Performance Study For Fat-Tree-Based Optical Networks-on-Chip With WDM

With the ever-increasing demand for computing performance and the eagerness for simultaneous processing of multiple tasks,the number of processing cores to be integrated on a single chip will continually increase.And on a chip with a limited power budget,high-speed information processing of processor cores on the chip and data parallel computing make multiprocessor system-on-chips(MPSoCs)urgently need a low-power,high-bandwidth,low-latency interconnection way.In the traditional MPSoCs,multi-cores communication is based on electrical interconnection,which is faced with many problems that are huge obstacles to the continuous development of MPSoCs,such as bit error,delay,bandwidth and power consumption.Currently,optical network-on-chips(ONoCs)are a new type of interconnect between multi-processor cores on a chip,which use optical connections instead of electrical connections and are expected to solve the problems faced by electrical interconnects.With the further demand for on-chip bandwidth in the fields of big data,artificial intelligence,and supercomputing in recent years,the use of single-wavelength ONoCs can no longer satisfy super-capacity data transmission,WDM-based optical networks-on-chip(WDM-ONoCs)has become the inevitable direction for the development of MPSoCs.WDM-ONoCs can effectively increase the communication bandwidth,reduce delay and power consumption.Therefore,related researches on WDM-ONoCs have become a hot topic in the study of inter-cores high-speed interconnection in recent years,and are the key technology for the continuing development of MPSoCs in the future,which have great application prospects in the fields of big data centers,multi-cores systems,high-speed communication networks,and ultra-large-scale integrated circuits.WDM-ONoCs integrate lasers,modulators,optical routers,photodetectors,optical wavelength conversion devices,and optical code-type conversion devices to achieve connection on a silicon on insulator(SOI)chip.However,due to the manufacturing processes of these basic devices and their own material properties,WDM-ONoCs inevitably suffer from a series of power loss and crosstalk noise.In particular,crosstalk is the most servere factor affecting bit error rate(BER)of WDM-ONoC,will continually accumulate to the network and thus affect the performance improvement of the network.Compared with traditional ONoCs employing single wavelength,WDM-ONoCs are more susceptible to crosstalk noise,especially the four-wave mixing(FWM)crosstalk noise generated by nonlinear FWM effect,which is more difficult to be separated and eliminated from original optical signals.These crosstalk noises accumulated to large-scale WDM-ONoCs will lead to optical signal distortion,degrad communication quality,reduce optical signal-to-noise ratio(OSNR)and bring information transmission errors,eventually cause network performance degradation and limite scalability of the network scale.Therefore,this thesis focus on the crosstalk noise characteristic of WDM-ONoCs,proposes a comprehensive crosstalk analysis model and researches on crosstalk characteristic for Fat-Tree-based ONoCs(Fat-Tree-ONoCs)with WDM.In addition,as far as the network performance,this thesis establishes a network performance analysis platform.These studies make a complete performance study from the physical level to the network level to Fat-Tree-ONoCs with WDM,will build theoretical basis for the next generation of ONoCs and provide reliable technical supports,and have high scalability and portability,it is suitable for any network size and any topology structure.The main content of this thesis is as follows:Firstly,according to the system composition of WDM-ONoCs,the related theoretical basis of the silicon-based waveguide,SOI micro-ring resonator,WDM technology foundation and FWM effect are introduced in detail,and the power calculation model of FWM crosstalk is established.Secondly,according to the network construction requirement of Fat-Tree-ONoCs with WDM,basic optical switching elements with WDM,the multi-ports,low-crosstalk,low-loss optical router,and the fat-tree-based ONoCs supporting WDM technology are designed.The crosstalk characteristic analysis methods at the device level,routing level,and network level are established hierarchically.Finally,WDM-based optical turnaround router optical router(WOTAR)is applied to the Fat-Tree-based ONoCs supporting WDM,and optical links with worst OSNR under different network sizes are determined.And the worst OSNR,bit error rate,crosstalk noise and power loss of this network are obtained.An on-chip multi-channel transmission system based on Optisystem is designed to view waveform changes of optical signals passing multi-channel transmission system on chip.Based on OPNET,a network feature simulation platform for Fat-Tree-based optical network-on-chips supporting WDM is built to verify the network performance on actual on-chip communication traffic patterns,such as the throughput and end-to-end delay of the network.The research results show that both of the traditional linear crosstalk noise and the FWM noise greatly affect the performance of Fat-Tree-ONoCs with WDM,such as reducing the OSNR,and limiting the network scalability.For example,in the worst case of crosstalk noise,when the input optical signal power of the network with 64 processing cores is 0 dBm,the average OSNR of eight wavelength optical signals is-9.47 dB,which means that the average crosstalk noise is slightly higher than the average signal power.However,when the number of processor cores reaches to 128,the average OSNR is 34.37 dB,which is 24.90 dB lower than that of the network with 64 processor cores.In addition,when the number of processing cores exceeds 64,the average worst OSNR of the Fat-Tree-ONoCs with WDM is less than 0,which means that the network design of Fat-Tree-ONoCs supporting WDM should not exceed 64 processing cores.The Fat-Tree-ONoCs with WDM has very excellent throughput and low latency under actual traffic patterns on chip.Compared to the Fat-Tree-based ONoCs employing single-wavelength,with the same packet size,the saturation point of Fat-Tree-based-ONoCs with WDM is more backward,the delay is lower,and the throughput is larger;Under the same network load,increasing the packet size can improve the network throughput and reduce the delay to a certain extent.