Wireless devices have long been our daily companions, and we rely on them more and more each day. Mobile and cordless phones, notebook PCs, wireless data networks and a wide variety of remote controllers make our lives more convenient and deliver precious flexibility.
This untethered convenience and flexibility is now coming to home video entertainment. A movie stored on a digital video recorder (DVR) located in the living room can be watched on a TV located in the bedroom, even as a live HDTV broadcast is viewed in the children’s room (Figure). A video clip or digital pictures stored on a notebook PC, digital camera, or camcorder can be viewed at any time, on any of the TV sets around the house.
With wireless entertainment technology, TV and video devices will no longer be linked to the location of the TV cable port. Any change to the TV-screen location will no longer require that new cable be rolled out. Full mobility throughout the home will become an everyday reality.
These capabilities require a number of new technological innovations. Wireless entertainment networks must provide higher bit rates that were previously possible with data networking technology, to support the distribution of multiply quality video and HDTV streams from a central location, along with total home coverage. Also, video applications cannot tolerate bandwidth fluctuations, so guaranteed bandwidth and quality-of-service (QoS) are essential requirements. Finally, a wireless entertainment network should provide wire-like performance regardless of changing environmental conditions.
802.11n IS THE FUTURE
These challenges in the new home environment cannot be met with existing IEEE 802.11 a/b/g-based wireless products. Products attempting to use current WLAN technology for video distribution have fallen well short of consumer expectations for link range and picture quality and, as a result, new techniques have been developed. In response to this challenge, the industry has developed the new IEEE 802.11n standard based on multiple input multiple output (MIMO) technology. The IEEE’s revised Draft 802.11n specification was ratified in January 2007 and is well on its way to final ratification with broad interoperability among various vendors’ chipsets and access point products.
According to market research firm In-Stat, while Draft n/802.11n chipsets are expected to be only 3.6 percent of total WLAN chipset shipments for 2006, this percentage will grow to almost 20 percent in 2007. According to senior analyst Gemma Tedesco, “Although 802.11g will remain strong in some segments, such as in portable consumer electronics devices, over the next three to four years, 802.11n is the future and eventually all product segments will shift to this standard.”
MIMO MAKES IT POSSIBLE FOR VIDEO
Video entertainment networking is one of the leading application candidates for 802.11n products, and MIMO technology is what will make it possible. The use of MIMO enables higher data transmission rates by a factor equal to the number of streams and the ability to establish a wireless connection with no line of sight.
In addition to MIMO technology, enhanced performance for video networking, along with much better immunity to interferences, is achieved through the following features:
• Channel bonding: Extending the bandwidth by bonding two adjacent 20MHz channels into a single 40MHz channel. Excess bandwidth can also be traded for extended reach and lower power consumption.
• Improved media access code (MAC) efficiency: Without a substantial increase in MAC efficiency even high physical layer (PHY) rates will fall short, as the effective throughput that is left for the application is insufficient.
• Use of low interference 5GHz band: Two spectrum bands are available for WLAN communication: the 2.4GHz band today by the IEEE 802.11b and IEEE 802.11g standards, and the 5GHz band, currently used by the IEEE 802.11a standard. The 2.4GHz band can accommodate up to three non-overlapping 20MHz channels, which imposes hard limitations on the number of users that can be served and the number of adjacent networks that can operate without interference. Since only three channels are available in the 2.4GHz band, channel boding is not a feasible option. Adding to the challenge is the interference resulting from home microwaves, Bluetooth devices and cordless phones, which all operate at the same band. Given these channel-bonding and interference issues, the 2.4GHz becomes irrelevant for quality home video distribution. The 5GHz band offers more than twenty 20MHz channels in most parts of the world, which allows the support of much higher numbers of users, much higher bandwidth per user, and higher immunity from interference.
• Advanced forward error correction (FEC) scheme – Low density parity check (LDPC): LDPC provides additional coding gain that can be used to extend the reach for the same data rate to increase the throughput or to increase the robustness and immunity to interference.
• Improved QoS technology: New jitter cancellation and clock recovery schemes ensure synchronization and prevent packet loss for latency-sensitive video networking applications. Additionally, the IEEE 802.11n QoS standard addresses the requirements of video, gaming and other applications that are intolerant to bandwidth fluctuations, while the addition of admission control scheme guarantees contention-free access to the wireless medium for further QoS guarantees.
The latest update to 802.11n technology came with the January 2007 IEEE 802.11 revised draft specification, which included a modification with the practical effect of pushing more video services into the 5GHz band. This modification specifies mandatory polling of the 2.4GHz band to check for legacy 40MHz services that might interfere with 802.11n services, particularly high-bandwidth services using bonded RF channels.
Mandatory scanning is quite challenging for video applications. Every 30 minutes, the device must temporarily switch off the operating channel to all adjacent channels, conduct measurements and bring any out-of-tolerance 40MHz channels back to20MHz operation. This scenario will likely result in noticeable data flow “hiccups” for video streaming devices, forcing them away from the 2.4GHz band and into the 5GHz for better performance and less interference. Obviously, a service requiring guaranteed bandwidth cannot rely on a scheme that might require a reduction in bandwidth by half in the presence of another neighboring network. Additionally, the 5GHz band has the capacity for significantly more bonded RF channels – up to 24, as compared to three in the 2.4GHz band.
CONCLUSION
The convergence of consumer electronics, telecommunications and networking is a key factor in moving the broadband revolution to the next level. As DVRs and personal video recorders (PVRs) grow in popularity, consumers expect to be able to access stored video content anywhere in the home. The challenge is to provide seamless connectivity for this multimedia and entertainment convergence. Since current standards can’t meet this challenge, new standards and techniques emerged. The 802.11n draft standard, supported by channel bonding, improved MAC efficiency, advanced FEC and enhanced QoS technologies – all operating in the 5GHz band – provides increased throughput, range and robustness, and creates an enhanced, reliable user experience. It will take the complete video networking technology package to deliver the abilities required to push the home broadband network to the next level, enabling reliable video delivery over WLAN.
Gil Ephstein is director of product marketing at Metalink Corp. He can be reached at GilE@metalinkBB.com.
Illustrations:
Figure 1 |
