Design Con 2015

FROM EDN EUROPE: Adaptive signalling scheme routes broadband content on power wiring

-August 03, 2006

Distributing data and multimedia content using power-line wiring is an attractive proposition. The power line network, in the home and elsewhere, is pervasive and offers a solution to the "no new wires" issue of providing a fast channel for distribution of new signal types without the major disruption of installing new cables. SiConnect, a fabless semiconductor vendor and entrant to this sector, has developed a technology that provides distribution of broadband signals within the confines of a home. The company says its design will provide the bandwidth needed for "triple-play" services, with "plug-and-play" simplicity for the user, while providing privacy and complying with all relevant EMC regulations. The company has a target price for the silicon per single node of $5.

Deriving many of its "use-case" requirements from the proposals of the Home Gateway Initiative, SiConnect notes that a common theme is that typical services need well-defined levels of quality-of-service (QoS). TV using compressed video needs freedom from dropped frames; multi-channel home-theatre audio requires a maximum latency of 20 msec before effects become audible; voice-over-IP calls need to be free from delays and drop-outs. It is one of SiConnect's contentions that transmission schemes in the Ethernet mould, which employ best-effort approaches with CSMA/CD protocols, cannot provide the necessary degree of managed QoS. The company's POEM technology provides 16-level fully managed QoS, employing a synchronous multiple access/contention resolution scheme. It has optional forward-error-correction, and 128-bit content encryption to protect privacy.

The home power network, according to CEO Trevor Sokell, typically exhibits almost complete unpredictability of the signal path between any two outlet sockets, in the up-to-30 MHz band the company employs for data transmission, as provided for under European and other regulations. Impedance, noise floor, signal-to-noise ratio, other signals picked up on the lines and local electrical interference are all variable and constantly changing. SiConnect believes that the OFDM (orthogonal frequency-division multiplexing) approach that some suppliers in this field use is not an appropriate solution to the problem and is too wasteful of power. Instead, POEM devices employ a set of four agile carriers that use a dynamic detect-and-avoid scheme to minimise the effects of other signals and noise sources. Each carrier occupies a narrow band (2.66 KHz) with power levels that are higher than those typical OFDM-based systems employ, but still under EMC regulatory limits. More than one POEM network can share the same power net, and the system supports up to 256 logical networks that can each have up to 255 nodes. The data network is synchronous, with constant re-synchronisation and packet-by-packet arbitration to allocate bandwidth to each point-to-point connection according to a 16-level QoS scheme.

To cater for the case in which the signal path between the two sockets—that the user has plugged his or her appliances into—is very poor, each SiConnect node is also a repeater. For that case, Sokell says, each of the sockets will invariably have a good signal path to some other point on the power network. Even if the initial usage is a single point-to-point connection, SiConnect recommends that equipment makers provide three nodes to the user, who will then simply plug the third one into various sockets until the network establishes the connection—the system is fully self-configuring. The first chip set that SiConnect releases, due later in 2006, will support data rates of 7 to 13 Mbit/sec—sufficient, Sokell says, for two streams of compressed standard-definition TV as well as other traffic. SiConnect will later upgrade the date rate to handle compressed HD TV. The $5 price point will be an objective for, initially, silicon cost per node (in high volume) and, later, for the complete bill-of-materials per node.

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