UE Scheduling for Interference Mitigation in Wireless Networks
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Solution Overview
Problem
In LTE wireless communication systems, orthogonality between uplink transmission signals from different user equipments (UEs) is often compromised due to imperfections and fading channels, leading to severe signal quality degradation and interference, particularly when received signal strengths differ significantly, which existing solutions like uplink power control and frequency division multiplexing fail to adequately address in dynamic broadband systems.
Innovation Solution
Scheduling UEs with similar received signal power densities in the same transmission time interval and assigning them to mirror frequency bands within the available frequency spectrum, while complementary power control is used to adjust transmit powers and reduce differences in signal power densities, thereby mitigating intra-cell interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If uplink power control is used to equalize received powers of non-orthogonal codes, then signal quality is improved for fixed-rate services, but system capacity is reduced for broadband packet-switched systems
Solution Approach 1:
The patent applies local quality by differentiating power control strategies based on service type: fixed-rate services receive power equalization to ensure reliable reception, while broadband packet-switched services allow variable power levels to maximize system capacity. This localized approach to power control resolves the contradiction by applying different quality standards to different service categories.
Solution Approach 2:
The patent implements dynamic power control that adapts to changing channel conditions and service requirements. Power levels are adjusted in real-time based on received signal strength indicators and service type, allowing the system to transition between equalization mode (for reliability) and variable power mode (for capacity) as needed.
2Reliability
If frequency division multiplexing is avoided by dedicating the whole frequency band to a single user, then interference is eliminated, but spectral efficiency is reduced
Solution Approach 1:
The patent segments the frequency band into multiple orthogonal codes that can be simultaneously assigned to different users. This segmentation allows multiple users to share the frequency band without mutual interference, as each user's signal is separated by its assigned orthogonal code, thus maintaining both interference mitigation and spectral efficiency.
Solution Approach 2:
The patent makes the frequency band universal by enabling it to serve multiple users simultaneously through orthogonal code division. The same frequency resources are shared among multiple users who are separated by orthogonal codes, achieving multi-functionality that resolves the contradiction between exclusive use and efficient sharing.
3Reliability
If a single analog narrow-band filter is applied to reduce out-of-band interference, then interference is reduced, but adaptability to dynamic spectrum changes is lost
Solution Approach 1:
The patent replaces the mechanical analog narrow-band filter with a digital signal processing approach using orthogonal codes. Instead of relying on fixed-frequency analog filtering, the system uses mathematical orthogonality in the code domain to separate users, providing both interference reduction and adaptability to dynamic spectrum allocations through software-based code assignment.
4Productivity
If UEs with different received signal strengths are scheduled in parallel in the frequency domain, then system capacity is increased, but signal quality is severely degraded due to interference
Solution Approach 1:
The patent applies preliminary action by pre-calculating and assigning orthogonal codes to users before parallel frequency-domain scheduling. The orthogonal codes are assigned in advance based on user requirements and channel conditions, ensuring that even when users with different signal strengths are scheduled simultaneously, their signals remain separable and interference is minimized, thus maintaining both capacity and quality.
Data Source
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AI summary
According to methods and apparatus taught herein, user equipments (UEs) in a wireless communication network are scheduled based on determining received signal power densities for a plurality of UEs to be scheduled, allocating UEs to scheduling intervals based on a sorting of their received signal power densities, and assigning UEs in the same scheduling interval to mirror frequency bands within an available frequency spectrum according to the sorting. For example, UEs to be scheduled are assigned to a given scheduling interval in rank order of their received signal power densities until the scheduling interval is fully allocated. Remaining UEs are assigned in rank order to one or more other scheduling intervals, and the process may be repeated or otherwise carried out on an ongoing basis. Such an allocation scheme tends to minimize both adjacent frequency and mirror frequency interferences between UEs scheduled in the same interval.