Cellular Power Controller SIR Target Optimization
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Solution Overview
Problem
In cellular networks, particularly those following the UMTS standard, there is a persistent need to increase capacity due to high data traffic, and existing power control methods struggle to optimize HARQ re-transmissions and BLER, leading to reduced cell capacity and interference between users.
Innovation Solution
A power controller that determines a maximum SIR target for each user equipment based on the number of users in the cell and granted data rate, limiting transmission power to enhance cell capacity and peak rates, using a lookup table and ramp function to adjust SIR targets dynamically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the RNC controls the target number of HARQ re-transmissions and target BLER, then the air-interface load is reduced for a given user throughput, but it is not prevented that two or more users affect each others SIR by causing each other to raise power, potentially causing more re-transmissions and reducing cell capacity
Solution Approach 1:
The invention changes the parameter being controlled from the target number of HARQ re-transmissions to the maximum SIR target. By controlling the SIR target directly at the RBS level, the system can prevent inter-user interference while still reducing air-interface load. The RBS determines the maximum SIR target based on the number of users in the cell, allowing dynamic adjustment that prevents power raising by multiple users without requiring RNC-level control of HARQ re-transmission targets.
2Speed
If a low percentage of HARQ re-transmissions is targeted for high peak rate, then peak throughput is maintained, but cell capacity is reduced when there are multiple EUL users
Solution Approach 1:
The invention makes the maximum SIR target dynamic by determining it at the RBS based on the current number of users in the cell. When there are few users, a higher maximum SIR target is allowed to support peak rates. When there are many users, the maximum SIR target is reduced to optimize cell capacity. This dynamic adjustment resolves the contradiction by adapting the SIR target to the current cell conditions rather than using a fixed target.
3Device complexity
If the RNC sets a maximum SIR target for a given radio access bearer, then power control is simplified, but the RNC is not in control of the users rate as the granted rate is handled in the scheduler in the RBS
Solution Approach 1:
The invention segments the control functions between the RNC and RBS. The RNC sets the maximum SIR target for each radio access bearer, maintaining simplified power control architecture. The RBS uses this maximum SIR target in conjunction with the granted rate from its scheduler to determine the actual SIR target for each user. This segmentation allows the RNC to control power parameters while the RBS controls rate parameters, resolving the contradiction between simplified control and rate control adaptability.
Data Source
AI summary
It is presented a power controller which is adapted to be coupled to a fixed node of a cellular network, wherein at least one user equipment is adapted to be associated with the fixed node. The power controller comprises: a signal to interference ratio, SIR, determiner arranged to determine a maximum SIR target for each of the at least one user equipment, which maximum SIR target is arranged to limit maximum transmission power of the at least one user equipment; wherein the determiner determines a maximum SIR target for each of the at least one user equipment directly or indirectly based on the number of user equipments in the cell of each respective user equipment. A corresponding method, computer program and computer program product are also presented.