Femto Base Station Downlink Synchronization via Macro Reference Signals
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Solution Overview
Problem
Femto base stations in cellular OFDM systems face challenges in achieving downlink network synchronization due to inability to receive GPS signals and unreliable backhaul connections, leading to difficulties in maintaining orthogonality between subcarriers and preventing inter-carrier interference.
Innovation Solution
A method where the femto base station scans reference signals from neighboring macro base stations, determines a desired reference signal using digital signal processing and a timing detector, and configures its downlink transmission time to synchronize with neighboring macro base stations, ensuring arrival time differences are within the Guard Interval Duration of an OFDM symbol.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If GPS is used for network synchronization, then timing reference reliability is improved, but indoor femto base station ability to receive GPS signals deteriorates
Solution Approach 1:
The patent uses macro base stations as intermediary nodes to relay timing reference information to femto base stations. Instead of direct GPS reception at the femto base station (which is blocked by buildings), the timing reference is transmitted through macro base stations that have unobstructed GPS reception, thus mediating the timing synchronization process.
Solution Approach 2:
The patent replaces the direct GPS signal reception mechanism with an alternative synchronization mechanism using backhaul network signaling. Instead of relying on radio frequency GPS signal propagation through buildings, the system uses the backhaul communication network to transmit timing reference information, substituting one signal transmission path for another that is not affected by physical obstructions.
2Reliability
If backhaul signaling is used for synchronization, then timing reference acquisition is improved, but timing precision deteriorates due to time variant round trip delay
Solution Approach 1:
The patent applies preliminary timing adjustment at the macro base station before signal transmission to the femto base station. By pre-compensating for the known or estimated backhaul delay, the system reduces the impact of time-variant round trip delays on timing precision, allowing the femto base station to achieve more accurate synchronization.
Solution Approach 2:
The patent implements a feedback mechanism where the femto base station measures the actual arrival time of reference signals and reports timing offset information back to the macro base station or network controller. This feedback loop enables continuous refinement and correction of timing references, compensating for time-variant backhaul delays and improving overall timing precision.
Data Source
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AI summary
A method of downlink synchronization for a femto base station in a cellular orthogonal frequency division multiplexing (OFDM) system is provided. The femto base station first scans one or more received reference signals transmitted from a plurality of neighboring macro base stations. The femto base station then determines a desired reference signal from the received 5 one or more reference signals based on the scanning result. Finally, the femto base station configures its downlink radio signal transmission time based on the desired reference signal such that the femto base station is synchronized with the plurality of neighboring macro base stations.