My experience is that both of you are right: It is true that there are not millions of unawarded scholarship dollars annually. They're awarded, all right--usually to the first warm body that shows up at the last minute, by an awarding body/committee that would otherwise be embarassed that they couldn't give their money away. This is because most scholarship programs are a just a sideline of the sponsoring organization, and often don't get the attention and publicity they need. As has already been noted, the golden area to mine for scholarships is the local area: Check the employers, unions, church groups, social organizations, technical groups/clubs, etc. of all family members for scholarship plans; many of them are limited to relatives of their members--which keeps the applicant pool down.
I went to school in the pre-web days, and supported myself via scholarships. I found most of my scholarships by avid bulletin-board surfing: For example, I got a two-year, $5000/yr. scholarship (in 1977 dollars) by replying to a 3 x 5 card tacked on a bulletin board outside the department office. It was supported by the foundation of a guy who started the Florida frozen orange juice industry (go figure); they had three scholarships to give away, and had four applicants in total--the 3 x 5 card being the limit of the scholarship publicity. I had several similar examples.
Speaking now to the original poster, and related to the above, exert your geek-inhibited personal relations skills to the utmost, and get on good terms with the school staff. Show your face regularly around the department and financial aid offices, say hello to the secretaries and, when both you and they can spare the time, engage in (dare I say it) small talk. Let the word out that you'd be interested in any scholarships or fellowships that happen to come down the pike. A good relationship with the university staff can give you insight into applicant selection procedures, early awareness of future opportunities, and the ability to avoid bureaucratic pitfalls. Schools often receive notice of obscure scholarships; the staff is often under no particular motivation to publicize them (ergo the 3 x 5 card above).
Another factor to keep in mind with scholarships is that it pays to keep your grades and test scores up. Not only does this improve your scholarship application itself, but it earns you friends among the University faculty. Once you've started at school, and do well (even a semester or two), you're in a position to put the word out to a professor or two that their prized student may have to drop out if the financial situation doesn't improve. While you have less leverage as an undergraduate than you would as a graduate student, you still have some; most instructors would at least make inquiries for a student showing an effort and doing well. Note that the professor could offer you help in the form of work in his lab; this is can be characterized anywhere in the range from "all that's missing is the salt mine," to "preferable to handing out french fries," to "fascinating--so that's where this technology is going." YMMV.
A final question I have is about your comment that the school is "still getting itself off the ground." What is the school's accreditation status? If you're looking to attend a four-year institution, be sure that the school is accredited in your field. Nothing's worse than doing all that work and ending up with a diploma no one accepts.
As the article says, the treebot is part of a "Networked Infomechanical System", a type of wireless sensor network, developed by the UCLA Center for Embedded Networked Sensing. The forest network is used to develop practical wireless sensing technology while simultaneously providing an example of its utility. The use of a mobile network node in a wireless sensor network requires some engineering of the multihop message routing protocol, since such networks are usually assumed to have stationary nodes. I don't know what they've done to address this; it could be anything from MANET-style routing (e.g., AODV, in which they accept the resulting increase in route establishment overhead), to a quasi-static approach in which the treebot reassociates to the network every time it stops.
I can't speak to what Delphi is doing, but the product design and engineering of XM radio is done in beautiful Boca Raton, Florida, US of A, in a building on Glades Road just off the Florida Turnpike, and they aren't going anywhere. Most of the major movers and shakers in the outfit (both engineering and management) are refugees from Motorola's defunct Paging Products Group, in nearby Boynton Beach, Florida, and have long ties to the area.
My understanding at this point is digital phones are easier to track because they're always in communication with the towers, but older analog-only phones are only trackable when they're being used, because they can go passive. I may be mistaken on that.
Yes, you are mistaken. Both types communicate regularly (every few seconds) with the cell infrastructure whenever they are on.
While you're working on your wife's site, you might want to remove the unneeded apostrophe in the boilerplate: "Sam McGees specializes in premium quality hot sauces, hot salsa's . ..".
A more practical alternative is energy scavenging--the use of alternative energy sources available in the node's environment.
One example is the use of piezoelectric techniques to recover energy from vibration (the famous shoe generator). (Electromechanical and magnetomechanical conversion means may also be used.) Others have already suggested photoelectrics. Other possibilities include changes in air temperature and pressure (which powers the Atmos clock) and even consumption of sugar.
A book on energy scavenging, authored by three Berkeley wireless sensor network researchers, will soon be published.
Exactly right. Security, in wireless sensor networks, means more than just encryption (for privacy), however. In many applications it's more important to have message integrity and sender authentication, meaning that the recipient is guaranteed that the message hasn't been altered, and that it was from who it says it was from. For example, having an encrypted message from a short-range wireless light switch is often of little utility; people around can see the light come on (perhaps through a window), so you're not really protecting anything. However, as the parent poster says, you really don't want some car of script kiddies driving through your neighborhood randomly turning lights on and off at 2 AM. The wireless lights need to know that the messages they receive are from their associated switches, not from some 3l33t d00dz; that's the function of message integrity and source authentication checking.
Recognizing the importance of these types of security, the IEEE 802.15.4 standard, available here, employs the Advanced Encryption Standard for encryption, message integrity, and sender authentication. The ZigBee Alliance specifies key transport protocols, key management, and other higher layer security functions.
There are many potential applications for wireless sensor networks. A major one is industrial monitoring and control. The cost of monitoring and controling many industrial processes is not determined by the cost of either the sensor or the readout device, but by the cost of the armored cable needed to send the signal from the process to the control point. In certain industries, like the automotive industry, these cables must be regularly torn out as the factory re-tools for the next new model. Wireless sensors, with their inherent low cost, low power, multihop routing capability, can greatly reduce factory capital expense in such cases.
Around the home, there are many places where one wants low data rate communication. Wireless light switches are one example; they can be placed where the user wants them, rather than the home builder, or even just carried around. Wireless thermostats can give the HVAC system a much better idea of which rooms are hot and which are cold; there can be more of them than the wired version since there are no wiring costs. One can imagine a wireless key fob, like the Remote Keyless Entry (RKE) device in cars, that the homeowner could use to lock the house at night before retiring; the single button press could lock the doors and windows, lower the heat to the "sleeping" temperature, etc., and give the user feedback that all is well.
There are additional applications in the intelligent agriculture, automotive, health care, and military markets, plus many others. The list is endless and, like discussing PCs in 1980, I probably haven't hit the killer ap, because someone in his garage hasn't invented it yet.
The IEEE 802.15.4 standard, available here, was designed to support such networks. The ZigBee Alliance, an industrial consortium of over 60 companies, is the marketing and compliance arm of the 802.15.4 standard, as the Wi-Fi Alliance is to 802.11. The vitality of the ZigBee Alliance, which had over 350 attendees at its recent open house in Silicon Valley, is an indication that this technology is moving from research into commercialization; the commercialization of wireless sensor networks is the real significance of the Wired article.
The heat you feel in a cell phone after talking on it for a time likely is due to the heating of the radio frequency (RF) power amplifier (PA) in the phone's transmitter, not the battery.
The PA must generate (depending on the type of phone you have--GSM, CDMA, etc.--the range to the cell tower, and other factors) somewhere between 0.2 and 1.0 Watts of RF power output. For lots of good reasons, and despite the best efforts of lots of engineers at lots of places, the conversion efficiency of battery power to RF power of cell phone PAs is around 35%--meaning that approximately two-thirds of the battery power consumed by the PA is converted to heat, instead of RF power, as you talk. Since everyone likes a small, light-weight cell phone, there is no dedicated heat sink (or external fan!) for the phone's PA; instead, most designs usually use the cell phone's frame to conduct the waste heat away from the PA. The frame, of course, conducts the heat to the outside world, which in this case includes your ear.
In many cases, to avoid the loss of an RF transmission line from the bottom to the top of the phone (which would result in even more inefficiency) the PA is placed next to the antenna, near the top of the phone--thus exacerbating the ear-heating effect. Since the heat generated by the PA has remained more-or-less constant over the years but the mass of the phone has decreased, the temperature the phone reaches in this situation has increased, making it more noticable. Handling this temperature rise is part of cell phone design, and one of the many tradeoffs that occur in them. Keep in mind that, since it is produced by energy stored in the battery that could otherwise be used to extend talk or standby time--two selling factors near and dear to the hearts of cell phone manufacturers--designers would eagerly reduce generated heat if they could do so without violating other design parameters, like product cost.
The type of heating you're experiencing sounds completely normal and safe to me. I would expect that heating of the battery itself would be unrelated to whether you talked on the phone or not. Rather, it would occur either (a) during charging with a defective or improperly designed charger, or (b) randomly, as a cell shorts out and its stored energy heats itself (and its neighbors) up, and the built-in protection circuitry either fails or (in off-brand batteries) is nonexistent. You can protect yourself against both of these possibilities (to below the lightning-strike and meteorite-collision probability levels) by simply buying and using name-brand batteries and chargers.
I could throw a pile of math at you, but the basic idea is that an accellerating charge (i.e., a changing current, a.k.a. alternating current or a.c.) along a loop of wire produces:
-- magnetic fields in the radial direction that weaken as (1/r^2) and (1/r^3), where r is the distance from the source;
-- magnetic fields perpendicular to the radial direction that weaken as (1/r), (1/r^2) and (1/r^3), and
-- electric fields perpendicular to both of these that weaken as (1/r) and (1/r^2).
It turns out that the electric and magnetic (1/r) terms can form a propagating wave that moves radially away from the source. This is the "radiating" wave with which we're all familiar. The power in the wave is the product of the electric and magnetic field strength (the electromagnetic equivalent to the Power == Voltage * Current equation in circuit theory), so the power falls off as (1/r)*(1/r) = (1/r^2), the inverse-square law.
What you don't hear about often is what happens to those other terms--the (1/r^2) and (1/r^3) terms. They fade away quickly with distance, so once you're a wavelength away or so they're hard to detect. If you're close to the antenna (in terms of wavelengths), however, they can be very strong. Usually this is a problem, because lossy materials near an antenna can dissipate power in these modes that would otherwise radiate in the usually desired (1/r) mode (see [1] for a longer discussion). Aura, however, is using the (1/r^3) magnetic field mode, and turning the range liability into assets--increased privacy, and physically close reuse without interference. The main problem I expect they had to overcome was the difficulty in generating a strong enough field from an integrated product--the usual way requires a very large coil of wire.
________ [1] Edgar H. Callaway, Jr., Wireless Sensor Networks: Architectures and Protocols. Boca Raton, Florida: CRC Press. 2003. Chapter 8.
This goes to the heart of Moore's Law. Moore's Law isn't about transistor size per se. Rather, it's about the number of components that can be built on an integrated circuit at minimum cost.
In his original paper, Moore examines the effects the defect density (the number of defects in the silicon per unit area) and the size of the chip have on the economics of chip production. As you make larger and larger chips, you can put more and more transistors on them. However, the wafers have unavoidable defects in them; a physically larger chip is therefore more likely to contain one or more of the fatal defects, and be worthless.
Moore's key insight (and one that is usually overlooked) was that at any given level of technology (i.e., lithography or transistor size) there is an economically optimum number of components (almost exclusively transistors, today) per chip--that is, a number of components that minimizes the manufacturing cost per component (see the first figure of his paper). If the chip is too small, you spend too much time handling and packaging too many chips, driving up costs; if the chip is too big, the yield is low due to the wafer defects, and costs are driven up again. Crucially, Moore noted that this economically optimum number of transistors increases markedly over time, as integration technology improves; this led to his more famous second figure, showing the base 2 log of the number of components per integrated function growing without bound over time (and doubling every year, a slope that has since been reduced to doubling every 18-24 months). What is unstated in the figure itself is that this represents the economically optimum number of components per integrated fuction.
So the short answer to your question is that a chip 3 inches on a side could be made, but the yield would be so low, due to the unavoidable defects in the silicon wafer itself, that it would be fabulously expensive. It would be cheaper to make several smaller chips perform the same function, which is what is done today, if you stop to think of how many different chips are in the average PC.
Moore's paper is a marvel of prognostication; he notes in it, among many other keen insights:
Clearly, we will be able to build such component-crammed equipment. Next, we ask under what circumstances we should do it. The total cost of making a particular system function must be minimized. To do so, we could amortize the engineering over several identical items, or evolve flexible techniques for the engineering of large functions so that no disproportionate expense need be borne by a particular array [i.e., chip design]. Perhaps newly devised design automation procedures
could translate from logic diagram to technological realization without any special engineering.
He soon got his "flexible techniques for the engineering of large functions" by the invention of the microprocessor; the use of automated design techniques for digital circuits is, of course, now commonplace.
ZigBee and the IEEE 802.15.4 Task Group are both well aware of security. No one wants to relive the WEP debacle in any 802 working group, and ZigBee has gone to the point of establishing a Security Working Group, to make sure things are done correctly in the upper layers.
15.4 specifies the well-known AES-128 algorithm for encryption, source authentication, and message integrity. ZigBee will also use AES-128 (enabling reuse of the hardware/software to minimize implementation cost), plus add a public-key algorithm and other techniques to control key distribution and other security policies a needed by specific applications.
IEEE 802.15.4 systems (which are direct sequence spread spectrum) perform a channel scan prior to network establishment, to identify unused spectrum space and avoid interference with existing services. Further, they perform a carrier sense multiple access with collision avoidance (CSMA-CA) routine prior to the transmission of data packets, so they avoid transmitting on a busy channel. Finally, the 15.4 physical layer generates a link quality indication (LQI) value for each received packet. The LQI is sent with the packet to the upper layers of the stack, and can be used to identify impaired channels.
Keep in mind that 15.4 by design supports very low duty cycle operation--that's one way it gets its low average power consumption (by being asleep a lot). For this reason it will produce very little interference in most 2.4 GHz applications. In addition, 15.4 has a second physical layer, covering the European 868.0-868.6 MHz and the North/South American/Australian/etc. 902-928 MHz bands, so if 2.4 GHz interference troubles you, you can always move to the other bands.
Yes. ZigBee is based on IEEE 802.15.4, which supports multi-hop networks with an arbitrary number of hops. 15.4 has a 16-bit logical address field, so network order is limited in practice by the application's tolerance for multi-hop message latency--which, in most of the applications for which it is designed, is relatively high.
It's a myth that the free space path loss increases with frequency. The free space path loss is independent of frequency. Think about it: If the path loss of electromagnetic radiation increased with frequency, we'd never see any light from the sun--at 500,000,000 MHz, it'd be severely attenuated!
The effect often seen is due to the antennas used, not the frequency of operation. WLANs often use resonant dipole antennas. Such antennas have constant gain with frequency; a 900 MHz resonant dipole has the same gain as a 2.4 GHz resonant dipole. However, the 900 MHz resonant dipole is physically larger than the 2.4 GHz resonant dipole. The 900 MHz resonant dipole can therefore collect more of the incident electromagnetic energy than the 2.4 GHz resonant dipole. Said a different way, the effective area of the 900 MHz resonant dipole is greater than the 2.4 GHz resonant dipole. The sunlight thought experiment works here, too: A larger solar cell collects more of the incident electromagnetic energy (sunlight) than does a smaller cell. In fact, the effective area of dipole falls inversely with the square of the frequency of operation.
There are antennas that have a constant aperture with frequency. The parabolic dish is one example. Its effective aperture remains constant (a function of the physical size of the dish), but its gain increases with the square of the operating frequency. Two radios using parabolic dishes would find that the apparent "path loss" actually decreased with increasing frequency. If they then switched to resonant dipole antennas, they would find the apparent "path loss" increased with increasing frequency. If one used a dipole and the other used a parabolic dish, they would find the apparent "path loss" independent of frequency.
At the high school physics level (i.e., no calculus), the first thing that comes to mind is the ARRL antenna book. It has a good chapter on theory, and another one on measurement techniques. A book more narrowly focussed on HF antennas is Carr's Practical Antenna Handbook, but it lacks the breadth of the ARRL book. A book devoted to the antennas and propagation common to handheld, portable products (including indoor propagation and measurement of the effects of the human body on radiation patterns) is Radiowave Propagation and Antennas for Personal Communications by Siwiak. I've used it for years; it's an excellent reference. If you'd like to "learn from the simulator," Makarov's book seems like a good introduction to antenna analysis with Matlab, but I've not used it. But really, the calculus you must have to get a mechanical engineering degree is sufficient for the general theory sections of most antenna texts, such as Bolanis, Kraus, or Stutzman and Thiele.
The general rule, of course, is that in free space the radiation intensity goes down with the square of the distance, while in indoor environments the "path loss exponent" increases to something between two and and four.
The open spectrum concept raises its ugly head again. I suppose I shouldn't be surprised; it combines the sexiest of terms (Moore's Law! Metcalfe's Law! SDR! UWB! Spread Spectrum! Mesh Networks! Open Source!) in one neat package, tied with a bow. If only they could work in the magnetic bracelet that cures arthritis, it would be a marketer's dream.
There are other reasons for spectrum allocation besides the "technology limitations" cited in the ACM article. Two of the most significant are:
1. The spectrum is used for many different services, with differing Quality of Service (QoS) requirements. Some of these, like the Instrument Landing Systems at airports, emergency services, GPS, etc. I'd like to have dedicated spectrum available solely to them 24x7; the idea that a trapped fireman's call on his handheld 2-way radio is not heard because of interference from a nearby mesh network providing video packets of a football game (or, if you like, the trapped fireman's call on his limited-range Open Spectrum radio is not heard because the burning building's network is already down) is not very appealing.
Other services, like industrial heating (and even microwave ovens) do not even use the RF spectrum for communication at all; if not limited in spectrum these large transmitted power services can render people incommunicado over large physical areas. Open Spectrum advocates will claim that this last problem will be overcome by the processing gain of the Open Spectrum radio itself; I merely note that increasing processing gain is increasingly expensive, and getting 60 dB of processing gain is a severe pain at wideband bit rates, while it is a trivial exercise for a tuned circuit if the spectrum is allocated properly.
2. The spectrum has different physical properties that make certain frequencies (and frequency bands) more suitable for certain services. Services that require ionospheric refraction need to operate below 30 MHz; systems using satellite-earth links must operate above 30 MHz. Systems requiring a lot of antenna gain, such as space probes and terrestrial point-to-point links, need to be a high frequency (multiple GHz), where high gain can be achieved in a small physical size by the use of parabolic antennas. Systems requiring worldwide underwater coverage must be below 100 Hz. There are atmospheric attenuation peaks at 24 and 60 GHz (and others higher) caused by oxygen absorption that make these frequencies useless for any trans-atmospheric links, but ideal for short-range unlicensed systems (that's why there are ISM unlicensed bands there). Rain (a.k.a. hydrometeors) becomes a significant attenuator above 5-20 GHz, depending on the rate at which it falls; this affects systems in tropical regions more than those in more temperate areas (see a graph of atmospheric attenuation). The hydrogen line (1420.40575 MHz), used by astronomers, is a fixed frequency. Etc.--this is just a partial list. All frequencies are not created equal.
However, if you'd like to stick to technical problems, consider the multiple access problem for these systems.
The success of 802.11b is often cited as an example for the Open Spectrum initiative--an unlicensed band being used productively. However, 11b has now become the 800-lb. gorilla in the 2.4 GHz ISM band; other services attempting to use that band must coexist with it, but it doesn't have to coexist with them. Any interference it causes to these new services must be borne by them; as a result, we have created a de facto allocated band.
Yeah, you get a chemical engineer who's never done anything out of the defense sector (i.e., never had to meet the needs of the commercial market).
For me to take the open spectrum concept seriously I'd have to hear the people that have designed communication products and networks (and therefore have demonstrated that they understand the problems with existing systems) espouse it. Having non-specialists declare that the status quo is all wrong, and that they have a much better way, is one of the hallmarks of pseudoscience.
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My experience is that both of you are right: It is true that there are not millions of unawarded scholarship dollars annually. They're awarded, all right--usually to the first warm body that shows up at the last minute, by an awarding body/committee that would otherwise be embarassed that they couldn't give their money away. This is because most scholarship programs are a just a sideline of the sponsoring organization, and often don't get the attention and publicity they need. As has already been noted, the golden area to mine for scholarships is the local area: Check the employers, unions, church groups, social organizations, technical groups/clubs, etc. of all family members for scholarship plans; many of them are limited to relatives of their members--which keeps the applicant pool down.
I went to school in the pre-web days, and supported myself via scholarships. I found most of my scholarships by avid bulletin-board surfing: For example, I got a two-year, $5000/yr. scholarship (in 1977 dollars) by replying to a 3 x 5 card tacked on a bulletin board outside the department office. It was supported by the foundation of a guy who started the Florida frozen orange juice industry (go figure); they had three scholarships to give away, and had four applicants in total--the 3 x 5 card being the limit of the scholarship publicity. I had several similar examples.
Speaking now to the original poster, and related to the above, exert your geek-inhibited personal relations skills to the utmost, and get on good terms with the school staff. Show your face regularly around the department and financial aid offices, say hello to the secretaries and, when both you and they can spare the time, engage in (dare I say it) small talk. Let the word out that you'd be interested in any scholarships or fellowships that happen to come down the pike. A good relationship with the university staff can give you insight into applicant selection procedures, early awareness of future opportunities, and the ability to avoid bureaucratic pitfalls. Schools often receive notice of obscure scholarships; the staff is often under no particular motivation to publicize them (ergo the 3 x 5 card above).
Another factor to keep in mind with scholarships is that it pays to keep your grades and test scores up. Not only does this improve your scholarship application itself, but it earns you friends among the University faculty. Once you've started at school, and do well (even a semester or two), you're in a position to put the word out to a professor or two that their prized student may have to drop out if the financial situation doesn't improve. While you have less leverage as an undergraduate than you would as a graduate student, you still have some; most instructors would at least make inquiries for a student showing an effort and doing well. Note that the professor could offer you help in the form of work in his lab; this is can be characterized anywhere in the range from "all that's missing is the salt mine," to "preferable to handing out french fries," to "fascinating--so that's where this technology is going." YMMV.
A final question I have is about your comment that the school is "still getting itself off the ground." What is the school's accreditation status? If you're looking to attend a four-year institution, be sure that the school is accredited in your field. Nothing's worse than doing all that work and ending up with a diploma no one accepts.
Oh, and I forgot to mention the NIMS website, which has a lot more pretty pictures.
As the article says, the treebot is part of a "Networked Infomechanical System", a type of wireless sensor network, developed by the UCLA Center for Embedded Networked Sensing. The forest network is used to develop practical wireless sensing technology while simultaneously providing an example of its utility. The use of a mobile network node in a wireless sensor network requires some engineering of the multihop message routing protocol, since such networks are usually assumed to have stationary nodes. I don't know what they've done to address this; it could be anything from MANET-style routing (e.g., AODV, in which they accept the resulting increase in route establishment overhead), to a quasi-static approach in which the treebot reassociates to the network every time it stops.
I can't speak to what Delphi is doing, but the product design and engineering of XM radio is done in beautiful Boca Raton, Florida, US of A, in a building on Glades Road just off the Florida Turnpike, and they aren't going anywhere. Most of the major movers and shakers in the outfit (both engineering and management) are refugees from Motorola's defunct Paging Products Group, in nearby Boynton Beach, Florida, and have long ties to the area.
Yes, you are mistaken. Both types communicate regularly (every few seconds) with the cell infrastructure whenever they are on.
He's talking about fixed mirrors at the intersection, on the side of the road, so that drivers can see around blind corners.
While you're working on your wife's site, you might want to remove the unneeded apostrophe in the boilerplate: "Sam McGees specializes in premium quality hot sauces, hot salsa's . . .".
Phuket, a delightful resort in Thailand.
A more practical alternative is energy scavenging--the use of alternative energy sources available in the node's environment.
One example is the use of piezoelectric techniques to recover energy from vibration (the famous shoe generator). (Electromechanical and magnetomechanical conversion means may also be used.) Others have already suggested photoelectrics. Other possibilities include changes in air temperature and pressure (which powers the Atmos clock) and even consumption of sugar.
A book on energy scavenging, authored by three Berkeley wireless sensor network researchers, will soon be published.
Exactly right. Security, in wireless sensor networks, means more than just encryption (for privacy), however. In many applications it's more important to have message integrity and sender authentication, meaning that the recipient is guaranteed that the message hasn't been altered, and that it was from who it says it was from. For example, having an encrypted message from a short-range wireless light switch is often of little utility; people around can see the light come on (perhaps through a window), so you're not really protecting anything. However, as the parent poster says, you really don't want some car of script kiddies driving through your neighborhood randomly turning lights on and off at 2 AM. The wireless lights need to know that the messages they receive are from their associated switches, not from some 3l33t d00dz; that's the function of message integrity and source authentication checking.
Recognizing the importance of these types of security, the IEEE 802.15.4 standard, available here, employs the Advanced Encryption Standard for encryption, message integrity, and sender authentication. The ZigBee Alliance specifies key transport protocols, key management, and other higher layer security functions.
There are many potential applications for wireless sensor networks. A major one is industrial monitoring and control. The cost of monitoring and controling many industrial processes is not determined by the cost of either the sensor or the readout device, but by the cost of the armored cable needed to send the signal from the process to the control point. In certain industries, like the automotive industry, these cables must be regularly torn out as the factory re-tools for the next new model. Wireless sensors, with their inherent low cost, low power, multihop routing capability, can greatly reduce factory capital expense in such cases.
Around the home, there are many places where one wants low data rate communication. Wireless light switches are one example; they can be placed where the user wants them, rather than the home builder, or even just carried around. Wireless thermostats can give the HVAC system a much better idea of which rooms are hot and which are cold; there can be more of them than the wired version since there are no wiring costs. One can imagine a wireless key fob, like the Remote Keyless Entry (RKE) device in cars, that the homeowner could use to lock the house at night before retiring; the single button press could lock the doors and windows, lower the heat to the "sleeping" temperature, etc., and give the user feedback that all is well.
There are additional applications in the intelligent agriculture, automotive, health care, and military markets, plus many others. The list is endless and, like discussing PCs in 1980, I probably haven't hit the killer ap, because someone in his garage hasn't invented it yet.
Wireless sensor networks are not new; there is even a textbook published recently on them (Wireless Sensor Networks: Architectures and Protocols). Many corporations have active WSN programs, including:
Motorola
Ember and
Figure 8 Wireless.
University research programs, in addition to Berkeley, include:
UCLA WINS
MIT uAMPS
plus those sposored by DARPA.
The IEEE 802.15.4 standard, available here, was designed to support such networks. The ZigBee Alliance, an industrial consortium of over 60 companies, is the marketing and compliance arm of the 802.15.4 standard, as the Wi-Fi Alliance is to 802.11. The vitality of the ZigBee Alliance, which had over 350 attendees at its recent open house in Silicon Valley, is an indication that this technology is moving from research into commercialization; the commercialization of wireless sensor networks is the real significance of the Wired article.
The heat you feel in a cell phone after talking on it for a time likely is due to the heating of the radio frequency (RF) power amplifier (PA) in the phone's transmitter, not the battery.
The PA must generate (depending on the type of phone you have--GSM, CDMA, etc.--the range to the cell tower, and other factors) somewhere between 0.2 and 1.0 Watts of RF power output. For lots of good reasons, and despite the best efforts of lots of engineers at lots of places, the conversion efficiency of battery power to RF power of cell phone PAs is around 35%--meaning that approximately two-thirds of the battery power consumed by the PA is converted to heat, instead of RF power, as you talk. Since everyone likes a small, light-weight cell phone, there is no dedicated heat sink (or external fan!) for the phone's PA; instead, most designs usually use the cell phone's frame to conduct the waste heat away from the PA. The frame, of course, conducts the heat to the outside world, which in this case includes your ear.
In many cases, to avoid the loss of an RF transmission line from the bottom to the top of the phone (which would result in even more inefficiency) the PA is placed next to the antenna, near the top of the phone--thus exacerbating the ear-heating effect. Since the heat generated by the PA has remained more-or-less constant over the years but the mass of the phone has decreased, the temperature the phone reaches in this situation has increased, making it more noticable. Handling this temperature rise is part of cell phone design, and one of the many tradeoffs that occur in them. Keep in mind that, since it is produced by energy stored in the battery that could otherwise be used to extend talk or standby time--two selling factors near and dear to the hearts of cell phone manufacturers--designers would eagerly reduce generated heat if they could do so without violating other design parameters, like product cost.
The type of heating you're experiencing sounds completely normal and safe to me. I would expect that heating of the battery itself would be unrelated to whether you talked on the phone or not. Rather, it would occur either (a) during charging with a defective or improperly designed charger, or (b) randomly, as a cell shorts out and its stored energy heats itself (and its neighbors) up, and the built-in protection circuitry either fails or (in off-brand batteries) is nonexistent. You can protect yourself against both of these possibilities (to below the lightning-strike and meteorite-collision probability levels) by simply buying and using name-brand batteries and chargers.
I could throw a pile of math at you, but the basic idea is that an accellerating charge (i.e., a changing current, a.k.a. alternating current or a.c.) along a loop of wire produces:
-- magnetic fields in the radial direction that weaken as (1/r^2) and (1/r^3), where r is the distance from the source;
-- magnetic fields perpendicular to the radial direction that weaken as (1/r), (1/r^2) and (1/r^3), and
-- electric fields perpendicular to both of these that weaken as (1/r) and (1/r^2).
It turns out that the electric and magnetic (1/r) terms can form a propagating wave that moves radially away from the source. This is the "radiating" wave with which we're all familiar. The power in the wave is the product of the electric and magnetic field strength (the electromagnetic equivalent to the Power == Voltage * Current equation in circuit theory), so the power falls off as (1/r)*(1/r) = (1/r^2), the inverse-square law.
What you don't hear about often is what happens to those other terms--the (1/r^2) and (1/r^3) terms. They fade away quickly with distance, so once you're a wavelength away or so they're hard to detect. If you're close to the antenna (in terms of wavelengths), however, they can be very strong. Usually this is a problem, because lossy materials near an antenna can dissipate power in these modes that would otherwise radiate in the usually desired (1/r) mode (see [1] for a longer discussion). Aura, however, is using the (1/r^3) magnetic field mode, and turning the range liability into assets--increased privacy, and physically close reuse without interference. The main problem I expect they had to overcome was the difficulty in generating a strong enough field from an integrated product--the usual way requires a very large coil of wire.
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[1] Edgar H. Callaway, Jr., Wireless Sensor Networks: Architectures and Protocols. Boca Raton, Florida: CRC Press. 2003. Chapter 8.
This goes to the heart of Moore's Law. Moore's Law isn't about transistor size per se. Rather, it's about the number of components that can be built on an integrated circuit at minimum cost.
In his original paper, Moore examines the effects the defect density (the number of defects in the silicon per unit area) and the size of the chip have on the economics of chip production. As you make larger and larger chips, you can put more and more transistors on them. However, the wafers have unavoidable defects in them; a physically larger chip is therefore more likely to contain one or more of the fatal defects, and be worthless.
Moore's key insight (and one that is usually overlooked) was that at any given level of technology (i.e., lithography or transistor size) there is an economically optimum number of components (almost exclusively transistors, today) per chip--that is, a number of components that minimizes the manufacturing cost per component (see the first figure of his paper). If the chip is too small, you spend too much time handling and packaging too many chips, driving up costs; if the chip is too big, the yield is low due to the wafer defects, and costs are driven up again. Crucially, Moore noted that this economically optimum number of transistors increases markedly over time, as integration technology improves; this led to his more famous second figure, showing the base 2 log of the number of components per integrated function growing without bound over time (and doubling every year, a slope that has since been reduced to doubling every 18-24 months). What is unstated in the figure itself is that this represents the economically optimum number of components per integrated fuction.
So the short answer to your question is that a chip 3 inches on a side could be made, but the yield would be so low, due to the unavoidable defects in the silicon wafer itself, that it would be fabulously expensive. It would be cheaper to make several smaller chips perform the same function, which is what is done today, if you stop to think of how many different chips are in the average PC.
Moore's paper is a marvel of prognostication; he notes in it, among many other keen insights:
He soon got his "flexible techniques for the engineering of large functions" by the invention of the microprocessor; the use of automated design techniques for digital circuits is, of course, now commonplace.The relevant FAI is the Federation Aeronautique Internationale. The aeromodelling page is here; world records are available here.
ZigBee and the IEEE 802.15.4 Task Group are both well aware of security. No one wants to relive the WEP debacle in any 802 working group, and ZigBee has gone to the point of establishing a Security Working Group, to make sure things are done correctly in the upper layers.
15.4 specifies the well-known AES-128 algorithm for encryption, source authentication, and message integrity. ZigBee will also use AES-128 (enabling reuse of the hardware/software to minimize implementation cost), plus add a public-key algorithm and other techniques to control key distribution and other security policies a needed by specific applications.
IEEE 802.15.4 systems (which are direct sequence spread spectrum) perform a channel scan prior to network establishment, to identify unused spectrum space and avoid interference with existing services. Further, they perform a carrier sense multiple access with collision avoidance (CSMA-CA) routine prior to the transmission of data packets, so they avoid transmitting on a busy channel. Finally, the 15.4 physical layer generates a link quality indication (LQI) value for each received packet. The LQI is sent with the packet to the upper layers of the stack, and can be used to identify impaired channels.
Keep in mind that 15.4 by design supports very low duty cycle operation--that's one way it gets its low average power consumption (by being asleep a lot). For this reason it will produce very little interference in most 2.4 GHz applications. In addition, 15.4 has a second physical layer, covering the European 868.0-868.6 MHz and the North/South American/Australian/etc. 902-928 MHz bands, so if 2.4 GHz interference troubles you, you can always move to the other bands.
Yes. ZigBee is based on IEEE 802.15.4, which supports multi-hop networks with an arbitrary number of hops. 15.4 has a 16-bit logical address field, so network order is limited in practice by the application's tolerance for multi-hop message latency--which, in most of the applications for which it is designed, is relatively high.
It's a myth that the free space path loss increases with frequency. The free space path loss is independent of frequency. Think about it: If the path loss of electromagnetic radiation increased with frequency, we'd never see any light from the sun--at 500,000,000 MHz, it'd be severely attenuated!
The effect often seen is due to the antennas used, not the frequency of operation. WLANs often use resonant dipole antennas. Such antennas have constant gain with frequency; a 900 MHz resonant dipole has the same gain as a 2.4 GHz resonant dipole. However, the 900 MHz resonant dipole is physically larger than the 2.4 GHz resonant dipole. The 900 MHz resonant dipole can therefore collect more of the incident electromagnetic energy than the 2.4 GHz resonant dipole. Said a different way, the effective area of the 900 MHz resonant dipole is greater than the 2.4 GHz resonant dipole. The sunlight thought experiment works here, too: A larger solar cell collects more of the incident electromagnetic energy (sunlight) than does a smaller cell. In fact, the effective area of dipole falls inversely with the square of the frequency of operation.
There are antennas that have a constant aperture with frequency. The parabolic dish is one example. Its effective aperture remains constant (a function of the physical size of the dish), but its gain increases with the square of the operating frequency. Two radios using parabolic dishes would find that the apparent "path loss" actually decreased with increasing frequency. If they then switched to resonant dipole antennas, they would find the apparent "path loss" increased with increasing frequency. If one used a dipole and the other used a parabolic dish, they would find the apparent "path loss" independent of frequency.
At the high school physics level (i.e., no calculus), the first thing that comes to mind is the ARRL antenna book. It has a good chapter on theory, and another one on measurement techniques. A book more narrowly focussed on HF antennas is Carr's Practical Antenna Handbook, but it lacks the breadth of the ARRL book. A book devoted to the antennas and propagation common to handheld, portable products (including indoor propagation and measurement of the effects of the human body on radiation patterns) is Radiowave Propagation and Antennas for Personal Communications by Siwiak. I've used it for years; it's an excellent reference. If you'd like to "learn from the simulator," Makarov's book seems like a good introduction to antenna analysis with Matlab, but I've not used it. But really, the calculus you must have to get a mechanical engineering degree is sufficient for the general theory sections of most antenna texts, such as Bolanis, Kraus, or Stutzman and Thiele. The general rule, of course, is that in free space the radiation intensity goes down with the square of the distance, while in indoor environments the "path loss exponent" increases to something between two and and four.
I agree, and thank you for your support. My position is stated in this comment.
The open spectrum concept raises its ugly head again. I suppose I shouldn't be surprised; it combines the sexiest of terms (Moore's Law! Metcalfe's Law! SDR! UWB! Spread Spectrum! Mesh Networks! Open Source!) in one neat package, tied with a bow. If only they could work in the magnetic bracelet that cures arthritis, it would be a marketer's dream.
There are other reasons for spectrum allocation besides the "technology limitations" cited in the ACM article. Two of the most significant are:
1. The spectrum is used for many different services, with differing Quality of Service (QoS) requirements. Some of these, like the Instrument Landing Systems at airports, emergency services, GPS, etc. I'd like to have dedicated spectrum available solely to them 24x7; the idea that a trapped fireman's call on his handheld 2-way radio is not heard because of interference from a nearby mesh network providing video packets of a football game (or, if you like, the trapped fireman's call on his limited-range Open Spectrum radio is not heard because the burning building's network is already down) is not very appealing.
Other services, like industrial heating (and even microwave ovens) do not even use the RF spectrum for communication at all; if not limited in spectrum these large transmitted power services can render people incommunicado over large physical areas. Open Spectrum advocates will claim that this last problem will be overcome by the processing gain of the Open Spectrum radio itself; I merely note that increasing processing gain is increasingly expensive, and getting 60 dB of processing gain is a severe pain at wideband bit rates, while it is a trivial exercise for a tuned circuit if the spectrum is allocated properly.
2. The spectrum has different physical properties that make certain frequencies (and frequency bands) more suitable for certain services. Services that require ionospheric refraction need to operate below 30 MHz; systems using satellite-earth links must operate above 30 MHz. Systems requiring a lot of antenna gain, such as space probes and terrestrial point-to-point links, need to be a high frequency (multiple GHz), where high gain can be achieved in a small physical size by the use of parabolic antennas. Systems requiring worldwide underwater coverage must be below 100 Hz. There are atmospheric attenuation peaks at 24 and 60 GHz (and others higher) caused by oxygen absorption that make these frequencies useless for any trans-atmospheric links, but ideal for short-range unlicensed systems (that's why there are ISM unlicensed bands there). Rain (a.k.a. hydrometeors) becomes a significant attenuator above 5-20 GHz, depending on the rate at which it falls; this affects systems in tropical regions more than those in more temperate areas (see a graph of atmospheric attenuation). The hydrogen line (1420.40575 MHz), used by astronomers, is a fixed frequency. Etc.--this is just a partial list. All frequencies are not created equal.
However, if you'd like to stick to technical problems, consider the multiple access problem for these systems.
The success of 802.11b is often cited as an example for the Open Spectrum initiative--an unlicensed band being used productively. However, 11b has now become the 800-lb. gorilla in the 2.4 GHz ISM band; other services attempting to use that band must coexist with it, but it doesn't have to coexist with them. Any interference it causes to these new services must be borne by them; as a result, we have created a de facto allocated band.
Yeah, you get a chemical engineer who's never done anything out of the defense sector (i.e., never had to meet the needs of the commercial market).
For me to take the open spectrum concept seriously I'd have to hear the people that have designed communication products and networks (and therefore have demonstrated that they understand the problems with existing systems) espouse it. Having non-specialists declare that the status quo is all wrong, and that they have a much better way, is one of the hallmarks of pseudoscience.