Electronic Design

Powerline Modem Uses OFDM To Overpower Noise And Transmit Data Reliably

Powerline communications (PLC) has been available for many years, but it hasn’t always lived up to its expectations. Electrical utilities regularly use the technology to monitor and control ac power lines. Some companies have even tried offering broadband Internet services. But the high-speed limitations of the ac lines as well as noise and interference issues have impeded its progress.

Still, designers can use PLC for monitoring and control functions at low data rates, like automatic meter reading, energy management, and home automation. Maxim’s MAX2990 single-chip powerline modem not only targets these applications, it also provides exceptional data rates, reliability, and performance over long powerline runs (see the figure). The MAX2990 uses orthogonal frequency- division multiplexing (OFDM) with differential binary phase-shift keying (DBPSK) and forward error correction (FEC) to provide reliable data transfers in the presence of noise, narrowband interferers, group delays, jammer signals, impulse noise, and frequency selective attenuations.

Additionally, it operates from 10 kHz to 490 kHz and can achieve up to 100 kbits/s. The chip complies with powerline signaling regulations from CENELEC, the Federal Communications Commission (FCC), and the Association of Radio Industries and Businesses (ARIB) as well.

Advanced channel-coding methods such as Reed Solomon FEC and convolutional encoding give the MAX2990 its superior performance. These errorcorrecting codes are transmitted with the data on different OFDM tones within the band to maximize the chip’s datarecovery ability. As a result, it delivers a typical bit-error rate (BER) of 10–4 with a signal-tonoise ratio (SNR) of –4 dB at 32 kbits/s between 10 and 95 kHz.

A fast Data Encryption Standard (DES) engine serves as an encryption/ decryption coprocessor for very secure transmissions. When used in a network with many nodes, it employs the CDMA/CA channel access arbitration method and automatic repeat request (ARQ) to ensure reliable packet delivery.

The MAX2990 packages the physical layer (PHY) and media access control (MAC) layer in a single chip that additionally integrates Maxim’s 16-bit RISC MAXQ microcontroller. It includes 32 kbytes of flash to run the MAC code and user-defined application, as well as 8 kbytes of SRAM for data storage.

The chip also offers includes UART, SPI, and I2C serial interfaces. A real-time clock is included, along with a set of pulse-width modulation (PWM) counters for applications such as LED brightness control.

TAGS: Components
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