Wireless Access Point Time Synchronization for TDM Efficiency
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Solution Overview
Problem
In wireless communication systems using the TDM method, long guard times are necessary to avoid interference due to transmission delay, leading to reduced transmission efficiency, and measuring round trip time for each STA increases overhead, further deteriorating efficiency as the number of STAs increases.
Innovation Solution
The system synchronizes time using external time information, allowing the access point and wireless stations to adjust transmission start times based on calculated delay times, enabling earlier transmission start times and optimized time slot allocation, reducing the need for lengthy guard times and improving overall efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If long guard times are used to avoid interference due to transmission delay, then reliability is improved, but transmission efficiency deteriorates
Solution Approach 1:
The access point performs preliminary measurement of transmission delay times to all STAs before data transmission. Based on these pre-measured delays, the AP calculates and notifies each STA of its specific transmission start time in advance. This preliminary action eliminates the need for long guard times, as each STA transmits at precisely calculated times that account for their individual delays, thereby improving transmission efficiency while maintaining reliability.
2Reliability
If round trip time is measured for each STA to manage transmission timing, then transmission reliability is improved, but device complexity increases due to increased overhead
Solution Approach 1:
The access point combines multiple RTT measurements into a single comprehensive delay time notification sent to each STA. Instead of performing separate RTT measurement and compensation procedures for each transmission, the AP measures the total delay time once and notifies all STAs of their respective transmission start times in advance. This merging approach maintains precise transmission timing control while significantly reducing overhead and simplifying the system.
Data Source
AI summary
An AP 3 and STAs 5 acquire time information from an external device, and synchronize time. The AP 3 sets, in a first signal, a transmission start time of the first signal, and transmits the first signal to the STA 5. The STAs 5 transmit, to the AP 3, a second signal in which a delay time is set, the delay time being calculated from a difference between the transmission start time acquired from the first signal and a reception start time of the first signal at the own station. The AP 3 acquires delay time from the second signal of each STA 5, decides a timing for permitting transmission by each of the STAs 5 by time division, on the basis of the acquired delay time, and notifies the STAs 5 thereof. The STAs 5 each effect control to start transmission of signals to the AP 3 at the timing notified from the AP 3.