Basestation Frequency Error Correction Using Mobile Device Timing
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Solution Overview
Problem
Cellular basestations face challenges in achieving the required frequency accuracy for signal generation and demodulation, particularly in cost-effective ways, as high-accuracy oscillators like OCXO are expensive and not feasible for small coverage areas.
Innovation Solution
A method is introduced where a basestation detects signals from other basestations, estimates frequency errors, and adjusts its oscillator operation to minimize these errors using timing information from mobile devices, allowing the use of lower-cost oscillators like VCTCXO.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an OCXO crystal oscillator is used to achieve high frequency accuracy, then the frequency accuracy requirement is met, but the cost of the basestation increases significantly
Solution Approach 1:
The patent uses timing information from mobile devices as an intermediary to transfer frequency reference from external basestations. Instead of relying on an expensive internal OCXO oscillator, the femtocell basestation uses timing measurements reported by mobile devices to estimate frequency offsets and adjust its VCTCXO oscillator accordingly, achieving accurate frequency control through this intermediary measurement mechanism
Solution Approach 2:
The patent replaces the expensive OCXO oscillator with a cheaper VCTCXO oscillator. While the VCTCXO has lower inherent accuracy, it is compensated through the timing measurement method, achieving the required frequency accuracy at lower cost. The system accepts that the oscillator itself is less precise but uses external reference information to achieve the needed performance
2Ease of manufacture
If a low-cost oscillator is used in the basestation, then the cost is reduced, but the frequency accuracy cannot be maintained
Solution Approach 1:
The patent implements a feedback mechanism where timing information from mobile devices is continuously measured and used to estimate frequency offsets. The basestation adjusts its oscillator based on this feedback loop, comparing its timing against references from other basestations and correcting any drift. This closed-loop feedback enables a low-cost oscillator to achieve the required frequency accuracy
Solution Approach 2:
The patent replaces the mechanical/physical precision of an OCXO oscillator with an electronic/software-based frequency estimation and correction system. Instead of relying on the physical stability of a high-precision crystal oscillator, the system uses digital timing measurements, frequency offset estimation algorithms, and electronic oscillator adjustment to achieve the same frequency accuracy goal
Data Source
AI summary
A basestation in a cellular communication system corrects frequency errors in signals generated within the basestation. The frequency errors may be corrected on the basis of signals transmitted by one or more other basestation within the network. As an alternative, the basestation may request information from one or mobile devices that are also able to detect transmissions from other basestations.