Packet error rate
Another key parameter determining the quality of wireless links is packet error rate (PER). Wireless video networks must achieve the design goal of maintaining communication links with a packet error rate of less than 10-8. Translating this into application-level, utility must be able to deliver over two hours of high-definition video without an error.
This is important to understand in both static as well as changing environmental conditions. This measurement of link reliability can be done with software such as iPerf. iPerf was developed The 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 & 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.
Click here for Figure 2
Figure 2: Throughput plotted vs. time with microwave interferer controlled in time.
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.
About the author
Dr. Rajeev Krishnamoorthy is the founder and CTO of Tzero Technologies.
Before founding Tzero, Rajeev was at Iospan Wireless, where he was responsible for developing the first commercially available multiple-antenna (MIMO) wireless systems. Rajeev spent the early years of his career at Bell Labs (AT&T/Lucent/Agere). Part of his tenure included the wireless LAN division in the Netherlands, where he co-invented and developed the high-speed version of the system that resulted in the 802.11b (Wi-Fi) standard.
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