PLC solution enables voice communication over power lines

The new solution consists of Renesas’ PLC software modem (R9A06G037), which manages the PLC communications, and the RX651 microcontroller (MCU), which controls the audio codec processing. The new solution enables system manufacturers to enhance security systems by incorporating voice capabilities to an existing installation at low cost.

For a new installation that includes various sensors as well as voice communication, wiring costs can be reduced by approximately 60% while installation and maintenance costs can be reduced up to 40%.

Facilities such as office buildings have a variety of management systems installed including climate control systems, lighting, sensors of various types, building PA systems, and security systems.

In the past, each of these systems would have required their own dedicated wiring. Recently, trends have shifted toward utilising existing direct current (DC) power lines in configurations where these communication lines are shared with the power system.

However, earlier attempts to use power lines for voice communication have led to poor audio quality due to fluctuations in the delay time. To resolve this issue, the new voice-over-PLC solution uses priority control during audio transmission to virtually eliminate delay fluctuations in voice communication, even in cases where signal control communication and voice communication operate over the same power lines.

This ensures stable audio quality at all times. In addition, it combines the audio priority control feature with Renesas’ low-bandwidth PLC technology in an optimised manner to allow the use of signal lines exceeding one kilometer (km) in length without using repeaters.

By making it possible to combine data communication and voice communication over existing power networks, the new solution significantly reduces the amount of wiring required for building management systems and contributes to lower maintenance costs.

Main features of the voice-over-PLC solution

• Achieves priority control during audio transmission to suppress delay variation, ensuring stable audio quality
In a PLC system, where multiple devices use power lines as a common communication medium, it is essential to avoid data collisions. This is similar to collision-avoidance functions used in wireless communication where data is transmitted once it is confirmed that no other device is communicating. Renesas’ voice-over-PLC solution is utilising an optimised collision-avoidance feature that gives priority to devices that are performing “voice” transmission. This minimises fluctuations in the communication delay which ensures stable voice communication without dropouts.

• Support of long-distance transfers over wiring lengths exceeding one kilometer without relays, for wide-range coverage within each installation
PLC systems usually include repeating (hopping) mechanisms in order to extend distance coverage. However, these mechanisms also cause increased fluctuation during data transfers. The R9A06G037 PLC chip integrates an analog front-end circuit with a wide dynamic range, variable amplifiers for transmission and reception, as well as ADC and DAC peripherals. In addition, Renesas has boosted the operating frequency of the DSP for PHY layer processing and added special instructions for PLC processing. These enhancements provide improved sensitivity with very small signals and better immunity to noise generated by power lines, which ensure long-distance communication. The new voice-over-PLC solution has been tested and proven to support greater than one km distance on DC powerlines with more than 128 nodes connected without the need of repeaters.

• Easy-to-implement software stack shortens time required for system development
The new solution is paired with a flexible and configurable software stack running on Renesas’ RX651 MCU. This software stack allows the user to easily select and implement an audio codec with the desired characteristics, which greatly shortens the time required for system development.

The solution will be available from October 2017.