Wireless Systems Design

Competition For A Wireless Video Home Heats Up

As short range wireless technologies have gotten speedier over the years, most companies have been seeking ways for their technology to gain a foothold in the high volume consumer electronics market to transmit video over short distances to eliminate the gaggle of cables we’ve gotten used to. Existing technologies like 802.11n Wi-Fi and WiMedia's Wireless USB UWB have potential in this application but have limitations as well. Both of those technologies were designed for other uses, specifically LANs and USB data transmissions, so they have not been the best solution. Although we will see both used in some video distribution applications, several other wireless technologies have emerged and just could dominate the video distribution marketplace. Both were designed and optimized for video so they’re fast, simple, and cheap—something that the consumer electronics market appreciates. These two technologies are Amimon's WHDI and Pulse~Link's CWave, both of which are being demonstrated at the International Consumer Electronics Show in Las Vegas between January 7-10.

WHDI, or Wireless High Definition Interface is not an official standard but instead a technology developed by wireless chip vendor Amimon (www.amimon.com). It is a wireless technology designed specifically for transmitting uncompressed HD video. The growth in adoption of HDTV has been spectacular these past few years as large screen plasmas and LCDs have dropped in price. You can expect to see even more HDTV in the future as analog TV is totally cut off February 17, 2009. At that time, all TV transmissions will be digital and HD. If you don't buy a digital HD set you will need to add a converter box to your old analog TV set to watch television.

One of the big issues with HDTV is how to transmit it by wireless means to eliminate the mess of cables usually associated with home entertainment systems. Wireless is a great choice, but the available technologies tend to be borderline in performance. The new 802.11n Wi-Fi standard is capable of speeds up to 200 to 300 Mb/s, which seems like enough, but that technology was designed as a data transmission LAN and not for streaming video. The same goes for UWB. It is fast at its maximum rate of 480 Mb/s but the range is limited to only a few meters. To use either usually involves compressing the video for transmission then decompressing it at the receiving end. The compression/decompression process works but introduces some distortion and loss of detail. The most desirable transmission method is uncompressed video such as that carried over a cable.

The newer HDTV sets and other digital video devices like DVD players, DVRs, and game consoles use a DVI cable or the newer HDMI cable. But its length is limited to about 30 feet and such cables are very expensive. Wireless is a great way to eliminate the cable if you can transmit at speeds necessary to carry uncompressed video. This means data rates up to 3 Gb/s.

The WHDI system operates in the unlicensed spectrum from 4.9 to 5.9 GHz. At frequencies this high, you can achieve data rates suitable for uncompressed video. In a 40-MHz-wide channel you can get a rate to 3 GB/s to transmit uncompressed 1080p HDTV. In a 20-MHz-wide channel you can get a data rate to 1.5 Gb/s to transmit uncompressed 1080i and 720p digital HD or even standard VGA. And the latency is less than 1 ms, meaning you won't have lip sync problems that occur in some compressed formats.

The range for WHDI is about 30 meters max indoors with full penetration of walls. Outdoors with a clear line of sight you can get up to about 60 meters. The Amimon chipsets for WHDI are available now and are being built into some new TV sets and other video devices. You will also see some dongles that connect to HDMI connectors to replace these high ticket cables. Amimon's WHDI just recently received High-bandwidth Digital Content Protection (HDCP) certification. This means that Digital Content Protection LLC, the licensor of the HDCP content protection technology specification, has granted Amimon's WHDI solution authorization as an Approved Retransmission Technology.

Pulse~Link (www.pulselink.net) is one of the early pioneers in the UWB field and holds many original patents on the technology. Their pulse-type UWB has not been widely adopted nor has other impulse methods of UWB. Most of these technologies lost the early UWB battle to the WiMedia's OFDM version of UWB. Most UWB vendors use this technology and have focused their energy on the wireless USB niche with some success. Other WiMedia supporters have also worked on the video distribution applications with mixed results. Pulse~Link has stayed true to its pulse method and may just win a piece of the wireless video distribution battle.

Pulse~Link's CWave technology uses a carrier in the UWB spectrum, typically about 4 GHz (3.1 to 10.6 GHz in the U.S.). Then using a simple BPSK modulation scheme transmits data at a rate of 1.35 Gb/s. That translates into an 890 Mb/s rate at the applications layer which is fine for video.

A recently issued UWB test report from octoScope (www.octoscope.com), an independent wireless testing and consulting firm tested CWave against the WiMedia Wireless USB technology and found that CWave outperformed the W-USB. CWave achieved a data rate of about 500 Mb/s at a range of 8 feet and dropping to 115 Mb/s at 40 feet. W-USB was only able to achieve 50 Mb/s at those close ranges.

Another neat feature is that the Pulse~Link PL3100 chipset has also been used successfully in distributing video over coax. Using the existing in-home cable TV coax wiring, it is possible to send video over the whole house in both directions through the splitters normally used to distribute cable TV. Several home networking technologies like those from the Multimedia over Coax Alliance (MoCA) and the Home Phoneline Networking Alliance (HomePNA) systems are designed to use this installed base of coax to distribute video in the home. In most home situations a wireless component is needed. With a Pulse~Link system, all of the coax and wireless transmissions use the same format and protocol. Pulse~Link has also demonstrated how its technology can also be used to transmit Gigabit Ethernet, IEEE 1394 (Firewire/iLINK), and HDMI/DVI wirelessly.

Other technologies recently mentioned as a solution to the streaming video problem include those in the 60-GHz unlicensed band. Chips are just now being developed and are currently very expensive. Besides, these devices have a much shorter transmission range, although they can easily achieve the high data rates needed for uncompressed HDTV. It is expected that most versions when available will use highly directional gain antennas to achieve the desired range but that will limit their usefulness because you will have to point them in the right direction. Look for some 60 GHz products during the year. But I suspect with CWave and WHDI available now, one or both will win the consumer video distribution war.

Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.