Mesh-based Optical Networks-on-chip Research Articles

The Performance Analysis of Thermal Effect in Mesh-Based Optical Networks-on-Chips

Optical networks-on-chips (ONoCs) are the key technology for the sustainable development of multiprocessors system-on-chip (MPSoC) in the future. Micro-ring resonators (MRs) are widely used in ONoCs as key device to select and redirect optical signals. However, MRs have the inherent property of being sensitive to environmental temperature. With the fluctuation of environmental temperature, its resonance wavelength drifts, which can introduce more loss and crosstalk noise to ONoCs and make the network performance decline sharply. Therefore, it is very important to analyze the influence of thermal effect in ONoCs to solve this problem. In this paper, the theoretical models of loss and crosstalk noise changing with temperature are established from device level to network level, respectively. And a series of network performances of mesh-based ONoCs caused by thermal effect are systematically modeled and analyzed employing formal methods. Finally, we conduct case studies for mesh-based ONoCs using optimized crossbar optical router and crux optical router to evaluate the proposed method. The simulation results show that the performance of mesh-based ONoCs declines with the increase of temperature, such as the decrease of optical signal-to-noise ratio (OSNR) and the increase of bit error rate (BER), which severely limits the network scalability. The formal analytical models provide a criterion for the performance analysis of thermal effect in ONoCs. In addition, the formal methods have high portability and scalability, and can provide technical support for future research work.

Exploring a New Adaptive Routing Based on the Dijkstra Algorithm in Optical Networks-on-Chip.

The photoelectric hybrid network has been proposed to achieve the ultrahigh bandwidth, lower delay, and less power consumption for chip multiprocessor (CMP) systems. However, a large number of optical elements used in optical networks-on-chip (ONoCs) generate high transmission loss which will influence network performance severely and increase power consumption. In this paper, the Dijkstra algorithm is adopted to realize adaptive routing with minimum transmission loss of link and reduce the output power of the link transmitter in mesh-based ONoCs. The numerical simulation results demonstrate that the transmission loss of a link in optimized power control based on the Dijkstra algorithm could be maximally reduced compared with traditional power control based on the dimensional routing algorithm. Additionally, it has a greater advantage in saving the average output power of optical transmitter compared to the adaptive power control in previous studies, while the network size expands. With the aid of simulation software OPNET, the network performance simulations in an optimized network revealed that the end-to-end (ETE) latency and throughput are not vastly reduced in regard to a traditional network. Hence, the optimized power control proposed in this paper can greatly reduce the power consumption of s network without having a big impact on network performance.

A Novel Algorithm for Routing Paths Selection in Mesh-Based Optical Networks-on-Chips.

Optical networks-on-chips (ONoCs) is an effective and extensible on-chip communication technology, which has the characteristics of high bandwidth, low consumption, and low delay. In the design process of ONoCs, power loss is an important factor for limiting the scalability of ONoCs. Additionally, the optical signal-to-noise ratio (OSNR) is an index to measure the quality of ONoCs. Nowadays, the routing algorithm commonly used in ONoCs is the dimension-order routing algorithm, but the routing paths selected by the algorithm have high power loss and crosstalk noise. In this paper, we propose a all-pass optical router model for two-dimensional (2-D) mesh-based ONoCs. Based on the general optical router model and the calculation models of power loss and crosstalk noise, a novel algorithm is proposed in ordder to select the routing paths with the minimum power loss. At the same time, it can ensure that the routing paths have the approximately optimal OSNR. Finally, we employ the Cygnus optical router to verify the proposed routing algorithm. The results show that the algorithm can effectively reduce the power loss and improve the OSNR in the case of network sizes of and . With the increase of the optical network scale, the algorithm can perform better in reducing the power loss and raising the OSNR.

Ant Colony Optimization-Based Thermal-Aware Adaptive Routing Mechanism for Optical NoCs

Optical networks-on-chip (NoC) based on silicon photonics has been proposed as an emerging on-chip communication infrastructure of chip multiprocessors. However, due to thermal sensitivity of optical devices under on-chip temperature variations, significant thermal-induced optical power loss would offset the benefit of optical NoCs in power efficiency. In this work, we propose a thermal-aware adaptive routing scheme based on ant colony optimization (ACO) to alleviate the thermal issue. The proposed ACO-based routing scheme applies the ACO method to formulate and optimize the routing decisions with the objective of reducing optical power loss under temperature variations. The traditional implementation of the ACO-based routing scheme requires a table in each node to keep and update pheromone, and the table size increases linearly with the number of nodes in the network. To avoid the table overhead, we further propose an approximate ACO-based routing (AACO) scheme based on linear regression. A case study on an <inline-formula> <tex-math notation="LaTeX">$8\times 8$ </tex-math></inline-formula> mesh-based optical NoC under a series of synthetic traffic patterns and real applications shows that the proposed routing schemes are able to select near-optimal paths under varying on-chip temperature variations. We further verify the scalability of the proposed routing schemes in a larger network.

A Novel Virtual-Cluster Based Architecture of Double-Layer Optical Networks-on-Chip

Optical Networks-on-Chip (ONoCs) have been proposed as the most promising solution for on-chip multi-core processors interconnection infrastructure due to its low latency, low power dissipation, and high bandwidth density. In ONoCs, the mesh topology is a typical structure that is regarded as the one of the most primary choice in ONoCs design due to its regular structure, simplicity, and divinable scalability in terms of network performance and budget. However, mesh structure has low connectivity and high insertion loss and crosstalk noise, which severely reduce the energy efficiency and signal reliability. In this paper, we first propose a novel double-layer ONoCs structure based on a partition of Virtual-Cluster in mesh, named VCmesh, which contains two candidate communication modes: inter-cluster communication and non-cluster communication. Furthermore, we design the length-optimized-routing-protocol (LORP) to select the preferred with smaller number of hops. The analyses and simulation results indicate that the performance of the VCmesh network is better than that of the typical mesh structure, especially in terms of end-to-end (ETE) latency and throughput. In physical layer performance, the VCmesh has a higher signal-to-noise-ratio (SNR), which improves the transmission quality of the optical signal. In addition, compared with the typical mesh-based ONoCs, the VCmesh-based ONoCs reduce the minimum required laser output power for 16 nodes, 25 nodes, and 36 nodes by 52.4&#x0025;, 85.6&#x0025;, and 94.6&#x0025;, respectively.

A thermal-sensitive design of a 3D torus-based optical NoC architecture

In order to overcome limitations of traditional electronic interconnects in terms of power efficiency and bandwidth density, optical networks-on-chip (NoC) based on silicon photonics have been proposed as an emerging on-chip communication architecture for chip multiprocessors (CMPs) with large core counts. However, due to thermo-optic effects, wavelength-selective silicon photonic devices such as microresonators suffer from temperature-dependent wavelength shift. In this work, we propose a thermal-sensitive design of a 3D torus-based optical NoC architecture. For the 3D torus-based optical NoC architecture, we propose a hybrid optical-electronic router architecture with a fully-connected 7 × 7 optical switching fabric. Besides, a thermal-sensitive routing algorithm is proposed to optimize the optical power loss in the presence of on-chip temperature variations. Simulation results show that for a set of synthetic traffic patterns, the proposed 3D torus-based optical NoC with the thermal-sensitive routing reduces the average thermal-induced optical power loss by 14.3% and 17% respectively as compared to the matched 3D torus-based optical NoC and the 3D mesh-based optical NoC with the traditional XYZ routing. For a set of real applications, the proposed 3D torus-based optical NoC with the thermal-sensitive routing reduces the worst-case optical power loss by 7.9% and 14.6% respectively as compared to the matched 3D torus-based optical NoC and the 3D mesh-based optical NoC with the traditional XYZ routing.

Exploring Reliable Communication in Optical Networks-on-Chip Based on All-Optical Linear Block Codes Encoder

Crosstalk noise and insertion loss are important factors influencing the performance of optical networks-on-chip (ONoCs), especially in wavelength division multiplexing (WDM) based ONoCs. These factors lead to a high bit error rate (BER) of the communication system, thereby reducing the reliability of the communication in ONoCs. All-optical coding on chip is one of the important methods to solve this problem, so a high-reliability communication scheme that utilizes all-optical coding in ONoCs is implemented in this paper. The scheme mainly exploits the characteristics of linear block codes to implement the function of checking and correcting bit errors. As a core part of implementing this scheme, a micro-resonators (MRs)-based all-optical linear block codes encoder is designed to encode the information sequence before transmission. When the encoded data arrive at the receiving end, an error detection and correction (EDC) module can detect and correct the bit errors according to certain rules. In addition, for bit errors that exceed the error correction range, a retransmission mechanism (RT) is activated in communication system to denoise and retransmit the uncorrectable data group. In order to verify the validity of the proposed approach, a case study is conducted in mesh-based ONoCs with WDM. The simulation results manifest that the information transmission quality can be effectively optimized by applying the reliable communication scheme to the ONoCs. This approach reduces the BER and improves the optical signal-to-noise ratio (OSNR) of optical signals. Under the same condition that the scale of network reaches the maximum, the OSNR is increased by 9.8301 dB and the BER is reduced by 12.4499 dB compared with the traditional mesh-based ONoCs. Therefore, this work has a great impact on improving the reliability of communication systems.

Formal Analysis of Crosstalk Noise in Mesh-Based Optical Networks-on-Chip with WDM

Optical networks-on-chip (ONoCs) using wavelength division multiplexing (WDM) technology is one of the most promising candidates in tacking multichannel communication on the single waveguide in multicore systems-on-chip. However, compared to the traditional ONoCs with single wavelength transmitting, ONoCs employing WDM can be more susceptible to the influence of the crosstalk noise, especially the nonlinear noise generated by the four-wave mixing (FWM) effect. Consequently, the crosstalk noise can result in the signal distortion and performance degradation, even constrain the scalability of the WDM-based ONoCs. In this paper, a formal systematical analysis model including the crosstalk noise and optical signal-to-noise ratio (OSNR) analysis in mesh-based ONoCs using WDM is presented at device, router, and network levels. To demonstrate the feasibility of the proposed method, we exploit a numerical simulation example of mesh-based ONoCs using the optimized crossbar and Crux optical routers with eight optical wavelengths. The simulation results show that the crosstalk noise is the critical element for the OSNR diminution and the scalability constraint of the mesh-based ONoCs using WDM. For example, the input power is 0 dBm in the worst case, when the mesh-based WDM-based ONoCs size using optimized crossbar is 4 × 4, the average FWM noise power, linear noise power, and OSNR are –37.61 dBm, –38.86 dBm, and 4.26 dB, respectively, and these values are –37.78 dBm, –38.95 dBm, and –13.65 dB when the scale of network is 6 × 6.

Performance Optimization and Evaluation for Mesh-Based Optical Networks-on-Chip

Optical networks-on-chips (ONoCs) are burgeoning structures of communication that can give a solution to the bandwidth and latency for multiprocessor systems-on-chips. Furthermore, photonic devices are widely used in ONoCs but suffer from crosstalk noise. Therefore, crosstalk noise is the critical factor that affects signal transmission and limits the network scale of ONoCs. To reduce the crosstalk noise sharply, an angle optimization that uses the cross angle of 60 $^{\circ}$ or 120 $^{\circ}$ instead of the conventional angle of 90 $^{\circ} $ is proposed to optimize the Crux router. Furthermore, we present a signal transmission system simulation model for the mesh-based ONoC. For different routers applied to the mesh-based ONoC, the simulation model can present the time-domain waveform, eye diagram, and bit-error-rate (BER) curve clearly. On the basis of the analytical model, the results show that the minimum signal-to-noise ratio (SNR) of a 7 $\times$ 7 mesh-based ONoC is 20.9 dB when using optimized Crux routers, and the injection power is equal to 0 dBm, which is 2.1 dB better than using Crux routers. Therefore, the application of angle optimization to the Crux router and mesh network can minimize crosstalk noise and improve the scalability of mesh-based ONoCs.

Systematic Analysis of Crosstalk Noise in Folded-Torus-Based Optical Networks-on-Chip

Photonic devices are widely used in optical networks-on-chip (ONoCs) and suffer from crosstalk noise. The accumulative crosstalk noise in large scale ONoCs diminishes the signal-to-noise ratio (SNR), causes severe performance degradation, and constrains the network scalability. For the first time, this paper systematically analyzes and models the worst-case crosstalk noise and SNR in folded-torus-based ONoCs. Formal analytical models for the worst-case crosstalk noise and SNR are presented. The crosstalk noise analysis is hierarchically performed at the basic photonic device level, then at the optical router level, and finally at the network level. We consider a general 5 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\,\times\,$</tex></formula> 5 optical router model to enable crosstalk noise and SNR analyses in folded-torus-based ONoCs using an arbitrary 5 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\,\times\,$</tex> </formula> 5 optical router. Using the general optical router model, the worst-case SNR link candidates, which restrict the network scalability, are found. Also, we present a novel crosstalk noise and loss analysis platform, called CLAP, which can analyze the crosstalk noise and SNR of arbitrary ONoCs. Case studies of optimized crossbar and Crux optical routers using recent photonic device parameters are presented. Moreover, we compare the worst-case crosstalk noise and SNR in folded-torus-based and mesh-based ONoCs using optimized crossbar and Crux optical routers. The quantitative simulation results show the critical behavior of crosstalk noise in large scale ONoCs. For example, in folded-torus-based ONoCs using the Crux optical router, the noise power exceeds the signal power for network sizes larger than 12 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\,\times\,$</tex></formula> 12; when the network size is 20 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\,\times\,$</tex></formula> 20 and the injection signal power equals 0 dBm, the signal power and noise power are <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\rm 9.4}~{\rm dBm}$</tex></formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\rm 6.1}~{\rm dBm}$</tex></formula> , respectively.

Formal Worst-Case Analysis of Crosstalk Noise in Mesh-Based Optical Networks-on-Chip

Crosstalk noise is an intrinsic characteristic as well as a potential issue of photonic devices. In large scale optical networks-on-chips (ONoCs), crosstalk noise could cause severe performance degradation and prevent ONoC from communicating properly. The novel contribution of this paper is the systematical modeling and analysis of the crosstalk noise and the signal-to-noise ratio (SNR) of optical routers and mesh-based ONoCs using a formal method. Formal analytical models for the worst-case crosstalk noise and minimum SNR in mesh-based ONoCs are presented. The crosstalk analysis is performed at device, router, and network levels. A general 5 × 5 optical router model is proposed for router level analysis. The minimum SNR optical link candidates, which constrain the scalability of mesh-based ONoCs, are identified. It is also shown that symmetric mesh-based ONoCs have the best SNR performance. The presented formal analyses can be easily applied to other optical routers and mesh-based ONoCs. Finally, we present case studies of mesh-based ONoCs using the optimized crossbar and Crux optical routers to evaluate the proposed formal method. We find that crosstalk noise can significantly limit the scalability of mesh-based ONoCs. For example, when the mesh-based ONoC size, using optimized crossbar, is larger than 8 × 8, the optical signal power is smaller than the crosstalk noise power; when the network size is 16 × 16 and the input power is 0 dBm, in the worst-case, the signal power is -24.9 dBm and the crosstalk noise power is -11 dBm.

3-D Mesh-Based Optical Network-on-Chip for Multiprocessor System-on-Chip

Optical networks-on-chip (ONoCs) are emerging communication architectures that can potentially offer ultrahigh communication bandwidth and low latency to multiprocessor systems-on-chip (MPSoCs). In addition to ONoC architectures, 3-D integrated technologies offer an opportunity to continue performance improvements with higher integration densities. In this paper, we present a 3-D mesh-based ONoC for MPSoCs, and new low-cost nonblocking 4 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\,\times\,$</tex></formula> 4, 5 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\,\times\,$</tex></formula> 5, 6 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\,\times\,$</tex></formula> 6, and 7 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\,\times\,$</tex></formula> 7 optical routers for dimension-order routing in the 3-D mesh-based ONoC. Besides, we propose an optimized floorplan for the 3-D mesh-based ONoC. The floorplan follows the regular 3-D mesh topology but implements all optical routers in a single optical layer. The floorplan is optimized to minimize the number of extra waveguide crossings caused when merging the 3-D ONoC to one optical layer. Based on a set of real applications and uniform traffic pattern, we develop a SystemC-based cycle-accurate NoC simulator and compare the 3-D mesh-based ONoC with the matched 2-D mesh-based ONoC and 2-D electronic NoC for performance and energy efficiency. Additionally, we quantitatively analyze thermal effects on the 3-D 8 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\,\times\,$</tex></formula> 8 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\,\times\,$</tex></formula> 2 mesh-based ONoC.

System-Level Modeling and Analysis of Thermal Effects in Optical Networks-on-Chip

The performance of multiprocessor systems, such as chip multiprocessors (CMPs), is determined not only by individual processor performance, but also by how efficiently the processors collaborate with one another. It is the communication architecture that determines the collaboration efficiency on the hardware side. Optical networks-on-chip (ONoCs) are emerging communication architectures that can potentially offer ultra-high communication bandwidth and low latency to multiprocessor systems. Thermal sensitivity is an intrinsic characteristic of photonic devices used by ONoCs as well as a potential issue. This paper systematically modeled and quantitatively analyzed the thermal effects in ONoCs. We used an 8 × 8 mesh-based ONoC as a case study and evaluated the impacts of thermal effects in the average power efficiency for real MPSoC applications. We revealed three important factors regarding ONoC power efficiency under temperature variations, and proposed several techniques to reduce the temperature sensitivity of ONoCs. These techniques include the optimal initial setting of microresonator resonant wavelength, increasing the 3-dB bandwidth of optical switching elements by parallel coupling multiple microresonators, and the use of passive-routing optical router Crux to minimize the number of switching stages in mesh-based ONoCs. We gave a mathematical analysis of periodically parallel coupling of multiple microresonators and show that the 3-dB bandwidth of optical switching elements can be widened nearly linearly with the ring number. Evaluation results for different real MPSoC applications show that, on the basis of thermal tuning, the optimal device setting improves the average power efficiency by 54% to 1.2 pJ/bit when chip temperature reaches 85 °C. The findings in this paper can help support the further development of this emerging technology.