Software Ranging in Optical Line Terminals via Cycle Counting
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Solution Overview
Problem
In passive optical network systems, implementing precise ranging using software is challenging due to the difficulty in achieving nanosecond-level time measurement, which is typically achievable with hardware but not with central processing units (CPU) or graphics processing units (GPU), and is further complicated by fluctuations in processing time.
Innovation Solution
A communication device and method that includes a transmission timing calculation unit, a reception timing calculation unit, and a round trip time calculation unit, utilizing a processor and interface circuit to calculate and manage frame transmission and reception timings based on the number of transferred bits and throughput, enabling precise round trip time measurement without direct clock time acquisition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If ranging is implemented using software (CPU/GPU), then flexibility and ease of configuration are improved, but time measurement precision deteriorates (cannot achieve nanosecond level)
Solution Approach 1:
The patent introduces a cycle counter as an intermediary mechanism between the software processing unit and the time measurement function. The cycle counter, implemented in hardware, counts the number of cycles elapsed during frame transmission and processing, providing precise time measurement capability to the software-based ranging function without requiring the CPU/GPU to directly handle timing at nanosecond resolution.
2Measurement precision
If hardware implementation (ASIC) is used for OLT functions, then time measurement precision is improved (nanosecond level achievable), but device complexity and manufacturing cost increase
Solution Approach 1:
The patent segments the OLT functionality into two distinct parts: general processing functions implemented in software (CPU/GPU) for flexibility, and time measurement functions implemented in hardware (cycle counter) for precision. This segmentation allows each part to be optimized independently, avoiding the need for full hardware implementation while maintaining nanosecond-level timing accuracy.
Solution Approach 2:
The patent replaces complex hardware time measurement mechanisms with a simpler cycle counting approach. Instead of using sophisticated hardware timers or clocks, the system uses a basic cycle counter that simply counts the number of processor cycles elapsed, providing accurate time measurement with minimal hardware complexity.
3Ease of operation
If software processing is used for frame generation and physical layer processing, then ease of operation and flexibility are improved, but processing time fluctuation increases, making precise RTT measurement difficult
Solution Approach 1:
The patent implements a feedback mechanism where the cycle counter continuously monitors the actual time taken for frame processing and transmission. This measured time information is fed back to the ranging calculation unit, which uses it to compensate for processing time fluctuations and calculate accurate round-trip times despite variations in software processing speed.
Data Source
AI summary
Provided is a communication device including: a transmission timing calculation unit configured to calculate a transmission timing of a first frame using the number of transmitted bits from a predetermined timing to transmission of the first frame and a throughput; a transmission unit configured to transmit the first frame to an external device at the transmission timing; a reception unit configured to receive a second frame from the external device in response to the first frame; a reception timing calculation unit configured to calculate a reception timing of the second frame using the number of received bits from a predetermined timing to reception of the second frame by the reception unit and a throughput; and a round trip time calculation unit configured to calculate a round trip time using a processing time required by the external device from the reception of the first frame to the transmission of the second frame, the transmission timing, and the reception timing.