Survey of
Wireless Network-on-Chip Systems
Master’s Project Defense
Xi Li
Report Advisor: Dr. Vishwani D. Agrawal
Report Committee: Dr. Shiwen Mao and Dr. Jitendra Tugnait
Department of Electrical and Computer Engineering
Auburn 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 “packetbased (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 500GHz
Devices’ sizes
Millimeter order
Millimeter order
Micrometer order
Transmission range
Not 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 wireless
Limited wireless source
Limited transmission range
Therefore, hard to use in practice
 Hybrid: Combination of wired and wireless
Reduce the number of hop
Alleviate latency
Therefore, always used
Xi's M.E.E Presentation
※ Structure
※ Wireless insertion
※ Routing scheme and communication protocol
Xi's M.E.E Presentation
※ Structure of Hybrid Wireless NoC system: Hierarchical
 Bottom level: nodes form to a cluster via wired link
Top 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
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
※ Conclusion
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.
Xi's M.E.E Presentation
※ Future work
 Devices’ manufactory
 Topology and communication protocol
Other aspect: fault tolerant and
reconfiguration
Xi's M.E.E Presentation
Thank You
Xi's M.E.E Presentation
Question?
Xi's M.E.E Presentation