NOMA User Pairing for Fairness and Latency
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Solution Overview
Problem
The Proportional Fairness (PF) scheduler in Non-Orthogonal Multiple Access (NOMA) systems prioritizes users inversely proportional to their historical throughput, leading to situations where users with high historical rates are not assigned transmission rates for multiple slots, causing issues in applications requiring constant Quality of Experience (QoE) or low latency, and fails to account for the increased throughput at the cell edge compared to orthogonal multiple access schemes.
Innovation Solution
A system and method for attributing users to sub-bands by selecting a first user for each sub-band and identifying candidate pairs with complementary channel gains, provisioning power allocation, and iteratively assigning users to maximize throughput and fairness, ensuring all sub-bands are attributed within a time slot.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Proportional Fairness (PF) scheduler prioritizes users inversely proportional to their historical throughput, then user fairness is improved, but users with high historical rates are not assigned transmission rates for multiple slots causing latency issues
Solution Approach 1:
The patent applies dynamics by making the scheduling decision adaptive and time-varying. The base station dynamically selects users for each time slot based on current channel conditions, queue states, and fairness requirements, rather than using a static prioritization scheme. This allows the system to balance fairness and latency requirements in real-time by adjusting user selection criteria according to changing system conditions.
Solution Approach 2:
The patent changes parameters by introducing multiple scheduling parameters beyond just historical throughput, including current channel quality, queue length, latency requirements, and fairness metrics. By modifying the scheduling decision parameters to consider multiple factors simultaneously, the system can achieve both fairness for low-throughput users and low latency for high-throughput users with urgent data.
2Productivity
If multiple users are assigned to the same sub-band in NOMA systems, then system capacity is increased, but interference management complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the system into multiple sub-bands and assigning different user groups to different sub-bands. This frequency-domain segmentation reduces interference between user pairs by providing frequency separation, while still allowing multiple users per sub-band through NOMA. The segmentation approach manages complexity by localizing interference to specific sub-bands rather than system-wide.
Solution Approach 2:
The patent uses power allocation coefficients as intermediaries to manage interference. By introducing power coefficients that weight the contribution of each user's signal, the system can control the interference level between users in the same sub-band. These intermediary parameters allow flexible interference management without requiring complex signal processing at the receivers.
3Productivity
If users with complementary channel gains are paired in NOMA, then throughput is maximized, but the computational complexity of user pairing increases
Solution Approach 1:
The patent changes parameters by using channel gain ratios or differences as the pairing criterion instead of exhaustive throughput calculations. This parameter simplification allows the base station to quickly identify suitable user pairs based on channel conditions without computing complex throughput metrics for all possible user combinations, thereby reducing computational complexity while maintaining throughput optimization.
Solution Approach 2:
The patent applies partial action by considering only a subset of users for pairing in each sub-band, rather than evaluating all possible user combinations across the entire system. This partial evaluation approach reduces computational complexity by focusing on local optimization within each sub-band, accepting that global optimality may not be achieved but system-wide complexity is significantly reduced.
Data Source
AI summary
A mechanism is presented for attributing users to one or more of a plurality of sub-bands in a multiple access communications system, wherein in an initial assignment phase, a first user is selected for a sub band, for example on the basis of a user priority. Users having complementary channel gains to that of the first user are identified, and then a second sub-band user maximizing a performance metric reflecting the achieved throughput, and/or fairness across users, is selected to accompany the first user on that sub-band. The initial assignment phase may terminate once all users have been assigned to a sub-band once. After the first phase is complete, the first user for each sub-band may be the user whose achieved total throughput is furthest from a target throughput defined for that user, wherein each user is assigned to the remaining sub-band to which no first user is currently attributed offering the highest channel gain for that user. Mechanisms for determining user priority, making provisional and definitive power allocations, and performance metrics are proposed.