doc.: 15-08-0744-00-0thz submission november 2008 rick roberts, intelslide 1 project: ieee p802.15...
TRANSCRIPT
November 2008
Rick Roberts, IntelSlide 1
doc.: 15-08-0744-00-0thz
Submission
Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: Some THz System Issues – Part 2 – SafetyDate Submitted: November, 2008Source: Rick Roberts Company: Intel CorporationAddressVoice: FAX: E-Mail: [email protected]
Re:
Abstract: This contribution presents some desirable system performance issues
Purpose: for discussion
Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.
November 2008
Rick Roberts, IntelSlide 2
doc.: 15-08-0744-00-0thz
Submission
In this contribution we continue to try to answer the question “in regards to communications, what is the compelling reason to invest in THz”?
For instance, the THz band offers more bandwidth, but we can get more bandwidth using infrared and apparently infrared is easier to generate.
In this contribution, some regard is given to the safety issue. It is found that the maximum allowed power densities for THz are higher than that allowed for near infrared. But it is questionable if the results are compelling for THz since actually emitting signals at these maximum power densities may be impractical.
November 2008
Rick Roberts, IntelSlide 3
doc.: 15-08-0744-00-0thz
Submission
From 15-08-0410-01 …What will it take to get industry excited about THz?
THz will be exciting if and when …
1. THz offers wireless bit rates unmatched by any other wireless technologies• Bit rate sells … historically there has been interest in wireless
technology that offers more throughput (even at short ranges).
2. Costs are comparable to existing technologies• The market wants more for the same cost. Going 10x faster
captures the market, but it doesn’t allow charging 10x more.
3. Power/bit is less than existing technology• Going 10x faster has to be done with basically the same battery
used by the 1x technology.
November 2008
Rick Roberts, IntelSlide 4
doc.: 15-08-0744-00-0thz
Submission
In traditional radio one can postulate that there is a relationship between cost, data rate and operating frequency … but does bandgap generation of the operating frequency disrupt this model?
Below we assume that the data rate is 1% of the operating frequency (i.e. the higher the operating frequency, the more the bandwidth and hence higher the data rate.
Freq
Cos
t
1 GHz 10 GHz 100 GHz 1 THz(10 GHz BW)
10 THz(100 GHz BW)
100 THz
electronics photonics
ImplementationGap
At 10s of Gbps data rates, will photonic bandgap generation of wireless communications be cheaper than traditional radio?
November 2008
Rick Roberts, IntelSlide 5
doc.: 15-08-0744-00-0thz
Submission
1 THz
From 15-08-0410-01
But why THz and not near IR1?
Why should industry invest in multi-Gbps THz as opposed to multi-Gbps near-IR?• lowest cost?
- easier to generate?• better performance?
- lower intrinsic terrestrial noise?- higher bit rates, less loss, less power?
• Safety?We need a compelling argument!
1Forin, D.M., et. al., “On field test of a Wavelength Division Multiplexing Free Space Optics Transmission at very high bit rates’, 9th ICT, June, 2007 (where NIR FSO rates of 40 Gbps are reported)
Ref: http://en.wikipedia.org/wiki/Water_absorption
November 2008
Rick Roberts, IntelSlide 6
doc.: 15-08-0744-00-0thz
Submission
Ionizing Radiation vs. Non-Ionizing Radiation
The energy of an individual photon is given by E=hf (h is Planck’s constant and f is the frequency); and in analogy to Eb, free space optics measures performance by the number of photons per bit (b).
At a frequency of ~2420 Terahertz the photon energy approaches 12.4 eV. At this energy level water molecules can become ionized (body tissue damage). This frequency is well above visible light (450 THz to 750 THz) and is in the ultraviolet region.
So we are only concerned with non-ionizing radiation; that is, we are concerned about absorption of energy (power density) heating the human body.
November 2008
Rick Roberts, IntelSlide 7
doc.: 15-08-0744-00-0thz
Submission
Not all Wavelengths Enter the Eyeball
Visible light to near infrared (400 nm to 1400 nm) pass through the eye lens and forms an image on the retina.
The problem with passing through the eye lens isthat a very sharply focused image is formed on theretina which significantly increases the power density. If the power density is enough to cause localized“boiling” then a permanent blind spot occurs. Near Infrared (>700 nm) is particularly dangerous since the body’s protective “blink reflex” is triggered only by visible light and the retina feels no pain as it is damaged.
If the energy does not pass through the lens then the energy (density) is dispersed on the cornea and lens, where the danger is the formation of cataracts.
November 2008
Rick Roberts, IntelSlide 8
doc.: 15-08-0744-00-0thz
Submission
Photon Ionization of Water Molecule
Enters the eyeball
Absorbed by skin or cornea/lens
November 2008
Rick Roberts, IntelSlide 9
doc.: 15-08-0744-00-0thz
Submission
MPE1 as power density versus exposure time for various wavelengths.
1Maximum Permissible Exposure
At 1 THz, λ=300 um
Source: http://en.wikipedia.org/wiki/Laser_safety
= 16 dB
November 2008
Rick Roberts, IntelSlide 10
doc.: 15-08-0744-00-0thz
Submission
THzSource
distance D
THzSink
Beam area at distance D is D2.
=1 sr
Required Eb/No (dBm) (OOK) 13NF (dB) 10No (dBm) (not applicable above 10 THz) -164Eb (dBm) -151Bit Rate (Gbps) 100RX Power (dBm) -41
RX Aperature (mm2) 78.53981634
RX Power Density (W/cm2) 1.01137E-07Source Beam Solid Angle (steradians) 1Range (m) 1
Beam Area at Range (m2) 1Total TX Power (W) 0.010113701
TX Aperature (mm2) 78.53981634
TX Power Density (W/cm2) 0.012877164
Safety Link Budget Example(Safe harbor statement: may not be realistic, may not be correct)
Based upon the assumptions, it appears that wavelengths >2.9 um (1 THz is 300 um) could be safely deployed while near infrared wavelengths (<1 um) would exceed the safety limits.
Double Click to Activate Spreadsheet
November 2008
Rick Roberts, IntelSlide 11
doc.: 15-08-0744-00-0thz
Submission
Conclusion
Is the safety argument compelling; that is, is THz always safer than Near Infrared?
• In our contrived example, Near Infrared (NIR) exceeded safety limits, but not by much. And the parameters could have been easily adjusted to meet the NIR safety standards.
• In general THz will have more safety margin, but this is not to say that IR couldn’t be safely deployed at 100 Gbps data rates over a short range with a highly focused beam.
Call for Contributions: Of interest would be contributions establishing compelling reasons why THz is preferred for communications over IR.
November 2008
Rick Roberts, IntelSlide 12
doc.: 15-08-0744-00-0thz
Submission
The End – Thanks!