Interference Mitigation via Conjugate Symbol Repetition
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Solution Overview
Problem
Current wireless communication networks face limitations in interference mitigation, particularly in IEEE 802.16e and LTE standards, due to co-channel interference, which affects cell edge coverage and spectrum efficiency, and existing techniques are unsuitable for Rician or flat fading channels.
Innovation Solution
The method involves repeating incoming modulation symbols over multiple subcarriers, encoding using complex conjugation and phase variation synchronized across spatially separated transmitters, and assigning unique pilot patterns to enhance interference suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data is repeated multiple times in DL-MAP to meet target BLER, then cell edge coverage is improved, but spectrum efficiency deteriorates
Solution Approach 1:
The patent segments the repeated data transmissions across multiple DL-MAP instances, allowing the receiver to collect observations from different time instances. By dividing the repetition across multiple frames and using MMSE processing, the system achieves interference suppression while maintaining reliability, resolving the contradiction between cell edge coverage and spectrum efficiency
Solution Approach 2:
The patent employs MMSE (Minimum Mean Square Error) processing that uses feedback from channel estimates and interference observations to optimally combine multiple repeated transmissions. This feedback mechanism allows the receiver to adaptively suppress interference from synchronous base stations while maintaining signal quality, thus improving spectrum efficiency without sacrificing cell edge coverage
2Object-affected harmful factors
If MMSE receiver is used to suppress interference, then interference cancellation gain is improved, but effectiveness deteriorates in Rician or flat fading channels
Solution Approach 1:
The patent introduces dynamics by varying the phase of repeated data symbols across different DL-MAP instances. This phase variation ensures that even in Rician or flat fading channels where channel gains remain constant, the effective channel response changes over time, allowing the MMSE receiver to successfully suppress interference. The dynamic phase modulation transforms a static channel into an effectively time-varying channel
Solution Approach 2:
The patent changes the phase parameter of the transmitted symbols in a controlled manner across repetitions. By modifying the phase parameter while maintaining the same data content, the system creates observable differences in the received signals that enable MMSE processing to distinguish between desired signal and interference, thereby maintaining reliability in challenging channel conditions
3Reliability
If data is repeated on distinct subcarriers spaced far apart, then frequency diversity gain is improved, but coordination complexity between base stations deteriorates
Solution Approach 1:
The patent uses copying of the same data across multiple DL-MAP instances but transmits these copies on the same subcarriers rather than distinct subcarriers. This copying approach, combined with phase variation and MMSE processing, achieves interference suppression without requiring complex coordination for subcarrier allocation, thereby reducing base station coordination complexity while maintaining reliability through temporal diversity
Data Source
AI summary
Embodiments herein provide methods and systems for enhancing interference mitigation using conjugate symbol repetition and phase randomization on a set of subcarriers. The repeated data tone in the signal is complex-conjugated before transmission, when the repetition factor is two. When the repetition factor is greater than two, a combination of conjugate repetition and random/deterministic phase variation of the repeated tones is used to mitigate the interference mitigation. Embodiments further disclose Collision Free Interlaced Pilot PRU Structures that can be used with or without conjugate symbol repetition and phase randomization for interference mitigation.