Date: Aug 09, 2013 Source: Wireless-Mag (
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Ultraphase Coordination (UPC) technology is a new PLL (phased locked loop) technology developed by Colorada-based Gain ICs, which overcomes the limitations of existing PLL technology, specifically jitter peaking, to achieve 1,000 times faster phase coordination or tracking bandwidth. These limitations caused traditional PLLs to be too slow for FM demodulation, leading to the QAM architecture widely used at this time.
The QAM (quadrature amplitude modulation) determines the bit rate density carried within the RF wave. 802.11ac increases this to 256QAM from the previous 802.11n Wi-Fi standard's 64QAM. In theory, this along with other improvements in the standard will enable data transfer speeds of up to 1.3Gb/s.
UPC leapfrogs QAM to achieve higher data transfer rates by going back to using PLLs for FM demodulation. This is possible because UPC eliminates jitter peaking, the chief barrier to high speed data transmission using a PLL demodulator. Besides the higher speed than existing architectures, UPC inherits the much more reliable transmission of FM with much greater immunity to noise and longer range per power.
Demands for faster wireless data transmission are only going to increase. Today's technology has limitations which are hindering the effort to transfer data at 1Gb/s and above by requiring more power while hogging more bandwidth on an already crowded frequency spectrum.
Limitations of QAM technology
The limitations in QAM technology have become apparent with the release of IEEE spec 802.11ac and the awarding of the US Defense Advanced Research Projects Agency's (DARPA) "100Gb/s RF Backbone (100G)" [4]. This article focuses on the limitations of QAM, while introducing a new, disruptive technology that solves the problems associated with transitioning to data rates of 1Gb/s and beyond.
The implementation of IEEE 802.11ac has begun. The technology is in its infant stages as the hardware upgrades await the silicon availability of products with better signaling capability. Even before the specification was finalized, it had gathered its fair share of critics [2], [3] and rightly so. Now that some products have been released, the reality of the limitations of the QAM architecture are becoming all too real [1].
You see the problem is that you cannot outdo the laws of data transfer capacity which according to the Shannon-Hartley Theorem simply state that:
Equation 1. Capacity = (Number of Channels) x (Bandwidth) x (Spectral Efficiency)
802.11ac is being lauded for expanding the capacity in Equation 1 by taking bandwidth from 20 MHz and 40 MHz in 80211.n to 80 and even 160 MHz and allowing a QAM rate increase from 64 to 256. For those of you unfamiliar with QAM, it is a constellation number that allows more resolution to be packed onto a signal, or more data bits communicated per symbol. 802.11ac also increases the number of spatial streams from 4 to 8. Although all of these increases allow for more data to be streamed, they open up a myriad of problems in actually implementing working hardware.
QAM is a combined signal of amplitude and phase modulation [6]. Amplitude modulation in general has problems with poor signal to noise ratios. That is why your AM car radio stations have less clarity than Frequency Modulated (FM) channels. As the number of QAM constellations increases, the signal to noise ratio must increase [5].
This is because increasing the number of constellations lessens separation between points thus allowing noise to become more of a factor. QAM as a technology suffers from poor noise immunity. As a result, 802.11ac and the DARPA 100Gb/s backbone initiative both propose increasing the transmitting power, using highly tuned antennas, and implementing beam forming to "steer" signals between transmitter and receiver. As reference [3] puts it: "For 802.11ac to work as advertised, it's essential to have greater control over the signal paths within the RF spectrum."
Additional bandwidth required
The other problem associated with 802.11ac is its need for additional bandwidth. The specification allows transmission at the 5 GHz carrier frequency which is less crowded than the 2.4 GHz used by 802.11n. Is it really less crowded? A look at the specification shows that even among the 5 GHz availability, there are a limited number of channels available to use.
This limited number of channels and the fact that the wider 160 MHz bandwidth also uses up more spectrum are overloading an already crowded frequency spectrum. Because of this limitation of the number of available channels, other methods of using the allowed bandwidth such as 80+80 MHz are being sought however they introduce more problems than they solve. "In this case, 80+80 MHz allows the use of more spectrum but only uses that spectrum half as efficiently [8]."
The bandwidth problem is so intense that a second DARPA initiative [7] has begun in order to divide up the number of users in a method of spectrum sharing on the dedicated military frequency spectrums.
This initiative in effect forms a line that one must get into and wait their turn to transmit. The key take away is that in the pursuit of faster speed, additional bandwidth hogging has resulted in delays associated with spectrum sharing. So if you have a drone under attack, better wait in line for your signal to arrive that will steer you out of the danger. As the commercial sector increases in use, expect a similar solution to appear.
Although 802.11ac was an initiative that was based on available technology and created by a panel of industry masters, the end result is an example of the limitations of QAM technology. The situation is akin to squeezing a water bottle to omit a bulge only for the bulge to appear elsewhere in a tradeoff of the parameters in the capacity equation (Eq 1) between bandwidth, signal to noise ratio (spectral efficiency), and number of channels. A new technology is needed in order to solve the problem and enable clear, reliable 1Gb/s data transfer rates.
Introducing Ultraphase Coordination
Ultraphase Coordination (UPC) allows data transmission to return to phase modulation signals thus eliminating the problems with QAM's amplitude modulation based architecture. The secret for UPC is a new phase locked loop PLL technology that allows for much faster PLL blocks which in turn lowers jitter peaking while increasing transmission speeds orders of magnitude.
UPC can be transmitted as a single channel signal with a lower spectral bandwidth hence much higher spectral efficiency than QAM as shown in Figure 1. This technology solves a major problem with traditional PLLs that initially caused designs to favor QAM technology. UPC allows wireless data transmission to return to simple signaling methods thus avoiding rotating the flat tire around the car as one must do when using QAM.
Figure 1. UPC's Narrow Modulation Bandwidth Frees Up the FM Spectrum for More Transmitting Channels to Be Added
Figure 1 shows that for an equivalent data transfer rate of around 610 Mb/sec, UPC technology uses half of the bandwidth of 80 MHz versus 160 MHz when compared to QAM while having a higher link spectral efficiency of 8.13 (b/s)/Hz versus 3.8 (b/s)/Hz for QAM. The higher efficiency produces a longer transmission range due to phase modulation only.
In addition, the signal quality of the UPC's phase modulated signal combined with a much higher spectral efficiency lowers the power required to transfer the signal thus eliminating the need for beam forming and other tricks in the transmit receive section. Note that such methods could only enhance the performance of UPC also yet users are most likely to avoid the additional cost and complexity. If you don't need it, don't employ it!
This allows customers to greatly reduce cost in the power amplifier stage not to mention the antenna design and product costs, while still achieving very high transfer rates. The single signal of the UPC technology further drives down cost by using one set of hardware instead of several.
As mentioned, as QAM increases in constellations the technology requires more channels and wider bandwidth in order to transfer data. UPC actually frees up bandwidth thus increasing the number of available channels as shown in Figure 2. This means the air space is now more available to transfer the Gb of data the market is aggressively requesting.
Figure 2. UPC Technology Offers the Ability to Free Up the Crowded Frequency Spectrum and Transmit at a Rate of 650Mb/s
UPC is a new technology that provides an advantage to the limitations of QAM architecture. UPC doesn't just make sense in one factor of the capacity equation, it provides an entirely new overall solution to exceed Gb/s data transfer needs as shown in the comparison of parameters in Table 1.
Table 1. UPC is a Disruptive Technology That Will Enable Gb/s Data Transfer While Freeing Up Significant Portions of the Frequency Spectrum
Summary
A new technology has been introduced for industry to use in a graceful transition to Gb/s data transmission rates. This technology known as Ultraphase Coordination (UPC) allows the return to traditional phase modulation techniques thus avoiding the complications introduced by higher QAM constellations. The technology is available today as an IP block that is ready for integration into your silicon product. Contact info@gainicsfor further information.
- See more at: http://www.wireless-mag.com/Features/26307/New_UPC_technology_facilitates_transition_to_1Gbps_Wi-Fi_data_transfer_rates_.aspx#sthash.klX2wimj.dpuf
