Characterizing End to End Performance Of Indoor Power Line Networks Presented By: Alvika Gautam Deepika

What is Power Line Communication  It is a Communication Technology  It uses Power Line to supply both electric power and transmit data.  PLC access networks typically cover: public area from the transformer substations to the customer premises (outdoor) private area within the customer building (indoor).

Power Line Communication

A Basic PLC Transceiver

Modulation  Modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted.  WHY MODULATE?  E=Hv We want to send high energy Signals  Length of Antenna is proportional to wavelength

Modulation Schemes  Single Carrier PLC technologies  FSK (Frequency Shift Keying)  ASK(Amplitude Shift Keying)  BPSK(Binary Phase Shift Keying)

Modulation Schemes

Frequency Shift Keying

Amplitude Shift Keying

Modulation Schemes  Multi Carrier PLC Technologies OFDM:Orthogonal Frequency Division Multiplexing Basic FDM System

OFDM A large number of closely spaced orthogonal sub-carrier signals are used to carry data Each sub-carrier is modulated with a conventional modulation scheme (such as BPSK, QPSK or QAM)

X10 

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This digital data is encoded onto a 120 kHz carrier which is transmitted as bursts during the relatively quiet zero crossings of the 50 or 60 Hz AC alternating current waveform. Bits sent on zero crossing of 60 Hz AC wave. The digital data consists of an address and a command sent from a controller to a controlled device. More advanced controllers can also query equally advanced devices to respond with their status. This status may be as simple as "off" or "on", or the current dimming level, or even the temperature or other sensor reading.

X10 Protocol  Four bit house code (A-P) followed by one or more four bit unit code(1-16), finally followed by a four bit command.  Each controlled device is configured to respond to one of the 256 possible addresses and each device reacts to commands specifically addressed to it, or broadcast commands.  Ex: "select code A3", followed by "turn on", which commands unit "A3" to turn on its device.  Several units can be addressed before giving the command, allowing a command to affect several units simultaneously.

X10 Commands Code

Function

Description

One Way

Two Way

0000

All units off

Switch off all devices with the house code indicated in the message

X

0001

All lights on

Switches on all lighting devices (with the ability to control brightness)

X

0010

On

Switches on a device

X

0011

Off

Switches off a device

X

010x

Dim

Reduces the light intensity

X

0101

Bright

Increases the light intensity

X

0111

Extended code

Extension code

X

1000

Hail request

Requests a response from the device(s) with the house code indicated in the message

X

1001

Hail acknowledge

Response to the previous command

X

1010

Pre-set dim

Allows the selection of two predefined levels of light intensity

X

1101

Status is on

Response to the Status Request indicating that the device is switched on

X

1110

Status is off

Response indicating that the device is switched off

X

1111

Status request

Request requiring the status of a device

X

X10 Physical Layer  A bit value of one is represented by a 1 millisecond burst of 120 kHz at the zero crossing point (nominally 0°, but within 200 microseconds of the zero crossing point), immediately followed by the absence of a pulse.  A zero value is represented by the absence of 120 kHz at the zero crossing point, immediately followed by the presence of a pulse.  All messages are sent twice to reduce false signaling.  Every data frame transmitted always begin with a start code of 1110.

Why Power Line Communication?  No more wires, just plug in  Still viable for within home networking, especially in homes without Ethernet (expensive to wire).

 Has the potential to avoid problems with Wi-Fi (spectrum crowding and network  Easy to install and use  Secure data-encryption

 One wire offers both power and your high-speed communications needs

Why PLC Over Wireless Technologies  More reliable for streaming media  Faster speeds with fewer dropouts  Whole-home coverage  Extends the range of wireless technology through WiFi extenders that bridge your wireless and Power line networks  Greater security (all products are sold with encryption turned on)

Types Of Power Line Communication  Narrow Band Power Line Communication  Broad Band Power Line Communication PROPERTY

NARROWBAND PLC

BROADBAND PLC

Data Rate

Upto 200 kbps

Over 1 Mbps

Frequency

Upto 500 kHz

Over 2 MHz

Modulation

FSK, S-FSK, BPSK, SS, OFDM

OFDM

Applications

Building Automation Renewable Energy Advanced Metering Street Lighting Electric Vehicle Smart Grid

Internet HDTV Audio Gaming

Application of Narrow Band PLC  Smart Metering

Application of Broadband PLC PLC Deployment: An example

Focus Of Paper  Research conducted to see if PLC technology has matured enough for broad use. Study analyzes if Power line networks are:  Impacted by distance  Have high capacity  Low latency  Support multiple transmitters and heterogeneous traffic patterns  Can cope with interference from household electrical appliances.

Equipment : Linksys Homeplug AV PLK200 Physical Layer Data Rate: 200 Mbps Information Data Rate: 150 Mbps Frequency: 2-28 Mhz

HPAV Architecture

Testing Setup •

Same model adaptors used on all ends, no intermixing of standards or equipment.

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3 environments: dormitory, house, and office building.

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An ad hoc Wi-Fi network (802.11g) was also set up for performance comparison.

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The additional use of a 575 feet extension cable plugged into an AC outlet was selected as a control to isolate testing from noise (in the office).

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Standard tools were selected to perform analysis including iperf, ping, and tcpdump.

Effect Of Distance  TCP throughput(using IPERF) and RTT(using Ping) were measured.  Wi-Fi test was performed at sending and receiving locations, using a one hop ad hoc network  At furthest distance, Wi-Fi achieved 22 Kbps vs 14.81 Mbps for PLC.  Extension cord test was also performed.

 Throughput (80 Mbps) and RTT were steady all along the extension cord, likely due to relatively short length.

Effect Of Electrical Appliance • UDP transmission between two nodes was performed. • Appliances were turned on for short periods to gauge impact. • Long term simulation was performed to see impact of normal daily interference. • Throughput and RTT varied throughout the day as equipment changed modulation scheme to counteract noise. • Electrical equipment with more capacitive equipment seemed to have a bigger impact.

Simultaneous Traffic Over Cross Traffic • Simultaneous communication on a network is common and needs to be simulated. • First one device was selected as the sink with multiple sources. Multiple sinks were also tested. • Total network capacity was generally evenly divided between transmitters on the extension cord. • Different types of traffic require different bit rates (Skype vs checking email). • Test was set up to vary a cross traffic bit rate and see the impact of the rest of the network's performance. • Median RTT and RTT spread increased as cross traffic bit rate increased. • Certain active nodes could bring down performance the of whole system , but not as much as with a Wifi network

Alone = one sink Pairs = multiple sinks Better performance on the extension cord is observed.

Media Access Control • Set up two PLC nodes to constantly unicast data to a third node on the extension cord to determine how access to network is handled. • Plot consecutive data frames sent. • With Wi-Fi, each sender has equal access to network, meaning close to only one packet is sent at a time before another sender can transmit. • With PLC, once transmitter is granted access, multiples of 10 packets are sent

Channel Symmetry • Wi-Fi channels tend to be asymmetrical, while Ethernet is symmetrical. • Asymmetry can cause problems in higher networking layers. • Set up two nodes on either end of the extension cord and measure TCP throughput in both directions. • Took ratio of higher and lower throughputs. • Good symmetry with data rate of 60 Mbps. • Added a blender in the middle of the line and reran the tests. • Found that the blender not only reduced throughout, but introduced asymmetry in the communication channel. 40 Mbps one direction, 19 Mbps the other. • Significant asymmetry was also found in the office setting.

Conclusion • PLC devices are very sensitive to AC noise levels. • Common household devices will cause great variation in network performance throughout the day. • They also do no work across surge protectors or other voltage suppressing devices. • PLC devices should not be used for applications requiring very low RTT. • PLC performance is much lower than the figures advertised by manufacturers.

Thank You!