VFDM Precoders for Interference Alignment in Cognitive Small Cell Networks
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Solution Overview
Problem
Cognitive radio systems with multiple secondary networks experience significant interference between secondary signals, which existing techniques fail to adequately mitigate while maintaining interference avoidance with primary network communications.
Innovation Solution
The system employs interference alignment techniques by determining nullspaces induced by cyclic prefixes in primary data channels to derive precoders for secondary users, aligning secondary channel interference with primary interference channels, and using Vandermonde-subspace frequency division multiplexing to mitigate interference between secondary and primary networks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional cognitive radio communication techniques are used to avoid interference with primary network, then interference avoidance with primary network is achieved, but interference between secondary network communications increases significantly
Solution Approach 1:
The patent applies interference alignment by transforming the interference problem from a scalar power control issue into a vector subspace alignment problem. By operating in the signal subspace domain rather than simply adjusting transmission power, the system aligns secondary interference signals into specific subspaces that do not affect primary network reception, thereby resolving the contradiction between avoiding primary interference and managing secondary interference.
Solution Approach 2:
The patent introduces cyclic prefix nullspaces as an intermediary mechanism. These nullspaces, created by the primary system's cyclic prefix structure, serve as designated subspaces where secondary transmissions can be aligned without affecting primary communication. This intermediary subspace structure enables secondary networks to communicate while automatically avoiding primary network interference.
2Productivity
If multiple secondary networks operate simultaneously to increase spectral efficiency, then spectral efficiency improves, but interference between secondary signals worsens
Solution Approach 1:
The patent resolves the spectral efficiency versus interference contradiction by moving the problem into the subspace dimension. Instead of treating interference as a power management issue, the system uses interference alignment to project secondary signals into specific subspaces, allowing multiple secondary networks to operate simultaneously without mutual interference, thereby maintaining high spectral efficiency.
Solution Approach 2:
The patent segments the signal space into distinct subspaces using cyclic prefix nullspaces. By dividing the overall signal space into interference-free subspaces for secondary transmissions, the system enables multiple secondary networks to operate in parallel without interfering with each other, thus improving spectral efficiency while controlling interference.
3Object-generated harmful factors
If interference alignment techniques are implemented to mitigate secondary interference, then interference between secondary signals is reduced, but system complexity increases
Solution Approach 1:
The patent employs self-service by utilizing the cyclic prefix nullspaces that are already generated by the primary system's own transmission structure. The primary system's cyclic prefix automatically creates the interference-free subspaces needed for secondary transmissions, eliminating the need for complex external interference management mechanisms and reducing overall system complexity.
Data Source
AI summary
Aspects of this disclosure provide techniques for computing Vandermonde-subspace frequency division multiplexing (VFDM) precoders for secondary network transmissions that mitigate interference between secondary communication signals, while avoiding interference with the primary system altogether. A precoder for a secondary user (SU) is computed on accordance with a nullspace induced by cyclic prefixes communicated over a primary data channel, a primary interference channel between a second user (SU) and the primary receiver, and a secondary interference channel between the SU and a neighboring SBS. The precoder provides both frequency domain precoding and spatial domain precoding on secondary transmission signals communicated from the SU.