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NEWS

"Comparing 802.11n and UWB for video applications"

by Rajeev Krishnamoorthy (CTO, Tzero Technologies), Wireless Net DesignLine, 17 October:

"Video is coming to home networks. Its requirements for both high bandwidth and low latency will mean a re-evaluation of wireless distribution technologies that can potentially provide a market opportunity for UWB.

"As the number of home networks in the US approach 40 million, the potential for a massive technology shift is becoming apparent. Home networks will evolve from being focused on data applications - with email and Web surfing being the most predominant - to handling one of the most bandwidth intensive of all applications, video.

"Why? Because video content is king. According to market researcher Parks Associates, a growing number of people want to stream online multimedia from their PCs to a consumer electronics (CE) device like an HDTV. Many [are] planning to move entertainment content from one CE device to another without a PC involved at all. The demand for this kind of interoperability and interactivity is driving the need for an evolution in networking technology...

Home entertainment without wires

"...[The] any-to-any communication capability of a wireless network finally solves the problem of connecting the device where content is stored (such as a DVR, TiVo box or DVD) to the point of consumption such as a remote display in a bedroom, kitchen, family room or home office... The challenges a wireless video solution must overcome include:

• Link reliability - Link reliability well in excess of 99% is required for wireless video. This compares to 90% link reliability for data networks.
• Low packet error rate - High-definition video content requires exceptionally low packet error rates of 10^-8 for the wireless link to deliver hours of flawless video. Wireless data networks typically achieve a packet error rate of 5 percent to 8 percent. Additionally, when occasional errors occur, the compression scheme must be one which does not propagate errors through multiple frames.
• Robust to interference - The home environment has numerous forms of RF interference. To preserve perfect video quality, the wireless link must avoid or cancel interference (both in-band and out-of-band)...
• Low latency - Total latency is a function of both the wireless link and the video compression timeline.
• Standards compliant and content protection compliant - The solution must be compliant and interoperable with all associated standards, including HDMI, HDCP and others...

Ultra Wideband vs. Wi-Fi

"Although Wi-Fi has a large installed base, Ultra wideband (UWB) is emerging as a serious contender for home networking because of its ability to handle video. UWB is a standards-based (WiMedia Alliance) communication mechanism using unlicensed spectrum from 3.1 GHz to 10.6 GHz.

"In an unprecedented move, regulatory agencies worldwide are adopting UWB. The initial wave of UWB products will mostly occupy Band Group 1 (see Figure 1), representing approximately 1.7 GHz of spectrum...

"For a 'best efforts' data network (email or web browsing), losing all data carrying capacity in the network often goes unnoticed. By contrast, a network carrying video at a data rate of 30 or 60 frames per second will suffer serious image degradation (and possibly a complete lack of video) as the result of an outage due to fading. Fading is an unavoidable phenomenon in Wi-Fi networks... To overcome this severe problem, some companies have tried buffering video data on the television. While this can help the on-going delivery of video to the screen, there are other implications...

• Memory cost ...the video buffer for a 1080p, 12-bit color, 60 fps application requires approximately 560 MBs of buffer memory per second of video.
• Loss of lip sync
• Increased latency and buffering result in poor remote control performance and poor joystick control in gaming applications.

"New [UWB] solutions provide link reliability and availability significantly above 99 percent, enabling real-time data transfer without buffering video data...

"[A] measurement of link reliability can be done with software such as iPerf. iPerf was developed [by the US] National Laboratory for Applied Network Research as a modern alternative for measuring TCP and UDP bandwidth performance, and it can report bandwidth, delay jitter, datagram loss.

"For the purposes of this document, two systems were setup (802.11n and UWB). The 802.11n chipset was supplied by Marvell and the equipment under test was the Netgear WNR854T and WN511T. These systems were tested for packet error rate (measured as a percentage of total packets) based on data rate and distance. These initial results were measured in the absence of any interfering devices. The exact same tests were then repeated with a microwave oven as an interferer, located approximately 30 feet from the receiving device.

"Both tests were run for 100 seconds. During the 100-second test the throughput and PER were logged at one second intervals. The interfering device was a microwave oven and was turned on and off as follows: Turned on at T = 41 sec and off at T = 56 sec

"The chart below clearly shows two of the phenomenon common to Wi-Fi networks which make Wi-Fi wholly unsuitable for entertainment networks:

• The fading characteristics of narrowband result in deep fades causing a loss of up to 60 percent of throughput.
• Interference from the microwave oven result in the 802.11n throughput dropping to around two percent of total available bandwidth.

"In Figure 2, The blue line represents the Tzero UWB throughput with no effect from microscopic fading or interference. The red line shows network failure of a 802.11 (draft n) solution when the microwave oven is turned on. Additionally, the red line shows measured drops in throughput as a result of microscopic fading (unavoidable in narrowband networks).

Interference robustness

"As illustrated above, interference is a huge issue for Wi-Fi networks. And in UWB, it's been an area of concentration for manufacturers. New solutions can be used to cancel in-band interference of 10 dB or more above the desired signal power. Out-of-band interferers (such as 802.11 systems, Bluetooth, cell phones, microwave ovens, cordless phones, etc.) can be nulled almost completely, even if they are in close proximity, thereby virtually guaranteeing reliable data delivery.

Conclusion

"New solutions using advanced UWB are quickly coming to market. They meet all of the requirements set forth by the major consumer electronics manufacturers. One of the first was productized by Gefen, Inc., a top provider of consumer and professional audio/video connectivity solutions. Their Wireless HDMI Extender uses the UWB chipset from Tzero Technologies. Tzero is the first chipset supplier to employ advanced interference cancellation - the company's UltraMIMO technology - and other approaches that make UWB appropriate for wireless video. The wireless HDMI design features non-line-of-sight operation that enables devices to communicate wirelessly through walls and extend across multiple rooms. It truly answers the call of the consumer, providing a wireless solution with the same quality as a wired network."

[UWB: 20 October 2006]