Meeting the challenge of in-home powerline communication

The idea of a single wholehouse network providing immediate access to telephone, Internet and TV services from any location in the house is an incredibly attractive proposition - so why don’t we all already have one?



Well in Europe at least, solidly constructed houses built on multiple levels with thick brick or concrete walls can create significant problems for wireless technology, and re-wiring a house with Category 5 Ethernet cabling is likely just too costly and time-consuming an option for most of us.The domestic AC power cables have long held an intriguing promise in this respect – houses come with the network preinstalled and it generally covers the whole house! While this may well address the basic infrastructure challenge, the technical challenges faced in harnessing such a network to carry a complete complement of digital media services is significant. SiConnect’s POEM technology has been purpose-designed to tackle the inherent challenges.



WHOLE HOUSE COVERAGE

Creating some crucial design criteria for power line communication (PLC) networks, a number of these challenges, and SiConnect’s response to them, are considered here. However, as will be discussed, the success of inhome PLC vitally depends on the ability of competing solutions to co-exist.



Unfortunately, noisy domestic electrical cables were never designed for broadband data transmission, and while there are pairs of sockets that will provide a good signal to noise ratio link for even the highest data rates, there are always pairs with a much poorer response (Figure 1).



By using a peer-to-peer network topology, SiConnect's POEM technology is able to embrace all available power sockets in the home to achieve whole home coverage. Each node can act as a repeater, which not only maximises coverage but also optimises throughput.



The connection quality of each link is always known to every POEM-enabled node on the network, and as a result, the best path is always used to optimise throughput. New nodes are automatically authorized and up to 255 networks, each with 255 nodes, are supported.



A good consumer experience of in-home PLC networks will depend on all connected equipment working correctly all of the time. To this end, management of traffic priority and bandwidth is critical, within a single network or across several co-existing networks. What’s clear is that the "best effort" approach of Ethernet-like technologies falls short when the requirements for in home distribution of IPTV, VoIP, and data are taken into account. The asynchronous carrier sense multiple access/collision detection (CSMA/CD) protocol that they rely on cannot ensure the controlled latency and jitter that’s required. The POEM technology therefore takes a different approach in that it uses a synchronous multiple access/contention resolution (SMA/CR) protocol and a QoS management structure based on 16 different service levels for prioritising traffic.



EMS COMPLIANCE

Since existing PLC technologies sit in the 3 to 30MHz band, concern has often been expressed regarding the prospect of powerline communication interfering with radio broadcasts. Certainly, technologies using spread spectrum techniques or orthogonal division multiplexing (OFDM) across a large part of the short-wave band can cause problems (Figure 2).



Conversely, POEM technology's detect and avoid scheme effectively moves carrier signals to avoid interference with any amateur radio band in local use (Figure 3). This has long been demanded by the amateur radio and broadcast community as the only effective way of ensuring local radio users are not disturbed by powerline carriers.



Designed to operate within global EMC regulations, POEM technology complies with Europe's EN55022 regulation for conducted emissions and EN55024 regulation for immunity to interference. It meets the requirement of the USA's FCC part 15 regulations for radiated emissions, and CISPR 22 and CISPR 24 regulations in the rest of the world.



INSTALLATION, SECURITY, PRICE

Like any consumer electronic device, ease of use is a crucial design criterion for PLC networks. The inherent ability of a POEM technology enabled network to continuously self-configure, combined with the fact that it has no dependency on a network PC or central controller, means user installation will be simple and truly plug and play. As a result, the need for service providers to provide technical support and to incur costly home visits is eliminated.



POEM technology also includes encryption to provide privacy and security features that ensure broadcast and personal multimedia data remain protected.



Moreoever, even the most technically brilliant PLC solution will fail if the price point isn’t right. Because the POEM technology was designed specifically for in-home communications, it will achieve a chip price of $5 per node - less than half the cost of competitive solutions.



COEXISTENCE

In answering the question "Why don't we all have a PLC network in the home?," the aspect of coexistence is a vital consideration. Even the most technically brilliant technical solution in the world will have limited appeal if it cannot coexist on the same power lines as other PLC solutions.



PLC technologies use either OFDM or multiple carrier approaches. A characteristic of OFDM is that it uses many carriers across the entire bandwidth; therefore another PLC system on the same power lines is very likely to suffer RF interference and lose performance. This interference is mutual and will ultimately cripple the operation of both networks. Avoiding this by achieving active coexistence must be a key objective for all semiconductor manufacturers working in the field.



CEPCA, the Consumer Electronics Powerline Communications Alliance, (www.CEPCA.org) is a technology-agnostic industry body that has put coexistence very much at the top of its agenda. With a membership composed of all of the world's major consumer electronics manufacturers, it sees coexistence as the essential route to reliability and sustained consumer confidence and the only means by which power utility service calls can be reduced and CE product returns minimized.



Its philosophy is that with so much momentum behind PLC, there’s a real need to get global consensus on a PLC coexistence standard now, rather than wait the many years required for a single standards to be published. The long-term success of PLC in the home requires that coexistence be built into the different manufacturer's technology in the same home. This is not complex to achieve but does require a level of cooperation that only an independent industry body like CEPCA can achieve.