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Consumers are increasingly practicing the benefits of whole-home data networks for activities like web surfing and e-mail access. Now, the industry is pursuing the creation of home networks that enable not just web browsing and e-mail, but the ability to access movies, music, data and more — located anywhere in the home — from any other suitable device within the home. Market research firm ABI Research recently referred to the converging factors that are enabling the coming widespread adoption of home multimedia networks as a broadband video “perfect storm.”

The core network applications, such as multiple simultaneous streams of high-definition (HD) movies, TV and multichannel audio, all with “trick play” (e.g., pause, fast forward and fast rewind), present significant technical challenges. Networking HDTV around the home, for example, creates bandwidth and quality of service (QoS) hurdles. This also creates digital piracy concerns with content providers. To address these issues, industry groups such as the High Definition Audio-Video Network Alliance (HANA), comprised of a cross section of content and service providers, CE manufacturers, technology companies and more, are emerging.

Within this framework, ultrawideband (UWB) technology has been promoted as a wireless connectivity solution for HDTV. Despite the attention UWB wireless technology has garnered, it is still basically a short-range, single-room solution. At first glance, it hardly appears to be a solution fit to enable whole-home HD multimedia networks.

However, a whole-home network can be achieved by using a properly optimized wireless UWB chipset. Instead of coupling it to an antenna, the engineer would need to do an impedance match to 75 V and couple it to a coaxial cable. Being a shielded media, coax can handle higher transmit power levels and since the intended transmission receiver is not wireless, it is not subject to the constraints of the wireless UWB emissions regulations. Coax is also prevalent in approximately 80% of North American homes and more than 400 million homes worldwide.

Using a common chipset optimized to enable simultaneous coax and wireless HD multimedia networks, coupled with an isochronous 802.15.3 MAC optimized for managing multiple simultaneous streams of HD video with guaranteed QoS; a UWB chipset solution is created that overcomes the whole-home networking hurdles. It can network multiple simultaneous streams of HDTV with trick play functionality, at hundreds of feet around the home, while supporting acceptable content protection mechanisms.

Creating such a hybrid coax/wireless solution from a common chipset yields a number of advantages compared to the alternative; creating a bridge between two dissimilar wired and wireless technologies. Aside from cost reductions that result from the elimination of the requirement for two separate radios, a common chipset possesses a common MAC and, therefore, no bridging is required. This preserves critical QoS and content protection mechanisms across the separate wired and wireless transmission media.

Much has been written about UWB wireless technology over the past several years. This article, therefore, will focus on UWB over coax, its performance characteristics, common misconceptions, and collected data and test characterizations. The principles discussed address the concept of UWB over coax in general and as such a specific discussion of modulation, physical layer characteristics and MAC implementations will not be included. This article addresses the characteristics surrounding a UWB-coax home network.

It is limiting to think of UWB as an application. Its true definition is essentially any signal that occupies more than 500 MHz of spectrum simultaneously or more than 20% of the fractional bandwidth of the available transmission media. Thus, when referring to “UWB-over-coax,” keep in mind that what is being described is a signal through the coaxial cable that occupies more than 500 MHz of spectrum simultaneously. For the purpose of the measurements discussed in this article, a UWB signal from the CWave UWB chipset, which is just over 1.3 GHz wide, will be employed.

In the wireless world, the Federal Communications Commission (FCC) mandates UWB wireless signals operate above 3.1 GHz. At the same frequencies inside a coax no other application exists or is planned today, making the UWB-over-coax signal completely coexistent with all legacy coax applications. If operations on coax are at the exact same frequencies as used in UWB wireless communications, it also makes the implementation of a chipset that can handle coax and wireless communications simultaneously easier to architect. Therefore, what is described in this article is a signal of more than 500 MHz spread (>1.3 GHz herein), at frequencies greater than 3 GHz, transmitted and received inside of the coaxial cable instead of across antennas.

It is usually about this point in any explanation about UWB over coax that the first objections arise. Demonstrable silicon is making overcoming such objections much easier. The most common objection is:

• Objection: The RF splitters around every home with coax cable aren't designed to work above 1.5 GHz. The resultant attenuation at higher frequencies introduces echoes and multipath that is difficult to equalize and control. It, therefore, isn't feasible to transmit signals above 3 GHz over existing coax home networks, so UWB over coax must not be feasible. After all, any feasible coax networking technology must have the ability to contend with what already exists in people's homes.

• Response: This is an entirely appropriate initial objection — but from a narrowband perspective and not from a UWB perspective. While it is true that CATV RF splitters are typically rated for operation up to no more than 1 to 2 GHz, that is by no means the maximum frequency at which most are capable of operating. When spreading the UWB signal energy over 1.3 GHz of spectrum, any spectrum nulls or drop-outs are, for the most part, averaged out over the 1.3 GHz. A UWB signal in the frequency domain is low, but in the time domain can be fairly high, which provides for a reliable and robust link. As for echoes and multipath, these are typically a narrowband concern and cause less concern for several reasons.

First, any reflections are typically very low in amplitude and attenuated by the coax cable itself. Given the harsher requirements for reliable operations in UWB wireless communications, as a general rule, engineers actually like echoes and multipath and, in some cases, wish there was more of it. As an example, consider that the CWave UWB radio essentially has a RAKE receiver that is capable of capturing multipath and using it to coherently add energy and increase receiver sensitivity. A narrowband receiver might generally see this energy as uncorrelated noise, but for a UWB receiver processing in the time domain it represents potential signal gain.

What follows is a summary and overview of characterization and data-rate capabilities of UWB technology like CWave, measured in several over-coax scenarios. It includes the performance of various combinations of splitters and cable lengths, while maintaining application layer data-rate capabilities in excess of 400 Mbps after forward error correction (FEC), data framing and checksum overhead.

Modular tests for all the constituent components were performed in order to fully understand end-to-end characteristics of the link. An Anritsu 37269B vector network analyzer was used to perform an S21 sweep of the frequency range of interest (2 GHz to 6 GHz), to characterize cable segments for various segment lengths and the insertion loss of the splitters. Details of measurements are provided below.

• Splitters

  During testing, off-the-shelf two-way, four-way and eight-way splitters were characterized. Sample results are shown in graphs of Figures 1, 2 and 3. The sample two-way splitter part number is GQ 201-232, and the four-way splitter part number is GQ 201-234. As shown in Figure 1 and Figure 2, the insertion loss of various two-way splitter models varies in the band of interest (3 GHz to 5 GHz) over a 7 dB to 10 dB range. The insertion loss of the tested four-way splitter is in the 12 dB to 25 dB range, over the 3 GHz to 5 GHz band of interest.

  Several 8-way splitters were also characterized. The two sample models used for these figures are from CALRAD Electronics (model 75-713-8) and PDI (mega-splitter model PDI-8WMVS-5). Both of these 8-way splitters are rated up to 1 GHz. The performance test characterized each port for the best insertion loss characteristics from 3 GHz to 5 GHz band. Figure 3 shows each splitter's performance in this band.

• RG-6 quad-shielded and RG-59 coaxial cables

  Several segments of differing length (100, 200 and 300 feet) of RG-6 coaxial cable were characterized. Attenuation vs. frequency curves are shown in Figure 4. Attenuation slopes increase by 3 dB per 100 feet of cable segment. The absolute value of attenuation increases by 12 dB per 100 feet.

  For comparison purposes, an off-the-shelf standard RG-59/U coaxial cable (sample part numbers BV-14W, BV-15W, BV-16W) was used. Figure 5 represents a sweep of the BV-16W 100-feet segment. There is 5 dB more attenuation at 4 GHz, with approximately equal tilt from 3 GHz to 5 GHz of -10 dB, as compared to a 100-foot RG-6/U quad shield cable.

• Compliance with FCC rules for unintentional radiation

  The maximum transmitter power for the CWave chipset-based modem was determined so that it complies with FCC Part 15 regulations for unintentional emissions. The maximum permitted emissions are summarized in Table 1. Table 2 provides examples for CWave PHY layer data-rate performance assuming no additional amplifier is used at the receiver.

Pulse~LINK has experimented with several methods of extending the range for high data rate transmissions over coaxial cable, including the use of specially designed amplifiers at the receiver end. Such methods have been tested to provide a reliable PHY rate capability of 675 Mbps through more than 300 feet of cable including two splitters.

The above data illustrates that UWB, often considered a wireless-only technology, has the ability to serve as a broadband distribution backbone for in-home coax networks. Properly optimized UWB-coax solutions are capable of traversing coax splitters and distances throughout the home. By using the same chipset for both wireless and coax solutions, multimedia content obtained from any STB, DVD, PVR, media center PC, network attached storage device or other source within the home, can seamlessly be shared with any other TV or multiple other TVs simultaneously, anywhere else in the home. This solution can provide the necessary QoS and content protection assurances maintained on a common network platform solution.

Dan Friedman is the vice president of marketing at Pulse~LINK. He has more than 23 years of experience in marketing, sales and system engineering in the hi-tech sector, including defining system architecture solutions of new semiconductor products in the consumer electronics and wireless market. Friedman holds a MSEE and BSEE from UC Santa Barbara and a Graduate Certificate in Finance at UC San Diego.