Research Project- Power Line Communication

Introduction to Power Line Communication (PLC)

The ideal communication mechanism is wireless as it does not need any cabling. However, it fails to meet all the applications. If the range between two communicating nodes is larger or there are obstacles like walls, ceilings, or floors the signal gets attenuated. Although, wireless networks are the most prevalent one it fails to accommodate environments where range and obstructions are present. In such scenarios, cable technology such as Ethernet is preferred but it comes at a cost of running cables over a large distance which is difficult and expensive.

An alternative to the problems of drawing cables over long distances and signal attenuation over Wi-Fi is the use of Power Line Communication (PLC) devices where the access medium is the AC power line. PLC operates by adding a modulated carrier signal to the wiring system. Different PLC devices operate at different frequency bands. Since power distribution and cables were originally designed for the transmission of electrical signals at frequencies of AC lines i.

e. 50-60 Hz, they are limited to carrying high-frequency signals hence the propagation problem is a limiting factor for PLC technology. But with the use of certain modulation technique-techniques front, it can be overcome, and we can leverage the benefits of already deployed electrical lines for the transmission of data.

How does PLC Works?

PLC operates in a master-slave mode where they are paired together. A master device is plugged into a Home Gateway router and the slave device is connected in the room where one needs access to network connectivity.

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Like every other device, PLC also uses the transmitter to modulate a high-frequency carrier with user data and transmit it on the power cable. The PLC receiver on the other end will receive modulated data, it will demodulate the signal and extract user data. Every PLC unit has a transceiver to enable the bi-directional exchange of data. The significance of it is you do not need extra cabling whereas leveraging the existing power lines.

Application of PLC:

• Home Networking with PLC:

PLC can be used in home networking to connect computers and other peripherals like entertainment devices that have an ethernet port. Plug the PLC device into the power outlet and establish an ethernet connection using the existing electrical wiring in the home. This allows devices to share data without the need of running dedicated network cables.

Current PLC Types:

1. HomePlug (HP):

It is the trade name of the PLC technology and a standard developed by the HomePlug alliance [1]. HomePlugAV2 is the latest version and has higher data rates. Moreover, it provides an extended feature of the MIMO wireless technique that enhances link reliability. MIMO uses additional ac lines including the second phase of the 240-V line, neutral or ground for additional signal paths.

2. G.hn:

It is a standard of the International Telecommunication Union – Telecommunication (ITU-T) organization, promoted and certified by the HomeGrid forum [2]. It supports PLC but also takes into account other wired media like twisted-pair telephone wiring and cable TV coax.

Mainly used for home networking, Internet access, and connecting TV sets and other video equipment. G.hn uses the OFDM modulation technique to achieve a data rate of up to 1 Gb/s.

3. HD-PLC:

It uses Wavelet-OFDM to achieve highly efficient transmission via an appropriate modulation of the sub-carrier and without Guard Interval (GI). It is capable to provide a physical speed of 240 Mbps at a band of 26 Mhz. Moreover, it provides high reliability even in poor conditions due to its strong error detection and correction technique.

Comparison Table:

Parameters Home Plug AV G.Hn HD-PLC

Standard HPAV1.0, 1.1 & 2, IEEE 1901 specification ITU G.hn 9960/61 standard Complete IEEE 1901 specification

Frequency Band 2-30 MHz,2-68 MHz 2-80MHz

2-30 MHz

PHY Speeds 200Mbps, 500 Mbps, 1Gbps (HPAV2) 700 Mbps, 1Gbps

240 Mbps

UDP speeds 95 Mbps 700 Mbps

100 Mbps

MIMO support Not Supported

-Will be supported widely in HomePlugAV2 Supported

-Defined in G 9963

Not Supported

QoS(Latency) 30ms 5-6ms 10ms

Power consumption Approx 4W 3.67W (SISO 100MHz)

4.31W (MIMO 50MHz) Approx 1.6W

Modulation Windowed OFDM Windowed OFDM Wavelet OFDM

Encryption 128bit AES

128bit AES

128bit AES

Noise Sources:

There are many different sources of noise and disturbance on electrical power networks. These noise sources impact the behavior of PLC devices. Below are the various electrical appliances that generate noise on the electrical lines.

• Brush motors used in a hair dryer, drill, mixer, blender, etc. introduce sporadic noise due to the type of use.
• Frequent impulses are produced by switching power supply, lamps, etc
• Random noise generated from power system glitches or light dimmer switch
• Radio interference from FM radio transmitters.

Impact of Household appliances on PLC

To understand the impact of a household electrical appliance on PLC performance, a throughput test has been conducted. Setup and results are explained below.

Test Setup

The test was conducted on a  1BHK apartment with a single-phase power supply. PLCs of the following technologies were tested:

• HP-AVtechnique-techniques front
• G.Hn
• HD-PLC

The data performance test setup was as below:

Impact of Washing Machine

FrontAfront front the front loading washing machine was used in this testing. Turning the washing machine on or off did not affect the performance of any of the PLC technology.

Impact of TV, STB, and speakers

TV & STB did not have observable disturbance as they were connected to the stabilizer. However. when the speaker was turned on, performance dipped for all three technologies for 5-6 sec and then it stabilized thereafter. The impact on HP-AV was highest with a drop in throughput from ~ 90Mbps to ~25Mbps. In the second instance where speakers were turned on, the random impact was observed on the performance of HP-AV whereas G.hn and HD-PLC were relatively stable.

Impact of Immersible Water Heater

A slight dip in performance of HP-AV and HD-PLC was observed when the heater was turned ON. G.hn remained relatively stable.

Impact of Microwave Oven

HP-AV observed the highest (~90Mbps to ~70Mbps) impact when the microwave oven is turned ON. Impact on HD-PLC was minimal and G.hn remained relatively stable.

Impact of Light and Fan

Tube light and Fan severely affected G.hn, data performance dropped to 0 Mbps for 4-5 sec. The performance of HP-AV also dropped significantly. The HD-PLC performance was relatively stable. CFLs affected all three, the highest impact on HP-AV throughput dropped from ~95Mbps to ~80Mbps and HD-PLC where throughput dropped from ~70Mbps to ~50Mbps. G.hn performance drop was minimal (~5-7Mbps). The impact of CFL continued.

Impact of Refrigerator

A noticeable impact was observed on HP-AV and HD-PLC when the refrigerator was turned ON. The g.hn performance was relatively stable.

Impact of cumulative load

G.hn throughput dropped to 0 Mbps for about 5-7 sec when fan and CFLs were turned ON. Other PLCs showed dips in performance when appliances were turned ON.

Summary

The impact of fan and tube lights on G.hn can severely impact customer experience for voice/video calls and real-time gaming. Other applications like audio/video streaming can be impacted but application buffers may handle this communication break.

In all other scenarios, there is a throughput drop, and the minimum observed throughput is 40Mbps which can suffice normal home networking needs. If dedicated high throughput is required then wired Ethernet networking must be used.

Sources:

1. http://www.homeplug.org/
2. http://homegridforum.org/