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Raise UWB throughput for wireless HD video

Posted: 01 Apr 2008 ?? ?Print Version ?Bookmark and Share

Keywords:wireless HD video? UWB? HDMI? USB?

By Fanny Mlinarsky
octoScope Inc.

It is difficult to imagine a wireless technology with more innovation and dynamism at work than UWB, particularly for the delivery of HD video. After a period of relative quiet in the UWB arena, new products are now emerging to raise the throughput bar.

Testing by octoScope verified that Radiospire's AirHook technology achieved throughput of 1.6Gbit/sfast enough for uncompressed HD video distribution over distances of 15 feet.

This article will first review the promise and technical challenges facing UWB, report on the most recent test results, and analyze Radiospire's approach to UWB. It will also discuss the throughput and encryption considerations for high-definition (HD) video distribution.

Recent developments
It was less than a year ago that the industry eagerly anticipated the arrival of Certified Wireless USB (CW-USB) and wondered how close real-world systems would come to the advertised 480Mbit/s PHY rate quoted by the technology's trade association, the WiMedia Alliance. Some WiMedia companies were promoting their technologies for video distribution with the help of data compression.

In independent testing conducted by octoScope and published by EE Times and Wireless Net DesignLine, however, performance of CW-USB chips and systems proved to be disappointing. But the same testbed confirmed that Pulse-Link's CWave technology achieved a 675Mbit/s PHY rate and 500Mbit/s of application layer throughput.

This is where Radiospire took the lead. It remains to be seen how WiMedia and Pulse-Link will respond, not to mention the UWB technology community, which has already taken initial steps toward standardizing a 60GHz technology.

UWB video challenges
UWB operates in the noise floor of traditional wireless applications and is able to share the already allocated spectrum with other services while only negligibly raising their noise floor.

The low transmit power limit of -41.3dBm/MHz Effective Isotropic Radiated Power curtails the range of UWB to about 10m, but the wide available spectrum of 3.1- to 10.6GHz, enables high throughput applications, making UWB technology well suited for short range HD video transport, connecting devices such as the DVD players, STBs and displays.

After the Federal Communications Commission approved the UWB spectrum allocation in February 2002, the IEEE 802.15 committee attempted to standardize the MAC and PHY layers to operate in the UWB band, but abandoned this effort in January of 2006 for lack of consensus. Many of the companies originally working on the IEEE 802.15 standard joined the WiMedia Alliance and focused on the CW-UWB technology that was evaluated in octoScope's recent EE Times test.

In that test the WiMedia-based products exhibited an order of magnitude lower throughout than Pulse-LINK (675Mbit/s), the only non-WiMedia product tested. Radiospire, another player outside the WiMedia camp, has set a new record of 1.6Gbit/s.

Although WiMedia is regarded as the UWB standard, companies such as Pulse-LINK and Radiospire point out that other MAC and transport standards, such as the IEEE 802.15.3b, TCP/IP and HDMI can also bridge the gap between UWB PHY technologies.

The original goal of UWB was short range HD video distribution. HDMI, in particular, is an uncompressed video interface, requiring more throughput (Table 1) than was achievable in the UWB band until Radiospire came along.

 Table 1: Uncompressed video throughput requirements
Table 1: Audio bandwidth varies with the number of channels. 8-channel audo requires 74 additional Mbit/s of transport bandwidth.

Radiospire's AirHook UWB chipset has demonstrated the highest airlink throughput in the UWB industry of about 1.6Gbit/s. The top device in our recent EE Times test, Pulse-LINK's CWave, performed at 675Mbit/s PHY data rate and delivered approximately 500Mbit/s TCP throughput.

WiMedia devices, comprising most of the UWB market, reached around 50Mbit/s application layer throughput. We were unable to verify whether the WiMedia PHY data rate reached the advertised 480 Mbit/s.

The WiMedia vendors claim that the low throughput is due to early driver implementations. The top performing new generation WiMedia chipset from Alereon is expected to reach 160Mbit/s, but this is still an order of magnitude lower than Radiospire's 1.6Gbit/s.

octoScope has verified the 1.6Gbit/s performance of the Radiospire AirHook chipset both on the bench and working as an HDMI cable replacement. The airlink transport of uncompressed 1080p HD video and 8 channel audio worked at 15 feet of range, through obstructions and at any antenna orientation.

Figure 1: Testing verified studio grade performance of the Radiospire wireless UWB based HDMI cable replacement reference design.

The data converters worked at 1.92GSps with 5.5bit effective resolution. The Radiospire device handled 1.7GHz of bandwidth from 3.1- to 4.8GHz, per design.

The system test setup included two displays placed side by side for a visual comparison of signal quality on the airlink vs. the ideal cabled signal. One of the displays was connected to the video source through an HDMI cable and the other display was connected through the AirHook airlink (Figure 2).

Figure 2: Radiospire system test setupTwo displays side by side with one connected through an HDMI cable and the other via the Radiospire UWB link. The Radiient repeater was used to split the HDMI signal into two identical synchronized streams.

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