low computational complexity. Two preferred embodiments are described; one with coherent reception using pilot signals, and the second with incoherent receiver of differentially encoded signals.