<< Chapter < Page Chapter >> Page >

In order to design an effective analysis tool, we have to be familiar with the effects of all the parameters we make available (processing gain, sequence length, SNR of channel, number of users, degree of generator polynomial). We tested our model and concluded our results were consistent with what we would expect from a CDMA system. The following are some relationships between some parameters and the bit rate error we found especially interesting.

Generator polynomial vs number of users: For an polynomial of order x, the number of users must be less than 2x in order to minimize bit error ratio. For any number of users N, the minimum order polynomial that corresponds to the number of users>N must be used in order to minimize error.

A dog sitting on a bed

Number of users vs number of errors: As the number of users in a system increases, the bit error rate increases as well. Modulation sequences are assigned to each user by taking one PN sequence with a long period and assigning users delayed versions of the sequence. Increasing users will cause each user's sequence to be less orthogonal with the rest of the users, resulting in more errors at the receiving end.

Processing Gain vs number of errors: The processor gain (also referred to as spreading factor) is the ratio of the bandwidth of the pseudo-random code to the bandwidth of our desired signal. The processing gain is also the number of "chips" used to transmit a single simple. A greater the processing gain results in fewer errors in our received signal. However, in practical applications, processing gain is limited by the available bandwidth. We plotted the effect of different processing gains against the bit error rate to observe the trade off between error rate and processing gain. This plot is shown below:

A dog sitting on a bed

SNR vs number of users: In our model, SNR specifies the ratio of signal power to noise power in the additive white Gaussian noise channel. In a communication channel, we would like to have a high SNR. For the majority of our simulation, we set the SNR to 0(dB) to simulate a worst case scenario, where the power of the signal and the power of noise are equal. However, for a better understanding, we will show some of the effects of the SNR on few and multiple users.

First, we wanted to how SNR affected the bit error rate if the system had a small number of users (<40). Choosing 30 users for our simulation, we saw that SNR had a significant effect on bit error rate. As the SNR increases (e.x. from -5 to 5) we can see a close to quadratic relationship between the SNR and the number of errors.

A dog sitting on a bed

We chose to include 150 users in our system to demonstrate how SNR affected bit error rate for a large number of uers. We observe that the SNR seems to have no effect on the bit error rate. Overall, the bit error rate is high for all SNR values. When there are many users, the SNR of the channel becomes less important because the waveforms transmitted by other users look like noise. Even with a high SNR, the channel will appear noisy because of the other users. Due to the randomness of the channel the BER varies by +/- 0.5%

A dog sitting on a bed

Questions & Answers

What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Berger describes sociologists as concerned with
Mueller Reply
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Elec 301 projects fall 2011. OpenStax CNX. Jun 18, 2012 Download for free at http://cnx.org/content/col11431/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Elec 301 projects fall 2011' conversation and receive update notifications?

Ask