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• FDMA
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GLONASS - FDMA signals
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All GLONASS satellites transmit the
same code as their SP signal; however
each transmits on a different
frequency using a 15-channel
frequency division multiple access
(FDMA) technique spanning either
side from 1602.0 MHz, known as the
L1 band
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GLONASS - FDMA signals
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The L2 signals use the same FDMA as the
L1 band signals, but transmit straddling
1246 MHz with the center frequency
determined by the equation 1246 MHz +
n×0.4375 MHz, where n spans the same
range as for L1. Other details of the HP
signal have not been disclosed.
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OFDMA
'Orthogonal Frequency-Division
Multiple Access' ('OFDMA') is a
multi-user version of the popular
orthogonal frequency-division
multiplexing (OFDM) digital
modulation scheme. Multiple access
is achieved in OFDMA by assigning
subsets of subcarriers to individual
users as shown in the illustration
below. This allows simultaneous low
data rate transmission from several
users.
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OFDMA - Claimed advantages over CDMA
* OFDMA can achieve a higher MIMO
spectral efficiency due to providing flatter
frequency channels than a CDMA rake
receiver can.
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OFDMA - Characteristics and principles of operation
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OFDMA resembles code division multiple
access (CDMA) spread spectrum, where
users can achieve different data rates by
assigning a different code spreading factor
or a different number of spreading codes
to each user.
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OFDMA - Characteristics and principles of operation
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OFDMA can be seen as an alternative to
combining OFDM with time division
multiple access (TDMA) or time-domain
statistical multiplexing, i.e. packet
mode communication. Low-data-rate
users can send continuously with low
transmission power instead of using a
pulsed high-power carrier. Constant
delay, and shorter delay, can be
achieved.
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OFDMA - Characteristics and principles of operation
OFDMA can also be described as a
combination of frequency domain and
time domain multiple access, where
the resources are partitioned in the
time-frequency space, and slots are
assigned along the OFDM symbol
index as well as OFDM sub-carrier
index.
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OFDMA - Characteristics and principles of operation
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OFDMA is considered as highly suitable
for broadband wireless networks, due to
advantages including scalability and
MIMO-friendliness, and ability to take
advantage of channel frequency
selectivity.
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OFDMA - Characteristics and principles of operation
In spectrum sensing cognitive radio,
OFDMA is a possible approach to filling
free radio frequency bands adaptively.
Timo A. Weiss and Friedrich K. Jondral
of the University of Karlsruhe proposed
a spectrum pooling system in which
free bands sensed by nodes were
immediately filled by OFDMA
subbands.
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OFDMA - Usage
OFDMA is also a candidate access
method for the IEEE 802.22 Wireless
Regional Area Networks (WRAN). The
project aims at designing the first cognitive
radio based standard operating in the
VHF-low UHF spectrum (TV spectrum).
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OFDMA - Trademark and patents
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The term OFDMA is claimed to be a
registered trademark by Runcom
Technologies
Ltd.[http://www.runcom.com/], with
various other claimants to the
underlying technologies through
patents.
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Global navigation satellite systems - FDMA signals
1
All GLONASS satellites transmit the same
code as their standard-precision signal;
however each transmits on a different
frequency using a 15-channel frequency
division multiple access (FDMA) technique
spanning either side from 1602.0 MHz,
known as the L1 band
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Global navigation satellite systems - FDMA signals
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The L2 band signals use the same FDMA as
the L1 band signals, but transmit straddling
1246MHz with the center frequency
1246MHz + n×0.4375MHz, where n spans
the same range as for L1.GLONASS
transmitter specs In the original GLONASS
design, only obfuscated high-precision signal
was broadcast in the L2 band, but starting
with GLONASS-M, an additional civil
reference signal L2OF is broadcast with an
identical standard-precision code to the L1OF
signal.
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Channel access method - Frequency Division Multiple Access (FDMA)
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An example of FDMA systems were
the first-generation (1G) cell-phone
systems, where each phone call was
assigned to a specific uplink
frequency channel, and another
downlink frequency channel
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Channel access method - Frequency Division Multiple Access (FDMA)
An advanced form of FDMA is the
orthogonal frequency-division multiple
access (OFDMA) scheme, for example
used in 4G cellular communication
systems. In OFDMA, each node may use
several sub-carriers, making it possible
to provide different quality of service
(different data rates) to different users.
The assignment of sub-carriers to users
may be changed dynamically, based on
the current radio channel conditions and
traffic load.
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FDMA
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FDMA, like other Multiple Access systems,
coordinates access between multiple users
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FDMA - Features
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* In FDMA all users share the Transponder
(satellite communications)|satellite
transponder or frequency channel
simultaneously but each user transmits at
single frequency.
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FDMA - Features
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* FDMA can be used with
both analog and digital
signal.
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FDMA - Features
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* FDMA requires high-performing filters
in the radio hardware, in contrast to
Time division multiple access|TDMA
and CDMA.
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FDMA - Features
* FDMA is not vulnerable to the timing
problems that Time division multiple
access|TDMA has. Since a predetermined
frequency band is available for the entire
period of communication, stream data (a
continuous flow of data that may not be
packetized) can easily be used with
FDMA.
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FDMA - Features
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* Due to the frequency filtering,
FDMA is not sensitive to near-far
problem which is pronounced for
CDMA.
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FDMA - Features
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FDMA, on the other hand, is an
access method in the data link
layer.
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FDMA - Features
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FDMA also supports demand assignment
in addition to fixed assignment. Demand
assignment allows all users apparently
continuous access of the radio spectrum
by assigning carrier frequencies on a
temporary basis using a statistical
assignment process. The first FDMA
demand-assignment system for satellite
was developed by COMSAT for use on
the Intelsat series IVA and V satellites.
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SC-FDMA
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'Single-carrier FDMA' ('SC-FDMA') is a
frequency-division multiple access
scheme. Like other multiple access
schemes (TDMA, FDMA, CDMA,
OFDMA), it deals with the assignment
of multiple users to a shared
communication resource. SC-FDMA
can be interpreted as a linearly
precoded OFDMA scheme, in the sense
that it has an additional Discrete
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SC-FDMA
Goodman,
“[http://hgmyung.googlepages.com/Single
CarrierFDMA_VTmagSep06.pdf Single
Carrier FDMA for Uplink Wireless
Transmission]”, IEEE Vehicular
Technology Magazine, vol
1
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SC-FDMA
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6, June 2002 pp.947–955 Although the
performance gap is not much, SCFDMA's additional advantage of low
PAPR makes it a favorite especially
for uplink wireless transmission in
future mobile communication
systems where transmitter power
efficiency is of paramount
importance.
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SC-FDMA - Transmitter and Receiver Structure of LP-OFDMA/SC-FDMA
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The process transmission
of SC-FDMA scheme is
very similar to OFDMA
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SC-FDMA - Transmitter and Receiver Structure of LP-OFDMA/SC-FDMA
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In SC-FDMA, multiple access among
users is made possible by assigning
different users, different sets of nonoverlapping fourier-coefficients (subcarriers). This is achieved at the
transmitter by inserting (prior to
IFFT) silent fourier-coefficients (at
positions assigned to other users), and
removing them on the receiver side
after the FFT.
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SC-FDMA - Transmitter and Receiver Structure of LP-OFDMA/SC-FDMA
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The distinguishing feature of SC-FDMA is
that it leads to a single-carrier transmit
signal, in contrast to OFDMA which is a
multi-carrier transmission scheme.
Subcarrier mapping can be classified into
two types: localized mapping and
distributed mapping.
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SC-FDMA - Transmitter and Receiver Structure of LP-OFDMA/SC-FDMA
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A special case of distributed SC-FDMA
is called interleaved SC-FDMA (IFDMA),
where the occupied subcarriers are
equally spaced over the entire
bandwidth.Xixia Leader in Converged
IP Testing, Single Carrier FDMA in LTE,
915-2725-01 Rev A November 2009
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SC-FDMA - Transmitter and Receiver Structure of LP-OFDMA/SC-FDMA
Goodman, Peak-to-Average Power
Ratio of Single Carrier FDMA Signals
with Pulse Shaping, The 17th Annual
IEEE International Symposium on
Personal, Indoor and Mobile Radio
Communications (PIMRC ’06), Helsinki,
Finland, Sep
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SC-FDMA - Transmitter and Receiver Structure of LP-OFDMA/SC-FDMA
In OFDM as well as SC-FDMA,
equalization is achieved on the
receiver side after the FFT
calculation, by multiplying each
Fourier coefficient by a complex
number. Thus, frequency-selective
fading and phase distortion can be
easily combated. The advantage is
that FFT and frequency domain
equalization requires less
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SC-FDMA - Transmitter and Receiver Structure of LP-OFDMA/SC-FDMA
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4, April 2002, pp.58–66 The single carrier
transmission, unlike SC-FDMA and OFDM
employ no IFFT or FFT at transmitter, but
introduce the cyclic prefix to transform the
linear channel convolution into a circular
one
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Single-carrier FDMA - Transmitter and Receiver Structure of LP-OFDMA/SCFDMA
The transmission
processing of SCFDMA is very similar to
that of OFDMA
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Single-carrier FDMA - Transmitter and Receiver Structure of LP-OFDMA/SCFDMA
1
In SC-FDMA, multiple access among
users is made possible by assigning
different users different sets of nonoverlapping fourier-coefficients (subcarriers). This is achieved at the
transmitter by inserting (prior to
IFFT) silent fourier-coefficients (at
positions assigned to other users), and
removing them on the receiver side
after the FFT.
https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html
Single-carrier FDMA - Transmitter and Receiver Structure of LP-OFDMA/SCFDMA
1
A special case of distributed SC-FDMA is
called interleaved SC-FDMA (IFDMA),
where the occupied subcarriers are
equally spaced over the entire
bandwidth.Xixia Leader in Converged IP
Testing, Single Carrier FDMA in LTE, 9152725-01 Rev A November 2009
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Single-carrier FDMA - Transmitter and Receiver Structure of LP-OFDMA/SCFDMA
Goodman, Peak-to-Average Power
Ratio of Single Carrier FDMA Signals
with Pulse Shaping, The 17th Annual
IEEE International Symposium on
Personal, Indoor and Mobile Radio
Communications (PIMRC ’06),
Helsinki, Finland, Sep
1
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Single-carrier FDMA - Transmitter and Receiver Structure of LP-OFDMA/SC-FDMA
In OFDM, as well as SC-FDMA,
equalization is achieved on the receiver
side, after the FFT calculation, by
multiplying each Fourier coefficient by a
complex number. Thus, frequencyselective fading and phase distortion can
be easily combated. The advantage is that
frequency domain equalization using FFTs
requires less computation than
conventional time-domain equalization.
1
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