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| Everything from light to radio to x-rays (and much more) are all a part of the electromagnetic spectrum. | Everything from light to radio to x-rays (and much more) are all a part of the electromagnetic spectrum. These various sections are named, and discussed as separate elements based on the way the radiation interacts with physical matter. Visible light excites electrons at a frequency convenient to biochemical processes, so there are rods and cones in our eyes which detect it. Radio collectively oscillates materials, like all the electrons in an antenna. |
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| Individual components are broken up, and discussed as though they are separate components. These are not arbitrary distinctions, and | Think of the entire electromagnetic spectrum in the same way as the spectrum of visible light; there is a clear area which is "red" and a clear area which is "orange" but also a space in between, parts of which could be considered "red-orange" or red, or orange. Though the individual components are discussed as though they are separate components, they are also part of a continuum and certain interactions overlap quite strongly. |
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| XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX | Everything on the electromagnetic spectrum has a frequency, wavelength and power. Radio, especially, is very commonly discussed in these terms as they influence range and the speed and capacity of the information carried. |
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| Electromagnetic radiation interacts with matter in different ways in different parts of the spectrum. The types of interaction can be so different that it seems to be justified to refer to different types of radiation. At the same time, there is a continuum containing all these "different kinds" of electromagnetic radiation. Thus we refer to a spectrum, but divide it up based on the different interactions with matter. Region of the spectrum Main interactions with matter Radio Collective oscillation of charge carriers in bulk material (plasma oscillation). An example would be the oscillation of the electrons in an antenna. Microwave through far infrared Plasma oscillation, molecular rotation Near infrared Molecular vibration, plasma oscillation (in metals only) Visible Molecular electron excitation (including pigment molecules found in the human retina), plasma oscillations (in metals only) Ultraviolet Excitation of molecular and atomic valence electrons, including ejection of the electrons (photoelectric effect) X-rays Excitation and ejection of core atomic electrons, Compton scattering (for low atomic numbers) Gamma rays Energetic ejection of core electrons in heavy elements, Compton scattering (for all atomic numbers), excitation of atomic nuclei, including dissociation of nuclei High energy gamma rays Creation of particle-antiparticle pairs. At very high energies a single photon can create a shower of high energy particles and antiparticles upon interaction with matter. Electromagnetic radiation interacts with matter in different ways in different parts of the spectrum. The types of interaction can be so different that it seems to be justified to refer to different types of radiation. At the same time, there is a continuum containing all these "different kinds" of electromagnetic radiation. Thus we refer to a spectrum, but divide it up based on the different interactions with matter. Region of the spectrum Main interactions with matter Radio Collective oscillation of charge carriers in bulk material (plasma oscillation). An example would be the oscillation of the electrons in an antenna. Microwave through far infrared Plasma oscillation, molecular rotation Near infrared Molecular vibration, plasma oscillation (in metals only) Visible Molecular electron excitation (including pigment molecules found in the human retina), plasma oscillations (in metals only) Ultraviolet Excitation of molecular and atomic valence electrons, including ejection of the electrons (photoelectric effect) X-rays Excitation and ejection of core atomic electrons, Compton scattering (for low atomic numbers) Gamma rays Energetic ejection of core electrons in heavy elements, Compton scattering (for all atomic numbers), excitation of atomic nuclei, including dissociation of nuclei High energy gamma rays Creation of particle-antiparticle pairs. At very high energies a single photon can create a shower of high energy particles and antiparticles upon interaction with matter. XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX == Radio Frequency Spectrum == Everything on the electromagnetic spectrum has a frequency, wavelength and power. Radio, especially, is very commonly discussed in these terms. Radio all operates between X and X |
Radio is generally considered to be the frequencies between 3 kHz to 300 GHz. |
Although almost none of you will be able to influence the design of radio systems, understanding the underpinnings of mobile communications can be crucial to assuring your particular application, site or service works correctly.
*** I've gone out of my way to take RF engineering classes. And it's pretty arduous. Transcoding Walsh codes by pencil, and so on. So I boiled down a couple thousand pages of documents gathered over time into an about 20 page slideshow for internal use. It has no explanations, has bad branding, and half of the images are snagged off the internet. Instead of posting that, I intend to repurpose all the content into a cohesive story and put it all up here as an article, so you can just refer to it when you need to. ***
The Electromagnetic Spectrum
Everything from light to radio to x-rays (and much more) are all a part of the electromagnetic spectrum. These various sections are named, and discussed as separate elements based on the way the radiation interacts with physical matter. Visible light excites electrons at a frequency convenient to biochemical processes, so there are rods and cones in our eyes which detect it. Radio collectively oscillates materials, like all the electrons in an antenna.
Think of the entire electromagnetic spectrum in the same way as the spectrum of visible light; there is a clear area which is "red" and a clear area which is "orange" but also a space in between, parts of which could be considered "red-orange" or red, or orange. Though the individual components are discussed as though they are separate components, they are also part of a continuum and certain interactions overlap quite strongly.
Everything on the electromagnetic spectrum has a frequency, wavelength and power. Radio, especially, is very commonly discussed in these terms as they influence range and the speed and capacity of the information carried.
Radio is generally considered to be the frequencies between 3 kHz to 300 GHz.
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX General physics of radio signals
RF communication works by creating electromagnetic waves at a source and being able to pick up those electromagnetic waves at a particular destination. These electromagnetic waves travel through the air at near the speed of light. The wavelength of an electromagnetic signal is inversely proportional to the frequency; the higher the frequency, the shorter the wavelength.
Frequency is measured in Hertz (cycles per second) and radio frequencies are measured in kilohertz (KHz or thousands of cycles per second), megahertz (MHz or millions of cycles per second) and gigahertz (GHz or billions of cycles per second). Higher frequencies result in shorter wavelengths. The wavelength for a 900 MHz device is longer than that of a 2.4 GHz device.
In general, signals with longer wavelengths travel a greater distance and penetrate through, and around objects better than signals with shorter wavelengths.
How does an RF communication system work?
Imagine an RF transmitter wiggling an electron in one location. This wiggling electron causes a ripple effect, somewhat akin to dropping a pebble in a pond. The effect is an electromagnetic (EM) wave that travels out from the initial location resulting in electrons wiggling in remote locations. An RF receiver can detect this remote electron wiggling.
The RF communication system then utilizes this phenomenon by wiggling electrons in a specific pattern to represent information. The receiver can make this same information available at a remote location; communicating with no wires.
In most wireless systems, a designer has two overriding constraints: it must operate over a certain distance (range) and transfer a certain amount of information within a time frame (data rate). Then the economics of the system must work out (price) along with acquiring government agency approvals (regulations and licensing).
How is range determined?
In order to accurately compute range – it is essential to understand a few terms:
dB - Decibels
Decibels are logarithmic units that are often used to represent RF power. To convert from watts to dB: Power in dB = 10* (log x) where x is the power in watts.
Another unit of measure that is encountered often is dBm (dB milliwatts). The conversion formula for it is Power in dBm = 10* (log x) where x is the power in milliwatts.
Line-of-site (LOS)
Line-of-site when speaking of RF means more than just being able to see the receiving antenna from the transmitting antenna. In, order to have true line-of-site no objects (including trees, houses or the ground) can be in the Fresnel zone. The Fresnel zone is the area around the visual line-of-sight that radio waves spread out into after they leave the antenna. This area must be clear or else signal strength will weaken.
There are essentially two parameters to look at when trying to determine range.
Transmit Power
Transmit power refers to the amount of RF power that comes out of the antenna port of the radio. Transmit power is usually measured in Watts, milliwatts or dBm. (For conversion between watts and dB see below.)
Receiver sensitivity
Receiver sensitivity refers to the minimum level signal the radio can demodulate. It is convenient to use an example with sound waves; Transmit power is how loud someone is yelling and receive sensitivity would be how soft a voice someone can hear. Transmit power and receive sensitivity together constitute what is know as “link budget”. The link budget is the total amount of signal attenuation you can have between the transmitter and receiver and still have communication occur.
Example: Maxstream 9XStream TX Power: 20dBm Maxstream 9XStream RX Sensitivity: -110dBm Total Link budget: 130dBm.
For line-of-site situations, a mathematical formula can be used to figure out the approximate range for a given link budget. For non line-of-site applications range calculations are more complex because of the various ways the signal can be attenuated.
RF communications and data rate
Data rates are usually dictated by the system - how much data must be transferred and how often does the transfer need to take place. Lower data rates, allow the radio module to have better receive sensitivity and thus more range. In the XStream modules the 9600 baud module has 3dB more sensitivity than the 19200 baud module. This means about 30% more distance in line-of-sight conditions. Higher data rates allow the communication to take place in less time, potentially using less power to transmit.
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MTS (1946) & IMTS (1963)
When I ask XXX japan, finland, maybe the early 80s. In fact...
in-service 1946, all dates here are the first serious date in service, not generally counting trials, or lab tests
Automatic Handoff, Metroliner Experiments (1969)
overlaps
cells and sectors diagram
AMPS, TACS, NMT, Netz, et. al. (1983)
D-AMPS (1990s)
GSM & GPRS (1991)
IS-95 CDMA (1995)
Tacking on Data, 2.5G (2001)
3G (2001)
WiMax & LTE (2009)
...
LTE is becoming the de-facto world standard, and almost every major carrier is signing on. This will perhaps mean another world network (as promised by GSM), and easy roaming in most countries.
Practically, there may still be fragmentation, and multiple subsets of LTE, causing issues with travel.
The ubiquity of data does not mean that all service will be reliable, or that data roaming costs are likely to disappear or become low enough customers will not care. Continue building services to use data efficiently, and offer functions to warn users on ad hoc and prepaid plans about network usage.
REFERENCES:
http://www.howcdmaworks.com/ - Lots of stuff made by Scott Baxter & Associates, but not published (you have to take the training) so how to refer to it.
- article in Smithsonian or somewhere on the development, especially of Metroliner experiments, etc.