Among the options available for enabling a home network withouthaving to install new wires, both wireless and powerline communicationsstand out for their ubiquity. Powerline communications enables abroadband connection to be sent anywhere in a home by using theexisting electrical wiring available in every room.
Powerline communications can work regardless of the back-haultechnology used to provide a broadband connection. As long as abroadband connection is available, powerline technology can be used toextend this connection to any socket inside a house.
For example, Internet protocol television (IPTV) services, where thetechnology used for the back-haul technology is xDSL-based, usespowerline communications to create a secure home network. In this case,service providers need a cost-effective and easy-to-use solution toconnect a set-top box, located next to a television set, to thebroadband modem, which is usually located in a different room somewherein the house.
Similarly, cable companies are also using powerline communicationsfor broadband extension when the data rate and stability requirementsare higher than those offered by wireless technology.
In this case, the back-haul technology used by cable companies isDOCSIS-based. As a result, powerline technology is gaining traction asthe preferred solution to extend the service provider's network intothe subscriber's home and to guarantee the quality of experiencerequired for a competitive service offering.
Typically, the broadband connection is fed through a powerlineadapter, which can be plugged into any socket in the house. By doingthis, all the remaining sockets in the house automatically become aninterface to the home network.
Every electrical point in the home can now pick up a video stream,digital audio, digital data or a live Internet connection, instantlyand without interruptions. By simply connecting a pair of adapters toany existing socket in the house, a home network is created in a matterof seconds.
Powerline communications technology uses electrical wiring forhigh-speed transmission of data. It is a more competitive solution tothe connectivity problem faced by many applications than other wiredsolutions or wireless technologies. It has the capability of offeringthe data rate, performance, flexibility, reliability andcost-efficiency required to support whole-home multimedia networking.
The electrical wiring used by powerline communications for datatransmission is considered to be a harsh and unfriendly environment andone of the most difficult communications channels. It is a channelknown for real-time variations, impulsive and periodic noise sources,sudden impedance changes and several bifurcations creating reflectionsand other undesirable effects.
OFDM: Modulating the powerline
Most powerline communications technology implements advanced OFDM(Orthogonal Frequency Division Multiplexing) modulation, a scheme thatovercomes most channel difficulties to achieve high data rates whilekeeping power transmission levels low.
OFDM was selected as the most suitable modulation scheme for thepowerline channel in particular because it is:
1) The most immune tointerference, being able to cope with severe changes in channelconditions;
2) Provides the highestlevel of spectral efficiency and performance.
Several leading powerline communications technology providers useOFDM modulation based on the simultaneous transmission of more than onethousand carriers over a frequency band of 30MHz, usually starting at2MHz and ending at 32MHz. The data to be transmitted is divided betweenall sub-carriers which are independently modulated based on theavailable SNR of the channel.
A number of bits are assigned to each sub-carrier depending on thesituation in the communications channel at that very instance. SNRmeasurements are continuous and the OFDM signal changes the bit loadingto adapt to any changes in the channel instantaneously, avoiding lineerrors (by decreasing the bits/carrier), or increasing efficiency (byincreasing the bits/carrier).
One of the great advantages of some OFDM implementations is that thesignal strength and the frequency spectrum used are fully adaptable andconfigurable. This means that commercial products can be tuned, takinginto account any type of regulation either by adding notches to allowfor coexistence with Radio Amateur signals, reducing the signalstrength or limiting the frequency spectrum that is used.
At the same time, powerline communications uses some of the mostadvanced forward error correction (FEC) algorithms. These algorithmsenable semiconductor vendors to add redundant bits to every data frameand thus allow for the information recovery to be possible even withthe presence of errors in received frames.
Similarly, most noise sources found in the electrical network aresynchronous to the ac cycle, which allows powerline communicationstechnology vendors to design synchronous algorithms to improveperformance. Synchronizing to the ac cycle and not transmitting when aknown noise source will be present ensures that block errors areminimized and higher effective data rates are achieved.
All these very complex algorithms and their corresponding siliconimplementations are required to transmit in one of the most complexmediums if high data rates, in the order of 200+Mbit/s data rates, aredesired.
The best of wired and wireless
Powerline combines the best of wired and wireless connections.Consumers have a fast, reliable and secure connection, anywhere intheir home. Since transmissions are sent over a wired medium, lowerlatencies can be achieved benefiting real-time streaming applicationslike VoIP and IPTV and interactive services.
The powerline connection does not experience interference from 'lineof sight' issues, because it is a direct connection to every outletwithin the home. At the same time, it also has strong encryption and apush-button secure network configuration to enable a secure dataconnection.
Wireless can offer benefits as well, though. Like powerline, it doesnot require any additional wiring and can extend a broadband signalthrough the house. However, it is less stable and secure and the levelof bandwidth that it can deliver also limits it. It rarely has thecapability to deliver triple play services (video, voice and data)simultaneously. Another limiting factor for wireless technology is fullcoverage.
Every time a wireless signal encounters an obstacle, signal strengthis lost. This means that full coverage can be a problem depending onthe construction materials used and the size of the house. Powerlinetechnology can help improve wireless coverage by acting as a backbonefor wireless connectivity increasing coverage and available data rates.
IPTV: Powerline Opportunity?
One of the major applications for powerline communications is IPTV homenetworking. Traditional telephone companies have started to offer IPTVservices to consumers, an offering usually reserved to cable companiesand other television providers. This strategic decision was a result oftrying to provide existing and potential subscribers with a morecompetitive service offering to reduce subscriber churn rates and alsoa strategic response to cable companies.
The cable companies had also started to offer voice services, anapplication traditionally dominated by the telephone companies. In thiscompetitive environment, IPTV deployments require a home networkingtechnology that allows service providers to cost-effectively meetsubscriber acquisition targets.
In order to do this, home networking technology should be easy touse, capable of being installed by any subscriber without assistance(self-install), enable a two-way communication channel to the callcentre to improve customer support and service quality and operatewithout interfering with existing broadband access infrastructuretechnologies, like VDSL.
|Figure1: The use of IPTV in the home|
Once connectivity is established and a secure home network is inplace, the IPTV service provider is faced with an even bigger problem:how to manage the last few meters inside the subscriber's house in acost-effective way.
Well known network management solutions, such as SNMP, cannot offerservice providers the common platform they require for devicemanagement on the network because each vendor creates proprietarymechanisms (MIBs) for management. It becomes extremely important thatpower-line communications semiconductor vendors offer a technology thatenables advanced remote management capabilities.
On-chip support for a device-agnostic network management technologyis mandatory for service providers that want to offer subscribers acompetitively priced service with advanced features.
In this respect, the DSL Forum's TR-069 standard is becoming moreand more popular as service providers discover the cost savings thatcan be accomplished by deploying powerline adapters that supportTR-069-based remote management.
On-chip support for the TR-069 remote management standard ensuresthat an IPTV roll-out is scalable, efficient and competitive. TR-069 isa key feature for network management and control of end-user devices,including routers, IPTV set-top boxes, or VoIP adapters as it sets outa common method for network devices to communicate with an autoconfiguration server (ACS).
Through the ACS a service provider can enable remote management andthe delivery of new services for an array of residential devices andapplications. The ACS can also be used to avoid costly truck rolls tocustomer locations because it supports remote troubleshooting,auto-configuration and real-time monitoring.
In December 2008, the ITU-T, the International TelecommunicationsUnion's standardization arm, reached agreement on a new internationalstandard for high-speed transmission over power lines, phone lines andcoaxial cables to support up to 20 times the throughput of existingwireless technologies and three times that of existing wiredtechnologies.
This development is of great importance for the whole homenetworking industry and especially for powerline technology. For years,the powerline communications industry had been unable to converge on asingle standard. Previous attempts simply failed or were reduced toproposals that could not agree on a single PHY and MAC and fell shortof the goal of ensuring full interoperability, a prerequisite forworldwide applicability.
The ITU-T G.9960 standard, also known as G.hn, is a single PHY andMAC international standard that aims to unify the wired home networkingindustry under a single technology implementation. With the objectiveset at 1Gbit/s over coaxial cable and 500Mbit/s over the existingelectrical network, G.hn is well on the path to achieving industryconsolidation. Current work is focused on finalising the MACimplementation, which is scheduled to be finished by September 2009.
For the first time in years, an international standard will back thewired home networking industry, enabling it to finally achieve its fullgrowth potential. The HomeGrid Forum, which is the interoperability,certification and promotional effort supporting the G.hn standard, willprovide a certification process to guarantee that interoperabilitybetween all G.hn implementations is assured.
Pablo Gagliardo is product marketingmanager at DS2.