What’s The Difference Between Wireless HD And 802.11ad 60-GHz Technologies?

There are two competing standards for 60-GHz applications: Wireless HD and IEEE 802.11ad. Both target the short-range video transport market that provides products to connect HDTV sets, set-top boxes, DVRs, games, and other video devices capable of streaming uncompressed HD video over a short range.

Background

Dozens of wireless technologies are competing for consumer, business, and industrial applications. Most have found an application specific-niche that allows them to exist. These technologies can be divided by capability and specifications such as high speed, low speed, short range, long range, mesh capability, security, cost, low power, or some mix of these attributes. Some technologies compete, but most do not. Also, there’s considerable overlap in capabilities among them.

Most of these technologies compete for spectrum space. Wi-Fi, Bluetooth, ZigBee, and a few others, for example, all use the 2.4-GHz unlicensed band. In most cases, co-existence is possible thanks to technology innovations within the standards that let them work. But as competition increases, and higher speeds and less interference are demanded, the trend has been to move to the higher frequencies.

The best example is Wi-Fi moving to the 5-GHz band. That trend is continuing as some applications are moving to the 60-GHz band. With semiconductor technology now able to provide practical and affordable transceiver chips, the 60-GHz spectrum, once a wasteland, soon will be occupied by millions of devices.

The 60-GHz Spectrum

In most countries, including the U.S., the spectrum around 60 GHz is designated as unlicensed and can be used for a variety of wireless applications. In the U.S., that spectrum is a 7-GHz swath from 57 to 64 GHz. That’s a lot of bandwidth, and it’s ideal for transmitting high-speed digital data.

Data rates over 1 Gbit/s are easily achieved with basic binary phase shift keying (BPSK) or quadrature phase shift keying (QPSK) modulation. Data rates to 25 Gbits/s can be reached with higher-level modulation schemes.

That makes this band a high priority of those wishing to transmit high-definition (HD) video wirelessly. While HD video is now transferred by some wireless methods, most of it is compressed using the H.264 standard (MPEG4 variant). Uncompressed video is preferred as it still retains more detail and faithful reproduction of the material.

In most home consumer electronic systems using HDTV, the video is transferred with HDMI cables, which are expensive and have length restrictions. Also, multiple HDMI cables are bulky and just add to the already messy nest of cables in a typical home entertainment center installation. Wireless is a highly desirable option.

Already, some Wi-Fi 802.11n and 802.11ac capability has been added to TV sets and other products for video streaming. Most use compressed video. With video now competing for space in the 2.4- and 5-GHz bands, some interference is bound to occur. Many if not most consumer electronics manufacturers are already committing to some 60-GHz technology that will provide the spectrum space to transmit uncompressed video at high speed from box to box in an interference-free environment.

Wilocity, which makes 60-GHz chips, indicates that the key benefit of this technology is that it speeds most applications several times over. For example:

Transferring 1000 photos between notebooks in 5 seconds (versus ~1.5 minutes with 802.11n)
Downloading a single 1080p movie to a tablet in 3 minutes (versus ~1 hour with 802.11n)
Uploading a 2-minute HD clip from a camcorder in 3 seconds (versus ~1 minute with 802.11n)

A few downsides offset these benefits. First, the range of transmission is very short and restricted essentially by physics. The Friis wireless range formula clearly states that the received signal power is proportional to the square of the wavelength (λ):

P_r = P_tG_rG_tλ²/16π²r²

P_r = power received

P_t = power transmitted

G_r = receive antenna gain (power ratio)

G_t = transmit antenna gain (power ratio)

r = range or distance from antenna

The shorter the wavelength, the greater the attenuation and the shorter the range. This is usually offset by higher transmitter power as well as receive and transmit antenna gains. However, the range is still shorter than other technologies at the lower frequencies. A range of a few feet is typical with the goal to achieve a maximum range of about 10 meters. Adaptive beamforming is another technique that extends range while improving link reliability with highly directional antennas with very high gain.

Attenuation is also aggravated by H₂O absorption. Water (mainly oxygen molecules) in the atmosphere absorbs radio waves since the signal wavelength is about the size of the oxygen molecules. This absorption effect peaks at 60 GHz, making this a real issue for longer-range applications. For a range of less than 10 meters, it’s not much of a limitation.

In any case, even though short range is a limitation, it is also a benefit since nearby devices basically won’t interfere with one another. This allows frequency reuse and a multiplicity of standards to easily coexist without interference.

WirelessHD

WirelessHD is a standard of the WirelessHD Consortium. It uses the 60-GHz band but is not Wi-Fi compatible. In fact, it was designed from scratch to be used as a video transport method rather than using existing Wi-Fi or some other technology not optimized for video. It supports the 1080p/60-Hz video format with a 10^–9-pixel error rate in addition to all EIA-861 video formats. It also supports both picture-in-picture (PI) and single source to multiple displays.

As for audio capability, the support includes two channels of 192 kHz; linear pulse-code modulation (LPCM); 5.1 channels for 24-bit, 96-kHz multi-channel LPCM audio; and 13.1 channels of 24-bit, 192-kHz compressed Dolby TrueHD or DTS-HD audio.

The standard can achieve rates in the 10- to 28-Gbit/s range, which permits concurrent transmission of uncompressed HD video and multi-channel audio and data. The radio technology is orthogonal frequency division multiplexing (OFDM) with adaptive beamforming. It can achieve a transmission range up to 10 meters.

Furthermore, WirelessHD provides Digital Transmission Content Protection (DTCP) capability, which protects high-value digital movies, TV programs, and audio against unauthorized interception and copying. It also supports HDCP 2.0, a content protection specification associated with HDMI.

Target applications include HDTV sets including 3D, Blu-ray players, set-top boxes, games, and other video accessories. Chip sets (Omnilink60) are available from Silicon Image (SiBeam), and some end products are on the market.

WirelessHD was originally part of an effort to develop a high-speed option for the IEEE 802.15.3c standard. That development group went into hibernation in November 2009.

IEEE 802.11ad

The IEEE 802.11 standard for wireless LANs (WLANs) has many versions including 11b, 11a, 11g, 11n, 11ac, and now 11ad. The 11b/g/n standards operate in the 2.4-GHz band. The 11a/ac/n standards operate in the 5-GHz band, and the 11ad standard targets the 60-GHz band. All share a similar media access control (MAC) layer to provide interoperability. The IEEE 802.11ad working group developed the 11ad standard with input from the Wireless Gigabit Alliance (WiGig). It was fully ratified in 2010. Chip sets are in development by Wilocity. No end products are available yet.

The 11ad standard divides the 60-GHz band into four 2.16-GHz wide channels. Data rates of up to 7 Gbits/s are possible using OFDM with different modulation schemes. A single-channel version for low-power operation is available and can deliver a speed up to 4.6 Gbits/s.

The WiGig/11ad standard also specifies an adaptive beamforming option that provides high antenna gains and narrow directionality to minimize interference and the ability to adjust to the surrounding to optimize data rate and link reliability. It additionally allows the use of protocol adaption layers (PALs), which is software that provides a way for developers to interface to specific displays like HDMI and DisplayPort as well as interfaces such as PCI Express and USB.

The goal is tri-band Wi-Fi chips that can switch seamlessly from one standard to another in one of the three Wi-Fi bands: 2.4, 5, or 60 GHz. It is estimated that chips will be available next year with end products to follow as the Wi-Fi testing and certification process is established.

The figure shows an initial solution to the tri-band objective. It combines Wilocity’s Wil6100 60-GHz transceiver chip with the AR9462 802.11n dual-band (2.4/5 GHz) Wi-Fi chip from Qualcomm Atheros. The AR9462 features dual-stream capability and a PCI Express interface. The module targets laptops and consumer devices.

A tri-band Wi-Fi module featuring a 60-GHz transceiver chip from Wilocity implements the 802.11ad/WiGig standard combined with a dual-band 2.4/5-GHz 802.11n chip from Qualcomm Atheros. It has a PCI Express interface.

Other Competing Technologies

Other non-millimeter-wave technologies have also been vying for the wireless video streaming market (see the table). Some of them use compressed video methods including Ultra Wideband (UWB), WHDI, and the 802.11n and 802.11ac Wi-Fi standards.

UWB is a broadband wireless technology based on a standard created by the WiMedia Alliance. It uses OFDM in the unlicensed 3.1- to 10.6-GHz range. It provides data rates from 53.3 to 480 Mbits/s, but the range is very short, typically less than 10 feet for the higher speeds.

UWB streams compressed video and provides a wireless link for video monitors in docking stations and laptops. It has been around for 10 years but has not lived up to its original promise. Alereon continues to make chips for this niche. Recent developments are expected to boost data rates to 1 Gbit/s, keeping UWB as a viable option for some applications.

The Wireless Home Digital Interface (WHDI) standard is a proprietary specification developed by Amimon. It uses the 5-GHz unlicensed band and a 4x5 multiple-input multiple-output (MIMO) arrangement that delivers 1.5 Gbits/s in a 40-MHz channel. It has an exceptional range of more than 100 feet and is effective through walls, making it very robust for in-home use. It is useful as a wireless HDMI connection and supports the 3D formats of the HDMI 1.4a specifications. Several consumer TV providers sell WHDI products and interfaces.

Finally, older Wi-Fi standards are finding some use in the video streaming business. IEEE 802.11n is fast, reliable, and good for compressed video. The newest WLAN standard, 802.11ac, is even faster. Using the 5-GHz band and channels of 40, 80, or 160 MHz, it can deliver data rates of up to 7 Gbits/s, which is more than enough for uncompressed video.

Conclusion

The wireless streaming technology sector is continuing to develop. Some products are currently available using 802.11n, WirelessHD, WHDI, and UWB technologies. Products based on the 802.11ad/WiGig specifications are still in the works but expected to emerge in 2013. Some believe the 802.11ad specification will be the ultimate winner in the 60-GHz band, but that remains to be seen. Some companies are planning combined 2.4-, 5-, and 60-GHz modules that will work for video streaming as well as other standard WLAN applications.