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White Space Internet Device
Responsibilities:
Sean Iveson - Antenna systems on device. Research on wireless protocols.
Bill Sadler - Individual device components.
Introduction
Whitespace Radio is a critical topic right now in Internet access options. There is
currently a White Spaces Coalition for white space broadband Internet access with members
including Microsoft, Google, and Intel. Microsoft is undergoing research developing a similar
system to what we are providing. The technology is useful and versatile, though may show
limitations, including low (by today’s standards) data transfer rates.
Providing Internet over white space airways currently requires special permission from
the Federal Communications Commission (FCC). However, different organizations have
obtained permission to provide Internet access over the white space frequencies.
Current tests in providing Internet access over white space has been using IEEE standards
802.11 (Wireless Local Area Network or WLAN) or 802.22 (Wireless Regional Area Network
or WRAN) radio protocols. IEEE 802.11 WLAN provides higher speeds compared to IEEE
802.22 WRAN but a range similar to that of your ordinary router. 802.22 however provides
broadband speeds to an area of at least 20 kilometers, making this protocol ideal for use in rural
areas which otherwise would not have an affordable broadband Internet connection option.
A task-force to create an IEEE 802.11af standard designed for white space Internet access
has been created as of early 2010. Although IEEE 802.11af would not have as great a range as
IEEE 802.22, it still uses frequencies less than 1 GHz and would allow for increased range and
better travel through masonry and other obstacles compared to other wireless
protocols. 802.11af, like 802.22, utilizes cognitive radio technology and geographical sensing
(discussed further in Cognitive Radio section).
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The IEEE 802.22 Standard was specifically designed to provide broadband Internet
access to rural locations via whitespace radio frequencies 54 - 862 MHz on a non-interfering
basis with the primary users. It could also effectively be utilized to create a single large network
across some sort of campus. Because the signal is so low powered compared to other wireless
protocols (which often approx 3-5 GHz), the signal is able to travel further and through
obstructions such as buildings or forests (and as a result the signal has a cell radius of 10 - 20
miles. IEEE 802.22 WRAN uses approximately 282 MHz of bandwidth or 47 TV channels, and
is optimized for long distance travel and is designed to compensate for delays. IEEE 802.22
provides transfer speeds of approximately 1.5 Mbps Down, and 384 kbps up, which is slow by
today's broadband standards, but still faster than other internet solutions in some areas (dialup). There are 255 max users on a network, and multiple network can co-exist in the same area
on the same channel. (IEEE 802.22 Wireless Regional Area Networks).
The article Electromagnetic signal attenuation in construction materials outlines the
signal attenuation between high (1.5 GHz) and low (1 GHz) frequencies through common
construction materials. Most import to our cause, the study shows that lower power frequencies
travel pass best through objects.
Geographical sensing is one new technology being utilized in these protocols designed
for white space radio frequencies. The idea is the system has a geographical database and knows
what channels are available in that area so that the system can avoid used channels. Cognitive
Radio technologies can then allow the system to detect transmissions and move to alternate, open
channels.
Cognitive radio is a great technology to utilize because it streamlines and optimizes
the use of the system.
The nature of this technology itself raises concerns with marketability. The two best
environments in which white space Internet access would be best utilized would be a campus
situation, such as a corporate campus, school campus, or hospital, or a rural environment. Costs
for rural environments are a concern however because of the low population in those areas,
which is the reason other products haven’t been already implemented in those areas.
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Cognitive Radio
Recent FCC studies have shown great scarcity on licensed spectrum as a result of
traditional command-and-control spectrum regulation. Cognitive radio aims to solve this by
allowing networks to operate in areas where the spectrum normally reserved for licensed use
only for unlicensed use when under utilized.
IEEE 802.22 is the first cognitive radio, designed
to recognize other signals and operate on the same frequency without diminishing other signals,
which makes it ideal for our product. The sensing portion of the system can detect other uses of
the spectrum in that location and fairly prioritize and regulate use accordingly. Cognitive radio
works by using a seperate antenna to scan for and quickly detect other signals on the same
frequency. When a signal is recognized, it sends a message and determines the priority of the
signal, and shares or yields the spectrum in that area appropriately. Cognitive Radio allows for
fair and controlled use of otherwise unregulated radio frequencies.
Software-Defined Radio and Other Components
In order to use the white-space frequencies that are available in the public domain, some
sort of radio receiver will need to be built into this device. This receiver will consist of an
antenna, a tuner, and some sort of signal detector. The antenna will receive the signal that is
being broadcast over the white-space. The tuner will be used to set the frequency over which the
signal is being accepted. There is a strict spectrum of frequencies that are available for use by the
public. The detector will be built into the device to capture the proper data signal from the signal
being received, and to also help reduce the noise of the signal.
This sort of radio receiver is of similar construct to that of a television or audio radio. The
signal is received by the antenna, then the audio, visual, or which ever specified component of
the signal is desired, is filtered out from the signal and then that signal is usually amplified and
then output by the device. The particular radio receiver configuration that we would most likely
implement in our design is a “software-defined radio receiver”. In this circuit configuration, the
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antenna is connected to a radio frequency band-pass filter. This portion of the circuit filters out
all of the unwanted frequencies that are being transmitted across the spectrum. Connected to the
band-pass filter is a low-noise amplifier which amplifies the signal that is being received at the
specified frequencies. Following the low-noise amplifier is the analog-to-digital converter, which
converts the analog signal received by the antenna into a digital signal which can be processed.
This digital signal then passes through a digital signal processor, which will ultimately allow the
signal to be broadcast through some internet protocol. A micro-controller will be used to handle
the determination of the frequency that is desired by the user, and it was also handle the data
transfers that will be made across this connection. Once the signal has been captured, it will then
pass through a digital-analog converter, which will convert the desired digital signal back into an
analog signal which can then be transmitted (either through 802.11af or 802.22 protocol).
Reception Antenna
The device will require two antenna systems. The first stage is for receiving information
from the white space access point, and the second to transmit data from the device to any devices
requiring internet access. Modern small scale devices use a Multiple Input Multiple Output
(MIMO) system in order to establish a stronger and more reliable connection. However, having
multiple antennas located so close to each other creates a coupling effect, which dramatically
reduces the quality of the signal. For that reason, advanced techniques must be utilized in order
to isolate and decouple the signals.
802.22, a new IEEE standard being developed for white space internet access in rural
locations, calls for two separate antennas: a directional antenna for the link and an omnidirectional antenna for sensing. Since the whole idea behind white space is its operation on a
free frequency, steps must be utilized to distinguish different signals for one another, which is
why we need a second antenna for sensing. This issue has led to development of what is known
as cognitive radio. IEEE 802.22 WRAN standards specify the spectrum sensing period as 5 ms.
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There are multiple different techniques for decoupling two antennas in very close
proximity. In order for these to operate properly, an impedance matching circuit is necessary
between the antennas.
Variable Bandpass Filter
Innumerable amounts of frequencies can received by the antenna of the software-defined
radio. In order to receive only the frequencies that are desired by the user of this device, a
variable band-pass filter is implemented. The pass-band on this filter must be able to change as
per a user request, since many different frequencies could be broadcasting an internet signal.
These frequencies could change depending on location, internet service provider, and also based
upon the rules and regulations set in place by the FCC. This presents a problem, in that a single
band-pass filter does not have a variable pass-band, however, there is a fairly simple solution to
this issue.
A/D Converter
In this portion of the circuit for this device, an analog-to-digital converter is required. The
signal that is received by the antenna is an analog signal. This sort of signal can not be processed
by the digital signal processor, thus the signal must be converted before it can be analyzed and
manipulated as needed. In order for this converter to function properly in this device, the signal
needs to be sampled at a frequency equal to two times the frequency that is being received. From
this point, the signal is transferred to the digital signal processor.
Digital Signal Processor
The digital signal processor is the most important part of the device. This is where is
internet signal will be isolated from all of the other signals being transmitted over the set
frequency using a special fast spectrum sensing algorithm. This algorithm will also reduce the
amount of noise in the signal and theoretically eliminate any static being transmitted. The
processor will also play an important part in providing the user with data about their
connectivity, what frequencies are being being received and also power management (all in
conjunction with a microcontroller). This information will then be displayed by the digital
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readout that is attached onto the device. More information about the digital display will be
provided in later sections of this report.
Fast Spectrum Sensing Algorithm
The first section of this signal sifting algorithm is the “Discrete Wavelet Transform”
section. This part of the algorithm focuses on the decomposition of the received signal with
respect to approximate space, and detail space contained in the signal and its components.
Following this section is the “Discrete Wavelet Packet Transform”. This particular step in the
algorithm analyzes the approximate space and detail space that was isolated in the initial
decomposition transform, and further breaks the signal down and separates the frequency of
signal equally. Then the power of each individual sub-band is measured using scaling and
wavelet coefficients in analysis and computation of the power equation found in Appendix C.
Once the wavelet has been analyzed and its power computed, the energy of each sub-band can be
determined
This energy detection algorithm has a couple improvements over other energy detection
schemes. One improvement is that the algorithm can easily select unoccupied candidate channels
without confirming whether or not the channels are unused or not. Another improvement made
with in this algorithm is that complexity of the transform function.
Digital Display
The digital display on this device is an colorless LCD display. This display has no actual
affect on the signal itself, but it is be used to provide the user with plenty of useful information.
One important thing that will be displayed to the user is the frequency that the device is currently
set to receive. As this information is variable (changed by user as desired) it is important for the
user to see which frequency they are setting for the device to receive. Another piece of useful
information that will be shown on this display will be the connectivity status of the users (e.g.
how many users are currently connected to the device). The display will also show the user the
remaining amount of battery power left in the batteries powering the device (When the device is
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not plugged into the AC/DC power supply). Built into this digital display will be an optional
back-light feature which can be turned on and off using a button on the face of the device.
Design #1
D/A Converter
Once the internet signal has been isolated from the rest of the data being transmitted
across the white-space frequencies, the signal must be converted once again. The output signal of
the digital signal processor is fed into a digital-to-analog converter. This converts the signal from
the digital signal, which was required in order for the processor the analyze and manipulate the
signal, into an analog signal. This signal can then be transmitted from an antenna, but before this
is done, additional filtering of the signal is required.
Output Filter
The output filter which must be implemented for this device which will be another bandpass filter, however, this filter need not have the variable capabilities of the input filter. This
filter will output a signal of the frequency desired to broadcast the 802.22 wireless network.
Second Antenna
In order to connect to desired devices, we considered multiple different design iterations.
The one which seemed best for our product was to include another antenna system to transmit its
own wireless network on a usual IEEE 802.11 WLAN frequency. Since most devices today are
not capable of using IEEE 802.22 WRAN frequencies, our device will act as a middle man
between the signal and what ever devices someone wanted internet access on (laptops, tablets,
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hand helds, etc. The device would essentially act as a mobile wifi router, with the internet
connection being provided from the white space frequencies.
Alternate Design A
USB 3.0 Implementation
Originally, the plan was to make the device a USB dongle. USB has the advantage that it
could power our device, so we would not need an additional power supply. However, USB also
has several disadvantages versus other potential designs. First, only devices which have USB
ports would be able to utilize the technology. That basically leaves our marketability to
computers, as other devices usually do not include USB. Also, USB 2.0 (the most common
iteration of USB used today) is not capable of data transfer rates as high as the ideal transfer rates
we will be achieving over the white space frequencies, resulting in bottlenecking. Since speed is
one of the most important factors for an internet service provider, this is not ideal.
USB 3.0 is more than fast enough to fix this issue, but not enough computers come with
USB 3.0 yet for this to be very marketable.
Alternate Design B
In order to fix the bottlenecking effect of USB, we considered using ethernet as the data
transfer medium. Ethernet is common to most computers, but still has the problem of not
extending to other wireless devices. An ethernet iteration could, if necessary, still be powered
through USB in order to eliminate the need for a power supply.
Ethernet Algorithm
For this design, a special algorithm is required in order to separate the bits of the Ethernet
signal into their intended sub signals.
Ethernet Transfer
The transfer of data over wireless can be quite fast, as can data transfer through USB (at
least with 3.0), however, the fastest transfer of data of the proposed devices would be through the
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use of an Ethernet protocol. With the proper algorithm implemented within the processor, strong
and consistent gigabit connections are possible with Ethernet
Comparison of Design Possibilities
Quality Function Deployment
Quality
Portability
Security
Accessibilty
Connection
Quality
Power
Consumption
Connection
Speed
Weighted
Totals
Weight
8
4
5
3
Design 1
7
3
7
3
Alt. Design A
3
7
1
7
Alt. Design B
3
7
1
7
3
3
1
7
5
7
7
3
156
116
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As seen in the QFD above, the design that was chosen for this product had the highest
weighted score on the QFD, but this is not to say that each model was without its own
advantages and disadvantages.
Differences in Models and Their Effects on the Product Functionality
The second antenna we need is to transmit data from the device to the actual user. For
this part of the device, we considered three possible design iterations. The device can connect to
a laptop via either USB, Ethernet, or its own wifi network. USB seemed the most obvious, as
there are other USB dongles on the market for use on different types on networks. The problem
with these, however, is that the possible speeds achievable by our device are greater than USB
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2.0 allows, resulting in bottlenecking. When speed is one of the most important factors, this is
not ideal. USB 3.0 is more than fast enough to fix this issue, but not enough computers have
USB 3.0 yet for this to be marketable.
Using an Ethernet connection is a simple fix to this problem. If necessary, the device
could still be powered through USB. Ethernet is fast enough to keep the connection from bottle
necking. Both the USB and Ethernet versions of the device would be very inexpensive to
manufacture. The D/A Converter and output filter are not neccesary on board the ethernet or
USB versions of the device, as such signal processing can be done with software on the host
computer.
The wifi version of the device is the most expensive and complicated of the three designs.
However, it connects to the most devices and is the most diverse. The device could be carried in
a personal bag in order to create a personal wifi hotspot for your laptop, internet tablet, etc.
Considering the ever increasing popularity of hand held devices (which do not usually have USB
or ethernet) this is an increasingly important factor. Also, the device could be utilized in public
transportation such as a bus, where it could provide standard IEEE 802.11 wifi for a number of
customers while traveling through rural areas.
Internet protocol
Once it had been determined that the device would essentially act as a wireless router, a
decision had to be made on which internet protocol to implement in the device. The first is the
older of the two options; 802.11af. This protocol, by comparison, has reasonably faster speeds,
however, the area that the signal broadcasts over is much smaller than that of the alternative.
This would be useful in small households in which few people would be connecting in a small
contained area. The alternative to the 802.11af protocol is 802.22. This protocol is slightly
slower than 802.11af, however, it can broadcast over a much larger area and can handle many
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more users. This protocol would be useful when implement on a school campus or possibly a
public park area where many users will be attempting to connect over a large area.
Conclusion
A self contained device which recognizes and connects to a white space internet
frequency (IEEE 802.22 WRAN) is proposed. Cognitive radio allows for transmission of white
space internet in areas with little to no risk of signal interference. The device features a MIMO
antenna system in order to maximize quality of service. The device connects to desired devices
by creating its own wifi hotspot (IEEE 802.11 WLAN). Different components of the device can
be controlled by the included colorless LCD display.
References:
802.22 receiver requirements.
https://mentor.ieee.org/802.22/dcn/09/22-09-0031-01-0000-text-proposal-for-receiverrequirement.doc
A Technical Tutorial on IEEE 802.11 Protocol. Pablo Brenner. http://www.sssmag.com/pdf/802_11tut.pdf
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Cognitive Radios for Dynamic Spectrum Access: From Concept to Reality
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5675780
Electromagnetic Signal Attenuation in Construction Materials.
http://fire.nist.gov/bfrlpubs/build97/PDF/b97123.pdf
IEEE 802.11af White-fi. http://www.radio-electronics.com/info/wireless/wi-fi/ieee-802-11afwhite-fi-tv-space.php.
IEEE 802.22 Wireless Regional Area Networks. Apurva N. Mody. Gerald
Chouinard. http://www.ieee802.org/22/Technology/22-10-0073-03-0000-802-22-overview-andcore-technologies.pdf
Implementation Challenges for UHF White Space Cognitive Systems
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=4656353
Security Vulnerabilities in IEEE 802.22. Kaigui Bian. Jung-Min “Jerry” Park.
http://portal.acm.org/citation.cfm?id=1554126.1554138&preflayout=flat
Spectrum Sensing in IEEE 802.22. Stephen J. Shellhammer.
http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=BA4C26FAD27141BDC0DB64711A
B00881?doi=10.1.1.167.2849&rep=rep1&type=pdf
Wi-Fi in the TV White Spaces - 802.11af task group
underway. http://blogs.broughturner.com/2010/01/wi-fi-in-the-tv-white-spaces---80211af-taskgroup-underway.html
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An Effective MIMO–OFDM System for IEEE 802.22 WRAN Channel
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=4543880
A Feasible RF Bandpass Sampling Architecture of Single-Channel
Software-Defined Radio Receiver
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=4796959&isnumber=4796933
Design of a MIMO Antenna for USB Dongle Application Using Common Grounding
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5745801
An Effective MIMO–OFDM System for IEEE 802.22 WRAN Channel
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=4543880
Appendix A: Self-Analysis of Progress
Strengths: The ability to provide internet access to a larger area than previously possible, or to a
large area with fewer access points than previously possible. One wireless access point can
provide internet up to twenty miles using white space frequencies. This opens up cheap effective
ways of delivering affordable internet access to extreme rural areas. Signal attenuation is less
through trees than through buildings, so high tree densities in rural areas isn’t as much as a
problem as buildings area in urban areas for our wireless signal. Cognitive radio allows for this
to be implemented fairly, without affecting other commercial signals. Our device acting as a
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personal wifi router allows for it to be used across any wifi ready device on the market, without
having to purchase different components for every device. IEEE 802.22 or similar white space
frequencies could act as a substitute or replacement for current standard technologies such as 3G
internet in low population areas, due to its extremely high range at little cost.
Weaknesses: Due to the low power of the signal, although better range is possible, the speed
compared to other wireless technologies is lower. Larger wireless access points leads to a
problem with more people using the same access point. Over crowding an area will prove to be
a concern, especially if this is ever introduced in a very large scale. Security vulnerabilities also
arise with so many people sharing fewer wireless access points.
Opportunities: This technology provides affordable broadband internet access to rural areas
where it was otherwise not affordable. Many countries around the world which had been using
this spectrum for analog TV channels have likewise made the complete switch to digital, so it
may be possible to deploy white space internet in foreign countries where internet access is
otherwise not obtainable.
Threats: There is already competition from the White Space Coalition, but nothing has been
fully implemented anywhere yet. Live tests have been set up successfully in a few select cities,
however these are really not the ideal testing location (the technology is designed for rural
locations). The FCC has not yet actually “OK”’ed the use of the white space spectrum for
internet connections/access, although this should not be a problem because cognitive radio
allows for fair sharing of the spectrum. Further research must first be conducted to test for
interference created by use of the particular radio frequencies, however this should not be much
of a problem with cognitive radio.
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Appendix B: Drawings & Diagrams
Alternate Design A:
Alternate Design B:
Appendix C: Governing Equations
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P=Power
T=Period
cj0,k=Scaling Coefficients
dj,k=Wavelet Coefficients
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