# A Novel Decomposed Optical Architecture for Satellite Terrestrial Network Edge Computing
## 6 Conclusions  
We implement and experimentally investigate an optical computing prototype with decomposed hardware cubes for STN edge computing. In the proposed NOS-based flat terrestrial computing network, decomposed hardware cubes are interconnected, leveraging two parallel optical packet sending plane and control plane. Based on a four-cube computing prototype, the physical and network performance of the proposed computing architecture are experimentally assessed. Then, utilizing the experimentally measured parameters, the scalability of the decomposed computing network is numerically evaluated scaling up to 4096 hardware cubes. Finally, compared with the existing terrestrial computing networks, the superiority of the implemented optical computing network with decomposed hardware cubes is verified, and it is feasible to apply the proposed decomposed architecture as terrestrial infrastructures for STN edge computing.  
It is shown in experimental and numerical assessments:  
1. In the physical assessment, the implemented computing prototype with decomposed hardware cubes achieves none-error packet transmission based on the power compensation of 0.5 dB. Minimal signal interference across the optical channel is ensured with larger than 60 dB ON/OFF ratio of SOA-based gates.
2. For the network performance of the computing prototype with decomposed hardware cubes, an end-to-end access latency of 122.3 ns can be obtained in the experimental investigation, while there is zero packet loss after initial CDR procedure.
3. When scaling the NOS port count to 64, the NOS-based interconnect network provides optical signals with 30.5 dB OSNR at the receiver part of decomposed hardware cubes, while requiring power compensation of 1.5 dB for none-error packet transmission. Under a network scale of 4096 decomposed hardware cubes, numerical studies report an end-to-end access latency of 148.5 ns inside the same rack with an MCAR of 0.9 and TRX bandwidth of 40 Gb/s.  
Compared with current terrestrial computing networks, the proposed NOS-based flat decomposed computing network can provide high bandwidth optical interconnection among hardware cubes (even higher than hundreds of gigabits) and low access latency (tens nanoseconds). Benefiting from the parallel and flat structure, the performance is maintained when scaling the network (up to thousands of hardware cubes).  
Due to the broadcast and select structure of NOS, the SOA-based gates receive much lower optical power input when further increasing the port count of NOS. This limitation may introduce more noise when amplifying the optical signals and degrade the performance of the NOS-based decomposed computing network. Meanwhile, if the target data are non-uniformly distributed among hardware cubes, there are more potential optical packet contentions, leading to higher access latency. Therefore, it is necessary to designthe corresponding data management algorithm and packet routing policy to minimize the packet contention and access latency.  
Conceptualization, X.G. and Y.J.; methodology, X.G.; software, X.G.; formal analysis, X.G., Y.Z., Y.J., S.W. and H.L.; resources, X.G. and Y.Z.; data curation, X.G.; writing--original draft preparation, X.G.; writing--review and editing, X.G.; visualization, X.G.; supervision, X.G.; project administration, X.G. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Natural Science Foundation of China, grant number U21B2050.  
Not applicable.  
The authors declare no conflict of interest.