In Infrastructure for Enterprise Wir ireless Networks Vivek - - PowerPoint PPT Presentation

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In Infrastructure for Enterprise Wir ireless Networks Vivek - - PowerPoint PPT Presentation

Feb 08, 2024 476 likes •1.03k views

Vid idyut: Exploiting Power Lin ine In Infrastructure for Enterprise Wir ireless Networks Vivek Yenamandra and Kannan Srinivasan Motivation Increasing demand for wireless capacity Proliferation of BYOD in workplaces Data

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Vid idyut: Exploiting Power Lin ine In Infrastructure for Enterprise Wir ireless Networks

Vivek Yenamandra and Kannan Srinivasan

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Motivation

  • Increasing demand for wireless

capacity

  • Proliferation of BYOD in workplaces
  • Data Intensive applications: Video

Streaming, Teleconferencing, Surveillance etc.

  • Scare spectrum resources

Growing emphasis for spectrally efficient large capacity wireless networks

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Enterprise WLAN

Ethernet Backbone AP 1 2 3 4 Dense Client Distribution

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Enterprise WLAN

Ethernet Backbone AP 1 2 3 4 Dense Client Distribution

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Enterprise WLAN

Ethernet Backbone AP 1 2 3 4 Dense Client Distribution The APs share medium(time/frequency/code) to mitigate interference

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Alternative?

Ethernet Backbone 2 3 4 1 Multiple APs coordinate to emulate a single virtual AP with many antennas – Network MIMO

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Why Network MIM IMO?

Ethernet Backbone 2 3 4 1 All four APs can serve their clients simultaneously without needing to share the medium.

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Network MIM IMO Prerequisite

The coordinating APs need to be synchronized in frequency and time

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Cannot synchronize

Network MIM IMO Im Implementation1

Ethernet Backbone Lead AP Synchronization Header Synchronize 2 3 4 1

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Cluster

[1]. Hariharan et.al, JMB: Scaling Wireless Capacity with User Demands, SIGCOMM, 2012

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Network MIM IMO Im Implementation

Ethernet Backbone 2 3 4 1 Frequency mismatch causes interference

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Network MIM IMO Im Implementation

Ethernet Backbone 2 3 4 1 The transmission range of the lead AP limits the number of APs that can coordinate to emulate a single large virtual AP

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How can we synchronize across clusters?

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Vidyut

Power lines Reference Clock transmitted on the Power Lines Each AP uses the reference clock on the power lines to synchronize their

  • wn carrier clocks using a PLL.

2 3 4 1

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Vidyut

Power lines Reference Clock transmitted on the Power Lines Each AP uses the reference clock on the power lines to synchronize their

  • wn carrier clocks using a PLL.

2 3 4 1

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All APs are synchronized

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Vidyut

2 3 4 1 No Frequency mismatch = No interference

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Phase Locked Loop

Phase difference detector Phase Difference to Voltage Converter Low- pass filter VCO Fref Fo ÷ 𝑶 Feedback Path Distributed to the baseband clock, carrier clock Fo/N Reference clock from the power lines Power Line

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Phase Locked Loop

Phase difference detector Phase Difference to Voltage Converter Low- pass filter VCO Fref Fo ÷ 𝑶 Feedback Path Distributed to the baseband clock, carrier clock Fo/N Reference clock from the power lines Power Line

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Phase Locked Loop

Phase difference detector Phase Difference to Voltage Converter Low- pass filter VCO Fref Fo ÷ 𝑶 Feedback Path Distributed to the baseband clock, carrier clock Fo/N Reference clock from the power lines Power Line

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Phase Locked Loop

Phase difference detector Phase Difference to Voltage Converter Low- pass filter VCO Fref Fo ÷ 𝑶 Feedback Path Distributed to the baseband clock, carrier clock Fo/N Reference clock from the power lines Power Line

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Phase Locked Loop

Phase difference detector Phase Difference to Voltage Converter Low- pass filter VCO Fref Fo ÷ 𝑶 Feedback Path Distributed to the baseband clock, carrier clock Fo/N Reference clock from the power lines Power Line

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How to select the reference frequency?

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Selecting the Reference Frequency

  • Determined by the Power Distribution Network
  • Elements like transformers/distribution panels

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Measuring Characteristics

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Transformer Response

Primary Secondary

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Transformer Response

  • 20
  • 15
  • 10
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5 1 2 3 4 5 6 7 8 9 10 Gain(dB) Frequency(MHz) Same Phase

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Transformer Response

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5 1 2 3 4 5 6 7 8 9 10 Gain(dB) Frequency(MHz) Same Phase

Filtering effect

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Three-Phase Power Supply

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The three phases are physically isolated Do we need a separate reference clock for each phase?

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Transformer Response

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  • 20
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5 1 2 3 4 5 6 7 8 9 10 Gain(dB) Frequency(MHz) Same Phase Cross Phase

Transformer Response

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  • 20
  • 15
  • 10
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5 1 2 3 4 5 6 7 8 9 10 Gain(dB) Frequency(MHz) Same Phase Cross Phase

Transformer Response

Site of coupling across phases

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  • 20
  • 15
  • 10
  • 5

5 1 2 3 4 5 6 7 8 9 10 Gain(dB) Frequency(MHz) Same Phase Cross Phase

Transformer Response

Site of coupling across phases

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We need just a single reference clock

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Evaluation: How effective is Vidyut’s phase synchronization?

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Evaluating Phase Mismatch

Both APs synchronized using Vidyut

Φmismatch = (Freceived – Fpilot ) x T + Φinitial

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Freceived

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Evaluating Phase Mismatch

Both APs synchronized using Vidyut

Φmismatch = (Freceived – Fpilot ) x T + Φinitial

When both nodes are synchronized, Freceived = Fpilot making Φmismatch constant over time

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Freceived

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Phase Synchronization Over Time

No deteriorating trend over time

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Phase Synchronization Over Time

The randomness is introduced by the phase noise in the PLL

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Phase Synchronization Over Time

We observe a phase mismatch under 0.05 radians over 90% runs.

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Power Distribution Network

  • Power lines are designed to carry power at 50/60 Hz
  • The higher frequency of the reference clock

attenuates over distance.

Each AP regenerates the reference clock back on to the power lines

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Clock Regeneration

2 1 Reference Clock Ref In Ref In Each AP feeds back a Reference clock phase matched to Ref In back on to the power lines.

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Clock Regeneration

2 1 Reference Clock Ref In Ref In Each AP feeds back a Reference clock phase matched to Ref In back on to the power lines. Enables synchronization of spatially distant APs

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Clock Regeneration

2 1 Reference Clock Ref In Ref In Each AP feeds back a Reference clock phase matched to Ref In back on to the power lines. Enables synchronization of spatially distant APs Makes Vidyut robust against single point of errors

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Regeneration Effect on Clock Synchronization

  • Each clock regeneration adds a distinctive phase noise characteristics
  • The phase mismatch between a pair of nodes does not correlate with

the number of clock regenerating sources between them.

  • Details in the paper.

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Achieving Distributed Time Synchronization

  • We adopt the principles proposed in [1].
  • Utilize the stable power frequency to achieve distributed time

synchronization

  • Details in the paper.

[1]. Rowe et.al, Low-power clock synchronization using electromagnetic energy radiating from ac power lines, SENSYS, 2009

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Im Implementation

  • Eight NI based SDR nodes
  • NI-5791 RF Front End
  • Accepts Reference Input/ Drives PLL output
  • 10 MHz OFDM in the 2.4 GHz ISM Band
  • PXIe-7965R FPGA ..
  • Agilent 8648C : 10 MHz Reference Clock

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Testbed

We interface the nodes to random power outlets across all three phases of power supply

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32m 20m

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Evaluation: Performance gains of Vidyut-enabled Network MIMO.

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Setup

Divide the eight nodes into four APs and four clients. Place the nodes at random locations as before such that the APs are divided into two clusters Each cluster has clients to service Compared schemes: MegaMIMO, NEMOx1

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[1]. Zhang et.al, Scalable Network MIMO for wireless networks, Mobicom, 2013

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NEMOx

Ethernet Backbone 2 3 4 1 Frequency mismatch causes interference

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NEMOx

Ethernet Backbone 2 3 4 1

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Throughput Gain

0.2 0.4 0.6 0.8 1 0.5 1 1.5 2 Fraction Throughput Gain MegaMIMO NEMOx

Absence of Cross Cluster Interference

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As the Number of f Clusters In Increases

MATLAB based simulation Account for increase in noise at each client due to phase mismatch between APs as their number increases. Provisions slackness for variance in time synchronization MegaMIMO and NEMOx are implemented using a TDMA over CSMA type MAC

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2 4 6 8 2 3 4 6 8 10 12 15 18 20 Throughput Gain Number of Clusters

MegaMIMO NEMOx

As the Number of f Clusters In Increase

Higher Density Low Density

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Future Work

  • Client selection in the clusters is an important design decision that has

been left for future work.

  • As the number of nodes participating in Network MIMO increases, the

challenge of processing the resulting large volumes of data needs to be addressed.

  • Distributed synchronization across multiple collision domains can enable

scalable implementation of exciting theoretical and systems work.

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Thanks!

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Vidyut Language of Origin: Sanskrit Definition: Electricity Alternate Pronunciations: Probably will not help.