In Part 1, The Next BIG Thing was characterized as Whole-house Digital Media over AC Power Lines – instant digital media access from every, and any, location in the home. That includes whole-house access to the Internet, TV/IPTV/Video (both standard- and high-definition video), served-up streaming music, file sharing, security and more. HomePlug® AV technology is ushering in a whole new era of high-performance powerline home networking and enabling service providers to deliver data, voice and video to every corner of the customer’s home.

Lutron Electronics

In this, Part 2, HomePlug AV technology is examined on the physical layer to see how a 200-Mbps bit rate (a.k.a. channel rate) is accomplished. The residential house wiring is a very harsh and electrically noisy medium over which to attempt high-data-rate digital communications. Even so, HomePlug powerline communication coexists on the household power wiring along with 120 or 240 volts AC, appliance-generated line noise and other signals, such as security and lighting control signals and induced EMI/RFI.

What’s more, HomePlug AV is designed to provide robust high-speed powerline communications using very low transmit levels that satisfy regulations around the world. Despite the low transmit power in the presence of high voltage and intermittent noise and invading signals, HomePlug AV technology finds its own space to ride and work above and around would-be interference.

The AC Power Line

Figure 1 illustrates how the occupants of the AC power wiring coexist in the frequency domain. At the low end of the spectrum is the 50/60 Hz, 120/240 VAC followed by legacy security and control system signals such as X10. HomePlug AV spectrum ranges from approximately 2 to 30 MHz, above power and other carrier signals. Frequency separation allows the use of passive filtering to successfully isolate low-band signals from the HomePlug AV powerline communications spectrum. Figure 1 does not show the random wideband appliance-generated noise or any induced EMI or RFI that challenges powerline communications.

Figure 1: AC Line Spectrum HomePlug AV Separated in Frequency

The HomePlug AV spectrum is easily separated from low-band signals using passive filtering. However, high-pass filtering does not prevent in-band broad-spectrum noise, as generated by home appliances, or EMI/RFI. Clever techniques must be employed to mitigate the challenge that in-band noise presents. The first step is to use a robust and flexible broadband modulation scheme known as Orthogonal Frequency Division Multiplexing (OFDM).

Windowed OFDM

OFDM is a physical medium transmission technique composed of a large number of evenly spaced carriers (frequency division), each of which can be orthogonally modulated using Phase Shift Keying (PSK) or Quadrature Amplitude Modulation (QAM). The robustness and bit efficiency of this technique is emphasized when one considers that it is also used in DSL phone line based systems (tone modulation) and in both Wi-Fi and WiMAX wireless technologies. Figure 2 illustrates how OFDM is employed for HomePlug AV powerline communications – 1155 individual carriers are spaced at approximately 24.4 kHz.

Figure 2: HomePlug AV OFDM Spectrum

HomePlug AV technology utilizes ‘windowed’ OFDM, which means that selected carriers can be turned off (dropped) to remove interference to and from wireless services that occupy the same spectrum. Carriers, both used and not used, comprise what is known as the ‘tone map’, each carrier referred to as a tone. A firmware-enabled tone mask is used to mute carriers that would interfere with legacy services such as the Amateur Radio bands. In addition to masking, the HomePlug AV standard allows for individual tones (carriers) to be programmed over a range of amplitude, which allows for line equalization associated with various applications.

In practice, the HomePlug AV tone map consists of 917 active carriers comprising the channel. Channel efficiency is optimized using dynamic channel adaptation in which the channel is periodically analyzed for interference and other line conditions to establish an optimal tone map in which each carrier (tone) is intelligently loaded with data bits before data transfer begins.

Carrier Bit Loading

Each carrier is modulated (loaded) using either Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), 8-Quadrature Amplitude Modulation (QAM), 16-QAM, 64-QAM, 256-QAM, or 1024-QAM modulation, depending on channel conditions. 1024-QAM provides the highest bit rate per carrier because each of the 1024 unique analog phase/amplitude symbols represents 10 digital bits.

With 917 carriers active in the HomePlug AV tone map and each modulated with 1024 QAM (10-bit symbol), the channel bit rate is 10 X 917 = 9170 bits per symbol period. The symbol period is the inverse of the carrier spacing (1/24400 Hz = ~41 µs) plus a small guard period of approximately 5.5 µs. Thus, the total symbol period during which 9170 bits are conveyed is 41 µs + 5.5 µs = 46.5 µs. Using the 46.5 µs period, the channel bit rate is 9170 bits/46.5 µs = ~197 Mbps. Thus, HomePlug AV offers a maximum physical layer channel rate of approximately 200 Mbps. If all 1155 carriers were used, there would be 11550 bits per symbol period and the maximum channel rate would be approximately 248 Mbps.

In practice, not all carriers can be loaded with the maximum number of bits (10). In a process called ‘channel estimation’, bit loading for each channel is established when the communications path between two HomePlug AV devices is initialized and is continuously refreshed to adapt to changing channel conditions to achieve the highest throughput rates. Each carrier is dynamically loaded with the maximum number of bits that prevailing line conditions allow.

The individual carrier bit loading capability enables interesting flexibility. Under the very worst of line conditions, all carriers could be modulated with the same data using a low-bit rate loading, BPSK for example. This would ensure that the information gets through on one or more carriers. At the other extreme, each carrier can contain different data, each with the highest bit loading. This would yield the highest possible channel bit rate and information flow.

AC Line Synchronization

While windowed OFDM allows channel frequency-domain adaptation and individual-carrier bit loading, AC line synchronization is also employed to adapt to time domain characteristics. AC cycle synchronization allows the system to identify and work around periodic and intermittent appliance-generated line noise in relation to the AC waveform. Synchronization to the AC cycles allows the system to optimize channel capacity by adjusting bit loading during periodic noise events of significant amplitude.

Line noise, in general, tends to fluctuate during a line cycle period. Impulse noise tends to be synchronous and occurs in limited periods of the line cycle. HomePlug AV line synchronization capability utilizes multiple time slots that are synchronized with the AC cycle and evaluated for noise during channel estimation periods. This allows HomePlug AV devices to minimize the effects of the noise by optimizing carrier bit loading according to noise conditions. The carrier bit loading is part of the tone map that is generated with each channel estimation period, allowing the communications to adapt to the line and impulse noise in any network path.

Powerful Forward Error Correction Technology

HomePlug AV technology employs powerful advanced coding technology to accomplish

Forward Error Correction (FEC). This technology achieves exceptional performance and realizes greater throughputs in the presence of noise, allowing HomePlug AV home networks to operate at a lower SNR. This advanced FEC coding has power efficiencies approaching (within 1 dB of) the theoretical Shannon limit and is well proven, having been widely adopted in harsh communications environments such as cellular telecommunications (CDMA2000 and W-CDMA), satellite (DVB-RCS, CCSD), and broadband wireless (802.16, WiMAX).

Ready for ‘Next BIG Thing’ Rollout

HomePlug AV technology is now ready for primetime with service providers eager to rollout new systems, products and services. HomePlug AV technology is a key enabler of ‘The Next BIG Thing’, offering very high channel and data throughput bit rates because of advanced channel estimation, adaptive and flexible tone mapping, line synchronization and powerful FEC coding technology. HomePlug AV is making the home network truly ubiquitous and fully capable of delivering both service providers’ and home owners’ digital content throughout the home to every AC outlet – digital media over power – entertainment at every AC outlet.


AV Audio Video

BPSK Binary Phase Shift Keying

DSL Digital Subscriber Line

EMI Electromagnetic Interference

FEC Forward Error Correction

Mbps Mega-bits per second (Millions of bits of data per second)

OFDM Orthogonal Frequency Division Multiplexing

PSK Phase Shift Keying

PLC Powerline Communications

QAM Quadrature Amplitude Modulation

QoS Quality of Service

QPSK Quadrature Phase Shift Keying

RFI Radio Frequency Interference

About Intellon Corporation
Intellon is the world leader in powerline communications, providing HomePlug® compliant and other powerline integrated circuits for home networking, networked entertainment, BPL access and commercial applications. Intellon created and patented the baseline technology for HomePlug 1.0, and is a major contributor to the baseline technology for the new 200-Mbps HomePlug AV powerline standard. With over three million HomePlug ICs sold, Intellon holds the dominant market share of the rapidly growing HomePlug market. The company was founded in 1989 and is headquartered in Ocala, Florida, with offices in San Jose and Toronto. For additional information, visit

Intellon and No New Wires are registered trademarks of Intellon Corporation. HomePlug is a registered trademark of the HomePlug Powerline Alliance. All other trademarks are the property of their respective owners.