Broadband Over Power Line

Amazed!!!!! Don't be, Technology has provided a new gateway to Internet. Think of it this way. Suppose you want to be in Internet, you dont have a wired line, neither you want to use the mobile or wireless linefor the cost associated and the speed. Now suddenly you find this technology where you place a plugtop device on any of your wall socket, connect your laptop or desktop to this device and magic!!!!!! You are on to the NET.

May seem like a dream but today its a dream come true. Anybody having a power connection can actually have internet through the same line. Not only internet, the possibilities are immense. Telephone, IPTV, Home automation anything, you name it and it can be done, all through the same wire, the electric line. Imagine how jumble free your home will look!! No wires dangling, running throughout the house hold.

The Technology:

The technology is known to be existance since 1960's. Back then it was called Power line Communication(PLC). PLC was able to support few Kilobytes of data over the electrical line. It was only in late 2000 - 2001 when the technology actually have started supporting data rate in the Mbps scale. BPL/ PLC is a technology that utilizes electric power lines for high speed transmission of data, voice, video, etc. It works by transmitting high frequency signals through the same power cable used for carrying electricity to households. Theoretically, as the frequency of power and RF signals are wide apart, there is no mutual interference. BPL uses OFDM (Orthogonal Frequency Division Multiplexing) modulation which is a multi-carrier modulation technique with densely spaced orthogonal sub-carriers each being modulated by low bit-rate digital stream. It also uses adaptive modulation which ensures highest order modulation scheme (BPSK, QPSK, QAM16, QAM64, etc.) for each sub-carrier depending on the signal to noise (S/N) ratio. This results in maximum utilization of frequency band. Different types of modulation techniques used in OFDM are detailed below.

· BPSK (carries 1 bit/symbol)

Suitable for noisy channel where S/N >6-8 dB

· QPSK (carries 2 bits/symbol)

Suitable for less noisy channel where S/N >10-12 dB

· QAM 16 (carries 4 bits/symbol)

Suitable for channel where S/N >25 dB

· QAM 64 (carries 6 bits/symbol)

Suitable for almost noise free channel

As of now BPL technology utilizes the frequency band from 1 MHz to 34 MHz. However, entire frequency band may not be utilized on a particular circuit. The actual frequency band depends upon the circuit characteristics. In this technology two different duplexing schemes can be adapted – (i) Frequency Division Duplexing (FDD) and (ii) Time Division Duplexing (TDD). In FDD separate frequency band is used for up link and down link. In TDD the same frequency band is used for both up & down link.

I am covering a major player, Defidev, France in this field as my experience involves very keen association with them.

The key components of the BPL system are furnished below.

a) Head-End

b) Repeater

c) Customer Premise Equipment (CPE)

d) Coupler

e) NMS

HEAD-END / SIGNAL INJECTOR

The Head-End is the master element of the BPL system. Broadband service from ISP is fed to the Head-End. Head-End injects the broadband signal after OFDM modulation into the power mains through capacitive or inductive coupler for onward transmission to user’s premises through repeater and CPE. The specification of the Head-End is furnished below.

Specifications

Model : Ahes-202

Chipset : DS2 9002

Nos. of MAC supported : 1024

No of Supported PLC Nodes : 64

No. of Supported VLAN s : 256

Ports : RJ 45 x 2 (Ethernet)

Operating Voltage : 100 -240 V AC

Operating Frequency : 50 to 60 Hz

Power Consumption : 15 Watt

Modulation : OFDM

No. of Carriers : 1536

Power Spectrum Density : -50 dBmW / Hz

Dynamic Range : 90 dB

Frequncy Range : 2 to 34 MHz

Operating Temperature : -10 to +65 deg C

Relative Humidity: 10% to 95% non condensing

Dimensions : 251x128x41

Weight : 1.2 kg

Casing Type:- IP 53

MTBF : 72000 Hrs.

REPEATER

The Repeater is connected to the power mains through capacitive or inductive coupler. It uses the same port to receive signal from the Head-End / Repeater in the uplink direction and transmits its own signal to Repeater / CPE in the down link direction.

Specifications

Model : Amh-201 F

Chipset : DSS 9001

Nos. of MAC supported : 64

No of Supported PLC Nodes : 32

No. of Supported V LAN s : 16

Ports : RJ 45 (Ethernet)

Operating Voltage : 100 -240 V AC

Operating Frequency : 50 to 60 Hz

Power Consumption : 7 Watt

Modulation : OFDM

No. of Carriers : 1536

Power Spectrum Density : -56 dBmW / Hz

Dynamic Range : 90 dB

Frequncy Range : 2 to 34 MHz

Operating Temperature : -0 to +40 deg C

Relative Humidity: 20% to 95% non condensing

Dimensions : 93x62x37

Weight : 195 g

Casing Type:- IP 20

MTBF : 72000 Hrs.

CPE

The CPE is a BPL modem with an inbuilt coupler. It extracts broadband signal from the power line and feeds to the computer connected to its Ethernet port.

Specifications

Type 1:

Model : Amh-200 SP

Chipset : DSS 9010

Nos. of MAC supported : 32

No of Supported PLC Nodes : 15

No. of Supported V LAN s : 1

Ports : RJ 45 (Ethernet)

Operating Voltage : 100 -240 V AC

Operating Frequency : 50 to 60 Hz

Power Consumption : 7 Watt

Modulation : OFDM

No. of Carriers : 1536

Power Spectrum Density : -56 dBmW / Hz

Dynamic Range : 90 dB

Frequncy Range : 2 to 34 MHz

Operating Temperature : -0 to +40 deg C

Relative Humidity: 20% to 95% non condensing

Dimensions : 93x62x37

Weight : 195 g

Casing Type:- IP 20

MTBF : 72000 Hrs.

Type 2:

Model : Amh-200 V

Chipset : DSS 9010

Nos. of MAC supported : 32

No of Supported PLC Nodes : 15

No. of Supported V LAN s : 1

Ports : RJ 45 (Ethernet), RJ 11 (VoIP)

Operating Voltage : 100 -240 V AC

Operating Frequency : 50 to 60 Hz

Power Consumption : 15 Watt

Modulation : OFDM

No. of Carriers : 1536

Power Spectrum Density : -56 dBmW / Hz

Dynamic Range : 90 dB

Frequncy Range : 2 to 34 MHz

Operating Temperature : -0 to +40 deg C

Relative Humidity: 20% to 95% non condensing

Dimensions : 93x62x37

Weight : 195 g

Casing Type:- IP 20

MTBF : 72000 Hrs.

COUPLER

Couplers are passive devices which are used to inject/extract BPL signals to/from electrical lines. There are two types of couplers e.g. inductive and capacitive. Inductive coupler is basically a ferrite core wound with low loss cable and power line passes through it. It works on electromagnetic induction principle. Normally, Inductive couplers are used where direct access to power lines is not easily available.

Capacitive coupler is basically a LC circuit which bridges the power mains to RF circuit of the BPL equipment. Capacitive couplers are directly connected to power mains and they may be connected to all three phases and neutral.

Working of the system:

The BPL system starts its working from the master or the Head – End. All PLC equipments are IP enabled and intelligent devices. Most of them can be inter convertible which means a single device can act as a Head – End, Repeater or CPE. Keeping the above points in mind and the remote configurability of devices it is evident that there needs to be a device or controller that can instruct these elements about its working. A simple PLC network may consist of a Head – End or master, few repeaters and few CPEs or modems. The operation of a BPL network invariably starts with the Head – End which is directly connected to the NMS system.

Each BPL equipment have a NVRAM built in it to store its configuration files. As soon as the Head – End starts it reaches the NMS through the Ethernet connectivity. At this point of time it do not transmit or receive any BPL signal. First step is that it requests an IP from the NMS server. Then it asks the NMS whether any configuration file is available for it by stating its MAC address. In the NMS, if the particular device is declared, immediately sends the configuration file through Trivial File Transfer Protocol (TFTP) from its configuration pool. Once it gets its configuration file it realizes that it is in fact the first device in the PLC tree and starts transmitting OFDM signal in the allocated frequency band.

For other equipments like repeater or CPE the process is little different. The moment a device comes online it start searching for a present master on the allocated signal mode and selects the best master. The node then tries to connect to the master. Immediately the master launches an authentication in consultation with the RADIUS server. If the authentication is made open in the master this step is skipped. After this the nodes gets an IP address and the name of the configuration file it needs for its proper operation. Once the node gets the name it download the file using TFTP in its NVRAM. After the download it configures its firmware accordingly and starts to communicate.

The above process is only executed if the particular device is in Auto configuration mode. Otherwise the node has all the required settings in its NVRAM if it is in fixed mode.

Normally boot phase takes very short time if the equipment is set in fixed mode. But the difficulty is once in fixed mode it won’t search for any other file. This works well if a particular equipment always work in the same network. But if for some reason the IP schema of the network changes or the equipment is exported to be a part of any other with dissimilar IP schema and Signal mode in use, the device will never come alive rendering it useless. In automatic mode the equipment always searches for the best master and then can latch on the network. This process might be bit slow but is reliable.

Standard practice is to deploy a new network in open authentication mode. Then when deployment is over fixed mode can be used to render more stability to the network.

Advantage:

The first and formost advantage is the system abolishes the cost of laying out a new network. This reduces the establishment cost enabling a service provider to reduce its cost in installation and thus providing the service at a lower cost.

Secondly usage of electric lines gurantees a much better penetration as reach of electrical line is much more than any other form of wiring.

The network can be deployed in a very short time span and can be made operational quickly.

Equipments are robust and virtually gurantees zero maintainance.

Disadvantage:

The designing of the network is very site specific and varies with site. In other words there is no right hand thumb rule to design the network.

There is still no available standard to the system. This lack of standard are attracting less players in the field.