The question is not whether display interfaces will become wireless but how. The sheer number of standards makes that difficult to determine.

by Matthew Brennesholtz

THERE ARE LITERALLY DOZENS of ways to connect an image source to a display. All of the most familiar connections involve running a cable from the one to the other. Now, after years of promise, a number of wireless solutions are maturing that can actually meet the needs of users. As "display people," we may not be paying much attention to what is going on with these wireless interfaces – which is precisely why an article on this topic seemed like a good idea. I think readers will find there is a lot more going on and providing a higher level of performance than might be imagined.

In the computer world, the classic VGA cable or the somewhat newer but still venerable DVI cable are perhaps the most familiar connections. In the video world, there are older composite and component connections and HDMI, the new kid on the block who is rapidly becoming the elephant in the room. HDMI is expanding its reach beyond television applications into computer displays as well.

Looking at my desk while I write this article, I see my computer monitor and keyboard and … wires: a VGA cable, at least seven USB cables, a phone cable, and power cords. At least I use Wi-Fi so I am not burdened by a network cable at home. Is there some way to get rid of this clutter and do it wirelessly?

The answer is yes, especially for video and data. Sometimes wireless connectivity can even include power, as is familiar to anyone who has a wireless-handset charging station. Fujitsu demonstrated a complete wireless desktop at CeBIT 2011, which used UWB for video and data. The power was inductively coupled into the monitor inductively using SUPA^™ technology, as shown in Fig. 1.

Fig. 1: Fujitsu demonstrated a complete wireless desktop, including monitor power, at CeBIT 2011 using UWB/Wireless USB for video and data. Photo Credit: Robert Hollingsworth, SVP of SMSC.

The solutions are not simple, however. Part of the problem is not that there are no wireless display connectivity solutions but that there are too many of them. The four standards with the most industry support are two in the 5-GHz band: Wi-Fi, including Intel's WiDi variation on it and WHDI; plus two more in the 60-GHz band, WirelessHD and WiGig. These standards are discussed briefly in the following sections.

Wi-Fi

Wi-Fi is a trademark of the Wi-Fi Alliance (http://wi-fi.org/) for products based on the IEEE 802.11 standard that the Wi-Fi Alliance has certified as interoperable, allowing equipment from different suppliers to reliably talk to each other. Other products based on IEEE 802.11 may be interoperable with Wi-Fi devices, but the Wi-Fi Alliance does not certify them or allow them to use the "Wi-Fi" word or logo. Wi-Fi operates in the 5-GHz RF band and is nearly universal in mobile computers.

Intel has developed a way to use Wi-Fi to connect laptop and desktop computers to displays, calling its approach WiDi (WirelessDisplay). This proprietary system uses the normal Wi-Fi interface with video compression, employing Intel chips to fit the HD signal into the Wi-Fi bandwidth.

WHDI

Wireless Home Digital Interface (WHDI) is a wireless protocol specifically designed to stream uncompressed video, including HD video. It is championed by the WHDI Consortium (http://www.whdi.org/WHDISIG/) and has wide support among HDTV manu-facturers, including Haier, Hitachi, LG, Mitsubishi, Samsung, Sharp, Sony, and Toshiba. It also has strong support among component suppliers, including Amimon, Maxim, Motorola, and, presumably, the chip-making divisions of the standard's HDTV supporters.

WHDI technology is said to enable wireless delivery of uncompressed HDTV throughout the home with video rates of up to 3 Gbps, sufficient for uncompressed 1080p, in the 5-GHz unlicensed band, with the same quality as a wired connection and no latency. WHDI is specifically designed to wirelessly connect multiple devices throughout the home. Because of the need to penetrate walls, ceilings,etc., to meet this design goal, WHDI works in the same 5-GHz frequency band as Wi-Fi or WiDi.

Because WHDI and Wi-Fi use very similar technology in the 5-GHz frequency range, it is possible to build a single chip that integrates both WHDI and Wi-Fi, although to my knowledge, this has not been done yet. The WHDI consortium says that a combined WHDI/Wi-Fi chip would not cost much more than a Wi-Fi-only chip. In addition, software solutions are available that allow the WHDI protocol to be used over ordinary Wi-Fi connections.

WHDI 2.0 is scheduled for release in Q4 '11. This upgrade is expected to have three key improvements:

• Support for ultra-high-resolution video (4K x 2K pixels).

• WHDI/Wi-Fi integration and same channel co-existence.

• Mobile device integration.

60 GHz

60-GHz wireless technology has been adopted by two different consortia interested in wireless video connections, the WirelessHD Consortium (www.wirelesshd.org) and the Wireless Gigabit Alliance (WiGig) (www.wirelessgigabitalliance.org). Both consortia's technology is discussed further below. 60-GHz technology is in the early stages of adoption and, when fully implemented, is expected to be available worldwide.

The 60-GHz spectrum is unlicensed and is used for other things besides wireless video connectivity, just as the 5-GHz spectrum is unlicensed and used for more than Wi-Fi. Some of the applications that can benefit from use of the 60-GHz spectrum include wireless HDTV; wireless laptop docking stations; extremely fast downloading of files via wireless gigabit Ethernet, wireless USB 2.0, 3.0, or other non-video connectivity protocols; wireless telecommunications backhauls; etc.

Bandwidth in the 60-GHz spectrum in multiple countries/regions has been allocated for use by mobile computing systems. The allocated bandwidths do not completely overlap, as shown in Table 1, although the 59–64-GHz band is common to all nations and regions. Note that these specifications are for indoor use and some countries have a narrower spectrum allocated for outdoor use.

60-GHz technology is fundamentally shorter range than the 5-GHz technology used by Wi-Fi and WHDI. It also does not penetrate walls. These two properties make 60-GHz technology a suitable approach to point-to-point connection; for example, the connection of a video source such as a handset to a local display such as a pico-projector or micro-projector.

WirelessHD is a 60-GHz technology based on the IEEE 802.15.3c specification. Version 1.0 of the WirelessHD specification was launched on January 3, 2008, and the companion WirelessHD Compliance Test Specification version 1.0 was launched on January 7, 2009. WirelessHD has a long list of sponsors, supporters, and adopters, including Intel, which also supports (and likely prefers) WiDi. Multiple companies that support WirelessHD also support WHDI. These include LG, Samsung, Sharp, Sony, Toshiba, and others. The specification includes provisions for universal remote control of all WirelessHD compliant devices. While the specification is primarily for the transmission of video and audio, including content protection, it can also support data transfer.

An example of a WirelessHD network is shown in Fig. 2. Note that in any WirelessHD network, there is one component, in this case the HDTV that acts as coordinator for the network. All members of the network have low-bandwidth bidirectional contact with all other members of the network. Some members of the network also have high-bandwidth unidirectional links. In this example, both the DVR and the Blu-ray player can deliver high-bandwidth content (i.e., HD video, audio, and copy protection) to the HDTV display. Currently, WirelessHD-equipped HDTV systems are available from LG, Panasonic, and Sony.

Fig. 2: This WirelessHD configuration is a Wireless Video Area Network (WVAN) that is using the HDTV as the coordinating component. Source: Wireless HD Consortium.

WiGig is a different application of 60-GHz technology that is based on the same IEEE 802.11 protocol as Wi-Fi. Therefore, WiGig can be thought of Wi-Fi with a higher bandwidth in a different RF frequency band. This compatibility allowed the WiGig Alliance and Wi-Fi Alliance to establish a cooperation agreement in May 2010 to share technology specifications for the development of the next-generation Wi-Fi Alliance certification program. This agreement further encourages the development of products supporting 60-GHz technology to expand existing Wi-Fi capabilities (Fig. 3).

Fig. 3: The WiGig Alliance has proposed usage models for wireless displays and other connectivity configurations. Image courtesy WiGig Alliance.

In addition to working with the Wi-Fi alliance, WiGig is working with the Video Electronics Standards Association (VESA). In November 2010, VESA and WiGig announced that "VESA and the WiGig Alliance will share technology expertise and specifications to develop multi-gigabit wireless DisplayPort capabilities. A certification program for wireless DisplayPort products will be developed in parallel."

WiGig is intended to cover all devices that need a wireless link. According to the WiGig FAQ, "The WiGig specification was designed from inception to address the rigorous requirements of various platforms, including low-power handhelds and battery-operated CE devices. To be more specific, the WiGig specification will include a high-efficiency physical-layer mode for mobile devices, with error-control schemes and MAC-layer features that are optimized for energy efficiency."

Proprietary Interfaces

One possible scenario for mobile video connectivity is for a company with a strong position in the mobile handset market and a desire to establish a foot-hold in the mobile projector market to establish a proprietary wireless standard. Apple did this in the wired video market with the video output on the iPhone and iPod. This has been a profitable path for Apple and there are many companies building products with iPod docks and paying Apple a royalty on each one. Apple does not license the connector for output: if you want to use the iPod dock on your projector, external speakers, or other system, you must own an Apple iPod or other Apple product, not a similar device from an Apple competitor. Another possible scenario is for a chip maker to provide a complete range of support chips for a proprietary interface. Intel is trying to do this with its WiDi system, as discussed.

The technology to pursue this proprietary strategy exists. Probably the strategy would take the form of a minor variation on one of the non-proprietary standards, just as the iPod connector, from a video point of view, is a minor variation on composite video.

The proprietary strategy would overcome the video-format compatibility issues inherent in the use of a non-proprietary wireless data transfer protocol. If Apple or some other company chose to pursue this strategy, there likely would be no advance notice: Apple (at a major media event) would simply announce its products, which would include at least one wireless-equipped iPhone or iPad and a compatible wireless equipped projector or other external display system (iProjector?). LG, Samsung, and a (small) handful of major handset manufacturers possibly could also pursue this proprietary path. LG and Samsung's announced support of standard protocols makes it unlikely they will introduce proprietary systems, however.

Wireless Connectivity Summary

Table 2 shows a summary of the various wireless standards. For completeness, this table includes wireless standards that are clearly not suited for video-rate connection between a video source and a display. In the future, it is likely that mobile devices will have more than one wireless protocol, intended for different purposes. For example, it is not difficult to imagine a next-generation tablet computer having Wi-Fi, 3G, or 4G connectivity for Internet access; 60 GHz for display connectivity; Bluetooth for headset, keyboard, or mouse connectivity; and near-field communications (NFC) to make the handset a virtual debit card.

Source: Insight Media

What can be concluded from all this? First, wireless connectivity between video sources and video displays is coming. In fact, it is not only coming, but has already arrived in some cases. Second, there are at least four standards with major corporate support that allow wireless video connectivity at HD data rates. These include WiDi and WirelessHD in the 5-GHz band and WHDI and WiGig in the 60-GHz band. WHDI and WiDi are both longer range. Unfortunately, they are in the already crowded 5-GHz band with Wi-Fi. WirelessHD and WiGig are both in the newer 60-GHz band and are intended for short-range connections.

I suspect in the long run there will be one 60-GHz and one 5-GHz video communications protocol. At this point, I refuse to guess as to which of the two standards in each RF band will be winners and which will be losers, but it would behoove display makers to follow the market carefully in order to ensure compatibility down the line. •