Technology

 

Direct2Digital (D2D) Analysis

Related Terms:

ParkerVision believes that its ESP technology represents a completely new electronic circuit architecture that has the capability of replacing RF Heterodyne architectures, which allow “for a single-step direct conversion of an incoming RF carrier signal directly to its baseband data, eliminating the need for the RF heterodyne architecture” in RF receiver and transmitter design. The Company’s focus has been on the creation of “zero intermediate frequency (“zero IF”) radio system applications” based on the ESP technology. “Zero IF radios eliminate all of the intermediate frequency stages currently utilized in broadly deployed heterodyne transmitters and receivers.”

 

ParkerVision implemented ESP technology into D2D chipsets for WLAN in the early 2000s, and developed the Signalmax family of wireless WLAN cards for personal computers to demonstrate its technology. In 2003, ParkerVision introduced the PV-1000 D2D chipset and a 802.11 WLAN card product called SignalMAX (the WR1500). The company claimed that the PV-1000 products would “provide high performance benefits in a significantly lower cost, power efficient direct conversion architecture.” In a May 2004 press release, “ParkerVision touted its first product, the wireless network card, as a significant improvement over other products in the market in terms of performance (distance and speed), size, power consumption and cost. The company said its technology could maintain a wireless signal for up to 1 mile, compared with only 1,500 feet for competing products.” 

 

The ParkerVision SignalMAX products were found to offer a meaningfully better range only in very specific circumstances – open field testing – at the expense of an extremely low data rate at long distances. This made them a reasonable choice for a limited set of niche applications where modem-style data rates are acceptable and long, open field distances must be traversed. However, in more real-world tests (see Comparison of ParkerVision SignalMAX vs. Belkin Pre-N), the ParkerVision products did not show a significant improvement in range over the Pre-N products while the Pre-N offered much higher data rates. We predicted in early 2005 that the Belkin Pre-N products (using first generation Airgo MIMO chipsets) would be likely to dominate the market that ParkerVision products were targeting. This did prove to be the case.

 

Despite ParkerVision’s failure in the WLAN market, the question about D2D performance has remained. Can D2D technology, which implements the 802.11 standard, really achieve better RF performance, specifically better radio sensitivity?

 

Radio sensitivity is not just the maximum front end sensitivity (for more details see FAQ on WLAN Receiver Sensitivity and Range). The 802.11 standard is designed for a close range environment with many interferers (such as you find at a Wi-Fi hotspot), making receiver sensitivity a low priority. The IEEE specification requires -76 dbm sensitivity at 11 Mbps and -80 dbm sensitivity at 1 Mbps. Several chip vendors claim to better this by up to 20 db.

 

In the real world, radios suffer from interference from other radios and multiple transmission paths, which cause signal strength to increase and/or decrease rapidly over short distances. The presence of other radios effectively adds noise to the detector. Because the IEEE 802.11 specification was designed for multiple radios in one location, an extremely low noise figure is not necessary. This is why it is so easy to improve upon the 802.11 sensitivity.

 

Noise figure, interference, multi-path, modulation bandwidth, and data encoding all affect WLAN product range. One of the more significant effects on the radio signal is reflections from objects. The multiple paths caused by the reflections allow the signal to interfere with the reflections, either enhancing or reducing the signal strength. These variations rise and fall every half wavelength, or about 2.4 inches at 2.5 GHz. Having multiple antennas connected to multiple receivers, also called full diversity, can increase the range. In addition, redundant transmit paths can increase the product range, but at the expense of data rate and manufacturing cost (twice the part count) and increase power consumption (about double).

 

Maximum sensitivity of a WLAN card is set by the minimum signal to noise ratio at the detector. Receiver front ends add their own noise, given as the noise figure of the receiver. The receiver noise figure is usually given in dB and describes how many decibels of noise the front end adds to the incoming signal. A zero dB noise figure would not add any noise, and chips such as the Maxim 2820 have only a 3.5dB noise figure. At the detector, the radio bandwidth and the data encoding also affect the receiver sensitivity. Broadband noise, due to thermal and atmospheric sources, reduces the sensitivity in dB as 10 * log (bandwidth). Finally, encoding schemes, such as the spread spectrum technology in 802.11b use extra bits to reduce the effects of random noise and interferers.

 

Some Cisco cards (as compared to Linksys which is owned by Cisco), like most older 802.11 designs, use an off-chip low-noise-amplifier (LNA), also called the preamp, in front of the receiver. Nearly all of the most recent 802.11g cards are now built with a true, single-chip CMOS implementation that integrate the receiver, the LNA, the VCO (voltage controlled oscillator – also known as the PLL), and many of the filters in the same chip. ParkerVision, in the original white paper (no longer on the web site), also claimed that they were going to integrate all of these components into a single CMOS chip. They haven’t done this at all. Unlike the best of the existing, high-volume OEM chip suppliers, they have (after 8 years, and about $80M) implemented what appears to be a SiGe chip and which uses an off-chip LNA and an off-chip VCO. This is not an inexpensive implementation (see Highly Integrated CMOS 802.11 Radios).

 

In the end, despite the expense of the PV-1000 chipset, ParkerVision relied on everything but D2D to improve SignalMax range and sensitivity! Specifically, ParkerVision increased range in three ways (see Reasons for SignalMax Range Improvement):

  1. They used an external low noise amplifier to increase the sensitivity of their D2D IC. Thus the shipping ParkerVision products were not, in fact, “direct to digital” at all: they used an external, analog low-noise preamp in front of the the D2D receiver.
  2. For the WR1500 product, Parker used multiple receivers connected to multiple antennas. They used diversity techniques to maximize the received signal. Note that another form of diversity (MIMO) is also used by Belkin on their Pre-N, which gains both range and bitrate, as compared to the ParkerVision approach which significantly reduced the bitrate and increased range.
  3. In addition, the WR1500 product was designed to have redundant transmit paths (as described in ParkerVision patent #6,647,250). The redundancy increased product range at the expense of a significant decrease in data rate.

 

Other chipsets on the market (Infineon, Maxim 2820, Atheros, and now Airgo as well) proved to be significantly better than the IEEE 802.11 standard implemented by ParkerVision. The Infineon and Maxim chips are 16 and 17dB more sensitive than the IEEE specification and the Atheros chipset reaches a 20 dB improvement by doing additional data encoding (which also reduces the data rate).

 

Furthermore, ParkerVision did not gain superior performance by their avoidance of the traditional superheterodyne architecture. In fact, superheterodyne receivers can be as sensitive as the ParkerVision D2D architecture. Many companies have moved away from the superheterodyne architecture because it requires many filters and is not ideal for digital integration, not because it lacks sensitivity. The Horizons HZ1500 card with ParkerVision D2D technology used a low noise amplifier (Infineon BGA622 in the Horizon card) to improve the sensitivity of the ParkerVision 2000TR IC. The ParkerVision WR1500 also used low noise amplifiers in front of their 2000TR ICs. Moreover, the WR1500, implemented with D2D technology, had over twice as many ICs in its RF path as NetGear’s WLAN router.

 

In May 2002, David Sorrells stated that “We are confident that not only will our reference designs using the PV-1000 be Wi-Fi compliant, but they will meet or exceed the specifications of today’s best performing Super Heterodyne based designs. The PV-1000 will deliver a high performance, highly integrated, cost effective IC transceiver solution based on our direct conversion technology.” In reality, there is no evidence that D2D technology has greater sensitivity than other IC technologies, is more integrated or cost effective. ParkerVision never published the noise floor data for any of their receivers, so a quantitative comparison of performance could never be made. In their WLAN cards, the use of an external low-noise preamp, the use of multiple receivers connected to multiple antennas in the router and the use of redundant traffic paths to the PCMCIA card easily explained all of the improvement observed in the range tests. These are applicable to any competitor willing to pay the higher component cost and suffer the reduced bitrate resulting from these techniques.

 

In the end, the market made its decision on ParkerVision’s D2D technology and WLAN products. Not only did the revenues for the product lines never exceed $1M over its three-year life cycle, but ParkerVision never gained sufficient consumer confidence to create meaningful traction. Despite its commercialization efforts over the past five years, there is not a single OEM customer for D2D technology to date. This is consistent with statements from our industry sources, who state “ParkerVision was never a real player” in the RF IC marketplace.