Orthogonal Signal Demodulation for Co-Channel Interference Rejection
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Solution Overview
Problem
Communications systems face challenges with co-channel interference due to shrinking cell sites and increased proximity of frequency-reusing cells, which existing methods like receiver antenna diversity struggle to address effectively, especially in cost and complexity.
Innovation Solution
The use of orthogonal modulated signals, generated by combining multiple bit streams with independent quaternary modulation and weighted symbols, allows for effective interference rejection through orthogonal components, enabling efficient demodulation without the need for multiple antennas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If receiver antenna diversity is used to mitigate co-channel interference, then interference attenuation is improved, but device complexity and cost increase due to additional antennas
Solution Approach 1:
The transmitter signal is segmented into multiple orthogonal components (in-phase and quadrature components) that can be independently processed. This segmentation allows the receiver to separate and process different signal components through simple correlation operations rather than requiring multiple physical antennas, thereby reducing receiver complexity while maintaining interference mitigation capability
Solution Approach 2:
Orthogonal training sequences are introduced as intermediary elements that facilitate channel estimation and signal separation. These training sequences act as mediators between the transmitted signal and the receiver processing, enabling the receiver to distinguish between desired signal and co-channel interference through correlation operations without requiring complex hardware
2Productivity
If cell sites are shrunk to increase capacity, then communication capacity is improved, but co-channel interference increases due to reduced geographical isolation
Solution Approach 1:
The system transitions from spatial dimension interference management (relying on geographical isolation of cell sites) to signal dimension interference management (using orthogonal signal components). By encoding information in multiple orthogonal dimensions (in-phase and quadrature components with different training sequences), the system can maintain high capacity with closely spaced cell sites while rejecting interference through signal processing rather than spatial separation
3Object-affected harmful factors
If orthogonal modulated signals with training sequences are used, then interference rejection is improved, but signal processing complexity increases
Solution Approach 1:
Known training sequences are copied and transmitted within the signal structure at predetermined positions. The receiver uses these copied training sequence copies to perform correlation operations, comparing the received signal against the known original sequences to extract channel information and reject interference. This copying approach simplifies processing by using simple correlation rather than complex adaptive algorithms
Data Source
AI summary
Methods and corresponding systems for providing and demodulating an orthogonal modulated signal where demodulation includes separating a sampled orthogonal modulated signal into in phase and quadrature samples, deriving first and second equalizer coefficients based on corresponding in phase and quadrature samples and further, respectively, based on a first and second training sequence, programming a first plurality of equalizer filters with the first equalizer coefficients and a second plurality of equalizer filters with the second equalizer coefficients; and processing, after programming with first and second coefficients, the in phase samples and the quadrature samples through a first and second plurality of equalizer filters to provide demodulated symbols.