Xi's M.E.E Presentation

Report Advisor: Dr. Vishwani D. AgrawalReport Committee: Dr. Shiwen Mao and Dr. Jitendra Tugnait

Survey of Wireless Network-on-Chip Systems

Master’s Project DefenseXi Li

Department of Electrical and Computer EngineeringAuburn University, AL 36849 USA

Xi's M.E.E Presentation

Outline ※ Background ※ Problem Statement ※ General Solution ※ Contribution

- Experimental Results and Analysis

Latency vs. Injection Rate Latency vs. Number of Virtual Channels

※ Conclusion

Xi's M.E.E Presentation

Background

Xi's M.E.E Presentation

※ Network-on-Chip (NoC) is an approach to designing the communication subsystem between IP cores on a single chip, modules are interconnected via switches (routers) ※ Size: mm-scale ※ Numbers of processors: dozens of or even hundreds of ※ Communication method:“Point-to-point” and “packet-based (usually in flit)” ※ Layered protocol (MAC layer, network layer) ※ Modules’ structures should be as simple as possible

※ Variety kinds of topologies are used in NoC

Xi's M.E.E Presentation

A 4 by 4 regular mesh NoC topology

Xi's M.E.E Presentation

Problem Statement

Xi's M.E.E Presentation

※ High latency and power consumption will be introduced due to 1) the multi-hop in the communication path between two nodes and 2) high injection rate.

More nodes in a chip, more hops and higher injection ※rate will be in the communication.

Many hops, high injection rate, and results a high latency

Xi's M.E.E Presentation

General Solutions

Xi's M.E.E Presentation

※ Wireless link is introduced – reduce the number of hops in the path Some outstanding transmission ways: UWB, mm-wave, ※CNT

UWB-Based Mm-Wave-Based

CNT-Based

Bandwidth 3.6GHz Tens of GHz Around 500GHzDevices’ sizes Millimeter order Millimeter order Micrometer

orderTransmission

rangeNot enough

(1mm)enough Enough

# of Channels per link

multiple single multiple

Xi's M.E.E Presentation

※ Pure Wireless vs. Hybrid Wireless NoC system

Pure: All nodes are fully connected via wirelessLimited wireless sourceLimited transmission rangeTherefore, hard to use in practice

Hybrid: Combination of wired and wirelessReduce the number of hopAlleviate latencyTherefore, always used

Xi's M.E.E Presentation

※ Structure Wireless insertion※ Routing scheme and communication protocol※

Xi's M.E.E Presentation

clustercluster

cluster

clustercluster

cluster

cluster

※ Structure of Hybrid Wireless NoC system: Hierarchical Bottom level: nodes form to a cluster via wired linkTop level: some clusters are connected by wireless

(sometimes, clusters in neighbor are still connected by wired)

Structure of hybrid wireless NoC

Xi's M.E.E Presentation

※ Wireless insertion:Using SA (simulated annealing) to get the optimal configuration – the placement of the wireless links

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Xi's M.E.E Presentation

※ Routing scheme and communication protocol Should be as simple as possible Routing schemes’ examples: Location-based

(LBR), dimension-ordered, path length-based and some other adopting router scheme

Communication protocol: multi-channel protocol (combination of TDM and FDM)

Other used communication schemes: pulse position modulation, biphase modulation, on-off key modulation…

Xi's M.E.E Presentation

Contribution

Xi's M.E.E Presentation

※ Experiment

In this section, performance of both traditional NoC (wired) and wireless NoC will be simulated; then, a comparison between them will me make.

Some parameters: injection rate: bit/cycle per node latency: cycle virtual channel

Xi's M.E.E Presentation

※ Latency vs. Injection Rate (wired)

8 by 8 regular mesh:

Xi's M.E.E Presentation

※ Latency vs. Injection Rate (wired)

In order to reduce the distance between two nodes in wired communication, we can increase the concentration of the network.

Concentration stands for the number of nodes that share a single router. E.g. concentration 4 means a router is shared by 4 nodes.

Xi's M.E.E Presentation

※ Latency vs. Injection Rate (wired)

A 4 by 4 cmesh NoC topology

Xi's M.E.E Presentation

A 4 by 4 regular mesh NoC topology

Xi's M.E.E Presentation

※ Latency vs. Injection Rate (wired)

therefore, in cmesh topology, the average distance can reduce.

8 by 8 cmesh hop

8 by 8 regular mesh hop

Xi's M.E.E Presentation

※ Latency vs. Injection Rate (wired)

8 by 8 cmesh:

Xi's M.E.E Presentation

※ Latency vs. Injection Rate (wired) However, since every router has more work to do,

latency is still introduced Therefore, there is a trade-off between the distance

and number of nodes per router if we use wired link.

Comparison between8 by 8 regular mesh and cmesh:

Xi's M.E.E Presentation

※ Latency vs. Injection Rate (wireless)

Therefore, wireless NoC is needed Here, we use a kind of topology to simulate

wireless NoC system – flattened butterfly topology

Xi's M.E.E Presentation

※ Latency vs. Injection Rate (wireless)

A 4 by 4 flattened butterfly NoC topology

Xi's M.E.E Presentation

※ Latency vs. Injection Rate (wireless)

64 nodes 256 nodes

Xi's M.E.E Presentation

※ Latency vs. Number of Virtual Channels (wired)

8 by 8 regular mesh

Xi's M.E.E Presentation

※ Latency vs. Number of Virtual Channels (wireless)

Wireless NoC (64 nodes)

Xi's M.E.E Presentation

※ Comparison between wired and wireless

Xi's M.E.E Presentation

Conclusion

Xi's M.E.E Presentation

Comparison with traditional wired NoC, wireless NoC has a great improvement in performance (latency, maximum injection rate, so that the throughput)

In wireless NoC, before a specific level of injection rate, the latency increment is tiny.

Virtual channel plays a more important role in wireless NoC than in traditional NoC.

※ Conclusion

Xi's M.E.E Presentation

※ Future work

Devices’ manufactory Topology and communication protocolOther aspect: fault tolerant and

reconfiguration

Xi's M.E.E Presentation

Thank You

Xi's M.E.E Presentation

Question?