TDM-PON ONU Multiplexing for CPRI Fronthaul Bandwidth
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Solution Overview
Problem
Current cloud radio access network (C-RAN) fronthaul technologies, such as CPRI and eCPRI, face inefficiencies in bandwidth usage and latency, particularly in time-sensitive applications like 5G RAN, due to high transmission overhead and latency in mobile fronthaul connections.
Innovation Solution
Implementing a method and apparatus for low-latency eCPRI transmission using time division multiplexing-passive optical network (TDM-PON) systems, where an optical network unit (ONU) coordinates Ethernet packet transmission from remote radio units (RRUs) to a baseband unit (BBU) with pre-allocated time slots, minimizing latency and contention through just-in-time buffering and multiplexing, and maintaining packet order without idle bits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional CPRI or eCPRI technologies are used for fronthaul transmission, then connectivity between BBU and RRUs is established, but bandwidth efficiency is low and transmission latency is high
Solution Approach 1:
The patent implements pre-allocation of time slots for TDM-PON upstream transmission and pre-determines buffer starting times and sizes before actual data transmission. This preliminary setup allows Ethernet packets to be efficiently packaged into transport blocks without contention at the OLT, achieving approximately 10× bandwidth efficiency improvement while maintaining low latency by eliminating runtime allocation overhead
Solution Approach 2:
The patent changes the transmission parameter structure by transitioning from traditional CPRI/eCPRI framing to TDM-PON with pre-allocated time slots. By adjusting buffer starting time and size parameters, and packaging Ethernet packets into fixed-length transport blocks, the system achieves optimized bandwidth utilization and reduced latency compared to conventional fronthaul technologies
2Productivity
If Ethernet packets are transmitted without coordination to multiple RRUs, then transmission simplicity is maintained, but contention occurs at the OLT and bandwidth efficiency decreases
Solution Approach 1:
The patent segments the fronthaul transmission into dedicated time slots for different RRUs within the TDM-PON upstream transmission. Each RRU is assigned specific time slots and buffer parameters, allowing simultaneous transmissions without contention at the OLT. This segmentation approach achieves high bandwidth efficiency while keeping coordination manageable through structured time division
Solution Approach 2:
The system performs preliminary coordination by pre-allocating time slots and determining buffer parameters for each RRU before transmission begins. This upfront planning eliminates runtime contention at the OLT and optimizes bandwidth utilization, achieving approximately 10× efficiency improvement with controlled complexity through systematic pre-configuration
3Reliability
If packet buffering is implemented to maintain packet order, then packet sequence integrity is ensured, but additional latency is introduced
Solution Approach 1:
The patent determines buffer starting times and sizes in advance before actual packet buffering occurs. By pre-calculating these parameters based on the coordinated transmission schedule, the system maintains packet order for each RRU with minimal latency. The pre-planned buffer configuration ensures reliability while avoiding the need for extensive runtime buffering that would increase delay
Data Source
AI summary
A method of communication between a base band unit (BBU) and a plurality of remote radio units (RRUs) via a point-to-multipoint time division multiplexing passive optical network (TDM-PON) system is provided. The method can be performed by an ONU and comprises receiving Ethernet packets from the Ethernet interface of an RRU of the plurality of RRUs, performing time-division multiplexing of the Ethernet packets to generate multiplexed packets, storing in a buffer of the ONU the multiplexed packets based on a pre-determined buffer starting time and buffer size, packaging the multiplexed packets in the buffer to fixed length transmission blocks (TBs) having pre-allocated time slots for TDM-PON upstream transmission, and transmitting the TBs to an optical line terminal (OLT) that is communicatively coupled to the BBU such that no contention of TBs occurs at the OLT.