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This module introduces frequency shift keying (FSK) and describes components of an FSK transmitter block-diagram.

Frequency shift keying

Frequency Shift Keying ( FSK ) is a scheme to transmit digital information across an analogchannel. Binary data bits are grouped into blocks of a fixed size, and each block is represented by a unique carrierfrequency, called a symbol , to be sent across the channel.

The receiver then looks at the recovered symbol frequency to determine which block of bitswas sent and converts it back to the appropriate binary data.
This requires having a unique symbol for each possible combination of data bits in a block. In thislaboratory exercise each symbol represents a two-bit block; therefore, there will be four different symbols.

The carrier frequency is kept constant over some number of samples known as the symbol period( T symb ). The symbol rate, defined as F symb , is a fraction of the board's sampling rate, F s . For our sampling rate of 44.1 kHz and a symbol period of 32, the symbol rate is 44.1k/32 symbols per second.

Pseudo-noise sequence generator and FSK transmitter.

Pseudo-noise sequence generator

The input bits to the transmitter are provided by the special shift-register, called a pseudo-noise sequence generator ( PN generator ), on the left side of . A PN generator produces a sequence of bits that appears random. The PN sequence will repeat withperiod 2 B 1 , where B is the width in bits of the shift register. A more detailed diagram of the PN generator alone appears in .

PN generator.

As shown in , the PN generator is simply a shift-register and XOR gate. Bits 14 and 15 of theshift-register are XORed together and the result is shifted into the lowest bit of the register. This lowest bit isthe output of the PN generator.

The PN generator is a useful source of random data bits for system testing. We can simulate the bit sequence that wouldbe transmitted by a user as the random bits generated by the PN generator. Since communication systems tend to randomizethe bits seen by the transmission scheme so that bandwidth can be efficiently utilized, the PN generator is a good datamodel.

PN generators have other applications in communications, notably in the Code DivisionMultiple Access schemes used by cellular telephones.

Series-to-parallel conversion

The shift-register produces one output bit at a time. Because each symbol the system transmits will encode two bits, werequire the series-to-parallel conversion to group the output bits from the shift-register into blocks of two bits so thatthey can be mapped to a symbol.

Frequency look-up table

This is responsible for mapping blocks of bits to one of four frequencies as shown in . Each possible two-bit block of data from the series-to-parallel conversionis mapped to a different carrier frequency i

Note that the subscript i denotes a symbol's index in the transmitted signal; i.e. , the first symbol sent has index i 1 , the second symbol sent has index i 2 , and so on. Therefore, i denotes the frequency and i denotes the phase offset of the i th transmitted symbol.
These frequencies are then used to generate the waveforms. The mappings for thisassignment are given in .

Data Chunk Carrier Frequency i
00 9 32
01 13 32
11 17 32
10 21 32

One way to implement this mapping is by using a look-up table. The two-bit data block can be interpreted as an offsetinto a frequency table where we have stored the possible transmission frequencies. Note that since each frequencymapping defines a symbol, this mapping is done at the symbol rate F symb , or once for every T symb DSP samples.

The symbol bit assignments are such that any two adjacent frequencies map to data blocks that differ by only one bit.This assignment is called Gray coding and helps reduce the number of bit errors made in the event of areceived symbol error.

Phase continuity

In order to minimize the bandwidth used by the transmitted signal, you should ensure that the phase of your transmittedwaveform is continuous between symbols; i.e., the beginning phase of any symbol must be equal to the ending phase of theprevious symbol. For instance, if a symbol of frequency 9 32 begins at phase 0, the symbol will end 31 output samples later at phase 31 9 32 . To preserve phase continuity, the next output sample must be at phase 32 9 32 , which is equivalent to phase . Therefore, the next symbol, whatever its frequency, must begin at phase . For each symbol, you must choose i in the expression i n i to create this continuity.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
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
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
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.
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
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
characteristics of micro business
for teaching engĺish at school how nano technology help us
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
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
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.
what is the actual application of fullerenes nowadays?
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.
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.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
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.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
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what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
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Source:  OpenStax, Ece 320 spring 2004. OpenStax CNX. Aug 24, 2004 Download for free at http://cnx.org/content/col10225/1.12
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