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Within a single cell, the transmitter implements multiple users that send messages by sequencing them in time.In TDMA, where the signal intended for each user is transmitted during a designated time slot, all users employ the same band of frequencies.The frame structure for the B 3 I G TDMA is shown in [link] . This may be contrasted with the FDMA situation where users each employtheir own frequency range, as was discussed in [link] .

The Time Division Multiple Access (TDMA) frame structure used in the B^3IG. The indicated sizes are valid for the 8-bit ASCII encoding.
The Time Division Multiple Access (TDMA) frame structure used in the B 3 I G . The indicated sizes are valid for the 8-bit ASCII encoding.

Typically, adjacent cells transmit on different frequencies, though frequencies may be reused in cells that are sufficiently far away.Adjacent cells may use frequencies that are close to each other – and may even overlap slightly due to relaxed spectral masks.Consequently, it is not unreasonable to expect some interference from adjacent cells. B 3 I G makes it easy to study the effects of this kind of interference.

In Code Division Multiple Access (CDMA), each user is assigned a code which is mutually orthogonal to all of the other users. All users transmit at the same time and in the same frequency range, and the decoding relies on the orthogonality of the codes. B 3 I G does not currently implement a CDMA protocol.

Constructing the received signal

The B 3 I G Transmitter (i.e., the base station) simulates K simultaneous users using TDMA. Each receiver (i.e., each mobile device in [link] ) retains and decodes only its intended portion of the signal. For single-user operation, K = 1 .

Each of the three blocks in [link] is itself built from several components that are familiar from previous chapters. The system that generatesthe analog received signal (i.e. the actual transmitter and channel) is shown in block diagram form in [link] . This is, of course, the magical M 6 Transmitter from [link] . When the signal arrives at the front end of the receiver,it is transformed into a sampled IF signal as in [link] .

The front end of the B^3IG transmission system filters for the desired frequency range, adjusts the gain, and modulates to the IF frequency. After a final filtering, the samples give the received signal r.
The front end of the B 3 I G transmission system filters for the desired frequency range, adjusts the gain, and modulatesto the IF frequency. After a final filtering, the samples give the received signal r .

The original message in [link] is a character string of English text. Each character is mapped into asequence of 4-PAM symbols. The mappings may be made using the M atlab function letters2pam.m , which converts each letter to an eight-bit binary string, and hence tofour 4-PAM symbols as in [link] . Alternatively, the mappings may be made with the more terse text2bin.m , which converts each letter to a 7-bit binary string, thus assigning seven 4-PAM symbols to every pair of letters.This mapping is familiar from [link] .

In order to decode the message at the receiver, the recovered symbols must be properly grouped, thestart of each group must be located, and the desired user data must be extracted. To aid this TDMA frame synchronization, apreamble is inserted in the symbol stream at the start of every frame. The preamble is a short text message that starts each frameand it is assumed to be known at the receiver. Like the message, it is encoded in 4-PAM symbols.The unknown messages for each user are placed in sequence after the preamble, as in [link] .

Questions & Answers

what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
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.
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Source:  OpenStax, Software receiver design. OpenStax CNX. Aug 13, 2013 Download for free at http://cnx.org/content/col11510/1.3
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