LTE MAC Layer Carrier Permutation for Interference Robustness
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Solution Overview
Problem
LTE systems are vulnerable to mid/narrow band interference due to fixed Orthogonal Frequency Division Multiplexing (OFDM) carriers used for management traffic, affecting both downlink and uplink channels, leading to potential system failures even with maximal correction codes.
Innovation Solution
A method and system that modify the MAC layer to scramble resource mappings in the LTE protocol stack, using a carrier permutation that can be reversed at the receiving end, to enhance interference robustness by randomly reassigning fixed OFDM carriers, maintaining timing and ensuring synchronization between eNodeB and User Equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If fixed OFDM carriers are used for management traffic, then system simplicity and ease of operation are improved, but interference robustness deteriorates
Solution Approach 1:
The patent applies dynamics by transforming the static, fixed OFDM carrier allocation into a dynamic system where carrier indices are permuted according to a sequence. The MAC layer randomly assigns carriers from a permuted set, and the PHY layer applies time-varying phase shifts to the scrambled carriers. This dynamic behavior enables the system to adapt to interference conditions while maintaining operational simplicity through automated randomization.
Solution Approach 2:
The patent changes the parameter of carrier frequency assignment by introducing a permutation sequence that randomly reassigns carrier indices. Instead of using fixed carrier frequencies for management traffic, the system permutes the carrier index set and assigns scrambled carriers to different physical resources. This parameter change fundamentally alters the system's vulnerability to mid-band interference while preserving ease of operation through algorithmic randomization.
2Reliability
If carrier permutation and scrambling are applied, then interference robustness is improved, but device complexity increases
Solution Approach 1:
The patent segments the carrier allocation process into distinct functional layers: the MAC layer handles carrier permutation and scrambling of resource assignments, while the PHY layer handles the actual signal modulation and time-varying phase shifting. This segmentation allows each layer to perform its specific function independently, reducing overall system complexity through modular design while achieving robust interference mitigation.
Solution Approach 2:
The patent introduces an intermediary permutation sequence as a mediator between the MAC layer and PHY layer. This permutation sequence acts as a bridge that translates management traffic requirements into interference-resistant physical layer assignments. The intermediary enables coordinated randomization across layers without requiring complex cross-layer optimization, thus improving interference robustness while managing device complexity.
3Object-affected harmful factors
If random reassignment of fixed OFDM carriers is performed, then vulnerability to interference is reduced, but synchronization difficulty increases
Solution Approach 1:
The patent applies periodic action through time-varying phase shifts that are applied systematically across different time slots and subframes. The permutation sequence and phase shifting follow periodic patterns that are predetermined and known to both transmitting and receiving ends. This periodicity maintains synchronization by ensuring that randomization follows a predictable temporal structure, reducing synchronization difficulty while maintaining interference resistance.
Solution Approach 2:
The patent implements feedback mechanisms where the receiving end monitors the scrambled carriers and provides feedback to the transmitting end about synchronization status and interference conditions. This feedback loop enables the system to adjust the permutation sequence and phase shifting parameters dynamically, maintaining synchronization accuracy while preserving the interference-mitigating randomization. The feedback ensures that random reassignment does not compromise system coordination.
Data Source
AI summary
The present disclosure provides a method of improving interference robustness in a LTE based wireless communication system. At a transmitting side, a MAC layer outputs MAC data units each including a resource mapping assigning said MAC data units to resource blocks of an LTE frame. The method comprises, at the transmitting side, modifying the MAC data units output by the MAC layer to scramble the resource mapping of said MAC data units thereby providing corresponding scrambled MAC data units including a scrambled resource mapping to a PHY layer of the transmitting side, the scrambled resource mapping being obtained by using a carrier permutation retrievable by a receiving side.