# 6.37 Information communication problems  (Page 8/8)

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## Hdtv

As HDTV (high-definition television) was being developed, the FCC restricted this digital system to use in the samebandwidth (6 MHz) as its analog (AM) counterpart. HDTV video is sampled on a $1035\times 1840$ raster at 30 images per second for each of the three colors. The least-acceptable picture received bytelevision sets located at an analog station's broadcast perimeter has a signal-to-noise ratio of about 10 dB.

1. Using signal-to-noise ratio as the criterion, how many bits per sample must be used to guarantee that ahigh-quality picture, which achieves a signal-to-noise ratio of 20 dB, can be received by any HDTV set withinthe same broadcast region?
2. Assuming the digital television channel has the same characteristics as an analog one, how much compressionmust HDTV systems employ?

## Digital cellular telephones

In designing a digital version of a wireless telephone, you must first consider certain fundamentals. First of all, thequality of the received signal, as measured by the signal-to-noise ratio, must be at least as good as thatprovided by wireline telephones (30 dB) and the message bandwidth must be the same as wireline telephone. Thesignal-to-noise ratio of the allocated wirelss channel, which has a 5 kHz bandwidth, measured 100 meters from thetower is 70 dB. The desired range for a cell is 1 km. Can a digital cellphone system be designed according to thesecriteria?

## Optimal ethernet random access protocols

Assume a population of $N$ computers want to transmit information on a random access channel. The access algorithm works as follows.

• Before transmitting, flip a coin that has probability $p$ of coming up heads
• If only one of the $N$ computer's coins comes up heads, its transmission occurs successfully, and the others must wait until thattransmission is complete and then resume the algorithm.
• If none or more than one head comes up, the $N$ computers will either remain silent (no heads) or a collision will occur (morethan one head). This unsuccessful transmission situation will be detected by all computers once thesignals have propagated the length of the cable, and the algorithm resumes (return to the beginning).
1. What is the optimal probability to use for flipping the coin? In other words, what should $p$ be to maximize the probability that exactly one computer transmits?
2. What is the probability of one computer transmitting when this optimal value of $p$ is used as the number of computers grows to infinity?
3. Using this optimal probability, what is the average number of coinflips that will be necessary to resolve the access so that one computer successfully transmits?
4. Evaluate this algorithm. Is it realistic? Is it efficient?

## Repeaters

Because signals attenuate with distance from the transmitter, repeaters are frequently employed for both analog and digital communication. For example, let's assume that thetransmitter and receiver are $D$  m apart, and a repeater is positioned halfway between them ( [link] ). What the repater does is amplify its received signal to exactly cancel the attenuationencountered along the first leg and to re-transmit the signal to the ultimate receiver. However, the signal therepeater receives contains white noise as well as the transmitted signal. The receiver experiences the same amountof white noise as the repeater.

1. What is the block diagram for this system?
2. For an amplitude-modulation communication system, what is the signal-to-noise ratio of the demodulated signal atthe receiver? Is this better or worse than the signal-to-noise ratio when no repeater is present?
3. For digital communication, we must consider the system's capacity. Is the capacity larger with therepeater system than without it? If so, when; if not, why not?

## Designing a speech communication system

We want to examine both analog and digital communication alternatives for a dedicated speech transmission system. Assume the speech signal has a 5 kHz bandwidth.The wireless link between transmitter and receiver is such that 200 watts of power can be received at a pre-assigned carrier frequency. We have some latitude in choosing the transmission bandwidth, but the noise power added by the channel increases with bandwidth with a proportionality constant of 0.1 watt/kHz.

1. Design an analog system for sending speech under this scenario. What is the received signal-to-noise ratio under these design constraints?
2. How many bits must be used in the A/D converter to achieve the same signal-to-noise ratio?
3. Is the bandwidth required by the digital channel to send the samples without error greater or smaller than the analog bandwidth?

## Digital vs. analog

You are the Chairman/Chairwoman of the FCC. The frequency band 3 MHz to 3.5 MHz has been allocated for a new “high-quality” AM band.Each station licensed for this band will transmit signals having a bandwidth of 10 kHz, twice the message bandwidth of what current stations can send.

1. How many stations can be allocated to this band and with what carrier frequencies?
2. Looking ahead, conversion to digital transmission is not far in the future. The characteristics of the new digital radio system need to be established and you are the boss!Detail the characteristics of the analog-to-digital converter that must be used to prevent aliasing and ensure a signal-to-noise ratio of 25 dB.
3. Without employing compression, how many digital radio stations could be allocated to the band if each station used BPSK modulation? Evaluate this design approach.

#### Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
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
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Nikki Reply

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