TwenteSat Cognitive Radio Afterlife - ETSV Scintilla - Universiteit

24 Pages·2014·8.19 MB·Dutch

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Cognitive Radio
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for Dynamic Spectrum Access
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Afterlife

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In Memoriam
To our great regret we have had
to say farewell to
Dewi Bohlmeijer
1994 - 2013
presidential note
Facing a challenge
The study year 2013/2014 will be a unique and challenging year for both
the students and this association. First of all, the new educational model
is officially integrated in all the universities programs. Secondly the gover- President
nment is changing their policies again considering scholarship. In the re-
coil of these financial cuts, students were too hesitant to spend too much
of their time in side activities like the board resulting in a big shortcoming
of volunteers. 84rd Board of E.T.S.V. Scintilla
Luckily there is one bright star shining away teabags, coffee spoons, sugar bags and
through the dark clouds. One heroin wil- every other thinkable food encapsulations
ling to spend one year of her life serving in the trash bins that are located literally 20
not only as the backbone and exoskeleton cm away from the places where everybody Wine tasting evening
of our financial critter, but also as the new else is dumping their waste. Thursday 21 November
wailing wall of the students taking care of all
20:00h, Abscint
of the complaints about our education. One Enough of that. The first weeks were not
descendant of Educational Sciences called only busy but also very fun! A lot of con-
Dieuwertje ten Berg with whom I have the stitution drinks helped me to train my beer
honor of working with. Karim Kok is once muscle. After gaining way to much pounds
again the administrator of the STORES. its time to start losing them. After all, I have MILFBA
Erik de Wit is the last person we needed to to be able to run those 7km without leaving Thursday 28 November
satisfy the demands of our regulations, wil- too much craters in the pavement.
18:00h, Abscint
ling to sign a contract stating that he could All in all, one amazing year ahead of us! The
be held responsible for Scintilla. I am very new students al seem to be very cool and
grateful to work with this team the upco- I’m really looking forward to making this a
ming year and I’m looking forward to it! fun year!
Scinterklaas evening
When we started we immediately noticed Op de koningin, op Scintilla! Wednesday 4 December
how much work is ahead of us. Not only big
16:00h, Abscint
tasks but also the small ones are draining
a lot of our time. After a few weeks of ha-
ving to clean up people their mess on our
balcony, our members automatically started
helping us out with our daily chores. Ama- Christmas-dinner
zing!! I want to thank everybody who is hel- Thursday 19 December
ping us out for their time and I also want to Robert Fennis,
19:00h, Abscint
personally thank everybody who is not too President of E.T.S.V. Scintilla
lazy to rinse their coffee mugs and throw
3
year 32
edition 1
table of contents table of contents
In this edition of Afterlife, you can read another story
Masthead It was not an easy job to find them, but Scintilla finally
about how your life might look like after a study Elec-
got them: a new board for the coming year. Last year, the Editorial
trical Engineering. Maarten Segers, who used to be an
board was presented to you in a tale of the five knights,
EE student and active member of Scintilla, tells his story.
8. this year you can read about the new board in the tale of
Nowadays, he works at a company in Amsterdam. How
De Vonk the two musketeers. How did they come in the position
The 84th did Maarten ‘finish’ his study and how did life go for him 16.
A game with two
they are today and what can we expect from them?
Periodical of E.T.S.V. Scintilla. after he stopped?
Board Afterlife
Published four times a year in the sides
amount of 630 copies.
YDeeacre 3m2b, eedr i2ti0o1n3 1 OccupiedspectruThme main article in this Vonk comes from the chair Smoocscte pr,o itp uisl aprr ospboabrtl yi nth teh be ewsto krnldo. wAnc caonrd-
Editorial team ower quency ‘ScIapCneD ctr’r.e uaImdn etShveeinsr syiantrhgtii ncfloge r, aDwboiytnuhat mtwhiecir eStlipetlseesc t“rcCuommro msAsucconcreircseasl”ta,i toyinoosnu, Ivcfhe ryelodinu og hn, ay vtoheu ee mvbeaarcy vk hi soaitfv eeed an ctohhte imc Seocdin ntihttioellr as. m ThCahlelas mceo bsmoe-rpc uiantl leterhdse a tZthtiianl-- dttawinnogg u tteloaa rmW fise iklwdiip wtehid tehial e atv hsepenh geparlmiacyaeel ribss a pollln.a Thy ae dar etb ciyt-
Tim Broenink, Erwin Bronkhorst, PFre bandwidth and frequency spectrums. Why is the speed clients are used as a full workstation on a daily basis, but is very popular is noticeable when you are
Arno Geurts, Fieke Hillerström, of a 3G network limited and how fast can we go with they lack strong processing power, a lot of memory and new somewhere. You introduce yourself,
Maikel Huiskamp, Vera Nauta, 10. new wireless technologies? Mark Oude Alink will ans- even a physical hard drive. In this article, Koen of Scin- 24. make small talk and most of the time the
Rowan de Vries. Main article wer these questions. tilla Operator Team explains how these systems work. Thin Clients subject of soccer pops up. Personally I
PGriilndteprint, Enschede Spectrumhole Time cmoousltd snpohte rciacrael bleaslsl sw ihni cah g oteaal,m s ok imckoss tt hoef
the times I will nod my head until the
subject changes.
Editorial office 3 25
Presidential note SOT That the sport is very popular is also no-
E.T.S.V. Scintilla, University of Twente,
ticeable when the national team has to
Postbus 217, 7500 AE Enschede, Facing a Challenge
Scintillas thinclient play. Streets turn orange, the countries
0031 53 489 2810
How SOT does it national color, and almost the entire
0031 53 489 1068
country is confined to the television. We
[email protected] 6
flock to the country where the game is
News 28
MEEKI played and turn it orange. It may seem
Material News for the Electrical Engineer strange to the rest of the world, but at
Master Kick-In
[email protected] least this happening is peaceful. What
Wikipedia does not mention is what so-
8
metimes seems to be the second goal of
The 84th board
All members of Scintilla receive De 30 soccer: Hooliganism.
Tale of the two musketeers Junction Apparently it is “fun” to destroy city cen-
Vonk free of charge by post.
ters, cars and beat up people. Sometimes
Tjark Post
it seems martial law is applied when
Nothing in this magazine may be du- 10
games are played in some cities. There are
Main article
plicated or copied without explicit
policeman on every corner and during
permission from the editorial team of Crosscorrelation Spectrum Sensing for Dynamic 32 some games it won’t take long before the
De Vonk. Spectrum Access Baking pies riot control heads out to sweep the streets
clean. Once I could not enter my own
16 Solar powered baking
The editorial team reserves the right city without proper identification when
Afterlife
to change or exclude material pro- “our” club had to play against our arch
vided by third parties, in part or in Uncertiefied succes enemy. Riot control was at the bridge
34
blocking the entrance to the city because
whole. The opinions expressed in the TwenteSat
apparently it was needed.
articles are not necessarily shared by 18 IAC2013
A little bird told me that Scintilla appa-
the editorial team. Advertorial Thales
rently has a new soccer team. I want to
Een interview met Tom Griffioen en Hugo Anbeek
wish them luck and may you kick more
ISSN 0925-5421
spherical balls in your opponent’s goal
37 than they do in yours.
20 Advertorial Liander
Photo pages
Network automation
22 38
Bachelor assignment Puuzle
4 Bobby on wheels 5
year 32 year 32
edition 2 edition 2
news news
News for the MIT constructs self-
assembling robots
Researchers at MIT constructed small cubi-
cal robots that can form any arbitrary shape.
Electrical Engineer The cubes are capable of propelling them-
selves forward, jump on each other and snap
together to do self-assembly.
The cubes known as M-blocks have no ex-
ternal moving parts. The movement of the
M-blocks comes from an internal flywheel Stretchable OLEDs developed for displays
that reaches up to 20.000 revolutions per
minute. When the flywheel is braked it im- Researchers at the University of California sandwiched between the transparent silver
parts its angular momentum to the cube to demonstrated an elastic OLED prototype. nanowires composite electrodes made from
make it move forward. On each edge of the The stretchable OLED displays could be a rubber-like polymer. In the prototype the
M-block there are permanent magnets that used in smartphones, electronic clothing or electrode layers were patterned into rows on
allow cubes to attach to each other. wallpaper like lighting. top and columns on the bottom layer, thus
In the research for reconfigurable robots To accomplish the stretchable and bendable enabling each pixel to be addressed separa-
Nanotube computer integrated with CMOS researchers have long used an abstraction OLED the researchers had to change and tely.
called the sliding-cube model. If two cu- reengineer all the materials in the OLED To prove the concept two small stretchable
for the first time bes are facing each other than one robot stack. The two key elements were the de- OLEDS were fabricated, one lighting panel
can slide over the other one. This model velopment of a transparent compliant con- and the other one a passive 5x5 pixel dis-
For the first time a working computer using from metallic nanotubes. that use the same design infrastructure as is meant to simplify the development of ductor and a light-emitting electrochemical play. The both survived over 1000 trials of
carbon nanotube transistors on a silicon To circumvent these problems the resear- normal CMOS logic. self-assembly algorithms. Already existing cell that consists of a mixture of electronic stretching 30 percent larger than their ori-
wafer was demonstrated by the researchers chers used their so called “imperfection-im- The researchers from Stanford were able modular-robot systems can stop their mo- semiconductors and an ionic conductor. ginal size and 180 degrees bends.
at Stanford University. The researchers used mune design”. In this approach nanotubes to create a working RISC CPU using 178 tion any time they want, which makes it a The light emitting electrochemical cell is
a so called “imperfection-immune design” are grown on quartz with vapor deposition nanotubes that can execute 20 instructions. “statically stable” system. The new system of
to overcome the main difficulties when pro- on which 99.5% of all the nanotubes grow the MIT researches is not statically stable
ducing carbon-based semiconductors in a in a straight line. These grown nanotubes Source: http://www.eetimes.com/document. since at some point the robots actually fly
CMOS design process. are then placed on a CMOS wafer. asp?doc_id=1319660 through the air. To compensate for the sta-
A couple of decades ago the carbon nano- Even when 99.5% of all the transistors are tic instability the researchers placed cylin-
tubes were pushed as the new and ideal oke this would normally still result in a drical magnets on each edge that automati-
transistor because of their higher speed unacceptable number of defects. To solve cally rotate when two cubes approach one
and lower power consumption than their this problem the researchers use a circuit another. This way the north and south poles
CMOS equivalents. There were a couple layout technique that etches out pre-de- are aligned and every face can be connected
of problems with the carbon nanotubes fined regions for specific functions using to any other face of the cubes.
that prevented them from being used, the graph-theoretic algorithms. This results in To further increase the grip when a cube
inability to grow them in straight lines and the imperfection-immune standard cells flips onto another the edges are also beve-
the difficulty of sorting out semiconducting led. This way when one cube flips on top of
another the bevels and magnets touch, thus
Tape used for electronics manufacturing increasing the connection strength between
cubes.
Encrypted implants keep hackers out.
Scientists from the University of Minnesota the research is that tape is one of the key ele-
have discovered a technique for the manu- ments in realizing the small gaps. Etching
facturing of nanostructures that uses Scotch the one nanometer wide gaps is not yet fea- Modern medical devices such as defibrilla- heartbeat of the patient as verification if so-
Magic tape. This technique has the poten- sible with the existing tools. The nano gaps tors and insulin pumps now include wire- meone is in direct contact with the patient
tial to make electrical and optical devices where constructed by layering atomic-scale less connections that allow a doctor or tech- or not. In this method the doctor holds an
smaller. Combining several standard nano- thin films on the sides of the structures and nician to update the software or download device against the patient’s body that reads
fabrication techniques and tape the resear- then capping the structure with another data that can be used for medical purposes, the heartbeat and compares is with the
chers where able to create tiny gaps over the metal layer. The challenging part was to re- but could also be misused by hackers. Secu- heartbeat that is relayed in the wireless sig-
surface of a silicon wafer, where the smallest move the excess metals on top and expose rity researchers showed that it is possible to nal from the implant.
gap was 1nm wide. The width of the gaps the structures below. The researchers found reprogram the devices such as the defibrilla-
Source: http://www1.umn.edu/news/news- could in addition be controlled to the ato- out that this can be done with tape. tor to stay inactive or give a 700-volt shock Source: http://www.technologyreview.com/
releases/2013/UR_CONTENT_455024. mic level. The most surprising outcome of when it is not needed. news/519266/encrypted-heartbeats-keep-
html A solution to this problem is to use the hackers-from-medical-implants/
6 7
year 32 year 32
edition 1 edition 1
new board new board
The 84th board
Tale of the two musketeers
Once upon a time in the east of the country, there was a silver castle. The
silver castle was the home of a specific group of students and their student
association. Last year the castle was protected by five brave knights, but
the five brave knights where nowhere to be found. The knights had to be
found, and this is the story of the musketeers on their quest to save the
knights. Actief sinds 1965
There was one musketeer who was immedi- nights, and he had almost lost all hope of locked up in a cage, surrounded by food, happy with their freedom. And Fennis was musketeer, fighting with the wolf. “Watch sons of the goldsmith were kidnapped. They
ately ready for the challenge. He was ready ever finding anything when he heard some and knight Luuk was cleaning the house. declared freedomfighter of the Silver castle. out” the musketeer shouted, “the wolf is were twins, one, Tim, was very well spoken
for a new challenge, he was waiting for acti- voices. He heard three voices, two he recog- The witch was stirring in her kettle. “Is he He took the two knights back to the cas- evil!”. “No, it is not!” she shouted back, and and knew how to play people so that they
on. This brave young man is called Fennis. It nized, one he didn’t. The voices he didn’t ready to be cooked?” the witch wanted to tle, where they could rest and get strong she stepped in front of the wolf. The oath would do anything for him. His brother,
seems to be that he also listens to a different know sounded old, and not very nice. It was know. “Is he already fat enough?” Luuk ans- before the new year started. Before he left to the wood and it’s habitants was explained Mattanja, was the guardian of the money
name, but that will only bring confusion. an old witch and she was commanding a wered: “no, not yet milady”. the knights gave him the advice to go the and Fennis the musketeer understood why and the jewels they gathered. In their heart
person to clean and cook. When Fennis got west. So he rode to the west. It was a long the wolf had to live. they were good men, but they were forced
The young musketeer was walking through closer to the house he saw that is was made Fennis thought; this is not right. He rushed journey, he met many people and fought to use their talents for evil business. The
the woods, he was following a trail of lit- of candy. He also saw that knight Luuk and to the house, killed the witch and freed many battles before he entered into the new Both the musketeer and the girl in red had goldsmith was a well respected man in the
tle white stones. He walked for days and knight Koen were there. Knight Koen was Luuk and Koen. Koen and Luuk were very woods. The woods used to be a nice, kind tasted the world of heroism and were not silver castle, so the musketeers rode out to
looking place, but now it was terrorized by a ready to stop living the heroic live. So they save his sons.
evil wolf called TOM. Fennis heard of this strode together to save the world. In one of
monster and was planning to kill it. the villages they passed, a story was told. It So the musketeers were searching for the
was the story of a blond princess, captured twins, they were kidnapped by a traveling
But in the woods lived a girl with a red clo- in a tower. An evil witch stole her from her circus. But the musketeers didn’t give up,
ak and her grandmother. Their family had parents and captured her in a tower. She and they were halfway on their way to Ja-
lived in the woods for many generations. must be saved, the two thought. So after a pan when they found the circus. They pre-
They protected the woods and the creatures journey of weeks they found the tower. Hi- tended that they wanted to join the circus
that lived in the woods. They took good dden in a far away country, they found the and gained their trust. And one night, they
care of the habitants in the woods. But Tom princess. She was high up in tower, locked ran away with Tim and Mattanja. The twins
the wolf was getting more and more proble- away for anyone to see. The two musketeers were very happy to go back home, and to be
matic, so the girl in red, named Dieuwertje, tried to get into the tower, but that was not reunited with their friends from the silver
was done with the wolf problem. The wolf so easy. One day the witch came, and the castle.
should not be causing so much trouble, princess let her hair down, and the witch
it should live in peace. But her family had climbed up to the window. When the witch All the knights were back in the silver cas-
sworn an oath to protect the animals and was gone, the musketeers asked the princess tle. But after these traumatizing experiences
not to kill them. So the wolf had to be ta- to let her hair down. The princess her name they were in need of rest, so new protectors
med. was Laurie, and she was desperate to get out. had to be found. The two musketeers were
She was rescued and bought back to the sil- up for the task. They had proven their dedi-
So Dieuwertje rode out to tame the wolf. ver castle. cation while saving the knights.
After a few days she found the wolf, and the
taming process began. She was training the In the silver castle she met Koen and Luuk, So the castle was again protected for a year,
wolf for two weeks when she heard a stran- her long lost friends. While the musketeers by the brave musketeers named Fennis and
ge noise in the night. She woke up and took were off saving the princess a different kind Dieuwertje.
her armor. When she got outside she saw a of horrific event had taken place. The two
8 9
year 32 year 32
edition 1 edition 1
main article main article
Crosscorrelation Dynamic Spectrum
Detecting these spectrum holes is one of
Access Occupiedspectrum the main challenges in DSA. It is in prin-
ciple possible to use databases to hold this
wer ency information, but that requires additional
There is an alternative way to get access to o qu infrastructure, and may not work for ad-
more spectrum, known as Dynamic Spec- PFre hoc networks or bands with rapidly chan-
Spectrum Sensing
trum Access (DSA). Measurements show ging occupancy. Therefore, many people
that only 2% to 20% of the spectrum below focus on spectrum sensing, which measu-
3tiGmHe azn ids laocctaivtieolyn , beevienng iuns emda jaotr acnityi egs.i vAenn Spectrumhole Time rtoes dtehtee rcmurirneen tw ohcicchu pbaanncdys oafr eth aev aspileacbtlreu tmo
example of such a measurement in shown Figure 3: Dynamic spectrum access opportu- use. One can distinguish between several
in fig. 2, made by Swisscom in Bern. Thus, nistically uses unused spectrum main categories of spectrum sensing, such as
for Dynamic
although spectrum is a scarce resource, it is coherent sensing, cyclostationary sensing,
used in a very inefficient way. DSA promises new year, or for (HD)TV streaming to your and energy detection. The first two catego-
a much more efficient use of the spectrum smartphone. ries exploit known properties of the signal,
by letting unlicensed users opportunisti- which improves the signal-to-noise ratio
cally use bands that are licensed to primary Public safety services tend to have a very (SNR) and thereby offers better detection
users (PUs), but are temporarily and/or lo- high peak-to-average utilization, which performance. Unfortunately, this will be
Spectrum Access
cally unused, known as ‘spectrum holes’ or means that their dedicated spectrum more difficult for bands that have many dif-
‘white space’, see fig. 3. ferent and perhaps many unknown modu-
Have you ever wondered why the datarate on your 3G connection is typi-
cally limited to just a few Mbit/s? It is basically limited by three factors:
(1) limited bandwidth, (2) limited spatial reuse, and (3) limited spectral
efficiency.
Currently, spatial reuse is aggressively im- mand for wireless data communications
proved by operators using cell splitting: the- continues to increase by 75% each year, see
re are more (but smaller) masts to provide fig. 1. Squeezing more bits into the same 15
h 10.8
an area with coverage. In that way, the same spectrum is very inefficient in terms of po- t
n 10
frequency can be reused more often, which wer consumption, and we all know that bat- o 6.9
m
4.2
effectively means that each user can get a tery life is already an issue in our smartpho- / 5 2.4
B 1.3
larger portion of the capacity of each cell. nes. The increase in number of cells is also E
0
limited by cost and practical constraints. So Figure 2: Spectrum measurements in Bern (and many others) show that although virtually all of the spectrum has been assigned, the actual
2012 2013 2014 2015 2016
LTE (also known as 4G) is currently being in the end, the only viable way to improve usage is rather low in most bands. (Source: Swisscom)
Year
rolled out in the Netherlands. Compared the capacity even further is to use more
to 3G, it improves on spectral efficiency spectrum. Figure 1: Wireless cell phone data demand One of the main drivers of DSA is the pos- remains largely unused for most of the time. lation formats. Moreover, these algorithms
as well as bandwidth. Where UMTS uses in exabytes per month for recent history and sibility to get broadband wireless internet When they do need spectrum, they actually tend to be quite computationally complex.
only 5MHz of spectrum per channel, LTE Unfortunately, virtually all of the usable near future (1EB=1018 bytes). to areas that are too remote or geographi- need more than what is assigned to them. Therefore, my focus is on energy detection
increases this to 20MHz (and even 40MHz spectrum below 6GHz has been assigned, cally difficult to reach via a wired network. Think of the many rescue workers that had (ED), which does not rely on any know-
in the near future). LTE increases spectral which makes it very hard for new services By using the sub-GHz frequencies, one can to communicate with each other after the ledge of the signals to be detected, and can
efficiency by using 64-QAM, which puts to squeeze in. There is a lot more room at transmission power, and the fact that walls easily cover tens of kilometers at reasonable fireworks disaster in Enschede in 2000. Mo- thus be used anywhere in any band.
three times as many bits per second in the higher frequencies. For example, the first and other obstacles severely attenuate the transmission powers. DSA would also allow reover, the addition of multimedia transfer,
same spectrum as QPSK, which is used in commercial products of IEEE 802.11ad signal. This is great to avoid interference any wireless connection to offload peak de- such as photos and video, could be of great Energy detection
UMTS. (WiFi at 60GHz) are expected in 2014 with your neighbors, but not so great if you mands to other parts of the spectrum, the- help in saving lives. DSA can also enable
and promise up to 7Gb/s. The downsides at want a good connection and mobility eve- reby allowing it to obtain a higher datarate rescue workers inside buildings to switch to
But even this increase will only be enough such high frequencies are the much smaller rywhere you go. when it needs it. This is a useful feature for more favorable frequencies to prevent los- ED measures the power (or energy, hence
for a few years. Predictions are that the de- distances that can be covered for the same the GSM-network in the first hour of the ing connection. the name) in a frequency band to decide
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year 32 year 32
edition 1 edition 1
main article main article
whether a signal is present or not. The de- alarm (denoted as P ) and the probability plot the minimum SNR on the x-axis, and −160 ACrcv1 and only the bins that fall between 2MHz
FA
tector has to decide, based on the digital of missed detection (denoted as PMD). One the required number of samples on the y- Hz] ACrcv2 and 3MHz are used in our detection algo-
complex baseband receiver output r[k] (if way you can improve your decision is to axis, the graph seems to hit a wall: it has a / −165 XC rithms. The noise power is determined by
you don’t know what that means, think of ask me to repeat the experiment 10 times. vertical asymptote (as will be shown later). m adding the power in the 103 bins that fall
B
it as the waveform as shown on the screen If the average sum would be above 353, P d within that band. Fig. 8 shows the output
FA [
of an oscilloscope), which of the following is already a lot less than it was for a single Crosscorrelation D −170 noise floors of 13 measurements. The last
two hypotheses is true: experiment. Similarly, P is also reduced. PS measurement was done almost two hours
MD
So, by averaging more often (or for DSA, after the first measurement. As you can see,
−175
measuring longer / using more samples), In order to mitigate these problems (and −15 −10 −5 0 5 10 15 the noise level fluctuates over time! The
detection performance can be improved. some others, which are not discussed here), difference between the highest and lowest
Frequency[MHz]
This is done by estimating the power I propose to use crosscorrelation (XC), total power is what I use as the value for
(or energy) of r[k] using K samples. The You can imagine that it will be easier to which is a form of ED quite similar to AC Figure 6: Visual example of the benefit of crosscorrelation with respect to autocorrelation in the the noise power uncertainty, which in these
standard means to do this is a form of auto- distinguish between the two hypotheses if as we have discussed so far. The principle presence of noise power uncertainty. measurements is slightly more than 0.07dB.
correlation (AC). For those of you familiar I have tampered with more dice, since this is shown in fig. 5. Rather than conjugating
with this term, the autocorrelation function will imply a larger distance between the ex- and squaring the output of a single recei- respond to AC), and the combination of 10% for various K and SNR; The thresholds are determined for each of
at lag 0 is calculated. The process is visuali- pected values of the two hypotheses. Simi- ver, the outputs of the two receivers are the receiver outputs using XC. The noise 3) Find P for various K and SNR using the 13 experiments, and shown in fig. 9. The
MD
zed in fig. 4, and the equation reads larly, a larger signal s[k] is easier to detect multiplied (with one receiver output con- uncertainty is modeled as a noise floor that the thresholds from step 2. noise fluctuations cause the thresholds to be
than a smaller signal. Therefore, the SNR, jugated). As a result, the input signal itself is not perfectly flat over frequency. Our eyes The noise floor is determined by measuring slightly different for each of the measure-
K 1
Pˆ =Y = 1 − r[k]2 defined as |s|2 / |n|2, is a relevant parameter. undergoes exactly the same process as in can easily identify the 6MHz wide signal in the averaged output spectrum of the indi- ments. The maximum of all values is
ac K | | fig. 4, while the noise contributions of the the XC spectrum, but they cannot detect it vidual receivers without applying an input used as the final threshold to “guarantee”
k=0
(cid:31) individual receivers are crosscorrelated and in the individual receiver spectra. signal. The ADCs sample at 10 MS/s: the that P does not exceed our desired P of
FA FA
largely average out. The power estimation baseband frequency ranges from -5 MHz to 10%. Note how much lower the threshold
n(t) conj
process I use is Prototype 5 MHz. In every measurement, 1024-point for XC is! This is due to the fact that most
FFTs with rectangular windows are used, of the noise is being averaged out.
K−1
s(t) + 1
rin(t) W r[n] × K k=0 Y IIn h oavrde ebr utiolt vae rpifryo ttohteyspee t hine o6r5etnimca l CreMsuOltsS, fCLK
(cid:31) technology with two integrated RF recei- Divide D
Figure 4: Principle of energy detection: receive noise plus a signal (or just noise), filter it to only It can be shown that, theoretically, the vers. The baseband circuitry and analog-to- by 8 ... ... TIA ADC S
look at a certain band, digitize it, and perform power estimation.
SNR-wall of XC is lower than that of AC. digital converters (ADCs) are left off-chip,
P
If this power is below a certain threshold, In practice, the number of samples K will be The intuitive explanation is that n(t) and and the signal processing is performed on a
1
the detector decides H0: the band is free. limited, because you quickly want to make n(t) in fig. 5 are averaged out, because their PC in Matlab. The frontends can be used
2
Otherwise, it decides H1: the band is occu- a decision which band to use. This implies product has an expected value of 0 as they separately (for regular reception), or can be
spectrum
pied. In many cases, most of the noise that that for a certain maximum P and P , are independently generated by the indivi- put in parallel via on-chip switches to ena-
FA MD RF attenuator LNTA HR-mixer
arrives at the detector is from the receiver only signals above a certain SNR can be de- dual receivers. Therefore, any uncertainty in ble XC spectrum sensing. The receivers can
itself due to the noisy analog circuitry. tected. Interestingly, it turns out that when their power thus also disappears. Only n(t) receive signals anywhere between 300MHz
0
The problem here is how to set this thres- you do not exactly know the noise power, (which represents external noise and shared to 1GHz with a baseband bandwidth of
hold. Let us use a comparable problem that but only to within a limited accuracy, a mi- noise of the receivers) and its uncertainty about 40MHz.
f
CLK
we can all relate to. Suppose I throw 100 nimum SNR still exists, even when your eventually remains. By storing the outputs of both receivers and
Divide
dice and tell you only the sum of all eyes. measurement time is unlimited! This SNR Fig. 6 shows a simulated result of the indi- processing them offline, the power estima-
Now you have to decide whether or not one is known as the SNR-wall, because if you vidual receiver output spectra (which cor- tors and can be directly compared: the by 8 ... ...
of the dice has been tampered with such that samples, and thus any temperature and gain
it will always show ‘6’. How would you do + variations (which typically are the main
W Figure 7: The system setup and chip photo (integrated parts inside dashed box)
that? If they are all normal dice, the expec- causes for uncertainty in the noise power),
ted sum is 350, because 3.5 is the expected n0(t) r1[k] are identical.
vowauilttuh et o nf oobrre mo 3na5le 3 dd?ii ceIe.t BIi suw tn owouthl dua tng ilefit kt ehtlheyi sstu hnmaut m teubvreennrs. s(t) + n1(t) 1 K−1 Measurement proce- m/Hz] −−115522..86 Receiver1
So, if you put the threshold too low, you n (t) × K k=0 Y dure dB −153
can generate a false alarm: you say some r (t) 2 r [k] (cid:31) D[ Receiver2
dice have been tampered with, but that is in 2 S −153.2
P
not actually true. On the other hand, if you To measure the expected improved perfor- −153.4
+ conj
put the threshold too high, I may have tam- W mance of XC, I used a number of steps: 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3
pered with some dice, but you don’t notice. 1) Measure the noise floor and estimate the
Basebandfrequency[MHz]
This is a missed detection. Clearly, there is Figure 5: Principle of crosscorrelation: receive noise plus a signal (or just noise), split it to noise uncertainty;
a tradeoff between the probability of false process it independently with two receivers, and combine the receiver results for the power 2) Find the thresholds for desired P of Figure 8: Noise power spectra of the individual receivers (13 measurements)
FA
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1
main article main article
put of two receivers, and thus the XC-de- 109
ACrcv1
600 tector has more information. What is also Conclusions
interesting to see is that at SNR=-25dB, the 108 ACrcv2
Theory with noise
XC
] P for AC goes down rather than up. This
W D 107 power uncertainty
means that due to the noise power uncer- Dynamic spectrum access is a promising
f
[ Receiver1 tainty, it is better to throw a coin to decide way to use the scarce spectrum more effi-
λac 550 whether a signal is present or not, than to ciently. It can do this by sensing the spec- 106
K
rely on the detector! At SNR=-32dB, the trum and identifying locally and temporally 105
same happens for XC as well. unused bands, which can then be opportu-
Without noise
Receiver2 Why does this happen? Let us go back to nistically used. Sensing these holes is quite a 104
power uncertainty
the dice-experiment. Assume my ‘normal’ challenge, especially if you do not have any
80 dice are not perfectly normal, but on avera- knowledge of the signals you need to de- 103
15 ge I throw somewhere between 3.4 and 3.6 tect. The use of crosscorrelation spectrum
−30.7dB −17.9dB
102
60 per die. To be on the safe side (you don’t sensing, which uses two receivers rather
W] want to generate too many false alarms), than one to process the same signal, seems −32 −30 −28 −26 −24 −22 −20 −18 −16 −14 −12 −10 −8 −6
[f 14 you choose 3.6 as the expected value per to give a significant improvement in terms SNR[dB]
λxc 40 5.8·105 106 daniey.w Aacyt.u Halolyw, ethveer d, iIc ael stou rhna oveu to tnoe b tea mnopremreadl onfa ld meteeacntiso onf p eenreforgrmy danetceec otivoenr. tIhne tthraed miteioa-- FSNiguRr-ew 1a2ll Thfore ASCN.R-wall for XC is -30.7dB in this experiment, almost 13dB better than the
die that always returns 6. The expected va- surements performed with a prototype, the Ph.D. dissertation, University of Twente,
20
lue for 100 dice is thus . As I throw only a improvement is more than 12dB. or André Kokkeler at the CAES-group Enschede, May 2013.
few dice, there is still a reasonable chance Intrigued by any of the parts discussed in ([email protected]). [2] M.S. Oude Alink, A.B.J. Kokkeler,
102 103 104 105 106
that the value exceeds your threshold of . So, this article? You can find much more in- E.A.M. Klumperink, G.J.M. Smit, and
K your P >0. However, as I repeat the experi- formation in the references. If you would References B. Nauta, “Spectrum Sensing with High
D
ment, and you average the results, the pro- like to work on this topic for a research, Sensivity and Interferer Robustness Using
Figure 9 Obtained thresholds for autocorrelation (lac) and crosscorrelation (lxc)for P =0.1 bability that this average sum exceeds 362.4 Bachelor or Master project, feel free to Crosscorrelation Energy Detection,” IEEE
FA
in 13 measurements. becomes smaller and smaller, and P gets contact Eric Klumperink at the ICD- [1] M.S. Oude Alink, “RF Spectrum Sen- J. Emerg. Sel. Topics Circuits Syst., vol. 3,
D
Finally, the input signal is applied, and the closer and closer to 0. This is exactly what group ([email protected]) sing in CMOS Expoiting Crosscorrelation,” no. 4, December 2013.
threshold values found earlier are used to Measurement results happens in fig. 11.
determine P for several SNRs. As input
MD
signal, I have used a noise-like OFDM sig- With all the measurement results analyzed,
nal with a bandwidth of 1MHz. To create By using the thresholds found before, it is I can explicitly show the SNR-wall by plot-
a different SNR, I simply decrease the sig- relatively straightforward to find the mea- ting the required number of samples for
nal generator output. An example for high sured P . In fig. 11, the results are shown, different SNR. This is shown in fig. 12. The
MD
SNR is shown in fig. 10. In each measure- where the probability of detection P , ra- theoretical lines (see [1] for the derivation)
D
ment, 227 complex samples per receiver are ther than P , is shown (P =1-P ). As are also shown, and correspond very well
MD D MD
captured (limited by computer memory), explained before, increasing K will improve with the measurement results. Indeed, as ex-
which results in 13.5 million independent detection performance, and that is what you pected, we can detect significantly smaller
samples available to detect the signal. To see for the higher SNR in the left two parts signals in the presence of noise uncertainty
find a P of 10% (which I used as the de- of the figure. What you also see, is that the with XC! At low SNR, it is also much fas-
MD
sired maximum value), at least 10 indepen- two autocorrelations of the individual recei- ter, so it is not only better for your battery
dent realizations are needed. This leaves vers require higher K for the same detection life, but also enables faster response to avai-
maximally 1.35 million samples available performance as the XC process. This can be lable spectrum holes and thus improves data
per measurement. explained by the fact that XC uses the out- throughput.
] −140 1
z SNR=−25dB SNR=−32dB
H
/ 0.8
m −145
B
d 0.6 ACrcv1
[ −150 D
D P ACrcv2
S 0.4 XC
P −155
2 3
0.2
Basebandfrequency[MHz]
SNR=−9dB SNR=−17dB
0
103 104 105 106 103 104 105 106 103 104 105 106 103 104 105 106
Figure 10 Output spectrum with a signal
present between 2 and 3MHz at an SNR of K K K K
approximately 10dB Figure 11 Measured P for P =0.1 as a function of K for several SNRs
D FA
14 15
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afterlife afterlife
Uncertified succes
travel, leaving more room in my budget for
other things. The study tour ended in Hong
Kong from which I boarded a plane hea-
ding to the Malaysian part of Borneo. I did
not do much preparation for this trip and I
pretty much only booked my plane tickets
and would sort out the rest on location.
I spent the two weeks that followed moun-
tain climbing, jungle tracking, boat riding,
hiking, driving my motorbike across the
country and sitting on the beach doing no-
The previous two Afterlife articles (written by LarsZ and BramT respec-
thing and relaxing. I then boarded a plane
tively) have two mayor topics in common. They both include a period of
to India. Again I was totally unprepared and
after-graduation-travel-time (not to be confused with after-graduation- I only knew that I would land in Chennai
time-travel) and they both involve an actual graduation to start this pe- and that I would have to leave three weeks
later from New Delhi (several thousand ki-
riod off with. Although my story has plenty of travel in it, it really lacks in
lometres away). The time in between I spent
graduation. Because of this graduation deficiency, the story has no obvi-
doing pretty much the same things I did on
ous point to start at, so I’ll just start at the beginning.
Borneo all while slowly making my way to I started on my first LED driver designs. Watt). My designs kept evolving as well and
New Delhi on busses, boats, planes and the We moved to another building after my I wrote and filed a patent on one of them.
wold famous Indian railway system. first week and we had gotten a pretty de- The electronics design team got expanded
It was 2005 when I first set foot on the hal- Contrary to my roommates advice I had The email she forwarded was from LED- By the time I got back to the Netherlands I cent budget to furnish the new electronics with a support technician and we recently
lowed grounds that form the University of no exit strategy, I had to come up with one consultancy, the Amsterdam based LED had been away for two months. In that time lab, this meant I also got to spend some welcomed the newest member to our team
Twente. I had gotten through high school before the end of the semester. I usually got lighting company she did the assignment my job finding quest had not progressed at time shopping around for new equipment. and the 15th employee of LED consultan-
without much trouble and I figured Electri- pretty decent grades for practical assign- for and it stated that they had seen my work all. It was time to get that all back on track. I As my designs progressed more and more cy. None other than DenickM, who most of
cal Engineering would fare me equally well. ments and projects and I had some experi- and liked it and they asked if I might be in- got back in contact with LED-consultancy safety and normalisation issues arose so I you know, was hired as an electronics desig-
It did not… ence with hobby-level electronics design, so terested in a job. I was! So I contacted them and went in for a job interview. By that time took a couple of weeks to dive into to these ner/IT manager.
6 years passed and although at this point I figured I could probably get a low level job and a few days later I took a train to Amster- the company had grown from 2 to 4 em- issues and read up on European norms and We are now on our way to finalize our first
the first EE students of my year started to in an electrical engineering company some- dam and had an informal conversation on ployees. One of the new employees being regulations concerning LED lighting and real products and we hope to release them
graduate, I was nowhere near graduation where and slowly work my way up the cor- what we could do for each other. We agreed a senior electronics designer to whom I electronics in general. on a big lighting fair in March. No one
myself. I had spent most of my time on drin- porate ladder. I decided to stay in Enschede that I would work there for a couple of days, knows what the future will bring for this
king beer, traveling and sleeping and I only as it has a good concentration of suitable just to test the waters, and that we would see company and what my role in it will be. The
I was the only electrical
managed to pass the easy, the fun and the companies nearby and if I kept my (cheap) were we would go from there. main advantage of smaller companies is that
interesting courses leaving me the hard and room I required a lower wage to have a de- Then D-day was finally there, the first of you have more room to grow and you don’t
the boring ones. I decided, as so many times cent income. Both things increasing my September, the first day of civilian life. But engineer in the company follow a set career path. Jobs are not clearly
before, that the coming year would be the chances of finding something fast. instead of running to the nearest welfare defined and you might be expected to do all
year I finally got of my lazy ass and started Several months passed without much pro- office, as one might expect, I went to the sorts of things (or maybe even all of them!).
making an effort. It wasn’t… gress. It seemed I applied the same work bank to collect large quantities of Chinese would be a junior. I got hired and we agreed In the meantime the company kept on gro- This gives you the chance to diversify and
currency. There was still a study tour that that I would start 2 months later, giving me wing, by that time we were up to about 10 maybe find something you really like.
had to take place and there were only a few time to get my driver’s license and find a employees. The electronics department still In Christian folklore the afterlife is where
I only passed the easy, the fun
days left until it started. Those last few days place to live in Amsterdam. consisted of only my senior and me, but that souls go after the deaths of the mortal bo-
went by in a flash and that Friday we left On the 15th of February I finally started was about to change. Not that we grew. On dies that once housed them. Applying this
and interesting courses
for Beijing. The three weeks that followed my job and after a few weeks of orientation the contrary, my senior got fired! The main to student life could sketch the following
were filled with pretty standard study tour reasons for this were his passive attitude and depressing picture: At the moment of gra-
stuff. Visiting amazing companies, doing all his general incompetence. Not that I would duation (or at any other study terminating
Shortly after the start of the new semester ethics to finding a job as I did to my educa- sorts of fantastic cultural activities, eating really miss him, but from this time on I was event) the student soul goes to heaven
I decided to join the study tour commit- tion. I did do some searches on job websites delicious food and doing loads and loads of the only electrical engineer in the company leaving the soulless body to roam the earth
tee and go on one last study tour. Looking and I was satisfied with the overall abun- partying! For a full report on the study tour and I was therefore also the only one res- as a corporate zombie for what seems like an
back on it now it is easy to see, but it took dance of jobs that I was sure I would find I would like to direct you to ‘de Vonk’ from ponsible for all electronics related affairs. eternity. Yikes!
me quite some time to realise I was just something in due time. Some more time the beginning of this year, but trust me, it Months went by and the company kept Don’t worry, the real afterlife is not that
avoiding the real issues and that I was unli- passed and out of the blue I got a forwarded was pretty awesome. All in all a fitting end evolving. It now had two new companies bad. It pretty bad, but not thát bad! And
kely to graduate any time soon, if at all. The email from a friend. I had helped her with to my life as a student and a nice start of my in the same holding. One for measuring all then of course there is the money, the sweet,
amount of time invested demanded some her bachelor assignment which included life as a civilian. But wait there’s more! relevant parameters of LED lighting (lu- sweet money…!
kind of pay out, but investing more time some LED lighting and control electronics. As is usual with study tours I decided to men output, spectrum, emission pattern, Reference:
was not the answer. I had to come up with I assisted her with the electronics design attach a little vacation to the end of it. As etc.) and a one for packaging LED dies http://en.wikipedia.org/wiki/List_of_col-
an alternative. I had to abort! and I soldered the whole thing for her. I was already in Asia I saved the cost of air into high power LED modules (10 to 500 lege_dropout_billionaires
Birthday cake
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